A soft-switching DC/DC converter to improve performance of a PEM fuel cell system

This paper presents a soft-switching dc/dc converter with ZCS to improve the performance of a PEM fuel cell as a power generation system. The first part of the paper presents an appropriate model for the fuel cell behavior based on analytical formulation of chemical processes behind fuel cell operation and the design of an equivalent and analogue electrical circuit describing the fuel cell operation. A method to extract the set of parameters needed for modeling and to optimize their values is also presented. For the validation of this approach experimental tests are performed with a commercial fuel cell system. The dynamics of the fuel cell model and the dependency on operation point are analyzed. In fact, the dynamics of the fuel cell must be taken in account for an accurate characterization of the fuel cell as a power generation unit. As a power generation unit the fuel cell must be integrated with a dc/dc converter able of controlling the system operating as a dc regulated voltage source and controlling the fuel cell MPPT, maximizing the generated energy. Authors purpose in the second part of the paper a topology this dc/dc converter based on resonant operation, which allows a soft-switching commutation, and consequently a high efficiency operation. Analysis on selected topology choice, the control and design of the converter are performed. Carried out results show that the controller needs to have a dynamic derivative component in order to ensure a good regulation of output voltage for different load conditions and disturbances on them. The overall system is validated using Matlab/Simulink models.