Research On Longitudinal And Lateral Coordinative Control For Distributed Driving Electric Vehicle Under Extreme Condition

The automobile industry is an important mainstay industry of our country.With the maturity of battery,motor and control technologies,the development of electric vehicle is the fundamental means to solve traffic emissions and energy problems.Distributed driving electric vehicle(DDEV)is one configuration of electric vehicle.It chooses In-wheel motors as its driving units,which improves the torque response speed and execution accuracy.The redundant characteristic makes it convenient for DDEV to realise various dynamic behaviours.Hence,DDEV is believed to be a promising architecture for electric vehicle.However,the high frequency excitation and high torque characteristics of the in-wheel motor increase the probability of wheel slip when accelerating.The intervention of differential torque increases the lateral tire force,which arises the possibility of sideslip when turning on the low adhesion road.The existing control schemes are used to adopt the traditional centralized driving electric vehicle(CDEV),which makes the stability of DDEV more fragile.Hence,how to fully use the advantages of the four-wheel independent driving and ensure the safety of DDEV in extreme conditions,is an urgent problem which needs to be solved.In this paper,the safety of DDEV in extreme conditions,such as low adhesion,rapid acceleration and large steering,is studied from the perspective of longitudinal and lateral coordiative control.The main contents are as follows:(1).The acceleration slip regulation system is an important guarantee for the longitudinal driving safety of vehicles.However,the model and control method of DDEV are different from the traditional CEDV.Considering the influence of tire lag,an ASR control method based on linear-parameter-varying robust performance-guaranteed pole-palcement is proposed.It is pointed out that the relaxation characteristic is the cause of underdamped vibration of slip ratio.An ASR system based on performance-guaranteed pole-palcement method is designed,and the influence of parameter perturbation and parameter time-varying is allivated by robust gain scheduled algorithm.The simulation result proves the robustness and adaptability of the designed ASR as well as a better performance of suppressing the slip rate oscillation,which ensure acelectaion comfort of DDEV.(2).To slove the conflict between lateral stability and motion tracking of DDEV,a multi-mode torque distribution strategy for extreme steering condition is proposed.The model predictive control algorithm is used to design the lateral stability controller.Considering the road conditions,the state of the vehicle is divided into three driving modes and a linear matrix inequality based criterion for mode switching is designed.According to the results of mode division,three different torque distribution objective functions are designed in the form of soft and hard constraints.The simulation results show that the proposed multi-mode torque distribution algorithm can realize the adaptive mode-switch,which improves the accuracy of motion tracking as well as avoiding the instability of the body.(3).To slove the coupling and contradiction between the steering system and the driving/braking system,a DMPC path-tracking controller based on multi-agent system is designed.The multi-objective optimization problem is transformed into single-objective optimization problems in longitudinal and lateral directions.The function overlap and control contradiction between steering agent and driving/braking agent are reduced.By exchanging the historical optimal sequence,the parallel optimal solution of steering agent and driving/braking agent is realized.At the same time,the computation burden of the agent is reduced.The simulation results show that the path-tracking controller based on DMPC ensures the path tracking accuracy,and the computational efficiency is significantly improved compared with the traditional centralized MPC controller.(4).A DDEV experimental vehicle is developed.The chassis reform cheme is designed to match the hub motor with the original high and low voltage architecture and thermal management system.The CAN communication topology and communication protocol are defined,and the new CAN network is connected with the original vehicle network.Based on the V mode of vehicle control software,the application control software of DDEV is developed,and the system level,component level and unit level modules are tested and verified to ensure the logic rationality and functional integrity of vehicle control software.The handing performance is verified by experiments.It is proved that the anti sideslip,anti rollover ability and steering flexibility are improved in four-wheel drive mode.In the condition of low adhesion road,the driving anti-skid function is tested,which realizes the stable tracking of the target slip rate,and improves the safety of the vehicle in the limit condition.