A DC current flow controller for meshed modular multilevel converter multiterminal HVDC grids

This paper proposes the design of a novel DC current flow controller (CFC) and evaluates the control performance of balancing and regulating the DC branch currents using the DC CFC in a meshed multi-terminal HVDC (MTDC) grid. The DC CFC consists of two identical full bridge DC-DC converters with the capacitors of the two converters being connected in parallel. The scalability of the DC CFC is easily achievable due to the identical bridge converter topology; the cost of this DC CFC is also relatively low due to its simple physical structure and low voltage ratings. The control performance of the DC CFC is tested on a meshed 3-terminal (3-T) HVDC grid, which is based on modular multilevel converters (MMC). The DC branch current control in the meshed MTDC grid is achieved using the proposed control strategy of the DC CFC, and is verified through case studies on the real-time digital simulator (RTDS).