LAUSR

Modular multilevel converter (MMC) high-voltage direct current (HVdc) transmission is a promising method to integrate renewable energies. However, limiting the dc-link fault current and accelerating the fault-current clearance are critical issues for MMC-HVdc systems. In this article, we propose an air-core-transformer-based fault-current limiter (ACT-FCL) in cooperation with the dc circuit breaker to limit fault-current rising and decrease fault-clearing time. Compared with the conventional dc reactor, hybrid current-limiting circuit, current-commutation-based fault-current limiter (FCL), and magnetic coupling FCL, the ACT-FCL can increase the equivalent inductance during the dc fault stage to reduce the rising rate and peak of fault current. The ACT-FCL can also decrease the equivalent inductance during the fault-current-clearing stage to reduce the fault-clearing time. The simulations and laboratory experiments verify the effectiveness of the proposed ACT-FCL in the bidirectional HVdc systems. The ACT-FCL may be extended to more fields, such as dc microgrid and domestic dc transmission.