Integrated HVDC Circuit Breakers With Current Flow Control Capability

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.