Analysis of unipolar leakage flux in series-hybrid permanent magnet machines

A series-hybrid variable flux memory (VFM) machine employing two different kinds of permanent magnets (PMs) on alternate rotor poles is investigated. This machine features controllable PM flux and good flux-weakening capability, as well as improved torque density. However, the unipolar end leakage flux occurs when the fluxes produced by two different kinds of PMs are not balanced. Therefore, the series connection of two kinds of PMs is analyzed, based on which the mechanism of unbalanced rotor poles and the unipolar end leakage flux are revealed. The rule of obtaining balanced poles is identified. A series-hybrid VFM machine prototype is fabricated and tested.