Two-Phase SR Drive with Flux-Reversal Free Stator and Balanced Normal Forces

This paper presents a two-phase switched reluctance machine (SRM) topology which has no flux reversals in the stator and balanced normal forces. It is an extension of a machine topology which was recently presented with a flux-reversal free stator (6/3), but the previous concept has inherently imbalanced radial force acting between the rotor and stator. These topologies are proposed in response to greater emphasis by industry and consumers on low-cost and high-efficiency variable speed drives in numerous applications. As such, SR drives with one or two electrical phases have attracted interest due to the simplicity of the machine construction and the electronic converter configuration. The two phase machine with a flux-reversal free stator was previously designed, analyzed, and experimentally verified in order to improve machine efficiency and reduce acoustic noise. However, further investigation of the particular topology revealed an imbalance of normal forces on the rotor. This paper proposes an extension of this structure to eliminate the imbalanced radial forces. For comparison, three machine topologies are designed and analyzed: a conventional two-phase SRM (4/2), the previous 6/3, and the proposed SRM (12/6) with balanced normal forces. Two-dimensional electromagnetic finite element analysis (FEA) is applied to each design. Particular attention was paid to minimizing torque ripple in the 12/6 design through shaping of the rotor pole. The data from FEA analysis is examined and reinforces that, although the 6/3 flux-reversal free topology does have the highest machine efficiency, it has a significant force imbalance acting between the rotor and stator. The 4/2 and 12/6 topologies have balanced radial forces and are comparable in terms of machine efficiency. The 12/6 design has significantly lower ripple torque than the 6/3 and 4/2 designs.