Design And Application Of Fractional Order Disturbance Observer

High performance servo system not only needs good dynamic response performance,but also needs good anti-disturbance performance to deal with the system external disturbance and the uncertainty of model parameters.The most commonly used control method in industry is the traditional PID control,which is based on the accurate model of the controlled system.However,almost all the actual control systems are difficult to get its accurate mathematical model,which leads to the traditional PID control method is difficult to meet the accurate,fast and stable control requirements.In order to achieve accurate control of such systems as high-performance servo systems,this thesis combines the disturbance observer with fractional calculus control theory to study the design and application of fractional order disturbance observer.The main research work and achievements are as follows:(1)The robust stability and disturbance rejection principle of classical disturbance observer are analyzed.In order to solve the problem of amplifying the high frequency measurement noise caused by the existence of differential elements in the classical disturbance observer structure,an improved disturbance observer structure is studied,which can effectively observe the low frequency disturbance and effectively filter the high frequency noise.(2)The influence of parameters of low pass filter on system performance in the design of improved disturbance observer is analyzed.Based on the theory of fractional calculus control,the low-pass filter is extended to fractional-order filter,and the fractional-order disturbance observer based on the improved disturbance observer is designed.(3)The digital realization of fractional-order disturbance observer is studied,and the approximation effect of fractional-order filter treated by different discrete approximation methods is analyzed.The proposed perturbation rejection control strategy based on fractional-order disturbance observer is experimentally studied,and the proposed fractional-order disturbance observer is proved to be robust to the uncertainties in the system on the Quanser semi-physical experiment platform.(4)This thesis further studies the effect of the fractional-order disturbance observer in the practical application,selects the two-axis and two-frame airborne photoelectric stabilized aiming platform as the experimental object,analyzes the disturbance factors affecting the system stability,and provides more reference for the design of the simulation experiment.Experimental results show that the fractional-order disturbance observer designed in this thesis not only has the advantages of being unaffected by model errors and effectively compensating the disturbances,but also absorbs the characteristics of fast response and strong robustness of fractional-order control.