Sliding-Mode Observer based Direct Torque Control of an IPMSynchronous Motor Drive at Very Low Speed

Abstract

Fast torque and flux dynamic responses are delivered by direct torque control of interior permanentmagnet synchronous motors. However, the major drawback is being the poor flux estimation at very low speeds. A majority of flux observers have been proposed for flux estimation, but most of them fail to check in the lowspeed region. In this paper, to improve flux estimation at very low speeds, a sliding-mode stator flux observer is proposed. This observer does not require any speed adaptation mechanism unlike conventional flux observers and is immune to speed estimation error. A novel stator resistance estimator is incorporated into the sensor less drive to compensate the effects of stator resistance variation. DC-offset effects are reduced by introducing a small elemental component in the observer gains. Simulation results at very low speeds, including 0 and 2 r/min, without signal injection confirm the effectiveness of the proposed method.