Active Vibration Control For Vehicle Active Suspsension Systems With Uncertain Dynamics

Vehicle suspension systems,as one of the most important vehicle chassis components,mainly affect the ride comfort,vehicle maneuverability and safety for the drivers and occupants.In this topic,considerable research work has been carried out toward the vehicle suspension systems in both automotive indusrial sectors and academic communities.According to the vibration attenuation mechanisms,suspension systems can be grouped into three categories: passive suspension systems,semi-active suspension systems and active suspension systems.Unlike passive and semi-active suspension systems,active suspension systems are equipped with extra actuation devices to provide proper real-time force to eliminate the vibrations and/or shocks transmitted to the vehicle body from the irregular road roughness,thereby greatly improving the vehicle ride comfort and driving safety.In this thesis,active suspension systems are specifically studied,and several novle active vibration control methods with enhanced transient performance are investigated.The main research work of this thesis can be summarized as follows.(1)Adaptive finite-time fuzzy control of quarter-car active suspension systems with input delay.Nonlinear active suspension system with input time delay induced by actuators is studied.By developing a predictor based compensation scheme,the effect of input time delay in the closed-loop system can be compensated.Then,a fuzzy logic system(FLS)is employed and incorporated into adaptive control to address the unknown nonlinearities.Furthermore,we introduce a set of low-pass filte operations,auxiliary integral matrices and sliding mode type term to develop a parameter estimation errorbased finite-time(FT)adaptive estimation algorithm,by which faster parameter convergence rate and better transient suspension response can be achieved.Finally,a Lyapunov-Krasovskii functional is constructed to prove the closed-loop system stability.A combined dynamic simulator is built based on commerical vehicle software Carsim and Matlab/Simulink,which is used for numerical simulations to validate the effectiveness of the proposed control method.The simulation results show that the proposd control method can not only addreee both the input delay and unknown nonlinearities but also achieve improved ride comfort and reduced dynamic tire load and suspension stroke.(2)Active vibration control for quarter-car active suspension systems with hydraulic actuator.In the most existing active suspension control results,the dynamics of actuator used to create the required active suspension forces is neglected.To address the unknown nonlinearities of hydraulic actuator,we develop an active vibration control with prescribed transient performance(e.g.convergence rate,maximum overshoot and steady-state error)for nonlinear active suspension systems configured with a hydraulic actuator.Based on the obtained active suspension system model with hydraulic actuator,we introduce a prescribed performance function(PPF)and associated error transform mechanism.The function approximators(i.e.Neural Network(NN)and Fuzzy Logic Systems(FLSs))are not needed to accommodate the system nonlinearities.In this framework,a simple yet robust controller is obtained,so that the complexity and computational burden induced by the NNs and/or FLSs can be remedied,while guaranteeing the steady-state and transient suspension performance simultaneously.Finally,the stability of the closed-loop control system is proved based on the Extreme Value Theorem and Lyapunov theory.Simulation results based on a dynamic simulator built in professional vehicle software Carsim and Matlab/Simulink are provided to validate that th proposed control method can effectively improve the vehicle ride comfort and ensuring the driving safety.(3)Adaptive control for half-car active suspension systems with actuator saturation compensation.Based on the obtained parameter estimation error based adaptive control method,we further propose an adaptive control with PPF for half-car active suspension systems.By incorporating a PPF and the associate error transform into adaptive control design,a modified adaptive control strategy can be obtained.The key point of this method is to transform the tracking problem of the original system into the stabilization problem of the newly established coordinate system,such that the transient suspension responses can be quantitatively studied.Moreover,to address the saturation phenomenon induced by the actuator devices,the above proposed approach has been further tailored.Specificilly,we incorporate a low-order antiwindup structure into the adaptive controller to construct an augmented controller,where the effect of saturation can be tackled and the potential performance degradation can be guaranteed.Theoretical analysis and numerical simulations are carried out to demonstrate that the proposed control method can effectively compensate the effect of actuator satuaration,while improving the transient suspension performance and guaranteeing the dynamic tire load and suspension stroke.(4)Nonlinear control for full-car active suspension systems without function approximation.For multi-inputs-multi-outputs full-car active suspension system with uncertain nonlinearities,we propose a nonlinear control strategy for uncertain nonlinear full-car active suspensions without using any function approximations.By designing a coordinate suspension error transformation with PPFs,a simple proportional-like control structure can be designed.One salient feature of this method is that it can not only address the computational burden but also guarantee both the transient and steady-state suspension performance.Based on the Extreme Value Theorem and Lyapunov theorem,the stability of the closed-loop system is rigorously proved.To validate the effectiveness of the proposed control method and show its practical applicability,simulation results are provided,which reveal that the proposed control strategy can effectively suppress the vehicle body vibration and improve both the ride comfort and driving safety compared with some existing approaches.Finally,experimental valdiation based on a quarter-car active suspension test-rig equipped with an electro-hydraulic actuator is carried out to demonstrate the effectiveness of the proposed prescribed transient performance active vibration control method.Experimental results verify the superior performance of this method regarding at the reduced active suspension control error and improved ride comfort.Moreover,it also shows the potentional feasibility and applicability for the proposed active suspension control.