Research On Nonlinear Control Method For Small-Scale Unmanned Aerial Vehicle

The four-rotor aircraft is new type UAV which has a high performance and simple mechanical structure. It not only has small size, strong concealment, low noise and many other advantages, but also involves the fusion technology and research value in many areas. This paper take the attitude system and dynamic system of four rotor aerial vehicle as the research object, and we design strong robustness and height performance flight control system with external disturbance, model uncertainty and loss the part effectiveness of actuator failure. The main works in this dissertation are arranged as follows:1. Firstly, this paper analysis and establish the dynamic and kinematic equations of four rotor aircraft, and give the relationship of failure factor for four rotor aerial vehicle with loss the part effectiveness of actuator failure and normal work in general, and the mathematical model of aircraft was presented for control.2. We considered the flight control problem of attitude system and conventional dynamic system of four rotor aircraft with external disturbances and parameters uncertainty. First, for attitude system, a new adaptive back-stepping control method is developed. Using fuzzy logic system to approximate the uncertainty nonlinear part of model, and an adaptive robust term with fuzzy monitoring strategy is introduced to compensate the external disturbance, it can cancel the unfavorable effects on control system. Then a double closed loop control system is established for the conventional dynamic system. At the same time, the virtual control law in outer control loop is designed as the command signal within inner control loop. Through the coordination of the inner and outer control loop, the tracking error can converge to the small neighborhood of a stable point. Simulation results show the effectiveness of proposed control strategy.3. We considered the attitude system of four rotor aircraft under the double closed loop structure using adaptive finite time control strategy. In inner and outer loop, a terminal sliding surface with integral bias is introduced to improve the tracking speed, and using the adaptive online compensation term to cancel the unfavorable effects on control system. The proposed control method can guarantee the tracking error to converge a small neighborhood of the stable point in finite time. For the conventional dynamic system, we design the double closed loop control system using the same method. Finally, the double closed loop ensure the whole system stability. 4. Two kinds of adaptive control strategies based on sliding mode technique are presented to address the tracking problem of four rotor unmanned aerial vehicles with the partial loss of actuator effectiveness. For the attitude system of aircraft, the designed control mechanism is utilized to achieve self-online adjustment of compensation when the partial loss of actuator effectiveness occurs. For the dynamic system of aircraft, the online correction method is employed to estimate the failure factors when failure occurs. Furthermore, an auxiliary function is added in the controller design, it not only makes the controller gain can be changed according to the effective information of sliding mode, but also can soften chattering control signal. Through the coordination of the inner and outer control loop, the tracking error can converge to the small neighborhood of a stable point.