Inter-harmonic source positioning and propagation path tracking method for multi-terminal flexible direct current system

Abstract

The invention discloses an inter-harmonic source positioning and propagation path tracking method for a multi-terminal flexible direct-current system. The method comprises the following steps: acquiring an electrical main wiring diagram of the multi-terminal flexible direct-current system, alternating-current side frequency of each converter station, rated capacity and voltage; when inter-harmonics are monitored to exceed the standard in the multi-terminal flexible direct current system, acquiring frequency and amplitude data of inter-harmonic components at the ports of the alternating current side and the direct current side of each converter station; determining a direct current side inter-harmonic frequency needing to be tracked by the multi-terminal flexible direct current system, determining an inter-harmonic frequency and amplitude corresponding to an alternating current side of each converter station, and determining a source station generating inter-harmonics in the multi-terminal flexible direct current system; obtaining current intermediate harmonic amplitude data of each direct current line of the multi-terminal flexible direct current system, and realizing propagation path tracking according to the amplitude of direct current side inter-harmonics needing to be tracked in each line. According to the method, inter-harmonic source positioning of the multi-terminal flexible direct current system is realized, and path tracking of inter-harmonics of the multi-terminal flexible direct current system in a direct current transmission network is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of multi-terminal flexible DC transmission systems, and particularly relates to a method for locating inter-harmonic sources and tracking propagation paths in a multi-terminal flexible DC system. Background Art

[0002] A multi-terminal flexible DC transmission system is an energy conversion and transmission system composed of multiple flexible DC converter stations connected by DC lines, and has technical advantages in aspects such as asynchronous grid interconnection, weak grid connection, flexible access of new energy, and island power supply. The core of a flexible DC converter station is a non-linear power electronic device, so a large amount of harmonics will be generated when the converter station operates; at the same time, the background harmonics in the AC side grid will cause harmonics of other frequencies to be generated on the AC side and DC side of the converter station after flowing into the converter station, and are transmitted to the AC sides of other converter stations in the multi-terminal flexible DC transmission system.

[0003] Multiple flexible DC transmission projects have reported low-frequency oscillation accidents caused by inter-harmonics in the background harmonics of the AC grid. For example, during the process of the increasing output of the wind farm in the South Australia three-terminal flexible DC transmission line located on South Australia Island, oscillations with a frequency of about 30 Hz were also observed. In a multi-terminal flexible DC transmission system, due to the strong coupling interaction between converter stations, the transmission path of inter-harmonics in the DC network is more complex. Summary of the Invention

[0004] The object of the present invention is to propose a method for locating inter-harmonic sources and tracking propagation paths in a multi-terminal flexible DC system, to achieve the location of inter-harmonic sources in a multi-terminal flexible DC system, and to achieve the path tracking of inter-harmonics in a multi-terminal flexible DC system in the DC transmission network.

[0005] The technical solution of the present invention is: a method for locating inter-harmonic sources and tracking propagation paths in a multi-terminal flexible DC system, including the following steps:

[0006] A. Obtain the electrical main wiring diagram of the multi-terminal flexible DC system, the frequencies, rated capacities, and voltages of the AC sides of each converter station;

[0007] B. After inter-harmonics are detected to exceed the standard in the multi-terminal flexible DC system, obtain the frequency and amplitude data of the inter-harmonic components at the AC side and DC side ports of each converter station;

[0008] C. Determine the inter-harmonic frequency on the DC side that needs to be tracked in the multi-terminal flexible DC system, determine the corresponding inter-harmonic frequencies and amplitudes on the AC side of each converter station, and determine the source station that generates inter-harmonics in the multi-terminal flexible DC system;

[0009] D. Obtain the inter-harmonic amplitude data in the current of each DC line in the multi-terminal flexible DC system, and realize the tracking of the propagation path according to the amplitudes of the inter-harmonics on the DC side to be tracked in each line.

[0010] Furthermore, in step A, the electrical main connection diagram of the multi-terminal flexible DC system, the AC-side frequency, rated capacity, and voltage of each converter station are obtained. The specific process is as follows:

[0011] First, obtain the electrical main connection diagram of the multi-terminal flexible DC system involved;

[0012] Then, number all the converter stations in the system;

[0013] Next, obtain the rated capacity Ssk, phase voltage value Usk, and frequency value fsk of the AC side of each converter station in the multi-terminal flexible DC system, where k = 1, 2,..., n.

[0014] Furthermore, in step B, when interharmonics exceed the standard in the multi-terminal flexible DC system, current data acquisition is required. The specific process is as follows:

[0015] First, monitor whether the interharmonics of the harmonic monitoring devices of one or more converter stations in the multi-terminal flexible DC system exceed the standard;

[0016] Then, after interharmonics exceed the standard, measure the three-phase current data at the AC-side ports of each converter station;

[0017] Finally, measure the current data at the DC-side ports of each converter station.

[0018] Furthermore, in step B, obtain the frequency and amplitude data of the interharmonic components at the AC-side ports of each converter station. The specific process is as follows:

[0019] First, select an appropriate window function and perform sliding window fast Fourier transform on the three-phase current data measured at the AC-side ports of each converter station;

[0020] Then, set the window width and sliding width according to the low-frequency interharmonic resolution;

[0021] Finally, obtain the frequency and amplitude of the interharmonic current at the AC ports of each converter station.

[0022] Furthermore, in step B, obtain the frequency and amplitude data of the interharmonic components at the DC-side ports of each converter station. The specific process is as follows:

[0023] First, perform sliding window fast Fourier transform on the DC current data measured at the DC-side ports of each converter station;

[0024] Then, set the window width and sliding width according to the low-frequency interharmonic resolution;

[0025] Finally, obtain the frequency and amplitude data of the interharmonic current at the DC ports of each converter station.

[0026] Further, step C determines the inter-harmonic frequencies between the DC sides that the multi-terminal flexible DC system needs to track, and the specific process is as follows:

[0027] First, obtain the magnitudes of the inter-harmonic currents at the AC and DC side ports of each converter station obtained in step B;

[0028] Then, based on the above data, determine that the inter-harmonic frequency between the DC sides that the multi-terminal flexible DC system needs to monitor is f ih ,

[0029] Finally, usually the inter-harmonic frequency value f ih is lower than the rated frequency value of the AC side of the converter station.

[0030] Further, step C determines the inter-harmonic frequencies and magnitudes corresponding to the AC side of each converter station, and the specific process is as follows:

[0031] First, according to the spectral shifting relationship between the inter-harmonics on the AC and DC sides of the flexible DC converter station, obtain the inter-harmonic frequency corresponding to the AC side of converter station s k as f ih ±f sk , that is, two dual frequencies;

[0032] Then, obtain the result of step B, and obtain the magnitudes of the two dual inter-harmonic currents on the AC side of converter station s k as I(f ih +f sk ) and I(f ih -f sk );

[0033] Next, calculate the sum of the squares of the currents of these two inter-harmonics in converter station s k ;

[0034] Finally, perform normalization processing to obtain the equivalent inter-harmonic current magnitude.

[0035] Further, step C determines the source station that generates inter-harmonics in the multi-terminal flexible DC system, and the specific process is as follows:

[0036] First, summarize, analyze, and compare the normalized equivalent inter-harmonic current magnitudes of all converter stations in the multi-terminal flexible DC system;

[0037] Then, the converter station with the largest normalized equivalent inter-harmonic current magnitude is identified as the source station that causes inter-harmonics in the multi-terminal flexible DC system.

[0038] Further, the background inter-harmonics in the AC power grid of the source station cause inter-harmonics to appear in the entire multi-terminal flexible DC system.

[0039] The beneficial effects of the present invention are as follows:

[0040] The present invention proposes a method for inter - harmonic source location and propagation path tracking among multi - terminal flexible DC systems, realizing the location of inter - harmonic sources among multi - terminal flexible DC systems and the path tracking of inter - harmonics in the DC transmission network among multi - terminal flexible DC systems.

[0041] The present invention solves the problem that in a multi - terminal flexible DC transmission system, due to the strong coupling interaction between converter stations, the transmission path of inter - harmonics in the DC network is complex and cannot be tracked. Brief Description of the Drawings

[0042] Figure 1 is the flowchart of the method of the present invention;

[0043] Figure 2 is the inter - harmonic characteristic diagram of each converter station in the present invention. Detailed Embodiment

[0044] Hereinafter, the present invention will be described in detail with reference to the drawings and embodiments:

[0045] As Figures 1 to 2 shown, a method for inter - harmonic source location and propagation path tracking among multi - terminal flexible DC systems includes the following steps:

[0046] A. Obtain the electrical main wiring diagram of the multi - terminal flexible DC system, the AC - side frequency, rated capacity, and voltage of each converter station;

[0047] B. After inter - harmonics exceeding the standard are detected in the multi - terminal flexible DC system, obtain the frequency and amplitude data of inter - harmonic components at the AC - side and DC - side ports of each converter station;

[0048] C. Determine the DC - side inter - harmonic frequency that needs to be tracked in the multi - terminal flexible DC system, determine the corresponding inter - harmonic frequency and amplitude at the AC - side of each converter station, and determine the source station that generates inter - harmonics in the multi - terminal flexible DC system;

[0049] D. Obtain the inter - harmonic amplitude data in the current of each DC line in the multi - terminal flexible DC system, and realize the propagation path tracking according to the amplitude of the DC - side inter - harmonics to be tracked in each line.

[0050] The specific process of step A for obtaining the electrical main wiring diagram of the multi - terminal flexible DC system, the AC - side frequency, rated capacity, and voltage of each converter station is as follows:

[0051] First, obtain the electrical main wiring diagram of the involved multi - terminal flexible DC system;

[0052] Then, number all the converter stations in the system;

[0053] Subsequently, obtain the rated capacity Ssk, phase voltage value Usk, and frequency value fsk of the AC side of each converter station in the multi-terminal flexible DC system, where k = 1, 2, …, n.

[0054] Step B: When interharmonics exceed the standard in the multi-terminal flexible DC system, current data acquisition is required. The specific process is as follows:

[0055] First, monitor whether the interharmonics of the harmonic monitoring device of one or more converter stations in the multi-terminal flexible DC system exceed the standard;

[0056] Then, after the interharmonics exceed the standard, measure the three-phase current data at the AC side ports of each converter station;

[0057] Finally, measure the current data at the DC side ports of each converter station.

[0058] In step B, obtain the frequency and amplitude data of the interharmonic components at the AC side ports of each converter station. The specific process is as follows:

[0059] First, select an appropriate window function and perform a sliding window fast Fourier transform on the three-phase current data measured at the AC side ports of each converter station;

[0060] Then, set the window width and sliding width according to the low-frequency interharmonic resolution;

[0061] Finally, obtain the frequency and amplitude of the interharmonic current at each AC port of the converter station.

[0062] In step B, obtain the frequency and amplitude data of the interharmonic components at the DC side ports of each converter station. The specific process is as follows:

[0063] First, perform a sliding window fast Fourier transform on the DC current data measured at the DC side ports of each converter station;

[0064] Then, set the window width and sliding width according to the low-frequency interharmonic resolution;

[0065] Finally, obtain the frequency and amplitude data of the interharmonic current at each DC port of the converter station.

[0066] Step C: Determine the DC side interharmonic frequency that the multi-terminal flexible DC system needs to track. The specific process is as follows:

[0067] First, obtain the amplitude magnitudes of the interharmonic currents at the AC side and DC side ports of each converter station obtained in step B;

[0068] Then, based on the above data, determine that the DC side interharmonic frequency that the multi-terminal flexible DC system needs to monitor is f ih ,

[0069] Finally, the interharmonic frequency value f ih is usually lower than the rated frequency value of the AC side of the converter station.

[0070] Step C determines the interharmonic frequency and amplitude corresponding to the AC side of each converter station, and the specific process is as follows:

[0071] First, according to the spectral shifting relationship between the interharmonics on the AC side and the DC side of the flexible DC converter station, the interharmonic frequency corresponding to the AC side of converter station s k is f ih ±f sk , that is, two dual frequencies;

[0072] Then, obtain the result of step B, and the amplitudes of the two dual interharmonic currents on the AC side of converter station s k are I(f ih +f sk ) and I(f ih -f sk );

[0073] Next, calculate the sum of the squares of the currents of these two interharmonics in converter station s k ;

[0074] Finally, perform normalization processing to obtain the equivalent interharmonic current amplitude.

[0075] Step C determines the source station that generates interharmonics in the multi-terminal flexible DC system, and the specific process is as follows:

[0076] First, summarize, analyze, and compare the normalized equivalent interharmonic current amplitudes of all converter stations in the multi-terminal flexible DC system;

[0077] Then, the converter station with the largest normalized equivalent interharmonic current amplitude is identified as the source station that causes interharmonics in the multi-terminal flexible DC system.

[0078] The background interharmonics in the AC power grid of the source station cause interharmonics to appear in the entire multi-terminal flexible DC system.

[0079] Specifically, in step A, all converter stations in the system are numbered as follows:

[0080] Assume that there are n converter stations in the multi-terminal flexible DC system involved, then the numbers of each converter station are s1, s2,..., sn in sequence

[0081] Specifically, the equivalent interharmonic current amplitude in step B is as follows:

[0082]

[0083] Specifically, in step D, the intermediate harmonic amplitude data of the DC currents of each DC line in the multi-terminal flexible DC system is obtained, and the propagation path is traced according to the amplitudes of the inter-harmonics between the DC sides to be tracked, as follows:

[0084] First, when the harmonic monitoring devices of one or more converter stations in the multi-terminal flexible DC system detect that the inter-harmonics exceed the standard, the current data of each DC line in the multi-terminal flexible DC system is measured.

[0085] Then, a suitable window function is selected to perform a sliding window fast Fourier transform on the current data measured for each DC line.

[0086] After that, the window width and the sliding width are set according to the low-frequency inter-harmonic resolution, and the inter-harmonic frequencies and amplitudes in the currents of each DC line are obtained.

[0087] After that, the amplitudes of the inter-harmonic currents with frequency f in each DC line of the multi-terminal flexible DC system are obtained. According to the magnitude relationship of the inter-harmonic currents with frequency f in each DC line and the electrical main wiring diagram of the multi-terminal flexible DC system. ih the inter-harmonic currents with frequency f ih and the electrical main wiring diagram of the multi-terminal flexible DC system.

[0088] Finally, taking the amplitudes of the inter-harmonics with frequency f ih in each DC line of the flexible DC system as the characteristics, the propagation path of the inter-harmonics in the DC network of the multi-terminal flexible DC system is judged.

[0089] The present invention proposes a method for locating the inter-harmonic source and tracing the propagation path in a multi-terminal flexible DC system, which realizes the location of the inter-harmonic source in the multi-terminal flexible DC system and the path tracing of the inter-harmonics in the DC transmission network of the multi-terminal flexible DC system.

[0090] The present invention solves the problem that in a multi-terminal flexible DC transmission system, due to the strong coupling interaction between converter stations, the transfer path of inter-harmonics in the DC network is complex and cannot be traced.

Claims

1. A method for inter-harmonic source location and propagation path tracing in a multi-terminal flexible DC system, characterized in that: It includes the following steps: A. Obtain the electrical main connection diagram of the multi-terminal flexible DC system, the AC side frequency, rated capacity, and voltage of each converter station; B. After detecting that the interharmonics exceed the standard in the multi-terminal flexible DC system, obtain the frequency and amplitude data of the interharmonic components at the AC side and DC side ports of each converter station; C. Determine the DC side interharmonic frequency that the multi-terminal flexible DC system needs to track, determine the corresponding interharmonic frequency and amplitude on the AC side of each converter station, and determine the source station of the interharmonics in the multi-terminal flexible DC system; D. Obtain the intermediate harmonic amplitude data of the currents in each DC line of the multi-terminal flexible DC system, and track the propagation path according to the amplitudes of the DC side interharmonics to be tracked on each line.

2. A method for inter-harmonic source localization and propagation path tracing between multi-terminal flexible DC systems according to claim 1, characterized in that: The specific process of step A for obtaining the electrical main connection diagram of the multi-terminal flexible DC system, the AC side frequency, rated capacity, and voltage of each converter station is as follows: First, obtain the electrical main connection diagram of the multi-terminal flexible DC system involved; Then, number all the converter stations in the system; After that, obtain the rated capacity Ssk, phase voltage value Usk, and frequency value fsk of the AC side of each converter station in the multi-terminal flexible DC system, where k = 1, 2,..., n.

3. A method for inter-harmonic source location and propagation path tracking in a multi-terminal flexible DC system according to claim 1, characterized in that: The specific process of current data acquisition is required in step B when it is detected that the interharmonics exceed the standard in the multi-terminal flexible DC system: First, monitor whether the interharmonics exceed the standard in the harmonic monitoring devices of one or more converter stations in the multi-terminal flexible DC system; Then, after the interharmonics exceed the standard, measure the three-phase current data at the AC side ports of each converter station; Finally, measure the current data at the DC side ports of each converter station.

4. A method for inter-harmonic source location and propagation path tracing between multi-terminal flexible DC systems according to claim 1, characterized in that: The specific process of obtaining the frequency and amplitude data of the interharmonic components at the AC side ports of each converter station in step B is as follows: First, select an appropriate window function and perform a sliding window fast Fourier transform on the three-phase current data measured at the AC side ports of each converter station; Then, set the window width and sliding width according to the low-frequency interharmonic resolution; Finally, obtain the frequency and amplitude of the interharmonic current at each AC port of the converter station.

5. A method for inter-harmonic source localization and propagation path tracking in a multi-terminal flexible DC system according to claim 1, characterized in that: The specific process of obtaining the frequency and amplitude data of the interharmonic components at the DC side ports of each converter station in step B is as follows: First, perform a sliding window fast Fourier transform on the DC current data measured at the DC side ports of each converter station; Then, set the window width and sliding width according to the low-frequency interharmonic resolution; Finally, obtain the frequency and amplitude data of the interharmonic current at each DC port of the converter station.

6. A method for interharmonic source location and propagation path tracking in a multi-terminal flexible DC system according to claim 1, characterized in that: The specific process of determining the DC side interharmonic frequency that the multi-terminal flexible DC system needs to track in step C is as follows: First, obtain the amplitudes of the interharmonic currents at the AC side and DC side ports of each converter station obtained in step B; Then, based on the above data, determine that the inter-harmonic frequency on the DC side that needs to be monitored in the multi-terminal flexible DC system is f ih , Finally, the interharmonic frequency value f of the DC side is usually ih lower than the rated frequency value of the AC side of the converter station.

7. A method for inter-harmonic source localization and propagation path tracking in a multi-terminal flexible DC system according to claim 1, characterized in that: The specific process of determining the corresponding interharmonic frequency and amplitude on the AC side of each converter station in step C is as follows: First, according to the spectral shifting relationship between the interharmonics on the AC side and the DC side of the flexible DC converter station, the converter station s is obtained. k The interharmonic frequency corresponding to the AC side is f. ih ±f sk , that is, two dual frequencies. Then, obtain the result of step B to get the converter station s k The amplitudes of the two interharmonic currents between the two pairs on the AC side are I(f ih +f sk ) and I(f ih -f sk ); Next, calculate the sum of the squares of the currents of these two interharmonics in converter station s k ; Finally, perform normalization processing to obtain the equivalent interharmonic current amplitude.

8. A method for inter-harmonic source location and propagation path tracking between multi-terminal flexible DC systems according to claim 1, characterized in that: The specific process of determining the source station of the interharmonics in the multi-terminal flexible DC system in step C is as follows: First, summarize, analyze, and compare the normalized equivalent interharmonic current amplitudes of all converter stations in the multi-terminal flexible DC system; Then, the converter station with the largest amplitude of the normalized equivalent interharmonic current is identified as the source station that causes interharmonics in the multi-terminal flexible DC system.

9. A method for interharmonic source localization and propagation path tracing between multi-terminal flexible DC systems according to claim 8, characterized in that: The background interharmonics in the AC power grid of the source station cause interharmonics to appear in the entire multi-terminal flexible DC system.

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