Improved analytical modeling of commutation losses including space harmonic effects in permanent magnet brushless DC motors

An analytical method based on a two-dimensional electromagnetic field analysis in polar coordinates is developed to predict the commutation losses in permanent magnet brushless DC motors. These losses are essentially the eddy current losses induced in rotor magnets and core and are caused by the rotor sweeping the stationary stator magnetic field before each current commutation due to inverter switching takes place. The analytical model is able to include the space harmonic (slotting) and time harmonic effects of the stator resultant MMF on the losses and is applicable to motor constructions with either magnet segments or a magnet ring. The model was applied to an existing motor and good agreement (within 6.8%) with the finite element method was achieved.