Measurement of Magnet Losses in a Surface Mounted Permanent Magnet Synchronous Machine

Magnet losses in permanent magnet synchronous machines (PMSMs) decrease efficiency and increase thermal loading. This paper presents a measurement technique for measuring the magnet losses in PMSMs. Losses were determined by measuring the initial temperature rise rate of the magnets. Measurement of magnet temperature was achieved via a calibration relating temperature rise to voltage constant. Measurements were made on an inverter driven axial flux PMSM at a number of different operating points. The results were used to validate a finite-element analysis, which decomposed the total loss into component parts based on the source of the flux variation in the magnets. The analysis showed that although the magnetomotive force (MMF) induced losses increased with current loading, the harmonic content of the current waveform decreased, leading to only small changes in total loss. Measurements were made at different dc bus voltages; a 60% increase in dc bus voltage increased magnet losses by 32%.