Research On Nonlinear Models And Control Techniques For Valve-controlled Servo Systems

Valve-controlled servo systems are widely used in various fields such as aviation,military,and civil industry because of their high-power density,fast response time,and high shock resistance.Although the performance of electromechanical servo systems has been significantly improved in recent years,valve-controlled servo systems still play an irreplaceable role in some high-power systems such as material testing machines and load simulators.As the level of China's equipment manufacturing industry continues to improve,the performance of the valve-controlled servo system has put forward more and more demanding requirements and promotes the development of the theory of valve-controlled servo system research.By summarizing and organizing the existing literature,it can be seen that the model nonlinearities of the valve-controlled servo systems are the key factors that restrict its performance improvement.Based on the above problems,this dissertation conducts an in-depth study on the nonlinear models and control techniques of valve-controlled servo systems,specifically about the nonlinear models of valve-controlled servo systems,position control methods and loading control methods.In order to improve the model accuracy of the valve-controlled servo systems,a comprehensive system model based on Yang-Tobar and Trikha pipeline models is established.The model considers the dynamic characteristics of the hydraulic pump station,servo valves,and connecting pipelines(including the pipelines between the hydraulic pump station and servo valves and the pipelines between servo valves and hydraulic cylinders)based on the established nonlinear simplified model so that the proposed model can match the real system better.In order to reflect the accurate dynamic response of the system further,a joint simulation model of the valve-controlled servo system is developed by using MATLAB\Simulink,AMESim,and Adams softwares.The model can exhibit the actual operating characteristics of the valve-controlled servo system and simulate the structural stiffness of the mechanical platform as well as the influence of the assembly gaps on the system performance.Finally,the model accuracy of the established nonlinear simplified model,the system comprehensive model,and the joint simulation model are tested using sinusoidal signals,and the accuracy results are 72%,84%,and 92%,respectively.It can be concluded that the nonlinear simplified model is only applicable to the design of the controller,while the system synthesis model can be used to analyze the system and verify the preliminary controller qualitatively,and the joint simulation model can be used to quantitatively analyze the existing system and test in the hardware-in-the-loop of the controller due to its high model accuracy.Adaptive robust control can deal with the model uncertainties of the system better,but there are problems of “differential explosion” in the backstepping design process and chattering caused by high control gain.In order to solve these problems,an adaptive robust control method based on tangent tracking differentiation and adaptive output filtering feedback is proposed to simplify the controller design process and improve system tracking accuracy.A nonlinear adaptive robust control based on discrete disturbance observer is proposed to improve the control performance further.Since the disturbance force is difficult to measure and model,a total disturbance is estimated and compensated in real-time by a discrete observer.The proposed controller improves the system tracking accuracy and avoids the control gain fast growth problem of adaptive robust control when the external disturbance grows and exploits the advantage of asymptotic tracking capacity of adaptive robust control better.The effectiveness of all the above control methods is verified by simulation analysis.The results show that,compared with the traditional adaptive robust control method,the improved adaptive robust control method and the adaptive robust control method based on discrete disturbance observer have significantly improved system position tracking accuracy,thus proving the feasibility of the proposed control methods.The controller designed based on the structural invariance principle cannot fully compensate the position perturbation and deal with surplus force problem of the valve-controlled loading system because of its approximate physics implementation.Based on the fact,two kinds of loading controllers are designed for the situations whether the internal structure of position perturbation is known or not.For the case where the internal structure of the position disturbance is known,a dual-loop controller based on static gain compensation and adaptive filtering output feedback is proposed to achieve dynamic decoupling of position disturbance compensation and loading control,which improves the system control accuracy.For the case where the internal structure of the position disturbance is unknown,a hybrid control method based on impedance control and adaptive integral robust control is proposed,and the corresponding switching strategy is designed.The hybrid control effectively alleviates the problem of commutation shock caused by the surplus force and the gaps of the loading process and improves the system control accuracy.The effectiveness of all the above control methods is verified by simulation analysis.In order to verify the practical effects of the above control methods in engineering applications,a load simulation experimental platform is built.The essential components of the experimental platform and the critical techniques for the digital implementation of the controllers are introduced.All the position control methods and loading control methods proposed in this dissertation are experimentally tested with the constructed experimental platform.The experimental results show that the proposed control methods have better dynamic performance and robustness than the existing control methods and achieve the expected results.