An Introduction of On-Grid PV Inverter Protective Functions

1.Anti-Islanding Protection

An excellent anti-Islanding protective function makes sure the on-grid inverter can handle the unplanned islanding effect reliably. The protection of unplanned islanding effect of on-grid PV inverter should have both active and passive detection schemes. Once the unplanned islanding effect happens, the inverter should stop supplying power to the grid within 2s and send alarm message.

2.Over Current Protection On AC Side

When the short cut of grid side detected by the inverter, the inverter should stop supplying power to the grid within 0.1s and send alarm signal. The inverter can work again only if the trouble is solved.

3.Grid Recovery Protection

After the PV inverter stops working due to the grid fault, like grid blackout, voltage too high, the inverter should be able to automatically recover to on-grid status after the grid voltage and frequency return to the normal range for 20s to 5min.The power of inverter should increase slowly and should not impact the grid.

4.Insulation Monitoring Function

When the live part of the equipment is grounded, the insulation monitoring system should be able to immediately detect the fault status, the inverter should shut down and send an alarm.

5.Reverse polarity protection

When the polarity of PV string input is reversed, the inverter should have the ability to protect itself from damage. The inverter can work only when the polarity of PV module input is right.

6.Grid Over-voltage/Under-voltage

Over-frequency/Under-frequency protection The on-grid inverter should be able to accurately detect the over/under voltage, over/under frequency and other abnormal conditions of the grid (wiring). The PV inverter should be protected according to the required time. When the inverter stops working due to the over/under voltage and frequency, a warning message should be sent. When the grid voltage and frequency return to the normal voltage and frequency range, the inverter should be able to start normally.

7.Protection sensitivity and reliability

In the normal inverter operating environment and the grid environment that meets the requirements, the inverter should not accidental shutdown, false alarm and other unintended stoppages.

8.Anti-Discharging Protection

When the DC side voltage of the PV inverter is lower than the allowable working range or the inverter is in the off state, the DC side of the inverter should have no reverse current.

9.Internal Shortcut Protection

When internal shortcut is happened in the inverter, the protection of electronic circuits and fuses in the inverter should be reposed fast and reliable.

10.Fire Resistance

Flame retardant wires and cables should be used for inverter wiring, wire slots and number marking sleeves also need to use flame retardant material. There should equip temperature sensor internal the inverter so that the real-time temperature could be monitored. Make sure under no circumstance can the inverter produce invasive flame.

11.Overvoltage Protection of DC Side

When the DC side input voltage is higher than the maximum allowable DC access voltage of the inverter, it should not start or shut down within 0.1s (When the inverter is running) and meanwhile send an alarm message. When the input voltage is recover to a normal range, the inverter should start or running normally.

12.Over-Temperature Protection

PV inverter should have an alarm when the internal environment temperature is too high (For example, an environment temperature increasing in the chassi caused by fire) and also need an over-temperature protection of key components inside the machine.

13.Cooling Function

The inverter should have measures to ensure that the inverter does not damage due to excessive temperature when it continues to operate normally.

14.DC Input Overload Protection

If the inverter cannot limit the output power of the PV modules, the inverter need a protection when the PV modules output power is 1.1times than rated input power of the inverter. If the inverter has a power limit function, when the output power of the PV modules exceed the allowed DC input power, the inverter will automatically limit the power to the maximum allowable AC output power.

15.Surge Protection

Inverter should be equipped with Surge Protection Device (SPD) which can handle 6000V surge voltage.

16.Noise Reduction Function

The noise of inverter is required below 50dB.

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