Real-time detection method of three-phase grid impedance under the condition of grid asymmetry
A three-phase power grid, real-time detection technology, applied in the direction of measuring resistance/reactance/impedance, measuring electricity, measuring devices, etc., can solve the problem of no impedance detection method, no way to detect the grid impedance value, long detection time, etc.
Active Publication Date: 2018-01-12
CHINA UNIV OF MINING & TECH
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Problems solved by technology
[0003] At present, there are few methods for detecting the impedance of the symmetrical grid at home and abroad. Some literatures have proposed a method for detecting the impedance of the symmetrical grid based on a complex filter, but this method has no way to detect the grid impedance of the three phases under the condition of asymmetrical grid impedance.
In addition, some literatures have proposed a three-phase asymmetric grid impedance detection method based on FFT, but this method has a large amount of calculation and a long detection time, and does not propose a detection method for impedance under unbalanced grid conditions.
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[0043] Below is further described according to the implementation steps of the present invention:
[0044] like figure 1 figure 2 The voltage and current vectors for the 175Hz and 325Hz harmonics are shown:
[0045]
[0046] P in formula (1) ab-a as a vector exist projection on , Q ab-a for exist Projection in the vertical direction. ω x They represent the injected 175Hz harmonic current angular velocity of 350π and the 325Hz harmonic current angular velocity of 650π. In the case of different harmonic currents, four corresponding equations can be obtained, and then solved,
[0047]
[0048] In the same way, the expressions of A-phase impedance and C-phase impedance are
[0049]
[0050]
[0051] Symmetrical harmonic currents with the same RMS are injected twice, i.e. I 175 =I 325 . From the expression of grid impedance, it can be seen that it is only necessary to obtain the effective value of the grid line voltage and the angle between the line v...
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A method for real-time detection of three-phase grid impedance under the condition of grid asymmetry, which is suitable for rapid detection of grid impedance in solar grid-connected applications. The steps are: injecting three-phase symmetrical harmonics with two non-characteristic sub-frequency of 175Hz and 325Hz into the grid current; separate the two non-characteristic sub-frequency harmonic current components in the current; separate the two non-characteristic sub-frequency harmonic voltage components in the grid voltage; obtain the phases of the two non-characteristic sub-frequency harmonic currents respectively; solve them separately The RMS values of these two non-characteristic sub-frequency harmonic voltages; respectively calculate the angle between the harmonic voltage and harmonic current at these two non-characteristic sub-frequency; calculate the impedance of each phase grid respectively according to the voltage, current and angle information obtained above. Its calculation speed is fast and the calculation amount is small, and it is suitable for grid impedance detection under the condition of grid voltage and grid impedance asymmetry.
Description
technical field [0001] The invention relates to a real-time detection method of three-phase power grid impedance, which is especially suitable for the real-time detection method of three-phase power grid impedance under the condition of grid asymmetry used for fast detection of power grid impedance in solar energy grid connection. Background technique [0002] The grid-connected converter is a key part of the solar grid-connected power generation technology, and plays an important role in the grid-connected process. Under normal circumstances, the grid-connected converter needs to have the function of island detection, and the voltage collected by the grid-connected converter during operation needs to remove the voltage drop on the grid line, so it is particularly important to perform impedance detection on the grid. For a single power grid, since the material is constant and the length of the three-phase line is the same, the simple line impedance value is constant. Howeve...
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IPC IPC(8): G01R31/00G01R27/04
Inventor 王颖杰韩雪龙伍小杰闫浩浩柴玉硕王文超左慧芳许贺张永磊王康安
Owner CHINA UNIV OF MINING & TECH