Bi-directional switch for neutral point clamped pwm inverter

Abstract

Bi-directional switches for use with neutral point clamped PWM inverters have utilized clamping switches which are operated alternately with main power switches in the inverter to periodically connect an output terminal of the inverter to a neutral voltage. However, a delay period is typically interposed between turn-off of a main power switch and turn-on of the clamping switch to minimize the possibility of a potentially destructive shoot-through condition. This delay adversely affects the quality of the power developed by the inverter and leads to an undesired increase in the size of snubber circuits coupled across the power switches. In order to overcome these problems, a bi-directional switch according to the present invention includes circuitry for providing a high impedance path in series circuits including the main power switches and the clamping switch so that shoot-through currents are blocked even when one of the main power switches and the clamping switch are simultaneously on. The delays between turn-off of a main power switch and turn-on of the clamping switch can thereby be reduced or eliminated, thereby resulting in improved quality of the output power of the inverter and a reduction in the size of snubber circuits used therein.