Hybrid Excitation Stator PM Vernier Machines With Novel DC-Biased Sinusoidal Armature Current

Stator permanent magnet (PM) machines are gaining more research interest in recent decades. Since the permanent magnets (PMs) are moved from the rotor side to the stator side and the salient rotor structure is adopted, it is claimed that the stator permanent magnet machines exhibit several promising features, such as simple and robust rotor, and good ability of heat dissipation as the main losses are located in the stator. On the other hand, to improve the shortcomings of the inherent limited magnetic field adjustment ability, and the low efficiency and power factor of stator dc current excited machines, hybrid excitation PM machines with additional field windings are proposed. However, the complexity of the machine structure is increased inevitably. At present, it is found that both the stator PM and the stator dc current excited Vernier machines operate with the flux modulation principle, and generally, the armature windings of the stator PM machines are fed with pure sinusoidal current. In this paper, a novel hybrid excitation stator PM Vernier machine is analyzed. In addition to the features of the salient rotor structure, stator located PMs, and concentrated armature windings, the novelty of this machine is dc-biased sinusoidal phase current, which contains an ac component and a dc component. The fundamental theories of stator PM machines fed with dc-biased current are researched, operation principle and slot/pole combination is concluded, and the optimal current configuration is studied theoretically and by finite element analysis. Finally, a prototype was designed and manufactured; the experimental tests were done to validate the proposed analysis.