Harmonic analysis method and analysis system applicable to hybrid multi-terminal DC transmission system

Abstract

The present invention discloses a harmonic analysis method and analysis system suitable for a hybrid multi-terminal direct current transmission system, and relates to the technical field of harmonic analysis of multi-terminal direct current transmission. In a direct current transmission project, voltage and current measuring points at different positions are recorded by a recording device; according to the Shannon sampling theorem, each recorded information is subjected to Fourier decomposition to obtain the analysis results of amplitude and phase angle information of different frequencies to form harmonic data; the Cos function with the initial moment of the recording as the starting point is used as the reference vector to generate the recording phase angle information of the specified frequency, and the phase angle difference after Fourier decomposition is automatically compensated for the recording information of different starting times; by increasing the amplitude and phase angle information of the specified frequency of the recording, the phase angle difference of the voltage and current at different measuring points in the direct current transmission project is obtained, and the transmission direction of the harmonic current is judged in combination with the known impedance in the direct current transmission system.

Description

Technical Field

[0001] The present invention relates to the technical field of multi-terminal direct current transmission harmonic analysis, and in particular to a harmonic analysis method and analysis system suitable for a hybrid multi-terminal direct current transmission system. Background Art

[0002] With the rapid development of DC transmission technology, multi-terminal DC transmission technology has been gradually applied in engineering practice. The converter of the high-voltage DC transmission system has the characteristics of nonlinearity and frequency conversion, which easily leads to harmonic voltage and current in the system. In the hybrid transmission system, the low-frequency harmonic characteristics of the conventional DC converter are prominent, and the high-frequency harmonic characteristics of the flexible DC converter are prominent. The interaction between the two makes the harmonic characteristics of the hybrid DC transmission system complex. In addition, the DC system topology is more complex with the adoption of multi-terminal DC transmission, and the harmonic transmission path is difficult to determine. In the process of analyzing the harmonic problem of the DC system, it is necessary to analyze the source of the harmonic according to the device recording. The existing recording analysis tool only provides the analysis results of the amplitude of each frequency harmonic in the waveform and its proportion in the power frequency. This result alone cannot adapt to the characteristics of multiple harmonic sources and complex harmonic transmission paths in the hybrid multi-terminal DC transmission system. Therefore, a harmonic analysis method suitable for the hybrid multi-terminal DC transmission system is needed to assist in the analysis of harmonic sources and harmonic transmission paths.

[0003] Existing waveform analysis tools only provide the magnitude of harmonic amplitudes in the waveform and their proportion in the industrial frequency. The transmission direction of harmonics in the DC system cannot be determined by the magnitude of harmonic amplitudes in the DC voltage and current alone.

[0004] In addition, the harmonic current of each node can be analyzed according to Kirchhoff's law to obtain the harmonic current transfer path. However, this method is only applicable to the analysis of simulation results of specific frequencies in the simulation waveform. For the recording results of actual devices in the project, the recording analysis tool cannot extract the current waveform of a specific frequency band, so it is impossible to determine the size of the harmonic current at a certain moment, so it is impossible to analyze the harmonic current transfer path.

[0005] Early DC projects were mainly two-terminal DC transmission projects, in which harmonic transmission was relatively simple, with only two possibilities: from the sending end to the receiving end or from the receiving end to the sending end. Therefore, in the process of harmonic analysis of DC systems, harmonic problems encountered in projects can be better solved by relying solely on harmonic amplitude information. For example, in two-terminal DC projects, 12th harmonic problems often occur due to the switching on and off of DC filters. By comparing the 12th harmonic amplitudes at various locations based on the switching on and off of the filters, it can be determined whether the harmonic source is at the sending end or the receiving end.

[0006] However, with the maturity of engineering technology and the use of new technologies, especially after the Kunliulong hybrid multi-terminal DC project was officially put into operation, the harmonic frequency band of the flexible DC station is wider and more random, and the DC topology structure is more complex. It is impossible to determine the harmonic transmission path only by the harmonic amplitude information, such as Figure 7 As shown, the high-frequency harmonics at the sending end A exceed the standard. Based on the amplitude, it is impossible to determine whether it is transmitted from the receiving end B or the receiving end C. At this time, it is necessary to analyze the harmonic information of the T zone of the receiving end B. At this time, the harmonic transmission direction cannot be determined only by the amplitude, so it is impossible to determine whether the harmonic source is B or C. The method of analyzing the harmonic current in each node according to Kirchhoff's law and then obtaining the direction of the harmonic current requires manual judgment, which is labor-intensive, difficult to operate, and is only applicable to the situation where the magnitude of the harmonic current is known at a specific moment. Figure 8 Taking a multi-terminal DC transmission system as an example, the current waveform in the T zone can be compared, and the direction of the harmonic current can be determined by Kirchhoff's current law. However, the actual waveform on site is formed by the superposition of the fundamental frequency and each frequency harmonic, and it is difficult to compare the waveform of a specific frequency band, so the direction of the harmonic current cannot be effectively analyzed. The present invention can directly generate the harmonic amplitude and phase angle measured by each measuring device in batches, and combine the harmonic frequency and the impedance between the measuring devices to efficiently analyze the harmonic transmission information. Summary of the invention

[0007] In order to solve the above practical problems, the present invention provides a harmonic analysis method suitable for hybrid multi-terminal DC transmission systems. By increasing the amplitude and phase angle information of the specified frequency of the recording, the phase angle difference of the voltage and current at different measuring points in the DC transmission project is obtained, and the transmission direction of the harmonic current is judged in combination with the known impedance in the DC transmission system.

[0008] The technical solution is: a harmonic analysis method applicable to a hybrid multi-terminal direct current transmission system, comprising the following steps:

[0009] S1: In DC transmission projects, the voltage and current measuring points at different locations are recorded by a recording device;

[0010] S2: Each recording corresponds to each recording information, and different recording channels can be formed according to the recording information;

[0011] The recording information includes at least one of the recording start time, current, voltage, and sampling frequency;

[0012] The recording channel is any one of the recording start time, current, voltage, and sampling frequency in the recording information.

[0013] S3: Analyze harmonics: According to Shannon sampling theorem, the sampled information contains frequency information of 0.5 times the sampling frequency. Performing Fourier decomposition on each recorded information can obtain the analysis results of amplitude and phase angle information of different frequencies to form harmonic data.

[0014] S4: Taking the Cos function with the initial moment of recording as the starting point as the reference vector, generate the recording phase angle information of the specified frequency, and automatically compensate the phase angle difference after Fourier decomposition for the recording information with different starting times;

[0015] S5: Repeat steps S3-S4, and obtain the phase angle difference of voltage and current at different measuring points in the DC transmission project by increasing the amplitude and phase angle information of the designated frequency of the recording. Combined with the known impedance in the DC transmission system, the transmission direction of the harmonic current is judged.

[0016] Further: when the recording to be analyzed is recorded in two or more recording information with different starting times, at this time, the recording to be analyzed is in different recording information,

[0017] The phase angle of recording 1 is δ, and the phase angle of recording 2 is &, where the phase angle δ is the angle obtained by Fourier decomposition of recording 1, and the phase angle & is the angle obtained by Fourier decomposition of recording 2;

[0018] After Fourier decomposition, there will be a phase angle difference in the recorded phase angle, and the calculation method of the phase angle difference is: θ=2πf(t1-t2), where t1 and t2 are the recording start time of recording information 1 and recording information 2 respectively;

[0019] Recording 2 will automatically generate a phase angle value &'=&+θ based on the reference vector of recording information 1, thereby completing automatic phase angle compensation for different recording information.

[0020] Preferably: a certain recording is selected as a reference value to complete the phase angle compensation of the specified recording.

[0021] Furthermore: the recording channel includes a current recording channel;

[0022] According to the phase angle information of the specified frequency of current recording channel 1 and current recording channel 2, combined with the impedance between the measuring points, the harmonic transmission direction is determined;

[0023] The phase angle of current recording channel 1 is δ, the phase angle of current recording channel 2 is &, and the impedance is inductive or capacitive;

[0024] If δ-&=90°,

[0025] When the impedance between the measuring points is capacitive, the harmonic transmission direction is current 2 → current 1;

[0026] When the impedance between the measuring points is inductive, the direction of harmonic transmission is current 1 → current 2;

[0027] If δ-&=-90°,

[0028] When the impedance between the measuring points is capacitive, the harmonic transmission direction is current 1 → current 2;

[0029] When the impedance between the measuring points is inductive, the direction of harmonic transmission is Current 2 → Current 1.

[0030] Preferably, the transmission direction of the harmonic current is presented in a harmonic data chart, and the harmonic data chart can be used to visually determine the transmission direction of the harmonic current and monitor the harmonic data at different locations in the direct current transmission project.

[0031] The present invention discloses an analysis system applicable to a hybrid multi-terminal direct current transmission system, which adopts the harmonic analysis method applicable to the hybrid multi-terminal direct current transmission system, comprising: a recording device bidirectionally connected to a server, a server, a harmonic analysis terminal, a recording device and a harmonic analysis terminal; the harmonic analysis terminal is used for at least one of phase angle compensation, harmonic analysis, forming a harmonic data chart, and harmonic source positioning.

[0032] Beneficial Effects

[0033] 1. The present invention obtains the phase angle difference of voltage and current at different measuring points in the DC transmission project by adding the amplitude and phase angle information of the designated frequency of the recording, and judges the transmission direction of the harmonic current in combination with the known impedance in the DC transmission system.

[0034] 2. In the present invention, when the recordings to be analyzed are in different recording information, there will be a phase angle difference in the recording phase angle after Fourier decomposition. The phase angle information of different frequency amplitudes of the recordings can be obtained after Fourier decomposition. Different recordings will automatically generate phase angle values ​​based on the recording information reference vector to complete phase angle compensation. If phase angle compensation is not performed, the phase angle difference between different recordings is not a real phase angle difference. Using the phase angle difference to analyze the harmonic flow direction will result in errors. The phase angle difference after compensation is the real phase angle difference.

[0035] 3. The present invention can obtain the harmonic transmission path or current harmonic flow direction more accurately based on the phase angle information of the specified frequency of different current recording channels and the impedance between the measuring points, analyze the harmonic information at different positions of the multi-terminal DC transmission system, and assist in locating the harmonic source.

[0036] 4. In the present invention, the harmonic data chart can be used to visually determine the direction of harmonic current transmission and monitor the harmonic data at different locations in the DC transmission project. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0038] Figure 1 The Cos function described in the embodiment is used as a reference vector to generate a schematic diagram of the phase angle information of the recording of a specified frequency with the initial moment of the recording as the starting point;

[0039] Figure 2 is a schematic diagram of the phase angle difference between the reference vectors described in the embodiment;

[0040] Figure 3 is a harmonic data chart of the embodiment;

[0041] Figure 4 is a flow chart of the implementation method described in Example 3;

[0042] Figure 5 is a schematic diagram of an interaction scenario described in an embodiment;

[0043] Figure 6 This is a schematic diagram of the effect described in Example 3;

[0044] Figure 7 is a schematic diagram of a two-terminal direct current transmission system according to an embodiment;

[0045] Figure 8 The multi-terminal direct current transmission system described in the embodiment;

[0046] Fig. 9 The recording display interface setting of the embodiment;

[0047] Fig.10 is a harmonic data list described in the embodiment;

[0048] Fig.11 Schematic diagram of the amplitude and phase angle of the 50 Hz component in the DC voltage and current described in the embodiment;

[0049] Fig.12 It is a schematic diagram of manually compensating the phase angle described in the embodiment. DETAILED DESCRIPTION

[0050] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0052] Glossary:

[0053] Recording device: In actual DC projects, control and protection devices are equipped with recording devices, which can be used to record the electrical quantities connected to the control and protection devices;

[0054] Example 1: Figure 1-4 As shown, a harmonic analysis method applicable to a hybrid multi-terminal direct current transmission system comprises the following steps:

[0055] S1: In DC transmission projects, the voltage and current measuring points at different locations are recorded by a recording device;

[0056] S2: Each recording corresponds to each recording information, and different recording channels can be formed according to the recording information;

[0057] The recording information includes at least one of the recording start time, current, voltage, and sampling frequency;

[0058] The recording channel is any one of the recording start time, current, voltage, and sampling frequency in the recording information.

[0059] S3: Analyze harmonics: According to Shannon sampling theorem, the sampled information contains frequency information of 0.5 times the sampling frequency. Performing Fourier decomposition on each recorded information can obtain the analysis results of amplitude and phase angle information of different frequencies to form harmonic data.

[0060] S4: Taking the Cos function with the initial moment of recording as the starting point as the reference vector, generate the recording phase angle information of the specified frequency, and automatically compensate the phase angle difference after Fourier decomposition for the recording information with different starting times;

[0061] S5: Repeat steps S3-S4, and obtain the phase angle difference of voltage and current at different measuring points in the DC transmission project by increasing the amplitude and phase angle information of the designated frequency of the recording. Combined with the known impedance in the DC transmission system, the transmission direction of the harmonic current is judged.

[0062] The present invention obtains the phase angle difference of voltage and current at different measuring points in a DC power transmission project by adding the amplitude and phase angle information of the designated frequency of the recording, and judges the transmission direction of the harmonic current in combination with the known element impedance characteristics in the DC power transmission system.

[0063] Embodiment 2: This embodiment implements phase angle compensation of recording in different recording information on the basis of embodiment 1, such as Figure 1-2 As shown in the figure: When the recording to be analyzed is recorded with two or more recording information at different starting times, the recording to be analyzed is in different recording information.

[0064] The phase angle of recording 1 is δ, and the phase angle of recording 2 is &, where the phase angle δ is the angle obtained by Fourier decomposition of recording 1, and the phase angle & is the angle obtained by Fourier decomposition of recording 2;

[0065] After Fourier decomposition, there will be a phase angle difference in the recorded phase angle, and the calculation method of the phase angle difference is: θ=2πf(t1-t2), where t1 and t2 are the recording start time of recording information 1 and recording information 2 respectively;

[0066] Recording 2 will automatically generate a phase angle value &'=&+θ based on the reference vector of recording information 1, thereby completing automatic phase angle compensation for different recording information.

[0067] According to the present invention, when the wave recordings to be analyzed are in different wave recording information, there will be a phase angle difference in the wave recording phase angle after Fourier decomposition, and the phase angle information of different frequency amplitudes of the wave recordings can be obtained after Fourier decomposition. Different wave recordings will automatically generate phase angle values ​​based on the wave recording information reference vector to complete phase angle compensation. If phase angle compensation is not performed, the phase angle difference between different wave recordings is not a real phase angle difference, and the result of harmonic flow analysis using the phase angle difference will be wrong. The phase angle difference after compensation is a real phase angle difference.

[0068] Embodiment 3: Figure 1-5 As shown, this embodiment selects a certain recording wave as a reference value on the basis of Embodiment 2 to complete the phase angle compensation of the specified recording wave.

[0069] Embodiment 4: This embodiment is based on the second or third embodiment, and determines the harmonic transmission direction, such as Figure 1-6 As shown: the recording channel includes a current recording channel;

[0070] According to the phase angle information of the specified frequency of current recording channel 1 and current recording channel 2, combined with the impedance characteristics of the components between the measuring points, the harmonic transmission direction is determined;

[0071] The phase angle of current recording 1 is δ, the phase angle of current recording 2 is &, and the impedance characteristics of the components are inductive or capacitive;

[0072] If δ-&=90°,

[0073] When the element between the measuring points is capacitive, the harmonic transmission direction is current 2 → current 1;

[0074] When the components between the measuring points are inductive, the direction of harmonic transmission is current 1 → current 2;

[0075] If δ-&=-90°,

[0076] When the element between the measuring points is capacitive, the direction of harmonic transmission is current 1 → current 2;

[0077] When the components between the measuring points are inductive, the direction of harmonic transmission is Current 2 → Current 1.

[0078] The present invention can obtain the harmonic transmission path or current harmonic flow direction more accurately based on the phase angle information of the specified frequency of different current recording channels and the impedance between the measuring points, analyze the harmonic information at different positions of the multi-terminal direct current transmission system, and assist in completing the harmonic source positioning.

[0079] Embodiment 5: Figure 3 As shown, this embodiment realizes the transmission direction of harmonic current based on the embodiment 4 and presents it in the harmonic data chart;

[0080] In the present invention, the harmonic data chart can be used to visually determine the direction of harmonic current transmission and monitor harmonic data at different locations in a direct current transmission project.

[0081] Embodiment 6: Figure 3 , Figure 9-12 An analysis system suitable for a hybrid multi-terminal DC transmission system is shown, which adopts the harmonic analysis method suitable for the hybrid multi-terminal DC transmission system, including: a recording device bidirectionally connected to a server, a server, a harmonic analysis terminal, a recording device and a harmonic analysis terminal; the harmonic analysis terminal is used for at least one of phase angle compensation, harmonic analysis, forming a harmonic data chart, and harmonic source positioning.

[0082] Embodiment 7: This embodiment combines the above embodiments 1 to 6 with a computer and a server for implementation. Figure 1-4 As shown, a harmonic analysis method applicable to a hybrid multi-terminal direct current transmission system comprises the following steps:

[0083] S1: In DC transmission projects, the voltage and current measuring points at different locations are recorded by a recording device, and the recorded files are saved and uploaded to the server;

[0084] S2: Import the recording file of the server into the harmonic analysis software to obtain all the recordings in the recording file. Each recording is saved as recording information, and different recording channels can be formed according to the recording information;

[0085] The recording information includes at least one of the recording start time, current, voltage, and sampling frequency;

[0086] The recording channel is any one of the recording start time, current, voltage, and sampling frequency in the recording information.

[0087] S3: Analyze harmonics: According to Shannon sampling theorem, the sampled information contains frequency information of 0.5 times the sampling frequency. Performing Fourier decomposition on each recorded information can obtain the analysis results of amplitude and phase angle information of different frequencies to form harmonic data.

[0088] S4: Taking the Cos function with the initial moment of recording as the starting point as the reference vector, generate the recording phase angle information of the specified frequency, and automatically compensate the phase angle difference after Fourier decomposition for the recording files with different starting times;

[0089] S5: Repeat steps S3-S4, and obtain the phase angle difference of voltage and current at different measuring points in the DC transmission project by adding the amplitude and phase angle information of the designated frequency of the recording in the recording analysis software. Combined with the known component impedance characteristics in the DC transmission system, the transmission direction of the harmonic current is judged.

[0090] In this embodiment, by adding the amplitude and phase angle information of the designated frequency of the recording in the recording analysis software, the phase angle difference of the voltage and current at different measuring points in the DC transmission project is obtained, and the transmission direction of the harmonic current is judged in combination with the known component impedance characteristics in the DC transmission system.

[0091] like Figure 1-2 As shown in the figure: when the recordings to be analyzed are saved in different recording files, the starting time of the recording files is different, so there are differences in the reference vectors in the Fourier decomposition results, and there is a phase angle difference θ between the reference vectors;

[0092] The phase angle of recording 1 is δ, and the phase angle of recording 2 is &, where the phase angle δ is the angle obtained by Fourier decomposition of recording 1, and the phase angle & is the angle obtained by Fourier decomposition of recording 2;

[0093] As mentioned above, if recording 1 and recording 2 are not the same file, there will be a phase angle difference in the recording phase after Fourier decomposition, which cannot reflect the real phase angle relationship. The calculation method of the phase angle difference is: θ=2πf(t1-t2), where t1 and t2 are the recording start time of recording file 1 and recording file 2 respectively;

[0094] Recording 2 will automatically generate a phase angle value &'=&+θ based on the reference vector of recording file 1, thereby completing automatic phase angle compensation for different recording files.

[0095] like Fig.12 The manual phase angle compensation scheme is shown: manually select a certain recording as the reference value to complete the manual phase angle compensation of the specified recording file.

[0096] In this embodiment, the recording information of different measuring points is uploaded to the server, and the recording files of different recording devices are automatically synchronized to obtain the amplitude and phase angle information of different recording frequencies, and the phase angle compensation can be completed automatically or manually; if the phase angle compensation is not performed, the phase angle difference between different recordings is not the real phase angle difference, and the harmonic flow analysis result using the phase angle difference will be wrong. The phase angle difference after compensation is the real phase angle difference.

[0097] like Figure 1-6 As shown: the recording channel includes a current recording channel;

[0098] According to the phase angle information of the specified frequency of current recording channel 1 and current recording channel 2, combined with the impedance characteristics of the components between the measuring points, the harmonic transmission direction is determined;

[0099] The phase angle of current recording 1 is δ, the phase angle of current recording 2 is &, and the impedance characteristics of the components are inductive or capacitive;

[0100] If δ-&=90°,

[0101] When the element between the measuring points is capacitive, the harmonic transmission direction is current 2 → current 1;

[0102] When the components between the measuring points are inductive, the direction of harmonic transmission is current 1 → current 2;

[0103] If δ-&=-90°,

[0104] When the element between the measuring points is capacitive, the direction of harmonic transmission is current 1 → current 2;

[0105] When the components between the measuring points are inductive, the direction of harmonic transmission is Current 2 → Current 1.

[0106] In this embodiment, based on the phase angle information of the specified frequencies of different current recording channels and in combination with the impedance characteristics of the components between the measuring points, the harmonic transmission path or the current harmonic flow direction can be obtained more accurately, and the harmonic information at different positions of the multi-terminal DC transmission system can be analyzed to assist in the location of the harmonic source.

[0107] like Figure 3 As shown: The direction of harmonic current transmission is presented in the harmonic data chart;

[0108] In the present invention, the harmonic data chart can be used to visually determine the direction of harmonic current transmission and monitor harmonic data at different locations in a direct current transmission project.

[0109] like Figure 3 , Figure 9-12An analysis system suitable for a hybrid multi-terminal DC transmission system is shown, which adopts the harmonic analysis method suitable for the hybrid multi-terminal DC transmission system, including: a recording device bidirectionally connected to a server, a server, a harmonic analysis terminal, a recording device and a harmonic analysis terminal; the harmonic analysis terminal is used for at least one of phase angle compensation, harmonic analysis, forming a harmonic data chart, and harmonic source positioning.

[0110] like Fig. 9 As shown, set the "Harmonic Analysis" menu option in the waveform display interface. By selecting this option, the following Fig.10 The “Harmonic Data List” window is shown.

[0111] exist Fig.10 In the interface shown, enter the harmonic frequency to be analyzed in the "Generate Frequency" input box, click the "Generate Harmonic Data" button, and the list on the right will generate the amplitude and phase angle information of all waveforms in the recording channel at the specified frequency, such as Fig.11 Shown are the magnitude and phase angle of the 50Hz component in the DC voltage and current.

[0112] In addition, to facilitate analysis, a channel can be manually selected as the reference value (for example Fig.11 Manual compensation of phase angle, such as Fig.12 shown.

[0113] Recording file: The recording file is generated by the recording device and is generally stored as a Comtrade format file. The cfg suffix file in the standard Comtrade file stores information such as the recording start time and sampling rate.

[0114] Recording file import: According to the recording file information, the recording file can be imported into the software, and each recording channel will be saved as an array. (The recording channel is a certain quantity in the recording file, for example, the DC voltage in the recording file is a recording channel)

[0115] Harmonic analysis: The amplitude and phase angle information of the specified harmonic frequency are extracted from the recording channel to be analyzed through the Fourier decomposition algorithm, and the results are listed in a table, such as Fig.11 shown.

[0116] Automatic phase angle compensation for different recording files: The Fourier decomposition algorithm uses the cosine function starting from the initial recording time as the reference vector to generate the phase angle information of the specified recording channel, such as Figure 1 As shown, the cosine function is the reference vector, and the phase angle information of the IDLH is the phase angle difference δ with the reference vector.

[0117] In actual engineering, there are cases where the recordings to be analyzed are stored in two recording files. Since the starting times of the two recording files are different, the reference vectors are different. Therefore, the phase difference between the two channels obtained by Fourier decomposition is not the real phase difference, which also includes the phase difference between the reference vectors. Figure 2 As shown, the phase angles of recording channel 1 and recording channel 2 obtained by Fourier decomposition algorithm are δ and & respectively. Obviously, the phase angle difference θ between recording channel 1 and recording channel 2 cannot be obtained based on the above phase angle information alone.

[0118] This embodiment will automatically calculate the phase angle difference between the reference vectors according to the recording file information. The specific calculation formula is as follows: θ=2πf(t1-t2), where t1 and t2 are the recording start time of recording file 1 and recording file 2 respectively;

[0119] According to the phase angle difference of the reference vector, recording file 2 will automatically generate a phase angle value &'=&+θ based on the reference vector of recording file 1, thereby completing automatic phase angle compensation for different recording files.

[0120] (1) Set the right-click menu bar in the waveform name display bar of the recording channel and set the harmonic analysis function. When the user clicks this option, a harmonic data list window is generated;

[0121] The recording software detects that the user selects the harmonic analysis function, pops up the harmonic data list subroutine, enters the harmonic data list interface, and transmits the waveform data in the corresponding recording channel to the subroutine.

[0122] (2) Select the harmonic frequency to be analyzed, click Generate Harmonic Data, and generate the harmonic amplitude and phase angle information in the list area on the right;

[0123] The harmonic frequency information is input into the subroutine, which performs Fourier decomposition on the data transmitted by the recording software and lists the decomposition results in a table according to amplitude and phase angle.

[0124] (3) Perform phase angle compensation based on harmonic phase angle information to facilitate observation of phase angle difference

[0125] According to the required phase angle compensation size, all phase angles are calculated uniformly to obtain the phase angle information after phase angle compensation, and updated in the list on the right.

[0126] Interaction scenes such as Figure 5 shown.

[0127] Effects such as Figure 6 As shown, the current flowing through the inductive impedance will cause the phase to lag by 90°, and the capacitive impedance is opposite, as shown in the figure below. Therefore, the direction of the harmonic current can be confirmed by combining the current phase information before and after.

[0128] The present invention can obtain the amplitude and phase angle of the harmonics of the specified frequency in the waveform measured by each measuring device, and the information can be statistically analyzed as follows: Figure 6 As shown in the figure, combined with the impedance characteristics, the harmonic transmission direction can be determined, which can effectively solve the problem of being unable to determine the harmonic transmission direction during the harmonic analysis process and help locate the harmonic source. Figure 3 Taking the two measuring points IDCH and IDLH as examples, IDCH lags behind IDLH by nearly 90°. Considering that the intermediate smoothing reactor is an inductive element, it can be seen that the harmonic current flows from the IDLH measuring point to the IDCH measuring point.

Claims

1. A harmonic analysis method applicable to a hybrid multi-terminal direct current transmission system, characterized in that: The following steps are involved: S1: In DC transmission projects, the voltage and current measuring points at different locations are recorded by a recording device; S2: Each recording corresponds to each recording information, and different recording channels can be formed according to the recording information; The recording information includes at least one of the recording start time, current, voltage, and sampling frequency; The recording channel is any one of the recording start time, current, voltage, and sampling frequency in the recording information; S3: Analyze harmonics: According to Shannon sampling theorem, the sampled information contains frequency information of 0.5 times the sampling frequency. Performing Fourier decomposition on each recorded information can obtain the analysis results of amplitude and phase angle information of different frequencies to form harmonic data. S4: Taking the Cos function with the initial moment of recording as the starting point as the reference vector, generate the recording phase angle information of the specified frequency, and automatically compensate the phase angle difference after Fourier decomposition for the recording information with different starting times; S5: Repeat steps S3-S4, and obtain the phase angle difference of voltage and current at different measuring points in the DC transmission project by increasing the amplitude and phase angle information of the designated frequency of the recording, and judge the transmission direction of the harmonic current in combination with the known impedance in the DC transmission system; When the recording to be analyzed is recorded in two or more recording information with different start times, the recording to be analyzed is in different recording information. The phase angle of recording 1 is δ, and the phase angle of recording 2 is &, where the phase angle δ is the angle obtained by Fourier decomposition of recording 1, and the phase angle & is the angle obtained by Fourier decomposition of recording 2; After Fourier decomposition, there will be a phase angle difference in the recorded phase angle, and the calculation method of the phase angle difference is: θ = 2πf (t1-t2), where t1 and t2 are the recording start time of the recorded information 1 and the recorded information 2 respectively; Recording 2 will automatically generate a phase angle value &'=&+θ based on the reference vector of recording information 1, thereby completing automatic phase angle compensation for different recording information; Select a certain waveform as the reference value to complete the phase angle compensation of the specified waveform; The recording channel includes a current recording channel; According to the phase angle information of the specified frequency of current recording channel 1 and current recording channel 2, combined with the impedance between the measuring points, the harmonic transmission direction is determined; The phase angle of current recording channel 1 is δ, the phase angle of current recording channel 2 is &, and the impedance is inductive or capacitive; If δ-&=90°, When the impedance between the measuring points is capacitive, the harmonic transmission direction is current 2 → current 1; When the impedance between the measuring points is inductive, the direction of harmonic transmission is current 1 → current 2; If δ-&=-90°, When the impedance between the measuring points is capacitive, the harmonic transmission direction is current 1 → current 2; When the impedance between the measuring points is inductive, the direction of harmonic transmission is Current 2 → Current 1.

2. The harmonic analysis method applicable to a hybrid multi-terminal direct current transmission system according to claim 1, characterized in that: The transmission direction of the harmonic current is presented in a harmonic data chart, which can be used to visually determine the direction of the harmonic current transmission and monitor the harmonic data at different locations in the DC transmission project.

3. An analysis system suitable for a hybrid multi-terminal direct current transmission system, characterized in that: The harmonic analysis method applicable to a hybrid multi-terminal direct current transmission system as described in any one of claims 1 to 2 comprises: a recording device bidirectionally connected to a server, a server, a harmonic analysis terminal, a recording device and a harmonic analysis terminal; the harmonic analysis terminal is used for at least one of phase angle compensation, harmonic analysis, forming a harmonic data chart, and harmonic source positioning.

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