STABILITY ANALYSIS OF MULTILEVEL INVERTER FED INDUCTION MOTOR DRIVE

Abstract

The stability problem in an induction motor drive system has to be discussed essentially from two different angles. One is from the angle of the power source in relation to the achievement of quick response in electromagnetic torque. The other is closely related to the well known self-exitation phenomena in a self-exitated type induction generator.The former is associated with the interaction between electric transients and rotor dynamics. For an induction motor driven by a voltage source of adjustable amplitude and frequency such as a PWM inverter the problem of occurrence of sustained oscillation has often been observed in the light loaded state. The two problem which should be considered are 1) under what condition is the oscillation exited, and how is the oscillating range is determined in the stator voltage verses frequency (V/F) plane. If the matter is consider from the stand point of drive performance, the stability is quite easily be interpreted. Whenever the electromagnetic torque is so controlled as to be kept, without delay, at a desired value required from the load side, the stability problem never occurs. Hence factors deteriorating the stability are the existence of the stator resistance and leakage inductances in both stator and rotor circuits or transient inductance.