Research On Speed Observer And Flux Observer Based On SVM-DTC For An Induction Motor

Nowadays, frequency control based on direct torque control(DTC) is one of the hot research spots in the induction motor drive control. Precise motor speed, flux observer and low cost are research keys of high-performance motor control. Therefore, this paper mainly research and improve speed observer, flux observer, motor parameters and robust control in the process of speed adjustment. These measures are adopted to improve the performance of frequency control for an induction motor.Firstly, development statues, improvement strategy, speed observer and flux observer of induction motor control are summarized. Then the choice of basic voltage vector and mathematical model of the induction motor and inverter are analyzed. MATLAB/Simulink simulation model of the induction motor is set up, which provides theoretical basis for further study.According to the principle of direct torque control and simulation model of the induction motor, a classical model based on DTC for an induction motor is built. Then an improved control strategy combining SVPWM with DTC (SVM-DTC) is described in detail, which provides research foundation for designing and improving observers. To save cost, stator voltages are estimated according to switch tube duty ratio and DC voltage, achieving AC voltage sensorless control. To some extent, this way can also improve the reliability and robustness of the system.After analyzing basic principles of the model reference adaptive system(MRAS) and sliding mode control(SMC), two speed observers are designed respectively. Speed observer based on MRAS estimate the motor speed according to the voltage model and the current model. Speed observer based on SMC creates a sliding surface by the error of the observed stator current and the real stator current. The stability of speed estimation is assured by Lyapunov theory. Two simulation models are built by MATLAB/Simulink and compared results are obtained. Experiments by dSPACE 1104 platform further verify speed observers and the control of an asynchronous motor without speed sensor becomes possible.In the process of improving ripple at low speed, this paper proposes two new flux observers. One of which is the full-order flux observer, aiming at reducing ripples of the flux and torque. The other one is designed on the basis of the classical flux observer, ignoring the stator resistance. The pure integral is replaced by two one-order low pass filter in serial. The way is called as non-parametric flux observer. Specific physical experiments verify the feasibility of the two flux observers. Direct torque control does not depend on any parameters of the motor by using non-parametric flux observer, which improves the robustness and enlarges the practical application range of the system.