The first step is to use a multimeter to detect the voltage of the power grid. If the voltage is abnormal, it indicates a problem with the power grid;

The second step is to detect the AC switch. In the normal closed state, the switch is conducting up and down, and there is no voltage between the
incoming and outgoing lines. If the voltage is greater than 5V, it indicates that there is a problem with the switch;

Step 3: If there is no problem with the AC switch, check the AC output terminal of the inverter and use a multimeter to check the voltage between the
phase lines of the terminal. The voltage of the power grid should be consistent. If it is not consistent, it may be a problem with the cable from the switch
to the inverter, or a problem with the output terminal of the inverter;

Step 4: If the voltage measured at the AC output terminal is normal and the inverter also reports an AC voltage fault, it may be an internal sampling problem
with the inverter, which needs to be resolved by contacting the inverter manufacturer.