Photovoltaic power generation technology has been widely used in various fields of social production, and has completely solved the problems of human energy shortage and natural environmental pollution. Large-capacity photovoltaic power stations, in particular, are the core basis of regional photovoltaic power generation technology application, and have a far-reaching impact on the operation of regional-level power grids. Therefore, this paper takes the theory and characteristics of large-capacity photovoltaic power stations as the breakthrough point to further analyze the specific impact of large-capacity photovoltaic power stations on the operation of district-level power grids, hoping to provide effective suggestions for improving the operation quality of district-level power grids. Compared with traditional thermal power plants, there is a significant difference in the production characteristics of photovoltaic power stations. That is, affected by the access of large capacity photovoltaic power stations, the regulation and operation of the previous power grid, power grid planning, power flow distribution, voltage stability and other aspects are affected to varying degrees. At the same time, the installation of photovoltaic power stations in the distribution network can greatly reduce network loss and control the investment and construction costs of the power grid in remote areas. In other words, the impact and influence of photovoltaic power stations on thermal power generation are relatively far-reaching. The intelligent power grid built has the distinctive characteristics of small footprint and less investment, which not only improves the power production efficiency, but also reduces the network loss. Combined with the statistical data, it is found that the fluctuation of photovoltaic power stations is strong, especially the fluctuation of large-capacity photovoltaic power stations has already reached 100MW level, and the problem of preemption of power transmission channel between thermal power plants and photovoltaic power stations is easy to occur in the summer peak period. In view of this, it is of great practical significance to analyze and study the “influence of large capacity photovoltaic power station on regional power grid operation” in this paper.
1.Large capacity photovoltaic power station
1.1 Concept and power transmission mode of large-capacity photovoltaic power station
Large capacity photovoltaic power station by photovoltaic panels collect light energy, and then converted into electricity, and the output voltage and current of a single photovoltaic panel is small, often need to choose multiple photovoltaic panels, series or parallel connection, otherwise it is difficult to form a photovoltaic array, unable to achieve satisfactory power generation effect. It can be seen that large capacity photovoltaic power stations rely on photovoltaic arrays to produce and convert electric energy, greatly improving the overall work efficiency. At the same time, the power supply and distribution system of the photovoltaic power station can be divided into two types: 35kV and 110kV, which are connected with the main grid to form the regional grid architecture. Even though the photovoltaic power station has the design characteristics of receiving power grid, it cannot meet the demand of large-capacity power transmission, and even a few lines do not meet the N-1 standard. From the technical point of view, the power supply mode of large capacity photovoltaic power station still has technical limitations.
1.2 Working Principle
The power generation capacity of large-capacity photovoltaic power stations is generally megawatt level, with an independent and independent cluster control production system, which not only can effectively parallel several converters, but also can match with the central control system to control each subsystem of the photovoltaic power station and ensure the mutual communication between the photovoltaic power station and the converters through the power grid. At the same time, the converter has the control function that other tools do not exist, which basically realizes the target of active power or reactive power output, helps to control the change of active power and eliminate the negative influence of harmonics. At present, most of our photovoltaic power stations contain multiple basic unit combination systems, that is, the capacity of each photovoltaic power source exceeds 1MW. Especially, photovoltaic array modules in large-capacity photovoltaic power stations, after photoelectric conversion, the current can directly flow through and converge to the bus position, which can complete the electric energy transmission of the converter in a real sense.
2.Characteristics and status analysis of large capacity photovoltaic power stations
Different from other types of power stations, large-capacity photovoltaic power stations are more difficult to connect to the grid, especially the inverter types used in the system are relatively rich and diverse. For example, multiple inverters can be combined to form during the specific practice. At the same time, the scale of photovoltaic arrays of large-capacity photovoltaic power stations is huge, so it is difficult to ensure the consistent performance of all components. However, the above basic characteristics make large-capacity photovoltaic power stations extremely prone to technical problems in the grid-connected operation process, such as excessive harmonics or difficult to restrain. Thus, it can be seen that the harmonics generated by a single inverter in the photovoltaic power grid system have relatively slight influence on the power grid, but after the parallel processing of the inverter, the harmonics generated may have greater interaction. If the transportation distance is too long, it may cause the problem of harmonic wave seriously exceeds the standard, and the wave wave and power quality instead are the important problems faced by grid connected large-scale photovoltaic power station at present. The characteristic curve of photovoltaic array is complicated, which greatly increases the difficulty of analyzing the curve change. At the same time, photovoltaic array modules are relatively large in scale. Unlike a single module, they only show ideal characteristics and may have P-V temperature characteristics and basic transport characteristics, indicating that their change rules are complex. In particular, they have far-reaching influences on power grids in some regions, affecting their power generation operation efficiency to varying degrees, and even affecting power output and daily life and work of surrounding residents.
3.Specific Impact analysis of large-capacity photovoltaic power stations on regional-level power grid operation
As mentioned above, I have a certain understanding of the characteristics and current situation of large-capacity photovoltaic power stations. In practice, large capacity photovoltaic power stations have a wide range of influence on regional-level power grid operation. In summary, the specific impact is as follows:
3.1 Comprehensive Impact
There is a close relationship between the output range of large-capacity photovoltaic power station and the operation of district-level power grid. In other words, insufficient sunshine conditions will directly affect the output range of large-capacity photovoltaic power station and make it fluctuate all the time, which may lead to volt jump during the active power processing of photovoltaic power station. Specifically, when the installed capacity of the photovoltaic power station increases and the sunshine time of the regional power grid remains unchanged, the power grid type changes to the main power grid into the up-sending power grid, and when the environment is cloudy, the power grid type changes to the receiving end power grid. Therefore, based on various factors and considering the maximum and minimum power start-up mode of regional power supply, it is found that photovoltaic power generation and current transmission have obvious intermittent characteristics, indicating that the power supply volatility generated in this stage is strong, which may affect the operation cost of large capacity photovoltaic power station, and even affect its operation stability. The absorption and long-distance power transmission capacity of large-capacity photovoltaic power station have a far-reaching impact on the operation of regional power grid, especially the voltage and electric energy. Once the treatment measures are inappropriate, it will directly affect the normal life and work of surrounding residents. For example, taking voltage as an example, the resulting fluctuations and effects show a state of degree differentiation. At the same time, photovoltaic power stations are different from traditional thermal power generation, and there is a big difference in voltage adjustment. Especially, after large-capacity photovoltaic power stations are connected to the power grid, the difficulty of voltage control is greatly increased, causing the voltage to fluctuate too much, and even difficult to be processed and adjusted in the future. Even though reactive power compensation devices have been set up for regional-level grid debugging of large-capacity photovoltaic power stations in China, their original device scheduling capabilities may be weakened due to the inadequate dynamic capacity compensation and other factors.
3.2 Influence of thermal power group operation and reserve capacity
Large capacity photovoltaic power stations inevitably have certain fluctuations during operation, especially the maximum fluctuation value can reach 1000MW level, and it is easy to occur the phenomenon of thermal power plant output when the summer peak electricity consumption, such as: In the summer thunderstorm season, the output value of the photovoltaic power station always approaches to zero infinitely, so it is bound to require the thermal power plant to increase its output rapidly, otherwise it cannot guarantee the normal operation of the photovoltaic power station. At the same time, large capacity photovoltaic power stations use mostly distributed power sources, which may cause current fluctuations once connected to the grid. The cause of current fluctuation is relatively complex, which is closely related to small hydropower, solar photovoltaic and wind power generation. Under adverse production conditions, the active switching of distributed power supply can ensure the access of regional-level power grid to new distributed power supply and ensure its operation safety.
3.3 Impact on System Stability
After large-capacity photovoltaic power station is connected to the distributed power supply, it may cause various problems, such as: the distributed power supply does not generate power or cannot generate power, etc., which affects the voltage stability of the distribution network to varying degrees. However, the causes of the above problems are relatively complex, which is closely related to the obvious lack of reactive power. Generally speaking, the power of distributed power supply ranges from 0.97 to 0.99. When the installed capacity of wind farm or hydropower project is too large, reactive power shortage is easy to occur, which will destroy the original stability of grid voltage and even lead to the complete collapse of system voltage. At the same time, the distribution planning and design tend to take the receiving power grid as the reference basis to draw up the corresponding design and analysis scheme. However, unlike the large-capacity photovoltaic power station, the grid-connection operation is in the late stage of the distribution network connecting to the distributed power supply, and there is a possibility that the basic operation characteristics of the distribution network may change. At the same time, the combined operation of photovoltaic power station and distribution network will directly affect the system security, reliability and operation stability. Especially after the power flow changes, it is not conducive to the orderly development of the voltage regulation work of distribution network, and even leads to the increasingly complex and diversified protection value setting process. From the perspective of operation stability, photovoltaic power stations themselves have certain characteristics of power supply, while large capacity photovoltaic power stations are similar to ordinary photovoltaic power stations, with relatively strong performance of power supply attributes, but the performance of system stability constraints has not yet reached the ideal state.
Conclusion:
Through research in this paper, it is realized that the continuous promotion of the national photovoltaic poverty alleviation policy promotes the rapid development of new energy represented by large-capacity photovoltaic power stations. At the same time, photovoltaic grid-connection has a far-reaching impact on the regional power grid, and the regional power grid must attach great importance to structural design, construction and operation, take the initiative to meet the basic requirements of absorbing new energy, and form a scientific and reasonable power grid structure, in order to ensure the local absorption of the large capacity photovoltaic power generated, and even use the means of building ultra-high voltage power grid to carry out long-distance power transmission. Otherwise, it may hinder regional economic development in the long run. All in all, the construction of intelligent distribution network at the prefecture level of large capacity photovoltaic power station is an irresistible mainstream trend. It shows that intelligent distribution network can meet the requirements of photovoltaic power station production and operation, and further makes the transformation of future electric power industry into comprehensive, humanized and intelligent direction.
