A Non-destructive Islanding Detection Method for Microgrid Based on Harmonic Current Injection and Harmonic Impedance Measurement

Abstract

The invention discloses a non-destructive island detection method for a microgrid based on harmonic current injection and harmonic impedance measurement, using FFT algorithm to measure harmonic voltage, harmonic current and system frequency at PCC in real time, and combining harmonic voltage and The system frequency is compared with the predetermined voltage and frequency threshold in real time. If it exceeds the threshold, it is directly judged as an island state; otherwise, the harmonic voltage and harmonic current are used to calculate the equivalent harmonic impedance amplitude and phase angle, and the current harmonic The ratio of the wave impedance amplitude to the last harmonic impedance amplitude determines whether the harmonic impedance amplitude ratio is greater than the proportional coefficient. If it is greater, it is judged whether the impedance phase angle is less than zero. If it is less than zero, it is determined as an island. The invention uses the amplitude change and phase change of the harmonic impedance as the islanding detection criterion, improves the accuracy of the islanding detection, realizes the islanding detection without forcing the voltage and frequency to exceed the threshold value, and is non-destructive.

Description

technical field [0001] The invention relates to the technical field of island detection, in particular to a non-destructive island detection method for a microgrid based on harmonic current injection and harmonic impedance measurement. Background technique [0002] Islanding refers to the phenomenon that when the grid side disconnects the circuit breaker due to failure or maintenance, the distributed power supply still supplies power to the load. The occurrence of unplanned islands will not only affect the stable operation of the grid and the normal use of electrical equipment, but also endanger the personal safety of grid maintenance personnel. With the maturity of distributed power generation technology and the increasing proportion of new energy connected to the grid, unplanned islands have become a problem that cannot be ignored. Therefore, improving and innovating the islanding detection method to achieve more accurate and faster islanding detection is an important pre...

AI Technical Summary

Problems solved by technology

But the disadvantage is that additional communication equipment is required, the cost is high, and it is not suitable for large-scale investment

The passive detection method judges whether islanding occurs by detecting whether the voltage, phase, frequency and its change rate of the grid connection point (PCC) are within the allowable range of change. This method does not require additional equipment investment, is simple to implement, and will not affect the system power. The quality is affected, but there is a large detection blind spot

The active detection method usually applies a small disturbance on the output reactive or active signal by the inverter, and judges the operating status of the distributed system by detecting the change of the disturbance signal. This method can significantly reduce or even eliminate the detection blind zone. But at the same time, it also has a certain degree of influence on the power quality.

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