A Time-Delay Compensation Method for IPMSM Hybrid Sensorless Drives in Rail Transit Applications

This paper proposes a hybrid sensorless control strategy for rail transit application employing interior permanent magnet synchronous machine (IPMSM), which works under low switching frequency. Due to a long system time delay, the convergence rate of estimated position in the sensorless dynamic region is reduced. As the speed increases, the $dq$ axes currents coupling is more severe, and deteriorates the control performance. In order to solve these problems, the analysis of time-delay effect on the IPMSM sensorless drives is first derived. Then, using $q$-axis current error, a global time-delay compensation method is designed to eliminate the lag angle of estimated position. Furthermore, the effect of this compensation on audible noise reduction is also analyzed. Through a phase-locked loop, the hybrid estimated position is obtained from a normalized position error. Finally, a 3.7-kW IPMSM is tested to verify the feasibility of the proposed sensorless method.