Robust Control For Aerospace Vehicles Based On Multi-model

Aerospace vehicles (ASV) are a new type of aerospace planes. Many countries are devoting major efforts to develop this reusable flying vehicles. Aerospace vehicles have very important military values and civilian values. The United States and other countries have their own aerospace projects and have achieved significant research progress. However, the research on hypersonic vehicles in our country is still at in the initial stage, a good number of important problems in this field still call for deeper study. Aerospace vehicle's reentry has the characteristic of violent aero-dynamic parameters change and demands high control performance. These characteristics make the control system face with many grave challenges for aerospace vehicles. The flight attitude control system design methods are studied systematically and comprehensively in this dissertation by means of theoretical analysis and simulation validation. The results attained are as follows.First of all, the problems about the modeling of six degrees of freedom of an ASV under the reentry flight condition are studied. The proposed model includes the whole of kinetic equations and motion equations. Aerodynamic force and moment coefficients are given as functions of angle of attack, Mach number, altitude and control surface deflections. The thrusters of reaction control system (RCS) are of switch type and the control value is approximately switching constant. Open-loop dynamics and stability characteristics proves that the whole model can demonstrate the complex nonlinearity, coupling and rapid variation of ASV. Therefore, the proposed model can be used to investigate trajectory optimization, attitude control conceptual design and simulation for a new generation hypersonic vehicle.Secondly, the problems concerning the ASV's atmospheric reentry flight attitude control system are researched. Multiple region T-S fuzzy models are modeled for ASV reentry attitude dynamics, and then local T-S controllers are designed in every region. The approach precision improves as the fuzzy domain decreases under a constant fuzzy rule. During reentry through the atmosphere, the control moment is generated by thrusters of the reaction control system to control attitudes of the ASV, and to compensate for the shortage of aero-surfaces that fail to offer enough moment because of the partially or completely lost efficiency. Along with the increase in air density, aero-surfaces gradually intervene the control system, and the RCS drops out of use. Considering the air scarcity and the decreased efficiency of aero-surfaces, the flight attitude control system for the ASV based on thrust of reaction jets is designed.Thirdly, a T-S fuzzy descriptor tracking control design for an atmospheric reentry flight attitude control system of aerospace vehicles is discussed. Slack variables are introduced into the model by equivalent transforming of the ordinary fuzzy model to a fuzzy descriptor model, and then a H∞tracking controller design method which is based on linear matrix inequality (LMI) is obtained. Its advantages are to solve all the controlling variables in LMIs at the same time. This improves the feasibility and debases the limitation to solving LMIs.Then, for it is hard to obtain enough knowledge about disturbances generated by an exogenous system, a novel multi-model switching integrated control based on compensation is proposed. A nonlinear disturbance observer is designed to deduce external disturbances and then to compensate for the influence of the disturbances using proper feedback. Based on Lyapunov theory, it is proven that the closed-loop system is exponential stability. The simulation results demonstrate that the proposed method is not only effective but also can improve control performance and robustness under uncertainty condition.Finally, a non-fragile multi-model switching control for a class of nonlinear systems based on local T-S models is proposed. The design scheme of non-fragile state-feedback controllers is developed in the presence of additive controller gain perturbations. We apply the scheme to the flight attitude control system for the ASV and make simulation. The simulation results show that the scheme can debase the sensitiveness of the controller with respect to perturbation in its coefficients, in other words, the scheme improves the non-fragile of the controller.