With the deepening of PV poverty alleviation, many problems have begun to stand out. For example, in some remote areas, construction workers found that the grid voltage is always high, which not only triggers frequent voltage fault alarms, but also causes inverter shutdown protection, which seriously affects PV revenue. For such problems, manufacturers often give solutions from the inverter side, such as relaxing the protection voltage range (for different regions, the factory AC voltage is relaxed to 160-300AC adjustable). Although this method can solve the protection shutdown problem of the inverter, it will always cause damage to some household appliances because the output grid voltage is too high. It should be said that such phenomena are very common, and many forum posts have also done professional technical analysis on this, but there are still many practitioners who are confused. Here, the author wants to make a simple combing through some analogy to help everyone avoid the above situation from the power station design source. We all know that the photovoltaic grid-connected system is the process of converting direct current into alternating current through an inverter and transmitting it to the grid. If the grid is compared to the sea, the inverter can be seen as a trickle, and the grid is like a trickle into the sea. The AC cable used for grid connection is the river bed. In this regard, we may wish to make an analogy: In some remote areas or grid-connected power generation in weak grid areas, often due to the influence of line impedance (small river bed, more blockage), the inverter output AC voltage has to be raised (the river water level increases and a high water potential is formed). In order to flow to the sea), to ensure that the AC flows efficiently to the grid (the river flows into the sea). But this will inevitably lead to two types of problems: First, the output voltage is higher than the inverter's own protection voltage value, causing the inverter to report errors and perform protective shutdown; second, the grid-connected transformer has a small capacity (that is, "the sea water storage" Insufficient quantity, this is the reason why many places limit the grid-connected capacity to about 30%.) It is easy to overload the Internet due to over-loading of electricity, and raise the grid voltage (the reservoir has insufficient water storage capacity and overflow). In fact, the above two cases are the two main reasons for the excessive voltage of the grid, that is, the capacity of the grid connection point is small, the load consumption capacity is insufficient, or the grid weakly highlights the line impedance. So how do we solve the above problem? There is no doubt that the first is to increase the cable specifications and choose the grid connection point. The second is to increase the capacity of the transformer to improve the "water storage capacity". Among them, the reasonable choice of grid connection points and capacity transformers are easy to understand. For example, the selection of the grid point is the most common grid connection point selection method, and the capacity transformer is to increase the capacity of the transformer. In this way, only the cable specification is increased. Using an image metaphor, the river bed is enlarged and the mud is cleaned at a position close to the sea to significantly reduce the middle resistance of the river. In addition, there is another situation worth mentioning. When multiple devices are connected to the network, if they are concentrated on one phase, it is easy to raise the phase voltage (similar to a number of rivers remitted to a narrow riverbed, causing water overflow). , the grid is biased, resulting in a phenomenon similar to the grid voltage is too high. Therefore, it is recommended that when multiple grids are connected to the same grid, the equipment should be evenly distributed on the three phases (as shown below). The above, aiming at a simple analogy, let everyone have an image of the cause of the grid overvoltage fault. But the ultimate goal is to hope that in the construction of photovoltaic power plants, these potential hazards can be avoided at the beginning of design to improve design efficiency and help photovoltaic poverty alleviation. Guangzhou Yunge Tianhong Electronic Technology Co., Ltd , https://www.e-cigarettesfactory.com
