PERFORMANCE EVALUATION OF immer TORQUE CONTROLLED MULTI LEVEL INVERTER FED INDUCTION MOTOR DRIVE

Abstract

The control and estimation of ac drives in general are considerably more complex than those of dc drives, and this complexity increases substantially if high performances are demanded. In recent years Direct Torque Control is one of the actively researched control schemes, which is based on the decoupled control of flux and torque providing a very quick and robust response with a simple control scheme. In the classical DTC scheme using 2 level inverter, due to the limited number of voltage vectors large and small errors in torque or flux cannot be distinguished. In fact switching vectors chosen for large errors are same as for small errors. In this work in order to overcome this problem multi level inverter is used instead of 2 level inverter. This work presents a novel Direct Torque Control algorithm to be applied in induction motor electric drives supplied by Multi-level Diode Clamped inverters. Results obtained with numerical simulation show that the employment of a Multi level inverter in such a control scheme permits to obtain the same dynamic performances as those obtained with a 2 level inverter with resulting far lower torque and flux ripples as well as lower harmonic content in stator current.