An Optimized PLL With Time Delay and Harmonic Suppression for Improved Position Estimation Accuracy of PMSM Based on Levenberg-Marquardt

This article proposes an optimized phase-locked loop (OPLL) based on Levenberg-Marquardt (LM) to improve the estimation accuracy of the sliding mode observer-based position estimator. The position estimation suffers from dc bias caused by digital control delay, and harmonics caused by inverter nonlinearity and flux spatial harmonics. The OPLL is constructed in two parts to overcome the above negative effects. The delay phase is preliminary calculated based on linear prediction, so as to compensate for the lag phase in the estimated back electromotive force (back-EMF); secondly, the objective function is built based on the reference and feedback position errors, the former of which contains an unknown harmonic. The objective function can be minimized by the LM to solve for the harmonic amplitude, and then the obtained harmonic is used to offset the harmonic components in the estimated position. Wherein, the required partial derivatives of the LM method can be deduced based on the transfer function of PLL and the delay-compensation back-EMF to achieve a stable update of harmonic amplitude. Finally, the corresponding comparative experiments in steady state and dynamic conditions proved the superiority of the proposed method applied to permanent magnet synchronous motors.