Near-power-frequency impedance measurement method and system, storage medium and equipment

Abstract

The invention discloses a near-power-frequency impedance measurement method and system, a storage medium and equipment, and the method comprises the steps: obtaining the actual fundamental frequency of a three-phase voltage and current signal, building a wave trap based on the actual fundamental frequency, filtering the fundamental component of the three-phase voltage and current signal through the wave trap, and effectively separating the power frequency and near-power-frequency components in a measurement signal. In the early-stage actual fundamental wave frequency acquisition, the Taylor Fourier transform dynamic frequency measurement method adjusts the center frequency of the band elimination filter according to the dynamic frequency, so that the power frequency component in the measurement signal is effectively filtered out, the problems of deviation and dynamic change of the fundamental wave frequency are solved, and the measurement accuracy is improved. And the identification precision of the near-power-frequency impedance is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy equipment and relates to a near-power frequency impedance measurement method, system, storage medium and equipment. Background Art

[0002] With the continuous integration of renewable energy, the "double high" characteristics of the power system, characterized by a high proportion of renewable energy and a high proportion of power electronic equipment, have gradually emerged. The risk of small disturbance stability in the renewable energy grid-connected system has intensified, and oscillation accidents have continued to occur. The impedance method is the most commonly used method for assessing the broadband oscillation risk of renewable energy grid-connected systems. Accurately obtaining the broadband impedance of renewable energy equipment and the power grid is of great significance for the broadband stability analysis of the system. Scanning the broadband impedance of renewable energy equipment and the power grid by injecting disturbance signals is currently an effective means of accurately obtaining impedance. However, since near-power frequency signals cannot be effectively separated from power frequency signals during the data analysis process, accurate identification of near-power frequency impedance is difficult. Summary of the Invention

[0003] The purpose of the present invention is to solve the problems in the prior art that the fundamental frequency has offset and dynamic changes, the near-power frequency signal cannot be effectively separated from the power frequency signal during data analysis, and the accurate identification of the near-power frequency impedance is difficult. A near-power frequency impedance measurement method, system, storage medium and device are provided, specifically involving a dynamic frequency measurement method based on Taylor Fourier transform, which adjusts the center frequency of the band-stop filter according to the dynamic frequency to achieve effective filtering of the power frequency component in the measurement signal and improve the identification accuracy of the near-power frequency impedance.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A method for measuring near-power frequency impedance, comprising the following steps:

[0006] Acquire three-phase voltage and current signals excited by near-power frequency disturbance signals;

[0007] Calculate the actual fundamental frequency of the three-phase voltage and current signals;

[0008] A notch filter is constructed based on the actual fundamental frequency, and the fundamental components of the three-phase voltage and current signals are filtered out based on the notch filter to obtain filtered voltage and current signals;

[0009] Calculate the near-power frequency impedance based on the filtered voltage and current signals.

[0010] A further improvement of the present invention is:

[0011] The method of calculating the actual fundamental frequency of the three-phase voltage and current signals comprises the following steps:

[0012] Any voltage signal from the three-phase voltage and current signals is selected, Taylor Fourier transform is performed on the selected voltage signal, and the fundamental frequency of the voltage is identified using the least square method.

[0013] The method of constructing a notch filter based on the actual fundamental frequency includes the following steps:

[0014] Set the center frequency of the notch filter ω c =2πf m , f m Indicates the actual fundamental frequency of the three-phase voltage and current signals; notch width ω b =2πf b , f b Indicates the bandwidth of the signal to be filtered that deviates from the central frequency; for a sampling interval of T a The discretized sampling signal r(k) of the notch filter is expressed by the following formula:

[0015]

[0016] in,

[0017] The method of filtering out the fundamental components of the three-phase voltage and current signals based on the notch filter to obtain filtered voltage and current signals includes the following steps:

[0018] Calculate the positive sequence voltage, negative sequence voltage, positive sequence current and negative sequence current of three-phase voltage and current signals;

[0019] According to the positive sequence voltage, negative sequence voltage, positive sequence current and negative sequence current, the fundamental components of the three-phase voltage and current signals are filtered out in combination with a notch filter.

[0020] The filtered voltage and current signals are expressed by the following formula:

[0021]

[0022] in, U pos Represents the positive sequence voltage of the three-phase voltage and current signals; I pos Represents the positive sequence current of the three-phase voltage and current signals.

[0023] The positive-sequence voltage, negative-sequence voltage, positive-sequence current, and negative-sequence current of the three-phase voltage and current signals are calculated using the following formula:

[0024]

[0025] Among them, U pos Represents the positive sequence voltage of the three-phase voltage and current signals; I pos Represents the positive sequence current of the three-phase voltage and current signals; j represents the imaginary number symbol; Uneg Indicates the negative sequence voltage of the three-phase voltage and current signal; I neg Represents the negative sequence current of the three-phase voltage and current signals.

[0026] The method of calculating the near-power frequency impedance based on the filtered voltage and current signals comprises the following steps:

[0027] Performing discrete Fourier transform or Taylor Fourier transform on the filtered voltage and current signals respectively;

[0028] Based on the transformed voltage and current signals, the voltage amplitude V at the frequency close to the power frequency signal is extracted. f and the current amplitude I f ;

[0029] Based on the voltage amplitude V f and the current amplitude I f Calculate the near-power frequency impedance.

[0030] A near-power frequency impedance measurement system, comprising:

[0031] A three-phase voltage and current signal acquisition module is used to acquire three-phase voltage and current signals excited by a near-power frequency disturbance signal;

[0032] The actual fundamental frequency calculation module is used to calculate the actual fundamental frequency of the three-phase voltage and current signals;

[0033] A filtering module is used to construct a notch filter based on the actual fundamental frequency, and filter out the fundamental components of the three-phase voltage and current signals based on the notch filter to obtain filtered voltage and current signals;

[0034] The near-power frequency impedance calculation module is used to calculate the near-power frequency impedance based on the filtered voltage and current signals.

[0035] A terminal device comprises a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of any one of the methods of the present invention when executing the computer program.

[0036] A computer-readable storage medium stores a computer program, wherein the computer program implements the steps of any method described in the present invention when executed by a processor.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The present invention discloses a near-power frequency impedance measurement method, which obtains the actual fundamental frequency of three-phase voltage and current signals, constructs a notch filter based on the actual fundamental frequency, and filters out the fundamental component of the three-phase voltage and current signals through the notch filter. This method can effectively separate the power frequency and near-power frequency components in the measurement signal, facilitates the improvement of the identification accuracy of the near-power frequency impedance in the later stage, realizes the effective filtering of the power frequency component in the measurement signal, and improves the identification accuracy of the near-power frequency impedance.

[0039] Furthermore, in the present invention, any voltage signal is selected, Taylor Fourier transform is performed, the fundamental frequency of the voltage is identified using the least squares method, and the dynamic frequency measurement method of Taylor Fourier transform is used to adjust the center frequency of the band-stop filter according to the dynamic frequency to achieve effective filtering of the power frequency component in the measurement signal, overcome the problems of offset and dynamic change of the fundamental frequency, and improve the identification accuracy of the near-power frequency impedance. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0041] Figure 1 This is a flow chart of a method for measuring near-power frequency impedance according to an embodiment of the present invention;

[0042] Figure 2 2 is a schematic diagram comparing the filtered signal before and after processing according to an embodiment of the present invention. DETAILED DESCRIPTION

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0044] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0045] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0046] In the description of the embodiments of the present invention, it should be noted that if the terms "upper," "lower," "horizontal," "inner," etc. appear, the orientation or positional relationship indicated is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the inventive product is typically placed when in use. These terms are merely for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first," "second," etc. are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0047] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0048] In the description of the embodiments of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0049] The present invention is described in further detail below with reference to the accompanying drawings:

[0050] See also Figure 1 The embodiment of the present invention discloses a method for measuring near-power frequency impedance. Specifically, a data processing method based on a band-stop filter is proposed in the calculation, which can effectively separate the power frequency and near-power frequency components in the measurement signal. At the same time, in order to solve the problem of power frequency signal separation caused by the offset and dynamic change of the fundamental frequency in actual engineering applications, the invention proposes a dynamic frequency measurement method based on Taylor Fourier transform, which adjusts the center frequency of the band-stop filter according to the dynamic frequency, realizes the effective filtering of the power frequency component in the measurement signal, and improves the identification accuracy of the near-power frequency impedance.

[0051] The method disclosed in the embodiment of the present invention is applicable to near-power frequency impedance measurement of power grids and new energy power generation equipment. Taking new energy power generation equipment as an example, the embodiment of the present invention specifically includes the following steps:

[0052] A method for measuring near-power frequency impedance, comprising the following steps:

[0053] Step 1: Obtain three-phase voltage and current signals excited by a near-power frequency disturbance signal;

[0054] Specifically, it includes: injecting a near-power frequency disturbance signal into the new energy power generation equipment through a broadband impedance measuring device, and collecting the instantaneous values ​​of the three-phase voltage and current at the output port of the new energy power generation equipment.

[0055] The near-power frequency mentioned in the embodiment of the present invention refers to a frequency band whose frequency range differs from the fundamental frequency by no more than 10 Hz. Taking 50 Hz as an example, the near-power frequency signal refers to a signal with a frequency between 40 and 60 Hz.

[0056] Step 2: Calculate the actual fundamental frequency of the three-phase voltage and current signals;

[0057] Specifically, the method includes: selecting any voltage signal from the three-phase voltage and current signals, performing Taylor Fourier transform on the selected voltage signal, and identifying the fundamental frequency of the voltage using the least square method.

[0058] In this embodiment, the A-phase voltage U in the three-phase voltage and current signal is selected. a Perform subsequent calculations;

[0059] Step 2.1: Assume that the voltage signal of phase A is U a The sampling interval is T a , the data window length is N = 2N h +1, taking the center of the window as the Taylor expansion moment, assuming the order of Taylor expansion is K, then the following formula holds:

[0060]

[0061] Among them, p K The phasor composed of the 0th to Kth order Taylor expansion derivative of the signal and its conjugate can be expressed as: K =[p (0) …p (K) ,p *(0) …p *(K) ] T It is also a value that needs to be identified, and * represents conjugation.

[0062] in

[0063]

[0064]

[0065] Step 2.2: Based on the least squares criterion, we can get:

[0066] (4)

[0067] Among them, B H is the Hermitian matrix of matrix B, ω = 2πf, and f is the frequency. For the first calculation, f can be set to 50 Hz.

[0068] Step 2.3: Actual fundamental frequency ω of the voltage signal m It can be calculated by the following formula:

[0069] ω m =ω0+Δω

[0070]

[0071] Among them, ∠p (0) Represents the complex number p (0) The phase angle of . imag represents the imaginary part.

[0072] Step 2.4: Set ω to ω m Repeat steps 2.1-2.3 until Δω ≤ a specific threshold Δω th ,but is the fundamental frequency of the signal.

[0073] Step 3: Construct a notch filter based on the actual fundamental frequency, and filter out the fundamental components of the three-phase voltage and current signals based on the notch filter to obtain filtered voltage and current signals;

[0074] Step 3.1: According to the f obtained in step 2 m Designing a notch filter:

[0075] Design the center frequency ω of the notch filter c =2πf m , notch width ω b =2πf b , f b Indicates the bandwidth of the signal to be filtered that deviates from the central frequency. For a sampling interval of T a The transfer function of the notch filter can be expressed as follows:

[0076]

[0077] in:

[0078] Step 3.2: Calculate the positive and negative sequence voltage and current according to equations (7) and (8) based on the instantaneous values ​​of the three-phase voltage and current of the renewable energy power generation equipment.

[0079]

[0080] in, j is the imaginary number symbol.

[0081] Step 3.3: U pos and I pos The discrete sampling sequence of the signal can be used to obtain the data after filtering by the notch filter based on the following formula:

[0082]

[0083] Step 4: Calculate the near-power frequency impedance based on the filtered voltage and current signals

[0084] The filtered voltage and current signals are subjected to discrete Fourier transform or Taylor Fourier transform, and the amplitude V at the frequency of the injected near-power frequency signal is extracted. f and I f .

[0085] Then the impedance of the new energy power generation equipment near the power frequency can be expressed as:

[0086]

[0087] Among them, V0 and I0 are the results of Fourier transform of the voltage and current sampling signals of the new energy power generation equipment at this frequency point when no signal is injected. They can be calculated by f and I f The same method is used for calculation. Usually, when no signal is injected, the harmonic voltage and current components near the power frequency are relatively low, so V0 and I0 can also be ignored.

[0088] This embodiment also discloses a specific embodiment, taking the near-power-frequency signal measurement data with a sampling rate of 10 kHz and an injection frequency of 48 Hz as an example to calculate the near-power-frequency positive and negative sequence impedance of the wind turbine generator.

[0089] Step 1: Set Δω th =0.01Hz, T a =1e-4; the data window length is N=1e4, the Taylor expansion order is K=2, and the fundamental frequency is identified according to the above method to obtain the fundamental frequency f m is 50.002;

[0090] Step 2: Design the notch filter center frequency ω c =314.1718, notch width ω b =6.2832, according to formula (6), the transfer function of the notch filter is designed and the fundamental components of voltage and current are separated to obtain the sampling signal after filtering out the fundamental components. Taking the voltage of phase A as an example, the signals before and after filtering are as follows: Figure 2 As shown, the black dotted line is the original sampling signal, and the black implementation is the filtered sampling signal.

[0091] Step 3: Perform Fourier transform on the filtered signal to extract the voltage and current components at 48 Hz. Calculate the impedance of the new energy power generation equipment at 48 Hz according to formula (10).

[0092] The embodiment of the present invention discloses a near-power frequency impedance measurement system, comprising:

[0093] A three-phase voltage and current signal acquisition module is used to acquire three-phase voltage and current signals excited by a near-power frequency disturbance signal;

[0094] The actual fundamental frequency calculation module is used to calculate the actual fundamental frequency of the three-phase voltage and current signals;

[0095] A filtering module is used to construct a notch filter based on the actual fundamental frequency, and filter out the fundamental components of the three-phase voltage and current signals based on the notch filter to obtain filtered voltage and current signals;

[0096] The near-power frequency impedance calculation module is used to calculate the near-power frequency impedance based on the filtered voltage and current signals.

[0097] An embodiment of the present invention proposes a data processing method based on a band-stop filter, which can effectively separate the power frequency and near-power frequency components in the measurement signal. At the same time, in order to solve the problem of power frequency signal separation caused by the offset and dynamic change of the fundamental frequency in actual engineering applications, the invention proposes a dynamic frequency measurement method based on Taylor Fourier transform, which adjusts the center frequency of the band-stop filter according to the dynamic frequency, realizes the effective filtering of the power frequency component in the measurement signal, and improves the identification accuracy of the near-power frequency impedance.

[0098] A schematic diagram of a terminal device provided in one embodiment of the present invention. The terminal device in this embodiment includes: a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of each of the aforementioned method embodiments are implemented. Alternatively, when the processor executes the computer program, the functions of each module / unit in each of the aforementioned device embodiments are implemented.

[0099] The computer program may be divided into one or more modules / units, which are stored in the memory and executed by the processor to accomplish the present invention.

[0100] The terminal device may be a computing device such as a desktop computer, a notebook computer, a PDA, a cloud server, etc. The terminal device may include, but is not limited to, a processor and a memory.

[0101] The processor can be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc.

[0102] The memory may be used to store the computer programs and / or modules, and the processor implements various functions of the terminal device by running or executing the computer programs and / or modules stored in the memory and calling the data stored in the memory.

[0103] If the module / unit integrated in the terminal device is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the process in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by a processor, it can implement the steps of each of the above-mentioned method embodiments. The computer program includes computer program code, which can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, USB flash drive, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electric carrier signal, telecommunication signal and software distribution medium. It should be noted that the content contained in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electric carrier signals and telecommunication signals.

[0104] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for measuring near-power frequency impedance, characterized in that: The following steps are involved: Acquire three-phase voltage and current signals excited by near-power frequency disturbance signals; Calculate the actual fundamental frequency of the three-phase voltage and current signals; A notch filter is constructed based on the actual fundamental frequency, and the fundamental components of the three-phase voltage and current signals are filtered out based on the notch filter to obtain filtered voltage and current signals; Calculate the near-power frequency impedance based on the filtered voltage and current signals.

2. A near-power frequency impedance measurement method according to claim 1, characterized in that: The method of calculating the actual fundamental frequency of the three-phase voltage and current signals comprises the following steps: Any voltage signal from the three-phase voltage and current signals is selected, Taylor Fourier transform is performed on the selected voltage signal, and the fundamental frequency of the voltage is identified using the least square method.

3. The method for measuring near-power frequency impedance according to claim 1, wherein: The method of constructing a notch filter based on the actual fundamental frequency includes the following steps: Set the notch filter center frequency ω c =2πf m , f m Indicates the actual fundamental frequency of the three-phase voltage and current signals; notch width ω b =2πf b , f b Indicates the bandwidth of the signal to be filtered that deviates from the central frequency; for a sampling interval of T a The discretized sampling signal r(k) of the notch filter is expressed by the following formula: in, 4. The method for measuring near-power frequency impedance according to claim 3, wherein: The method of filtering out the fundamental components of the three-phase voltage and current signals based on the notch filter to obtain filtered voltage and current signals includes the following steps: Calculate the positive sequence voltage, negative sequence voltage, positive sequence current and negative sequence current of three-phase voltage and current signals; According to the positive sequence voltage, negative sequence voltage, positive sequence current and negative sequence current, the fundamental components of the three-phase voltage and current signals are filtered out in combination with a notch filter.

5. The method for measuring near-power frequency impedance according to claim 4, wherein: The filtered voltage and current signals are expressed by the following formula: in, U pos Represents the positive sequence voltage of the three-phase voltage and current signals; I pos Represents the positive sequence current of the three-phase voltage and current signals.

6. The method for measuring near-power frequency impedance according to claim 4, characterized in that: The positive-sequence voltage, negative-sequence voltage, positive-sequence current, and negative-sequence current of the three-phase voltage and current signals are calculated using the following formula: Among them, U pos Represents the positive sequence voltage of the three-phase voltage and current signals; I pos Represents the positive sequence current of the three-phase voltage and current signals; j represents the imaginary number symbol; U neg Indicates the negative sequence voltage of the three-phase voltage and current signal; I neg Represents the negative sequence current of the three-phase voltage and current signals.

7. The method for measuring near-power frequency impedance according to claim 1, wherein: The method of calculating the near-power frequency impedance based on the filtered voltage and current signals comprises the following steps: Performing discrete Fourier transform or Taylor Fourier transform on the filtered voltage and current signals respectively; Based on the transformed voltage and current signals, the voltage amplitude V at the frequency close to the power frequency signal is extracted. f and the current amplitude I f ; Based on the voltage amplitude V f and the current amplitude I f Calculate the near-power frequency impedance.

8. A near-power frequency impedance measurement system, characterized in that: include: A three-phase voltage and current signal acquisition module is used to acquire three-phase voltage and current signals excited by a near-power frequency disturbance signal; The actual fundamental frequency calculation module is used to calculate the actual fundamental frequency of the three-phase voltage and current signals; A filtering module is used to construct a notch filter based on the actual fundamental frequency, and filter out the fundamental components of the three-phase voltage and current signals based on the notch filter to obtain filtered voltage and current signals; The near-power frequency impedance calculation module is used to calculate the near-power frequency impedance based on the filtered voltage and current signals.

9. A terminal device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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