The lifetime of photovoltaic inverter is determined by the reliability of its components. Electrolytic capacitors are one of the key components to improve the reliability of photovoltaic inverters. In addition, photovoltaic inverters have high expectations for life, so there are also requirements for capacitors.
Photovoltaic inverter requirements for electrolytic capacitors
1. High voltage
Generally, high-power photovoltaic inverters directly merge the converted AC power into the high-voltage grid. However, from the perspective of safety regulations, the output voltage of the photovoltaic battery pack is generally not higher than 900V. You can choose two 450V electrolytic capacitors in series, but In order to improve safety, you can choose 2 500V electrolytic capacitors in series. Therefore, high-voltage capacitors are needed to reduce the series connection of capacitors and improve reliability.
2. High ripple resistance
Generally, the current flowing through the capacitor of a photovoltaic inverter is 0.44 times the effective value of the inverter output current. For example, the output voltage of the photovoltaic inverter is 250V line voltage, the output current corresponding to each output 1kW power is about 2.54A, and the current flowing through the DC bus capacitor is 1.12A. The DC bus capacitor of a 100kW photovoltaic inverter needs to flow 112A effective value current, and the rated current of the selected capacitor should not be lower than this value. If the rated current of an electrolytic capacitor cannot meet the requirements, it is necessary to select multiple electrolytic capacitors in parallel to obtain the required current value. Therefore, a single electrolytic capacitor with high ripple resistance is required to reduce the number of electrolytic capacitors in parallel and improve overall reliability.
3. Long life
In the solar power generation system, the service life of photovoltaic panels is as long as 25 years, and the inverter becomes a photovoltaic system generally only for 5 to 10 years, so the solar power system requires the life of the photovoltaic inverter system to be 25 years. For electrolytic capacitors with passive components, its negative electrode is electrolyte, which will slowly dry up and become invalid as the use time increases. This will inevitably require the electrolytic capacitor industry to manufacture longer-life electrolytic capacitors to meet the requirements of photovoltaic inverter.
