Comparative studies of torque performance improvement for different doubly salient synchronous reluctance machines by current harmonic injection

Three types of doubly salient synchronous reluctance machines have been comparatively studied to improve the torque performance using current harmonic injection methods. These machines are derived from the switched reluctance machines (SRMs) with different winding configurations, such as the double/single layer mutually coupled SRMs (MCSRMs) and fully pitched SRMs (FPSRMs), by supplying them with sinewave current. Such current supply mode can lead to higher torque/power density, lower vibrations and acoustic noise compared to the conventional rectangular current supply. The proposed torque analytical model can predict the instantaneous torque of the doubly salient SRMs with sinewave current excitation and the current harmonics also can be selected in order to reduce the torque ripple and/or increase the average torque. It has been found that the 3rd current harmonic injection shows the best performance for single-layer MCSRMs and FPSRMs because it improves the average torque and reduces the torque ripple at the same time. However, it has little influence on doubly-layer MCSRMs. To improve the torque performance of such machines, other harmonic currents, e.g. 5th and 7th, need to be used. Both static and dynamic tests have been carried out to validate the predictions.