Consuming chemical energy, fuel cells produce simultaneously heat, water and
useful electrical power [J.M. Andújar, F. Segura, Renew. Sust. Energy Rev. 13, 2309 (2009)], [J. Larminie, A. Dicks, Fuel Cell Systems Explained, 2nd edn.
(John Wiley & Sons, 2003)]. As a matter of fact, the voltage generated
by a fuel cell strongly depends on both the load power demand and the
operating conditions. Besides, as a result of many design aspects, fuel
cells are low voltage and high current electric generators. On the contrary,
electric loads are commonly designed for small voltage swing and a high V/I
ratio in order to minimize Joule losses. Therefore, electric loads supplied
by fuel cells are typically fed by means of an intermediate power voltage
regulator. The specifications of such a power converter are to be able to
step up the input voltage with a high ratio (a ratio of 10 is a classic
situation) and also to work with an excellent efficiency (in order to
minimize its size, its weight and its losses) [A. Shahin, B. Huang, J.P. Martin, S. Pierfederici, B. Davat, Energy Conv. Manag. 51, 56 (2010)].
This paper deals with the design of this essential ancillary device. It
intends to bring out the best structure for fulfilling this function.
Several dc-dc converters with large voltage step-up ratios are introduced. A
topology based on a coupled inductor or tapped inductor is closely studied.
A detailed modelling is performed with the purpose of providing designing
rules. This model is validated with both simulation and implementation.
The experimental prototype is based on the following specifications: the
fuel cell output voltage ranges from a 50 V open-voltage to a 25 V rated
voltage while the load requires a constant 250 V voltage. The studied
coupled inductor converter is compared with a classic boost converter
commonly used in this voltage elevating application. Even though the voltage
regulator faces severe FC specifications, the measured efficiency reaches
96% at the rated power whereas conventional boost efficiency barely
achieves 91.5% in the same operating conditions.