Optimization of Torque Tracking Performance for Direct-Torque-Controlled PMSM Drives With Composite Torque Regulator

Abstract

In this article, a composite torque regulator is proposed for optimizing the torque tracking performance in direct torque-controlled permanent-magnet synchronous motor drives. In the proposed composite torque regulator, two new variable hysteresis bands are designed and combined with two constant hysteresis bands. In the conventional direct torque control (DTC) scheme, the torque increasing rate and decreasing rate are changed with different speeds and loads. Thus, the average torque will deviate the reference torque seriously under some operation states. With torque deviation, the reference torque can hardly reflect the actual electromagnetic torque, and the torque tracking becomes more difficult and unsatisfactory in dynamic process. On the other hand, the time delay of one sampling period further deteriorates the precision of torque tracking. By introducing the proposed composite torque regulator, both torque deviation and the impact of time delay on the torque ripple can be eliminated. In addition, the advantages of the conventional DTC scheme, namely low switching frequency, fast dynamic response, simple structure, and independence of motor parameters, can be reserved in the proposed DTC scheme with a composite torque regulator. Experimental results are presented to verify the effectiveness of the proposed scheme and compare its performance with the conventional DTC scheme.