Rotor position and speed estimation of a variable structure direct torque controlled IPM synchronous motor drive at very low speeds

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