First, an overview of advanced power transmission technology
People's application and understanding of electricity and power science and technology are the first to start from the DC. Early DC transmission voltage transformation exists, the power is difficult to upgrade, the motor brush commutation, low reliability and other series operation. In 1895, the United States Niagara composite power system was completed, established the dominant position of AC transmission.
As the AC power transmission technology with easy voltage conversion, easy to achieve more off-point power, the current there is a natural zero-crossing, high current breaking easy to achieve and other advantages. In the early 20th century, the exchange system started to develop rapidly. Over the past 100 years, the AC transmission voltage has been gradually developed from the initial 13.8kV to 35,66,110,220,330,400,500,750,1000kV.
However, with the formation of wide-area AC power grids, the technical problems of AC power grids are constantly emerging. Large-scale power grid accidents in the world continue to occur: synchronization problems, stability problems, transmission distance problems, transmission efficiency problems and transmission corridors. Therefore, we can not help asking: is the AC power transmission system the only technical means of power transmission in the future?
Because of the inherent shortcomings of AC power transmission that can not be serviced, modern DC transmission technology overcomes some of the inherent disadvantages of AC power transmission technology. With the development of inverter technology, the voltage level and capacity of flexible DC transmission projects rapidly increase. In addition, the ever-decreasing system losses and costs greatly facilitate the application of flexible DC engineering.
With the development of power electronics and other technologies, the major technical problems restricting the development of modern HVDC transmission are expected to be solved in the next three to 10 years. Future HVDC technology ideas in two ways, AC - DC - AC and DC - DC - DC.
The reverse distribution of energy and load in our country determines the long-term strategy of long-distance and large-capacity transmission in China's power grid development. The increasing demand of trans-regional power transmission and the decrease of environmental carrying capacity have put forward higher requirements on the transmission efficiency and resource utilization level.
China has built the world's largest and most complex power grid. The large-scale development and utilization of renewable energy will further aggravate the complexity and control difficulty of the power grid. It is urgent to improve the safety, flexibility and controllability of the power grid.
To carry out advanced transmission technology research, that is, based on the traditional transmission technology, the transmission theory is developed to innovate the transmission mode and achieve high efficiency, environmental protection, intelligence and long-distance transmission of electric energy by means of raising the voltage level and converting the power forms.
The advanced power transmission technology represented by power electronics technology mainly carries out the following four aspects:
1) Ultra-high voltage flexible AC transmission technology to improve the transmission capacity of AC lines to enhance the operational flexibility and safety and stability of the power grid;
2) UHVDC transmission technology that can efficiently deliver 10,000 MW of power to two thousand kilometers away;
3) flexible DC transmission technology, the highest controllable most flexible new transmission mode;
4) DC grid technology, a new generation of power grid architecture, improve the efficiency of renewable energy use.
Second, ultra-high voltage flexible AC transmission technology
Flexible AC Power Transmission (FACTS) uses power electronics and control technology to flexibly control key system parameters such as voltage, current, phase, power and impedance to enhance system stability and safety.
Controllable series compensation device (TCSC) is used to improve transmission capacity of the AC transmission line and to enhance the stability of the system power electronics. The device is connected in series with the AC power transmission line to provide continuous smoothing of equivalent capacitance compensation by adjusting the firing angle of two sets of anti-parallel thyristor valves. Thyristor valve in TCSC multi-stage series crimping technology, the need to accurately trigger the thyristor, thyristor requirements not only high voltage, withstand dv / dt ability, but also trigger a small delay, high serial consistency.
Static synchronous reactive power compensator (STATCOM) is the use of full-controlled device converter generates the same AC frequency with the grid frequency, by regulating the size of the converter output voltage to the grid output or controllable input reactive power from the grid, the application Through the transformer in parallel with the system. STATCOM needs to control the size, frequency and phase of the voltage by controlling the full-controlled device, require the opening of the device to cut off the speed fast, the loss is low. The device uses multi-level modular IGBT connection, large volume at high voltage levels, the future if the use of high voltage level devices or crimp IGBT, can significantly reduce the volume.
The Unified Power Flow Controller (UPFC) enables simultaneous or controlled control of all parameters (voltage, impedance and phase angle) that affect the active and reactive power flow of the line at the same time and is flexible, fast and versatile to solve many problems of power transmission Of the control device. UPFC is the use of full-controlled devices to achieve VSC valve group to improve the line control, change the status of the two converters, the requirements of the composition of the VSC valve group requires high voltage level, low device loss, high reliability.
1, After more than 20 years of research and development accumulated by Chinese researchers, China now has led the development of flexible AC transmission technology.
Before 2004, China's flexible AC transmission equipment all rely on imports, the application of less than 10 sets; At present, we have solved the large-capacity valve components in series trigger, high potential to take, multi-state pulse coding and other challenges; proposed multi-objective coordinated control , Overvoltage and active insulation coordination and other methods to establish a complete system of flexible AC transmission system analysis, complete design, core device development and other complete technical system; breakthrough 500kV SVC, TCSC, STATACOM, CSR, FCL and other flexible AC transmission device common technology.
2, completed the first four sets of FACTS equipment research and development, and to achieve a demonstration application.
1) Static Reactive Power Compensation: In 2004, China's first set of static reactive power compensation equipment for independent intellectual property rights power transmission network (Anshan, Liaoning); and in 2008, the world's first 500 kV DC ice melting and SVC plant (Yiyang, Hunan).
2) Controllable Series Compensation: In 2004, the world's first hybrid multiplexed fixed and controllable series compensator (Gansu Cheng Bi); in 2007, the world's highest series complement, 500KV series compensator (Heilongjiang Feng Tun).
3) Controllable Shunt Reactance: The world's first set of 500kV magnetron shunt reactors (Hubei Jingzhou) in 2007; the world's first set of 750kV valve-controlled shunt reactors (Dunhuang, Gansu) in 2012.
4) Short circuit current limit: In 2010, the world's first 500kV short circuit current limiting device (Zhejiang bottle kiln).
3, the overall level of technical flexibility of AC power transmission in China is the international leader.
In 2006, "R & D and Application of Core Technology of Static Var Compensator (SVC)" won the second prize of National Science and Technology Progress; in 2008, the "Key Technology and Application of Flexible AC Transmission in Power Transmission System" won the first prize of National Science and Technology Progress Award In 2010, "a controlled series thyristor electronic trigger system" won the Chinese patent gold medal.
At present, more than 100 sets of SVCs have been applied in China, forcing ABB and SIEMENS companies to abandon the Chinese market and successfully enter the power grids such as Korea and the Philippines. Successfully developed series compensation device domestic engineering bidding prices dropped by more than 30%, the application of more than 50 sets, the total capacity of 28Gvar, accounting for more than 50% of global applications, and exported to Vietnam, Brazil and other countries.
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