A Multiterminal Active Resonance Circuit Breaker for Modular Multilevel Converter Based DC Grid

With the growing demands for flexible power supply, dc grids outstand with the advantages of simple structure, high efficiency and large capacity. However, the dc fault protection is one of the most critical issues in restriction of dc grids. The fault current interruption time of the existing dc circuit breakers (DCCBs) rises along with the increase of fault distance and a vast amount of energy would be dissipated in the DCCBs. To overcome these problems, this brief proposes a multiterminal active resonance circuit breaker (MAR-CB), which contains a converter-side breaker (CSB) for each modular multilevel converter (MMC) as well as multiple line-side breakers (LSBs) and ultra-fast disconnectors (UFDs) for dc lines. During the dc fault interruption, a reverse current is generated by the resonance of the CSB and LSB to extinguish the UFD arc. Afterwards, the converter-side current is interrupted by the CSB, while the line-side current is interrupted by the LSB. The proposed MAR-CB can handle the dc fault with the advantages of short interruption time, reduced energy dissipation, low conduction loss and absence of additional pre-charge dc source. A four terminal dc grid is simulated with PSCAD/EMTDC to verify the effectiveness of the MAR-CB and a down-scale prototype experimentally confirms the performance of fault interruption.