A Position Sensorless Drive System Using an IPM Motor and Analysis of its Operating Characteristics.

This paper describes a position sensorless brushless dc motor drive system, in which an interior permanent magnet (IPM) motor is used as a synchronous motor. It is characterized by the position-sensing technique based on current detection of the free wheeling diodes. A three-phase voltage-source inverter with the conducting interval of 120 degrees in each phase is employed in the drive system. Reluctance torque plays an important role in producing torque of the IPM motor, having q-axis inductance larger than d-axis inductance, so that the control of id=0 can not achieve the highest motor efficiency.The characteristic analyses of the position detection and the commutation overlapping angle are done, in which the saliency of the motor and harmonics of the back electromotive force are taken into consideration. It is shown that the detection angle and the commutation leading angle tend to lead with increase of the load torque, while the phase angle of the fundamental armature current lags by half of commutation overlapping angle. As the result, the total leading angle of the fundamental armature current exists near the optimal one which can attain the highest efficiency. The experimental results shows that higher efficiency is achieved at the rated speed without special phase angle control in relation to the load torque.