1868 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 26, NO. 7, JULY 2011 Simple Model and Experimental Identification of a Fuel-Cell-Based Power Supply Oriented to System-Level Analysis Cristina Fern´ andez, Member, IEEE, Pablo Zumel, Member, IEEE, Virgilio Valdivia, Student Member, IEEE, Angel Fern´ andez-Herrero, Member, IEEE, Marina Sanz, Member, IEEE, Antonio L´ azaro, Member, IEEE, and Andr´ es Barrado, Member, IEEE Abstract—Power electronics systems are becoming larger and more complex, involving a wide variety of loads, power sources, and power conditioning equipment. Simple behavioral models are required to perform a system-level analysis. These models can be parameterized from simple measurements or data supplied by the manufacturer. One of the emerging power sources are the fuel cells, which are being used in different power levels and applications. Some commercial products include not only the fuel cell stack, but also a dc–dc converter to provide a regulated output voltage despite the operation conditions of the fuel cell. In this paper, a behavioral model of a commercial fuel cell with a built-in front- end dc–dc converter is developed, based on load step tests. Model identification is carried out from experimental measurements using well-known identification algorithms. A validation of the obtained model has been performed by means of applying the same current patterns to the model and the actual fuel cell: steps; pulses; and sinusoids. Moreover, a simple power system has been built in order to validate the proposed model. A good trade-off between simplicity and accuracy is achieved. Index Terms—DC–DC power converters, fuel cell, power system modeling, system identification. I. INTRODUCTION T HE requirements regarding autonomy and energy density for the modern electric systems have driven the research of new energy storage devices and power sources, such as fuel cells [1]–[4]. These are electrochemical systems that obtain electric energy from a chemical reaction of oxygen and hydrogen. They are being applied in a wide range of power and applications, such as mobile, vehicular, power supply backup, etc. [5]–[12]. Fuel cells are a part of electronic power systems, which in the last years have become so complex that the system-level dynamic modeling and simulation have turned out to be very important to ensure proper performance and predict interactions Manuscript received June 10, 2010; revised September 14, 2010; accepted November 1, 2010. Date of current version August 5, 2011. This work was supported in part by the Spanish Ministry of Science and Innovation through the research project SAUCE under Grant DPI: 2009–12501. Recommended for publication by Associate Editor S. Choi. C. Fern´ andez, P. Zumel, V. Valdivia, M. Sanz, A. L´ azaro, and A. Barrado are with the Universidad Carlos III de Madrid, 28911 Leganes, Spain (e-mail: cristina.fernandez@uc3m.es). A. Fern´ andez-Herrero is with the Escuela T´ ecnica Superior de Ingenieros de Telecomunicaci´ on, Universidad Polit´ ecnica de Madrid, 28040 Madrid, Spain (e-mail: angelfh@die.upm.es). Digital Object Identifier 10.1109/TPEL.2010.2093538 Fig. 1. Simplified internal block diagram of the fuel-cell-based power supply. between regulated converters, instabilities due to load connec- tions, activation of protections, etc. [13]–[21]. Consequently, the designer requires knowing very well the fuel cell features to predict the dynamic and static behaviors of the overall system. A model of the power source, in this case the fuel cell, turns out to be extremely important for this system-level analysis [22]. Modeling a fuel cell is a difficult task due to its nonlinear na- ture: output voltage dependence on the working point; ambient temperature and fuel cell aging; existence of hysteretic effects; etc. [23]–[26]. Many of the already proposed models of fuel cells are based on the internal operation of the stack and the power plant, i.e., the physical-chemical processes produced inside the fuel cell [27]–[29]. In these cases, it is necessary to know many internal parameters of the fuel cell, which usually are difficult to determine. Moreover, considering commercial fuel cells, the internal structure is unknown, as well as some of the parameters of the internal processes. Consequently, it is very convenient to develop simple electrical models, independent of the internal parameters of the fuel cell, which can be characterized through simple electrical tests [30], [31]. Many commercial fuel cells include not only the fuel cell itself, but also a dc–dc converter in order to supply a regu- lated output voltage, despite aging and temperature effects of the fuel cell stack. The simplified schematic of this fuel-cell- based power supply is shown in Fig. 1, considering the fuel cell (stack, power plant, etc.) and a front-end dc–dc converter. Con- sequently, in this particular case, the system behavior and the model to be developed will be completely different to the previ- ously mentioned approaches, as the dc–dc converter completely modifies the behavior of the fuel cell. 0885-8993/$26.00 © 2011 IEEE