Sensorless Direct Torque and Flux-Controlled IPM Synchronous Motor Drive at Very Low Speed Without Signal Injection

This paper proposes a novel speed-sensorless direct torque and flux control scheme for an interior permanent-magnet synchronous motor drive. The drive uses a new stator flux observer based on the extended rotor flux concept. Due to the simultaneous implementation of stationary and rotating reference frames, the proposed observer does not require any speed adaptation and is inherently sensorless. Unlike speed adaptive observers, the proposed observer is immune to speed estimation errors; thus, its performance at very low speed is improved significantly. A novel stator resistance estimator is incorporated into the sensorless drive to compensate the effects of stator resistance variation. The global asymptotic stabilities of both the flux observer and stator resistance estimator are guaranteed by the Lyapunov stability analysis. Simulation and experimental results at very low speeds, including 0 and 5 r/min, confirm the effectiveness of the proposed method.