Analysis of one step delay in direct torque control of permanent magnet synchronous motor and its remedies

One-step delay in digital implementation of direct torque controlled (DTC) AC motor drives leads to large torque ripple and low switching frequency. Two remedies are proposed in this paper to eliminate the one-step delay. One is based on model-based prediction, which is complex and relies much on the model; the other is based on the multiple sampling of stator current. Different from the model-based method, the stator current prediction in the second method is achieved by using linear extrapolation, which does not require the motor model. By using the one-step compensation, the torque and flux ripples are reduced effectively and the switching frequency is increased, making better use of the power converters. The two remedies are firstly simulated in Simulink, and then experimentally verified in a permanent magnet synchronous motor (PMSM) DTC drive, validating the effectiveness of the proposed methods.