Compact multi-modular design of high power DC/DC resonant converters for offshore wind energy HVDC transmission

Besides research on reliability, efficiency and grid impact challenges imposed by the wind energy industry, research on compact design of multi-modular interfacing DC/DC converters is growing rapidly. This paper addresses the application of multi-modular resonant-type DC/DC converters for offshore wind high power HVDC transmission systems. The attractive feature about resonant converters is their soft switching characteristics which enables higher frequency operation and hereby reduced converter footprint. The paper focuses on one important aspect leading to increased power density; the output filter design. New analytical expressions are derived for filter ripple content in DC/DC resonant converters. This has not been investigated previously. Further mathematical relations are derived for multi-module interleaved operation of DC/DC resonant converters with both series and parallel connections of output filter. Results are demonstrated to validate the derived design equations highlighting the advantage of interleaving with multi-modular structures in achieving highly compact designs.