Commutation-caused eddy-current losses in permanent-magnet brushless DC motors

An analytical approach based on a two-dimensional electromagnetic field analysis in polar coordinates is developed to predict the commutation losses in a permanent magnet brushless dc (PMBD) motor. These losses are essentially the eddy-current losses induced in the PMBD motor's rotor magnets and core and are caused by the rotor sweeping of the stationary stator magnetic field before each current commutation due to inverter switching takes place. The approach is applicable to motor constructions with either magnet segments or a magnet ring and able to deal with ill-conditioned cases. The model was applied to an existing motor and good agreement (within 11%) with the finite element method was achieved.