Harmonic immunity assessment method and system for parallel grid systems considering frequency coupling

Abstract

This invention relates to the field of harmonic assessment technology, specifically disclosing a method and system for assessing harmonic immunity of a parallel grid system considering frequency coupling. The method includes: acquiring grid-connected current data for GFL and GFM converters under different background harmonics; calculating the harmonic coupling admittance matrices of the GFL and GFM converters to obtain the harmonic coupling admittance matrix of the parallel system at the common coupling point; calculating 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; and calculating the assessment index of the parallel system's ability to resist background harmonic interference based on the grid-side harmonic coupling admittance matrix, thereby achieving the assessment of the harmonic immunity of the parallel system. This invention introduces harmonic mutual impedance, fully considering the influence of harmonic coupling, and effectively improves the accuracy of harmonic immunity assessment in some scenarios.

Description

Technical Field

[0001] This invention relates to the field of harmonic assessment technology, and in particular to a method and system for assessing harmonic immunity in a parallel grid system that takes into account frequency coupling. Background Technology

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

[0003] Typical control modes for renewable energy can be divided into two categories: grid-following (GFL) and grid-forming (GFM). GFL converters have good dynamic response performance and high renewable energy utilization rate. Grid-forming control methods such as virtual synchronous machines enable GFM converters to exhibit dynamic characteristics similar to synchronous generators and voltage source characteristics, possessing certain voltage, frequency, and inertia support capabilities. Due to the complementary advantages of GFL and GFM converters, parallel systems of grid-following / GFM converters, which combine system support capabilities with high renewable energy utilization rate, may become one of the mainstream forms of future power grids.

[0004] Currently, research on grid-connected and grid-connected converter parallel systems mainly focuses on system stability. Existing research utilizes stability criteria to set the lower limit of the GFM converter's proportion, and allows for flexible switching between GFL / GFM control modes to adapt to the system's stability requirements under different grid intensities.

[0005] Compared to GFL converters, GFM converters are less affected by voltage distortion in their current waveform. Therefore, increasing the proportion of GFM converters in parallel systems can effectively improve grid-connected power quality; however, an excessively high GFM converter proportion will increase investment and construction costs and reduce the utilization rate of renewable energy. Current capacity matching settings mainly obtain the minimum GFM converter proportion that ensures system stability through stability criteria and phase margin assessments, neglecting the superior performance of GFM converters in improving power quality.

[0006] For grid-connected and grid-connected converter parallel systems, existing technologies mainly evaluate their harmonic immunity by calculating the harmonic impedance or admittance of the grid-connected and grid-connected converters. However, the impact of harmonic coupling on the evaluation results is ignored. 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 1A fifth harmonic current, it will also generate a 0.3A seventh harmonic current). Ignoring this will make the harmonic immunity evaluation result higher than the actual value, affecting the evaluation accuracy. Summary of the Invention

[0007] To address the aforementioned issues, this invention proposes a harmonic immunity assessment method and system for parallel grid systems that takes into account frequency coupling. This method fully considers the harmonic coupling effect, calculates the harmonic admittance matrix of the parallel system by combining the voltage at the common coupling point, and corrects the harmonic admittance matrix of the parallel system using the power grid line impedance, thereby achieving an accurate assessment of the parallel system's ability to resist background harmonic interference.

[0008] In some implementations, the following technical solutions are adopted:

[0009] A harmonic immunity assessment method for a parallel grid system considering frequency coupling includes:

[0010] The grid-connected current data of GFL converter and GFM converter under different background harmonics were obtained respectively. The harmonic coupling admittance matrix of GFL converter and GFM converter was calculated, and then the harmonic coupling admittance matrix of the parallel system at the common coupling point was obtained.

[0011] Based on the harmonic coupling admittance matrix of the parallel system at the common coupling point and the power grid line impedance, calculate the harmonic coupling admittance matrix on the power grid side.

[0012] Based on the harmonic coupling admittance matrix on the power grid side, the evaluation index of the parallel system's ability to resist background harmonic interference is calculated, thereby realizing the evaluation of the harmonic immunity of the parallel system.

[0013] As a further solution, the process of capacity tuning for parallel systems connected to the network and those in the network structure is also included, specifically:

[0014] Based on the harmonic components in the grid voltage and the total installed capacity of the parallel system, calculate the minimum background harmonic interference immunity evaluation index required to ensure the grid-connected power quality of the parallel system;

[0015] The minimum GFM converter ratio required to meet the minimum background harmonic interference immunity assessment index is calculated recursively.

[0016] The minimum background harmonic interference immunity evaluation index required to ensure the grid-connected power quality of the parallel system satisfies the following:

[0017] The minimum evaluation index for background harmonic interference immunity shall not be less than the ratio of the harmonic voltage in the grid voltage to the total installed capacity of the parallel system by a set multiple.

[0018] As a further approach, the harmonic coupling admittance matrix of the parallel system at the common coupling point is calculated. Specifically:

[0019] ;

[0020] in, Y GFLHere is the harmonic coupling admittance matrix of the GFL converter. Y GFM Here is the harmonic coupling admittance matrix of the GFM converter. K M The impact factors of parallel operation on the harmonic coupling admittance matrix of GFL and GFM converters. K L The effect of output power on the harmonic coupling admittance matrix of the GFL converter is given by the following factor. denoted as 'gf', where 'a' represents the total number of GFM converters in the renewable energy power plant.

[0021] 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 output power of the GFL converter to the harmonic coupling admittance matrix of the GFL converter at rated power.

[0022] The influence factor of parallel operation on the harmonic coupling admittance matrix of 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.

[0023] As a further approach, the harmonic coupling admittance matrix on the grid side is calculated. Y The method is as follows:

[0024] ;

[0025] in, , , , and These are the harmonic coupling admittance matrices of the parallel system at the common coupling point. The corresponding element in; Z gm and Z gn These represent the line impedance to the m-th and n-th 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,...

[0026] The method for calculating the evaluation index of the anti-background harmonic interference capability of the parallel system is as follows:

[0027] When evaluating the immunity to the 6k-1st harmonic: ;

[0028] When evaluating the immunity to the 6k+1th harmonic: ;

[0029] in, Ah h is an evaluation index for the ability of a parallel system to resist background harmonic interference, where h represents the harmonic order to be evaluated.

[0030] In other embodiments, the following technical solutions are adopted:

[0031] A harmonic immunity assessment system for a parallel grid system considering frequency coupling, comprising:

[0032] The data acquisition module is configured to acquire grid-connected current data of GFL converter and GFM converter under different background harmonics, respectively.

[0033] The harmonic coupling admittance matrix calculation module is 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; based on the harmonic coupling admittance matrix of the parallel system at the common coupling point and the power grid line impedance, the harmonic coupling admittance matrix on the power grid side is calculated.

[0034] The harmonic immunity assessment module is configured to calculate the evaluation index of the parallel system's ability to resist background harmonic interference based on the grid-side harmonic coupling admittance matrix, thereby realizing the assessment of the harmonic immunity of the parallel system.

[0035] In other embodiments, the following technical solutions are adopted:

[0036] A terminal device includes a processor and a memory, the processor being used to implement instructions; the memory being used to store multiple instructions adapted to be loaded and executed by the processor to perform the above-described harmonic interference immunity assessment method for a parallel network system considering frequency coupling.

[0037] Compared with the prior art, the beneficial effects of the present invention are:

[0038] (1) This invention uses the harmonic coupling admittance matrix of the power grid side to calculate the evaluation index of the ability of the parallel system to resist background harmonic interference. It introduces harmonic mutual impedance and fully considers the influence of harmonic coupling. In some scenarios, the accuracy of harmonic interference resistance evaluation is effectively improved. At the same time, the influence of line parameters is considered, so that the proposed method still maintains a good evaluation effect in different line length scenarios.

[0039] (2) This invention calculates the minimum background harmonic interference resistance required to ensure the grid-connected power quality of the parallel system, and then calculates the minimum GFM converter ratio required to meet the background harmonic interference resistance requirement by recursion. The algorithm has a small computational load and low requirements for equipment performance. Furthermore, the obtained minimum GFM converter ratio can minimize the investment and construction costs and maximize the utilization rate of new energy sources while ensuring the grid-connected power quality of the system.

[0040] (3) Compared with traditional methods that only consider the response characteristics between harmonic voltage and current at the same frequency, this invention introduces harmonic mutual admittance when calculating harmonic immunity, fully considers multi-frequency coupling characteristics, can more accurately evaluate the grid-connected power quality level of grid-connected and grid-connected systems, and minimize the loss of new energy utilization rate under given harmonic constraints, providing a new technical solution for capacity setting of grid-connected and grid-connected systems.

[0041] (4) In calculating the HCAM of a parallel system, the present invention proposes a phase alignment method, which significantly improves the calculation accuracy of HCAM.

[0042] Other features and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0043] Figure 1 This is a flowchart of the harmonic interference immunity assessment method for a parallel grid system considering frequency coupling in an embodiment of the present invention.

[0044] Figure 2 This is a schematic diagram illustrating the capacity tuning process for the parallel system of the grid and the network in an embodiment of the present invention;

[0045] Figure 3 This is a diagram of the parallel system architecture of the network and the network structure in an embodiment of the present invention. Detailed Implementation

[0046] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0047] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0048] Example 1

[0049] The architecture of this embodiment, which is connected in parallel with a grid / grid-type converter, is as follows: Figure 3 As shown, both the GFL converter and the GFM converter adopt a three-phase two-level topology, connected to the common coupling point PCC via an LCL filter, and then through the line impedance Z. g Connect to the AC power grid.

[0050] Under this architecture, this embodiment discloses a harmonic immunity assessment method for a parallel network system considering frequency coupling, combined with... Figure 1 Specifically, it includes the following processes:

[0051] S101: Obtain grid-connected current data for GFL converter and GFM converter under different background harmonics.

[0052] In this embodiment, grid-connected current data of the GFL converter and GFM converter under different background harmonics are obtained through frequency sweep testing. Specifically, frequency sweep experiments are performed under no background harmonics and under 6K±1 harmonics.

[0053] The grid connection point voltage and the grid connection current of the branches where the GFL and GFM converters are located are collected and calculated as follows: U c , I c,GFL and I c,GFM The subscripts c=0 and 6K±1 (K=0,1,2,…) are used to indicate the operating conditions under which the measured data are located; where c=0 indicates the measured data under the condition of no background harmonics, and c=6K±1 indicates the measured data under the condition of the 6K±1th harmonic.

[0054] 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.

[0055] In this embodiment, the specific process for calculating the harmonic coupling admittance matrix HCAM of the GFL converter is as follows:

[0056] By performing Fourier decomposition on the grid-connected voltage and the measured grid-connected current data of the GFL converter, the frequency domain components of the voltage and current data in the fundamental and 6K±1 harmonics were obtained, and were respectively denoted as... U x，y and I x，y The subscripts x=0 and 6K±1 are used to indicate the operating conditions under which the measured data is conducted (representing the experiment conducted under no background harmonics or under 6K±1 background harmonics), and the subscripts y=1 and 6K±1 are used to indicate the corresponding frequency domain components (representing the fundamental component or the 6K±1 harmonic component after Fourier decomposition).

[0057] The measured data are phase-aligned using the frequency domain component (fundamental component) of the measured grid-connected voltage signal of the GFL converter at the fundamental frequency as a reference. The specific method is as follows:

[0058] First, the fundamental component of the voltage signal under each operating condition is vector-rotated so that the phase of the fundamental component is 0 degrees after rotation, and the rotation angle is recorded. φ h Then, the frequency domain components (harmonic components) of the grid-connected voltage signal under harmonic conditions are vector-rotated by an angle of y*. φ h For example, the frequency domain component of the grid-connected voltage under the 5th harmonic needs to be rotated by 5*φ. h .

[0059] Phase alignment can avoid the calculation error of the harmonic coupling admittance matrix (HCAM) caused by asynchronous sampling time.

[0060] Then, by subtracting the frequency domain components of the voltage and current measured under 6K±1 background harmonics from the frequency domain components of the voltage and current measured without background harmonics, the changes in harmonic voltage and harmonic current are calculated as shown in equation (1):

[0061] (1)

[0062] in, This represents the frequency domain component of the voltage measured by the GFL converter under 6K±1 background harmonics. This represents the frequency domain component of the voltage measured by the GFL converter in the absence of background harmonics. This indicates the amount of change in harmonic voltage; This represents the frequency domain component of the current measured by the GFL converter under 6K±1 background harmonics. This represents the frequency domain component of the current measured by the GFL converter in the absence of background harmonics. It represents the change in harmonic current.

[0063] Furthermore, based on equation (2), the harmonic coupling admittance matrix HCAM of the GFL converter is calculated by least squares fitting. The specific fitting formula is as follows:

[0064] (2)

[0065] in, HCAM is the harmonic coupling admittance matrix of the GFL converter;

[0066] and Self-admittance reflects the response relationship between voltage and current at the same frequency (e.g., Y 5,5 (This is the ratio of the 5th harmonic current response to the 5th harmonic voltage disturbance). and Mutual admittance reflects the response relationship between voltage and current at different frequencies, with a frequency difference of 100Hz (e.g., Y 5,7 This is the ratio of the 7th harmonic current response to the 5th harmonic voltage disturbance, whileY 7,5 (This is the ratio of the 5th harmonic current response to the 7th harmonic voltage disturbance).

[0067] and These represent the changes in the negative sequence (nth) harmonic current and the positive sequence (mth) harmonic current of the GFL converter, respectively. and These represent the changes in negative-sequence and positive-sequence harmonic voltages 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 The solution requires four equations. First, substitute the data obtained under the 5th background harmonic condition, and let... I 5= I 5,5 , I 7= I 5,7 ,

[0068] V 5= U 5,5 , V m = U 5,7 This yields two equations. Then, by incorporating 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 7,7This yields the remaining two equations, which are then used to calculate the 5th and 7th harmonic coupling admittance matrices.

[0069] The specific process for calculating the harmonic coupling admittance matrix (HCAM) of the GFM converter is the same as described above and will not be detailed here again.

[0070] After calculating the harmonic coupling admittance matrices of the GFL and GFM converters, the harmonic coupling admittance matrix of the parallel system at the common coupling point PCC is calculated as follows:

[0071] (3)

[0072] in, HCAM is the harmonic coupling admittance matrix of a parallel system. Y GFL HCAM is the harmonic coupling admittance matrix of the GFL converter. Y GFM HCAM is the harmonic coupling admittance matrix of the GFM converter.

[0073] K M The impact factors of parallel operation on GFL and GFM converter HCAM. K L The output power is the HCAM effect factor of the GFL converter. a 1 represents the number of GFM converters, and a represents the total number of converters in the new energy power station.

[0074] In this embodiment, the influence factor of output power on the HCAM of the GFL converter is calculated by measuring the HCAM of the GFL converter under different power levels. K L Specifically, as shown in equation (4):

[0075] (4)

[0076] In the formula, Y GFLN HCAM for GFL converter at rated power. Y GFL HCAM is the harmonic coupling admittance matrix of the GFL converter (at the current output power P). K L The output power is the HCAM effect factor of the GFL converter.

[0077] By measuring the HCAM of the parallel system and the HCAM of the GFL and GFM converters during stand-alone operation, the influence factor of parallel operation on the HCAM of the GFL and GFM converters is calculated. K MSpecifically, as shown in equation (5):

[0078] (5)

[0079] in, Y M HCAM for parallel systems, Y GFL HCAM is the harmonic coupling admittance matrix of the GFL converter. Y GFM For GFM converters HCAM. K M The impact factors of parallel operation on GFL and GFM converter HCAM.

[0080] S103: Calculate the harmonic coupling admittance matrix on the grid side based on the harmonic coupling admittance matrix of the parallel system at the common coupling point PCC and the grid line impedance.

[0081] Specifically, the impedance of the power grid lines is calculated by looking up tables based on the data sampling results. Z g .

[0082] The combined impedance of the power grid lines Z g And the HCAM of the parallel system at the point of common coupling (PCC), the HCAM on the grid side is calculated as follows:

[0083] (6)

[0084] (7)

[0085] In the formula, HCAM characterizing a parallel system from the network side. Ign and Igm represents the change in negative-sequence (nth) harmonic current and positive-sequence (mth) harmonic current in a parallel system, respectively. Vgn and Vgm represents the changes in negative-sequence harmonic voltage and positive-sequence harmonic voltage of the power grid, respectively, while Zgm and Zgn represent the impedance of the line to the m-th and n-th harmonic voltage disturbances, respectively. , , , These are the corresponding elements in the parallel system YM, and the above variables are known quantities. Each element in the table represents a variable to be determined; the subscripts “m=6k+1” and “n=6k-1” are used to distinguish harmonic frequencies, where k=0,1,2,…

[0086] S104: Based on the harmonic coupling admittance matrix of the power grid side, calculate the evaluation index of the parallel system's ability to resist background harmonic interference, and realize the evaluation of the harmonic immunity of the parallel system.

[0087] In this embodiment, key variables are defined. A h The specific calculation formula used to represent the harmonic immunity of a parallel system is as follows:

[0088] When evaluating the immunity to the 6k-1st harmonic: ;

[0089] When evaluating the immunity to the 6k+1th harmonic: ;

[0090] in, A h h is the evaluation index for the ability of a parallel system to resist background harmonic interference, where h is the harmonic order to be evaluated.

[0091] Based on the evaluation index of the background harmonic interference resistance capability of parallel systems, the harmonic interference resistance capability of parallel systems can be evaluated; the larger the index value, the stronger the system's interference resistance capability.

[0092] The method for evaluating the harmonic immunity of parallel systems in this embodiment fully considers the multi-frequency coupling effect. By introducing harmonic mutual impedance, the accuracy of harmonic immunity evaluation can be improved by more than 20% in some scenarios.

[0093] Example 2

[0094] In this embodiment, the evaluation index is based on the one calculated in Embodiment 1. A h The capacity tuning process for parallel systems connected to the grid and those in the network is as follows:

[0095] S201: Obtain local power grid voltage distortion data through historical data, and calculate the minimum background harmonic interference immunity required to ensure the grid-connected power quality of the parallel system, in accordance with relevant national standards. The specific calculation formula is as follows:

[0096] (8)

[0097] in, U h This represents the harmonic components in the local power grid voltage, with the subscript h indicating the harmonic order. S This represents the total installed capacity of the parallel system. k a It is a constant, given in accordance with national standards. k a The lower the value, the higher the requirement for the parallel system to resist background harmonic interference.

[0098] S202: As Figure 2 As shown, it is first assumed that the number of GFM converters is 0. Then, the harmonic immunity assessment method of the parallel system considering frequency coupling in Example 1 is used to calculate the background harmonic interference immunity of the parallel system. The result obtained by comparing with equation (9) is... A hf The lower limit is compared to determine whether the power quality requirements are met.

[0099] If the requirements are not met, the number of GFM converters will be increased until the requirements for the parallel system's ability to resist background harmonic interference are met. If the requirements are met, the number of GFM converters at this point will be output. If setting all renewable energy converters in the renewable energy power station to GFM control mode still does not meet the grid-connected power quality requirements, then all of them will be set to GFM control mode.

[0100] The grid-connected and parallel-connected system capacity setting method in this embodiment obtains the minimum GFM converter ratio while fully ensuring the power quality of the grid-connected system, thereby effectively reducing investment and construction costs and improving the utilization rate of new energy sources. Furthermore, the setting method involves minimal computation and has low requirements for computing equipment performance.

[0101] Example 3

[0102] In one or more embodiments, a harmonic immunity assessment system for a parallel grid system considering frequency coupling is disclosed, comprising:

[0103] The data acquisition module is configured to acquire grid-connected current data of GFL converter and GFM converter under different background harmonics, respectively.

[0104] The harmonic coupling admittance matrix calculation module is 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; based on the harmonic coupling admittance matrix of the parallel system at the common coupling point and the power grid line impedance, the harmonic coupling admittance matrix on the power grid side is calculated.

[0105] The harmonic immunity assessment module is configured to calculate the evaluation index of the parallel system's ability to resist background harmonic interference based on the grid-side harmonic coupling admittance matrix, thereby realizing the assessment of the harmonic immunity of the parallel system.

[0106] The system capacity tuning module is configured to perform capacity tuning for grid-connected and grid-connected parallel systems, specifically as follows:

[0107] Based on the harmonic components in the grid voltage and the total installed capacity of the parallel system, calculate the minimum background harmonic interference immunity evaluation index required to ensure the grid-connected power quality of the parallel system;

[0108] The minimum GFM converter ratio required to meet the minimum background harmonic interference immunity assessment index is calculated recursively.

[0109] The minimum background harmonic interference immunity assessment index required to ensure the grid-connected power quality of the parallel system satisfies the following: the minimum background harmonic interference immunity assessment index is not less than the ratio of the harmonic voltage in the grid voltage to the total installed capacity of the parallel system by a set multiple.

[0110] As a specific implementation method, the harmonic coupling admittance matrix of the parallel system at the common coupling point is calculated. Specifically:

[0111] ;

[0112] in, Y GFL Here is the harmonic coupling admittance matrix of the GFL converter. Y GFM Here is the harmonic coupling admittance matrix of the GFM converter. K M The impact factors of parallel operation on the harmonic coupling admittance matrix of GFL and GFM converters. K L The effect of output power on the harmonic coupling admittance matrix of the GFL converter is given by the following factor. denoted as 'gf', where 'a' represents the total number of GFM converters in the renewable energy power plant.

[0113] As a specific implementation method, 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 at the current output power to the harmonic coupling admittance matrix of the GFL converter at the rated power.

[0114] As a specific implementation method, the influence 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.

[0115] As a specific implementation method, the harmonic coupling admittance matrix on the power grid side is calculated. Y The method is as follows:

[0116] ;

[0117] in, , , , and These are the harmonic coupling admittance matrices of the parallel system at the common coupling point. The corresponding element in; Z gm and Z gn These represent the line impedance to the m-th and n-th 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,...

[0118] As a specific implementation method, the method for calculating the evaluation index of the anti-background harmonic interference capability of the parallel system is as follows:

[0119] When evaluating the immunity to the 6k-1st harmonic: ;

[0120] When evaluating the immunity to the 6k+1th harmonic: ;

[0121] in, A h h is the evaluation index for the ability of a parallel system to resist background harmonic interference, where h is the harmonic order to be evaluated.

[0122] It should be noted that the specific implementation methods of the above modules are the same as those in Example 1, and will not be described in detail again.

[0123] Example 4

[0124] In one or more embodiments, a terminal device is disclosed, comprising a processor and a memory, the processor being used to implement instructions; the memory being used to store multiple instructions adapted to be loaded by the processor and executed by the processor to perform the harmonic interference immunity assessment method for a parallel network system considering frequency coupling as described in Embodiment 1.

[0125] It should be understood that in this embodiment, the processor can be a central processing unit (CPU), or it can be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor, etc.

[0126] Memory may include read-only memory and random access memory, and provides instructions and data to the processor. A portion of memory may also include non-volatile random access memory. For example, memory may also store information about the device type.

[0127] In the implementation process, each step of the above method can be completed by the integrated logic circuits in the processor hardware or by software instructions.

[0128] The specific implementation of the method in this embodiment is the same as that in Embodiment 1, and will not be described in detail again.

[0129] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this 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 without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for evaluating harmonic immunity in a parallel network system considering frequency coupling, characterized in that, include: Obtain grid-connected current data for GFL and GFM converters under different background harmonics, calculate the harmonic coupling admittance matrices of the GFL and GFM converters, and then obtain the harmonic coupling admittance matrix of the parallel system at the common coupling point. Specifically: in, Y GFL Here is the harmonic coupling admittance matrix of the GFL converter. Y GFM Here is the harmonic coupling admittance matrix of the GFM converter. K M The impact factors of parallel operation on the harmonic coupling admittance matrix of GFL and GFM converters. K L The effect of output power on the harmonic coupling admittance matrix of the GFL converter is given by the following factor. denoted as the number of GFM converters, where a is the total number of converters in the new energy power station. Based on the harmonic coupling admittance matrix of the parallel system at the common coupling point and the power grid line impedance, calculate the harmonic coupling admittance matrix on the power grid side. Based on the harmonic coupling admittance matrix on the power grid side, the evaluation index of the parallel system's ability to resist background harmonic interference is calculated, thereby realizing the evaluation of the harmonic immunity of the parallel system.

2. The harmonic immunity assessment method for a parallel network system considering frequency coupling as described in claim 1, characterized in that, It also includes the process of capacity tuning for parallel systems connected to the grid and those connected to the network, specifically: Based on the harmonic components in the grid voltage and the total installed capacity of the parallel system, calculate the minimum background harmonic interference immunity evaluation index required to ensure the grid-connected power quality of the parallel system; The minimum GFM converter ratio required to meet the minimum background harmonic interference immunity assessment index is calculated recursively.

3. The harmonic interference immunity assessment method for a parallel network system considering frequency coupling as described in claim 2, characterized in that, The minimum background harmonic interference immunity evaluation index required to ensure the grid-connected power quality of the parallel system meets the following requirements: The minimum evaluation index for background harmonic interference immunity shall not be less than the ratio of the harmonic voltage in the grid voltage to the total installed capacity of the parallel system by a set multiple.

4. The harmonic immunity assessment method for a parallel network system considering frequency coupling as described in claim 1, characterized in that, 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 at the current output power to the harmonic coupling admittance matrix of the GFL converter at the rated power.

5. The harmonic immunity assessment method for a parallel network system considering frequency coupling as described in claim 1, characterized in that, The influence factor of parallel operation on the harmonic coupling admittance matrix of 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.

6. The harmonic immunity assessment method for a parallel network system considering frequency coupling as described in claim 1, characterized in that, Calculate the harmonic coupling admittance matrix on the power grid side Y The method is as follows: ； in, , , , and These are the harmonic coupling admittance matrices of the parallel system at the common coupling point. The corresponding element in; Z gm and Z gn These represent the line impedance to the m-th and n-th 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,...

7. The harmonic immunity assessment method for a parallel network system considering frequency coupling as described in claim 6, characterized in that, The method for calculating the evaluation index of the anti-background harmonic interference capability of a parallel system is as follows: When evaluating the immunity to the 6k-1st harmonic: ; When evaluating the immunity to the 6k+1th harmonic: ; in, A h h is an evaluation index for the ability of a parallel system to resist background harmonic interference, where h represents the harmonic order to be evaluated.

8. A harmonic immunity assessment system for a parallel network system considering frequency coupling, employing the harmonic immunity assessment method for a parallel network system considering frequency coupling as described in any one of claims 1-7, characterized in that, include: The data acquisition module is configured to acquire grid-connected current data of GFL converter and GFM converter under different background harmonics, respectively. The harmonic coupling admittance matrix calculation module is 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. Based on the harmonic coupling admittance matrix of the parallel system at the common coupling point and the power grid line impedance, calculate the harmonic coupling admittance matrix on the power grid side. The harmonic immunity assessment module is configured to calculate the evaluation index of the parallel system's ability to resist background harmonic interference based on the grid-side harmonic coupling admittance matrix, thereby realizing the assessment of the harmonic immunity of the parallel system.

9. A terminal device comprising a processor and a memory, the processor for implementing instructions; the memory for storing multiple instructions, characterized in that, The instructions are adapted to be loaded by a processor and executed by the harmonic immunity assessment method for a parallel network system considering frequency coupling, as described in any one of claims 1-7.

Images