Event-triggered Control For Nonlinear Systems With Unknown Disturbances

Almost all practical engineering systems are nonlinear.As the controlled system becomes more complex and the requirements for control accuracy continue to increase,the linear system control theory has been unable to meet the demand.And it is difficult to avoid the influence from different types of disturbances such as environmental disturbances,model uncertainties and cyber attacks in the practical application.Therefore,the control problem of nonlinear systems with unknown disturbances is a current research hotspot in the control field.Connecting system nodes such as the actuator and the controller through networks can enhance the scalability of the system and break through the space constraints between the controller and the controlled system.It is one of the important structures of the engineering system in the future.In this system structure,the event-triggered control method can effectively solve the problem of the waste of communication resources caused by the traditional high-frequency sampling control method.Meanwhile,the cooperation of multiple nonlinear systems can effectively overcome the problems of low robustness,weak autonomy and incomplete capability of a single system.Therefore,this paper mainly aims at the cooperative tracking problem of nonlinear multi-agent systems with unknown disturbances,and proposes an event-triggered control scheme to ensure that all signals of the closed-loop system are semi-globally uniformly ultimately bounded.The main research contents are as follows:(1)A disturbance observer-based event-triggered control algorithm is proposed to solve the consensus tracking problem of multi-agent systems with unknown system parameter vectors.First,a disturbance observer is designed based on the system model to estimate the mismatched external disturbances.Then,the control law is designed by backstepping to estimate the unknown parameter vectors as well as to compensate for the disturbances.In order to avoid input saturation due to compensation,the amplitude of the control signal is limited,and a new type of saturation compensation subsystem is designed to compensate for the over-saturation control,thereby ensuring the control performance.Finally,an event triggering mechanism is designed based on a relative threshold strategy to reduce the information transmissions from the controller to the actuator.The effectiveness of the proposed method is verified by design numerical simulation and manipulator system simulation.(2)An event-triggered control algorithm based on prescribed performance is proposed to solve the formation control problem of underactuated surface vessels(USVs)under directed communication.First,the upper bound of the environmental disturbance is estimated by designing an adaptive law and compensated by the controller.Second,the prescribed performance control is used to constrain the distance errors to avoid collisions and maintain communication.Then,neural networks and auxiliary variables are constructed to deal with the problems of uncertain nonlinearity and underactuation of USVs,respectively.Finally,the actual controllers are designed through adaptive backstepping and relative threshold event-triggered strategy.The effectiveness of the control method is verified by the simulation of the Cyber Ship II system.(3)A data selector-based event-triggered control algorithm is proposed to solve the secure consensus tracking problem of nonlinear multi-agent systems.First,in order to deal with the problem of sparse attacks on sensor measurements,a data selector is designed to pick out sensor data that has not been attacked.Then,based on the obtained sensor data and neural networks,a state observer is constructed to estimate the unavailable system states.And the convex combination theorem is applied to reduce the difficulty of solving the observation gains.Finally,a novel event-triggered strategy is designed to regulate the update of the control signals,and the updated signals are transmitted by the 1-bit signal transmission mechanism to further reduce the occupation of communication bandwidth.The effectiveness of the proposed method is verified by the simulation of the UAV attitude system.