Shanghai Nanhui flexible DC transmission project, Zhoushan ± 200 kV five-terminal flexible DC transmission technology demonstration project, Xiamen ± 320 kV flexible DC transmission technology demonstration project, Zhangbei renewable energy ± 500 kV flexible DC grid demonstration project ......All above projects that lead innovation and science and technology are of great significance. They significantly improve the overall science and technology content of the power grid and upgrade and leapfrog the traditional power grid to a safe, efficient, economical and clean modern interactive power grid,which provides strong protection for economic construction, social development and livelihood improvements.
The flexible DC transmission technology is a new generation of DC transmission technology based on insulated gate bipolar transistor (IGBT), which has the characteristics of fast response, good controllability, flexible operation mode and small coverage of area with the same capacity. It is the most controllable and adaptable transmission technology in the world at present. It has technical advantages when applied in large-scale renewable energy grid interconnection, AC system interconnection, DC network construction, weak system interconnection, urban distribution grid capacity transformation, island power supply and other occasions.
However, the flexibleDC transmission technology is strictly confidential in the international community.Facing the difficulties and challenges,SGCC insisted on independent innovation and continued to exert its utmost efforts toward the most advanced, the most urgent, the most challenging and the most promising high-end technologies in the field of electric power. SGCC starts from scratch the R & D and engineering applications , and will climb to a higher technological peak.
Independent innovation leads the technological development
The flexible DC transmission technology can improve the stability of the power system, enhance the system's ability to absorb clean energy and improve the reliability and flexibility of the distribution network. More importantly, HVDC can carry clean energy such as wind and solar power from multiple sites to reach the load centers of multiple cities through large-capacity and long-distance power transmission channels, and provide effective solutions in the fields of new energy network and large cities power supply and so on.
The importance of flexible DC transmission technology for power grid development goes without saying. However, conquering the peak of flexible DC transmission technology is not easy.
All beginnings are hard. Due to the late start of the research on the technology of flexible DC transmission in our country, combined with the international strict secrecy of the technology, there is no publication of a drawing or a photo, nor publication of academic articles in journals. The related materials are extremely scarce.
In May 2006, Beijing was in early summer. State Grid Corporation of China organized the domestic authoritative experts to hold a seminar on "The Key Technology Framework of Flexible DC Transmission Systems". The meeting systematically proposed the overall planning of the research on flexible DC transmission technology, the major science and technology project of flexible DC transmission started in an all-round way, and the prelude to the development of flexible DC transmission technology in China formally played.
In line with the scientific attitude to deepen and solid the foundation , the State Grid Corporation through the mechanism analysis, formula derivation, model building and simulation verification repeated verification, created China's flexible HVDC basic technology system at the end of 2007. This is the first time that China has conducted systematic and comprehensive research on the theory of flexible DC transmission technology.
At the end of the same year, State Grid Corporation of China conducted a demonstration project of flexible DC transmission technology in Shanghai Nanhui Wind Farm and started the exploration and attempt of a suitable rout in high-voltage and large-capacity flexible DC transmission technology. At that time, the two-level and three-level technology adopted by ABB Company had the problems of high operating loss and difficult capacity expansion. The modular multi-level converter topology proposed by German scholars was still in the stage of concept development and the technology application in the world was in blank situation. Facing on the difficulties, State Grid Corporation in April 2009 innovatively proposed the idea of use modular multi-level converter topology . Meanwhile, multinational companies such as Siemens and ABB started the exploration of high-voltage and large-capacity flexible HVDC technology at about the same time. Since then, our country had successfully entered the field of high-end electric equipment in the world and was on the same starting line with the world's leading multinational corporations.
In July 2011, Shanghai Nanhui flexible DC transmission project put into operation. This is the first HVDC transmission project in Asia to be applied to wind power access, which can greatly improve the failure through ability of wind farms. It is cited as a typical case of grid connection of wind farms in CIGRE Guideline 370,which outbreaks the scratch of our country’s flexible DC transmission technology,marking the company to become the world's third company who completely control the flexible DC transmission equipment design, testing, debugging and production of a full range of core technology.
So far, China's flexible DC transmission is rapidly to large capacity, multi-terminal, bipolar, back to back and many other research directions to carry out the practice and exploration. Anting, a member of the Global Energy Internet Research Institute, said that the next few years will be a period of rapid development of flexible DC transmission technology research and engineering construction in China. The AC-DC power grid with strong cross-connect will become the basic form of China's power grid architecture. Flexible DC Power transmission will be the most important form of transmission in the DC grid. On the road of exploring new energy sources, flexible DC transmission has become the next high ground grabbed by the global power industry.
Leading technology to create quality projects
Shanghai Nanhui flexible DC transmission project achieved the cross of China's flexible DC transmission technology from concept to application. Since then, the State Grid Corporation has greatly enhanced the intelligence level of the power grid and built a batch of smart grid projects with world-advanced level, such as multi-terminal flexible DC, making it a leader in the construction of flexible DC projects.
Zhejiang Zhoushan Islands has more than 1,300 islands dotted. The unique natural environment here provides excellent conditions for scientific exploration. On July 4, 2014, the world's largest terminal flexible HVDC project - Zhejiang Zhoushan ± 200 kV five-terminal flexible DC transmission technology demonstration project put into operation, marking the State Grid Corporation smart grid high-end equipment development capability is up to a new Step.China's flexible DC transmission technology is in the forefront of the world,which achieves the "China created" and "China's leading".
It is understood that State Grid Corporation now fully mastered the systematic digital simulation, converter electrical design, equipment parameters selection and other flexible multi-terminal HVDC complete sets of design techniques, breaking the high-pressure high-capacity DC converter, HVDC cable, multi-terminal flexible DC Control and protection system dynamic test and joint commissioning and other key technologies to enhance the international competitiveness of China's HVDC industry, which has good demonstration effect on the large-scale promotion of the flexible DC and marine transmission technology.
On December 29, 2016, Zhoushan once again witnessed a new breakthrough in the field of China's power frontier technology. State Grid independently developed the world's first 200 kV HVDC circuit breakers and rapid recovery devices and has been successfully applied to Zhoushan five-terminal flexible HVDC transmission project. The circuit breaker can break up 15,000 amperes of fault current in a 200 kilovolt HVDC transmission line in 3 milliseconds at speeds 100 times faster than human blinks. It overcomes the world-class technical problems that the HVDC transmission current can not be quickly disconnected and realizes a major breakthrough in the R & D and manufacturing of the core HVDC equipment.
On the spot when Zhoushan soft DC system circuit breaker and damping recovery technology put into operation,the academician Zheng Jian Chao from Chinese Academy of Engineering excitedly said: "The DC circuit breakers has been successfully researched and passed all tests and was put into engineering applications.It provides a key technical support for future higher voltage DC grid Development. "
It is the first flexible bipolar DC transmission project in China Xiamen that is 900 kilometers away from Zhoushan. It is also the true bipolar flexible DC transmission project with the highest voltage transmission capacity and the largest transmission capacity so far in the world. The Xiamen demonstration project of ± 320kv flexible HVDC transmission technology was put into operation on December 17, 2015, marking that China has fully mastered the high-voltage large capacity flexible HVDC key technologies and engineering capabilities, and has achieved the international lead in the field of flexible HVDC transmission technology.
This project which covers an area of less than 30 acres can provide Xiamen Island 50% of the electricity supply. According to Zheng Guoshun, director of the soft-DC converter station of Fujian Power Co., Ltd., a branch of the State Grid, if the project is likened to the "bridge of electricity" across Xiamen Island and outside, the power delivered is likened to the traffic flow, the true bipolar design is equivalent to the addition of a two-way spare "lane" in a conventional two-way "lane" (power path). When any "lane" fails or overhaul, the use of a backup channel will ensure normal passage of current. Even if either direction "lanes" are completely blocked for any reason, half of the electric energy can be guaranteed to pass smoothly when the backup channel is enabled.
In the same year from July 27 to 29, Zhangbei renewable energy ±500 kV flexible DC grid demonstration project pre-complete design and preliminary design passed the review. This is the world's highest voltage level, transmission capacity of the largest flexible DC project, and is also the world's first network DC grid demonstration project,which is expected to be completed and put into operation in 2018. By then, the project will meet the demand for reliable delivery and consumption of renewable energy in Zhangbei, serve the green low-carbon winter Olympics, promote independent innovation in the DC power grid and increase the share of renewable energy in the power consumption in Beijing, Tianjin and Hebei so as to provide "re-electrification" with strong guarantee.
Guided by the "Belt and Road Initiatives," SGCC has been steadily going abroad to win overseas markets with technology. On June 13, 2017, State Grid Corporation of China announced that its flexible DC transmission technology, independently developed by the Global Energy Internet Institute, has won the bid for the Shetland Flexible HVDC Transmission Project. This is the first project that China's flexible DC transmission technology goes to the world and is also an important manifestation of the international competitiveness of China's high-end transmission technology. In the "Belt and Road", an important link between the Asia-Pacific Economic Circle and the European Economic Circle, the flexible DC transmission technology penetrates into the market and promotes the deep participation of the power grid enterprises in the development of the European power grid. It also drives the equipment enterprises to successfully enter the European high-end market, which brings a new historic opportunity for China power industry to develop into stronger and bigger companies in the global competiton.
Original title: State Grid flexible DC transmission technology achieved "China leading"