MATHEMATICAL MODELS FOR A PWM INVERTER FED INDUCTION MOTOR.

Preliminary results are presented of an investigation into the transient and harmonic behavior of a three-phase induction motor supplied from a pulse-width-modulated (PWM) voltage source inverter. It evaluates the use of the two-axis theory and the simpler ac equivalent circuit method as two alternative mathematical models to represent the PWM voltage wave and the motor circuits. Results are presented for a case study and they indicate that the two methods yield virtually the same answers for the steady cyclic motor current and torque oscillations. The ac equivalent circuit method has simpler equations and may safely be used by drive designers, but it fails to predict the starting-up transients accurately.