Study On Some Issues For Direct Torque Control Technology Of Induction Motor

Direct Torque Control (DTC) is a fairly new quality control velocity means for induction motors, which has the advantages of simple control idea and good stable and dynamic performance. However, as a kind of the new theory and technology, it not perfect. Owing to the reasons above, DTC has become one of increasing hot points for AC motor drive. In order to sustain the rapid response of DTC and overcome the flux and torque ripples, the dissertation focuses on the theory of DTC.Firstly, we investigate the mathematical model of asynchronous motors and analyze the traditional theory of DTC. And through MATLAB / Simulink modeling and simulation for the motor and direct torque control system, validate the fast response performance of direct torque control.Secondly, based on the effects of changes in stator resistance, proposes an improvement strategy of stator resistance estimation. The stator resistance estimation strategy is to proceed from the motor model, according to the stator current change with the stator resistance, using PI regulator to compensate for resistance to turn torque and flux linkage back to a stable state. Through MATLAB /Simulink modeling and simulation, the strategy verifies the correctness of the theory.Thirdly, this paper based on flux, torque ripple is larger in the traditional direct torque control, proposes an improvement strategy of direct torque control based on space vector modulation (SVM-DTC). SVM-DTC is that space vector combine with direct torque control, using of two PI controllers to replace the hysteresis loop control of conventional direct torque control system, it can get an accurate reference voltage vector to compensate for the current stator flux and torque errors. Then, space vector modulation technology will convert the reference voltage vector to corresponding PWM switching signal. So it realizes continuous real-time control to reduce the torque ripple. Through MATLAB /Simulink modeling and simulation, the strategy verifies the correctness of the theory.Finally, we illustrate a variety of control theory of induction motors in details, and design a DTC system via digital signal processor (DSP). The SVM-DTC experiment is conducted on an experiment platform, which realizes the AC variable speed and validates the effectiveness and the feasibility of the proposed technique. In the end, we sum up the insufficiency of the whole system and predict the direction of DTC as well.