An Integrated Control and Protection Scheme to Inhibit Blackouts Caused by Cascading Fault in Large-Scale Hybrid AC/DC Power Grids

Cascading fault is one of the serious challenges in hybrid ac/dc power grids, which initiates from a dc or a severe inverter ac fault and leads to a blackout in the inverter ac side. However, owing to the fact that dc faults do not cause commutation failure, the existing commutation failure inhibition approaches are not effective in the prevention of cascading faults caused by dc fault. In order to resolve the challenge, this paper first develops a hybrid ac/dc relay (HADR) based on the positive-sequence component, which can detect and locate the fault events in hybrid ac/dc networks. Subsequently, an integrated control and protection scheme is presented using the developed HADR and a thyristor-controlled series compensator. The proposed scheme has the ability to prevent the blackouts caused by cascading fault using transmission capacity enhancement of the ac line and load-shedding in the inverter ac system. The salient feature of the proposed scheme is that it provides a very economical way to compensate for the loss of power caused by HVdc line outage. In addition, it does not require communications among the relays. The practical performance and feasibility of the proposed scheme is validated by laboratory testing, using the real-time Opal-RT hardware prototyping platform. The experimental results demonstrate that the proposed strategy can effectively inhibit the blackouts caused by cascading fault in hybrid ac/dc networks.