Method and apparatus for suppressing dc side frequency coupling effect for grid-connected inverters

Abstract

The application discloses a DC side frequency coupling effect suppression method and device for a grid-connected inverter, and the method comprises the following steps: obtaining a forward channel transfer function according to LCL filter parameters of the inverter; obtaining a conversion matrix according to a phase angle difference between a power grid dq coordinate system and a phase-locked loop controller dq coordinate system; obtaining an output admittance matrix according to a current loop transfer function of the inverter, the forward channel transfer function and the conversion matrix; obtaining a transfer function model according to a DC voltage loop transfer function of the inverter and the output admittance matrix; taking a first proportional coefficient of a PI controller in the DC voltage loop transfer function as a variable, and drawing a preset number of Bode diagrams according to the transfer function model; selecting the first proportional coefficient corresponding to the Bode diagram with a harmonic current amplitude meeting a preset requirement as a parameter of the transfer function model to obtain a first model; and performing inverter control according to the first model.

Description

Technical Field

[0001] This invention relates to the field of grid-connected inverter technology, and in particular to a method and apparatus for suppressing DC-side frequency coupling effects in grid-connected inverters. Background Technology

[0002] New energy power generation mainly uses grid-connected inverters as interfaces to connect to the power grid. When a large number of grid-connected inverters are connected to the power grid, the interaction between the power grid and the grid-connected inverters becomes stronger and more frequent, which can easily cause subsynchronous / supersynchronous oscillation problems in specific frequency ranges.

[0003] In subsynchronous / supersynchronous oscillations, a harmonic component of one frequency often appears simultaneously with a harmonic component of another frequency, and the harmonic frequencies of the two are symmetrical about the fundamental frequency, exhibiting a mirror symmetry relationship. This phenomenon is called frequency coupling effect. Some researchers believe that the frequency coupling effect in grid-connected inverters is caused by phase-locked loops (PLLs) and have established impedance models for analysis, but the mechanism analysis is still incomplete. Other researchers believe that the frequency coupling effect in grid-connected inverters is caused by the asymmetry of the d-axis and q-axis controllers, but they have not pinpointed the exact source of the frequency coupling effect. Because the source of the frequency coupling effect in grid-connected inverters is still unclear in existing research, there are no targeted suppression methods in current technology.

[0004] Therefore, a new solution is urgently needed to address the technical problem of how to suppress the frequency coupling effect of grid-connected inverters. Summary of the Invention

[0005] This invention provides a method and apparatus for suppressing the frequency coupling effect on the DC side of a grid-connected inverter, in order to solve the technical problem of how to suppress the frequency coupling effect of a grid-connected inverter.

[0006] To achieve the above objectives, the present invention provides a method for suppressing DC-side frequency coupling effects in grid-connected inverters, comprising:

[0007] The forward transfer function is obtained based on the LCL filter parameters of the inverter; the transformation matrix is ​​obtained based on the phase angle difference between the grid dq coordinate system and the phase-locked loop controller dq coordinate system; the output admittance matrix is ​​obtained based on the inverter's current loop transfer function, forward transfer function, and transformation matrix; the transfer function model is obtained based on the inverter's DC voltage loop transfer function and output admittance matrix; a preset number of Bode plots are drawn based on the transfer function model, using the first proportional coefficient of the PI controller in the DC voltage loop transfer function as a variable; the first proportional coefficient corresponding to the Bode plot whose harmonic current amplitude meets the preset requirements is selected as the transfer function model parameter to obtain the first model; the inverter is controlled based on the first model.

[0008] Preferably, the forward channel transfer function is obtained based on the LCL filter parameters of the inverter, including:

[0009] The first transfer function and the second transfer function are constructed based on the LCL filter parameters of the inverter.

[0010] The first transfer function G1(s) reflects the transfer relationship between the inverter-side filter inductor and filter capacitor, including:

[0011] ;

[0012] The second transfer function G2(s) reflects the transfer relationship between the inverter-side filter inductor, filter capacitor, and grid-side filter inductor, including:

[0013] ;

[0014] in, Represents the identity matrix; , and These represent the capacitance transfer function impedance matrix of the LCL filter, the inductance transfer function admittance matrix of the inverter output port, and the inductance transfer function admittance matrix at the grid connection point, respectively. That is, the first transfer function.

[0015] Preferably, the transformation matrix obtained based on the phase angle difference between the power grid dq coordinate system and the phase-locked loop controller dq coordinate system includes:

[0016] Considering the influence of phase angle disturbance of the phase-locked loop output in the dq domain, the first transformation matrix and the second transformation matrix are obtained based on the phase angle difference between the grid dq coordinate system and the phase-locked loop controller dq coordinate system.

[0017] First transformation matrix Used for conversion between grid-connected output current and phase-locked loop controller, including:

[0018] ;

[0019] Second transformation matrix Used for conversion between grid-connected voltage and phase-locked loop controller, including:

[0020] ;

[0021] in, This is the transfer function of the PI controller in the phase-locked loop; For the Laplace operator; and The output modulation signal of the PI controller in the current loop of the inverter is respectively... shaft and Steady-state value on the axis; and The output current of the inverter is respectively shaft and Steady-state values ​​of the axis components; For the inverter grid connection point voltage at Steady-state values ​​of the axis components.

[0022] Preferably, the output admittance matrix is ​​obtained based on the inverter's current loop transfer function, forward path transfer function, and transformation matrix, including:

[0023] The output admittance matrix is ​​derived by using the inverter's current loop transfer function, forward path transfer function, and transformation matrix. ,include:

[0024] ;

[0025] in, For pulse width modulation gain; The delay generated during the calculation and modulation process includes:

[0026] ;

[0027] in, Indicates the sampling period.

[0028] Preferably, the transfer function model obtained based on the inverter's DC voltage loop transfer function and output admittance matrix includes:

[0029] Based on the DC voltage loop transfer function and output admittance matrix of the inverter, the equivalent output admittance matrix on the DC side of the inverter, i.e., the transfer function model, is derived and calculated. ,include:

[0030] ;

[0031] Based on the transfer function model There is a relationship between DC-side voltage disturbance and the actual output current of the inverter:

[0032] ;

[0033] ;

[0034] in, This is the DC side current; This is the actual output current of the inverter. For DC-side voltage disturbance; The magnitude of the disturbance voltage. ; This is the DC voltage amplitude. and These are the disturbance angular frequency and the disturbance phase angle, respectively. Indicates time.

[0035] Preferably, using the first proportional coefficient of the PI controller in the DC voltage loop transfer function as a variable, the predetermined number of Bode plots are drawn based on the transfer function model, including:

[0036] The proportional coefficient of the PI controller in the DC voltage loop transfer function is denoted as the first proportional coefficient. Using the first proportional coefficient as a variable, a preset number of parameter combinations are set within a preset parameter range. Based on the preset number of parameter combinations and the transfer function model, a preset number of Bode plots are drawn.

[0037] Preferably, the first scaling factor corresponding to the Bode plot whose amplitude of the harmonic current meets the preset requirements is selected as the transfer function model parameter, resulting in a first model including:

[0038] Frequency coupling effect analysis is performed based on a preset number of Bode plots. Bode plots in which the harmonic current amplitude, harmonic disturbance and their coupled harmonic content all meet the expected values ​​are selected to obtain the result plot. The first proportional coefficient corresponding to the result plot is selected as the proportional coefficient of the PI controller in the DC voltage loop transfer function of the transfer function model to obtain the first model.

[0039] The present invention also provides a DC-side frequency coupling effect suppression device for grid-connected inverters, which is used to implement the method of the present invention. The device includes a first module, a second module, a third module, a fourth module, and a fifth module.

[0040] The first module is used to obtain the forward transfer function based on the LCL filter parameters of the inverter; and to obtain the transformation matrix based on the phase angle difference between the grid dq coordinate system and the phase-locked loop controller dq coordinate system.

[0041] The second module is used to obtain the output admittance matrix based on the inverter's current loop transfer function, forward path transfer function, and transformation matrix.

[0042] The third module is used to obtain the transfer function model based on the inverter's DC voltage loop transfer function and output admittance matrix;

[0043] The fourth module is used to draw a preset number of Bode plots based on the transfer function model, using the first proportional coefficient of the PI controller in the DC voltage loop transfer function as the variable.

[0044] The fifth module is used to select the first proportional coefficient corresponding to the Bode plot whose amplitude of the harmonic current meets the preset requirements as the transfer function model parameter to obtain the first model; and to control the inverter according to the first model.

[0045] The present invention has the following beneficial effects:

[0046] The present invention provides a method for suppressing DC-side frequency coupling effects in grid-connected inverters. It derives the output admittance matrix based on the inverter's current loop transfer function, forward path transfer function, and transformation matrix. Furthermore, it constructs a transfer function model based on the inverter's DC voltage loop transfer function and output admittance matrix, enabling the transfer function model to reflect the relationship between DC-side voltage disturbances and the actual grid-connected output current. Using the first proportional coefficient of the PI controller in the DC voltage loop transfer function as a variable, a predetermined number of Bode plots are drawn based on the transfer function model, revealing the harmonic disturbance coupling characteristics caused by DC-side voltage fluctuations. The first proportional coefficient corresponding to the Bode plot where the harmonic current amplitude meets predetermined requirements is selected as the transfer function model parameter, resulting in a first model. Inverter control is performed based on the first model, enabling the method of the present invention to effectively suppress the frequency coupling effect of the grid-connected inverter.

[0047] The DC-side frequency coupling effect suppression device for grid-connected inverters of the present invention, used in the method of the present invention, has the same beneficial effects as the method of the present invention.

[0048] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0049] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0050] Figure 1 This is a schematic diagram of the control structure of a three-phase LCL grid-connected converter system in the dq domain according to a preferred embodiment of the present invention.

[0051] Figure 2 This is a schematic diagram of the method flow of a preferred embodiment of the present invention.

[0052] Figure 3 This is a control block diagram of the transfer function model of a grid-connected converter in the dq domain, according to a preferred embodiment of the present invention.

[0053] Figure 4 This is the transfer function model of a preferred embodiment of the present invention. Different parameters Bode plot under certain conditions.

[0054] Figure 5 This is a preferred embodiment of the present invention. A schematic diagram of the actual grid-connected output current harmonics when the value is 0.25.

[0055] Figure 6 This is a preferred embodiment of the present invention. A schematic diagram of the actual grid-connected output current harmonics when the value is 0.35.

[0056] Figure 7 This is a preferred embodiment of the present invention. A schematic diagram of the actual grid-connected output current harmonics when the value is 0.75.

[0057] Figure 8 This is a preferred embodiment of the present invention. Actual grid-connected output current when it is 0.25 Waveform diagram.

[0058] Figure 9 This is a preferred embodiment of the present invention. Actual grid-connected output current when it is 0.35 Waveform diagram.

[0059] Figure 10 This is a preferred embodiment of the present invention. Actual grid-connected output current when it is 0.75 Waveform diagram. Detailed Implementation

[0060] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0061] In a preferred embodiment of the present invention, the control structure of the three-phase LCL grid-connected converter system in the dq domain is described below. Figure 1 .exist Figure 1 middle, DC power supply For the inverter-side filter inductor, For grid-side filter inductance, For filtering capacitors, For damping resistor, Indicates the voltage at the grid connection point. Indicates the power grid impedance. This indicates the grid voltage, PLL is the phase-locked loop, and PCC is the grid connection point. This is the DC-side disturbance voltage. DC side voltage This is the reference value for the DC side voltage. This is the DC voltage loop transfer function of the inverter. This refers to the actual grid-connected output current of the grid-connected inverter. and for Reference value for grid-connected output current in the domain. and for The actual grid-connected output current of the grid-connected inverter in the domain. Let be the current loop transfer function of the inverter. and The modulated signal output by the controller in the dq domain. For pulse width modulation gain, and These are the dq transform and the inverse dq transform, respectively. This is the output of the phase-locked loop.

[0062] DC voltage loop transfer function of inverter include:

[0063] ;

[0064] in, and These are the proportional and integral coefficients of the PI controller in the DC voltage loop, respectively. For the Laplace operator.

[0065] Inverter current loop transfer function include:

[0066] ;

[0067] in, and They represent The proportional and integral coefficients of the PI controller in the shaft current control loop; and They represent The proportional and integral coefficients of the PI controller in the shaft current control loop.

[0068] See Figure 2 In a preferred embodiment of the present invention, a method for suppressing DC-side frequency coupling effects in a grid-connected inverter is provided, comprising:

[0069] F1. Obtain the forward channel transfer function based on the LCL filter parameters of the inverter; obtain the transformation matrix based on the phase angle difference between the grid dq coordinate system and the phase-locked loop controller dq coordinate system.

[0070] In a preferred embodiment of the present invention, obtaining the forward channel transfer function based on the LCL filter parameters of the inverter includes:

[0071] The first transfer function and the second transfer function are constructed based on the LCL filter parameters of the inverter.

[0072] First transfer function The transmission relationship between the inverter-side filter inductor and filter capacitor is illustrated, including:

[0073] ;

[0074] Second transfer function The transmission relationship between the inverter-side filter inductor, filter capacitor, and grid-side filter inductor is illustrated, including:

[0075] ;

[0076] in, Represents the identity matrix; , and These represent the capacitance transfer function impedance matrix of the LCL filter, the inductance transfer function admittance matrix of the inverter output port, and the inductance transfer function admittance matrix at the grid connection point, respectively. That is, the first transfer function. In a preferred embodiment of the present invention, , and Represented as:

[0077] ;

[0078] ;

[0079] ;

[0080] in, For the inverter-side filter inductor, For grid-side filter inductance, For filtering capacitors, This represents the damping resistor in an LCL filter. This represents the power grid frequency, with a value of 50Hz.

[0081] In a preferred embodiment of the present invention, obtaining the transformation matrix based on the phase angle difference between the power grid dq coordinate system and the phase-locked loop controller dq coordinate system includes:

[0082] In the dq domain, the influence of phase angle disturbance at the PLL output is considered, i.e., the phase angle difference between the grid dq coordinate system and the PLL controller dq coordinate system is taken into account. The first transformation matrix and the second transformation matrix are obtained based on the phase angle difference between the grid dq coordinate system and the PLL controller dq coordinate system.

[0083] First transformation matrix Used for conversion between grid-connected output current and phase-locked loop controller, including:

[0084] ;

[0085] Second transformation matrix Used for conversion between grid-connected voltage and phase-locked loop controller, including:

[0086] ;

[0087] in, Let be the transfer function of the PI controller in the phase-locked loop. , and These are the proportional and integral coefficients of the PI controller in the phase-locked loop, respectively. For the Laplace operator; and The output modulation signal of the PI controller in the current loop of the inverter is respectively... shaft and Steady-state value on the axis; and The output current of the inverter is respectively shaft and Steady-state values ​​of the axis components; For the inverter grid connection point voltage at Steady-state values ​​of the axis components.

[0088] F2. The output admittance matrix is ​​obtained based on the inverter's current loop transfer function, forward path transfer function, and transformation matrix. In a preferred embodiment of the present invention, F2 specifically includes:

[0089] The output admittance matrix is ​​derived by using the inverter's current loop transfer function, forward path transfer function, and transformation matrix. ,include:

[0090] ;

[0091] in, For pulse width modulation gain; The delay generated during the calculation and modulation process includes:

[0092] ;

[0093] in, Indicates the sampling period.

[0094] F3. Obtain the transfer function model based on the inverter's DC voltage loop transfer function and output admittance matrix. In a preferred embodiment of the present invention, F3 specifically includes:

[0095] Based on the DC voltage loop transfer function and output admittance matrix of the inverter, the equivalent output admittance matrix on the DC side of the inverter, i.e., the transfer function model, is derived and calculated. ,include:

[0096] ;

[0097] Based on the transfer function model There is a relationship between DC-side voltage disturbance and the actual output current of the inverter:

[0098] ;

[0099] ;

[0100] in, This is the DC side current; This is the actual output current of the inverter. For DC-side voltage disturbance; The magnitude of the disturbance voltage. ; This is the DC voltage amplitude. and These are the disturbance angular frequency and the disturbance phase angle, respectively. Indicates time.

[0101] In a preferred embodiment of the present invention, see [reference needed]. Figure 3 The transfer function model of the grid-connected converter in the dq domain according to the method of the present invention is described, including:

[0102] Actual value of grid-connected output current Feedback coefficients of feedback control Multiply to obtain the feedback quantity ; feedback quantity Subtract the DC side voltage reference value and DC side disturbance voltage The DC voltage loop transfer function input to the inverter after summation The grid-connected output current reference value is obtained. .

[0103] Grid-connected voltage With the first transformation matrix Multiply and then subtract the actual grid-connected output current. and the grid-connected output current reference value After addition, the current loop transfer function of the input inverter is obtained. , obtain the controller in Modulation signal output in the domain ; grid-connected voltage With the second transformation matrix After multiplication, it is combined with the controller. Modulation signal output in the domain Add them together to get the power grid's position. Modulation signal output in the domain ; to put the power grid in Modulation signal output in the domain The delay generated during the calculation and modulation process in sequence Pulse width modulation gain and the first transfer function Multiplying these together yields the first forward channel signal.

[0104] Subtract the grid voltage from the first forward channel signal. After the second transfer function Multiply to obtain the actual value of the grid-connected output current. .

[0105] F4. Using the first proportional coefficient of the PI controller in the DC voltage loop transfer function as a variable, plot a preset number of Bode plots based on the transfer function model. In a preferred embodiment of the present invention, F4 specifically includes:

[0106] The proportional coefficient of the PI controller in the DC voltage loop transfer function is denoted as the first proportional coefficient. Using the first proportional coefficient as a variable, a preset number of parameter combinations are set within a preset parameter range. Based on the preset number of parameter combinations and the transfer function model, a preset number of Bode plots are drawn.

[0107] F5. Select the first proportional coefficient corresponding to the Bode plot whose amplitude of the harmonic current meets the preset requirements as the transfer function model parameter to obtain the first model; perform inverter control based on the first model. In a preferred embodiment of the present invention, F5 specifically includes:

[0108] Frequency coupling effect analysis was performed using a predetermined number of Bode plots. The analysis revealed that harmonic disturbances and their coupled harmonics are expressions of the transfer function model, demonstrating the coupling characteristics of harmonic disturbances caused by DC-side voltage fluctuations. Fast Fourier analysis based on the actual grid-connected output current showed that the output harmonics and their coupled harmonics of the actual grid-connected output current are symmetrical about the fundamental frequency, with almost identical harmonic amplitudes. In the actual analysis, as the proportional gain of the PI controller in the DC voltage loop transfer function increases, the amplitude of the harmonic current gradually decreases, and the content of harmonic disturbances and their coupled harmonics gradually diminishes.

[0109] Bode plots were selected to ensure that the harmonic current amplitude, harmonic disturbance, and their coupled harmonic content all met the desired values, resulting in a graph. The first proportional coefficient corresponding to the graph was selected as the proportional coefficient of the PI controller in the DC voltage loop transfer function of the transfer function model, thus obtaining the first model. Inverter control was then performed based on the first model.

[0110] The present invention provides a method for suppressing DC-side frequency coupling effects in grid-connected inverters. It derives the output admittance matrix based on the inverter's current loop transfer function, forward path transfer function, and transformation matrix. Furthermore, it constructs a transfer function model based on the inverter's DC voltage loop transfer function and output admittance matrix, enabling the transfer function model to reflect the relationship between DC-side voltage disturbances and the actual grid-connected output current. Using the first proportional coefficient of the PI controller in the DC voltage loop transfer function as a variable, a predetermined number of Bode plots are drawn based on the transfer function model, revealing the harmonic disturbance coupling characteristics caused by DC-side voltage fluctuations. The first proportional coefficient corresponding to the Bode plot where the harmonic current amplitude meets predetermined requirements is selected as the transfer function model parameter, resulting in a first model. Inverter control is performed based on the first model, enabling the method of the present invention to effectively suppress the frequency coupling effect of the grid-connected inverter.

[0111] In a preferred embodiment of the present invention, a DC-side frequency coupling effect suppression device for a grid-connected inverter is also provided, which is used in the method of the present invention. The device includes a first module, a second module, a third module, a fourth module, and a fifth module.

[0112] The first module is used to obtain the forward transfer function based on the LCL filter parameters of the inverter; and to obtain the transformation matrix based on the phase angle difference between the grid dq coordinate system and the phase-locked loop controller dq coordinate system.

[0113] The second module is used to obtain the output admittance matrix based on the inverter's current loop transfer function, forward path transfer function, and transformation matrix.

[0114] The third module is used to obtain the transfer function model based on the inverter's DC voltage loop transfer function and output admittance matrix;

[0115] The fourth module is used to draw a preset number of Bode plots based on the transfer function model, using the first proportional coefficient of the PI controller in the DC voltage loop transfer function as the variable.

[0116] The fifth module is used to select the first proportional coefficient corresponding to the Bode plot whose amplitude of the harmonic current meets the preset requirements as the transfer function model parameter to obtain the first model; and to control the inverter according to the first model.

[0117] The frequency coupling effect suppression device for grid-connected inverters of the present invention, used in the method of the present invention, has the same beneficial effects as the method of the present invention.

[0118] Verification section:

[0119] A three-phase LCL grid-connected inverter system was built in MATLAB / Simulink. The main parameters are shown in Table 1.

[0120] Table 1 Main System Parameters

[0121] ;

[0122] To verify the method of the present invention, Figure 4 The transfer function model is based on the relationship between DC-side voltage disturbance and actual grid-connected output current. Different parameters Bode plot under certain conditions.

[0123] observe Figure 4 Adjust the parameters of the PI controller in the DC voltage loop. ,when When increasing, The amplitude gradually decreases, and the harmonic current... The amplitude gradually decreases, thus suppressing harmonic disturbances to a degree of 17%.

[0124] Figures 5 to 7 For different parameters A schematic diagram of the actual grid-connected output current harmonics. Figures 8 to 10 For different parameters Schematic diagram of actual grid-connected output current waveform. When a 40Hz disturbance amplitude is injected into the DC side, the disturbance value is... Harmonic voltage disturbances were observed. Fast Fourier analysis of the actual grid-connected current revealed that the actual grid-connected output current contained a 40Hz harmonic and its coupled 60Hz harmonic, exhibiting a frequency coupling effect.

[0125] observe Figures 5 to 7 It can be seen that when When = 0.25, the 40Hz harmonic accounts for 28.778% of the fundamental frequency, and the coupled 60Hz harmonic accounts for 29.062% of the fundamental frequency; when When = 0.35, the 40Hz harmonic accounts for 26.568% of the fundamental frequency, and the coupled 60Hz harmonic accounts for 26.818% of the fundamental frequency; when When the value is 0.75, the 40Hz harmonic accounts for 23.920% of the fundamental frequency, and the coupled 60Hz harmonic accounts for 24.090% of the fundamental frequency.

[0126] observe Figures 8 to 10 It can be seen that adjusting the parameters of the PI controller in the DC voltage loop... ,according to =0.25、 =0.35、 As the value of 0.75 increases, the total harmonic distortion (THD) decreases from 29.20% to 24.22%, and the amplitude of the harmonic current gradually decreases, thus suppressing the harmonic disturbance to a degree of 17%.

[0127] Therefore, by adjusting the PI controller parameters in the voltage loop ,when As the harmonic current increases, its amplitude gradually decreases, verifying that... Figure 4 The theoretical analysis is correct. The method of this invention can suppress harmonic disturbances to a degree of 17%.

[0128] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for suppressing DC-side frequency coupling effects in grid-connected inverters, characterized in that, include: The forward channel transfer function is obtained based on the LCL filter parameters of the inverter. The transformation matrix is ​​obtained based on the phase angle difference between the grid dq coordinate system and the phase-locked loop controller dq coordinate system; the output admittance matrix is ​​obtained based on the inverter's current loop transfer function, the forward path transfer function, and the transformation matrix; the transfer function model is obtained based on the inverter's DC voltage loop transfer function and the output admittance matrix; a preset number of Bode plots are drawn based on the transfer function model, using the first proportional coefficient of the PI controller in the DC voltage loop transfer function as a variable; the first proportional coefficient corresponding to the Bode plot whose harmonic current amplitude meets the preset requirements is selected as the transfer function model parameter to obtain the first model; Inverter control is performed based on the first model; Based on the inverter's DC voltage loop transfer function and the output admittance matrix, the transfer function model is obtained as follows: Based on the inverter's DC voltage loop transfer function and the output admittance matrix, the equivalent output admittance matrix on the inverter's DC side, i.e., the transfer function model, is derived. ,include: ； in, I dc This is the DC side current; U m0 For the inverter grid connection point voltage at d Steady-state values ​​of the axis components; This is the output admittance matrix; This is the DC voltage loop transfer function for the inverter.

2. The method for suppressing DC-side frequency coupling effect in a grid-connected inverter according to claim 1, characterized in that, The forward channel transfer function, derived from the LCL filter parameters of the inverter, includes: The first transfer function and the second transfer function are constructed based on the LCL filter parameters of the inverter, respectively. The first transfer function G1(s) reflects the transfer relationship between the inverter-side filter inductor and filter capacitor, including: ； The second transfer function G2(s) reflects the transfer relationship between the inverter-side filter inductor, filter capacitor, and grid-side filter inductor, including: ； in, Represents the identity matrix; , and These represent the capacitance transfer function impedance matrix of the LCL filter, the inductance transfer function admittance matrix of the inverter output port, and the inductance transfer function admittance matrix at the grid connection point, respectively. That is, the first transfer function.

3. The method for suppressing DC-side frequency coupling effect in a grid-connected inverter according to claim 2, characterized in that, The transformation matrix obtained based on the phase angle difference between the power grid dq coordinate system and the phase-locked loop controller dq coordinate system includes: Considering the influence of phase angle disturbance of the phase-locked loop output in the dq domain, the first transformation matrix and the second transformation matrix are obtained based on the phase angle difference between the grid dq coordinate system and the phase-locked loop controller dq coordinate system. The first transformation matrix Used for conversion between grid-connected output current and phase-locked loop controller, including: ； The second transformation matrix Used for conversion between grid-connected voltage and phase-locked loop controller, including: ； in, This is the transfer function of the PI controller in the phase-locked loop; For the Laplace operator; and The output modulation signal of the PI controller in the current loop of the inverter is respectively... shaft and Steady-state value on the axis; and The output current of the inverter is respectively shaft and Steady-state values ​​of the axis components; For the inverter grid connection point voltage at Steady-state values ​​of the axis components.

4. The method for suppressing DC-side frequency coupling effect in a grid-connected inverter according to claim 3, characterized in that, The output admittance matrix is ​​obtained based on the inverter's current loop transfer function, the forward path transfer function, and the transformation matrix, including: The output admittance matrix is ​​obtained by derivation and calculation based on the inverter's current loop transfer function, the forward path transfer function, and the transformation matrix. ,include: ； in, For pulse width modulation gain; The delay generated during the calculation and modulation process includes: ； in, Indicates the sampling period.

5. The method for suppressing DC-side frequency coupling effect in a grid-connected inverter according to claim 4, characterized in that, Also includes: According to the transfer function model There is a relationship between DC-side voltage disturbance and the actual output current of the inverter: ； ； in, This is the actual output current of the inverter. For DC-side voltage disturbance; The magnitude of the disturbance voltage. ; This is the DC voltage amplitude. and These represent the perturbation angular frequency and the perturbation phase angle, respectively; t represents time.

6. The method for suppressing DC-side frequency coupling effect in a grid-connected inverter according to claim 5, characterized in that, Using the first proportional coefficient of the PI controller in the DC voltage loop transfer function as a variable, drawing a predetermined number of Bode plots based on the transfer function model includes: The proportional coefficient of the PI controller in the DC voltage loop transfer function is denoted as the first proportional coefficient. Using the first proportional coefficient as a variable, a preset number of parameter combinations are set within a preset parameter range. A preset number of Bode plots are drawn based on the preset number of parameter combinations and the transfer function model.

7. The method for suppressing DC-side frequency coupling effect in a grid-connected inverter according to claim 6, characterized in that, The first scaling factor corresponding to the Bode plot whose amplitude of the harmonic current meets the preset requirements is selected as the transfer function model parameter, resulting in the first model including: Frequency coupling effect analysis is performed based on the preset number of Bode plots. A Bode plot in which the harmonic current amplitude, harmonic disturbance, and their coupled harmonic content all meet the expected values ​​is selected to obtain the result plot. The first proportional coefficient corresponding to the result plot is selected as the proportional coefficient of the PI controller in the DC voltage loop transfer function of the transfer function model to obtain the first model.

8. A DC-side frequency coupling effect suppression device for a grid-connected inverter, used to implement the method according to any one of claims 1 to 7, characterized in that, The device includes a first module, a second module, a third module, a fourth module, and a fifth module; The first module is used to obtain the forward transfer function based on the LCL filter parameters of the inverter; and to obtain the transformation matrix based on the phase angle difference between the grid dq coordinate system and the phase-locked loop controller dq coordinate system. The second module is used to obtain the output admittance matrix based on the inverter's current loop transfer function, the forward path transfer function, and the transformation matrix; The third module is used to obtain the transfer function model based on the DC voltage loop transfer function of the inverter and the output admittance matrix. The fourth module is used to draw a preset number of Bode plots based on the transfer function model, using the first proportional coefficient of the PI controller in the DC voltage loop transfer function as a variable. The fifth module is used to select the first proportional coefficient corresponding to the Bode plot whose amplitude of the harmonic current meets the preset requirements as the transfer function model parameter to obtain the first model; and to perform inverter control based on the first model.

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