China Electric Power Research Institute Co., Ltd. (hereinafter referred to as China Electric Power Research Institute) is a scientific research unit directly under the State Grid Corporation of China. The company provides comprehensive technical support. Since its establishment, the China Electric Power Research Institute has undertaken nearly 400 various national science and technology projects, and gradually formed the world’s most complete UHV and large power grid test and research system with the most complete functions, the strongest test capabilities, and the highest technical level. A number of innovations have been achieved in the fields of DC transmission and transformation, large-scale grid control, and smart grids. In 2012, he won the national special prize for scientific and technological progress, and in 2016, he won one first prize and three second prizes of national scientific and technological progress.

The 19th National Congress of the Communist Party of China proposed that it is necessary to aim at the frontiers of world science and technology, strengthen basic research, and achieve major breakthroughs in forward-looking basic research and leading original results; strengthen applied basic research, expand the implementation of major national science and technology projects, and highlight key common technologies and cutting-edge leading technologies , Modern engineering technology, disruptive technological innovation. The State Grid Corporation of China focuses on the overall situation of the party and the country, and in-depth advances its scientific and technological development strategy to build a modern company with “one strong and three excellent”. In accordance with the requirements of the State Grid Corporation of China, the China Electric Power Research Institute has set the goal of "fully implementing the new requirements of the'two transformations', focusing on key development directions, comprehensively improving technological innovation capabilities and supporting service capabilities, and accelerating the creation of'two centers'".

Under the guidance of the company's scientific and technological innovation strategy, the China Electric Power Research Institute has proposed a series of innovation management measures to further improve the efficiency of scientific and technological research and development. The first is to strengthen the top-level design of scientific research and make innovation resources more concentrated. Initially formed a R&D planning model of "top-level design first, guide application implementation, and strategic planning compatibility", relying on top-level design to condense and focus on new technological directions, cultivate future business growth points, and support top-level design in the selection of major strategic directions, and promote scientific and technological resources Further gathering in the direction of core technology, under the condition of limited resources, enhanced the systematic, overall and synergistic nature of scientific research investment. Through the top-level design of scientific research, 47 key research directions, 376 key technologies, 38 core technologies, and 8 medium and long-term strategic scientific research directions have been condensed, which basically established the core key technical directions of the China Electric Power Research Institute in the next few years. The second is to optimize the R&D organization to make the comprehensive advantages more prominent. Initially establish a cross-professional joint research mechanism of "overall design, centralized research, and decentralized implementation" to form a collaborative research system in which units within the hospital complement each other, promote each other, and exchange what is needed. Explore the pilot project leader system, strengthen the control and assessment power of the project leader in terms of personnel and resources, and mobilize and stimulate the enthusiasm of scientific research personnel for innovation. By optimizing the R&D organization model, in the past five years, it has overcome a large number of power system dynamic simulations, UHV substation equipment status early warning, large-scale new energy generation and grid connection, distribution network self-healing control, large-scale energy storage system integration, etc. Key technical problems.

With the gradual implementation of the national science and technology plan reform plan, relevant state departments used the national key research and development plan for the first time in 2016 to organize project declarations. With the strong support and orderly organization of the State-owned Assets Supervision and Administration Commission and State Grid Corporation of China, the China Electric Power Research Institute has actively participated in various related special declarations. In 2016 and 2017, it participated in the declarations of 8 special projects and 47 projects, of which 31 projects ( 8 leading projects and 23 cooperation projects) have been approved for project establishment, and have become the unit that has undertaken the most projects in the field of smart grid for two consecutive years.

[Realize the localization of high-end insulation materials to improve the reliability of electrical equipment-nano composite insulation materials for UHV electrical equipment and key applications]

Epoxy composites are key insulating materials for UHV electrical equipment, and they are used in large quantities and are irreplaceable. During the construction of UHV projects in my country, the key parts of UHV electrical equipment-epoxy insulators and saturated reactors have encountered the problem of the gap between the performance of insulating materials and foreign countries.

At the beginning of the construction of UHV projects, most of the basin insulator materials were mainly imported. Foreign countries such as ABB, Mitsubishi, Toshiba, Hitachi, etc. have mastered the key technology of UHV basin insulator materials. Among them, Toshiba UHV basin insulator materials have high resistance It has the characteristics of heat and high toughness, the glass transition temperature reaches 130℃, and the tensile strength reaches 80MPa. It is widely used in the construction of UHV projects. Domestic switch manufacturers such as Pinggao, Xikai, and New Northeast Electric have a large gap in epoxy casting formula, design structure and process technology. The material strength is below 75MPa, and the glass transition temperature is about 120°C.

UHV basin insulators need to solve many control problems such as stress control, defect control, temperature field control, etc. during the casting and molding process. When deep into the epoxy resin castable level for insulators, the cross-linked network structure of the cured product from the castable is required. , Multi-level microstructure, organic-inorganic interface compatibility, nanoparticle dispersion and modification, etc. to optimize the formulation of the castable. The national key R&D project "Nano-composite insulating materials and key technologies for UHV electrical equipment" will design and simulate the molecular structure of epoxy resin and its curing agent, the synthesis and surface control and dispersion of nanoparticles, and the surface of inorganic fillers. The formulation and mass production of modified and epoxy composite insulating material castables, systematic research at multiple levels, and a comprehensive grasp of the formulation and mass production technology of epoxy composite insulating materials.

For the saturable reactor used in the converter valve, the hollow coil turns and the turns need to be fixed with resin, and its thermal conductivity will directly affect the temperature distribution inside the reactor. According to reports, the thermal conductivity (0.7-0.8W/(m˙K)) and heat resistance grade (glass transition temperature of 90℃-100℃) of the resin insulating materials for reactors are relatively low. If its thermal conductivity can be doubled or even higher, reaching 1.5W/(m˙K) or more, it will greatly improve the heat dissipation effect of the iron core, greatly reduce the temperature of the iron core, and increase the service life of the insulating material. It can effectively control the difficulty of reactor insulation design and manufacturing cost, and ensure the safe and stable operation of the equipment.

The project will carry out research on the key technologies of high thermal conductivity insulating packaging materials for DC converter valve saturated reactors, to overcome the current bottleneck problem of improving the thermal conductivity of insulating packaging materials, and effectively reduce the working temperature of the existing valve reactor cores, making them in the design Stable, safe and reliable operation within the temperature range. The research results will provide directions for manufacturers to make targeted improvements in the formulation technology and preparation process of reactor packaging materials, enhance my country’s technology and production capacity in the field of reactors, and completely get rid of foreign companies’ high-voltage DC transmission equipment. Lay the foundation for the constraints in China.

In recent years, using imported epoxy resin, domestically developed UHV basin insulators and other epoxy insulators have been widely used in UHV AC projects. However, whether it is domestically made or imported insulators made of imported materials, the insulation fails. It has always been the main reason for the failure of UHV electrical equipment. In addition, because my country is a country that has a complete grasp of UHV transmission technology in the world, and is also the only country in the world that has experience in the commercial operation of UHV projects. UHV basin insulators produced with imported epoxy composite materials have also experienced multiple flashover problems, which still cannot meet the operational requirements well. Among the failures of epoxy insulators, the flashover problem of the gas-solid interface accounts for more than 80% of the failures of epoxy insulators, and it is difficult to predict. The flashover of epoxy insulators has become a bottleneck restricting the further improvement of the reliability of UHV electrical equipment. In order to solve this kind of problem, in addition to the above-mentioned strengthening of the research on the performance of the basic material itself, it is also necessary to systematically solve it from the aspects of design, manufacturing, operation, maintenance and diagnosis.

This project studies the influence of preparation process and nano-addition on the characteristics of gas-solid interface, masters the field strength tolerance characteristics of gas-solid interface and electric field design criteria; through the establishment of multi-field coupling simulation model of epoxy composite insulation system, researches multi-field collaborative design method. Combined with the control of the surface state of the insulating parts, the field strength of the gas-solid interface is improved.

With current inspection methods, many small defects inside or along the insulating parts are difficult to find. Therefore, the project researches pulse current partial discharge detection and ultra-high frequency partial discharge detection optimization methods, as well as X-ray insulation defect excitation technology and new optical fiber ultrasonic partial discharge detection. Technology, steep wave impulse test technology, and the development of a metal-enclosed steep wave impulse voltage generator to improve the sensitivity of the micro-defect detection technology for insulating parts.

At the same time, study the occurrence and development of surface defects of insulating parts under multi-field coupling conditions, grasp the principle of insulation failure of insulating parts, and propose a multi-source information fusion defect detection technology for insulating parts, so as to realize early diagnosis of defects and establish defects of insulating parts in operation Hazard status assessment methods and operation and maintenance strategies. Reduce the failure rate of insulators and improve the reliability of equipment operation.

The implementation of this project will enable my country to reach the international advanced level in key materials, design and manufacturing, operation and maintenance diagnosis, etc., and form a domestically-made epoxy nanocomposite formulation system for UHV electrical equipment, which can fully replace UHV and UHV import. At the same time, it will cultivate a group of innovative talents engaged in UHV electrical equipment key materials and application and testing related technologies, promote the technological progress of the domestic UHV electrical industry, and provide solid technology, equipment and talent guarantee for the development and application of UHV electrical equipment.

The global warming coefficient value of the environmental protection gas developed by the project is only 5% of SF6, which can drive the environmental protection upgrade of gas insulation equipment.

The research and development of a new type of insulating gas, to deliver fresh blood to power equipment, and to be environmentally friendly, poses a huge challenge to power workers.

All major power equipment giants in the world are actively researching and developing new environmentally friendly gases. The US 3M, GE and ABB have all made breakthroughs and are gradually forming a technological monopoly advantage. Facing the strong leading advantages of foreign companies, several generations of domestic electric power workers have worked hard, but they are still mainly in the laboratory research stage. "The research on environmental protection gases to replace sulfur hexafluoride in my country is still in the exploratory stage, which is far behind similar foreign technologies. The relevant research urgently needs to be speeded up and deepened.” said Gao Kli, the person in charge of the key national key research and development program project "Environmental protection pipeline transmission key technology" and vice president of the China Electric Power Research Institute.

When the transmission line encounters special geographical conditions such as high drop and river crossing, the use of gas-insulated pipelines for power transmission has gradually become an important supplement to overhead lines in recent years. China Electric Power Research Institute organized Pinggao Group, Xikai Electric and other units to take the lead in developing UHV (1000kV) transmission pipelines insulated with sulfur hexafluoride were successfully used in 3 substations in the Huainan-Nanjing-Shanghai UHV AC project; at the same time, the sulfur hexafluoride mixed gas UHV transmission pipeline independently developed by the State Grid Corporation of China The prototype was tested on-line at Wuhan UHV AC Test Base. China has accumulated rich experience in the research and development and manufacturing of UHV switchgear for many years, laying a solid foundation for the development of new environmentally friendly gas transmission pipelines.

At present, GE has applied the new environmentally friendly gas to 420kV power transmission pipelines and has achieved engineering applications, declaring the feasibility of applying the new environmentally friendly gas to power transmission pipelines. However, the 1000kV environmental protection transmission pipeline has a high voltage level, strict environmental protection and insulation requirements, and many factors that need to be considered in design, manufacturing and operation, and there is no relevant technology at home and abroad. "If the new environmentally friendly insulating gas is applied to the ultra-high voltage 1000kV voltage level, the problem of'three saturations and one breakthrough' needs to be solved. As the voltage level increases, the gap insulation, creeping insulation and flow capacity tend to be saturated, and the mechanical strength is difficult to break through. "The project leader Gokley said.

Based on the research and development of 1000kV sulfur hexafluoride power transmission pipeline, the project learns from the development experience of 420kV new environmental protection gas transmission pipeline, overcomes the key technology of environmental protection pipeline power transmission, and develops new environmental protection gas for 1000kV environmental protection transmission pipeline, supporting insulators and transmission pipeline prototype. "The project needs to solve the contradiction between the new gas insulation and environmental protection and the design problems of the gas-solid insulation system based on the new gas, focusing on breaking through the discharge law and gas-solid compatibility of the gas-solid insulation system in the environmentally friendly insulation gas, and the three pillars for 1000kV transmission pipelines The key technology of insulator design and manufacturing, and the maintenance and repair technology of environmental protection transmission pipeline." The project leader Zhou Wenjun introduced.

At home and abroad, only a small amount of potential sulfur hexafluoride substitute gases and mixed gases have been studied on the discharge characteristics of gas-solid insulation systems. my country has not yet mastered the new environmentally friendly mixed gas insulation technology. It is necessary to conduct research on discharge physical parameters, insulation characteristics and dielectric recovery characteristics. Gas-solid material compatibility is a prerequisite for ensuring the reliability of power transmission pipelines. It is necessary to master the interaction law of new environmentally friendly gases and their decomposition gases with solid materials, and propose gas-solid compatibility control methods.

Transmission pipelines need to withstand multiple stresses such as electricity, heat and force during operation. The characteristics of new environmentally friendly gases make it difficult to design environmental protection transmission pipelines and supporting insulators for insulation, flow and structural strength; three pillars for 1000kV transmission pipelines The manufacturing process control of insulators, the regulation of the surface morphology of insulators, and the suppression of metal particles in transmission pipelines are facing greater challenges. It is necessary to overcome the design and manufacturing technology of three-pillar insulators for the new 1000kV environment-friendly gas transmission pipeline, and provide key components for the development of the prototype of the transmission pipeline unit.

The mixed preparation, performance testing, storage and transportation of new environmentally friendly gases, as well as the fault detection and location of power transmission pipelines, operation status monitoring and evaluation, and other technologies are quite different from the existing sulfur hexafluoride and its equipment operation and maintenance technology. , It is necessary to carry out research on the operation and maintenance monitoring technology of new environmental protection gases to provide sufficient guarantee for the reliable operation of environmental protection transmission pipelines.

Focusing on the above three scientific and key technical problems, the project carries out research on the physical parameters and insulation characteristics of environmentally friendly insulating gas dielectric discharge, research on the compatibility of gas-solid materials in environmentally friendly gases and interfacial insulation performance, and the design and manufacturing technology of supporting insulators for 1000kV transmission pipelines , Research on 1000kV environmental protection pipeline power transmission system development and operation and maintenance technology.

The project is expected to develop a standard unit prototype for 1000kV environmental protection transmission pipelines with environmental protection gas, basin insulators and three-pillar insulators, and 18m long transmission pipelines. The gas insulation performance of the environmental protection gas used under the same pressure reaches 80% of that of sulfur hexafluoride, and the liquefaction temperature is not higher than -15°C. The research results of the project will provide strong support for solving the transmission bottleneck in the UHV, long-distance, and complex geographic environment, and can be promoted to other power equipment, continue to lead the upgrade of environmental friendliness of the equipment, and have significant economic and social benefits.

Install a smart brain for my country's UHV AC/DC hybrid large-scale power grid-research and application of key technologies for smart dispatch and safety early warning of large-scale power grids

Dispatching is the brain that controls the safe and stable operation of the power grid, the foundation of maintaining the power production process, and an important means to ensure the operation and development of smart grids. Compared with foreign countries, my country's power grid dispatching control technology research started late, but it has developed rapidly, and many technologies have reached the world's leading level. Among them, the Smart Grid Dispatching Control System (D5000) organized by the State Grid Corporation of China in 2008, based on an integrated platform that integrates four major applications including real-time monitoring and early warning, won the second prize of the National Science and Technology Progress Award, and has now been promoted to the State Grid operation All power grid dispatching agencies above the provincial level and many regions within the scope.

At present, the scale of my country's UHV AC/DC hybrid power grid is continuously expanding, and the operation characteristics of the power grid have undergone profound changes. The power grid dispatching control is also facing new and greater challenges. On the one hand, UHV long-distance, high-power transmission, across multiple climate zones, and the operating environment is complex and changeable. Dispatching at all levels is urgently required to simultaneously control the grid operation situation; on the other hand, UHV grid transmission and receiving end, AC and DC strong coupling, There are security risks that local failures affect the overall situation, and cross-regional integrated security early warning and risk prevention and control are required at the entire network level in real time; in addition, the optimal configuration of large-scale source-network-load resources requires urgent improvement of the entire network under market conditions Decision support ability of lean control.

New architecture and new technology to escort the safe and economic operation of large power grids

According to the national key research and development plan project "Key Technology Research and Application of Intelligent Dispatching and Safety Early Warning for Large Power Grids", Xu Hongqiang, deputy director of the National Electric Power Dispatching Control Center, introduced: "The existing dispatching control system follows the system architecture of the weak interconnection stage of the power grid. Support the needs of large-scale AC/DC hybrid power grid dispatching operation. It is urgent to carry out research on key technologies of integrated intelligent dispatching and safety early warning for large-scale AC/DC hybrid power grids, and build an intelligent control platform based on the concept of cloud computing of “physical distribution and logical unity”. Realize the overall coordinated control of the large power grid, and improve the early warning capability of large power grid operation safety."

The project has set up five topics around the major requirements of UHV large-scale AC/DC hybrid power grid dispatching operation control, namely, intelligent control platform architecture and real-time transparent access technology, control system on-demand modeling and wide-area data distributed processing technology, including The development and application of intelligent dispatching and control technology for large power grids with uncertainties on both sides of source and load, integrated online security risk prevention and control and intelligent decision-making technology for large power grids, and the development and application of integrated operation intelligent control platform for large power grids.

The intelligent control platform architecture and real-time transparent access technology are oriented to the business needs of monitoring, control and decision-making in the integrated dispatching operation of large-scale AC-DC hybrid power grids, guided by theories of cloud computing, network science, and cyber-physical integration, and proposed support " "Physical distribution and logical unity" distributed remote multi-active intelligent control platform architecture; based on the network and service of data resources, it can transparently access grid information at any location according to permissions and needs, and realize data resources can be used when needed , Provide basic technical support for follow-up topics.

Control system on-demand modeling and wide-area data distributed processing technology focuses on the flexible definition of large power grid models, multi-version management of graphs and models, distributed source-end maintenance and on-demand sharing, and proposes data streaming methods to realize wide-area data If needed, it can be used and high-speed parallel processing, data distributed storage and efficient access technology to realize large-data-based wide-area collaborative processing and fault diagnosis of master and sub-stations, and provide model and data support for subsequent topics.

The intelligent dispatching control technology of large power grids that takes into account the uncertainties of both sources and loads. Through the study of the unified model of heterogeneous power sources and flexible load response uncertainty, and the calculation method of large-scale analysis and optimization of the power system, it adopts multi-period considering the confidence interval. The multi-objective dispatching plan generates the economic operation domain of the power grid, and combines data mining and intelligent learning technology to perform multi-dimensional real-time evaluation of the operation status of the large power grid, so as to obtain the optimal operation point of the power grid, and guide and implement the coordinated optimization control of the source and load of the district power grid.

Power grid integrated online security risk prevention and control and intelligent decision-making technology proposes a large power grid security risk assessment method that takes into account the uncertainties of both sides of the source and load, and uses data mining technology to carry out multi-time scale fast security risk forward warning for large power grids, and to prevent high risks Early warning scenarios optimize the security risk prevention and control strategy of the large power grid, and track the system status to coordinate the three lines of defense and system protection to realize the integrated security risk prevention and control and intelligent decision-making of the large power grid.

The project is expected to develop a highly scalable and high-performance intelligent control platform and implement demonstration applications, reducing the peak-to-valley difference of the grid load by 5% and increasing the capacity of new energy consumption by 3%. The implementation of the project will change the current situation of independent analysis and decision-making by the control centers, put a smart brain into my country's UHV AC/DC hybrid large-scale power grid, realize lean control and control decisions across the entire network, and significantly improve the large-scale power grid dispatching "predictions" , Pre-judgment, pre-control" capabilities and intelligent level, to achieve "automatic cruise" for optimized operation of the power grid and "intelligent decision-making" for safety risk prevention and control. It can produce significant economic and social benefits in terms of saving system construction costs, reducing the peak-to-valley load of the grid, improving the level of new energy consumption, and avoiding major power outages.

[Overcome the stable control of the sending end system and promote the cross-regional consumption of renewable energy-the stability control technology of the DC transmission system of the renewable energy power generation base]

Vigorously developing renewable energy is an important measure for my country to ensure energy security and respond to climate change. Wind power and photovoltaic power generation are the main ways of using renewable energy in my country. According to the "13th Five-Year Plan", my country's installed wind and solar power generation capacity will reach 320 million kilowatts by 2020, of which 200 million kilowatts will be located in the "Three Norths" area. In order to solve the problem of renewable energy consumption in the "Three Norths" area, there are 8 UHV DC transmission channels that have been built, under construction and planned to be constructed. At present and in the future, large bases and DC transmission will be the development of my country's renewable energy. The dominant form of utilization.

Compared with the traditional power system dominated by synchronous generators, the biggest feature of the DC transmission system of the renewable energy power generation base is the high proportion of power electronic equipment access, including wind and solar power generation, dynamic reactive power compensation, DC transmission, etc. Taking the Hami Tianzhong DC transmission system in Xinjiang as an example, the wind and solar power generation capacity exceeds 10GW, the dynamic reactive power compensation capacity exceeds 2GW, and the DC transmission capacity is 8GW, while the synchronous generator capacity is only 5GW, and the power electronic equipment capacity is much larger than the synchronous generator capacity. .

Under the leading role of the control characteristics of power electronic equipment, the dynamic characteristics of the DC transmission system of the renewable energy power generation base are very different from the traditional power system, and the stability analysis and control of the system are facing severe challenges. The problems that have begun to highlight are mainly in two aspects: frequent oscillation accidents under normal operating conditions, Xinjiang Hami-Zhengzhou DC transmission-end power grid has occurred more than 100 times/super-synchronous oscillations, which caused 3 DC supporting thermal power units to trip at the same time. The risk of chain disconnection accidents under AC and DC failures increases. Preliminary calculations show that the power sent by the Jiuquan-Hunan DC from Gansu Province will be restricted as a result.

According to Professor Kang Yong, the person in charge of the National Key R&D Project "Renewable Energy Power Generation Base DC Transmission System Stability Control Technology", this project focuses on solving the above two major problems in the current system, and overcomes two major scientific problems and one. Key technologies:

1. Dynamic interaction of diversified equipment and wide-band oscillation mechanism

In the DC transmission system of the renewable energy power generation base, the number of power electronic power generation equipment is huge, the control is complex, and there are multiple time-scale couplings. The dynamic interaction between the bases and the DC transmission is intensified, leading to the unclear mechanism of broadband oscillation, modeling and Analysis faces great challenges.

2. Multi-machine and multi-time scale transient process coupling mechanism and system transient behavior evolution law

Under complex control, multiple time scales of voltage and power angle coupling appear among diverse equipment. The dynamic characteristics of renewable energy power generation equipment are very different from those of synchronous generators. When AC/DC faults occur, there is a nonlinear switching phenomenon in the control, which leads to the evolution of system transient behavior. The law is more complicated, and it is urgent to explore the mechanism of system transient stability under new conditions.

3. Broadband oscillation suppression and transient stability control technology

Due to the unclear system stability mechanism and complex dynamic interaction, the current lack of effective broadband oscillation suppression methods, and the difficulty in controlling transient stability of bases in weakly synchronized grids, restrict the cross-regional absorption of renewable energy, and it is urgent to break through broadband oscillation suppression And transient stability control technology.

The project lead unit, China Electric Power Research Institute, is the most powerful multi-disciplinary and comprehensive scientific research institution in my country's electric power industry. The team members include my country's 5 first-level national key disciplines of electrical engineering, and 16 national R&D platforms including 6 national key laboratories. The project leader, Professor Kang Yong, has long been engaged in scientific research on the application of power electronics in power systems. He is currently the executive deputy director of the State Key Laboratory of Strong Electromagnetic Engineering and New Technology.

The project will propose a stable control theory and method for the DC transmission system of a renewable energy power generation base in a weakly synchronized power grid, and form a series of independent intellectual property rights including papers, invention patents, national/industry standards, etc.; develop 35kV/1MVA broadband impedance measurement equipment Developed a 35kV/5MW dynamic simulation platform containing wind/photovoltaic power generation, synchronous generators and DC transmission to verify the effectiveness of the control method under the condition that the short-circuit ratio is less than 2; the project results are directly applied to Xinjiang and Gansu's tens of thousands of kilowatts of renewable energy Base, solve the problem of broadband oscillation and DC power limitation, and promote the application, improve the level of China's large-scale grid-connected renewable energy consumption, and promote the sustainable development of the economy and society.

[Promote the structural reform of the energy supply side to promote the flexible and efficient consumption of distributed energy-AC and DC hybrid renewable energy technology based on power electronic transformers]

In recent years, my country's distributed renewable energy has grown rapidly, and large-scale distributed renewable energy has been connected to the grid, which has put forward new challenges and higher requirements for the flexible access and effective management and control of the system.

At present, there are many AC-DC conversion links in renewable energy access technology, which reduces efficiency and affects the convenience of access. In addition, the lack of interconnection and flexibility of the distribution network also limits the full consumption and efficient use of distributed renewable energy. The use of two-way multi-port power electronic transformers to construct an AC/DC hybrid system can achieve flexible networking, integrate distributed renewable energy at multiple AC and DC voltage levels, and achieve flexible and safe access; and reduce conversion links, improve energy efficiency, and enhance The system control capability realizes interconnection and complementarity on a larger scale and fully consumes renewable energy.

Researcher Kong Li, former director of the Institute of Electrical Engineering of the Chinese Academy of Sciences and head of the national key R&D project "Research on AC and DC Hybrid Renewable Energy Technology Based on Power Electronic Transformers", said: "The AC and DC hybrid system based on power electronic transformers, etc., It can provide effective technical means for the flexible access, optimized configuration and safe operation control of a large number of renewable energy in the future. It is an important development direction in the future and has broad application prospects."

The State Grid Jiangsu Electric Power Company, the Institute of Electrical Engineering of the Chinese Academy of Sciences, the China Electric Power Research Institute and Zhejiang University formed the project's production, learning, research, and application research team. The team has 5 national key laboratories for new energy and energy storage operation control, new energy power systems, and 5 national engineering research centers for power electronics application technology, power electronics technology and equipment research and development. The project team has presided over more than 30 national-level projects in related fields in recent years, and has successfully developed a 1MVA power electronic transformer prototype and connected to the grid. At the same time, it is the initiator of the IEC Technical Subcommittee of "High-capacity Renewable Energy Power Generation Connected to the Grid". Leading units of many national standards and IEC international standards, the R&D team has a strong scientific research level in this field, and the supporting conditions are perfect to ensure the smooth completion of the project.

Aiming at key technical issues such as flexible access, complementary optimization, and coordinated control of the AC/DC hybrid distributed renewable energy system, the research team develops key technologies from five aspects: "system analysis, optimized configuration, equipment development, operation control, and integrated demonstration" Tackling key problems.

In terms of system analysis, in view of the operational diversity and dynamic complexity of AC/DC coupling of key equipment such as power electronic transformers, the focus is on the structure and dynamic characteristics analysis methods of AC/DC hybrid systems based on key equipment such as power electronic transformers. The problem of dynamic analysis method of coupled and nonlinear AC/DC hybrid system.

In terms of optimal configuration, consider the complex and multi-dimensional problems caused by the complexity and flexibility of the AC-DC hybrid system grid structure and operation mode, and tackle the multi-level planning method for the complementary optimal configuration of AC-DC hybrid distributed renewable energy, and Propose an energy efficiency evaluation method suitable for AC and DC systems.

In terms of equipment development, for multi-port power electronic transformers, focus on high-efficiency and high-reliability circuit topology and wide-load range efficiency optimization control technology, so that its efficiency can reach 96%; for fault current controllers, focus on integrating current limiting and breaking The power electronic current limiter topology and fast response control integrated with line voltage regulation can quickly limit and break the DC fault current, and enhance the system voltage control capability.

In terms of operation control, make full use of the power electronic transformer measurement information and flexible control capabilities, focus on the AC-DC hybrid renewable energy system sequential progressive optimization scheduling method, and solve the multi-dimensional, strong nonlinear complex system optimization and control problems, and give full play to The flexible networking and flexible control capabilities of power electronic transformers enhance the access and absorption capabilities of renewable energy and ensure the stable operation of the system.

In terms of integration demonstration, aiming at the multi-device and multi-parameter integration of AC and DC distributed renewable energy, focus on key equipment integration, system information interaction integration and other technologies, and research system testing and verification technologies, develop corresponding test platforms and complete demonstrations .

The expected results of the project include 3MW two-way four-port power electronic transformer, 1.2MW/±750Vdc DC fault current controller, optimized operation control system, planning and design software, etc. The project results will be demonstrated at the permanent site of the International Energy Reform Forum in Tongli, Suzhou. The demonstration and verification combines the high proportion of renewable energy in the area and connects it to the different voltage level ports of power electronic transformers. It will be presented to the International Energy Reform Forum for a permanent meeting. Power supply for important DC loads such as sites, effectively improving energy utilization efficiency and absorbing capacity, while ensuring the reliability of energy supply.

The implementation of the project will promote the technological development of AC and DC distributed renewable energy, and provide core technologies and empirical experience for improving the level of access and consumption of distributed renewable energy in my country, and improving the safe operation and control capabilities of the system.

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