Sliding Mode Adaptive Control Of Nonlinear System And Application To Electro-Hydraulic Control System

Since sliding mode variable structure control and Backstepping control have some drawbacks, this paper presents nonlinear derivative and integral sliding mode adaptive control scheme, a time-varying sliding mode adaptive control scheme and a multiple sliding mode robust adaptive control scheme, and these proposed methods are applied to tracking control of electro-hydraulic control system respectively .Chapter One expatiates the development history of nonlinear system control theory and electro-hydraulic system modern control, including precise stable feedback control, sliding mode variable structure control and Backstepping control, and points out the drawbacks of these control laws. The research work of this thesis is presented.Chapter Two proposes a derivative and integral sliding mode variable control scheme, and a derivative and integral sliding mode adaptive control scheme for a class of nonlinear system with uncertain parameters. The two control approaches introduce integral control to avoid the assumption that the derivative of desired signal must be known in conventional sliding mode variable structure control. The integral of tracking error is introduced into switching function to eliminate the [every item?] involving desired signal derivative. A nonlinear derivative control is introduced to avoid system chattering.The two proposed methods are applied to velocity tracking control and position tracking control of two electro-hydraulic servo systems respectively. Simulation results indicate that the two control approaches both are robust and improve tracking accuracy considerably and the control inputs are smooth. In addition, the energy consumption of DI-SMAC is smaller.In Chapter Three, since the reaching stage of sliding mode control can not guarantee to remain insensitive to parameter uncertainties and disturbances, a time-varying sliding mode adaptive control is presented for a second-order nonlinear system. Moreover, a two layer time-varying sliding mode adaptive control technique is developed for a high-order nonlinear system. Time-varying sliding surface and two layer time-varying sliding surface are defined, and the design method of adaptive controller and adaptation law are given.The proposed two layer time-varying sliding mode adaptive control method is applied to velocity tracking control of an electro-hydraulic servo system. Simulation results indicate that the control approach is robust and improves tracking accuracyconsiderably, and eliminates chatting phenomena.Chapter Four introduces the concepts of fictitious controller and fictitious adaptation law. Combining robust control method, a multiple sliding mode robust adaptive control strategy is proposed for a class of high-order uncertain nonlinear system including model parameters uncertainty and model structure uncertainty. Compared with standard Backstepping control, all fictitious controllers and actual controller of the proposed control method only have the desired output and parameters of the current step subsystem. So the proposed control method is decoupled control in some sense.The performance of the variable displacement pump controlled invariable displacement motor electro-hydraulic system is analyzed. Using the multiple sliding mode robust adaptive control strategy, a position tracking controller is designed. Simulation results show that the control approach has nice robustness and improves position tracking accuracy considerably.Chapter Five gives the vehicle active suspension control system research. A low-pass nonlinear filter and a high-pass nonlinear filter are used to optimize the aim function which includes the car body vertical acceleration and suspension travel to make adapt to different road, A nonlinear adaptive controller of hydraulic active suspension is designed by adopting multiple sliding mode robust adaptive control technique. In addition, the zero dynamic system feature and frequency feature of the control system are analyzed.The simulation results indicate that the control approach can greatly improve ride quality and manipulate performance for different input singles.Chapter Six summarizes the research work of this thesis and points out its shortage. The future research aim and direction are presented.