The paper describes the development of a brushless motor drive consisting of a permanent-magnet synchronous motor and an electronic commutator. Normally this type of drive requires a position sensor to trigger the electronic commutator in the proper sequence, however, in this case voltage feedback is used that eliminates the requirement for a sensor. Also, a half wave inverter with three transistors instead of the usual six is used to reduce the cost of the electronics. The increase in motor loss by the half wave operation is offset by the reduced losses in the inverter.
The calculation of the performance, although based on a simple model of the motor, agrees well with test data. Knowledge of the harmonic components of the open circuit voltage of the motor is required which can be obtained from analysis of the magnetic field distribution. The efficiency of the drive is higher than that of the dc motor it replaces, and the whole drive including the electronics occupies only slightly higher volume.