An extended rotor-flux model for sensorless direct torque and flux control of interior permanent-magnet synchronous motor drives

Direct torque and flux control (DTFC) of interior permanent-magnet synchronous motors (IPMSMs) 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 the extended rotor flux concept, which does away with the saliency in an IPMSM. This observer is combined with the DTFC scheme to achieve a high performance sensorless IPMSM drive over a wide-speed range, including standstill. Experimental results at very low speeds - 0 rpm and 5 rpm without signal injection confirm the effectiveness of the proposed approach.