Dynamic response analysis of dc-dc converter with supercapacitor for direct borohydride fuel cell power conditioning system

The direct borohydride fuel cell (DBFC) is directly fed sodium borohydride as a fuel and hydrogen peroxide as an oxidant. The output voltage of the DBFC drops with respect to current demand. Therefore, it requires a dc-dc converter for a regulated voltage. The dc dc converter should be designed considering both the impact of the fuel cell and load disturbances to achieve a wide range voltage response. This paper analyzes the impact on the dc-dc converter due to the DBFC impedance. Based on the small signal model with the DBFC impedance, the boost converter was evaluated. Impacts of the voltage and current control loops on the boost converter were investigated. Improved speed and stability of the DBFC dc-dc converter was observed by adding a supercapacitor between the DBFC and the dc-dc converter. Finally, two converter controllers, a nonlinear feedforward controller and a state feedback controller are proposed for the further improvement of the dc-dc converter response time. A prototype 20W dc-dc converter was built and tested to show the response improvement of the proposed analysis and control scheme.