Control Strategies For Different Drive Modes Of Four-Wheel Ndependent Drive Electric Vehilces

Four-wheel independent drive(4WID) electric vehicle(EV) will be the most important key technology in the near future because of its advantage in vehicle dynamics over internal combustion engine vehicle. As the four wheels can be controlled independently, 4WID EV can work in different drive modes by distributing the driving torque among the four wheels. In this thesis, some control strategies for different drive modes of 4WID EV have been proposed.(1) A cubature Kalman filter(CKF) based vehicle state estimation method for 4WID EVs is proposed. Based on a nonlinear three degrees of freedom vehicle model and cubature Kalman filter, an estimator for 4WID EVs is designed to estimate longitudinal velocity, side slip angle and yaw rate. The estimated longitudinal velocity and side slip angle can be used in energy management, fail safe control and vehicle stability control of 4WID EVs.(2) A drive mode switch method for 4WID EV is presented. Motor drive system Energy management based dive mode active switch strategy and fail safe based drive mode passive switch strategy are studied. First, a genetic algorithm based dive mode active switch strategy is proposed to maximize the efficiency of motor drive systems by switching among different drive mode. Second, a drive mode passive switch strategy is designed to maintain the vehicle stability by controlling the remaining normal working motor drive systems.(3) A vehicle stability control strategy for different drive modes of 4WID EV is proposed. A two-layer-control-model(direct yaw-moment control layer and torque distribution layer) is presented to maintain the performance and stability of the vehicle for different drive mode; In the upper layer, a fuzzy logic based direct yaw-moment controller is proposed to calculate deviation torque for the purpose of stability; In the lower layer, an algorithm is designed to distribute torque to the motor drive systems.(4) A vehicle control unit and hardware in loop(HIL) simulation system are designed. First, a Tricore based vehicle control unit is designed. Second, a dSPACE and CarSim RT based hardware in loop simulation system is constructed. And the control strategies for different drive modes of 4WID EVs are verified using the HIL simulation system.For the control strategies proposed in this paper, not only the fuel economy and fail safe but also vehicle stability are considered by using the four independent drive wheels. This study would be useful to the development of 4WID EVs.