Full Speed Range Sensorless Drive of Nonsalient PMSMs Based on PLL-Type Speed and Position Estimator

In the drive system of nonsalient permanent magnet synchronous motors, sensorless control at low speed remains challenging, since the existing saliency-based and model-based methods may be ineffective. To address this issue, this article proposes a sensorless control method capable of full-speed-range operation. In the proposed method, an extended state observer estimates the back-electromotive force in the γ-δ frame, while a phase-locked loop-type estimator extracts the rotor position and speed. Experimental results demonstrate that the motor can start up from any initial position under rated load and achieve reliable speed reversal. Moreover, the method maintains high estimation accuracy even when the motor runs at 2% rated speed. This indicates that a single-method full-speed-range sensorless solution is feasible.