Bi-Directional DC - DC Converters for Battery Buffers with Supercapacitor

Abstract

Sources of electrical energy for industry, agriculture or military use are different with respect to the purpose, place, sort of appliance, type of supplied systems. Fixed military facilities, for example, bases and camps are supplied by common electrical network system. Uninterruptible power sources are used to span short network black-outs and to maintain the power quality supplied to computers and other sensitive electronic equipment due to dips, surges and voltage reductions (Kurka & Leuchter, 2008). In vehicles and aircraft various types of accumulator batteries are used for starting of engines, on-board generators as main source of electrical energy are driven by operating engines. Stable electrical power generating sets are used for power supply in military bases and camps, where the connection to network is not possible. Mobile generating sets are also used for general use to supply various appliances, facilities, systems, for heating, illumination, and other purposes in industry, agriculture or military units. Most of up to date systems are equipped by specialized built-in generating sets. In studies focused on this problem the sources based on the small nuclear generators, sun and wind energy are speculated, but no one from these technologies is suitable from the mobility, safety and operativity of corresponding application point of view. The majority of above mentioned electrical energy sources use some means of energy accumulation (electrical energy buffers or accumulators) to secure the reliable operation under all possible circumstances and conditions. It is considered as self-evident that fuel cells become another mobile power sources and electrical energy buffers (batteries). Fuel cells were marked as one of the new energetic source alternatives for military applications. In the comparison with classical conversion of fuel (where the efficiency reaches 15 to 35%, and with the gas turbine with max. 40%), fuel cells based on the direct conversion of chemical energy to the electric one reach efficiency 50 to 70%, according to the type, power, used chemicals and design. In the combination with semiconductor converters, systems based on the fuel cells become practically the universal source of electric energy (Kurka & Leuchter, 2008). With the development of new technologies in transportation, vehicles, renewable energy sources, UPS, mobile electrical energy generating sets and in other branches the accumulation of electrical energy, its transformation and transportation represents one common problem. For this purposes various types of electrical energy buffering methods and converters including buffers are used. As will be shown, supercapacitors are well suited to replace classical batteries and conventional capacitors in many applications. Electrical