Segmentation of Magnets to Reduce Losses in Permanent-Magnet Synchronous Machines

This paper studies the losses in the magnets of a permanent-magnet synchronous machine (PMSM) with surface magnets caused by square voltage pulse width modulation (PWM) waveforms. First, the conductivity of the magnets is determined. Second, the effect of segmentation on the losses is calculated by a 3-D time-harmonic finite element model for sinusoidal waveforms. More segmentation of the magnets in axial and circumferential direction results in much lower losses in the magnets, but more losses in the massive rotor yoke. In a third step, the losses are simulated and measured on an experimental PMSM for square waveforms generated by PWM. Superposition of appropriate sinusoidal losses obtained by a time-harmonic FEM seems to be acceptable in order to predict losses in a PMSM for square voltage waveforms.