Power Factor Improvement of a Linear Vernier Permanent-Magnet Machine Using Auxiliary DC Field Excitation

Vernier permanent-magnet (VPM) machines attract more and more attention recently because of the high-torque density and low-speed operation features. Due to the vernier structure for field modulation, its power factor (PF) usually is lower than that of the conventional PM machines. In this paper, a new linear VPM machine for improving the PF is proposed. By using an auxiliary dc field winding to provide an additional excitation, the air-gap flux excited by PMs is compensated. The proposed machine has a similar structure to the split-pole VPM machines with surface-mounted PMs. For implementing the auxiliary dc field winding, a parallel-hybrid excitation topology and consequent-pole PM machine structure are adopted. The machine topology, modeling, and operating principle are discussed. Both simulation and experimentation show that the PF of the machine can be improved by the auxiliary dc field excitation.