Sensorless Control of Permanent Magnet Synchronous Motors for Zero- and Low-Speed Region

The study presents results from the evaluation of sensorless control techniques for permanent magnet synchronous motors (PMSM). The focus is on achieving low mechanical rotor speed using a high frequency (HF) signal injection method and signal demodulation in a dq system. Injecting pulsating voltage into the dq system allows the flux-producing and torque-producing components of the voltage and current to be separated, unlike injecting rotating voltage into the two-phase stationary reference frame αß, which causes increased noise and torque ripple. Utilizing pulsating voltage is more preferable than solely utilizing the d-axis, as it doesn't have as significant an impact on the motor torque. This technique estimates various individual quantities necessary to complete the current transformation between three-phase stationary reference frame abc, two-phase stationary reference frame αß, and rotational reference frame dq, including estimated mechanical rotor speed and estimated electrical rotor position. The study utilises actual measurements and simulations. Additionally, the research exhibits how this was implemented on an actual motor. The results show that the investigated method is able to control the motor at low and zero speed with relatively low amplitude of the injected signal and relatively low saliency of the motor. Conclusion is that this technique is highly appropriate for controlling the motor at low and zero speeds without having a major impact on the torque ripple.