An extended rotor flux model for sensorless direct torque and flux control of IPM synchronous motor drives

Direct torque control (DTC) of interior permanent magnet (IPM) synchronous motors is known to deliver fast torque and flux dynamic responses. However, the poor flux estimation at very low speeds has been its largest drawback. A multitude of flux observers have been proposed for flux estimation but most of them fail to fare in the low speed region. This paper proposes a new stator flux observer for improved flux estimation at very low speeds. The observer is based on a novel extended rotor flux concept which does away with the saliency in an IPM motor. This observer is combined with the direct torque and flux control (DTFC) scheme to achieve a high performance sensorless IPM motor drive over a wide speed range. Experimental results at very low speeds -5 rpm and 10 rpm without signal injection confirm the effectiveness of the proposed approach.