Investigation on Contribution of Inductance Harmonics to Torque Production in Multiphase Doubly Salient Synchronous Reluctance Machines

Abstract

including the URL of the record and the reason for the withdrawal request.Abstract-This paper investigates the contribution of each order inductance harmonic to the torque (both average torque and torque ripple) of multiphase doubly salient synchronous reluctance machines (DS-SRMs). Such machines are similar to switched reluctance machines but supplied with sinewave currents. The investigations in this paper are as follows: first, a general analytical torque model based on Fourier Series analysis of inductances has been built for machines with different phase numbers, slot/pole number combinations and also winding configurations. The instantaneous torque for DS-SRMs with any given phase number can then be accurately predicted. Using such model, contribution of each order inductance harmonic to torque can be investigated separately. It is found that the torque ripple frequency of the DS-SRM only depends on phase number. For example, for a m-phase machine, there will be m×k th order torque ripple if , where m is phase number and k is a natural number. This study also explains why certain phase numbers inherently produce lower torque ripple than others. The findings in this paper provide a future direction for potential torque ripple reduction methods either from machine design or advanced control. The simulations have been validated by experiments using a 6-phase DS-SRMs.Index Terms-Doubly-salient, multiphase machine, synchronous reluctance machine, torque harmonic.

Impact of Current Harmonic Injection on Performance of Multi-Phase Synchronous Reluctance Machines

“…As can be proved that the 𝑇 ℎ only contains the mk th order torque harmonic, which is the same as that of 𝑇 𝑓 (as detailed in [15]). Therefore, it is possible to compensate for torque ripple produced by the fundamental current using a contribution produced by a current harmonic.…”

“…𝜃 𝑒 is the electrical rotor position. Based on the study in [15], there will be one type of self-inductance waveform and Z types of mutual-inductance waveform for an m-phase DS-SRM. The factor 𝑍 depends on the phase number and is be the minimum integer which is no less than (𝑚 − 1) 2 ⁄ .…”

“…where the subscripts 'f' and 'h' represent the components due to fundamental and harmonic currents; 'sel' and 'mut' are the torques produced by self-and mutual-inductances; '0' and 'rip' are the average torque and torque ripple, respectively. The torque produced by sinewave current for m-phase machines has been investigated in [15]. This section will further detail the torque components produced by the interaction between current harmonics and self-/mutual-inductances, which can be decoupled into two terms: 𝑇 ℎ (𝐼 𝑓 𝐼 𝑣 ) and 𝑇 ℎ (𝐼 𝑣 2 ).…”

“…Since current shaping or harmonic current injection will introduce higher order harmonic currents, it is likely to increase core losses in the machines, and hence lead to reduced efficiency. Therefore, if maintaining sinewave current is deemed desirable, increasing the phase number (m) may be another effective means of reducing torque ripple [14]- [15]. In addition, machines with higher phase number (m>3) can also achieve higher torque density and enhanced fault-tolerant capability [16]- [17].…”

“…Previous studies have demonstrated that the multiphase DS-SRM also have different characteristics compared to their 3-phase counterparts with sinewave current supply, e.g. more different types of mutual-inductances [15]. Hence, if harmonic current is injected into a multi-phase DS-SRMs, it is likely that it will behave differently compared to its 3-phase counterpart.…”