06,10,2026 54views
Abstract: Under the new power system, the installed capacity of distributed photovoltaics in various provinces and cities has been increasing year by year. Due to the volatility of distributed photovoltaics, the integration of photovoltaics into the power grid has added great instability to the original distribution network, posing a threat to the safe operation of the power system. The "Management Measures for the Development and Construction of Distributed Photovoltaic Power Generation" issued by the National Energy Administration stipulate that distributed photovoltaics with a capacity of 6MW or more must be self used. For distributed photovoltaics with a capacity of less than 6MW, self use and surplus electricity grid connection are required. For distributed photovoltaics with a capacity of less than 6MW in some areas, self use is also required, and anti backflow control requirements must be implemented. In response to this issue, this article conducts a case analysis from the perspective of the background, technical solutions, and product configuration of photovoltaic anti backflow, providing a solution for photovoltaic anti backflow projects.
Keywords: distributed photovoltaics, anti backflow control, energy management, protective devices.
1. Overview
At present, the installed capacity of distributed photovoltaics is increasing, and there are red zones in some places. Local power companies require the construction of new distributed photovoltaics for self use and take measures to prevent backflow. The main reason for preventing backflow in distributed photovoltaic power generation systems is to ensure the stability and safety of the power grid, while meeting the regulations and requirements of local power companies. Here are several main reasons:
(1) Grid stability:
When the power generation of a distributed photovoltaic system exceeds the demand of local loads, excess electricity will flow back into the grid. This backflow phenomenon may have an impact on the voltage and frequency of the power grid, thereby threatening the stability of the power grid.
(2) Equipment and personnel safety:
Reverse current may cause overheating or damage to user side electrical equipment (such as inverters, transformers, etc.), and may even lead to safety accidents such as fires.
For maintenance personnel of the power grid, backflow may also pose a safety hazard, as they do not expect current to flow from the user side to the grid during maintenance or inspection.
(3) Policy and regulatory requirements:
In some regions, due to legal requirements, it is not allowed to feed excess electricity back to the grid. For example, due to capacity limitations of the previous transformer or policy restrictions in specific regions, new grid connections are not allowed.
If reverse power is found to be connected to the grid, the power grid company may impose fines or other forms of punishment on users.
(4) Economic benefits considerations:
In some cases, although technology allows for reverse flow back to the grid, it is not economically viable. For example, if the filing materials are incomplete, resulting in the inability to obtain the grid connection permit from the power grid company, and the cost of installing energy storage systems is too high, then taking anti backflow measures is particularly important in this situation.
(5) Energy management optimization:
Anti backflow devices can help optimize energy use, ensuring that all generated electricity is effectively utilized instead of being wasted in unnecessary backflow. This is particularly important for users who wish to increase their self use ratio to reduce their electricity bills.
2. Project situation
The total installed capacity of the distributed photovoltaic power generation project of Jiangxi Yanjing Beer Co., Ltd. is 1MW, and the construction area is located in Fenghuang Park, Ji'an High tech Zone, Ji'an County, Ji'an City, Jiangxi Province. This project includes a photovoltaic power generation system (photovoltaic cell modules, with unknown total installed capacity on the DC side), 3 transformers, and 16 50kW inverters. Among them, there are three grid connection points. Grid connection point 1 is equipped with 5 50kW inverters, grid connection point 2 is equipped with 5 50kW inverters, and grid connection point 3 is equipped with 6 50kW inverters.
Each inverter will convert the DC power output from the battery components into AC power (0.4kV), which will be led to the box type transformers (10kV) at their respective grid connection points through cables. After each box transformer is further boosted to 10kV, it is connected to the local power grid through a transmission line and converges with the 10kV external line.
According to local power supply requirements, this distributed photovoltaic project can only be consumed on-site and is prohibited from being transmitted to the power grid.
3. Solution
In order to achieve the above goals, anti backflow protection devices are installed at the public connection points. Once backflow is detected, a signal will be sent to the energy management system through a communication interface. By monitoring the power at the main incoming line and real-time power generation, corresponding inverter adjustment instructions are generated through system calculations to achieve flexible regulation of photovoltaic anti backflow. This method can ensure that the power system operates according to the design, protect the safety and stability of the power grid, and also greatly utilize photovoltaic power generation to reduce energy consumption costs for users. The control scheme is as follows:
The typical configuration of the plan is as follows:
The system networking diagram is as follows:
4. Plan effect
The energy management system integrates distributed energy sources for unified monitoring and management. Through an intelligent control system, the output power of each photovoltaic unit can be adjusted in real time according to the power demand of the load, ensuring that the power of the photovoltaic system is not transmitted in reverse to the grid. Before the anti backflow comprehensive protection system trips the grid cabinet, the system issues inverter power adjustment commands to achieve flexible adjustment, thereby improving the stability and reliability of the microgrid system. The following figure shows the anti backflow regulation effect. By controlling the output of the inverter, the power value of the common connection point is kept at the set value of 15kW, preventing photovoltaic backflow and avoiding assessment and fines from the power company.
At the same time, the human-machine interface of the energy management system is friendly, which can visually display the operating status of each electrical circuit in the form of a system electrical diagram, monitor the voltage, current, power, power factor and other electrical parameter information of the photovoltaic circuit in real time, and manage the power generation of distributed power sources, enabling management personnel to grasp the output information, revenue information and operating power settings of the power generation units in real time.
5. Conclusion
With the increase of distributed photovoltaic installed capacity, more and more regions require distributed photovoltaics to be self used. This article introduces a scheme of energy management system combined with anti backflow protection device, and its application in the Yanjing Beer distributed photovoltaic project provides a reliable solution for the demand of self use in distributed photovoltaic power plants without connecting surplus electricity to the grid. It provides assistance for the construction and grid connection acceptance of distributed photovoltaics.
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