Novel grid-forming control for black start restoration using MMC-HVdc systems

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Fazel Darbandi, Arash
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System-wide power outages are fortunately very rare. However, when they do occur, they can catastrophically affect tens or even hundreds of millions of customers. To minimize this impact, a “black start” power restoration, must be achieved in the minimum possible time. Challenges during restoration can include overvoltage or overcurrent in equipment, and the frequency transitioning outside the acceptable range. Though the ac transmission is at present the method of choice for black start restoration, HVdc transmission, where available, is proving to be an attractive alternative. Earlier research has investigated connections to simplified systems. Real world systems can be more complex and have regions that are completely blacked out and remote islands of generation which have been started earlier, or were never blacked out. This thesis considers methods for restarting in such networks, and presents a novel grid-forming approach that allows the converter to be synchronized to a local generation with synchronous generators, inverter-based generation and/or an external energized network during the restoration process. The method provides fault ride-through capability during black start restoration and operation in a very weak system. This thesis demonstrates the key attributes and effectiveness of the proposed methods through a series of Electromagnetic Transient (EMT) simulation study in both steady-state and dynamic conditions.
MMC, grid-forming, black start restoration, HVdc