This article is transferred from Wechat Official Account, Tsinghua University

On January 8, 2018 The state science and technology awarding meeting of the People's Republic of China was held in the Great Hall of the People. A total of 24 outstanding scientific and technological achievements in Tsinghua University won the 2018 State Science and Technology Prizes, including 5 National Natural Science Awards, 3 National Technological Invention Awards and 16 National progress prize in scientific Awards. As the first unit or the unit where the first finisher works, Tsinghua University won 15 prizes in national science and technology award, ranking first in the number of prizes in universities in the country. Among them, there were 4 first prizes, including 1 in the first prize in China's State Natual Science Award and 3 in progress prize in scientific (including 1 in the innovation team). Both the total number of awards and the number of first-class awards reached record highs. In addition, Tsinghua alumnus and radar and signal processing technology expert Liu Yongtan won the 2018 Highest Science and Technology Awards.

Today, we will show you Sun Hongbin and his automatic voltage control team from the Department of Electrical Engineering and Applied Electronics of Tsinghua University, which installed "super brain" in the power grid, and their "Complex Power Grid Self-discipline-Collaborative Automatic Voltage Control Key Technologies, System Development and Engineering Application" project.

Sun Hongbin has a habit of recording the things to be done and the solutions to the problems in his mobile phone memo inside every day, and ticking off each item. In the past six months, his mobile phone inside has a total of 1,447 memos. He started to take notes as early as during his doctor's term. The notebooks ticked over the past 20 years are still in good condition, full of contents related to grid voltage control.

From being "shelved" to being widely used, Professor Sun Hongbin led his team through more than 20 years of continuous research and joint research of industry, university and research. He built the "self-discipline cooperation" complex grid AVC technology system, developed the world's first complex grid AVC system, realized the "leap from manual to automatic" of modern grid voltage control, effectively guaranteed the safety and economic operation of China's grid, and realized the first output to the United States. However, the project "Key Technologies, System Development and Engineering Application of Complex Power Grid Self-discipline-Cooperative Automatic Voltage Control" won the first prize of progress prize in scientific at the 2018 National Science and Technology Award Conference on January 8.

I. Do scientific research with indomitable spirit

One of the keys to the quality of electricity is the quality of voltage. For the power system, the load often changes and faults are inevitable. To maintain the voltage safety of the system, real-time regulation is needed. In the past, all countries adopted the method of manual decentralized control. In the control centers of power grids at all levels and in power plants, substations and other places, there were 24-hour dispatching operators. They kept an eye on the voltage situation of the power grid at all times. Once problems were found, they would dial the phone step by step and require the corresponding units to make adjustments. This method not only consumes huge manpower, but also is not conducive to coordinating the safety of the entire power grid from a global perspective.

"Especially in economically developed areas with large electricity consumption, electricity is transported from far away, just like pouring deep pools into waterfalls, which is easy to form depressed areas of voltage. This kind of sunken area is very prone to chain reaction if it encounters sudden failure, just like knocking down dominoes, causing large-scale power failure. "Sun Hongbin said that the blackouts in the United States and Canada and Brazil all reflect that the voltage safety of the power grid system is a worldwide problem.

Therefore, it is more and more urgent to install a "super brain" on the power grid, let it collect the power grid data in real time for analysis, use effective algorithms to form decisions, and coordinate and control all kinds of reactive power and voltage control equipment in the power grid, so as to make the power grid in the best state at all times. This "super brain" is an automatic voltage control system.

In the 1980s, France first put into use the automatic voltage control system in the world, but this technology cannot be directly used in China. The most important thing is that the development of China's power grid is very rapid. In the new century, for 10 years, the installed capacity of China's power grid in inside is about the same as that of Britain. However, France's automatic voltage control technology is a solidified control system and cannot adapt to the rapid changes in China's power grid.

In 1995, under the guidance of professors Xiang Niande and Zhang Boming, Sun Hongbin, a doctoral candidate, began to set foot in this research field. He participated in the research of the national 85 science and technology research project "Research and demonstration project of global quasi-steady-state voltage optimization closed-loop control for power system" and began inside's tireless search in this field for 20 years. To solve the problem that French automatic voltage control system is difficult to solve, Sun Hongbin's team is committed to making the control system have certain adaptive characteristics, so that the control mode and method of the system can change with the changes of the power grid, and become a flexible system with automatic strain control mode. At the same time, potential faults of the power grid are also considered, so that the control strategy of the system can be automatically responded to.

It is a major problem to realize system-level automatic voltage control in complex power systems. On the one hand, the control objects are complex, especially in recent years, large-scale intermittent renewable energy has been fed into the already very complex super-large power grid, further causing new problems; Second, the control mode is complex. China's interconnected large power grids are jointly dispatched by spatially distributed multilevel control centers. The power grids are interconnected to control the distribution. How to make the computer make the best decision in the shortest time, through the cooperation of 300 or 400 control centers, it is a difficult problem to keep the voltage of each node on the super-large power grid within the safe range at all times. The third is the complexity of the mathematical problem, which is a mixed integer dynamic programming problem with large-scale complex constraints and is difficult to solve by itself.

"In order to cope with this complexity, we have adopted the technical route of' self-discipline and coordination'.” Sun Hongbin described this technical route as a "seesaw": one side is self-discipline and the other side is coordination. Self-discipline simplifies, makes control reliable and agile, and through coordination ensures consistent goals and global optimization. What they do is how to find the delicate balance between self-discipline and coordination. Sun Hongbin said: "We are stepping on the most difficult place between self-discipline and coordination."

So how to simplify the complicated problem? Sun Hongbin skillfully used the knowledge of physics to put forward the master-slave split theory. "According to the master-slave physical characteristics of a large-scale power grid, the master-slave system will be torn apart and self-regulated respectively, and then it will be coordinated through mutual communication. And the coordination is good or not, that is, the optimality depends on the physical mechanism of system interaction."

On the one hand is physics, on the other hand is mathematics. The perfect integration of the two has become a breakthrough in solving complex power grid problems, laying a solid theoretical foundation for the wide application of AVC technology. The habit of thinking about mathematical problems with physical thinking has also been fully reflected in Sun Hongbin's national excellent course, Power System Analysis: in a PPT page, the physical network is on the left and the mathematical equation is on the right. Equation is the complete mathematical representation of network. According to physical network, complete mathematical equation can be written, and according to mathematical equation, it can also be reduced to physical network. Sun Hongbin thinks that such a symmetrical form can at least ensure that students have a comprehensive understanding of physical mechanism and mathematical methods.

However, due to the lack of relevant conditions for voltage control application in China at that time, the master-slave split theory proposed by Sun Hongbin did not find a corresponding application stage and was "shelved". Until Jiangsu Power Grid found Sun Hongbin and became "the first person to eat crabs". "The work that Mr. Sun did at that time really played a fundamental role in laying the foundation.” Guo Qinglai, an associate professor in the electrical engineering department, who spent the longest time on the project site and was the second person to complete the project, was deeply touched. "This is also a feature of the engineering discipline. To do indomitable research, one may have to go through such a stage, with forward-looking thinking and basic research first, followed by solid application and promotion. "

"Someone has to sit on the bench", for Sun Hongbin, "this research is the need of national development."

II. Let Power Grid Control System Out of Laboratory

In 2002, Jiangsu Power Grid, which is in urgent need of automatic voltage control system, found Sun Hongbin and hoped to cooperate. Before that, Jiangsu Power Grid had also looked for other research institutions, but they did not reach cooperation because of the difficulty and great responsibility in the research and development of the system. However, relying on the existing accumulation and courage not afraid of failure, Sun Hongbin accepted the challenge without hesitation and combined theoretical research with engineering practice in depth.

However, the gap between practice and theory still poses a big challenge to the Sun Hongbin team. For example, because of the problem of equipment acquisition accuracy, there is an error between the voltage measured by the control center and the actual voltage. If the voltage is directly adjusted based on the measurement, the safety problem will be caused because the voltage exceeds the reasonable range. Therefore, the team should add many protective measures in the test in combination with the field requirements. "Electricity is very fast, and its foundation can't tolerate any mistakes, so for the first time we did closed-loop control in Jiangsu, we didn't dare to sleep at night, staring at the screen in shifts, staring at the control instructions and the final effect feedback." Sun Hongbin recalled working in Jiangsu power grid, "because this is the first time we tried it on the spot, and we don't know that the consequence of such global closed-loop control is What?.” Is there any unexpected potential safety hazard? Therefore, ensuring the reliability of the closed-loop control is the most risky place besides real-time and optimality. "

In this closed-loop experiment, Guo Qinglai, as a doctoral student, stayed in the computer room for 72 hours and did not dare to leave. "At that time, the debugging was still quite tense.” Guo Qinglai said, "What I did before was theoretical analysis and simulation tests. This time it was a real engineering application. The pressure was very great, and I could only stare at the control curve and effect on the spot. However, as an engineering researcher, I will never forget the sense of accomplishment of that moment when I really see that the control instructions are sent to the actual power grid system and the equipment acts according to the expected strategy and achieves the ideal control effect. “ It was this sense of accomplishment that made Guo Qinglai stay in the control room of Jiangsu Power Grid for nearly 3 years, almost every day in a large computer room in inside, where he programmed and watched the system by himself, often without even a speaker from morning till night. Guo Qinglai smiled. "Because I can't find anyone to talk to, I can't help talking to people when I see the' living' who can talk, so all the people on duty in the small hotel I live in know me very well."

Where there's a will, there's a way. When other students were using the simulation data, Guo Qinglai had already obtained the first-hand field voltage control data and completed his doctoral thesis, continuing the tradition of the automatic voltage control team-from engineering to engineering. "This is the characteristic of engineering, I think the engineering teachers in Tsinghua must first understand the scene, otherwise it is difficult to do original work. From paper to paper is to forbid the pulse of industrial development, because you don't know the real new demand on the spot. “In order to ensure the reliability of control, Sun Hongbin led the team to combine the characteristics and needs of different power grids and invented a series of control technologies, authorizing 108 special items.

The successful operation in Jiangsu Power Grid has given Sun Hongbin's team great incentives. They did not stop, they started to continuously improve and upgrade the system based on the experience accumulated and problems found in practical engineering applications. More and more power grids at all levels are beginning to apply the systems they have developed. Through the combination of production, teaching and research with many partners, up to now, their systems have all covered 7 major regional power grids in China, and have been applied to 40 provincial power grids and 306 regional power grids in China on a large scale. They have closed-loop control over 81% of water/thermal power plants, 88% of substations above 220kV and 55% of centralized grid-connected fans/photovoltaic plants in the country.

III. Let Power Grid Control System Go to the World

If the successful application in China is Sun Hongbin's goal all along, it is somewhat beyond his expectation to successfully export the system to the United States. All this started with an e-mail from PJM, North America's largest regional power grid, to Sun Hongbin seeking cooperation.

PJM was the world's largest regional power grid company at that time. It was responsible for the safe operation of the power grid in Washington, D.C., and the 13 eastern states and the electricity market service, with the total electricity consumption accounting for 1/6 of the United States. The introduction of automatic voltage control system is a key project for PJM to implement smart grid. They have carried out research cooperation with American professors for this purpose, but the effect is not ideal. Against this background, they turned their eyes to Tsinghua University.

PJM power grid is a complex large power grid with 13,000 nodes and 19,000 branches. According to the requirements of the power market, the automatic voltage control system also ensures that after 5,500 complex expected faults occur, the voltage operation of all nodes is still safe and qualified. "5500 faults multiplied by 13000 nodes need to be quickly calculated by the system and used for decision-making and control. If the nonlinear optimization problem is completely modeled, it cannot be directly solved, let alone used for real-time control.” Guo Qinglai said in an interview.

"During that time, in inside, everyone in our research group basically worked until early morning. Whenever there was any progress, they were very excited and often tested all night.” Sun Hongbin said. Fortunately, in the face of this huge mathematical optimization problem, everyone finally came up with the game method, regarding the safety and economy of the power grid as both sides of the game, and then using the safety scanning method to reach a new equilibrium point. The realization of this idea requires a strong computing capability for optimization and security assessment, which are the advantages of the Sun Hongbin team. They have been engaged in research work in these two fields for a long time. Therefore, when this new idea was established, the team quickly realized it and applied for a series of patents from the United States and China, successfully solving this difficult problem.

However, the door of the United States is not so easy to open. Next, Sun Hongbin's team also faced PJM's harsh six-month continuous online testing and the US Federal Energy Regulatory Commission's harsh three-year and four-month information security checks. "We need to pay close attention to the evaluation results at all times, because the tests do not stop. Once problems are found, we need to solve them in a series of ways to avoid affecting the subsequent tests.” Sun Hongbin said. "This is an important opportunity for us to go out. The pressure is very great, and the Spring Festival has always been focused on the United States."

This series of persistence and efforts have made the system developed by the Sun Hongbin team the first automatic voltage control system in the US power grid. Bose, consultant of the US Department of Energy, power grid operation and control authority and academician of National Academy of Engineering, said that the achievement "makes China far ahead of the world in the field of voltage control".

IV. The new challenge in the power grid is the new mission.

Looking back on the 20 years of research on this achievement, Sun Hongbin described it as "four Fermentation starter". He called his tutors Professor Xiang Niande, Professor Zhang Boming and his initial research work the starting and foundation-laying stage. Starting from Sun Hongbin's doctoral thesis, the graduation thesis of several doctoral students in inside, the research group, has always carried out in-depth research around this research. Associate Professor Guo Qinglai's doctoral thesis has realized the application of this achievement from theory to practice and realized closed-loop operation in the control center. Wang Bin's doctoral thesis realized the cooperative operation from a single control center to a multi-level multi-control center. However, Zhang Mingye's doctoral thesis has solved the problem of the operation of the system in the PJM power grid in the United States, and has realized the application from the China power grid to the United States power grid. In addition, several doctors and masters have worked together to solve the voltage control problem of large-scale intermittent renewable energy sources such as wind and photovoltaic power generation connected to the power grid.

Each landing of the project will bring new problems to Sun Hongbin and his team and give birth to new technological inventions and thoughts. "When you get to the scene, you will find that the original assumption or the thing that has no problem may be the most challenging, which may be the source of the next innovation.” Guo Qinglai was inspired by a communication error during voltage control and began to lead his team to explore a new research direction-Cyber Physical Systems.

"It is not only the academic frontier, but also, more importantly, it is completely oriented to the major needs of the country.” In the minds of students, some "strict" teacher sun always lets everyone participate in the voltage control test on the spot. "sometimes the wind power and photoelectric bases are on the top or at the foot of the mountain in the village, and they can't buy anything. they stay there for several months. But there is no way. We will go to the scene to solve the problem."

Twenty years of intensive cultivation have brought great economic and social benefits to the operation of the power grid and significantly reduced the losses in the transmission process of the power grid. According to statistics, after the system is put into operation in Jiangsu power grid, inside can save nearly 100 million kilowatt-hours of electricity loss in one year, equivalent to an annual saving of about 50 million RMB. "China's power grid currently consumes about 360 billion kilowatt-hours of electricity per year, which is equivalent to 1 kilowatt-hour of electricity per person per day and 150 million tons of coal.” Sun Hongbin said, "Through our automatic voltage control system, we do not need to increase any equipment investment, but only through control means, we can significantly reduce losses and achieve the effect of Skillfully Deflected."

On the other hand, Sun Hongbin team proposed and implemented voltage control technology for large-scale wind power integration. Up to now, AVC system has been applied in all 13 large-scale wind/light integration areas, effectively ensuring the safe operation of new energy bases and power grids, and significantly improving the grid's ability to absorb intermittent new energy.

"Safety, high quality, economy and environmental protection are the four major goals of power grid operation. Our continuous research over the past 20 years has always focused on how to enable operators to better control the increasingly complex power grid through automatic control technology.” Sun Hongbin said, "Our system has become an indispensable and powerful tool for operators. This requires us not to stop for a moment. The new challenge in the power grid is our new mission."

"Without so many years of basic research accumulation, we would not have achieved today's results. If it were only theoretical research, we would not be able to achieve today's results without China's complicated power system as a stage for us to carry out engineering practice. "Sun Hongbin said, "As an engineering discipline, facing the main battlefield of the national economy and doing scientific research with indomitable spirit, this is what my mentor Professor Zhang Boming often taught me in those days. I also remind the young people in the team all the time now. I hope this can be passed down from generation to generation as a spirit and a value of our entire team."