What Is an EV Charging Capacitor?

An EV charging capacitor is a high-reliability capacitor used in electric vehicle charging power modules to stabilize DC voltage, suppress ripple current, and ensure efficient energy conversion.

It is widely applied in:

• PFC (Power Factor Correction) circuits
• DC-link filtering stages
• On-board chargers (OBC)
• DC-DC converters
• DC fast charging power modules

In modern high-power charging systems, the performance of the capacitor for EV charger directly affects charging efficiency, system stability, and long-term operating cost.

Why EV Charging Capacitors Matter in Charging Stations

In a DC fast charging station, power modules operate continuously under:

• High voltage conditions
• High ripple current stress
• Elevated operating temperatures

Under these conditions, the EV charging capacitor is not a passive component — it is a key factor that determines:

• Charging stability
• System efficiency
• Equipment uptime
• Maintenance frequency

A small degradation in capacitor performance can lead to system-level failures.

What Does EV Charging Capacitor Failure Cost Operators?

When an EV charging capacitor degrades or fails, the impact is not limited to component replacement. It creates a chain of operational losses:

• Reduced charging efficiency and higher electricity cost
• Slower charging speed and unstable output
• Excessive ripple voltage triggering vehicle BMS alarms
• Charging interruption or system shutdown
• Emergency maintenance and technician dispatch
• Lost charging revenue during downtime
• Customer complaints and reduced station utilization

In real operation, the biggest cost is not the capacitor itself, but:

Hidden operational losses:

• Downtime revenue loss
• Repeated maintenance costs
• User experience degradation
• Brand reputation impact

For multi-station operators, these losses can accumulate into significant annual operating expenses.

Why Do EV Charging Capacitors Fail Early?

Compared with laboratory conditions, real charging environments are far more severe.

High Temperature Stress

Inside charging cabinets, temperatures often reach 70°C–85°C.

At high temperatures:

• ESR increases rapidly
• Capacitance decreases
• Internal heat accelerates aging

This significantly shortens capacitor lifetime.

High Ripple Current Overload

In 30kW–350kW DC fast chargers, ripple current can reach 20–50 Arms.

If the EV charging capacitor cannot handle high ripple:

• Internal heating increases
• Thermal stress accumulates
• Early failure occurs

This often leads to system instability or shutdown protection.

Space Constraints in High-Power Modules

Modern EV chargers are designed for:

• Higher power density
• Smaller cabinet size
• Modular architecture

This places higher requirements on capacitor size and thermal design.

Vibration and Outdoor Conditions

Outdoor charging stations and mobile charging systems are exposed to:

• Mechanical vibration
• Thermal cycling
• Environmental stress

This may cause:

• Solder joint fatigue
• Internal structural loosening
• Connection instability

Why Snap-In Capacitors Are Commonly Used in EV Chargers

In high-power charging systems, snap-in capacitors are widely used as EV charging capacitors due to their balance of performance and reliability.

They offer:

• High capacitance density
• Strong ripple current capability
• Stable PCB mounting structure
• Excellent thermal performance
• Long operational life

Typical applications include:

• PFC circuits
• DC-link energy storage
• EV charger power modules
• 800V fast charging systems

Compared with conventional capacitor structures, snap-in capacitors provide better suitability for high-power industrial environments.

How to Choose an EV Charging Capacitor

Selecting the right EV charging capacitor is critical for system reliability and cost control.

Voltage Rating

Common ranges:

• 450V
• 500V
• 550V
• 600V

Higher voltage margin improves reliability.

Ripple Current Capability

High-power EV chargers require:

20–50 Arms ripple current capability

Insufficient ripple performance leads to overheating and early failure.

Temperature Resistance

Recommended range:

-40°C to +105°C

Higher temperature tolerance improves lifespan in real operating conditions.

Lifetime Expectancy

A standard rating:

105°C / 6000h

At lower operating temperatures, real service life can extend significantly.

ESR Performance

Low ESR is critical because it:

• Reduces heat generation
• Improves efficiency
• Extends service life

Xuansn EV Charging Capacitor Solution

The Xuansn XTN Series EV Charging Capacitors are designed specifically for:

• EV charger power modules
• PFC stages
• DC-link applications
• High-power industrial systems

Each feature is engineered to reduce operational cost and improve system reliability.

High Power Density Design

• Up to 25% smaller size
• Supports 800V EV charging systems
• Improves cabinet layout efficiency

High Ripple + Low ESR Performance

• Ripple capability improved by 30%
• Temperature reduced by 8–12°C
• Lower failure risk in continuous operation

Long Lifetime Operation

At 85°C ambient temperature, lifetime can reach:

Up to 24,000–32,000 hours equivalent

Under real charging usage (6–8h/day), service life can reach:

8–12 years

Automotive-Grade Reliability

• 10G vibration resistance
• AEC-Q200 compliant design
• Reinforced terminal structure

Lower Total Operating Cost

• Reduced maintenance frequency
• Lower downtime cost
• Faster delivery (2–4 weeks)

FAQs About EV Charging Capacitors

What is an EV charging capacitor used for?

It is used in EV charger power modules to stabilize voltage, filter ripple current, and ensure efficient power conversion.

Why do EV charging capacitors fail?

Main reasons include high temperature, high ripple current, vibration stress, and insufficient thermal design.

Are snap-in capacitors suitable for EV chargers?

Yes, snap-in capacitors are widely used in EV charging systems due to their high capacitance, strong ripple capability, and reliable mounting structure.

What is the lifespan of an EV charging capacitor?

Depending on operating conditions, lifespan can range from 3 years to over 10 years in optimized systems.

Conclusion

The performance of an EV charging capacitor directly determines the reliability, efficiency, and operating cost of EV charging stations.

Capacitor failure leads to:

• Downtime
• Revenue loss
• Increased maintenance cost
• Poor user experience

By using high-reliability, low-ESR, high-ripple capacitors such as the Xuansn XTN Series, charging station operators can significantly reduce hidden operational costs and improve long-term system stability.

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These capacitors, installed between the IGBT power modules and the DC input, perform several vital functions:

• Absorb high-frequency ripple currents generated by IGBT switching
• Stabilize the DC bus voltage to prevent fluctuations that may affect downstream equipment
• Suppress grid harmonics that can stress capacitors and other components

As energy storage systems evolve toward higher voltage and higher power applications, the performance and reliability of aluminum electrolytic capacitors in power conversion system are becoming increasingly important. Selecting the right capacitor requires more than just considering voltage and capacitance—it requires understanding ripple current, thermal performance, and long-term reliability under real operating conditions.

Why Aluminum Electrolytic Capacitors Fail in PCS

In practical operation, when a PCS operates at full power or during grid fluctuations, the DC bus voltage often experiences excessive variations; when superimposed with grid harmonics, this generates high-frequency ripple current surges. Consequently, capacitors frequently suffer from issues such as abnormal overheating, bulging, or even catastrophic rupture. Capacitors designed for a 15-year service life may fail after less than five years of actual use. In some instances, this leads directly to overvoltage breakdown of the IGBTs, triggering a system-wide fault shutdown. Such failures result in the energy storage system frequently disconnecting from the grid—rendering it unable to respond to grid dispatch commands—while the cost of replacing capacitors incurs high operation and maintenance expenses and damages brand reputation, prompting system owners to question the overall lifecycle reliability of the equipment.

Analysis of the Root Causes

From a technical perspective, the root causes of these issues include:

① Mismatch in Ripple Current Absorption: During PCS operation, the high-frequency switching of the IGBTs generates significant ripple currents on the DC bus. The capacitors are required to absorb these ripples; however, if the capacitance value or the number of capacitors is insufficient, the ripple current may exceed the capacitors’ tolerance limits, leading directly to internal overheating.

② Excessive ESR (Equivalent Series Resistance): The ESR of aluminum electrolytic capacitors varies with changes in temperature and frequency. If the ESR under actual operating conditions is not adequately considered during the component selection phase, high-frequency ripple currents flowing through the ESR will generate Joule heating (P = I²R). This causes the internal temperature of the capacitor element to rise excessively, thereby accelerating the evaporation of the electrolyte.

③ Failure to Meet Key Parameter Specifications: Ripple Current—Under harsh environmental conditions and actual operating loads, the ripple current value exceeds the capacitor’s rated ripple current limit, leading to overheating. Temperature Rise (△T) at Rated Ripple Current—The capacitor’s allowable temperature rise (typically 5°C to 10°C) is exceeded, with actual temperature rises reaching over 20°C. High-Frequency Performance—At high frequencies (e.g., >10 kHz), the Equivalent Series Resistance (ESR) is excessively high, resulting in severe heat generation. Thermal Resistance (RtH)—The thermal resistance between the capacitor’s internal “hot spot” and its outer casing is too high, hindering effective heat dissipation.

④ Flaws in Component Selection Methodology
The customer originally utilized general-purpose aluminum electrolytic capacitors, selecting them solely based on rated voltage and capacitance values. They failed to calculate the actual ripple current and temperature rise under real-world operating conditions, and also neglected to account for the impact of high-frequency ripple currents resulting from the superposition of grid harmonics.

Xuansn Technical Solution

The Xuansn XSN/XTN series is specifically designed to meet the challenges of PCS DC-link applications, providing reliable operation under high ripple current and thermal stress:

These features directly address the main failure mechanisms in PCS, ensuring both electrical and thermal reliability.

Recommended Application Design

• Parallel capacitor configurations for even ripple current distribution
• Adequate spacing and airflow to maintain safe operating temperatures
• Proper ripple current calculation to ensure capacitors operate within ratings

Field Verification Results

Actual field tests confirm the XSN/XTN series improves PCS reliability:

• Temperature rise remains ≤ 10°C under extreme ripple current conditions
• Service life restored to 15 years, compared to <5 years for standard capacitors
• Failures eliminated: overheating, bulging, and rupture no longer occur
• IGBT overvoltage problems resolved
• PCS system stability maintained during grid fluctuations and dispatch commands

Conclusion

Choosing the right aluminum electrolytic capacitors for PCS DC-link applications is critical for long-term system stability. Key considerations include:

• Low ESR for reduced heat generation
• High ripple current tolerance for handling surge conditions
• Effective thermal management to maintain safe operating temperatures

The Xuansn XSN/XTN series provides a proven solution, enabling high-voltage, high-power PCS systems to operate reliably over their full service life.

FAQ

Q1: What is a DC-link capacitor in PCS?
A: It is a capacitor placed between the DC input and IGBT module, stabilizing DC bus voltage and absorbing ripple currents.

Q2: How long do aluminum electrolytic capacitors last in PCS?
A: With proper design and selection, capacitors can meet a 15-year service life.

Q3: How to prevent overheating in DC-link capacitors?
A: Use low ESR capacitors, distribute ripple current, and ensure effective thermal management.

The post Aluminum Electrolytic Capacitors in Power Conversion System (PCS): Selection, Reliability & Failure Analysis appeared first on DongGuan Xuansn Electronic Tech Co.,LTD.

Electrolytic capacitors are essential components in modern electronics, widely used for energy storage, voltage stabilization, and filtering. But what exactly is an electrolytic capacitor, and how does it work? In this guide, we’ll explain everything you need to know, including types, structure, applications, and best practices for using these critical components in industrial, automotive, and consumer electronics worldwide.

In simple terms:
An electrolytic capacitor is a polarized electronic component that stores electrical energy and smooths voltage in circuits requiring high capacitance, making it ideal for power supplies, LED drivers, automotive electronics, and industrial systems.

2.How Does an Electrolytic Capacitor Work?

An electrolytic capacitor is a type of capacitor that stores and releases electrical energy to stabilize voltage in electronic circuits. It consists of a metal anode, a thin oxide layer that acts as the dielectric, and an electrolyte serving as the cathode. When voltage in the circuit rises, the capacitor charges and stores energy in its electric field, like filling a small energy reservoir. When the voltage drops, it discharges the stored energy back into the circuit, smoothing out voltage fluctuations and reducing ripple. This continuous process of charging and discharging is how electrolytic capacitors work to provide a steady and reliable power supply, making them essential components in power supplies, LED drivers, industrial electronics, automotive systems, and other devices requiring stable energy.

3.Structure of an Electrolytic Capacitor

The structure of an electrolytic capacitor is carefully designed to provide high capacitance in a compact size. At its core, it consists of a metal anode (usually aluminum or tantalum), a thin oxide layer acting as the dielectric, and an electrolyte that. The anode is often etched or roughened to increase its surface area, whstore large amounts of energy even in small dimensionsseparator prevents direct contact between the anode and the electrolyte while allmetal can or plastic casing with clearly marked positive and negative terminals, as electrolytic capacitors are polarized. This unique internal structure not only enables efficient energy storage and voltage smoothing, but also provides a self-healing property, where the electrolyte helps repair minor damage to the dielectric. Understanding the internal structure of an electrolytic capacitor is essential for engineers and designers who need reliable high-capacitance capacitors for power supplies, LED drivers, automotive electronics, and industrial systems.

The structure of aluminum electrolytic capacitors determines their high capacitance and energy storage capabilities. To explore the principle and production process behind these capacitors, check out: Principle of Aluminum Electrolytic Capacitors and Production

4.Types of Electrolytic Capacitors

Electrolytic capacitors are fundamental components in modern electronic systems, widely used for energy storage, voltage smoothing, and signal filtering. To fully understand what is an electrolytic capacitor, it is not enough to know its definition—its classification also plays a critical role in determining how it performs in real-world applications.

In practice, electrolytic capacitors are classified based on two key dimensions:

• Material composition, which determines electrical performance
• Package and mounting type, which determines mechanical integration

This dual classification reflects the trade-off between performance requirements and physical design constraints, which is essential for engineers when selecting components.

1. Classification by Material

The material used in the anode and electrolyte directly influences the capacitor’s capacitance density, leakage current, stability, lifespan, and frequency characteristics. Among all types, aluminum and tantalum electrolytic capacitors are the most widely used in the industry.

Aluminum Electrolytic Capacitors

Aluminum electrolytic capacitors are the most common and cost-effective solution for applications requiring high capacitance values. Structurally, they consist of etched aluminum foil as the anode, a thin aluminum oxide layer as the dielectric, and a liquid or solid electrolyte that serves as the cathode.

From an engineering perspective, their biggest advantage lies in their ability to deliver very high capacitance within a relatively small volume, making them ideal for bulk energy storage and power conditioning.

Performance:

• High capacitance-to-volume ratio, suitable for large energy storage
• Capable of handling relatively high voltage levels
• Effective for low-frequency filtering and ripple suppression

Characteristics:

• Limited operational lifespan due to gradual electrolyte evaporation
• Performance degradation under high temperature and high ripple current conditions
• Higher leakage current compared to solid-state capacitors

Because of these characteristics, aluminum electrolytic capacitors are extensively used in:

• Power supply circuits (AC-DC and DC-DC conversion)
• Industrial equipment and motor drives
• LED lighting systems and consumer electronics

Tantalum Electrolytic Capacitors

Tantalum electrolytic capacitors are designed for applications that require higher stability, reliability, and compact size. They use tantalum metal as the anode and a solid electrolyte, typically manganese dioxide or conductive polymer.

Compared to aluminum capacitors, tantalum capacitors offer more consistent electrical characteristics over time, making them suitable for precision and sensitive electronic systems.

Performance:

• Excellent capacitance stability across temperature and time
• Low leakage current, beneficial for low-power circuits
• Superior performance in higher-frequency applications

Characteristics:

• Smaller size for equivalent capacitance values
• Higher reliability under controlled conditions
• More expensive due to material cost
• Sensitive to surge voltage and reverse polarity, which may lead to failure

These capacitors are commonly found in:

• Smartphones, tablets, and portable electronics
• Medical devices and instrumentation
• Automotive electronics and aerospace systems

2. Classification by Package and Mounting Type

While material determines electrical performance, the package and mounting style define how the capacitor is physically integrated into a circuit. This is especially important in modern electronics, where space constraints and automated manufacturing play a major role.

Radial Electrolytic Capacitors

Radial electrolytic capacitors have two leads emerging from the same end of the component, allowing them to be mounted vertically on a printed circuit board.

This design is highly compatible with modern PCB layouts and automated assembly processes, making radial capacitors the most widely used package type today.

Integration:

• Through-hole mounting with vertical orientation
• Strong mechanical stability on PCB
• Suitable for automated insertion processes

SMD (Surface Mount) Electrolytic Capacitors

SMD electrolytic capacitors are designed for surface mounting directly onto PCBs without the need for through-hole leads. This makes them essential for modern electronics where miniaturization and high-density layouts are required.

Their compatibility with automated pick-and-place machines significantly improves manufacturing efficiency.

Integration:

• Surface mount technology (SMT)
• Optimized for compact and high-density PCB designs
• Enables fully automated production

5.Applications of Electrolytic Capacitors

Electrolytic capacitors are essential components in modern electronics, providing stable voltage, energy storage, and support for transient currents. Their high capacitance and reliability make them widely used across industrial, automotive, consumer, and audio electronics worldwide.

1. Power Supply Circuits: Rectification, filtering, and smoothing AC ripple in sw.
2. DC Link & Energy Storage: In inverters, motor drives, and frequency converters, capacitors store instantaneous energy and sup
3. Audio Equipment: Used for signal coupling, decoupling, and bass frequency filtering in speakers, power amplifiers, and preamps.
4. Consumer Electronics: Motherboards, TVs, refrigerators, air conditioners, and chargers rely on electrolytic capacitors for voltage stabilization and transient current support.
5. Automotive Electronics: Capacitors in car battery management systems, ignition circuits, and on-board power modules (low ESR types preferred).
6. Industrial Control: Used in PLCs, servo drives, and industrial power distribution for anti-interference and voltage holding.

6.How to Identify Polarity in Electrolytic Capacitors

Most electrolytic capacitors are polarized, meaning connecting them backward can cause bulging, leakage, explosion, or permanent damage. Methods to identify polarity include:

1. Marked Negative Stripe: Aluminum shell often has a silver/black vertical stripe with a “-”, indicating the negative pin.
2. Pin Length (Radial Type): Longer lead = positive (+), shorter lead = negative (-).
3. PCB Silkscreen: Circuit boards mark “+” for positive, hollow or outlined pad for negative.
4. SMD Capacitors: Color bar or square mark indicates the negative electrode.
5. Datasheet Verification: For high-voltage or special models, always cross-check polarity with the manufacturer datasheet.

Correctly identifying polarity in electrolytic capacitors is vital for circuit reliability and safety. For a deeper understanding of why polarity matters and its effects in electronic circuits, you can read our detailed guide: Understanding Capacitor Polarity: Unveiling Its Significance in Electronic Circuits

7.Common Failures and Lifespan

Electrolytic capacitors have a limited lifespan due to the nature of their electrolyte and dielectric materials. Understanding common failure modes and aging factors is critical to ensure reliable operation in power supplies, automotive electronics, LED drivers, and industrial equipment.

7.1 Standard Lifespan

• General aluminum electrolytic capacitors: 1,000–5,000 hours at rated temperature (85–105℃).
• High-temperature / long-life models: 10,000–20,000 hours; lifespan halves with every 10℃ increase above rated temperature.

7.2 Common Failure Modes

• Electrolyte Drying: Loss of internal electrolyte → capacitance drops, ESR rises → ripple increases, circuit instability.
• Bulging & Bursting: Reverse polarity, overvoltage, or overheating → internal gas expansion → top vent bulges or ruptures.
• Leakage & Corrosion: Electrolyte seeps out → corrodes PCB pads and nearby components.
• Short Circuit: Dielectric breakdown from overvoltage or aging → direct short → fuse burnout or board damage.
• Open Circuit: Lead detachment or internal drying → circuit loses power holding → equipment fails to start.

7.3 Main Causes of Aging

• Long-term over-temperature operation.
• Exceeding rated voltage or ripple current.
• Frequent hot-swap or instantaneous voltage spikes.
• Poor heat dissipation in enclosed equipment.

5. FAQ

Q1: Can I use an electrolytic capacitor in AC circuits?
A: Standard electrolytics are polarized and designed for DC. Use non-polarized electrolytic or film capacitors for AC.

Q2: What does low ESR mean?
A: Low ESR capacitors have lower internal resistance, improving high-current ripple filtering. Common in motherboard power modules and high-power chargers.

Q3: Can I replace a bulging capacitor with a higher voltage model?
A: Yes, as long as voltage rating is equal or higher; keep capacitance the same. Do not use lower voltage than original.

Q4: Why do capacitors fail in high-temperature devices?
A: Heat accelerates electrolyte volatilization and dielectric aging. Heat dissipation design directly affects actual service life.

6. Conclusion

What Is an Electrolytic Capacitor? It is a low-cost, high-capacitance component vital for energy storage and voltage stabilization in modern electronics. Correct polarity, voltage derating, and thermal management are key for long-term reliability.

Xuansn offers globally shipped, ISO-certified aluminum and tantalum electrolytic capacitors for engineers and electronics manufacturers in the US, Europe, Brazil, and Asia. Contact us for high-quality capacitors to power your devices safely and efficiently.

The post What Is an Electrolytic Capacitor? Types, Working Principle, Applications & Lifespan appeared first on DongGuan Xuansn Electronic Tech Co.,LTD.

Introduction

The uses of capacitors are essential to modern electronics, making capacitors one of the most widely used passive components in electrical and electronic systems.

From simple household devices to complex industrial machinery, the uses of capacitors span across nearly every industry. They play a key role in ensuring stable voltage, efficient energy transfer, signal integrity, and reliable system performance.

Understanding the different uses of capacitors is crucial for engineers, designers, and buyers, as choosing the right capacitor directly affects the performance, lifespan, and safety of electronic systems.

What Are the Main Uses of Capacitors in Circuits?

The uses of capacitors in circuits go far beyond merely storing electrical energy. Capacitors are versatile, multifunctional components that play a critical role in regulating voltage, filtering noise, stabilizing power supplies, coupling and decoupling signals, and controlling timing and frequency. By efficiently storing and releasing energy, capacitors help protect sensitive components from voltage spikes, reduce electromagnetic interference (EMI), improve signal integrity, and enhance overall circuit performance. They are essential in nearly every type of electronic system, from consumer electronics and computers to automotive electronics, industrial machinery, LED lighting, and renewable energy systems, ensuring reliable and stable operation under a wide range of conditions.

🔋 1. Energy Storage

One of the most fundamental uses of capacitors in circuits is storing electrical energy in an electric field. Unlike batteries, which store energy chemically and release it slowly, capacitors can charge and discharge almost instantaneously, providing short bursts of energy when needed.

How It Works:
A capacitor stores energy by accumulating opposite charges on two conductive plates separated by a dielectric material. When a load requires energy, the capacitor releases the stored charge quickly, helping maintain voltage stability in the circuit.

Typical Applications:

• Backup power for memory modules in electronics
• Flash circuits in cameras
• Pulse power systems in industrial machinery
• Energy harvesting devices and regenerative systems in electric vehicles

Recommended Capacitor Types:

• Supercapacitors for high-capacity, rapid discharge applications
• Film or ceramic capacitors for low-power, fast-response circuits

Design Tips:

• Ensure voltage rating exceeds operating voltage by 20–50%
• For high-frequency pulses, low ESR capacitors improve efficiency and reduce heat

🔌 2. Voltage Smoothing

Capacitors are widely used for voltage smoothing, especially in power supplies. After AC power is converted to DC, the output often contains ripples—small voltage fluctuations—that can destabilize sensitive circuits. Capacitors absorb peaks and fill in dips, producing a stable DC voltage.

How It Works:
By acting as a reservoir, a capacitor stores excess voltage during peaks and releases it during dips. In switching power supplies, low-ESR capacitors also help filter high-frequency noise, improving efficiency and preventing voltage spikes.

Typical Applications:

• Switching Mode Power Supplies (SMPS)
• AC-DC adapters
• Solar inverters and battery chargers
• LED driver circuits

Recommended Capacitor Types:

• Aluminum electrolytic capacitors for bulk filtering
• Ceramic for high-frequency decoupling

Design Tips:

• Combine bulk and bypass capacitors for best results
• Ensure proper layout on PCB to minimize inductance

🌊 3. Noise Filtering & EMI Suppression

Electronic circuits generate unwanted noise that can interfere with performance. Capacitors are a key component in filtering this noise and suppressing electromagnetic interference (EMI), ensuring signals remain clean and reliable.

How It Works:
Capacitors provide a low-impedance path for high-frequency noise, effectively bypassing it to ground while allowing desired signals to pass. This prevents noise from propagating through the power lines or signal paths.

Typical Applications:

• Audio amplifiers and signal processing circuits
• RF communication devices
• Digital microcontroller boards
• Automotive ECUs and infotainment systems

Recommended Capacitor Types:

• Ceramic capacitors for high-frequency filtering
• Film capacitors for industrial EMI suppression

Design Tips:

• Place decoupling capacitors as close as possible to IC power pins
• Use multiple capacitors in parallel to cover a wider frequency range

🔄 4. Signal Coupling & Decoupling

Capacitors control the way signals move through circuits, making them essential for signal integrity.

Coupling:

• Allows AC signals to pass from one stage to another while blocking DC
• Common in audio amplifiers, RF circuits, and ADC/DAC interfaces

Decoupling:

• Removes noise from power lines and stabilizes voltage at ICs
• Protects sensitive components from sudden current changes

Typical Applications:

• Microcontroller and FPGA boards
• Audio signal chains
• RF communication modules
• Sensor systems

Recommended Capacitor Types:

• Ceramic for high-frequency decoupling
• Film for precise analog signal coupling

Design Tips:

• Use a 0.1–0.01µF ceramic capacitor near each IC for high-speed digital circuits
• Combine decoupling and bulk capacitors for both high-frequency and low-frequency noise suppression

⏱ 5. Timing & Frequency Control

Capacitors are widely used with resistors to form RC (resistor-capacitor) circuits, which control timing and oscillation frequencies.

How It Works:
In an RC circuit, the capacitor charges and discharges through a resistor, creating predictable time delays or oscillations. This is the basis for timers, pulse generators, and oscillators.

Typical Applications:

• Timer circuits using 555 ICs
• PWM (pulse-width modulation) for motor and LED control
• Clock oscillators in microprocessors and digital systems
• Audio tone generation and waveform shaping

Recommended Capacitor Types:

• Ceramic for stable timing and frequency control
• Film capacitors for precision oscillators

Design Tips:

• Timing is proportional to T = R × C; choose components with tight tolerance
• Consider temperature stability for precision applications

Typical Uses of Capacitors Across Different Industries

The uses of capacitors vary widely across industries, but their core function remains the same: to store energy, stabilize voltage, filter signals, and improve system reliability. From consumer electronics to aerospace systems, capacitors play a critical role in ensuring performance, efficiency, and safety in modern technology.

📱 Uses of Capacitors in Consumer Electronics

In consumer electronics, the uses of capacitors are essential for maintaining stable operation and high-quality signal performance in compact and high-speed devices.

Typical Applications:

Filtering and decoupling in power supply circuits to smooth voltage fluctuations
Signal coupling and bypassing to ensure clean audio and video transmission
Timing and oscillation in RC circuits for clocks and control systems

Why It Matters:
Capacitors help prevent noise, voltage instability, and signal distortion in devices such as smartphones, laptops, TVs, and gaming systems.

Common Capacitor Types:

Ceramic capacitors for high-frequency decoupling
Tantalum capacitors for compact and stable performance

🚗 Uses of Capacitors in Automotive Industry (Especially EVs)

The automotive sector, particularly electric vehicles, relies heavily on advanced capacitor technologies.

Typical Applications:

Rapid energy storage and release in regenerative braking systems
Instant power support in start-stop systems
DC-link capacitors in motor drive controllers for voltage stabilization
Infotainment systems and airbag triggering circuits

Why It Matters:
Capacitors ensure reliability under extreme conditions such as high temperature, vibration, and voltage fluctuations.

Key Requirements:

High reliability and long lifespan
Resistance to heat and mechanical stress
Compliance with automotive standards (e.g., AEC-Q200)

🔋 Uses of Capacitors in Renewable Energy & Power Systems

Capacitors are critical in modern energy infrastructure, especially in renewable energy systems.

Typical Applications:

Filtering and smoothing in solar inverters and wind power converters
Power factor correction to improve energy efficiency
Energy buffering in high-voltage DC (HVDC) transmission systems

Advanced Functions:

Harmonic filtering to protect grid stability
Voltage regulation and transient suppression

Why It Matters:
Capacitors help increase system efficiency, reduce energy loss, and ensure stable integration of renewable energy into the grid.

🏭 Uses of Capacitors in Industrial Manufacturing & Automation

Industrial systems require capacitors that can handle high power, high voltage, and harsh environments.

Typical Applications:

Motor start and run capacitors in single-phase AC motors
Pulse power discharge in welding machines and laser equipment
Energy storage and voltage regulation in UPS systems
DC bus capacitors in variable frequency drives (VFDs) to suppress voltage spikes

Benefits:

Improved energy efficiency
Reduced downtime and maintenance
Enhanced system stability and performance

🏥 Uses of Capacitors in Medical Equipment

In medical technology, capacitors play a life-critical role where precision and reliability are essential.

Typical Applications:

Energy storage in defibrillators for delivering life-saving electric shocks
Timing pulses in pacemakers using miniature capacitors
High-voltage stabilization in X-ray and CT imaging systems

Why It Matters:
Capacitors ensure accurate operation, patient safety, and reliable performance in sensitive medical environments.

📡 Uses of Capacitors in Telecommunications & Aerospace

Capacitors are indispensable in high-frequency and high-reliability systems such as communication networks and aerospace equipment.

Typical Applications:

Resonance, impedance matching, and filtering in RF circuits (base stations, satellites)
Signal isolation and DC blocking (coupling/decoupling)
Temperature compensation and radiation-resistant capacitors in aerospace systems

Why It Matters:
These applications demand extreme precision, stability, and durability under harsh environmental conditions.

🏠 Uses of Capacitors in Home Appliances & Lighting

Capacitors are widely used in household appliances and lighting systems to improve efficiency and reliability.

Typical Applications:

Start capacitors in air conditioners and refrigerators
Motor operation in washing machines and fans
Power factor correction and EMI suppression in fluorescent lamps and LED drivers

Why It Matters:
Capacitors help reduce energy consumption, improve performance, and extend the lifespan of household devices.

How to Choose the Right Capacitor

Choosing the right capacitor ensures stable performance, efficiency, and long lifespan. The key is to match the capacitor’s specifications with your application.

🔑 Key Factors to Consider:

• Capacitance (μF / nF / pF)
  Determines how much energy is stored.
  👉 Power supply: higher capacitance | Signal circuits: lower capacitance
• Voltage Rating
  Should be 20%–50% higher than actual working voltage to avoid failure
• ESR (Equivalent Series Resistance)
  👉 Low ESR = better efficiency, less heat
  Ideal for power supplies, LED drivers, automotive electronics
• Temperature Rating
  👉 85°C (general) / 105°C (industrial & automotive)
  Lower temperature = longer lifespan
• Capacitor Type
  Electrolytic → power filtering
  Ceramic → high frequency
  Film → high voltage
  Supercapacitor → energy storage
• Ripple Current
  High ripple applications require high ripple-rated capacitors

✅ Quick Tip

The best capacitor is not the most expensive one, but the one that fits your circuit requirements perfectly.

❓ FAQ About Uses of Capacitors

What are the main uses of capacitors?

The main uses of capacitors include energy storage, voltage smoothing, noise filtering, signal control, and timing in electronic circuits.

Why are capacitors important?

Capacitors ensure stable voltage, reduce noise, and improve circuit efficiency and reliability across all electronic systems.

Where are capacitors used?

They are used in electronics, automotive systems, industrial equipment, renewable energy, LED lighting, and computer hardware.

How do I choose the right capacitor?

Select based on voltage, capacitance, ESR, temperature, lifespan, and application requirements.

How long do capacitors last?

Depending on type and conditions, capacitors can last from a few years to over 10–15 years in industrial applications.

Can a bad capacitor damage a circuit?

Yes, a failed capacitor can cause instability, overheating, or damage to other components.

Conclusion

The uses of capacitors are fundamental to modern electronics, supporting everything from energy storage and voltage smoothing to noise filtering, signal control, and power management.

Whether in consumer electronics, automotive systems, industrial equipment, renewable energy, or LED lighting, capacitors ensure stable performance, improved efficiency, and long-term reliability.

Choosing the right capacitor is critical. By understanding different capacitor types, applications, and key parameters such as capacitance, voltage rating, ESR, and temperature, engineers and buyers can optimize both performance and cost.

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Bipolar electrolytic capacitors (BECs), also known as non-polarized electrolytic capacitors, are a special type of aluminum electrolytic capacitor. Their core advantage lies in their ability to operate stably under both positive and negative voltages, eliminating the need to distinguish between positive and negative terminals, thus breaking the polarity limitations of standard polarized electrolytic capacitors.

Compared to conventional polarized electrolytic capacitors, the key difference of bipolar electrolytic capacitors lies in their internal structure—they form a symmetrical electrical structure by connecting two identical polarized electrolytic capacitors in reverse series, thereby safely handling AC signals or circuits with frequent voltage polarity reversals.

This unique structure fundamentally avoids damage problems such as dielectric breakdown, capacitor expansion, and even explosion caused by voltage polarity reversal, balancing practicality and safety.

2. Internal Structure and Working Principle

The internal structure of a bipolar electrolytic capacitor can be simplified to “two polarized electrolytic capacitors connected back-to-back in reverse series,” interconnected through their respective negative terminals. Only two non-polar external leads are led out, eliminating the need to distinguish between positive and negative terminals, greatly simplifying the installation process. The core principle behind its stable operation under AC voltage is as follows:

When a voltage is applied to a bipolar electrolytic capacitor, regardless of the voltage polarity, one of the two series-connected polarized capacitors is always forward-biased (meeting the normal operating conditions of a polarized capacitor, allowing for stable charging and discharging), while the other is in a zero-biased or weakly reverse-biased state (not reaching the breakdown threshold and will not be damaged).

It is this characteristic of “always having one capacitor working normally” that allows bipolar electrolytic capacitors to withstand polarity changes in alternating voltage, making them suitable for AC or bidirectional voltage circuits. This is the core logic that distinguishes them from conventional polarized electrolytic capacitors.

A bipolar electrolytic capacitor is a type of aluminum electrolytic capacitor that does not have polarity and can operate with both positive and negative voltages.

Unlike conventional electrolytic capacitors, it can safely handle AC signals or bidirectional voltage without causing breakdown or damage.

Because of this feature, bipolar capacitors are commonly used in audio circuits, motor circuits, and signal coupling applications.

3. Key Characteristics of Bipolar Electrolytic Capacitors

The core advantages of bipolar electrolytic capacitors are “combining large capacitance, non-polarity, and low cost,” perfectly filling the market gap between conventional polarized capacitors and non-polarized film capacitors. Their specific characteristics are shown in the table below:

Based on these characteristics, bipolar electrolytic capacitors are widely used in various circuits that are cost-sensitive, require large capacitance, and need to handle AC or bidirectional voltage, making them a preferred device that balances performance and cost.

4. Comparison of Bipolar Capacitors, Polarized Capacitors, and Film Capacitors

To more clearly illustrate the positioning of bipolar electrolytic capacitors, a comprehensive comparison is provided below with conventional polarized electrolytic capacitors and film capacitors, clarifying the differences in their applicable scenarios:

In summary, the core value of bipolar electrolytic capacitors lies in “filling a gap”—they solve the problem that polarized electrolytic capacitors cannot handle AC signals, and they also make up for the high cost of large-capacity film capacitors, making them the optimal solution for specific scenarios.

5. Main Applications of Bipolar Electrolytic Capacitors

The core applications of bipolar electrolytic capacitors revolve around three main requirements: large capacitance, non-polarity, and low cost. They are primarily used in circuits that need to process AC signals or bidirectional voltages. Below are six of the most common application areas, covering multiple industries including consumer electronics, industrial, and automotive:

5.1 Audio and Speaker Systems

This is the most core and largest application market for bipolar electrolytic capacitors. Their non-polarity perfectly suits the transmission requirements of AC audio signals. Typical applications include:

– Speaker crossover networks: Separate high and low frequency audio signals to optimize sound quality output;

– Audio signal coupling: Enable signal transmission between modules in audio equipment, blocking DC interference;

– Power amplifier output coupling: Connect the power amplifier and the speaker, protecting the speaker from damage caused by DC components;

– Headphone signal blocking capacitors: Filter DC signals to ensure headphone sound quality and safety;

– Subwoofer audio circuits: Provide large-capacity energy storage to enhance bass output.

In these types of circuits, the core function of bipolar electrolytic capacitors is to “block DC and conduct AC,” ensuring pure audio signal transmission while achieving high capacitance at a relatively low cost, thus balancing sound quality and cost-effectiveness.

5.2 Household Appliances and Motor Circuits

Many household single-phase motors (especially low-power motors) require AC signals for starting and operation. Bipolar electrolytic capacitors, with their non-polarity and high capacitance, become core components in these circuits. Typical applications include:

– Electric fans and range hoods: assisting in motor starting and stabilizing operating speed;

– Washing machine and air conditioner fan motors: providing starting capacitor support to ensure smooth motor start-up and shutdown;

– Small water pumps: assisting in motor commutation and ensuring continuous and stable pump operation.

In these applications, the core value of bipolar electrolytic capacitors lies in adapting to the AC characteristics of motor circuits while providing sufficient starting capacitance at low cost, reducing the overall manufacturing cost of household appliances.

5.3 Consumer Electronics and Instruments

In various consumer electronics and measuring instruments, bipolar electrolytic capacitors are mainly used for AC coupling or DC blocking to ensure the stability of signal transmission. Common applications include:

– Televisions and audio equipment: Audio signal processing, filtering DC interference;

– Measuring instruments and oscilloscopes: AC signal sampling and DC blocking to ensure measurement accuracy;

– Portable audio amplifiers: Signal coupling and energy storage, optimizing audio output.

5.4 Automotive Electronics

In automotive electronic systems, voltage fluctuations are significant, and some circuits involve bidirectional voltage. Bipolar electrolytic capacitors can effectively stabilize signals and absorb voltage spikes. Typical applications include:

– Car audio systems and power amplifiers: Audio crossover and signal coupling to improve in-vehicle sound quality;

– Window motors and wiper motor drive circuits: Stabilizing drive signals to ensure smooth motor operation;

– HVAC fan controllers: Absorbing voltage fluctuations to protect the control module.

5.5 Industrial Equipment and Power Circuits

In industrial settings, bipolar electrolytic capacitors are primarily used to buffer bidirectional voltage ripple and absorb surges, ensuring reliable equipment operation. Typical applications include:

– Small inverters and servo control systems: Ripple absorption, stabilizing output voltage;

– UPS power supplies: Bidirectional voltage buffering, ensuring power supply stability during power outages;

– Switching power supply ripple absorption: Filtering noise in the power output, improving power quality.

5.6 Lighting and Security Systems

In lighting and security equipment, bipolar electrolytic capacitors are used to ensure stable signal transmission and suppress DC offset. Typical applications include:

– LED driver circuits and fluorescent lamp ballasts: DC blocking and coupling, protecting light sources from DC damage;

– Surveillance cameras and audio monitoring systems: Stabilizing audio/video signals, improving monitoring effectiveness.

6. Disadvantages of Bipolar Electrolytic Capacitors

While bipolar electrolytic capacitors (BECs) offer significant advantages in low-to-medium frequency and cost-sensitive applications, as a branch of the electrolytic capacitor family, they still possess structural and performance limitations. These shortcomings are determined by their internal “two capacitors in reverse series” structure and electrolyte characteristics, and must be carefully avoided in high-frequency, high-voltage, and long-life precision applications.

6.1 Higher Equivalent Series Resistance (ESR)

The ESR (Equivalent Series Resistance) of bipolar electrolytic capacitors is significantly higher than that of film capacitors of the same capacitance, which is their core performance weakness.

Causes: They contain two electrolytic cores connected in series, and the electrolyte’s limited conductivity leads to a higher overall series resistance.

Specific Impacts:

– Increased Heat Generation: During circuit operation, ripple current generates power loss across the ESR (P=I²×ESR), causing the capacitor to heat up. Prolonged high temperatures accelerate its aging.

– Reduced High-Frequency Efficiency: In high-frequency signal transmission, a higher ESR results in voltage loss, weakening filtering or coupling effects.

– Signal Loss: In applications sensitive to signal purity, such as audio, excessively high ESR can introduce slight distortion, affecting sound quality details.

6.2 Limited Rated Voltage

Bipolar electrolytic capacitors have a relatively narrow and generally low rated voltage range, making them unsuitable for high-voltage applications.

Typical Range: Only covers 6.3V – 100V, with mainstream specifications concentrated in the low-to-medium voltage range (10V-50V).

Application Limitations: Completely unsuitable for high-voltage applications such as direct filtering of 220V AC mains or industrial high-voltage drives. Forced use in high-voltage circuits will immediately cause capacitor breakdown, bulging, or even explosion, posing serious safety hazards.

6.3 Poor High-Frequency Performance

Due to limitations in internal structure and material properties, bipolar electrolytic capacitors exhibit extremely poor high-frequency performance, making them completely unsuitable for high-frequency applications.

Core Reason:

– High Parasitic Inductance: The dual-capacitor series structure and lead layout introduce greater parasitic inductance, creating an “LC resonance” limitation that leads to a sharp decline in high-frequency performance.

– ESR Increases with Frequency: At high frequencies (typically exceeding 100kHz), ESR increases significantly, further weakening the filtering effect.

Application Contraindications: Strictly prohibited for use in radio frequency (RF) circuits, high-frequency switching power supplies, ultra-high-speed signal processing, and other similar applications. For these applications, ceramic or film capacitors with excellent high-frequency performance should be prioritized.

6.4 Larger Physical Size

Due to the integration of two independent electrolytic capacitor cores in series packaging, bipolar electrolytic capacitors are significantly larger than single-polar (polarized) electrolytic capacitors of the same capacitance and voltage rating.

Specific Performance: Under the same package specifications, bipolar electrolytic capacitors typically have a smaller capacitance; to achieve the same capacitance, their volume will be 30%-100% larger than that of single-polar electrolytic capacitors.

Application Limitations: In space-constrained PCB designs (such as small consumer electronics and high-density circuit boards), bipolar electrolytic capacitors occupy more layout space, potentially limiting circuit integration.

6.5 Limited Lifespan

Like all liquid electrolyte electrolytic capacitors, the lifespan of bipolar electrolytic capacitors is strictly limited by environmental and operating conditions, making long-term stable operation impossible.

Key Influencing Factors:

– Temperature: High temperatures are lifespan killers. For every 10°C exceeding the rated maximum operating temperature, the lifespan is typically halved (following the “10°C halving rule”).

– Ripple Current: Prolonged exposure to excessive ripple current causes the electrolyte to heat up and evaporate, accelerating capacitor performance degradation.

– Natural Aging: Over time, the liquid electrolyte gradually dries out and deteriorates, leading to decreased capacitance, increased ESR, and ultimately, loss of function.

Scenario Limitations: Unsuitable for scenarios with extremely high lifespan requirements (such as server power supplies and long-running industrial equipment). For these scenarios, longer-lifespan solid-state or film capacitors should be selected.

7. How to Select Bipolar Electrolytic Capacitors

Correct selection is crucial for ensuring reliable circuit operation and extending equipment lifespan. The selection of bipolar electrolytic capacitors should revolve around four core dimensions: voltage, capacitance, frequency, and packaging, following these principles:

7.1 Rated Voltage Selection

Core Principle: The rated voltage of the selected bipolar electrolytic capacitor should be ≥ 1.5~2 times the actual operating voltage.

Example: If the actual operating voltage of the circuit is 12V, it is recommended to select a bipolar electrolytic capacitor with a rated voltage of 25V or 35V to handle voltage spikes during circuit startup and prevent capacitor breakdown.

7.2 Capacitance Value Selection

The required capacitance value must be accurately calculated based on the circuit design requirements to avoid the capacitor being too large or too small, which would affect circuit performance. Common capacitance values ​​for bipolar electrolytic capacitors include: 4.7µF, 10µF, 47µF, 100µF, 220µF, and 470µF.

Note: For applications with high signal performance requirements, such as audio circuits, products with smaller tolerances (e.g., ±10%) should be selected to ensure stable sound quality or signal transmission.

7.3 ESR and Frequency Characteristics Considerations

Bipolar electrolytic capacitors have a higher equivalent series resistance (ESR) than film capacitors and moderate frequency characteristics. For high-frequency applications (such as high-frequency filtering and precision signal processing), bipolar electrolytic capacitors are not recommended as a first choice; film capacitors, which offer better performance, should be considered instead. For mid-to-low frequency applications (such as audio and motor starting), bipolar electrolytic capacitors are a cost-effective option.

7.4 Package and Size Selection

Common package types for bipolar electrolytic capacitors include radial leads and snap-fit ​​types; surface mount (SMD) is relatively less common. When selecting a product, the PCB space and assembly method should be considered to choose a product with a suitable size. This avoids situations where the package is too large to install or too small, affecting heat dissipation and stability.

8. Summary

The core competitiveness of bipolar electrolytic capacitors lies in their perfect integration of three major advantages: large capacitance, non-polarity, and low cost, effectively filling the market gap between polarized electrolytic capacitors and film capacitors.

With its unique internal structure, it can stably handle AC signals or bidirectional voltages, and is widely used in audio circuits, motor control, home appliances, automotive electronics, industrial equipment, lighting and security, and many other fields, becoming the preferred device for various cost-sensitive applications requiring large-capacity non-polar capacitors.

FAQ

Q1: What is the difference between bipolar and unipolar electrolytic capacitors?

A1: The core difference lies in polarity restrictions and applicable voltage types. Unipolar (polarized) electrolytic capacitors must be connected with the correct polarity and can only be used in DC circuits; bipolar electrolytic capacitors have no polarity restrictions, can be connected bidirectionally, and can handle AC signals or bidirectional voltage circuits without being damaged by reverse polarity connection.

Q2: Can bipolar electrolytic capacitors be used in AC circuits?

A2: Yes. The internal structure of a bipolar electrolytic capacitor (two polarized capacitors connected in reverse series) is specifically designed for AC or bidirectional voltage circuits. This is the core difference between it and a standard polarized electrolytic capacitor—standard polarized electrolytic capacitors are prohibited from use in AC circuits, otherwise they will break down and be damaged.

Q3: Why are bipolar capacitors used in speaker crossovers?

A3: Because the driving signal of a speaker is an AC audio signal, bipolar capacitors, with their non-polarity and large capacitance, allow the AC audio signal to pass through smoothly while effectively blocking DC components, preventing DC signals from flowing into the speaker and causing damage. This balances sound quality and cost.

Q4: Are bipolar capacitors better than film capacitors?

A4: Not necessarily. Both have their advantages and disadvantages, and the choice depends on the application. Film capacitors have advantages in high-frequency performance, accuracy, and stability, making them suitable for high-frequency and precision circuits. However, bipolar electrolytic capacitors can provide larger capacitance at a lower cost, making them suitable for mid-to-low frequency applications, cost-sensitive applications, and applications requiring large-capacity non-polar capacitors (such as audio equipment and motor starting).

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From the 1870s to the present, the development of super capacitors has gone through many important processes: In the late 1950s, some scientists proposed replacing double-layer electrochemical capacitors made of metal sheets with capacitors made of porous carbon materials, and It has been proven by practice. In other words, electrochemical capacitors have made rapid progress at this time. The world’s first commercial super capacitor came out in 1971, which marked that super capacitors have begun to enter the market operation stage; in the 1980s, In the 1990s, due to the introduction of pseudocapacitive electrode materials, the energy density of super capacitors has been greatly improved, reaching a farad level that has never been reached before. Only then did the so-called electrochemical capacitors be called true super capacitors. Name; In the 1990s, the development prospects of super capacitors were valued by Western developed countries, and they have proposed major projects related to it.

In 1879, Helmholz discovered the properties of double-layer capacitance and proposed the concept of electric double layer. However, the use of double-layer super capacitors for energy storage has only been in recent decades. In 1957, Becker (General Electric Co.. GE) proposed using capacitors with a specific capacity close to the battery as energy storage components. In 1968, Sohio (The Standard Oil Company) used high specific surface area carbon materials to produce electric double layer capacitors. In 1978, Japan’s Osaka Company produced gold capacitors, which were the earliest commercialized and mass-produced carbon electric double layer capacitors. In 1979, Nippon Electric Company, Limited began producing supercapacitors and used them in starting systems for electric vehicles. In 1980, Japan’s Panasonic Corporation studied super capacitors using activated carbon as electrode material and organic solution as electrolyte. After this, super capacitors began to be industrialized on a large scale.

1. Advantages of super capacitors

(1) High capacitance: The capacity of supercapacitors can reach up to several thousand farads, which is thousands of times higher than the capacity of platinum electrolytic capacitors and aluminum electrolytic capacitors of the same volume.

(2) Long cycle life: The charging and discharging process of supercapacitor is divided into two types according to its energy storage mechanism: one is the physical process of electric double layer, that is, there is only the transfer of ions or charges during the charging and discharging process, and no chemical or electrochemical reaction occurs. Another situation that triggers electrode phase change is the electrochemical reaction process. This reaction process has good reversibility and is not prone to phenomena such as crystalline transformation and shedding of active materials that affect the service life. All in all, no matter which of the above processes occurs, the capacitance of the supercapacitor decreases very little, and the number of cycles can reach tens of thousands of times, which is 5 to 20 times the number of cycles of the battery.

(3) Short charging time: Supercapacitors use high current to charge and can be quickly charged in a few seconds to minutes, while batteries require dozens of minutes to charge quickly, and frequent rapid charging will also affect the service life.

(4) High power density and high energy density: While supercapacitors provide a power density of 1000~2000W/kg, they can also output an energy density of 1~10Wh/kg. For this reason, supercapacitors are suitable for applications where short-term high power output is required. The mixed use of supercapacitors and battery systems can form a system with both high power density and high energy density.
energy storage system.

(5) Wide operating temperature range: The operating temperature range of supercapacitors is -40~70°C, while the operating temperature range of general batteries is between -10~50C. (6) Reliable operation, maintenance-free and environmentally friendly: Supercapacitors have a certain ability to resist overcharge and will not have much impact on their work in a short period of time, ensuring the reliability of system operation.

2. Disadvantages of super capacitors

(1) Low monomer working voltage: The working voltage of aqueous electrolyte supercapacitor monomer is generally 0~1.0V. The high output voltage of supercapacitors is achieved by connecting multiple single capacitors in series, and the series capacitors are required to have good consistency. The working voltage of a non-aqueous electrolyte supercapacitor monomer can reach 3.5V, but in actual use the maximum is only 3.0V. At the same time, the purity of non-aqueous electrolytes is high, and it needs to be produced in an assembly environment such as anhydrous and vacuum conditions.

(2) Possible leakage: Although the materials used in supercapacitors are safe and harmless, if the installation location is unreasonable, electrolyte leakage may still occur, affecting the normal performance of the supercapacitor.

(3) Supercapacitors are generally used under DC conditions and are not suitable for use in AC situations.

(4) Higher price: The cost of supercapacitors is much higher than that of ordinary capacitors

Supercapacitors are a new type of energy storage device between traditional capacitors and batteries, with capacities ranging from hundreds to thousands of farads. Compared with traditional capacitors, it has larger capacity, higher energy, wider operating temperature range and extremely long service life; compared with batteries, it has higher power density and no pollution to the environment. . Therefore, supercapacitor is an efficient, practical and environmentally friendly energy storage device. The performance comparison of several energy storage devices is shown in Table 1-2.

Table 1-2 Performance comparison of several energy storage devices

Currently, the indicators used to describe the performance of supercapacitors are:

1) Rated capacity: refers to charging to the rated voltage according to the specified constant current (for example, the charging current specified for super capacitors above 1000F is 100A, and those below 200F is 3A) for 2~3 minutes, and then discharged under the specified constant current discharge conditions. The product of the time until the terminal voltage is zero and the current is divided by the rated voltage value, in farads (F).

2) Rated voltage: the highest safe terminal voltage that can be used. Breakdown voltage, its value is much higher than the rated voltage, about 1.5 to 3 times the rated voltage, the unit is volts (V) 3) Rated current: refers to the current discharged to half of the rated voltage within 5 seconds, the unit is Ampere A)

4) Maximum stored energy: refers to the energy released when discharging to zero at rated voltage, the unit is Joule (J) or Watt-hour (Wh).

5) Energy density: also called specific energy. Refers to the energy given by the capacitor per unit mass or unit volume, in Wh/kg or w·h/L.

6) Power density: also called specific power. It refers to the discharge power of a super capacitor per unit mass or unit volume when it produces half and half electrical/heating effects under matching loads. It represents the ability of the super capacitor to withstand current, and the unit is kw/kg or kW/L.

7) Equivalent Series Resistance (ESR): Its value is related to supercapacitor electrolyte and electrode materials, preparation process and other factors. Generally, AC ESR is smaller than DC ESR and decreases as the temperature rises. Units are ohms (Q).

8) Leakage current: refers to the static loss caused by the internal equivalent parallel impedance when the supercapacitor maintains a static energy storage state. It is usually the current measured after applying the rated voltage for 72 hours, and the unit is Ampere (A).

9) Service life: refers to the length of time when the capacitance of the super capacitor is less than 20% of the rated capacity or the ESR increases to 1.5 times the rated value.

10) Cycle life: A super capacitor experiences one charge and discharge, which is called one cycle or one cycle. The cycle life of supercapacitors is very long, up to more than 100,000 times.

In the development of supercapacitors, the current focus is on liquid electrolyte electric double layer capacitors and composite electrode material/conductive polymer electrochemical super capacitors. The development of foreign supercapacitors is shown in Table 1-3.

Table 1-3 Development of supercapacitors abroad

In terms of the industrialization of super capacitors, the earliest products were products from NEC and TOKIN in 1980 and Panasonic and Mitsubishi in 1987. The nominal voltage of these capacitors is 2.3~6V, with an annual output of millions. In the 1990s, Russian ECOND Company and ELIT produced SC brand electrochemical capacitors with nominal voltages from 12 to 450V and capacitances from 1F to several hundred F, which are suitable for occasions requiring high-power starting power. In general, products from the United States, Japan, and Russia currently occupy almost the entire super capacitor market, and industrialized super capacitors are basically electric double layer capacitors. Some performance parameters of some electric double layer supercapacitor products are listed in Table 1-4.

Table 1-4 Some performance parameters of electric double layer super capacitor products

In my country, Beijing Nonferrous Metal Research Institute, Jinzhou Power Capacitor Co., Ltd., University of Science and Technology Beijing, Beijing University of Chemical Technology, Beijing Institute of Technology, Beijing Jinzhengping Technology Co., Ltd., Army Chemical Defense College, Harbin Jurong New Energy Co., Ltd., Shanghai Ao Wei Technology Development Co., Ltd. and others are conducting research on super capacitors. In 2005, the 863 project “Research on Key Technologies of Supercapacitor Energy Storage Systems for Renewable Energy Power Generation” undertaken by the Institute of Electrical Engineering of the Chinese Academy of Sciences passed expert acceptance. This project completed the research and development of a 300W·h/kW super capacitor energy storage system for photovoltaic power generation systems. In addition, relevant research groups such as North China Electric Power University are studying the application of supercapacitor energy storage system (Super capacitor Energy Storge System, SESS) to the distribution network of distributed power generation systems. But overall, my country’s research and application level in the field of supercapacitors clearly lags behind the world’s advanced level.

When using supercapacitors, you should pay attention to the following issues: 1. Supercapacitors have fixed polarity, and the polarity should be confirmed before use; 2. Super capacitors should be used at nominal voltage because when the capacitor voltage exceeds the nominal voltage It will cause the electrolyte to decompose, and the capacitor will heat up, reduce the capacity, and increase the internal resistance, shortening its life; 3. Due to the existence of ESR, supercapacitors cannot be used in high-frequency charging and discharging circuits: when using supercapacitors in series When there is a voltage balance problem between cells, simple series connection will cause one or several cell capacitors to be damaged due to overvoltage, thus affecting their overall performance.

With the development of power systems, distributed power generation technology has attracted more and more attention. As a necessary energy buffer link in distributed power generation systems, energy storage systems play an increasingly important role. The supercapacitor energy storage system uses multiple groups of supercapacitors to store energy in the form of electric field energy. When energy is urgently lacking or needed, the stored energy is released through the control unit to accurately and quickly compensate for the active and reactive power required by the system. work, thereby achieving balance and stable control of electrical energy. In 2005, a 450kW supercapacitor energy storage device was built in California, USA, to reduce fluctuations in the power delivered by a 950kW wind turbine to the grid. In addition, energy storage systems can also play an important role in improving the power quality of power system distribution networks. Through the inverter control unit, the reactive power and active power provided by the supercapacitor energy storage system to users and the network can be adjusted to achieve the purpose of improving power quality.

In the 35kV substations and 10kV switch stations built in my country from the 1960s to the 1980s, the operating mechanisms of most high-voltage switches (circuit breakers) are electromagnetic operating mechanisms. The corresponding DC system is equipped in the power distribution room of the substation or distribution station, which is used as the DC power supply for opening and closing operation, control and protection. These DC power equipment are mainly capacitor energy storage silicon rectifier opening and closing devices and DC panels partially composed of batteries. Capacitor energy storage silicon rectifier opening and closing devices were widely used at that time due to their simple structure, low cost, and low maintenance. However, there was a fatal flaw in actual use: poor reliability of accident opening and closing. The reason is that the capacity of electrolytic capacitors for energy storage is limited and the leakage current is large. Although DC panels composed of batteries can store a large amount of electrical energy and have become necessary devices in some important transformation and distribution stations, due to their extremely high operating costs and short service life, these devices can only be used at the 110kV level. It is difficult to promote the use of substations.

Supercapacitors make it possible to solve the above problems with their ultra-long service life, frequent and fast charge and discharge characteristics, and cheap price. If two 0.85F, 240/280V supercapacitors are connected in parallel, they can completely replace the bulky, frequent maintenance, and polluting battery pack. Since the energy consumption of one closing is only equivalent to 3% of the energy stored in the supercapacitor (70kJ), and this energy can be quickly replenished in the floating charge circuit, it is fully adaptable to continuous and frequent operations, and has extremely high High reliability.

Although many users choose Uninterrupted Power Supply (UPS) as a rescue device for equipment power supply when the grid is out of power or the grid voltage drops instantaneously, UPS is overqualified for instantaneous voltage drops. UPS is powered by batteries and has a long working time. However, due to the shortcomings of the battery itself (requires regular maintenance, short life), the UPS needs to always pay attention to the status of the battery during operation. The duration of power system voltage drops is often very short (10ms ~ 60s), so the advantage of using supercapacitors in this case is obvious over UPS: its output current can rise to hundreds of amps with almost no delay, and the charging speed is very fast It is fast and can store energy within minutes to facilitate the next power failure. Therefore, although the energy storage of the supercapacitor can be maintained for a short time, when it is used for about 1 minute, it has incomparable advantages – 500,000 cycles, no care required, and economical. In Singapore, a dynamic voltage recovery device (DVR) produced by ABB that uses supercapacitor energy storage is installed in a 4MW semiconductor factory to achieve 160ms fault ride-through.

The static synchronous compensator (STATCOM) is one of the main devices of Flexible AC Transmission Technology (FACTS) and represents the new development direction of reactive power compensation technology in the power system at this stage. It can quickly and continuously provide capacitive and inductive reactive power, achieve appropriate voltage and reactive power control, and ensure stable, efficient and high-quality operation of the power system. STATCOM based on double-layer capacitor energy storage can be used to improve the voltage quality of distributed power generation systems. It will gradually replace traditional superconducting energy storage in distributed power generation systems with power levels of 300~500kW. In terms of economics, the cost of an electric double layer capacitor energy storage device of the same capacity is almost the same as that of a superconducting energy storage device, but the former requires almost no operating costs, while the latter requires considerable cooling costs.
For supercapacitors, the direction and focus of future research is: utilizing the high specific power characteristics and rapid discharge characteristics of super capacitors to further optimize the application of supercapacitors in power systems. In addition, under the guidance of my country’s policy of vigorously developing new energy, in the fields of photovoltaic power generation and wind power generation, super capacitors provide favorable conditions for the improvement and development of key equipment with their fast charging and fast discharging characteristics.

1.2 Classification of super capacitors

As a new green energy storage component, supercapacitor has broad application prospects in electric vehicles, distributed power generation systems and other fields. Supercapacitors can be divided into three categories: electric double layer supercapacitors, pseudocapacitors and hybrid supercapacitors according to different energy storage principles.

1. Electric double layer super capacitors

Electric double layer supercapacitors use the interface double layer formed between electrodes and electrolytes to store energy. Electric double layer supercapacitors have made changes in manufacturing materials, such as: activated carbon electrode materials, which are processed with high specific surface area activated carbon materials to make electrodes, carbon airgel electrode materials, which are combined with precursor materials to prepare gels, and then carbonized Activation treatment serves as an electrode. When the electrode and the electrolyte come into contact, due to the action of Coulomb force, intermolecular force or interatomic force, a stable double layer of charges with opposite signs appears at the solid and liquid interface, which is called the interface double electric layer.

2. Pseudocapacitance

Pseudocapacitance, also known as Faraday quasicapacitance in general, refers to the capacitance on the electrode surface or body.
On the two-dimensional or quasi-two-dimensional space in the phase, the active material undergoes under-potential deposition and highly reversible chemical adsorption/desorption or oxidation/reduction reactions occur, thereby generating Faradaic capacitance. Pseudocapacitive super capacitors generally use metal oxide electrode materials and polymer electrode materials. They can be divided into adsorption eagle capacitors and redox eagle capacitors.

3. Hybrid super capacitors

Hybrid super capacitors can be divided into the following 3 types (based on different types of electrode materials):
1) It consists of an electrode with both electric double layer capacitance characteristics and an electrode with pseudocapacitance characteristics, or is composed of two different types of pseudocapacitance electrode materials.

2) Composed of super capacitor electrodes and battery electrodes

3) It consists of the anode of the electrolytic capacitor and the cathode of the super capacitor. The two poles of hybrid supercapacitors generally use “battery-type” materials with high energy density as active materials and “capacitor-type” materials with high power density, so they have the advantages of both.

1.3 Application prospects of super capacitors

Supercapacitors are also called electrochemical capacitors. They have stable performance, specific capacity is 20 to 200 times that of traditional capacitors, and specific power is generally greater than 1000W/kg. The cycle life and storable energy are much higher than traditional capacitors, and they charge quickly. Due to their extremely long service life, they can be used throughout the entire life cycle of the end product. When high-energy batteries and fuel cells are combined with supercapacitor technology, high power density, high energy density characteristics and long operating life can be achieved.

In recent years, high-power supercapacitors have shown a rising industry trend in the fields of electric vehicles, solar energy devices, heavy machinery and other fields. Many developed countries have regarded supercapacitor projects as national key research and development projects. The domestic and foreign markets of supercapacitors are showing a trend. Unprecedented prosperity.

The application of supercapacitors has become increasingly mature and has been widely used in fields such as industry, communications, medical equipment, military equipment, and transportation [4]. From small-capacity emergency energy storage to large-scale power energy storage, from independent energy storage to hybrid energy storage systems with batteries or fuel cells, supercapacitors have shown unique advantages. To sum up, the application directions of supercapacitors can be divided into the following four fields:

1. Main power supply, replacement power supply or backup power supply for low-power electronic equipment

1) Main power supply: Supercapacitors are suitable for use in main power supplies. Typical applications include electric toys, which have the advantages of being small in size, light in weight, high in power density and able to start quickly as the main power supply.

2) Replacement power supply: Supercapacitors are also suitable for use in replacement power supplies. Typical applications include road signs, solar watches, traffic lights and bus stop timetable lights.

3) Backup power supply: Supercapacitors are widely used in backup power supplies. Typical applications include vehicle meters, vehicle fare meters, radio wave receivers and cameras, etc.

2. Hybrid electric vehicles and electric vehicles

The lifespan of supercapacitors is hundreds of times that of electrochemical batteries (storage batteries and potassium-ion batteries, etc.) and does not require maintenance. Therefore, the total cost of supercapacitors applied to electric vehicles is much lower than that of general electrochemical batteries. Currently, countries all over the world are investing the most in developing electric vehicles, of which hybrid electric vehicles (Hybrid Electric Vehicles) are the ones that invest the most. Hybrid electric vehicles use batteries to provide normal operating power for electric vehicles. Supercapacitors are used to supplement power when accelerating and climbing, and ultracapacitors are used to store regenerative energy generated during braking. Therefore, electric vehicles using supercapacitors have the advantages of fast starting, fast acceleration and strong climbing ability.

3.Renewable energy power generation systems and distributed power systems

Supercapacitors can give full play to the advantages of high energy storage density, high power density, long cycle life and no need for maintenance. They can store energy alone or be mixed with other energy storage systems to store energy. Supercapacitors can be combined with solar cells and used in street lights, traffic warning signs, traffic lights, etc. They can also be used in distributed power generation systems, such as wind power stations, hydropower stations, etc. Energy storage through supercapacitors can improve the system. It plays the role of instant power compensation to improve the stability and reliability of the power supply system. This power supply method can well compensate for the unstable and unpredictable output power of power generation equipment.

4. Energy buffer

The energy buffer consists of a supercapacitor and a power converter. It is mainly used in variable frequency drive systems such as elevators. When the elevator accelerates up, the energy buffer supplies power to the DC bus in the drive system to provide the peak power required by the motor. When the elevator decelerates and descends, the energy buffer absorbs the energy fed back by the motor.

Supercapacitors can replace batteries in portable instruments such as driving micromotors, relays, and solenoid valves. It can avoid misoperation due to instantaneous load changes. Supercapacitors can also be used to power camera flashes, allowing the flash to achieve continuous use performance, thereby improving the camera’s ability to continuously shoot. It is applied to camera phones, allowing camera phones to use high-power LEDs. Supercapacitor technology can also be used in mobile wireless communications equipment. These devices often use pulses to maintain communication. Because supercapacitors have strong instantaneous charge and discharge capabilities and can provide high power, they have a wide range of applications in this field. Supercapacitors are almost irreplaceable components in important power systems of many large petrochemical, electronic, textile and other enterprises, especially in transient voltage and current stabilization of high-power systems. In addition, it is also very important for chip companies to consider power fluctuations when selecting sites, and supercapacitor systems can completely solve this problem.

Supercapacitors also play an irreplaceable role in short-term UPS systems, electromagnetic operating mechanism power supplies, solar power car anti-theft, car audio and other systems. In wind power or solar power systems, due to the instability of wind and solar energy, the battery will be repeatedly charged frequently, resulting in shortened life. Supercapacitors can absorb or supplement the fluctuations in electrical energy to solve this problem. Supercapacitors also have huge application value and market potential in electric vehicles, hybrid fuel vehicles and special load-carrying vehicles. As a power source for electric and hybrid vehicles, supercapacitors can be used alone or in combination with batteries. In this way, when the supercapacitor is used as a short-term drive power supply for electric vehicles, it can quickly provide a large current when the vehicle starts and climbs a hill to obtain power to provide powerful power; it can be quickly charged by the battery during normal driving; and it can be quickly charged by the battery during braking. Quickly store the large warm-time current generated by the generator, thereby reducing the restrictions on high-current discharge of the battery by electric vehicles, extending the cycle life of the battery, and improving the practicality of electric vehicles. The application of supercapacitors in the electric moped market is also expanding. The battery on an electric moped has strict charging and discharging current requirements, making it difficult to recover energy instantaneously. Supercapacitors can easily meet these requirements. The supercapacitor supplements the energy of the system when the electric moped is starting, accelerating and climbing, and completely recovers energy during braking to improve system performance.

As one of the key new energy storage products developed in the 21st century, super capacitors are being developed and produced by more and more countries and companies, and their rapid progress is obvious to all. At the 1st International Annual Conference on Electric Double Layer Capacitors and Hybrid Energy Storage held in 1991, the large single capacitor was a capacitor with a capacity of 470F designed and developed by Panasonic, and its voltage was 2.3V. Today, the capacity of single capacitors of the same size produced by Panasonic has exceeded 2000F. At the same time, not only Panasonic, but many companies around the world have begun to enter this field. These companies are mainly engaged in the development of large-scale manufacturing technology and marketing so that capacitor products can be used with portable electronic equipment and pulse power appliances on the market. It can be said that today’s super capacitor market has entered an era of competition: Maxwell’s company in San Diego is the leading manufacturer of large-scale electrochemical capacitors in the United States; PowerStor was developed from the carbon aerogel technology of Lawrence Livermore’s laboratory , and is now quite large-scale; South Korea’s Ness Company has been interested in small energy storage devices since the beginning. Its products have spread throughout the market, from small ones to the largest ones, and have now developed into a company. The company that leads the way in the pulse power performance of electrochemical capacitors; the products of Germany’s Siemens Matsushita also greatly surpass all its previous products. It is a subsidiary of Maxwell and later became EPCOS; recently, as one of the important members of the world’s electrolytic capacitor industry One Japanese chemical company has now officially joined the super capacitor industry-Power System Company founded by Mr. Okamura now has a production line of large-scale products; certain products of Russia’s ECOND Company, ELIT Company and ESMA Company It is also a force that cannot be underestimated in the super capacitor team. Among them, Russia’s ESMA company is the representative of the production of inorganic hybrid super capacitors. In recent years, some companies in our country have also begun to actively get involved in this industry, and have already possessed certain technical strength and industrialization capabilities. Important companies include Jinzhou Fu Company, Beijing Jixing Company, Beijing Hezhong Huineng, Shanghai Aowei Company, Jinzhou Jinrong Company, Shijiazhuang Gaoda Company.

Beijing Jinzhengping Company, Jinzhou Kaimei Company, Daqing Zhenfu Technology, Harbin Jurong Company, Nanjing Jihua Company, Xinzhoubang Company, etc. Among them, Xinzhoubang Company has now become a qualified supplier of the world’s mainstream super capacitor manufacturers, such as the American Maxwell Company, REDI Company and other upstream manufacturers, and has gradually realized batch supply; domestic customers mainly include Beijing Jixing and Beijing Hezhonghui Neng, Jinzhou Kaimei and other companies. Since 2009, the company’s customers and orders have continued to increase, and it is expected to become one of the main suppliers to the world’s mainstream super capacitor manufacturers.

With the application of super capacitors in electric vehicles in recent years, their market has become increasingly broad. The current automotive power battery market is mainly composed of the following four parts: lead-acid batteries are currently mostly used in electric bicycles; metal oxide nickel batteries are expensive and have short driving distance and have no prospects in electric vehicles; potassium iron phosphate batteries are relatively expensive and It has been used in electric vehicles and can travel 100~120km on a single charge. It needs to start the hybrid power of the gasoline engine to extend the mileage; super capacitor power battery is cheap, maintenance-free and has a charge-discharge cycle life of 100,000~500,000 times, maybe Power batteries will soon become the mainstream. Compared with metal oxide nickel batteries/potassium iron phosphate power batteries, super capacitors made of high-purity barium titanate have the advantages of high energy density, high power utilization, safety, and low price. The U.S. Department of Energy first issued a statement in the “Business Daily” in the 1990s, strongly recommending the development of capacitor technology and its application in electric vehicles. At the time, California had enacted a near-term plan for zero-emission vehicles, and these electric vehicles using capacitors were generally considered to be cars that just met that standard. Capacitors are the most potential and most effective technology for realizing the practical use of electric vehicles. The DOE’s announcement has prompted companies such as Maxwell Technologies to enter the field of electrochemical capacitor technology. Fast forward to 2016, and advances in technology have paved the way for the use of electrochemical capacitors to recover regenerative braking energy in hybrid vehicles. These hybrids are now being used in highly hybrid city bus systems.

The electric vehicles of Japan’s Fuji Heavy Industries use a combination device of potassium-ion batteries produced by Hitachi Electric Corporation and energy storage capacitors produced by Panasonic Corporation: Japan’s Honda Corporation has even combined super capacitors with gasoline engines to develop a comprehensive motor booster The system greatly reduces the emissions of the internal combustion engine and can recycle braking energy. By being installed on the passenger car, it greatly reduces the fuel consumption of the gasoline engine and makes it a low-emission energy-saving vehicle: the hybrid electric vehicle developed by Japan’s Toyota Company, whose emissions Compared with traditional gasoline locomotives: CO is reduced by 50%, CO and NO are reduced by 90%, and fuel is saved by half.

In my country, with the official introduction of financial subsidy policies for private purchases of new energy vehicles, market participants pointed out that this will become an opportunity for the further development of super capacitors. In the field of new energy vehicles, super capacitors are usually used in combination with carp-ion batteries. The perfect combination of the two forms a power source with stable performance, energy saving and environmental protection, which can be used in hybrid vehicles and pure electric vehicles. Potassium-ion batteries solve the problem of car charging and energy storage and provide long-lasting power for the car. The mission of the super capacitor is to provide high-power auxiliary power for starting and accelerating the car, and to collect and store energy when the car is braking or running rapidly. Among domestic manufacturers involved in new energy vehicles, many have chosen the technical route of combining super capacitors with potassium-ion batteries. For example, Ankai Bus’ pure electric buses and Haima parallel pure electric sedan MPe use potassium-ion battery/super capacitor power systems. In addition, the technology developed by Shanghai Aowei Technology Development Co., Ltd. to modify ordinary activated carbon into high-purity activated carbon through high technology and make new electrical storage materials for use in super capacitors has been industrialized. The super capacitors they produce are beginning to be used in new energy vehicles.

In the face of ever-expanding market demand, the super capacitor industry is still in its infancy. Existing supercapacitor products still have imperfections. It is necessary to look for new technology solutions that can serve the insufficient functions of existing products, improve product performance, reduce product prices, and broaden product offerings. Application in new fields and strengthening its cooperation with power batteries are the future development trend and direction of super capacitors. In particular, its application in the field of new energy vehicles determines its strategic value and attracts a large amount of manpower and material resources around the world for research and development Some companies in the United States, Japan and other countries are currently in a leading position in the industrialization of super capacitors with their years of development experience and technology accumulation. With the in-depth adjustment of my country’s economic structure, I believe we will eventually discover its value and will successively introduce strong industrial support policies to promote the development of the upstream and downstream industrial chains of this strategic product.

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The application of AC capacitor in air conditioning is very important.It is one of the core components of the air conditioning system. It is usually used as the starting and running capacitor of the compressor motor and the fan motor, and plays an important role in the starting and operation of the compressor and the fan motor. Once the capacitor fails, the air conditioner will not work properly. Therefore, whether the AC motor capacitor is reliable and whether the selection is reasonable directly affects the performance and safety of the air conditioner. In the development and design of the air conditioner, we must pay attention to the reasonable selection of capacitors, and special attention should be paid to the requirements for explosion protection.

2 The Application of AC capacitor in air conditioners

AC capacitors are usually used as the starting and running capacitors of compressor motors and fan motors, and play an important role in the starting and operation of compressors and fan motors. For air conditioner compressor motors and fan motors, single-phase capacitor-operated asynchronous motors are the most commonly used. When a single-phase asynchronous motor works, it does not have only one phase winding, because one winding cannot generate a rotating magnetic field, and the motor cannot rotate. According to the conditions for the formation of the rotating magnetic field, it is necessary to try to make the motor generate a rotating magnetic field, so the motor must have two-phase windings, one phase is the main winding (working winding), and the other phase is the auxiliary winding (starting winding). Applying different phase currents to the two windings produces a rotating magnetic field. In order to generate different phase currents, it is realized by connecting AC capacitors in series in the secondary winding, as shown in Figure 1.

（Figure 1  Schematic diagram of single-phase capacitor run asynchronous motor）

The application of AC capacitors is crucial in air conditioning systems, as they play a vital role in the starting and running of compressors and motors. The role of the AC capacitor is to make the secondary winding loop impedance capacitive, so that the current of the secondary winding leads the power supply voltage.
Because the main winding is inductive, its current lags behind the power supply voltage, so the secondary winding current leads the main winding current by a 90° phase difference, that is, a phase-separated induction current is generated, and a rotating magnetic field is generated to start and keep the motor running.
The AC capacitor connected in series is the starting and running capacitor of the motor. From the above analysis, it can be seen that this capacitor is essential for the starting and running of the compressor and the motor, and plays an important role in the starting and running of the compressor and the fan.

 (Figure 2)

3 Introduction to CBB61 and CBB65 AC capacitors

The application of AC capacitor is evident in the specific types used in air conditioning systems. Air conditioner fan motors generally use CBB61 metallized polypropylene film AC motor capacitors (Figure 2 left); compressors generally use CBB65 metallized polypropylene film AC motor capacitors (Figure 2 right). This kind of capacitor is a non-polar capacitor with a negative temperature coefficient (that is, its capacity becomes smaller when the temperature rises) made of polypropylene film as the medium.

Advantages of metallized polypropylene film capacitors: wide capacity range, high insulation resistance, extremely wide operating voltage range, and wide operating temperature range. Can be metallized and has self-healing properties. Especially suitable for high frequency, high voltage, high stability, high pulse and AC occasions.

The capacity of CBB61 type fan capacitor is relatively small, and it is usually encapsulated into a sealed type with epoxy resin, a square plastic shell, the two electrodes are generally inserts (187 or 250), and welding leads are used as lead-outs.

The CBB65 type compressor capacitor has a relatively large capacity and is mainly used for starting and running a single-phase compressor. Its shape is generally designed as a cylinder, packaged with a metal shell, and filled with insulating oil inside for heat dissipation and sealing (anti-metal coating oxidation) , is a sealed structure. The two electrodes are generally welded by wires and 250 inserts are used as the lead-out ends. In addition, because of its large capacity, CBB65 series capacitors have an explosion-proof structure for safety reasons.

4 Safety and reliability requirements for AC capacitors used in air conditioners

The application of AC capacitor, such as CBB61 capacitor and CBB65 capacitor, is crucial in ensuring compliance with air conditioner safety standards.CBB61 and CBB65 AC capacitors are one of the key components of the air conditioner safety standards, and must meet the following requirements: (1) In the normal heating test, the surface temperature is required not to exceed the upper limit of the capacitor’s operating temperature, generally 70 ℃ . (2) In the abnormal test, capacitor opening and short circuit tests are required for compressor and fan capacitors, and the surface temperature during the test cannot exceed 150°C. (3) When the compressor and motor are at 1.1 times the rated voltage and rated frequency, the voltage across the capacitor during the start-up and operation of each gear should not exceed 1.1 times the rated voltage of the capacitor. (4) In terms of explosion-proof level, the new version of electrical safety standards has required that the application of fan capacitors must meet one or more of the following conditions:

——A capacitor with explosion-proof grade of P2/S2 or above is used;
——The capacitor is covered by a metal or ceramic case;
——The distance from the outer surface of the capacitor to the adjacent non-metallic parts should exceed 50mm;
——Adjacent non-metallic parts 50mm away from the outer surface of the capacitor can pass the needle flame test;
——Adjacent non-metallic parts 50mm away from the outer surface of the capacitor are at least V-1 level;

The above requirements mainly focus on the surface temperature and voltage of the capacitor, and the last one mainly examines the safety requirements of the capacitor and whether it is explosion-proof. The working temperature and voltage of the capacitor directly affect the service life and reliability of the capacitor. For the outdoor unit of the split type air conditioner, the capacitor is installed outdoors, and the operating environment is very harsh, with high temperature and high humidity in summer and low temperature and high humidity in winter, and is exposed to wind and sun all year round. Especially in the hot summer, the full-load running time of the air conditioner increases, and the running time of the compressor and the fan capacitor at high temperature also increases accordingly. Therefore, it is one of the important measures to improve the quality and safety of the air conditioner to select a capacitor that can maintain excellent electrical performance for a long time in a harsh environment, and will not explode or cause danger when it fails.

Conclusion

In conclusion, the application of AC capacitor in air conditioning systems is crucial for their proper functioning. AC capacitors serve as starting and running capacitors for compressor motors and fan motors, playing a vital role in initiating and maintaining motor operation. Capacitor selection should prioritize reliability, safety, and explosion-proof requirements to ensure optimal performance in the harsh environments faced by air conditioning units. By considering the specific application of AC capacitors in air conditioning, the overall quality and safety of these systems can be significantly improved.

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Capacitors play a crucial role in various electronic systems, offering storage and release of electrical energy. As diverse as their applications, capacitors come in various types and constructions. In this article, we will delve into the different types of capacitors and explore their applications in different industries and everyday life.

Types of Capacitors:

Ceramic Capacitors:

• Ceramic capacitors are constructed using a ceramic dielectric material with metal electrodes. They are widely used due to their small size, high capacitance values, and low cost. Ceramic capacitors find applications in decoupling, bypassing, timing circuits, and RF filtering.

Electrolytic Capacitors:

• Electrolytic capacitors consist of two conductive plates separated by an electrolyte-soaked paper. They offer high capacitance values and low equivalent series resistance (ESR). Electrolytic capacitors are commonly used in power supplies, audio amplifiers, motor circuits, and energy storage applications.

Film Capacitors:

• Film capacitors utilize a plastic film as the dielectric material between metal electrodes. They come in different types such as polyester, polypropylene, and polycarbonate capacitors. Film capacitors are employed in various applications, including coupling, filtering, motor start-up, and AC/DC circuits.

Tantalum Capacitors:

• Tantalum capacitors utilize tantalum pentoxide as the dielectric material. They offer high capacitance values, stability, and low leakage current. Tantalum capacitors find applications in portable electronics, telecommunications, and medical devices.

Supercapacitors:

• Supercapacitors, also known as ultracapacitors or electric double-layer capacitors (EDLCs), are a type of capacitor that stores and releases electrical energy. They have electrodes made of high-surface-area materials, such as activated carbon, and use an organic solvent or ionic liquid as the electrolyte. Supercapacitors offer high energy storage capacity, rapid charging and discharging, long cycle life, and good temperature performance.

Difference Between Types of Capacitors :

Each types of capacitors has its own unique construction, materials, capacitance values, and specific applications. Ceramic capacitors excel in compact designs and cost-effectiveness, while electrolytic capacitors offer high capacitance values. Film capacitors provide excellent frequency response, and tantalum capacitors offer stability and low leakage. Aluminum electrolytic capacitors provide high capacitance and voltage ratings. The choice of capacitor depends on factors such as size, cost, capacitance requirements, operating conditions, and desired performance characteristics.

Applications of Capacitor:

• Energy Storage: Capacitors store electrical energy and release it quickly when needed, making them suitable for applications such as flash cameras, power backup systems, and energy harvesting devices.
• Power Conditioning: Capacitors improve power quality by filtering out noise, reducing ripple in power supplies, and correcting power factor issues in electrical systems. They play a crucial role in power factor correction, motor starting, and smoothing voltage fluctuations.
• Timing and Oscillation: Capacitors, in conjunction with resistors, enable precise timing and oscillation in circuits such as timing circuits, oscillators, and RC filters. They are used in applications requiring accurate timekeeping or frequency generation.
• Signal Coupling and Filtering: Capacitors enable the coupling of signals between different stages of electronic circuits. They also act as filters, allowing certain frequencies to pass while blocking others. Capacitors are essential components in audio amplifiers, radio receivers, and telecommunications equipment.
• Motor Start-Up: Capacitors provide the initial high-current boost required to start electric motors efficiently. They help overcome the high inrush current during motor startup, ensuring smooth and reliable operation in various industrial and household appliances.

Applications in Daily Life and Electronics:

Capacitors are present in various everyday devices, highlighting their widespread applications in electronics. Here are a few examples:

• Air Conditioning Units: Capacitors are used in air conditioning systems for motor start-up. They provide the initial high-current boost required by the compressor to start efficiently.
• Audio Systems: Capacitors play a vital role in audio equipment, such as amplifiers and speakers. They are used for coupling signals between stages, filtering out unwanted frequencies, and ensuring accurate reproduction of sound.
• Television Sets: Capacitors are employed in television sets for power conditioning. They help smooth out fluctuations in the power supply, ensuring stable and high-quality performance.
• Electronic Appliances: Capacitors are used in various electronic appliances to improve performance and reduce electrical noise. They are essential for noise reduction, power factor correction, and stabilizing voltage levels.

The Most Commonly Used Capacitor:

The most commonly used capacitor in various electronic applications is the ceramic capacitor. Ceramic capacitors offer several advantages that make them widely preferred in the industry:

1. Small Size: Ceramic capacitors are available in compact sizes, allowing for efficient use of space on circuit boards, especially in compact electronic devices such as smartphones, tablets, and wearables.
2. High Capacitance Values: Ceramic capacitors offer a wide range of capacitance values, from picofarads (pF) to microfarads (µF), making them suitable for various applications that require different capacitance levels.
3. Low Cost: Ceramic capacitors are cost-effective compared to other capacitor types, making them a popular choice for mass-produced electronic devices.
4. High Voltage Ratings: Ceramic capacitors can handle high voltage levels, allowing for their use in applications that require voltage regulation and filtering, such as power supply circuits.
5. Wide Temperature Range: Ceramic capacitors exhibit stable performance over a wide temperature range, ensuring their reliability in diverse environmental conditions.
6. Excellent High-Frequency Performance: Ceramic capacitors have low equivalent series resistance (ESR) and equivalent series inductance (ESL), making them suitable for high-frequency applications such as RF filters and decoupling.
7. Low Leakage Current: Ceramic capacitors have minimal leakage current, ensuring efficient and reliable operation.

Due to their versatility, small size, and cost-effectiveness, ceramic capacitors find extensive usage across different industries and electronic devices. They are utilized in power supply filtering, decoupling, timing circuits, noise suppression, coupling applications, and more. However, it’s important to consider the specific requirements of your application to determine the most suitable capacitor type for optimal performance.

Capacitor and Capacitance:

Different types of capacitors have capacitance.To clarify the difference between a capacitor and capacitance, it’s essential to understand their respective definitions. A capacitor refers to the physical device that consists of two conductive plates separated by a dielectric material. Capacitance, on the other hand, is the measure of a capacitor’s ability to store electrical charge and is expressed in Farads. In simple terms, capacitance is the inherent property of a capacitor.

AC and DC Capacitor Operation:

Different types of capacitors are used in both AC and DC circuits and their performance depends on the frequency and voltage applied to them.Capacitors can be used in both AC (alternating current) and DC (direct current) circuits, but their operation and behavior differ in each case.

AC Capacitor Operation: When a capacitor is connected to an AC circuit, its behavior depends on the frequency of the alternating voltage. Here are some key points:

1. Charging and Discharging: In an AC circuit, a capacitor charges and discharges continuously as the voltage alternates. During the positive half-cycle of the AC voltage, the capacitor charges, and during the negative half-cycle, it discharges.
2. Reactance: Capacitors in AC circuits exhibit reactance, which is the opposition to the flow of alternating current. Reactance depends on the capacitance value and the frequency of the AC signal. The reactance of a capacitor decreases with increasing frequency.
3. Phase Shift: Capacitors introduce a phase shift between voltage and current in an AC circuit. The voltage across the capacitor leads the current by 90 degrees. This phase shift is utilized in various AC applications, such as in phase shifters and AC motor start circuits.

DC Capacitor Operation: When a capacitor is connected to a DC circuit, its behavior is different from that in an AC circuit. Here’s how capacitors operate in a DC circuit:

1. Charging and Discharging: When a capacitor is connected to a DC voltage source, it charges until it reaches the same voltage as the source. Once fully charged, the capacitor blocks the flow of DC current as it acts as an open circuit.
2. Energy Storage: Capacitors store energy in their electric field when connected to a DC circuit. This stored energy can be discharged when the
3. Time Constant: The time it takes for a capacitor to charge or discharge in a DC circuit is determined by the RC time constant, where R is the resistance in the circuit and C is the capacitance. The time constant represents the rate at which the voltage across the capacitor changes.

It’s important to note that certain types of capacitors, such as electrolytic capacitors, are polarized and have a specific voltage polarity requirement. They are typically used in DC circuits where the voltage is constant and unidirectional.

In summary, capacitors in AC circuits continuously charge and discharge, exhibit reactance, and introduce phase shifts. In DC circuits, capacitors charge, store energy, and block the flow of current once fully charged. Understanding the differences in capacitor behavior in AC and DC circuits is crucial for selecting the appropriate capacitor for a specific application.

Types of Capacitors Behavior and Characteristics:

Capacitors serve two main functions in electronic systems: energy storage and signal conditioning. They store electrical energy, which can be discharged when needed, providing instantaneous power. Additionally, capacitors are used for signal coupling, filtering out unwanted frequencies, and improving the performance and efficiency of electronic circuits.

When it comes to high frequencies, the impedance of capacitors decreases, making them more effective for filtering and coupling applications. Capacitors exhibit different behaviors based on the frequency range they are designed for.

Regarding voltage, capacitors can withstand certain voltage ratings. If the applied voltage exceeds the capacitor’s rating, it can lead to failure or breakdown. It is crucial to select capacitors with appropriate voltage ratings for the intended application.

Over time, capacitors may experience aging, changes in capacitance values, and possible deterioration due to environmental factors, temperature, and voltage stress. These factors can affect the performance and reliability of capacitors, emphasizing the importance of considering their lifespan and operating conditions.

Conclusion:

Understanding the different types of capacitors and their applications is crucial in selecting the right component for specific electronic systems. Whether it’s ceramic capacitors for compact designs, electrolytic capacitors for high capacitance applications, or film capacitors for precise signal conditioning, each type has its unique advantages. Capacitors are ubiquitous in various industries and everyday life, contributing to the efficiency, stability, and performance of electronic devices and systems. By comprehending their characteristics and applications, engineers and enthusiasts can make informed decisions when choosing capacitors for their projects.

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1 Supercapacitors improve car starting performance

Supercapacitors, also known as ultra-capacitors, are energy storage devices that offer high power density, fast charge/discharge cycles, and long cycle life. Automotive application of supercapacitor can be combined with traditional lead-acid batteries to improve vehicle starting performance.

During the engine start-up process, the starter motor draws a large amount of current from the battery, causing a rapid voltage drop at the battery terminals. By adding a supercapacitor in parallel with the battery, the voltage drop during start-up can be reduced, which increases the available power to the starter motor and improves the engine starting performance. This is especially useful in situations where frequent starts are required, such as at stop lights or in heavy traffic.

Supercapacitors can also be used to improve engine starting performance in cold weather conditions. At low temperatures, the battery’s available power decreases, which can make it difficult to start the engine. However, the high power density and fast charge/discharge cycles of supercapacitors make them well-suited for providing the additional power needed to start an engine in cold weather.

In addition to improving starting performance, supercapacitors can also be used to capture and store energy during regenerative braking, which can then be used to power electrical accessories or assist the engine during acceleration. Overall, the use of supercapacitors in automotive applications offers a promising avenue for improving vehicle performance and efficiency.Therefore, the application of supercapacitor in automobiles is very critical and important

1.1  Problems with the battery

The battery is a crucial component in cars and its performance directly affects the starting of the vehicle. The current required for starting the engine is very high, leading to a significant drop in the battery voltage during the start-up process. This sudden drop in voltage causes strong electromagnetic interference that can affect the electrical equipment in the car, potentially leading to malfunction or damage. Due to its size and weight, increasing the battery capacity is not a practical solution. Therefore, using a supercapacitor in parallel with the battery can effectively solve this problem.

1.2 The combination of supercapacitor and battery improves the starting performance of automobiles

1.2.1 Application of supercapacitor-Improvement of electrical performance

The selection of supercapacitors mainly depends on the equivalent series resistance of the supercapacitor. In the application of small cars, the total equivalent series resistance can be used below 10mΩ, while for heavy-duty vehicles, it is hoped to choose 5mΩ or even below 2mΩ. If it can reach 1mΩ then It is even more desirable.
The current and output power waveforms are shown in Figure 6.26. Compared with Figure 6.24, the voltage drop at the moment of starting is increased from 3.2V to 7.2V when only the battery is used; the starting current is increased from 560A to 1200A; the output power of the power supply at the moment of starting is increased from 2kW to 8.7kW; the steady voltage during starting is increased from 7V Increased to 9.4V; the steady current of the starting process increased from 280A to 440A; the steady output power of the power supply during the starting process increased from 2.44kw to 4.12kW.

1.2.2 Improvement of startup performance

Using a supercapacitor in parallel with the battery can improve the starting performance of the car. Taking a car equipped with a 19L diesel engine as an example, a 250F/16.2V supercapacitor is used in parallel with a 12V, 45A battery, and it can start smoothly at minus 10 degrees Celsius. Although the battery can be started alone, when the supercapacitor is used in parallel with the battery, the starting speed and performance have been significantly improved. The parallel connection of supercapacitors can also increase the output power so that the starting speed can be increased from 300/min to 450/min. In addition, the use of supercapacitors is very meaningful in low-temperature environments, because the performance of the battery will be greatly reduced, which may lead to failure to start normally or multiple starts. When using a supercapacitor in parallel with the battery, it only needs one ignition to start successfully.

1.2.3 Improvement of battery application status

When the supercapacitor is connected in parallel with the battery since the equivalent series resistance of the supercapacitor is much lower than the internal resistance of the battery, most of the starting current is provided by the supercapacitor, which improves the stable voltage during the starting process. This not only effectively reduces the polarization of the battery plate and prolongs the battery’s service life but also frequent starting will no longer have a great impact on the life of the battery. Therefore, from the perspective of energy saving, the engine can be turned off when the red light is stopped and then restarted when the green light is turned on. Especially when the bus stops at the station and turns off the engine, and restarts when leaving the station, it will not have too much impact on the life of the battery.

2 Application of supercapacitor in hybrid electric vehicles and electric vehicles

2.1 Series-Parallel Hybrid Technology

There are many stops for urban buses, and each station needs to stop, start, and accelerate. Frequent braking and start-up acceleration are its biggest characteristics when encountering traffic lights. Due to the characteristics of the internal combustion engine, not only the fuel consumption is high when starting, but also the exhaust emissions are the largest. When accelerating, because the engine works in a high power output state, its fuel consumption and exhaust emissions are also very large. However, during braking, the kinetic energy obtained by accelerating the engine is converted into heat energy by braking and consumed in vain. According to the above, the fuel consumption and exhaust emissions of urban buses are very high. To reduce fuel consumption and exhaust emissions, the best way is to use hybrid technology or fuel cell power technology.

The connection between the electric drive and the internal combustion engine of a hybrid vehicle can be divided into series hybrid technology and parallel hybrid technology. The basic structure of the series hybrid technology is shown in 6.27, and the parallel hybrid technology is shown in Figure 6.28.

In hybrid electric vehicles, two types of hybrid technology are used: series hybrid and parallel hybrid. In a series hybrid, the wheels are powered solely by the drive motor, which is fed by a diesel engine operating at a constant speed to drive a synchronous generator and an energy storage unit (such as a supercapacitor) through a two-way power conversion converter circuit. This setup allows the drive motor to receive power from both the diesel engine and the energy storage unit. In contrast, in a parallel hybrid, the internal combustion engine and the drive motor share the responsibility of powering the wheels. The electric motor is used to drive the vehicle at low speeds, while the internal combustion engine takes over at higher speeds and under heavy load conditions. Both types of hybrid technology can help reduce the required power output of the drive motor and the energy storage unit, leading to more efficient and cost-effective vehicles.

For example, the electric energy provided by the 336V/12F supercapacitor bank is enough to drive a 40kW electric motor with a current of 300A for the 20s, which can easily complete the electric start and electric auxiliary acceleration functions of hybrid vehicles. Not only that but the drive motor can also be used to work in the power generation feedback state to recover the kinetic energy of braking and convert it into electrical energy and store it in the supercapacitor.

The control method can be as follows: when the car starts, the speed is lower than 20km/h, the supercapacitor is discharged when the output power of the diesel engine is less than a certain power value under the acceleration state; when the car is braking, the braking energy (charged) is transferred to the drive motor converted into electrical energy to charge the supercapacitor. Due to the existence of the supercapacitor energy storage unit, both the diesel engine and the storage unit can always run in an efficient state. As a result, fuel consumption can be reduced by more than 20%. In this way, the total energy demand of the city center can be reduced by about 18%. The application of  supercapacitor is not limited to hybrid buses, they are also suitable for frequent acceleration and braking cycles of all subways and various cars, which can save a lot of energy.

The application of supercapacitor is particularly beneficial in urban traffic.The use of braking energy feedback in motor vehicles, particularly in urban traffic, has significant benefits. During stop-and-go traffic or when stuck at traffic lights, vehicles frequently brake and accelerate, and the kinetic energy generated during braking is usually dissipated as heat energy, leading to increased energy loss. To reduce environmental pollution, it is essential to save energy during braking and reuse it. This is particularly beneficial for hybrid vehicles using internal combustion engines, where AC motors can be used as brake generators.

Supercapacitors are ideal devices for these applications due to their high energy storage capacity and strong ability to handle current. Unlike traditional lead-acid batteries, which have limited charge and discharge life, supercapacitors can be charged frequently and rapidly, and they can be discharged to 0V with a time constant of only about 2s without any risk of fault.

Supercapacitors have capacitance values in the thousands of Farads, making them highly efficient at storing energy generated in a short amount of time and releasing it efficiently. In the following example, the cost-effectiveness and rationality of supercapacitors are illustrated.

For example, a 2-ton car stops at a red light. In this process, all the kinetic energy is converted into electric energy and stored in the supercapacitor. When braking, the car goes from a speed of 50km/h until the final speed becomes 0. The following calculation shows that the 19.3kJ energy generated during braking (supercapacitor voltage from 25~46V during constant current braking) stored in the capacitor can make the capacitive energy of the capacitor reach 260F.

            The kinetic energy of the car

E_k=0.5m·V2  

In the formula, mass m=2000kg, speed v=50km/h=13.89m/s, braking energy (vehicle kinetic energy) E_k is 193kJ.

           Capacitors required to store braking energy

E₁=0.5C·（V_E²-V_A²)

In the formula, V_E is the initial charging voltage of the capacitor, and V_A is the final charging voltage of the capacitor. When E = 193kJ, the required capacitance is 260F.

        The corresponding braking current is

△Q=I·△t=C·△V

       When △t=10s, △V=21V, I_c=546A

From the above calculations, a supercapacitor suitable for this application requires a capacitance of 260F and a surge voltage of 46V. It can be formed by connecting 18 5000F/2.7V supercapacitors in series.

During post-braking acceleration, the supercar starts to discharge and the voltage drops, discharging from 46V to 25V at a constant current of 546A. In terms of the energy loss in the above case, the supercapacitor can still provide an additional 14kW of power for 10s, which makes the total efficiency 72%, because the acceleration power of 7.5kW can be maintained for the 20s, and the capacitance loss is very low, making the overall efficiency increase to 78%. This idea can naturally be applied to all similar braking processes, but the braking process should be less than 1min. This example shows that the application of supercapacitor can improve the range and acceleration of motor vehicles.

Applying a supercapacitor-based regenerative braking device to a diesel-driven bus can reduce fuel consumption by 25% and reduce exhaust emissions by about 20%. At the same time, the life of the supercapacitor can be the same as or higher than that of the car itself.

It should be noted that the electric part of the hybrid vehicle only provides auxiliary power for a short time, such as a few minutes or ten minutes. Therefore, hybrid electric vehicles are suitable for urban road applications where high-speed continuous driving or frequent braking and starting are not possible. If it is continuous driving on the highway, the battery or supercapacitor at this time will not be able to provide continuous power. At this time, the energy-saving effect of the hybrid vehicle will be negative, because the charging of the battery or supercapacitor requires the engine to provide power, and the energy efficiency at this time is not as good as that of the mains charging or the engine directly providing power.

In electric vehicles, fuel cells have gradually become one of the electric energy supply methods for electric vehicles. Due to the relatively slow response speed of fuel cells, a short-term power balance device is required, and the ideal device is a supercapacitor. The supercapacitor can absorb or release the redundant or insufficient power part of the fuel cell when the power changes. It should be noted that to reduce the fuel cell cost of fuel cell electric vehicles, an additional power source (such as a storage battery) and a fuel cell combination are required. Part of it needs to be provided by the battery (such as 20% of the power).

3 Application of supercapacitor-Supercapacitor electric vehicles

The application of supercapacitor in electric vehicles has been a topic of interest due to their long life and high number of charge and discharge cycles. While the energy density of supercapacitors is lower than that of batteries, they can still be used to complement or combine with a storage battery or internal combustion engine to form a hybrid vehicle.

However, organic system electric double-layer supercapacitors are not practical for electric vehicles due to their high cost and low energy density. Aqueous electric double layer supercapacitor also do not meet the requirements as their energy density is lower than that of organic systems.

The electrochemical supercapacitor shows potential with higher energy density, but it introduces an electrochemical process and needs to address the battery’s shortcomings, such as poor low-temperature characteristics, short cycle life, and inability to withstand high-rate charge and discharge.

Supercapacitors can be used to absorb or release high-rate current in electric vehicles, such as in starting, acceleration, deceleration, and braking. However, their single-charge mileage is limited, and they need to be used in conjunction with other power sources.

If electrochemical supercapacitors can make breakthroughs in lifespan and power density, they may become the sole power source for electric vehicles, extending the application of supercapacitor in the automotive industry.

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🌿At present, characteristics of capacitors used in DC converter stations mainly include the following seven types: ① shunt capacitors installed in the AC field of the converter station; ② capacitors for filters installed in the AC field of the converter station; DC filter capacitors installed in the DC field; ⑤ capacitors for DC PLC noise filters (the capacitors have been basically replaced by ceramic sleeve type or silicone rubber type coupling capacitors); ⑥ neutral line impulse capacitors; ⑦ DC circuit breaker capacitors.

1. Parallel capacitors

☘️The DC shunt capacitor device is only used to compensate the reactive power required by the converter. It is different from the capacitors used in the ordinary AC power system in the following points:

🍀(1) The rated voltage is high, which includes the arithmetic sum of each harmonic voltage, that is, =+. Therefore, the calculation of the shunt capacitor used in the DC converter station is 20%~40% higher than that of the conventional AC power system capacitor without considering the harmonics. For example, the single-phase rated voltage of the AC 500kV shunt capacitor is as high as 357%. ~411 kV, sometimes in the design, considering the uneven voltage distribution between the series sections, it is also necessary to multiply the rated voltage of the capacitor unit by a redundancy factor of 1.02~1.05.

🎍(2) The rated working field strength of the capacitor unit is higher than that of the ordinary AC capacitor unit. Due to the high value, it is necessary to select a high dielectric field strength. Generally, domestic capacitors are selected to be 60 MV/m and above to ensure the reliability of operation.

🍂(3) The series reactance value is very small, usually the K value is less than 0.1%, and even in some projects, a shunt capacitor without series reactor at the tail end is used, that is, K=0. In China, basically, in the new DC projects after 2004, the capacitor switching switch adopts the synchronous opening and closing device (this book will be described in the following chapters), the closing inrush current is greatly reduced, and under normal circumstances, the capacitor will not be fused inside. wire damage.

💐(4) The capacitor used on the capacitor bridge arm of the converter station has more stringent requirements on the difference in capacitance value. The allowable deviation of the capacitance value of the conventional capacitor is -5%~+10% (the capacitance value of the DC capacitor is generally also followed), but some special Under such circumstance, if the capacitor of the switching switch of the phase selection closing controller was not installed in the early stage, and there were some deficiencies in the manufacture of the capacitor used for the DC converter station in the early stage of the same period, in practice, only the capacitance deviation of the capacitor used in the DC project was controlled. At 2%, the stable operation of the capacitor after switching can be ensured (and the improvement of the capacitor manufacturing quality of domestic capacitor manufacturers has also relaxed the limit of capacitance value deviation). The essence of controlling the capacitance value deviation of the capacitor is to ensure that each phase is connected in series Inter-segment voltage uniformity. Strict requirements for deviations make higher requirements for the design, manufacture and quality control of capacitors.

🌷(5) The structure of the capacitor tower of the DC converter station, the structure of 1 to 3 towers per phase can be selected according to the specific situation, and generally 1 to 2 towers are in the majority in China. Of course, if the floor space allows, use a multi-tower structure as much as possible to reduce the height of the capacitor tower and facilitate installation and operation and maintenance. This is also the difference between DC capacitors and AC compensation capacitors in the tower structure.

🌹(6) The annual damage rate of capacitors used in DC converter stations is much lower than that of ordinary AC capacitors. Because the power failure of capacitors has a certain impact on the operation of the DC system, the general bidding specifications have made mandatory requirements. The annual damage rate of capacitors is less than 0.2%, which puts forward higher requirements on the design and manufacturing process of DC capacitors.

🌺(7) The protection configuration is different from that of ordinary AC capacitors. The DC capacitor adopts bridge differential current protection, and the unit adopts internal fuse protection.

2. AC filter capacitors

In addition to providing reactive power for the converter, the AC filter capacitor is also used to filter out the various harmonics generated by the converter valve to the AC power grid. In addition, it has the same characteristics as shunt capacitors in terms of protection methods and protection methods. In addition, it has its own characteristics:

🌸(1) It needs to cooperate with reactors and resistors to form a filter that filters out specific frequency harmonics. Due to the need for tuning, there are stricter requirements on the tolerance and temperature characteristics of capacitors. Usually, the tolerance of capacitor units is controlled at ±2%, each phase tolerance is controlled at ±1%.

🌼(2) In addition to high-voltage capacitors, AC filter capacitors generally have low-voltage capacitors. The selection of rated voltage has its own characteristics. The largest of the following three requirements should be selected: ① Continuous working voltage value (fundamental voltage and The arithmetic sum of each harmonic voltage); ② the voltage value calculated according to the capacity sum of the fundamental wave and each harmonic; ③ the voltage value obtained by dividing the impulse withstand level value by 4.3.

🌻(3) When the capacitor unit on the low-voltage side of the AC filter cannot be protected by an internal fuse, the dielectric working field strength should be appropriately reduced in order to obtain higher operational reliability.

🌞(4) AC filter capacitors are noisy during operation. In general AC power systems, the noise level of capacitors will not attract people’s attention. However, AC filter capacitors operating in converter stations are not affected by the installation capacity. If it is large, the high-order harmonic current passing through is large, and the noise problem will be particularly prominent. In the bidding design specification for the new converter station, strict restrictions are put forward on the noise of the filter capacitor device. Therefore, the capacitor device adopts noise reduction measures and reduces the height of the capacitor tower to meet the requirements of noise reduction.

3. DC filter capacitors

🌝The DC filter capacitor is installed on the DC side to filter out the harmonics on the DC side. The demand for the DC filter capacitor itself is not high, but it has higher technical and production requirements than the capacitor used in the AC system of the converter station. , and even foreign countries have produced products with stable quality after many repeated improvements. At present, domestic manufacturers such as Xirong and Guirong are also capable of producing DC-side capacitors with performance that meets operating requirements. DC filter have the following characteristics of capacitors:

🌛The rated voltage is high, and its calculation formula is

In the formula ，

U—the maximum continuous operating voltage of the DC line, kV;

U—Each harmonic voltage on the DC side, kV;

K—voltage coefficient, the value is greater than or equal to 1.3.

⭐️According to formula (1-8), we take the conventional ±500kV DC converter station as an example, take 511kV, and the rated voltage of the 6/12th and 24/36th order DC filter capacitors will be as high as 836kV and 751kV, respectively.

🌟(2) The DC filter protection method, the capacitor unit adopts the internal fuse protection, and the capacitor bank adopts the bridge difference unbalanced current protection (the details will be introduced in the later chapters of this book).

✨(3) Voltage equalization measures: There are voltage equalization resistors and discharge resistors inside the capacitor unit, and the resistance value must consider the voltage equalization effect in the design. The current can also keep the voltage distribution basically uniform, and at the same time, the design can prevent overheating inside the DC characteristics of capacitors.

⚡️(4) The creepage distance of external insulation should be at least greater than 50mm/kV.

🌈(5) The design of the DC filter capacitor tower is different from that of the AC filter capacitor tower. In order to reduce the influence of the insulation leakage current on the voltage distribution, the DC filter capacitor tower can only adopt a single tower structure, and the capacitor unit can be installed flat on the tower. Decrease the height of the tower. Suspended installation can also be used if necessary (±80 kV DC converter stations have been put into operation in China, such as the Suidong converter station of the Chusui DC project, because the single tower of the DC filter capacitor is too high, the support type installation is unstable. , only the suspension installation method can be selected).

☀️(6) The low-voltage capacitor of the DC filter actually bears the AC voltage of each spectral wave during the operation, and its technical requirements are the same as those of the capacitor for the AC filter.

4.The AC converter transformer incoming line PLC capacitor

❄️At present, this type of capacitor is no longer designed and installed in many newly built converter stations. The early converter stations were designed to filter out the 30-500 kHz harmonics in the PLC frequency range on the AC bus, to prevent high-order harmonics generated by the converter. Harmonics cause noise interference to the PLC system on the AC side and the carrier communication on the connected and adjacent AC lines. Here is a brief introduction to its characteristics:

🍓(1) Its rated voltage is high, mainly including harmonic voltage. For example, the phase voltage of some conventional ±500 V DC engineering PLC capacitors in China is as high as 441 kV, which is 1.45 times the rated voltage of power frequency.

🍒(2) In terms of structure, if the capacitance of the PLC capacitor is small (generally below 1 nF), the column structure of the porcelain jacket is used, and when the capacitance is large (greater than 30 nF), the tower structure is used.

5. DC PIC characteristics of capacitors

🍑DC PLC capacitors include coupling capacitors for carrier communication of the DC side power line of the converter station (the new DC project is not used for carrier communication) and filter capacitors. Its essence is a low-pass filter. Its function is to filter out the harmonics in the frequency range of the DC line PLC and prevent noise interference to the adjacent line carrier communication. Its technical characteristics are the same as those of the AC PLC. Voltage equalization measures to offset the adverse effect of insulation leakage current on voltage distribution in the case of external pollution. The creepage distance of the external insulation is generally required to be greater than 50 mm/kV.

6. Neutral line impulse capacitors

🥭Also known as a surge capacitor, this capacitor protects the DC neutral and has the same characteristics as a DC filter capacitor.

7. DC circuit breaker characteristics of capacitors

🍍Before the DC circuit breaker breaks the current, the capacitor discharges to form a sinusoidal alternating current, and the principle of the AC circuit breaker can be used to cut off the DC current. This kind of capacitor has short working time, high operating overvoltage, and its demand is very small. Generally, it is specially designed according to the project.

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