Dsp-based Three-phase Asynchronous Motor Direct Torque Control System

The thesis first explains the basic running principle and the characteristic of the Direct Torque Control (DTC), and presents the arithmetic model of the three-phase asynchronous motor, as well as its basic equation of voltage and flux. The knowledge about DSP is simply introduced. The basic principle and the characteristic of fuzzy control and the design method of fuzzy logic controller are also introduced. Considering the response of ordinary DTC is slower during start-up and change in load, a fuzzy controller is proposed. Flux position & error in flux magnitude and error in torque are used as fuzzy state variables. Fuzzy logic is used for choosing the switching state. A fuzzy logic controller can choose the switching states according to a set of fuzzy rules based on both specialists' experience and knowledge, which improves the response performance of the system effectively during start-up and change in load. In following two chapters, the hardware and software design of the digital control system developed by author are dissertated in detail. The chapter of hardware design first expounds the whole design. The several primary circuit are designed, including power circuit, controlling circuit, detecting circuit and the DSP quadrature encode circuit. The chapter of software design firstly introduces the flowing chart of whole system, and discusses the whole design idea, giving the flowing chart of main program and interrupting service sub-routine of timer and part of program code. Then interrupting service sub-program and velocity measuring sub-program are expatiated in detail. At last, the restricting current of start-up and weak magnetism technology are introduced simply. After we apply the design scheme of this paper to a three-phase asynchronous motor, the simulating experiment result indicates that the digital control system realizes the motor's stable running and fast response during the start-up and unexpected change in load; moreover, it realizes the good dynamical performance. Integrating the intelligent control with AC-timing, this paper apply fuzzy control in Direct Torque Control, therefore improving the speed of controlling system and the capacity of resisting change of parameters, with good practical value.