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 second-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.