Under the new energy and distributed power system) Chengming Southeast University Electric Power Demand Side Management Institute Nanjing Nanjing 210096, Jiangsu Province, the basic principles, key technical content and development status of the domestic and international development of power systems, reviewed the impact of distributed power supply on the power system and Prospects.
23 Wind power Wind is a natural phenomenon that people are very familiar with. It is because the sun heats the air, the hot air rises, and the cold air replenishes the air to form a huge amount of energy. Therefore, wind energy, like solar energy, is an inexhaustible and clean renewable energy source. However, wind energy is a kind of process energy. Unlike fossil fuels such as coal, oil and natural gas, wind energy cannot be stored directly. Only when it is converted into other energy can it be stored. According to different needs, wind energy can be converted into other different forms of energy, such as mechanical energy, electrical energy, thermal energy and so on. Due to the unparalleled superiority of electric energy, converting wind energy into electric energy, that is, using wind power, has become the first choice for people to use wind energy, and has been rapidly developed in recent years. At the end of 1997, the global installed capacity of wind power was 7,636 MW. By the end of 2001, it had increased to 24,000 MW. In just four years, the capacity has increased by 214X, making it the fastest growing power generation method in the world.
Wind power generation is currently the most mature and most promising commercial development prospect in new energy development. The principle of wind power generation is: natural wind blowing blades, driving generator rotor rotation, professor, doctoral tutor, department head JEEE senior member, China Electric Power Education Association, electrical engineering subject teaching committee, deputy director, vice chairman of Jiangsu Electric Power Technology Society Long and Secretary General. The main research directions are: micro-motors and their measurement and control systems, power electronics and motor integration systems, electric vehicle drive and control, distributed power technology.
Electricity. Wind turbines for wind turbines mostly use a horizontal axis and a three-blade structure. The diameter of the blade is lengthened with the increase of the capacity of the single machine. The largest rotating blade in the world has a diameter of 66m and a height of 80m16. The power regulation is one of the key technologies of the wind turbine. Adjustment mode: one type is fixed pitch stall control; the other type is variable pitch control. Most wind turbines have an alignment mechanism that automatically winds the turbine. With the development of technology, new wind turbine systems such as wind-enhanced wind turbine wind-up and speed-limiting automatic control systems have emerged. 2.3.1 Wind turbine type According to whether the wind turbine generator speed is constant, wind power generation can be divided into There are two modes of fixed speed operation and variable speed operation; according to the structure of generators, there are asynchronous generators, synchronous generators, permanent magnet generators, brushless doubly-fed generators and switched reluctance generators. Early wind turbines mostly used asynchronous generators with speed-increasing devices. The power frequency AC power of the asynchronous generator structure can be directly used or input to the grid via a transformer. In most cases, the asynchronous wind turbine fixed-speed rotary line asynchronous motor can adjust the torque by low-frequency excitation by connecting the variable resistor to the rotor, and can also operate at variable speed. Because the excitation current is to be obtained from the grid, asynchronous wind power cannot generally be run separately from the grid unless the excitation is obtained in some way.
Synchronous wind turbines do not require a speed-increasing transmission structure, and the overall structure is simple. With the advancement of power electronic converter technology, advanced synchronous wind power generation often adopts the AC-DC-AC access method, that is, the communication between the new technology and the distributed power system (below) is turned into DC. And then inverting into a power frequency AC access user or grid. The advantage of this type of power generation is that the generator speed does not have to be synchronized with the speed required by the grid frequency.
A permanent magnet generator is a synchronous generator that uses a permanent magnet instead of an excitation magnetic field and has no excitation system. With the high-performance, low-cost NdFeB magnets, the popularity of the dFeB magnets has become more excellent. The permanent magnet synchronous wind turbines with good structure and simpler structure have become possible.
The brushless doubly-fed motor is actually composed of two wound-type asynchronous motors. The coaxial connection of the two rotors eliminates the slip ring and the brush. The generator can control the excitation current of the exciter under the condition of varying rotor speed. The frequency is to ensure that the generator output current frequency is kept at 50H - so the brushless doubly-fed generator can realize variable-speed constant-frequency power generation. 2.3.2 Operation mode of wind power generation/4 The operation mode of wind power generation can be divided into independent operation, grid-connected operation, and complementary operation with other power generation modes. Independent operation means that the electric energy output by the wind turbine is stored by the battery and then supplied to the user. This method can be used in remote rural areas, pastoral areas, islands and other areas that cannot be reached by the power grid. Generally, hundreds of to single-unit capacity of single-machine capacity is connected to the grid. In wind-rich areas, wind turbines are installed in a certain arrangement to become wind power. The electric energy generated by the electric field is sent to the power grid through the transformer. This is the main way of wind power generation. Wind power is complementary to other power generation methods, such as wind-diesel unit complementary power generation, wind-solar photovoltaic power generation, wind-fuel battery power generation, etc. This method not only compensates for the sudden change in power generation caused by wind speed changes, but also ensures balanced power supply throughout the year, and can extend battery life. At the same time, it can also reduce the power generation cost of off-grid small-user power generation systems. Natural resources Get the most out of it.
2.3.3 Overview of domestic and international development of wind power generation In the early 1970s, due to the oil crisis in the Middle East, wind power started in a difficult time. In the 1980s, wind farms began to be built around the United States and Denmark. In the 1990s, wind power installed capacity increased at an average annual rate of 203. Europe is the world's most developed region for wind power generation. Last year, Europe's wind power generation capacity increased by 4,500 MW, making the total power of wind power generation in Europe reach 17 000 MW, accounting for more than 703 of the world's wind power generation capacity. As the scale of production of wind power equipment expands and the level of technology increases, the cost of wind power is declining. For example, the cost of wind power in the United States has decreased by 803 in the past 20 years. When the first batch of wind turbines were installed in the 1980s, each dry tile The cost of wind power is 30 cents and now it is only 4 cents. At the same time, people are studying various new wind power technologies. It is reported that three British institutions and the University of Stuttgart in Germany have recently begun to experiment with wind power technology between high-rise buildings. The principle of this technology is not complicated. People will feel the wind suction as long as they stand between the buildings. The wall between the two floors is vertical, the wind will not be blown away here, and it will be blown directly into the turbine, which is more concentrated than the wind in the open area. According to the calculation, this method can generate 253 more electric energy than the ordinary wind turbine. If the research is successful, it will hopefully change the power supply structure of the city.
China is a country rich in wind energy resources. The total amount of wind energy resources available for development and utilization in the country is 253 million kW. The southeast coast and nearby islands of Xinjiang, Inner Mongolia and Gansu Hexi Corridor are rich in China's wind resource-rich areas. value. China's wind power generation started from the 1980s. By the end of 2000, the national wind power installed capacity was only 344MW. During the 10th Five-Year Plan period, China plans to add 1 192 MW of wind power. The development focus is as follows: First, build 3~5 seas for 100MW wind farms. Antagonize offshore wind farms and achieve economies of scale; second, encourage wind power projects that have wind energy resources but have not yet built a wind farm area to develop wind power projects.
In order to encourage the development of wind power, the State Council recently approved a preferential policy for wind power generation to be levied at half the value-added tax. According to this new policy, China's wind power prices will be reduced by 0.05~0.06 yuan/Wh on average, and the price of new wind farms is expected to fall below 0.5 yuan/fcWh). The introduction of this policy will have a positive impact on the development of wind power industrialization in China.
2.4 High-speed flywheel energy storage system High-speed flywheel technology was a hot spot in technology development from the 1970s to the early 1980s. After the Middle East oil crisis, people's interest in it slowly declined. In recent years, with the development of high-strength composite materials and low-cost bearings, as well as the needs of distributed power and electric vehicle applications, high-speed flywheels have once again become a research hotspot.
The high-speed flywheel energy storage system is a typical high-tech mechatronic system that combines the latest magnetic levitation technology, high-speed motor technology, power electronics technology and new material technology to support high-intensity flywheels that operate at ultra-high speeds. The basic structure of an 18-gas high-speed flywheel such as a magnetic suspension bearing capable of efficiently and bidirectionally converting electric energy and mechanical energy with a small loss of a magnetic suspension bearing is shown.
Unlike the traditional mass flywheel, the ultra-high speed flywheel is light in weight and extremely high in speed because of the wheel speed. It can be seen from the above formula that the stored energy is proportional to the moment of inertia, and the Science and Technology Xinyuan is proportional to the square of the flywheel speed. Therefore, in order to increase the energy, the flywheel speed should be increased as much as possible under the conditions of the flywheel strength. At present, the maximum speed of a typical ultra-high speed flywheel is 30 000~50000r/min. The most advanced high-speed recording is 600,000 r/min. The conversion between electric energy and mechanical energy in the flywheel energy storage system is based on the motor and its control system. In the process of storing and releasing energy, the speed of the motor and the flywheel is constantly changing. Therefore, in addition to the high-efficiency motor, a high-efficiency power electronic power conversion device must be equipped to ensure the flywheel energy storage system. The speed of the motor can be controlled continuously during energy storage, and the load can meet the frequency and voltage requirements when the energy is released. The motor-generator in the flywheel energy storage system has been integrated into one component. When charging, it acts as a motor, absorbing energy from the outside to accelerate the flywheel, and "discharging" acts as a generator, converting kinetic energy into electrical energy and outputting it to the outside. At this time, the speed of the flywheel is continuously decreasing. For the high-speed flywheel energy storage system, there are a variety of motors to choose from: induction motor, switched reluctance motor, permanent magnet brushless DC motor and double salient permanent magnet motor. It is worth mentioning that the new double salient permanent magnet (DSPM) motor that has appeared in recent years has a potential characteristic i3*2 which is very suitable for the energy storage of the flywheel. It is a schematic diagram of the structure of the DSPM motor. The motor not only has the traditional permanent magnet brushless DC. High motor efficiency, no commutator and brush, no maintenance, etc. The most outstanding advantage is that the permanent magnet is placed on the stator of the motor. There is no permanent magnet on the salient pole rotor, and there is no high mechanical strength of the winding. It runs at high speed and there is almost no loss or heat on the rotor, which is very important for the flywheel rotor that is vacuumed to reduce wind and friction losses. Because the heat generated by the rotor loss under vacuum conditions is difficult to dissipate.
One of the characteristics of flywheel energy storage is that the flywheel continues to rotate at high speed during a fairly long standby time. Therefore, it is necessary to maintain the rotating function of the flywheel and eliminate the friction loss of the bearing. This is also the key to achieving the efficient flywheel of the eyebrow necessary to extend the life of the bearing. The traditional mechanical bearing has a large friction coefficient and is not suitable for the flywheel rotor load-bearing in the high-speed, heavy-duty flywheel energy storage device, but its structure is simple, compact and strong, and it is generally used as a backup bearing in an emergency state. In recent years, magnetic suspension bearings have outstanding advantages such as high speed, no mechanical contact, no friction, no lubrication, long life and adjustable dynamic characteristics. They are especially suitable for use in flywheel energy storage systems because magnetic bearings are non-contact. The use of such a bearing can greatly reduce the friction loss of the flywheel. Recently, superconducting technology has also been introduced into such bearings, and friction loss is expected to further reduce the application prospects of 22 flywheel energy storage technology. First, it can be used for power grid peaking. When the grid load is at a low point, the flywheel system's motor drags the flywheel to accelerate the conversion of 2 electric energy into kinetic energy. At the peak of power consumption, the flywheel drags the generator to convert the kinetic energy into electrical energy.
Compared with pumped storage, flywheel energy storage system is superior to pumped storage power station, especially in areas where water resources are lacking. After the flywheel energy storage system is put into operation in the power grid, the power system load level can be effectively adjusted and the static stability and transient stability level of the power system can be greatly improved.
The flywheel energy storage unit can also effectively improve the voltage level and power supply reliability of the system as an adjustable reactive power source and an accident backup power supply. B. Secondly, the flywheel energy storage system is combined with new energy power generation systems such as wind energy and solar energy, which can effectively overcome The shortcomings of wind and solar energy vary greatly with seasons and time, and the advantages of fast response of the flywheel system are fully utilized to make full use of the stable energy generation of the new energy power generation system.
Furthermore, the flywheel energy storage system can be installed in an electric vehicle as a power source, which is called a flywheel battery, and the flywheel system can also be applied to transportation vehicles such as trains and ships. When braking, the braking energy is stored by the motor into the mechanical kinetic energy of the flywheel, which becomes a renewable energy. When high-power work is required, the kinetic energy is released for the system to use 2 braking energy for reuse, which improves transportation. The efficiency of the tool. In addition, the flywheel system has important application value in aerospace, military equipment, medical equipment, computer stations and other places.
3 Conclusion In summary, the distributed power system closely related to new energy is a typical high-tech system, involving today's new materials technology, power electronics technology, motor drive technology, semiconductor technology, electrochemical technology, demand side management, etc. . It has a series of advantages such as small scale, short construction period, small land occupation, easy operation and maintenance, high efficiency, economy, reliability, and low pollution. It can not only provide users in industrial and commercial enterprises, residential quarters, high-rise buildings, but also users in isolated and remote areas. Electricity, and can be incorporated into the demand side management DSM system of existing power systems to provide emergency power support services for power companies. The complementary and coordinated supply of distributed power supply and large-scale power supply is an ideal way to comprehensively utilize existing resources and equipment to provide users with reliable and high-quality power. As a result, distributed power sources will have an increasing share of the power market, especially new loads, and have a huge and far-reaching impact on the entire power system. First, a significant portion of the new load will be met by distributed power sources. The demand for centralized power plants and long-distance transmission lines will be reduced. And because of the role of distributed power sources with peak-shaving and balancing loads, existing power transmission facilities The utilization rate will be greatly improved, and those that have extremely low utilization rate and only meet the needs of the peak load technology Xinyuan will no longer have to be built. Secondly, the introduction of distributed power supply will completely change the planning and operation of traditional distribution network junctions. Then the popularity of distributed power sources will have a profound impact on the direction and final pattern of the power market. Since the user can buy electricity from the power company, or use his own distributed power supply to sell electricity to the power company or provide services such as paid peaks for the power company, a new relationship will be formed between the power company and the user. In other industries, the postal gas company has opened the door to the electricity market, and the competition in the entire power market will become more intense. Therefore, the development of new energy and distributed power systems is both an opportunity and a challenge for both technical personnel engaged in research and development of new energy and distributed power systems, as well as for traditional power companies. mouth
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