Non-power-frequency disturbance measuring and distinguishing method for power-frequency coupling impedance of converter

Abstract

The invention discloses a non-power-frequency disturbance measuring and distinguishing method for power-frequency coupling impedance of a converter. According to the method, a subsynchronous / supersynchronous disturbance testing method is adopted to apply a disturbance signal with the frequency close to the power frequency; wherein the frequency components contained in the disturbance signal are fs1 = f1 + deltaf and fc = f1-deltaf, f1 is the power frequency, and deltaf is the disturbance signal; a frequency coupling impedance / admittance model under the frequency of fs1 = f1 + deltaf and fc1 = f1-deltaf is obtained through a disturbance test, so that a frequency coupling impedance / admittance model under the frequency of fs2 = f1 + deltaf and fc2 = f1 + deltaf is obtained; determining a frequency coupling impedance / admittance model at a power frequency based on the above two types of frequency coupling impedance / admittance models; and evaluating the value of the disturbance signal delta f to select a proper delta f value so as to ensure the extraction precision of the disturbance component and the identification precision of the frequency coupling impedance / admittance model at the power frequency.

Description

Technical Field

[0001] The present invention relates to the technical field of disturbance detection, and particularly to a non-power-frequency disturbance detection method for the power-frequency coupling impedance of a converter. Background Art

[0002] The interaction between new energy units based on power electronic converters such as wind power and photovoltaic power and the AC power grid may cause serious oscillation problems. Through frequency-domain analysis of the oscillogram data of the oscillation, it is found that there are always multiple oscillation components in the output current of devices such as direct-drive wind turbines, and they are interdependent, that is, the "frequency coupling" phenomenon, and the two are symmetrically distributed about the power frequency. Frequency coupling has a significant impact on the medium and low frequency oscillation characteristics of the new energy system, and it needs to be fully considered when conducting oscillation stability analysis. Among them, identifying the impedance model through disturbance testing has become an effective impedance construction method. Among them, the measurement and identification of the frequency coupling impedance model at the power frequency is relatively special. If a power-frequency disturbance is injected, the frequency coupling component is also the power frequency, so it is difficult to measure the frequency coupling impedance model. Existing methods have proposed a method of injecting a power-frequency disturbance. However, there are problems such as changing the operating conditions, endangering the system stability, and it is difficult to apply to the power-frequency impedance identification of a "black box" system.

[0003] The invention with the authorized publication number CN113447717B relates to a method for measuring and identifying the frequency coupling impedance of a converter under power-frequency disturbance. It includes: constructing a platform of a converter to be measured, a converter grid connection topology, a data measurement module, and an impedance calculation module; applying a power-frequency disturbance at the common coupling point where the converter is connected to the system, and the measurement module collects the three-phase power-frequency voltage and current before and after the disturbance, and then uses the impedance calculation module to generate a power-frequency frequency coupling impedance model. The present invention can obtain the coupling impedance model at the power frequency of the converter by changing the power-frequency operating point, making up for the defect that the existing impedance model is inaccurate in measurement at the power frequency.

[0004] The existing technology measures the impedance by changing the power-frequency operating point of the converter, which is easy to change the system operating point, and then change the stable operating boundary of the system, which may affect the system stability. In addition, this method has high requirements for the system to be measured, requires knowing the internal control and parameters of the converter, and is not applicable to the "black box" system.

[0005] The measurement and identification of the frequency coupling impedance model has become an effective solution for the small-signal stability analysis of a power system with a high proportion of new energy and a high proportion of power electronic devices ("dual high"). However, the impedance model at the power frequency (50 Hz) is relatively special. According to the frequency coupling effect, if the disturbance signal is the power frequency, the power-frequency disturbance is likely to change the system operating point and may reduce the stability margin. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems in the related art to some extent.

[0007] To this end, the present invention proposes a method for detecting and identifying the power frequency coupling impedance of a converter by non-power frequency disturbance, providing an idea for measuring the power frequency coupling impedance. That is, the sub / supersynchronous disturbance test method is still used, but instead of directly applying a power frequency disturbance, a near-power frequency disturbance is applied to realize the identification of the coupling impedance at the power frequency.

[0008] To achieve the above object, on the one hand, the present invention proposes a method for detecting and identifying the power frequency coupling impedance of a converter by non-power frequency disturbance, including:

[0009] Applying a disturbance signal with a frequency close to the power frequency by using the sub / supersynchronous disturbance test method; wherein, the frequency components contained in the disturbance signal are respectively f s1 = f1 + Δf and f c1 = f1 - Δf, where f1 is the power frequency and Δf is the disturbance signal;

[0010] Obtaining the frequency coupling impedance / admittance model at f s1 = f1 + Δf and f c1 = f1 - Δf through the disturbance test, so as to directly obtain the frequency coupling impedance / admittance model at frequencies of f s2 = f1 + Δf and f c2 = f1 + Δf;

[0011] Based on the above two types of frequency coupling impedance / admittance models, determining the frequency coupling impedance / admittance model at the power frequency;

[0012] Evaluating the numerical value of the disturbance signal Δf and selecting an appropriate Δf value to ensure the extraction accuracy of the disturbance component and the identification accuracy of the frequency coupling impedance / admittance model at the power frequency.

[0013] The method for detecting and identifying the power frequency coupling impedance of a converter according to the embodiment of the present invention may further have the following additional technical features:

[0014] In an embodiment of the present invention, obtaining the frequency coupling impedance / admittance model at f s1 = f1 + Δf and f c1 = f1 - Δf through the disturbance test, that is

[0015]

[0016] Directly obtaining the frequency coupling impedance / admittance model at f s2 = f1 - Δf and f c2 = f1 + Δf, that is:

[0017]

[0018] In one embodiment of the present invention, when Δf is less than a preset threshold, an approximate frequency coupling impedance / admittance model at power frequency is obtained, that is:

[0019]

[0020] In one embodiment of the present invention, the method further includes:

[0021] Connect the controller of the wind turbine to be measured to the real-time simulation system of RTDS or RT-Lab, and construct an impedance model identification device;

[0022] Based on the impedance model identification device, inject a near-power-frequency disturbance signal at the grid connection point of the wind turbine in the system to be measured, and simultaneously collect the output voltage and current data of the wind turbine;

[0023] Use the impedance model identification algorithm formulas (1)-(3) to calculate the impedance model of the wind turbine.

[0024] In one embodiment of the present invention, all components of the wind turbine are modeled in RTDS, and the converter controller uses a hardware control cabinet.

[0025] In one embodiment of the present invention, the impedance model identification device integrates software and hardware; the hardware part is used to support the operation of the software and realize the information interaction between the device and the external system RTDS.

[0026] In one embodiment of the present invention, the anti-model identification device is further used for:

[0027] Generate a disturbance configuration file containing information such as the disturbance frequency to be measured, signal amplitude, phase, and disturbance duration according to user needs, and control the device to output corresponding three-phase disturbance voltages to RTDS according to the configuration file. At this time, the three controlled voltage or current sources in RTDS output disturbances that meet user requirements; for power frequency impedance identification, output disturbance components of near power frequency f s1 = f1 + Δf and f c1 = f1 - Δf;

[0028] While outputting three-phase disturbance currents to RTDS, record the three-phase voltage and current signals from RTDS, automatically segment the recorded data according to the different characteristics of the disturbance signals, and store the corresponding files in the built-in or external hard disk of the device;

[0029] After the disturbance ends, automatically detect whether the disturbance configuration file and the recorded file match, that is, detect whether the number of recorded files and the data volume of each recorded file conform to the disturbance frequency to be measured and the disturbance duration information in the disturbance configuration file;

[0030] If it is determined that the disturbance profile and the oscillogram file match correctly, all oscillogram files are processed one by one through the built-in impedance model identification program to calculate the frequency coupling impedance model; if the disturbance profile and the oscillogram file do not match, a prompt message is output.

[0031] The off-power frequency disturbance measurement and identification method for the power frequency coupling impedance of the converter according to the embodiment of the present invention provides an idea for the measurement of the power frequency coupling impedance. That is, the sub / supersynchronous disturbance test method is still used, but instead of directly applying the power frequency disturbance, a near-power frequency disturbance is applied to realize the identification of the coupling impedance at the power frequency.

[0032] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0034] Figure 1 is a flowchart of the off-power frequency disturbance measurement and identification method for the power frequency coupling impedance of the converter according to the embodiment of the present invention;

[0035] Figure 2 is a control hardware-in-the-loop test system architecture diagram of the impedance model measurement and identification device according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0037] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0038] The off-power frequency disturbance measurement and identification method for the power frequency coupling impedance of the converter according to the embodiment of the present invention will be described below with reference to the accompanying drawings.

[0039] Figure 1 is a flowchart of the off-power frequency disturbance measurement and identification method for the power frequency coupling impedance of the converter according to the embodiment of the present invention, as Figure 1 shown, the method includes but is not limited to the following steps:

[0040] S1. Apply a disturbance signal with a frequency close to the power frequency using the sub / supersynchronous disturbance test method. Among them, the frequency components contained in the disturbance signal are f s1 = f1 + Δf and f c1 = f1 - Δf, where f1 is the power frequency and Δf is the disturbance signal;

[0041] S2. Obtain the frequency coupling impedance / admittance model at frequencies f s1 = f1 + Δf and f c1 = f1 - Δf through the disturbance test, so as to directly obtain the frequency coupling impedance / admittance model at frequencies f s2 = f1 + Δf and f c2 = f1 + Δf;

[0042] S3. Determine the frequency coupling impedance / admittance model at the power frequency based on the above two types of frequency coupling impedance / admittance models;

[0043] S4. Evaluate the numerical value of the disturbance signal Δf and select an appropriate value of Δf to ensure the extraction accuracy of the disturbance component and the identification accuracy of the frequency coupling impedance / admittance model at the power frequency.

[0044] Specifically, use the sub / supersynchronous disturbance test method to apply a disturbance with a frequency close to the power frequency. Suppose the frequency components contained in the applied disturbance signal are f s1 = f1 + Δf and f c1 = f1 - Δf, then the frequency coupling impedance / admittance model at this frequency can be obtained through the disturbance test, that is:

[0045]

[0046] The frequency coupling impedance / admittance model at f s2 = f1 - Δf and f c2 = f1 + Δf can be directly obtained, that is

[0047]

[0048] When Δf is small enough, the frequency coupling impedance / admittance model at the power frequency can be approximately obtained, that is

[0049]

[0050] Evaluate the numerical value of the disturbance signal Δf. When actually establishing the frequency coupling impedance model at power frequency based on the disturbance test of the simulation model or physical device, if Δf is too small, the frequency of the injected disturbance signal will be very close to the power frequency. Moreover, since the amplitudes of the voltage and current disturbances generated by its excitation are usually much smaller than the power frequency components, the disturbance components will be interfered by the power frequency signal when extracting the disturbance components from the recorded wave data, resulting in a large deviation in the actually extracted disturbance components, and further leading to a decrease in the identification accuracy of the frequency coupling impedance / admittance model at power frequency. Therefore, using the non-power frequency disturbance test method to establish the frequency coupling impedance / admittance at power frequency is an approximate method. When actually applying it, an appropriate Δf should be selected. Both too large and too small may cause large errors, but this method has low requirements for the system to be measured. It does not require any internal control and parameters to be known and is applicable to a completely "black box" system.

[0051] Furthermore, in this embodiment, the impedance measurement and identification are carried out in an offline manner, that is, in the laboratory, methods such as software simulation and control hardware-in-the-loop experiments are used to obtain the impedance model, which can be used for the impedance model measurement and identification of unconnected units.

[0052] Taking the impedance measurement and identification of the grid-connected converter of a wind turbine as an example, first, connect the controller of the wind turbine to be measured to a real-time simulation system such as RTDS or RT-Lab to construct an impedance model measurement and identification platform. Then, inject a near-power frequency disturbance signal at the grid connection point of the wind turbine in the system to be measured, and at the same time collect the output voltage and current data of the wind turbine. Finally, use the impedance model measurement and identification algorithm: formulas (1)-(3) to calculate the impedance model of the wind turbine. Figure 2 Shown is a control-hardware-in-the-loop (CHIL) system. Among them, Figure 2 (a) in it is the functional structure, Figure 2 (b) in it is the experimental platform. Except for the converter controller, all components of the wind turbine (filters, generators, AC / DC and DC / AC converter power circuits, etc.) are modeled in RTDS. The converter controller uses an actual hardware control cabinet. Since its manufacturer strictly keeps the internal detailed control parameters and structure confidential, the converter controller can be regarded as a "black box". The AC power grid can be represented in the form of "voltage source + impedance". In order to apply disturbances, three controlled voltage or current sources are connected to the system in series or parallel at the grid connection point as disturbance sources, and the control signals of the controlled voltage or current sources come from the impedance model measurement and identification device.

[0053] The impedance model identification device integrates software and hardware. The hardware part is used to support the operation of the software and realize the information interaction between the device and external systems such as RTDS, such as digital to analog conversions (DAC), etc. With the cooperation of software and hardware, the impedance model identification device can achieve the following functions.

[0054] 1) Generate a disturbance configuration file containing information such as the disturbance frequency to be measured, signal amplitude, phase, and disturbance duration according to user needs, and control the device to output corresponding three-phase disturbance voltages to the RTDS according to this configuration file. At this time, the three controlled voltage or current sources in the RTDS will output disturbances that meet the user's requirements; for power frequency impedance identification, disturbances with frequencies f s1 = f1 + Δf and f c1 = f1 - Δf will be output.

[0055] 2) While outputting three-phase disturbance currents to the RTDS, record the three-phase voltage and current signals from the RTDS, automatically segment the recorded wave data according to the different characteristics (i.e., frequency and amplitude) of the disturbance signals, and store the corresponding files in the built-in or external hard disk of the device;

[0056] 3) After the disturbance ends, automatically detect whether the disturbance configuration file and the recorded wave file match, that is, detect whether the number of recorded wave files and the data volume of each recorded wave file conform to the information such as the disturbance frequency to be measured and the disturbance duration in the disturbance configuration file;

[0057] 4) If the disturbance configuration file and the recorded wave file match correctly, process all recorded wave files one by one through the built-in impedance model identification program to calculate the frequency-coupled impedance model; if the disturbance configuration file and the recorded wave file do not match, prompt the user that there are problems in the identification process and possible sources of problems.

[0058] The control of the hardware-in-the-loop test is carried out according to the following process. First, according to the disturbance configuration file, the impedance model identification device generates three-phase disturbance voltages with corresponding frequencies (f s1 = f1 + Δf and f c1 = f1 - Δf), transmits them to the RTDS through analog-to-digital conversion, controls the three-phase controlled voltage or current sources to inject disturbances into the system, and at the same time records the three-phase voltage and current at the point of common coupling and stores the recorded wave data. Finally, the impedance model identification program performs subsequent operations according to the matching situation between the disturbance configuration file and the recorded wave file. If the match is correct, it processes all recorded wave data one by one, calculates the frequency-coupled impedance / admittance model and the non-coupled impedance / admittance model at all disturbance frequencies, and draws curves.

[0059] The above impedance model identification device and the control hardware-in-the-loop test platform can be applied to establish the frequency coupling impedance models of 14 different types of direct-drive and doubly-fed wind turbines in 9 large-scale wind farms in Ximeng area, providing an important model basis for the sub- / supra-synchronous oscillation risk assessment work after the grid connection of the wind farms. In addition to wind turbines, the device and the platform are also applicable to identifying the frequency coupling impedance models of photovoltaic generating units, STATCOM and other devices.

[0060] The non-power-frequency disturbance identification method for the power-frequency coupling impedance of the converter in the embodiment of the present invention. Aiming at the problem that it is difficult to ensure the accuracy of the power-frequency impedance identification of the converter, establishing a frequency coupling impedance / admittance model at the power frequency is an approximate method. When actually applied, a suitable disturbance test signal frequency Δf should be selected, which is selected near 50 Hz, and the measured impedance is used to equivalent the impedance model at 50 Hz. This method has low requirements for the system to be measured. It does not require any internal control and parameters to be known, is applicable to a completely "black box" system, and will not change the operating conditions of the converter, and has little influence on the system stability.

[0061] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0062] In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically defined.

Claims

1. A non-power-frequency disturbance detection and identification method for the power-frequency coupling impedance of an inverter, characterized in that, include: Apply a disturbance signal with a frequency close to the power frequency by using the sub / supersynchronous disturbance test method; wherein, the frequency components contained in the disturbance signal are respectively f s1 = f1 + Δf and f c = f1 - Δf, where f1 is the power frequency and Δf is the disturbance signal; The frequency coupling impedance / admittance models at frequencies f s1 = f1 + Δf and f c1 = f1 - Δf are obtained through perturbation tests, thereby obtaining the frequency coupling impedance / admittance models at frequencies f s2 = f1 + Δf and f c2 = f1 + Δf; Based on the above two types of frequency coupling impedance / admittance models, determine the frequency coupling impedance / admittance model at the power frequency; The numerical value of the disturbance signal Δf is evaluated and an appropriate Δf value is selected to ensure the accuracy of the disturbance component extraction and the identification accuracy of the frequency-coupled impedance / admittance model at the power frequency.

2. The method according to claim 1, characterized in that, Obtained through perturbation testing are the frequency coupling impedance / admittance models at frequencies f s1 = f1 + Δf and f c1 = f1 - Δf, that is Directly obtain at f s2 = f1 - Δf and f c2 = f1 + Δf, the frequency coupling impedance / admittance model, that is:

3. The method according to claim 2, wherein When Δf is less than the preset threshold, the frequency coupling impedance / admittance model at the power frequency is approximately obtained, that is:

4. The method according to claim 3, characterized in that The method further comprises: Connect the controller of the wind turbine to be tested to the real-time simulation system of RTDS or RT-Lab, and construct an impedance model measurement and identification device; Based on the impedance model measurement and identification device, a near-power frequency disturbance signal is injected at the grid connection point of the wind turbine in the system to be tested, and the output voltage and current data of the wind turbine are collected at the same time; The impedance model of the wind turbine is calculated using the impedance model identification algorithm formulas (1)-(3).

5. The method according to claim 4, characterized in that, All components of the wind turbine are modeled in RTDS, and the converter controller uses a hardware control cabinet.

6. The method according to claim 5, wherein The impedance model identification device integrates two parts: software and hardware; the hardware part is used to support software operation and realize information interaction between the device and the external system RTDS.

7. The method according to claim 6, characterized in that, The impedance model identification device is also used for: Generate a disturbance configuration file containing information on the disturbance frequency to be measured, signal amplitude, phase, and disturbance duration according to user needs, and control the device to output the corresponding three-phase disturbance voltage to the RTDS according to the configuration file. At this time, the three controlled voltage or current sources in the RTDS output disturbances that meet the user's requirements; for power frequency impedance discrimination, disturbances with frequencies of f s1 = f1 + Δf and f c1 = f1 - Δf are output. While outputting the three-phase disturbance current to the RTDS, the three-phase voltage and current signals from the RTDS are recorded. The recorded data is automatically segmented according to the characteristics of the disturbance signal and the corresponding files are stored in the device's built-in or external hard disk. After the disturbance is over, the system automatically detects whether the disturbance configuration file and the recording file match, that is, whether the number of recording files and the amount of data in each recording file are consistent with the disturbance frequency and duration information to be measured in the disturbance configuration file; If the disturbance configuration file and the recording file are judged to match correctly, all the recording files are processed one by one through the built-in impedance model identification program to calculate the frequency-coupled impedance model; if the disturbance configuration file and the recording file do not match, a prompt message is output.

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