Research On Nonlinear Control Of Hydraulic Launcher With Consideration Of Various Uncertainties

With the improvement of the performance of air-raid weapons and the enhancement of low-altitude penetration capabilities,the speed and maneuverability of weapons against ground weapon equipments and surface warships have all been improved significantly.Therefore,higher requirements have been put forward for the targeting,tracking,and interception capabilities of medium-low altitude air defense missile weapon systems.The control performance of the electro-hydraulic servo system of missile launcher directly determines the tracking and interception accuracy of the air defense missile weapon system.Therefore,it is necessary to study its high performance control approach to shorten the turnaround time of the launcher and improve the tracking accuracy.The missile launcher electro-hydraulic servo system is highly nonlinear.Its nonlinear characteristics are mainly reflected in the nonlinearity of the missile launcher's mechanism(the nonlinear relationship between the displacement of the piston of the hydraulic cylinder and the rotation angle of the load),the nonlinear pressure-flow characteristics of valve and the valve dead-zone nonlinearity,etc.In addition,there exist lots of model uncertainties in the electro-hydraulic servo system of missile launcher,which can be generally divided into parametric uncertainty and uncertain nonlinearity.Parametric uncertainties mainly include the variation of the moment of inertia of the load caused by the reduction of the mass of the load and the offset of the center of mass due to the launch of missiles,changes in viscous and Coulomb friction coefficients due to component wear or lubrication conditions,and change of oil bulk modulus caused by the environment,etc.Uncertain nonlinearities mainly include external disturbances,unmodeled leakage characteristics of hydraulic cylinder and valve,nonlinear frictions,valve dynamics,etc.The nonlinear characteristics and uncertainties of the missile launcher electro-hydraulic servo system have become the determinate factor limiting its tracking performance improvement.Traditional linearization-based control methods have gradually failed to meet the high-performance requirements of the system.Therefore,researching on the advanced high-performance nonlinear control method to overcome the effect of nonlinearity and model uncertainty on control performance,and then to improve the tracking performance of the missile launcher electro-hydraulic servo system is the main content of this dissertation.Specifically,the following works are focused:1.According to the technical requirements,the preliminary design of the main parameters of the missile launcher electro-hydraulic servo system and the selection of components are completed.The nonlinear mathematical model of the electro-hydraulic servo system of missile launcher is established,which takes into account the main nonlinear characteristics and model uncertainties of the system and describes the dynamic and static physical characteristics of the actual system more accurately.The nonlinear mathematical model of the electro-hydraulic servo system of missile launcher is the basis of the subsequent high-performance nonlinear controller deisgn.2.In order to overcome the effect of nonlinear characteristics and model uncertainty on the system performance,a nonlinear adaptive integral robust controller is proposed based on the nonlinear model of the electro-hydraulic servo system of missile launcher.The semi-global asymptotic stability of the control strategy is proved.The controller adopts an integral robust gain self-tuning mechanism to effectively avoid the randomness,conservativeness,and potential high gain feedback of the integral robust gain adjustment,so that the control strategy is more suitable for engineering applications.Considering that the heavy measurement noise of load acceleration signal has nonnegligible influence on the control performance,and the actual electro-hydraulic servo system has both matched and mismatched model uncertainties,a new continuous integral robust control strategy is proposed,which can handle smooth and bounded matched and mismatched model uncertainties simultaneously,and does not need the heavy noise-comtaminated load acceleration signals.The proposed continuous integral robust controller guarantees that the system achieves a globally asymptotic stability result.3.Dead-zone characteristics are common in various control valves,especially proportional valves.The presence of valve dead-zone may deteriorate the achievable control performance,leading to undesirable control accuracy,limit cycles,and even instability.Therefore,it is of great practical significance to carry out reasonable and effective valve dead zone compensation for high-performance control of electro-hydraulic servo system.In this dissertation,based on two common control methods for dealing with dead-zone problems,two different nonlinear control strategies for electro-hydraulic servo system considering valve dead-zone are proposed.Specifically,by considering the valve dead-zone model as a combination of a control input with time-varying gain and a bounded disturbance term,an active disturbance rejection adaptive control strategy is propsed which integrates the adaptive control with an extended state observer.The proposed control strategy preserves the advantages of adaptive control and extended state observer-based active disturbance rejection control while overcoming their performance limitations,and improves the tracking performance of the system.When the system is subjected to parametric uncertainty,matched and mismatched time-varying uncertain nonlinearity and valve dead-zone,the proposed active disturbance rejection adaptive control strategy can guarantee the uniformly ultimately bounded stability of the system.In addition,in the presence of parametric uncertainty and constant uncertain nonlinearity only,an asymptotic tracking performance can also be achieved by the proposed active disturbance rejection adaptive control strategy.In order to achieve more accurate dead-zone compensation and further improve the steady-state tracking performance,the valve dead-zone characteristics are also explicitly considered,meanwhile taking into account the effects of various model uncertainties.The valve dead-zone characteristics are linearly parameterized based on a smooth dead-zone inverse,and a robust adaptive control strategy with valve dead-zome compensation is proposed.The control strategy adopts an adaptive method to deal with unknown system parameters and dead zone parameters.Meanwhile,a novel nonlinear robust control law with disturbance upper bound estimation is incorporated to overcome the effects of unmodeled disturbances.Closed-loop system asymptotic tracking performance is guaranteed by the proposed control strategy.4.Investigate reasonable and effective valve dynamics compensation control for electro-hydraulic servo system.For electro-hydraulic servo system,its valve dynamics should theoretically be third-order,including first-order electrical dynamics and second-order spool dynamics equation.However,if the third-order valve dynamics are directly taken into account in the nonlinear model of the hydraulic system,the "exploration of terms" of the controller design based on backstepping method will be caused,which greatly increases the complexity of the controller design.It is even impossible to complete this mission.Therefore,how to consider the effect of valve dynamics in the design of the controller and fully utilize the bandwidth of the valve is of great significance for high-performance of electro-hydraulic servo system.By analyzing the frequency domain response of the valve,it is recognized that the amplitude-frequency characteristic of the valve dynamics is almost zero within the interesting frequency range,and its core effect is the phase lag effect.Therefore,a time-delay model/element is proposed to approximate the valve dynamics.The problem of valve dynamics compensation is theoretically transformed to input delay compensation.Since the time-delay model does not affect the order of the system,the backstepping-based controller design of the electro-hydraulic servo system is simplified.Based on the proposed time-delay model,meanwhile taking into account the influence of measurement noise of velocity and pressure signals on the control performance,an extended state observer based output feedback control strategy with valve dynamics compensation is proposed.The designed extended state observer can simultaneously estimate unmeasured system states and unmodeled disturbances.The input delay caused by the valve dynamics is effectively compensated by a robust delay compensation feedback control law.The uniformly ultimately bounded stability of the closed-loop system is proved based on Lyapunov stability theorem by using Lyapunov-Krasovskii functional.For the more general case of unknown time-delay constant in the valve dynamic time-delay model,an adaptive control strategy with valve dynamics compensation is proposed.In the controller design,adaptive laws are synthesized to handle the unknown parameters of the system.Meanwhile,an unknown time-delay estimation algorithm based on gradient method is designed to achieve on-line estimation of the unknown time-delay constant in the time-delay model of the valve dynamics.The proposed controller achieves uniformly bounded tracking performance.5.Experimental verifications of the proposed control algorithms(continuous integral robust control,robust adaptive control with valve dead-zone compensation,and time-dealy-model-based output feedback control with valve dynamics compensation)are presented by using a double-rod hydraulic cylinder position servo experimental platform.The proposed control algorithms were experimentally compared with other existing control methods.The effectiveness of the proposed control methods are verified by the analysis and comparison of the experimental results,.