What is the islanding effect?

Simply put: if the low-voltage side of the photovoltaic power station is connected to the power grid, the commercial power you use can be used as the main power, while the solar power station is equivalent to the standby power. When you are overhauling, you just turn off the main power supply, while the photovoltaic power station is still transmitting electricity. "Early development of benevolence and property and grandchildren" is the island effect. In order to prevent this situation, it is necessary to add an anti-islanding device to ensure that if the mains power is cut off, the photovoltaic power station will immediately stop supplying power. \x0d\\x0d\ In electronic circuits, islanding refers to the phenomenon that there is a current path in a certain area of the circuit, but no current actually flows. In the communication network, there may be coverage of wireless mobile base stations. \x0d\ Principle \x0d\ In a circuit with capacitors connected in series, only two plates connected to the external circuit (note: not the plates of the same capacitor) have current flow (charge exchange), and the total charge of the other plates is constant, so it is called an island. Islanding is an electrical phenomenon. When a part of the power grid is disconnected from the main power grid, this part of the power grid is completely powered by photovoltaic system. This is still a controversial issue in the international standardization of photovoltaic grid connection, because islanding will damage the safety of the public and the maintenance personnel of power companies and the quality of power supply, and may damage the equipment when automatically or manually reclosing the power switch to re-supply power to the islanded power grid. Therefore, inverters usually have devices to prevent islanding. Passive technology (detecting voltage and frequency changes of power grid) is not enough to prevent islanding under the condition of good load balance, so it must be combined with active technology, which is based on sampling frequency offset, impedance monitoring of flowing current, phase jump and harmonic monitoring, positive feedback method or controller of unstable current and phase. There are many ways to prevent it. There are 16 patents in the world, some of which have been obtained and some of which are still in the process of application. Some of these methods, such as monitoring the current pulse flowing through the power grid, have proved inconvenient, especially when multiple inverters work in parallel, which will reduce the quality of the power grid and have a negative impact on islanding detection due to the interaction of multiple inverters. In other occasions, the working range of voltage and frequency becomes wider, and the installer can usually set these parameters through software, or even turn off ENS (a monitoring device, which is mandatory in Germany) in order to work in the weak current network. \x0d\ Editing this section \x0d\ In general, resonance is used to simulate the load circuit, and a quality factor "Q factor" is defined. Nevertheless, these tests are still difficult to carry out, especially for those high-power inverters that need large laboratories. The circuit and parameters of the test will vary from country to country, and the test results depend largely on the technical level of the tester. Some studies have been carried out to evaluate the possibility of islanding and its related risks. The research shows that islanding effect is actually impossible for low-density photovoltaic power generation system, because the load and power generation capacity are far from matching. However, for the power grid with high-density photovoltaic power generation system, active island protection is necessary, supplemented by voltage and frequency control, to ensure that the risk brought by photovoltaic is minimal. This data must be compared with the estimated annual electric shock of the power grid without photovoltaic. Most photovoltaic inverters have active and passive islanding protection. Although there are few examples of photovoltaic entering the power grid, foreign standards in this regard have not been relaxed. Islanding is the coverage problem of base stations. When the base station covers a large water surface or special terrain such as mountains, an "enclave" appears in the distance on the basis of the original coverage, but the adjacent base station with handover relationship cannot cover it due to the obstacle of terrain, resulting in no handover relationship between the "enclave" and the adjacent base station, so the "enclave" becomes an island. When the mobile phone occupies the "enclave", \x0d\ edit this. Due to various reasons (the wireless transmission environment is too good, the base station is too high or the antenna inclination angle is small), the service cell cannot cover the adjacent cells, which leads to a lonely area (so-called umbrella coverage) in the coverage area of some cells, and there are no adjacent cells in geography, which is similar to an "island". If the mobile station moves in this area, because there is no adjacent cell, the mobile station cannot switch to other cells, resulting in dropped calls. "Islanding effect" often appears after network expansion. As the new base station cuts into the access network, the coverage of the original cell needs to be adjusted. However, if the cell coverage shrinks too fast, the coverage of the two cell handover areas will be poor, otherwise it is easy to form an "island effect". Usually, we can find a solution to this kind of problem through a large number of DT tests, which can generally reduce the coverage of the cell and increase the neighbor list. Eliminate the "islands" of redundant adjacent relations and reduce dropped calls. Wireless optimization mainly solves the problems of dropped calls, frequency interference, handover and network congestion. Here, we discuss the method of reducing dropped calls by using redundant neighbor relations. There are many reasons for dropped calls, such as frequency interference in-band and out-of-band, missed judgment and wrong judgment of switching relationship, hardware failure, weak signal drop caused by insufficient coverage, and power failure of user's mobile phone. Many colleagues have discussed these issues. Here I want to talk about the method to solve dropped calls in the definition of switching relationship. Because our network coverage has been good, the inter-frequency interference is much smaller than before after frequency hopping. In practical work, it is often found that many dropped calls are caused by switching relationships. For example, in general, CELL3 of Base Station B only defines CELL 1 and CELL2 of Base Station A as adjacent cells, which is generally defined in CDD. We often think that CELL3 of base station B will only switch with CELL 1 and CELL2 of base station A. However, in actual road test, it is often found that the signal of base station B will cross base station A and run to the coverage area of CELL3 of base station A, and the signal strength will be higher than that of CELL3 of base station A, becoming the strongest cell locally, which is the common "island effect". Especially in places with dense base stations, there will be many repeated coverage, forming many "islands" (small circles in the figure). Because these islands are small in area and change with the change of wireless environment, it is often difficult to find them if they follow a fixed route in road test. Only when you happen to stay on these islands for a while, will your mobile phone be re-selected to CELL3 in Community B.. At this time, when you make a phone call, you will usually drop the call because there is no better neighborhood. On the other hand, if there is another base station C and the base station A is located between B and C, there will be no direct handover relationship from B: Cell 3 to C when the base station A is congested or blocked. Therefore, users who move from base station B to base station C may eventually give up the call because they can't find a better cell handover or still switch to a worse cell. Because these "small islands" have strong concealment, we tend to ignore them. It is often difficult to reflect on indicators. Common solutions include increasing antenna inclination, reducing transmission power or using TALIM parameters to limit the maximum coverage of the cell, but these methods all have their shortcomings. In practical work, we often use the method of adding redundant one-way switching relationship to solve it. For example, in the above example, we can add the one-way switching relationship between B: Cell 3 and A: Cell 3 or C: Cell 1 and CELL2, and even add the one-way switching relationship between B: Cell 3 and C. However, due to high-frequency reuse, it may happen that A: Cell 3 is the same as C: Cell 3 BCCHNO. At this time, it is necessary to change the BCCHNO of one of the cells to avoid the same BCCHNO of the adjacent cells.