Island detection method

Abstract

Provided is an island detection method. A passive method and an active method are matched, an island can be detected out fast according to an overfrequency / underfrequency and an overvoltage / undervoltage method, and the quality of electric energy is not affected; when islanding occurs and power matching is formed in an island system, power matching of the system can be destroyed according to a capacitor switching method with harmonic detection as a criterion, voltage and frequency in the system are made to change, and consequently the island is detected out.

Description

technical field [0001] The invention belongs to the field of anti-islanding protection for large-scale new energy centralized grid connection, is an anti-islanding protection detection scheme combining passive detection and active detection, and particularly relates to an islanding detection method for voltage / frequency detection and harmonic detection capacitor switching . Background technique [0002] Islanding means that after the power grid fails, the distributed generation system still supplies power to the surrounding loads, thus forming an uncontrollable local power supply network. Unplanned islands will bring some serious problems to the safe and stable operation of the power system. For example, the voltage and frequency in the island cannot be controlled, which may cause damage to the user's equipment; the lines in the island are still live, which may endanger the maintenance personnel. personal safety etc. The main function of island detection is to disconnect t...

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Problems solved by technology

However, if the method of periodically inputting capacitors is adopted, if the input capacitor is large, the grid-connected operation may cause uninterrupted voltage shocks to the distribution network system with a small capacity, which will have a certain impact on the power quality; secondly, this method The reliability of the switch is high, and periodic switching will shorten the service life of the switch

The second is to cooperate with the switch at the PCC point, such as figure 1 The middle switch S1, when the switch S1 is turned off, the switch S2 is closed, and the external capacitor is incorporated into the system, which destroys the power balance of the system

The disadvantage of this method is that the switching of the capacitor needs to cooperate with the switch at the PCC point, and the capacitor must be detected that the switch at the PCC point has been disconnected. If the detection device fails, the island detection will fail.

In addition, this method must find the power matching point, but the power flow of the power system changes frequently, and it is difficult to find a fixed power matching point

[0007] Based on the above analysis, it can be seen that the voltage / frequency detection method can effectively detect islands when the output power of the DG system inverter and the local load power are unbalanced, but when the output power of the DG system inverter and the local load power are balanced, the method failure

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