Mode definition and operation strategies for secondary battery assisted Hybrid-type DMFC systems

In relatively small allowable volume fuel cells are unable to provide the average power and essentially high peak power demanded by specific electric load. Hybrid-type direct methanol fuel cell (DMFC) systems composed of fuel cells and secondary batteries could combine the high power density of clean fuel cells and the high energy density of convenient batteries which exist already within the original system. This paper presents a study on operational strategies for passive power sharing in such a hybrid fuel cell/battery power source and external adaptor. We define the eight operational modes and specify the condition on which the mode transitions occur. Also, emergency mode is defined and activated at each abnormal condition. To implementation purpose four electric switches are appended at specific power paths, i.e. fuel cell stack output, secondary battery output, electric load input, and charger input.