Method and system for suppressing oscillation of grid-connected inverter of three-phase unbalanced system

Abstract

The invention discloses a grid-connected inverter oscillation suppression method and system for a three-phase unbalanced system. The method comprises the steps of constructing a state equation of the system according to a third-order nominal model and lumped interference; according to the lumped interference suppression function, constructing a filter structure in which two time-delay filters subjected to phase compensation are connected in series to obtain a series-connected time-delay filter; constructing a vector proportional-integral controller formed by combining a proportional-integral controller and a resonance controller; and according to control signals output by the series time-delay filter and the vector proportional-integral controller, the control signals are converted into switching tube driving signals for controlling the inverter. The influence of three-phase imbalance and background harmonic waves of the power grid can be effectively suppressed, and the control accuracy of the network access current is improved.

Description

TECHNICAL FIELD

[0002] The application belongs to the technical field of safe operation of power systems, and particularly relates to a grid-connected inverter oscillation suppression method and system for a three-phase unbalanced system. BACKGROUND

[0004] After large-scale new energy is connected to an alternating current power grid, a power distribution network system contains a large number of power electronic converter interface circuits, and devices for power quality management, and a large number of power electronic devices are concentrated in a relatively closed small area to form a nonlinear environment, which can cause grid distortion and three-phase voltage / current imbalance, and can also cause an increase in grid current harmonic distortion.

[0005] There are two main methods for suppressing grid three-phase imbalance and harmonics: the first method is to improve the traditional feedback control, for example, by using a repetitive control strategy to control the grid current to achieve zero-error tracking of the current signal, but the dynamic response speed of this method is slow, and it cannot suppress specific harmonics; the other method is to improve the anti-disturbance control, for example, by optimizing the linear active disturbance rejection control (LADRC) technology, which can achieve accurate tracking of the reference current without relying on an accurate mathematical model, but the LADRC structure is complex and the parameter tuning is difficult. SUMMARY

[0007] The application provides a grid-connected inverter oscillation suppression method and system for a three-phase unbalanced system, which is used to solve the technical problem of three-phase imbalance and harmonics of the grid-connected inverter current when the grid is three-phase unbalanced.

[0008] In a first aspect, the application provides a grid-connected inverter oscillation suppression method for a three-phase unbalanced system, which includes: Modeling a three-phase LCL grid-connected inverter in a d-q coordinate system, using capacitor current feedback active damping to suppress the resonance peak of the LCL filter, obtaining an actual model of the grid-connected inverter based on active damping, and constructing a three-order nominal model with the same order as the actual model of the grid-connected inverter; According to the twice-frequency component disturbance caused by the three-phase imbalance of the grid in the d-q coordinate system, the background harmonics of the grid as external disturbances of the system, the difference between the actual model of the grid-connected inverter and the nominal model of the grid-connected inverter, and other uncertain disturbances in the digital control system, a lumped disturbance is constructed; According to the three-order nominal model and the lumped disturbance, a state equation of the system is constructed, wherein the state equation contains a lumped disturbance suppression function; The second construction module is configured to construct a filter structure of two time delay filters in series according to the lumped interference suppression function, and obtain a series type time delay filter. The third construction module is configured to construct a vector proportional integral controller combined by a proportional integral controller and a resonance controller. The control module is configured to convert the control signals output by the series type time delay filter and the vector proportional integral controller into switch tube driving signals for controlling the inverter.

[0009] In a second aspect, the present application provides a grid-connected inverter oscillation suppression system of a three-phase unbalanced system, comprising: The construction module is configured to model a three-phase LCL grid-connected inverter in a d-q coordinate system, suppress the resonance peak of the LCL filter by using a capacitor current feedback active damping, obtain an actual model of the grid-connected inverter based on the active damping, and construct a three-order nominal model with the same order as the actual model of the grid-connected inverter. The first construction module is configured to construct a lumped interference according to the twice-frequency component disturbance caused by the grid three-phase imbalance in the d-q coordinate system, the grid background harmonic as external interference of the system, the difference between the actual model of the grid-connected inverter and the nominal model of the grid-connected inverter, and other uncertain interference in the digital control system. The determination module is configured to construct a state equation of the system according to the three-order nominal model and the lumped interference, wherein the state equation contains a lumped interference suppression function. The second construction module is configured to construct a filter structure of two time delay filters in series according to the lumped interference suppression function, and obtain a series type time delay filter. The third construction module is configured to construct a vector proportional integral controller combined by a proportional integral controller and a resonance controller. The control module is configured to convert the control signals output by the series type time delay filter and the vector proportional integral controller into switch tube driving signals for controlling the inverter.

[0010] In a third aspect, an electronic device is provided, which includes at least one processor and a memory connected with the at least one processor in communication, wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to perform the steps of the grid-connected inverter oscillation suppression method of any embodiment of the present application.

[0011] Fourthly, the present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein when the program instructions are executed by a processor, the processor performs the steps of the grid-connected inverter oscillation suppression method for a three-phase unbalanced system according to any embodiment of the present invention.

[0012] This application discloses a method and system for suppressing oscillations in a grid-connected inverter for a three-phase unbalanced system. The method obtains an actual model of the three-phase LCL grid-connected inverter in a two-phase rotating coordinate system (dq). Based on this model, a third-order nominal model is constructed. An SSUDE (Support Optimization Subsystem) is designed based on this nominal model. During the design, the second harmonic disturbance caused by the three-phase imbalance of the power grid and background harmonic interference are considered as external disturbances to the system. The unmodeled dynamics of the system are also considered to obtain the system's state equations. An equivalent transformation of the state equations yields the system's lumped interference. This lumped interference is then combined with a low-pass filter to estimate the lumped interference, thus completing the SSUDE design. The designed SSUDE has a two-degree-of-freedom structure and can be considered a patch to a traditional feedback controller. The outer-loop feedback controller can be designed independently. Therefore, a vector proportional-integral (PI-VPI) control is designed based on traditional proportional-integral (PI) control to improve the stability and accuracy of the current closed-loop control. The designed controller can effectively suppress the influence of three-phase imbalance and background harmonics in the power grid, improving the control accuracy of the grid-connected current. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 A flowchart of a grid-connected inverter oscillation suppression method for a three-phase unbalanced system provided in an embodiment of the present invention; Figure 2 A system control block diagram of a grid-connected inverter oscillation suppression method according to a specific embodiment of the present invention is provided; Figure 3 A dq control block diagram of a grid-connected inverter oscillation suppression method according to a specific embodiment of the present invention; Figure 4 Bode plot of interference suppression function of time delay filter in grid-connected inverter oscillation suppression method provided in a specific embodiment of the present invention; Figure 5Bode plot of interference suppression function of time delay filter after delay compensation in a specific embodiment of the grid-connected inverter oscillation suppression method provided in an embodiment of the present invention; Figure 6 A schematic diagram of interference suppression functions for a conventional time-delay filter and a series-type time-delay filter according to a specific embodiment of the present invention; Figure 7 This is a structural block diagram of a grid-connected inverter oscillation suppression system for a three-phase unbalanced system provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of the structure of an electronic device provided in an embodiment of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0018] Please see Figure 1 The diagram shows a flowchart of a grid-connected inverter oscillation suppression method for a three-phase unbalanced system according to this application.

[0019] like Figure 1 As shown, the method for suppressing oscillations in a grid-connected inverter of a three-phase unbalanced system specifically includes the following steps: Step S101: Model the three-phase LCL grid-connected inverter in the dq coordinate system, use active damping with capacitor current feedback to suppress the resonance peak of the LCL filter, obtain the actual model of the grid-connected inverter based on active damping, and construct a third-order nominal model with the same order as the actual model of the grid-connected inverter.

[0020] Please see Figure 2 The UDE control strategy is the method for suppressing unbalanced current in a three-phase LCL grid-connected inverter provided in this embodiment. For capacitor current, This refers to the current at the grid connection point PCC. , , The three-phase voltage components at the grid connection point PCC. For the load inductance on the grid side, and These are the filter inductors on the inverter side and the grid side, respectively. For filter capacitors, PLL, A phase-locked loop and its phase angle; This is the reference current for the grid-connected system.

[0021] It should be noted that the expression for the LCL filter transfer function in the dq coordinate system of the actual grid-connected inverter model is as follows: , In the formula, Let be the transfer function of the LCL filter in the dq coordinate system. For the Laplace operator at the fundamental frequency, For the inverter side inductor, For grid-side inductance, For filtering capacitors, This is the active damping coefficient of the capacitor current. System switching frequency The expression for the third-order nominal model is: , In the formula, Let be the transfer function of the LCL filter in the dq coordinate system. For the Laplace operator at the fundamental frequency, For the inverter side inductor, For grid-side inductance, For filtering capacitors, This is the active damping coefficient of the capacitor current. This refers to the system switching frequency.

[0022] Step S102: Based on the second harmonic component disturbance caused by the three-phase imbalance of the power grid in the dq coordinate system, the background harmonics of the power grid as external interference to the system, the difference between the actual model and the nominal model of the grid-connected inverter, and other uncertainties in the digital control system, a lumped interference is constructed.

[0023] It should be noted that the digital control system is a PWM digital control system.

[0024] Step S103: Construct the state equation of the system based on the third-order nominal model and the lumped disturbance, wherein the state equation includes a lumped disturbance suppression function.

[0025] In this step, based on the differences between the actual model and the nominal model, and considering other uncertainties and disturbances in the digital control system as lumped disturbances, the state equation of the grid-connected inverter system is established as follows: In the formula, For system state variables, The d-axis component of the grid-connected current. The first derivative of the d-axis component of the grid-connected current. The second derivative of the d-axis component of the grid-connected current. , For the unmodeled parts of the system, including dq-axis coupling, This includes external system interference, such as the second harmonic component interference generated when the three phases of the power grid are unbalanced, and background harmonic interference from the power grid. For inverter output, For system control delay, Given the known state matrix of the system, The known input matrix of the system is: , , Furthermore, the system's control signals It is separated into a two-degree-of-freedom structure, with one part used to compensate for lumped disturbances and the other part used to control the nominal model, expressed as: In the formula, For the controller output, This is an estimate of the lumped disturbance. For the lumped disturbance of the system, the relationship between the expressions is as follows: In the formula, The delay includes control delay and PWM delay. For time; When the estimated value of the lumped disturbance is equal to the lumped disturbance of the system, that is, when the condition is met... At that time, the system will become an ideal state unaffected by disturbances, and the above equation will become: , The lumped disturbance of the system can be indirectly estimated by using known quantities of the system. ,Right now: , Lumped interference is estimated by combining it with a low-pass filter. Combining the above equation with the low-pass filter yields: , In the formula, represents the convolution operation. For a third-order low-pass filter, after being combined with a low-pass filter, the left side of the equation becomes an estimate of the lumped interference, while the right side of the equation is directly achievable.

[0026] Furthermore, substituting the known state matrix M and input matrix N into the above equation and transforming it into complex frequency domain form, we can finally obtain the following through simplification and rearrangement: , In the formula, This is an estimate of the lumped disturbance; By simply rearranging the terms in the above equation, we get: The above equation is still a two-degree-of-freedom structure. At that time, the lumped interference on the left side of the equation was completely eliminated.

[0027] Please see Figure 3 ,in This is a practical model of the inverter system. For the purpose of creating a nominal model. It is a third-order low-pass filter. It is a traditional feedback controller.

[0028] Step S104: Based on the lumped interference suppression function, construct a filter structure consisting of two phase-compensated time-delay filters connected in series to obtain a series-type time-delay filter.

[0029] In this step, the low-pass filter introduces phase hysteresis, causing the time-delay filter to have a shift at a specific harmonic frequency. Phase compensation is then performed on the time-delay filter.

[0030] Furthermore, the expression for the low-pass filter is: , In the formula, This is the filter cutoff frequency. This represents the filter bandwidth.

[0031] The expression for phase compensation of a time-delay filter is: , The expression for the compensated time-delay filter is: , Based on the lumped interference suppression characteristics, a filter structure consisting of two low-pass filters cascaded together is designed. The interference suppression function of the cascaded time-delay filter in the discrete domain is: In the formula, It is a third-order low-pass filter. This is the first third-order low-pass filter. This is the second third-order low-pass filter; From the lumped interference suppression function in the above equation, the expression for the corresponding series time-delay filter can be derived as follows: .

[0032] Step S105: Construct a vector proportional-integral controller composed of a proportional-integral controller and a resonant controller.

[0033] In this step, the designed series-type time-delay filter has a two-degree-of-freedom structure. To address the second-harmonic AC classification caused by three-phase imbalance in the power grid, a vector proportional-integral (PI-VPI) controller, composed of a proportional-integral (PI) controller and a resonant controller, is designed. Its expression is: , In the formula, This is the expression for the vector proportional integral. For an integral system, For the Laplace operator, This is the vector scaling factor. The resonant coefficient of the vector controller. For the resonant frequency bandwidth, This is the proportionality coefficient. The cutoff frequency, This represents the harmonic order.

[0034] Considering that the coefficients of the quadratic and cubic terms in the inverter transfer function are much smaller than the coefficients of the first-order terms, they are ignored for ease of parameter tuning. This effectively transforms the third-order system into a first-order system with time delay. Based on the above equation, the PI controller parameters are designed by first determining the system's corner frequency. The phase angle corresponding to the system loop gain at the corner frequency is: in, This refers to the phase margin, i.e.: In the formula, The integral coefficient is... It is the symbol for imaginary numbers; When the phase margin of the system is determined, the maximum corner frequency of the system is: , The condition for the above formula to be true is: The limit value is 90°, therefore we have: , Based on the characteristics of the corner frequency, the loop gain of the system is unity gain at the corner frequency, that is: Therefore, the three steps for PI controller parameter design can be summarized as follows: Step 1: First, based on the phase margin To determine the maximum transition frequency, we need to select a suitable [favorite frequency]. value; Step 2: Confirm Then, calculate the value of kp in the PI controller; Step 3: Confirm Then, according to and Determine The maximum value, and then selected according to the actual situation. The reasonable value is therefore taken in this application. , .

[0035] The VPI controller parameter design employs the optimal damping ratio design method, using zero-pole cancellation to reduce the order of the control system and enhance its stability. The PI-VPI controller expression can be transformed into: , In the formula, , This is the parasitic resistance of the filter. , .

[0036] The closed-loop transfer function of the system, considering only the VPI controller, is: , because The value is very small, and the cubic term of s can be ignored after expanding the denominator. At this time, the closed-loop transfer function of the system is approximately a second-order system, and its damping ratio is: Therefore, the parameters of the VPI controller can be designed.

[0037] Please see Figure 4 and Figure 5 The interference suppression function of the time-delay filter before and after compensation.

[0038] Please see Figure 6 This is the interference suppression function for ordinary time-delay filters and series time-delay filters.

[0039] Step S106: Based on the control signals output by the series time-delay filter and the vector proportional-integral controller, the control signals are converted into switching transistor drive signals for controlling the inverter.

[0040] In summary, the method of this application obtains the actual model of a three-phase LCL grid-connected inverter in a two-phase rotating coordinate system (dq); a third-order nominal model is shaped based on the obtained actual inverter model; and an SSUDE is designed based on the nominal model. During the design, the second harmonic disturbance caused by the three-phase imbalance of the power grid and background harmonic interference are considered as external disturbances to the system. The unmodeled dynamics of the system are also considered to obtain the system's state equations. An equivalent transformation is performed on the state equations to obtain the system's lumped disturbance. The lumped disturbance is combined with a low-pass filter to estimate the lumped disturbance, thus completing the SSUDE design. The designed SSUDE has a two-degree-of-freedom structure and can be considered a patch to a traditional feedback controller. The outer-loop feedback controller can be designed independently. Therefore, vector proportional-integral (PI-VPI) control is designed based on traditional proportional-integral (PI) control to improve the stability and control accuracy of the current closed-loop control. The designed controller can effectively suppress the influence of three-phase imbalance and background harmonics in the power grid, improving the control accuracy of the grid-connected current.

[0041] Please see Figure 7 The diagram shows a structural block diagram of a grid-connected inverter oscillation suppression system for a three-phase unbalanced system according to this application.

[0042] like Figure 7 As shown, the grid-connected inverter oscillation suppression system 200 includes a construction module 210, a first construction module 220, a determination module 230, a second construction module 240, a third construction module 250, and a control module 260.

[0043] The construction module 210 is configured to model a three-phase LCL grid-connected inverter in the dq coordinate system, using capacitor current feedback active damping to suppress the resonance peak of the LCL filter, obtaining an actual model of the grid-connected inverter based on active damping, and constructing a third-order nominal model with the same order as the actual model of the grid-connected inverter; the first construction module 220 is configured to construct lumped interference based on the second harmonic component disturbance caused by three-phase imbalance in the grid in the dq coordinate system, the grid background harmonics as external interference to the system, the difference between the actual model and the nominal model of the grid-connected inverter, and other uncertainties in the digital control system; the determination module 23... 0. The first construction module is configured to construct the system's state equation based on the third-order nominal model and the lumped interference, wherein the state equation includes a lumped interference suppression function; the second construction module 240 is configured to construct a filter structure consisting of two phase-compensated time-delay filters connected in series based on the lumped interference suppression function, thereby obtaining a series-type time-delay filter; the third construction module 250 is configured to construct a vector proportional-integral controller composed of a proportional-integral controller and a resonant controller; the control module 260 is configured to convert the control signal output by the series-type time-delay filter and the vector proportional-integral controller into a switching transistor drive signal for controlling the inverter.

[0044] It should be understood that Figure 7 The modules and references described in the document Figure 1 The steps described in the text correspond to those in the method described above. Therefore, the operations, features, and corresponding technical effects described above also apply to the method described in the text. Figure 7 The various modules in the document will not be described in detail here.

[0045] In other embodiments, the present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein when the program instructions are executed by a processor, the processor performs the grid-connected inverter oscillation suppression method for a three-phase unbalanced system in any of the above method embodiments. In one embodiment, the computer-readable storage medium of the present invention stores computer-executable instructions, which are configured as follows: A three-phase LCL grid-connected inverter is modeled in the dq coordinate system. Active damping with capacitor current feedback is used to suppress the resonance peak of the LCL filter, resulting in an actual model of the grid-connected inverter based on active damping. A third-order nominal model with the same order as the actual model of the grid-connected inverter is then constructed. Based on the second harmonic component disturbance caused by three-phase imbalance of the power grid in the dq coordinate system, the background harmonics of the power grid as external interference of the system, the difference between the actual model and the nominal model of the grid-connected inverter, and other uncertainties in the digital control system, a lumped interference is constructed. The system's state equation is constructed based on the third-order nominal model and the lumped disturbance, wherein the state equation includes a lumped disturbance suppression function; Based on the lumped interference suppression function, a filter structure consisting of two phase-compensated time-delay filters connected in series is constructed to obtain a series-type time-delay filter. Construct a vector proportional-integral controller composed of a proportional-integral controller and a resonant controller; The inverter is controlled by the control signals output by the series time-delay filter and the vector proportional-integral controller, and the control signals are converted into switching transistor drive signals.

[0046] Computer-readable storage media may include a stored program area and a stored data area, wherein the stored program area may store an operating system and an application program required for at least one function; the stored data area may store data created based on the use of the grid-connected inverter oscillation suppression system of the three-phase unbalanced system, etc. Furthermore, the computer-readable storage medium may include high-speed random access memory, and may also include memory, such as at least one disk storage device, flash memory device, or other non-volatile solid-state storage device. In some embodiments, the computer-readable storage medium may optionally include memory remotely disposed relative to a processor, which can be connected to the grid-connected inverter oscillation suppression system of the three-phase unbalanced system via a network. Examples of such networks include, but are not limited to, the Internet, corporate intranets, local area networks, mobile communication networks, and combinations thereof.

[0047] Figure 3 This is a schematic diagram of the structure of the electronic device provided in the embodiment of the present invention, such as... Figure 3 As shown, the device includes a processor 310 and a memory 320. The electronic device may also include an input device 330 and an output device 340. The processor 310, memory 320, input device 330, and output device 340 can be connected via a bus or other means. Figure 3Taking a bus connection as an example, the memory 320 is the computer-readable storage medium described above. The processor 310 executes various server functions and data processing by running non-volatile software programs, instructions, and modules stored in the memory 320, thereby implementing the grid-connected inverter oscillation suppression method for the three-phase unbalanced system described in the above embodiment. The input device 330 can receive input digital or character information and generate key signal inputs related to user settings and function control of the grid-connected inverter oscillation suppression system for the three-phase unbalanced system. The output device 340 may include a display screen or other display device.

[0048] The aforementioned electronic device can execute the method provided in the embodiments of the present invention, and has the corresponding functional modules and beneficial effects for executing the method. Technical details not described in detail in this embodiment can be found in the method provided in the embodiments of the present invention.

[0049] In one implementation, the above-described electronic device is applied to a grid-connected inverter oscillation suppression system for a three-phase unbalanced system, serving as a client, and includes: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to: A three-phase LCL grid-connected inverter is modeled in the dq coordinate system. Active damping with capacitor current feedback is used to suppress the resonance peak of the LCL filter, resulting in an actual model of the grid-connected inverter based on active damping. A third-order nominal model with the same order as the actual model of the grid-connected inverter is then constructed. Based on the second harmonic component disturbance caused by three-phase imbalance of the power grid in the dq coordinate system, the background harmonics of the power grid as external interference of the system, the difference between the actual model and the nominal model of the grid-connected inverter, and other uncertainties in the digital control system, a lumped interference is constructed. The system's state equation is constructed based on the third-order nominal model and the lumped disturbance, wherein the state equation includes a lumped disturbance suppression function; Based on the lumped interference suppression function, a filter structure consisting of two phase-compensated time-delay filters connected in series is constructed to obtain a series-type time-delay filter. Construct a vector proportional-integral controller composed of a proportional-integral controller and a resonant controller; The inverter is controlled by the control signals output by the series time-delay filter and the vector proportional-integral controller, and the control signals are converted into switching transistor drive signals.

[0050] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods of various embodiments or some parts of embodiments.

[0051] 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 them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for suppressing oscillations in a grid-connected inverter of a three-phase unbalanced system, characterized in that, include: A three-phase LCL grid-connected inverter is modeled in the dq coordinate system. Active damping with capacitor current feedback is used to suppress the resonance peak of the LCL filter, resulting in an actual model of the grid-connected inverter based on active damping. A third-order nominal model with the same order as the actual model of the grid-connected inverter is then constructed. Based on the second harmonic component disturbance caused by three-phase imbalance of the power grid in the dq coordinate system, the background harmonics of the power grid as external interference of the system, the difference between the actual model and the nominal model of the grid-connected inverter, and other uncertainties in the digital control system, a lumped interference is constructed. The system's state equation is constructed based on the third-order nominal model and the lumped disturbance, wherein the state equation includes a lumped disturbance suppression function; Based on the lumped interference suppression function, a filter structure consisting of two phase-compensated time-delay filters connected in series is constructed to obtain a series-type time-delay filter. Construct a vector proportional-integral controller composed of a proportional-integral controller and a resonant controller; The inverter is controlled by the control signals output by the series time-delay filter and the vector proportional-integral controller, and the control signals are converted into switching transistor drive signals.

2. The method for suppressing oscillations in a grid-connected inverter of a three-phase unbalanced system according to claim 1, characterized in that, The expression for the LCL filter transfer function in the dq coordinate system of the actual model of the grid-connected inverter is as follows: ， In the formula, Let be the transfer function of the LCL filter in the dq coordinate system. For the Laplace operator at the fundamental frequency, For the inverter side inductor, For grid-side inductance, For filtering capacitors, This is the active damping coefficient of the capacitor current. This refers to the system switching frequency.

3. The method for suppressing oscillations in a grid-connected inverter of a three-phase unbalanced system according to claim 1, characterized in that, The expression for the third-order nominal model is: ， In the formula, For the third-order nominal model of the grid-connected inverter system, For the Laplace operator at the fundamental frequency, For the inverter side inductor, For grid-side inductance, For filtering capacitors, This is the active damping coefficient of the capacitor current. This refers to the system switching frequency.

4. The method for suppressing oscillations in a grid-connected inverter of a three-phase unbalanced system according to claim 1, characterized in that, The expression for the lumped interference suppression function is: ， In the formula, For the inverter side inductor, For grid-side inductance, For filtering capacitors, For the Laplace operator at the fundamental frequency, This is the active damping coefficient of the capacitor current. For the system switching frequency, It is a low-pass filter. This is an estimate of the lumped disturbance. The grid-connected current is the d-axis current. This is the actual output of the controller.

5. The method for suppressing oscillations in a grid-connected inverter of a three-phase unbalanced system according to claim 1, characterized in that, The expression for the series time-delay filter is: ， ， ， ， ， In the formula, It is a series time delay. Here is the interference suppression function for a series time-delay filter. It is a low-pass filter. For the first low-pass filter, For the second low-pass filter, It is a third-order low-pass filter. This is the first third-order low-pass filter. This is the second third-order low-pass filter. For a normal period, the value is 0.02s. As compensation for the delay, For the Laplace operator, This is the bandwidth of a typical third-order filter.

6. The method for suppressing oscillations in a grid-connected inverter of a three-phase unbalanced system according to claim 1, characterized in that, The expression for the vector proportional-integral controller is: ， In the formula, This is the expression for the vector proportional integral. For an integral system, For the Laplace operator, This is the vector scaling factor. The resonant coefficient of the vector controller. For the resonant frequency bandwidth, This is the proportionality coefficient. The cutoff frequency, This represents the harmonic order.

7. A grid-connected inverter oscillation suppression system for a three-phase unbalanced system, characterized in that, include: The construction module is configured to model a three-phase LCL grid-connected inverter in the dq coordinate system, use active damping with capacitor current feedback to suppress the resonance peak of the LCL filter, obtain the actual model of the grid-connected inverter based on active damping, and construct a third-order nominal model with the same order as the actual model of the grid-connected inverter. The first construction module is configured to construct lumped interference based on the second harmonic component disturbance caused by the three-phase imbalance of the power grid in the dq coordinate system, the background harmonics of the power grid as external interference of the system, the difference between the actual model of the grid-connected inverter and the nominal model of the grid-connected inverter, and other uncertain interferences in the digital control system. The determination module is configured to construct the state equation of the system based on the third-order nominal model and the lumped disturbance, wherein the state equation includes a lumped disturbance suppression function; The second construction module is configured to construct a filter structure consisting of two phase-compensated time-delay filters connected in series based on the lumped interference suppression function, thus obtaining a series-type time-delay filter. The third building module is configured to build a vector proportional-integral controller composed of a proportional-integral controller and a resonant controller; The control module is configured to convert the control signals output by the series time-delay filter and the vector proportional-integral controller into switching transistor drive signals for controlling the inverter.

8. An electronic device, characterized in that, include: At least one processor, and a memory communicatively connected to the at least one processor, wherein the memory stores instructions executable by the at least one processor to enable the at least one processor to perform the method according to any one of claims 1 to 6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by a processor, it implements the method described in any one of claims 1 to 6.

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