How to Solve the AC Overvoltage Problem of On Grid Inverter

Nowadays, photovoltaic grid-connected power generation is becoming more and more popular, and ordinary people's homes can also see photovoltaic power stations in real time. However, for ordinary people, they are still not as familiar with photovoltaic grid-connected systems, especially grid-connected inverters, as they are with TV refrigerators, and even some technicians of installation companies can't do decisive and rapid troubleshooting of common inverter faults.

Therefore, when the inverter feeds back some system fault information, everyone will be helpless. Therefore, it is an important condition to know the tips to solve the inverter faults to ensure the normal operation of the inverter.

In principle, the photovoltaic inverter itself will not generate voltage. The voltage displayed by the inverter comes partly from photovoltaic modules, which is called DC voltage, and partly from the power grid, which is called AC voltage. What to do if "Grid-connected inverter shows AC overvoltage problem".

According to the relevant regulations, the grid-connected PV inverter must work within the specified grid voltage range, which 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, the inverter must trip and stop working, in order to ensure the equipment safety and protect the personal safety of operators.

According to years of experience, when AC overvoltage occurs in the inverter, there are only the following three situations:

Situation 1: The grid-connected distance is too far, resulting in the voltage rising.

If the distance between the grid-connected inverter and the grid-connected point is too far, the voltage difference at the AC terminal side of the inverter will increase. When it exceeds the grid-connected voltage range specified by the inverter, the inverter will display the grid overvoltage. In addition, the cable used by the inverter to the grid connection point is too long, too thin, winding or substandard materials, etc., which will all lead to the increase of the AC terminal voltage difference of the inverter, so the cable selection and rational layout are particularly important. In view of this situation, it is first necessary to check whether the grid-connected distance is too long, and it is best to choose the nearest grid-connected scheme; Secondly, check cable distribution and cable quality, and select reasonable wiring mode and qualified AC cable.

Situation 2: Multiple inverters are centralized in one access point.

In fact, photovoltaic power generation in China has not been on the rise for a long time. The power supply bureau does not have much experience in selecting inverters for grid connection, and sometimes it appears unprofessional or thoughtless. It is often the case that multiple single-phase inverters are connected to the same phase, which will easily lead to unbalanced grid voltage, and the grid voltage will rise, which will naturally lead to too high grid-connected voltage. This situation is relatively easy to solve, so it is necessary to consider allocating the grid-connected capacity of the project to the three phases of the power grid and selecting multi-point grid connection.

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

With the national policy getting better and better, and the financing channels of photovoltaic finance expanding, many people are scrambling to install it. As a result, there may be too much installed photovoltaic capacity in the same district (the power supply range or area of one transformer) and insufficient load digestion capacity of the power grid. Because the electric energy generated by photovoltaic system can't be consumed nearby, and it can't be transported to a long distance point, naturally the grid voltage will rise continuously, and the inverter will show that the grid-connected voltage is too high.

The solutions to this situation are as follows: 

1. Reduce the capacity of photovoltaic power stations; 

2. Increase the capacity of transformers; 

3. Take precautions: survey the power grid in the early stage to evaluate the appropriate grid-connected capacity (the best method).