1. Current situation of user side grid connected power generation system

With the development of new energy, many users will choose to install distributed photovoltaic power generation, wind power generation, energy storage and other power generation systems on the basis of the existing public power grid distribution system. However, due to fluctuations in power generation and continuous changes in user side electricity load, in order to prevent reverse power generation from the user side grid connected power generation system and reverse power transmission to the public grid, it is necessary to scientifically and reasonably use the user side grid connected power generation system, and at the same time, perform safety control on the user side grid connected power generation system to achieve anti backflow function.

2. Anti backflow solution for user side grid connected power generation system

According to 6.3.2 of GB/T 50865-2013 "Design Specification for Photovoltaic Power Generation and Distribution Network", "When the photovoltaic power generation system is designed as an irreversible grid connection mode, reverse power protection equipment should be configured. When the reverse current exceeds 5% of the rated output, the photovoltaic power generation system should automatically reduce its output or stop supplying power to the grid line within 2 seconds. ”

According to section 10.7 of GB/T 43526-2023 "Technical Regulations for User Side Electrochemical Energy Storage Systems Connected to Distribution Networks", "For user side electrochemical energy storage systems that do not allow reverse power transmission to the grid, the common connection point should have reverse power protection function

2.1 Design Standards and Basis

GB/T 19964-2024 "Technical Regulations for Connecting Photovoltaic Power Stations to Power Systems"

GB/T 29319-2024 "Technical Regulations for Photovoltaic Power Generation System Access to Distribution Network"

GB/T 50865-2013 "Design Specification for Photovoltaic Power Generation Connected to Distribution Network"

GB/T 43526-2023 "Technical Regulations for User Side Electrochemical Energy Storage Systems Connected to Distribution Networks"

GB/T 31366-2015 "Technical Requirements for Photovoltaic Power Station Monitoring System"

GB/T 50052-2009 "Design Specification for Power Supply and Distribution Systems"

GB/T 50053-2013 "Design Specification for 20kV and Below Substations"

GB/T 50062-2008 "Code for Design of Relay Protection and Automatic Devices of Power Equipment"

GB/T 50063-2017 "Design Specification for Electrical Measuring Instrument Devices of Power Equipment"

GB/T 19939-2005 "Technical Requirements for Grid Connection of Photovoltaic Systems"

GB/T 31366-2015 "Technical Requirements for Photovoltaic Power Station Monitoring System"

2.2 Anti backflow solution for user side grid connected power generation system

When using a user side grid connected power generation system that does not allow reverse power transmission to the grid, anti backflow protection devices need to be installed at the common connection point. Through a combination of anti backflow software flexible adjustment and anti backflow protection rigid tripping, the grid cabinet can be quickly disconnected when reverse power is generated and transmitted to the public grid, preventing the user side grid connected power generation system from continuously generating power and transmitting it back to the public grid.

The configuration schemes for anti backflow protection devices in different application scenarios are as follows:

1) When the cable laying distance between the backflow monitoring point and the grid connected cabinet is within 100 meters, a single machine version device AM5SE-IS is used to achieve backflow protection function;

2) When the cable laying distance between the backflow monitoring point and the grid connected cabinet is between 100 meters and 40 kilometers, the AM5SE-PV series master-slave device is used, and fiber optic connections can be used between the master and slave to achieve remote backflow prevention function.

3. System topology

The user side grid connected power generation system is designed according to a three-layer architecture of station control layer, interval layer, and equipment layer. Through the interval layer communication management machine and network switch, real-time data of secondary equipment such as anti backflow protection device, microcomputer protection device, power quality monitoring, metering, and remote control system is collected to achieve monitoring and automation management of multiple regional user side grid connected power generation systems. At the same time, a communication system, a timing system, and a remote control system are configured in the monitoring room to meet the internal communication and superior scheduling needs of the system. An integrated power supply system is configured to provide stable and reliable power for the operation of important equipment such as secondary equipment and monitoring hosts, achieving safe and stable operation of the entire user side grid connected power generation system.

4. Anti backflow software function

The anti backflow software can monitor the power changes of anti backflow monitoring points in real time, including the current total power of photovoltaic power generation, real-time discharge power and charging power of energy storage, as well as the real-time power of each grid connected unit and grid connection point.

The anti backflow software can set the power threshold and tripping action time for reverse power tripping, the power threshold and adjustment time for low-power regulation, and the power value and restoration closing action time for judging the closing after the power returns to normal.

4.1 Low power flexible adjustment

The anti backflow software sets a power threshold for low-power regulation (which is the off grid power used by the user side on the public grid). When the off grid power of the public grid is low and reverse power may occur due to load fluctuations, the anti backflow software flexibly adjusts and sends a command to reduce the power generation to the grid connected units of the user side parallel power generation system to prevent reverse power generation.

4.2 Reverse power trip

The anti backflow software sets the power threshold for reverse power tripping (which is the grid connected power supplied by the user side grid connected power generation system in reverse to the public grid). When the grid connected power supplied by the user side grid connected power generation system in reverse to the public grid triggers the reverse power tripping power threshold, the anti backflow software sends a tripping instruction to the grid connected unit of the user side grid connected power generation system, cutting off the grid connected unit of the user side grid connected power generation system and preventing continuous reverse power supply to the public grid.

4.3 Power restoration closing

When the grid connected unit of the user side grid connected power generation system trips due to reverse power, and the user side uses the off grid power of the public grid to restore the normal threshold, and the grid connected unit still fails to close within the power restoration closing time, the anti backflow software sends a closing instruction to the grid connected unit of the tripped user side grid connected power generation system to restore the power generation of the grid connected unit of the user side grid connected power generation system, improve the utilization rate of the user side grid connected power generation system, and reduce the use of the public grid.

5. Anti backflow protection device

5.1 Single machine version anti backflow protection device

AM5SE-IS anti backflow protection device

The AM5SE-IS anti backflow protection device is mainly suitable for new energy grid connected power supply systems such as 35kV, 10kV, and low-voltage 380V photovoltaic power generation, wind power generation, energy storage charging and discharging. When there is a reverse power supply phenomenon to the public power grid, the grid connection point can be quickly cut off to prevent the station from continuously supplying power in reverse to the grid, ensuring that the use of the power station meets the requirements of the grid.

10kV grid connection

0.4kV grid connection

Ø Main functions

Ø Technical parameters

Ø Appearance and opening size

5.2 Master slave version anti backflow protection device

5.2.1 Fiber Optic Direct Jumping Scheme

AM5SE-PV series anti backflow protection device

The AM5SE-PV series anti backflow protection device adopts a fiber optic connection between the master and slave machines, and achieves anti backflow by remotely switching in and out through a fiber optic link.

1) When the cable laying distance between the reverse flow monitoring point and the grid connected cabinet of the user side grid connected power generation system grid connected unit is between 100 meters and 1.5 kM, the AM5SE-PV series master-slave scheme can be used. Multi mode optical fiber with a wavelength of 850 nm and ST interface connection can be used between the master and slave units;

2) When the cable laying distance between the backflow monitoring point and the grid connected cabinet of the user side grid connected power generation system grid connected unit is between 1.5kM and 20km, the AM5SE-PV series master-slave scheme can be used. Single mode fiber optic wavelength 1310nm and ST interface connection can be used between the master and slave units;

3) When the cable laying distance between the backflow monitoring point and the grid connected cabinet of the user side grid connected power generation system grid connected unit is between 20km and 40km, the AM5SE-PV series master-slave scheme can be used. Single mode fiber optic wavelength 1550nm and ST interface can be used between the master and slave.

Dual city power incoming line

Main functions

Technical Specifications

Appearance and opening size

5.2.2 COOSE Communication Scheme

AM5SE-PV series anti backflow protection device

The AM5SE-PV series anti backflow protection device uses fiber optic connection between the master and slave devices, and achieves anti backflow through the GOOSE communication network of the fiber optic link group.

1) When the cable laying distance between the reverse flow monitoring point and the grid connected cabinet of the user side grid connected power generation system grid connected unit is between 100 meters and 20 kilometers, the AM5SE-PV series master-slave scheme can be used. Single mode optical fiber with a wavelength of 1310nm and FC interface connection can be used between the master and slave units;

2) When the cable laying distance between the reverse flow monitoring point and the grid connected cabinet of the user side grid connected power generation system grid connected unit is between 20km and 40km, the AM5SE-PV series master-slave scheme can be used. Single mode optical fiber with a wavelength of 1550nm and FC interface connection can be used between the master and slave.

Topology diagram of fiber optic direct connection in master-slave communication network

Master-slave communication network borrowing fiber ring network switching unit fiber ring network topology diagram

Main functions

Technical Specifications

Appearance and opening size

6. Typical configuration scheme

7. Typical case

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Anti backflow solution for the 34.8MW distributed photovoltaic project at Jiangnan Shipyard