When the public grid is powered off, the grid side is equivalent to a short-circuit state. At this time, the grid-connected inverter will be automatically protected due to overload. When the microprocessor detects an overload, in addition to blocking the SPWM signal, it will also disconnect the circuit breaker connected to the grid. At this time, if the solar battery array has energy output, the inverter will run in a separate operating state. The control is relatively simple when running alone, that is, the negative feedback state of the AC voltage. The microprocessor detects the inverter output voltage and compares it with the reference voltage (usually 220V), and then controls the PWM output duty cycle to achieve inverter and stability. pressure operation.