A mobile harmonic source based on-line impedance scanning method for medium and high voltage DC power grid

Abstract

The application discloses an online medium and high voltage DC power grid impedance scanning method based on a mobile harmonic generator, which comprises a harmonic generator, measuring points 1 to measuring points n and remote impedance analysis software. The harmonic generator comprises a harmonic generator controller and an Ethernet port, which is used for sending a harmonic disturbance signal to a to-be-measured power grid node; the measuring points comprise the to-be-measured power grid node, a wave recording device and an Ethernet port, which are used for obtaining voltage and current signals of the measuring points after the disturbance signal is injected into the to-be-measured power grid node; the remote impedance analysis software is communicated with the Ethernet ports of the harmonic generator and the measuring points through a local area network to transmit data, and calculates the amplitude and phase angle of the to-be-measured node through a DFT program algorithm, so as to calculate the amplitude-frequency curve and the phase-frequency curve of the to-be-measured impedance and obtain the to-be-measured impedance model. The DC power grid impedance of multiple measuring points can be obtained on line through the mobile harmonic generator, information is transmitted through 4G local area network communication, and the method is not limited to the power grid internal network. During the current stable period of the disturbance signal injection, the remote impedance analysis software can calculate the impedance model at the last frequency point on line, and the efficiency of obtaining the power grid impedance is improved.

Description

Technical Field

[0001] This invention belongs to the field of power electronics and relates to an online impedance scanning method for medium and high voltage DC power grids based on a mobile harmonic generator. Background Technology

[0002] As the penetration rate of converters connected to the power grid increases, and in the future it will develop into a converter network system dominated by local converters or even a power electronic power system, rather than a converter-connected grid system, impedance measurement of the power grid is of great significance in order to avoid or solve potential stability problems.

[0003] With the rapid development of flexible DC systems, new stability issues have gradually emerged. In recent years, multiple oscillation phenomena have occurred in flexible DC systems both domestically and internationally, with oscillation frequencies ranging from a few Hz to several kiloHz. For example, in 2013, the BARD Offshore 1 flexible DC system in Beihai experienced a sudden oscillation at around 200Hz, generating extremely large harmonic currents that even damaged the filter capacitors, causing a complete system shutdown. In 2014, during commissioning of the Nan'ao three-terminal flexible DC project, oscillations of around 20Hz appeared in the system as the wind farm's output power gradually increased.

[0004] Impedance scanning of DC power grids requires scanning multiple measurement points, necessitating the use of mobile harmonic generators. Furthermore, data transmission presents a significant challenge in impedance scanning. Therefore, there is an urgent need for an online impedance scanning method for medium- and high-voltage DC power grids based on mobile harmonic generators. This method should enable impedance scanning at multiple measurement points and utilize local area network (LAN) communication to avoid data confinement within the power grid itself. Summary of the Invention

[0005] The technical solution of this invention is used to solve the problem of difficulty in simultaneously measuring the impedance of multiple DC grid nodes online, and realizes impedance scanning of multiple nodes without data transmission through the internal network of the power grid.

[0006] The present invention solves the above-mentioned technical problems through the following technical solutions:

[0007] An online impedance scanning method for medium- and high-voltage direct current (HVDC) grids based on a mobile harmonic generator includes a harmonic generator, measurement points 1 to n, and remote impedance analysis software. The harmonic generator includes a harmonic generator controller and an Ethernet port to emit harmonic disturbance signals to the grid node under test. The measurement points include the grid node under test, a waveform recording device, and an Ethernet port to obtain voltage and current signals after the disturbance signal is injected into the grid node. The remote impedance analysis software transmits data with the harmonic generator and the Ethernet ports of the measurement points via local area network communication and calculates the impedance model using algorithms such as DFT.

[0008] Furthermore, the harmonic generator uses a single sinusoidal disturbance signal. The Ethernet port in the harmonic generator obtains information such as the amplitude, phase, and frequency of the disturbance signal from remote impedance analysis software via local area network communication, and transmits the disturbance signal information to the harmonic generator controller to generate the disturbance frequency signal.

[0009] Furthermore, the signal amplitude and frequency range are set according to the actual required measurement range and accuracy. The amplitude of the disturbance signal is 0.5% to 1% of the DC side voltage; to facilitate the calculation of the impedance model by the remote impedance analysis software, the frequency of the disturbance signal is an integer multiple of the change in the fundamental frequency, which is 50Hz, thus forming a frequency point array F[]. A single-frequency sinusoidal disturbance signal is injected into the grid node under test each time.

[0010] Furthermore, after a harmonic source injects a disturbance into the circuit under test, if it is the first time a disturbance signal has been injected, the remote impedance analysis software sends a trigger command for the waveform recording device to the Ethernet port of the measurement point via local area network communication after the injected harmonic current stabilizes. Upon receiving the trigger signal, the waveform recording device begins to record the voltage and current signals of the grid node under test at the current disturbance frequency. If it is not the first time a disturbance signal has been injected, the remote impedance analysis software calculates the impedance model of the previous frequency point using the obtained voltage and current signals during the period when the injected harmonic current stabilizes. After the harmonic current stabilizes, the remote impedance analysis software sends a trigger command for the waveform recording device to the Ethernet port of the measurement point via local area network communication. Upon receiving the trigger signal, the waveform recording device begins to record the voltage and current signals of the grid node under test at the current disturbance frequency.

[0011] Furthermore, the remote impedance analysis software obtains voltage and current signals at a frequency point from the Ethernet port of the measurement point through local area network communication, and uses the DFT algorithm to convert the voltage and current signals of the power grid node under test from the time domain to the frequency domain, thereby obtaining the amplitude and phase angle of the voltage and current signals at this frequency.

[0012] Furthermore, based on the voltage and current signals in the frequency domain, the impedance amplitude and phase angle at the current frequency point are calculated. After all frequency point arrays have been read, the remote impedance analysis software can derive the amplitude-frequency curve and phase-frequency curve of the grid impedance based on the impedance amplitude and phase angle at all frequency points, thereby obtaining the impedance model of the DC grid.

[0013] Furthermore, for a data sequence {x(n)} of length N, the corresponding frequency domain sequence {X(k)} can be calculated using DFT:

[0014] in, For phase factor:

[0015] Furthermore, to meet the requirement of online acquisition of impedance characteristics, the DFT algorithm is simplified to an FFT algorithm to reduce complexity:

[0016]

[0017] Where X1(k) and X2(k) are both N / 2-point DFTs, and the value of k ranges from 0, 1, 2...N / 2-1. Only the first half of the result can be obtained, based on the periodicity of the phase factor. We can obtain X1(N / 2+k)=X1(k) and X2(N / 2+k)=X2(k), that is, the value of the latter half is...

[0018] Furthermore, the voltage signal at frequency point f obtained by the remote impedance analysis software is converted to the frequency domain using the FFT algorithm, and the amplitude and phase angle are V, respectively. mag and V deg The amplitude and phase angle of the current signal at frequency point f, after being converted to the frequency domain by the FFT algorithm, are respectively I... mag and I deg Then the impedance model at frequency point f is:

[0019]

[0020] Among them, Z mag and Z deg The impedance magnitude and phase angle are given.

[0021] After all the frequency points in the array have been read and the impedance amplitude and phase angle at each frequency point have been calculated, the impedance amplitude and phase angle at all frequency points can be combined in frequency order to obtain the amplitude-frequency curve and phase-frequency curve of the grid impedance, thus obtaining a DC grid impedance model with a wide frequency range.

[0022] The advantages of this invention are:

[0023] (1) A movable harmonic generator was used during impedance scanning, which can simultaneously measure multiple DC grid nodes, thus improving the efficiency of impedance scanning.

[0024] (2) Local area network communication was used in the data transmission to avoid the measured data being confined to the power grid network, making data transmission more convenient;

[0025] (3) During the period of harmonic current stability, the remote impedance analysis software will obtain the impedance model when the disturbance signal is injected at the previous frequency point, which reduces the time to obtain the impedance model and greatly improves efficiency. Attached Figure Description

[0026] Figure 1This is a schematic diagram of the DC grid impedance scanning method of the present invention.

[0027] Figure 2 This is the impedance scanning flowchart of the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0030] like Figure 1 As shown, the online impedance scanning method for medium- and high-voltage DC power grids based on a mobile harmonic generator includes a harmonic generator, measurement points 1 to n, and remote impedance analysis software. The harmonic generator includes a harmonic generator controller and an Ethernet port, used to send harmonic disturbance signals to the grid node under test. The measurement points include the grid node under test, a waveform recording device, and an Ethernet port, used to obtain the voltage and current signals at the measurement points after the disturbance signal is injected into the grid node under test. The remote impedance analysis software transmits data with the harmonic generator and the Ethernet ports of the measurement points via local area network communication, and calculates the impedance model using algorithms such as DFT.

[0031] Specifically, the harmonic generator uses a single sinusoidal disturbance signal. The Ethernet port in the harmonic generator obtains information such as the amplitude, phase, and frequency of the disturbance signal from remote impedance analysis software via local area network communication, and transmits the disturbance signal information to the harmonic generator controller to generate the disturbance frequency signal.

[0032] Specifically, the signal amplitude and frequency range are set according to the actual required measurement range and accuracy. The amplitude of the disturbance signal is 0.5% to 1% of the DC side voltage; to facilitate the calculation of the impedance model by the remote impedance analysis software, the frequency of the disturbance signal is an integer multiple of the change in the fundamental frequency, which is 50Hz, thus forming a frequency point array F[]. A single-frequency sinusoidal disturbance signal is injected into the grid node under test each time.

[0033] Specifically, after a harmonic source injects a disturbance into the circuit under test, if it is the first time a disturbance signal has been injected, the remote impedance analysis software sends a trigger command for the waveform recording device to the Ethernet port of the measurement point via local area network communication after the injected harmonic current stabilizes. After receiving the trigger signal, the waveform recording device begins to record the voltage and current signals of the grid node under test at the current disturbance frequency. If it is not the first time a disturbance signal has been injected, during the period when the injected harmonic current stabilizes, the remote impedance analysis software calculates the impedance model of the previous frequency point using the obtained voltage and current signals. After the harmonic current stabilizes, the remote impedance analysis software sends a trigger command for the waveform recording device to the Ethernet port of the measurement point via local area network communication. After receiving the trigger signal, the waveform recording device begins to record the voltage and current signals of the grid node under test at the current disturbance frequency.

[0034] Specifically, the remote impedance analysis software obtains voltage and current signals at a frequency point from the Ethernet port of the measurement point through local area network communication, and uses the DFT algorithm to convert the voltage and current signals of the power grid node under test from the time domain to the frequency domain, thereby obtaining the amplitude and phase angle of the voltage and current signals at this frequency.

[0035] Specifically, based on the voltage and current signals in the frequency domain, the impedance amplitude and phase angle at the current frequency point are calculated. After all the frequency point arrays have been read, the remote impedance analysis software can derive the amplitude-frequency curve and phase-frequency curve of the grid impedance based on the impedance amplitude and phase angle of all frequency points, thereby obtaining the impedance model of the DC grid.

[0036] Specifically, for a data sequence {x(n)} of length N, the corresponding frequency domain sequence {X(k)} can be calculated using the DFT:

[0037] in, For phase factor:

[0038] Specifically, to meet the requirement of online acquisition of impedance characteristics, the DFT algorithm is simplified to the FFT algorithm to reduce complexity:

[0039]

[0040] Where X1(k) and X2(k) are both N / 2-point DFTs, and the value of k ranges from 0, 1, 2...N / 2-1. Only the first half of the result can be obtained, based on the periodicity of the phase factor. We can obtain X1(N / 2+k)=X1(k) and X2(N / 2+k)=X2(k), that is, the value of the latter half is...

[0041] Specifically, the voltage signal at frequency point f obtained by the remote impedance analysis software is converted to the frequency domain using the FFT algorithm, and the amplitude and phase angle are V, respectively. mag and V deg The amplitude and phase angle of the current signal at frequency point f, after being converted to the frequency domain by the FFT algorithm, are respectively I... mag and I deg Then the impedance model at frequency point f is:

[0042]

[0043] Among them, Z mag and Z deg The impedance magnitude and phase angle are given.

[0044] After all the frequency points in the array have been read and the impedance amplitude and phase angle at each frequency point have been calculated, the impedance amplitude and phase angle at all frequency points can be combined in frequency order to obtain the amplitude-frequency curve and phase-frequency curve of the grid impedance, thus obtaining a DC grid impedance model with a wide frequency range.

[0045] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An online impedance scanning method for medium- and high-voltage DC power grids based on a moving harmonic generator, characterized in that: This includes harmonic sources, measurement points 1 to n, and remote impedance analysis software; The harmonic generator includes a harmonic generator controller and an Ethernet port, used to send harmonic disturbance signals to the power grid node under test; the measurement point includes the power grid node under test, a waveform recording device, and an Ethernet port, used to obtain the voltage and current signals of the measurement point after the disturbance signal is injected into the power grid node under test; the remote impedance analysis software transmits data with the harmonic generator and the Ethernet port of the measurement point through local area network communication, and calculates the amplitude and phase angle of the node under test through the DFT program algorithm, thereby calculating the amplitude-frequency curve and phase-frequency curve of the impedance under test, and obtaining the impedance model of the impedance under test; The harmonic generator uses a single sinusoidal disturbance signal. The Ethernet port in the harmonic generator obtains the amplitude, phase and frequency information of the disturbance signal from the remote impedance analysis software through local area network communication, and transmits the disturbance signal information to the harmonic generator controller to generate the disturbance frequency signal. After a harmonic source injects a disturbance into the circuit under test, if it is the first time a disturbance signal is injected, after the injected harmonic current stabilizes, the remote impedance analysis software sends a trigger command for the waveform recording device to the Ethernet port of the measurement point via local area network communication. After receiving the trigger signal, the waveform recording device begins to record the voltage and current signals of the power grid node under test at the current disturbance frequency. If it is not the first time a disturbance signal is injected, during the stabilization period of the injected harmonic current, the remote impedance analysis software calculates the impedance model of the previous frequency point through the obtained voltage and current signals. After the circuit stabilizes, the remote impedance analysis software sends a trigger command for the waveform recording device to the Ethernet port of the measurement point through local area network communication. After receiving the trigger signal, the waveform recording device begins to record the voltage and current signals of the grid node under test at the current disturbance frequency. The remote impedance analysis software obtains voltage and current signals at a frequency point from the Ethernet port of the measurement point through local area network communication, and uses the DFT algorithm to convert the voltage and current signals of the power grid node under test from the time domain to the frequency domain, thereby obtaining the amplitude and phase angle of the voltage and current signals at this frequency.

2. The online impedance scanning method for medium and high voltage DC power grids based on a moving harmonic generator according to claim 1, characterized in that: Based on the voltage and current signals in the frequency domain, calculate the impedance amplitude and phase angle at the current frequency point; After all the frequency point arrays have been read, the remote impedance analysis software can derive the amplitude-frequency curve and phase-frequency curve of the grid impedance based on the impedance amplitude and phase angle of all frequency points, thereby obtaining the impedance model of the DC grid.

3. The online impedance scanning method for medium and high voltage DC power grids based on a moving harmonic generator according to claim 1, characterized in that: For a data sequence of length N The corresponding frequency domain sequence can be calculated using DFT. : ; in, For phase factor: .

4. The online impedance scanning method for medium and high voltage DC power grids based on a moving harmonic generator according to claim 3, characterized in that: To meet the requirement of online acquisition of impedance characteristics, the DFT algorithm is simplified to an FFT algorithm to reduce complexity: in, and Both are N / 2-point DFTs, and the value of k ranges from 0, 1, 2...N / 2-1. Only the first half of the result can be obtained, based on the periodicity of the phase factor. You can get That is, the value of the second half is .

5. The online impedance scanning method for medium and high voltage DC power grids based on a moving harmonic generator according to claim 2, characterized in that: The voltage signal at frequency point f obtained by the remote impedance analysis software is converted to the frequency domain using the FFT algorithm, and the amplitude and phase angle are respectively... and The amplitude and phase angle of the current signal at frequency point f after being converted to the frequency domain by the FFT algorithm are respectively... and Then the impedance model at frequency point f is: in, and The magnitude and phase angle of the impedance; After all the frequency points in the array have been read and the impedance amplitude and phase angle at each frequency point have been calculated, the impedance amplitude and phase angle at all frequency points can be combined in frequency order to obtain the amplitude-frequency curve and phase-frequency curve of the grid impedance, thus obtaining a DC grid impedance model with a wide frequency range.

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