Small-Scale Unmanned Helicopter Modeling And Controller Design

Small-scale unmanned helicopter has unique flight characteristics that other aircraft hasn't, such as vertical take-off and landing, hovering, cruising, low altitude and aggressive flight, and so on. Further more, it has the advantages of small size, small weight, low cost and high performance of concealment. It is widely used in both military and civil fields. However, small-scale unmanned helicopter model is a typical under-actuated, strongly coupled, unstable and time-varying nonlinear system, therefore, the design and development of an autonomous flight control system is of great theoretical significance and practical utility.The key parts of this dissertation are research on small-scale unmanned helicopter modeling and design for autonomous flight controller based on theoretical analysis and numerical simulation.Firstly, a full state nonlinear equation for the small-scale unmanned is established which combines first-principles and system identification methods. In order to solve the shortcomings of linear control methods, a novel observer-based gain scheduling controller based on the established helicopter model is presented. The design of the individual controllers for gain scheduling is time-consuming and it lacks flexibility with respect to its applicability in the other cases. Considering the structural features of the unmanned helicopter, a hierarchical inner-outer loop-based flight controller is proposed, which takes advantages of both model predictive control and adaptive backstepping method, then a simulation analysis is conducted. The stability of the hierarchical controller as described in previous chapter is hard to prove theoretically, therefore, a newly nonlinear cascaded control strategy is proposed and the stability of the feedback control system is proved via Lyapunov theory. From a practical perspective, considering the constraints on the helicopter states, we present a filtering backstepping flight controller. This method has solved the complicated and tedious calculation of the virtual control signal derivatives in standard backstepping, and the constraint problem.In general, the main contents and primary innovations of this dissertation can be summarized as follows:1. We give the background of the small-scale unmanned helicopter at home and abroad, then we give an emphasis introduction to the development status of the modeling and flight control.2. A very specific analysis for the dynamic characteristics of the small-scale unmanned helicopter is given. Combining first-principles method and system identification technology, the mathematical models of rotor flap motion and aerodynamic forces are built, then a full state nonlinear equation for the small-scale unmanned helicopter is obtained. And later, the flight experiment confirms the correctness of the model.3. Based on the model that was established in Chapter 2, we first linearize the nonlinear equation in the selected equilibrium points, and then a series of observer-based LQI feedback control law are designed. Considering the drawback of linear controller and conventional gain scheduling method, a novel observer-based gain scheduling helicopter flight controller is presented which based on Youla parameterization theory.4. In terms of the structural features of the unmanned helicopter, a hierarchical inner-outer loop-based flight controller is proposed. The outer loop employs model predictive controller to track the reference trajectory, while the inner loop controller is designed by means of adaptive backstepping techniques that allow stabilization of the attitude. The obtained control method takes advantages of both model predictive control and adaptive backstepping method. Finally, a simulation analysis is conducted.5. The stability of the trajectory tracking controller as described in Chapter 5 is not easy to prove theoretically, therefore, a newly nonlinear cascaded control strategy is proposed. The intermediate control signals related to the attitude dynamics exploit the structural properties of the transform matrix; therefore it avoids the model errors introduced by attitude model reduction. The stability of the feedback control system is proved via Lyapunov theory. Finally, an“8”trajectory tracking simulation is conducted to illustrate the efficiency of the proposed control method.6. Considering the high order of the small-scale unmanned helicopter's model, it is very complicated and tedious to calculate the virtual control signal derivatives in standard backstepping. The present paper designs a filtering backstepping controller, which significantly simplifies the backstepping implementation. While in the process of filter design, system states and control constraints can be enforced by limiting the magnitude, rate and bandwidth of the virtual control signals. Then the exponential stability of the compensated tracking errors are proved in the sense of Lyapunov theory. Finally, the numerical simulation is conducted to verify the effectiveness of the proposed control method.At last, some problems are proposed for further research and exploration after the summary of this dissertation.