Patent ID: 8896260

Claim:
A power supply unit for a press machine having a converter connected to a commercial AC power supply, and an inverter connected to a press motor, and generating and outputting a motor drive power for driving the press motor, an electrical capacity of the converter during power-running operation being smaller than an electrical capacity of the inverter during power-running operation, the converter being formed by a converter circuit, and the inverter being formed by an inverter circuit that implements a regeneration operation, and the power supply unit comprising: an electrical energy bank that is provided in a DC current path and stores electrical energy, the DC current path connecting the converter circuit and the inverter circuit; an inrush prevention circuit that includes inrush prevention resistors and contactors that are respectively connected in parallel to AC phase current paths that connect the commercial AC power supply and the converter circuit; an inrush prevention instruction signal generation section that generates an inrush prevention instruction signal when a detected actual DC voltage of the DC current path is lower than a comparison reference voltage; and a contactor switch section that switches the contactors of the inrush prevention circuit from an ON state to an OFF state on condition that the inrush prevention instruction signal generation section has generated and output the inrush prevention instruction signal.