Harmonic resonance determination method and system for multiple grid-connected inverters based on modal analysis

Abstract

The present disclosure provides a modal analysis-based multi-grid-connected inverter harmonic resonance determination method and system, which belongs to the technical field of multi-grid-connected inverter harmonic resonance determination, and comprises: obtaining a system node admittance matrix based on a pre-constructed multi-grid-connected inverter equivalent model; obtaining a system modal impedance based on the system node admittance matrix by using a modal analysis method, wherein the system modal impedance is the reciprocal of the eigenvalue of the system node admittance matrix; calculating a damping ratio based on the obtained system modal impedance by using a half-power bandwidth method; and performing resonance degree calculation based on the system modal impedance and the damping ratio to realize determination of multi-grid-connected inverter harmonic resonance.

Description

TECHNICAL FIELD

[0001] The present disclosure belongs to the technical field of harmonic resonance determination of multi-grid-connected inverters, and particularly relates to a harmonic resonance determination method and system of multi-grid-connected inverters based on modal analysis. BACKGROUND

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

[0003] With the access of multi-grid-connected inverters to the power grid, the harmonic resonance problem caused by the multi-grid-connected inverters is highlighted. The modal analysis method is one of the effective methods for analyzing the mechanism of the problem. The inventors have found that the existing modal analysis method only determines the degree of harmonic resonance according to the amplitude of modal impedance, and the modal analysis result obtained has a large error with the simulation result, which is easy to lead to an incorrect analysis conclusion. SUMMARY

[0004] In order to solve the above problems, the present disclosure provides a harmonic resonance determination method and system of multi-grid-connected inverters based on modal analysis. When the modal analysis method is used to analyze the harmonic resonance problem, the common influence of the modal impedance amplitude and the damping ratio is considered, which effectively improves the applicability of the modal analysis method for analyzing the harmonic resonance problem. At the same time, the damping ratio is calculated by the half-power bandwidth method, only the frequency data of the peak point and two half-power points are needed, and the identification method is simple and has high identification accuracy.

[0005] According to a first aspect of an embodiment of the present disclosure, a harmonic resonance determination method of multi-grid-connected inverters based on modal analysis is provided, comprising:

[0006] obtaining a system node admittance matrix based on a pre-constructed equivalent model of multi-grid-connected inverters;

[0007] obtaining a system modal impedance based on the system node admittance matrix by using a modal analysis method, wherein the system modal impedance is the inverse of the eigenvalue of the system node admittance matrix;

[0008] calculating a damping ratio based on the obtained system modal impedance by using a half-power bandwidth method;

[0009] calculating the degree of resonance based on the system modal impedance and the damping ratio to realize the determination of the harmonic resonance of the multi-grid-connected inverters.

[0010] Further, the calculation of the degree of resonance based on the system modal impedance and the damping ratio specifically uses the following formula:

[0011] RD=(0.01f0) 2 |Z m |ξ

[0012] wherein RD is the resonance degree, |Z m is the peak of the modal impedance curve, ξ is the damping ratio obtained by the half-power bandwidth method, and f0 is the frequency corresponding to the peak of the modal impedance curve.

[0013] Further, the system modal impedance is obtained by using the modal analysis method, specifically, the reciprocal of the eigenvalue of the system node admittance matrix is used as the system modal impedance, and the modal corresponding to the smallest eigenvalue is used as the key modal of resonance.

[0014] Further, the damping ratio is calculated by using the half-power bandwidth method, specifically, the following formula is used:

[0015]

[0016] wherein ω1 and ω2 are the damped resonance frequencies corresponding to the half-power points of the current source amplitude-frequency characteristic curve, f1 and f2 are the frequencies corresponding to the half-power points of the modal impedance curve, and f0 is the frequency corresponding to the peak of the modal impedance curve.

[0017] Further, the system node admittance matrix is obtained based on the pre-constructed equivalent model of the multiple grid-connected inverters, specifically, the multiple grid-connected inverters are connected to the power grid through a common connection point, and the equivalent output admittance of the grid-connected inverter is obtained based on the Norton equivalent transformation.

[0018] According to a second aspect of the embodiments of the present disclosure, a multiple grid-connected inverter harmonic resonance determination system based on modal analysis is provided, comprising:

[0019] An admittance matrix solving unit is configured to obtain a system node admittance matrix based on a pre-constructed equivalent model of the multiple grid-connected inverters;

[0020] A modal impedance calculation unit is configured to obtain a system modal impedance by using a modal analysis method based on the system node admittance matrix, wherein the system modal impedance is the reciprocal of the eigenvalue of the system node admittance matrix;

[0021] A damping ratio calculation unit is configured to calculate a damping ratio by using a half-power bandwidth method based on the obtained system modal impedance;

[0022] A resonance degree calculation unit is configured to calculate a resonance degree based on the system modal impedance and the damping ratio, so as to determine the harmonic resonance of the multiple grid-connected inverters.

[0023] According to a third aspect of the embodiments of the present disclosure, a computer readable storage medium is provided, which stores a program to be executed by a processor to implement the multiple grid-connected inverter harmonic resonance determination method based on modal analysis.

[0024] According to a fourth aspect of the embodiments of the present application, an electronic device is provided, comprising a memory, a processor, and a program stored in the memory and capable of running on the processor, and the processor implements the modal analysis based harmonic resonance determination method for multi-grid-connected inverters when executing the program.

[0025] Compared with the prior art, the present disclosure has the following beneficial effects:

[0026] The present disclosure provides a modal analysis based harmonic resonance determination method and system for multi-grid-connected inverters, which considers the joint influence of modal impedance amplitude and damping ratio when analyzing the harmonic resonance problem by modal analysis method, thereby improving the applicability of modal analysis method in analyzing the harmonic resonance problem.

[0027] The advantages of the additional aspects of the present disclosure will be partially given in the following description, partially will become obvious from the following description, or will be understood through the practice of the present disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0028] The accompanying drawings, which form a part of the present disclosure, are used to provide further understanding of the present disclosure, and the illustrative embodiments of the present disclosure and their description serve the purpose of explaining the present disclosure, and do not constitute improper limitations on the present disclosure.

[0029] Figure 1 A modal analysis based harmonic resonance determination method for multi-grid-connected inverters described in the embodiments of the present disclosure;

[0030] Figure 2 A multi-grid-connected inverter topology structure described in the embodiments of the present disclosure;

[0031] Figure 3 A grid-connected inverter control block diagram of each inverter in the alpha-beta coordinate system described in the embodiments of the present disclosure;

[0032] Figure 4 A Norton equivalent model of multi-grid-connected inverters described in the embodiments of the present disclosure;

[0033] Figure 5 An RLC parallel circuit diagram described in the embodiments of the present disclosure;

[0034] Figure 6 A modal analysis result diagram described in the embodiments of the present disclosure;

[0035] Figure 7 A Norton equivalent model of two grid-connected inverters described in the embodiments of the present disclosure;

[0036] FIG. 8(a) and FIG. 8(b) are respectively modal analysis results of two grid-connected inverters according to an embodiment of the present disclosure;

[0037] FIG. 9(a) and FIG. 9(b) are respectively voltage spectrum diagrams of node 1 in different resonance modes according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0038] The present disclosure will be further described below with reference to the accompanying drawings and embodiments.

[0039] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the present disclosure. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this present disclosure belongs.

[0040] It should be noted that the terms used herein are only intended to describe specific embodiments and are not intended to limit exemplary embodiments according to the present disclosure. As used herein, the singular form is intended to include the plural form unless the context clearly indicates otherwise, and it should also be understood that when the terms "comprise" and / or "include" are used in the specification, they indicate the presence of the features, steps, operations, devices, components and / or combinations thereof.

[0041] The embodiments in the present disclosure and the features in the embodiments can be combined with each other without conflict.

[0042] Embodiment One:

[0043] The purpose of the present embodiment is to provide a multi-grid-connected inverter harmonic resonance determination method based on modal analysis.

[0044] A multi-grid-connected inverter harmonic resonance determination method based on modal analysis, comprising:

[0045] Obtaining a system node admittance matrix based on a pre-constructed equivalent model of multi-grid-connected inverters;

[0046] Based on the system node admittance matrix, a modal analysis method is used to obtain a system modal impedance, wherein the system modal impedance is the inverse of the eigenvalue of the system node admittance matrix;

[0047] Based on the obtained system modal impedance, a half-power bandwidth method is used to calculate a damping ratio;

[0048] Based on the system modal impedance and the damping ratio, resonance degree calculation is performed to determine the harmonic resonance of multi-grid-connected inverters.

[0049] Further, the resonance degree calculation based on the system modal impedance and the damping ratio specifically uses the following formula:

[0050] RD = (0.01f0) 2 |Z m |ξ

[0051] Where RD is the degree of resonance, |Z m | represents the peak value of the modal impedance curve, ξ is the damping ratio obtained by the half-power bandwidth method, and f0 is the frequency corresponding to the peak value of the modal impedance curve.

[0052] Furthermore, the modal analysis method is used to obtain the system modal impedance. Specifically, the reciprocal of the eigenvalues ​​of the system node admittance matrix is ​​used as the system modal impedance, and the mode corresponding to the smallest eigenvalue is used as the key mode of resonance.

[0053] Furthermore, the damping ratio is calculated using the half-power bandwidth method, specifically using the following formula:

[0054]

[0055] Where ω1 and ω2 are the damped resonant frequencies corresponding to the half-power points of the current source amplitude-frequency characteristic curve, f1 and f2 are the frequencies corresponding to the half-power points of the modal impedance curve, and f0 is the frequency corresponding to the peak value of the modal impedance curve.

[0056] Furthermore, the process of obtaining the system node admittance matrix based on the pre-constructed equivalent model of multiple grid-connected inverters specifically involves: multiple grid-connected inverters being connected to the power grid through a common coupling point, and the equivalent output admittance of the grid-connected inverters being obtained based on the Norton equivalent transformation.

[0057] Specifically, for ease of understanding, the following detailed description of the solution in this embodiment is provided in conjunction with the accompanying drawings:

[0058] like Figure 1 As shown, this embodiment provides a method for determining harmonic resonance in multi-grid-connected inverters based on modal analysis. The main technical concept is as follows: establishing a multi-grid-connected inverter model and constructing the system node admittance matrix → analyzing the harmonic resonance caused by the multi-grid-connected inverters using modal analysis → proposing an improved modal analysis method and introducing a resonance degree index to determine the degree of harmonic resonance → building a simulation system in MATLAB / Simulink for verification. Specifically, it includes the following steps:

[0059] Step 1: Establish a multi-grid-connected inverter model and construct the system node admittance matrix, specifically including:

[0060] Multiple LCL grid-connected inverters are connected to the power grid through a point of common coupling. The equivalent output admittance Y of the i-th grid-connected inverter can be obtained by performing Norton equivalent transformation. si The expression for (s) is

[0061]

[0062] where L1, C and L2 are the inverter-side inductor, filter capacitor and grid-side inductor, respectively; K C is the capacitor current feedback coefficient; K PWM is the proportional gain of the PWM link; G QPR (s) is the current regulator.

[0063] The expression of the node admittance matrix of the multi-grid-connected inverter system is

[0064]

[0065] Step 2: The modal analysis method is used to analyze the harmonic resonance, which specifically includes:

[0066] The modal analysis method is a method of analyzing the eigenvalues of the node admittance matrix. When a network containing multiple nodes occurs parallel resonance at a certain frequency, part of the node voltage rises, and part of the eigenvalues of the admittance matrix decreases, so the reciprocal of the eigenvalues increases.

[0067] When the system occurs parallel resonance at the frequency f, the node voltage equation is

[0068]

[0069] where V f represents the node voltage matrix; I f represents the node injection current matrix; Y f represents the node admittance matrix of the grid-connected system at a certain frequency f. Y f can be decomposed into

[0070] Y f =LΛT (4)

[0071] where L=[L1,L2,…,L n ] is the left eigenvector matrix; L n is the nth column element of L; Λ=diag(λ1,λ2,…,λ n ) is the diagonal eigenvalue matrix of Y f ; T=[T1,T2,…,T n ] T is the right eigenvector matrix; T n is the nth row element of T; L=T -1 .

[0072] Substituting equation (4) into equation (3) can obtain:

[0073] TV f =Λ -1 TI f (5)

[0074] Definition U f = TV f is the modal voltage vector, J f = TI f is the modal current vector, then U f = A -1 J f . The n-node circuit can be represented as:

[0075]

[0076] The reciprocal of the eigenvalue is defined as the modal impedance Z m When the frequency is f1, f1 is equal to or close to zero, even if J f1 is very small, it can produce a very large U f1 , and the modal voltage at other frequencies will not be affected by the modal current at that frequency. Therefore, the resonance frequency and degree can be determined according to the reciprocal of the eigenvalue, that is, the modal impedance. The modal corresponding to the smallest eigenvalue is called the key modal of resonance.

[0077] Step 3: Propose an improved modal analysis method, introduce a resonance degree index to determine the degree of harmonic resonance, which specifically includes:

[0078] Through modal analysis method, it can be found that harmonic resonance occurs in a specific modal, and each modal has its specific resonance frequency and damping ratio. However, the current modal analysis method only determines the resonance frequency through the modal impedance amplitude-frequency characteristic, and does not consider the influence of damping ratio. The half-power bandwidth method is a commonly used damping ratio identification method, so the present application takes the parallel resonance of RLC parallel circuit as an example, and analyzes the resonance based on the half-power bandwidth method. The frequency response function H(jw) of the equivalent impedance between the current source can be expressed as

[0079]

[0080] where G, L and C represent the conductance, inductance and capacitance in the RLC parallel circuit respectively; ω represents the frequency variable; ω0 is the resonance frequency with damping; ξ is the damping ratio; G0 is the amplification coefficient; ω n represents the resonance frequency without damping; Q is the quality factor of parallel resonance, which is specifically expressed as:

[0081] When parallel resonance occurs, the input impedance is maximum. Since the output amplitude of the output signal of the circuit is large in the neighborhood of the resonance point frequency, the region within 0.707 times of the maximum input impedance is called the resonance band, and the critical point of the resonance band is the half-power point. The amplitude-frequency response of the frequency response function at the half-power point satisfies

[0082]

[0083] Combining formula (7) and formula (8), the bandwidth of the resonance band can be obtained as

[0084]

[0085] where ω1, ω2 are the damped resonant frequencies corresponding to the half-power points of the current source amplitude-frequency characteristic curve, respectively.

[0086] The half-power bandwidth method is introduced to further solve and improve the modal analysis results. Based on the modal impedance curve obtained by the modal analysis method, the damping ratio is calculated according to formula (10) to assist in determining the resonance characteristics. The damping ratio ξ can be expressed as

[0087]

[0088] where f1, f2 are the frequencies corresponding to the half-power points of the modal impedance curve, respectively; f0 is the frequency corresponding to the peak value of the modal impedance curve.

[0089] In order to analyze the influence of modal impedance amplitude and damping ratio on the harmonic resonance degree of multi-grid-connected inverters, the resonance degree (RD) is defined as

[0090] RD=(0.01f0) 2 |Z m |ξ (11)

[0091] where |Z m | is the peak value of the modal impedance curve, and ξ is the damping ratio obtained by the half-power bandwidth method.

[0092] Step 4: Build a simulation system in MATLAB / Simulink to verify the limitations of the existing modal analysis method and the effectiveness of the method in this paper, which includes the following specific steps:

[0093] The modal analysis results are realized by MATLAB programming, and a model of two grid-connected inverters is built in MATLAB / Simulink. Considering that the damping ratio may affect the harmonic resonance degree, the improved modal analysis method is used to analyze the harmonic resonance of the two grid-connected inverters, and the results are shown in Table 1.

[0094] Table 1 Calculation results of improved modal analysis method

[0095]

[0096] From Table 1, it can be seen that when the resonance ranges of two different modes in the system are close, even for different resonance modes of the system (such as K CThe damping ratio of the low-frequency and high-frequency modes decreases with the decrease of the capacitance current feedback coefficient, and the corresponding modal impedance amplitude increases, so does the RD and the harmonic voltage.

[0097] When the resonance ranges of different modes in the system hardly coincide, such as K C When K is 15, the damping ratio of the low-frequency resonance mode is larger and the modal impedance amplitude |Z m.3 It can be seen that the modal impedance amplitude is the main factor affecting the harmonic resonance degree, and the harmonic resonance degree is less affected by the damping ratio. According to formula (11), the RD corresponding to the low-frequency mode is higher, which is consistent with the result that the low-frequency harmonic voltage is higher in Fig. 9(a).

[0098] When K C When K is reduced to 10, the damping ratio of the high-frequency resonance mode is smaller and the modal impedance amplitude |Z m.3 It can be seen that the modal impedance value is the main factor affecting the harmonic resonance degree, and the harmonic resonance degree is less affected by the damping ratio. Therefore, when judging the occurrence degree of system harmonic resonance through modal analysis, the modal impedance amplitude and the damping ratio should be considered at the same time. According to formula (11), the RD corresponding to the high-frequency mode is higher, which is consistent with the result that the high-frequency harmonic voltage is higher in Fig. 9(b).

[0099] Figure 2 Fig. 1 is a topology diagram of a multi-grid-connected inverter. A plurality of LCL grid-connected inverters are connected through a common connection point and a power grid. In the figure, U dci is a DC voltage source (i = 1, 2, …, n), the inverter-side inductance L 1i , the capacitance C i and the grid-side inductance L 2i together constitute an LCL filter, I Ci and I gi are the filter capacitance current and the grid-connected current respectively, Z fi is the line impedance, Z g and V g are the grid impedance and the three-phase grid voltage respectively.

[0100] Figure 3 Fig. 2 is a control block diagram of the grid-connected inverter in the ab coordinate system. A double-closed-loop control mode is adopted, which feeds back the grid-connected current and the capacitance current. The system first samples the grid current, compares it with the reference current generated by the phase-locked loop in the current regulator, and then outputs a modulation signal. The on-off of the thyristors of the inverter is controlled through PWM, so as to realize inverter grid connection. In the figure, I g.ref is the grid current command value; G i (s) is the current regulator; a quasi-proportional resonant regulator is adopted; K Cis the feedback coefficient of the capacitor current; Z L1 (s) = sL1, Z L2 (s) = sL2, Z C (s) = 1 / (sC).

[0101] Figure 4 is the Norton equivalent model of multiple grid-connected inverters. In the figure, I si and Y si (i = 1, 2, …, n) are the equivalent current source and output admittance of the ith grid-connected inverter, respectively; Y fi is the line equivalent admittance; Y g is the grid equivalent admittance.

[0102] Figure 5 is the RLC parallel circuit diagram. In the figure, represents the voltage across the current source, represents the current source current, G represents the conductance, X L , X C represent the inductive reactance and capacitive reactance, respectively, and represent the current flowing through the conductance, inductive reactance, and capacitive reactance, respectively.

[0103] Figure 6 is the modal analysis result diagram. In the figure, f0 is the resonance frequency; |Z m (f0)| is the peak value of the modal impedance curve; f1, f2 are the frequencies corresponding to the half-power points of the modal impedance curve, respectively.

[0104] Figure 7 is the Norton equivalent model of two grid-connected inverters. The two grid-connected inverters are inverter A and inverter B, respectively, and their parameters are shown in Table 2.

[0105] Table 2 Grid-connected inverter parameters

[0106]

[0107] Figures 8(a) and 8(b) are modal analysis result diagrams of two grid-connected inverters. When the feedback coefficient of the capacitor current in inverter A is 15 or 10, there are two resonance peaks in the modal analysis results, respectively in the low frequency and high frequency ranges, and the modal impedance peak in the low frequency range is higher than that in the high frequency range. Since the existing modal analysis method considers that the modal impedance peak represents the resonance degree, according to the existing modal analysis method, the harmonic resonance degree in the low frequency range is the highest.

[0108] Figures 9(a) and 9(b) are node 1 voltage spectrum diagrams. Based on MATLAB / Simulink, a grid-connected inverter system simulation model is built, and 10-35 harmonic currents are injected into the PCC. In both cases, two resonance peaks appear in the system, which is consistent with the modal analysis results. When KC When K is 15, the harmonic voltage generated at low frequency of node 1 is higher than that generated at high frequency, which corresponds to the result that the modal impedance value at low frequency is higher in the modal analysis result. When K is reduced to 10, the harmonic voltage generated at low frequency of node 1 is lower than that generated at high frequency, which is contrary to the result that the modal impedance value at low frequency is higher in the modal analysis result, so the degree of harmonic resonance cannot be determined only according to the amplitude of the modal impedance curve, and the existing modal analysis method has limitations. C When K is 15, the harmonic voltage generated at low frequency of node 1 is higher than that generated at high frequency, which corresponds to the result that the modal impedance value at low frequency is higher in the modal analysis result. When K is reduced to 10, the harmonic voltage generated at low frequency of node 1 is lower than that generated at high frequency, which is contrary to the result that the modal impedance value at low frequency is higher in the modal analysis result, so the degree of harmonic resonance cannot be determined only according to the amplitude of the modal impedance curve, and the existing modal analysis method has limitations.

[0109] The embodiment introduces the resonance degree index to determine the degree of harmonic resonance, and the following conclusions are obtained through simulation.

[0110] (1) The degree of harmonic resonance is affected by the amplitude of modal impedance and the damping ratio, and the main influencing factors are different in different cases.

[0111] (2) When the modal analysis method is used to analyze the harmonic resonance problem, the resonance degree can be determined according to the proposed index RD.

[0112] Embodiment two:

[0113] The purpose of the embodiment is to provide a multi-grid inverter harmonic resonance determination system based on modal analysis.

[0114] A multi-grid inverter harmonic resonance determination system based on modal analysis, comprising:

[0115] An admittance matrix solving unit for obtaining a system node admittance matrix based on a pre-constructed equivalent model of the multi-grid inverter;

[0116] A modal impedance calculation unit for obtaining a system modal impedance based on the system node admittance matrix by using the modal analysis method, wherein the system modal impedance is the reciprocal of the eigenvalue of the system node admittance matrix;

[0117] A damping ratio calculation unit for calculating the damping ratio by using the half-power bandwidth method based on the obtained system modal impedance;

[0118] A resonance degree calculation unit for calculating the resonance degree based on the system modal impedance and the damping ratio to determine the harmonic resonance of the multi-grid inverter.

[0119] Further, the system described in the embodiment corresponds to the method described in embodiment one, and the technical details have been described in detail in embodiment one, so this will not be repeated here.

[0120] In more embodiments, the following is also provided:

[0121] An electronic device includes a memory and a processor, and computer instructions stored on the memory and run on the processor, when the computer instructions are run by the processor, the method described in embodiment one is completed. For the sake of brevity, it will not be repeated here.

[0122] It should be understood that in the embodiments, the processor can be a central processing unit CPU, and the processor can also be other general-purpose processors, digital signal processors DSPs, application-specific integrated circuits ASICs, ready-to-program gate arrays FPGA or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or the processor can also be any conventional processor.

[0123] The memory can include read-only memory and random access memory, and provide instructions and data to the processor, and a part of the memory can also include non-volatile random access memory. For example, the memory can also store device type information.

[0124] A computer readable storage medium for storing computer instructions, when the computer instructions are executed by the processor, the method described in embodiment one is completed.

[0125] The method in embodiment one can be directly embodied as hardware processor execution completion, or executed by a combination of hardware and software modules in the processor. The software module can be located in a mature storage medium in the art such as random access memory, flash memory, read-only memory, programmable read-only memory or electrically erasable programmable memory, register, etc. The storage medium is located in the memory, and the processor reads the information in the memory, and combines the hardware to complete the steps of the above method. To avoid repetition, it will not be described in detail here.

[0126] Those of ordinary skill in the art can realize that the units of the examples described in combination with the embodiments, i.e. the algorithm steps, can be realized in electronic hardware or in a combination of computer software and electronic hardware. Whether the functions are executed in hardware or software mode depends on the specific application and design constraints of the technical solution. The skilled person can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the disclosure.

[0127] The multi-grid-connected inverter harmonic resonance determination method and system based on modal analysis provided by the above embodiments can be realized, and has a wide application prospect.

[0128] The above only describes the preferred embodiments of the disclosure and is not intended to limit the disclosure. Those skilled in the art can make various modifications and changes to the disclosure. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the disclosure shall be included in the protection scope of the disclosure.

Claims

1. A method for determining harmonic resonance of multiple grid-connected inverters based on modal analysis, characterized in that, The method comprises the following steps: obtaining a system node admittance matrix based on a pre-constructed equivalent model of multiple grid-connected inverters; obtaining a system modal impedance based on the system node admittance matrix by using a modal analysis method, wherein the system modal impedance is the reciprocal of an eigenvalue of the system node admittance matrix; calculating a damping ratio by using a half-power bandwidth method based on the obtained system modal impedance; calculating a resonance degree based on the system modal impedance and the damping ratio to determine harmonic resonance of the multiple grid-connected inverters; specifically, the following formula is used: wherein RD is the degree of resonance, Z m is the peak of the modal impedance curve, is the damping ratio obtained by the half-power bandwidth method, f 0 is the frequency corresponding to the peak of the modal impedance curve.

2. The method of claim 1, wherein the method is based on modal analysis. The system modal impedance is obtained by using the modal analysis method, specifically, the reciprocal of the eigenvalue of the system node admittance matrix is used as the system modal impedance, and a mode corresponding to the smallest eigenvalue is used as a key mode of resonance.

3. The method of claim 1, wherein the method is based on modal analysis of the plurality of grid-tied inverters. The damping ratio is calculated by using the half-power bandwidth method, specifically, the following formula is used: wherein, , f0and f0are the damped natural frequencies corresponding to the half-power points of the current source amplitude-frequency characteristic curve, respectively, f 1, f 2are the frequencies corresponding to the half-power points of the modal impedance curve, respectively; f 0is the frequency corresponding to the peak value of the modal impedance curve; f0is the damped natural frequency.

4. The method of claim 1, wherein the method is based on modal analysis of the plurality of grid-tied inverters. The system node admittance matrix is obtained based on the pre-constructed equivalent model of the multiple grid-connected inverters, specifically, equivalent output admittance of the grid-connected inverters is obtained based on Norton equivalent transformation, and the multiple grid-connected inverters are connected to a power grid through a common connection point.

5. A harmonic resonance determination system for multi-grid-connected inverters based on modal analysis, characterized in that, The method comprises the following steps: an admittance matrix solving unit configured to obtain a system node admittance matrix based on a pre-constructed equivalent model of multiple grid-connected inverters; a modal impedance calculating unit configured to obtain a system modal impedance based on the system node admittance matrix by using a modal analysis method, wherein the system modal impedance is the reciprocal of an eigenvalue of the system node admittance matrix; a damping ratio calculating unit configured to calculate a damping ratio by using a half-power bandwidth method based on the obtained system modal impedance; a resonance degree calculating unit configured to calculate a resonance degree based on the system modal impedance and the damping ratio to determine harmonic resonance of the multiple grid-connected inverters; specifically, the following formula is used: wherein RD is the degree of resonance, Z m is the peak of the modal impedance curve, is the damping ratio as determined by the half-power bandwidth method, f 0 is the frequency corresponding to the peak of the modal impedance curve.

6. A modal analysis based multi-grid inverter harmonic resonance determination system as claimed in claim 5, wherein, The system modal impedance is obtained by using the modal analysis method, specifically, the reciprocal of the eigenvalue of the system node admittance matrix is used as the system modal impedance, and a mode corresponding to the smallest eigenvalue is used as a key mode of resonance.

7. A computer-readable storage medium having stored thereon a program, characterized in that, The program is executed by the processor to implement the method for determining harmonic resonance of multiple grid-connected inverters based on modal analysis according to any one of claims 1-4.

8. An electronic device comprising a memory, a processor, and a program stored in the memory and executable on the processor, characterized by The processor executes the program to implement the method for determining harmonic resonance of multiple grid-connected inverters based on modal analysis according to any one of claims 1-4.

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