Reduced number of switch direct torque control of induction machine with bidirectional capability

Abstract

In the middle of 1980s a novel technic for alternating current (AC) machine control is proposed, this technic is known as direct torque control (DTC). It happens that the control algorithm of this technic is simple and less sensitive to machine parameters compared to others technics. It is based on direct determination of suitable switching states according to the error of the torque and flux. However, since the switching frequency of basic DTC is not constant then high torque and flux ripples are produced which in turns degrade the performance of this technic, especially at low speed regions.

This work introduces and compare between DTC or induction motor (IM) using six switch three phase inverter (SSTPI) and DTC for IM using four switch three phase inverter (FSTPI). The basic FSTPI results in four unbalanced voltage vectors, which in turns divide the ?? plane into four sectors. These unbalanced voltage vectors generated by the FSTPI leads to high torque and flux ripples, in order to improve these performances, effective vectors are introduced; this strategy is based on the emulation of the operation of the conventional SSTPI. This has been achieved by suitable combination of the four unbalanced voltage vectors. This approach allows using the well-known established switching table of SSTPI for FSTPI. The simulation results comparaison of the proposed FTSTPI fed IM drive with the conventional SSTPI system shows that the proposed technic is quite acceptable considering its performance such as fast speed response, cost reduction and other advantages features.