Study On The Steering Stability Control Of Four-Wheel-Drive Electric Vehicle

adoption of motor traction by Electric Vehicle (EV). In particular, by employing the electric wheel technique, vehicles get rid of the complex mechanical structure. This innovative vehicle structure, together with traction style, while providing a space for the electric vehicles of exceeding the traditional ones, makes the traditional chassis control method difficult to adapt. Multi-wheel drive EV with simple mechanical structure needs to rely mostly on advanced control strategies to achieve the control of vehicle.This thesis takes four-wheel drive EV as its researching object in dynamic control scheme. On one hand, the driving command can be tracked by vehicle path through multi-motor traction control and differential control; on the other hand, for the problem that vehicle can't keep the best driving posture when the process of moving is affected by nonlinear factors under different operating conditions, the method which combines model matching adaptive control structure and robust control strategy is adopted to correct the driving path and vehicle dynamic posture and improve vehicle stability, maneuverability and safety.The main work of the thesis is provided as follows:Considering the essence of vehicle dynamics and structure of electric vehicle, a vehicle dynamics model with three degrees of freedom is built which adopts Pacejka model as vehicle tire model, analyzes the simulation result which is simulated with same operating conditions under Matlab/Simulink and Carsim respectively. And both correctness and feasibility of the vehicle dynamics model is proved to be achieved.This thesis adopts Direct Torque Control (DTC) as control strategy for permanent magnet synchronous motor, and Ackermann-Jeantand model as differential model for EV. To achieve the four-wheel independent drive control, differential and traction performance in the process of steering and going straight have been verified under Matlab / Simulink simulation platform. To tackle with the difficulty of keeping vehicle stable under limit control condition, this paper takes the attitude of vehicle as control target, yaw rate and vehicle slip angle as attitude parameters, model matching control as control structure to construct the vehicle stability control system. Ideal model adopts the output with slight understeer under linear situation. And its controller regards the robust issue of Linear Matrix Inequation (LMI) as its theoretical basis and a controller is designed. Under two different testing conditions of fish-hook and J-turn, the close loop simulation that the Robust Model Matching Control (R-MMC) strategy can improve the stability and safety of vehicle under nonlinear condition and the system has a good robustness to the nonlinearity of the vehicle's parameter.Finally, this thesis employs a two-wheel drive model vehicle to execute the differential experiment. This model vehicle is controlled by a MCU. And it is controlled independently by two DC motors on its rear wheels, and adopts independent controlled steering gear to steer. The test has obtained a good differential performance.