Optimization of PMSMs Considering Multi-Harmonic Current Waveforms: Theory, Design Aspects, and Experimental Verification

This paper is about investigating the potential of multi-harmonic design of permanent magnet synchronous machines. Thereby, multi-harmonic refers to the temporal periodic characteristics of linked fluxes and currents of the stator phases in order to ensure high-efficient operation with very low torque ripple. At first, a suitable model allowing for multi-harmonic currents evaluation is derived. Consequently, an interior-rotor IPM machine is studied. In order to have a fair comparison with conventional PMSMs featuring sinusoidal currents, an optimization scenario is defined where the same outer dimensions as well as magnet and copper volume for both design variants are considered. The use of multiple current harmonics requires a dedicated strategy for evaluating machine designs, as the conventional dq-grid analysis cannot be utilized. The introduced approach is applied and results of the optimization are illustrated. Prototypes were manufactured and machine designs were subsequently evaluated through experiments. A valuable lesson learned during practical implementation regarding rotor angle determination is highlighted. Measurement results reveal that adding more degrees of freedom in terms of multiple harmonics can give significant improvements for performance measures efficiency and torque ripple. This particularly holds if the harmonics are already considered throughout the machine design and optimization process, rather than only at post-processing stage.