Design Concepts for Medium Voltage DC Networks supplying the Future Circular Collider (FCC)

In the frame of the feasibility studies for the construction of the Future Circular Collider (FCC), a new particle accelerator of 90 km of circumference under design, the use of Medium Voltage DC Grids (MVDC) for distribution has attracted attention considering their potential advantages in terms of transmission losses, power flow control and energy storage integration. Traditionally, the main concerns of the DC networks have been their reliability and robustness. In this sense, a DC network where the AC/DC and DC/DC converters are based on the MMC (Modular Multi-level Converter) could offer advantages, thanks to the modularity, the easy maintenance, the possibility of integrating distributed energy storage and the redundancy. However, there is little knowledge about how a network for such a large power should be implemented. Accordingly, this work describes the design aspects of a Medium Voltage DC network based on the MMC topology for the FCC, focusing on the specificities of non-isolated step-down DC/DC converters and examining how their control should be implemented to power a magnet chain and recover its energy. Additionally, a method to mitigate the impact of DC pole-to-pole and pole-to-ground faults is proposed.