Direct Torque Control Of Induction Motor Based On Anfis,

With the development of power electronics and computer technique , regulating-speed methods and technique of AC induction-motor gradually substitute the traditional regulating-speed methods of DC motor. In the mid-1980s, after development of vector transform control technique, the direct torque control (DTC) technique, as a new rising advanced regulating speed method, is developed. According to the method the complexity of control calculation in vector control technique is decreased, the influence of motor parameter changes on the performance of motor is reduced, in the great extend, and the question of which the practice performance of controlled motor is difficult to achieve to the results of theoretical analysis is saved. By using the method the best static and dynamical performance can be obtained. By directly controlling stator flux and electromagnetic torque the higher quality of dynamical performance is achieved. The method possesses of such advantages as simplicity of control construct, rapidity of response on motor toque, and good robustness of motor parameters, and so on. But there are many difficult problems, such as greater torque ripple and bad controllability in the low speed area, non-stability of switching frequency, and so on, in the engineering area in which quick response and regulating speed of higher quality of precise are necessary. All of shortcomings are caused by the bang-bang regulator, the discrete voltage switching vector table, increase of the influence of the stator resistances in low speed, and so on.To the questions that are such defect as big torque ripple in the traditional direct torque control system, bad control performance in low-speed and unstable switching frequency, a number of theoretical analysis and simulation test are present in the paper. Firstly, by transforming mathematical models of induction-motor under different reference coordinate the inherence relationship of the model is researched. Secondly, by software MATLAB/SIMULINK a simulation model of the DTC system is set up and the basic theory of the system is researched and analyzed deeply. Finally, the Adapted Neural Fuzzy Inference System (ANFIS) and the Space-Vector Pulse Width Modulation (SVPWM) technique are applied into the traditional DTC system and the performance of the DTC system is improved. 1) On the basis of three inputs: The errors of torque and stator flux and the angles of flux, by using ANFIS voltage vectors with random magnitude and direction are produced; and 2) then the voltage vectors are applied to the voltage vector pulse width modulator. And by SVPWM technique the synthesized voltage vectors control switch status of inverter, as a result the errors of toque and stator flux are compensated and the switch frequency of inverter is invariable.Because in ANFIS system the voltage vectors with random magnitude and direction are produced on the basic of synthesizing the magnitude and the direction of the toque errors and stator flux errors, the toque ripple is reduced effectively in the improved Direct Toque Control system. Whereas in the traditional Direct Toque Control system the voltage vectors are produced just on the basic of considering the direction of the toque errors and stator flux errors, and by using the comparator of lagging phase the one of six reference voltage vectors, which are 60 degree apart in space, is selected to control the inverter. The simulation results show that the control method is effective on decreasing torque ripple greatly and increasing the stable performance of the induction motor, especially in the low speed.