Disturbance Observer Based Control For A Three Degree Freedom Of Model Helicopter

The helicopter flight control system is a typical multi-input and multi-output(MIMO) system, with strong channel couplings and nonlinear characteristics, which is considered as a complex control object in control engineering. As simple structure and low cost experimental devices, the three degree of freedom(3DOF) model helicopter systems can be used to verify a variety of linear and nonlinear control methods for the development of helicopter flight control method, and provide guidance for helicopter flight control study and design. In this thesis, based on a 3DOF model helicopter made by Googol Technology Ltd, robust control methods are developed for the motion control of 3DOF model helicopter with unknown external disturbance, modeling uncertainties, input and output saturation. The main research contents are as follows:First of all, the nonlinear mathematical model is established based on the motion characteristics of 3DOF model helicopter. And, linear equations are obtained in an equilibrium state linearization.Secondly, a disturbance observer based generalized proportional integral(GPI) attitude controller is designed for the motion control of linear model of 3DOF model helicopter. A disturbance observer is designed to estimate the system suffered external disturbance, which can be compensated in the controller. The designed controller is simple, easy to implement, and the parameters of the controller can be directly obtained by the method of pole assignment. The simulation results show that the designed controller has good robustness and tracing property in the presence of external disturbance in the system. The real time simulation results verify that the GPI controller has better robustness and tracking performance than traditional proportion-integral-derivative(PID) controller, and can effectively solve the noise introduced by derivative term in traditional PID controller.Then, backstepping control method is applied in the control design for a class of nonlinear systems with unknown external disturbance and modeling uncertainties, and applied to the motion control system of 3DOF model helicopter. Taking into account of the existence of unknown external disturbance and modeling uncertainties, a disturbance observer is designed to approximate the unknown external disturbance and unknown modeling uncertainties, which will be compensated in the controller. At the same time, the stability of closed-loop system is proved by Lyapunov method. Simulation results for the motion control design of the pitch channel with unknown external disturbance and modeling uncertainties show that the designed controller is effectively to ensure the stability of the pitch angle control. The real time simulation results verify that the designed controller has good tracking control performance.Following, a backstepping control method based on observer is studied to the motion control design of the nonlinear model for 3DOF model helicopter with unknown external disturbance and modeling uncertainties. Based on the motion characteristics of the 3DOF model helicopter, the whole system is divided into two subsystems. Agmented state observers are applied to estimate the unknown states and composite disturbance which is considered as an augmented state composed by unknown external disturbance and modeling uncertainties. At the same time, the stability of closed-loop system is proved by Lyapunov method. Simulation results show that the designed control scheme is effective to deal with the motion control of 3DOF model helicopter in the case of unknown external disturbance and modeling uncertainties.Finally, a backstepping control method is devolped for the motion control design of 3DOF model helicopter with unknown external disturbance, modeling uncertainties, input and output saturation. Augmented state observers are applied to estimate the unknown states, unknown external disturbance and modeling uncertainties. An auxiliary system is designed to deal with input saturation. Barrier lyapunov function(BLF) is applied to process the output saturation. The stability of closed-loop system is proved by Lyapunov method. Simulation results show that the designed control scheme is effective to deal with the motion control of 3DOF model helicopter in the presence of unknowm external disturbance and modeling uncertainties, input and output saturation.