Modified Direct Torque Control of PMSM Drives using Dither Signal Injection and Non-Hysteresis Controllers

Abstract

International audienceThe DTC of voltage source inverter fed PMSM is based on hysteresis controllers of torque and flux. It has several advantages, namely, elimination of the mandatory rotor position sensor, less computation time and fast torque response. In addition, the stator resistance is the only parameter, which should be known and no reference frame transformation is required. The implementation of DTC in PMSM drives is described and the switching tables specific for an interior PMSM are derived. The conventional eight voltage-vector switching table, which is namely used in the DTC of induction motor, does not seem to regulate the torque and stator flux in PMSM well when the motor operates at low speed. Modelling and simulation studies have both revealed that a six voltage-vector switching table is more appropriate for PMSM drive at low speed. Different switching algorithms using hysteresis and non-hysteresis controllers are proposed and the effectiveness of the strategies are analyzed and discussed. In addition, a modified method is propoed which introduces dither signal injection so that the flux and torque ripples are reduced