As a new energy source, solar energy can provide clean and pollution-free energy for people's daily life. Due to the fact that the current generated by photovoltaic power generation systems is DC, but civil power is mainly AC powered, and solar power generation will eventually move towards grid connection, which means that solar power generation must convert DC power into AC power through inverters to drive loads such as household appliances. Therefore, inverters play an important role in solar power generation systems. So, what are the specific applications of aluminum electrolytic capacitors in photovoltaic inverter products in the new energy field?
Requirements for photovoltaic inverters for solar power generation
According to the usage of inverters in existing photovoltaic systems, they can generally only be used for 5 to 10 years, while photovoltaic panels have a service life of up to 25 years, making inverters the most reliable components in photovoltaic systems. The solar inverter technology industry has high expectations for product life, generally guaranteeing a service life of 20 to 25 years, so special emphasis is placed on the reliability of each component.
Key to improving the life of photovoltaic inverters
The lifetime of photovoltaic inverters is determined by the reliability of their components. Although semiconductor components typically achieve this level of reliability, it can be a challenge for passive components, especially electrolytic capacitors. Improving the reliability of electrolytic capacitors has become one of the keys to improving the reliability of photovoltaic inverters.
The role of electrolytic capacitors in photovoltaic inverters
Photovoltaic inverters can be seen as special purpose inverters powered by DC power, with an output frequency of 50Hz or 50Hz synchronized with the power grid. Their function is to absorb the switching frequency extremely high harmonic current generated by the inverter and the third harmonic current and high harmonic current of the output frequency.
Requirements of photovoltaic inverters for electrolytic capacitors
Generally, high-power photovoltaic inverters incorporate the converted AC power directly into the high-voltage power grid. However, from the perspective of safety regulations, the output voltage of photovoltaic battery packs is generally not higher than 900V, and two 450V electrolytic capacitors can be selected in series. However, to improve safety, two 500V electrolytic capacitors can be selected in series. Therefore, it is necessary to use high voltage level capacitors to reduce the series connection of capacitors and improve reliability.
Generally, the current flowing through the capacitor of a photovoltaic inverter is 0.44 times the effective value of the inverter output current. If the rated current of one 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 parallel electrolytic capacitors and improve overall reliability.
In solar power generation systems, the service life of photovoltaic panels can be as long as 25 years, while inverters can only be used as photovoltaic systems for 5 to 10 years. Therefore, solar power generation systems require a service life of 25 years for photovoltaic inverter systems.
For passive element aluminum electrolytic capacitors, their negative electrode is electrolyte, which will slowly dry up and become invalid as the service time increases. This is bound to require the electrolytic capacitor industry to manufacture electrolytic capacitors with longer life to meet the requirements of photovoltaic inverters.
The interior of an electrolytic capacitor has an electrolyte material that stores electric charges, with positive and negative polarity, similar to a battery, and cannot be connected in reverse. The positive electrode is a metal substrate adhered with an oxide film, and the negative electrode is connected to the electrolyte (solid and non solid) through a metal electrode plate. Electrolytic capacitor paper, also known as capacitor separator paper, serves as an isolation and insulation between the anode and cathode aluminum foil of an electrolytic capacitor. The better the quality of electrolytic capacitor paper, the better it can meet the requirements of capacitor voltage resistance, low impedance, and low loss.
The (bipolar) electrolytic capacitor adopts a double oxide film structure, similar to two polar electrolytic capacitors formed by connecting two negative electrodes. The two electrodes are connected by two metal electrode plates (both bonded with oxide films), and the middle of the two groups of oxide films is an electrolyte. Polarized electrolytic capacitors usually function as power filters, decoupling, signal coupling, time constant setting, and DC lamp isolation in power supply circuits or intermediate and low frequency circuits. Non polar electrolytic capacitors are commonly used in audio frequency divider circuits, television S correction circuits, and single-phase engine starting circuits.