Modified SVPWM based torque ripple reduction in permanent magnet synchronous motor

Abstract

In steady state operation of Permanent Magnet Synchronous Motor (PMSM), torque decreases when Direct Torque Control (DTC) is applied. It results in deterioration of system performance. To fix this problem, this paper proposes a modified Space Vector Pulse Width Modulation (SVPWM) method by introducing speed feedback. In the proposed strategy, the prediction of stator flux is divided into two parts which can make PI controller work more effective. The DTC scheme is an inherent sensorless control technique. Its implement does not need the continuous rotor position information and requires only the initial position. Moreover the initial position is obtained by a method called High-Frequency Voltage Injection. In recent years, the performance of DTC has been greatly improved by the use of SVPWM technique. With the combination of SVPWM, the torque ripple can be reduced to an acceptable extent, especially in the low speed range of PMSM. The simulation results shows that both the steady state and dynamic state system performance are improved with the modified control method. An effective modality for reducing the torque ripple, proper reference voltage vector is calculated to produce the desired torque and flux values, and then applied to the inverter using SVPWM. This approach is known in the literature as DTC-SVPWM. This paper proposes a simple method for the calculation of the reference voltage vector, which preserves the conventional DTC principle regarding the decoupled torque and flux control.