Islanding detection method based on voltage harmonic fault component

A voltage harmonic and island detection technology, applied in the field of grid-connected distributed power sources, can solve problems such as power quality impact, and achieve the effect of low sampling frequency requirements and easy hardware implementation.

Inactive Publication Date: 2016-06-01
XIAN UNIV OF SCI & TECH
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Problems solved by technology

Local islanding detection methods can be further divided into two types: passive and active: the passive method only judges the occurrence of islanding based on the abnormal voltage or frequency output by the grid-connected inverter, and usually the passive method has relatively large detection blind spots; and The active method injects disturbances into the power grid, and uses the corresponding changes in system voltage, frequency, and impedance caused by the disturbance signals to judge the occurrence of islanding. Although this method can effectively reduce detection blind spots, it will have certain impact on power quality. Impact

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  • Islanding detection method based on voltage harmonic fault component
  • Islanding detection method based on voltage harmonic fault component
  • Islanding detection method based on voltage harmonic fault component

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Embodiment Construction

[0053] The present invention will be described in further detail below in conjunction with the accompanying drawings.

[0054] When the grid is connected with distributed power, the grid can be regarded as a voltage source with a large capacity, and the harmonic current generated by the grid-connected inverter will flow into the grid with lower impedance. Low grid impedance at the output terminal voltage response u of the grid-connected inverter a Contains only a small amount of harmonics, that is, the voltage distortion rate is close to zero.

[0055] When the grid is disconnected, there will be two factors that make u a Increased content of mid-harmonics:

[0056] Harmonic currents flow into loads whose impedance is much higher than the grid impedance, making u a produce greater distortion.

[0057] If the switch disconnecting from the grid is located on the primary side of the transformer, the current output by the grid-connected inverter will flow through the secondary...

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Abstract

The invention discloses an islanding detection method based on voltage harmonic fault component. Through detecting differences presented by voltage signals at specific frequencies of 150 Hz, 250 Hz and 350 Hz in the case of normal grid-connected operation and islanding operation, the islanding operation state is detected. A sliding data window is used for calculating absolute values |DeltaU3|, |DeltaU5|, and |DeltaU7| for voltage specific subharmonic fault components at the grid-connected inverter end, and whether islanding happens according to the sizes of the |DeltaU3|, the |DeltaU5|, and the |DeltaU7|. The quality of electric energy outputted by the grid-connected inverter is not influenced, the transient response of the system is not disturbed, the sampling frequency is lowly required, and hardware realization is facilitated. The method of the invention can quickly and effectively detect islanding effects in the most serious islanding condition defined by the IEEE Std.1547.1 standard, is applicable to various broken circuit conditions, and has good practicality.

Description

technical field [0001] The invention belongs to the technical field of grid connection of distributed power sources, and in particular relates to an island detection method based on voltage harmonic mutation. Background technique [0002] The island effect means that in the distributed power generation system, when the grid power supply trips due to a fault accident or power outage maintenance, the distributed grid-connected power generation system at each user end fails to detect the power outage in time and cuts itself off from the mains network. A self-sufficient power supply island power generation system is formed by the grid-connected power generation system of distributed power stations and its connected loads. [0003] The island effect makes the voltage and frequency out of control. If the distributed generation system does not have the ability to adjust the voltage and frequency, and there is no voltage and frequency protection relay to limit the deviation of the v...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G01R31/00
CPCG01R31/00
Inventor 高淑萍李文浩罗娟杨忠礼付周兴谢晶
Owner XIAN UNIV OF SCI & TECH
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