Research On Optimum Torque Distribution Algorithm For Fourwheel-Independent-Drive Electric Vehicle

’Electric drive’ and ’intelligent’ is the developing treads of the vehicle.Four-wheel-independent-drive electric vehicle is one of the new research fields of modern electric vehicles due to its unique structure and technical characteristic.The classical control algorithm and the intelligent control algorithm are combined in this paper to design an optimum torque distribution algorithm,which takes advantages of the four-wheel-independent-drive vehicle.The designed optimum torque distribution algorithm is divided into torque distribution algorithm under linear-stable condition and nonlinear-emergency condition.Firstly,a dynamical model for FWID-EV with closed-loop control of driver is established based on Car Sim and Matlab/Simuink.For verifying the accuracy of the model,a simple and effective torque distribution algorithm is given.The simulation results show that the dynamical model has good performance on power and stability,which lays a foundation for developing complicated control algorithm.Secondly,this paper presents a torque distribution algorithm aiming to improve both the energy economy and vehicle performance for FWID-EV under linear-stable condition.To incorporate energy management issue into the torque distribution problem,a mathematical energy efficiency model for the driving motor is built based on experimental data.The design of the multi-objective optimization problem considering the following three factors: energy consumption,road handling and ride comfortability.To solve this complex objective function,an Adaptive Particle Swarm Optimization(APSO)algorithm is adopted to figure out this multiobjective optimization problem.Thirdly,a torque distribution algorithm is presented to improve the handling and stability of FWID-EV under nonlinear-emergency condition.The proposed torque distribution algorithm is constructed using three hierarchical controllers.The upper controller is designed to judge whether the vehicle is in the stable state and whether the wheels are slipping.The middle controller aims to calculate the demands for the desired traction force and yaw moment,whereas the lower controller is designed to translate the demands from the middle controller into actual actuator commands.When designing the middle controller,a sliding mode control method is adopted to guarantee system stability and robustness by taking into account various factors,including lateral wind and sensor noise.For the lower controller,a control allocation optimization method is utilized to determine an appropriate control input for each motor with respect to the road conditions,adhesion utilization and maximum output torque of the motor.Finally,numerical simulation studies are conducted to evaluate the performance of the torque distribution algorithm using a co-simulation of Car Sim and Matlab/Simulink software.Results indicate the proposed torque distribution algorithm under linear-stable condition can improve energy economy,road handling and ride comfortability of vehicle,the proposed torque distribution algorithm under nonlinear-emergency condition is able to distribute the appropriate torque to each wheel and ensure the stability of vehicle,compared with the even-distribution algorithm.The research in this paper is useful for the development of control theory and electric vehicle control system.