New energy flexible direct-current grid-connected transient harmonic detection method and new energy flexible direct-current grid-connected transient harmonic detection system

Abstract

The invention provides a new energy flexible direct-current grid-connected transient harmonic detection method and a new energy flexible direct-current grid-connected transient harmonic detection system. The number K of VMD decomposition mode components is determined by adopting a Pearson correlation coefficient method, the start time and stop time of signal disturbance are accurately positioned by utilizing a singular value decomposition (SVD), and finally instantaneous amplitude frequency information is extracted through Hilbert transformation and least square fitting, so that the algorithmadaptability and the calculation efficiency are improved while the high-precision detection and disturbance positioning of transient harmonic signals are realized. The efficiency and accuracy of harmonic detection are improved, the system is beneficial to harmonic treatment according to a detection result, the power loss of a power grid is reduced, the impact of transient disturbance on the steady-state operation of the power grid is reduced, and the stability of the operation of the power grid is improved.

Description

technical field [0001] The present disclosure relates to the related technical field of grid harmonic detection, and in particular, relates to a new energy flexible DC grid-connected transient harmonic detection method and system. Background technique [0002] The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art. [0003] In recent years, with the continuous development of my country's smart grid, new energy generation represented by wind power and photovoltaics has been continuously connected to the power grid, and a large number of non-linear electrical equipment and impact loads have been put into use, which has brought serious power quality pollution problems to the power grid. Mainly harmonic pollution. The existence of harmonics increases the power loss of the power grid, and the randomness of transient disturbances has an impact on the steady-state operation of the power gri...

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Problems solved by technology

At present, the methods of harmonic detection mainly include Fourier transform, instantaneous reactive power theory, wavelet transform and Hilbert-Huang transform (HHT), etc. Under non-synchronous sampling, Fourier transform detection harmonics will have spectrum leakage and fence effect, and transient harmonics cannot be detected; the instantaneous reactive power theoretical calculation speed is fast, the calculation amount is small, and the real-time performance is good, but the signal waveform is required to be undistorted; the wavelet transform time-frequency local analysis effect is better, but the decomposition is excessive Relying on the selection of wavelet basis and decomposition layers; HHT can adaptively decompose nonlinear and non-stationary signals, and has the ability to analyze stable transient harmonics, but it is prone to modal aliasing problems when decomposing harmonic signals with similar frequencies

[0005] Variational Mode Decomposition (VMD) uses alternating direction penalty factors in the variational problem framework to continuously update each mode and its center frequency, but VMD generally pre-judges the number K of components in the original signal through fast Fourier transform , requires manual observation of the center frequency of the spectrum, which makes the method less adaptable and less computationally efficient

And for the transient harmonics that appear in the new energy flexible DC grid-connected grid, it is not only necessary to detect its instantaneous amplitude and frequency, but also to locate the start and end moments of the disturbance, which requires higher detection accuracy and noise robustness, which cannot be met by current detection methods. Requirements for transient harmonic detection

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