A current flow control apparatus for meshed multi-terminal DC grids

The absence of a reliable current flow control method is one of the main problems that need to be solved to allow the realization of multi terminal high-voltage direct current (HVDC) transmission. Industry leaders and researchers have introduced a few methods of power flow control based on either the control of converter station or the connection of new power electronic equipment to the grid. This paper presents the operation and control of an extended three-port IGBT based current flow control (CFC) device suitable for multi terminal HVDC systems. Features and functionalities of the proposed controller including the balancing of cable currents, limiting the magnitude of cable current and current nulling are demonstrated. The three-port CFC is simulated using PSCAD/EMTDC, network simulation software to evaluate its steady state and dynamic performance. Simulation studies explore the fast dynamic response and the results show that the CFC studied may have a significant role to play in the control a of power flows in multi terminal high voltage DC systems.