A Novel Protection Scheme without DC Circuit Breaker for VSC-Based DC Grids

Dc grid is extremely promising in the future development of electrical power systems and has attracted research interests due to its distinct advantages. In dc grids, voltage source converters (VSCs) are widely used as rectifiers or inverters for electrical power conversion. However, the VSC is vulnerable to the high discharge current from the dc-link capacitor caused by the dc-cable short-circuit fault, which severely threatens the security of system operation. The high discharge current can be eliminated by a dc circuit breaker (CB), but high-capacity dc CBs are not well developed and cost a lot, which constrains the development of the VSC-based dc grid. In this paper, based on the analysis of the dc-cable short-circuit fault in the VSC-based dc grid, a novel fault protection scheme without dc CBs is proposed. With the cooperation of a high-speed switch and an ac CB separately installed in front of and behind the dc-link capacitor, the dc cable where the short-circuit fault occurs can be quickly and securely cut off. The process for the proposed protection scheme to cut off the fault current is divided into two steps and the actuation time of the high-speed switch and the ac CB is provided. The validity and the superiority of the proposed protection scheme are confirmed by simulation results.