Low-speed Performance. Direct Torque Control Of Induction Motor Based On Dsvm Strategy Improvement Research

This paper is against the disadvantages of the induction motor basedon direct torque control which has large torque ripple, current distortion,flux depression and unstable switching frequency in the low speed range.By integrating method of voltage space vector with direct torque control,It introduces a method based on discrete space vector modulation (DSVM)which more voltage vector chosen in per controlling period is integratedto target voltage vector according to different torque, flux and speedrange. This method increases the number of voltage vector withoutadding complexity of circuit and system.Based on the analysis of DSVM, in order to improve the fault ofpositive bias of actual average torque, which caused by the zero voltagevector frequently be used in low speed. This paper proposes a modifiedstrategy of DSVM-DTC to optimize the '-' part of sector switching table,which is used to reduce the torque and current ripples and improve theperformance of system in the low speed range. At the same time, byintegrating the technology of fuzzy control, a fuzzy logic controller isadopted instead of the conventional hysteresis controllers of torque andflux. It solves the problems that the variation range of stator flux andtorque can not be distinguished accurately and some small changescaused by indefinite factors could not be controlled timely inconventional direct torque control. Furthermore, an angle mappingstrategy is used in the fuzzy DSVM-DTC to reduce the fuzzy controlrules steadily, which availably improves the whole performance of thesystem.At last, simulation models of the conventional DTC, theconventional DSVM-DTC, the improved DSVM-DTC and the fuzzyDSVM-DTC are separately established based on the MATLAB/Simulinkplatform. Simulation results can prove that the large torque tipple, currentdistortion, flux depression have been overcame remarkably whilemaintaining the switching frequency constant through the application ofthe improved DSVM-DTC and the fuzzy DSVM-DTC strategy. The low speed performance of direct torque control has been improved effectively.