Sensorless direct torque controlled drive of brushless DC motor based on fuzzy logic

Investigations were carried out on a sensorless fuzzy direct torque control (DTC) which drives brushless DC motors (BLDC). It is deduced that the amplitude of stator flux linkage can not been controlled in BLDC-DTC since it is automatically determined by every 60 electrical degrees commutation. Then, the control of the flux linkage is unused in the proposed system. For the sake of improving the static and dynamic performance of the system, fuzzy logic is introduced into the system, which the torque error and flux linkage angle of BLDC were all properly fuzzified into several subsets to accurately select the voltage space vector in order to smooth the torque and quicken the torque response. A state observer is designed to estimate the back-EMF, the torque and rotor speed can be derived from the estimated back-EMF. Simulations illustrate the operation and performance of the proposed scheme.