Development of a Performance Prediction Program for EVs Powered by Lithium-ion Batteries

The performance capabilities which hold the key to the acceptance of electric vehicles (EVs) includes range and acceleration. Range can be effectively extended by increasing the size of the batteries used, but it requires a trade-off with acceleration performance which deteriorates due to the increased weight. The FEV-II and Prairie Joy EV exhibited at the 1995 Tokyo Motor Show were equipped with high-performance lithium-ion batteries that achieve both high energy and power densities, to provide an excellent balance of range and acceleration. Futher more, the batteries exceptionally high charging efficiency enables them to accept regenerative energy effectively. This feature improves range, and also allows the battery state of charge (SOC) to be determined accurately. This characteristic was used to develop a highly accurate battery model which was incorporated in a simulation program for predicting EV performance. This simulation program provides accurate predictions of range and acceleration performance based on calculations of the constantly charging battery SOC. The calculations are performed by inputting the vehicle specifications (vehicle weight, number of passengers, drag coefficient, front-end projection area, dynamic tire radius, gear ratio and gear efficiency) and information on the charge/discharge conditions (initial SOC, upper limit of discharge current and discharge cut-off voltage). The accuracy of the simulation program was verified experimentally, and it is now being used as a performance design tool in the development of EVs that make the most of the advantages of lithium-ion batteries.