Investigation of performance improvement of doubly salient synchronous reluctance machine with current harmonic injection

This thesis investigates some novel current harmonic injection methods to improve the electromagnetic performance of doubly salient synchronous reluctance machines (DS-SRMs). These machines will have different winding configurations, slot/pole number combinations and phase numbers. The theoretical analyses (both static and dynamic) are carried out based on Fourier Series analysis, and validated by 2-dimensional finite element method and also experiments using several prototype machines.
Based on the analytical torque model in abc-axis frame, a powerful insight into the mechanism of torque generation of the DS-SRMs with pure sinewave current supply can be achieved. The electromagnetic torque (both magnitude and phase angle) produced by each order of inductance harmonic can be predicted, which allows us to obtain the dominant torque ripple components for such machines. Therefore, the appropriate current harmonic (3rd, 5th and 7th) can be injected to generate torque ripple components in order to compensate that produced by the fundamental current, and hence to achieve an overall reduced torque ripple. On the other hand, the average torque of the DS-SRMs can also be improved by properly selecting the current harmonics in terms of harmonic order, amplitude and phase angle. However, it is found that the current harmonics, although can improve torque performance, will often cause extra losses (both copper and iron losses) and undesirable distortion in the phase voltages, which could lead to negative impact on the machine efficiency and dynamic performance. Therefore, in order to fully evaluate the potential of the proposed harmonic current injection method, comprehensive studies about losses, efficiency and dynamic performances such as torque-speed curves of 3-phase and multi-phase DS-SRMs have been carried out. In order to simplify the investigation of dynamic performance analyses such as the torque speed curves and efficiency maps, novel analytical torque model in dq0-axis frame has also been proposed. The findings in this thesis can provide some useful guidelines for torque performance improvement of DS-SRMs using harmonic current injections.