Rotor Eddy Current Loss in Single-Phase Permanent Magnet Brushless DC Motor

Due to spatial harmonics in the pulsating stator mmf and temporal harmonics in the excitation current, a significant eddy current loss may be induced in the rotor of a single-phase permanent magnet brushless dc (BLDC) motor. The eddy current loss is also dependent on the level of airgap asymmetry which is employed to facilitate unidirectional rotation. The paper investigates the eddy current loss which results in the permanent magnets and retaining sleeve of a 1.1 kW, 45 krpm, single-phase BLDC motor, and considers the influence of the phase current waveform and the level of airgap asymmetry, as well as the effectiveness of segmenting the magnets in reducing the loss.