Power conversion system

A power conversion system (PCS) is provided. A micro-control unit of the PCS obtains a current charged ratio of a rechargeable battery according to a state-of-charge (SOC) signal received from the rechargeable battery, and obtains an output power of the PCS according to the voltage and current detected by a voltmeter-and-current meter of the PCS. When the micro-control unit detects that the mains off-grid occurs, the following steps are performed: judging whether a current charged ratio of the rechargeable battery is greater than the first ratio; when it is determined that the current charged ratio is greater than the first ratio, judging whether the output power is less than a first power; and when it is judged that the output power is less than the first power, increasing a frequency of an alternating current output from an alternating current (AC) power port of the PCS, so that a photovoltaic (PV) inverter coupled to the AC power port stops outputting power.