Constructing network parallel system harmonic wave anti-interference evaluation method and system considering frequency coupling

Abstract

The invention relates to the technical field of harmonic wave evaluation, and particularly discloses a follow-up network parallel system harmonic wave anti-interference evaluation method and system considering frequency coupling, and the method comprises the steps: obtaining grid-connected current data of a GFL converter and a GFM converter under different background harmonic waves, calculating the harmonic wave coupling admittance matrix of the GFL converter and the GFM converter, and calculating the harmonic wave coupling admittance matrix of the GFL converter and the GFM converter; obtaining a harmonic coupling admittance matrix of the parallel system at the common coupling point; calculating a power grid side harmonic coupling admittance matrix based on the harmonic coupling admittance matrix of the parallel system at the common coupling point and the power grid line impedance; and based on the power grid side harmonic coupling admittance matrix, calculating an evaluation index of the anti-background harmonic interference capability of the parallel system, and realizing evaluation of the harmonic anti-interference capability of the parallel system. According to the method, harmonic mutual impedance is introduced, the influence of harmonic coupling is fully considered, and the harmonic anti-interference capability evaluation precision is effectively improved in part of scenes.

Description

Technical Field

[0001] The present invention relates to the technical field of harmonic evaluation, and in particular to a method and system for evaluating harmonic interference immunity of a parallel network system taking frequency coupling into account. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Typical control modes for renewable energy can be categorized as grid-following (GFL) and grid-forming (GFM). GFL converters offer excellent dynamic response and high renewable energy utilization. Grid-forming control methods such as virtual synchronous machines enable GFM converters to exhibit dynamic characteristics similar to synchronous generators, exhibiting voltage source characteristics and possessing sufficient voltage, frequency, and inertia support capabilities. Due to the complementary strengths of GFL and GFM converters, parallel systems of grid-following / GFM converters, combining system support capabilities with high renewable energy utilization, are likely to become a mainstream form factor for future power grids.

[0004] Currently, research on grid-following and grid-forming parallel converter systems primarily focuses on ensuring stable operation. Existing research uses stability criteria to set the lower limit for the GFM converter's load. Flexible switching between the converter's GFL and GFM control modes allows for adaptability to varying grid strengths.

[0005] Compared to GFL converters, GFM converter current waveforms are less affected by voltage distortion. Therefore, increasing the proportion of GFM converters in parallel systems can effectively improve grid power quality. However, an excessively high proportion of GFM converters increases investment and construction costs and reduces renewable energy utilization. Existing capacity ratio setting methods primarily rely on stability criteria and phase margin assessment to determine the minimum GFM converter ratio that ensures system stability, ignoring the superiority of GFM converters in improving power quality.

[0006] For parallel systems of grid-following and grid-forming converters, existing technologies mainly evaluate their harmonic immunity capabilities by calculating the harmonic impedance or admittance of the grid-following and grid-forming converters. However, this ignores the impact of harmonic coupling on the evaluation results. In some scenarios, the degree of harmonic coupling can reach more than 30% (taking the fifth background harmonic voltage as an example, in addition to generating a fifth harmonic current of 1A, a seventh harmonic current of 0.3A is also generated). Ignoring this will cause the harmonic immunity capability evaluation results to be higher than the actual value, affecting the evaluation accuracy. Summary of the Invention

[0007] In order to solve the above problems, the present invention proposes a harmonic immunity evaluation method and system for a parallel grid system taking into account frequency coupling. The method fully considers the harmonic coupling effect, calculates the harmonic admittance matrix of the parallel system in combination with the voltage at the common coupling point, and uses the grid line impedance to correct the harmonic admittance matrix of the parallel system, thereby achieving an accurate evaluation of the parallel system's ability to resist background harmonic interference.

[0008] In some embodiments, the following technical solutions are adopted: A method for evaluating harmonic interference immunity of a parallel grid system taking frequency coupling into account includes: The grid-connected current data of the GFL converter and the GFM converter under different background harmonics are obtained respectively, and the harmonic coupling admittance matrix of the GFL converter and the GFM converter is calculated, and then the harmonic coupling admittance matrix of the parallel system at the common coupling point is obtained; Calculate the grid-side harmonic coupling admittance matrix based on the harmonic coupling admittance matrix of the parallel system at the common coupling point and the grid line impedance; Based on the grid-side harmonic coupling admittance matrix, an evaluation index of the parallel system's ability to resist background harmonic interference is calculated to implement an evaluation of the parallel system's harmonic immunity capability.

[0009] As a further solution, the capacity adjustment process for the grid-connected and grid-connected parallel systems is also included, specifically: Based on the harmonic components in the grid voltage and the total installed capacity of the parallel system, calculate the minimum anti-background harmonic interference capability evaluation index required to ensure the grid-connected power quality of the parallel system; The minimum GFM converter ratio required to meet the minimum anti-background harmonic interference capability evaluation index is calculated recursively.

[0010] The minimum background harmonic interference resistance evaluation index required to ensure the grid-connected power quality of the parallel system meets the following requirements: The minimum anti-background harmonic interference capability evaluation index shall not be less than the ratio of the harmonic voltage in the grid voltage to the set multiple of the total installed capacity of the parallel system.

[0011] As a further approach, the harmonic coupling admittance matrix of the parallel system at the common coupling point is calculated as , specifically: ; in, Y GFL is the harmonic coupling admittance matrix of the GFL converter, Y GFM is the harmonic coupling admittance matrix of the GFM converter, K M is the impact factor of parallel operation on the harmonic coupling admittance matrix of GFL and GFM converters,K L is the influence factor of output power on the harmonic coupling admittance matrix of GFL converter, is the number of GFM converters, and a is the total number of converters in the new energy station.

[0012] The influence factor of the output power on the harmonic coupling admittance matrix of the GFL converter is specifically: the ratio of the harmonic coupling admittance matrix of the GFL converter output power to the harmonic coupling admittance matrix of the GFL converter at rated power.

[0013] The impact factor of the parallel operation on the harmonic coupling admittance matrix of the GFL and GFM converters is specifically: the ratio of the harmonic coupling admittance matrix of the parallel system at the common coupling point to the sum of the harmonic coupling admittance matrices of the GFL converter and the GFM converter.

[0014] As a further solution, the grid-side harmonic coupling admittance matrix is calculated Y 'The method is: ; in, , 、 、 and They are the harmonic coupling admittance matrices of the parallel system at the common coupling point The corresponding elements in ; Z gm and Z gn They represent the impedance of the line to the mth and nth harmonic voltage disturbances respectively; the subscripts “m=6k+1” and “n=6k-1” are used to distinguish the harmonic frequencies, where k=0, 1, 2, …

[0015] The method for calculating the evaluation index of the parallel system's ability to resist background harmonic interference is as follows: When evaluating 6k-1 harmonic immunity: ; When evaluating the 6k+1 harmonic immunity capability: ; in, A h It is an evaluation index of the parallel system's ability to resist background harmonic interference, and h represents the harmonic number to be evaluated.

[0016] In other embodiments, the following technical solutions are adopted: A harmonic interference immunity evaluation system for a parallel grid system taking frequency coupling into account, comprising: A data acquisition module is configured to respectively acquire grid-connected current data of the GFL converter and the GFM converter under different background harmonics; a harmonic coupling admittance matrix calculation module configured to calculate the harmonic coupling admittance matrix of the GFL converter and the GFM converter, thereby obtaining the harmonic coupling admittance matrix of the parallel system at the common coupling point; and calculate the grid-side harmonic coupling admittance matrix based on the harmonic coupling admittance matrix of the parallel system at the common coupling point and the grid line impedance; The harmonic immunity evaluation module is configured to calculate the parallel system's background harmonic interference resistance evaluation index based on the grid-side harmonic coupling admittance matrix, thereby evaluating the parallel system's harmonic immunity.

[0017] In other embodiments, the following technical solutions are adopted: A terminal device includes a processor and a memory, wherein the processor is used to implement instructions; the memory is used to store multiple instructions, wherein the instructions are suitable for being loaded by the processor and executed by the above-mentioned harmonic interference immunity evaluation method for a parallel network system taking into account frequency coupling.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses the grid-side harmonic coupling admittance matrix to calculate the evaluation index of the parallel system's ability to resist background harmonic interference, introduces harmonic mutual impedance, and fully considers the influence of harmonic coupling. In some scenarios, the accuracy of harmonic anti-interference ability evaluation is effectively improved; at the same time, the influence of line parameters is taken into account, so that the proposed method can still maintain a good evaluation effect in scenarios with different line lengths.

[0019] (2) The present invention calculates the minimum anti-background harmonic interference capability required to ensure the grid-connected power quality of the parallel system, and then recursively calculates the minimum GFM converter ratio required to meet the anti-background harmonic interference capability requirement. The algorithm has a small amount of calculation and low requirements on equipment performance; and the obtained minimum GFM converter ratio can minimize investment and construction costs and maximize the utilization rate of new energy while ensuring the grid-connected power quality of the system.

[0020] (3) Compared with the traditional method that only considers the response characteristics between the voltage and current of harmonics of the same frequency, the present invention fully considers the multi-frequency coupling characteristics by introducing harmonic mutual admittance when calculating the harmonic anti-interference capability. It can more accurately evaluate the grid-connected power quality level of the grid-connected and grid-connected parallel systems, and minimize the loss of new energy utilization under the given harmonic constraints, providing a new technical solution for the capacity adjustment of the grid-connected and grid-connected parallel systems.

[0021] (4) When calculating the HCAM of a parallel system, the present invention proposes a phase alignment method, which significantly improves the calculation accuracy of HCAM.

[0022] Other features and advantages of additional aspects of the present invention will be given in part in the following description and in part will become obvious from the following description or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Flowchart of a method for evaluating harmonic interference immunity of a parallel grid-connected system taking frequency coupling into account in an embodiment of the present invention; Figure 2 Schematic diagram of the capacity adjustment process for the grid-following and grid-forming parallel systems according to an embodiment of the present invention; Figure 3 This is a diagram of the parallel system architecture for following the network and building the network in an embodiment of the present invention. DETAILED DESCRIPTION

[0024] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0025] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0026] Example 1 This embodiment follows the architecture of the grid / grid-type converter parallel system. Figure 3 As shown in the figure, both the GFL converter and the GFM converter adopt a three-phase two-level topology, connected to the common coupling point PCC via the LCL filter, and then connected to the line impedance Z g Connect to the AC grid.

[0027] Under this framework, this embodiment discloses a method for evaluating harmonic interference immunity of a parallel network system taking frequency coupling into account. Figure 1 , specifically including the following process: S101: Obtain grid-connected current data of the GFL converter and the GFM converter under different background harmonics respectively.

[0028] In this embodiment, the grid-connected current data of the GFL converter and the GFM converter under different background harmonics are obtained through frequency sweep tests. Specifically, the frequency sweep experiments are performed under no background harmonics and 6K±1 harmonics.

[0029] The grid connection point voltage and the grid connection current of the branch where the GFL converter and GFM converter are located are collected and calculated as U c 、 I c,GFL and I c,GFM The subscripts c=0, 6K±1 (K=0, 1, 2, …) are used to indicate the working conditions of the measured data; among them, c=0 indicates the measured data under the working conditions without background harmonics, and c=6K±1 indicates the measured data under the working conditions of 6K±1 subharmonics.

[0030] S102: Calculate the harmonic coupling admittance matrix of the GFL converter and the GFM converter, and then obtain the harmonic coupling admittance matrix of the parallel system at the common coupling point PCC.

[0031] In this embodiment, the specific process of calculating the harmonic coupling admittance matrix HCAM of the GFL converter is as follows: By performing Fourier decomposition on the grid-connected point voltage and the grid-connected current data of the measured GFL converter, the frequency domain components of the voltage and current data in the fundamental wave and 6K±1 harmonics are obtained, which are respectively calculated as U x，y and I x，y , the subscript x=0, 6K±1 is used to indicate the working conditions of the measured data (representing experiments without background harmonics or with 6K±1 background harmonics), and the subscript y=1, 6K±1 is used to indicate the corresponding frequency domain components (representing the fundamental component or the 6K±1 harmonic component after Fourier decomposition).

[0032] The measured data is phase aligned based on the frequency domain component (fundamental component) of the measured GFL converter grid-connected voltage signal at the fundamental wave. The specific method is as follows: First, perform vector rotation on the fundamental component of the voltage signal under each working condition so that the phase of the fundamental component after rotation is 0 degrees, and record the rotation angle φ h Then the frequency domain component (harmonic component) of the grid voltage signal under harmonics is vector-rotated, and the rotation angle is y* φ h For example, the frequency domain component of the grid voltage under the 5th harmonic needs to be rotated by 5*φ h .

[0033] By phase alignment, the calculation error of the harmonic coupling admittance matrix (HCAM) caused by asynchronous sampling time can be avoided.

[0034] Then, by taking the difference between the frequency domain components of the voltage and current measured under 6K±1 background harmonics and the frequency domain components of the voltage and current measured under no background harmonics, the changes in harmonic voltage and harmonic current are calculated as shown in formula (1): (1) in, It represents the frequency domain component of the voltage measured by the GFL converter under the 6K±1 background harmonic; It represents the frequency domain component of the voltage measured by the GFL converter without background harmonics; Indicates the change in harmonic voltage; It represents the frequency domain components of the current measured by the GFL converter under the 6K±1 background harmonics; Represents the frequency domain components of the current measured by the GFL converter without background harmonics; Indicates the change in harmonic current.

[0035] Then, based on formula (2), the harmonic coupling admittance matrix HCAM of the GFL converter is calculated by least square fitting. The specific fitting formula is as follows: (2) in, is the harmonic coupling admittance matrix HCAM of the GFL converter; and is the self-admittance, which reflects the response relationship between voltage and current at the same frequency (for example, Y 5,5 is the ratio of the 5th harmonic current response to the 5th harmonic voltage disturbance); and is the mutual admittance, which reflects the response relationship between voltage and current at different frequencies, and the frequency difference between the two is 100Hz (for example, Y 5,7 is the ratio of the 7th harmonic current response to the 5th harmonic voltage disturbance, and Y 7,5 is the ratio of the 5th harmonic current response to the 7th harmonic voltage disturbance).

[0036] and are the changes in the negative sequence (nth order) harmonic current and the positive sequence (mth order) harmonic current of the GFL converter, and are the changes in the negative-sequence harmonic voltage and positive-sequence harmonic voltage of the GFL converter, respectively. The subscripts "m=6k+1" and "n=6k-1" are used to distinguish harmonic frequencies, where k=0, 1, 2, .... n and m appear in pairs. When K=1, n=5 and m=7. The harmonic coupling admittance matrix is also solved in pairs. Taking K=1 as an example, the unknown quantity Y 5,5、Y 7,7 、Y 7,5 、Y 5,7 Four equations need to be solved. First, substitute the data obtained under the 5th background harmonic condition, and let I 5= I 5,5 、 I 7= I 5,7 、 V 5= U 5,5 、 V m = U 5,7 , thus we get two equations. Then we input the data obtained under the 7th background harmonic condition, let I 5= I 7,5 、 I 7= I 7,7 、 V 5= U 7,5 、 V m = U 7,7 , thus obtaining the remaining two equations, and then completing the calculation of the 5th and 7th harmonic coupling admittance matrices.

[0037] The specific process of calculating the harmonic coupling admittance matrix HCAM of the GFM converter is the same as the above process and will not be described in detail.

[0038] After calculating the harmonic coupling admittance matrix of the GFL converter and the GFM converter, the harmonic coupling admittance matrix of the parallel system at the common coupling point PCC is calculated, which is: (3) in, is the harmonic coupling admittance matrix HCAM of the parallel system, Y GFL is the harmonic coupling admittance matrix HCAM of the GFL converter, YGFM is the harmonic coupling admittance matrix HCAM of the GFM converter.

[0039] K M is the impact factor of parallel operation on HCAM of GFL and GFM converters. K L is the impact factor of output power on HCAM of GFL converter. a 1 is the number of GFM converters, and a is the total number of converters in the new energy station.

[0040] In this embodiment, the HCAM of the GFL converter is measured at different powers to calculate the influence factor of the output power on the HCAM of the GFL converter. K L , as shown in formula (4): (4) Where, Y GFLN is the HCAM of the GFL converter at rated power, Y GFL is the harmonic coupling admittance matrix HCAM of the GFL converter (at the current output power P). K L is the impact factor of output power on HCAM of GFL converter.

[0041] By measuring the HCAM of the parallel system and the HCAM of the GFL converter and GFM converter in single-machine operation, the impact factor of parallel operation on the HCAM of GFL and GFM converters is calculated. K M , as shown in formula (5): (5) in, Y M HCAM for parallel systems, Y GFL is the harmonic coupling admittance matrix HCAM of the GFL converter, Y GFM This is the GFM converter HCAM. K M is the impact factor of parallel operation on HCAM of GFL and GFM converters.

[0042] S103: Calculate the grid-side harmonic coupling admittance matrix based on the harmonic coupling admittance matrix of the parallel system at the common coupling point PCC and the grid line impedance.

[0043] Specifically, the grid line impedance is calculated by looking up the table based on the data sampling results. Zg .

[0044] The grid line impedance obtained by combining Z g As well as the HCAM of the parallel system at the point of common coupling PCC, the HCAM on the grid side is calculated as follows: (6) (7) Where, Characterize the HCAM of the parallel system from the grid side, Ign and Igm is the change of negative sequence (nth order) harmonic current and positive sequence (mth order) harmonic current of parallel system, Vgn and Vgm represents the change of the negative-sequence harmonic voltage and the positive-sequence harmonic voltage of the power grid, Zgm and Zgn represent the impedance of the line to the mth and nth harmonic voltage disturbances, respectively. 、 、 、 are the corresponding elements in the parallel system YM respectively, and the above variables are known quantities. The elements in are the quantities to be determined; the subscripts “m=6k+1” and “n=6k-1” are used to distinguish harmonic frequencies, where k=0, 1, 2, ….

[0045] S104: Based on the grid-side harmonic coupling admittance matrix, an evaluation index of the parallel system's ability to resist background harmonic interference is calculated to evaluate the parallel system's harmonic immunity capability.

[0046] In this embodiment, key variables are defined A h It is used to indicate the harmonic immunity capability of the parallel system. The specific calculation formula is as follows: When evaluating 6k-1 harmonic immunity: ; When evaluating the 6k+1 harmonic immunity capability: ; in, A h It is an evaluation index of the parallel system's ability to resist background harmonic interference, and h is the harmonic number to be evaluated.

[0047] Based on the evaluation index of the parallel system's ability to resist background harmonic interference, the parallel system's harmonic interference immunity is evaluated; the larger the index value, the stronger the system's interference immunity.

[0048] The parallel system harmonic immunity capability assessment method of this embodiment fully considers the multi-frequency coupling effect and introduces harmonic mutual impedance, which improves the harmonic immunity capability assessment accuracy by more than 20% in some scenarios.

[0049] Example 2 In this embodiment, based on the evaluation index calculated in Example 1, A h , perform capacity adjustment on the parallel systems of the grid and the grid-connected systems. The specific process is as follows: S201: Obtain the local grid voltage distortion through historical data and, in combination with relevant national standards, calculate the minimum anti-background harmonic interference capability required to ensure the grid-connected power quality of the parallel system. The specific calculation formula is as follows: (8) in, U h is the harmonic component in the local grid voltage, and the subscript h represents the harmonic order. S is the total installed capacity of the parallel system; k a is a constant, given in combination with the national standard. k a The lower it is, the higher the requirement for the parallel system's ability to resist background harmonic interference.

[0050] S202: If Figure 2 As shown, first assume that the number of GFM converters is 0, and then calculate the parallel system's ability to resist background harmonic interference by using the harmonic interference evaluation method of the parallel grid system taking into account frequency coupling in Example 1. By comparing it with the result obtained by formula (9) A hf to determine whether the power quality requirements are met.

[0051] If not, increase the number of GFM converters until the parallel system meets the requirements for background harmonic interference resistance. If so, output the current number of GFM converters. If all renewable energy converters in the renewable energy station are set to GFM control mode and still do not meet the grid power quality requirements, set all of them to GFM control mode.

[0052] The capacity calibration method for grid-connected and grid-connected parallel systems in this embodiment achieves the minimum GFM converter ratio while fully ensuring grid-connected power quality, thereby effectively reducing investment and construction costs and improving the utilization of renewable energy. Furthermore, this calibration method requires minimal computation and low computing equipment performance.

[0053] Example 3 In one or more embodiments, a harmonic interference immunity evaluation system for a parallel grid system taking frequency coupling into account is disclosed, comprising: A data acquisition module is configured to respectively acquire grid-connected current data of the GFL converter and the GFM converter under different background harmonics; a harmonic coupling admittance matrix calculation module configured to calculate the harmonic coupling admittance matrix of the GFL converter and the GFM converter, thereby obtaining the harmonic coupling admittance matrix of the parallel system at the common coupling point; and calculate the grid-side harmonic coupling admittance matrix based on the harmonic coupling admittance matrix of the parallel system at the common coupling point and the grid line impedance; The harmonic immunity evaluation module is configured to calculate the parallel system's background harmonic interference resistance evaluation index based on the grid-side harmonic coupling admittance matrix, thereby evaluating the parallel system's harmonic immunity.

[0054] The system capacity adjustment module is configured to adjust the capacity of the grid-connected and grid-connected parallel systems. Specifically: Based on the harmonic components in the grid voltage and the total installed capacity of the parallel system, calculate the minimum anti-background harmonic interference capability evaluation index required to ensure the grid-connected power quality of the parallel system; The minimum GFM converter ratio required to meet the minimum anti-background harmonic interference capability evaluation index is calculated recursively.

[0055] Among them, the minimum anti-background harmonic interference capability evaluation index required to ensure the grid-connected power quality of the parallel system meets the following requirements: the minimum anti-background harmonic interference capability evaluation index is not less than the ratio of the harmonic voltage in the grid voltage to the set multiple of the total installed capacity of the parallel system.

[0056] As a specific implementation method, the harmonic coupling admittance matrix of the parallel system at the common coupling point is calculated as follows: , specifically: ; in, Y GFL is the harmonic coupling admittance matrix of the GFL converter, Y GFM is the harmonic coupling admittance matrix of the GFM converter, K M is the impact factor of parallel operation on the harmonic coupling admittance matrix of GFL and GFM converters, K L is the influence factor of output power on the harmonic coupling admittance matrix of GFL converter, is the number of GFM converters, and a is the total number of converters in the new energy station.

[0057] As a specific implementation, the influence factor of the output power on the harmonic coupling admittance matrix of the GFL converter is specifically: the ratio of the harmonic coupling admittance matrix of the current output power of the GFL converter to the harmonic coupling admittance matrix of the GFL converter at rated power.

[0058] As a specific implementation, the impact factor of the parallel operation on the harmonic coupling admittance matrix of the GFL and GFM converters is specifically: the ratio of the harmonic coupling admittance matrix of the parallel system at the common coupling point to the sum of the harmonic coupling admittance matrices of the GFL converter and the GFM converter.

[0059] As a specific implementation method, the grid side harmonic coupling admittance matrix is calculated Y 'The method is: ; in, , 、 、 and They are the harmonic coupling admittance matrices of the parallel system at the common coupling point The corresponding elements in ; Z gm and Z gn They represent the impedance of the line to the mth and nth harmonic voltage disturbances respectively; the subscripts “m=6k+1” and “n=6k-1” are used to distinguish the harmonic frequencies, where k=0, 1, 2, …

[0060] As a specific implementation, the method for calculating the evaluation index of the parallel system's ability to resist background harmonic interference is: When evaluating 6k-1 harmonic immunity: ; When evaluating the 6k+1 harmonic immunity capability: ; in, A h It is an evaluation index of the parallel system's ability to resist background harmonic interference, and h is the harmonic number to be evaluated.

[0061] It should be noted that the specific implementation of the above modules is the same as that in Example 1 and will not be described in detail.

[0062] Example 4 In one or more embodiments, a terminal device is disclosed, comprising a processor and a memory, wherein the processor is configured to implement instructions; and the memory is configured to store a plurality of instructions, wherein the instructions are suitable for being loaded by the processor and executed by the method for evaluating harmonic interference immunity of a parallel network system taking into account frequency coupling described in Example 1.

[0063] It should be understood that in this embodiment, the processor may be a central processing unit (CPU), or may be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), off-the-shelf field-programmable gate arrays (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or any conventional processor, etc.

[0064] The memory may include a read-only memory and a random access memory, and provides instructions and data to the processor. A portion of the memory may also include a non-volatile random access memory. For example, the memory may also store information about the device type.

[0065] During implementation, each step of the above method may be completed by an integrated logic circuit of hardware in a processor or by instructions in the form of software.

[0066] The specific implementation of the method in this embodiment is the same as that in the first embodiment and will not be described in detail.

[0067] Although the above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without any creative work are still within the scope of protection of the present invention.

Claims

1. A method for evaluating harmonic interference immunity of a parallel grid system taking into account frequency coupling, characterized in that: include: The grid-connected current data of the GFL converter and the GFM converter under different background harmonics are obtained respectively, and the harmonic coupling admittance matrix of the GFL converter and the GFM converter is calculated, and then the harmonic coupling admittance matrix of the parallel system at the common coupling point is obtained; Calculate the grid-side harmonic coupling admittance matrix based on the harmonic coupling admittance matrix of the parallel system at the common coupling point and the grid line impedance; Based on the grid-side harmonic coupling admittance matrix, an evaluation index of the parallel system's ability to resist background harmonic interference is calculated to achieve an evaluation of the parallel system's harmonic immunity.

2. The method for evaluating harmonic interference immunity of a parallel grid system taking frequency coupling into account according to claim 1, wherein: It also includes the process of capacity adjustment for the grid-following and grid-connected parallel systems, specifically: Based on the harmonic components in the grid voltage and the total installed capacity of the parallel system, calculate the minimum anti-background harmonic interference capability evaluation index required to ensure the grid-connected power quality of the parallel system; The minimum GFM converter ratio required to meet the minimum anti-background harmonic interference capability evaluation index is calculated recursively.

3. The method for evaluating harmonic interference immunity of a parallel grid system taking frequency coupling into account according to claim 2, wherein: The minimum background harmonic interference resistance evaluation index required to ensure the grid-connected power quality of the parallel system meets the following requirements: The minimum anti-background harmonic interference capability evaluation index shall not be less than the ratio of the harmonic voltage in the grid voltage to the set multiple of the total installed capacity of the parallel system.

4. The method for evaluating harmonic interference immunity of a parallel grid system taking frequency coupling into account according to claim 1, wherein: Calculate the harmonic coupling admittance matrix of a parallel system at the common coupling point , specifically: ； in, Y GFL is the harmonic coupling admittance matrix of the GFL converter, Y GFM is the harmonic coupling admittance matrix of the GFM converter, K M is the impact factor of parallel operation on the harmonic coupling admittance matrix of GFL and GFM converters, K L is the influence factor of output power on the harmonic coupling admittance matrix of GFL converter, is the number of GFM converters, and a is the total number of converters in the new energy station.

5. The method for evaluating harmonic interference immunity of a parallel grid system taking frequency coupling into account according to claim 4, wherein: The influence factor of the output power on the harmonic coupling admittance matrix of the GFL converter is specifically: the ratio of the harmonic coupling admittance matrix of the current output power of the GFL converter to the harmonic coupling admittance matrix of the GFL converter at rated power.

6. The method for evaluating harmonic interference immunity of a parallel grid system taking frequency coupling into account according to claim 4, wherein: The impact factor of the parallel operation on the harmonic coupling admittance matrix of the GFL and GFM converters is specifically: the ratio of the harmonic coupling admittance matrix of the parallel system at the common coupling point to the sum of the harmonic coupling admittance matrices of the GFL converter and the GFM converter.

7. The method for evaluating harmonic interference immunity of a parallel grid system taking frequency coupling into account according to claim 1, wherein: Calculate the grid-side harmonic coupling admittance matrix Y 'The method is: ； in, , 、 、 and They are the harmonic coupling admittance matrices of the parallel system at the common coupling point The corresponding elements in ; Z gm and Z gn They represent the impedance of the line to the mth and nth harmonic voltage disturbances respectively; the subscripts "m=6k+1" and "n=6k-1" are used to distinguish the harmonic frequencies, where k=0, 1, 2, … 8. The method for evaluating harmonic interference immunity of a parallel grid system taking frequency coupling into account according to claim 7, wherein: The method for calculating the evaluation index of the parallel system's ability to resist background harmonic interference is: When evaluating 6k-1 harmonic immunity: ; When evaluating the 6k+1 harmonic immunity capability: ; in, A h It is an evaluation index of the parallel system's ability to resist background harmonic interference, and h represents the harmonic number to be evaluated.

9. A harmonic interference immunity evaluation system for a parallel grid system taking frequency coupling into account, characterized in that: include: A data acquisition module is configured to respectively acquire grid-connected current data of the GFL converter and the GFM converter under different background harmonics; a harmonic coupling admittance matrix calculation module configured to calculate the harmonic coupling admittance matrix of the GFL converter and the GFM converter, thereby obtaining the harmonic coupling admittance matrix of the parallel system at the common coupling point; Calculate the grid-side harmonic coupling admittance matrix based on the harmonic coupling admittance matrix of the parallel system at the common coupling point and the grid line impedance; The harmonic immunity evaluation module is configured to calculate the parallel system's background harmonic interference resistance evaluation index based on the grid-side harmonic coupling admittance matrix, thereby evaluating the parallel system's harmonic immunity.

10. A terminal device comprising a processor and a memory, wherein the processor is used to implement instructions; the memory is used to store multiple instructions, characterized in that: The instructions are suitable for being loaded by a processor and executed by the harmonic interference immunity evaluation method for a parallel grid system taking into account frequency coupling as described in any one of claims 1-8.

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