Analysis of DC-DC converter stability in fuel cell powered portable electronic systems

Fuel cell is an emerging power source for portable electronic systems. The steady state DC output of a fuel cell suffers from a 2 to I voltage variation from no load to full load. A boost type DC-DC converter is employed to generate a regulated output voltage. The internal impedance of the fuel cell consists of a membrane resistance R-m, and two parallel resistor/capacitor (R-p1-C-1; R-p2-C-2) elements related to the electron transport phenomena in the anode and cathode. It is shown that this internal impedance can influence the dynamic response of the DC-DC converter, often in a manner that degrades regulator performance. In this paper the effect of the fuel cell internal impedance on the dynamic performance of the power converter is fully analyzed. Design inequalities are reviewed in per-unit quantities to better understand the interaction between the converter, fuel cell and potential instability conditions. An approach to utilize supercapacitors to enhance stability and improve dynamics is explored. A method to calculate the value of the supercapacitor required is also detailed. Finally, experimental results obtained on a 30W PEM fuel cell system powering a DC-DC boost converter are discussed in detail.