Novel sensorless control for permanent magnet synchronous machines based on carrier signal injection

In this thesis, the carrier signal injection methods are in focus for the sensorless control of permanent magnet synchronous machines (PMSMs), utilising alternative types of carrier responses, i.e., the carrier current and zero sequence carrier voltage, respectively. For the carrier current sensing based carrier signal injection methods, this study investigates the combined effects of signal processing delays and HF resistance, which generates large position estimation errors. Accordingly, a new compensation strategy by modifying the phase angle of the demodulation signal is proposed. The influence of machine parameter asymmetries on the conventional carrier injection methods is also investigated. The 2 nd harmonic position estimation errors will arise due to the asymmetries. To mitigate the resistance asymmetry, the selection of the proper injection frequency is discussed. Besides, a new dual frequency injection strategy is also proposed for inductance asymmetry suppression. Furthermore, a novel carrier signal injection strategy with zero sequence carrier voltage sensing is proposed. This injection strategy is performed on the estimated reference frame, anti-rotating at twice the estimated electrical speed of the rotor. It combines the synergies of both the zero sequence method (i.e., high bandwidth and stability) and the pulsating injection (i.e., high accuracy and fast dynamic response). Then, the proposed anti-rotating injection strategy is further applied for the square-wave signal injection. The anti-rotating square-wave injection with zero sequence voltage sensing can also integrate the merits of both zero sequence voltage sensing and square-wave injection. In addition, magnetic polarity identification using the zero sequence voltage responses is also performed. The amplitude variation-based polarity detection method using the zero sequence voltage has a higher detection sensitivity than the conventional method using the carrier current. The secondary harmonic based detection method using the zero sequence voltage has the advantages of simple signal demodulation, fast response, and a large signalto-noise (S/N) ratio. Considering that the secondary harmonics of the zero sequence voltage contain the actual magnetic polarity information and have less distortion, they are directly utilised to estimate the rotor position. This removes the time-consuming process of the polarity detection, and enhances the robustness and stability of the estimation. The final part of the thesis presents full comparisons for the different carrier signal injection methods with alternative types of carrier responses sensing. The influence of signal processing delays, the cross-coupling magnetic saturation effects, inverter nonlinearity effects, and multiple saliency effects, etc., will be investigated.