Fuzzy Control Algorithm Research And Application Of Direct Torque Control System

The induction motor is a system of high-order, non-linear, strong coupling and many variables. It is well known that the rotor parameters of induction motor are subjected to variability and hard to be detected, which more or less deteriorates the performance of such a speed control system based on the mathematical mode depending upon the rotor parameters. Direct torque control (DTC) system is of robustness and simplicity by employing stator flux orientation. The main reason is that the only parameter in stator flux estimation model is the resistance of stator, which can be easily measured, without any parameters of rotor. In practice, comparing to field-orientation control (FOC) system, DTC system can hardly have the broad speed range. It is because that DTC system cannot have large load capability and there are torque ripples.Since the traditional DTC system is not so good at a low speed range, many methods are presented in order to solve the problem. According to changement of the stator current causing changement of the stator resistance, a fuzzy estimator of the stator resistance is adopted to measure the changement of the stator resistance on-line. It is easy to get accurate value of the stator resistance. Then by means of U-I stator flux model of induction motor, it can work out the value of the stator flux and lessen its error caused by changement of the stator resistance. Another scheme, fuzzy logic control, is also presented to select the state of the inverter instead of the traditional Band-Band control. In this way, the inverter can decrease torque ripples. Thus the speed range of DTC system can be expanded greatly.TMS320F240 chip of TI Corporation is contributed to digital control of the motor. We build a digital fuzzy logic DTC system based on it. It makes research of DTC system from emulation to practice. In the software programming of DSP, I adopt the language of structurization: C language, which carries out realization of control strategy. Thus the program is of structurization and consecution.In the thesis, the stator resistance fuzzy estimator and stator fluxand torque fuzzy logic controller have improved steady performance of induction motor in the experiment of speed control, have reduced the steady torque ripples, have enlarged the scope of speed control.