Robust Magnet Polarity Estimation for Initialization of PM Synchronous Machines with Near Zero Saliency

This paper investigates magnet polarity estimation of permanent magnet synchronous machines. Because the magnet polarity is estimated from low signal-to-noise ratio signals, it is sensitive to additional signal content, affecting the robustness of magnet polarity estimate. An evaluation of eight low saliency machines identifies a dc-offset vector in the positive 2^nd harmonic carrier signal current as the primary source of magnet polarity estimation error. Angular offset is a secondary limitation to the polarity estimation robustness. By estimating and decoupling the dc-offset vector and the angular offset the robustness is improved and applicability to a wide set of the machines is enabled