With the advancement of power electronics technology and the increasing integration of microgrids into the power grid, flexible DC distribution networks are becoming a research focus worldwide due to their advantages, such as lower line construction costs, reduced power loss, higher power supply reliability, and lower microgrid integration costs.

To conduct in-depth research on flexible DC distribution technology, Shenzhen Power Supply Bureau Co., Ltd. took the lead, collaborating with institutions like Tsinghua University and Zhejiang University to undertake the research for the Ministry of Science and Technology's 863 Program project—"Research and Application of Key Technologies for Smart Distribution Based on Flexible DC." This project addresses prominent issues in urban AC distribution networks, such as power quality problems and the rapid development of distributed generation. It investigates the use of flexible DC technology in urban distribution networks, including dedicated power supply to specific users and using voltage source converters (VSC) to improve AC distribution power quality. Additionally, it explores technical solutions like directly connecting distributed generation and energy storage devices on the DC side to supply DC loads directly. These approaches aim to solve several critical problems in urban distribution networks and expand the application areas of flexible DC technology.

KeLiang utilized the RT-LAB real-time simulator to establish a hardware-in-the-loop (HIL) research and testing platform for a flexible DC distribution control and protection system. This platform played a crucial role in the project, assisting Shenzhen Power Supply Bureau in successfully completing the first-phase simulation experiments for the flexible DC distribution network.

With the development of power electronics technology and the continuous advancement of renewable energy integration technologies, supportive policies have propelled the rapid growth of the wind power industry. Series capacitor compensation technology reduces line losses, increases transmission capacity, and enhances system stability. It is a mature and cost-effective solution for long-distance power transmission and has become a primary measure for delivering large-scale wind farm power to the grid.

Since the Gezhouba–Nanqiao Project, the number of HVDC transmission lines, converter stations, and transmission distances in China’s highvoltage direct current (HVDC) power transmission systems have increased sharply. Accordingly, the overvoltage fault rate in AC/DC transmission systems has also risen. Especially in regions such as Hubei Province, Shanghai, and Guangdong Province, which host multiple HVDC systems, the complexity of the AC/DC grid results in more intricate faultcausing factors. However, the simulation of largescale AC/DC grids has mainly been applied to the development and verification of control strategies and power flow analysis. During modeling, extensive equivalent processing is often adopted, with many primary equipment simplified or even omitted, making it impossible to obtain actual overvoltage conditions on the equipment.

With the development and commissioning of hydropower in western Yunnan Province, the main power transmission grid for the west-to-east power transmission in the Southern Power Grid during the 12th Five-Year Plan period will form a configuration of eight AC and eight DC lines. The transmission distance between the eastern and western AC grids is increasing, and the grid structure with hybrid AC/DC operation is becoming more complex. Implementing asynchronous grid interconnection between Yunnan Grid and the Southern Power Grid can effectively mitigate grid security and stability issues caused by AC/DC power transfer, thereby improving power supply reliability.