Slot-by-slot brushless DC motor commutation technique

The commutation technique used for the optimal operation of a special brushless DC motor is presented. The machine has a wound rotor, 12 armature phases, 4 poles and a nominal power of about 30 kW. Electronic commutation ensures a nearly 90 electric degrees angle difference between the resultant stator magnetomotive force (MMF) and the rotor field. An optical rotor position sensor is mounted on the rotor to gauge its angular position. It determines the slot commutation instant as well as the motor speed. This paper presents a description of the electronic commutation and the motor control system that uses a microprocessor (DSP) and the closed-loop PI control procedures. The results obtained when using bipolar and unipolar voltage switching in a full bridge inverter are also reported.