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Loss investigation of slotless bearingless disk drives

Losses are often a limiting factor for the application of bearingless motors, especially at high rotational speeds. In this paper the loss mechanisms in slotless bearingless disk drives with toroidal windings are identified and analyzed. Although the slotless topology already features comparably low losses, a detailed comprehensive analysis of the loss portion enables a further reduction of these losses. To obtain the loss composition, computationally efficient simulation and calculation methods as well as simple measurement methods are presented for each loss component, considering iron losses, eddy current losses in the coils, PWM induced losses, copper losses, windage losses, and inverter losses. This allows for optimization of the motor geometry towards minimized losses. The analysis results are compared with loss measurements of four different motors with different rotor sizes, pole pair numbers, and coil configurations.