Investigation of Delta-Type Variable Flux Memory Machines Considering Magnetizing Current Limits

A simple delta-type interior-permanent magnet (PM) variable flux memory (VFM) machine exhibiting series-parallel magnetic coupling is investigated, and the limits of magnetizing current capacity are considered. The series-parallel coupled high coercive force (HCF) PMs and low coercive force (LCF) PMs integrate the merits of stable PM working point in series-type VFM machines with the high torque output in parallel-connected cases. Moreover, it is revealed that the iron bridges between the two kinds of the PMs play an essential role on magnetic coupling, de-/re-magnetization and torque capability. The VFM machines with wider iron bridges normally require higher magnetizing currents. The effects of the iron bridges are investigated based on the theoretical analysis and finite element methods. It is found that the narrower iron bridges contribute to the more significant series coupling and wider flux variation range, while the wider iron bridges sacrifice the flux variation but facilitate the torque improvement. A prototype machine is manufactured and the experiments are carried out to verify the investigations.