Robust Control Of Fractional Active Suspension System For In-Wheel Motor Electric Vehicle

When the vehicle is disturbed by the road excitation in the process of driving,the driving conditions such as vehicle speed and driving direction will change,which will easily lead to violent vibration of the whole vehicle or part of the vehicle.Vehicle vibration will produce a series of adverse effects,such as the loss of vehicle components,poor ride comfort and ride comfort,etc.As an important part of the vehicle,and also the main damping component of the vehicle,suspension can bear the force between the body and the wheels,effectively reduce the impact caused by road excitation disturbance to the body,which is one of the important indicators to measure vehicle performance.In this paper,a more accurate model of automobile suspension system with fractional order is established,and the active control of automobile suspension system is studied.The main research contents can be summarized as follows:First of all,vehicle suspension damping devices not only have hysteresis and nonlinear characteristics,but most dampers have similar viscoelastic constitutive relations.These viscoelastic materials are between elasticity and damping characteristics,and ordinary integer-order theory cannot accurately describe them.The constitutive relationship of this material.For this reason,many researchers have begun to describe viscoelastic materials using fractional-order theory.Studies have shown that it is more accurate to describe the constitutive relationship of damping materials with memory characteristics using differential equations containing fractional-order differential terms.Based on this,the theory of fractional calculus is introduced into the automobile suspension system,and a mathematical model that can describe the fractional active suspension system more objectively and truly is established.Secondly,the definition and basic properties of fractional calculus are introduced.For different road excitations,first of all,we need to deal with the fractional order micro sub items in the fractional order active suspension system through the algorithm.Generally,there are three kinds of methods to deal with the fractional calculus term,which are approximate analytical method,numerical method and filter algorithm.In this paper,the approximate analytic method and the filter algorithm of the fractional calculus term processing method are derived in detail,and their effectiveness is verified.Then,combined with the mathematical model of 1/4 vehicle three degree of freedom fractional active suspension system,considering the vehicle performance constraints and some related physical system constraints,the control problem of fractional active suspension system is simplified into a robust disturbance suppression problem with two constraints,namely output constraints and control constraints.For different types of road disturbance inputs,the H_∞norm is used as the performance optimization index of the closed-loop system to design and optimize the controller system,and the corresponding linear matrix inequality form is obtained.Matlab simulation shows the obvious advantages of active suspension compared with passive suspension.The robustness of fractional active suspension system is verified by analyzing the simulation results.In addition,considering that the spring load mass is not a fixed value when the actual vehicle is driving,it is an indefinite value that varies with the actual use of the vehicle.Therefore,when building a three degree of freedom fractional active suspension system model of 1/4 vehicle,the influence of the variation of spring load mass on the dynamic characteristics and robust control effect of the system should also be considered.Therefore,considering the change of spring mass,the range of the variation of spring mass is set up,and the fractional order active suspension system model based on T-S fuzzy model is established.The difference between the output constraint and control constraint of the passive suspension,the traditional active suspension and the fractional active suspension system based on T-S fuzzy model is analyzed by simulation and comparison,and the difference between the passive suspension and the transmission suspension system is verified The performance of the system dynamics is better than the traditional active suspension and the active suspension based on T-S fuzzy model.Finally,considering that in the actual control system,due to the increasing number of components,the system function requirements are getting higher and higher,and the correlation between different links is getting closer and closer,and any one of the components or links may fail directly.As a result,the performance of the entire control system is drastically deteriorated,or even completely lost,so that the suspension system cannot meet the required ideal results,and thus cannot meet the riding comfort and driving stability of the vehicle during the driving process.Therefore,a fault-tolerant fuzzy controller is designed in this paper,and the superiority of the fault-tolerant fuzzy controller under different actuator thrust losses is verified by comparison.