In Shanghai, a mega city with a permanent population of over 20 million, the electricity safety of thousands of households is directly related to the Gezhouba Nanqiao (hereinafter referred to as "Genan") DC transmission project. The electricity generated from the Gezhouba Hydropower Station in Hubei Province spans over a thousand kilometers and is converted from direct current to alternating current through a high-voltage direct current converter valve at the ± 500 kV Nanqiao Converter Station located in Nanqiao Town, Fengxian District, Shanghai. More than 5 billion kilowatt hours of electricity are imported into Shanghai every year, lighting up the lights of every household. Therefore, high-voltage DC converter valves are known as the "heart" of DC transmission engineering. This summer, the Nanqiao converter station once again passed the peak summer "big test". Unlike in previous years, through the Ge'nan DC transmission renovation project, the Nanqiao converter station has just undergone a successful heart replacement surgery. On September 18th, Yang Jun, the technical backbone of State Grid Smart Grid Research Institute Co., Ltd. (hereinafter referred to as "Intelligent Research Institute"), which was responsible for the renovation of the converter valve, introduced to the reporter of Science and Technology Daily that the renovation project used the world's first controllable commutation converter valve. The team has been working hard for more than ten years to create this world first. Shanghai, located at the mouth of the Yangtze River, is one of the regions with the strongest economic vitality in China, and its strong demand for electricity is self-evident. Heading upstream along the Yangtze River, China's unique three-level stepped terrain has created rich hydropower resources in the western region, which has nurtured the West to East Power Transmission Project, weaving an unprecedented huge power grid. The Ge'nan DC transmission project is an important link in this network. In 1983, with the first large-scale water conservancy hub on the main stream of the Yangtze River in China, the Gezhouba Hydropower Station generator units were successively put into operation for power generation. As a demonstration project for cross regional power grids, the construction of the Genan DC transmission project began. In 1989, the project was put into operation and became the first ± 500 kV ultra-high voltage direct current transmission line in China. This project is like a power transmission highway - the water from the Three Gorges starts from Yichang, Hubei and takes about 16 days to reach Shanghai, while the hydropower from the Three Gorges only takes 0.0038 seconds to reach Shanghai, becoming an important channel for external electricity to enter Shanghai. With the increase of years, equipment such as converter valves are severely aging, posing risks to the safety and stability of system operation. The renovation of the Ge'nan DC transmission project has been put on the agenda by State Grid Corporation of China. What kind of high-voltage direct current transmission converter valve to use has become a top priority. At the beginning of the construction of the Ge'nan DC transmission project, China's power industry was still relatively backward, and traditional high-voltage DC transmission converter valves could only be imported from abroad. The converter valve uses a thyristor switching element, but the thyristor has an inherent "semi control" characteristic, which can only be controlled on and off, and can easily lead to a large loss of system transmission power, or even drop to zero. This phenomenon is called "commutation failure". Since the birth of high-voltage direct current transmission technology in 1954, the "stubborn illness" brought about by this "mother child" has been troubling the academic and engineering communities. For Shanghai, the need to completely solve the problem of commutation failure is particularly urgent. At that time, Shanghai had already built four DC converter stations in a limited area, and the problem of multiple DC converter failures at the same time was prominent. Traditional equipment could no longer meet the requirements for safe and stable operation of the system. The problem of phase change failure has become a constraint on the large-scale energy supply to China's East China and other power consumption areas