Fault Detection of Irreversible Demagnetization Based on Space Harmonics According to Equivalent Magnetizing Distribution

This paper proposes a detection technique for irreversible demagnetization using the harmonics characteristics of the back electromotive force (BEMF) in brushless dc motors (BLDCMs). We analyze the harmonics characteristics of the BEMF that are obtained for fault types encountered by interior permanent magnet (PM)-type BLDCMs according to the magnetization pattern of irreversible demagnetization. An irreversible demagnetized PM is represented as an equivalent magnetizing distribution by applying space harmonics analysis using both the finite element method and the space harmonics method. Furthermore, we analyze flux linkage and BEMF waveforms for different demagnetization ratios.