Research On Stability Control Strategies Of In-wheel Motor Drive Electric Vehicles

In the form of vehicle-driven layout,in-wheel motor drive electric vehicle is a new type of drive layouts of the new energy vehicles,which are characterized by independent control of each wheel torque and remove the mechanical transmission system.And the wire-controlled chassis applications have a strong advantage of vehicle lightweight.Also because the four-wheel torque is independently controllable,new requirements are put forward for vehicle driving parameters acquisition,acceleration slip regulation,stable yaw moment control,integrated control of tire lateral force and longitudinal force,and fault tolerant control of the driving motor.In the form of vehicle system dynamics,vehicle dynamics can be divided into longitudinal dynamics and maneuver dynamics.Because the vehicle adopts the form of four-wheel independent driving,which makes the vehicle's driving state parameters difficult to measure,a low-cost and high-precision soft measurement method needs to be proposed to realize the measurement of the vehicle state.When the vehicle accelerates straight ahead,the vehicle needs to be driven with acceleration slip regulation to ensure that the vehicle wheel slip ratio is around the ideal value and sufficient tire lateral force can resist the interference from the lateral force.However,most acceleration slip regulation is to control the ideal slip ratio around a fixed value and does not adapt well to change road conditions.When the vehicle is steering will be subject to a large lateral force,easy to produce unstable yaw moment,it is necessary to control the stability of the yaw moment based on the torque distribution according to the characteristics that the in-wheel motor drives the four-wheel torque of the vehicle independently and controllable.However,different solution methods have different characteristics and need to be compared,summarized and induction.Independent drive of four wheels and independent steering makes it possible to integrate the control of lateral and longitudinal force of the tire.However,it is necessary to consider the goal that the integrated control should meet and propose the corresponding target control function,and the analysis of the existence of the driving torque energy consumption problem less consideration in most studies.At present,the research on the control of fault tolerance in the drive motor is based on the reconstruction of the objective function,the constraints and the solution method.This method is laborious and difficult to implement,and an easy to implement fault tolerance method needs to be explored.In response to the above problems,this paper did the following research:(1)In the current research,the soft measurement of vehicle driving condition parameter is mostly estimated by the method of linearizing the nonlinear problem,such as the extended Kalman filter.However,this method introduces the truncation error in the process of linearizing the nonlinear problem.In order to improve the truncation error,this paper studied the application of unscented Kalman filter in the vehicle state estimation.Unscented Kalman filter uses UT variation to approximate the probability density distribution of nonlinear function.It does not need to derive the Jacobian matrix and avoids the truncation error caused by Taylor expansion.(2)In this paper,the control of acceleration slip regulation based on the optimal slip ratio and maximum adhesion coefficient of the pavement was studied.The purpose of acceleration slip regulation based on the changed pavement conditions was achieved.The accuracy of acceleration slip regulation was improved by subdividing the pavement condition.(3)In this paper,a stable yaw moment controller based on sliding mode variable structure and a torque distribution controller based on optimization method were established.The advantages and disadvantages of three mathematical programming methods,including constrained nonlinear programming,quadratic programming and weighted least squares were compared.Explored the intelligent optimization algorithm in the field of application.It provides reference for the selection of optimization methods in this aspect.(4)In this paper,aiming at the integrated control of tire lateral force and longitudinal force,a method of control the longitudinal force of the driving motor to control the longitudinal force and the active steering control of the rear wheel to indirectly control the lateral force were adopted in the actuator.At the controller level,the objective functions and constraints were redesigned.A multi-objective unified optimization objective function that could meet the minimum tire utilization rate,the smallest distribution of tire utilization rate,and the least torque loss was established.Improve the accuracy of integrated control.(5)Aiming at the problem of fault tolerance,a fault-tolerant method which is easier to implement was proposed.The method was based on a new form of motor failure expression.Fault tolerant control could be realized only by modifying the constraints of the objective function of the controller.The method does not need to modify the objective function and the solution method.The proposed control strategies for each simulation were verified.It can be concluded that the control method designed can achieve the control objective well.