1.Output voltage stability
In a photovoltaic system, the energy emitted by the solar cell is first stored by the battery and then inverted by the inverter into 220V or 380V AC. However, the battery is affected by its own charge and discharge, and its output voltage varies widely. For example, a nominal 12V battery can vary its voltage from 10.8 to 14.4V (beyond this range, it may cause damage to the battery). For a qualified inverter, when the input voltage changes within this range, the change of the steady-state output voltage should not exceed the rated value of Plusmn; 5%, and when the load is abrupt, the output voltage deviation should not Exceeding ±10% of rated value.
2.Waveform distortion of the output voltage
For sine wave inverters, the maximum allowable waveform distortion (or harmonic content) should be specified. Usually expressed as the total waveform distortion of the output voltage, its value should not exceed 5% (single-phase output allows 10%). Because the high-order harmonic current output from the inverter will generate additional losses such as eddy currents on the inductive load, if the waveform distortion of the inverter is too large, the load components will be seriously heated, which is not conducive to the safety of electrical equipment and seriously affects the system. Operating efficiency.
3.Rated output frequency
For loads including motors, such as washing machines, refrigerators, etc., because the motor's optimal frequency operating point is 50Hz, the frequency is too high or too low, which will cause the equipment to heat up, reduce the system operating efficiency and service life, so the inverter The output frequency should be a relatively stable value, usually 50Hz for power frequency. Under normal working conditions, the deviation should be within Plusmn; l%.
4.Load power factor
Characterizes the ability of an inverter with inductive or capacitive loads. The sine wave inverter has a load power factor of 0.7 to 0.9 and a nominal value of 0.9. In the case of a certain load power, if the power factor of the inverter is low, the capacity of the required inverter is increased, on the one hand, the cost is increased, and the apparent power of the AC circuit of the photovoltaic system is increased, and the circuit is increased. As the current increases, the losses increase and the system efficiency decreases.
The efficiency of the inverter refers to the ratio of the output power to the input power under the specified working conditions, expressed as a percentage. Under normal circumstances, the nominal efficiency of the PV inverter refers to the pure resistance load, 80% load s efficiency. Due to the high overall cost of the photovoltaic system, it is necessary to maximize the efficiency of the photovoltaic inverter, reduce the system cost, and improve the cost performance of the photovoltaic system. At present, the nominal efficiency of mainstream inverters is between 80% and 95%, and the efficiency of low power inverters is not less than 85%. In the actual design process of the photovoltaic system, not only should the high-efficiency inverter be selected, but also the reasonable configuration of the system should be used to make the photovoltaic system load work near the best efficiency point.