The instability induced by high voltage direct current (HVdc) contingencies is challenging operation of ac/dc synchronous system. The asynchronization of ac/dc synchronous system can be a promising strategy for this concern which, however, is lack of practical applications. This paper analyzed the necessity of replacing the existing parallel ac/dc interconnection by pure dc interconnection in China Southern Power Grid (CSG), Guangzhou, China. A comprehensive solution is proposed to mitigate the risk of frequency instability in a small power grid with large amount of power sending out by HVdcs. Meanwhile, the strategy that combines the use of line-commuted converter-HVdc, voltage source converter-HVdc, and flexible ac transmission system is proposed to ensure the secure operation of HVdc feeding in weak ac system. The principle and application of asynchronous operation of CSG provide a reference for other grid development.
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Zhou et al. (2018) studied this question.