Lateral Stability Control And Optimal Torque Distribution For Electric Vehicles

The global energy crisis,air pollution is serious.Especially in recent years,our incidence of allergic asthma on the rise,fog seriously affects people's physical and mental health.So electric vehicles have received much research interest nowadays?Four wheel independent drive electric vehicles has become the new direction with its unique advantages.Because it's no transmission system,which can control the four wheels independently and has fast torque response.Vehicle stability affected by structural parameters,speed,steering wheel angle which is a nonlinear problem.Especially in the cornering condition,vehicle rear axle load transfer to the front axle and the inside of the wheel load transfer to the outer,so that the vehicle structure parameters are constantly changing,such as cornering stiffness.In this case,the vehicle will lose the vehicle lateral stability such as under-steer problem and plow out of the desired path.In this paper,This work is supported by National Key R&D Program of China(2016YFB0101102)research on parameter uncertainty and torque distribution in the stability control of electric vehicles.Following works have been done in the paper:Firstly,we establish the vehicle dynamics model,tire model,wheel dynamics model,motor model,electronic hydraulic brake system based on four-wheel independent drive electric vehicle.Where,permanent magnet synchronous motor is established in AMESim,and the method of space vector control is used for tracking control motor torque.Electronic hydraulic brake system control the braking torque based on fuzzy PI controller.Secondly,for electric vehicles with in-wheel motors parameters uncertainties problem in different road conditions,this paper proposes an adaptive sliding-mode algorithm to guarantee vehicle lateral stability and compensate parameter uncertainties.A sliding control law is effective to trace the desired yaw rate and the side-slip angle,and reduce the errors of them simultaneously.Adaptive control law is designed to update the whole control law for parameter uncertainties compensation.The adaptive sliding-mode algorithm has the asymptotic stability of the adaptive system and the transient characteristic of the sliding mode control system simultaneously.The torque distribution algorithm is designed to use the constrained optimal control theory based on quadratic programming method.A Car Sim/Simulink simulation is conducted for algorithm verification.It is found from the simulation results that the proposed control scheme which is effective to compensate system uncertainties as well as guaranteed the vehicle lateral stability.Finally,the lower controller includes torque distribution and coordination optimization.Four independent variable torque,the desired yawing moment from upper controller under various constraint conditions is distributed at each wheel.Considering the influence of vertical load transfer counter rotating for torque distribution,our optimal objective is the minimization of tire utilization,constrained optimization can be solved using the quadratic programming method.The objective is to engage the electric motor only during braking,up to the point at which the motor reaches its performance limit.The insufficient braking torque is supplemented with hydraulic brake.