The Study On Disturbance Observer In The AC Position Servo System

The AC position servo systems are extensively used in the industrial control systems. The disturbance is the main factor which influences the performance of the systems, and the major sources of disturbance in servo systems are: (1) The parametric uncertainties in the nominal model, parameter variations during operation, and structure uncertainty in modeling such as nonlinear friction (static friction and Coulomb friction); (2) The external disturbances such as the load variations and the change in operation conditions etc..The observation and compensation of the above disturbances in the AC position servo system based on the 3-phase induction motor is studied in this thesis. The dynamic model of the 3-phase induction motor is obtained first, and the vector control theory is introduced. Then the two-loop position servo system composed of current loop and position loop as well as the triple-loop position servo system composed of current loop, speed loop and position loop are designed. The conventional PID controller together with the disturbance observer is adopted in the AC position servo system to reject the disturbance.The basic concept, design principle and method of DOB are introduced. The stabilities of the whole system and DOB are analyzed respectively, and stability conditions are given with Routh-Hurwitz stability criterion. Within certain parametric uncertainties in the nominal model, the DOB has the advantages of rapid respond and independent regulation. Compared with other control methods, DOB without extra sensors can be implemented easily. The parameters such as the order, the relative degree and the bandwidth of the low-pass filter in DOB can be adjusted with ease.Finally, issues related to the implementation of DOB in the numerical simulation and in a digital signal processing board (TMS320F2812) are also presented.Through numerical simulation and real experiments, it is proved that the disturbance observer in the AC position servo system can reject disturbance effectively, and provide strong robustness to the parameter variation.