Research On Hierarchical Optimization Of Distributed Electric Vehicle Stability Control System

At present,the consumption of natural resources is increasing,and the environmental pollution is more and more serious.Many countries have begun to focus on the development of pure electric vehicles.Meanwhile,due to the economic development,the quality of life of the people is improving.Car ownership was being in a state of continuous growth.People have been no longer satisfied with the current vehicle dynamic and comfort requirements,more inclined to have active and passive safety,intelligent driving and other technologies of the car.The development of automobile industry technology is continuously promoted.Distributed electric vehicles not only save the main components of engines and transmissions,but also adopt the way of in-wheel-motors to drive independently.The distributed electric vehicle greatly reduces the quality of the vehicle and improves the space of the carriage.More importantly,the distributed electric vehicle driven by the hub motor could precisely control each in-wheel-motor according to the actual working conditions,in order to achieve the optimal state of the current vehicle operation.This paper takes the distributed electric vehicle as the research object,and makes a hierarchical optimization research on the vehicle stability control system.The main contents of this paper are as follows:(1)The research background and current situation of distributed electric vehicle,the structure and key technologies of distributed electric vehicles were introduced,and the research status at home and abroad in recent years were introduced.In this paper,the estimation of vehicle sideslip angle and stability were summarized and classified.(2)Based on the Car Sim and Matlab/Simulink platform,The whole vehicle dynamics model was established in this paper.Considering the influence of the vehicle stability system,the vehicle model was simplified as the lateral,longitudinal,yaw,pitch,frontwheels steering and the rotation of the four wheel.In addition,a "magic formula" tire model,simplified motor model and brake model were established in this paper also.Finally,the whole vehicle model is simulated and verified.The simulation results shown that the proposed model in this paper can reflect the vehicle's dynamic characteristics of(3)The stability of vehicle and the influence of yaw rate,slip ratio and sideslip angle on vehicle stability were analyzed.The steady state response and transient response of the front wheel step input were analyzed.Calculating the ideal sideslip angle and the ideal yaw rate sideslip angle when vehicle was running steadily.Finally,the vehicle stability criterion was formulated.(4)The vehicle sideslip angle has been estimated by Luenberger observer and the sliding mode observer.The effect of switching function,saturation function and hyperbolic tangent function on chattering reduction of sliding mode observer were analyzed and proved the convergence of the sliding mode observer in this paper.Finally,the simulation results shown that the Luenberger observer and the sliding mode observer can accurately estimate the center-of-mass deflection.(5)The principle and structure of distributed electric vehicle stability control system,was analyzed and the stability control system was optimized.The optimization algorithm of speed controller based on PID control,the optimization algorithm of sliding rate controller based on fuzzy adaptive PID control,and the optimization algorithm of yaw rate controller based on LQR theory were designed.The optimization algorithm of single wheel control,two wheel control and coordinated control were designed for the torque distributor.Finally,using Car Sim and Matlab/Simulink platform for the high adhesion coefficient,low adhesion coefficient,double lane change and slalom contrast simulation,the simulation results shown that the optimized control system can improve vehicle stability.