Abstract
Electric vehicle is considered to be the solution for energy crisis and environment pollution in individual transportation. However, electric vehicles are still not competitive with conventional vehicles limited by the driving range with the state-of-art power battery technology. Therefore, energy efficiency is of crucial importance for battery electric vehicles due to the limited stored energy. In order to optimize the energy efficiency of a four-wheel independently driven electric vehicle, the model consisting of the vehicle dynamics model, wheel motor model and PNGV model of LiFePO4 power battery was developed in Matlab/Simulink. As the motor efficiency is low in small torque range, motors should work as much as possible in high efficiency range in order to extend the driving range. A new control algorithm was developed to distribute the total torque requirement dynamically to four wheel motors. When the total torque requirement is low, only two motors drive the vehicle and when the total torque requirement is high, four motors should work together to deliver the required torque. The vehicle switches between 2-wheel drive mode and 4-wheel drive mode according to the driving condition using the new control algorithm. Simulations of the new control algorithm were carried out on a modified urban drive cycle. The result showed that an improvement in driving range was achieved with the new control algorithm.