Bidirectional LCL-T Resonant DC–DC Converter for Priority Loads in Undersea Distribution Networks

In undersea long-distance dc power distribution networks, power converters are distributed over the length of the trunk cable carrying constant dc current. Under regular circumstances, these series-connected isolated dc–dc converters deliver power from the constant current feed to their respective loads while regulating their output voltage or current. However, in the event of a cable or other faults, the converters in the string lose power from the source, and hence bidirectional load(s) could be employed for continuing power delivery to the priority loads. In this article, it is shown how a dual active bridge (DAB) based LCL-T resonant converter can be designed to meet the requirements of driving such bidirectional loads to provide constant voltage to the load from a constant current source under regular operation and convert a voltage source to a constant current drive for the priority loads in the event of loss of power from the main feed. Steady-state modeling and analysis are furnished for the DAB LCL-T converter with three-angle modulation to derive all the dc and ac signals of the converter. Detailed design and modulation angle control are presented to minimize the overall VA rating of the resonant tank, transformer, and H-bridges. Experimental validation is provided for a prototype hardware system converting 1-A input current to 150-V output voltage in the forward direction and 1-A current drive from 150-V dc source in reverse power transfer, operating at 250-kHz switching frequency over a 50–500 W load range.