Signal injection method without torque ripple based on maximum torque control frame

This paper presents a new signal injection method without torque ripple for sensorless controls of salient-pole synchronous motors at low speeds. At low speeds, since the back electromotive force (EMF) including position information decreases, additional signals are injected to estimate position information of saliency. The torque ripple caused by the injections of signal currents can be represented by a cross product of a virtual flux and a differential current vector. An f-axis of maximum torque control frame is defined to the direction of the virtual flux. Therefore, signal injection without torque ripple is realized by using the f-axis current. In this paper, a signal injection method with f-axis current is proposed, and the effects of the estimation error are discussed to apply the method for position-sensor-less controls. The proposed injection method allows us to flexibly design frequencies of the signal current. The validity of the proposed method and applicability to position estimation are confirmed by experimental tests. (c) 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.