LCL DC/DC converter for DC grids

This paper proposes an LCL dc-dc converter concept which is capable of achieving very high stepping ratios with megawatt-level power transfers. The converter can find potential application in connecting high-power dc sources to high-voltage dc transmission including future dc transmission networks. This converter is based on two ac/dc insulated-gate bipolar transistor-based converters and an internal passive LCL circuit without internal ac transformers. The LCL circuit is designed to enable voltage stepping without any reactive power circulation and with potentially soft switching operation which minimizes the switching losses. The designed converter has the ability to achieve current regulation even under extreme external dc faults and, therefore, the converter can operate through dc faults. The switch utilization is better than similar topologies and losses are reasonably low. A dual-active-bridge transformer-based converter design is presented to compare with the proposed LCL converter. A detailed PSCAD model confirms conclusions using a 100-MW 20-kV/300 kV test system. An LCL 200-W 20-V/100-V dc/dc prototype converter is built to validate the proposed topology.