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In meshed High Voltage Direct Current (HVDC) grids, Current Flow Controllers (CFC) may be required to avoid bottlenecks or line overloads. The present paper proposes the concept of installing Distributed Current Flow Controllers (DCFCs) in different nodes of a meshed HVDC grid that are operated selectively. This concept allows to use simplified DCFC devices to prevent the overloads, with a reduction of the required CFC voltage compared with a single CFC in the grid. First, a methodology to investigate the effect of installing DCFCs in a generic meshed HVDC grid is presented. Several case studies with a 3-terminal and a 7-terminal meshed HVDC grids are conducted and the most suitable topology for the DCFCs is derived based on the previous analysis. Then, this work analyses the increase in the operational area brought by installing DCFCs in a 3-terminal HVDC grid and it is compared with the increase achieved by a Dual H-bridge CFC in one node. The CFC losses and voltage requirement depending on the location of the DCFCs are investigated. Finally, the operation and control of the DCFCs are designed and tested in a 3-terminal meshed HVDC grid using dynamic simulations. [ABSTRACT FROM AUTHOR]

This paper proposes a DC/DC current flow controller (CFC) for meshed high voltage direct current (HVDC) grids. The CFC has the advantage of a simplified structure that allows us to use the minimum number of switches when unidirectional current flows through the DC lines are expected. An extended CFC topology that is able to operate with all possible current flows is also presented. Then, the operating principle of the CFC is discussed and its structure is compared with a dual H-bridge analyzing advantages and disadvantages. This paper also details the applied modulation strategy and the control methodology. Finally, a five-terminal meshed HVDC grid is used to validate the CFC by means of simulations. [ABSTRACT FROM PUBLISHER]

Two key problems in meshed high-voltage direct current (HVDC) transmission grids are managing line power flows and protection against dc faults. Current flow controllers (CFCs) will be required to balance cable currents in meshed dc grids, in order to prevent individual line power capacity limits restricting overall power flow in the grid. Direct current circuit breakers (DCCBs) will be also required to protect HVDC grids from dc faults. This paper demonstrates that the current flow controller functionality can be added into a hybrid CB's design. This paper proposes integrating an interline CFC into the load commutation switch (LCS) of a hybrid DCCB. The integrated design LCS/CFC is analyzed and a state-space model is derived. The control of the CFC is designed and the performance of the LCS/CFC during normal operation is verified by means of MATLAB Simulink and PSCAD simulations. A comparison of the integrated LCS/CFC and the separate design is given. The case studies show a reduction in total power losses, and improved protection operation times can be achieved. [ABSTRACT FROM PUBLISHER]

• An interline current flow controller (CFC) is able to reduce the operating costs of hybrid AC/DC meshed grids by alleviating the congestions within the DC lines. • The CFC is modelled taking into account its restrictions regarding the current unidirectionality and voltage rating. • The best connection arrangement of the CFC to the grid is assessed based on the current unidirectionality of the device. • The case studies address the impact of the CFC in the operating costs under two different scenarios: on one hand, considering normal operation without line overloads and on the other hand, considering an overload in one of the DC lines. This paper is meant to show that an interline current flow controller (CFC) is able to reduce the operating costs of hybrid AC/DC meshed grids by alleviating the congestion within the DC lines. The work considers a unidirectional DC/DC CFC with a simple structure and its average model is introduced into the mathematical formulation of the Optimal Power Flow (OPF) problem of an hybrid AC/DC meshed grid, which also considers the losses of the Voltage Source Converters (VSC). The CFC restrictions and the different connection arrangements of the device into the AC/DC grid are also included in the model and show an important effect on the OPF solution. The case studies are conducted in a 5-terminal AC/DC meshed grid and point out that the CFC has a reduced capability to reduce the operating costs of the system if there are no overloads in the DC lines. However, when the power limit of one of the lines is reached, the CFC can redirect part of the DC current and, therefore, reduce the operating costs compared to the case without CFC. [ABSTRACT FROM AUTHOR]