Fuel Cells are becoming a more attractive option for many remote power applications. One of the main well-known problems of a fuel cell system is related to its slow dynamic response: the fuel-cell system needs significant time to reach a new steady state condition after a load change. This slow dynamic response must be compensated when a quick load variation occurs. Notice that fuel cell dynamics, in terms of time-constants, may be in the order of seconds while electrical loads are usually in the millisecond range. Clearly this wide gap requires some kind of compensation to support all transient periods in which the fuel cell is adapting its state according to the load request. This problem has been analyzed and an active filter has been designed to compensate for the fast needs of the load while the fuel cell system adjusts the fuel flow to deliver the necessary energy. A general, seven-step design procedure has been implemented to design the active filter. Simulations in SIMULINK have been developed to obtain insight about several control strategies, as well as the behavior of the bi-directional converter. Finally, a hardware prototype for D35 PEM fuel cell has been built to verify the performance of the controls and validate the control strategies.