Back EMF-Based Dynamic Position Estimation in the Whole Speed Range for Precision Sensorless Control of PMLSM

Back electromotive force (EMF)-based sensorless control strategies for permanent-magnet linear synchronous motor (PMLSM) have the potential to simplify the mechatronic system, reduce the cost and prolong the service life. However, the poor performance in the low-to-zero speed region limits their application range. In this article, a novel back EMF-based mover position estimator is proposed to achieve consistent good accuracy in the whole speed range including high speed, medium speed, low speeds, temporary standstill, and speed reversals. The three-phase flux linkages are obtained by directly calculating the integration of back EMF. To overcome the curve drift caused by the integrator, this article proposes a jumping correction algorithm and a uniform correction algorithm. The mover position is calculated from the corrected flux linkages. This article also realizes a closed-loop sensorless trajectory tracking control system using the proposed position estimator. Experimental results on a PMLSM demonstrate that the proposed position estimator can guarantee the stability and accuracy in the whole speed range. Compared with the existing back EMF-based methods working only well in high-speed region and usually with mm-level accuracy, the proposed method achieves an accuracy of sub-200 mu m regardless of the reference trajectory, and has exciting prospect in industrial applications.