Accuracy-Enhanced Sensorless Control of Permanent Magnet Linear Synchronous Motor Under Asymmetric Back Electromotive Force

Sensorless control of permanent magnet linear synchronous motors (PMLSMs) offers advantages such as reduced cost, stronger robustness, and easier maintenance. Existing back electromotive force (BEMF)-based sensorless control methods often assume three-phase circulant symmetry, which is not valid due to end effects, thereby losing accuracy. To reduce the reliance on symmetry assumptions and improve accuracy, this article first proposes a jumping curve jumping amplitude (JCJA) algorithm to reconstruct asymmetric three-phase flux linkages. Next, instead of using the traditional Clarke transform, this work proposes a new cotangent transform (CotT), which can precisely extract orthogonal and equal-amplitude$\boldsymbol{\alpha}$-$\boldsymbol{\beta}$components without requiring three-phase symmetry. Experimental results on a PMLSM show a significant improvement in position and speed estimation accuracy compared with existing methods assuming symmetry. Finally, sensorless trajectory-tracking control is realized with accuracy and robustness, providing new insights into the field of precision sensorless control of linear motors.