1. Definition and working principle of photovoltaic inverter
1) Photovoltaic inverter definition:
Inverter, also known as power regulator, is a power regulator composed of semiconductor devices. It is mainly used to convert DC power into AC power.
The inverter is composed of a boost circuit and an inverter bridge circuit. The boost circuit boosts the SOLAR cell dc voltage to the inverter output control required DC voltage; The inverter bridge circuit will boost the DC voltage equivalent to the common frequency of the AC voltage.
2) Working principle of photovoltaic inverter:
Inverters turn DC inputs into AC outputs by regularly turning switching elements such as transistors ON and OFF repeatedly. Of course, inverter output waveform generated solely by on and off circuits is not applicable. Generally adopt high-frequency pulse width modulation, make the near at the ends of the sine wave voltage width narrow, central sine wave voltage width wider, and always let the switch element in half cycle according to certain frequency moves in one direction, thus formed a pulse wave train (quasi sine wave), and then let the form sine wave pulse through a simple filter.
2. Function summary of photovoltaic inverter
1) The functions of photovoltaic inverter are summarized as follows:
The inverter not only has the function of direct AC conversion, but also has the function of maximizing the performance of solar cells and system failure protection.
To sum up, it has automatic operation and shutdown function, maximum power tracking control function, independent operation function, automatic voltage adjustment function, DC detection function, DC grounding detection function. The direct ac conversion function, automatic running and shutdown function and maximum power tracking control function are briefly introduced here.
(1) Direct AC conversion function:
The main function of the inverter is to transform the variable DC voltage input of the power supply into a non-interfering AC sine wave output, which can be used by the equipment and can also be fed back to the power grid.
② Automatic operation and shutdown function:
After sunrise in the morning, the solar radiation gradually increases, and the output of the solar cell also increases. When the output power required by the inverter is reached, the inverter automatically starts to run. After entering the operation, the inverter will always monitor the output of the solar cell module, as long as the output power is greater than the output power required by the inverter work, the inverter will continue to run until the sunset shutdown. When the inverter output is close to 0, it forms the standby state.
Maximum power tracking control function:
The output power of the solar cell module changes with the solar radiation intensity, so there is an optimal working point that can obtain the maximum power. Relative to the radiation intensity change, the working point of the solar cell module is always at the maximum power point, and the system always obtains the maximum power output. This control is the maximum power tracking control.
3. Classification and industry status of photovoltaic inverters
1) Photovoltaic inverter classification:
According to the use in the photovoltaic power generation system is divided into independent power supply and grid-connected.
② According to the waveform modulation mode is divided into square wave inverter, step wave inverter, sine wave inverter, combined three-phase inverter.
③ According to whether there is a transformer, it is divided into transformer inverter and transformer - free inverter.
2) Current situation of photovoltaic inverter industry:
(1) Industry situation of photovoltaic inverter:
At present, the industry leader of photovoltaic inverter is Germany ESMA (SMA) company, technology in the industry peak;
② The world's top ten famous photovoltaic inverter manufacturers:
SMA (Germany); Power-one (US); KACOKACO New Energy (Germany); Ruifuso (China); Inhotean (Spain); ABB (Switzerland); Hefei Sunshine Power Supply Co., LTD. (China); ENPHASE ENERGY (USA); Tbea Electric (China); Chase Day Electric appliance (China).
Requirements for aluminium electrolytic capacitors for photovoltaic inverters
1) Requirements of photovoltaic inverters for electrolytic capacitors:
① High voltage:
General high-power photovoltaic inverters directly integrate the converted AC power into the high-voltage grid. However, from the perspective of safety regulations, the output voltage of photovoltaic cells is generally not higher than 900V. Two 450V electrolytic capacitors can be selected in series, but in order to improve safety, two 500V electrolytic capacitors can be selected in series. In recent years, 550V electrolytic capacitors with high voltage grade have been developed to meet the market demand.
② High ripple resistance:
Generally, photovoltaic inverters have high ripple current through electrolytic capacitors. In this case, if the rated ripple current of an electrolytic capacitor cannot meet the requirements, multiple electrolytic capacitors should be connected in parallel to obtain the required current value. Therefore, the ripple resistance of a single electrolytic capacitor should be high, so as to reduce the number of parallel electrolytic capacitors and improve the overall reliability.
③ Long life:
In the solar power generation system, the service life of photovoltaic panels is as long as 25 years, while the inverter can only be used for 5 to 10 years. This is mainly limited to the passive components of electrolytic capacitors (electrolytic capacitors are negative electrolyte, which will slowly dry up and fail with the growth of use time). This will inevitably require the electrolytic capacitor industry to produce electrolytic capacitors with longer life to meet the requirements of photovoltaic inverters.