Investigation of Rotor Loss Due to Current Commutation in a Permanent Magnet Brushless DC Motor

This paper summarises the commutation losses in a permanent magnet brushless DC motor. These losses are essentially the eddy current losses induced in the motor´s rotor magnets, metallic sleeve and shaft. The losses are caused by the rotor sweeping the stationary stator magnetic field before each current commutation due to inverter switching. These losses generate heat which needs to be dissipated in order to not exceed a defined temperature level for the magnet to avoid demagnetisation, which if it occurs will reduce the motor performance, hence not meet requirements.