CN110887994A - Method and system for obtaining system harmonic impedance - Google Patents
Method and system for obtaining system harmonic impedance Download PDFInfo
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- CN110887994A CN110887994A CN201911191828.9A CN201911191828A CN110887994A CN 110887994 A CN110887994 A CN 110887994A CN 201911191828 A CN201911191828 A CN 201911191828A CN 110887994 A CN110887994 A CN 110887994A
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Abstract
The invention discloses a method and a system for acquiring system harmonic impedance, which comprises the following steps: s1: acquiring harmonic signals of a wind power plant and a photovoltaic power plant after grid connection, and inhibiting self-excited oscillation of the harmonic signals to generate preprocessed harmonic signals; s2: constructing a filter function by adopting a Fokker-Planck equation, and decomposing the preprocessed harmonic signal according to the filter function to obtain a periodic component; s3: performing Hilbert transform on each component in the periodic components, extracting harmonic characteristic parameters and obtaining the harmonic characteristic parameters according to the harmonic characteristic parameters; the harmonic characteristic parameters include frequency, amplitude and phase. According to the method and the system for obtaining the harmonic impedance of the system, the harmonic impedance analysis of the power system is simplified, the mode aliasing problem existing in an empirical mode decomposition algorithm can be effectively avoided, and the analysis efficiency of the harmonic impedance is improved.
Description
Technical Field
The invention relates to an electrical engineering technology, in particular to a method and a system for acquiring harmonic impedance of a system.
Background
At present, the problems of non-stationarity and increasingly outstanding complexity of harmonic components of a power system and difficulty in identification and detection caused by wide application of a large number of nonlinear loads and power electronic equipment
The existing harmonic analysis of the power system needs to deduce a mathematical theoretical formula for realizing harmonic superposition under the condition of unknown phase, obtain the relationship between the square of the amplitude of the total harmonic and each superposed component, and establish the function relationship between the square of the amplitude of the total harmonic and the cosine expectation of the phase angle difference between the two superposed components, and the theoretical derivation has certain difficulty. Secondly, solving the harmonic superposition coefficient by using a numerical value statistical method through a large amount of harmonic actual measurement data of wind power and photovoltaic power generation does not necessarily directly show a specific rule, and the harmonic sources may need to be classified, discussed in different periods and summarized in the superposition coefficient.
Meanwhile, the coefficient is related to the harmonic emission characteristic of the harmonic source and the number of the harmonic sources of the same bus, and in addition, the coefficient may also be related to seasons, different harmonic times may have different simultaneous coefficients, and multiple factors need to be considered and the simultaneous coefficients need to be discussed in different harmonic times, so that certain difficulty is achieved.
Disclosure of Invention
The technical problem to be solved by the invention is that the technical difficulty of harmonic impedance analysis of a power system in the prior art is very high, and the invention aims to provide a method and a system for obtaining the harmonic impedance of the system, so as to solve the problems.
The invention is realized by the following technical scheme:
a method for obtaining system harmonic impedance comprises the following steps: s1: acquiring harmonic signals of a wind power plant and a photovoltaic power plant after grid connection, and inhibiting self-excited oscillation of the harmonic signals to generate preprocessed harmonic signals; s2: constructing a filter function by adopting a Fokker-Planck equation, and decomposing the preprocessed harmonic signal according to the filter function to obtain a periodic component; s3: performing Hilbert transform on each component in the periodic components, extracting harmonic characteristic parameters and obtaining the harmonic characteristic parameters according to the harmonic characteristic parameters; the harmonic characteristic parameters include frequency, amplitude and phase.
When the method is applied, firstly, a pre-processing harmonic signal is generated, the pre-processing signal needs to suppress the harmonic wave of the photovoltaic grid-connected point and eliminate the nonlinear self-oscillation, and the post-analysis can be carried out after the pre-processing is finished; in the analysis process, a filter function is constructed by utilizing a Fokker-Planck equation, and an intrinsic mode component with stable characteristics is obtained through filtering and screening, so that the method has a solid mathematical foundation and can effectively avoid the mode aliasing problem existing in an empirical mode decomposition algorithm. Firstly, a periodic component is obtained by decomposition through an improved adaptive iterative filtering algorithm, Hilbert transformation is carried out on each component, harmonic characteristic parameters including frequency, amplitude and phase are extracted, and the strong adaptability of the method in the harmonic detection of the power system is fully verified through a comparison result of the harmonic characteristic parameters and empirical mode decomposition. By setting the steps, the harmonic impedance analysis of the power system is simplified, the mode aliasing problem of the empirical mode decomposition algorithm can be effectively avoided, and the harmonic impedance analysis efficiency is improved.
Further, step S1 includes the following sub-steps:
s11: obtaining harmonic signals of a wind power plant and a photovoltaic power plant after grid connection, and performing park transformation on the harmonic signals to generate d-axis and q-axis signals;
s12, transforming the d-axis and q-axis signals to obtain α -axis and β -axis signals, and separating alternating components in the α -axis and β -axis signals;
and S13, obtaining estimated values of the frequency, the amplitude and the phase of each alternating component on the α axis and the β axis after processing the alternating components through windowing interpolation Fourier transform.
Further, step S1 further includes the following sub-steps:
s14: separating the harmonic signals from the alternating components with the overlimit estimated values in real time, and taking the alternating components with the overlimit estimated values separated as preprocessing alternating component signals;
s15: and carrying out inversion processing on the preprocessed alternating component signals to generate preprocessed harmonic signals.
When the method is applied, the inventor finds that the generated nonlinear self-oscillation is the reason for generating the grid-connected point harmonic wave, so that the alternating component separation method based on the windowed interpolation Fourier transform can effectively eliminate the nonlinear self-oscillation and restrain the photovoltaic grid-connected point harmonic wave.
Further, the periodic component is an IMF component.
A system harmonic impedance acquisition system comprising:
a pretreatment unit: the harmonic suppression device is used for acquiring harmonic signals of a wind power plant and a photovoltaic power plant after grid connection and suppressing self-excited oscillation of the harmonic signals to generate preprocessed harmonic signals;
a decomposition unit: the system is used for constructing a filter function by adopting a Fokker-Planck equation and decomposing the preprocessed harmonic signal according to the filter function to obtain a periodic component;
a transformation unit: the harmonic characteristic parameters are extracted after Hilbert transform is carried out on each component in the periodic components and are obtained according to the harmonic characteristic parameters; the harmonic characteristic parameters include frequency, amplitude and phase.
The method comprises the steps of obtaining harmonic signals of a wind power plant and a photovoltaic power plant after grid connection by a preprocessing unit, carrying out park transformation on the harmonic signals to generate d-axis and q-axis signals, obtaining α -axis and β -axis signals after the d-axis and q-axis signals are transformed by the preprocessing unit, separating alternating components in the α -axis and β -axis signals, and obtaining estimated values of frequency, amplitude and phase of each alternating component on the α -axis and β -axis after the alternating components are processed by the preprocessing unit through windowing interpolation Fourier transformation.
Further, the preprocessing unit separates the harmonic signal from the alternating component with the over-limit estimated value in real time, and takes the alternating component with the over-limit estimated value separated as a preprocessed alternating component signal; and the preprocessing unit is used for generating a preprocessing harmonic signal after carrying out inversion processing on the preprocessing alternating component signal.
Further, the periodic component is an IMF component.
Compared with the prior art, the invention has the following advantages and beneficial effects:
according to the method and the system for obtaining the harmonic impedance of the system, the harmonic impedance analysis of the power system is simplified, the mode aliasing problem existing in an empirical mode decomposition algorithm can be effectively avoided, and the analysis efficiency of the harmonic impedance is improved.
Drawings
The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:
FIG. 1 is a schematic diagram of the process steps of the present invention;
FIG. 2 is a schematic diagram of an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.
Examples
As shown in fig. 1, the method for obtaining the harmonic impedance of the system of the present invention includes the following steps: s1: acquiring harmonic signals of a wind power plant and a photovoltaic power plant after grid connection, and inhibiting self-excited oscillation of the harmonic signals to generate preprocessed harmonic signals; s2: constructing a filter function by adopting a Fokker-Planck equation, and decomposing the preprocessed harmonic signal according to the filter function to obtain a periodic component; s3: performing Hilbert transform on each component in the periodic components, extracting harmonic characteristic parameters and obtaining the harmonic characteristic parameters according to the harmonic characteristic parameters; the harmonic characteristic parameters include frequency, amplitude and phase.
When the embodiment is implemented, a pre-processing harmonic signal is generated firstly, the pre-processing signal needs to suppress the photovoltaic grid-connected point harmonic and eliminate the nonlinear self-oscillation, and the post-analysis can be performed after the pre-processing is finished; in the analysis process, a filter function is constructed by utilizing a Fokker-Planck equation, and an intrinsic mode component with stable characteristics is obtained through filtering and screening, so that the method has a solid mathematical foundation and can effectively avoid the mode aliasing problem existing in an empirical mode decomposition algorithm. Firstly, a periodic component is obtained by decomposition through an improved adaptive iterative filtering algorithm, Hilbert transformation is carried out on each component, harmonic characteristic parameters including frequency, amplitude and phase are extracted, and as shown in fig. 2, the strong adaptability of the method in the harmonic detection of the power system is fully verified by the comparison result of the embodiment and empirical mode decomposition. By setting the steps, the harmonic impedance analysis of the power system is simplified, the mode aliasing problem of the empirical mode decomposition algorithm can be effectively avoided, and the harmonic impedance analysis efficiency is improved.
To further explain the operation of the present embodiment, step S1 includes the following sub-steps:
s11: obtaining harmonic signals of a wind power plant and a photovoltaic power plant after grid connection, and performing park transformation on the harmonic signals to generate d-axis and q-axis signals;
s12, transforming the d-axis and q-axis signals to obtain α -axis and β -axis signals, and separating alternating components in the α -axis and β -axis signals;
and S13, obtaining estimated values of the frequency, the amplitude and the phase of each alternating component on the α axis and the β axis after processing the alternating components through windowing interpolation Fourier transform.
To further explain the working process of the present embodiment, step S1 further includes the following sub-steps:
s14: separating the harmonic signals from the alternating components with the overlimit estimated values in real time, and taking the alternating components with the overlimit estimated values separated as preprocessing alternating component signals;
s15: and carrying out inversion processing on the preprocessed alternating component signals to generate preprocessed harmonic signals.
In the implementation of the embodiment, the inventor finds that the generated nonlinear self-oscillation is the reason for generating the grid-connected point harmonic wave, so that the alternating component separation method based on the windowing interpolation fourier transform, which is provided by the invention, can effectively eliminate the nonlinear self-oscillation and suppress the photovoltaic grid-connected point harmonic wave.
To further illustrate the operation of this embodiment, the periodic component is an IMF component.
A system harmonic impedance acquisition system comprising:
a pretreatment unit: the harmonic suppression device is used for acquiring harmonic signals of a wind power plant and a photovoltaic power plant after grid connection and suppressing self-excited oscillation of the harmonic signals to generate preprocessed harmonic signals;
a decomposition unit: the system is used for constructing a filter function by adopting a Fokker-Planck equation and decomposing the preprocessed harmonic signal according to the filter function to obtain a periodic component;
a transformation unit: the harmonic characteristic parameters are extracted after Hilbert transform is carried out on each component in the periodic components and are obtained according to the harmonic characteristic parameters; the harmonic characteristic parameters include frequency, amplitude and phase.
To further illustrate the working process of the embodiment, the preprocessing unit obtains harmonic signals of a wind power plant and a photovoltaic power plant after grid connection, performs park transformation on the harmonic signals to generate d-axis and q-axis signals, the preprocessing unit obtains α -axis and β -axis signals after transforming the d-axis and q-axis signals and separates out alternating components in the α -axis and β -axis signals, and the preprocessing unit obtains estimated values of the frequency, the amplitude and the phase of each alternating component on the α -axis and β -axis after processing the alternating components through windowing interpolation Fourier transformation.
To further illustrate the working process of this embodiment, the preprocessing unit separates the harmonic signal from the alternating component with the estimation value exceeding the limit in real time, and uses the alternating component with the estimation value exceeding the limit as the preprocessed alternating component signal; and the preprocessing unit is used for generating a preprocessing harmonic signal after carrying out inversion processing on the preprocessing alternating component signal.
To further illustrate the operation of this embodiment, the periodic component is an IMF component.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (8)
1. A method for obtaining system harmonic impedance is characterized by comprising the following steps:
s1: acquiring harmonic signals of a wind power plant and a photovoltaic power plant after grid connection, and inhibiting self-excited oscillation of the harmonic signals to generate preprocessed harmonic signals;
s2: constructing a filter function by adopting a Fokker-Planck equation, and decomposing the preprocessed harmonic signal according to the filter function to obtain a periodic component;
s3: performing Hilbert transform on each component in the periodic components, extracting harmonic characteristic parameters and obtaining the harmonic characteristic parameters according to the harmonic characteristic parameters; the harmonic characteristic parameters include frequency, amplitude and phase.
2. The method for obtaining the system harmonic impedance according to claim 1, wherein the step S1 includes the following sub-steps:
s11: obtaining harmonic signals of a wind power plant and a photovoltaic power plant after grid connection, and performing park transformation on the harmonic signals to generate d-axis and q-axis signals;
s12, transforming the d-axis and q-axis signals to obtain α -axis and β -axis signals, and separating alternating components in the α -axis and β -axis signals;
and S13, obtaining estimated values of the frequency, the amplitude and the phase of each alternating component on the α axis and the β axis after processing the alternating components through windowing interpolation Fourier transform.
3. The method for obtaining the system harmonic impedance according to claim 2, wherein the step S1 further comprises the following sub-steps:
s14: separating the harmonic signals from the alternating components with the overlimit estimated values in real time, and taking the alternating components with the overlimit estimated values separated as preprocessing alternating component signals;
s15: and carrying out inversion processing on the preprocessed alternating component signals to generate preprocessed harmonic signals.
4. The method of claim 1, wherein the periodic component is an IMF component.
5. A system harmonic impedance acquisition system, comprising:
a pretreatment unit: the harmonic suppression device is used for acquiring harmonic signals of a wind power plant and a photovoltaic power plant after grid connection and suppressing self-excited oscillation of the harmonic signals to generate preprocessed harmonic signals;
a decomposition unit: the system is used for constructing a filter function by adopting a Fokker-Planck equation and decomposing the preprocessed harmonic signal according to the filter function to obtain a periodic component;
a transformation unit: the harmonic characteristic parameters are extracted after Hilbert transform is carried out on each component in the periodic components and are obtained according to the harmonic characteristic parameters; the harmonic characteristic parameters include frequency, amplitude and phase.
6. The system harmonic impedance obtaining system of claim 5, wherein the preprocessing unit obtains harmonic signals of a wind power plant and a photovoltaic power plant after grid connection, performs park transformation on the harmonic signals to generate d-axis and q-axis signals, the preprocessing unit obtains α -axis and β -axis signals after transforming the d-axis and q-axis signals and separates out alternating components in the α -axis and β -axis signals, and the preprocessing unit obtains estimated values of frequency, amplitude and phase of each alternating component on the α -axis and β -axis after processing the alternating components through windowing interpolation Fourier transformation.
7. The system harmonic impedance acquiring system according to claim 6, wherein the preprocessing unit separates the harmonic signal from the alternating component with the estimation value exceeding the limit in real time, and uses the alternating component with the estimation value exceeding the limit separated as a preprocessed alternating component signal; and the preprocessing unit is used for generating a preprocessing harmonic signal after carrying out inversion processing on the preprocessing alternating component signal.
8. The system harmonic impedance acquisition system of claim 5 wherein the periodic component is an IMF component.
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Application publication date: 20200317 |