Large-scale access to new energy, flexible and direct technology is essential

The proposal of the global energy internet is based on many global problems such as resource shortage, environmental pollution, climate change and so on caused by the large-scale development and utilization of fossil energy, as well as the increasingly severe fossil energy dilemma facing human society. In the future, it is necessary to vigorously develop various renewable energy sources with wide distribution and great potential in the world to ensure a long-term stable supply of energy. Transforming energy production, allocation and consumption patterns, large-scale development and utilization of clean energy, will optimize the energy structure, improve energy efficiency, improve the ecological environment, and achieve clean development. As a high-quality, clean and efficient secondary energy, electric energy is one of the most important forms of energy in the future. Clean energy such as wind energy and solar energy will become the leading energy. There are many technologies required by the global energy internet, such as uhv ac/DC transmission technology and big data technology. Among them, the demand for flexible DC transmission technology is particularly urgent. At present, China's power generation mode has changed and the proportion of renewable energy has increased; In the future, the global energy internet can access renewable energy on a large scale. Therefore, flexible DC transmission technology is essential. In the future, DC power grid will efficiently connect new energy base and load center. DC power grid is a transmission and distribution system composed of multiple converters, DC transmission lines, DC circuit breakers, DC transformers and other equipment. DC power grid technology and equipment are important means to promote power grid reform and are hot spots in the international power field. Flexible DC transmission is a new generation of transmission technology, and it is also the transmission technology with the highest controllability and the best adaptability in the world. Flexible DC transmission technology can be used for large-scale renewable energy efficient reception, large cities and islands and other regional transmission networks and efficient transmission and distribution networks. Its advantages are: greatly reducing the number of converter stations; The converter station can transmit power independently and can flexibly switch the transmission state; It has redundancy and high reliability. It can be predicted that the DC power grid in the future will include multiple voltage levels and various power supply connections, forming an efficient energy allocation system connecting the global renewable energy base to the load center. Flexible DC has significant technical advantages in renewable energy grid connection, DC transmission network construction, weak system networking, large city power supply and other occasions. It does not need reactive power support equipment, can flexibly adjust the export voltage of the wind farm, ensure the continuous operation of the fan in the event of system failure, and improve system stability and energy utilization rate. The network composed of flexible DC can realize the intermittent output complementary of multiple wind farms and ensure the efficient collection, flexible transmission and decentralized absorption of wind energy in a large range. The power of the flexible DC transmission system is flexible and controllable, can realize the power receiving and power supply of the weak current network, and the transmission distance is not limited by the cable charging power, which is the best technical means to realize the collection and transmission of the offshore wind power base. After years of independent research and development, China has fully mastered the basic theory and key engineering technologies of flexible DC transmission. The Xiamen flexible DC transmission project currently under construction has a voltage level of 320 kV and a transmission capacity of 100 kilowatts. This shows that the voltage level and transmission capacity of the flexible DC transmission equipment independently designed and developed by China have already taken the lead in the world. In addition, China's self-developed flexible DC transmission high-end equipment has been recognized by the European market. The challenge of flexible DC transmission is to meet the demand of grid connection for the development of large-scale renewable energy bases in the global energy internet. It requires a power transmission method with longer transmission distance, higher performance, more flexibility and reliability, carry out a lot of technical research. -- UHV, super large capacity flexible DC converter technology and equipment. Break through the key technologies and equipment of flexible DC transmission of ± 800 kV, ± 1100 kV and above, and realize the grid connection of large-scale renewable energy bases with larger capacity, longer distance and higher efficiency. --Flexible DC transmission technology based on overhead lines. The rapid DC fault removal and system recovery technology in overhead line applications can remove the new converter topology with DC fault current and low loss, and overcome the reliability and economic optimization technology required in system capacity improvement. -- Research on basic theory and key technologies of DC power grid, especially power grid simulation technology including large-scale DC system and DC power grid protection technology. We need to build a simulation platform and a dynamic closed-loop test platform to meet the requirements of UHVDC, flexible DC and DC power grid equipment systems. --DC circuit breaker with higher voltage grade. With the increasing capacity and voltage level of global energy interconnection, DC circuit breakers need higher voltage level, larger breaking current and faster breaking speed, in the future, it is necessary to break through the key technologies of ± 800 kV to ± 1100 kV DC circuit breakers. -- New DC equipment such as high voltage DC converter and new power electronic device technology will realize the interconnection of ultra-high voltage, ultra-high voltage, high voltage, medium and low voltage DC systems in the future. It can be said that the global energy internet is the fundamental solution to the contradiction between human sustainable development and energy demand. The State Grid Corporation of China has successfully explored and practiced related technologies and equipment, laying a solid foundation for the construction of a global energy internet. The continuous improvement of technology and equipment will provide more powerful support for the construction of the global energy internet.