Wavelet packet extraction method for grid-connected inverter network-side harmonic current information

Abstract

The invention discloses a wavelet packet extraction method for grid-connected inverter network-side harmonic current information. The method is based on a wavelet tree optimized decomposition and reconstruction algorithm for db4 wavelet packets. A maximum harmonic current component real-time extraction technology based on wavelet packet transform is put forward. According to the method of the invention, the wavelet frequency band, the maintaining frequency band and the zero-setting frequency band are judged by the threshold criterion after each layer of decomposition, and only the wavelet frequency band is decomposed during next layer of decomposition. The method has the advantages of small amount of decomposition operation and high wavelet decomposition precision. Compared with the prior harmonic current information extraction method, the method of the invention takes into consideration the computation limit of a digital processor, the amount of computation of decomposition and reconstruction in the process of harmonic information extraction is reduced without sacrificing the amount of maximum harmonic current information, and the method is more practical in engineering and has the advantage of high harmonic information extraction precision.

Description

technical field [0001] The invention belongs to the technical field of power quality detection. , especially relates to a wavelet packet extraction method for grid-side resonant current information of grid-connected inverters. Background technique [0002] The large-scale grid connection of renewable energy based on voltage source grid-connected inverters is increasingly widely used, such as the centralized grid connection of large-scale photovoltaic power plants in western my country, and the large number of household photovoltaic grid-connected inverters at the end of the distribution network in European countries. Connect to the grid, etc. In these applications, the output terminals of multiple grid-connected inverters are connected in parallel at the common terminal (Point of Common Coupling, PCC) of the grid, and the resonance generated by the grid-connected filter excited by the switching action of each grid-connected inverter converges at the PCC, resulting in The cu...

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Problems solved by technology

In these applications, the output terminals of multiple grid-connected inverters are connected in parallel at the common terminal (Point of Common Coupling, PCC) of the grid, and the resonance generated by the grid-connected filter excited by the switching action of each grid-connected inverter converges at the PCC, resulting in The current resonance of each grid-connected branch and PCC is intensified, which endangers the operation safety of the grid-connected inverter and the grid

[0003] Traditionally, active damping is used for filter resonance suppression, which satisfies the application of single-unit integration into the ideal grid. However, multiple single-units are connected in parallel in the PCC. The interaction of their respective resonance sources and the consideration of nearby capacitive loads will produce more complex problems. resonance phenomenon

The single unit with damping measures still has resonance in large-scale applications. In the prior art, the resonance is generally suppressed based on the idea of ​​"detection-feedback-compensation". In view of the complexity and variability of the resonance current of large-scale grid-connected inverters, Generally, the wavelet packet complete decomposition algorithm is used to extract resonance information, which has a large amount of calculation, consumes a lot of digital processor resources, and has low engineering practicability.

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