Recently, the flexible DC project at the Yunnan Mile Wind Farm, invested and constructed by the Three Gorges Group, was successfully put into operation. This project was implemented jointly by the Three Gorges Group, Tsinghua University, the South China Power Grid Research Institute, Xidian Power Systems, XJ Electric, and NARI Group Corporation. It is part of the National Development and Reform Commission’s key technological research and development project. The project is the world’s first to use IGCT devices in a new energy flexible DC project and the world’s first to use 6.5kV power semiconductor devices in a flexible DC project. Following significant breakthroughs in IGCT flexible DC technology such as the Zhuhai DC distribution, Dongguan medium-voltage interconnection, and Ulanqab source-network-load-storage projects, this marks another key advancement, which will strongly promote the large-scale application of IGCT flexible DC technology in scenarios like desert, offshore wind power, and urban power grids.

Flexible DC technology is a strategic core technology supporting China’s “dual carbon” goals. The IGBT flexible DC technology route was first proposed in Europe and the United States and has been widely applied globally. In recent years, the voltage and capacity of flexible DC projects have been rapidly improving, particularly with China accelerating the implementation of its dual carbon goals, which has led to a hundredfold increase in the voltage and capacity of domestic flexible DC projects.

China has been the first to propose the IGCT flexible DC technology route internationally. Since IGCT devices are low-frequency, large-capacity devices, they are naturally suitable for flexible DC transmission applications. In recent years, the technical bottlenecks of IGCT flexible DC converter valves have gradually been overcome. Compared to existing flexible DC projects, the use of larger capacity IGCT devices, such as 6.5kV and 8kV, will reduce the cost, volume, and loss of converter valves by over 30%. As whole wafer devices, IGCT devices’ surge current tolerance and inherent explosion-proof characteristics make the flexible DC converter valves more resilient to transient faults and have stronger active support capabilities.

Currently, manufacturers such as Xidian, XJ Electric, NARI Group, TBEA, and Rongxin Huike have launched IGCT converter valve products, laying an industrial foundation for the large-scale application of IGCT flexible HVDC transmission. With the mature application of four-inch IGCT devices in flexible DC projects, larger capacity IGCT devices based on six-inch chips, such as 4.5kV/12.5kA (current 6.25kA) and 6.5kV/10kA (current 5kA), will soon be launched. The advantages of the IGCT flexible DC technology route—low cost, low loss, high reliability, and intrinsic safety—will become more prominent.

Figure 1: IGCT Whole Wafer Chip and Device

The Yunnan Mile project is located in Shiwan Village, Hongxi Town, Mile City, with an altitude of 2500 meters. The IGCT converter valve components are fully aligned with the offshore wind power flexible HVDC transmission projects and use 288 domestically produced 6.5kV/4kA (current 2kA) IGCT-Plus devices, which is a comprehensive engineering test of IGCT devices and converter valve technology. During the commissioning phase, the project was rigorously tested against offshore wind power projects, undergoing over 100 steady-state, transient, and protection function tests. The project showed reliability exceeding existing technologies and entered the official operation phase after a continuous 168-hour trial operation, passing on December 24, 2024.

This project will provide valuable operational experience for the future application of IGCT flexible DC converter valves in desert areas, offshore wind power, urban power grids, and other fields, driving China’s leadership in the next-generation flexible DC technology route.

Figure 2: Three Gorges Group Yunnan Mile IGCT Flexible DC Converter Station

Figure 3: IGCT Converter Valve Hall

Figure 4: IGCT Flexible DC Rectifier and Inverter Valves