QFT/TECS Application In Aircraft Automatic Landing Control System

This dissertation mainly investigates robust control and velocity/altitude decoupling control strategies wich is a key technology in the research of safty and reliable automatic landing control systems. Considering that during aircraft landing phase there are drastic changes in velocity and altitude and fluences of wind turbulence, a quantitative feedback theory (QFT) is applied in the design of a robust automatic landing system. On the other hand the coupling effect between air speed and altitude may mess up the landing performance of the aircraft, in order to get a smooth landing, total energy control system (TECS) design method is applied in the velocity/altitude decoupled automatic landing system.The main work of this dissertation includes:1. QFT method is studied and applied in flight control system. First the quantitative feedback theory is systematically studied. The main character and the designing process of QFT controller are presented. A pitch angle control system is designed based QFT, and take this as the inner-loop system a longitude landing system is designed. Simulation shows, intergrated with thrust controller, this landing system gets a robust performance.2. A non-diagonal QFT controller degign methodology is presented and applied in attitude control mode. Based on the study of the shortcomings of MIMO systems QFT diagonal controllers, the non-diagonal QFT controller is thoroughly discussed. Sience there are a lot of 2 × 2MIMO systems in nature plants, in this paper a robust non-diagonal controller design methodology for 2×2MIMO systems is presented. A quality function is introduced to check the effect of the non-diagonal controller. Then a sequential design methodology of the fully populated matrix controller is proposed in the quantitative feedback theory (QFT) robust control frame. Finally, an application in an attitude control of a plane is included to show the practical use of this technique.3.Two improvements are proposed to enhance the TECS control performance. First, the structure and principle of total energy control system are systematically presented. Based the basic ideas and core control structure of TECS, an error controlmethod was adopted to eliminate the stable error of airspeed and altitude when decoupling control through TECS theory. A new feedback loop based on the cooperation error between aircraft total energy rate and energy distribution rate is proposed. This method adopts several simple PI controller to achieving good decoupling effect. Finally, digital simulations of this new control method is conducted with an aircraft on four of its typical situations, the result validated this method's availability.4. Based on QFT and TECS methods, the longitude automatic landing laws are designed. A glide mode and a flare mode are studed and proposed to join with the core control structure of TECS. The set of longitude flight control modes is redesigned. Take TECS as the whole control structure and apply QFT in pitch angle controller design, the longitude landing control system is designed. Two flight modes were tested to check this automatic landing laws and the result shows satisfactory landing performance.5. Based on QFT method, the lateral automatic landing laws are designed. First, appling QFT in roll angel controller design of the aircraft's lateral direction. Take the roll angle control mode as the inner-loop, then a lateral deflection modification system is designed joined with the cooperation of aileron controller. Simulation shows this system meets the demands on lateral deflection, roll angle, yawing angle, sideslip angle during the landing phase.6. Considering the total demands on the longitude and lateral directiong of the aircraft during landing phase, a total system joined longitude and lateral modes is proposed and a common design approach and process are presented. Aircraft system dynamics under wind disturbance are studied. Since wind turbulence is the commonest disturbance during aircraft landing, the total automatic landing system is tested under middle severe wind turbulences. Simulations show satisfactory landing performance in both longitude and lateral directions.