Research On The Strategy Of The Direct Self Control Of Brushless DC Motor

The greatest feature of Brushless DC motor was that using electronic commutator based on position sensor constituted by electronic logic circuits and power switching circuits to replace commutator consisted of mechanical commutator and brushes. It not only had the advantages of AC motors, such as reliable operation, simple structure, convenient maintenance and so on, but also possessed the advantages of DC motors, such as high running efficiency, low noise and good speed performance. It also had the advantages of small bulk, light weight and long life, so it was widely used in the field of national economic departments, military industry, aviation and spaceflight, appliances and so on. However, Brushless DC motor could not be applied to the field of high-performance speed control, high-precision position control and low noise. Therefore, running performance of Brushless DC motor was improved by improving control methods.Direct Torque Control had lots of advantages of simple control structure, fast torque response, excellent dynamic and static performance. It was holding the simple structure while the high performance was achieved which Direct Torque Control was proposed to Brushless DC motor. Up to now, Direct Torque Control had used successfully in asynchronous motor and permanent magnet synchronous motor, but not in brushless direct current motor. Therefore, the research of this paper had theory and practical meaning. This paper would focus on the strategy of Direct Self Control of Brushless DC motor.Because of off-phase, Direct Torque Control of Brushless DC motor strategy was difficult to achieve and complicated to calculation. To eliminate off-phase, Direct Self Control was introduced in Brushless DC motor systems. Direct Self Control of Brushless DC motor strategy used three phase conduction mode, which had simple combination, easily realization and smaller calculation. It improved the running performance of Brushless DC motor. First of all, the basic structure and working principle of Brushless DC motor were introduced. As the back-EMF was trapezoidal wave, Brushless DC motor contained a large number of high-order harmonics, its air-gap magnetic field was non-sinusoidal distribution. However, d-q axis coordinate system transformation principle only applied to the motor which air-gap magnetic field was sinusoidal distribution. Therefore, this paper established the mathematic model of Brushless DC motor using the original phase variables of the motor directly, which was easy to use, had small calculation and accurate results. In the basis of understanding of the principle of Direct Self Control, simulated the whole system by Matlab/Simulink and obtained the simulation results. The waves of the stator flux-linkage trace, torque dynamic response, back-EMF, phase current, speed and torque were analyzed. They showed: The stator flux-linkage trace was hexagon. The system had fast dynamic response. The back-EMF was trapezoidal wave. The running performance was greatly improved. The above analysis results showed that it was feasible that Direct Self Control was introduced to Brushless DC motor. Finally, the experimental system of the strategy of Direct Self Control of Brushless DC motor, including hardware circuit design and software design. The corresponding experiments were made using this system. The results were obtained and analyzed. Through comparing the simulation results and experimental results, we could see, they were matched, which verified that It was feasible that Direct Self Control was proposed to Brushless DC motor.