Investigation of Harmonic Losses in a Two-Pole Slotless Permanent-Magnet Motor Due to Wide Bandgap Inverter Supply

The recent emergence of wide bandgap power devices enables higher switching frequencies in electric motor drives. The subsequent possibility for higher efficiency and smaller size requires accurate prediction of harmonic losses in motors. Therefore, in this article, an original analysis of harmonic losses arising in inverter-fed two-pole slotless permanent-magnet machines with axially segmented ring magnets is presented. The developed three-dimensional time-efficient numerical model is successfully validated under high-speed no-load operation using a silicon carbide based three-phase inverter and rotors carrying a broad range of magnet segment thicknesses (3-12.6 mm). The model enables harmonic loss prediction capability (including loss separation) with an accuracy of 15% over a wide frequency range (8-120 kHz), which is a unique contribution. The sensitivity analysis primarily emphasizes the importance of taking into account the axial segmentation, and secondarily the rotor-shaft magnetoelasticity effects for accurate modeling of harmonic losses. The conducted case study demonstrates that wide bandgap transistors effectively can contribute to eliminating the need for inductive filters in motor drives.