Impedance-based islanding detection method for parallel operation of multiple inverters

Abstract

The invention discloses an island detection method suitable for multi-inverter parallel operation and based on impedance measurement, and belongs to the field of large-scale new energy station integrated grid connection islanding protection. The method includes the steps that firstly, the opening state and the closing state of a PCC point circuit breaker are detected in real time; secondly, if the PCC point circuit breaker is disconnected, the third step is executed, or else the first step is executed; thirdly, delay is conducted, and if a switch is kept in the disconnected state within one-second delay, the fourth step is executed, or else the first step is executed; fourthly, uncharacteristic harmonic currents are injected, timing is started, and time is set as t; fifthly, the impedance Z of uncharacteristic harmonic is measured; sixthly, if Z is larger than Zset, it is judged that an island exists, and the eighth step is executed, or else the seventh step is executed; seventhly, if t is larger than or equal to one second, the eighth step is executed, or else the fifth step is executed; eighthly, injection of the uncharacteristic harmonic currents is stopped. According to the method, harmonic is injected only when the island exists, and the quality of electric energy is not affected in the DG system grid connection operation process; an inverter is not needed for injection, mutual interference between injected harmonic is avoided, and therefore misjudgment and blind regions are avoided.

Description

technical field [0001] The invention belongs to the field of anti-islanding protection for large-scale new energy centralized grid connection, and in particular relates to an impedance measurement-based islanding detection method suitable for parallel operation of multiple inverters. Background technique [0002] Islanding means that when the distributed system (DG system) is disconnected from the main grid, the distributed generation system still supplies power to the local loads it carries, thus forming a self-sufficient power supply network that cannot be controlled by the power company. Islands are divided into planned islands and unplanned islands. Planned islands refer to islands that have been predicted at the beginning of grid planning and corresponding measures have been taken in advance for their safe and stable operation. Unexpected islands during planning, when unplanned islands occur, will bring some serious problems to the safe and stable operation of the power...

AI Technical Summary

Problems solved by technology

Similarly, for other inverters, if the phase angles meet the above conditions, there may be a detection blind zone

[0013] (2) Cases of misjudgment

[0017] It can be seen from the analysis that although the islanding detection scheme based on the impedance method has many advantages in the case of a single or a small number of inverters running in parallel, its detection performance is greatly reduced in the case of multiple inverters in parallel, which will not only affect Power quality during normal operation, and due to the influence of injected harmonics, its detection capability will be greatly weakened, and blind spots may increase or misjudgments may occur

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