Grid Security from the System Perspective

When Hurricane Sandy struck the United States, two nuclear power plants stopped working and about 3.1 million users stopped power. In the snowstorm in Yanqing, Beijing, on November 4, 15 high-voltage power lines failed.

Globally, grid security incidents caused by severe natural disasters such as hurricanes, earthquakes, and heavy snowstorms occur every year. In addition, factors such as equipment failure rate, long-distance power transmission, wind power access, and vibration of interconnected power grids all affect grid security. How to take scientific and effective measures to reduce the impact of disasters on the power system has become a major national strategic demand.

Grid Security Urgently Needs New Technology

“The major events that affect the safe operation of the power grids occur every year, such as the earthquake in Wenchuan, China. Last year's earthquake and tsunami in Japan and the hurricane 'Sandy' that hit the United States all brought serious grid safety accidents.” Professor Sun Yuanzhang, Dean of the School of Electrical Engineering of Wuhan University and a professor at Tsinghua University, told reporters of the China Science Journal.

On August 14, 2003, the largest blackout in the history of North America occurred in the United States and eastern Canada. After the electricity was interrupted in eight US states and Ontario, Canada, the United States closed nine nuclear power stations. At the same time, in the rapid economic development of our country, there has also been a large-scale power shortage, and 22 provinces and cities have severely lacked electricity.

On August 16, 2003, Chinese President Hu Jintao made instructions: “Be prepared to be free of danger, learn the lessons of the US and Canada blackouts, carefully study the power system security issues, and improve the emergency handling mechanism to ensure the safety of power production and distribution. ”

However, the interconnection of China's power grids makes the network structure more complex, more geographically distributed, and more components. It is more difficult for the analysis and safety early warning of this kind of nonlinear ultra-large-scale power system with dynamic and static uncertainties. The long-term use of local information-based power system control and static security defense systems is difficult to meet the safety requirements.

In order to improve the prevention and control function of power system security, it is urgent to study new theories and methods for dynamic safety assessment of large-scale power systems.

“The wide-area security defense system provides a possible technical platform for grid security. Its features are the use of computers, networks, communications, global satellite positioning systems and other technologies to develop new online power systems with advantages in data acquisition, transmission, and processing. Real-time monitoring and analysis methods. Among them, the acquisition of key information and online dynamic security analysis based on these key information are crucial for decision-making, said Sun Yuanzhang.

In the United States, the increase in power outages resulted from an abnormality in the energy management system of the dispatch center, resulting in “a lot of data, insufficient information”, followed by a chain failure, which eventually led to a blackout.

Sun Yuanzhang believes that to achieve the purpose of wide-area security defense of power systems, it is necessary not only to build highly informatized and automated information support systems, but also to use wide-area measurement technologies to realize online dynamic security analysis and control of ultra-large-scale power systems. Moreover, this has also become the main direction for the development of power systems in various countries.

Targeting major strategic needs

In order to solve the major strategic needs in the development of national power, based on Sun Yuanzhang’s completion of the Young Scientists Fund, Outstanding Youth Fund, and Science Foundation project, the Fund Committee has funded the “Basic Theory of the Wide-area Security Defense System for Power Systems” proposed by the Sun Yuanzhang team. And key technology research project applications.

“To completely avoid the effects of major disasters is extremely difficult, but from the perspective of power grid safety, building a good power grid structure and power supply structure, and strengthening measures to prevent plans can minimize the impact of such special natural disasters on the safe operation of power grids. Degree." Sun Yuanzhang said.

Under the funding of the Science Foundation, Sun Yuanzhang's team established a complete nonlinear control theory system for power systems. The theory has made breakthroughs in four long-standing unsolved problems, such as the unity of small interference and large disturbance stability control in power systems, and the control of grid sensitivity, and has developed a fully digital non-linear optimal excitation controller with independent intellectual property rights.

Sun Yuanzhang's team built a microgrid system in the laboratory that can measure electricity and non-electricity and connect the data directly to the Internet. Combining model structure, parameter identification, and digital simulation and dynamic phasor measurement technology, they explored the systematic modeling of multi-scale power system dynamic safety analysis and the comprehensive simulation theory method of multi-time scales, creating the power system security and On-line dynamic early warning theory of stability, proposed the theory and method of early warning, protection and control based on wide area information, and provided the basic theory and key technology for China's ultra-large-scale power system online dynamic security defense system.

With the help of the Automation Committee of the China Electric Power Association and the Hydroelectric Power Association, the team and the Institute of Automation of the Institute of Hydraulic Sciences, Huazhong Electric Power Corporation, Northeast Electric Power Group Corporation, Inner Mongolia Electric Power Company, Guangdong Electric Power Group Corporation, Gezhouba Nengda Company and other units Cooperation, after more than ten years of hard work, developed a GEC-I all-digital nonlinear optimal excitation adjustment device. The device has been used in more than 100 units such as Fengman Hydropower Plant, Haibowan Power Plant, Shajiao Power Plant, Jiaozuo Power Plant, Shalingzi Power Plant, Lianzhou, Guangdong, Shaoguan, Datong Power Plant, Zhejiang Zhenhai Power Plant, etc., which improves the safety and stability of the power grid It has produced major economic and social benefits.

For the first time, the team conducted closed-loop continuous control based on wide-area information in the actual interconnected power grid. The oscillating signals were measured in real time at six substations in Yunnan, Guizhou, and Guangdong, and transmitted to the control master station in Guangzhou. The resulting control commands were then issued. For DC rectifier stations in Gaochun and Xing'an, Guizhou, effective suppression of interval oscillations is achieved by rapid adjustment of DC power. The results of Tianguang Guangzhou's 700MW blocking disturbance test and grid dispatch department calculations show that this system is equivalent to adding a 500km line of 1000km, saving the country hundreds of millions of dollars in investment.

Sun Yuanzhang and others proposed a new concept and system integration method for the new generation of grid energy management systems for three-dimensional coordination of space, time, and objectives, and realized online global, real-time closed-loop, comprehensive early warning, and optimal control of the grid. The key technologies are at the domestic 18 provincial-level or higher grids. In the promotion, some of the key technologies were adopted by the largest PJM grid in the United States.

Minimize harm

There are many factors that affect the safety of power grids. In order to improve the operational safety of the equipment, Sun Yuanzhang’s team is currently working on the research of power grid condition maintenance. The study is expected to reduce the failure rate of the equipment.

“From my personal research, we mainly studied the reasonable structure of the power grid, such as the establishment of a strong transmission network with a voltage rating of 500kV and above, the establishment of a 110kV to 220kV distribution network with a reasonable structure, and the establishment of a microgrid with various small-scale safe and efficient power supplies. Can effectively resist the attacks of special natural disasters." Sun Yuanzhang said.

In terms of large-scale remote transmission of hydropower, the team is strengthening the research and construction of the first-end power grid construction and operation of hydropower. For the safe operation of wind power connected to the power grid, the researchers have started to carry out high-precision wind power forecasting and reserve capacity optimization. , Energy storage, safety analysis theory and methods, and research work on coordinated control of the entire network to cope with the impact of wind power fluctuations on the safe operation of the power grid.

“After relying on the funding provided by the Fund, a large number of experts and scholars have invested in the basic theory and key technologies of the wide-area security defense system of the power system, stabilized a team of professionals engaged in basic research in the country, and trained a group of PhDs in this direction. Master Sun Yuanzhang said, "The Science Foundation has played a fundamental role in the research of myself and my team. Every year, our team has doctoral students to participate in research in developed countries, or participate in international conferences to exchange scientific research results."