Harmonic impact on rotor losses in fault-tolerant interior permanent-magnet machines

Fractional-slot permanent-magnet (FCSPM) machines offer several advantages, but they suffer from the high content of space harmonics in the air-gap magnetic motive force (MMF) distribution. The MMF space harmonic amplitude and frequency depend on the particular combination of numbers of slots and poles. Such harmonics induce losses in the rotor since they are not synchronous with the rotor speed. The aim of this paper is to analyze the MMF and its space harmonic distribution in the air-gap, in which both finite element method and analytical method are employed. Also, it is explained why PMs segmented can reduce the eddy current losses. The rotor eddy current losses of three fault-tolerant permanent-magnet machines, including one surface type and two interior types, are calculated and predicted.