Detecting uniform and partial demagnetization for an interior permanent magnet machine

Partial demagnetization is studied in detail in this paper to understand its effects and develop a robust detection method. The voltage and current harmonics can be used to indicate that a fault exists but this method cannot always differentiate demagnetization from eccentricity. The inductance characteristics of the direct rotor oriented axis are used to verify the harmonic-based detection findings. The detection of partial demagnetization is improved by determining the incremental inductance over a range of direct axis currents; this way secondary `knees' caused by asymmetrical rotor saturation are found. This asymmetrical saturation can be determined with the inductance. A detailed discussion and observation of the effect of partial demagnetization is novel compared to the literature. Three types of demagnetization are discussed in this paper: uniform demagnetization, partial demagnetization of one magnet and removal of three magnets from the rotor. Finite elements analysis is used to simulate the changes in the incremental inductance waveforms under each type of demagnetization. Experimental data is introduced in this paper to validate the incremental inductance results for the removal of three magnets.