Sensorless initial rotor position identification for non-salient permanent magnet synchronous motors based on dynamic reluctance difference

Due to the equivalence between the d-axis and q-axis static reluctance in non-salient permanent magnet synchronous motors (PMSMs), the traditional saliency-tracking self-sensing strategies appear powerless for rotor position identification. However, the nonlinear magnet saturation characteristic results in much larger d-axis dynamic reluctance than that in q-axis, then two novel methods based on the dynamic reluctance difference are proposed for sensorless initial rotor position detection. In the high frequency rotating voltage injection method, the positive-sequence and negative-sequence second-harmonic carrier current components are used to estimate two pre-angles simultaneity and separately, where the final estimated rotor position is calculated with the offset angle caused by q-axis dynamic reluctance eliminated. In the high frequency pulsating voltage injection method, the cosine second-harmonic carrier current component contains rotor position and magnet polarity information. The position signal is employed to estimate the possible pre-angles from three symmetrical and equidistant initial estimated angles respectively, where the pre-angle with the largest and negative polarity signal is the final estimated rotor position. Both methods can accomplish the rotor position estimation without an additional polarity detecting process. The simulation and confirmatory experimental results on a surface-mounted PMSM demonstrated the proposed methods can estimate initial position reliably and fast at standstill.