A resonance peak suppression method, device and inverter parallel system

Abstract

This application provides a method, device, and inverter parallel system for suppressing resonance peaks. Applied to an inverter parallel system, multiple inverters are connected to the power grid in parallel via corresponding LCL filters. The grid-connected current has a first resonance peak. This method determines the target value of virtual damping based on the first frequency of the first resonance peak, a preset bandpass filter transfer function model, and a preset virtual damping suppression coefficient. The first frequency is determined based on the number of inverters. According to the target value of virtual damping, the first resonance peak is suppressed through the inverter control loop. Thus, the target value of virtual damping effectively suppresses the first resonance peak and avoids affecting the current gain of other frequency bands in the grid-connected current, ensuring the stability of the power system.

Description

Technical Field

[0001] This application relates to the field of photovoltaic power generation technology, and in particular to a method, device and inverter parallel system for suppressing resonance peaks. Background Technology

[0002] With the rapid development of the photovoltaic industry, more and more power electronic devices are being connected to the power grid, making the characteristics of the grid more complex. In long-distance power transmission, the grid impedance gradually increases, leading to a gradual decrease in the short-circuit impedance ratio and creating a weak grid, a harsh operating condition. When multiple inverters with LCL (inductor-capacitor-inductor) filters are connected to a weak grid, the large grid impedance and harsh grid environment cause the grid current to easily oscillate. Especially when multiple inverters have different capacities, the imbalance of grid-connected currents can easily lead to coupling between inverters, resulting in multiple resonance peaks in the inverter's grid-connected current, which seriously affects the stability of the power system.

[0003] When multiple LCL inverters are connected in parallel and not synchronously, the resonance characteristics of the entire system are extremely complex due to the excitation of the inverters themselves, the coupling of multiple inverters, and the influence of the large power grid, and the resonance peak is difficult to suppress. Summary of the Invention

[0004] To address the aforementioned technical problems, this application provides a method, apparatus, and inverter parallel system for suppressing resonance peaks, thereby resolving the issue that existing technologies cannot effectively suppress resonance peaks in the grid-connected current of inverters.

[0005] To achieve the above technical objectives, the embodiments of this application provide the following technical solutions:

[0006] Firstly, this specification provides a resonance peak suppression method applied to a parallel inverter system. Multiple inverters are connected in parallel via corresponding LCL filters and then connected to the power grid. The grid-connected current has a first resonance peak. The method includes:

[0007] Based on the first frequency of the first resonant peak, the preset bandpass filter transfer function model, and the preset virtual damping suppression coefficient, the target value of the virtual damping is determined, wherein the first frequency is determined based on the number of inverters;

[0008] The first resonance peak is suppressed by the control loop of the inverter according to the target value of the virtual damping.

[0009] In one implementation, the target value of virtual damping is determined based on the first frequency of the first resonant peak, a preset bandpass filter transfer function model, and a preset virtual damping suppression coefficient, including:

[0010] The first frequency is used as the center angular frequency and input to the transfer function model of the bandpass filter to obtain the damping value of the bandpass filter at the first frequency.

[0011] The product of the damping value of the bandpass filter at the first frequency and the virtual damping suppression coefficient is taken as the target value of the virtual damping.

[0012] In one embodiment, the bandpass filter transfer function model includes a bandwidth, which is determined based on the bandwidth of the first resonant peak.

[0013] In one implementation, the first frequency is determined based on the number of inverters, including:

[0014] The first frequency is determined based on the number of inverters, the current impedance of the power grid, and the configuration information of the LCL filter.

[0015] In one embodiment, the grid-connected current further has a second resonant peak; the method further includes:

[0016] Based on the second frequency of the second resonant peak and the preset notch filter transfer function model, the feedback coefficient of the capacitor current is determined, wherein the second frequency is greater than the first frequency.

[0017] The second resonant peak is suppressed by the control loop of the inverter based on the feedback coefficient of the capacitor current.

[0018] In one implementation, the feedback coefficient of the capacitor current is determined based on the second frequency of the second resonant peak and a preset notch filter transfer function model, including:

[0019] The second frequency is used as the notch filter frequency and input into the notch filter transfer function model to obtain the feedback coefficient of the capacitor current.

[0020] In one embodiment, the notch filter transfer function model includes a notch width, which is determined based on the bandwidth of the second resonant peak.

[0021] In one implementation, the second frequency is obtained by the following method:

[0022] The second frequency is obtained based on the configuration information of the LCL filter.

[0023] In one embodiment, the control loop of the inverter includes a first subtractor, a current closed-loop controller, a second subtractor, a current amplitude-frequency controller, a first feedback controller, and a second feedback controller.

[0024] The current amplitude-frequency controller is used to output the inverter-side current of the LCL filter, the grid-connected-side current of the LCL filter, and the capacitor current of the LCL filter.

[0025] The first subtractor is used to output a first current difference between the target output current of the inverter and the inverter-side current.

[0026] The current closed-loop controller is used to output a voltage regulation value based on the first current difference;

[0027] The first feedback controller is used to generate a feedback value of the grid-connected current based on the grid-connected current and the target value of the virtual damping;

[0028] The second feedback controller is used to generate a feedback value for the capacitor current based on the capacitor current and the feedback coefficient of the capacitor current;

[0029] The second subtractor is used to output a first voltage difference to the current amplitude-frequency controller based on the voltage adjustment value, the feedback value of the grid-connected current, and the feedback value of the capacitor current.

[0030] In one embodiment, the current amplitude-frequency controller includes a gain controller, a third subtractor, an inverter-side current calculation unit, a fourth subtractor, a capacitor voltage calculation unit, a fifth subtractor, and a grid-connected current calculation unit.

[0031] The gain controller is used to output the inverter port voltage based on the first voltage difference and the equivalent gain of the inverter;

[0032] The third subtractor is used to generate a second voltage difference based on the inverter port voltage and the capacitor voltage of the LCL filter;

[0033] The inverter-side current calculation unit is used to output the inverter-side current based on the second voltage difference and the inverter-side filter inductor impedance of the LCL filter.

[0034] The fourth subtractor is used to generate a second current difference between the inverter-side current and the grid-connected current, and uses the second current difference as the capacitor current.

[0035] The capacitor voltage calculation unit is used to output the capacitor voltage based on the capacitor current and the capacitor impedance of the LCL filter;

[0036] The fifth subtractor is used to output the third voltage difference between the capacitor voltage and the grid connection point voltage of the inverter;

[0037] The grid-connected current calculation unit is used to output the grid-connected current based on the third voltage difference and the grid-connected filter inductor impedance of the LCL filter.

[0038] Secondly, this specification provides a resonance peak suppression device applied to a parallel inverter system. Multiple inverters are connected in parallel via corresponding LCL filters and then connected to the power grid. The grid-connected current has a first resonance peak. The device includes:

[0039] The first processing module is used to determine the target value of virtual damping based on the first frequency of the first resonant peak, a preset bandpass filter transfer function model, and a preset virtual damping suppression coefficient, wherein the first frequency is determined based on the number of inverters.

[0040] The second processing module is used to suppress the first resonance peak through the control loop of the inverter according to the target value of the virtual damping.

[0041] In one embodiment, the grid-connected current further has a second resonant peak; the device further includes:

[0042] The third processing module is used to determine the feedback coefficient of the capacitor current based on the second frequency of the second resonant peak and a preset notch filter transfer function model, wherein the second frequency is greater than the first frequency.

[0043] The second processing module is also used to suppress the second resonance peak through the control loop of the inverter based on the feedback coefficient of the capacitor current.

[0044] In one embodiment, the control loop of the inverter includes a first subtractor, a current closed-loop controller, a second subtractor, a current amplitude-frequency controller, a first feedback controller, and a second feedback controller.

[0045] The current amplitude-frequency controller is used to output the inverter-side current of the LCL filter, the grid-connected-side current of the LCL filter, and the capacitor current of the LCL filter.

[0046] The first subtractor is used to output a first current difference between the target output current of the inverter and the inverter-side current.

[0047] The current closed-loop controller is used to output a voltage regulation value based on the first current difference;

[0048] The first feedback controller is used to generate a feedback value of the grid-connected current based on the grid-connected current and the target value of the virtual damping;

[0049] The second feedback controller is used to generate a feedback value for the capacitor current based on the capacitor current and the feedback coefficient of the capacitor current;

[0050] The second subtractor is used to output a first voltage difference to the current amplitude-frequency controller based on the voltage adjustment value, the feedback value of the grid-connected current, and the feedback value of the capacitor current.

[0051] In one embodiment, the current amplitude-frequency controller includes a gain controller, a third subtractor, an inverter-side current calculation unit, a fourth subtractor, a capacitor voltage calculation unit, a fifth subtractor, and a grid-connected current calculation unit.

[0052] The gain controller is used to output the inverter port voltage based on the first voltage difference and the equivalent gain of the inverter;

[0053] The third subtractor is used to generate a second voltage difference based on the inverter port voltage and the capacitor voltage of the LCL filter;

[0054] The inverter-side current calculation unit is used to output the inverter-side current based on the second voltage difference and the inverter-side filter inductor impedance of the LCL filter.

[0055] The fourth subtractor is used to generate a second current difference between the inverter-side current and the grid-connected current, and uses the second current difference as the capacitor current.

[0056] The capacitor voltage calculation unit is used to output the capacitor voltage based on the capacitor current and the capacitor impedance of the LCL filter;

[0057] The fifth subtractor is used to output the third voltage difference between the capacitor voltage and the grid connection point voltage of the inverter;

[0058] The grid-connected current calculation unit is used to output the grid-connected current based on the third voltage difference and the grid-connected filter inductor impedance of the LCL filter.

[0059] Thirdly, the embodiments of this specification provide an inverter parallel system, including: multiple inverters and a control device;

[0060] The multiple inverters are connected in parallel through corresponding LCL filters and then connected to the power grid.

[0061] The control device performs the resonance peak suppression method as described in any of the preceding claims to suppress the resonance peak of the grid-connected current through the control loop of the inverter.

[0062] Fourthly, embodiments of this specification provide a computer-readable storage medium storing a computer program that, when executed by a processor, implements the resonance peak suppression method as described in any of the preceding claims.

[0063] Fifthly, embodiments of this specification provide a computer program product or a computer program, the computer program product including a computer program stored in a computer-readable storage medium; a processor of the computer device reads the computer program from the computer-readable storage medium, and when the processor executes the computer program, it implements the resonance peak suppression method as described in any of the preceding claims.

[0064] As can be seen from the above technical solutions, the embodiments of this application provide a resonance peak suppression method, device, and inverter parallel system, which are applied to an inverter parallel system. Multiple inverters are connected to the power grid in parallel through corresponding LCL filters. The grid-connected current has a first resonance peak. The resonance peak suppression method determines the target value of virtual damping based on the first frequency of the first resonance peak, a preset bandpass filter transfer function model, and a preset virtual damping suppression coefficient. The first frequency is determined based on the number of inverters. According to the target value of virtual damping, the first resonance peak is suppressed through the control loop of the inverter. Thus, the first resonance peak can be effectively suppressed by the target value of virtual damping, and the influence on the current gain of other frequency bands in the grid-connected current is avoided, ensuring the stability of the power system. Attached Figure Description

[0065] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0066] Figure 1 This is a flowchart illustrating a resonance peak suppression method provided for implementation of this specification.

[0067] Figure 2 This is a schematic diagram of an equivalent circuit model of n inverters connected in parallel, provided for the implementation of this specification.

[0068] Figure 3 This is a schematic diagram of the Norton equivalent model of an inverter provided for the implementation of this specification.

[0069] Figure 4 A G provided for the implementation of this specification x Bode plot of (s).

[0070] Figure 5 A G provided for the implementation of this specification y Bode plot of (s).

[0071] Figure 6 A G provided for the implementation of this specification z Bode plot of (s).

[0072] Figure 7 This is a schematic diagram of the control circuit of an inverter provided for the implementation of this specification.

[0073] Figure 8 A schematic diagram of the control circuit of another inverter provided for an embodiment of this specification.

[0074] Figure 9 A flowchart illustrating another resonance peak suppression method provided for the implementation of this specification.

[0075] Figure 10 The G-suppression of the first resonance peak provided for the embodiments of this specification x Bode plot of (s).

[0076] Figure 11 The G-shaped peak suppression provided for the embodiments of this specification x Bode plot of (s).

[0077] Figure 12 The embodiment provided in this specification provides G that simultaneously suppresses the first and second resonance peaks. x Bode plot of (s).

[0078] Figure 13 This is a schematic diagram of a resonance peak suppression device provided for the implementation of this specification. Detailed Implementation

[0079] Unless otherwise defined, the technical or scientific terms used in the embodiments of this specification shall have the ordinary meaning understood by one of ordinary skill in the art to which this specification pertains. The terms "first," "second," and similar terms used in the embodiments of this specification do not indicate any order, quantity, or importance, but are merely used to avoid confusion of constituent elements.

[0080] Unless the context otherwise requires, throughout this specification, "a plurality of" means "at least two," and "including" is interpreted as open-ended or encompassing, that is, "including, but not limited to." In the description of this specification, terms such as "one embodiment," "some embodiments," "exemplary embodiment," "example," "specific example," or "some examples" are intended to indicate that a particular feature, structure, material, or characteristic associated with that embodiment or example is included in at least one embodiment or example of this specification. The illustrative representations of the above terms do not necessarily refer to the same embodiment or example.

[0081] The technical solutions in the embodiments of this specification will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this specification, and not all embodiments. Based on the embodiments in this specification, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this specification.

[0082] Overview

[0083] As described in the background section, with the rapid development of the photovoltaic industry, more and more power electronic devices are being connected to the power grid. This makes the characteristics of the power grid more complex. Furthermore, the construction of photovoltaic power stations in the Gobi Desert has led to long-distance power transmission lines, causing the grid impedance to gradually increase and the short-circuit impedance ratio to gradually decrease, resulting in a weak grid and other severe operating conditions. When multiple inverters with LCL filters are connected to a weak grid, the large grid impedance and harsh grid environment make the grid current prone to oscillations. Especially when multiple inverters have different capacities, the imbalance of grid-connected currents can easily lead to coupling between inverters, resulting in multiple resonance peaks in the inverter's grid-connected current, which seriously affects the stability of the power system.

[0084] When multiple LCL inverters are connected in parallel and not synchronously, due to their own inverter excitation, multi-inverter coupling and the influence of the large power grid, the grid-connected current will have a low-frequency resonance peak. The resonance frequency of the low-frequency resonance peak changes with the number of inverters connected and the grid impedance. As a result, the resonance characteristics of the entire system are extremely complex, the resonance peak is difficult to suppress, the possibility of grid-connected current oscillation is greatly increased, and the stability of the power system is difficult to guarantee.

[0085] Currently, the DD-Σ method, or a combination of PI control and capacitor current feedback, is commonly used to suppress resonance peaks. However, the DD-Σ method requires knowledge of the LCL filter parameters and the grid inductance, and necessitates the use of an impedance identification algorithm, making control complex. Furthermore, the grid inductance changes with the current, leading to significant control errors during resonance peak suppression and thus failing to effectively suppress resonance peaks in the grid-connected current. Additionally, due to the increased complexity of the resonance characteristics, simply adding capacitor current feedback to PI control is insufficient for effective resonance peak suppression and may suppress current gain in other frequency bands.

[0086] Therefore, it is necessary to provide a method for effectively suppressing the resonance peak in the grid-connected current of the inverter.

[0087] To address the problem that traditional methods cannot effectively suppress resonant peaks in the grid-connected current of inverters, and that suppressing resonant peaks can affect the current gain of other frequency bands in the grid-connected current, the inventors discovered that the virtual admittance control method has a better effect on suppressing low-frequency resonant peaks. Therefore, in this application's technical solution, the virtual admittance control method is improved to effectively suppress low-frequency resonant peaks. Specifically, it includes: determining a target value for virtual damping based on the first frequency of the first resonant peak, a preset bandpass filter transfer function model, and a preset virtual damping suppression coefficient. The first frequency is determined based on the number of inverters. According to the target value of virtual damping, the first resonant peak is suppressed through the inverter's control loop. Thus, the target value of virtual damping effectively suppresses the first resonant peak and avoids affecting the current gain of other frequency bands in the grid-connected current, ensuring the stability of the power system.

[0088] Meanwhile, the inventors discovered through research that high-frequency resonance peaks also exist in the grid-connected current. The resonant frequency of these high-frequency resonance peaks remains constant, mainly due to the connected LCL filter, and the capacitor current feedback control method shows good suppression effect on these peaks. Therefore, in this application's technical solution, the capacitor current feedback control method has been improved to effectively suppress high-frequency resonance peaks.

[0089] In addition, in order to further improve the suppression effect and response speed of the resonance peak in the grid-connected current, the resonance peak suppression method provided in the embodiments of this specification also defines the specific method for determining the first frequency of the first resonance peak and the second frequency of the second resonance peak.

[0090] Based on the above inventive concept, the resonance peak suppression method provided in the embodiments of this specification will be described exemplarily below.

[0091] Exemplary methods

[0092] This specification provides a resonance peak suppression method applied to a parallel inverter system. Multiple inverters are connected in parallel via corresponding LCL filters and then connected to the power grid. The grid-connected current exhibits a first resonance peak. Figure 1 As shown, the method includes:

[0093] S101. Based on the first frequency of the first resonant peak, the preset bandpass filter transfer function model, and the preset virtual damping suppression coefficient, determine the target value of the virtual damping, wherein the first frequency is determined based on the number of inverters.

[0094] Specifically, the inverter can receive direct current (DC) from solar panels and other sources, convert it to alternating current (AC), and then connect it to the power grid. Each inverter is connected to the grid via a corresponding LCL filter. The power grid can be a three-phase grid, for example, it can include phases a, b, and c, each with identical characteristics; that is, each phase in the grid-connected current can be individually suppressed for resonance peaks.

[0095] For any one of the three phases a, b, and c, the target value of the virtual damping can be determined based on the first frequency of the first resonant peak of that phase in the grid-connected current of the inverter, the preset bandpass filter transfer function model, and the preset virtual damping suppression coefficient.

[0096] The first resonant peak can be a low-frequency resonant peak, and its first frequency is the resonant frequency of the first resonant peak. This first frequency can be adaptively updated based on the current number of inverters. The current number of inverters refers to the number of inverters currently connected to the grid. For example, the number of inverters connected to the grid can be updated based on their operating status (e.g., fault status), external environment (e.g., light intensity), and grid connection requirements. It is understandable that the first frequency can also be determined based on both the current number of inverters and the current impedance of that phase in the grid. The current impedance of that phase in the grid is the impedance of the equivalent circuit of the grid at the current transmission distance. In practice, the equivalent impedance of the grid in each phase can be pre-configured, and updated when the transmission distance of the grid changes.

[0097] In practice, the first frequency can be determined based on the current number of inverters, the current impedance of the phase in the grid, and the target correspondence. The target correspondence can be used to characterize the correspondence between the number of inverters, the equivalent impedance of the grid, and the first frequency.

[0098] The transfer function model of a bandpass filter can be the transfer function model H(s) of a bandpass filter in the s-domain, for example, as shown in equation (1):

[0099]

[0100] In the formula, D is the bandwidth coefficient of the passband, which can be a preset value; ω d denoted as the center angular frequency of the bandpass filter, and s is the Laplace operator.

[0101] The virtual damping suppression coefficient can include parameters used to simulate the damping effect, reflecting the effect of virtual damping. The value of the virtual damping suppression coefficient can be pre-configured. For example, the damping suppression effect under different virtual damping suppression coefficients can be simulated experimentally, and the value of the virtual damping suppression coefficient can be determined based on the damping suppression effect under different virtual damping suppression coefficients. Thus, the first resonance peak can be effectively suppressed based on the target value of virtual damping determined by the virtual damping suppression coefficient.

[0102] In practice, the first frequency of the first resonant peak can be used as the center angular frequency input to the bandpass filter transfer function model to obtain the damping value of the bandpass filter at the first frequency. Based on the damping value of the bandpass filter at the first frequency and the virtual damping suppression coefficient, the target value of the virtual damping is determined. Since the bandpass filter has passband characteristics, it can suppress a single frequency band without affecting the gain of other frequency bands. Thus, the target value of the virtual damping can suppress the current gain only at the first frequency, avoiding the impact on the current gain of other frequency bands in the grid-connected current, thereby effectively improving the stability of the power system.

[0103] S102. Based on the target value of virtual damping, suppress the first resonance peak through the control loop of the inverter.

[0104] Specifically, the target value of virtual damping can be superimposed on the control circuit of the corresponding inverter in that phase to suppress the first resonance peak through the target value of virtual damping, thereby achieving effective suppression of the first resonance peak in the grid-connected current.

[0105] In one feasible implementation, based on the first frequency of the first resonant peak, a preset bandpass filter transfer function model, and a preset virtual damping suppression coefficient, the target value of the virtual damping is determined, including:

[0106] By inputting the first frequency as the center angular frequency into the bandpass filter transfer function model, the damping value of the bandpass filter at the first frequency is obtained.

[0107] The product of the damping value of the bandpass filter at the first frequency and the virtual damping suppression coefficient is used as the target value of the virtual damping.

[0108] Specifically, the first frequency can be used as the center angular frequency input to the bandpass filter transfer function model to obtain the damping value of the bandpass filter at the first frequency. For example, the first frequency can be substituted into ω in equation (1). d And H(s) after substituting into the first frequency is used as the damping value of the bandpass filter at the first frequency.

[0109] After obtaining the damping value of the bandpass filter at the first frequency, the damping value of the bandpass filter at the first frequency can be multiplied by the virtual damping suppression coefficient, and the product of the two can be used as the target value of the virtual damping. This allows for the rapid and effective determination of the target value of the virtual damping. Furthermore, based on the target value of the virtual damping, the current gain at the first frequency can be suppressed only, avoiding the impact on the current gain of other frequency bands in the grid-connected current, and effectively improving the stability of the power system.

[0110] In practice, the target value Z of the virtual damping can be determined using equation (2). X (s):

[0111]

[0112] In the formula, z n The virtual damping suppression coefficient is used, and thus, the first frequency can be substituted into ω in equation (2). d The target value of virtual damping can be obtained directly.

[0113] In one feasible implementation, the bandpass filter transfer function model includes a bandwidth determined based on the bandwidth of the first resonant peak.

[0114] Specifically, the transfer function model of a bandpass filter can include the center angular frequency and the bandwidth. The bandwidth is the bandwidth coefficient of the passband of the bandpass filter, which can characterize the width of the current signal used for damping suppression.

[0115] In practice, the specific value of the bandwidth coefficient of the passband can be determined based on the bandwidth of the first resonant peak. For example, without resonant peak suppression, the bandwidth of the first resonant peak in the grid-connected current at multiple historical moments can be detected, and the bandwidth coefficient of the passband can be determined based on the bandwidth of the first resonant peak at multiple historical moments. For example, the mean or median of the bandwidth of the first resonant peak at multiple historical moments can be used as the bandwidth coefficient of the passband. Thus, based on the target value of the virtual damping determined by the bandpass filter transfer function model, the first resonant peak can be effectively suppressed, and the impact on the current gain of other frequency bands in the grid-connected current can be effectively avoided, thereby effectively improving the stability of the power system.

[0116] In one feasible implementation, the first frequency is determined based on the number of inverters, including:

[0117] The first frequency is determined based on the number of inverters, the current impedance of the grid, and the configuration information of the LCL filter.

[0118] Specifically, the number of inverters connected to the grid can be obtained in real time through communication with each inverter or with the grid control unit. At the same time, it can detect in real time whether the configuration value of the grid's equivalent impedance has changed. For example, when the grid's equivalent impedance changes, the user can update the grid's equivalent impedance through human-computer interaction.

[0119] The configuration information of the LCL filter may include the capacitance value of the filter capacitor in each phase and the inductance value of each filter inductor. The filter inductors may include grid-side filter inductors and inverter-side filter inductors.

[0120] Specifically, when at least one of the following data changes—the number of inverters connected to the grid, the equivalent impedance of the grid, and the configuration information of the LCL filter—the first frequency can be updated based on the current number of inverters, the current impedance of the grid, and the configuration information of the LCL filter. This enables adaptive updating of the first frequency, improves the effectiveness of determining the target value of the virtual damping, and allows for effective suppression of the first resonance peak based on the target value of the virtual impedance.

[0121] Understandably, when the number of inverters connected to the grid, the equivalent impedance of the grid, and the configuration information of the LCL filter remain unchanged, it is not necessary to update the first frequency. Instead, the target value of the virtual damping can be determined based on the latest update result of the first frequency, thus avoiding repeated calculations of the first frequency. This allows for an effective improvement in the response speed to the first resonance peak while ensuring effective suppression of the first resonance peak.

[0122] In implementation, the first frequency is determined based on the number of inverters, the current impedance of the grid, and the configuration information of the LCL filter. This may include:

[0123] The first frequency is determined based on the number of inverters, the current impedance of the power grid, the configuration information of the LCL filter, and a preset first correspondence.

[0124] The first correspondence is used to characterize the correspondence between the number of inverters, the equivalent impedance of the power grid, the configuration information of the LCL filter, and the first frequency.

[0125] Specifically, a first correspondence can be pre-constructed. This first correspondence can be used to characterize the correspondence between the number of inverters connected to the grid, the equivalent impedance of the grid, the configuration information of the LCL filter, and the first frequency. The first correspondence can be a function model, a mapping table, etc., which can be set according to actual needs.

[0126] In implementation, the first grid-connected current data of the inverter can be obtained under different grid configuration data. The grid configuration data may include the number of inverters connected to the grid, the equivalent impedance of the grid, and the configuration information of the LCLs connected to each inverter. The first grid-connected current data may include the detection result of the first frequency of the first resonant peak. A first correspondence is obtained by fitting the first grid-connected current data under different grid configuration data. In addition, the first correspondence can also be determined based on the pole characteristics of the inverter's transfer function model, thereby enabling the rapid and accurate construction of the first correspondence.

[0127] In determining the first frequency, the current number of inverters, the current impedance of the power grid, and the configuration information of the LCL filter can be input into the function model representing the first correspondence to obtain the determination result of the first frequency. Alternatively, the current number of inverters, the current impedance of the power grid, and the configuration information of the LCL filter can be matched with the data in the mapping table representing the first correspondence, and the first frequency can be determined according to the matching result. This allows the first frequency to be obtained quickly and accurately, effectively suppressing the first resonance peak and further improving the response speed to the first resonance peak.

[0128] In one feasible implementation, the grid-connected current also has a second resonant peak; the method further includes:

[0129] Based on the second frequency of the second resonant peak and the preset notch filter transfer function model, the feedback coefficient of the capacitor current is determined, and the second frequency is greater than the first frequency.

[0130] Based on the feedback coefficient of the capacitor current, the second resonant peak is suppressed through the control loop of the inverter.

[0131] Specifically, the second frequency of the second resonant peak is the resonant frequency of the second resonant peak. The second frequency can be greater than the first frequency; that is, the second resonant peak can be a high-frequency resonant peak. The second frequency of the second resonant peak can be a fixed value. For example, the magnitude of the second frequency can be determined based on the configuration information of the LCL filter connected to the inverter in that phase. It is understood that the structure and configuration information of each inverter, as well as the configuration information of the LCL filter connected to each inverter, can be the same, and the configuration information of the LCL filter in each phase can be the same to ensure the uniformity of the system.

[0132] For any one of the three phases a, b, and c, the feedback coefficient of the capacitor current can be determined based on the second frequency of the second resonant peak of that phase in the inverter's grid-connected current and a preset notch filter transfer function model. The notch filter transfer function model can be the notch filter transfer function model Z in the s-domain. G (s), for example, can be shown as in equation (3):

[0133]

[0134] In the formula, d is the notch width, ω o This is the notch frequency of the notch filter, i.e., the center frequency.

[0135] In implementation, the second frequency of the second resonant peak can be used as the notch filter frequency input to the notch filter transfer function model to obtain the feedback coefficient of the capacitor current. Based on the feedback coefficient of the capacitor current, the second resonant peak is suppressed through the inverter control loop. For example, the feedback coefficient of the capacitor current can be superimposed on the corresponding inverter control circuit for that phase to suppress the second resonant peak through the feedback coefficient of the capacitor current, thereby effectively suppressing the second resonant peak in the grid-connected current. Since the notch filter can trap the gain of a fixed frequency band and thus filter harmonics of that fixed frequency band, the current gain at the second frequency can be suppressed only based on the feedback coefficient of the capacitor current, avoiding the impact on the current gain of other frequency bands in the grid-connected current, and effectively improving the stability of the power system.

[0136] Meanwhile, by suppressing the first resonance peak through the target value of virtual damping and by suppressing the second resonance peak through the feedback coefficient of capacitor current, the first and second resonance peaks can be suppressed independently through different methods.

[0137] In one feasible implementation, the feedback coefficient of the capacitor current is determined based on the second frequency of the second resonant peak and a preset notch filter transfer function model, including:

[0138] The second frequency is used as the notch filter frequency and input into the notch filter transfer function model to obtain the feedback coefficient of the capacitor current.

[0139] Specifically, the second frequency can be used as the notch filter frequency input to the notch filter transfer function model to obtain the feedback coefficient of the capacitor current. For example, the second frequency can be substituted into ω in equation (3). o And substitute the Z after the second frequency G (s) serves as the feedback coefficient for the capacitor current, enabling the rapid and effective determination of the capacitor current feedback coefficient. Furthermore, based on the capacitor current feedback coefficient, the current gain at the second frequency can be suppressed, avoiding the impact on the current gain of other frequency bands in the grid-connected current, thus effectively improving the stability of the power system.

[0140] In one feasible implementation, the notch filter transfer function model includes the notch width, which is determined based on the bandwidth of the second resonant peak.

[0141] Specifically, the notch filter transfer function model can include the notch frequency and the notch width, whereby the notch width can characterize the width of the current signal used for resonance suppression.

[0142] In practice, the specific value of the notch width can be determined based on the bandwidth of the second resonant peak. For example, without resonant peak suppression, the bandwidth of the second resonant peak in the grid-connected current at multiple historical moments can be detected, and the notch width can be determined based on the bandwidth of the second resonant peak at multiple historical moments. For example, the average or median of the bandwidth of the second resonant peak at multiple historical moments can be used as the notch width. Thus, based on the feedback value of the capacitor current determined by the notch filter transfer function model, the second resonant peak can be fully suppressed, and the impact on the current gain of other frequency bands in the grid-connected current can be effectively avoided, thereby effectively improving the stability of the power system.

[0143] In one feasible implementation, the second frequency is obtained by the following method:

[0144] The second frequency is obtained based on the configuration information of the LCL filter.

[0145] Specifically, a second correspondence can be pre-constructed, which can be used to characterize the correspondence between the configuration information of the LCL filter and the second frequency. The second correspondence can be a function model, a mapping table, etc., which can be set according to actual needs.

[0146] In implementation, the second grid-connected current data of the inverter can be obtained under different LCL configuration information. The second grid-connected current data can include the detection result of the second frequency of the second resonant peak, and a second correspondence can be obtained by fitting the second grid-connected current data under different LCL configuration information. In addition, the second correspondence can also be determined based on the pole characteristics of the inverter's transfer function model, thereby enabling the rapid and accurate construction of the second correspondence.

[0147] Specifically, after the configuration information of the LCL filter is determined or updated, the second frequency can be determined based on the configuration information of the LCL filter and the second correspondence. During the process of suppressing the resonance peak of the grid-connected current, the second frequency can remain unchanged until the updated value of the second frequency is received, thereby effectively suppressing the second resonance peak and further improving the response speed to the second resonance peak.

[0148] In one feasible implementation, the first correspondence and the second correspondence are determined by the following method:

[0149] Obtain the transfer function model of the inverter. The transfer function model is used to characterize the correspondence between the inverter's output current and the inverter's control coefficient and equivalent parallel admittance, the grid's equivalent admittance and target voltage, and the target output current of each inverter.

[0150] Based on the pole characteristics of the transfer function model, the first and second correspondences are determined.

[0151] Specifically, the inverter's output current is the current connected to the grid, i.e., the grid-connected current. The inverter's control coefficient is the parameter used to control the inverter's output current. The inverter's equivalent parallel admittance can be considered as the admittance of the equivalent circuit between the inverter and the grid.

[0152] The equivalent admittance of a power grid is the admittance of its equivalent circuit. The target voltage of a power grid is the voltage of the grid under ideal conditions (i.e., without interference and noise).

[0153] For any inverter, its target output current is the current that the inverter expects to provide to the grid, i.e., the grid-connected reference current.

[0154] In the parallel asynchronous operation mode of multiple inverters, to ensure system uniformity, all hardware and software parameters of each inverter are identical except for the grid-connected reference current. Therefore, the control coefficients of each inverter are equal, i.e., G. sk1 (s)=G sk2 (s)=…=G skn (s), G skj (s) represents the control coefficient of the j-th inverter, 1 ≤ j ≤ n, where n is the number of inverters connected to the grid; simultaneously, the equivalent parallel admittance of each inverter is equal, i.e., Y dx1 (s)=Y dx2 (s)=…=Y dxn (s), Y dxj (s) represents the equivalent parallel admittance of the j-th inverter in each phase; furthermore, the grid-connected reference currents of each inverter are not equal, i.e., I xg1f (s)≠I xg2f (s)≠…≠I xgnf (s), I xgjf (s) represents the grid-connected reference current of the j-th inverter in each phase.

[0155] For example, the structure of the equivalent circuit model of n inverters connected in parallel can be as follows: Figure 2 As shown, Figure 2 Middle,U dcL is the DC bus voltage. ij For the LCL filter connected to the j-th inverter, C is the inverter-side filter inductance in each phase. j Let L be the filter capacitor in each phase of the LCL filter connected to the j-th inverter. gj Z is the grid-side filter inductance in each phase of the LCL filter connected to the j-th inverter. xg U is the equivalent impedance of the power grid in each phase. PCC e is the grid connection point voltage in each phase. g This represents the grid voltage in each phase.

[0156] Based on the Norton equivalent model of a single inverter, when n inverters are connected in parallel asynchronously, the Norton equivalent model of each inverter is also connected to the same grid connection point (PCC). Specifically, this can be seen as follows: Figure 3 As shown. Figure 3 in,i dxj (s) represents the equivalent current source of the j-th inverter in each phase under a weak power grid. To meet the requirements of asynchronous operation of multiple inverters in parallel, the equivalent current source of each inverter is different, i.e., i dx1 (s)≠i dx2 (s)≠…≠i dxn (s), Y dxj (s) represents the equivalent parallel admittance of the j-th inverter in each phase under weak grid conditions, L xg (s) represents the equivalent inductance of the power grid in each phase, R xg (s) represents the equivalent resistance of the power grid in each phase.

[0157] In practice, the inverter's transfer function model can be used to characterize the relationship between the inverter's output current and the inverter's control coefficient and equivalent parallel admittance, the grid's equivalent admittance and target voltage, and the target output current of each inverter. For example, the inverter's transfer function model can be shown in equation (4):

[0158]

[0159] In the formula, i xgj (s) represents the output current of the j-th inverter in each phase; Y xg (s) represents the equivalent admittance of the power grid in each phase; I xghf (s) represents the grid-connected reference current in each phase of the h-th inverter, excluding the j-th inverter, where 1 ≤ h ≤ n-1, j ≠ h; e g (s) represents the target voltage of the power grid in each phase.

[0160] By performing a format conversion on equation (4), we can obtain:

[0161]

[0162] Among them, G x (s), G y (s) and G z (s) are all simplified expressions, as shown in equation (6):

[0163]

[0164] From equations (5) and (6), it can be seen that when n inverters of different capacities are connected in parallel and operated asynchronously, their resonance peak is mainly determined by G. x (s), G y (s) and G z (s) Caused by three resonant excitation factors. Among them, G x (s) represents the resonant excitation effect of its own inverter, G y (s) represents the parallel coupling resonant excitation effect between different inverters, G z (s) represents the series coupling resonant excitation effect between the microgrid and the main grid. G x (s), G y (s) and G z The Bode plots of (s) can be respectively as follows: Figure 4 , Figure 5 and Figure 6 As shown. According to Figures 4-6 It can be seen that there are two resonance peaks in a parallel asynchronous operation system of multiple inverters. One is a low-frequency resonance peak, whose resonant frequency changes with the number of inverters connected, i.e., the first resonance peak. The other is a high-frequency resonance peak, whose resonant frequency remains constant, i.e., the second resonance peak.

[0165] In implementation, the number of inverters, the equivalent impedance of the grid, the configuration information of the LCL filter, and the first correspondence between the first frequency and the second correspondence between the LCL filter configuration information and the second frequency can be determined based on the pole characteristics of the inverter's transfer function model. That is, the first and second correspondences can be determined when the denominator of the inverter's transfer function model is zero, thereby effectively ensuring the reliability of the determination results of the first and second correspondences. Furthermore, based on the first and second correspondences, the first frequency of the first resonance peak and the second frequency of the second resonance peak can be accurately determined, further improving the suppression effect on the first and second resonance peaks.

[0166] For example, it can be based on G x (s), G y (s) and G z The denominator of (s) is analyzed for resonance characteristics to obtain the first and second correspondences. It is understandable that, due to G... x(s), G y (s) and G z The denominators of (s) are the same, so only G can be used. x (s), G y (s) or G z The resonance characteristic analysis of the denominator of (s) yields the first and second correspondences as shown in equations (7) and (8), respectively:

[0167]

[0168] In the formula, f1 is the first frequency and f2 is the second frequency.

[0169] In one feasible implementation, such as Figure 7 As shown, the control loop of the inverter includes a first subtractor 701, a current closed-loop controller 702, a second subtractor 703, a current amplitude-frequency controller 704, a first feedback controller 705, and a second feedback controller 706.

[0170] The current amplitude-frequency controller 704 is used to output the inverter-side current of the LCL filter, the grid-connected-side current of the LCL filter, and the capacitor current of the LCL filter.

[0171] The first subtractor 701 is used to output the first current difference between the target output current of the inverter and the inverter-side current.

[0172] The current closed-loop controller 702 is used to output a voltage regulation value based on a first current difference;

[0173] The first feedback controller 705 is used to generate a feedback value of the grid-connected current based on the target value of the grid-connected current and the virtual damping.

[0174] The second feedback controller 706 is used to generate a feedback value of the capacitor current based on the capacitor current and the feedback coefficient of the capacitor current.

[0175] The second subtractor 703 is used to output the first voltage difference to the current amplitude-frequency controller 704 based on the voltage regulation value, the feedback value of the grid-connected current, and the feedback value of the capacitor current.

[0176] Specifically, the inverter-side current of the LCL filter is the current output by the inverter-side filter inductor of the LCL filter. The grid-connected current of the LCL filter is the current output by the grid-side filter inductor of the LCL filter, i.e., the grid-connected current of the inverter. The capacitor current of the LCL filter is the current flowing into the filter capacitor of the LCL filter. The target output current of the inverter is the grid-connected reference current of the inverter.

[0177] The current closed-loop controller 702 can output a voltage regulation value based on the first current difference between the target output current of the inverter and the inverter-side current to perform closed-loop control of the inverter-side current.

[0178] The first feedback controller 705 can use the product of the grid-connected current and the target value of the virtual damping as the feedback value of the grid-connected current and output it to the second subtractor 703.

[0179] The second feedback controller 706 can use the product of the capacitor current and the feedback coefficient of the capacitor current as the feedback value of the capacitor current and output it to the second subtractor 703.

[0180] The second subtractor 703 can output the first voltage difference to the current amplitude-frequency controller 704 based on the voltage regulation value, the feedback value of the grid current, and the feedback value of the capacitor current.

[0181] The current amplitude-frequency controller 704 can adjust the amplitude and frequency of the grid-connected current based on the first voltage difference to reduce the difference between the inverter-side current and the target output current, and to suppress the first and second resonant peaks.

[0182] In one feasible implementation, such as Figure 8 As shown, the current amplitude-frequency controller 704 includes a gain controller 801, a third subtractor 802, an inverter-side current calculation unit 803, a fourth subtractor 804, a capacitor voltage calculation unit 805, a fifth subtractor 806, and a grid-connected-side current calculation unit 807.

[0183] The gain controller 801 is used to output the inverter port voltage based on the first voltage difference and the equivalent gain of the inverter.

[0184] The third subtractor 802 is used to generate a second voltage difference based on the inverter port voltage and the capacitor voltage of the LCL filter.

[0185] The inverter-side current calculation unit 803 is used to output the inverter-side current based on the second voltage difference and the inverter-side filter inductor impedance of the LCL filter.

[0186] The fourth subtractor 804 is used to generate a second current difference between the inverter-side current and the grid-connected current, and uses the second current difference as the capacitor current.

[0187] The capacitor voltage calculation unit 805 is used to output the capacitor voltage based on the capacitor current and the capacitor impedance of the LCL filter;

[0188] The fifth subtractor 806 is used to output the third voltage difference between the capacitor voltage and the inverter's grid connection point voltage;

[0189] The grid-connected current calculation unit 807 is used to output the grid-connected current based on the third voltage difference and the grid-connected filter inductor impedance of the LCL filter.

[0190] Specifically, the equivalent gain of the inverter can be the ratio between the inverter's output voltage and input voltage, and can be a pre-configured value, such as 1. Understandably, the equivalent gain of the inverter can also be updated in real time according to control requirements. The gain controller 801 can output the inverter port voltage based on the first voltage difference and the inverter's equivalent gain; the inverter port voltage is the voltage output by the inverter to the connected LCL filter.

[0191] The capacitor voltage of the LCL filter is the voltage at the output terminal of the filter capacitor in the LCL filter. The inverter-side current calculation unit 803 can output the inverter-side current based on the second voltage difference between the inverter port voltage and the capacitor voltage of the LCL filter and the inverter-side filter inductor impedance of the LCL filter.

[0192] The fourth subtractor 804 can be used to calculate the second current difference between the inverter side current and the grid-connected side current, and input the second current difference as the capacitor current to the second feedback controller 706 and the capacitor voltage calculation unit 805.

[0193] The capacitor voltage calculation unit 805 can output the capacitor voltage based on the capacitor current and the capacitor impedance of the LCL filter.

[0194] The inverter's grid connection point voltage is the voltage at the common node where the inverter connects to the grid. The grid-connected current calculation unit 807 can output the grid-connected current based on the third voltage difference between the capacitor voltage and the inverter's grid connection point voltage, as well as the grid-connected filter inductor impedance of the LCL filter, to reduce the difference between the inverter-side current and the target output current, and to suppress the first and second resonant peaks.

[0195] The following example illustrates the specific implementation process and effects of the resonance peak suppression method applied to a parallel inverter system, using an optional implementation method. (Reference) Figure 9 Resonance peak suppression methods may include:

[0196] S901. Construct the transfer function model of the inverter, as shown in Equations (5) and (6).

[0197] S902. Based on the inverter's transfer function model, determine the function expression of the first frequency of the first resonant peak (i.e., the first correspondence between the number of inverters, the equivalent impedance of the grid, the configuration information of the LCL filter and the first frequency) and the function expression of the second frequency of the second resonant peak (i.e., the second correspondence between the configuration information of the LCL filter and the second frequency), as shown in Equations (7) and (8).

[0198] S903. Based on the function expression of the first frequency, the first resonance peak is suppressed by an adaptive damping control method;

[0199] S904. Based on the function expression of the second frequency, the second resonance peak is suppressed by an improved capacitor current feedback control method.

[0200] In step S903, the current number of inverters connected to the grid can be obtained through communication with each inverter or with the grid control unit. The current number of inverters is then substituted into equation (7) to obtain the first frequency of the first resonant peak. The first frequency of the first resonant peak is then substituted into equation (2) as the center angular frequency to obtain the target value of the virtual damping. The product of the target value of the virtual damping and the current value of the inverter's grid-connected current is then superimposed onto the inverter's control loop as a feedback value of the grid-connected current to suppress the first resonant peak. After suppressing the first resonant peak, G... x The Bode plot of (s) can be as follows Figure 10 As shown, by Figure 10 It can be seen that the adaptive damping control method can effectively suppress the first resonance peak without affecting the current gain of other frequency bands.

[0201] In step S904, the second frequency of the second resonant peak obtained through equation (8) can be substituted into equation (3) as the notch filter frequency to obtain the feedback coefficient of the capacitor current. The product of the feedback coefficient of the capacitor current and the current value of the capacitor current is used as the feedback value of the capacitor current. The feedback value of the capacitor current is then superimposed on the control loop of the inverter to suppress the second resonant peak. After suppressing the second resonant peak, G x The Bode plot of (s) can be as follows Figure 11 As shown, by Figure 11 It can be seen that the improved capacitor current feedback control method can effectively suppress the second resonance peak without affecting the current gain of other frequency bands.

[0202] Among them, after simultaneously suppressing the first resonance peak through an adaptive damping control method and suppressing the second resonance peak through an improved capacitor current feedback control method, G x The Bode plot of (s) can be as follows Figure 12 As shown, by Figure 12It can be seen that the adaptive damping control method and the improved capacitor current feedback control method can effectively suppress the first and second resonance peaks without affecting the current gain of other frequency bands, thereby effectively improving the stability of the power system.

[0203] Exemplary device

[0204] In one exemplary embodiment of this specification, a resonance peak suppression device is also provided, applied to a parallel inverter system, wherein multiple inverters are connected in parallel through corresponding LCL filters and then connected to the power grid, and the grid-connected current has a first resonance peak; such as Figure 13 As shown, the device includes:

[0205] The first processing module 1301 is used to determine the target value of virtual damping based on the first frequency of the first resonant peak, a preset bandpass filter transfer function model, and a preset virtual damping suppression coefficient, wherein the first frequency is determined based on the number of inverters.

[0206] The second processing module 1302 is used to suppress the first resonance peak through the control loop of the inverter according to the target value of the virtual damping.

[0207] In one feasible implementation, the first processing module 1301 is specifically used for:

[0208] The first frequency is used as the center angular frequency and input to the transfer function model of the bandpass filter to obtain the damping value of the bandpass filter at the first frequency.

[0209] The product of the damping value of the bandpass filter at the first frequency and the virtual damping suppression coefficient is taken as the target value of the virtual damping.

[0210] In one feasible implementation, the bandpass filter transfer function model includes a bandwidth determined based on the bandwidth of the first resonant peak.

[0211] In one feasible implementation, the first processing module 1301 is further configured to:

[0212] The first frequency is determined based on the number of inverters, the current impedance of the power grid, and the configuration information of the LCL filter.

[0213] In one feasible implementation, the grid-connected current also has a second resonant peak; the device further includes:

[0214] The third processing module 1303 is used to determine the feedback coefficient of the capacitor current based on the second frequency of the second resonant peak and a preset notch filter transfer function model, wherein the second frequency is greater than the first frequency.

[0215] The second processing module 1302 is also used to suppress the second resonance peak through the control loop of the inverter based on the feedback coefficient of the capacitor current.

[0216] In one feasible implementation, the third processing module 1303 is specifically used for:

[0217] The second frequency is used as the notch filter frequency and input into the notch filter transfer function model to obtain the feedback coefficient of the capacitor current.

[0218] In one feasible implementation, the notch filter transfer function model includes a notch width, which is determined based on the bandwidth of the second resonant peak.

[0219] In one embodiment, the third processing module 1303 is further configured to:

[0220] The second frequency is obtained based on the configuration information of the LCL filter.

[0221] In one feasible implementation, the control loop of the inverter includes a first subtractor, a current closed-loop controller, a second subtractor, a current amplitude-frequency controller, a first feedback controller, and a second feedback controller.

[0222] The current amplitude-frequency controller is used to output the inverter-side current of the LCL filter, the grid-connected-side current of the LCL filter, and the capacitor current of the LCL filter.

[0223] The first subtractor is used to output a first current difference between the target output current of the inverter and the inverter-side current.

[0224] The current closed-loop controller is used to output a voltage regulation value based on the first current difference;

[0225] The first feedback controller is used to generate a feedback value of the grid-connected current based on the grid-connected current and the target value of the virtual damping;

[0226] The second feedback controller is used to generate a feedback value for the capacitor current based on the capacitor current and the feedback coefficient of the capacitor current;

[0227] The second subtractor is used to output a first voltage difference to the current amplitude-frequency controller based on the voltage adjustment value, the feedback value of the grid-connected current, and the feedback value of the capacitor current.

[0228] In one feasible implementation, the current amplitude-frequency controller includes a gain controller, a third subtractor, an inverter-side current calculation unit, a fourth subtractor, a capacitor voltage calculation unit, a fifth subtractor, and a grid-connected-side current calculation unit.

[0229] The gain controller is used to output the inverter port voltage based on the first voltage difference and the equivalent gain of the inverter;

[0230] The third subtractor is used to generate a second voltage difference based on the inverter port voltage and the capacitor voltage of the LCL filter;

[0231] The inverter-side current calculation unit is used to output the inverter-side current based on the second voltage difference and the inverter-side filter inductor impedance of the LCL filter.

[0232] The fourth subtractor is used to generate a second current difference between the inverter-side current and the grid-connected current, and uses the second current difference as the capacitor current.

[0233] The capacitor voltage calculation unit is used to output the capacitor voltage based on the capacitor current and the capacitor impedance of the LCL filter;

[0234] The fifth subtractor is used to output the third voltage difference between the capacitor voltage and the grid connection point voltage of the inverter;

[0235] The grid-connected current calculation unit is used to output the grid-connected current based on the third voltage difference and the grid-connected filter inductor impedance of the LCL filter.

[0236] The resonance peak suppression device for parallel systems provided in this embodiment belongs to the same concept as the resonance peak suppression method for parallel systems provided in the above embodiments of this application. It can execute the resonance peak suppression method for parallel systems provided in any of the above embodiments of this application, and has the corresponding functional modules and beneficial effects for executing the resonance peak suppression method for parallel systems. Technical details not described in detail in this embodiment can be found in the specific processing content of the resonance peak suppression method for parallel systems provided in the above embodiments of this application, and will not be repeated here.

[0237] In one exemplary embodiment of this specification, a parallel inverter system is also provided, including: a control device and multiple inverters;

[0238] The multiple inverters are connected in parallel through corresponding LCL filters and then connected to the power grid.

[0239] The control device performs the resonance peak suppression method as described in any of the above embodiments to suppress the resonance peak of the grid-connected current through the control loop of the inverter.

[0240] Exemplary computer program products and storage media

[0241] In addition to the methods and devices described above, the resonance peak suppression method provided in the embodiments of this specification can also be a computer program product, which includes computer program instructions that, when executed by a processor, cause the processor to perform the steps in the resonance peak suppression method according to the various embodiments of this specification as described in the "Exemplary Methods" section above.

[0242] Computer program products can be written in any combination of one or more programming languages ​​to perform the operations of the embodiments described herein. Programming languages ​​include object-oriented programming languages ​​such as Java and C++, as well as conventional procedural programming languages ​​such as C or similar languages. The program code can be executed entirely on a semiconductor process device, partially on the device, as a standalone software package, partially on a semiconductor process device and partially on a remote semiconductor process device, or entirely on a remote semiconductor process device or server.

[0243] Furthermore, embodiments of this specification also provide a computer-readable storage medium having a computer program stored thereon, the computer program being executed by a processor of the steps in the resonance peak suppression methods according to various embodiments of this specification as described in the "Exemplary Methods" section above.

[0244] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium. When executed, the computer program can include the processes of the embodiments of the methods described above. Any references to memory, storage, databases, or other media used in the embodiments provided in this specification can include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), RAMbus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and RAMbus dynamic RAM (RDRAM), etc.

[0245] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0246] The embodiments described above are merely illustrative of several implementation methods outlined in this specification. While the descriptions are specific and detailed, they should not be construed as limiting the scope of the solutions provided in this specification. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this specification, and these all fall within the scope of protection of this specification. Therefore, the scope of protection for this patent should be determined by the appended claims.

Claims

1. A method for suppressing resonance peaks, characterized in that, This method is applied to inverter parallel systems, where multiple inverters are connected in parallel through corresponding LCL filters and then connected to the power grid, with the grid-connected current exhibiting a first resonant peak. The method includes: Based on the first frequency of the first resonant peak, the preset bandpass filter transfer function model, and the preset virtual damping suppression coefficient, the target value of the virtual damping is determined, wherein the first frequency is determined based on the number of inverters; The first resonance peak is suppressed by the control loop of the inverter according to the target value of the virtual damping.

2. The method according to claim 1, characterized in that, Based on the first frequency of the first resonant peak, the preset bandpass filter transfer function model, and the preset virtual damping suppression coefficient, the target value of the virtual damping is determined, including: The first frequency is used as the center angular frequency and input to the transfer function model of the bandpass filter to obtain the damping value of the bandpass filter at the first frequency. The product of the damping value of the bandpass filter at the first frequency and the virtual damping suppression coefficient is taken as the target value of the virtual damping.

3. The method according to claim 1, characterized in that, The bandpass filter transfer function model includes a bandwidth, which is determined based on the bandwidth of the first resonant peak.

4. The method according to claim 1, characterized in that, The first frequency is determined based on the number of inverters, including: The first frequency is determined based on the number of inverters, the current impedance of the power grid, and the configuration information of the LCL filter.

5. The method according to any one of claims 1 to 4, characterized in that, The grid-connected current also has a second resonant peak; the method further includes: Based on the second frequency of the second resonant peak and the preset notch filter transfer function model, the feedback coefficient of the capacitor current is determined, wherein the second frequency is greater than the first frequency. The second resonant peak is suppressed by the control loop of the inverter based on the feedback coefficient of the capacitor current.

6. The method according to claim 5, characterized in that, Based on the second frequency of the second resonant peak and the preset notch filter transfer function model, the feedback coefficient of the capacitor current is determined, including: The second frequency is used as the notch filter frequency and input into the notch filter transfer function model to obtain the feedback coefficient of the capacitor current.

7. The method according to claim 5, characterized in that, The notch filter transfer function model includes the notch width, which is determined based on the bandwidth of the second resonant peak.

8. The method according to claim 5, characterized in that, The second frequency was obtained by the following method: The second frequency is obtained based on the configuration information of the LCL filter.

9. The method according to claim 5, characterized in that, The control loop of the inverter includes a first subtractor, a current closed-loop controller, a second subtractor, a current amplitude-frequency controller, a first feedback controller, and a second feedback controller. The current amplitude-frequency controller is used to output the inverter-side current of the LCL filter, the grid-connected-side current of the LCL filter, and the capacitor current of the LCL filter. The first subtractor is used to output a first current difference between the target output current of the inverter and the inverter-side current. The current closed-loop controller is used to output a voltage regulation value based on the first current difference; The first feedback controller is used to generate a feedback value of the grid-connected current based on the grid-connected current and the target value of the virtual damping; The second feedback controller is used to generate a feedback value for the capacitor current based on the capacitor current and the feedback coefficient of the capacitor current; The second subtractor is used to output a first voltage difference to the current amplitude-frequency controller based on the voltage regulation value, the feedback value of the grid-connected current, and the feedback value of the capacitor current.

10. The method according to claim 9, characterized in that, The current amplitude-frequency controller includes a gain controller, a third subtractor, an inverter-side current calculation unit, a fourth subtractor, a capacitor voltage calculation unit, a fifth subtractor, and a grid-connected-side current calculation unit. The gain controller is used to output the inverter port voltage based on the first voltage difference and the equivalent gain of the inverter; The third subtractor is used to generate a second voltage difference based on the inverter port voltage and the capacitor voltage of the LCL filter; The inverter-side current calculation unit is used to output the inverter-side current based on the second voltage difference and the inverter-side filter inductor impedance of the LCL filter. The fourth subtractor is used to generate a second current difference between the inverter-side current and the grid-connected current, and uses the second current difference as the capacitor current. The capacitor voltage calculation unit is used to output the capacitor voltage based on the capacitor current and the capacitor impedance of the LCL filter; The fifth subtractor is used to output the third voltage difference between the capacitor voltage and the grid connection point voltage of the inverter; The grid-connected current calculation unit is used to output the grid-connected current based on the third voltage difference and the grid-connected filter inductor impedance of the LCL filter.

11. A resonance peak suppression device, characterized in that, This device is applied to inverter parallel systems, where multiple inverters are connected in parallel through corresponding LCL filters and then connected to the power grid. The grid-connected current has a first resonant peak. The device includes: The first processing module is used to determine the target value of virtual damping based on the first frequency of the first resonant peak, a preset bandpass filter transfer function model, and a preset virtual damping suppression coefficient, wherein the first frequency is determined based on the number of inverters. The second processing module is used to suppress the first resonance peak through the control loop of the inverter according to the target value of the virtual damping.

12. The apparatus according to claim 11, characterized in that, The grid-connected current also has a second resonant peak; the device further includes: The third processing module is used to determine the feedback coefficient of the capacitor current based on the second frequency of the second resonant peak and a preset notch filter transfer function model, wherein the second frequency is greater than the first frequency. The second processing module is also used to suppress the second resonance peak through the control loop of the inverter based on the feedback coefficient of the capacitor current.

13. The apparatus according to claim 12, characterized in that, The control loop of the inverter includes a first subtractor, a current closed-loop controller, a second subtractor, a current amplitude-frequency controller, a first feedback controller, and a second feedback controller. The current amplitude-frequency controller is used to output the inverter-side current of the LCL filter, the grid-connected-side current of the LCL filter, and the capacitor current of the LCL filter. The first subtractor is used to output a first current difference between the target output current of the inverter and the inverter-side current. The current closed-loop controller is used to output a voltage regulation value based on the first current difference; The first feedback controller is used to generate a feedback value of the grid-connected current based on the grid-connected current and the target value of the virtual damping; The second feedback controller is used to generate a feedback value for the capacitor current based on the capacitor current and the feedback coefficient of the capacitor current; The second subtractor is used to output a first voltage difference to the current amplitude-frequency controller based on the voltage adjustment value, the feedback value of the grid-connected current, and the feedback value of the capacitor current.

14. The apparatus according to claim 13, characterized in that, The current amplitude-frequency controller includes a gain controller, a third subtractor, an inverter-side current calculation unit, a fourth subtractor, a capacitor voltage calculation unit, a fifth subtractor, and a grid-connected-side current calculation unit. The gain controller is used to output the inverter port voltage based on the first voltage difference and the equivalent gain of the inverter; The third subtractor is used to generate a second voltage difference based on the inverter port voltage and the capacitor voltage of the LCL filter; The inverter-side current calculation unit is used to output the inverter-side current based on the second voltage difference and the inverter-side filter inductor impedance of the LCL filter. The fourth subtractor is used to generate a second current difference between the inverter-side current and the grid-connected current, and uses the second current difference as the capacitor current. The capacitor voltage calculation unit is used to output the capacitor voltage based on the capacitor current and the capacitor impedance of the LCL filter; The fifth subtractor is used to output the third voltage difference between the capacitor voltage and the grid connection point voltage of the inverter; The grid-connected current calculation unit is used to output the grid-connected current based on the third voltage difference and the grid-connected filter inductor impedance of the LCL filter.

15. An inverter parallel connection system, characterized in that, include: Control unit and multiple inverters; The multiple inverters are connected in parallel through corresponding LCL filters and then connected to the power grid. The control device performs the resonance peak suppression method as described in any one of claims 1 to 10 to suppress the resonance peak of the grid-connected current through the control loop of the inverter.

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