A method and system for suppressing grid-connected oscillation in a three-phase inverter

Abstract

This invention belongs to the field of grid-connected oscillation suppression technology, specifically disclosing a method and system for suppressing grid-connected oscillation in a three-phase inverter. The method includes: acquiring signal data at the grid connection point; setting a voltage feedforward channel in the current control inner loop of the three-phase inverter, the voltage feedforward channel generating a feedforward compensation signal based on the input signal; applying the feedforward compensation signal to the current control inner loop to obtain a corrected current control signal; establishing a sequence admittance model including the voltage feedforward channel based on the corrected current control signal, treating the portion generated by the voltage feedforward channel as virtual admittance, and connecting it in parallel with the original sequence admittance; determining the gain parameter of the voltage feedforward channel based on the parallel relationship between the virtual admittance and the original sequence admittance, ensuring that the real part of the parallel admittance is positive at the target frequency band; and adjusting the sequence impedance of the three-phase inverter using the reshaped sequence admittance. The transfer function of this application is simple and reliable, requiring only a separate gain stage to achieve the desired reshaping effect.

Description

Technical Field

[0001] This invention belongs to the field of grid-connected oscillation suppression technology, specifically relating to a method and system for suppressing grid-connected oscillation in a three-phase inverter. Background Technology

[0002] With the demands of energy transition and development, renewable energy sources, represented by wind and solar power, will gradually dominate the energy structure. Unlike traditional power systems, large-scale power electronic devices are constantly being connected to the grid, and the power system is gradually showing a trend towards power electronics. Therefore, the broadband oscillation problem caused by the interaction between power electronic devices and the grid is becoming increasingly serious. Such oscillations can cause damage to various devices in the power system at best; at worst, they can lead to large-scale disconnection of new energy units from the grid, system shutdowns, or even partial grid disconnection, posing a significant threat to the stable operation of the power system.

[0003] Existing oscillation suppression technologies primarily rely on adding additional damping channels. Additional damping control, without altering the original control structure, changes the original impedance characteristics by feeding electrical quantities back to the control loop through a compensator, thereby increasing damping.

[0004] However, most of the proposed additional damping channels have the following shortcomings: First, their transfer function is complex, often requiring the introduction of higher-order elements or multi-parameter compensators, which increases the design and implementation difficulty of the controller; second, the design ideas rely on specific modeling assumptions or specific operating conditions, resulting in poor applicability. When the grid impedance or operating conditions change, the original control effect may be significantly weakened; third, existing methods usually only suppress oscillations in a narrow frequency band, lacking consideration for non-target frequency bands, and may even introduce adverse effects in other frequency bands, leading to a decrease in the overall stability margin of the system. Summary of the Invention

[0005] This invention addresses the problems in the prior art by providing a method and system for suppressing grid-connected oscillations in three-phase inverters. This solves the problem in the background art where the introduction of additional high-order elements or multi-parameter compensators increases the design and implementation difficulty of the controller.

[0006] The technical solution adopted in this invention is as follows:

[0007] In a first aspect, this application provides a method for suppressing grid-connected oscillations in a three-phase inverter, the method comprising the following steps:

[0008] Step S1: Obtain the three-phase voltage signal at the grid connection point, and obtain the direct-axis voltage component and quadrature-axis voltage component through coordinate transformation calculation;

[0009] Step S2: Set up a voltage feedforward channel in the current control inner loop of the three-phase inverter;

[0010] Step S3: Input the direct-axis voltage component and the quadrature-axis voltage component into the voltage feedforward channel. The voltage feedforward channel generates a feedforward compensation signal based on the input signal.

[0011] Step S4: Apply the feedforward compensation signal to the inner loop of the current control to obtain the corrected current control signal;

[0012] Step S5: Based on the corrected current control signal, establish a three-phase inverter sequence admittance model including a voltage feedforward channel. In the sequence admittance model, the part generated by the voltage feedforward channel is regarded as virtual admittance and connected in parallel with the original sequence admittance.

[0013] Step S6: Determine the gain parameter of the voltage feedforward channel based on the parallel relationship between the virtual admittance and the original sequence admittance, so that the real part of the admittance after parallel connection is greater than zero in the target frequency band.

[0014] Step S7: Adjust the sequence impedance of the three-phase inverter using the sequence admittance after real part reshaping.

[0015] Furthermore, based on the harmonic linearization method, the sequence admittance of the three-phase grid-connected inverter after adding the voltage feedforward channel is calculated as follows:

[0016]

[0017] in, is the positive-sequence perturbation frequency; s is a complex frequency domain variable; This is the first filter inductor; This is the second filter inductor; , These are the inverter's DC-side capacitor and DC voltage, respectively. For filtering capacitors; This represents the amplitude of the fundamental component of the grid-connected voltage when the inverter is operating in steady state. The dq decoupling coefficients; It is the closed-loop transfer function of the phase-locked loop; , These are the first and second steady-state operating points of the system, respectively. , It is a DC quantity related to the first steady-state operating point and the second steady-state operating point of the system; The transfer function of the inner current loop; The angular frequency of the fundamental voltage; The transfer function of the voltage feedforward channel; This is the capacitor current feedback coefficient.

[0018] Furthermore, the expressions for the phase-locked loop closed-loop transfer function, the system's first steady-state operating point, the system's second steady-state operating point, and the DC quantity are as follows:

[0019]

[0020]

[0021]

[0022] in, This represents the amplitude of the fundamental component of the grid-connected current when the inverter is operating in steady state. The phase angle in which the fundamental grid-connected voltage leads the grid-connected current; The phase angle in which the fundamental grid-connected voltage leads the capacitor current; This represents the amplitude of the fundamental component of the filter capacitor current.

[0023] Furthermore, Transfer function for phase-locked loop controller;

[0024] and The expressions are as follows:

[0025]

[0026]

[0027] in, This refers to the proportional coefficient of the inner current loop controller. The integral coefficient of the inner current loop controller; This refers to the proportional gain of the phase-locked loop controller; is the integral coefficient of the phase-locked loop controller.

[0028] Furthermore, in step S5, the isolated virtual admittance The expression is:

[0029]

[0030] Original admittance The expression is:

[0031]

[0032] Virtual Admittance With original admittance The overall admittance of a three-phase grid-connected inverter connected in parallel after adding a voltage feedforward path is, among which, For the original admittance The real part, For the original admittance The imaginary part; among which For virtual admittance The real part, For virtual admittance The imaginary part.

[0033] Furthermore, in step S6, the parallel virtual admittance real part is... Expressions of imaginary parts for:

[0034]

[0035] Primitive Order Admittance Real Part and virtual part for:

[0036]

[0037] The denominators of the virtual admittance and the original sequence admittance are the same, and the real part of the denominator is... and the virtual part The expression is:

[0038]

[0039] The real part of the parallel virtual admittance The expression is:

[0040]

[0041] Real part of primitive sequential admittance The expression is:

[0042]

[0043] Voltage feedforward channel The specific method for determining the value is as follows:

[0044] .

[0045] Furthermore, in step S3, the voltage feedforward channel performs proportional calculations on the direct-axis voltage component and the quadrature-axis voltage component to obtain a feedforward compensation signal corresponding to the grid voltage change. The feedforward compensation signal is used to reflect the impact of voltage disturbance on inverter current control.

[0046] Furthermore, in step S4, the feedforward compensation signal is introduced into the signal combination stage of the current control inner loop, and works together with the original control signal of the inner loop to enable the corrected current control signal to simultaneously include grid-connected voltage information and the original current control information.

[0047] Secondly, this application provides a three-phase inverter grid-connected oscillation suppression system for implementing the steps of the three-phase inverter grid-connected oscillation suppression method as described in the first aspect, including:

[0048] The voltage acquisition unit is used to acquire the three-phase voltage signal at the grid connection point and obtain the direct-axis voltage component and quadrature-axis voltage component through coordinate transformation calculation.

[0049] The current control unit is used to set up a voltage feedforward channel in the current control inner loop of the three-phase inverter, and input the direct-axis voltage component and the quadrature-axis voltage component to the voltage feedforward channel, so that the voltage feedforward channel generates a feedforward compensation signal according to the input signal;

[0050] The signal processing unit is used to apply the feedforward compensation signal to the inner loop of the current control to obtain the corrected current control signal.

[0051] The modeling unit is used to establish a three-phase inverter sequence admittance model including a voltage feedforward channel based on the corrected current control signal, and in the sequence admittance model, the part generated by the voltage feedforward channel is regarded as virtual admittance and connected in parallel with the original sequence admittance;

[0052] The parameter determination unit is used to determine the gain parameters of the voltage feedforward channel based on the parallel relationship between the virtual admittance and the original sequence admittance, so that the real part of the admittance after parallel connection is positive in the target frequency band.

[0053] The impedance adjustment unit is used to adjust the sequence impedance of the three-phase inverter using the sequence admittance after real part reshaping.

[0054] Furthermore, the modeling unit is configured as follows:

[0055] When separating virtual admittance from original sequential admittance, virtual admittance is expressed as a fraction with the same denominator as original sequential admittance, and virtual admittance and original sequential admittance are defined as admittance quantities containing real and imaginary parts, respectively, so as to form equivalent sequential admittance through parallel relationship.

[0056] As can be seen from the above technical solutions, the advantages of the present invention are:

[0057] This invention adds a voltage feedforward channel to the inner current loop of a three-phase grid-connected inverter to reshape the sequence impedance. The purpose of this invention is to make the real part of the sequence admittance of the three-phase grid-connected inverter greater than zero. The voltage feedforward channel transfer function is designed so that the transfer function is simple and reliable, and only a separate gain stage is needed to achieve the desired reshaping effect.

[0058] This invention has a good effect on improving the phase margin of grid-connected systems across a wide frequency range. Compared with traditional sequence impedance reshaping suppression methods, it has less impact on the stability of non-oscillating frequency bands and can suppress broadband oscillations over a wider frequency range. Attached Figure Description

[0059] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0060] Figure 1 This is a flowchart illustrating the steps of the three-phase inverter grid-connected oscillation suppression method in the embodiment.

[0061] Figure 2 This is a schematic diagram of the structure of the three-phase grid-connected inverter with LCL-type filtering in the embodiment;

[0062] Figure 3 This is a schematic diagram of the current inner loop structure of the additional voltage feedback channel of the three-phase grid-connected inverter in the embodiment;

[0063] Figure 4 The diagram shows the theoretical and swept frequency values ​​of the admittance model for the LCL-type three-phase grid-connected inverter in the embodiment.

[0064] Figure 4 (a) is a graph showing the theoretical and swept-frequency values ​​under the admittance model amplitude;

[0065] Figure 4 (b) shows the theoretical and swept-frequency values ​​under the admittance model phase.

[0066] Figure 5 The equivalent admittance diagram of the three-phase inverter grid-connected system after adding a voltage feedforward channel in the embodiment is shown.

[0067] Figure 6 For different examples The value of under different frequency bands A diagram illustrating the values;

[0068] Figure 7 This is a diagram showing the stable regions corresponding to the positive and negative signs of the real part of the admittance of the three-phase grid-connected inverter in the embodiment.

[0069] Figure 8 The phase diagram shows the sequence impedance of the three-phase grid-connected inverter before and after the addition of the voltage feedforward channel in the embodiment.

[0070] Figure 9 To illustrate this, a voltage feedforward channel is added when the grid impedance is 3e-3H in the example. Nyquist diagram of a front- and rear-connected grid system;

[0071] Figure 10 To illustrate this, a voltage feedforward channel is added when the grid impedance is 3e-3H in the example. Time-domain simulation diagrams of grid-connected voltage and current at the grid connection point of the three-phase grid-connected inverters;

[0072] Figure 10 (a) When the grid impedance is 3e-3H, add a voltage feedforward path. Time-domain simulation diagram of the grid connection point voltage and current of the three-phase grid-connected inverter;

[0073] Figure 10(b) When the grid impedance is 3e-3H, add a voltage feedforward path. The time-domain simulation diagram of the grid connection point voltage and current of the three-phase grid-connected inverter. Detailed Implementation

[0074] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0075] Please see Figures 1 to 10 As shown, the present invention provides a method for suppressing grid-connected oscillation in a three-phase inverter, comprising the following steps:

[0076] Step S1: Obtain the three-phase voltage signal at the grid connection point, and obtain the direct-axis voltage component and quadrature-axis voltage component through coordinate transformation calculation;

[0077] Step S2: Set up a voltage feedforward channel in the current control inner loop of the three-phase inverter;

[0078] Step S3: Input the direct-axis voltage component and the quadrature-axis voltage component into the voltage feedforward channel. The voltage feedforward channel generates a feedforward compensation signal based on the input signal.

[0079] Step S4: Apply the feedforward compensation signal to the inner loop of the current control to obtain the corrected current control signal;

[0080] Step S5: Based on the corrected current control signal, establish a three-phase inverter sequence admittance model including a voltage feedforward channel. In the sequence admittance model, the part generated by the voltage feedforward channel is regarded as virtual admittance and connected in parallel with the original sequence admittance.

[0081] Step S6: Determine the gain parameter of the voltage feedforward channel based on the parallel relationship between the virtual admittance and the original sequence admittance, so that the real part of the admittance after parallel connection is greater than zero in the target frequency band.

[0082] Step S7: Adjust the sequence impedance of the three-phase inverter using the sequence admittance after real part reshaping.

[0083] In some embodiments, the sequence admittance of the three-phase grid-connected inverter after adding a voltage feedforward channel is calculated using the harmonic linearization method as follows:

[0084]

[0085] in, is the positive-sequence perturbation frequency; s is a complex frequency domain variable; This is the first filter inductor; This is the second filter inductor; , These are the inverter's DC-side capacitor and DC voltage, respectively. For filtering capacitors; This represents the amplitude of the fundamental component of the grid-connected voltage when the inverter is operating in steady state. The dq decoupling coefficients; It is the closed-loop transfer function of the phase-locked loop; , These are the first and second steady-state operating points of the system, respectively. , It is a DC quantity related to the first steady-state operating point and the second steady-state operating point of the system; The transfer function of the inner current loop; The angular frequency of the fundamental voltage; The transfer function of the voltage feedforward channel; This is the capacitor current feedback coefficient.

[0086] In some embodiments, the expressions for the phase-locked loop closed-loop transfer function, the first steady-state operating point of the system, the second steady-state operating point of the system, and the DC quantity are as follows:

[0087]

[0088]

[0089]

[0090] in, This represents the amplitude of the fundamental component of the grid-connected current when the inverter is operating in steady state. The phase angle in which the fundamental grid-connected voltage leads the grid-connected current; The phase angle in which the fundamental grid-connected voltage leads the capacitor current; This represents the amplitude of the fundamental component of the filter capacitor current.

[0091] In some embodiments, Transfer function for phase-locked loop controller;

[0092] and The expressions are as follows:

[0093]

[0094]

[0095] in, This refers to the proportional coefficient of the inner current loop controller. The integral coefficient of the inner current loop controller; This refers to the proportional gain of the phase-locked loop controller; is the integral coefficient of the phase-locked loop controller.

[0096] In some embodiments, in step S5, the isolated virtual admittance The expression is:

[0097]

[0098] Original admittance The expression is:

[0099]

[0100] Virtual Admittance With original admittance The overall admittance of a three-phase grid-connected inverter connected in parallel after adding a voltage feedforward path is, among which, For the original admittance The real part, For the original admittance The imaginary part; among which For virtual admittance The real part, For virtual admittance The imaginary part.

[0101] In some embodiments, in step S6, the parallel virtual admittance real part is... Expressions of imaginary parts for:

[0102]

[0103] Primitive Order Admittance Real Part and virtual part for:

[0104]

[0105] The denominators of the virtual admittance and the original sequence admittance are the same, and the real part of the denominator is... and the virtual part The expression is:

[0106]

[0107] The real part of the parallel virtual admittance The expression is:

[0108]

[0109] Real part of primitive sequential admittance The expression is:

[0110]

[0111] Voltage feedforward channel The specific method for determining the value is as follows:

[0112] .

[0113] In some embodiments, in step S3, the voltage feedforward channel performs a proportional calculation on the direct-axis voltage component and the quadrature-axis voltage component to obtain a feedforward compensation signal corresponding to the grid voltage change. The feedforward compensation signal is used to reflect the impact of voltage disturbance on inverter current control.

[0114] In some embodiments, in step S4, the feedforward compensation signal is introduced into the signal combination stage of the current control inner loop and works together with the original control signal of the inner loop to enable the corrected current control signal to simultaneously include grid-connected voltage information and the original current control information.

[0115] A simulation model of a three-phase grid-connected inverter was built in the simulation software, and an admittance scan was performed on it. The results are as follows. Figure 4 As shown. Figure 4 The solid lines in the diagram represent the theoretical values ​​of the three-phase grid-connected inverter model established by S1, while the circles represent the simulated frequency sweep test values; the two correspond perfectly. Therefore, the correctness of the admittance model established by S1 can be verified.

[0116] Virtual Admittance Expressions and primitive admittance The denominators of the expressions are the same, therefore the admittance system of the three-phase grid-connected inverter after adding the voltage feedforward channel is as follows: Figure 5 As shown.

[0117] Figure 6 Showing different Under the value of , Values ​​at different frequency bands. The curve transitions from red to black to represent... From -10 to 10.

[0118] Depend on Figure 6 It can be seen that in the frequency band below 1000Hz, as Changes, The value also changes from positive to negative, and from... Figure 1 It can be seen that the unstable region of a three-phase grid-connected inverter is approximately 100Hz to 1000Hz, therefore, we take... A suitable value will enable this frequency band to... A value greater than 0 ensures that the phase of this sequence impedance is in the first or second quadrant, increasing the stability margin of the grid-connected system. The principle of stabilizing the grid-connected inverter system by changing the phase through altering the sign of the real part of the admittance is as follows: Figure 7 As shown.

[0119] Depend on Figure 7 It is known that the grid impedance is often equivalent to a constant inductance, so the phase angle of its sequence impedance is always 90°. According to existing impedance theory, when the phase angle of the sequence impedance of a three-phase grid-connected inverter differs from the phase angle of the grid impedance by more than 180°, it is an unstable region. Therefore, the system is stable when the sequence impedance of the three-phase grid-connected inverter falls in the first or second quadrant. When the real part of the sequence admittance of the three-phase grid-connected inverter is greater than 0, its sequence impedance phasor can fall in the first or second quadrant.

[0120] Specifically, the voltage feedforward channel in S5 When -2 is taken, by Figure 6 The results show that this occurs in the frequency band below 1000Hz. That is, the phase angle of the sequence impedance of a three-phase grid-connected inverter can be reshaped to the first and second quadrants, and the reshaping result is as follows: Figure 8 As shown.

[0121] Figure 8 In the diagram, the solid black line represents the sequence impedance phase of the feedforward channel of the three-phase grid-connected inverter without voltage application. It can be seen that a large frequency band of the phase lies in the third and fourth quadrants. At that time, the sequence impedance phase of the grid-connected inverter is reshaped into a solid blue line, and it can be seen that the phase that was originally in the third and fourth quadrants is reshaped into the first and second quadrants.

[0122] Figure 9 When the grid impedance is 3e-3, The Nyquist curves of the system before and after reshaping the phase of the three-phase grid-connected inverter are shown, where the solid black line represents the unrestored phase. The Nyquist curve of the system during remodeling includes the point -j1; the solid blue line represents the increase. The Nyquist curve of the reshaped system does not include the point -j1. Therefore The time-domain simulation diagrams of a three-phase inverter grid-connected system with a grid impedance of 3e-3 are shown below, transforming it from unstable to stable. Figure 10 As shown.

[0123] Depend on Figure 10 It can be seen that when the grid impedance is 3e-3, no increase is made. During remodeling, the voltage and current at the grid connection point of the three-phase grid-connected inverter oscillate, causing system instability and increasing [the risk of damage]. The oscillations disappeared after reshaping. The time-domain simulation results are consistent with... Figure 8 , Figure 9 The theoretical simulation results are consistent, demonstrating the effectiveness of this method.

[0124] In some embodiments, the present invention also provides a three-phase inverter grid-connected oscillation suppression system, comprising the steps of a three-phase inverter grid-connected oscillation suppression method, including:

[0125] The voltage acquisition unit is used to acquire the three-phase voltage signal at the grid connection point and obtain the direct-axis voltage component and quadrature-axis voltage component through coordinate transformation calculation.

[0126] In a specific implementation, the voltage acquisition unit can consist of a voltage sensor and a processing circuit. The voltage sensor is used to detect the three-phase AC voltage signal in real time, and the processing circuit is used to convert the acquired three-phase signal into a digital quantity and perform coordinate transformation calculations in the control chip to obtain the direct-axis and quadrature-axis components. In one embodiment, the voltage sensor is installed at the grid-connected port of the inverter, and the processing circuit is connected to a DSP or FPGA control chip to ensure that the voltage signal can be quickly and accurately converted into direct-axis and quadrature-axis components.

[0127] The current control unit is used to set up a voltage feedforward channel in the current control inner loop of the three-phase inverter, and input the direct-axis voltage component and the quadrature-axis voltage component to the voltage feedforward channel, so that the voltage feedforward channel generates a feedforward compensation signal according to the input signal;

[0128] In a specific implementation, the current control unit may include a controller chip and a signal interface. The feedforward channel is preset as an adjustable computation path to process the voltage components and generate a feedforward compensation signal. In one embodiment, the controller of the current control unit sets the gain coefficient of the feedforward channel through software, so that the direct-axis and quadrature-axis components are amplified or attenuated in the channel, ultimately forming a feedforward compensation signal. The compensation signal is output to the current control loop through a digital interface.

[0129] The signal processing unit is used to apply the feedforward compensation signal to the inner loop of the current control to obtain the corrected current control signal.

[0130] In a specific implementation, the signal processing unit can be combined with the adjustment module within the controller to inject a feedforward compensation signal at the input of the control loop. In one embodiment, the signal processing unit combines the feedforward compensation signal with the existing control signal in the inner loop, enabling the current control signal generated by the controller to simultaneously include voltage information and the original control information, thereby achieving signal correction.

[0131] The modeling unit is used to establish a three-phase inverter sequence admittance model including a voltage feedforward channel based on the corrected current control signal, and in the sequence admittance model, the part generated by the voltage feedforward channel is regarded as virtual admittance and connected in parallel with the original sequence admittance;

[0132] In a specific implementation, the modeling unit can be implemented in the software layer of the controller to perform frequency domain modeling of the inverter's current control process and form a corresponding sequence admittance model. In one embodiment, the modeling unit inputs the corrected current control signal into the modeling program, which generates the admittance model according to the set calculation process, automatically distinguishes the part generated by the voltage feedforward channel as virtual admittance, and the remaining part as original admittance, and then performs parallel operations to obtain the equivalent admittance.

[0133] The parameter determination unit is used to determine the gain parameters of the voltage feedforward channel based on the parallel relationship between the virtual admittance and the original sequence admittance, so that the real part of the admittance after parallel connection is positive in the target frequency band.

[0134] In a specific implementation, the parameter determination unit can select the gain parameter through offline calculation or online adjustment. In one embodiment, the parameter determination unit performs numerical calculations on the real parts of the virtual admittance and the original admittance based on the admittance characteristics within a preset frequency band, and adjusts the gain coefficient of the voltage feedforward channel according to the calculation results to ensure that the real part of the equivalent admittance remains positive within the target frequency band.

[0135] The impedance adjustment unit is used to adjust the sequence impedance of the three-phase inverter using the sequence admittance after real part reshaping.

[0136] In a specific implementation, the impedance adjustment unit can perform the adjustment by updating the impedance parameter table inside the controller, so that the output characteristics of the inverter match the grid impedance. In one embodiment, the impedance adjustment unit receives the equivalent admittance result provided by the modeling unit, and based on the gain parameter set by the parameter determination unit, modifies the inverter control strategy, thereby adjusting the equivalent sequence impedance of the inverter during operation.

[0137] In some embodiments, the modeling unit is configured as follows:

[0138] When separating virtual admittance from original sequential admittance, virtual admittance is expressed as a fraction with the same denominator as original sequential admittance, and virtual admittance and original sequential admittance are defined as admittance quantities containing real and imaginary parts, respectively, so as to form equivalent sequential admittance through parallel relationship.

[0139] In a specific implementation, the modeling unit uses the same denominator structure when separating the virtual admittance from the original admittance, thereby ensuring consistency among the admittance quantities during the calculation process. In one embodiment, the modeling unit decomposes both the virtual admittance and the original admittance into real and imaginary components through software programming, and then stores these components in the controller's modeling database in fractional form, so that they can be directly called during operation to realize the real-time calculation of the equivalent order admittance.

[0140] It should be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0141] It should be understood that although the terms first, second, third, etc., may be used to describe various information in one or more embodiments of this specification, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, first information may also be referred to as second information without departing from the scope of one or more embodiments of this specification, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "in response to a determination," or "when," or "in the event of a determination."

[0142] The above description is merely a preferred embodiment of one or more embodiments of this specification and is not intended to limit the scope of one or more embodiments of this specification. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments of this specification should be included within the protection scope of one or more embodiments of this specification.

Claims

1. A method of grid-connection oscillation suppression for a three-phase inverter, characterized by, The method comprises the following steps: Step S1, acquiring three-phase voltage signals of a grid connection point, and obtaining a direct-axis voltage component and a quadrature-axis voltage component through coordinate transformation operation; Step S2, setting a voltage feedforward channel in a current control inner loop of a three-phase inverter; Step S3, inputting the direct-axis voltage component and the quadrature-axis voltage component into the voltage feedforward channel, and generating a feedforward compensation signal by the voltage feedforward channel according to the input signals; Step S4, applying the feedforward compensation signal to the current control inner loop to obtain a modified current control signal; Step S5, establishing a three-phase inverter sequence admittance model containing the voltage feedforward channel based on the modified current control signal, and regarding a part generated by the voltage feedforward channel as a virtual admittance in parallel with an original sequence admittance in the sequence admittance model; Step S6, determining a gain parameter of the voltage feedforward channel according to a parallel relationship between the virtual admittance and the original sequence admittance, so that a real part of the admittance after parallel connection is greater than zero at a target frequency band; Step S7, adjusting a sequence impedance of the three-phase inverter by using the sequence admittance after the real part is reshaped. The sequence admittance of the three-phase grid-connected inverter after the voltage feedforward channel is added is calculated according to a harmonic linearization method as follows: wherein, is the positive sequence disturbance frequency; s is a complex frequency variable; is the first filter inductance; is the second filter inductance; is the inverter DC voltage; is the filter capacitance; is the amplitude of the fundamental component of the grid- connected voltage when the inverter is in steady state operation; is the dq decoupling coefficient; is the phase-locked loop closed loop transfer function; , are the first and second steady state operating points of the system, respectively; , is the direct current quantity related to the first and second steady state operating points of the system; is the current inner loop transfer function; is the angular frequency of the fundamental voltage; is the transfer function of the voltage feed forward channel; is the capacitance current feedback coefficient; Expressions of the phase-locked loop closed-loop transfer function, the first stable working point of the system, the second stable working point of the system and the direct current flow are as follows: wherein, is the amplitude of the fundamental component of the grid current when the inverter is operating in steady state; is the phase angle by which the fundamental grid voltage leads the grid current; is the phase angle by which the fundamental grid voltage leads the capacitor current; is the amplitude of the fundamental component of the filter capacitor current; for the phase-locked loop controller transfer function; and The expressions for the above are respectively: wherein, is a current inner loop controller proportional coefficient; is a current inner loop controller integral coefficient; is a phase locked loop controller proportional coefficient; is a phase locked loop controller integral coefficient; separated virtual admittance The expression is: original admittance The expression is: Virtual admittance With original admittance Overall admittance of three-phase grid-connected inverter with parallel connection and voltage feed-forward channel Parallel virtual admittance real part sub And virtual part sub expression Is: original sequence admittance real part sub-particle and imaginary part sub-particle is: The denominators of the virtual admittance and the original sequence admittance are the same, and the real part of the denominator and the imaginary part The expression is: the real part of the parallel virtual admittance is given by the expression Real part of the original sequence admittance The expression for the real part of the original sequence admittance is Voltage feedforward channel The specific value method is: 。 2. The three-phase inverter grid-connected oscillation suppression method according to claim 1, characterized by, In step S3, the voltage feedforward channel proportionally operates on the direct-axis voltage component and the quadrature-axis voltage component to obtain a feedforward compensation signal corresponding to a grid voltage change, and the feedforward compensation signal is used to reflect an influence of voltage disturbance on inverter current control.

3. The three-phase inverter grid-connected oscillation suppression method according to claim 1, characterized by, In step S4, the feedforward compensation signal is introduced into a signal combination link of the current control inner loop, and acts together with original control signals of the inner loop, so that the modified current control signal can contain grid voltage information and original current control information at the same time.

4. A three-phase inverter grid-connected oscillation suppression system for implementing the steps of the three-phase inverter grid-connected oscillation suppression method according to claim 1, characterized by, The method comprises the following steps: A voltage acquisition unit is configured to acquire three-phase voltage signals of a grid connection point, and obtain a direct-axis voltage component and a quadrature-axis voltage component through coordinate transformation operation; A current control unit is configured to set a voltage feedforward channel in a current control inner loop of a three-phase inverter, and input the direct-axis voltage component and the quadrature-axis voltage component into the voltage feedforward channel, so that the voltage feedforward channel generates a feedforward compensation signal according to the input signals; A signal processing unit is configured to apply the feedforward compensation signal to the current control inner loop to obtain a modified current control signal; A modeling unit is configured to establish a three-phase inverter sequence admittance model containing the voltage feedforward channel based on the modified current control signal, and regard a part generated by the voltage feedforward channel as a virtual admittance in parallel with an original sequence admittance in the sequence admittance model; A parameter determination unit is configured to determine a gain parameter of the voltage feedforward channel according to a parallel relationship between the virtual admittance and the original sequence admittance, so that a real part of the admittance after parallel connection is positive at a target frequency band; An impedance adjustment unit is configured to adjust a sequence impedance of the three-phase inverter by using the sequence admittance after the real part is reshaped.

5. The three-phase inverter grid-tie oscillation suppression system of claim 4, wherein, The modeling unit is configured to: In separating the virtual admittance from the original sequence admittance, the virtual admittance is expressed in a fractional form with the same denominator as the original sequence admittance, and the virtual admittance and the original sequence admittance are respectively defined as admittance quantities containing real parts and imaginary parts, so as to form an equivalent sequence admittance through the parallel relationship.

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