A Study of System Losses in a Transistorized Inverter-Induction Motor Drive System

A study is described of the system losses in a transistorized pulsewidth modulated (PWM) inverter and induction motor in a traction drive system and the development of a strategy for minimizing them. The losses include inverter losses, conventional fundamental frequency motor losses, and motor harmonic losses. The losses in both PWM and six-step square wave (SSSW) inverter operation are studied. The loss models are introduced into a motor performance analysis program allowing the computation of the drive system performance over the entire speedtorque range. The study shows that a strategy for minimizing drive system losses is a function of torque. The air gap flux density should be held at its maximum level until the torque requirement is reduced to a low value, and then the air gap flux level is reduced.