A method and system for fast frequency scanning of a wind farm via flexible direct transmission system

Abstract

The application provides a kind of wind farm through flexible sending out system's fast frequency scanning method and system, comprising: based on the time domain simulation of pre-constructed injection signal disturbance model respectively obtained voltage steady waveform and current steady waveform of flexible system and wind farm port;Injection disturbance source is injected into injection signal disturbance model respectively to obtain the voltage steady waveform and current steady waveform of flexible system and wind farm port after injection disturbance;The voltage steady waveform, current steady waveform of flexible system and wind farm port are analyzed with the voltage steady waveform and current steady waveform of flexible system and wind farm port after injection disturbance, and disturbance voltage and disturbance current are obtained;Frequency domain data is obtained by fast Fourier calculation method to disturbance voltage and disturbance current, and corresponding impedance curve is obtained based on frequency domain data;The application adopts the method of injecting disturbance source into injection signal disturbance model, solves the coupling problem of frequency scanning method, improves the rapidity, and avoids the coupling of frequency.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system stability analysis, and particularly relates to a fast frequency scanning method and system for a wind farm through flexible direct transmission system. BACKGROUND

[0002] With the increase of flexible direct current transmission (hereinafter referred to as flexible direct current) projects, and the large-scale grid connection of wind turbine generators and photovoltaic power generation equipment, a high proportion of power electronic equipment is contained in the power system, which brings complex changes to the stability analysis of the power system. Multiple wind farms and flexible direct current projects have appeared oscillation phenomena with frequencies ranging from 1-2000Hz. For example, the subsynchronous oscillation of 3-12Hz in Hebei Guyuan wind farm, the subsynchronous oscillation of 20-34Hz in Xinjiang direct-drive wind farm, and the high-frequency oscillation of 1270Hz in Luxi flexible direct current. At present, a fast and effective method for system stability analysis is frequency scanning method. This method is to analyze the stability of the system by reflecting the impedance characteristics of the system and using stability criteria. Through a simulation tool, the impedance characteristic curve of the system can be quickly obtained, thereby guiding the implementation of measures to avoid resonance points.

[0003] The frequency scanning method is different from the impedance analysis method and the eigenvalue analysis method which can reveal the mechanism of oscillation. The main purpose of this method is to quickly obtain the impedance characteristics, which reflects the rapidity and accuracy. In addition, this method can also be used as an auxiliary tool to verify the conclusion of the impedance analysis method. Therefore, how to make the frequency scanning method achieve the rapidity and accuracy in different occasions is one of the key technologies for analyzing the stability of the system by using the impedance analysis method.

[0004] Existing research results: CN109782068B proposes a wideband impedance scanning method and system based on a real-time digital simulator, which generates three-phase disturbance signals for multiple operating conditions, and sequentially injects them into the real-time digital simulator to generate three-phase voltage disturbance and three-phase current disturbance signals corresponding to the port of the system under test, and calculates the wideband impedance of the system under test through an impedance model identifier; the present invention discloses a wideband impedance scanning method and system based on a real-time digital simulator, wherein the method comprises: when the power grid system model and the system under test are stably running, the impedance scanning signal generator and the collector obtain a configuration file containing scanning signals for multiple operating conditions, and generate three-phase disturbance signals for multiple operating conditions according to the start and stop signal instructions of the impedance model identifier; the three-phase disturbance signals for multiple operating conditions are sequentially injected into the real-time digital simulator to make the disturbance source generate three-phase voltage disturbance and three-phase current disturbance signals corresponding to the port of the system under test; the impedance model identifier calculates the wideband impedance of the system under test according to the collected three-phase voltage and three-phase current signals. This method can efficiently and quickly obtain the impedance characteristics of the power device in the wideband domain, and the obtained scanning results provide an important basis for the influence analysis of the access of various power equipment to the power grid. CN110867889A proposes an oscillation stability discrimination method and system for wind farms or units connected to an AC power grid, which obtains a power grid impedance model through frequency scanning and proposes a new stability criterion. The present invention relates to an oscillation stability discrimination method and system for wind farms / units connected to an AC power grid, belonging to the technical field of power system analysis and control. The present invention obtains a power grid impedance model through frequency scanning, and obtains the impedance model of a wind turbine or a wind farm through signal injection testing, and calculates the aggregated impedance after the wind turbine or the wind farm is connected to the grid, and judges the oscillation stability of the entire system after the wind turbine or the wind farm is connected to the grid according to the aggregated impedance characteristics. The criterion used to judge the oscillation stability is very simple and easy to operate, and can accurately judge whether the system is oscillation stable after the wind turbine or the wind farm is connected to the AC power grid, making up for the deficiency of the current research on the oscillation stability evaluation of the wind turbine and the wind farm connected to the AC power grid, and providing a method for judging whether the system is oscillation stable after the wind turbine and the wind farm are connected to the AC power grid, which provides an important basis for the design and grid connection of the wind turbine and the wind farm.

[0005] The existing frequency scanning methods mainly include point-by-point scanning and scanning method of simultaneously injecting full-band disturbance, but each has its own shortcomings. For the complex system of wind farms sent out by flexible transmission, the impedance modeling process needs to verify each link by frequency scanning. For the point-by-point scanning method, since oscillation occurs in a wide frequency band, it will take a lot of time if simulation is done at each frequency point, and simultaneous injection of full-band disturbance may cause frequency coupling, making the curve obtained by frequency scanning not smooth and the result inaccurate. SUMMARY

[0006] In order to solve the problems of time-consuming, frequency coupling and low accuracy of the existing frequency scanning method, the application provides a fast frequency scanning method for a wind farm through a flexible transmission sending-out system, which comprises the following steps:

[0007] Based on the pre-constructed injection signal disturbance model, time domain simulation is performed to obtain voltage steady-state waveforms and current steady-state waveforms of the flexible transmission system and the wind farm port respectively.

[0008] A disturbance source is injected into the injection signal disturbance model to obtain voltage steady-state waveforms and current steady-state waveforms of the flexible transmission system and the wind farm port after the injection of the disturbance.

[0009] The voltage steady-state waveforms and current steady-state waveforms of the flexible transmission system and the wind farm port are analyzed with the voltage steady-state waveforms and current steady-state waveforms of the flexible transmission system and the wind farm port after the injection of the disturbance to obtain the disturbance voltage and the disturbance current.

[0010] The disturbance voltage and the disturbance current are subjected to fast Fourier calculation to obtain the frequency domain data, and the corresponding impedance curve is obtained based on the frequency domain data.

[0011] The injection signal disturbance model is constructed based on the parameters of the flexible transmission system and the wind farm.

[0012] Preferably, the step of injecting a disturbance source into the injection signal disturbance model to obtain voltage steady-state waveforms and current steady-state waveforms of the flexible transmission system and the wind farm port after the injection of the disturbance comprises the following steps:

[0013] The disturbance frequency bands are divided based on the disturbance sources of the flexible transmission system and the wind farm port.

[0014] One of the disturbance frequency bands is injected into the flexible transmission system and the wind farm port at the same time, and time domain simulation is performed to obtain the voltage steady-state and current steady-state waveforms of the flexible transmission system and the wind farm port after the injection of the disturbance.

[0015] Preferably, the step of analyzing the voltage steady-state waveforms and current steady-state waveforms of the flexible transmission system and the wind farm port with the voltage steady-state waveforms and current steady-state waveforms of the flexible transmission system and the wind farm port after the injection of the disturbance to obtain the disturbance voltage and the disturbance current comprises the following steps:

[0016] The voltage steady-state waveforms and current steady-state waveforms of the flexible transmission system and the wind farm port are introduced into data analysis software to extract data containing voltage and current after the injection of the disturbance.

[0017] The disturbance voltage and the disturbance current are obtained by subtracting the extracted data containing voltage and current respectively.

[0018] Preferably, the frequency domain data is obtained by a fast Fourier calculation method based on the disturbance voltage and the disturbance current, and the corresponding impedance curve is obtained based on the frequency domain data, comprising:

[0019] The amplitude and the phase angle of the HVDC system and the wind farm port impedance are obtained based on the frequency domain data;

[0020] The function image of the amplitude and the phase angle of the HVDC system and the wind farm port impedance with respect to frequency is respectively drawn;

[0021] The impedance curve corresponding to the frequency domain data is obtained based on the function image.

[0022] Preferably, the disturbance voltage is calculated as follows:

[0023] ΔV p = V p -V st ;

[0024] In the formula, ΔV p is the disturbance voltage; V p is the port voltage after the disturbance is injected; and V st is the steady-state port voltage.

[0025] Preferably, the disturbance current is calculated as follows:

[0026] ΔI p = I st -I p ;

[0027] In the formula, ΔI p is the disturbance current; I st is the steady-state port current; and I p is the port current after the disturbance is injected.

[0028] Preferably, the port impedance is calculated as follows:

[0029]

[0030] In the formula, Z p is the port impedance; is the disturbance voltage frequency domain; is the disturbance current frequency domain.

[0031] Preferably, the port impedance amplitude is calculated as follows:

[0032]

[0033] In the formula, Z p is the port impedance amplitude.

[0034] Preferably, the port impedance phase angle is calculated as follows:

[0035]

[0036] wherein ∠Z p is the port impedance phase angle.

[0037] The application also provides a fast frequency scanning system of a wind farm through a flexible transmission system based on the same inventive concept, comprising:

[0038] a time domain simulation module, configured to perform time domain simulation on a pre-constructed injection signal disturbance model to obtain voltage steady-state waveforms and current steady-state waveforms of the flexible transmission system and the wind farm port respectively;

[0039] an injection module, configured to inject a disturbance source into the injection signal disturbance model to obtain voltage steady-state waveforms and current steady-state waveforms of the flexible transmission system and the wind farm port after injection disturbance respectively;

[0040] an analysis module, configured to analyze the voltage steady-state waveforms and the current steady-state waveforms of the flexible transmission system and the wind farm port and the voltage steady-state waveforms and the current steady-state waveforms of the flexible transmission system and the wind farm port after injection disturbance to obtain disturbance voltage and disturbance current;

[0041] a calculation module, configured to obtain frequency domain data of the disturbance voltage and the disturbance current through a fast Fourier calculation method, and obtain corresponding impedance curves based on the frequency domain data.

[0042] The injection signal disturbance model is constructed based on the flexible transmission system and the wind farm.

[0043] Compared with the prior art, the application has the following beneficial effects:

[0044] The application provides a fast frequency scanning method and system of a wind farm through a flexible transmission system, comprising: performing time domain simulation on a pre-constructed injection signal disturbance model to obtain voltage steady-state waveforms and current steady-state waveforms of the flexible transmission system and the wind farm port respectively; injecting a disturbance source into the injection signal disturbance model to obtain voltage steady-state waveforms and current steady-state waveforms of the flexible transmission system and the wind farm port after injection disturbance respectively; analyzing the voltage steady-state waveforms and the current steady-state waveforms of the flexible transmission system and the wind farm port and the voltage steady-state waveforms and the current steady-state waveforms of the flexible transmission system and the wind farm port after injection disturbance to obtain disturbance voltage and disturbance current; obtaining frequency domain data of the disturbance voltage and the disturbance current through a fast Fourier calculation method, and obtaining corresponding impedance curves based on the frequency domain data; the application injects a disturbance source into the injection signal disturbance model, solves the problems of time and labor consumption and frequency coupling of the frequency scanning method, improves the rapidity and accuracy, and avoids the frequency coupling. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 is a flow chart of a rapid frequency scanning method of a wind farm through flexible transmission system provided by the present application;

[0046] Figure 2 is a schematic diagram of a rapid frequency scanning system of a flexible transmission provided by the present application;

[0047] Figure 3 is a schematic diagram of a frequency scanning system of a direct drive wind turbine of the prior art;

[0048] Figure 4 is a comparison result diagram of a frequency scanning of a direct drive wind turbine of the present application and a point-by-point frequency scanning amplitude-frequency characteristic of the prior art;

[0049] Figure 5 is a comparison result diagram of a frequency scanning of a direct drive wind turbine of the present application and a point-by-point frequency scanning phase-frequency characteristic of the prior art;

[0050] Figure 6 is a comparison result diagram of a frequency scanning of a direct drive wind turbine of the present application and a full-band injection disturbance scanning amplitude-frequency characteristic of the prior art;

[0051] Figure 7 is a comparison result diagram of a frequency scanning of a direct drive wind turbine of the present application and a full-band injection disturbance scanning phase-frequency characteristic of the prior art;

[0052] Figure 8 is a flow chart of a stability analysis method of a wind farm through flexible transmission system provided by the present application. DETAILED DESCRIPTION

[0053] In order to better understand the present application, the content of the present application will be further described below in combination with the accompanying drawings and examples.

[0054] Example 1:

[0055] The present application provides a rapid frequency scanning method of a wind farm through flexible transmission system, as shown in Figure 1 , comprising:

[0056] Step 1: based on a pre-constructed injection signal disturbance model, time domain simulation is performed to obtain voltage steady-state waveforms and current steady-state waveforms of a flexible transmission system and a wind farm port respectively;

[0057] Step 2: a disturbance source is injected into the injection signal disturbance model to obtain voltage steady-state waveforms and current steady-state waveforms of the flexible transmission system and the wind farm port after injection disturbance respectively;

[0058] Step 3: the voltage steady-state waveforms and the current steady-state waveforms of the flexible transmission system and the wind farm port are analyzed together with the voltage steady-state waveforms and the current steady-state waveforms of the flexible transmission system and the wind farm port after injection disturbance to obtain the disturbance voltage and the disturbance current;

[0059] Step 4: the disturbance voltage and the disturbance current are subjected to fast Fourier calculation method to obtain the frequency domain data, and the corresponding impedance curve is obtained based on the frequency domain data;

[0060] The injection signal disturbance model is constructed based on the parameters of the HVDC system and the wind farm.

[0061] The voltage steady-state waveform and the current steady-state waveform of the HVDC system and the wind farm port are obtained respectively by time-domain simulation based on the pre-constructed injection signal disturbance model in step 1, and the specific steps include:

[0062] A fast frequency scanning method for a wind farm HVDC transmission system, the embodiment of the present application provides a simplified model of a direct-drive wind farm HVDC transmission system. In impedance modeling, the HVDC side is simplified as a wind farm side inverter and a DC voltage source, the direct-drive wind farm is simplified as a grid-connected inverter and a DC current source, and the direct-drive wind farm output power is adjusted by changing the size of the DC current source.

[0063] Step 101: establish an injection disturbance signal model. The wind farm side converter station of the HVDC adopts a constant voltage and constant frequency (V / f) control mode, and the HVDC and an ideal AC current source should be connected when the HVDC is frequency scanned, the ideal AC current source replaces the wind farm to transmit power to the HVDC, and the disturbance source should be a disturbance current provided by the controlled current source in Figure 2 When the wind farm is frequency scanned, the wind farm should be connected to an ideal AC grid, and the disturbance source should be a disturbance voltage provided by the controlled voltage source in Figure 3 .

[0064] Step 102: obtain the port voltage and current steady-state operating waveform of the HVDC system and the wind farm to be tested respectively by PSCAD / EMTDC time-domain simulation, the model enters the steady state at 1.5s, the simulation time can be 3s, the simulation step is 10us, the drawing step is 10us, the waveform data can be saved in a text file by taking the waveform of 2-3s.

[0065] Step 2: obtain the voltage steady-state waveform and the current steady-state waveform of the HVDC system and the wind farm port after injection disturbance respectively by injecting the disturbance source in the injection signal disturbance model, and the specific steps include:

[0066] Divide the disturbance frequency band based on the disturbance source of the HVDC system and the wind farm port;

[0067] Inject one of the disturbance frequency bands into the HVDC system and the wind farm port at the same time, and obtain the voltage steady-state and current steady-state waveform of the HVDC system and the wind farm port after injection disturbance by time-domain simulation.

[0068] Step 103: Inject a disturbance source into the HVDC system and the wind farm respectively, the amplitude of the disturbance source is 0.5%-5% of the peak value of the rated phase voltage of the AC side of the system, the effective value of the line voltage of the AC side of the system is 66kV, considering that multiple disturbances are injected at the same time, the amplitude of the disturbance will be superimposed, so the amplitude of the injected disturbance voltage is 0.1kV, the amplitude of the disturbance current is 0.01kA, there is a phase difference for each frequency corresponding disturbance source, which reduces the amplitude of the superimposed disturbance and avoids destroying the linearization of the system. The power frequency is set to 50Hz, 50 disturbances of different frequencies are injected at the same time each time starting from the lowest frequency 1Hz, the interval between the frequencies is 1Hz, and the initial phase angle of the a-phase disturbance source with a frequency of f is π / 180(f-1) in this embodiment. 2 The system port voltage and voltage waveform after injecting the disturbance are obtained through simulation, and the waveforms of 2-3s are still taken.

[0069] Step 104: The method can quickly and accurately obtain the impedance characteristics in the subsynchronous / super-synchronous frequency band, and the step 103 can be repeated to obtain the impedance characteristics in a wide frequency band. In fact, the impedance characteristics in the medium-high frequency band above 500Hz tend to be smooth, and the frequency coupling interference is small, so 500-2000 disturbances of different frequencies can be injected at the same time.

[0070] In step 3, the disturbance voltage and the disturbance current are obtained by analyzing the voltage steady-state waveform and the current steady-state waveform of the HVDC system and the wind farm port and the voltage steady-state waveform and the current steady-state waveform of the HVDC system and the wind farm port after injecting the disturbance, and specifically comprising:

[0071] The voltage steady-state waveform and the current steady-state waveform of the HVDC system and the wind farm port and the voltage steady-state waveform and the current steady-state waveform of the HVDC system and the wind farm port after injecting the disturbance are respectively introduced into a data analysis software to extract data containing voltage and current;

[0072] The disturbance voltage and the disturbance current are obtained by subtracting the extracted data containing voltage and current respectively.

[0073] The disturbance voltage is calculated as follows:

[0074] ΔV p =V p -V st ;

[0075] In the formula, ΔV p is the disturbance voltage; V p is the port voltage after injecting the disturbance; and V st is the steady-state port voltage.

[0076] The disturbance current is calculated as follows:

[0077] ΔI p =I st -Ip ;

[0078] where ΔI p is the disturbance current; I st is the steady-state port current; I p is the port current after injecting the disturbance.

[0079] Step 105: importing the data obtained in steps 102 and 103 into Matlab for analysis. The programming idea of Matlab is as follows:

[0080] 1) If the system is three-phase balanced, only one-phase impedance can be considered. Taking the analysis of a-phase impedance as an example, the data containing voltage and current waveforms in the data are extracted, and four groups of data are obtained, which are: steady-state port voltage V ast , steady-state port current I ast , port voltage V ap after injecting the disturbance, and port current I ap after injecting the disturbance. Since the drawing step is 10 μs, the waveform data has 100000.

[0081] 2) The disturbance current corresponding to the injected disturbance voltage (the disturbance voltage corresponding to the injected disturbance current) can be obtained by making a difference, i.e. disturbance voltage ΔV ap = V ap -V ast , and disturbance current ΔI ap = I ast -I ap .

[0082] In step 4, the disturbance voltage and disturbance current are calculated by a fast Fourier calculation method to obtain the frequency domain data, and the corresponding impedance curve is obtained based on the frequency domain data, which specifically includes:

[0083] Based on the frequency domain data, the amplitude and phase angle of the HVDC system and the port impedance of the wind farm are obtained;

[0084] The amplitude and phase angle of the HVDC system and the port impedance of the wind farm are plotted as a function of frequency, respectively;

[0085] Based on the function image, the impedance curve corresponding to the frequency domain data is obtained.

[0086] 3) The fft function is applied to ΔV ap and ΔI ap to obtain the frequency domain data and The port impedance amplitude is: and the phase angle is The data has 50001.

[0087] The port impedance is calculated as follows:

[0088]

[0089] wherein Z p is the port impedance; is the perturbation voltage frequency domain; is the perturbation current frequency domain.

[0090] The port impedance amplitude is calculated as follows:

[0091]

[0092] wherein |Z p | is the port impedance amplitude.

[0093] The port impedance phase angle is calculated as follows:

[0094]

[0095] wherein ∠Z p is the port impedance phase angle.

[0096] 4) Draw the impedance amplitude and phase angle as functions of frequency f, respectively. The frequency f is in the frequency band of the injected perturbation, and for the 1-50Hz frequency band, f should be set to 2-51, because the second data in the amplitude and phase angle corresponds to the 1Hz perturbation, and the same is true for the subsequent data, so that the effective data can be extracted from Z p and ∠Z p , so as to obtain the correct impedance characteristic curve.

[0097] Compared with the point-by-point sweep method, the time required for obtaining the impedance characteristics of the 1-100Hz frequency band is about 5 minutes, while the point-by-point sweep method requires nearly 1 hour, which can obviously improve the speed of obtaining the impedance characteristics (computer configuration: 64-bit operating system; RAM: 16.0GB; processor: Intel(R) Core(TM) i5-1035G1 CPU@1.00GHz 1.19GHz), and the invention effect comparison is shown in Figure 4 and Figure 5 Compared with the simultaneous injection of full-band perturbation sweep method, the invention obviously improves the accuracy of the impedance characteristics, and the invention effect comparison is shown in Figure 6 and Figure 7 .

[0098] Example 2:

[0099] Based on the same inventive concept, the application also provides a fast frequency scanning system for a flexible direct transmission system of a wind farm, comprising:

[0100] a time-domain simulation module, configured to perform time-domain simulation on the pre-constructed injection signal disturbance model to obtain voltage steady-state waveforms and current steady-state waveforms of the HVDC system and the wind farm port respectively;

[0101] an injection module, configured to inject a disturbance source into the injection signal disturbance model to obtain voltage steady-state waveforms and current steady-state waveforms of the HVDC system and the wind farm port after injection of the disturbance;

[0102] an analysis module, configured to analyze the voltage steady-state waveforms and the current steady-state waveforms of the HVDC system and the wind farm port and the voltage steady-state waveforms and the current steady-state waveforms of the HVDC system and the wind farm port after injection of the disturbance to obtain the disturbance voltage and the disturbance current;

[0103] a calculation module, configured to obtain the frequency domain data by using a fast Fourier calculation method on the disturbance voltage and the disturbance current, and obtain the corresponding impedance curve based on the frequency domain data;

[0104] The injection signal disturbance model is constructed based on the HVDC system and the wind farm.

[0105] The injection module comprises:

[0106] a frequency band division sub-module, configured to divide the disturbance source of the HVDC system and the wind farm port into disturbance frequency bands;

[0107] an injection frequency band sub-module, configured to inject one disturbance frequency band of the HVDC system and the wind farm port at the same time and obtain voltage steady-state waveforms and current steady-state waveforms of the HVDC system and the wind farm port after injection of the disturbance by using time-domain simulation.

[0108] The injection module will be described in detail as follows:

[0109] The disturbance source is injected into the HVDC system and the wind farm respectively, and there is a phase difference between the disturbance source corresponding to each frequency, so as to reduce the amplitude of the superimposed disturbance and avoid destroying the linearizability of the system. Starting from the lowest frequency f L The frequency band is divided according to the power frequency and its multiple frequencies, the disturbance source of one small frequency band is injected at a time, the voltage and current waveforms of the system port after injection of the disturbance are obtained by simulation, and the time-domain simulation module is used to obtain the waveforms of the system after entering the steady state for T seconds.

[0110] The time-domain simulation module is specifically configured to:

[0111] perform time-domain simulation on the pre-constructed injection signal disturbance model to obtain voltage steady-state waveforms and current steady-state waveforms of the HVDC system and the wind farm port respectively;

[0112] The injection disturbance signal model is established. Since the wind farm side converter station of the flexible direct current adopts a constant voltage and frequency (V / f) control mode, the flexible direct current and an ideal alternating current source are connected when the frequency scanning of the flexible direct current is performed, the ideal alternating current source replaces the wind farm to transmit power to the flexible direct current, and the disturbance source to be injected is a disturbance current. When the frequency scanning of the wind farm is performed, the wind farm is connected to an ideal alternating current grid, and the disturbance source to be injected is a disturbance voltage.

[0113] The port voltage and current steady-state operation waveforms of the to-be-tested flexible direct current system and the wind farm are obtained through time domain simulation respectively, and the waveforms of T seconds after the system enters a steady state are taken. The value of T is determined by the lowest frequency f L to be injected, and there is a relationship: T = 1 / f L .

[0114] The injection module is specifically configured to inject a disturbance source into the injection signal disturbance model to obtain voltage steady-state waveforms and current steady-state waveforms of the ports of the flexible direct current system and the wind farm after the injection of the disturbance.

[0115] If the impedance characteristics of a wide frequency band are to be obtained, the steps of the injection module can be repeated. In fact, since the impedance characteristics of the high frequency band tend to be smooth, the frequency coupling interference is small, and more frequencies can be injected at one time, and the flowchart is as shown in Figure 8 .

[0116] The analysis module is specifically configured to analyze the voltage steady-state waveforms and current steady-state waveforms of the ports of the flexible direct current system and the wind farm and the voltage steady-state waveforms and current steady-state waveforms of the ports of the flexible direct current system and the wind farm after the injection of the disturbance to obtain the disturbance voltage and the disturbance current.

[0117] The data obtained by the injection module and the time domain simulation module are imported into a data analysis software for data post-processing. The data containing the voltage and current waveforms in the simulation are extracted respectively, and four groups of data are obtained, which are: steady-state port voltage V st , steady-state port current I st , port voltage V p after the injection of the disturbance, and port current I p after the injection of the disturbance. The disturbance current corresponding to the injected disturbance voltage (the disturbance voltage corresponding to the injected disturbance current) can be obtained by difference, that is, disturbance voltage ΔV p = V p -V st , and disturbance current ΔI p = I st -I p .

[0118] The calculation module is configured to obtain the frequency domain data of the disturbance voltage and the disturbance current by a fast Fourier calculation method, and obtain the corresponding impedance curve based on the frequency domain data.

[0119] Afterwards, AV p and AI p The frequency domain data is solved by applying fast Fourier transform (FFT) and The port impedance is: The amplitude is |Z p | and the phase angle is ∠Z p Finally, the impedance amplitude and phase angle are plotted as functions of frequency f, and the frequency f is in the frequency band of the injected disturbance.

[0120] Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0121] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROMs, optical storage devices, etc.) containing computer-usable program code.

[0122] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of the flows and / or blocks in the flowcharts and / or block diagrams can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing apparatus to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing apparatus generate a means for implementing the functions specified in the flowcharts and / or block diagrams. Figure 1 The functions specified in the flow or multiple flows and / or blocks Figure 1 The functions specified in the flow or multiple flows and / or blocks

[0123] These computer program instructions can also be stored in a computer-readable memory capable of causing the computer or other programmable data processing apparatus to work in a specific manner, so that the instructions stored in the computer-readable memory produce a manufactured product including instruction means, which implements the functions specified in the flowcharts and / or block diagrams. Figure 1 The functions specified in the flow or multiple flows and / or blocks Figure 1 The functions specified in the flow or multiple flows and / or blocks

[0124] These computer program instructions can also be loaded into a computer or other programmable data processing devices, so that a series of operational steps are generated to realize the computer-implemented processes in the computer or other programmable devices, and the instructions executed in the computer or other programmable devices provide operational steps for implementing the functions specified in the flowchart Figure 1 one flow or a plurality of flows and / or the functions specified in the block Figure 1 one flow or a plurality of flows and / or the functions specified in the block

[0125] The above merely illustrates the embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall fall within the scope of the claims of the present application.

Claims

1. A method for fast frequency scanning of a wind farm through flexible transmission system, characterized in that, The method comprises the following steps: based on the pre-constructed injection signal disturbance model, time domain simulation is performed to obtain the voltage steady-state waveform and the current steady-state waveform of the HVDC system and the wind farm port respectively; a disturbance source is injected into the injection signal disturbance model to obtain the voltage steady-state waveform and the current steady-state waveform of the HVDC system and the wind farm port after the injection of the disturbance respectively; the voltage disturbance and the current disturbance are obtained by analyzing the voltage steady-state waveform and the current steady-state waveform of the HVDC system and the wind farm port and the voltage steady-state waveform and the current steady-state waveform of the HVDC system and the wind farm port after the injection of the disturbance; the frequency domain data is obtained by using the fast Fourier calculation method on the voltage disturbance and the current disturbance, and the corresponding impedance curve is obtained based on the frequency domain data; wherein, the injection signal disturbance model is constructed based on the parameters of the HVDC system and the wind farm; the voltage steady-state waveform and the current steady-state waveform of the HVDC system and the wind farm port after the injection of the disturbance are obtained by injecting a disturbance source into the injection signal disturbance model, which comprises the following steps: based on the disturbance source of the HVDC system and the wind farm port, the disturbance frequency band is divided; one of the disturbance frequency bands is injected into the HVDC system and the wind farm port at the same time, and the voltage steady-state waveform and the current steady-state waveform of the HVDC system and the wind farm port after the injection of the disturbance are obtained by time domain simulation; the voltage disturbance and the current disturbance are obtained by analyzing the voltage steady-state waveform and the current steady-state waveform of the HVDC system and the wind farm port and the voltage steady-state waveform and the current steady-state waveform of the HVDC system and the wind farm port after the injection of the disturbance, which comprises the following steps: the voltage steady-state waveform and the current steady-state waveform of the HVDC system and the wind farm port and the voltage steady-state waveform and the current steady-state waveform of the HVDC system and the wind farm port after the injection of the disturbance are imported into a data analysis software respectively to extract the data containing voltage and current; the voltage disturbance and the current disturbance are obtained by making difference based on the extracted data containing voltage and current respectively; the frequency domain data is obtained by using the fast Fourier calculation method on the voltage disturbance and the current disturbance, and the corresponding impedance curve is obtained based on the frequency domain data, which comprises the following steps: the amplitude and the phase angle of the impedance of the HVDC system and the wind farm port are obtained based on the frequency domain data; the function images of the amplitude and the phase angle of the impedance of the HVDC system and the wind farm port with respect to frequency are drawn respectively; the impedance curve corresponding to the frequency domain data is obtained based on the function images; the port impedance is calculated according to the following formula: ； wherein is the port impedance; is the perturbation voltage frequency domain; is the perturbation current frequency domain; the port impedance amplitude is calculated according to the following formula: ； In the formula, Z0is the port impedance magnitude; the port impedance phase angle is calculated according to the following formula: ； In the formula, is the port impedance phase angle; The frequency domain data And Is to And The application of fast Fourier decomposition fft function solution obtained; Wherein: The disturbance voltage; The disturbance current.

2. The method of claim 1, wherein, the voltage disturbance is calculated according to the following formula: ； wherein is the perturbation voltage; is the perturbation voltage; is the steady state port voltage.

3. The method of claim 1, wherein, the current disturbance is calculated according to the following formula: ； wherein is the disturbance current; is the steady state port current; is the post-injection disturbance port current.

4. A fast frequency scanning system for a wind farm through flexible transmission system for carrying out the method of fast frequency scanning of a wind farm through flexible transmission system as claimed in claim 1, characterized in that, The method comprises the following steps: a time domain simulation module is used to perform time domain simulation on the pre-constructed injection signal disturbance model to obtain the voltage steady-state waveform and the current steady-state waveform of the HVDC system and the wind farm port respectively; an injection module is used to inject a disturbance source into the injection signal disturbance model to obtain the voltage steady-state waveform and the current steady-state waveform of the HVDC system and the wind farm port after the injection of the disturbance respectively; An analysis module is configured to analyze the voltage steady-state waveform and the current steady-state waveform of the HVDC system and the wind farm port before and after the disturbance injection to obtain a disturbance voltage and a disturbance current; A calculation module is configured to obtain frequency domain data by using a fast Fourier calculation method on the disturbance voltage and the disturbance current, and obtain a corresponding impedance curve based on the frequency domain data. The injection signal disturbance model is constructed based on the HVDC system and the wind farm.

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