Enhanced rotor position/speed observer for sensorless control of salient-pole permanent-magnet synchronous machines

Reliable rotor position/speed estimation is one of the key issues in the position/speed sensorless control of permanent-magnet synchronous machines (PMSM). In this paper, a quasi-sliding-mode observer (QSMO) with an online observer parameter adaption scheme is employed to estimate the extended electromotive force of a salient-pole PMSM. Due to machine parameter variations, inverter nonlinearities and digital delays, a pulsating position estimation error or even instability might be observed in the closed-loop sensorless control during extreme loading conditions. This work proposes an enhanced speed/position estimator, which utilizes a phase-locked loop (PLL)-type observer with a proportional-integral plus integral structure. To further mitigate the pulsating position estimation error and improve the transient stability, an online phase compensator using the γ-axis (i.e., the estimated d-axis) current tracking error is proposed to compensate the rotor position estimation error of the PLL-type observer. Experimental results are provided to validate the effectiveness of the proposed rotor position/speed estimator and the sensorless control system for a salient-pole PMSM.