DC Capacitors in Photovoltaic Inverters

Solar photovoltaic power generation will play an important role in the world's energy consumption in the near future, not only to replace some conventional energy sources, but also to become the main source of the world's energy supply.

Photovoltaic inverters are inverters that convert the variable DC voltage generated by photovoltaic (PV) solar panels into utility frequency alternating current (AC), which can be fed back into the commercial transmission system or used in off-grid system. Since inverters are generally used in outdoor condition and require long-term reliable operation and less maintenance, end users and designers have extremely stringent quality and reliability requirements for the components used in these devices. As the carrier and support in the energy conversion process, film capacitors play a vital role in all aspects of photovoltaic inverters. If they are not selected properly, they will have a fatal impact on the stability and lifetime of the equipment.

For the use in the inverter circuit, please refer to the application example in the figure below:

The role of the DC-link capacitor:

1) In the inverter circuit, the output voltage of the rectifier is mainly smoothed and filtered;

2) Absorb the high-amplitude pulsating current requested by the inverter from "DC-Link", prevent it from generating high-amplitude pulsating voltage on the impedance of "DC-Link", and keep the voltage fluctuation on the DC bus within the allowable range scope;

3) Prevent the voltage overshoot and transient overvoltage of the "DC-Link" from affecting the IGBT.

Therefore, the requirements for capacitors:

1) Ensure sufficient withstand voltage

2) Enough capacitance

3) Sufficient over-current capability, low ESR as possible

4) Need good frequency characteristics, low ESL as possible

5) Satisfy the harsh outdoor high temperature and high humidity application condition

Wuxi CRE New Energy Technology Co., Ltd. has been focusing on the application of film capacitors in power electronics for a long time. Aiming at the harsh application condition in photovoltaic inverters, based on CRE's DC-supported high-resistance film technology, it adopts low-loss, high-temperature-resistant Polypropylene Dielectric has designed and developed a series of film capacitors with high temperature and high humidity resistance, low ESR (lower heat generation), high reliability and long life.

Among them, the performance characteristics of DMJ-PS DC bus capacitor are as follows: