All simulations were performed using PSIM Version 6.0 from Powersim Inc. at the currents and voltages of the IRENE system. The following two diagrams show the circuits that were used to simulate the buck and boost integration circuits.
The next two figures show the simulated transient response of the two circuits. The last two figures show the steady-state response of the circuits. For both the buck and boost simulations the conversion was started at 1mS, to demonstrate the turn on time of the circuits. A 0.5 Ohm load was switched onto the battery bank after 3.5 mS. Both circuits behaved nearly identically. The buck FCIC has a slightly larger current ripple than the boost but both are well within tolerances of the fuel cell. Response times of both circuits were nearly identical; however, the boost fuel cell output current is not allowed to change instantaneously because it is filtered by an inductor. The buck output current is also filtered by the inductor and cannot change instantaneously; but the fuel cell after the buck output is not filtered by an inductor allowing the characteristic capacitance of the fuel cell (or any parallel capacitance) to supply current to the load. This property could be used to improve the response time with the buck circuit. The buck circuit would also have a superior turn on time and response to reduction in loads if the fuel cellís very slow response time along the polarization curve could be properly simulated.
Because the two circuits behaved so similarly in simulation, it was decided that the circuits should be built and the differences should be measured.