Voltage Fed and Current Fed Full Bridge Converter for the Use in Three Phase Grid Connected Fuel Cell Systems

Fuel cells for low or medium power deliver comparatively low voltages compared to the mains voltage at high currents. A high dc-link voltage is needed to feed in electrical energy from fuel cells to the mains via a voltage source inverter. Several well known DC/DC converters can be used to transform the varying fuel cell voltage to the requested amplitude of the dc-link-voltage. Besides transformerless converters like the boost converter, converters with high frequency transformers can be used. In the considered higher power range, the full-bridge converter circuit is the appropriate solution. Depending on their input circuit, the converters are classified between voltage fed and current fed full bridge converter. In this paper, full bridge converters of the voltage type and of the current type as active front end for fuel cell inverters in the power range of 20 kW and higher are analysed and compared to each other. The focus is set on the operating behavior, the system complexity and the efficiency of the different converters