The Integreted Research Of Direct Torque Control Of Brushless DC Motors

The core content was direct torque control of brushless direct current motor, including theory and experiment. 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 creation. Direct torque control had excellent dynamic performance, easy realization, convenient for realization of non-velocity sensor. For the simple structure brushless direct current motor,application of direct torque control would acquire two result: firstly, the dynamic and stable performance of brushless direct current motor get improvement, secondly, the complex of brushless direct current motor control system did not increase. So the research of this paper get practical meaning.The direct torque control strategy of brushless direct current motor was proposed. The optimal voltage space vector was chosen to control the motor by torque comparator and flux comparator. The locus of stator flux was sawtoothed circle. The direct torque control strategy created whole fundamental theory, and solved three problem: voltage vector's calculation under two-phase conduction mode; the flux calculation under two-phase conduction mode; the coordinate transformation of non-sinusoidal variable. That was the foundation of next research.To solve the complex of direct torque control strategy, the direct self control strategy of brushless direct current motor was proposed. The strategy used three phase conduction mode to eliminate turn-off phase, as a result, the control system get simplified. The stator flux followed hexagon locus. The system's combination was simple and easily realization.The direct torque control strategy was complicated, and the direct self control strategy had the deficiency of current pulsation. To solve these two problems, a newly theory: hyper space vector theory of brushless direct current motor was proposed. The theory used two phase conduction mode, and three dimension space coordinate was applied. The voltage of turn-off phase was put on the z axis, which perpendicular to xy plane. The voltage space vector and flux space vector moved in three dimension space. The project of voltage space vector were used to control the project of flux space vector. The control system of hyper space vector theory was simplest within the three mentioned strategy. It had bright development in practice.The motor was only a fraction of speed control system, it was not a scientific method to research only one part of a whole system. Besides the control strategy, the aim of this paper was to research the motor, so as the whole system performance get optimized. The relation between the brushless direct current motor parameters and current pulsation was analyzed firstly, including stable current pulsation and start-up current shock. The critical parameter was induction. As the induction of brushless direct current motor was always small, the paper analyzed the method how to increase the induction, with their merits and disadvantage.The permanent magnet synchronous motor was analysed according to the whole system theory, and three critical parameters were selected: direct axis reactance, quadrature axis reactance, permanent magnet flux. The effects of these three parameter on speed control performance was analyzed, furthermore, a graphic method was proposed to optimize these three parameter, as a result, the control system maintained maximum utilization.