Rare-Earth and AlNiCo Magnets Interaction in Hybrid Magnet Variable Flux Machines

This work investigates the interactions between the rare-earth permanent magnet (PM) and the AlNiCo PM in hybrid magnet variable flux motors (VFMs) in the absence of stator winding excitation. These interactions are responsible for reducing the magnetization current of the series hybrid VFMs and widening the field regulation range (FRR) of the parallel hybrid VFMs. Initially, key conditions of these interactions are derived from basic principles. Then, the concept of optimal working point trajectory line (WPTL) for the low coercivity magnets is introduced based on the transferability of generic hybrid magnet VFMs to the classical rare-earth-free VFMs. The limitations of realizing the optimal WPTLs for the generic series and parallel structures are highlighted. Then, two hybrid structures are investigated for increasing the on-load demagnetization withstand ability along with extending the field regulation range. These two structures are then combined to construct a novel two-layer hybrid magnet VFM with wide FRR and improved on-load demagnetization capabilities. It is revealed that to develop hybrid magnet VFMs, approaching the optimal series and parallel WPTL in a two-layer hybrid magnet structure can be a promising design choice.