DC-DC converter topology in a 5kW PEM fuel cell

A proton exchange membrane (PEM) fuel cell´s output power depends nonlinearly on its output current and voltage. The output current of a PEM fuel cell stack depends on the load placed on that stack. There exists a unique maximum power point (MPP) that varies with the temperature and hydration of the membrane among other factors. One use of PEM fuel cells is backup power, often with long intervals between fuel cell operation cycles where the fuel cell is called when the prime power is unavailable. The maximum power output of a PEM fuel cell is not instantaneous; time is required for the fuel cell stack to come up to optimum operating conditions and achieve maximum operating power. Trying to force the fuel cell stack to provide more power than it is instantaneously capable of generating may force operation in a region that may cause damage to its PEM membranes. This paper presents a control system and DC - DC converter topology used in a 5kW PEM fuel cell to ensure that the maximum available output power from a PEM membrane fuel cell is delivered to a load during a power outage bridging the startup time as well as to optimize the health of the fuel cell membrane stack. The overall electrical efficiency of the fuel cell is shown to deliver over 90% of the electrical power produced by the PEM fuel cell stack to the load inclusive of the parasitic power required to operate the electronics and fan. The DC - DC converter contributes to the overall system electrical efficiency by achieving over 97% efficiency.