Stator Flux Online Observe Method Of There-phase Induction Motor

The Direct Torque System (DTC) is a high performance control method which has been put forward after vector control and developed together with it. The basic principle of DTC is using an analytical method of space vector to observe and control the torque of asynchronous motor under the stator coordinate directly, in order to achieve high dynamic performance of torque. DTC is a novel method with simple structure and direct control method. As AC drive control technique, it has high static and dynamic performance.In DTC system, control of torque is actualized by controlling the stator flux, so the accurate observation of stator flux is the basic of guarantee the system performance. In this thesis, the method of stator flux observation has been analyzed bases on the study of stator flux observation theory in AC drive and DTC system. First, to assure the accuracy of flux observation, this thesis studies the method of basic motor state parameters (such as current, voltage) acquisition and processing. Then, in allusion to the shortage of common u-i model and i-n model, a closed-loop flux observer bases on MRAS has been put forward. The observer is designed bases on the state equation of AC motor inα-βcoordinate system, uses iαs,iβs,ψαs,ψβs as state parameters, compares the real current to the observed current outputted by flux observer, uses PI generator to adjust them, thereby achieves the accurate observation. Thirdly, the thesis analyzes the structure and arithmetic of DTC system with MRAS stator flux observer in it, demonstrates that the real-time performance of flux observer designed in this paper can satisfy the need of DTC system..Finally, bases on the analysis of DTC system, MATLAB/SIMULINK software is used in this thesis to construct a simulation DTC system with stator flux observer bases on MRAS in it, and then analyzes its performance. The results demonstrate that this system has high static and dynamic performance and can guarantee the accuracy.The analysis of DTC system performance with MRAS stator flux observer has demonstrated: the stator flux observer based on MRAS puts forward in this thesis can be used in DTC real-time control system.