Rotor Position and Speed Estimation of a Variable Structure Direct-Torque-Controlled IPM Synchronous Motor Drive at Very Low Speeds Including Standstill

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 (HF) 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 the estimated rotor position information for stator flux and torque estimation purposes. Experiments were performed to test the effectiveness of the proposed HF signal injection algorithm, and results show that the sensorless drive is capable of accurately estimating the position and speed at very low speeds including standstill. The implementation of the changeover algorithm to switch between the two observers at low and high speeds has enabled sensorless operation of the drive from zero to base speed.