As we all know, photovoltaic power generation generates direct current, and there is no problem of reactive power or power factor itself. However, after photovoltaic power generation is converted into an AC grid by an inverter, a series of problems will arise in matching with the grid. The problem of reactive power is One of the main problems.
In fact, the connection methods of photovoltaic power plants are different, and the problem of reactive power reflected is also very different. At present, photovoltaic power generation systems can be divided into large-scale photovoltaic power stations connected to the high-voltage grid side and distributed photovoltaic power stations connected to the user side. Due to the different access methods and load conditions in the power grid, the reflected reactive power problems and reactive power compensation requirements are completely different, and measures should be taken according to the actual situation.
- Large-scale photovoltaic power plants connected to the high-voltage grid side
This type of power station often adopts a dedicated line design to directly connect the power of the power station to the transformer of the upper substation. Therefore, the reactive power problem of this type of power station is relatively small and relatively simple. During the day, when the photovoltaic power station generates electricity, since there is no other load between the photovoltaic power station and the substation, the inductance of the step-up transformer on the upper stage is the main factor of reactive power in the grid, but due to the large amount of power generated during the day, the transformer is almost at full load Therefore, the proportion of reactive power is relatively small, and most photovoltaic power plants can meet the requirements of the grid.
However, at night, the inverter of the photovoltaic power station is in a stop state, while the transformer in the station is always connected to the high-voltage power grid. At this time, the transformer in the station becomes an inductive load, which not only consumes part of the Reactive power loss occurs in the high-voltage circuit of the power station and the upper substation. The light-load operation of the outgoing cable lines and main transformers of large-scale photovoltaic power plants will generate reactive power. Usually, a set of reactive power compensators can be added to the high-voltage bus to absorb the reactive power generated by the line at night, so that the power factor of the photovoltaic power station at night can meet the requirements of the grid.
- Distributed photovoltaic power station connected to the user side
The problem of reactive power factor is a more prominent problem encountered in distributed photovoltaic power plants going online in recent years, especially industrial and commercial photovoltaic power plants. Because such power stations are usually connected to the low-voltage or medium-voltage power grid inside the enterprise, there are many electrical equipment connected to the network, especially inductive loads such as motors. When the photovoltaic power generation system was not installed originally, the reactive power compensation system in the network automatically adjusts and compensates according to the active power supply power of the grid and the reactive power in the network, so the reactive power problem in the network can be set through the network The reactive power compensation equipment achieves the purpose of automatic compensation, so that the reactive power in the network meets the requirements of the power grid.
When the photovoltaic power generation system is connected to the network, it means that there is a second or even multiple power sources in the network. When the light is strong, the photovoltaic power generation system will generate strong power, which will greatly reduce the power supply load of the power grid. The active power displayed by the meter will decrease as the power of the photovoltaic system increases, and even the surplus power of photovoltaic power generation will be sent out. At this time, if the load in the grid remains unchanged, especially when the inductive load is relatively large, the original reactive power compensation system in the grid will make wrong instructions and actions according to the power supply load and power load of the large grid, resulting in The proportion of reactive power increases, resulting in a decrease in power factor.
In recent years, many companies that install photovoltaics have been charged high power adjustment fees by the grid company because the power factor of the user-side grid cannot meet the requirements of the grid company.
In order to solve this problem, in addition to ensuring that the original reactive power compensation device of the power grid is configured correctly, installed correctly and running well. For the photovoltaic power generation system whose matching capacity is greater than 50% of the transformer capacity, and there are many inductive loads such as motors in the network, special attention should be paid to the selection of photovoltaic grid-connected points. If conditions permit, the access point of photovoltaic power generation should be set At point A at the front end of the original reactive power compensation equipment (as shown in the figure below), this connection method can make full use of the original reactive power compensation system and reduce investment.
However, if the construction site of the photovoltaic power station is far away from point A, or due to some other reasons, it is impossible to connect at point A, and it has to be connected at point B or other parts, the sampling of the original reactive power compensation equipment Although the point can perceive the reactive power in the grid, it refers to the power supply of the grid and cannot perceive the output power of photovoltaic power generation, which may not meet the function of correctly adjusting reactive power.
To solve this problem, it is necessary to install a special reactive power compensation device for this photovoltaic power generation system. Usually, this reactive power compensation device should be installed on the output side of the photovoltaic power station to supplement the lack of large-capacity reactive power compensation of the photovoltaic power generation system. ability to meet the needs of the grid.
Most industrial and commercial photovoltaic inverters have a power factor adjustment capability of about 20%. For a system with a small installed capacity of photovoltaic power generation in the grid and a small inductive load in the grid, it is not necessary to consider the problem of reactive power compensation equipment. Part of the reactive power compensation is provided by the inverter. However, when the reactive power in the grid is too large, exceeding the tolerance and adjustment capacity of the inverter, configuring an appropriate amount of reactive power compensation equipment becomes the main means to improve the efficiency of the grid and the effective power generation of the photovoltaic power station.
From the perspective of photovoltaic system operation stability, it is also best to choose the grid-connected point of photovoltaic power generation as close to the transformer as possible. The closer to the transformer, the more stable the voltage, and the farther away from the end of the transformer, the greater the voltage fluctuation. Frequent voltage and power fluctuations will cause the reactive power compensation device to fail to operate normally or malfunction.
The power factor problem is one of the important problems in many photovoltaic power plants, especially industrial and commercial photovoltaic power plants. In the design process, the original transformer, reactive power compensation device, transmission cable, load type and power should be fully considered. For industrial and commercial photovoltaic power plants connected to the grid on the user side, attention should be paid to the location of the access point to ensure that the reactive power compensation device can function normally, and the power quality meets the requirements of the power grid, so that the photovoltaic power plant can operate efficiently and stably to achieve maximum economic benefits.