A critical evaluation of the problem of reverse bipolar transistor conduction in high current PWM inverters

Almost all PWM converters using bipolar transistors experience the problem of reverse transistor conduction. This effect is analysed for various types of base drive. It is shown to be most serious for low impedance direct drives. A mathematical model is developed for this case and verified experimentally. Problems associated with turn-on and turn-off in the reverse conduction mode are investigated.