Stability Control And Energy Efficiency Optimation For Distributed Drive Electric Vehicle Based On State Estimation

With the advantages of short power chain,fast and controllable response and easy to obtain higher driving efficiency,the distributed electric vehicle has become one of the current research hotspot.With the increase of control degree of freedom,higher handling stability and energy efficiency can be obtained,and the control difficulty is also increased.On the one hand,the control difficulty is reflected in the coordination of four wheel drive/brake,on the other hand,it is reflected in the sensitivity of vehicle state parameters.Therefore,it has important theoretical significance and application value to study the handling stability control and energy efficiency optimization of distributed electric drive vehicle based on vehicle state parameter estimation method.In this paper,with the support of National Natural Science Foundation of China and graduate research and innovation foundation of Chongqing,the distributed electrical vehicle is considered as the research target,a multi parameter nonlinear observer is designed to estimate the state parameters of the vehicle considering as the problem that the state parameters of the vehicle are difficult to measure.Based on the mentioned above,in order to improve the vehicle stability,a hierarchical controller integrated with active steering and direct yaw moment control(DYC)is proposed to reduce the impact of DYC control on the longitudinal velocity of the vehicle while ensuring the vehicle stability.In order to reduce the energy consumption of the vehicle,an integrated control strategy is proposed to reduce the energy consumption of the vehicle,improving the vehicle stability.The main research contents and conclusions are shown as follows:(1)A multi parameter nonlinear observer is designed and its effectiveness is verified.Based on the 7-DOF vehicle dynamics model,considering the highly nonlinear characteristics of tires,taking the longitudinal acceleration,lateral acceleration,yaw rate and the rotational speed of four wheels as observable variables,taking the longitudinal velocity,lateral velocity,yaw rate,rotational speed of four wheels,longitudinal tire forces and lateral tire forces as state variables,the UKF algorithm is adopted to design the multi-parameter nonlinear observer.The simulation results show that the observer can effectively estimate the longitudinal velocity,lateral velocity,tire longitudinal tire forces and lateral tire forces.(2)A hierarchical controller based on DYC control method is designed and its effectiveness is verified.In order to improve the vehicle stability,a hierarchical controller including the upper controller and the lower controller is designed based on the 7-DOF vehicle dynamics model.The sliding mode control method(SMC)is adopted in the upper controller to calculate the desired additional yaw moment.The attachment ellipse and driving intention are considered as the constraints in lower controller,taking the vehicle stability as optimization objective,and the weighted least square(WLS)method is adopted to achieve the optimal distribution of the additional yaw moment.The desired longitudinal force of each wheel is obtained and fed back to the vehicle.Through the simulation analysis and comparison on Simulink and Car Sim platform,it can be seen that the hierarchical controller can effectively track the ideal state of the vehicle,improving the vehicle stability.(3)The integrated controller of four-wheel independent steering and DYC is designed,and the effectiveness of the controller is verified.Considering the DYC control has a great influence on the longitudinal velocity,the differential braking system will make the longitudinal velocity sharply reduce,affecting the driver's driving experience.Considering the influence of 4WIS system and DYC system on vehicle stability,the multi-objective optimization of four longitudinal tire forces is realized by using model predictive control(MPC)method,taking the vehicle stability and the increment of optimization variables as the optimization objective,taking the attachment ellipse as the constraint.In addition,in order to apply the target value of the longitudinal tire forces to the vehicle,the lower controller is designed to calculate the desired braking pressure of the four wheels.The simulation results show that the controller can effectively track the ideal vehicle state,improving the vehicle stability and reducing the impact of DYC system on the longitudinal velocity.(4)A hierarchical controller is designed to reduce vehicle energy consumption and improve vehicle stability,and the effectiveness of the controller is verified.The controller consists of the upper controller and the lower controller.The SMC method is adopted in the upper controller to calculate the desired additional yaw moment.The lower controller is designed based on the efficiency map characteristic of the permanent magnet synchronous motor.Considering the energy consumption of the four driving motors as the optimization objective,according to the relationship between the left front wheel and the left rear wheel and the right front and the right rear wheel can be obtained respectively,considering constraint conditions such as the attachment ellipse and the maximum torque of the drive motor,looking up the efficiency map of the drive motor,a set of tire forces which can minimize the energy consumption of the drive motor are optimized.According to the simulation analysis under different working conditions on Simulink and Car Sim platform,the controller can not only improve the handling stability of the vehicle,but also save nearly 32% energy at low longitudinal velocity.