A grey-box aggregation method and system for new energy power generation networks

Abstract

The application provides a grey box aggregation method and system for a new energy power generation network, comprising: obtaining equivalent impedance of electrical elements for constructing the new energy power generation network based on a VF algorithm; constructing the new energy power generation network by aggregating the equivalent impedance, wherein the aggregation comprises parallel aggregation and series aggregation; selecting subsystems without the same zero point for aggregation in the parallel aggregation process; and selecting subsystems without the same pole for aggregation in the series aggregation process; the application is based on a grey box background, uses the VF algorithm to fit discrete impedance data of main electrical equipment such as inverters to obtain an initial impedance network of the system, and elaborates the impedance network aggregation process and a stability analysis method for the network after aggregation; the application prevents the system stability misjudgment caused by the zero-pole cancellation phenomenon existing in the impedance network aggregation process, and provides a basis for correctly selecting an impedance aggregation path.

Description

Technical Field

[0001] This invention relates to the field of power distribution network emergency recovery technology, and more specifically, to a gray box aggregation method and system for new energy power generation networks. Background Technology

[0002] As the penetration rate of new energy power generation networks gradually increases, harmonic instability becomes a prominent issue. Impedance analysis is one of the effective methods for analyzing this problem, and its core application is impedance aggregation. However, if the aggregation path is not properly selected during impedance aggregation, zero-pole cancellation may occur, leading to misjudgment of stability. To address this deficiency, there is an urgent need for a gray-box aggregation method and system for new energy power generation networks that considers zero-pole cancellation during impedance aggregation. This method provides a solution for zero-pole cancellation during impedance aggregation and is suitable for stability analysis of new energy power systems. Summary of the Invention

[0003] To address the above technical problems, this invention provides a gray box aggregation method for new energy power generation networks, comprising the following steps:

[0004] Based on the VF algorithm, the equivalent impedance of electrical components used to construct new energy power generation networks is obtained;

[0005] A new energy power generation network is constructed by aggregating equivalent impedances, where aggregation includes parallel aggregation and series aggregation.

[0006] In the parallel aggregation process, subsystems that do not have the same zero point are selected for aggregation;

[0007] In the tandem aggregation process, subsystems that do not have the same poles are selected for aggregation.

[0008] Preferably, in the process of obtaining the equivalent impedance of electrical components, the equivalent impedance of electrical components is obtained using the vector matching method based on the gray box background, and a new energy power generation network is generated by constructing an equivalent impedance model.

[0009] Preferably, in the process of obtaining the equivalent impedance, voltage disturbances are injected on the series side and current disturbances are injected on the parallel side to stabilize the DC side voltage.

[0010] Injecting a voltage / current disturbance under a specific harmonic into the electrical component under test, generating a current / voltage response after passing through the electrical component's circuit, and obtaining impedance data under that harmonic;

[0011] Based on the impedance data, the impedance of electrical components is fitted with a gray box using the VF algorithm to obtain the equivalent impedance and construct an equivalent impedance model.

[0012] Preferably, in the process of constructing a new energy power generation network, the network is generated by connecting the electrical components according to the system topology based on the equivalent impedance model of the electrical components and performing harmonic stability analysis using impedance analysis.

[0013] Preferably, during the harmonic stability analysis, the harmonic stability analysis is performed by obtaining the source-side equivalent impedance and load-side equivalent impedance of the node to be analyzed, wherein the expression for the harmonic stability analysis is:

[0014]

[0015] In the formula, T m V is the minimum loop gain of the system. S It is the output voltage of the power supply subsystem when it is running alone; V L Z is the input voltage of the load subsystem. S and Z L These are the source-side equivalent impedance and the load-side equivalent impedance, respectively.

[0016] Preferably, during the harmonic stability analysis, based on the Middlebrook stability criterion, an improved criterion, represented by the GMPM criterion, is used. By defining prohibited regions for the amplitude margin and phase margin of the new energy power generation network system, the stability of the new energy power generation network is determined. The conditional expression for the prohibited regions is as follows:

[0017]

[0018] In the formula, GM represents the gain margin.

[0019] Preferably, in the process of constructing a new energy power generation network, the transfer function expression before and after the first aggregation in parallel aggregation is as follows:

[0020]

[0021]

[0022] In the formula, Z C For the equivalent impedance of the parallel aggregation network, N A N B D A D B The polynomials formed by the zeros and poles of the independent networks A and B before aggregation are N′ and N′ respectively. A =N A / (s-λ0), N′ B =N B / (s-λ0), where λ0 is the right half-plane zero shared by systems A and B;

[0023] The transfer function expressions for the second aggregation in cascade aggregation are:

[0024]

[0025]

[0026] In the formula, Z D For the equivalent impedance of the series-converged network, D′ A =D A / (s-γ0), D′ B =D B / (s-γ0), where γ0 is the right half-plane pole shared by systems A and B;

[0027] Based on the transfer function expressions before and after the first aggregation and the second aggregation, it is determined whether zero-pole cancellation occurs during the aggregation process. Specifically, in the parallel aggregation process, subsystems without the same zeros are selected for aggregation to avoid zero-pole cancellation; in the series aggregation process, subsystems without the same poles are selected for aggregation to avoid zero-pole cancellation.

[0028] This invention provides a gray box aggregation system for new energy power generation networks, comprising:

[0029] The equivalent impedance generation module is used to obtain the equivalent impedance of electrical components used to build new energy power generation networks based on the VF algorithm.

[0030] The power generation network construction module is used to construct a new energy power generation network by aggregating equivalent impedances, wherein the aggregation includes parallel aggregation and series aggregation;

[0031] In the parallel aggregation process, subsystems that do not have the same zero point are selected for aggregation;

[0032] In the tandem aggregation process, subsystems that do not have the same poles are selected for aggregation.

[0033] Compared with existing technologies, it has the following beneficial effects:

[0034] (1) Based on the actual situation of information confidentiality inside power generation equipment in engineering sites, the present invention uses the VF algorithm to fit the discrete impedance data of major electrical equipment such as inverters to obtain the initial impedance network of the system.

[0035] (2) Based on the initial impedance network of the system, the impedance network aggregation process is described in detail and the stability analysis method of the aggregated network is presented.

[0036] (3) This invention focuses on a detailed discussion of how to correctly select the impedance aggregation path, points out that the zero-pole cancellation phenomenon in the impedance network aggregation process may lead to misjudgment of system stability, and provides the basis for correctly selecting the impedance aggregation path.

[0037] (4) A multi-parallel grid-connected inverter model was built in Matlab / Simulink to reproduce the phenomenon that the analysis conclusions were inconsistent when the path selection was wrong, and to further verify the effectiveness and practicality of the method proposed in this invention. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 The following is a general flowchart illustrating the implementation of the method described in this invention;

[0040] Figure 2 This is a schematic diagram illustrating the principle of discrete impedance data measurement and calculation as described in this invention.

[0041] Figure 3 This is a flowchart of the VF algorithm described in this invention;

[0042] Figure 4 This is a model diagram of distributed photovoltaic grid connection as described in this invention;

[0043] Figure 5 This is the impedance network diagram of the new energy power generation described in this invention;

[0044] Figure 6 This is a diagram illustrating the aggregation process of the impedance network for new energy power generation as described in this invention.

[0045] Figure 7 This is a circuit structure diagram of the multi-parallel GCI system described in this invention;

[0046] Figure 8 The Bode plot of the impedance frequency response of the inverter described in this invention;

[0047] Figure 9 This is the aggregation path diagram of the multi-parallel GCI system described in this invention;

[0048] Figure 10 This is the Z4 Bode plot fitted using the VF algorithm as described in this invention;

[0049] Figure 11 This is a voltage waveform diagram of node ④ in the multi-parallel GCI system following the aggregation path described in this invention.

[0050] Figure 12 The Z-value based on VF algorithm fitting described in this invention Linei Bode plot (i = 1, 2);

[0051] Figure 13 The Z-value based on VF algorithm fitting described in this invention 4_1 Bode plot;

[0052] Figure 14 This is the aggregation path diagram of the improved multi-parallel GCI system described in this invention;

[0053] Figure 15 This is the Z3 Bode plot fitted based on the VF algorithm as described in this invention;

[0054] Figure 16 The voltage waveform of node ③ in the multi-parallel GCI system after the improved aggregation path described in this invention. Detailed Implementation

[0055] To fully describe the technical content, structural features, objectives, and effects of this invention, the following detailed description of a specific implementation method for a gray box aggregation method for a new energy power generation network is provided in conjunction with the accompanying drawings in the embodiments of this invention.

[0056] As the penetration rate of new energy power generation networks gradually increases, harmonic instability becomes a prominent issue. Impedance analysis is one of the effective methods for analyzing this problem, and its core application is impedance aggregation. However, if the aggregation path is not properly selected during impedance aggregation, zero-pole cancellation may occur, leading to misjudgment of stability. To address this shortcoming, a gray-box aggregation method for new energy power generation networks is proposed, which can effectively solve this problem.

[0057] like Figure 1-16 As shown, the present invention provides...

[0058] Figure 1 The following is a flowchart illustrating the overall implementation of the method of the present invention. Figure 1 As shown, the gray box aggregation method provided by the present invention includes the following steps:

[0059] Step 1: Obtain the equivalent impedance of electrical components based on the VF algorithm;

[0060] Step 2: Establish a new energy power generation network and perform impedance aggregation;

[0061] Step 3: Judge and analyze the zero-pole cancellation phenomenon in the impedance polymerization process;

[0062] Step 4: Build a multi-parallel grid-connected inverter system in Matlab / Simulink for simulation to further verify the effectiveness and practicality of the proposed aggregation method.

[0063] Step 1: Obtain the equivalent impedance of electrical components based on the VF algorithm, specifically including:

[0064] For the method of obtaining the impedance model of circuit devices such as inverters, the proposed approach is to use an algorithm to fit the transfer function. First, this invention injects voltage disturbance on the series side and current disturbance on the parallel side to stabilize the DC side voltage. The disturbance injection device injects voltage / current disturbance under a specific harmonic into the grid-connected inverter under test, which generates a current / voltage response after passing through the grid-connected inverter circuit. The impedance data under the harmonic is obtained by calculation. The basic principle is shown in Equation (1).

[0065]

[0066] In the formula: Z f U is the impedance value of the grid-connected inverter at frequency f. f and I f For the grid-connected inverter port voltage u abc i abc Voltage and current components at frequency f obtained through FFT decomposition.

[0067] Based on the acquired discrete impedance data, this invention uses a rational function approximation algorithm to perform gray-box fitting on the impedance of electrical components such as grid-connected inverters. The rational function approximation algorithm selected is the VF algorithm, which means that a set of discrete impedance frequency responses can be fitted into a continuous transfer function in the form of partial fraction expansion or polynomial expression using the VF algorithm.

[0068] The basic idea of ​​the VF algorithm is that any rational function can be expressed as a fractional summation, as shown in equation (2):

[0069]

[0070] In the formula, N is the initial order (which can be determined through trial and error), and r m For the residue, a m Let be the initial pole (determined by the least squares method), and d and e are both rational numbers.

[0071] The linear problem is represented by equations (3)-(6):

[0072] σ(s)f(s)=p(s) (3)

[0073]

[0074]

[0075] {a m}=eig(Ab·c T (6)

[0076] In the formula, σ(s) is a scalar, p(s) is a vector, and f(s) is the initial set of zeros. The poles of f(s) are the zeros of s, and can also be represented as the eigenvalues ​​of a specific matrix, where A is {q}. m A diagonal matrix consisting of}, where b is a unit column vector, and c T For the residue {r m The row vector formed by}

[0077] Equation (2) can also be expressed as Equation (7), and the two equations have different meanings and set parameters. Equation (2) is mainly used to analyze the right half-plane poles of stability, while Equation (7) is mainly used to identify the control parameters of the grid-connected inverter circuit.

[0078]

[0079] In the formula, i is the inverter designation.

[0080] Step 2: Establish a new energy power generation network and perform impedance aggregation, specifically including:

[0081] Each component in a new energy power generation network is essentially an impedance model. Connecting the impedances of each component according to the system topology forms a complete new energy power generation impedance network. When performing harmonic stability analysis on the new energy power generation impedance network using impedance analysis, it is necessary to first determine the "source side" and "load side" impedances of the node to be analyzed through impedance aggregation. The basic idea of ​​impedance analysis is to obtain the equivalent impedances of the "source side" and "load side" respectively.

[0082] To evaluate the system stability, the transfer function of the simplified system is written as shown in equation (8).

[0083]

[0084] In the formula T m Defined as the minimum loop gain of the system, V S It is the output voltage of the power supply subsystem when it is running alone; V L Z is the input voltage of the load subsystem. S and Z L These are the equivalent impedance on the "source side" and the equivalent impedance on the "load side".

[0085] The mainstream method for stability determination is still the Nyquist criterion. In addition, the Middlebrook stability criterion determines the stability of the system through equation (9), which overcomes the complexity of the Nyquist criterion and is also widely used.

[0086]

[0087] In the formula, GM represents the gain margin.

[0088] The Middlebrook stability criterion uses the forbidden zone representation, that is, when T m When the system is confined within a unit circle on the complex plane, it can be determined that the system is stable; in this case, the outer gray region is T. m The restricted area, if T m If the Nyquist curve is located outside its forbidden region, and the number of times the curve encircles the point (-1, j0) counterclockwise is zero, then the system can be determined to be stable.

[0089] Based on the Middlebrook stability criterion, this invention adopts an improved criterion represented by the GMPM criterion, which defines forbidden regions for the system's gain margin and phase margin, as shown in equation (10):

[0090]

[0091] Currently, based on the GMPM criterion, the stability of a system can be intuitively judged by the Bode plot. That is, if the phase angle in the Bode plot is between -90° and 90°, the system can be determined to be in a stable state. If the maximum amplitude of the phase angle exceeds 90° or the minimum amplitude is less than -90°, the system is determined to be unstable.

[0092] Based on the principle of impedance analysis, harmonic stability analysis can be performed. When studying the global harmonic stability of a grid-connected inverter and grid interaction system, impedance analysis treats them as two independent subsystems. Impedance models are established separately based on their respective control structures and parameter characteristics. Changes in the structure and parameter characteristics of any component on one side will not affect the other, thus eliminating the need to rebuild the impedance model and reducing the difficulty of system analysis. After obtaining the impedance model, the equivalent circuit of the interaction system is represented by a linear network structure, and then the impedance stability criterion is used to analyze the system stability.

[0093] The above analysis shows that applying impedance analysis in new energy power generation networks relies on the establishment of impedance networks and the accurate formation of aggregated impedances; however, both face the following challenges:

[0094] 1) The establishment of an impedance network requires the impedance model of all network components as a foundation. However, current equipment suppliers have technical confidentiality requirements, making the internal control structure or parameters of power electronic devices "black box" or "grey box," making it difficult to establish detailed mechanistic state space or electromagnetic models. The "grey box" method can obtain the broadband impedance characteristics of the grid-connected inverter by relying solely on port voltage and current data, provided that the confidential information inside the grid-connected inverter is unknown.

[0095] 2) The formation of aggregated impedance needs to consider the aggregation path. Generally, it is assumed that power systems are both controllable and observable, so the zero-pole cancellation phenomenon in the impedance transfer function is not considered when aggregating impedance. However, in reality, there are still a few uncontrollable or unobservable power systems that may experience zero-pole cancellation during the aggregation process. Therefore, it is necessary to change the aggregation path; otherwise, the mode information of the system will be missed, resulting in misjudgment.

[0096] Step 3: Identify and analyze the zero-pole cancellation phenomenon during the impedance polymerization process, specifically including:

[0097] After obtaining the impedance transfer function by fitting discrete impedance values, we can then obtain the impedance model of each device. The large-scale integration of power electronic equipment and the expansion of power system scale have made the grid structure of power systems, especially new energy power systems, more complex. Therefore, before using impedance models to analyze related problems, it is necessary to first simplify the analysis based on the interconnection structure between the impedance models of each part, preserving their dynamic characteristics. This simplifies the analysis process and improves efficiency without introducing errors or large inaccuracies in the analysis results.

[0098] Currently, existing aggregation paths for impedance networks assume that the aggregated system possesses both observability and controllability, but they do not consider the unobservability and uncontrollability issues caused by pole-zero cancellation of the transfer function during aggregation. When pole-zero cancellation occurs, the aggregated network loses some of its original information, rendering the observability-and-controllability-based analysis method ineffective. To ensure the reliability of subsequent analyses, a different aggregation path should be chosen.

[0099] For parallel aggregation of independent impedance networks, the transfer functions before and after aggregation can be expressed by equations (11) and (12) respectively, provided that the impedance values ​​remain unchanged after aggregation.

[0100]

[0101]

[0102] In the formula, Z C For the equivalent impedance of the parallel aggregation network, N A N B D A D B The polynomials formed by the zeros and poles of the independent networks A and B before aggregation are N′ and N′ respectively. A =N A / (s-λ0), N′ B =N B / (s-λ0), where λ0 is the right half-plane zero shared by systems A and B.

[0103] Similarly, when independent impedance networks are aggregated in series, the numerical values ​​remain unchanged, and the transfer functions before and after aggregation can be expressed by equations (13) and (14), respectively.

[0104]

[0105]

[0106] In the formula, Z D For the equivalent impedance of the series-converged network, D′ A =D A / (s-γ0), D′ B =D B / (s-γ0), where γ0 is the right half-plane pole shared by systems A and B.

[0107] Z A and Z B Each pair of conjugate complex poles corresponds to a peak value in the amplitude-frequency response curve, and each pair of conjugate complex zeros corresponds to a valley value. For parallel connections, if Z A and Z B If the amplitude-frequency response curves of systems A and B have the same valley frequency, then the amplitude-frequency response curves of the subsystem resulting from the aggregation of systems A and B have no peak values ​​at the same frequency, indicating that zero-pole cancellation occurred during the aggregation process. For series connections, if Z A and Z B If the amplitude-frequency response curves of systems A and B have the same peak frequency at the same frequency, then the amplitude-frequency response curves of the subsystem after aggregation of systems A and B have no valley at the same frequency, that is, zero-pole cancellation occurs during the aggregation process.

[0108] Based on the above analysis, in order to avoid zero-pole cancellation during impedance aggregation, it is necessary to avoid aggregating two parallel subsystems with the same valley value of the amplitude-frequency response curve or two series subsystems with the same peak value of the amplitude-frequency response curve. In other words, in the parallel aggregation process, select subsystems that do not have the same zero point, and in the series aggregation process, select subsystems that do not have the same pole point, that is, change the impedance aggregation path.

[0109] Step 4: Build a multi-parallel grid-connected inverter system in Matlab / Simulink for simulation. Select different impedance aggregation paths and use impedance analysis to perform system stability analysis to further verify the effectiveness and practicality of the proposed aggregation method.

[0110] This invention takes a multi-parallel GCI system as an example. First, the impedance model of the inverter system under gray box background is obtained by using the VF algorithm and compared with the system impedance model obtained after frequency sweep to obtain discrete data. Second, the Bode plot of the system under different aggregation paths is analyzed with or without considering zero-pole cancellation. Finally, the system stability is determined.

[0111] Figure 2 This is a schematic diagram illustrating the discrete impedance data measurement and calculation principle of this invention. This invention injects voltage disturbances on the series side and current disturbances on the parallel side to stabilize the DC-side voltage. The disturbance injection device injects voltage / current disturbances under specific harmonics into the grid-connected inverter under test. After passing through the grid-connected inverter circuit, a current / voltage response is generated, and the impedance data under that harmonic is calculated. The disturbance injection process is as follows: Figure 2 As shown in the figure, V dc U is a DC voltage. h For the injected series voltage, I h The injected parallel current is represented by L1, which is the inverter-side inductance, L2, which is the grid-side inductance, and C is the filter capacitor Z. inv i is the output impedance of the inverter. abc and u abc These represent the input frequency response analyzer's voltage and current based on the abc axes, with PCC as the common coupling point, and Z... g U is the grid-side impedance. g This is the grid-side voltage.

[0112] Figure 3 This is a flowchart of the VF algorithm of this invention. It details how to use the VF algorithm to obtain the equivalent impedance of electrical components.

[0113] Figure 4 This is a schematic diagram of the distributed photovoltaic grid connection model of the present invention. The system includes a wind farm, a photovoltaic power station, and an equivalent AC grid.

[0114] Figure 5 This is the impedance network diagram for new energy power generation in this invention. Figure 4 Each component in the illustrated new energy power generation network is essentially an impedance model. By connecting the impedances of each component according to the system topology, a complete new energy power generation impedance network can be formed, such as... Figure 5 As shown.

[0115] Figure 6 This is a diagram illustrating the impedance network aggregation process of the new energy power generation system according to the present invention. When performing harmonic stability analysis on the impedance network of the new energy power generation system, it is necessary to first determine the "source side" and "load side" impedances of the node to be analyzed through impedance aggregation. Figure 6 Taking node X as an example, the impedance polymerization process of each part and the final polymerization result are shown in detail.

[0116] Figure 7 This is a circuit diagram of the multi-parallel GCI system used in the verification phase of this invention. This invention uses a multi-parallel GCI system as an example, where Z... i Z represents the line impedance between node i and node ④. is Z is the source-side impedance of node i. ilLet i be the load-side impedance at node i, where i = 1, 2, 3. First, the impedance model of the inverter system under gray box background is obtained using the VF algorithm and compared with the system impedance model obtained after frequency sweep to obtain discrete data. Second, the Bode plots of the system under different aggregation paths are analyzed, whether or not zero-pole cancellation is considered. Finally, the system stability is determined.

[0117] Figure 8 This is the Bode plot of the inverter impedance frequency response of the present invention. The Bode plot of the inverter impedance transfer function obtained using discrete impedance data is shown as the black dashed line. The Bode plot of the impedance transfer function obtained using the VF algorithm is shown as the solid line. The purple solid line represents the impedance frequency response Bode plot obtained by fitting the initial order N=1 using the VF algorithm; the blue solid line represents the impedance frequency response Bode plot obtained by fitting the initial order N=2 using the VF algorithm; and the red solid line represents the impedance frequency response Bode plot obtained by fitting the initial order N=3 using the VF algorithm. As can be seen from the figure, the first-order and second-order fitted curves have significant errors in impedance amplitude and phase compared to the impedance curve obtained using discrete impedance data. However, the third-order fitted curve basically coincides with the impedance curve obtained using discrete impedance data. That is, in this example, the impedance fitting curve calculated by the VF algorithm in the gray box model with an initial order N=3 has an error within the allowable range and can be used for further experiments.

[0118] Figure 9 This is the aggregation path diagram for the multi-parallel GCI system of this invention. To simplify the stability analysis of the multi-grid-connected inverter system, it is necessary to aggregate the equivalent impedance network of the multi-grid-connected inverter system. The multi-grid-connected inverter system has four nodes. This invention first obtains the system impedance aggregation path starting from node ④. The impedance aggregation process is as follows: Figure 10 As shown, the source-side impedance and Z g All grounded, Z Line1 =Z 1S +Z1, Z Line2 =Z 2S +Z2, Z Line3 =Z 3S +Z3. Z 4_1 Z 4_2 These are the first and second steps of obtaining the system aggregate impedance starting from node ④, respectively, where Z4 is the system aggregate impedance obtained starting from node ④.

[0119] Figure 10 The figure shows the Bode plot of Z4 fitted by the VF algorithm in this invention, with its amplitude and phase characteristics. The impedance Z4 obtained by aggregation has a harmonic frequency of 1702 Hz and a phase angle between -90° and 90°, indicating that the multi-parallel GCI system is stable after the formation of Z4.

[0120] Figure 11The figure shows the voltage waveform of node ④ in the multi-parallel GCI system after the aggregation path of this invention. As can be seen from the figure, the voltage waveform output by node ④ is not a standard sine wave. At about 1.5s, the voltage waveform begins to oscillate and gradually becomes out of control. This indicates that the multi-parallel GCI system after aggregation is unstable. This phenomenon is inconsistent with the aforementioned theoretical analysis results, and the reasons for the inconsistency need to be analyzed.

[0121] Figure 12 This invention provides Z-fitting based on the VF algorithm. Linei (i=1,2) Bode plot. From the plot, we can see that Z... Line1 and Z Line2 They share a common valley frequency of 1671 Hz, and their phase angles are not within the range of -90° to 90°, indicating that the Z-wave pattern formed after simple cascading... Line1 Small system and Z Line2 The small system is not stable. This may affect the determination of system stability.

[0122] Figure 13 This invention provides Z-fitting based on the VF algorithm. 4_1 Bode plot. (Z) Line1 and Z line2 After parallel processing, as shown in the figure, in Z... 4_1 During the formation of Z Line1 and Z line2 There is no peak at the valley frequency (1671Hz), and its phase angle is between [-90°, 90°], which is consistent with Z. Line1 and Z line2 The inconsistency in stability indicates that impedance transfer functions with the same zero point cannot be used for parallel connection.

[0123] Figure 14 This is the improved aggregation path diagram for a multi-parallel GCI system according to the present invention. The aforementioned aggregation path, due to the parallel connection of two equivalent impedances with the same zero point in the first aggregation step, exhibits zero-point cancellation during aggregation, leading to discrepancies between theoretical and practical results in system stability analysis and causing misjudgments. To address this, the aggregation path should be modified to avoid parallel connection of devices with the same zero point in their impedance transfer functions. The improved multi-parallel GCI system aggregation path is as follows: Figure 14 As shown. Z 3_1 Z 3_2 These are the first and second steps of obtaining the system aggregate impedance starting from node ③, respectively, and Z3 is the system aggregate impedance obtained starting from node ③.

[0124] Figure 15This is the Bode plot of Z3 obtained by fitting the VF algorithm according to the present invention. The figure shows its amplitude and phase. The impedance Z3 obtained by aggregation has a harmonic frequency of 1506Hz. Its phase angle is not all in the range of [-90°, 90°]. Near the harmonic frequency, the maximum phase angle is greater than 90° and the minimum phase angle is less than -90°, indicating that the multi-parallel GCI system is unstable after Z3 is formed.

[0125] Figure 16 The figure shows the voltage waveform at node ③ of the multi-parallel GCI system after the improved aggregation path of this invention. As can be seen from the figure, the voltage waveform output by node ③ is a standard sine wave, indicating that the multi-parallel GCI system after aggregation is unstable. This phenomenon is consistent with the aforementioned theoretical analysis results, that is, the impedance aggregation path that avoids zero-pole cancellation is correctly selected.

[0126] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0127] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0128] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A gray-box aggregation method for new energy power generation networks, characterized in that, Includes the following steps: Based on the VF algorithm, the equivalent impedance of electrical components used to construct new energy power generation networks is obtained; The new energy power generation network is constructed by aggregating the equivalent impedances, wherein the aggregation includes parallel aggregation and series aggregation; In the parallel aggregation process, subsystems that do not have the same zero point are selected for aggregation; In the tandem aggregation process, subsystems that do not have the same poles are selected for aggregation; In the process of constructing the new energy power generation network, the electrical components are connected according to the system topology based on the equivalent impedance model. After harmonic stability analysis is performed using impedance analysis, the new energy power generation network is generated. In the process of harmonic stability analysis, the source-side equivalent impedance and load-side equivalent impedance of the node to be analyzed are obtained to perform harmonic stability analysis. The expression for harmonic stability analysis is as follows: In the formula, T m To achieve the minimum loop gain of the system, V S It is the output voltage of the power supply subsystem when it is running alone; V L It is the input voltage of the load subsystem. Z S and Z L These are the source-side equivalent impedance and the load-side equivalent impedance, respectively. In the process of harmonic stability analysis, based on the Middlebrook stability criterion, an improved criterion represented by the GMPM criterion is adopted. By defining prohibited regions for the amplitude margin and phase margin of the new energy power generation network system, the stability of the new energy power generation network is determined. The conditional expression for the prohibited regions is as follows: In the formula, GM This is the gain margin; In the process of constructing the new energy power generation network, the transfer function expression before and after the first aggregation of the parallel aggregation is as follows: In the formula, Z C For the equivalent impedance of the parallel aggregation network, N A 、N B 、D A 、D B These are the polynomials composed of the zeros and poles of the independent networks A and B before aggregation. , , This is the right half-plane zero point shared by systems A and B; The transfer function expressions before and after the second aggregation in the cascade aggregation are as follows: In the formula, Z D The equivalent impedance of the series-connected aggregation network, , , The pole in the right half-plane is shared by systems A and B. Based on the transfer function expressions before and after the first aggregation and the transfer function expressions before and after the second aggregation, it is determined whether zero-pole cancellation occurs during the aggregation process. Specifically, in the parallel aggregation process, subsystems without the same zeros are selected for aggregation to avoid zero-pole cancellation; in the series aggregation process, subsystems without the same poles are selected for aggregation to avoid zero-pole cancellation.

2. The gray box aggregation method for new energy power generation networks according to claim 1, characterized in that: In the process of obtaining the equivalent impedance of electrical components, the equivalent impedance of the electrical components is obtained using the vector matching method based on the gray box background. The new energy power generation network is generated by constructing the equivalent impedance model.

3. The gray box aggregation method for new energy power generation networks according to claim 2, characterized in that: In the process of obtaining the equivalent impedance, voltage disturbances are injected on the series side and current disturbances are injected on the parallel side to stabilize the DC side voltage. Injecting voltage / current disturbances into the electrical component under test generates a current / voltage response after passing through the electrical component's circuit, thus obtaining impedance data under harmonic conditions; Based on the impedance data, the impedance of the electrical components is fitted with a gray box using the VF algorithm to obtain the equivalent impedance and construct the equivalent impedance model.

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