Research And Simulation Of Vector Control System For Induction Machine

In AC drive control system, in order to obtain the high dynamic response of an induction machine, the magnetizing and torque components of stator current must be decoupled suitably respective to the rotor flux vector . In terms of cost and reliability, the indirect vector control system , which estimates the position of the rotor flux vector from the machine parameters, is widely used. But it is machine parameters dependent since the model of the machine is used for flux estimation. The variations of machine parameters, due to operation temperature, saturation level of rotor flux , rotor time constant, etc., lead to poor dynamic performance and incorrect stationary point of operation. To solve this problem, various approaches have been proposed. However , most of these methods still use some machine parameters values , obviously have limitations in practical applications. For example, a recent work reports that a simple and effective approach based on regulating the energy stored in the magnetizing inductance is still in need of machine parameters values . Another approach compares the torque signal obtained from stator current and estimated stator flux with the torque signal obtained stator current and estimated rotor flux to adjust the rotor constant, but this method has less superiority in low speed operation. Based on extend Kalman filter approach or recursive least square algorithm, several adaptive algorithms which are independent of machine parameters have been proposed , but the computations of these algorithms are too heavy and the inherent characteristics of machine can not be exploited sufficiently.In this paper , a new method of designing rotor flux adaptive observer is introduced, and a simulation study is made for both the Vector-inverter model of squirrel-cage induction rotor and vector control system which takes model as its controller object. In simulation model, classical PID controller, and vector control with rotor flux adaptive observers in rotor reference frame are deeply studied. A lot of simulation experiments are done. System performance is studied, such as steady-state characteristics, dynamic characteristics and the effects of disturbance and parameters variation. The necessary structure diagrams , algorithm, and results from simulation have been shown in this paper. The results demonstrates that this method effectivelyovercomes the problem of the performance degradation due to parameters variations in the vector control of an induction machine. In this method , the value of rotor flux can be estimated only by using the rotor speed, stator current and voltage, no machine parameters values are needed. So this method is obviously not sensitive to variations of machine parameters. The stability and convergence of the algorithm are guaranteed by the parameter adaptive algorithm with strictly positive real error transfer function. The effectiveness is also verified by simulation results.In general, vector control system based on rotor flux adaptive observer has the advantage of restraining nonlinearity and parameters variation to vector control system, clearly improving system robustness.