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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 varies with respect to current demand. Therefore, it requires a dc-dc converter for a regulated output voltage. The dc-dc converter should be designed considering both the impact of the fuel cell and load disturbances to achieve wide range voltage regulation. This paper analyzes the impact of the DBFC impedance on the dc-dc converter. Based on the converter's small signal model including the DBFC impedance, the boost converter was evaluated. Impacts of the voltage and current control loops on the boost converter were investigated. Improved response time and stability of the DBFC dc-dc converter were 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 further improvement of the dc-dc converter response time. A prototype 20-W dc-dc converter was built and tested to show the response improvement of the proposed analysis and control scheme.
Date of Publication: Aug. 2012