Estimation Method Of Sideslip Angle For In-wheel-motor Electric Vehicle

In-wheel-motor electric vehicle(IWMEV)represents the future of electric vehicle with its fundamental change of chassis structure and driving mode from the traditional.Sideslip angle is an important parameter of the IWMEV stability control system which can not be measured directly through sensors due to cost and technical constraints.This paper focuses on estimation for sideslip angle of IWMEV with theoretical and practical significance.Considering,the vehicle has the characteristics of large dynamic variation,linear and nonlinear interaction under all operating condition,which makes the modeling complex,and leads to difficulties in designing and considerable computation.Therefore,the nonlinear dynamic characteristics of vehicle under full working conditions are analyzed,and the decomposition method for different dynamic characteristics is proposed.Then,a method for estimating the sideslip angle of IWMEV is designed to meet the requirement of the sideslip angle estimation under all operating condition.Aiming at the low speed,high friction coefficient road surface and small steering angle conditions,a method of sideslip angle estimation is proposed.Due to the condition of the wheel lateral force is linear and weakly nonlinear,linear estimator design method to solve the problem of side slip angle estimation is feasible.In this paper,a vehicle dynamics model describing longitudinal,lateral and yaw motion is established according to the Dugoff tire model and the vehicle body dynamic model.Through the simplification of the nonlinear term in the model,a LPV model of sideslip angle estimation is obtained.Then,based on the parameter dependent Lyapunov stability theory,a LPV angle estimator for the sideslip angle of the centroid is designed to meet the needs of real-time computation.Simulation results under high precision vehicle dynamics simulation software veDYNA show that the design of the estimator is effective.In view of the poor estimation accuracy of side slip angle,results of nonlinear saturation characteristics of the lateral force under limit conditions,a PWA(piece-wise affine)method is applied to modeling.Then,combined with the two-track model describing the yaw rate and side slip of the vehicle,a piecewise affine vehicle dynamics model describing the nonlinear dynamic characteristics of wheel saturation is established.To facilitate real-time computation,Furtherconsidering the complexity of the estimator design,the PWA estimator is designed on the basis of the global Lyapunov function of the switching system.Through simulation on conditions of high speed,different road friction coefficient and different steering angles,it is proved that the designed PWA estimator can accurately estimate the sideslip angle.In this paper,the adaptive analysis of the LPV and PWA estimation methods is carried out to test their applicable range.And the fusion strategy is presented based on condition of tire by calculating the tire sideslip angle.The effectiveness of the fusion strategy presented in this paper is verified by simulation of multiple operating conditions.