Sensorless Control of a Linear Permanent-Magnet Motor Based on an Improved Disturbance Observer

Linear permanent-magnet (PM) motors incorporate the merits of high efficiency, simple mechanism, and low cost, which have a bright future in urban rail transit. However, the position sensor costs are huge, which is the main barrier against a wider implementation. In this paper, a type of modified disturbance observer is newly proposed to improve the precision. Two disturbance observers are utilized to estimate the back electromotive force. Then, position information is detected by a phase-locked loop. Finally, the linear PM motor runs with the feedback of estimated position and speed instead of position encoder measuring. The algorithm avoids designing filters and injecting signals. Experimental results based on a linear primary PM vernier motor demonstrate the accuracy and dynamic performance. The comparisons in the aspect of the robustness to measurement errors certify that the modified disturbance observer is superior to the conventional disturbance observer.