Photovoltaic "islanding effect" can be interpreted as when the inverter is connected to the grid, the mains cannot supply power to the local load due to various reasons. At this time, if there is no islanding judgment technology, the inverter will continue to supply the local load and local Grid load power supply.

Generally speaking, the photovoltaic island effect may have adverse effects on the entire power distribution system equipment and user-side equipment, mainly including:

1. Endanger the personal safety of the power company transmission line maintenance personnel.

2. Affect the protection switch action program on the power distribution system.

3. Instability of power supply voltage and frequency in the power island area.

4. The phase out-of-synchronization problem caused when the power supply of the power company is restored.

5. The solar power supply system has the problem of under-phase power supply for the three-phase load of the system due to single-phase power supply.

The basic and key point to prevent the photovoltaic island effect is the detection of grid power failure.

In order to quickly detect power outages in the grid, two "island effect" detection methods, passive and active, are generally required. Once the power outage of the grid is confirmed, it is necessary to disconnect the inverter from the grid within a few cycles and stop the inverter. device operation.

With the further widespread application of photovoltaic grid-connected power generation systems, when multiple photovoltaic inverters are connected to the grid at the same time, the output of different inverters varies greatly, which may cause the above method to fail. Therefore, research on grid-connected communication and cooperative control of various photovoltaic inverters has become a research trend in the detection and control of photovoltaic islanding effects.