Analysis and Design of an LCL–T Resonant DC–DC Converter for Underwater Power Supply

Constant dc current distribution is preferred over dc voltage distribution in under-sea power distribution networks due to ruggedness over long distance cable impedance and faults. DC--DC converters with constant current input have different design constraints from their constant voltage input counterparts. Considering these constraints, an LCL-T resonant network based isolated dc-dc converter is analyzed in this article to operate as a load independent constant voltage source when supplied with constant dc current at the input. It is shown that use of passive rectification for this converter can limit converter operating load range, which is overcome through use of an active rectifier. A three-angle modulation strategy for a dual-active bridge (DAB) based LCL-T resonant converter is presented to achieve minimum VA rating for tank elements, transformer and the bridges. Detailed analysis and design method are provided for a converter regulating its output voltage at 150 V fed from a 1 A source, operating with 250 kHz switching frequency, over the load range of 50 to 500 W. Experimental results from prototype hardware are presented to show the accuracy of the analysis.