Analysis and design of bi-directional DC-DC converters for ultracapacitors management in EVs

The on-board energy-storage system of an electric vehicle (EV) should be able to collect large amounts of energy and to deal with fast load variations. The use of hybrid power sources as storage devices is an attractive solution, aiming at maximizing both energy and power density. The battery/ultracapacitors (UCs) combination promises to provide significant benefits. An accurate design of bi-directional converters, capable of proplery managing the charge/discharge of the UCs from/to a voltage bus, is essential. In this paper, a bi-directional DC-DC converter connected to a bank of UCs is described and the simulation results are given as well. The designed converter is a buck-boost type, able to manage a 40kW peak power for a duration of 3s, required by a 48 V bus-connected load.