Minimization of torque ripple of direct-torque controlled induction machines by improved discrete space vector modulation

Abstract

In this paper, discrete space vector modulation (DSVM) technique for induction machine drives is developed, and then a fuzzy logic direct torque control (DTC) scheme based on the proposed DSVM technique is presented. In DSVM technique, new voltage vectors are synthesized by applying three standard voltage space vectors for three equal time intervals at each sampling period. Rearranging the sequence of the three voltage space vectors does not change final synthesized voltage vectors, but has an influence on torque ripple. By comparing torque waveforms in one sampling period, an analysis is carried out to determine the influence. Based on the analysis, new switching tables used in DSVM-DTC are defined. In the switching tables, the three components of each synthesized voltage vector are arranged in optimized sequence. Finally, a fuzzy logic controller is designed to select synthesized voltage vectors. Its control rules are established based on the proposed switching tables. The proposed scheme is verified by simulations. Simulation results show that a reduction of torque ripples is achieved in a whole speed range.