A Novel Duty-Controlled DTC of a Surface PMSM Drive With Reduced Torque and Flux Ripples

Abstract

Direct torque control (DTC) is a widely used method for the control of permanent magnet synchronous motor (PMSM) drive. DTC suffers the drawback of high ripples in torque and flux. Various duty-cycle-controlled DTC methods have been introduced in the recent past to improve the steady-state response of the PMSM. However, the existing duty-cycle-controlled DTC methods are complex and result in higher switching frequencies. This article introduces a novel duty-controlled DTC for reducing the ripple in torque and flux without giving considerable rise in the switching frequency and computation burden. The proposed DTC applies two separate voltage vectors (VVs) for individual control of stator flux and torque during two different sampling intervals. A look-up table is proposed to select candidate VVs and their duty ratios are calculated to achieve the reference values of stator flux and torque in two sampling intervals. This causes a major reduction in the torque and stator-flux ripples. Also, the proposed method decides the sequence of candidate VVs to reduce the number of switching and thereby reduce the switching frequency. The proposed method is experimentally tested and compared with conventional DTC, an existing duty-based DTC, and deadbeat DTC to verify its effectiveness.