Standstill Position Estimation of SPMSM Robustness to Manufacturing Tolerances

A calibration method is presented to overcome phase unbalance and eccentricity effects in zero speed position estimation of surface-mount permanent magnet synchronous motors (SPMSM). Mechanical tolerances and random nature of winding cause sample to sample variation in phase inductances and saturation saliencies. Finite element simulations were performed to investigate the effects of eccentricity and winding unbalances on phase inductances. To confirm this behavior, experiments were performed on a set of SPMSMs manufactured in the same batch to measure actual sample to sample variation of saliency ratios and offsets. The simulation and experimental results indicate a significant variation in the average value of the phase inductances from sample to sample, which evince the need for separate calibration of each motor unit for accurate initial position estimation. The paper proposes six calibration parameters to model the inherent unbalances, which can be used to estimate the standstill position of SPSM.