When installing a photovoltaic system, some people will hold the mentality of "even if the power grid fails, if there is sun, their home can still use electricity". The reality is that when the power grid fails, the photovoltaic system of their home will only be exposed to the sun , will also stop running, and will not use electricity.

The reason for this phenomenon is the grid-connected inverter, which must be equipped with an anti-islanding device. When the grid voltage is zero, the inverter will stop working. The anti-islanding device is an essential device for all photovoltaic grid-connected inverters. The reason for this is mainly for the safety of the grid. When the grid is powered off, the maintenance personnel are ready to overhaul the circuit. Electricity can easily cause safety accidents. Therefore, the national standard stipulates that the photovoltaic grid-connected inverter must have the detection and control functions of the islanding effect.

The detection methods of the islanding effect include passive detection and active detection. The passive detection method detects the amplitude of the voltage and current at the output of the grid-connected inverter. The inverter does not add interference signals to the grid, and detects the current phase offset and frequency Whether the parameter exceeds the specified value is used to judge whether the power grid is out of power; this method does not cause grid pollution, and there will be no energy loss; and active detection means that the grid-connected inverter actively and regularly applies some interference signals to the grid. Such as frequency shift and phase shift, since the power grid can be regarded as an infinite voltage source, these interference signals will be absorbed by the power grid when there is a power grid. If the voltage exceeds the standard, it can be judged whether the island effect has occurred.

At present, the anti-islanding function technology of grid-connected inverters is fully mature. Therefore, in household grid-connected projects, there is no need to add anti-islanding devices. In some places, not only photovoltaic grid-connected inverters are connected to the grid, but also possible It is a distributed power source such as wind power generation, biomass power generation, and energy storage system. The State Grid Corporation of China stipulates that when the access capacity of the grid connected to the power grid exceeds 25% of the rated capacity of the distribution transformer in the station area, the main switch of the low-voltage side of the distribution transformer should be Transform it into a low-voltage main switch, and install an anti-islanding device at the low-voltage busbar of the distribution transformer; the low-voltage main switch should have an operation locking function with the anti-islanding device, and when there is communication between the busbars, the connection switch should also have an operation with the anti-islanding device Latching function.