PURPOSE: To suppress the zero phase components of an inverter output current and the distortion of voltage waveform by placing a link transformer between a multiple transformer and a system, and making the output side of the multiple transformer and the input side of the link transformer respectively Y connections, and connecting the neutral points by a means which suppresses zero phase components.

CONSTITUTION: The output side of the multiple transformer 2 connected to the output of an inverter 1 is made Y connection. On the other hand, the input side of a link transformer 3 is made Y connection, and the output side connection. Furthermore, the neutral points of the multiple transformer 2 and the link transformer 3 are connected by a reactor 4. And the zero phase components, which occurs due to the one pulse PWM control of the inverter 1, flows through the reactor 4, and is suppressed by the impedance of the reactor.