Study Of Direct Torque Control System Of Brushless DC Motor

Brushless DC motor(BLDCM) not only has the advantage of light weight, smallvolume, small moment of inertia and high efficiency, so it is widely used in the field ofelectric vehicles, CNC machine tools, robots, household appliances, medicalequipment and aerospace. BLDCM has a large torque ripple problem in the runningprocess. The torque ripple makes the motor and the load device produce vibration andnoise. It influences the performance of the system seriously, limits position precision,speed precision and reliability of BLDCM at high requirements places, especially inthe application of direct drive, the torque ripple makes motor control performancedeterioration. So how to restrain the torque ripple becomes the key to improving theperformance of BLDCM.Direct Torque Control (DTC) technology is a high-performance AC speed controlmethod. It has good dynamic, static performance, fast torque response, simple controlstructure and strong robustness. DTC not only saves the complicated vectortransformation in calculation, but also realizes digital easily. It has attractedwidespread attention when it appeared. Flux and torque comparator use Schmidttrigger in the traditional direct torque control, so its tolerance size has a great influenceon the performance of the system. Against this shortcoming, DTC is applied into thecontrol of BLDCM in this paper. DTC uses fuzzy logic control strategy, in which thespace voltage vector selection is adopted. It significantly improved the performance ofthe system. The design of fuzzy controller has a certain blindness and subjective.Therefore, we use genetic algorithm to optimize the fuzzy controller in order to furtherimprove the control performance of the system.In order to verify the effectiveness and feasibility of the proposed method, webuild the simulation model of BLDCM direct torque control system in Simulinkenvironment, and do the simulations study. The simulation results show that，BLDCM direct torque control strategy proposed in this paper, not only retains the high dynamic and static performance of DTC, but also effectively restrains the torque ripple.