Research On Networked Control Systems Of Flight Vehicle

As a new kind of control system, networked control systems (NCS) satisfies intelligent and autonomous requests of modern flight vehicle by the good system architecture, and represents the future development of flight vehicle control system. This thesis focuses on NCS of flight vehicle (FV-NCS) both the common problems of NCS and the special problems for flight vehicle application.The control network which is adapted to flight vehicle control system is studied. 1553B bus,CAN bus and Ethernet are analyzed and compared, and CAN bus is selected to build FV-NCS. The examples of CAN bus being applied to flight vehicle control system indicate the feasibility of flight vehicle system applying CAN bus.The delay characteristic of NCS based on CAN (CAN-NCS) are researched by simulation experiments and theoretical analysis. Two methods of analyzing the components of NCS delay are discussed and their relationship is described. NCS is simulated by TrueTime and message delay characteristic which is affected by network protocol, network load and other factors is discussed. For CAN-NCS, the formula of continuous scheduling and discrete scheduling for the worst case message waiting time of CAN are given by methods of real-time system task scheduling, the formula of the longest transmission time of CAN data frame is defined, the generic characteristic of CAN-NCS delay is obtained. Real-time capability of CAN-NCS is improved by TTCAN, the feasibility of flight vehicle system applying TTCAN is analyzed.The influences of CAN-NCS delay to flight vehicle control system are researched by output response and bandwidth of closed loop system. It is discovered that CAN-NCS delay can not affect centroid movement and attitude movement of flight vehicle, but CAN-NCS delay can affect many servo mechanisms which always have higher bandwidth. As the representation of these type of plants which are sensitive to CAN-NCS delay, DC motor is used as the control plant in this thesis to develop the controller study, in order to ensure the whole performance of complex and multiple loops of FV-NCS. As the basic of analyzing and designing of NCS by generic methods, the uniform augmented plant model and closed loop system model of short delay NCS are built for four different cases.Adaptive control of FV-NCS is studied. Error-integral LQG controller is designed as the basic controller, in order to solve the problem that standard LQG controller can not track the giving input. The simulation of DC motor NCS with basic controller based on TrueTime is realized, the influences by sampling period and network delay to control system performance are analyzed. For fixed network delay, fixed parameter LQG controller is designed by state argumentation. For time-varying network delay, adaptive parameter LQG controller is designed. The methods of increasing the update period of controller parameter and automatically switching control strategies are put forward and the problem of serious oscillation of system response is solved . Considering sensor package loss and time- varying network delay, adaptive parameter LQG controller with package loss managing is designed by mixed event/time driving mode and arithmetic of package loss managing. The simulation experiments for the three kinds of controller are made based on TrueTime, the results indicate that the three kinds of controller all achieve good control effect for the certain case.Robust control of FV-NCS is investigated. Uniform robust control model of CAN-NCS is built for a generic system matrix. A calculate method of the bound value for uncertain matrix is brought forward to satisfy the demand for uncertain matrix in the robust control model. For direct state feedback, sufficient conditions of stability and H_∞control of NCS are deduced, the restricts of LMI form are obtained by appropriate transformation. For state feedback with observer, because parameter matrix contains matrix variables, the approximate linearization method of inverse matrix of matrix variable is presented, and the arithmetic of LMI form for stability and H_∞control of NCS are given. For DC motor NCS, the feasible solutions are obtained by LMI toolbox of MATLAB, the simulation experiments are made based on TrueTime. The results indicate that the feasible solutions of robust stability can guarantee the closed loop system stable and the feasible solutions of H_∞control can restrain the external disturbances effectively.Gain scheduling control of FV-NCS is studied. The generic method for original controller to schedule output is discussed. Error-integral LQR controller is used as the original controller, gain scheduling method for fixed network delay is researched, the multilevel searching strategy is put forward and the optimal gain is quickly found, cost function is modified and the problem is solved that system performance of the optimal gain is not the best when sum of error square is the cost function. Gain scheduling control for time-varying network delay is realized by on-line delay estimation and dynamic scheduling gain coefficient. The simulation experiments are made based on TrueTime, the results indicate that the system performances are improved by gain scheduling control comparing to original controller and gain scheduling control can make original controller to adapt the network environment with the possible little expense.