Very low speed operation of a variable structure direct torque controlled IPM synchronous motor drive using combined HF signal injection and sliding observer

The performance of a speed sensorless variable structure direct torque controlled interior permanent magnet synchronous motor drive is investigated in this paper. The speed is estimated using position information extracted using high frequency signal injection at low speeds and a sliding observer at high speeds. The changeover between these two algorithms is performed using a weighting function which smoothly hands over position information used for speed, torque and flux estimation. Experiments were performed to test the effectiveness of the proposed algorithm and results show that the sensorless drive is capable of accurately estimating position and speed at very low speeds including zero speed.