On December 25th, the National Science and Technology Ministry’s 863 Plan major special project, the Nanao ±160 kV multi-end flexible DC demonstration project, officially began operations. This milestone marks a significant breakthrough for China Southern Power Grid, as it has successfully addressed global challenges in the control and protection of multi-terminal flexible DC transmission. It also highlights China's leadership in mastering the full range of core technologies for designing, testing, commissioning, and operating multi-terminal high-voltage direct current (HVDC) systems.
As a world-first achievement, the Nanao project serves as a model for integrating production, research, and learning in China’s power grid development. It represents a new technological advancement in international HVDC transmission, following the ±800kV UHV DC project. The South Australia multi-end flexible DC project is designed to enable long-distance, large-capacity power transmission, accommodate large-scale intermittent renewable energy sources, and support multiple DC feed-in points, offering safe and efficient solutions for modern grids.
Flexible DC transmission has become the preferred technology for integrating wind power into the grid. Compared to traditional HVDC, it can reduce investment by over 10% in certain cases with capacities ranging from 10,000 to 1 million kW. It is especially beneficial for offshore wind farms located far from shore. Experts predict that the global market for flexible DC transmission could exceed 100 billion yuan in the next decade.
Since 1997, ABB pioneered the world's first flexible DC transmission test project in Sweden. Since then, research on flexible HVDC has gained momentum globally, but progress has been slow. In 2006, the State Grid Corporation of China launched the "Framework for Key Technologies for Flexible HVDC Power Transmission Systems," initiating comprehensive research on this technology. This effort was nearly concurrent with Siemens' own developments.
Flexible DC technology is more complex than conventional DC, offering broader applications and greater technical advantages. Due to its strategic importance in energy transformation, it has attracted significant attention from developed countries like Europe and the United States. The complexity of the research is evident in the challenges faced during its development.
Multi-terminal flexible DC projects are more advanced than two-terminal systems. Xu Shuzheng, an engineer involved in the Nanao project, explained that two-terminal systems cannot connect multiple power sources or supply multiple loads simultaneously. However, multi-terminal systems can link several offshore wind farms and isolated islands to the mainland, forming a DC network. This approach reduces costs and minimizes the use of marine resources, allowing islands to meet their electricity needs while exporting surplus power to the mainland.
In simple terms, a flexible HVDC system acts like a smart valve in the existing power grid. It not only controls the flow of electrical energy but also isolates faults within the grid. It can quickly send or absorb energy based on grid requirements, providing flexibility, efficiency, and adaptability. Dr. He Zhiyuan from the China Academy of Electric Power emphasized that this technology plays a key role in optimizing grid distribution, enhancing stability, and improving the intelligence and controllability of modern power systems.
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