Distributed Drive Electric Vehicle Dynamics Control Considering Braking Energy Recovery

Since the beginning of the 21 st century,the automobile industry has developed rapidly.At the same time,along with the fossil energy crisis,new car manufacturers and traditional car companies around the world have begun to transform to electric vehicles,and the development of electric vehicles has become a new trend.Electric vehicles have obvious advantages over traditional fuel vehicles in terms of energy saving and controllability.Therefore,electric vehicles provide new possibilities for energy saving control and handling stability.Distributed drive electric vehicles are driven by in-wheel motors,which have the advantages of high controllable freedom,rapid response,and high transmission efficiency.The cruising range of electric vehicles is currently one of the issues that everyone is concerned about.Traditional vehicles do not have energy storage devices.The kinetic energy of the vehicle is converted into heat and energy consumption through friction braking,while the distributed drive electric vehicles can store braking energy through braking energy recovery to increase the mileage of the vehicle,so making good use of this feature and dealing with the core issue of electro-hydraulic hybrid braking is the key to this article.In addition,in terms of vehicle stability control,traditional vehicle electronic stability system(ESP)is another major advancement after vehicle anti-lock brake control(ABS).It controls wheel slip by reducing engine torque or adjusting the brake fluid pressure of each wheel.It can also generate additional yaw moment to maintain vehicle stability,but this control method is at the expense of vehicle power loss,and the hydraulic response is relatively slow,which does not satisfy the driver’s expectations.Based on the in-wheel motor-driven electric vehicle equipped with Booster to achieve vehicle braking energy recovery and vehicle stability control,the specific research in this paper is as follows:First,an electro-hydraulic compound braking strategy based on Booster electronic assisted brakes is designed,and models of motors,batteries,and hydraulic systems are established,which can realize vehicle braking force distribution under normal operating conditions,and verify the Effectiveness of dynamic energy recovery algorithm through simulations of different braking strengths.Second,a three-degree-of-freedom vehicle model that can describe vehicle dynamics is established,which provides a reference for the development of vehicle speed estimation and control algorithms.A nonlinear vehicle speed observer is proposed,combined with the Unitire tire model based on the three-degree-of-freedom vehicle model,and the tire force is used as the state feedback to estimate the vehicle speed more accurately under normal and extreme conditions.In addition,a PI controller design based on the estimated vehicle speed was developed to realize anti-lock braking control with in-wheel motors as actuators under low adhesion conditions,and simulation verification was performed on low adhesion single roads and split roads.Third,hierarchical control is used to develop Torque Vector Contol(TVC)to improve handling stability control,which treats the vehicle as a second-order control system model.In the simulation environment,the inherent characteristics of the vehicle are parameterized through the steering wheel angle step test.The upper-level controller of the vehicle makes the decision of the yaw moment in combination with the real-time state of the vehicle.This article discusses and derives in detail the first-order sliding mode control,the second-order sliding mode control,and the second-order adaptive sliding mode control to determine the required yaw moment of the vehicle.The effectiveness and advantages and disadvantages of these three types of control are analyzed through simulation.Fourth,a detailed analysis of the vehicle state under low-adhesion conditions is carried out.The instability under this special condition is mainly caused by the conflict of decisionmaking torques of the upper control.Therefore,the lower torque distribution controller is designed to coordinate the defense The torque conflict between lock control and torque vector control can better find a balance point between vehicle braking performance and stability.Finally,the brake energy recovery strategy was verified based on the wheel-driven test vehicle equipped with Booster.Through the Booster characteristic test and the brake test of different braking intensities,the results show that the brake energy recovery strategy can perform various conditions smoothly.Under the electro-hydraulic brake switch,the professional driver feels good on the pedal,and the energy-saving effect is verified through the rotating hub test bench.