Isolated Multilevel HVDC Converter for Off-shore DC Distribution

This paper proposes a new multilevel converter structure to add the benefits of higher power density and robustness in future DC subsea electric transmission and distribution systems. To reduce reactive power consumption impacts without a significant increase in the footprint, this paper also proposes a new HVDC subsea configuration. In order to have medium frequency switching with high current capability, a SiC-MOSFET based 6 MW, 36/6 kV modular stacked DC/DC converter is proposed and analyzed to operate on the seabed. The proposed structure renders the system with fault tolerance and capability to operate in a degraded mode. Compared to existent HVAC subsea configurations, eliminating huge line transformer (LT) on the seabed results in reducing the overall system size. Real-time simulations were done on Typhoon HIL and the results verify the validity and feasibility of the proposed DC/DC structure and control system.