Research On Dynamic Modeling And Active Fuzzy Control Of Large Flexible Space Truss

Active control of Large Flexible Space Truss (LFST) is a challenging subject in the domain of the dynamics and control of spacecrafts. LFST is a kind of large discrete structures made of structural elements, such as bars, beams, joints, its payloads and so on, according to given specific needs of space missions. LFST is widely used in space structures for its excellence of easily loading and unloading, high reliability, good suitability to missions. However, as a typical kind of large discrete structures, LFST is of complex dynamic characteristics, and the control methods based on custom and modern control theories are difficult to suit the control problem of this large complex system. However, fuzzy control theory doesn't depend on the accurate mathematical model and it is suitable to the control of the large complex system. From this point of view, this dissertation researches the dynamics of LFST and brings forward the research topic of active fuzzy control for LFST, which are deeply studied and discussed in this dissertation.This dissertation mainly covers two aspects of works. One is the topic of the dynamic modeling, characteristics analysis and computation of LFST, and the other is the topic of active control of LFST based on fuzzy control methods. In a word, based on the two aspects, this dissertation includes:1. Aiming at LFST, a typical kind of discrete structures, this dissertation nails down the background and characteristics of the researched object, and LFST is classified as several kinds of structures, such as truss type of space station, stretched-out support truss, paraboloid truss antennas, ring-tension truss deployable antennas, tetrahedral truss antennas and variable geometry truss. This dissertation reviews three aspects of the research topics: (1) dynamics and active control of LFST; (2) fuzzy control; (3) active fuzzy control of structures.2. The dynamics of LFST is researched thoroughly and entirely.(1)Considering the problem and challenge brought by the vibration when spacecrafts with LFST in orbit, and aiming at several general materials, this dissertation analyses the feasibility to building a scaled model of LFST in lab, which is of the same or near dynamic characteristics as the LFST in orbit.(2)The dynamic characteristics based on modal analysis of some general types of space truss structures, such as paraboloid truss antennas, ring-tension truss deployable antennas, tetrahedral truss antennas and variable geometry truss, are researched.(3)Truss type of space station and stretched-out support truss structures are modeled and computed by finite element method, which mainly includes large distributed type of flexible structures for truss type of space station, flexible spacecraft with LFST, intelligent space truss model for stretched-out support truss and its active members. Because the optimal location of active members is a discrete problem, this dissertation designs Integer Coded Genetic Algorithms (ICGA) for the discrete problem.3. According to the research actuality of fuzzy control theory domestic and overseas, and combining fuzzy control theory with the custom control theory, modern control theory and intelligent control theory, this dissertation designs some advanced fuzzy controllers.(1)Based on the explanation of fuzzy control concisely, this dissertation emphasizes four kinds of advanced fuzzy controllers. Combining to the PID control principle, this dissertation adopts fuzzy inference mechanism to tune PID parameters. To improve the dynamic capability, the conception of Scaling Universes of Discourse (SUD) is inducted during the fuzzification of input parameters. Based on ICGA to the optimization of the fuzzy rules base, the control law of the fuzzy controller could be improved radically. To reduce the stable error, this dissertation designs a kind of fuzzy controller with intelligent integral introduced.(2)Now days, fuzzy control theory has not get the perfect and systemic theory, especially in the aspects of stableness and robustness. This dissertation aims at the characteristics that the control of spacecrafts gets better to adopt the self-adaptive control, and basing on the center values of input and output membership functions, adopting the analysis method of Lyapunov function, designs the stableness and robustness of self-adaptive fuzzy control system based on SUD.4. Based on the dynamic computation of LFST, several advanced fuzzy controllers (fuzzy PID controller, fuzzy controller with intelligent integral introduced, self-adaptive fuzzy controller based on SUD, fuzzy control based on ICGA to the optimization of the fuzzy rules base) are simulated for the active control of LFST. This dissertation chooses a kind of fuzzy inference mechanism according to the principle of fuzzy inference during simulation, adopts the method that combines the rules got from experience and knowledge with the rules got from ICGA for the optimization of fuzzy control of LFST, and finally chooses a kind of defuzzification method by comparison during the simulation. Furthermore, fuzzy controllers are compared with the custom PID controller, optimal controller and H∞output feedback controller for the active control of LFST, respectively. The simulation results show that the fuzzy control methods designed in the dissertation are much more suitable and superior than custom and modern control methods for the LFST.