Microgrid non-destructive island detection method based on harmonic current injection and harmonic impedance measurement

Abstract

The invention discloses a microgrid non-destructive island detection method based on harmonic current injection and harmonic impedance measurement. The method comprises the steps of utilizing an FFT algorithm to real-timely measure a harmonic voltage, a harmonic current and a system frequency at a PCC, comparing the harmonic voltage and the system frequency with a preset voltage threshold value and a preset frequency threshold value in real time, and if the harmonic voltage and the system frequency exceed the threshold values, judging as an island state directly; otherwise, utilizing the harmonic voltage and the harmonic current to calculate an equivalent harmonic impedance amplitude and a phase angle, calculating a ratio of the harmonic impedance amplitude to the last harmonic impedance amplitude, judging whether the ratio of the harmonic impedance amplitude is greater than a proportionality coefficient or not, if so, judging whether the impedance phase angle is less than zero or not,and if not, judging as an island. According to the method, the amplitude change and phase change of the harmonic impedance are used as the island detection criteria, so that the island detection accuracy is improved, the island detection can be realized without needing to force the voltage and frequency to exceed the threshold values, and the island detection method 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.

Images