Ningbo Dingnuo Electric Reveals: How Do Capacitors Serve as the “Heart and Voltage Regulator” of New Energy Systems?

Ningbo Dingnuo Electric Reveals: How Do Capacitors Serve as the “Heart and Voltage Regulator” of New Energy Systems?

  Within the entire power system, there is a seemingly unremarkable yet indispensable core component—the capacitor. It serves not only as a reliable voltage stabilizer in circuits but also as an invisible guardian that ensures the efficient grid integration and long-term safe operation of renewable energy systems.

  With nearly two decades of deep expertise in the power capacitor sector, Dingnuo Electric leverages its extensive experience in R&D and project implementation to provide a comprehensive analysis of capacitor classifications, functional roles, and application solutions across various scenarios, following the complete power chain from the generation side → grid side → load side → energy storage side.

  

Classification by Power Source

  

  A centralized power supply is a power supply architecture in which the functions of power conversion, distribution, and control are consolidated into a single area. Typical examples include large-scale thermal power, hydroelectric, and nuclear power plants. The core capacitors used in such systems include generator circuit breaker (TRV)  capacitors and power plant output capacitive voltage transformers (CVT).

  

•  Power Plant Output CVT: Connected in parallel between the AC system phase line and ground, it provides accurate voltage signals for measuring instruments and relay protection devices, while also serving as a power line carrier coupling capacitor.

•  Generator Circuit Breaker TRV Capacitors: Installed across the generator protection circuit breaker, these effectively suppress overvoltage steepness, limit the transient recovery voltage (TRV) and voltage rise rate (RRRV), and ensure the safety of the switching equipment.

 

   Distributed power sources, such as solar and wind power, have a power range spanning from several kilowatts to 50 MW. They feature a modular layout and are designed forlocal consumption. The mainstream applications in this context include DC-link capacitors and damping capacitors.

  DC-Link Capacitors: Installed on the inverter’s DC bus, these capacitors absorb pulsating surge currents, stabilize the bus voltage, withstand transient overvoltages, and protect power devices.

  Damping Capacitors: Installed in close proximity to IGBT modules, these capacitors absorb spike voltages induced by stray inductance in the busbar, preventing breakdown and damage to semiconductor devices.

Grid Side | Capacitors Vary Depending on the Grid Application

  

  AC transmission lines are responsible for long-distance power transmission from large-scale energy generation bases to load centers, as well as for interconnecting regional power grids. Capacitors are primarily used to optimize power quality and enhance grid stability. The specific categories are as follows:

  High-Voltage Shunt Capacitors: Connected to the AC power grid to compensate for inductive reactive power, improve power factor, stabilize voltage levels, reduce line energy losses, and fully utilize transformer transmission capacity;

  AC Filter Capacitors: Provide a low-impedance path for specific harmonic frequencies to suppress harmonic distortion in the power grid while simultaneously providing reactive power compensation;

  Series Capacitors: Connected in series with transmission lines to offset the line’s inherent inductive reactance, thereby reducing voltage drops and increasing the line’s transmission capacity;

  Circuit Breaker Voltage Equalization/TRV Capacitors: Connected in parallel across the opening of high-voltage circuit breakers to equalize voltage distribution across the break and suppress transient recovery voltages caused by the breaking process.

LCC-HVDC transmission

  LCC-HVDC transmission refers to high-voltage direct-current transmission technology based on grid-synchronous commutation. It uses semiconductor devices such as thyristors to form converters; the technology is mature and features low losses, making it primarily suitable for ultra-high-capacity, long-distance point-to-point DC transmission scenarios, in which as many as 15 different types of capacitors are used.

  

  Capacitive Voltage Transformers: Installed in the AC-side switchyard of a converter station or in the vicinity of the converter transformer, they provide voltage signals to electrical measuring instruments, control and protection devices, or the converter transformer’s control system.

  AC/DC PLC/RI Capacitors: Installed on the AC and DC sides of the converter station, respectively, to filter out harmonics within the PLC frequency range of (30–500) kHz and prevent noise interference caused by higher-order harmonics generated by the converter valves from affecting carrier communication and wireless communication in the AC system.

  

  Damping capacitors for commutator valves: Together with reactors, resistors, and other components, they form a DC filter and work in conjunction with smoothing reactors and neutral busbar surge capacitors to reduce harmonic voltages and currents in the 3rd to 50th order range generated by the converter.

  Voltage-balancing Capacitors for Converter Valves: Connected between the neutral busbar and ground, these capacitors absorb the energy generated at this point during lightning strikes or other faults, and provide a low-impedance path for currents on the rectifier side that consist primarily of harmonics in multiples of 3.

  

  DC Filter Capacitors: These, together with reactors, resistors, and other components, form a DC filter. They work in conjunction with smoothing reactors and neutral busbar surge capacitors to reduce harmonic voltages and currents in the 2nd to 50th order range generated by the converter.

  Neutral Bus Surge Capacitors: Connected between the neutral bus and ground, these capacitors absorb the energy generated at this point during lightning surges or other faults, and provide a low-impedance path for DC-side currents consisting primarily of harmonics in multiples of 3.

  Capacitors for DC Circuit Breakers: As auxiliary equipment for DC circuit breakers on the neutral busbar, these capacitors, together with inductors, generate a sinusoidal AC current through charging and discharging before the DC circuit breaker interrupts the current, thereby interrupting the current at the zero-crossing point.

  

Load Side | Classification by Voltage Load

  

  Low-voltage power distribution consists of distribution substations, high-voltage distribution lines, distribution transformers, low-voltage distribution lines, and corresponding control and protection equipment. Capacitors are widely used in low-voltage power distribution applications for reactive power compensation and power quality improvement, including the following four types.

  Low-voltage shunt capacitors: Connected in parallel within a low-voltage AC system, they are used to compensate for inductive reactive power, improve power factor and voltage quality, and reduce line losses.

  Low-voltage filter capacitors: Used for power factor correction in low-voltage circuits, while reducing voltage distortion caused by harmonics and mitigating the interference of harmonics on the normal operation of loads.

  Smart Capacitors: By combining traditional low-voltage capacitors with power electronics, modern communication technology, and smart technology, these capacitors provide faster and more precise reactive power compensation.

  DC Capacitors for SVG/APF/UPFC: The DC side uses DC capacitors as energy storage elements. By switching the power semiconductor switches in the inverter on and off, the    DC-side voltage is converted into an AC-side output voltage that matches the grid’s frequency.

Vehicle Transportation

  

   In the transportation sector, capacitors meet requirements such as high performance, compact size, and high reliability, and are therefore widely used.

  DC capacitors for traction converters: Used in traction converters for rail transit, trolleybuses, and mining locomotives, these capacitors must be compact, have high capacitance, be capable of withstanding high inrush currents, and feature low inductance, low temperature rise, and resistance to vibration and shock.

  DC Capacitors for New Energy Vehicles: Used in the converters of electric drive systems for hybrid and electric vehicles, these capacitors must feature compact and lightweight designs with low inductance, as well as resistance to extreme temperature fluctuations and high safety standards.

Energy Storage Side | Classification Based on Capacitor Energy Storage Applications

  Super capacitors: Designed for applications requiring power supplementation on a scale of seconds to minutes—such as load following, system frequency regulation, reactive power support, mechanical energy recovery, and rotating mass in renewable energy stations—they feature fast response times and high cycle life.

  Pulse capacitors: Utilize the short-term release of energy stored in capacitors to generate high voltages or large currents; they are used in fields such as electromagnetic propulsion, high-power lasers, and controlled nuclear fusion.