Performance analysis of switched-flux machines with hybrid NdFeB and ferrite magnets

Switched-flux permanent magnet machines excited with NdFeB magnets have high torque density and efficiency but the disadvantage of a high magnet usage and consequently high cost. A hybrid NdFeB and ferrite switched-flux permanent magnet machine is proposed. This machine offers significant flexibility to achieve a desired cost/performance trade-off due to the use of a hybrid of high performance NdFeB magnets and comparatively low cost ferrites. Two magnet configurations: (a) series-excited and (b) parallel-excited machine are investigated for their electromagnetic performance and demagnetization withstand capability. It is shown that although their electromagnetic performance is similar, the series magnet configuration has a much better demagnetization withstand capability. Finally, in comparison to the conventional switched-flux machine utilizing only NdFeB magnets, it is shown that the series-excited hybridmagnet machine can achieve the same torque with an 18.5% increase in axial length and a cost saving of 12% when the NdFeB/ferrite volume ratio is 1:1.