Research Of Strategy And Engineering Method About Direct Torque Control For Asynchronous Motor

Since the field-oriented control scheme for induction machine has been developed from 1970s, it has gained huge success in perfecting control theory and improving control algorithm. However, it remains the problem of too complicated control system and the precision be affected by rotator parameters. In the midst time of 1980s, Germany and Japan scientists firstly developed a novel AC machines control scheme named as direct torque control. This scheme is characterized by concise control structure and robust to the variance of an AC motors parameters. It is also characterized by the rapid response of torque and flux. Then this method is evoking the great interest of many researchers. However, the applications of this method are limited due to some disadvantages, such as the large ripple of electromagnetic torque, the problem of low speep characters, and the distortion of the stator flux track.How to remain good performance and to eliminate the disadvantages of conventional direct torque control causes greate interest of many researchers. The key discussions of this dissertation are described as follows.This dissertation firstly makes the feasibility design and study of the DTC system based on analyzing some important parts. Introducing a stator flux calculation method with hysteresis band exchange of two different models. Having vector sub-division and using an optimized voltage vector selection table in DTC system.By analyzing the characteristic of torque performance in DTC system, a scheme of soft starting and the method of limiting the starting current are proposed in this dissertation.An idea of replacing Schmitt trigger by fuzzy controller for regulators is describe in this dissertation in order to make the system responses to the instruction rapidly.In the simulation system, the performances have been analyzed when theparameters of torque hysteretic comparator or the hysteretic band of stator flux are changed. The simulation of swiching between hexagon flux control and circle flux control is also completed. Results of simulating indicated that better system performance could be derived from introduction of fuzzy controller under the same condition with the traditional method.At last, the author chooses TMS320LF2407A to complete system design both in hardware and software. These include some detail circuites design and a detail analysis on the DTC algorithm such as generating of PWM signals, improving of the PI regulator for speed control and the improvement of M/T method speed detecting.This dissertation rearches the realization of building a lib system of DTC based on DSP and it is also a valuable attempt to realize the DTC in actual production.