Explain in detail the anti-islanding protection of the inverter

　　As the global demand for clean energy continues to rise, the photovoltaic industry is developing rapidly, and the safety issues of power stations have received extensive attention, including the islanding effect protection that reverses the inverter.

　　A: What is the "islanding effect"

　　According to the relevant regulations of industry standards, photovoltaic grid-connected inverters should have anti-islanding protection functions, that is, they should have the ability to quickly monitor islands and immediately disconnect from the grid. The protection action time should not exceed 2s, and a warning signal should be issued at the same time and the islanding protection should also be coordinated with the line protection on the grid side. Therefore, the inverter must have an anti-islanding protection function! Before introducing the inverter anti-islanding protection, let's first understand what the "islanding effect" is.

　　The popular understanding of "islanding effect" refers to the phenomenon that power generation equipment is still used as an isolated power source to supply power to the load when the power grid loses voltage or is disconnected, forming a power supply island.

　　B: What are the hazards of the "islanding effect"

　　The "islanding effect" has huge hidden dangers to the safety of equipment and personnel, including the following aspects:

　　(1) When the power grid is out of service for maintenance, the maintenance personnel may not necessarily be aware of the existence of the distributed system. If the inverter of the grid-connected photovoltaic power station continues to supply power, the safety of the maintenance personnel may be endangered;

　　(2) When the islanding effect occurs, the power grid cannot control the voltage and frequency of the power supply island, and the drift of the voltage amplitude and frequency will cause damage to the electrical equipment;

　　(3) If the inverter is still generating electricity, due to the phase difference between the output voltage of the grid-connected system and the grid voltage, inrush current will be generated when the grid is restored to power supply, which may cause another trip or damage to the distributed generation system. Damage to the load and power supply system.

　　C: How does the inverter realize anti-islanding protection

　　How does the photovoltaic inverter, which is the core of the photovoltaic system, realize anti-islanding protection?

　　The key point of the anti-islanding effect is the detection when the power grid is out of power. Two detection methods are usually adopted, passive or active. The grid is disconnected and the inverter is stopped. In fact, in order to ensure the safety of personnel and equipment, the protection time will be shorter.

　　D: Summary

　　Although grid-connected photovoltaic inverters have islanding protection functions, according to actual conditions and specific requirements, in general, large and medium-sized photovoltaic power stations will install islanding protection devices at grid-connected points.

　　As for distributed photovoltaic power plants, due to the relatively small installed capacity and low-voltage grid connection, in order to ensure the safety of the grid, according to local requirements, there are generally anti-islanding protection devices. The installation of anti-islanding protection device is mainly to realize the secondary protection of anti-islanding, ensuring more safety and reliability.

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