A system and method for pre-charging the DC bus of a utility connected
power converter. In one embodiment, a full-wave rectifier circuit is
coupled to the utility grid through an isolation transformer and circuit
protector. The rectifier circuit output is connected to the DC bus of the
power converter to provide a pre-charging current to the DC bus
capacitors. The output from the rectifier circuit also supplies power to
the control circuit power supply for the converter. When the control
circuit closes the contactor of the converter system and activates the
converter, the voltage across the DC bus capacitors is increased above
the level of the rectified power grid voltage provided at the output of
the pre-charge circuit. This reverse-biases the rectifier diodes, placing
the pre-charge circuit into an inactive state. The impedance of the
isolation transformer limits the in-rush current into the DC bus
capacitors during the pre-charge.