Low-Speed Rotor Angle Estimation of Multi-Salient Railway Propulsion Motors at Any Torque

Providing reliable and efficient electric drives for rolling stocks are two key objectives within the railway industry. Accordingly, industries are putting relentless efforts in increasing drives’ reliability and reducing their cost and volume. In this sense, encoderless motor drives can notably contribute to these targets. While high-speed encoderless operation can be successfully ensured by fundamental-wave models, stable control at speeds around zero speed is still challenging and, as yet, not standard. At near-zero speeds, the use of spatial saliencies of induction motors (IMs) opens up new horizons of encoderless control methods since saliencies provide information on the rotor angle or flux. In particular, the standard design of railway propulsion IMs occasionally involves the creation of three dominant spatial saliencies: saturation, slotting and intermodulation. This intermodulation saliency has been previously compensated in available literature. In this work, the intermodulation saliency is used to obtain a rotor position, harnessing its distinct characteristics of high signal strength and high estimation accuracy even at the challenging point of overload. Two standard railway traction motors with different ratings serve to experimentally validate the suitability of the intermodulation saliency for high-precision rotor position extraction at near-zero speeds under a wide torque range even beyond rated load.