Dynamics Analysis And Nonlinear Control Of Model-Scale Unmanned Helicopters

Model-scale unmanned helicopters have unique flight characteristics, such as hov-ering, vertical take-off and landing, law altitude and aggressive flight. Furthermore, they have significant advantages of small size, light weight, low cost and high performance of concealment. So they are widely used in military and civilian fields, such as battleground monitoring, search and rescue, aerial photography and architecture topography etc. How-ever, the model-scale helicopter is a special and sophisticate control object. Its dynamics model has the characteristics of multiple-input multiple-output (MIMO), strong coupling, time varying, nonlinearity, underactuation and stationary unstabilization. It is very dif-ficult to achieve the autonomous flight control for model-scale helicopters. Therefore, the design and development of an autonomous flight control system is of theoretical and practical significance.The main parts of this dissertation are research on autonomous flight control based on dynamics model of model-scale unmanned helicopters. This work researches and de-velops a flight control testbed, which can validate attitude control algorithm based on Align TREX 450 radio-controlled (RC) helicopter. Considering the problems of non-linearity, strong coupling, underactuation, parametric uncertainties and external distur-bances existing in the dynamics model, this dissertation proposes three nonlinear flight control schemes. Lyapunov-based stability theorem is utilized to prove that the proposed control algorithm can achieve stable tracking of reference trajectories while keeping all the closed-loop signals bounded. Furthermore, MATLAB/Simulink numerical simula-tions are performed based on the nonlinear dynamics model to demonstrate the tracking performance of the proposed controller, and highlight the robustness with respect to the parametric uncertainties and external disturbances. Specifically, the major contributions of this work can be summarized as follows:Firstly, according to the available researches on the dynamics modeling of model-scale helicopters, this dissertation introduces the nonlinear dynamics model of model-scale unmanned helicopters in detail. We follows a component buildup approach in de-vising the model, which includes rigid-body kinematics, rigid-body dynamics, force and moment generation processes and main rotor flapping dynamics. Based on the analy-sis of each component of the model, we obtain a generic complete nonlinear parametric dynamics model.Secondly, using the small electric RC helicopter as the main body, a helicopter testbed is developed. This work investigates the servo actuators coordinated control method with separate channel of the new-style electric helicopter, which is named as elec-tronic collective-cycle pitch mixing (ECCPM). A modified digital incremental proportional-integral-derivative (PID) control algorithm which is free of servo actuators saturation is-sue is proposed for the attitude control of helicopter. Experiment results are provided to verify the testbed and control design.Thirdly, according to the translational dynamics and rotational dynamics of model-scale helicopters, this dissertation presents an adaptive backstepping control design for flight trajectory tracking. In order to facilitate the control design, we divide the heli-copter’s dynamics model into three subsystems, which are the altitude subsystem, the heading subsystem and the horizontal subsystem. An adaptive updating law is designed to evaluate the uncertain parameters of mass and inertia moments, which solves the prob-lems of parametric uncertainties in the dynamics model. The global asymptotic stability of the closed-loop system is proved via the Lyapunov-based stability analysis.Fourthly, based on the general dynamics model of a class of model-scale heli-copter including main rotor flapping dynamics and external disturbances, this dissertation presents a new sliding mode control scheme. The control objective is to let the helicopter track some pre-defined time varying velocity and yaw reference trajectories. In order to facilitate the control design, the linearized model is divided into two subsystems, such as the longitudinal-lateral subsystem and the heading-altitude subsystem. The proposed controller employs sliding mode control technique to compensate for the unmeasurable flapping angles dynamic effects and external disturbances. The global exponential stabil-ity of the closed-loop system is proved via the Lyapunov-based stability analysis.Finally, a nonlinear robust controller for model-scale helicopters is developed using sliding mode control structure combined with feedback linearization procedure. The con-trol objective is to let the helicopter track some pre-defined time varying position and yaw reference trajectories. The approximate feedback linearization controller with dynamic decoupling is designed based on the simplified nonlinear dynamics model. Besides, the proposed controller employs sliding mode adaptive control technique to compensate for the parametric uncertainties, small body forces and external wind gust disturbances. The global asymptotic stability of the closed-loop system for the un-simplified complete non-linear model under the proposed control algorithm is proved via Lyapunov-based stability analysis.