A Study of the Methods of Charging Electric Vehicle' s Nickel/Metal Hydride Battery

摘要

In this study, the methods of charging nickel/metal hydride (Ni/MH) batteries for an electric vehicle were investigated. Charging and discharging conditions were varied in an attempt to improve high-energy efficiency and to increase the cycle life. The effects of the amount of current, the frequency of the equalizing charge on the charge and the shallow depth of discharge were estimated. A battery system with 12 modules was subjected to a cycling test with a discharge by dynamic stress test (DST) 120 patterns and a one- or two-step charge more than 800 cycles, and was found to have a longer cycle life than a valve-regulated lead-acid battery. Two-step charging with the first-step current of 0.5CA was completed in less than two and half hours after discharging by DST 120 patterns to 80%DOD. Reduction in frequency of equalizing charge from every time to every 10 cycles enhances the energy efficiency by 3 Wh% to about 83 Wh%. Discharge and charge with shallow depth of discharge reduced the energy efficiency to 78 Wh%, by 5 Wh% less than that with discharge until 80 % DOD. After repeated discharging to shallow depth of discharge, the system underwent decreases in the discharge capacity by 5 % and power density of 10 % due to the memory effect.