Torque ripple minimization strategy for direct torque control of production motor

In this paper, a torque ripple minimization technique with constant switching frequency is proposed for direct torque control (DTC) of an induction motor. Some drawbacks of conventional DTC are the generation of relatively large torque ripple in a low speed region and a variation of switching frequency according to the amplitudes of torque and flux hysteresis bands. In this proposed strategy, an optimal switching instant during one switching cycle is calculated for torque ripple minimization which is derived from the RMS torque ripple equation based on an instantaneous torque equation. The proposed strategy improves the performance of the DTC by combining a low torque ripple characteristic in the steady state and the conventional fast torque dynamic characteristic. Experimental results prove the feasibility of the proposed strategy compared with the conventional method.