A novel strategy of direct torque control for PMSM drive reducing ripple in torque and flux

An improved scheme is proposed to solve the torque and the stator flux linkage ripples of direct torque control (DTC) for a permanent magnet synchronous motor in this paper. Based on the analysis of the basic DTC theory, the space vector pulse width modulation (SVPWM) strategy for permanent magnet synchronous motor is designed. In the scheme, the error between the reference stator flux linkage and the estimated stator flux linkage is calculated during each sampling period, and the two nonzero adjacent voltage vectors are selected and then the operation time is calculated accurately. Finally the linear combination method is used to synthesize a new voltage vector. Compared with several fixed voltage vectors in the basic DTC, the voltage vectors in this strategy can trace the torque and the stator flux linkages very well because of their random, so the torque ripple may be reduced. This algorithm can also ensure the constant switch frequency. The simulation results show that this method is very feasible. It can dramatically reduce the torque and the stator flux linkage ripples of the basic DTC, and at the same time, the dynamic responses of the torque and the angular velocity are very fast. The control effect, thereby, is obtained very well.