SVM direct torque control of IPM synchronous machines at very low speeds

The performance of direct torque control (DTC) of interior permanent magnet(IPM) machines at low speed is poor due to a few reasons, namely limited accuracy of stator voltage acquisition and the presence of offset and drift components in the acquired signals. Factors such as forward voltage drop and dead-time across switching devices in the three phase inverter become significant problems at very low speed as their magnitude becomes comparable with the back-emf used for accurate stator flux and torque estimation. High frequency signal injection in the d-q frame is implemented and the current model is used for flux and torque estimation at very low speeds. Results show very good dynamic and steady state performance of the SVM-DTC IPM drive at very low speeds including zero speed.