The document discusses key technologies for flexible HVDC that have been breakthroughs in China. It covers two areas: 1) System analysis and packaged design technology, including flexible HVDC access analysis, control and protection technology, and device parameter design. Breakthroughs have allowed optimized design of hybrid systems considering power stability and economics. 2) Core device key technologies, including converters, valve control equipment, and control/protection devices. Flexible HVDC will allow applications such as island power supply, new energy access, and multi-terminal systems to improve power grid stability and capacity.