The Design And Implementation Of Three-phase Asynchronous Induction Motor Direct Torque Control System

In recent years, with the fast development of power electronics technology, high-precision modern control strategies, as well as the high-speed digital signal processors controller, there are many new control algorithms of the three-phase asynchronous AC induction motor. Direct torque control algorithm is the latest one in these control algorithms, it became the focus because of its simple control structure, easy to implement, as well as the fast response of torque and flux. It was recognized as the mainstream of the development in the field of AC motor drive in future.In this paper, the basic theory of classical direct torque control is studied first. Then, we use the Matlab/Simulink to build the simulation model and carry out the motor experiment. Through the theoretical and experimental analysis, we pointed out three main problems of the classical direct torque control algorithm. To solve these problems, we adopted an improved algorithm which is based on stator flux-oriented method and space vector modulation. In this new algorithm, a double-closed-loop controller is used for the control of flux and torque; meanwhile, the hysteresis comparators are replaced by the PI controllers. All of these improvements make the control performance of flux and torque much more accurate than the classical one.What's more; the method of space vector modulation is used to output the voltage space vector which is expected. This method can fix the switching frequency, reduces the stator current ripple, extend the useful life of the inverter.For the key part of the algorithm—stator flux observing, a low pass filter with an adaptive compensation is used for the flux-observer, which can not only take full advantage of the low-pass filter for the inhibition of the DC offset and noise, but also compensate the phase and amplitude distortion caused by the low-pass filter in such a short period of time. What's more, this method can be applied to many input signals whose amplitudes are different; it is of great value in practice.This paper is based on the project of Wuhan Guide Electric Co. Ltd-The R&D of inverter based on direct torque control. Though the theoretical researches, simulation experiments and implement of the control system, this improved algorithm is implemented in the model machine finally. The final motor experiment shows that, compare with the classical algorithm, the performance of the improved algorithm has been greatly improved, and there have been a better solution to the three main problems of classical direct torque control algorithm.