An input rectifier supplies d-c energy for an auxiliary-commutated inverter. A logic circuit provides gating signals for the semiconductor switches in the input rectifier circuit and in the inverter circuit. A pre-charge circuit provides an independent path to charge the commutating capacitor in the inverter when the system is energized. The gating signals to the input rectifier are delayed by a predetermined time interval, allowing the commutating capacitor in the inverter to be charged and thus ensure effective commutation when the inverter commences operation.