Sensorless Control for Induction Machines Based on Square-Wave Voltage Injection

This paper presents a sensorless control for induction machines, using square-wave voltage injection. Multiple saliencies are considered, as well as saliency orientation shift according to loading conditions. These two nonideal phenomena severely degrade the performance of sensorless controls for induction machines. Multiple saliencies cause the position error signal to become distorted and make estimation of the rotor flux position difficult. Saliency orientation shift causes the estimated rotor flux position to drift from the actual rotor flux position, depending on the torque and speed. In this study, a sensorless algorithm based on square-wave voltage injection is adopted for induction machine control. When square-wave voltage is injected into the estimated synchronous reference frame, the harmonics of the error signal are lower than those of the conventional sinusoidal injection method. In addition, by injecting a square wave into the q-axis of the estimated synchronous reference frame instead of the d-axis, the saliency orientation shift is made smaller. Based on this study using square-wave voltage injection into the q-axis, the flux can be estimated with less error. Because of its enhanced rotor flux estimation performance, the proposed method provides better torque controllability than the conventional sinusoidal voltage injection method. Experimental results confirm the effectiveness of the proposed technique.