Voltage source inverter stability control method and system for direct current micro-grid

Abstract

The invention provides a stability control method and system for a voltage source type inverter of a direct-current micro-grid, and the method comprises the steps: selecting a corresponding double-loop control strategy to control the current according to an inverter architecture when a dq-axis direct current is sent to a control link, i.e., when an additional sensor exists in the inverter architecture, selecting a corresponding double-loop control strategy to control the current; a direct current signal is introduced to the output end of the outer ring PI controller through a proportional element, and current control is carried out; otherwise, the grid-connected current is introduced to the output end of the outer ring PI controller through the corresponding transfer function, and current control is carried out; on the basis of easy implementation, the problem of DC bus voltage oscillation caused by interaction between VSC equivalent DC impedance and line impedance can be effectively avoided, and the stability of the voltage source type inverter is further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of DC microgrid converter control, and particularly relates to a stability control method and system for a voltage source inverter in a DC microgrid, which is used to avoid the DC bus voltage oscillation problem caused by the mismatch between the DC equivalent impedance of the inverter and the grid line impedance. Background Art

[0002] The statements in this part merely provide background technical information related to the present invention and do not necessarily constitute prior art.

[0003] The development of renewable energy is an important part of the power field. New energy has the characteristics of randomness and intermittency, and a microgrid can connect new energy to the public grid with the least impact. Due to the advantages of high energy conversion efficiency, small harmonic interference, and simple system structure, the DC microgrid has become an important development direction of modern power systems.

[0004] In a DC microgrid, the interaction between converters and line impedance, converters and grid impedance, and between converters will cause stability problems. The mismatch between the equivalent DC impedance of the VSC (voltage source inverter) and the line impedance will lead to DC bus voltage oscillation. For such instability problems, many countermeasures have emerged.

[0005] However, these existing technologies for dealing with DC bus voltage oscillation still generally have some technical problems, such as:

[0006] (1) Most of the existing methods model the DC side impedance of the VSC from the perspective of small signals. This method introduces the common coupling point voltage to the output end of the current controller through a corresponding transfer function. Although it has a certain stabilizing effect, the transfer function design of this method is too complex, and the parameters to be designed are too cumbersome.

[0007] (2) Among the existing methods, there are also those based on the active virtual impedance reshaping method for control. This control method can improve the stability of the VSC in the middle frequency band. However, in the high frequency band, due to the need to add a lead link, the phase of the inverter impedance increases sharply, resulting in unpredictable negative effects in the high frequency band. Summary of the Invention

[0008] To overcome the deficiencies of the above-mentioned existing technologies, the present invention provides a stability control method and system for a voltage source inverter in a DC microgrid, which can effectively avoid the DC bus voltage oscillation problem caused by the interaction between the equivalent DC impedance of the VSC and the line impedance on the basis of being easy to implement, and further improve the stability of the voltage source inverter.

[0009] To achieve the above object, one or more embodiments of the present invention provide the following technical solutions:

[0010] The first aspect of the present invention provides a stability control method for a voltage source inverter in a DC microgrid.

[0011] The stability control method for a voltage source inverter in a DC microgrid includes:

[0012] Collecting three-phase voltage signals at the point of common coupling by using a first sensor, and inputting the three-phase voltage signals into a phase-locked loop to obtain the angle value required for coordinate transformation; collecting grid-connected current information by using a second sensor, and converting the three-phase current into dq-axis DC current according to the angle value required for coordinate transformation.

[0013] Feeding the obtained dq-axis DC current into a control link, and selecting a corresponding double-loop control strategy according to the inverter architecture to control the current. Specifically: when there are sensors other than the first sensor and the second sensor in the inverter architecture, introducing the DC current signal into the output end of the outer-loop PI controller through a proportional link for current control; otherwise, introducing the grid-connected current into the output end of the outer-loop PI controller through a corresponding transfer function for current control.

[0014] Further, the proportional link is: adjusted according to the magnitude and direction of the power transmitted by the voltage source inverter, the size of the DC microgrid and the filter capacitor to cope with different working conditions.

[0015] Further, the parameter design of the proportional link includes multiple parameter value settings, that is:

[0016]

[0017] where K i and K p respectively represent the parameter values of the integral link and the proportional link in the current inner-loop PI controller, and L represents the value of the filter inductor.

[0018] Further, the parameter design of the proportional link is determined based on phase requirements, including: first, determining the operating condition of the voltage source inverter and solving the DC-side impedance; then, determining the approximate range of the impedance intersection frequency according to the obtained DC-side impedance value; finally, calculating the K value according to the phase margin requirement, and determining whether to further solve the DC-side impedance of the voltage source inverter or solve the transfer function by judging whether to additionally add a new sensor.

[0019] Further, the DC side of the voltage source inverter under the double-loop control strategy is expressed as:

[0020]

[0021] where R and X respectively represent the real part and the imaginary part of the equivalent admittance of the DC side of the voltage source inverter under the double-loop control strategy; I gdrepresents the effective value of the grid-connected current on the d-axis, D d represents the effective value of the modulation wave on the d-axis; ω represents the frequency, L g represents the value of the grid inductor, I gd represents the effective value of the grid-connected current on the d-axis, K pwm represents the modulation ratio of the PWM modulation link.

[0022] Furthermore, the transfer function is determined based on the inverter transmission power and the relationship between the DC side and the AC side of the PWM modulation link.

[0023] Furthermore, the determined transfer function is expressed as:

[0024]

[0025] wherein, H x and H y represent the transfer functions required for the grid-connected current, I gd represents, L represents the value of the filter inductor, s represents the quantity of the physical loop, ω represents the frequency, D d represents the effective value of the modulation wave on the d-axis; I g represents the value of the grid inductor, I gd represents the effective value of the grid-connected current on the d-axis, K pwm represents the modulation ratio of the PWM modulation link.

[0026] The second aspect of the present invention provides a stability control system for a voltage source inverter for a DC microgrid.

[0027] The stability control system for a voltage source inverter for a DC microgrid includes:

[0028] A coordinate transformation module, configured to: collect three-phase voltage signals of the common coupling point by using a first sensor, and input the three-phase voltage signals into a phase-locked loop to obtain the angle value required for coordinate transformation; collect grid-connected current information by using a second sensor, and convert the three-phase current into dq-axis DC current according to the angle value required for coordinate transformation;

[0029] A stability control module, configured to: send the obtained dq-axis DC current into a control link, and select a corresponding double-loop control strategy according to the inverter architecture to control the current. Specifically: when there are sensors other than the first sensor and the second sensor in the inverter architecture, introduce the DC current signal into the output end of the outer-loop PI controller through a proportional link for current control; otherwise, introduce the grid-connected current into the output end of the outer-loop PI controller through the corresponding transfer function for current control.

[0030] The third aspect of the present invention provides a computer-readable storage medium, on which a program is stored, and when the program is executed by a processor, the steps in the voltage-source inverter stability control method for a DC microgrid as described in the first aspect of the present invention are implemented.

[0031] The fourth aspect of the present invention provides an electronic device, including a memory, a processor, and a program stored on the memory and executable on the processor. When the processor executes the program, the steps in the voltage-source inverter stability control method for a DC microgrid as described in the first aspect of the present invention are implemented.

[0032] The above one or more technical solutions have the following beneficial effects:

[0033] (1) By introducing a feedforward control strategy containing only a proportional link, the present invention abandons the complex integral-differential transfer function structure in traditional methods. Specifically, the present invention directly introduces the feedforward quantity of the DC current or grid-connected current (through a proportional link or an equivalent transfer function) at the output end of the voltage outer-loop PI controller, significantly simplifying the mathematical model of the control system. Among them, the parameter design of the proportional link only needs to be adjusted according to the operating conditions of the VSC transmission power, grid inductance, and filter capacitor, without complex multi-link parameter tuning. Therefore, compared with the prior art, the control strategy of the present invention can greatly reduce the implementation complexity and engineering commissioning difficulty while ensuring stability.

[0034] (2) The present invention adopts a feedforward control method with a pure proportional link, completely avoiding the defect of adding a lead link in the active virtual impedance reshaping technology. Since no high-frequency phase compensation link is introduced, the phase characteristic of the equivalent impedance on the DC side of the VSC remains unchanged in the high-frequency band, thus eliminating the high-frequency oscillation risk caused by the sharp increase in phase in traditional methods. In addition, the present invention further ensures the natural attenuation of the system impedance characteristic in the high-frequency band by optimizing the scheme to equivalently replace the DC current feedforward with the grid-connected current, without additional adjustment of the high-frequency response characteristic of the controller. Therefore, the control strategy of the present invention can maintain the inherent robustness in the high-frequency band while improving the stability in the middle frequency band, solving the problem that the negative impact in the high-frequency band in the prior art is uncontrollable.

[0035] The advantages of the additional aspects of the present invention will be partially given in the following description, partially will become obvious from the following description, or will be understood through the practice of the present invention. Description of the Drawings

[0036] The specification drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0037] Figure 1It is a flowchart of the stability control method for the voltage source inverter used in the DC microgrid in the first embodiment of the present invention.

[0038] Figure 2 It is the topology diagram of the DC microgrid in the first embodiment of the present invention.

[0039] Figure 3 It is the schematic diagram of DC current feedforward in the first embodiment of the present invention.

[0040] Figure 4 It is the schematic diagram of grid-connected current feedforward in the first embodiment of the present invention.

[0041] Figure 5 It is a flowchart of the parameter design of the proportional link in the first embodiment of the present invention. Detailed implementation mode

[0042] It should be noted that the following detailed descriptions are all exemplary and are intended to provide further descriptions of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0043] It should be noted that the terms used herein are only for describing the specific implementation mode and are not intended to limit the exemplary implementation mode according to the present invention.

[0044] Without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0045] In addition, for the convenience of understanding the technical solution of the present invention, first, the parameters and related variables involved in the present invention are explained, and the specific explanations are shown in Table 1.

[0046] Table 1 Explanation of variables related to VSC and microgrid

[0047]

[0048] Embodiment 1

[0049] This embodiment discloses a stability control method for the voltage source inverter used in the DC microgrid.

[0050] As Figure 1 shown, the stability control method for the voltage source inverter used in the DC microgrid includes:

[0051] Step S1: Use the first sensor to collect the three-phase voltage signals at the point of common coupling, and input the three-phase voltage signals into the phase-locked loop to obtain the angle value required for coordinate conversion; use the second sensor to collect the grid-connected current information, and convert the three-phase current into the dq-axis DC current according to the angle value required for coordinate conversion;

[0052] Step S2: Feed the obtained dq-axis DC current into the control link, and select the corresponding double-loop control strategy according to the inverter architecture to control the current. Specifically: when there are sensors other than the first sensor and the second sensor in the inverter architecture, introduce the DC current signal to the output end of the outer-loop PI controller through a proportional link for current control; otherwise, introduce the grid-connected current to the output end of the outer-loop PI controller through the corresponding transfer function for current control.

[0053] Based on the above process, the problem of DC bus voltage oscillation caused by the interaction between the DC equivalent impedance of the VSC and the line impedance can be effectively solved; at the same time, this control method is relatively easy to implement and the parameter design is relatively simple. For the convenience of understanding the technical solution of the present invention, the following further explains and illustrates the specific implementation steps of the technical solution of the present invention.

[0054] As Figure 2 shown is a typical DC microgrid topology structure, where photovoltaic, energy storage, DC and AC loads are connected to the same DC bus through converters, and the VSC is applied in the DC microgrid as a power exchange device between the public grid and the microgrid. The DC side of the VSC is connected to the DC bus, but the inductive line impedance between the DC bus and the DC side port of the VSC cannot be ignored; the AC side of the VSC is connected to the public grid, and at the same time, considering the condition of a weak grid, that is: the inductive grid impedance cannot be ignored.

[0055] For this, the present invention provides a voltage source inverter stability control method for a DC microgrid, which can be specifically implemented through Step S1 - Step S2.

[0056] In Step S1, use the first sensor to collect the three-phase voltage signals at the point of common coupling, and input the three-phase voltage signals into a phase-locked loop to obtain the angle value required for coordinate transformation; use the second sensor to collect the grid-connected current information, and convert the three-phase current into dq-axis DC current according to the angle value required for coordinate transformation.

[0057] As an optional embodiment, the voltage information at the point of common coupling PCC can be collected by a three-phase voltage sensor, and the signal is transmitted to the phase-locked loop PLL to obtain the angle value required for coordinate transformation, so as to achieve the static error-free control of the dq-axis DC current by the PI controller.

[0058] As an alternative embodiment, grid-connected current information can be collected by a three-phase current sensor, and the three-phase current can be transformed into dq-axis DC current through coordinate transformation and sent to the control link. The current inner loop controls the grid-connected current, and the voltage outer loop generates the reference value of the current inner loop. Among them, the dq-axis is a key coordinate system used to simplify the control of alternating quantities in power electronics control. By converting three-phase alternating quantities into two-phase direct current quantities (d-axis and q-axis), decoupled control of active and reactive power is achieved; in this embodiment, the dq-axis DC current (such as the current in a two-phase rotating coordinate system) is the control variable obtained through Park transformation.

[0059] It should be noted that VSCs generally operate at unity power factor. Therefore, the reference value of the q-axis current is 0; the information of the DC side voltage of the VSC is collected by a voltage sensor and sent to the voltage outer loop, and the reference value of the voltage outer loop and the reference value of the DC bus voltage are given, so that the VSC can support the DC bus voltage.

[0060] In the context of a weak grid, the grid impedance cannot be ignored, so the control method needs to consider the influence of this resistive-inductive impedance; at the same time, in order to improve the stability of the DC side of the VSC and suppress the oscillation of the DC bus voltage, the present invention is improved on the basis of the traditional method, and innovative improvements are made in step S2, that is: to meet the above requirements, through the modeling and analysis of the DC side impedance of the VSC, a feedforward method with a simpler transfer function that only has a proportional link instead of a complex integral-differential link is designed. This method will not affect the characteristics of the VSC in the high-frequency band. At the same time, for the case where no additional sensors are added, this method can also make corresponding equivalent improvements with the same effect. Among them, the DC side impedance of the VSC can be obtained by frequency sweeping with simulation software.

[0061] In step S2, the obtained dq-axis DC current is sent to the control link, and the corresponding double-loop control strategy is selected according to the inverter architecture to control the current. Specifically: when there are sensors other than the first sensor and the second sensor in the inverter architecture, the DC current signal is introduced into the output terminal of the outer-loop PI controller through a proportional link for current control; otherwise, the grid-connected current is introduced into the output terminal of the outer-loop PI controller through the corresponding transfer function for current control.

[0062] A. The DC current signal is introduced into the output terminal of the outer-loop PI controller through a proportional link for current control.

[0063] As Figure 3 shown, the improvement made by the present invention on the basis of the basic control strategy of the grid-connected inverter is the direct current control strategy in the dq coordinate system. From Figure 3It can be seen that, compared with the existing inverter control architecture design, a proportional link is added in this invention. Specifically, in order to improve the stability of the DC side of the VSC and suppress the oscillation of the DC bus voltage, the collected DC current signal is introduced into the output end of the outer-loop PI controller through the proportional link in this invention. This proportional link can be adjusted according to the magnitude and direction of the power transmitted by the VSC, the magnitude of the grid inductance and the filter capacitance to cope with different working conditions. In this scheme, one more sensor is introduced compared with the traditional VSC control strategy.

[0064] Among them, the proportional link includes the design of multiple parameter values, that is:

[0065]

[0066] Among them, K i and K p respectively represent the parameter values of the integral link and the proportional link in the current inner-loop PI controller, and L represents the value of the filter inductance. For the convenience of representation in calculation, two parameters α and β without specific physical meanings are defined. Both α and β are process parameters characterizing the VSC.

[0067] At the same time, the proportional link also includes the definition of multiple parameters, that is:

[0068]

[0069] Among them, ω represents the frequency, and the impedance model is expanded in the frequency domain. On this basis, the real part and the imaginary part of the equivalent admittance of the DC side of the voltage source inverter VSC under the double-loop control strategy can be respectively expressed as. For the convenience of representation in calculation, two parameters m and n without specific physical meanings are defined. Both m and n are process variables.

[0070]

[0071] Among them, R and X respectively represent the real part and the imaginary part of the equivalent admittance of the DC side of the voltage source inverter under the double-loop control strategy; I gd represents the effective value of the grid-connected current in the d-axis, D d represents the effective value of the modulation wave in the d-axis; ω represents the frequency, L g represents the value of the grid inductance, I gd represents the effective value of the grid-connected current in the d-axis, K pwm represents the modulation ratio of the PWM modulation link.

[0072] Thus, only by determining the parameter K value of the proportional link, the DC current signal can be introduced into the output end of the outer-loop PI controller through the proportional link for current control. As Figure 5As shown, the parameter design of the proportional link is determined based on the phase requirement, including: First, determine the operating conditions of the voltage source inverter and solve the DC-side impedance; then, determine the approximate range of the impedance intersection frequency according to the obtained DC-side impedance value; finally, calculate the value of K according to the phase margin requirement, and determine whether to further solve the DC-side impedance of the voltage source inverter or solve the transfer function by judging whether to add a new sensor additionally.

[0073] First, determine the operating conditions of the VSC and determine I gd and L g . Among them, Igd represents the power transmitted by the inverter and can be obtained through the load prediction of the microgrid; L g can be obtained through corresponding measurement techniques. As an optional embodiment, L g can be obtained by the direct measurement method. For example: ① Disconnect the grid connection: Under safe conditions, isolate the part of the grid to be measured (such as lines, transformers) from the main grid; ② Apply a test signal: Inject an AC signal with a specific frequency (usually 50 / 60 Hz of the power frequency or the harmonic frequency band) through the equipment; ③ Measure the voltage V and the current I: Record the amplitude and phase difference of the voltage and the current; ④ Calculate L g , that is: where θ is the phase difference between the voltage and the current.

[0074] Subsequently, solve the DC-side impedance. As an optional embodiment, the solution of the DC-side impedance can be achieved by: ① Inject a perturbation signal: Inject a small-signal voltage perturbation RA at the DC bus; ② Measure the response: Record the current response RB after the perturbation and calculate the impedance amplitude ③ Frequency-domain fitting: Analyze the impedance characteristics through the Bode diagram or Nyquist diagram to identify the resonant frequency and the stability boundary to solve the DC-side impedance.

[0075] Then, judge whether PM is greater than 0. If it is not greater than 0, further determine the approximate range of the impedance intersection frequency, that is, draw the Bode diagram of the VSC DC impedance and the impedance of the rest of the microgrid, and the approximate range of the intersection frequency can be obtained; if it is greater than 0, directly end.

[0076] Then, solve the value of K according to the phase margin requirement through Equation (3). After obtaining the value of K, judge whether a new sensor is added. If so, re-solve the DC-side impedance of the VSC and re-judge whether PM is greater than 0 again; after calculating the value of K, multiply the DC current idc by this coefficient K and introduce it to the output end of the outer-loop PI controller to achieve current control. If not, directly introduce the grid-connected current to the output end of the outer-loop PI controller through the corresponding transfer function, that is, perform current control based on the transfer function.

[0077] B. The grid-connected current is introduced to the output of the outer-loop PI controller through the corresponding transfer function for current control.

[0078] As Figure 4 shown, the improvement made by the present invention based on the basic control strategy of the grid-connected inverter is the grid-connected current control strategy in the dq coordinate system. As can be seen from Figure 4 this, compared with the existing inverter control architecture design, the present invention adds a transfer function control on this basis and no longer requires an additional sensor design. Specifically, the present invention optimizes the solution by introducing the grid-connected current to the output of the outer-loop PI controller through the corresponding transfer function. This introduction effect is equivalent to the introduction of a DC current through a proportional link. The optimized solution reduces the use of sensors, and the transfer function is not complex.

[0079] Without additionally introducing new sensors, the above Scheme A can be equivalent. Since the transfer function is determined based on the relationship between the inverter transmission power, the DC side and the AC side of the PWM modulation link, the equivalence basis can be as follows:

[0080] ① The inverter transmission power can be expressed as:

[0081]

[0082] where s represents the quantity in the physical loop; p dc represents the power transmitted by the inverter VSC, and T represents the transpose calculation of the matrix vector.

[0083] ② The relationship between the DC side and the AC side of the PWM modulation link can be expressed as:

[0084]

[0085] Combining Equation (4) and Equation (5) and performing small-signal analysis, we can obtain:

[0086]

[0087] Thus, the transfer function required for introducing the grid-connected current as a feedforward is obtained, that is

[0088]

[0089] where H x and H y represent the transfer functions required for the grid-connected current, I gd represents, L represents the value of the filter inductor, s represents the quantity in the physical loop, ω represents the frequency, D dIt represents the effective value of the d-axis modulation wave. After calculating the transfer function, the grid-connected currents id and iq are introduced into the output of the outer-loop PI controller through this transfer function, and current control can be achieved.

[0090] Based on the above design, it can be seen that the present invention takes into account the operating conditions of the VSC and the grid inductance, introduces DC current feedforward on the basis of double-loop control, improves the stability of the DC side of the VSC, and can effectively avoid the DC bus voltage oscillation problem caused by the interaction between the equivalent DC impedance of the VSC and the line impedance; at the same time, the parameters of this control method are easy to design. If additional sensors need to be avoided in engineering, corresponding equivalent alternative solutions can be used, that is, introducing the grid-connected current into the feedforward, and the effect is the same as introducing the DC current into the feedback.

[0091] Embodiment 2

[0092] This embodiment discloses a stability control system for a voltage source inverter in a DC microgrid.

[0093] A stability control system for a voltage source inverter in a DC microgrid includes:

[0094] A coordinate transformation module, configured to: collect three-phase voltage signals at the point of common coupling using a first sensor, and input the three-phase voltage signals into a phase-locked loop to obtain the angle value required for coordinate transformation; collect grid-connected current information using a second sensor, and convert the three-phase current into dq-axis DC currents according to the angle value required for coordinate transformation.

[0095] A stability control module, configured to: send the obtained dq-axis DC currents into the control link, and select a corresponding double-loop control strategy to control the current according to the inverter architecture. Specifically: when there are sensors other than the first sensor and the second sensor in the inverter architecture, introduce the DC current signal into the output of the outer-loop PI controller through a proportional link for current control; otherwise, introduce the grid-connected current into the output of the outer-loop PI controller through a corresponding transfer function for current control.

[0096] Embodiment 3

[0097] The purpose of this embodiment is to provide a computer-readable storage medium.

[0098] A computer-readable storage medium, on which a computer program is stored, and when the program is executed by a processor, it implements the steps in the method for stabilizing the control of a voltage source inverter in a DC microgrid as described in Embodiment 1 of the present disclosure.

[0099] Embodiment 4

[0100] The purpose of this embodiment is to provide an electronic device.

[0101] An electronic device includes a memory, a processor, and a program stored in the memory and executable on the processor. When the processor executes the program, it implements the steps in the voltage source inverter stability control method for a DC microgrid as described in Embodiment 1 of the present disclosure.

[0102] In the devices of Embodiments 2, 3, and 4 above, the steps involved correspond to those in Method Embodiment 1. For specific implementation manners, reference may be made to the relevant description part of Embodiment 1. The term "computer-readable storage medium" should be understood to include a single medium or multiple media containing one or more instruction sets; it should also be understood to include any medium that can store, encode, or carry an instruction set for execution by a processor and enable the processor to execute any method in the present invention.

[0103] Those skilled in the art should understand that the above-mentioned modules or steps of the present invention can be implemented by a general-purpose computer device. Optionally, they can be implemented by program codes executable by a computing device, so that they can be stored in a storage device and executed by the computing device, or they can be separately fabricated into individual integrated circuit modules, or multiple modules or steps among them can be fabricated into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0104] Although the specific implementation manners of the present invention have been described above in conjunction with the accompanying drawings, it is not a limitation on the protection scope of the present invention. Those skilled in the art should understand that, based on the technical solutions of the present invention, various modifications or deformations that can be made without creative efforts by those skilled in the art are still within the protection scope of the present invention.

Claims

1. A stability control method for a voltage source inverter in a DC microgrid, characterized in that Including: Collecting three-phase voltage signals of the common coupling point by using a first sensor, and inputting the three-phase voltage signals into a phase-locked loop to obtain the angle value required for coordinate transformation; Collecting grid-connected current information by using a second sensor, and converting the three-phase current into dq-axis DC current according to the angle value required for coordinate transformation; Sending the obtained dq-axis DC current into a control link, and selecting a corresponding double-loop control strategy to control the current according to the inverter architecture. Specifically: when there are sensors other than the first sensor and the second sensor in the inverter architecture, introducing the DC current signal into the output end of the outer-loop PI controller through a proportional link for current control; Otherwise, introducing the grid-connected current into the output end of the outer-loop PI controller through a corresponding transfer function for current control.

2. The voltage source inverter stability control method for a DC microgrid according to claim 1, characterized in that, The proportional link is: adjusted according to the magnitude and direction of the power transmitted by the voltage-source inverter, the size of the DC microgrid and the filter capacitor to cope with different working conditions.

3. The voltage source inverter stability control method for a DC microgrid according to claim 1, characterized in that The proportional link includes multiple parameter value designs, that is: Among them, K i and K p respectively represent the parameter values of the integral link and the proportional link in the current inner-loop PI controller, and L represents the value of the filter inductor.

4. The stability control method for a voltage source inverter used in a DC microgrid according to claim 1, wherein, The parameter design of the proportional link is determined based on phase requirements, including: first, determining the operating condition of the voltage-source inverter and solving the DC-side impedance; then, determining the approximate range of the impedance intersection frequency according to the obtained DC-side impedance value; finally, calculating the K value according to the phase margin requirement, and determining whether to further solve the DC-side impedance of the voltage-source inverter or solve the transfer function by judging whether to additionally add a new sensor.

5. The voltage source inverter stability control method for a DC microgrid according to claim 1, characterized in that, The DC side of the voltage-source inverter under the double-loop control strategy is expressed as: wherein, R and X respectively represent the real part and the imaginary part of the equivalent admittance of the DC side of the voltage source inverter under the double-loop control strategy; I gd represents the effective value of the grid-connected current on the d-axis, D d represents the effective value of the modulation wave on the d-axis; ω represents the frequency, L g represents the value of the grid inductance, I gd represents the effective value of the grid-connected current on the d-axis, K pwm represents the modulation ratio of the PWM modulation link.

6. The voltage source inverter stability control method for a DC microgrid according to claim 1, characterized in that The transfer function is determined based on the relationship between the power transmitted by the inverter, the DC side and the AC side of the PWM modulation link.

7. The voltage source inverter stability control method for a DC microgrid according to claim 6, characterized in that, The determined transfer function is expressed as: Among them, H x and H y represent the transfer functions required for grid-connected current, I gd represents, L represents the value of the filter inductor, s represents the quantity of the physical loop, ω represents the frequency, D d represents the effective value of the d-axis modulation wave; L g represents the value of the grid inductor, I gd represents the effective value of the d-axis grid-connected current, K pwm represents the modulation ratio of the PWM modulation link.

8. A stability control system for a voltage source inverter used in a DC microgrid, characterized in that, Including: A coordinate transformation module, configured to: collect three-phase voltage signals of the common coupling point by using a first sensor, and input the three-phase voltage signals into a phase-locked loop to obtain the angle value required for coordinate transformation; collect grid-connected current information by using a second sensor, and convert the three-phase current into dq-axis DC current according to the angle value required for coordinate transformation; A stability control module, configured to: send the obtained dq-axis DC current into a control link, and select a corresponding double-loop control strategy to control the current according to the inverter architecture. Specifically: when there are sensors other than the first sensor and the second sensor in the inverter architecture, introducing the DC current signal into the output end of the outer-loop PI controller through a proportional link for current control; Otherwise, introducing the grid-connected current into the output end of the outer-loop PI controller through a corresponding transfer function for current control.

9. A computer-readable storage medium having a program stored thereon, characterized in that, When the program is executed by a processor, it implements the steps in the method for stabilizing the voltage-source inverter for a DC microgrid according to any one of claims 1-7.

10. An electronic device, comprising a memory, a processor, and a program stored on the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps in the method for stabilizing the voltage-source inverter for a DC microgrid according to any one of claims 1-7.

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