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

The discrete or hopping nature of magnetic field, produced by the nonsinusoidal square-wave stator currents of permanent magnet brushless DC motors, gives rise to eddy current losses in the rotor magnets and core. These losses, referred to as commutation losses, can be substantial in large propulsion motors. This paper presents a further refinement in the analytical model derived and presented in an earlier paper. The improved model is able to account for the space harmonic effect of the stator resultant magnetomotive force (MMF) on commutation losses and consequently can lead to a more accurate prediction of the commutation loss. The model was verified by comparing its results with those obtained using the finite element method at several operating speeds and current levels. The results show good improvement (an average value of 6.8% for the total losses) compared with the earlier model (an average value of 11.7%).