1. Input overvoltage protection: When the input voltage of the DC side is higher than the maximum allowable DC array access voltage of the grid-tied inverter, the inverter cannot start or stop within 0.1s ( running) and a warning signal is emitted. released at the same time. After the DC side voltage is restored to the allowable working range of the inverter, the inverter should power on and operate normally.
2. Input reverse connection protection: When the positive input terminal and negative input terminal of the solar inverter are reversely connected, the inverter should be able to protect itself automatically. When the polarities are correctly connected, the equipment should be able to work normally.
3. Input overcurrent protection: After connecting the PV modules in series and parallel, each string is connected to the DC side of the solar PV inverter. After MPPT interference, when the input current is higher than the maximum allowable DC input current set by the inverter, the inverter (in operation) stops the MPPT interference and sends a warning signal. After the DC side current returns to the operating range allowed by the solar inverter, the inverter should be able to start up and operate normally.
4. Output over-current protection: Over-current protection needs to be set on the AC output side of the grid-tied inverter. When a short circuit is detected on the grid side, the grid-tied inverter should stop supplying power to the grid within 0.1s and send out a warning signal. After removing the fault, the grid-tied inverter should work normally.
5. Output short circuit protection: In case of inverter output short circuit to the grid, short circuit protection measures must be taken. The short circuit protection action time of the inverter should not exceed 0.5s. After removing the short circuit fault, the equipment should work normally.
6. AC/DC surge protection: The on-grid solar inverter must have lightning protection function, and the technical index of the lightning protection device must ensure that it absorbs the expected impact energy.
7. Anti-islanding protection: The grid-tied inverter must have complete and reliable anti-islanding protection function. The grid-tied inverter generally has passive or active detection methods. Passive island protection: Detects the magnitude, frequency and phase of the network voltage in real time. When the grid is without power, it will generate a jump signal in the grid voltage amplitude, frequency and phase parameters, and the jump signal will be detected to judge whether the grid is without power or not. Active island protection: generate small interference signals through inverter time to observe whether or not the power grid is affected as a basis for judgment, such as pulse current injection method, power change detection method output, active frequency compensation method and sliding frequency compensation method and so on. When the grid is powered, the interference has no effect on the grid voltage frequency. When the network is without power, the interference will cause a large change in the frequency of the network voltage, which determines whether the network is without power or not.
8. Output overvoltage/undervoltage, overfrequency/underfrequency protection: On the AC output side of the grid-tied inverter, the grid-tie inverter must be able to accurately determine the overvoltage/undervoltage, overfrequency/ underfrequency and other abnormal conditions of the power supply network (wiring). The inverter connected to the grid must protect according to the required time. A warning signal should be issued when cutting. When the grid voltage and frequency return to the allowable voltage and frequency range, the inverter should be able to start normally.
9. Internal short-circuit protection: When a short circuit occurs inside the grid-tied inverter, the protection of the inverter's electronic circuits and fuses must be fast and reliable.
10. Overheat protection: The grid connected inverter must have overheat protection functions, such as internal ambient temperature too high alarm (such as temperature too high in case of fire), too high temperature of key components in the machine (such as IGBT, Mosfet, etc.).
11. Grid-tied protection automatic recovery: After the grid-tied inverter stops supplying power to the grid due to grid failure, the grid-tied inverter should be able to automatically send power to the grid 5 minutes after the mains voltage and frequency return to normal range for 20 s. In power supply, the output power should increase slowly, but without affecting the network.
12. Insulation resistance monitoring: The grid tied inverter has a complete insulation resistance monitoring function. When the electrical part of the equipment is grounded, the insulation monitoring system should be able to immediately monitor the status of inverter fault, shutdown and alarm. The inverter calculates the grounding resistance of PV+ and PV– by detecting the grounding voltage of PV+ and PV-. If the resistance of any side is less than the threshold, the inverter will stop working and the alarm will display "low PV insulation resistance".
13. Leakage current monitoring and protection: The solar grid tie inverter has perfect leakage current monitoring function. In the process of inverter operation, it monitors the leakage current in real time. When the monitored residual current exceeds the following limits, the inverter should be disconnected from the grid within 0.3s, and a fault signal should be sent: As for inverters with rated output less than or equal to 30KVA: 300mA; As for inverters with nominal power greater than 30KVA: 10mA/KVA.
14. Zero (Low) Voltage Transversal Function: Zero (Low) Voltage Transversal Function: When the power system has an accident or interference, causing voltage drop at the grid connection point of the plant PV power station, within a certain voltage drop range and time interval, the PV power station can guarantee continuous operation without disconnection from the grid. This function is performed by the inverter. The cause of the voltage drop is that when a short circuit fault occurs in a branch of the power system, the current increases sharply. At this time, the protection device on the fault branch acts to isolate the fault point, so the voltage recovers. From fault generation to detection and then disconnection, it takes a while, which will cause the voltage of each branch to drop suddenly, forming a short-term voltage drop. At this time, if the solar power station is cut off immediately, the stability of the power grid will be affected, and even other branches without faults will also be cut off, resulting in a large-scale power grid blackout. At this time, the solar PV inverter is required to support for a period of time (within 1s) until the grid voltage recovers. The zero (low) voltage transverse function is suitable for large-scale land-based power plants. The grid voltage level is above 10KV, and the solar power is connected to the Internet and is not directly supplied to the load. However, in distributed PV plants, the zero (low) voltage transverse function is not necessary.