An overview of DC-DC converter topologies for fuel cell-ultracapacitor hybrid distribution system

DC microgrids have recently attracted research interest. A DC microgrid is composed of different dispatchable and non-dispatchable power generators and energy buffers, such as fuel cells and ultracapacitors, which are employed to provide the steady-state and transient power demanded by the load. To interface these generation resources to a common DC bus-bar, different configurations of power electronic converters have been proposed in the literature. For the fuel cell, a unidirectional DC-DC converter is utilised, for the ultracapacitor, however, a bidirectional DC-DC converter is needed to maintain the state-of-the-charge of the ultracapacitor. The overall efficiency of the microgrid will depend on the efficiency of these converters. High efficiency and low cost converters are very important to obtain a cost-effective solution. In addition, the power electronics converters must be chosen in respect to the characteristics of these generation resources. In this regard, this paper introduces an overview on different of DC-DC converter topologies and investigates their applicability for fuel cell and ultracapacitor electricity generators based on the electrical output characteristics of these resources. Thus, the fuel cell and ultracapacitor characteristics and properties are presented in this paper. A number of configurations that can be employed to interface the ultracapacitor with the fuel cell generator forming part of a DC bus microgrid are also presented.