Research On Three-Axis Hydraulic Simulator Control System Based On H_∞ Control Theory

Three-axis simulator is a kind of high-tech hardware-in-the-loop simulation equipment of great economic value and is important for national defense. It can reproduce various postures of flying weapons in laboratory. Its performance indexes directly relate to the fidelity of simulation results. With the increasingly austere international situation and the development of modern military technologies in China, the demands on technical level, application range and application requirements of simulator become higher and higher. Three-axis hydraulic simulator is a complex multiple-input-multiple-out nonlinear system. Its inner and outer gimbals are directly driven by a set of hydraulic servo system respectively, and its middle gimbal is directly driven by dual hydraulic motors servo system. The performance of hydraulic control system is very important to the simulator's. Under certain working conditions, for example, when system oil source power capacity, machine structure and system components are fixed, the selection of suitable control strategy can guarantee maximum performance of the system. Therefore, it is necessary to study the properties and control strategies of single channel hydraulic servo system and dual hydraulic motors driving system.After synthesizing numerously relevant literatures and reference material at home and abroad, the simulator development at home and abroad is summarized in this paper, simulator configuration and some key techniques deciding the general technology level of simulator are introduced, and the current trend of research on hydraulic control system applied to simulator is reviewed. In the meantime, the development outline of H∞control theory and robust design method is also introduced.The mathematical model of single channel hydraulic servo system of simulator is established, and the influence of model parameters on single channel system performance is analyzed. A kind of system model identification method suitable for robust control design is proposed, and some identification results for inner and outer single channel systems of simulator are obtained. In fact, the proposed identification method is model set identification method composed of nominal model parameters identification for single channel system based on general stochastic state space grey-box identification model and estimation of uncertainty bound based on model error modeling.The basic theory of H∞control is introduced. Based on the property and performance requirement of hydraulic simulator, the identification results of nominal models and their uncertainty bounds of single channel systems in inner and outer gimbals as well as the flexible and systematic robust controller design frame provided byμ-synthesis, the robust feedback controllers withμ-synthesis are designed for single channel systems in hydraulic simulator's inner and outer gimbals. The principle and property of input signal feedforward compensator based on the inversed model is analyzed and its realization problem is discussed. The anti-windup problem of control system is studied and the anti-windup compensators for single channel systems in simulator's inner and outer gimbals are designed by using H∞control theory. Simulation results of single channel system in inner gimbal are obtained and prove that the proposed control approaches are correct and effective.Several synchro-driven control schemes of dual hydraulic motors are introduced. And at the same time, the mathematical model of dual motors synchro-diven system is constructed and the reasons for causing synchro-error are systematically analyzed. Considering the coupling effect, the difference between two motors'transfer functions, and so on, a kind of robust synchro-control scheme with synchro-error direct feedback correction is put forward and designed usingμ-synthesis. Simulation results prove that the synchro-scheme is very effective to improve synchro-motion precision of the synchro-driven system in simulator's middle gimbal.The performance experiments of single channel systems in inner and outer gimbals, synchro-driven system in simulator's middle gimbal and attenuating coupling disturbances among channels are performed on three-axis hydraulic simulator. Some practical conclusions are obtained. Research results further prove that the theories and views set forth are right, and the model identification algorithm and the controllers designed are reasonable and feasible.