Directional stability and control of four-wheel independent drive electric vehicles

Abstract The innovative powertrain configuration of modern electric vehicles with four-wheel independent drive (4WID) provides the possibility of simple and exact yaw moment control by controlling the electric motor of every wheel independently. In this study, a genuine control strategy for optimum direct yaw moment control is proposed. Although this can be considered as a global control system for traction control of 4WID electric vehicles, the analysis is quite general and can be applied to other types of vehicle. The directional vehicle model is derived and, in accordance with the optimal control theory, an optimum yaw moment controller is designed. Two versions of the control law are developed and the dynamic performance of each one is determined and compared. Numerical simulation of the vehicle directional model, with and without the use of the optimal yaw moment controller, is carried out. Results indicate that considerable improvement in the directional stability of the vehicle can be achieved when the optimal yaw moment controller is engaged.