Power converter system and method of controlling power converter

A power converter system includes: a circuit breaker (3a) having one terminal connected to a power system and another terminal connected to a load (20); a transformer (6a) for interconnection; a power converter (30); and a controller (50) for controlling the power converter, wherein, during a return to grid connected operation, the power converter is controlled such that the phase of an output voltage of the power converter matches the phase of the system voltage, and the circuit breaker is closed, so as to prevent an overcurrent during a changeover from the self commutated operation to the grid connected operation of the power converter.