Sensorless control for induction machines using square-wave voltage injection

This paper presents a sensorless control for induction machines using a square-wave voltage injection. Multiple saliencies and a saliency orientation shift are considered in this paper. The multiple saliencies make the position error signal distorted and the estimation of the flux position difficult. And, due to the saliency orientation shift, the estimated rotor flux position drifts from the actual rotor flux position according to torque and speed. When the square-wave voltage is injected into the estimated synchronous reference d-q frame, the error signal has lower harmonics than that of the conventional sinusoidal injection method. In addition, by injecting the square-wave into q axis of the estimated synchronous reference frame, the flux can be estimated with less error compared to the injection into d axis. Because of the enhanced rotor flux estimation performance, the square wave injection into q axis reveals better torque controllability compared to the sine wave injection into d axis.