Composite Nonlinear Feedback Controllerfor UAV With Input Saturation

The rapid development of UAV has benefited from the continuous optimization of control algorithms that increase the usability and safety of UAV.For a long time,control algorithms have always been one of the hotspots and difficulties in the field of UAV research.Due to the complex characteristics of UAV system itself and its controller is under-actuated,so it is difficult to obtain satisfactory control effect by traditional linear controller.In addition,the UAV will be affected by uncertain interference such as its own friction and external airflow during flight,which further increases the difficulty of controller design.In this paper,composite nonlinear feedback control technology is used to solve the problem of driver saturation of UAV controller,and the transient performance of the system is improved under the premise of ensuring the steady state performance of the system.For the uncertainty disturbance,the robustness of the composite nonlinear feedback control technique is improved by combining the disturbance observer and the sliding mode control respectively,so as to ensure that the control output of the UAV can accurately track the given reference signal in the presence of disturbances..The main research work is as follows:1.Composite nonlinear feedback control technology is introduced for the problem that the system control input saturation problem and transient performance are difficult to balance.Starting from the composite nonlinear feedback control of steady-state trajectory tracking in single-input and single-output systems,the design method and design idea of composite nonlinear feedback control are studied.On this basis,the technology is extended to the time-varying trajectory tracking problem of high-order multiple input and multiple output systems.The design method is given and the stability is analyzed.Finally,the simulation results show that the designed controller can make full use of the driving performance of the controller and improve the adverse effects of driving saturation.At the same time,the control output can be tracked to a given time-varying reference signal quickly and smoothly.2.A robust composite nonlinear feedback control method based on disturbance observer is proposed for a class of time-varying disturbances.The method first uses the observer to estimate the external time-varying disturbances,and then the external interference is cancelled by combining the estimation with the compensation itemsadded in the controller.Finally,a composite nonlinear feedback controller without disturbance and a robust composite nonlinear feedback controller with disturbance for UAV are designed and simulated.The simulation results show that the UAV’s transient performance under the composite nonlinear feedback control is obviously better than that of the PID combined LQR control scheme proposed in the literature,and the robust combined nonlinear feedback controller proposed in this paper can effectively eliminate the influence of time-varying disturbances and achieve fast and accurate tracking of time-varying trajectories.3.Considering the more general complex uncertainty interference,a robust composite nonlinear feedback control strategy based on integral sliding mode is proposed.The specially designed sliding surface function and the approach method ensure that the system state trajectory can reach the sliding surface and remain stable,thus reducing the influence of uncertainty interference on the controller performance.After reaching the sliding surface,the system can quickly and smoothly track the reference signal under the action of composite nonlinear feedback control.The control method is used in the UAV model with uncertain interference,and it is proved by simulation that the control strategy can make the attitude angle of the UAV track to a given time-varying trajectory with a very small error.