The Aircraft Track Angle High-precision Tracking Control Algorithm Research

Unmanned aerial vehicles (UAVs) are now increasingly used in military and civilian fields due to their inherent quality of being cheap, agile and the ability to carry out a variety of missions without man loss. The study on the automatic flight control technology of the UAVs has been more and more important due to the rapid development of the UAVs.As one of the several control approaches for achieving height maneuver, the flight-path-angle control based scheme is not sensitive with respect to external aerodynamic disturbances, and hence is widely used in practical flight. This control mode is hence one of the most important modes considered by the control-law designers. However, for the conventional PID-based control scheme (without feed forward compensator), the non-minimum phase characteristics lead to internal-state oscillation and unacceptable tracking error and, moreover, this may in turn induce saturation of the elevator control surface due to feedback and hence endanger the flight. This dissertation is devoted to investigating the high-precision tracking control problem of flight-path-angle. Firstly, the total equation of motion of the airplane model, which will be trimed and linearized to analyze the non-minimum phase characteristics of airplane, has been established. Furthermore, the difficulties of the flight-path-angle control have been expounded in detail. Secondly, the conventional PID-based controller has been designed and verified by digital simulation. According to the simulation results, further analysis on the causes and specific phenomenon has been executed to figure out why this control scheme cannot solve the non-minimum phase problem. A novel control technology based on Ideal Internal Dynamics (IID) also has been proposed subsequently. Then, the Sliding Mode Controller (SMC) based on IID and UDE (Uncertainty and Disturbance Estimator) has been designed to solve the non-minimum phase control problem combined with internal-state disturbances. The effectiveness of IID, UDE and SMC has been verified by linear simulation. Afterwards, according to the comprehensive analysis and evaluation of conventional PID controller and SMC based on IID and UDE, the IID-based PID controller has been designed. The performance of the controller has been verified by simulation and by comparison with the conventional PID-based controller. Lastly, nonlinear simulation platform has been developed to simulate and verify the three control schemes. Further analysis and comparison of the three control schemes are also made concerning the performance and the control cost.The IID-based SMC and IID-based PID controller, whose validity and accuracy have been verified by linear and nonlinear simulation, can be applied to solve the non-minimum phase problem of flight-path-angle control.