Finite-time Sliding Mode Variable Structure Control For Model-scale Helicopters

With the development of flight control technology of the unmanned helicopter in recent ten years, the finite-time control technology of unmanned helicopter get more and more attention. And in some applications which need the unmanned helicopter to get hovering in the limited time, such as formation flight for unmanned helicopters. This paper designs hover and forward flight controllers via finite-time sliding mode variable structure control under this background.Firstly, this paper presents the mathematical model of model-scale helicopter under some reasonable assumptions. For this purpose, the model-scale helicopter is broken down into six subsystems, which include the fuselage, the main rotor, flybar and tail rotor, the tail plane and vertical fin. And, we present mathematical model for the six subsystems respectively. Finial, the complete mathematical model of the model-scale helicopter is established by analyzing the coupling relationship among these subsystems. Besides, we formulate the wave kinematic equations of the flybar, and analyze the relationship between the main rotor and flybar. At the same time, we carry on the partial linearization based on reasonable assumptions under the conditions of approximate hovering for aerodynamics model.Secondly, under the multi-loop control framework, hovering controller for the model-scale helicopter is designed in this thesis. Considering the under-actuated property of the model-scale helicopter and the cascade characteristics of the translation and rotation subsystems, the finite-time sliding mode controller and PID controller are synthesized for the translation and rotation subsystems to construct the multiple-loop hovering controller. After compare, a suitable terminal sliding mode surface and reaching law are used to design hovering controller. Instead of the sign function in the terminal sliding mode, this thesis uses continuous function to reject the chattering phenomenon. In the end, this thesis verifies the robustness of the controller by the simulation.Finally, this thesis designs forward flight controller for model-scale helicopter via finite-time sliding mode variable structure approach. Based on the definition of forward flight state, we use the same method to design forward flight controller, and verifies the robustness of the controller by simulation.