Nonlinear Domination And Constrained Disturbance Rejection Control Methods With Applications In Thermal Power Engineering

It is challenging to control thermal power processes or systems with appropriate performance due to strong nonlinearities and various unknown uncertainties.Recently,most existing advanced controllers are interesting to solve tracking problem based on modelling the behaviors of thermal power processes,but few focus on how to directly deal with these nonlinearities and uncertainties,in particular on how to analyze the stabilities of the closedloop systems.This thesis intends to investigate how to deal with the strong nonlinearities and unknown uncertainties,and thus to propose two new controller design methods,called nonlinear domination control and disturbance rejection control with constraints(on inputs).The main contributions and novelties are summarized as follows:(1)To regulate a class of nonlinear system with unknown but bounded uncertainties,this paper proposes a robust nonlinear controller design method in a recursive manner using nonlinear domination based on Lyapunov theory and homogeneous system theory.This new method extends the conventional homogeneity to interval homogeneity,and gives stable conditions on the boundaries of time-varying parameters as well as a kind of Lyapunov function with interval parameters.Simulation results show that the proposed method can be used to control a class of typically thermal power systems when their parameters vary in a certain boundaries.(2)To solve tracking problem of a class of nonlinear thermal power processes with unknown disturbances,this paper proposes a state feedback controller in a composite manner based on high-order sliding mode observer,where the state feedback controller was designed based on the nominal model,whereas the high-order sliding mode observer is used to estimate the lumped disturbances in the channels of states and outputs and thus to compensate the influences of lumped disturbances on the performance.Simulation results indicate that the outputs can track given references rapidly in the presence of various unknown disturbances but without sacrificing its nominal performance in the absence of unknown disturbances.(3)To solve tracking problem of a class of nonlinear thermal power processes with unknown disturbances as well as some constrains on control inputs,this paper proposes a receding Galerkin optimal controller design method in following two different ways: the former designs a state observer to estimate unmeasured states and then uses an independent model to estimate just constant disturbances in the output channel,whereas in the later one,the highorder sliding mode observer is used to estimate unmeasured state as well as various unknown disturbances existing in both channels of state and output,as similarly do above in(2).Simulation results suggest that appropriate performance can be achieved by both ways when imposing constraints on control inputs.