Grid-connected inverter impedance modeling method and system in multivariable control mode

Abstract

The invention provides a grid-connected inverter impedance modeling method and system in a multivariable control mode. The method comprises the following steps: firstly, carrying out two-port equivalence on a to-be-analyzed and modeled grid-connected inverter to obtain a main circuit core equation; secondly, after disturbance is added, a harmonic linearization method is used for modeling a phase-locked loop under current response of voltage disturbance to obtain a corresponding phase-locked loop model considering coupling, coupling components of all frequency bands are fully considered, and the frequency coupling rule of the inverter is revealed; and finally, based on a multivariable control mode, introducing different control parameters to obtain grid-connected inverter impedance models in different control modes. Compared with a traditional inverter impedance modeling method, the grid-connected inverter impedance modeling method not only considers coupling response mechanisms under various frequencies, but also considers the impedance model under the influence of different control variables, and improves the precision and accuracy of the grid-connected inverter impedance model.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system control, and in particular relates to a method and system for modeling impedance of a grid-connected inverter under a multivariable control mode. Background Art

[0002] With the increasing application of renewable energy generation systems in power grids, grid-following (GFL) control, the interface between renewable energy generation systems and the grid, is increasingly becoming a key component of grid-connected systems. In practical applications, impedance analysis is a common method for studying the stability of grid-connected inverter systems. Its modular approach offers advantages in studying the interaction between the grid and the inverter, along with its clear physical meaning. However, the choice of different inverter control methods significantly impacts not only the dynamic response but also the impedance characteristics and grid stability. Currently, detailed GFL inverter impedance modeling has not been considered, nor has a detailed impedance model that considers frequency coupling under multivariable control modes been established. Therefore, developing an impedance modeling method for grid-connected inverters under multivariable control modes is crucial for studying grid-connected system stability. Summary of the Invention

[0003] The purpose of the present invention is to provide a method and system for modeling the impedance of a grid-connected inverter under a multivariable control mode, so as to solve the technical problem that the traditional modeling method does not consider the impact of the multivariable control mode on the impedance model, while ensuring the modeling precision and accuracy.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] In a first aspect, the present invention provides a method for modeling impedance of a grid-connected inverter in a multivariable control mode, comprising:

[0006] According to the LCL type three-phase grid-connected inverter system structure, the core equation of the three-phase circuit of the grid-connected inverter is established;

[0007] Without considering the influence of the phase-locked loop frequency characteristics, the three-phase grid-connected inverter system is decomposed into two positive and negative sequence subsystems using the harmonic linearization method. Positive and negative sequence small signal disturbances are injected into the grid-connected output terminal. Based on the core equations of the three-phase circuit of the grid-connected inverter, the positive and negative sequence output impedances of the grid-connected inverter are obtained when the positive and negative sequence small signal disturbances are injected but the phase-locked loop disturbance is not considered.

[0008] Based on the three-phase positive and negative sequence output impedance of the grid-connected inverter injected with positive and negative sequence small signal disturbance but without considering the phase-locked loop disturbance, while injecting the positive and negative sequence small signal at the grid-connected output end, a phase angle disturbance is introduced into the phase-locked loop phase angle, thereby obtaining a grid-connected inverter output impedance model under the conditions of injecting positive and negative sequence small signal disturbance and considering the phase angle disturbance;

[0009] Multivariable feedback control is introduced, and the output impedance model of the grid-connected inverter is reshaped using the above method to obtain the output impedance model of the grid-connected inverter under the multivariable control mode.

[0010] Preferably, the core equation of the three-phase circuit of the grid-connected inverter is expressed as:

[0011] , in, Modulate the voltage of the three-phase bridge arm; is the DC input voltage; is the inverter voltage modulation ratio; and Constructing a filter; Connect the filter capacitor in series with the damping resistor; is the three-phase grid voltage containing fundamental frequency components and small disturbance components; is the three-phase grid current containing fundamental frequency component and small disturbance component; Represents complex frequency.

[0012] Preferably, injecting positive and negative sequence small signal disturbances at the grid-connected output end, and obtaining the positive and negative sequence output impedance of the grid-connected inverter injected with positive and negative sequence small signal disturbances but without considering phase-locked loop disturbances based on the core equation of the three-phase circuit of the grid-connected inverter, comprises:

[0013] Without considering the influence of the phase-locked loop frequency characteristics, the three-phase grid-connected inverter system is decomposed into two subsystems with positive and negative sequences using the harmonic linearization method. Positive and negative sequence small signal disturbances are injected into the grid-connected output terminal to obtain the grid-connected current response components at the disturbance frequency.

[0014] Obtaining the frequency domain form of the grid-connected current response component at the disturbance frequency through Fourier transform;

[0015] Based on the frequency domain form of the grid-connected current response component at the disturbance frequency and according to the grid-connected inverter circuit control structure, the dq axis current closed-loop control is performed to obtain the dq axis voltage output by the current regulator, and the voltage is input into the space vector pulse width modulation module to obtain the dq axis bridge arm modulation voltage;

[0016] Based on the dq-axis bridge arm modulation voltage and the core equation of the three-phase circuit of the grid-connected inverter, the positive and negative sequence output impedances of the grid-connected inverter are obtained when positive and negative sequence small signal disturbances are injected but phase-locked loop disturbances are not considered.

[0017] Preferably, the grid-connected current response component at the disturbance frequency is expressed as:

[0018] ,

[0019] in, is the fundamental current peak value; is the fundamental wave phase angle; 、 are the positive and negative sequence current disturbance phase angles respectively; and are the positive and negative sequence current disturbance peaks respectively;

[0020] The frequency domain form of the grid-connected current response component at the disturbance frequency is expressed as:

[0021] ,

[0022] ,

[0023] in 、 are the dq axis grid-connected current after Fourier transformation, is the frequency in the frequency domain expression, 、 and are the fundamental frequency and positive and negative sequence current disturbance frequencies respectively, is the fundamental current phase, and are the frequency domain expressions of the positive and negative sequence current disturbance peaks, and are the positive and negative sequence current disturbance phases respectively;

[0024] The dq axis bridge arm modulation voltage is expressed as:

[0025] ,

[0026] ,

[0027] in, 、 、 、 are respectively the positive and negative sequence dq axis bridge arm modulation voltages under the injection of positive and negative sequence small signal disturbances, and correspond and , is the equivalent transfer function of the current sampling delay link, is the current loop regulator, is the current loop regulation coefficient;

[0028] The positive and negative sequence output impedance of the grid-connected inverter injected with positive and negative sequence small signal disturbance but without considering the phase-locked loop disturbance is expressed as:

[0029] ,

[0030] ,

[0031] in, and is the positive and negative sequence output impedance of the grid-connected inverter when positive and negative sequence small signal disturbances are injected but the phase-locked loop disturbance is not considered.

[0032] Preferably, while injecting positive and negative sequence small signals at the grid-connected output end, a phase angle disturbance is introduced into the phase-locked loop phase angle, to obtain a grid-connected inverter output impedance model under the injection of positive and negative sequence small signal disturbances and the consideration of phase angle disturbances, including:

[0033] Under the frequency characteristics of the phase-locked loop, the phase-locked angle introduces phase angle disturbance, and the closed-loop transfer function of the phase-locked loop with phase angle disturbance is obtained;

[0034] Based on the closed-loop transfer function of the phase-locked loop that introduces the phase angle disturbance and the grid-connected current response component at the disturbance frequency, a frequency domain form of the grid-connected current response component that takes into account the phase angle disturbance of the phase-locked loop is obtained;

[0035] Based on the frequency domain form of the grid-connected current response component considering the phase-locked loop phase angle disturbance, according to the grid-connected inverter circuit control structure, the dq axis current closed-loop control is performed to obtain the dq axis voltage output by the current regulator, and the voltage is input into the space vector pulse width modulation module to obtain the dq axis bridge arm modulation voltage;

[0036] Based on the dq-axis bridge arm modulation voltage and the core equation of the three-phase circuit of the grid-connected inverter, an output impedance model of the grid-connected inverter under the injection of positive and negative sequence small signal disturbances and consideration of phase angle disturbances is obtained.

[0037] Preferably, the closed-loop transfer function of the phase-locked loop that introduces phase angle disturbance is expressed as:

[0038] ,

[0039] in, is the closed-loop transfer function of the phase-locked loop, is the system fundamental DC voltage, and is the relationship expression between positive and negative sequence voltage and phase angle disturbance,

[0040] and Expressed as:

[0041] ,

[0042] in, is the phase angle perturbation, 、 is the positive and negative sequence disturbance component in the frequency domain;

[0043] The frequency domain form of the grid-connected current response component considering the phase-locked loop phase angle disturbance is expressed as:

[0044] ,

[0045] ,

[0046] in, and are the dq axis frequency domain forms of the grid current response components considering the phase angle disturbance of the phase-locked loop, 、 are the positive and negative sequence transfer functions of the phase-locked loop, respectively, which are derived from the closed-loop transfer function of the phase-locked loop;

[0047] The dq axis bridge arm modulation voltage is expressed as:

[0048] ,

[0049] ,

[0050] in, 、 、 and The positive and negative sequence dq axis bridge arm modulation voltage is injected with positive and negative sequence small signal disturbance and considering phase angle disturbance;

[0051] The output impedance model of the grid-connected inverter under the injection of positive and negative sequence small signal disturbances and the consideration of phase angle disturbances is expressed as:

[0052] ,

[0053] ,

[0054] in, and is the positive and negative sequence output impedance of the grid-connected inverter under the injection of positive and negative sequence small signal disturbance and considering phase angle disturbance.

[0055] Preferably, the multivariable feedback control is introduced, and the output impedance model of the grid-connected inverter is reshaped in the above manner to obtain the output impedance model of the grid-connected inverter under the multivariable control mode, including:

[0056] By introducing grid voltage feedforward, inverter side inductor current feedforward, and inverter side capacitor current feedforward respectively, the output impedance model of the grid-connected inverter under the injection of positive and negative sequence small signal disturbances and the consideration of phase angle disturbances is reshaped to obtain the output impedance model of the grid-connected inverter under different variable control modes, which is expressed as:

[0057] In the grid voltage feedforward control mode, we get:

[0058] ,

[0059] ,

[0060] ,

[0061] Then the positive sequence output impedance is: ;

[0062] In the inverter side inductor current feedforward control mode, we get:

[0063] , ,

[0064] , ,

[0065] ,

[0066] ,

[0067] Then the positive sequence output impedance is: ;

[0068] In the inverter side capacitor current feedforward control mode, we get:

[0069] , ,

[0070] ,

[0071] ,

[0072] Then the positive sequence output impedance is: ;

[0073] above 、 、 、 、 、 、 、 、 、 、 、 、 are all process parameters, is the grid voltage feedback transfer function, Inductor on the inverter side Current transfer function, is the capacitor current transfer function.

[0074] In a second aspect, the present invention provides a grid-connected inverter impedance modeling system under a multivariable control mode, for implementing the above-mentioned grid-connected inverter impedance modeling method under a multivariable control mode, the system comprising:

[0075] The circuit analysis module is used to establish the core equations of the three-phase circuit of the grid-connected inverter based on the system structure of the LCL three-phase grid-connected inverter;

[0076] The first model output module is configured to decompose the three-phase grid-connected inverter system into two positive-sequence and negative-sequence subsystems using a harmonic linearization method without considering the influence of the phase-locked loop frequency characteristics, inject positive-sequence and negative-sequence small signal disturbances at the grid-connected output terminal, and obtain the positive-sequence and negative-sequence output impedances of the grid-connected inverter when the positive-sequence small signal disturbances are injected but without considering the phase-locked loop disturbance based on the core equations of the three-phase circuit of the grid-connected inverter;

[0077] A second model output module is configured to inject positive and negative sequence small signal disturbances at the grid-connected output terminal while introducing a phase angle disturbance into the phase-locked loop phase-locked angle based on the three-phase positive and negative sequence output impedance of the grid-connected inverter without considering the phase-locked loop disturbance, thereby obtaining a grid-connected inverter output impedance model under the conditions of injecting positive and negative sequence small signal disturbances and considering the phase angle disturbance;

[0078] The multivariable reshaping module is used to introduce multivariable feedback control and reshape the output impedance model of the grid-connected inverter using the above method to obtain the output impedance model of the grid-connected inverter under the multivariable control mode.

[0079] In a third aspect, the present invention provides a computer-readable storage medium storing one or more programs, wherein the one or more programs include instructions, which, when executed by a computing device, enable the computing device to perform any of the methods for grid-connected inverter impedance modeling under the above-mentioned multivariable control mode.

[0080] In a fourth aspect, the present invention provides a computing device comprising one or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include instructions for executing any one of the methods for grid-connected inverter impedance modeling under the above-mentioned multivariable control mode.

[0081] The beneficial effects achieved by the present invention are as follows:

[0082] Compared with traditional inverter impedance modeling methods, the grid-connected inverter impedance modeling method provided by the present invention, which takes into account the coupling response mechanism at various frequencies, also considers the impedance model under the influence of different control variables, thereby improving the precision and accuracy of the grid-connected inverter impedance model. First, the grid-connected inverter to be analyzed and modeled is subjected to two-port equivalence to obtain the core equation of the main circuit; second, after adding disturbances, the harmonic linearization method is used to model the phase-locked loop under the current response of the voltage disturbance to obtain a phase-locked loop model that takes into account the coupling, fully considering the coupling components of each frequency band and revealing the frequency coupling law of the inverter; finally, based on the multivariable control mode, different control parameters are introduced to obtain the grid-connected inverter impedance model under different control methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] Figure 1 A schematic flow chart of a method for modeling impedance of a grid-connected inverter in a multivariable control mode provided by an embodiment of the present invention;

[0084] Figure 2 Schematic diagram of the control loop and main circuit structure of the grid-following inverter provided in an embodiment of the present invention;

[0085] Figure 3 A flow chart for verifying modeling accuracy through frequency sweeping provided by an embodiment of the present invention;

[0086] Figure 4 A diagram showing the comparison results between the positive sequence impedance theoretical model and the measured model of a grid-connected inverter modeling method considering multivariable control provided by an embodiment of the present invention;

[0087] Figure 5 A diagram showing the comparison results between the positive-sequence impedance theoretical model and the measured model of a grid-connected inverter modeling method considering multivariable control provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0088] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and the accompanying drawings. Here, the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0089] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, the accompanying drawings only show structures and / or processing steps closely related to the solutions according to the present invention, while other details that are not closely related to the present invention are omitted.

[0090] It should be emphasized that the term "include / comprises" when used herein refers to the existence of features, elements, steps or components, but does not exclude the existence or addition of one or more other features, elements, steps or components.

[0091] It should be emphasized here that the step marks mentioned below do not limit the order of the steps, but it should be understood that the steps can be executed in the order mentioned in the embodiment, or in a different order from the embodiment, or several steps can be executed simultaneously.

[0092] Example 1

[0093] This embodiment 1 provides a grid-connected inverter impedance modeling method under a multivariable control mode, see Figure 1 , including the following steps:

[0094] S1. Currently, most new energy generators use a grid-following control strategy when connected to the grid. In actual circuits, an LCL filter (Inductor-Capacitor-Inductor Filter) is used, which takes into account the frequency characteristics of a phase-locked loop (PLL). Based on the LCL three-phase grid-connected inverter system structure, the three-phase circuit core equations and the single-phase frequency domain core equations of the grid-connected inverter are established. The LCL filter is a filter circuit consisting of two inductors and one capacitor.

[0095] S2. Based on the three-phase circuit core equations and single-phase frequency-domain core equations of the grid-connected inverter established in step S1, and without considering the influence of the phase-locked loop frequency characteristics, the three-phase grid-connected inverter system is decomposed into two positive-sequence and negative-sequence subsystems using the harmonic linearization method. Positive and negative-sequence small-signal disturbances are injected into the grid-connected output terminal, and the grid-connected current response components at the disturbance frequency are derived. Based on the relationship between the small-signal disturbance voltage excitation and the output current response, the core equations of step S1 are used to obtain the three-phase positive- and negative-sequence output impedances of the grid-connected inverter.

[0096] S3. Based on the three-phase positive and negative sequence output impedance of the grid-connected inverter derived in step S2, while considering the influence of the phase-locked loop frequency characteristics, injecting small positive and negative sequence signals at the grid-connected output terminal, considering the introduction of phase angle disturbance in the phase-locked loop phase angle, and deriving the output impedance model of the grid-connected inverter when considering the phase-locked loop;

[0097] S4. To further improve the stability margin of the grid-connected inverter and improve its stability under weak grid conditions, based on the output impedance model of the grid-connected inverter considering the phase-locked loop derived in step S3, multivariable feedback control is introduced to perform impedance reshaping to obtain the impedance model of the grid-connected inverter under the multivariable control mode.

[0098] The system structure of LCL three-phase grid-connected inverter is as follows: Figure 2 As shown, 、 、 are the three-phase voltages at the grid connection point; 、 、 They are three-phase output currents respectively; 、 are the filter inductors respectively; is the filter capacitor; 、 、 is a three-phase modulated signal; 、 are the dq axis voltages at the grid connection point respectively; 、 are dq axis output current respectively; Control the output phase angle for the phase-locked loop; , , , , , Respectively represent the switching signals of the upper and lower bridge arms of each phase; 、 Represents the grid connection point voltage after Park transformation; 、 Represents the current loop transfer function. In this embodiment, based on the LCL type three-phase grid-connected inverter system structure, it is decomposed into positive and negative sequence subsystems, and the three-phase circuit core equation and single-phase frequency domain core equation of the grid-connected inverter are established. This is the basis for solving the impedance modeling of the grid-connected inverter under the multivariable control mode, and is specifically expressed as follows:

[0099] The core equation of the three-phase circuit of the grid-connected inverter is expressed as:

[0100] (1)

[0101] Where, Modulate the voltage of the three-phase bridge arm; is the DC input voltage; is the inverter voltage modulation ratio; and It constitutes an LCL filter; Connect the filter capacitor in series with the damping resistor; is the grid voltage containing fundamental frequency component and small disturbance component; is the grid current containing the fundamental frequency component and the small disturbance component, and the frequency domain expression is Refers to the complex frequency, which is the key parameter in the corresponding relationship between Laplace transform and Fourier transform.

[0102] Taking phase A as an example, the single-phase frequency domain core equation can be obtained according to formula (1), which is expressed as:

[0103] (2)

[0104] In formula (2), is the modulation voltage of the A-phase bridge arm; and are the A-phase grid voltage and grid current respectively.

[0105] In this embodiment, without considering the influence of the phase-locked loop frequency characteristics, the harmonic linearization method is used to decompose the three-phase grid-connected inverter system into two positive and negative sequence subsystems. Positive and negative sequence small signal disturbances are injected into the grid-connected output terminal, and the grid-connected current response component at the disturbance frequency is derived. According to the relationship between the small signal disturbance voltage excitation and the output current response, the core equation of step S1 is used to obtain the positive and negative sequence output impedance of the three-phase grid-connected inverter, which is specifically as follows:

[0106] According to formula (1), the positive and negative sequence small signal disturbances are injected into the grid output terminal to obtain the grid current response components at the disturbance frequency as follows:

[0107] (3)

[0108] Where, is the fundamental current peak value; is the fundamental wave phase angle; 、 are the positive and negative sequence current disturbance phase angles respectively; and are the peak values ​​of positive and negative sequence small signal disturbances respectively.

[0109] By performing coordinate transformation on the above-mentioned grid-connected current response components, its frequency domain expression can be obtained through Fourier transform, which can be expressed in the form of equations (4) and (5):

[0110] (4)

[0111] (5)

[0112] Where, 、 are the dq axis grid-connected current after Fourier transform respectively; is the frequency in the frequency domain expression, 、 and are the fundamental frequency and positive and negative sequence current disturbance frequencies respectively, is the fundamental current phase, and They are the frequency domain expressions of the positive and negative sequence current disturbance peaks, respectively. and , and are the positive and negative sequence current disturbance phases respectively.

[0113] After obtaining equations (4) and (5), according to the inverter circuit control structure, the dq axis current closed-loop control is performed to obtain the dq axis voltage output by the current regulator, which is then input into the space vector pulse width modulation module. Finally, the dq axis bridge arm modulation voltage is obtained, as shown in equations (6) and (7):

[0114] (6)

[0115] (7)

[0116] Where, 、 、 、 are the positive and negative sequence dq axis bridge arm modulation voltages under the injection of positive and negative sequence small signal disturbances respectively; and correspond and , is the equivalent transfer function of the current sampling delay link, is the current loop regulator, is the current loop regulation coefficient.

[0117] In this embodiment, without considering the influence of the phase-locked loop frequency characteristics, the positive and negative sequence output impedances of the three-phase grid-connected inverter are obtained as follows:

[0118] Substituting equations (6) and (7) into equation (2), we can obtain the positive and negative sequence output impedances of the three-phase grid-connected inverter as shown in equations (8) and (9).

[0119] (8)

[0120] (9)

[0121] and is the positive and negative sequence output impedance of the three-phase grid-connected inverter when positive and negative sequence small signal disturbances are injected but the phase-locked loop disturbance is not considered.

[0122] In this embodiment, while considering the influence of the frequency characteristics of the phase-locked loop, a small positive and negative sequence signal is injected into the grid-connected output terminal, and a phase angle disturbance is introduced into the phase-locked angle of the phase-locked loop to derive the closed-loop transfer function of the phase-locked loop. The specific implementation process is as follows:

[0123] Phase-locked loop frequency characteristics under phase-locked angle Introducing phase angle perturbation back, , is the grid phase-locking angle in steady state, and the derivation is The transfer function of the positive and negative sequence voltage disturbances is obtained, thereby deriving the closed-loop transfer function of the phase-locked loop.

[0124] After Park transformation, the frequency-shifted dq-axis three-phase grid voltage is obtained as shown in equations (10) and (11):

[0125] (10)

[0126] (11)

[0127] and They are the d-axis three-phase grid voltage and the q-axis three-phase grid voltage respectively; is the system fundamental DC voltage; 、 are the positive and negative sequence disturbance components of the system in the frequency domain.

[0128] To seek , assuming 、 is the positive and negative sequence voltage and The relationship between is shown in formula (12).

[0129] (12)

[0130] Based on formulas (10) and (11), the positive and negative sequence q-axis voltages after Park transformation are As shown in formula (13):

[0131] (13)

[0132] After linearization, the positive and negative sequence q-axis voltages and As shown in formula (14):

[0133] (14)

[0134] At the same time, by substituting formula (12) into formula (14), considering the phase-locked loop control block diagram, we can get 、 The expression is shown in formula (15):

[0135] (15)

[0136] Where, is the closed-loop transfer function of the phase-locked loop.

[0137] In this embodiment, taking into account the influence of the phase-locked loop frequency characteristics, the output impedance model of the grid-connected inverter is derived when the phase-locked loop is considered, as follows:

[0138] According to equations (4) and (5) in step S2, the three-phase grid-connected current expression after considering the phase angle disturbance is obtained and the dq axis frequency domain expression is obtained after coordinate transformation as follows:

[0139] (16)

[0140] (17)

[0141] in, and are the dq axis frequency domain forms of the grid current response components considering the phase angle disturbance of the phase-locked loop, 、 are the positive and negative sequence transfer functions of the phase-locked loop, respectively, which are derived according to formula (15).

[0142] After obtaining equations (16) and (17), according to the inverter circuit control structure, the dq axis current closed-loop control is performed to obtain the dq axis voltage output by the current regulator, which is then input into the space vector pulse width modulation module. Finally, the dq axis bridge arm modulation voltage is obtained, as shown in equations (18) and (19):

[0143] (18)

[0144] (19)

[0145] in 、 、 and It is the positive and negative sequence dq axis bridge arm modulation voltage under the injection of positive and negative sequence small signal disturbance and considering phase angle disturbance.

[0146] Finally, according to the response relationship between small signal disturbance voltage excitation and output current, the three-phase bridge arm modulation voltage is substituted into the core equation of the main circuit to obtain the positive and negative sequence output impedance of the three-phase grid-connected inverter considering the phase angle disturbance of the phase-locked loop, as shown in Equations (20) and (21).

[0147] (20)

[0148] (twenty one)

[0149] in, and is the positive and negative sequence output impedance of the grid-connected inverter under the injection of positive and negative sequence small signal disturbance and considering phase angle disturbance.

[0150] In this embodiment, in order to further improve the stability margin of the grid-connected inverter and improve its stability under weak grid conditions, based on the output impedance model of the phase-locked loop grid-connected inverter derived in step S3, multivariable feedback control is introduced to perform impedance reshaping, and the impedance model of the grid-connected inverter under the multivariable control model is obtained, which is specifically as follows:

[0151] By sampling the three-phase grid voltage at PCC point, the inductance on the inverter side The current of the filter capacitor The current is introduced into the grid voltage feedback transfer function , inverter side inductor Current transfer function and the capacitor current transfer function After filtering and Park transformation, the sampled parameters are transformed into the dq coordinate system and fed back into the current loop. The impedance model is re-derived according to the above steps S2-S3. Taking the positive sequence impedance model as an example, three different control variables are introduced respectively, as follows. In addition, to simplify the expression of the formula, some formulas are simplified in alphabetical form:

[0152] 1) Grid voltage feedforward control mode

[0153] (twenty two)

[0154] (twenty three)

[0155] (twenty four)

[0156] 2) Inverter side inductor current feedforward control mode

[0157] 、 (25)

[0158] 、 (26)

[0159] (27)

[0160] (28)

[0161] 3) Capacitor current feedforward control mode

[0162] 、 (29)

[0163] (30)

[0164] (31)

[0165] In summary, the positive sequence output impedance is derived as The derivation process of negative sequence impedance is the same as that of positive sequence, so it will not be described in detail in this patent.

[0166] Further, according to Figure 3 The steps shown are based on the harmonic perturbation injection method to perform impedance sweep measurement to verify the accuracy of the established model. After the system reaches steady state, the perturbation frequency and model parameters are set and the perturbation is injected to obtain the voltage and current response of the system port. The steps are repeated to calculate the amplitude and phase of the impedance model under this perturbation and compare them with the derived theoretical output impedance. The comparison results of the impedance measurement value obtained based on the frequency sweep and the impedance analytical value obtained by numerical calculation based on equations (20) and (21) are shown as follows: Figure 4 and Figure 5 As shown in the figure, the theoretically calculated values ​​of the positive and negative sequence impedance characteristics are represented by purple solid lines, and their measured results are represented by red discrete points. The comparison results show that the theoretical model and the scan results are in good agreement, verifying the accuracy of the established theoretical impedance model.

[0167] Example 2

[0168] Based on the above-mentioned inventive concept, this embodiment 2 provides a grid-connected inverter impedance modeling system under a multivariable control mode, which is used to implement the grid-connected inverter impedance modeling method under the multivariable control mode of the above-mentioned embodiment. The system includes:

[0169] The circuit analysis module is used to establish the core equations of the three-phase circuit of the grid-connected inverter based on the system structure of the LCL three-phase grid-connected inverter;

[0170] The first model output module is configured to decompose the three-phase grid-connected inverter system into two positive-sequence and negative-sequence subsystems using a harmonic linearization method without considering the influence of the phase-locked loop frequency characteristics, inject positive-sequence and negative-sequence small signal disturbances at the grid-connected output terminal, and obtain the positive-sequence and negative-sequence output impedances of the grid-connected inverter when the positive-sequence small signal disturbances are injected but without considering the phase-locked loop disturbance based on the core equations of the three-phase circuit of the grid-connected inverter;

[0171] A second model output module is configured to inject positive and negative sequence small signal disturbances at the grid-connected output terminal while introducing a phase angle disturbance into the phase-locked loop phase-locked angle based on the three-phase positive and negative sequence output impedance of the grid-connected inverter without considering the phase-locked loop disturbance, thereby obtaining a grid-connected inverter output impedance model under the conditions of injecting positive and negative sequence small signal disturbances and considering the phase angle disturbance;

[0172] The multivariable reshaping module is used to introduce multivariable feedback control and reshape the output impedance model of the grid-connected inverter using the above method to obtain the output impedance model of the grid-connected inverter under the multivariable control mode.

[0173] It is worth noting that this embodiment corresponds to the above-mentioned method embodiment, and the implementation methods of the above-mentioned method embodiment are applicable to this device embodiment and can achieve the same or similar technical effects, so they will not be described in detail here.

[0174] Example 3

[0175] This embodiment 3 provides a computer-readable storage medium storing one or more programs, wherein the one or more programs include instructions, which, when executed by a computing device, enable the computing device to perform any one of the grid-connected inverter impedance modeling methods under the multivariable control mode according to the above embodiments.

[0176] Example 4

[0177] This embodiment 4 provides a computing device, including one or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include instructions for executing any one of the grid-connected inverter impedance modeling methods under the multivariable control mode according to the above embodiments.

[0178] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present application may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0179] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0180] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0181] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0182] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A grid-connected inverter impedance modeling method under multivariable control mode, characterized in that: include: According to the LCL type three-phase grid-connected inverter system structure, the core equation of the three-phase circuit of the grid-connected inverter is established; Without considering the influence of the phase-locked loop frequency characteristics, the three-phase grid-connected inverter system is decomposed into two positive and negative sequence subsystems using the harmonic linearization method. Positive and negative sequence small signal disturbances are injected into the grid-connected output terminal. Based on the core equations of the three-phase circuit of the grid-connected inverter, the positive and negative sequence output impedances of the grid-connected inverter are obtained when the positive and negative sequence small signal disturbances are injected but the phase-locked loop disturbance is not considered. Based on the three-phase positive and negative sequence output impedance of the grid-connected inverter injected with positive and negative sequence small signal disturbance but without considering the phase-locked loop disturbance, while injecting the positive and negative sequence small signal at the grid-connected output end, a phase angle disturbance is introduced into the phase-locked loop phase angle, thereby obtaining a grid-connected inverter output impedance model under the conditions of injecting positive and negative sequence small signal disturbance and considering the phase angle disturbance; Multivariable feedback control is introduced, and the output impedance model of the grid-connected inverter is reshaped using the above method to obtain the output impedance model of the grid-connected inverter under the multivariable control mode.

2. The impedance modeling method for a grid-connected inverter in a multivariable control mode according to claim 1, characterized in that: The core equation of the three-phase circuit of the grid-connected inverter is expressed as: ， in, Modulate the voltage of the three-phase bridge arm; is the DC input voltage; is the inverter voltage modulation ratio; and Constructing a filter; Connect the filter capacitor in series with the damping resistor; is the three-phase grid voltage containing fundamental frequency components and small disturbance components; is the three-phase grid current containing fundamental frequency component and small disturbance component; Represents complex frequency.

3. The impedance modeling method for a grid-connected inverter in a multivariable control mode according to claim 2, wherein: The positive and negative sequence small signal disturbance is injected at the grid-connected output end, and based on the core equation of the three-phase circuit of the grid-connected inverter, the positive and negative sequence output impedance of the grid-connected inverter injected with the positive and negative sequence small signal disturbance but without considering the phase-locked loop disturbance is obtained, including: Without considering the influence of the phase-locked loop frequency characteristics, the three-phase grid-connected inverter system is decomposed into two subsystems with positive and negative sequences using the harmonic linearization method. Positive and negative sequence small signal disturbances are injected into the grid-connected output terminal to obtain the grid-connected current response components at the disturbance frequency. Obtaining the frequency domain form of the grid-connected current response component at the disturbance frequency through Fourier transform; Based on the frequency domain form of the grid-connected current response component at the disturbance frequency and according to the grid-connected inverter circuit control structure, the dq axis current closed-loop control is performed to obtain the dq axis voltage output by the current regulator, and the voltage is input into the space vector pulse width modulation module to obtain the dq axis bridge arm modulation voltage; Based on the dq-axis bridge arm modulation voltage and the core equation of the three-phase circuit of the grid-connected inverter, the positive and negative sequence output impedances of the grid-connected inverter are obtained when positive and negative sequence small signal disturbances are injected but phase-locked loop disturbances are not considered.

4. The impedance modeling method for a grid-connected inverter in a multivariable control mode according to claim 3, wherein: The grid-connected current response component at the disturbance frequency is expressed as: ， in, is the fundamental current peak value; is the fundamental wave phase angle; 、 are the positive and negative sequence current disturbance phase angles respectively; and are the positive and negative sequence current disturbance peaks respectively; The frequency domain form of the grid-connected current response component at the disturbance frequency is expressed as: ， ， in 、 are the dq axis grid-connected current after Fourier transformation, is the frequency in the frequency domain expression, 、 and are the fundamental frequency and positive and negative sequence current disturbance frequencies respectively, is the fundamental current phase, and are the frequency domain expressions of the positive and negative sequence current disturbance peaks, and are the positive and negative sequence current disturbance phases respectively; The dq axis bridge arm modulation voltage is expressed as: ， ， in, 、 、 、 are respectively the positive and negative sequence dq axis bridge arm modulation voltages under the injection of positive and negative sequence small signal disturbances, and correspond and , is the equivalent transfer function of the current sampling delay link, is the current loop regulator, is the current loop regulation coefficient; The positive and negative sequence output impedance of the grid-connected inverter injected with positive and negative sequence small signal disturbance but without considering the phase-locked loop disturbance is expressed as: ， ， in, and is the positive and negative sequence output impedance of the grid-connected inverter when positive and negative sequence small signal disturbances are injected but the phase-locked loop disturbance is not considered.

5. The impedance modeling method for a grid-connected inverter in a multivariable control mode according to claim 4, characterized in that: The method of injecting a small positive and negative sequence signal at the grid-connected output terminal and introducing a phase angle disturbance into the phase-locked loop phase angle obtains a grid-connected inverter output impedance model under the conditions of injecting a small positive and negative sequence signal disturbance and considering the phase angle disturbance, including: Under the frequency characteristics of the phase-locked loop, the phase-locked angle introduces phase angle disturbance, and the closed-loop transfer function of the phase-locked loop with phase angle disturbance is obtained; Based on the closed-loop transfer function of the phase-locked loop that introduces the phase angle disturbance and the grid-connected current response component at the disturbance frequency, a frequency domain form of the grid-connected current response component that takes into account the phase angle disturbance of the phase-locked loop is obtained; Based on the frequency domain form of the grid-connected current response component considering the phase-locked loop phase angle disturbance, according to the grid-connected inverter circuit control structure, the dq axis current closed-loop control is performed to obtain the dq axis voltage output by the current regulator, and the voltage is input into the space vector pulse width modulation module to obtain the dq axis bridge arm modulation voltage; Based on the dq-axis bridge arm modulation voltage and the core equation of the three-phase circuit of the grid-connected inverter, an output impedance model of the grid-connected inverter under the injection of positive and negative sequence small signal disturbances and consideration of phase angle disturbances is obtained.

6. The impedance modeling method for a grid-connected inverter in a multivariable control mode according to claim 5, characterized in that: The closed-loop transfer function of the phase-locked loop with phase angle disturbance is expressed as: ， in, is the closed-loop transfer function of the phase-locked loop, is the system fundamental DC voltage, and is the relationship expression between positive and negative sequence voltage and phase angle disturbance, and Expressed as: ， in, is the phase angle perturbation, 、 is the positive and negative sequence disturbance component in the frequency domain; The frequency domain form of the grid-connected current response component considering the phase-locked loop phase angle disturbance is expressed as: ， ， in, and are the dq axis frequency domain forms of the grid current response components considering the phase angle disturbance of the phase-locked loop, 、 are the positive and negative sequence transfer functions of the phase-locked loop, respectively, which are derived from the closed-loop transfer function of the phase-locked loop; The dq axis bridge arm modulation voltage is expressed as: ， ， in, 、 、 and The positive and negative sequence dq axis bridge arm modulation voltage is injected with positive and negative sequence small signal disturbance and considering phase angle disturbance; The output impedance model of the grid-connected inverter under the injection of positive and negative sequence small signal disturbances and the consideration of phase angle disturbances is expressed as: ， ， in, and is the positive and negative sequence output impedance of the grid-connected inverter under the injection of positive and negative sequence small signal disturbance and considering phase angle disturbance.

7. The impedance modeling method for a grid-connected inverter in a multivariable control mode according to claim 6, characterized in that: The multivariable feedback control is introduced, and the output impedance model of the grid-connected inverter is reshaped in the above manner to obtain the output impedance model of the grid-connected inverter under the multivariable control mode, including: By introducing grid voltage feedforward, inverter side inductor current feedforward, and inverter side capacitor current feedforward respectively, the output impedance model of the grid-connected inverter under the injection of positive and negative sequence small signal disturbances and the consideration of phase angle disturbances is reshaped to obtain the output impedance model of the grid-connected inverter under different variable control modes, which is expressed as: In the grid voltage feedforward control mode, we get: ， ， ， Then the positive sequence output impedance is: ; In the inverter side inductor current feedforward control mode, we get: ， ， ， ， ， ， Then the positive sequence output impedance is: ; In the inverter side capacitor current feedforward control mode, we get: ， ， ， ， Then the positive sequence output impedance is: ; above 、 、 、 、 、 、 、 、 、 、 、 、 are all process parameters, is the grid voltage feedback transfer function, Inductor on the inverter side Current transfer function, is the capacitor current transfer function.

8. A grid-connected inverter impedance modeling system under multivariable control mode, characterized in that: A system for implementing the impedance modeling method for a grid-connected inverter in a multivariable control mode according to any one of claims 1 to 7, the system comprising: The circuit analysis module is used to establish the core equations of the three-phase circuit of the grid-connected inverter based on the system structure of the LCL three-phase grid-connected inverter; The first model output module is configured to decompose the three-phase grid-connected inverter system into two positive-sequence and negative-sequence subsystems using a harmonic linearization method without considering the influence of the phase-locked loop frequency characteristics, inject positive-sequence and negative-sequence small signal disturbances at the grid-connected output terminal, and obtain the positive-sequence and negative-sequence output impedances of the grid-connected inverter when the positive-sequence small signal disturbances are injected but without considering the phase-locked loop disturbance based on the core equations of the three-phase circuit of the grid-connected inverter; A second model output module is configured to inject positive and negative sequence small signal disturbances at the grid-connected output terminal while introducing a phase angle disturbance into the phase-locked loop phase-locked angle based on the three-phase positive and negative sequence output impedance of the grid-connected inverter without considering the phase-locked loop disturbance, thereby obtaining a grid-connected inverter output impedance model under the conditions of injecting positive and negative sequence small signal disturbances and considering the phase angle disturbance; The multivariable reshaping module is used to introduce multivariable feedback control and reshape the output impedance model of the grid-connected inverter using the above method to obtain the output impedance model of the grid-connected inverter under the multivariable control mode.

9. A computer-readable storage medium storing one or more programs, characterized in that: The one or more programs include instructions, which, when executed by a computing device, cause the computing device to perform any one of the grid-connected inverter impedance modeling methods in a multivariable control mode according to claims 1 to 7.

10. A computing device, characterized in that include, One or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include instructions for executing any one of the grid-connected inverter impedance modeling methods in a multivariable control mode according to claims 1 to 7.

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