Sensorless Direct Torque Control for Saliency Permanent Magnet Brushless DC Motors

Sensorless technology cannot only reduce the cost of motor drive system, but also improve system reliability. In the sensorless direct torque control (DTC) drive system of permanent magnet brushless dc motor (BLDCM), the estimations of instantaneous electromagnetic torque and stator flux linkage are two key issues. Additionally, some BLDCMs with salient-pole phenomenon make the estimations of torque and flux linkage even harder. A sensorless salient-pole BLDCM-DTC drive system is proposed in this paper. A stator current estimator with back electromotive-force (EMF) self-adaptation is first constructed according to stator current state equations and the back EMF is obtained by adaptive law. Then, a phase-locked loop is used to output smooth estimated value of rotor position angle based on the identified back EMF. At last, according to the estimated rotor position angle, the torque and stator flux linkage are calculated to realize saliency BLDCM-DTC running smoothly. Experimental results show that the estimated torque and stator flux linkage are very close to their actual values. The novel sensorless DTC drive system has nice dynamic and static performances, and the lowest steady-state speed can be decreased to 33 r/min.