Research On Nonlinear Control Method Of Positive Displacement Hydraulic Actuator Based On Speed Adjustment

Hydraulic systems have been used widely in modern industries due to their advantages of small size-to-power ratios and large force/torque output capability,typical applications including vehicle hydraulic turbines,robot manipulators,active suspensions,hydraulic manipulators,load simulators and so on.The demand of high accuracy control of hydraulic systems is happening with or as a result of the rapid development of the industry.However,nonlinear behaviors and model uncertainties,which are inherent in hydraulic systems,limit the tracking performance improvement for hydraulic systems.Traditional linear control theory(e.g.,proportional-integral-derivative(PID)type controllers)has an important impact on control engineering in the past,but it is limited to satisfy the demand of modern hydraulic servo system since it is hard to deal well with heavy nonlinear behaviors and/or model uncertainties.Therefore,researching on the advanced high-performance nonlinear control method to overcome the influence of nonlinearity(e.g.,input saturation,dead-zone,etc.)and model uncertainties(e.g.,heavy disturbances modeling errors etc.),and then to improve the tracking performance of the closed pump-controlled hydraulic servo system is the main content of this dissertation.Specifically,the following works are focused:1.Considering the main nonlinear characteristics and model uncertainties of each part of the system,the mechanism model of closed pump-controlled hydraulic servo system with nonlinear uncertainties is established firstly.Compared with the traditional linearization model,it more accurately reflects the physical characteristics of the system and provides a model paradigm for the study of nonlinear control strategies in the later stage.2.A model predictive control strategy is proposed for the high-accuracy tracking control of hydraulic servo system with strong heavy disturbances.In this method,an optimal control law is obtained by solving the objective quadratic function including the output prediction equation,which will be adjusted in real time based on the mechanism of receding horizon and repeating optimization.Therefore,it can effectively resist the effect of heavy disturbances on the controlled system.Besides,to address the problem of unmeasured state and various model uncertainties,an output feedback model predictive control with the integration of an extended state observer is proposed based on the method of traditional model predictive control.This way effectively avoids the use of speed and acceleration signals polluted by noise and achieves active disturbances compensation.The effectiveness of the designed control strategy is verified by simulation results.3.A robust adaptive control is proposed for pump-controlled hydraulic system with input saturation,parametric uncertainties and uncertain disturbances,in which input saturation increment is firstly fed back to the design of the model compensation item through the dynamic auxiliary system.On this basis,to deal with the problem of input saturation and valve dead-zone simultaneously,the designed anti-windup is integrated with the compensation of the dead-zone nonlinearity effectively via a combined and comprehensive inverse model.A dynamic auxiliary system and a smooth dead-zone inverse model,which are utilized to attenuate input saturation and compensate the nonlinearity of dead-zone,are synthesized into the design of the robust adaptive controller based on backstepping technology.Meanwhile,the adaptive law and the nonlinear robust control law are conducted to handle parametric uncertainties and various disturbances.Based on the Lyapunov stability theory,the closed-loop asymptotic stability of the designed control strategy is proved,and the boundedness of all the signals are ensured.The excellent tracking performance of the proposed control scheme is verified by comparative simulation results.4.Experimental verifications of the proposed control algorithms(output feedback model predictive control,model predictive control,robust adaptive control with input saturation and dead-zone,and robust adaptive control with input saturation)are tested by using a double-rod hydraulic cylinder position servo experiment platform.Through the analysis and comparison of the experimental results,the effectiveness and rationality of the proposed control methods are verified.