Insight into the development of the smart grid in the 21st century in China

Smart grid is a new trend and a new concept. At present, many research institutes and enterprises in China have started the research and development of smart grids.

Facing the fiery situation of domestic smart grid development, Yu Jixin, an academician at Tianjin University, believes that smart grid is not a purely technical issue. It involves many basic concepts, and the current confusion in smart grid recognition in China is precisely based on these basic concepts. This article attempts to clarify the development of China's smart grid at the level of basic concepts.

The smart grid is an automatic and widely distributed energy exchange network. It has the characteristics of two-way flow of electricity and information, and can monitor all components from power plants to consumer electronics. Smart grids use the superiority of distributed computing and communication to provide real-time information to the grid and enable it to maintain an immediate supply-demand balance at the equipment level.

At present, the western countries led by the United States are investing more in the research of smart grids. In China, relevant research and layout have also started.

However, the procedural and technical challenges of smart grids are enormous. In order to promote the smart grid, long-term continuous research and development is needed. Regulations aiming at incentives for smart grids need to be introduced , and national standards must be established in an open manner and the active participation of many related industries encouraged.

The driving force of the smart grid

There are five main driving forces behind the implementation of the smart grid, of which the first four are from the perspective of the grid, and the last one is from the perspective of national economic and industrial development perspectives.

1 ) Achieve safe and stable operation of large systems and reduce the risk of large-scale blackouts.

In recent years, large-scale chain power cuts in the world have occurred frequently and the losses have been enormous. For example, the economic loss caused by the blackout in the northeastern United States in 2003 was about US$ 6 billion, which fully exposed the vulnerability of traditional grids. It is generally believed that improving the system's global visibility and early warning capabilities, as well as achieving self-healing, is the key to enhancing the reliability of the grid and avoiding system crashes caused by accidents. Considering the vulnerability of complex large-scale power grids to natural disasters and man-made malicious attacks, the future grid will become more robust — autonomous and self-adaptive infrastructure, able to reduce power outage range and recover quickly through self-healing response. powered by.

2 ) A large number of distributed power supply access and full use.

At present, many countries in the world have raised the development of renewable energy technologies to the height of national strategies. President Barack Obama also believes that " the countries that lead the world in creating a clean energy economy will lead the global economy in the 21st century. "

Distributed generation is a small-scale power generation technology near the load side, which can reduce costs and improve reliability. Among renewable clean energy sources, solar energy and wind energy are distributed naturally because of their geographical distribution. Therefore, distributed solar and wind power generation technologies have received extensive attention.

Also among the distributed power sources are small, micro gas turbines (such as cogeneration systems, CHP ), as well as small-scale energy storage and the demand response described below. The future of tens of thousands of kilowatts of micro nuclear power is also in the field of vision.
With the advancement of technology, it can be foreseen that the future power grid will gradually get rid of the model of single centralized power generation in the past and turn to the mode of distributed generation-assisted centralized power generation. Such as Denmark or a centralized power grid system in the mid-1980s, and today has become more decentralized system.

When a large number of distributed power sources are integrated into large power grids, most of them are directly connected to distribution networks at all levels, making the power grids from top to bottom a power flow system capable of bi-directional flow on the branches, but the current distribution network It is based on one-way flow design and does not have the potential to effectively integrate a large number of distributed power sources. It is difficult to deal with the uncertainty and intermittent nature of distributed power sources, and it is difficult to ensure the reliability and safety of the power grid.

3 ) Peak load problem and demand side management.

Because there are no economical and efficient means of large-capacity energy storage, the occurrence and consumption of electricity must always be balanced. The power load changes with time. To meet the balance between supply and demand, power facilities must be planned and constructed based on the peak load throughout the year.

However, due to the fact that the time around the peak load of the system is very short each year, the utilization rate of power assets is low. U.S. real power grid assets have a utilization factor of about 55% , while the utilization of power generation assets is not high. The utilization of distribution network assets, which account for 75% of the total assets of the entire grid, is even lower. The annual average load rate is only about 44% , and a large amount of investment in fixed assets is wasted.

The survey shows that China’s current 10kV distribution asset utilization rate is lower than the United States. The average annual load rate of 10kV distribution lines and transformers in most cities is less than 30%; under the condition that the main grid component can also guarantee safety after a mains failure, the line load rate at peak load is below 50% . One way to solve the above problem is to reduce the peak-to-valley difference in the load curve.

At the same time, in order to cope with the unforeseen events of the grid and the uncertainty of the power load, the power system must maintain (10%~13%) capacity margin ( also called spin-standby ) at any time to ensure reliability and peak load demand , which also increases the Power generation costs and demand for power generation capacity.

Fortunately, there are a lot of loads in the real system that can be friendly with the grid. Such as air conditioners, refrigerators, washing machines and other appliances can be suspended during periods of peak power load ( high electricity prices ) , and properly translated to the low-power period when the power supply is not tight ( low electricity prices ) to help use the grid to achieve the power load curve. Peak clipping and filling.

At the time of the peak load of the typical peak load in the United States, the residential electricity use accounted for 30% of the peak load, of which 2/3 , or 20%, belongs to the load that can be friendly with the grid, and its value exceeds 13% of the peak load. Spare capacity. If the corresponding technical support can be provided, and through the interaction between the power company and the end user ( demand response or power consumption management ) , peak load shedding of the power load curve can be achieved.

Residual electricity consumption in cities in China accounts for 15%~20% of the peak load at the peak load of the typical annual load day. About half of these are the translatable loads that can be friendly with the grid. It should be noted that if we can reduce the peak load of 6% to 8% , the amount of power assets it saves is already very large. What's more, business users and industrial users have the potential to cooperate friendly with the grid.

This friendly cooperation between the demand side user and the power grid can also replace the rotation reserve if necessary to support the safe operation of the system. For example, in the afternoon of the beginning of 2008 , Texas in the United States experienced a sudden and unexpected drop in wind power: a 1.3 million kW drop in power generation in three hours. An emergency-responsive demand response program at this time enabled large industrial and commercial users to recover most of the lost power within 10 minutes, acting as a buffer for intermittent power fluctuations. The premise of this emergency response program is a pre-signed agreement between the grid company and the user.

4) Increasingly stringent constraints on the grid ( improvement of reliability, improvement of power quality, energy conservation, loss reduction, and environmental protection ) are increasingly strict.

In the past 20 years, communication and information technology have made great progress. United States in the 1980s, the electrical load embedded chip computerized systems, installations and equipment, as well as sensitive electronic equipment automated production line is still very limited. Today, the share of this part of the power load has risen above 40% , and it is expected that it will exceed 60% in 2015 , placing high demands on the power supply reliability and power quality of the power grid.

The survey shows that US companies spend more than US$ 100 billion each year on power outages and power quality problems, which is equivalent to a user spending $ 1 on every purchase of electricity and a loss of 30 cents on power outages. Among them, the annual cost of disturbances and power interruptions ( excluding blackouts ) amounts to 79 billion U.S. dollars. Table 1 shows the forecast of the power reliability requirements of the users of the American Academy of Electric Power (EPRI) for the next 20-30 years. The current power grid not only fails to meet these needs of the digital society, but it also lags behind in the application of digital technologies, especially in distribution networks.

With the adjustment of industrial structure and industrial upgrading, there will be an increasing number of digital companies in China that place higher demands on power supply reliability and power quality.

In fact, the distribution network is also a bottle that improves the reliability of the user's power supply. Surveys have shown that the impact of power outage time on users of power grids below 10kV in China accounts for 70%~80% . Even minus the planned outage time, China's large cities the annual average outage time users mostly in one hour, mostly a few hours, or even longer. In Tokyo, Japan, because of its flexible network topology and distribution automation, the average annual power outage of its users is only 2 to 5 minutes ; in the event of a major component failure in the power grid, the peak can still be guaranteed. Line load rate up to 75%~85% ( as stated earlier, the value in China is less than 50%) .

5) Especially worthy of our attention is: due to a wide range of technologies, a key goal of the smart grid is to create new technologies and business models, provide new support for economic and technological development, and achieve industrial revolution. Cisco predicts that the smart grid has a larger market space than the Internet.