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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]

High voltage direct current (HVDC) grids may be protected from dc faults through the application of HVDC circuit breakers. Recent advances in dc circuit breaker technologies may allow faults in the dc grid to be cleared without a permanent loss of power to the connected ac grids. The requirements for the protection have yet to be fully defined; especially where half-bridge modular multilevel converter (MMC) controls are concerned. This paper investigates integrating dc circuit breakers with half-bridge MMC converters, specifically looking to at how to recover from a pole-to-pole fault. The fault response of the converter to a fault is analyzed in depth. This analysis highlights key stages in the converter response to a dc fault, allowing the MMC fault currents to be predicted. This analysis is then verified in PSCAD simulations and the power flow recovery is shown. The converter controls are investigated, improvements made to the power flow recovery, and the need for arm current controllers highlighted. [ABSTRACT FROM PUBLISHER]

Circuit breakers for high voltage direct current (HVDC) applications are seen as a required technological step in the development of HVDC grids. The development of several new HVDC circuit breaker prototypes indicate that this step may be achieved in the years to come. In order to facilitate the installation of HVDC circuit breakers, appropriate standards and tests need to be developed. These tests and standards must ensure that the technology is capable of functioning as required. In cases where direct testing cannot be carried out, a synthetic test circuit is used to recreate the conditions of the power system. Testing envelopes which encapsulate the fault currents for two types of voltage source converter under fault conditions are analytically derived in this study and compared with simulations. Testing envelopes allow specifications for HVDC breaker test circuits to be defined. Discussion is also given to the worst type of fault and protection operation time estimates. [ABSTRACT FROM AUTHOR]