In the photovoltaic system, the electric energy produced by the solar cell is first stored by the battery and then converted into 220V or 380V alternating current by the inverter. However, the output voltage of a battery varies widely due to its own charging and discharging. For example, for a nominal 12V battery, its voltage can vary between 10.8 and 14.4V (exceeding this range may cause damage to the battery). For a qualified inverter, the steady-state output voltage shall not change more than ±5% of the rated value when the input voltage varies within this range, and the output voltage deviation shall not exceed ±10% of the rated value when the load changes abruptly.