Rotor Flux Online Observe Method Of Three-phase Induction Motor

Vector control, also named magnetic field oriented control, is a control method which establishes the rotating coordinate on rotor flux direction, sets up the model of motor, regards the induction motor as DC motor after a series of coordinate transformation, finally to achieve the decoupling of excitation component and torque component of stator current. This method optimizes the speed control system. In recent years, computer control technology has been improved a lot, so the vector control system which had been limited by computation condition is now being used in a wide domain.The realization of vector control bases on accurate observation of rotor flux. If the observation of rotor flux is not exact enough, the advantage of control system will not be visualized. So the high dynamic performance of vector control system depends on correct observation of rotor flux.In this dissertation, vector control theory has been analyzed. It shows the importance of real-time observe the rotor flux, introduces calculation methods of motor state parameters, sets up math models of induction motor in three-phase static coordinate, two-phase static coordinate and two-phase rotating coordinate system. Then, to guarantee the accuracy and real-time performance of system, a state observer bases on model reference adaptive method has been put forward. It uses motor as reference model and observer equation as adjustable model to construct a MRAS system, observes rotor flux of induction motor on-line. Then, the structure and arithmetic equation have been analyzed to demonstrate that its real-time performance is suitable for on-line observation of rotor flux in vector control system. At last, Matlab/Simulink software has been used to analyze the performance of this method, compare the results of several observers, and demonstrate the accuracy and real-time performance of the method.