Rotor Polarity Detection and Tracking for Slotless Permanent Magnet Synchronous Motors

This paper presents a novel rotor polarity detection algorithm for permanent magnet synchronous motors with slotless stator windings that exhibit low magnetic anisotropy and saturation effects. The proposed algorithm can be used together with existing injection-based rotor position detection methods that deliver rotor position with 180° ambiguity. It uses the estimated angle provided by such methods and determines the right orientation of the rotor. The algorithm is based on injecting voltage pulses along the q-axis of the assumed rotor reference frame and estimating the sign of the q-component of the induced back electromotive force (back-emf) in the same frame. The algorithm determines rotor polarity at standstill with only a very small rotor movement, which can be tolerated in many practical applications. In addition to this algorithm, the paper describes a method to track rotor polarity during motion. The effectiveness of the presented algorithm is illustrated experimentally.