Cancellation And Suppression Of Multiple Disturbances Based On Output Feedback

This note provides the method of disturbance cancellation and suppression based on output feedback scheme in presence of multiple disturbances.Through the output information of the system,the disturbance observer is designed to obtain the disturbance estimation value and compensate in the feedforward channel.By adjusting the parameters of the observer and analyzing the stability of the closed-loop system,the control characteristics and robustness of disturbance observer can be guaranteed in the presence of multiple disturbances.Otherwise,the disturbance observer method is extended to a class of second-order non-minimum phase systems.Combined with the nominal controller,the tracking control of disturbance can be realized.The innovative research of this thesis is listed as follows:(1)This chapter provides a sinusoidal disturbance estimation method based on reverse recursive scheme.A low-pass filter is introduced to excite the disturbance characteristics,and series of cascaded unmeasurable signals are then obtained.Particularly,the signals can be decomposed into three parts,including standard sinusoidal virtual signal,equivalent bounded disturbance and decay term.In case of the frequency is known,the auxiliary filter is designed to establish the relationship between frequency and virtual disturbance,with which the input disturbance can be reconstructed based on reverse recursive scheme.The disturbance observer design method removes the nessarity to estimate the disturbance state and is completely independent of the controller structure.In condition that equivalent bounded disturbance is absent,the sinusoidal disturbance can be tracked asymptotically.Otherwise,the uniformly ultimately bounded of estimation error can be guaranteed in presence of multiple disturbances.(2)Under the condition that the controlled system includes regular or modelable bounded disturbance,such as constant or slow time-varying disturbances,which is described or approximated as the sinusoidal disturbances with offset.Then the disturbances is equivalent to a third-order modelableexternal system to be estimated based on reverse recursive structure.a low-pass filter and a novel auxiliary filter are utilized to reconstruct the input disturbance in the relationship of the frequency and disturbance.Afterwards,combined with the Lyapunov's theorem,the stability of the method is analyzed.The effectiveness of the disturbance observer structure has been verified by simulation and experiment.(3)An anti-disturbance control and compensation for a class of second-order non minimum phase system is studied.The disturbance cannot be directly estimated because of the zero dynamic instability of the system.Therefore,firstly,an auxiliary observer is designed to obtain the disturbance characteristic.Then,based on the relationship of frequency,system parameters and disturbance,the disturbance synthesizer is constructed by utilizing the output signal of auxiliary observer and corresponding derivative to estimate the external modelable periodic disturbance.This method makes full use of system characteristic and possess strong robustness under the condition of bounded noise.