Operating DC Circuit Breakers With MMC

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.