Integrated fuel cell hybrid test platform in electric forklift

Materials handling vehicles are considered one of the potential early markets for fuel cells. In this application, lifetime and reliability have been identified as key parameters to be maximized. However, typical work cycle of many materials handling and other industrial vehicles, like forklifts, is characterized by heavy and fast variations in power demand. This sort of fast transient operation is not ideal for a fuel cell and hence hybridizing it with different energy storages is preferred. A hybrid power source consisting of PEMFC, ultracapacitors and lead-acid battery has been developed on a large counter-weight forklift. The energy storages were connected directly in parallel without actual power electronics in order to achieve simple structure and avoid conversion losses. In this arrangement, the lead-acid battery SoC and the internal resistance of energy storages directly dictate the load distribution between them. Only high current rated relays and a Schottky-diode are used to control current flow between energy storages and protect the fuel cell stacks.