PhD student Samith Sirimanna with Advisor K. Haran

Magnet eddy currents are generated from two main sources in permanent magnet synchronous machines: spatial and time harmonics. Discrete winding distribution in the stator generates spatial harmonics that are asynchronous with the main rotor field while inverter switching creates time harmonics in the current waveform. Generally, resistance-limited magnet-loss models are accurate in predicting losses under relatively low fundamental frequencies. However, with the new thrust towards light-weight, large pole-count machines with high fundamental frequencies, using resistance-limited models to capture slot-harmonic magnet losses may not be applicable for capturing slot-harmonic magnet losses as we move to higher frequencies.
In this work, the surface-mount permanent magnet quasi-3D reactance limited model is extended with inputs from the planar-resistive limited model to compute the slot-harmonic magnet losses. Figure 1 shows the flow chart for the magnet-loss calculation algorithm taking inputs from both resistance- and reactance-limited models. The results showed good agreement between loss prediction with finite element analysis for a wide range of fundamental frequencies.
This research is funded by the Grainger Center for Electric Machinery and Electromechanics.

Figure 1. Extended quasi-3D magnet loss model.