Research On Integrated Control Method Of Handling And Stability For Distributed Electric Vehicle

With the increasing number of vehicles in the world,the environmental problems caused by vehicle exhaust pollutants are widely concerned.Atmospheric environment is seriously threatened.To this end,governments and auto manufacturers have proposed to push out electric vehicles as a solution to this problem.With the development of science and technology,and the continuous improvement of people's pursuit of automotive performance,the distributed driving electric vehicles came into being.This new type of electric vehicle is different from internal combustion engine vehicle,the distributed electric vehicle eliminates the transmission system of the vehicle and is driven by a wheel hub motor mounted on the wheel directly.And the controllable degree of freedom of vehicle is greatly improved.It also has a significant advantage in improving vehicle handling and stability.It also means that the control strategy of distributed electric vehicle needs to be redesigned and researched.In order to ensure the safety performance of distributed electric vehicle,a new control strategy and method is put forward based on the research of traditional vehicle stability control strategy.This Ph.D.dissertation is based on the project of National Key Research and Development Plan named Research on the Key Issues of Sensing Environment,Dynamic Decision-making and Controlling for Intelligent Electric Vehicle(No.2016YFB0100900),and the project of China Automotive Technology and Research Center,Research on the coordinated control strategy of driving,steering and braking of electric intelligent vehicle(No.3R217R802417).In this paper,based on the premise of improving the stability and stability of the vehicle,a distributed electric vehicle is studied,this paper makes an in-depth study of the rear wheel active steering system,the distributed drive system control method and the distributed electric vehicle handling and stability integrated control system.By analyzing the current status of relevant research at home and abroad,the problems and shortcomings in the current related research are summarized,and the main contents of this paper are determined.The main contents of this paper include a few aspects:1.A distributed electric vehicle dynamic model is established.Based on Darren Bell's principle and Newton's second law,a dynamic simulation model with 8 degrees of freedom for a distributed electric vehicle is established,which includes Gim tire model,steering system model,drive motor model and driver model.The open loop and closed loop simulation test and analysis of the vehicle dynamics model are carried out.By comparing and analyzing the vehicle models with Carsim software,the rationality of the proposed vehicle dynamic model is verified,which provides a foudation for the simulation test for later study.2.Acquire vehicle driving state parameter information and judge the vehicle driving stability state.The extended Kalman filtering principle(EKF)is used to establish the state estimator to estimate the side slip angle of the vehicle and the adhesion coefficient between the tire and road.The effectiveness and accuracy of the estimation algorithm under linear and nonlinear conditions are verified by simulation experiments.Based on the phase plane rule,the phase plane stability region of the side slip angle and its change rate under the conditions with different velocity and road ashesion is obtained.Then the phase plane region of the vehicle side slip angle and its change rate is divided into three parts: "stable region","critical area" and "unstable region".As a basis for the design for the vehicle stability integrated control system.3.A variable weight coefficient of LQR rear wheel active steering control system was designed.Based on the traditional LQR control theory to design the rear-wheel active steering controller,a rear-wheel active steering controller is designed to adjust the weight coefficient of the Q matrix according to the condition of the road surface adhesion coefficient.The relationship between yaw rate,side slip angle and vehicle stability is analyzed.With the different road-adhesion conditions,the weight coefficient of the Q matrix is dynamically adjusted.When the vehicle driving on low road-adhesion surface,the weight coefficient of q? is increased and the weight coefficient of qwr is reduced;accordingly,the weight coefficient of qwr is increased and q? is reduced while vehicle traveling on high road-adherent surface.Based on the fuzzy control theory,a Q-matrix weight coefficient adjuster is designed,and a variable weight coefficient of LQR rearwheel active steering controller is designed.Through step response open-loop and double lane change closed-loop simulation tests,the adaptability of the variable weight coefficient of LQR rear-wheel active steering controller under different road-adhesion conditions was verified.And then not only reduce the degree of driver fatigue,but also has a better trajectory tracking ability.According to the evaluation indicators of vehicle handling stability proposed by previous scholars,compared to the traditional LQR rearwheel active steering controller,the variable weight coefficient of LQR rear-wheel active steering controller has advantages in all evaluation indicators,and the comprehensive performance also has more advantage.4.An immune genetic optimization algorithm is proposed to optimize the fuzzy controller used to ESC controller.The problems of over-reliance on the experience of designers in the process of designing fuzzy controllers and the problems of “explosive” and “premature” for populations resulting from the optimization of fuzzy controllers by means of traditional genetic algorithms can not obtain the “optimal” individuals.The immune genetic optimization algorithm was selected,and on the premise of maintaining the diversity of the population,the vaccine information was used to improve the optimization efficiency of the genetic algorithm.Optimized for the ESC controller designed with fuzzy control,including the distribution of its membership function,the proportional coefficient and the quantization factor optimization.Through the open-loop step response and sinusoidal simulation tests,the performance of the ESC controller before and after optimization was compared.The optimized ESC fuzzy controller improved the lateral response of the vehicle,and the yaw rate and the side slip angle reached the steady state.The vibration amplitude is significantly reduced,and the time required to reach the steady state value is shorter and the overall performance is improved.5.An integrated control system for vehicle stability is designed.In order to give consideration to vehicle stability and driver's intention of acceleration and deceleration.There are two subsystem of "integrated control system designed for vehicle stability control" and "integrated control system designed for vehicle handling stability" are designed respectively.With the real-time change of the side slip angle and its change rate of the vehicle,the two subsystems play a role at the right moment.When the side slip angle and its chang rate phase plane is in the “critical area” or “unstable region”,the variable weight coefficient of LQR rear wheel active steering controller is integrated with the ESC controller which optimized by immune genetic optimization.Designing and coordinating the two controllers separately or together play a role in controlling the vehicle.And then an integrated control system based on vehicle stability control is designed.Through the sine gain open-loop simulation test,the effectiveness of this integrated control system under the nonlinear conditions of the vehicle is verified,the driving stability of the vehicle under the extreme working conditions is improved,and the ESC intervention can be reduced during the vehicle stability control process.The decline of the vehicle velocity is reduce and the vehicle runs steadily.When the side slip angle and its chang rate phase plane is in the “stable region”,the vehicle is in stable state,the yaw moment distributor is designed through the quadratic programming principle,which will maintain the vehicle driving stable.The yaw moment which maintain the vehicle driving stable is coordinated with the generalized longitudinal force required by driver's acceleration and deceleration intention,and then is allocated to the driving/braking torque of the 4 wheels.So that the distributed electric vehicle driving system is integrated with the braking system,the “Integrated control system based on vehicle handling stability control” is designed.Through double lane change simulation test,it is verified that under the premise of ensuring the vehicle does not lose stability,the stability margin of the vehicle is improved,and the driver's control requirements for the vehicle speed can be satisfied in some extent.6.The hardware in the loop test platform is built,and the hardware in the loop test is carried out.The NI PXIe real-time system hardware is selected as a real-time test platform for the Hi L(Hardware-in-the-loop)platform.The hardware in the loop test platform is built after matching of the hardware and the related controller to the underlying actuator system of the vehicle.The vehicle stability control system based on the Matlab/Simulink platform is properly processed in real time.Through the hardware in the loop simulation test,the simulation results demonstrate that the variable weight coefficient of LQR active rear wheel steering system,vehicle stability integrated control system,vehicle stability control system can run well in real-time environment,improve the vehicle handling stability under various working conditions effectively.It also further proves the effectiveness and rationality of the proposed strategy of vehicle stability integrated control system.In this paper,the proposed variable weight coefficient of LQR rear wheel active steering controller,ESC controller based on immune genetic optimization,the integrated controller based on vehicle stability control,the integrated controller based on vehicle handling stability control have a certain reference significance for distributed electric vehicle.The proposed control system can be used alone or in combination,which provide the basis and reference for the study of vehicle active safety technology and vehicle dynamics control system.