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How to solve the problem of AC overvoltage of photovoltaic inverter?

2020-06-18

Photovoltaic grid-connected power generation is becoming more and more popular and photovoltaic power plants can be seen in ordinary people's homes. However, common people are still not familiar with the photovoltaic grid-connected system, especially the grid-connected inverter as the TV refrigerator. Even the technicians of some installation companies have not been able to solve the common faults of the inverter quickly and decisively. Therefore, knowing the tips to solve the inverter fault is an important condition to ensure the normal operation of the inverter.

 

In principle, the photovoltaic inverter itself does not generate voltage. Part of the voltage displayed by the inverter comes from the photovoltaic component, called DC voltage, and the other part comes from the grid called AC voltage. What to do if "Grid-connected inverter displays AC overvoltage problem"?

 

According to relevant regulations, the PV grid-connected inverter must work within the specified grid voltage range, and can be monitored in real time and synchronized with the grid voltage. When the inverter detects that the grid voltage (AC voltage) exceeds the specified range, it must be tripped to stop working to ensure the safety of the equipment and protect the personal safety of the operator.

 

According to many years of "clinical experience", when AC overvoltage occurs in the inverter, there are only the following three cases:

 

Case 1: The grid connection distance is too far, causing the voltage to rise

If the grid-connected inverter is too far from the grid connection point of the grid, the voltage difference on the AC terminal side of the inverter will increase. When the grid-connected voltage range specified by the inverter is exceeded, the inverter will display grid overvoltage. In addition, if the cable used from the inverter to the grid connection point is too long, too thin, entangled or the material is not in compliance, etc., it will lead to an increase in the voltage difference of the AC terminal of the inverter, so the cable selection and reasonable layout using are very important.

In view of this situation, we must first check whether the grid connection distance is too long, it is best to choose the nearest grid connection scheme; secondly, check the cable distribution and cable quality, select a reasonable wiring method and qualified AC cable.

 

Case 2: Multiple inverters are concentrated in one access point

In fact, the rise of domestic photovoltaic power generation is not long. The power supply bureau does not have much experience in selecting inverters for grid connection, and sometimes it seems unprofessional or under-considered. It is common that multiple single-phase inverters are connected to the same phase, which can easily cause the grid voltage to be unbalanced, and the grid voltage will increase, which naturally causes the grid-connected voltage to be too high.

This situation is relatively easily to solve, and it is necessary to consider allocating the grid-connected capacity of the project to the three phases of the power grid, and select multi-point grid-connection.

 

Case 3: The installed photovoltaic capacity in the same area is too large

With the improvement of national policies and the expansion of photovoltaic financial financing channels, many people are rushing to install, so that there may be too much photovoltaic installed capacity in the same area (the power supply range or area of a transformer). Since the electrical energy generated by the photovoltaic system cannot be consumed nearby, and the long-distance transmission point cannot be achieved, then the grid voltage will continue to rise, and the inverter will show that the grid-connected voltage is too high.

The solution to this situation is:

1. Derating of photovoltaic power station

2. Transformer capacity increase

3. Do a good job of prevention: pre-prospecting the power grid to evaluate the appropriate grid-connected capacity (the best method)


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