Hybrid Encoderless Control of Multi-Salient Induction Motors in Parallel Connection at Variable Flux and Torque

Abstract

Saliencies that contain information about the rotor position offer a direct replacement signal for the shaft encoder. Some designs of induction motors feature a visible rotor-slotting saliency, which, in combination with the magnetic saturation saliency, gives rise to the commonly-referred intermodulation saliency. These saliencies modulate the transient current response resulting from active inverter switching, and so saliencies can be observed by calculating the phase current slopes. In recent works, intermodulation saliency has been utilized for extracting the rotor position. The primary advantage of the intermodulation saliency is the increasing amplitude with torque, what makes it a suitable saliency for the overload region. However, at light loads or reduced flux, intermodulation signal-to-noise ratio tends to decrease, what can decrease the performance of rotor position extraction. This often occurs in dual induction motors connected in parallel and fed by a single inverter. In this work, a hybrid saliency-based encoderless control scheme is proposed, employing the slotting and intermodulation saliencies depending on the actual torque and flux level. Experimental validation is conducted on a test stand consisting of two multi-salient induction motors used in railway applications and fed by a single inverter.