Research On Active Safety Control Strategy Of Electric Vehicle Based On Active Front Steering(AFS) And Direct Yaw Moment Control(DYC)

With the complexity of vehicle driving conditions,the number of deaths caused by traffic accidents is increasing every year.The active safety control of vehicles has attracted much attention in recent years.In order to further improve the stability of the vehicle,the active safety control system design has been considered for in-wheel electric vehicles.The active front steering(AFS)control scheme is first discussed,and then the integrated control strategy by combining the active front steering and direct yaw-moment control is also been proposed.The main contents of this thesis can be summarized as follows.On the one hand,taking into account that the AFS system with the linear controllers may not provide the satisfactory disturbance rejection property under some extreme conditions,three kinds of nonlinear robust control methods for AFS system will be proposed.Firstly,combining the PI controller with the disturbance observer(DOB),a composite AFS control scheme is designed.This control method is simple and significantly improves the anti-disturbance performance of the closed-loop system.Secondly,a kind of nonsingular terminal sliding mode(TSM)control scheme is proposed.The given nonsingular TSM control strategy not only possesses a rapid dynamic performance and is easy to be implemented,but also offers a stronger anti-disturbance performance by comparing with the traditional PI control.Thirdly,considering the fact that the control parameters in the TSM controller are usually required to be turned very largely,a composite nonlinear control scheme is also designed in combination with the disturbance observer technique.Meanwhile,through CarSim and MATLAB/Simulink,the advantages and disadvantages of the proposed methods are also discussed under the same operating conditions.On the other hand,for the drawback of AFS control system at a high speed,the integrated control strategy by combining the active front steering and direct yaw-moment control is also discussed in this thesis.Consider that the fundamental reason of the vehicle instability is the saturation characteristic of the tire,and the AFS control highly depends on the lateral force of the vehicle tire,which can be easily restricted by the lateral force of the tire and the saturation characteristic of the sideslip angle.On the basis of the AFS control system,the direct yaw-moment control scheme is first designed by non-smooth control technique.According to the recognition of the vehicle state,the task of AFS and DYC are separately allocated.The purpose of the control strategy is to make sure that the actual yaw rate and sideslip angle will track their ideal values and thus improve the vehicle's handing stability.Similarly,simulation test is carried out through CarSim.The simulation results show that by comparing with the AFS control,the integrated control scheme ensures a better stability performance,especially at a high speed.