Active discharge circuit for link capacitor using phase leg switches

Abstract

A DC link capacitor in a drive system for an electric vehicle is quickly discharged using only local action within an inverter module and without any extra components to dissipate the charge. The inverter has a phase leg comprising an upper switching device and a lower switching device coupled across the capacitor. A gate driver is coupled to the phase leg to alternately switch the switching devices to ON state according to a PWM signal during pulse-width modulation of the drive system. The gate driver is configured to discharge the link capacitor during a discharge event by simultaneously activating the upper and lower switching devices to transitional states. Thus use of transitional states ensures that the switching devices provide an impedance that dissipates the capacitor charge while protecting the devices from excessive temperature.