Low-Speed Performance And Predictive Functional Control Of Hydraulic Simulator

Hydraulic simulator is a set of key high-tech hardware-in-the-loop simulation equipment on ground used to reproduce the flying posture of flying weapons. The performance index of hydraulic simulator directly relate to the precision of flying weapons and defense capacity of our country. Therefore, the study of super-low speed, high frequency response, high precision hydraulic simulator plays an important role to the development of aerospace industry of our country. However, hydraulic simulator has many disadvantageous factors influencing the performance improvement. First, high nonlinear friction torque decreases the low-speed performance index and tracking precision, but decrease of friction moment is limited to technological level and experiment funds. Secondly, it is difficult to obtain the accurate plant model due to the nonlinearity and uncertainty of hydraulic simulator, but the performance improvement of hydraulic simulator depends on the accuracy of its model for traditional control methods. Therefore, it is necessary to study new friction compensation methods and control strategies that can acquire desirable performance of hydraulic simulator without accurate plant model.After synthesizing numerous relevant literatures and references home and abroad, this paper introduces some decisive techniques in simulator design and provides a general discussion of simulator development. Then the current control strategies to the hydraulic system and the development of electro-hydraulic system of hydraulic simulator are also introduced. In the meantime the development of low-speed theories are detailed such as friction characters, friction models and their peculiarities, the common friction compensation methods. And the development history of predictive control is introduced.The mathematical model of hydraulic simulator is constructed, the factors impacting the low-speed performance index of electro-hydraulic servo system of hydraulic simulator are analyzed. It is necessary to identify and compensate the dynamic friction torque because the dynamic friction torque influnences the performance index of hydraulic simulator. However, the complexity and nonlinearity of the LuGre dynamic friction model make it difficult to identify its parameters. Therefore, a two-step genetic simulated annealing parameter identification algorithm of LuGre model based on hybrid optimization strategy is proposed. The method identifies the parameters of the dynamic friction model accurately for its strong local searching ability and good global search capacity. Then the LuGre model of outer framen is identified by this method. And it is beneficial to the analysis and compensation of dynamic friction of hydraulic simulator.The dynamic model of hydraulic simulator with friction disturbance is constructed for solving the problems that nonlinear friction torque influences tracking precision and low-speed performance. An adaptive dynamic friction compensation strategy is proposed and simulated based on the identified LuGre model. The method can achieve good compensation results with the fluctuation of dynamic friction parameters. But the method is not quite satisfying with disturbances. Thus the adaptive robust friction compensation strategy is proposed that utilizes the discontinuous projection mapping to improve the stability of parameter adaptation and friction state and uses robust feedback terms to assure the robustness. Simulation results show the method can attenuate the influence of disturbances and uncertainties and obtain desirable tracking precision and dynamic performance.Predictive functional control (PFC) is applied to hydraulic simulator servo system based on the characteristic of hydraulic simulator. Firstly the mean idea, the internal model structure of predictive control is listed and the concept and principle of PFC and the design method of sliding model control (SMC) are introduced. Based on the theories, a PFC-SMC hybrid control strategy is proposed. According the hybrid control strategy the predictive functional controller is used to improve the tracking performance of the control plant and the sliding model controller can restrain disturbances as the feedback filter of the internal model controller. Then the detailed design approach of the hybrid controller of hydraulic simulator is offered. Simulation shows that the method can satisfy the low-speed performance and enhance the double-ten performance index of hydraulic simulator.Experiments are made on the hydraulic simulator model machine. The experiments include the compensation experiments of the outer frame of hydraulic simulator, the frequency characteristics experiments and low-speed performance experiments of the three frames and the coupled disturbance attenuation experiment among three frames. Experiment results show the efficiency and feasibility of the theories and control strategies.