I. Introduction
Significant challenges to the development of multiterminal HVDC transmission systems are protection during a dc fault and postfault operation. In the event of a dc short circuit, high current flows through the freewheeling diodes in half-bridge (HB) modular multilevel converters (HB-MMCs), which are currently the preferred HVDC converter configuration, from the ac grid to the dc side. The low impedance of the short-circuit path leads to a steep rise in fault current which may cause serious damage to the converters or a complete shutdown of the entire HVDC network [1]–[3].