Research And Practice Of Direct Torque Control System Of AC Induction Motor

During the recent 20 years, Direct Torque Control (DTC) for induction motor has been developed greatly because of its simple system scheme and excellent dynamic and static performances. In this scheme, the torque of motor is calculated and controlled in the staler reference frame. By using stator field orientation, the optimum switching mode is achieved to control the inverter. In this dissertation, the author has accomplished the simulation of the DTC system and analyzed the corresponding results. The software of the digital control system, in which the digital signal processor (DSP) is used, has also been designed in the thesis.The Direct Torque Control scheme is studied in the paper, and the simulation models of hexagon flux control system and approximate circle flux control system are presented based on the application of MATLAB/Simulink. In the simulation system, the performances have been analyzed when the parameter of torque hysterelic comparator or the hysteretic band of stator flux is changed. The simulat ion of switching between hexagon flux control and circle flux control is also compl eted. In addition, the traditional PI regulator is improved in the paper.The digital DTC system is implemented easily using TMS320F210, which is a fixed-point DSP and developed specially for motor&motion control by Texas Instruments Inc. It combines high-performance processing capabilities and several advanced peripherals that include the event manager module and a dual 10-bit analog-to-digital converter. The design of the control software becomes easy and the performance and reliability of the control system are greatly improved due to the application of DSP. In the thesis, the software of control system withspeed sensor is complied in DSP assembly language. This software has realized functions of the sampling of stator phase current, calculating of the phase voltage, the observing of stator flux and the output of switching signal etc.According to the analysis of the theory of DTC scheme and the design of the control software, the author of this paper has done the primary experiments of the open-loop hexagon flux control system using the DSP test-bed for experimentation and development of motor control. The experiments of motor without and with load on a given frequency are completed in this paper. These results are compared and analyzed. The feasibility of the scheme is validated through the analysis of the results.