Three-phase grid-connected inverter output power ripple suppression method and system

Abstract

The invention discloses a three-phase grid-connected inverter output power ripple suppression method and system, and the method comprises the steps: collecting the data of a power grid, and calculating the voltage and current components under the imbalance of the power grid; and calculating the power under the unbalanced power grid, and performing quantitative analysis on virtual phase current modulation. And suppressing the two-phase voltage fault working condition, and adding a compensation coefficient. And designing a controller, drawing a Bode diagram of an open-loop transfer function expression, and judging the stability of the system. According to the three-phase grid-connected inverter output power ripple suppression method and system provided by the invention, a virtual phase current modulation method is adopted, a compensation item is added to a current feedback loop of a fault voltage, a positive sequence or negative sequence component does not need to be considered, a compensation value is consistent with a voltage drop rate of the fault voltage, and active power ripples can be effectively counteracted. The method is not only suitable for a single-phase voltage fault working condition, but also suitable for a two-phase voltage fault working condition. The problems of power oscillation, current imbalance and the like caused by power grid imbalance are solved, and the operation performance of the system is improved.

Description

Technical Field

[0001] The present invention relates to the field of new energy technology, and in particular to a method and system for suppressing output power ripple of a three-phase grid-connected inverter. Background Art

[0002] In recent years, due to the constraints of the environment and traditional energy, the pursuit of green and low-carbon development has become a general consensus of the international community. Under this situation, seeking to use renewable energy such as solar energy and wind energy as power supply is an effective solution. However, with the increasing degree of access to the grid for renewable energy, grid failures and unbalanced load access, the grid voltage is unbalanced. The unbalanced grid voltage will cause a significant increase in the DC bus voltage ripple, deterioration of the total harmonic distortion of the current, and fluctuations in the output power, thereby damaging the power equipment and even threatening the safety of the power system. At this time, the traditional inverter grid-connected control strategy will no longer be applicable to this working condition. Therefore, it is of great significance to conduct in-depth research on the control technology of three-phase grid-connected inverters under unbalanced grids.

[0003] Regarding the control technology of three-phase grid-connected inverters under unbalanced power grids, some literatures proposed self-regulating filters and multivariable filters for DC bias and grid distortion conditions in order to enhance the robustness of the system under unbalanced power grids, but this method requires complex positive and negative sequence component extraction and more control parameter adjustments. Some literatures proposed a dual synchronous reference system control for inverters under unbalanced power grids, in which the positive and negative sequence components of the grid current are controlled by their corresponding synchronous reference systems, but the control process is relatively complicated and the entire control system requires four proportional integral controllers. Some literatures proposed a third-order harmonic reference power compensation method based on PIR and a model prediction direct power control method with different power compensation targets, both of which can eliminate current harmonics or power ripple. However, the calculation process of the above control methods is complex and sensitive to parameter changes. Therefore, the problem of maintaining stable operation of three-phase inverter grid-connected systems under unbalanced power grids needs further study. Summary of the invention

[0004] In view of the above-mentioned problems, the present invention is proposed.

[0005] Therefore, the technical problem solved by the present invention is that the above control method has a complex calculation process and is relatively sensitive to parameter changes. Therefore, the problem of maintaining stable operation of the three-phase inverter grid-connected system under unbalanced power grids needs further research.

[0006] To solve the above technical problems, the present invention provides the following technical solutions: A method for suppressing output power ripple of a three-phase grid-connected inverter, comprising: collecting grid data, and calculating voltage and current components under unbalanced grid conditions.

[0007] Calculate the power under unbalanced grid and quantitatively analyze the virtual phase current modulation.

[0008] The two-phase voltage fault condition is suppressed and a compensation coefficient is added.

[0009] Design the controller, draw the Bode diagram of the open-loop transfer function expression, and determine the system stability.

[0010] As a preferred solution of the method for suppressing output power ripple of a three-phase grid-connected inverter according to the present invention, wherein: the collecting of grid data and calculating the voltage and current components under unbalanced grid conditions include: the d-axis voltage component under unbalanced grid conditions It is expressed as:

[0011]

[0012] Among them, u d Indicates the d-axis voltage under normal operating conditions, u a Indicates the voltage of phase A under normal working conditions, u b Indicates the voltage of phase b under normal working conditions, u c Indicates the phase C voltage under normal working conditions, Represents the Park transformation matrix of the d-axis, the formula is simplified to:

[0013]

[0014] D-axis compensation current component It is expressed as:

[0015]

[0016] Among them, i d represents the d-axis current under normal operating conditions, i a,gain Indicates i d With l a The ratio of b,gain Indicates i d With l a The ratio of c,gain Indicates i d With l a ratio.

[0017] The d-axis compensation current component is simplified and expressed as:

[0018]

[0019] Among them, λ a Represents the virtual phase current gain in the current feedback loop.

[0020] As a preferred solution of the method for suppressing output power ripple of a three-phase grid-connected inverter according to the present invention, the calculation of the power under unbalanced grid includes obtaining the output power expressed as:

[0021]

[0022] Among them, P o,VPCR Represents the power ripple component obtained by using the virtual phase current modulation method.

[0023] As a preferred solution of the method for suppressing output power ripple of a three-phase grid-connected inverter according to the present invention, the quantitative analysis of virtual phase current modulation includes: the oscillation component P o,VPCR This will degrade the performance of the suppression method, and a quantitative analysis of the virtual phase current modulation method is needed.

[0024] Define the output power ripple ΔP when no suppression method is used o,ripple And the average output power P avg The ratio λ e , expressed as:

[0025]

[0026] Define the output power ripple ΔP when the proposed suppression method is used o,VPCR And the average output power P o The ratio λ VPCR , expressed as:

[0027]

[0028] Combined with Lambda e and λ VPCR , the improvement ratio λ of power ripple by using virtual phase current modulation method is obtained imp , expressed as:

[0029]

[0030] By changing λ a The value of is obtained, and the improvement of power ripple by using virtual phase current modulation method under slight voltage fault and severe voltage fault is obtained.

[0031] As a preferred solution of the method for suppressing output power ripple of a three-phase grid-connected inverter described in the present invention, wherein: the suppression of the two-phase voltage fault condition and the addition of the compensation coefficient include: under the two-phase voltage fault condition, the voltage fluctuation affects the stability of the system and the balance of the output power, and it is necessary to compensate the two-phase voltage, and add an additional compensation coefficient to suppress the power ripple. When the voltage of phase a and phase b fails, the compensation coefficients λ are added respectively.a and λ b .

[0032] According to the virtual phase current modulation method, the fault voltage expression is corrected to:

[0033] u d,fault =u d +λ a ·u a +λ b ·u b

[0034] The expression of the d-axis compensation current component is corrected to:

[0035] i d,fault =i d +λ a ·i a,gain +λ b ·i b,gain

[0036] The compensation coefficient is set based on the specific parameters of the system and the fault conditions. Assume that the voltage fluctuation of phase A caused by the fault is Δu a , the voltage fluctuation of phase b is Δu b According to Park transformation, the fluctuation of d-axis voltage is expressed as:

[0037] Δu d =k a Δu a +k b Δu b

[0038] Among them, k a k represents the conversion factor, which depends on the system topology. b Represents the conversion coefficient, which depends on the system transformation matrix.

[0039] Determine the compensation coefficient, expressed as:

[0040] k a λ a +k b λ b =-1

[0041] Solve to obtain the compensation coefficient.

[0042] As a preferred solution of the method for suppressing output power ripple of a three-phase grid-connected inverter according to the present invention, the controller design includes designing a current loop controller using a proportional-integral controller, and the transfer function of the controller is expressed as:

[0043]

[0044] Among them, kp represents the proportionality coefficient, k i Represents the integral coefficient.

[0045] As a preferred solution of the method for suppressing output power ripple of a three-phase grid-connected inverter according to the present invention, wherein: the drawing of the Bode diagram of the open-loop transfer function expression to judge the system stability includes obtaining the open-loop transfer function according to the controller transfer function, which is expressed as:

[0046]

[0047] Where L represents the system inductance, R represents the resistance, and s represents the complex variable in the Laplace transform.

[0048] Use the open-loop transfer function to draw the Bode plot of the system. The Bode plot includes both magnitude and phase plots.

[0049] The magnitude of the amplitude margin and phase margin is used to determine whether the system is in a stable state. When the amplitude margin is greater than or equal to 6dB, it means that the system has sufficient gain margin in the frequency domain to resist external interference. When the phase margin is between 30° and 60°, it means that the system has good dynamic response characteristics. Otherwise, adjust k p and k i , so that the system meets the stability requirements.

[0050] A three-phase grid-connected inverter output power ripple suppression system, characterized in that: it includes:

[0051] The calculation module collects grid data and calculates the voltage and current components under unbalanced grid conditions.

[0052] The analysis module calculates the power under unbalanced power grid and quantitatively analyzes the virtual phase current modulation.

[0053] The adjustment module suppresses the two-phase voltage fault condition and adds a compensation coefficient.

[0054] Determine the module, design the controller, draw the Bode diagram of the open-loop transfer function expression, and determine the system stability.

[0055] A computer device comprises a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps of the above method when executing the computer program.

[0056] A computer-readable storage medium stores a computer program, which implements the steps of the method described above when executed by a processor.

[0057] Beneficial effects of the present invention: By adopting a virtual phase current modulation method, a compensation term is added to the current feedback loop of the fault voltage, and the compensation value is made consistent with the fault voltage drop rate without considering the positive sequence or negative sequence components, so that the active power ripple can be effectively offset. This method is not only applicable to single-phase voltage fault conditions, but also to two-phase voltage fault conditions. The active power ripple suppression method of the present invention solves the problems of power oscillation and current imbalance caused by unbalanced power grids, and improves the operating performance of the system. The main advantage of the present invention is that the control is simple and can be implemented by a digital signal processor without adding additional hardware circuit costs and control complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. Among them:

[0059] Figure 1 The present invention provides an overall flow chart of a method and system for suppressing output power ripple of a three-phase grid-connected inverter according to the first embodiment of the present invention.

[0060] Figure 2 A conventional grid-connected inverter control system structure diagram of a three-phase grid-connected inverter output power ripple suppression method and system provided in the first embodiment of the present invention.

[0061] Figure 3 A design diagram of a positive-sequence component phase-locked loop based on a synchronous reference system using a positive-sequence component is provided for a three-phase grid-connected inverter output power ripple suppression method and system provided in the first embodiment of the present invention.

[0062] Figure 4 A method and system for suppressing output power ripple of a three-phase grid-connected inverter provided in the first embodiment of the present invention and a structure diagram of a grid-connected inverter control system using a virtual phase current modulation method under an unbalanced power grid.

[0063] Figure 5 A control block diagram of a virtual phase current modulation method of a three-phase grid-connected inverter output power ripple suppression method and a system provided in the first embodiment of the present invention. DETAILED DESCRIPTION

[0064] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0065] Example 1, reference Figure 1 to Figure 5 , is an embodiment of the present invention, and provides a method for suppressing output power ripple of a three-phase grid-connected inverter, comprising:

[0066] S1: Collect grid data and calculate voltage and current components under unbalanced grid conditions.

[0067] It should be noted that the main circuit topology and traditional control structure of the three-phase grid-connected inverter are shown in the figure below. Figure 2 As shown. Among them, U dc Indicates the DC bus voltage, V T1 -V T6 To form a three-phase inverter bridge, i kabc Indicates the inverter side current, i abc Indicates the grid-connected current, u abc represents the grid voltage, q represents the phase of the grid voltage obtained by the phase-locked loop, Gc(s) represents the current loop controller, k d Represents the proportionality coefficient. The traditional three-phase inverter control system mainly includes a dual current loop, which is responsible for the grid-connected current inverter control and realizes the unity / constant power factor grid-connected requirements.

[0068] The traditional control principle is: First, collect the inverter side current i kabc , grid-connected current i abc and voltage u abc , perform Park transformation on it to get d q Inverter side current i in axis coordinate system kd 、i kq , grid-connected current i d 、i q and voltage u d 、u q ; Then, the grid-connected current reference value i is given dref 、i qref , the grid-connected current reference value is compared with the actual value and then enters the current loop controller, and the output signal is then compared with the inverter side current i kd 、i kq After comparison, enter the inner loop controller k dFinally, the output signal of the inner loop controller is subjected to an inverse Park transform, and the obtained signal is input into the SPWM modulation to obtain the PWM modulation signal of the three-phase inverter, thereby controlling the three-phase inverter accordingly.

[0069] It should be noted that, since the conventional phase-locked loop based on the synchronous reference system cannot accurately detect the amplitude and phase of the positive-sequence fundamental voltage, the present invention adopts the corresponding positive-sequence fundamental component extraction algorithm to extract the grid voltage phase component, such as Figure 3 As shown. The main idea is: first, the grid voltage is converted to the ab coordinate system, then the positive and negative sequences of the grid voltage in the ab coordinate system are separated, and finally only the positive sequence component is controlled by PI to obtain the grid voltage phase. Compared with the traditional phase-locked loop based on the synchronous reference system, this method can more accurately detect the voltage phase and is more conducive to the grid-connected control of the three-phase inverter.

[0070] The virtual phase current modulation method of the three-phase inverter under unbalanced power grid proposed by the present invention controls the overall structure as follows: Figure 4 As shown, the control structure of the virtual phase current modulation method is as follows Figure 5 The main idea is to use dq axis transformation to control the inverter output active and reactive power. When a phase voltage fails in the three-phase three-wire inverter control structure, the amplitude and phase of its phase current should be precisely controlled by adding a virtual phase current gain λ in the current feedback loop. a ,λ a The compensated d-axis current signal is automatically adjusted by the virtual phase current modulation method, which can eventually eliminate the active power ripple.

[0071] D-axis voltage component under unbalanced grid It is expressed as:

[0072]

[0073] Among them, u d Indicates the d-axis voltage under normal operating conditions, u a Indicates the voltage of phase A under normal working conditions, u b Indicates the voltage of phase b under normal working conditions, u c Indicates the phase C voltage under normal working conditions, Represents the Park transformation matrix of the d-axis, the formula is simplified to:

[0074]

[0075] D-axis compensation current component It is expressed as:

[0076]

[0077] Among them, i d represents the d-axis current under normal operating conditions, i a,gain Indicates i d With l a The ratio of b,gain Indicates i d With l a The ratio of c,gain Indicates i d With l a ratio.

[0078] The d-axis compensation current component is simplified and expressed as:

[0079]

[0080] Among them, λ a Represents the virtual phase current gain in the current feedback loop.

[0081] S2: Calculate the power under unbalanced grid and quantitatively analyze the virtual phase current modulation.

[0082] According to the voltage component and compensation current component under unbalanced power grid, the output power is expressed as:

[0083]

[0084] Among them, P o,VPCR Represents the power ripple component obtained by using the virtual phase current modulation method.

[0085] Oscillation component P o,VPCR This will degrade the performance of the suppression method, and a quantitative analysis of the virtual phase current modulation method is needed.

[0086] Define the output power ripple ΔP when no suppression method is used o,ripple And the average output power P avg The ratio λ e , expressed as:

[0087]

[0088] Define the output power ripple ΔP when the proposed suppression method is used o,VPCR And the average output power P o The ratio λ VPCR , expressed as:

[0089]

[0090] Combined with Lambda e and λ VPCR , the improvement ratio λ of power ripple by using virtual phase current modulation method is obtained imp , expressed as:

[0091]

[0092] By changing λ a The value of is obtained, and the improvement of power ripple by using virtual phase current modulation method under slight voltage fault and severe voltage fault is obtained.

[0093] S3: Suppress the two-phase voltage fault condition and add a compensation coefficient.

[0094] Under the condition of two-phase voltage fault, the voltage fluctuation affects the stability of the system and the balance of output power. It is necessary to compensate the two-phase voltage and add additional compensation coefficients to suppress power ripple. When the voltage of phase a and phase b fails, the compensation coefficients λ are added respectively. a and λ b .

[0095] According to the virtual phase current modulation method, the fault voltage expression is corrected to:

[0096] u d,fault =u d +λ a ·u a +λ b ·u b

[0097] The expression of the d-axis compensation current component is corrected to:

[0098] i d,fault =i d +λ a ·i a,gain +λ b ·i b,gain

[0099] The compensation coefficient is set based on the specific parameters of the system and the fault conditions. Assume that the voltage fluctuation of phase A caused by the fault is Δu a , the voltage fluctuation of phase b is Δu b According to Park transformation, the fluctuation of d-axis voltage is expressed as:

[0100] Δu d =k a Δu a +k b Δu b

[0101] Among them, k a k represents the conversion factor, which depends on the system topology. b Represents the conversion coefficient, which depends on the system transformation matrix.

[0102] Determine the compensation coefficient, expressed as:

[0103] k a λ a +k b λ b =-1

[0104] Solve to obtain the compensation coefficient.

[0105] S4: Design the controller, draw the Bode diagram of the open-loop transfer function expression, and determine the system stability.

[0106] The current loop controller is designed using a proportional-integral controller, and the transfer function of the controller is expressed as:

[0107]

[0108] Among them, k p represents the proportionality coefficient, k i Represents the integral coefficient.

[0109] The open-loop transfer function is obtained according to the controller transfer function, which is expressed as:

[0110]

[0111] Where L represents the system inductance, R represents the resistance, and s represents the complex variable in the Laplace transform.

[0112] Use the open-loop transfer function to draw the Bode plot of the system. The Bode plot includes both magnitude and phase plots.

[0113] The magnitude of the amplitude margin and phase margin is used to determine whether the system is in a stable state. When the amplitude margin is greater than or equal to 6dB, it means that the system has sufficient gain margin in the frequency domain to resist external interference. When the phase margin is between 30° and 60°, it means that the system has good dynamic response characteristics. Otherwise, adjust k p and k i , so that the system meets the stability requirements.

[0114] The above embodiments also include a three-phase grid-connected inverter output power ripple suppression system, specifically:

[0115] The calculation module collects grid data and calculates the voltage and current components under unbalanced grid conditions.

[0116] The analysis module calculates the power under unbalanced power grid and quantitatively analyzes the virtual phase current modulation.

[0117] The adjustment module suppresses the two-phase voltage fault condition and adds a compensation coefficient.

[0118] Determine the module, design the controller, draw the Bode diagram of the open-loop transfer function expression, and determine the system stability.

[0119] The computer device may be a server. The computer device includes a processor, a memory, an input / output interface (I / O for short) and a communication interface. The processor, the memory and the input / output interface are connected via a system bus, and the communication interface is connected to the system bus via the input / output interface. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store data cluster data of a power monitoring system. The input / output interface of the computer device is used to exchange information between the processor and an external device. The communication interface of the computer device is used to communicate with an external terminal via a network connection. When the computer program is executed by the processor, a method is implemented.

[0120] A person of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiment method can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memory. Non-volatile memory may include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory may include random access memory (RAM) or external cache memory, etc. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. Non-relational databases may include distributed databases based on blockchains, etc., but are not limited to this. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but are not limited to this.

[0121] Embodiment 2, an embodiment of the present invention, provides a method and system for suppressing output power ripple of a three-phase grid-connected inverter. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through simulation experiments.

[0122] The experimental equipment includes a three-phase grid-connected inverter, a voltage fault simulation device, a data acquisition system, and a PI controller. The experiment is carried out in a controlled laboratory environment to avoid external electromagnetic interference.

[0123] The voltage and current data of the power grid are recorded using a data acquisition system. Under normal operating conditions, the voltage data of phase a, phase b, and phase c are recorded. A virtual phase current gain is introduced in the current feedback loop to simplify the control. When a phase voltage fails, the active power ripple is eliminated by adjusting the virtual phase current gain. In the case of an unbalanced power grid, the voltage and current components are calculated, and the output power and its ripple components are further calculated. In the case of a two-phase voltage fault, the compensation coefficients of phase a and phase b are added respectively, and the power ripple suppression effect is optimized by adjusting the compensation coefficients. A proportional integral controller (PI controller) is used to design the current loop controller to optimize the system response characteristics. The design of the controller needs to consider the inductance and resistance parameters of the system. According to the transfer function of the controller, the Bode diagram of the system is drawn. By analyzing the amplitude margin and phase angle margin in the Bode diagram, it is determined whether the system is in a stable state. Ensure that the amplitude margin is greater than or equal to 6dB and the phase angle margin is between 30° and 60°. The experimental results are shown in Table 1.

[0124] Table 1 Experimental results

[0125]

[0126] From the above experimental data, it can be seen that under different compensation coefficients, the output power ripple under unbalanced grid conditions is significantly suppressed. The specific analysis is as follows:

[0127] Power ripple before compensation: Without compensation, the output power ripple is between 8% and 12%, the fluctuation caused by grid imbalance is large, and the system stability is poor.

[0128] Compensated power ripple: By introducing the compensation coefficient, the output power ripple is significantly suppressed and reduced to between 3% and 6%.

[0129] By calculating the improvement ratio under different compensation coefficients, it can be seen that when the compensation coefficient is 0.35 and 0.3, the system's power ripple suppression effect is the best, and the improvement ratio reaches 60%. This shows that by reasonably adjusting the compensation coefficient, the stability and response characteristics of the system can be significantly improved.

[0130] It should be noted that during the experiment, certain errors may be introduced due to environmental factors, equipment accuracy, etc. Nevertheless, the experimental results still show obvious improvement effects, verifying the effectiveness of the method of the present invention.

[0131] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for suppressing output power ripple of a three-phase grid-connected inverter, characterized in that: include: Collect grid data and calculate voltage and current components under unbalanced grid conditions; Calculate the power under unbalanced grid and conduct quantitative analysis on virtual phase current modulation; Suppress the two-phase voltage fault condition and add compensation coefficient; Design the controller, draw the Bode diagram of the open-loop transfer function expression, and determine the system stability.

2. The method for suppressing output power ripple of a three-phase grid-connected inverter according to claim 1, characterized in that: The collecting of grid data and the calculation of voltage and current components under unbalanced grid conditions include: a d-axis voltage component under unbalanced grid conditions; It is expressed as: Among them, u d Indicates the d-axis voltage under normal operating conditions, u a Indicates the voltage of phase A under normal working conditions, u b Indicates the voltage of phase b under normal working conditions, u c Indicates the phase C voltage under normal working conditions, Represents the Park transformation matrix of the d-axis, the formula is simplified to: D-axis compensation current component It is expressed as: Among them, i d represents the d-axis current under normal operating conditions, i a,gain Indicates i d With l a The ratio of b,gain Indicates i d With l a The ratio of c,gain Indicates i d With l a The ratio of The d-axis compensation current component is simplified and expressed as: Among them, λ a Represents the virtual phase current gain in the current feedback loop.

3. The method for suppressing output power ripple of a three-phase grid-connected inverter according to claim 2, characterized in that: The calculation of the power under unbalanced grid conditions includes obtaining the output power expressed as: Among them, P o,VPCR Represents the power ripple component obtained by using the virtual phase current modulation method.

4. The method for suppressing output power ripple of a three-phase grid-connected inverter according to claim 3, characterized in that: The quantitative analysis of virtual phase current modulation includes the oscillation component P o,VPCR This will reduce the performance of the suppression method, and a quantitative analysis of the virtual phase current modulation method is needed; Define the output power ripple ΔP when no suppression method is used o,ripple And the average output power P avg The ratio λ e , expressed as: Define the output power ripple ΔP when the proposed suppression method is used o,VPCR And the average output power P o The ratio λ VPCR , expressed as: Combined with Lambda e and λ VPCR , the improvement ratio λ of power ripple by using virtual phase current modulation method is obtained imp , expressed as: By changing λ a The value of is obtained, and the improvement of power ripple by using virtual phase current modulation method under slight voltage fault and severe voltage fault is obtained.

5. The method for suppressing output power ripple of a three-phase grid-connected inverter according to claim 4, characterized in that: The suppression of the two-phase voltage fault condition and the addition of the compensation coefficient include: under the two-phase voltage fault condition, the voltage fluctuation affects the stability of the system and the balance of the output power, and the two-phase voltage needs to be compensated, and an additional compensation coefficient is added to suppress the power ripple; when the voltage of phase a and phase b fails, the compensation coefficient λ is added respectively a and λ b ; According to the virtual phase current modulation method, the fault voltage expression is corrected to: in d,fault =in d +λ a ·in a +λ b ·in b The expression of the d-axis compensation current component is corrected to: i d,fault =i d +λ a ·i a,gain +λ b ·i b,gain The compensation coefficient is set based on the specific parameters of the system and the fault conditions. Assume that the voltage fluctuation of phase A caused by the fault is Δu a , the voltage fluctuation of phase b is Δu b ; According to Park transformation, the fluctuation of d-axis voltage is expressed as: Δu d =k a Δu a +k b Δu b Among them, k a represents the conversion coefficient, which depends on the system topology; k b represents the conversion coefficient, which depends on the system transformation matrix; Determine the compensation coefficient, expressed as: k a l a +k b l b =-1 Solve to obtain the compensation coefficient.

6. The method for suppressing output power ripple of a three-phase grid-connected inverter according to claim 5, characterized in that: The controller design includes designing a current loop controller using a proportional-integral controller, and the transfer function of the controller is expressed as: Among them, k p represents the proportionality coefficient, k i Represents the integral coefficient.

7. The method for suppressing output power ripple of a three-phase grid-connected inverter according to claim 6, characterized in that: The drawing of the Bode diagram of the open-loop transfer function expression to determine the system stability includes obtaining the open-loop transfer function according to the controller transfer function, which is expressed as: Where L represents the system inductance, R represents the resistance, and s represents the complex variable in the Laplace transform; Use the open-loop transfer function to draw the Bode diagram of the system. The Bode diagram includes the magnitude diagram and the phase diagram. The system is judged whether it is in a stable state according to the magnitude of the amplitude margin and the phase margin. When the amplitude margin is greater than or equal to 6dB, it means that the system has sufficient gain margin in the frequency domain to resist external interference. When the phase margin is between 30° and 60°, it means that the system has good dynamic response characteristics. Otherwise, adjust k p and k i , so that the system meets the stability requirements.

8. A three-phase grid-connected inverter output power ripple suppression system using the method according to any one of claims 1 to 7, characterized in that: The calculation module collects grid data and calculates the voltage and current components under unbalanced grid conditions; The analysis module calculates the power under unbalanced grid conditions and conducts quantitative analysis on virtual phase current modulation; Adjustment module, suppresses two-phase voltage fault conditions and adds compensation coefficients; Determine the module, design the controller, draw the Bode diagram of the open-loop transfer function expression, and determine the system stability.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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