Improved rotor position estimation in sensorless-controlled permanent-magnet synchronous machines having asymmetric-EMF with harmonic compensation

This paper investigates the performance of sensorless control of switched-flux permanent-magnet synchronous machines (SFPM) with different stator winding topologies, such as all poles wound (double-layer winding) and alternate poles wound (single-layer winding), whose back electromotive force (EMF) exhibit different waveform characteristics, i.e., sinusoidal, asymmetric, and non-sinusoidal waves. Most importantly, it is found that the single-layer SFPM machine is with asymmetric back-EMFs, due to which the performance of sensorless control will deteriorate. In order to minimize this influence, a control strategy is developed for the improvement of accuracy of rotor position estimation, which is based on the elimination of back-EMF harmonics and not sensitive to the machine parameters. In addition, it also shows that the developed strategy is easy for implementation and the experimental results confirm that the influence of asymmetric and non-sinusoidal back-EMF can be effectively compensated. Consequently, an improvement in the accuracy of rotor position estimation is achieved at both steady and dynamic states as compared with those conventionalmethods without compensation.