Flux-Modulated Relieving-DC-Saturation Hybrid Reluctance Machine With Synthetic Slot-PM Excitation for Electric Vehicle In-Wheel Propulsion

Abstract

The reluctance machine with dc field coils in stator is an emerging brushless candidate for the in-wheel direct drive for its wide speed range and robust mechanical structure, while it suffers from relatively low torque density and efficiency, due to the poor excitation ability of dc field coils and worse extra dc saturation effect in the stator core. To address this issue, a new hybrid reluctance machine is proposed in this article, in which an integrated dual-layer PM source is introduced into stator slots, aiming to relieve dc saturation and, meanwhile, evoke flux modulation effect. In this way, the stator core utilization factor can be boosted due to dc saturation elimination by inner-layer slot permanent magnets (PM). On the other side, extra PM torque is generated by the flux modulation effect of outer-layer slot PMs. Hence, with synthetic assistance from dual-layer slot PMs, the torque density is improved distinctly especially under relatively high current density. Besides, slot PMs share a parallel magnetic circuit with dc field coils, which enables a bidirectional dc magnetization control for speed range extension. In this article, the proposed new topology is fully evaluated by both finite element (FE) analysis and prototype experiments.