Based on new technologies, the system utilizes and develops renewable energy sources such as nuclear energy, wind energy, solar energy, ocean energy, hydrogen energy, biomass energy, geothermal energy, and so on. Unconventional energy is usually referred to as new energy sources other than traditional energy sources. Compared with fossil energy, new energy has two distinct advantages. One is that the amount of pollutants is relatively small and the reserves are large. Another advantage is that new energy sources are recyclable and renewable. Since the beginning of the 21st century, the massive use of fossil energy has brought environmental pollution, energy depletion and climate change to the society. The development and progress of human society have been seriously challenged. However, renewable energy and new energy have entered a period of rapid development, and will certainly become the strategic direction of social development and the new force of the world energy system in the future. One of the key points of China's future development is to master new energy technologies.
Because China's technology research on new energy power generation develops late and has certain limitations, it causes China's lack of stability in the use of new energy power generation, mainly in strong discontinuity, volatility and randomness, and new energy. The control technology of power generation is very difficult. At this stage, the capacity of the grid is still insufficient, and it is difficult to accept the power generated by the new energy on a large scale, mainly in the following aspects:
For wind power generation, the output power of a wind turbine is related to the magnitude of the wind speed. Since the energy of the wind is directly proportional to the cube of the wind speed, and the wind speed in the natural world is extremely unstable, it is difficult to artificially control the wind power, resulting in a large change in the output power of the wind turbine. For photovoltaic power generation, the output power of the PV array is related to the intensity of the light, so it is greatly affected by the weather and temperature, and is as volatile as wind power. The incorporation of large amounts of volatile wind power and photovoltaic power into traditional power grids can cause large current surges in the grid, causing grid frequency deviations, voltage fluctuations and flicker. For example, when the voltage of the wind farm drops, if the wind turbine does not have low voltage ride-through capability, it is easy to have a transient fault. Therefore, in order to avoid these situations, it is first required that the new energy equipment incorporated into the grid has the specified grid-connected technical performance, and secondly, the grid needs to have sufficient peak-shaving capacity and power-receiving capability. The most indispensable of the new energy power generation system devices are active power adjustment and dynamic reactive power adjustment. In addition, reactive power loss is likely to occur in wind farms and photovoltaic power station stations. Therefore, reactive power compensation functions need to be configured in the functions of new energy power generation system configuration applications.
In the new energy power generation system, there are two main ways to bring harmonics to the power grid. Taking a wind power generation system as an example, one is that the power electronic device equipped with the wind power generator itself brings harmonic problems. For a constant-speed wind turbine directly connected to the grid, a certain amount of harmonics is generated by connecting the power electronic device to the grid during the soft start phase. For the variable speed wind turbine, it is connected to the grid system through the rectification and inverter device. If the switching frequency of the power electronic device is just within the range of generating harmonics, it will cause a serious harmonic problem; the other is wind power generation. The parallel compensation capacitor of the machine may resonate with the line reactance. In order to balance the reactive power, the wind power system needs to be equipped with a parallel compensation device, but due to the constant changes of harmonics and the complexity of the power grid, under certain conditions, harmonic amplification or even system resonance may occur.
Therefore, in the wind farm, a single variable speed or constant speed wind turbine should be avoided as much as possible. This will cause excessive harmonic voltages locally, and different types of fan hybrid configurations should be used. Secondly, the power system should properly configure the filtering device to reduce the harmonic content in the power grid, and use the dynamic or static reactive power compensation device while suppressing harmonics.
When the large power grid loses pressure, the grid-connected wind power generation and photovoltaic power generation will continue to supply power to a certain part of the power grid, and form a connection with the local load to achieve a new supply and demand balance state, forming an isolated network operation. At this time, the voltage and frequency in the isolated network are not controlled by the large power grid, and the adjustment support of the large power grid is not obtained. When the load on the load side changes or the output power of the power generation side changes, the supply and demand of the isolated network will be unbalanced, resulting in an isolated network. The voltage and frequency are prone to fluctuations. If the fluctuation range exceeds the allowable safety range, the safety of the equipment will be seriously affected. When the supply is greater than necessary, the voltage and frequency may exceed the allowable range and may cause damage to the user's equipment. When the supply is less than necessary, the inverter will be overloaded and the inverter may be burnt. Therefore, before the new energy is integrated into the power grid, the power dispatch must be strictly checked and audited. For the wind power generation system and the photovoltaic power generation system, the power prediction function is one of the necessary access conditions.
The distribution of new energy is broader, but the distribution is not uniform. It is difficult for our country to achieve a relatively unified grid of new energy generation grids. According to the current state of technology development in China, only the technical standards of large-scale grid-connected systems can be unified, but their detection technology is not unified, and there are certain defects in system testing. Therefore, system certification should be further improved.
At this stage, China lacks professional knowledge to analyze the main reasons for the destruction of power system stability and the reduction of power quality in the integration of large and medium-sized new energy sources. Even the factors affecting grid dispatching and affecting grid operation are lack of reasonable identification. Moreover, the problems existing in the grid receiving technology are still being researched and explored. At present, there is no real unified conclusion. It is still difficult to complete the detection of the access system in China. For example, we need to constantly improve the detection of inverters and controllers. In addition, although we are constantly developing and exploring the detection technology of transmission and distribution equipment and two-way metering equipment, compared with the technology of some developed countries in the West, there is still a big gap in China's technology.
From the perspective of the impact of new energy grid-connected on power quality of power grids in China, the research and development of China's grid-connected technology in four aspects of DC transmission technology, grid-connected mode, intelligent control technology and scheduling technology are needed. Make greater efforts and enhancements, play a pillar role in renewable energy in the grid-connected mode, and carry out effective operation and control in terms of technology. With the continuous development of more and more widely used information technology and the continuous advancement of technology, artificial control will be replaced by intelligent control one day in the future. In order to effectively improve the technical level of grid system security, it is necessary to use intelligent control technology; in the transmission technology, the research and development of DC transmission technology and large-scale energy storage technology must be continuously strengthened and improved, and then the grid will be operated. The reliability and stability of the system are demonstrated by DC transmission technology, which will reduce the damage to the grid when connected to the grid through large-scale energy storage technology. At the same time, when inter-scheduled work is carried out in areas where new energy is relatively poor or where there is more new energy, the scheduling technology is also widely used at work, and the corresponding technical level will also increase.
Summary: Due to the new energy characteristics and the low level of technology in China at this stage, the new energy grid connection in the current stage has some negative impacts on the power grid application in China, which threatens the safe and stable operation of the power system to a large extent. . (Note: According to the experience of developed countries in Europe, when photovoltaic power generation and wind power generation exceed 6% of the total power grid power, it will affect the stable operation of the power grid, and it is necessary to install energy storage devices.) Therefore, in the face of this situation, Relevant personnel and relevant government departments will improve relevant technologies and standards to ensure that the development of China's power system will be effectively promoted while eliminating the adverse effects of new energy grids on the power grid of China's power grid, and ultimately provide people with security and stability. The power resources ensure the normal production and life needs of people, improve and improve people's quality of life.