| Distributed-Drive Electric Vehicles(DDEVs)driven by in-wheel motors have the advantages of high driving efficiency,compact structure,small environmental pollution,fast control response and large degree of control freedom,etc.It is an ideal carrier to achieve driverless driving,represents an important direction of future automobile development,and has gradually become a research hotspot both in academic and industrial circles at home and abroad.Under the background of energy conservation and environmental protection,how to give full play to the independent and controllable advantages of each wheel of the DDEVs and further reduce energy loss to improve the driving range is a subject worthy of in-depth study.In this paper,a DDEV is taken as the research object,with the goal of reducing the energy consumption in the driving process,the eco-driving strategy considering the road curvature and the energy-oriented torque optimization are studied.The main work and research achievements of the paper include the following aspects:(1)A seven degree-of-freedom(7-DOF)nonlinear dynamic model of distributed-drive electric vehicle is established,including the body model,wheel model,tire model,battery model and motor model.Based on the established dynamic model,a seven degree of freedom forward Simulink model is built,and a multi-body dynamic vehicle model is built using the Carsim as well.Through the simulation tests of steering angle step input,doublelane change and Slalom test,it is verified that the established nonlinear 7-DOF vehicle model can represent the input-output response of the real vehicle well.In addition,a driver model consists of longitudinal speed and trajectory tracking is established to form a "driver-vehicle-road" closed-loop control system,which lays a foundation for the design and verification of control strategies.(2)Study on the state estimation and handling stability analysis of distributed drive electric vehicles.Firstly,a EKF state observer is designed to estimate the sideslip angle,yaw rate and longitudinal speed of the vehicle.Then,based on the Carsim,double-lane change and slalom test simulations are carried out to verify the effectiveness and accuracy of the designed EKF under general and extreme conditions.Finally,based on the sideslipsideslip angular velocity phase plane analysis method,the influence of road adhesion coefficient,longitudinal speed and front wheel angle on the handling stability is studied.Double parallel lines are used as the boundary lines to divide the stable and unstable regions of the phase plane diagram,the mathematical expressions of the slope,intercept of the boundary line with respect to the road adhesion coefficient,longitudinal speed and front wheel angle are established,it provides a basis for the determination of vehicle stability under different working conditions.(3)Study on the energy-saving driving strategy considering road curvature.In order to further improve the energy-saving performance of DDEVs,an energy-saving driving strategy considering road curvature was proposed.Firstly,the generation mechanism of turning resistance is revealed theoretically,the influence of cornering resistance on the energy consumption of DDEVs is expounded,and it is pointed out that optimizing the driving speed can save energy consumption under cornering conditions.Then,an adaptive variable step Newton iteration method with fast convergence speed and high accuracy is proposed to calculate the cornering resistance under both linear and nonlinear working conditions,and the mathematical expressions of the cornering resistance with respect to the front wheel steering angle and vehicle speed are fitted.On this basis,the speed optimization problem considering the road curvature is established,and an optimization algorithm based on dynamic programming is proposed to solve it.The simulation results show that the proposed energy-saving driving strategy can generally save energy consumption compared with the typical driving modes under the same constraints.(4)Study on the energy-oriented torque optimization control strategy.In order to reduce the energy consumption while ensuring braking and handling stability,an energyoriented torque optimization control strategy was proposed.First,based on the LQR(Linear Quadratic Regulator)and PI(Proportional Integral)control,the upper controller is designed to calculate the generalized force,that is,the additional yaw moment and the expected total driving moment.Then,three optimal drive torque allocation strategies are designed for the lower controller according to the driving conditions: 1)For the straight driving conditions,an optimal drive torque allocation strategy based on exhaustive search method is proposed based on the motor efficiency MAP;2)An enhanced regenerative braking strategy is proposed to meet the requirements of braking regulations and improve the energy recovery rate at the same time;3)For cornering conditions,in order to ensure the controllability and stability control while reducing energy consumption,a yaw moment adjustment factor(AF)is proposed.On this basis,a multi-objective convex optimization problem is established to minimize the tracking error of generalized force and the energy loss.The global optimal solution is obtained by using the active set method and a proposed analytical method based on the Karush-Kuhn-Tucker condition,respectively.Finally,the simulation results under NEDC(New European Driving Cycle)and DLC(Double-Lane Change)scenarios show that the proposed torque optimization control strategy can improve the energy recovery and reduce the energy consumption while ensuring braking and handling stability.(5)In order to verify the effectiveness and practicability of the energy-saving driving strategy considering road curvature and the energy-oriented torque optimization control strategy,a hardware-in-the-loop(HIL)test platform and a real vehicle test platform were built,and the double-lane change HIL tests and single-curve field tests were conducted.The experiment tests further prove that the proposed energy-oriented torque optimization control strategy can achieve online real-time control and save energy while ensuring stability control;The test vehicle can track the optimized speed curve with a small error.Under the same constraint conditions,compared with the typical driving modes,the proposed energy-saving driving strategy can generally reduce the energy consumption when driving through curves,and thus improve the driving range of EVs. |
PDF Full Text Request