The future is a combination of large power grids and microgrids

Lu Qiang Professor of the Department of Electrical Engineering at Tsinghua University, a member of the Chinese Academy of Sciences, a member of the Royal Swedish Academy of Engineering Sciences, a member of the Standing Committee of the Eighth, Nine, and Tenth CPPCC National Committee, and a vice chairman of the eighth and ninth Central Committee of the Democratic League. His books include "Optimum Control of Power Systems," "Nonlinear Control of Power Systems," and "Nonlinear Control Theory and Power System Dynamics (British)", and are considered as the subject of linear optimal control and nonlinear optimal control of power systems. Trailblazers and founders. He used to be the chief scientist of the 973 program “Control of Catalyzed Disasters in the Power System” and successively presided over more than ten major scientific researches such as “non-linear robust stability control of power systems”, “intelligent control of power systems” and “non-linear excitation of Three Gorges generator sets”. project. In recent years, the power system hybrid control theory has been established, which provides the theory and method for the construction of China's intelligent dispatch system. It is applied to the northeast, Shanghai power system and Shenzhen power grid intelligent dispatch automation system.

China Electric Power News: What do you think is the reason for haze weather? What is the relationship with the burning of fossil fuels such as coal and oil?

Lu Qiang: There are many reasons for haze weather: coal-fired power plants and automobile exhaust (while the road is blocked, its exhaust gas is 4 to 5 times normal), and the construction is savage. The construction (disposal of cement and sand, and cleanup after “completed”) and decentralized heating methods in winter still exist, together with China’s unique way of cooking hot oil and kebabs spread all over the streets. When it comes to the use of coal, I think at least one-fifth or one-quarter of the coal should be turned into coal gas for utilization. It should be more gas-fired than coal-fired, so coal gasification and liquefaction projects should Become the mainstream of the coal revolution. The coal revolution does not mean that coal is not used, but rather good coal (with low ash content and sulfur content) is used. We should change the way we use coal. Now we also cooperate with many countries in oil and gas. The shale gas revolution in the United States has reduced its dependence on oil by about 30%. In the future, our third industrial revolution may also become a coal gas giant. Some people say that coal gasification costs money. There is a fundamental problem to solve here. What is our development? The people’s yearning for the blue sky and white clouds is our goal.

"Development of Southwest Hydropower is not to be delayed"

China Electric Power: What role do you think the grid should play in the energy revolution?

Lu Qiang: The power grid should play a backbone role in the energy revolution, because in a country's use of terminal energy, the higher the percentage of electrical energy, the more mature the country’s economic, technological and social development. Therefore, the energy revolution must first focus on electricity, through the promotion and application of electricity to drive the revolution of the entire energy system.

China Electric Power News: What kind of relationship should the grid and power supply be in the entire revolution?

Lu Qiang: I think the relationship between the power grid and power supply is like the relationship between the human nervous system and the digestive system and the brain. It is a complete system. Therefore, the power supply and power grid cannot be separated during operation. To talk about the revolution, we must talk about power supply.

China Electric Power News: What is your opinion or suggestion on the development of China's power supply?

Lu Qiang: In the energy revolution of the future, we should make up for the lack of development of major hydropower in the past 10 years, such as the development of the Nu River and the Brahmaputra. There is a total of about 500 million kilowatts of hydropower in China that has not yet been developed. Hydropower is the cleanest renewable energy source without any carbon emissions. If we do not put enough manpower, energy, and financial resources into the active development of hydropower in China, the empty energy revolution is meaningless.

When I graduated from university, that is, in the 1960s, the geological exploration of the Nu River and the selection of the site began. However, there is an unpredictable force in foreign countries that has hindered the development of China. They established the so-called environmental protection fund under the banner of environmental protection. To blind people who do not know the truth. Because once the Nujiang River is developed, its total installed capacity will be no less than that of the Three Gorges, and its immigration is only one-fifth to one-hundredth of that of the Three Gorges. In the future, the development of the Nujiang cascade hydropower station will play a huge role in the revitalization of China's energy resources. The role. Over the past decade or so, the Nu River has remained unmoved. Our golden period of development is not long enough for us to delay.

China Electric Power News: But there are people both at home and abroad who question the impact of hydropower development on the ecology.

Lu Qiang: I went to Nujiang to see that the people had to use fire to eat. Therefore, they cut wood on the mountains. Now that the trees that can be cut around have been cut almost, they begin to cut trees in the mountains, destroying the ecology of the Nu River. Seriously, it is poverty and lack of electricity. Regarding the issue of immigration development, the development of the Lancang River has brought a good start to the destruction of an acre of forest or grassland to replant an acre or even two acres. There is now a good mechanism, which is related to economics and gives immigrants shares so that they can make them rich and their children and grandchildren benefit from the development of the Nu River. Therefore, the Nu River must be developed. This is China's sovereignty. The absence of sovereignty amounts to the loss of sovereignty. Even if it is developed now, it takes about 10 years before the first unit goes into production.

China Power News: Is it related to previous failures in hydropower development?

Lu Qiang: Some people are now questioning some problems in the Three Gorges. In fact, these problems are not insurmountable, nor are they out of control. For example, Poyang Lake and Dongting Lake will show “inverted” phenomenon when the water level in the lower reaches of the Yangtze River is low. We learn that water conservancy knows that if we calculate and dynamically simulate a given “minimum allowable water level in the lower reaches of the Yangtze River,” we can solve this problem. questionable.

In fact, the Three Gorges is not dominated by electricity generation. Its main functions are flood control, drought prevention, and shipping.

Regarding Sanmenxia’s situation in Sanmenxia, ​​I don’t think it will. Sanmenxia was designed by former Soviet experts. At the time, Soviet experts took the collected information to Ukraine and designed it in the office. The collected data gives an optimistic estimate of the upstream soil erosion, which is 10 times lower than the current loss. So Soviet experts designed Sanmenxia on the basis of the design method of the Volga River. This was related to the historical conditions and institutions at that time. It is impossible to happen now.

Regarding the development of the Yarlung Tsangpo, it should be carried out at the same time as the Nu River. Even so, its first unit will be put into operation 10 years later than the Nu River, because the project is too large. There is actually a way to solve the earthquake problem. Instead of a concrete gravity dam, we can use a rockfill dam. This type of dam is not afraid of earthquakes and there is no risk of collapse, and the stone can be sourced locally. By the way, the number of immigrants Yajiang developed was less than 51% of the Three Gorges.

Also don't forget to use nuclear power. The root cause of major nuclear power plant accidents in various countries is the destruction of the cooling water system. However, the “high-temperature gas-cooled reactor” is inherently safe. It does not use cooling water and is cooled by gas convection. In the worst case, it is air convection cooling. . The unit capacity of such a nuclear power plant should not be too large. This distributed nuclear power plant site with inherent safety can be closer to the load, and it can be built anywhere without the need to sit on the seashore.

"Shanghai should not have too many UHV DC landing points"

China Electric Power News: After the development, it is the problem of power transmission.

Lu Qiang: Yes, this time it is connected to the power grid. How to send? One of the major destinations is the Yangtze River Delta, and the other is the Pearl River Delta. This requires UHV. At present, the maximum safety distance for 1000 kV AC UHV transmission is about 600 kilometers, and the maximum power is 6 million kilowatts. If a compact line is used, it can be sent to 700 kilometers to 800 kilometers. Even so, the distance is still not enough, so UHVDC must be used. . The ±800 kV DC line can be sent over 2000 kilometers because it has no synchronization stability issues.

The current UHV DC transmission can only be a "point-to-point" approach. On its way, it cannot distribute electricity on the spot. This is a big problem. In addition, if under certain special circumstances, the “Ultrapolar Lockout” occurs twice in UHV DC transmission lines sent to Shanghai, then Shanghai will lose millions of kilowatts in an instant. Can East China Grid withstand this? In addition, the Shanghai AC power grid at the end of the HVDC transmission needs to support a sufficient amount of dynamic reactive power compensation capacity. To sum up, we can see that East China Power Grid should have a strong AC grid to take its responsibility. It seems that in the future, more ±800 kV DC lines will be sent to the southwest, and scattered spots will be better. Another idea is that it can be sent to Central China with some DC UHV first, and then sent to East China with AC UHV. This is also a good solution.

China Power News: Why must the process of sending Huazhong from Huazhong be an exchange UHV?

Lu Qiang: Because this distance is the most suitable distance for UHV exchanges. We need to consider comprehensive factors such as safety and economics, including the issue of transmission corridors, as UHVs are more intensive. In the future, we also need to encourage the use of compact UHV lines. Now our UHV transmission corridor is about 20 meters, and the compact one is 9 meters to 10 meters. This technology must be applied. There are already some test routes. It is not high in terms of total cost, but many construction companies do not have experience in this area.

"The essence of smart grid is optimization"

China Electric Power News: Now that the concept of smart grid is hot, how do you understand it?

Lu Qiang: Until now, the United States has not given a clear definition of smart grid. I think the essence of smart grid should be optimization. Until now, both the high-voltage grid and the low-voltage grid have been controlled by dispatchers. Take the example of the United States' “8̇14” blackout. In the United States, if the dispatcher has made a wrong instruction, he must be held liable. In the event of an emergency, the dispatcher should make the right decision within 10 seconds and then move backwards. In this case, the dispatcher dared not make a decision. As a result, no dispatcher sent any authoritative instruction within 29 hours.

Therefore, in the future power grid, we cannot rely mainly on people for dispatch. We must conduct automatic control through information technology and computer science to achieve a complete closed-loop system for the entire power system. China's current dispatch is a five-level dispatching system. The upper and lower contacts are based on traditional methods such as telephone calls. Once there is a major accident, it may not be possible to control it.

The following is a multi-index optimization problem. One thing is from "good" to "better" to "best". This is mathematically an optimization category. The establishment of a smart grid also belongs to the category of optimization. There are two types of optimization, one is single-indicator optimization, and the other is multi-indicator optimization. The requirements of the power system are safety, economy, high power quality, etc. Therefore, the optimization of the power system is a multi-indicator optimization. The multi-index optimization of power large-scale systems is a macro variation problem in mathematics, because each generator is described by a five- to seven-order differential equation, and 10,000 generators are 50,000-70,000 differential equations. In addition, the constraint conditions of the upper and lower bound nonlinear algebraic equations of tens of thousands of nodes, and then the analytical solution of an extreme value, which can not be solved mathematically.

When the power system is so complicated that pure mathematics cannot solve it, we need to find a new way of thinking.

We proposed hybrid control theory, which is to put people's needs for the power system (safety, economy, quality, etc.) all together and write it into multi-index optimization software into the control system.

The third industrial revolution proposed that information science and traditional science embrace each other. Therefore, we need to collect data from each power plant and sensor of each important node in a power system to a large database. The SCADA unit fetches data from the database. After it is fetched, there is a process to remove the pseudo-faith, called the state estimation. Then use these reliable data to compare with the pre-agreed optimal state. If the difference is greater than the predetermined value, an “accident” is formed, and control must be started. Before the control, you need to test whether this control scheme is effective. If the effect is good, you can control the power plant, substation, control the load, control the charge and discharge of the electric vehicle, and control the household appliances. After the control, the new operating status is generated. New data If the optimal control criteria are met, the incident is eliminated.

So it becomes one of the simplest theories: events start control and control eliminate events. Throughout all this, people did not participate.

The current communication technology can do it. For example, the dispatch in Shanghai has already been done initially. Shanghai's dispatchers originally monitored and now become primarily surveillance. Therefore, communication and mathematics entered the classical power system, resulting in the third industrial revolution of the power system, resulting in a smart power system.

This power system is essentially a "robot". Because the essence of the robot is the automated electromechanical system created by man, and this electromechanical system must obey man's original will. Achieving multi-target self-optimization is called an intelligent robot. The power system is not a general form of robot, but a wide-area robot. Therefore, the task we have to accomplish is to build China's power system into an intelligent wide-area robot. That is, we must establish an intelligent dispatch system for our five-level dispatch. .

China Electric Power News: Is there a difference between the smart grid we are building and foreign countries?

Lu Qiang: The smart grid proposed by Mr. Obama mainly refers to the power grid that is equivalent to China's 110 kilovolts and is part of the distribution network. While our large units are all connected to a 500-kilovolt grid, we need to build smart power systems and smart grids in China, not just smart grids. Now that Shanghai has almost achieved, Shanghai's original dispatch center has only automatic power control (AGC), no AVC, and now realizes intelligence. The two are cooperatively controlled, which puts the possibility of accidents in Shanghai's power system, especially the breakdown of voltages. The chance of accidents is significantly reduced. A man-machine interface that is most welcomed by the dispatcher is to dynamically mark the operating point and the boundary of the stable domain in real time. If there is an accident, the dispatcher automatically gives and executes the control strategy. The dispatcher also has the right to make manual adjustments.

"The future will be a combination of large grid and micro grid."

China Power News: With the development of micro-grid, will the self-sufficient model later replace the current large-scale power grid?

Lu Qiang: Microgrids are feasible in local areas such as schools, families, large-scale playgrounds, and hotels. Now our country's power is greater than the sum of the entire European electric power, so the future development mode of China's power grid must be a combination of super-large backbone network and distributed micro-grid.

China Power News: Will microgrids play a leading role in the future?

Lu Qiang: The microgrid will dominate in the future when it is peaking. We now have low power after midnight, and the power in the peak hours is insufficient. We need to use large-scale thermal power plants and pumped storage power stations to adjust the load curve.

In the future, we will transition to the main body that uses load as the peak load adjustment, so that the demand side will actively respond to the needs of the economic operation and emergency control of the large-scale power system and solve it from the perspective of demand.

China Electric Power News: This puts forward higher requirements for the development of energy storage.

Lu Qiang: At present, the construction of pumped-storage power stations requires relatively strict geographical conditions and is not suitable for the development of distributed energy storage in the future. The use of storage batteries for energy storage has the disadvantages of high price and short life. If we want to store the electricity generated by the Three Gorges for ten hours, we will need to use a large number of dedicated buildings to store the batteries. It will be necessary to replace them once again in three or four years. It is obviously unrealistic.

Now, there is a better idea to use a compressed air compressor to store energy, use air from abandoning the wind, discarding water, and disposing of light to compress the air, compress the air in a container capable of holding 200 atmospheres, and wait until it is used. Then the compressed air is blown out and the turbine is impulsively driven to generate electricity. At the beginning of September this year, we will conduct a test of compressed air energy storage in the Wuhu National High-tech Development Zone in Anhui Province.

Now a better project is to construct a large-scale air-pressure storage room underground. After thorough investigation and research, this type of underground construction is not a difficult task for our country. The above scientific experiment project is supported by the State Grid Corporation of China.

China Electric Power News: How do you see the future development of electric vehicles?

Lu Qiang: Electric cars have an irreplaceable role, that is, lithium batteries are mature, although lithium batteries are not feasible for centralized large-scale energy storage, but they can be used in distributed energy storage of electric vehicles. An electric vehicle is almost 5000 kilowatts of storage power, developed, the country is a huge amount. If electric vehicles are storing energy when the grid is down, the benefits are enormous.

However, electric vehicles must use smart meters and can display the electricity price curve with a half-hour ladder.

And the charging pile and the charging station must be two-way: the owner can sell electricity at high electricity prices, and charge at low prices, which becomes a "cash backcar", which is very conducive to the purpose of peaking the grid. .

China Electric Power News: But now the recycling of lithium batteries is a problem.

Lu Qiang: Yes. Therefore, we need to pay close attention to the project and study the recycling of lithium batteries to prevent pollution.

China Electric Power News: In this case, the electricity price system also needs to be adjusted accordingly.

Lu Qiang: From the point of view of economics, the price of electricity should be similar to the stock market in the future. There is a daily power price curve. Its change can be sent to each owner’s smart meter in hours.

China Electric Power News: On a global scale, you are observing the changes or innovations that are taking place in the energy industry in terms of production concepts and technologies.

Lu Qiang: I think it is the shale gas in the United States. The geological conditions in the United States are very good and the potential for future development is very great.

China still has 500 million kilowatts of hydropower to be urgently developed. It is coal gasification and the establishment of distributed small and medium-sized nuclear power plants with inherent safety.