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Flexible direct current (DC) grids face a serious challenge in terms of rapidly isolating DC faults. A DC circuit breaker is an effective solution for DC fault isolation. To improve the fault-isolation and reclosing capability of flexible DC systems, a new high voltage direct current (HVDC) circuit breaker topology with adaptive reclosing capability is proposed in this paper. The topology of the circuit breaker is a T-shaped structure, which has the ability to break the current in both directions and effectively reduce the cost of components. Meanwhile, after the fault is cleared, the circuit breaker is controlled to inject a voltage signal into the line. Based on this, to prevent the circuit breaker reclosing in the event of a permanent fault from having an impact on the system, a method for fault identification based on Euclidean distance that uses the voltage signal to identify the fault properties is proposed. Finally, the performance of the circuit breaker is simulated and verified by PSCAD/EMTDC simulation software, and compared with the typical existing circuit breakers to verify the effectiveness of the circuit breaker and reclosing scheme. [ABSTRACT FROM AUTHOR]

DC circuit breaker is the key equipment to deal with the interruption of short-circuit current. Compared with the mechanical switch, the solid circuit breaker and the hybrid circuit breaker using the semiconductor device to interrupt the short-circuit current exhibit superiorities in response duration and arc-less characteristics. Massive power devices controlled by corresponding gate drivers which make the semiconductors-based dc circuit breaker bulky and costly are required to withstand the high dc-bus voltage. In this article, the master−slave concept based modular circuit breaker is proposed to simplify the gate driver topology. Only one single gate driver is required to control highly compact modular submodules consisting of power devices, passive components, and diodes. Moreover, the proposed topology can be easily implemented with high flexibility and low cost. Specifically, the gate control function and voltage equalization for series-connected devices can be realized reliably. The master−slave concept and operation principle of the proposed topology are elaborated and the effectiveness has been demonstrated by both simulation and experimental test. [ABSTRACT FROM AUTHOR]

To improve the reliability of power supply, reclosing schemes are required after transient faults, which commonly occur in overhead line based high voltage DC (HVDC) systems. However, in the event of permanent faults, the auto-reclosing scheme may cause a severe strike. To avoid the severe impacts caused by permanent faults, the fault type should be discriminated before activating the reclosing scheme. Therefore, an adaptive reclosing scheme based on phase characteristics is proposed in this paper. Firstly, the modulation of a periodic voltage by actively controlling the hybrid DC circuit breaker (DCCB) is introduced. Then, a cascaded π equivalent model and its decoupling algorithm are presented to analyze the frequency-domain characteristics of the measured impedance of the coupled overhead lines. From the frequency-domain characteristics, the frequency of the periodic detecting voltage is determined to analyze the phase features of the measured impedance at primary frequency. The permanent or transient faults can thus be accurately identified by using these different phase characteristics, with negligible influence on the healthy lines. In addition, the proposed scheme is robust to various fault resistances, leading to improved reliability. The effectiveness of the proposed scheme is verified in PSCAD/EMTDC. [ABSTRACT FROM AUTHOR]