Robust Fault Tolerant Constrained Control For Unmanned Autonomous Helicopter

Compared with the fixed-wing aircraft,unmanned autonomous helicopter(UAH)has obvious advantages because of its special abilities of hovering at a desired altitude,vertical take-off and landing,flexible flight,and coordinated turn.Consequently,it possesses broad application prospect in many military and civilian fields.In particular,owning to the tremendous merits of long cruise,large payload,fast speed,high altitude,and strong robustness,medium-scale UAH has received more attention by experts and scholars and become one of the research hotspots in aerospace domain.However,the UAH is in nature a multivariable nonlinear system with underactuation and strong coupling.Meanwhile,there are numerous downsides in the actual flight,such as external disturbance,system uncertainty,actuator fault and nonlinear constraint.Therefore,it is of far-reaching significance to study the robust fault-tolerant constrained control problem of UAH system.Focusing on the single-rotor medium-scale UAH with a tail rotor,this paper investigates the issues of nonlinear modeling and robust fault-tolerant constrained control.The main contributions of the thesis are summarized as follows:(1)For the medium-scale UAH hovering and low-speed cruise flight modes,the main rotor flapping dynamics are introduced into the kinematics and dynamics equations of the medium-scale UAH.Finally,the medium-scale UAH nonlinear model with 6-degree-of-freedom and 14-states is established.Meanwhile,the validity and applicability of the established model are verified by simulation experiments,which provides the corresponding basis for the subsequent investigation of the robust fault-tolerant constrained control problem of helicopter.(2)An adaptive robust fault-tolerant tracking control scheme is proposed for the medium-scale UAH in presence of external disturbance and actuator fault.Firstly,external disturbance and actuator fault are incorporated into the medium-scale UAH nonlinear model.Then,in order to the design the fault observers,different auxiliary systems are then constructed for the translational motion subsystem,the rotational motion subsystem,and the rotor flapping motion subsystem,respectively.Meanwhile,the adaptive method is combined with the projection function to estimate the unknown actuator loss of effectiveness fault,and the robust term is designed to improve the anti-disturbance ability of the system.Finally,based on the backstepping control approach,a robust fault-tolerant control strategy is developed to ensure the tracking control performance of the whole closed-loop system.(3)A global finite-time fault-tolerant tracking control scheme is presented for the medium-scale UAH in presence of system uncertainty and multiple actuator faults.Firstly,considering system uncertainty and multiple actuator faults,the medium-scale UAH altitude and attitude combination model is provided.Secondly,a fault detection and identification algorithm is proposed to detect and recognize different types of actuator faults.Meanwhile,the radial basis function neural network(RBFNN)is adopted to approximate the system uncertainty.Finally,an adaptive neural network fault-tolerant tracking control scheme is developed to guarantee the finite-time convergence of the closed-loop system error signals.In addition,by integrating a switching function into the control design,the traditional semiglobally uniformly ultimately bounded stability is extended to globally uniformly ultimately bounded stability.(4)A robust fault-tolerant compensation control scheme is developed for the medium-scale UAH in presence of external disturbance,actuator fault and input constraint.To improve the robustness of the UAH system in actuator healthy case,the corresponding nominal controllers are respectively designed for the position motion subsystem and the attitude motion subsystem with external disturbance.Whereafter,additional compensation control inputs are designed to reduce the negative effects derived from actuator fault and input saturation.Finally,by combining with the backstepping control and adaptive control methods,a robust fault-tolerant control scheme is proposed to guarantee the boundedness of the closed-loop system tracking errors.(5)A prescribed performance-based fault-tolerant tracking control scheme is proposed for the medium-scale UAH in presence of external disturbance,actuator fault and output constraint.Firstly,an error transformation function is introduced to convert the UAH system with output constrained into an unconstrained system.Then,the parameter adaptation method is utilized to handle the unknown external disturbance and the RBFNN is employed to approximate the unknown nonlinear function.Meanwhile,an auxiliary system is constructed to tackle the actuator fault in view of the approximation results.Finally,a robust fault-tolerant control scheme is presented to guarantee the transient and steady-state performance of the closed-loop system,and the output tracking errors satisfy the specified restricted conditions.(6)An adaptive robust fault-tolerant control scheme is presented for the medium-scale UAH in presence of external disturbance,actuator fault and full state constraints.First,the whole closed-loop system is divided into three subsystems: translational motion,rotational motion and rotor flapping motion.Subsequently,a fault tolerant control strategy is proposed for each subsystem to cope with the actuator fault,which can effectively overcome the singularity problem in many adaptive estimation approaches by using projection function.Meanwhile,the adaptive method is employed to restrain the unknown bounded disturbance.Finally,based on the barrier Lyapunov function method,a robust faulttolerant control scheme is developed to ensure that all closed-loop system states change within the prescribed constrained conditions.The proposed various robust fault-tolerant constrained control strategies have been applied to the medium-scale UAH nonlinear system model to verify the validity.Simulation results show that the robust fault-tolerant constrained controller designed in this paper can not only guarantee the system stability effectively,but also enable the system outputs to track the reference trajectory signals.