China's energy and power grid characteristics
With the rapid development of China's technology and economy, energy and power grids have carried many unprecedented pressures. There are many problems in energy conservation and emission reduction, energy structure, energy distribution, power distribution, disaster prevention capability, and power supply reliability.
In terms of energy conservation and emission reduction, on November 25, 2009, the State Council held a standing meeting and decided that by 2002, China's GDP per unit of GDP would fall by 40%-50% compared with 2005; according to the growth rate of 7.5%, China's GDP problem will be It will reach 74.3 trillion yuan in 2020. China's GDP energy consumption will be reduced from 1.222 tons of coal in 2005 DFP to 0.672 tons in 2020, with an annual energy consumption of 5 billion tons of standard coal, close to the sum of the United States, the European Union and Japan. If China's energy structure is not adjusted, carbon dioxide emissions will reach 12 billion tons. By then, the United States, the European Union, and Japan will have a total emissions of 8 billion tons, and the global total emissions limit will be 30 billion tons. It can be seen that China has high requirements on the road of energy conservation and emission reduction, heavy tasks, and bears enormous pressure to reduce emissions.
In terms of energy structure, the results of the 2008 global energy structure analysis show that the ratio of oil, natural gas and coal is relatively average, while China's energy is mainly coal, accounting for 70.23%, almost the global energy structure of oil and natural gas. The sum of the three categories of coal. The comparison with the global energy structure shows that China's energy structure is highly biased and its structure is irrational. It needs to adapt to the trend and make huge adjustments.
In terms of energy distribution, China's primary energy and electricity demand distribution is extremely uneven. Power flow mainly consists of northwestern and southwestern coal-fired power and hydropower bases to the eastern receiving end center. The transmission distance is long and the transmission capacity is large, forming multiple receiving ends. Center, in the future, as energy development moves westward and northward, the distance between large energy bases and energy consumption sites will be farther and farther, the scale of energy transmission will become larger and larger, and the technical requirements for transmission will also be Higher and higher.
In terms of power distribution, China's load has grown rapidly. As of March 2010, the installed capacity of power generation has reached 870 million kilowatts, and it is expected to reach 1.6 billion kilowatts by 2020. However, per capita installed capacity is still at the world average. Although power growth has slowed down this year, overall, power installation and power consumption are still in a period of rapid development for a long period of time to come. Corresponding to the rapid growth of the load is the lag of the power grid, especially the construction of urban distribution networks. In developed countries such as the United States, the United Kingdom, and Japan, the ratio of power generation, transmission, and distribution investment is 1:0.43:0.7, 1:0.45:0.78, and 1:0.47:0.68, and the proportion of power distribution investment is quite large, while China is in these three The investment ratio of the link is 1:0.21:0.12 (before 2000), and most of the investment is used for the transmission part. However, this issue has gradually received attention. In 2009, China's power grid investment surpassed power investment for the first time. Among them, the power grid above 330kV accounted for 24%, and the power grid below 220kV accounted for 76%.
In addition, in recent years, many serious natural disasters (such as the 2008 major snowstorm, the 5.12 earthquake, etc.) and power grid blackouts (such as Henan Power Grid 2006.7.1 power outage accident, Hainan Power Grid 2005.9.26 power outage accidents, etc.) on China's power grid The ability to prevent disasters poses a huge challenge, and power interruptions caused by power quality problems are not uncommon.
In summary, the characteristics of China's energy and power grid are characterized by uneven distribution of energy resources, rapid development of load, coal-based power supply structure, insufficient regulation capacity and high environmental pressure. These factors constitute the driving force for the development of China's smart grid.
New problems facing China's power grid
First, China's power grid is increasingly complex, load growth is rapid, and load characteristics are more constant. The proportion of external power receiving in the load center has gradually increased, and the problem of safety and stability has become increasingly prominent. How to prevent large-scale power outages and ensure the safe and stable operation of the power grid?
Second, in the face of large-scale renewable energy (large wind farms) and access to a wide range of distributed power sources (solar, wind, gas turbines, electric vehicles, distributed energy storage), how the grid handles all types of renewable energy, Coordinated operation after intermittent power supply and heavy load access?
Third, how to meet the increasing demands of customers on power supply reliability, power quality and other power services?
Finally, in the face of continuous improvement of the transparency of the user interface, to meet more flexible load demand, how can the power company and the user work more friendly, realize the interaction between the power grid and the user, and improve the operational efficiency, reduce the electricity price and improve the service level?
Safe and stable operation, full acceptance of new energy sources, improved power supply reliability and flexible interaction capabilities are all new issues before us. We need to increase efforts and quickly seek relevant solutions.
Microgrid technology
With the development of smart grids, microgrids and their key technologies have also become the focus of attention.
When the microgrid is connected to the grid, all micro power supplies adopt a constant PQ control strategy. When the main network fails to operate the microgrid, one of the micro power supplies will switch to the V/f control strategy. The voltage and frequency of the microgrid system will be supported until the other micro power supplies maintain PQ control operation, and cannot be adjusted with voltage and frequency. In the isolated network operation mode, the power supply and demand balance of the V/f control unit can be achieved in the microgrid, while ensuring high voltage and frequency quality. When the microgrid is connected to the grid again, the phase-locked loop control ensures that the phase angles of the frequency and voltage phases between the microgrid and the main network are consistent, and the smooth and flexible grid connection is basically realized. The PSCAD simulation study also proves the effectiveness of the control strategy. With a reasonable control strategy, the microgrid can be operated on the grid or isolated network, and can achieve smooth transition and conversion of the two operating states.
The grid adjustment based on the microgrid structure can facilitate large-scale distributed energy interconnection and access to medium and low voltage distribution systems, providing a mechanism for fully utilizing distributed energy generation.
The microgrid can be used as the third-level power grid after the transmission grid and distribution network; compared with the current large grid, this structure has significant socio-economic and environmental benefits. By establishing a microgrid, distributed power generation can be applied to the power system and exert its maximum potential.
Opportunities and Challenges
Smart grid and microgrid technologies will contribute to the development of clean energy, reduce carbon emissions, improve the efficiency of power companies, and solve the contradiction between the rapid development of China's power grid and weak grid structure; for equipment manufacturers, power companies and power Users offer new opportunities and challenges.
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