Research Of A High Performance Direct Torque Control System

The direct torque control(DTC) theory is a kind of new control method after vector control theory in the field of AC drive system. It calculates and controls the torque of AC motor in stator coordinate using the space vector analysis method. With the stator-flux-oriented scheme, it controls the switch state of the inverter directly to get the high dynamic performance of the torque by the pulse width modulation signal that produced by discrete Pang-pang control. It leaves out the complex vector transform, and the simplified mathematical model of the motor with a rapid dynamic response, and it is simple and easy to realize the advantages. However, there are also some disadvantages. For example, the characteristic of the torque is not very good at a low speed, and the steady-state torque ripple is greater and the load capacity declines.In this paper, Firstly, the theory of the DTC was introduced based on analyzing AC motor mathematic model. Aiming at the improvement of the DTC technology, the fuzzy control technology is applied into the traditional DTC to improve the system performance. To facilitate the usage of the method into digital control system, we calculated off-line to get a fuzzy control table, and by using a table look-up operation to choose the switch state the simulation, to realize the fuzzy DTC; because of the lag of the digital control system, the steady output torque ripple often exceeds the set tolerance. So we propose to use vector subdivision technology in the fuzzy DTC in order to increase the data of the available voltage space vector, at the same time, the Flux Sector is subdivided to optimize the choice of the voltage space vector. In the MATLAB/SIMULINK software, the integrated usage of the fuzzy DTC and the technology of vector analysis, and building the simulation module prove the effectiveness of the algorithm.In this paper, we use the TMS320LF2407A DSP chip as the core platform for the experiment. The results of the experiment show that, in the fuzzy DTC the responsive speed of the torque is faster and the robustness performance and the dynamic performance are better. After the application of the technology of the vector subdivision analysis into the fuzzy DTC, the torque fluctuation can be reduced under the condition of no increase of the frequency of the sampling system and accuracy of the speed control. In the actual motor control system, it is very suitable to be realized in the digital control system because of the simplicity and the direct control of the DTC algorithm. So, this control method has good prospects for development.