Method and device for suppressing arm current of flexible DC power transmission system

Abstract

The present invention discloses a method and device for suppressing arm current in a flexible direct current (HVDC) transmission system. The method comprises: obtaining arm current values and average voltages of each submodule in all phases of the HVDC transmission system in real time; dynamically adjusting the virtual impedance value of a controller that incorporates a virtual impedance based on the maximum arm current value among all phase arm current values when an unbalanced fault occurs in the HVDC transmission system or when the fault is restored; the virtual impedance value is positively correlated with the arm current value, with the larger the arm current value, the larger the virtual impedance value; performing balanced control on the submodule voltages based on the average voltage of each phase submodule; and collaboratively suppressing the arm current based on the dynamically adjusted virtual impedance value and the balanced submodule voltages. The present invention can reduce the impact of arm current during unbalanced faults, address the limitations of single control in the prior art, and enhance the suppression effect of arm current.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible direct current transmission of power systems, and in particular to a method and device for suppressing arm current of a flexible direct current transmission system. Background Art

[0002] This section is intended to provide a background or context to the embodiments of the invention that are recited in the claims. No statement herein is admitted to be prior art by virtue of its inclusion in this section.

[0003] Flexible DC transmission systems utilize voltage-source converters, enabling independent control of active and reactive power while avoiding the commutation failures common in conventional DC systems. Modular multilevel converters employ a modular design and nearest-level modulation, reducing harmonic content and switching losses, and are widely used in HVDC transmission systems. However, simulations have shown that when a two-phase unbalanced fault occurs in a Flexible DC transmission system operating in the sending-end DC voltage-controlled mode, the sudden change in system voltage generates large arm currents. Existing technologies for suppressing arm currents are limited and cannot meet practical requirements. Summary of the Invention

[0004] An embodiment of the present invention provides a method for suppressing arm current in a flexible direct current transmission system, to address the problem of poor arm current suppression when a two-phase unbalanced fault occurs in the prior art. The method includes:

[0005] Obtain the bridge arm current values of all phases and the average voltage of each phase submodule in the flexible DC transmission system in real time;

[0006] When an unbalanced fault occurs in the flexible DC transmission system or the fault is restored, the virtual impedance value in the controller that adds the virtual impedance is dynamically adjusted according to the maximum bridge arm current value among all phase bridge arm current values. The virtual impedance value is positively correlated with the bridge arm current value. The larger the bridge arm current value, the larger the virtual impedance value.

[0007] The submodule voltage is balanced and controlled according to the average voltage of each phase submodule;

[0008] Based on the dynamically adjusted virtual impedance value and the balanced controlled sub-module voltage, the bridge arm current is cooperatively suppressed.

[0009] An embodiment of the present invention further provides a bridge arm current suppression device for a flexible direct current transmission system, which is used to solve the problem of poor bridge arm current suppression effect when a two-phase unbalanced fault occurs in the prior art. The device includes:

[0010] The bridge arm current value and each phase submodule voltage average value acquisition module is used to obtain the bridge arm current value and each phase submodule voltage average value of all phases in the flexible DC transmission system in real time;

[0011] The virtual impedance dynamic adjustment module is used to dynamically adjust the virtual impedance value in the controller that adds virtual impedance according to the maximum bridge arm current value among all phase bridge arm current values when an unbalanced fault occurs or the fault is restored in the flexible DC transmission system. The virtual impedance value is positively correlated with the bridge arm current value. The larger the bridge arm current value, the larger the virtual impedance value.

[0012] The inter-phase submodule voltage balancing control module is used to balance the submodule voltages according to the average voltage of each phase submodule;

[0013] The bridge arm current cooperative suppression module is used to cooperatively suppress the bridge arm current based on the dynamically adjusted virtual impedance value and the sub-module voltage after balanced control.

[0014] An embodiment of the present invention further provides a computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the above-mentioned method for suppressing the bridge arm current of the flexible direct current transmission system is implemented.

[0015] An embodiment of the present invention further provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the method for suppressing the bridge arm current of the flexible direct current transmission system is implemented.

[0016] An embodiment of the present invention further provides a computer program product, which includes a computer program. When the computer program is executed by a processor, the method for suppressing the bridge arm current of the flexible direct current transmission system is implemented.

[0017] In an embodiment of the present invention, the bridge arm current values of all phases and the average voltage of each phase submodule in the flexible direct current transmission system are obtained in real time; when an unbalanced fault occurs in the flexible direct current transmission system or the fault is restored, the virtual impedance value in the controller with the virtual impedance is dynamically adjusted according to the maximum bridge arm current value among the bridge arm current values of all phases; the virtual impedance value is positively correlated with the bridge arm current value, and the larger the bridge arm current value, the larger the virtual impedance value; the submodule voltage is balanced according to the average voltage of each phase submodule; based on the dynamically adjusted virtual impedance value and the balanced controlled submodule voltage, the bridge arm current is collaboratively suppressed. In the above process, the embodiment of the present invention reduces the impact of the bridge arm current during an unbalanced fault by dynamically adjusting the synergistic effect of the virtual impedance and the voltage balancing control, thereby solving the limitations of the single control in the prior art and improving the suppression effect of the bridge arm current. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0019] Figure 1 Flowchart of a method for suppressing bridge arm current in a flexible DC transmission system according to an embodiment of the present invention;

[0020] Figure 2 Schematic diagram of suppressing bridge arm current by virtual impedance in an embodiment of the present invention;

[0021] Figure 3 This is a flow chart of calculating the d-axis reference wave and the q-axis reference wave after adding virtual impedance in an embodiment of the present invention;

[0022] Figure 4 This is a flow chart of obtaining reference waves of the upper bridge arm and the lower bridge arm after balanced control in an embodiment of the present invention;

[0023] Figure 5 Schematic diagram of suppressing bridge arm current through inter-phase sub-module voltage balancing control in an embodiment of the present invention;

[0024] Figure 6 Schematic diagram of a bridge arm current suppression device for a flexible DC transmission system in an embodiment of the present invention. DETAILED DESCRIPTION

[0025] To make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the embodiments of the present invention are further described in detail below with reference to the accompanying drawings. Here, the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0026] The acquisition, storage, use, and processing of data in this application's technical solution comply with relevant national laws and regulations.

[0027] Figure 1 Flowchart of a method for suppressing arm current of a flexible DC transmission system according to an embodiment of the present invention. The method includes:

[0028] Step 101: obtaining in real time the arm current values of all phases and the average voltage of each phase submodule in the flexible DC transmission system;

[0029] Step 102: When an unbalanced fault occurs in the flexible HVDC system or the fault is restored, dynamically adjust the virtual impedance value in the controller that adds the virtual impedance according to the maximum bridge arm current value among the bridge arm current values of all phases; the virtual impedance value is positively correlated with the bridge arm current value, and the larger the bridge arm current value, the larger the virtual impedance value.

[0030] Step 103, performing balancing control on the submodule voltages according to the average value of the submodule voltages of each phase;

[0031] Step 104: Based on the dynamically adjusted virtual impedance value and the balanced controlled submodule voltage, the bridge arm current is cooperatively suppressed. Each step is described in detail below.

[0032] In step 101, the bridge arm current values of all phases and the average voltage of each phase submodule in the flexible direct current transmission system are obtained in real time.

[0033] In a specific embodiment, when an unbalanced fault occurs or a fault is recovered, the voltage at the midpoint of the upper and lower bridge arms will suddenly change, the capacitors in the upper and lower bridge arms will charge and discharge respectively, and the bridge arm current will increase rapidly. To solve the above problems, the present invention proposes the following when an unbalanced fault occurs or a fault is recovered in the flexible DC transmission system:

[0034] In step 102, when an unbalanced fault occurs in the flexible direct current transmission system or the fault is restored, the virtual impedance value in the controller adding the virtual impedance is dynamically adjusted according to the maximum bridge arm current value among the bridge arm current values of all phases; the virtual impedance value is positively correlated with the bridge arm current value, and the larger the bridge arm current value, the larger the virtual impedance value.

[0035] In one embodiment, dynamically adjusting the virtual impedance value in the controller adding the virtual impedance according to the maximum bridge arm current value among the bridge arm current values of all phases includes:

[0036] Based on the maximum bridge arm current value among all phase bridge arm current values, the virtual impedance value is adjusted in sections according to the following threshold rules:

[0037]

[0038] Among them, X1 is 1.1 times the rated value of the bridge arm current, X2 is 1.2 times the rated value of the bridge arm current, and X3 is between 1.2 times the rated value of the bridge arm current and the preset value of the bridge arm current protection. armMax is the maximum current value in each bridge arm, R x is the virtual impedance, and R1 is the preset resistance value. Generally, R1 is an empirical value, such as 0.2.

[0039] In a specific embodiment, Figure 2 FIG2 is a schematic diagram showing a method of suppressing the bridge arm current by virtual impedance according to an embodiment of the present invention, wherein Udcref is the DC voltage reference value, U dc is the actual value of DC voltage, Q ref is the reactive power reference value, Q is the actual reactive power value, wL, w is the fundamental frequency angular frequency, and L is the equivalent inductance on the AC side. An adaptive virtual impedance is added to the controller to adaptively adjust the virtual impedance according to the bridge arm current. The larger the bridge arm current value, the larger the virtual impedance value, thereby suppressing the impact of the bridge arm current. Since the larger the bridge arm current, the larger the virtual impedance required to better reduce the bridge arm current impact, where R1 <R2<R3<R4。

[0040] Figure 3 This is a flow chart of calculating the d-axis reference wave and the q-axis reference wave after adding virtual impedance in an embodiment of the present invention. In one embodiment, after dynamically adjusting the virtual impedance value in the controller adding virtual impedance according to the maximum bridge arm current value among all phase bridge arm current values, the process includes:

[0041] Step 301, obtaining a d-axis reference wave and a q-axis reference wave of a controller without adding a virtual impedance;

[0042] Step 302 : Calculate the d-axis reference wave and the q-axis reference wave after adding the virtual impedance according to the d-axis reference wave, the q-axis reference wave and the virtual impedance value.

[0043] In one embodiment, the d-axis reference wave and the q-axis reference wave after adding the virtual impedance are calculated according to the following formulas:

[0044]

[0045] Among them, V dref 、V qref are the d-axis reference wave and q-axis reference wave of the controller without adding virtual impedance, 、 are the d-axis reference wave and q-axis reference wave after adding virtual impedance, i d 、i q are the d-axis current value and the q-axis current value respectively, R x is the virtual impedance.

[0046] In step 103, the submodule voltages are balanced and controlled according to the average value of the submodule voltages of each phase.

[0047] Figure 4 This is a flow chart of obtaining reference waves of the upper bridge arm and the lower bridge arm after balanced control in an embodiment of the present invention. In one embodiment, balanced control of the submodule voltage is performed based on the average value of the submodule voltage of each phase, including:

[0048] Step 401, obtaining reference waves of the upper bridge arm and the lower bridge arm respectively;

[0049] Step 402: Using a PI regulator, obtain the reference wave superposition of the upper bridge arm and the lower bridge arm according to the average voltage of each phase submodule;

[0050] Step 403 : performing balanced control on the inter-phase submodule voltages according to the reference waves of the upper bridge arm and the lower bridge arm and the superposition of the reference waves of the upper bridge arm and the lower bridge arm to obtain the reference waves of the upper bridge arm and the lower bridge arm after balanced control.

[0051] In one embodiment, the reference wave after equalization control is calculated according to the following formula:

[0052]

[0053] in, 、 are the reference waves of the upper bridge arm and the lower bridge arm respectively, 、 are the reference wave superposition amounts of the upper bridge arm and the lower bridge arm respectively, 、 They are the reference waves of the upper bridge arm and the lower bridge arm after balanced control.

[0054] like Figure 5 FIG. 1 is a schematic diagram showing how to suppress the bridge arm current by controlling the voltage balancing of the phase submodules in an embodiment of the present invention. 、 are the reference waves of the upper bridge arm and the lower bridge arm respectively, 、 are the reference wave superposition amounts of the upper bridge arm and the lower bridge arm respectively, 、 These are the reference waves for the upper and lower bridge arms after balanced control. To further suppress the bridge arm current, balanced control of the interphase submodule voltage is added to reduce the charging and discharging of the capacitors when the voltage at the midpoint of the upper and lower bridge arms suddenly changes, thereby reducing the bridge arm inrush current.

[0055] In a specific embodiment, Figure 4 As shown, the inter-phase submodule voltage balancing control is explained by taking phase A as an example. First, the total average value U of the six bridge arm voltages is obtained. cav , and the average voltage of phase A U cav_A The difference is made, and the bridge arm voltage reference wave superposition amount duref is obtained after passing through the PI regulator. When the average voltage of phase A is lower than the preset voltage value, the reference waves of the upper and lower bridge arms of phase A are increased, phase A is charged, and the average voltage of phase A is increased. When the average voltage of phase A is higher than the preset voltage value, the reference waves of the upper and lower bridge arms of phase A are reduced, phase A is discharged, and the average voltage of phase A is reduced.

[0056] In step 104 , the bridge arm current is cooperatively suppressed based on the dynamically adjusted virtual impedance value and the balanced controlled submodule voltage.

[0057] In one embodiment, the bridge arm current is cooperatively suppressed based on the dynamically adjusted virtual impedance value and the balanced controlled submodule voltage, including:

[0058] The bridge arm current is cooperatively suppressed according to the reference waves of the upper bridge arm and the lower bridge arm after balanced control, and the d-axis reference wave and the q-axis reference wave after adding virtual impedance.

[0059] In this embodiment of the present invention, an adaptive virtual impedance is first added to the controller. The virtual impedance is adaptively adjusted based on the arm current. The larger the arm current, the larger the virtual impedance, thereby suppressing the arm current surge. Because the voltage at the midpoint of the upper and lower arms can experience significant voltage changes when an unbalanced fault or fault recovery occurs in the AC system, the current surge in the upper or lower arms of that phase can also be significant. To further suppress arm current surges, interphase submodule voltage balancing control is implemented to reduce the voltage surge at the midpoint of the upper and lower arms, thereby further minimizing arm current surges.

[0060] The present invention also provides a device for suppressing arm current in a flexible DC transmission system, as described in the following embodiments. Because the principles underlying the device are similar to those of the method for suppressing arm current in a flexible DC transmission system, the implementation of the device can be referenced to the implementation of the method for suppressing arm current in a flexible DC transmission system, and any repetitions will not be repeated.

[0061] Figure 6 Schematic diagram of a bridge arm current suppression device for a flexible DC transmission system according to an embodiment of the present invention, the device comprising:

[0062] The bridge arm current value and average voltage value of each phase submodule are obtained by the module 601, which is used to obtain the bridge arm current value and average voltage value of each phase submodule in the flexible DC transmission system in real time;

[0063] The virtual impedance dynamic adjustment module 602 is used to dynamically adjust the virtual impedance value of the controller that adds the virtual impedance according to the maximum bridge arm current value among all phase bridge arm current values when an unbalanced fault occurs or the fault is restored in the flexible DC transmission system. The virtual impedance value is positively correlated with the bridge arm current value. The larger the bridge arm current value, the larger the virtual impedance value. The inter-phase submodule voltage balancing control module 603 is used to balance the submodule voltage according to the average voltage of each phase submodule.

[0064] The bridge arm current cooperative suppression module 604 is configured to cooperatively suppress the bridge arm current based on the dynamically adjusted virtual impedance value and the balanced controlled sub-module voltage.

[0065] In one embodiment, the virtual impedance value dynamic adjustment module 602 is specifically configured to:

[0066] Based on the maximum bridge arm current value among all phase bridge arm current values, the virtual impedance value is adjusted in sections according to the following threshold rules:

[0067]

[0068] Among them, X1 is 1.1 times the rated value of the bridge arm current, X2 is 1.2 times the rated value of the bridge arm current, and X3 is between 1.2 times the rated value of the bridge arm current and the preset value of the bridge arm current protection. armMax is the maximum current value in each bridge arm, R x is the virtual impedance, and R1 is the preset resistance value.

[0069] In one embodiment, the virtual impedance value dynamic adjustment module 602 is further configured to:

[0070] Obtain the d-axis reference wave and q-axis reference wave of the controller without adding virtual impedance;

[0071] According to the d-axis reference wave, the q-axis reference wave and the virtual impedance value, the d-axis reference wave and the q-axis reference wave after adding the virtual impedance are calculated respectively.

[0072] In one embodiment, the d-axis reference wave and the q-axis reference wave after adding the virtual impedance are calculated according to the following formulas:

[0073]

[0074] Among them, V dref 、V qref are the d-axis reference wave and q-axis reference wave of the controller without adding virtual impedance, 、 are the d-axis reference wave and q-axis reference wave after adding virtual impedance, i d 、i q are the d-axis current value and the q-axis current value respectively, R x is the virtual impedance.

[0075] In one embodiment, the inter-phase sub-module voltage balancing control module 603 is specifically configured to:

[0076] Obtain the reference waves of the upper bridge arm and the lower bridge arm respectively;

[0077] The PI regulator is used to obtain the superposition of the reference waves of the upper and lower bridge arms according to the average voltage of each phase submodule;

[0078] According to the reference waves of the upper bridge arm and the lower bridge arm and the superposition of the reference waves of the upper bridge arm and the lower bridge arm, the inter-phase sub-module voltages are balanced controlled to obtain the reference waves of the upper bridge arm and the lower bridge arm after balanced control.

[0079] In one embodiment, the reference wave after equalization control is calculated according to the following formula:

[0080]

[0081] in, 、 are the reference waves of the upper bridge arm and the lower bridge arm respectively, 、 are the reference wave superposition amounts of the upper bridge arm and the lower bridge arm respectively, 、 They are the reference waves of the upper bridge arm and the lower bridge arm after balanced control.

[0082] In one embodiment, the bridge arm current cooperative suppression module 604 is specifically configured to:

[0083] The bridge arm current is cooperatively suppressed according to the reference waves of the upper bridge arm and the lower bridge arm after balanced control, and the d-axis reference wave and the q-axis reference wave after adding virtual impedance.

[0084] An embodiment of the present invention further provides a computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the above-mentioned method for suppressing the bridge arm current of the flexible direct current transmission system is implemented.

[0085] An embodiment of the present invention further provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the method for suppressing the bridge arm current of the flexible direct current transmission system is implemented.

[0086] An embodiment of the present invention further provides a computer program product, which includes a computer program. When the computer program is executed by a processor, the method for suppressing the bridge arm current of the flexible direct current transmission system is implemented.

[0087] In an embodiment of the present invention, the bridge arm current values of all phases and the average voltage of each phase submodule in the flexible direct current transmission system are obtained in real time; when an unbalanced fault occurs in the flexible direct current transmission system or the fault is restored, the virtual impedance value in the controller with the virtual impedance is dynamically adjusted according to the maximum bridge arm current value among the bridge arm current values of all phases; the virtual impedance value is positively correlated with the bridge arm current value, and the larger the bridge arm current value, the larger the virtual impedance value; the submodule voltage is balanced according to the average voltage of each phase submodule; based on the dynamically adjusted virtual impedance value and the balanced controlled submodule voltage, the bridge arm current is collaboratively suppressed. In the above process, the embodiment of the present invention reduces the impact of the bridge arm current during an unbalanced fault by dynamically adjusting the synergistic effect of the virtual impedance and the voltage balancing control, thereby solving the limitations of the single control in the prior art and improving the suppression effect of the bridge arm current.

[0088] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0089] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0090] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0091] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0092] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for suppressing arm current of a flexible direct current transmission system, characterized in that: include: Real-time acquisition of all-phase bridge arm current values and average voltage values of each phase submodule in the flexible DC transmission system; When an unbalanced fault occurs in the flexible DC transmission system or the fault is restored, the virtual impedance value in the controller that adds the virtual impedance is dynamically adjusted according to the maximum bridge arm current value among all phase bridge arm current values. The virtual impedance value is positively correlated with the bridge arm current value. The larger the bridge arm current value, the larger the virtual impedance value. The submodule voltage is balanced and controlled according to the average voltage of each phase submodule; Based on the dynamically adjusted virtual impedance value and the balanced controlled submodule voltage, the bridge arm current is collaboratively suppressed. Dynamically adjust the virtual impedance value of the controller adding the virtual impedance according to the maximum bridge arm current value among the bridge arm current values of all phases, including: Based on the maximum bridge arm current value among all phase bridge arm current values, the virtual impedance value is adjusted in sections according to the following threshold rules: in, X1 1.1 times the rated current of the bridge arm, X2 1.2 times the rated current of the bridge arm, X3 The value is between 1.2 times the rated value of the bridge arm current and the preset value of the bridge arm current protection. i armMax is the maximum current value in each bridge arm, R x is the virtual impedance, R 1 is the preset resistance value.

2. The method according to claim 1, wherein After dynamically adjusting the virtual impedance value in the controller adding the virtual impedance according to the maximum bridge arm current value among the bridge arm current values of all phases, the method includes: Get the controller without adding virtual impedance d Axis reference wave and q Axis reference wave; according to d Axis reference wave, q Axis reference wave and virtual impedance value, respectively calculate the value after adding virtual impedance d Axis reference wave and q Axis reference wave.

3. The method according to claim 2, wherein Calculate the value after adding virtual impedance according to the following formulas d Axis reference wave and q Axis reference wave: in, V dref 、 V qref are the controllers without virtual impedance. d Axis reference wave and q Axis reference wave, 、 After adding virtual impedance d Axis reference wave and q Axis reference wave, i d 、i q They are d Shaft current value and q Shaft current value, R x is the virtual impedance.

4. The method according to claim 2, wherein Based on the average voltage of each phase submodule, the submodule voltage is balanced and controlled, including: Obtain the reference waves of the upper bridge arm and the lower bridge arm respectively; The PI regulator is used to obtain the superposition of the reference waves of the upper bridge arm and the lower bridge arm according to the average voltage of each phase sub-module; According to the reference waves of the upper bridge arm and the lower bridge arm and the superposition of the reference waves of the upper bridge arm and the lower bridge arm, the inter-phase sub-module voltages are balanced controlled to obtain the reference waves of the upper bridge arm and the lower bridge arm after balanced control.

5. The method according to claim 4, wherein The reference wave after equalization control is calculated according to the following formula: in, 、 are the reference waves of the upper bridge arm and the lower bridge arm respectively, 、 are the reference wave superposition amounts of the upper bridge arm and the lower bridge arm respectively, 、 They are the reference waves of the upper bridge arm and the lower bridge arm after balanced control.

6. The method according to claim 4, wherein Based on the dynamically adjusted virtual impedance value and the balanced submodule voltage, the bridge arm current is collaboratively suppressed, including: According to the reference wave of the upper bridge arm and the lower bridge arm after balanced control, the virtual impedance is added d Axis reference wave and q Axis reference wave, cooperatively suppressing the bridge arm current.

7. A bridge arm current suppression device for a flexible direct current transmission system, characterized in that: include: The bridge arm current value and each phase submodule voltage average value acquisition module is used to obtain the bridge arm current value and each phase submodule voltage average value of all phases in the flexible DC transmission system in real time; The virtual impedance dynamic adjustment module is used to dynamically adjust the virtual impedance value in the controller that adds virtual impedance according to the maximum bridge arm current value among all phase bridge arm current values when an unbalanced fault occurs or the fault is restored in the flexible DC transmission system. The virtual impedance value is positively correlated with the bridge arm current value. The larger the bridge arm current value, the larger the virtual impedance value. The inter-phase submodule voltage balancing control module is used to balance the submodule voltages according to the average voltage of each phase submodule; The bridge arm current cooperative suppression module is used to cooperatively suppress the bridge arm current based on the dynamically adjusted virtual impedance value and the balanced controlled sub-module voltage; The virtual impedance value dynamic adjustment module is specifically used for: Based on the maximum bridge arm current value among all phase bridge arm current values, the virtual impedance value is adjusted in sections according to the following threshold rules: in, X1 1.1 times the rated current of the bridge arm, X2 1.2 times the rated current of the bridge arm, X3 The value is between 1.2 times the rated value of the bridge arm current and the preset value of the bridge arm current protection. i armMax is the maximum current value in each bridge arm, R x is the virtual impedance, R 1 is the preset resistance value.

8. The device according to claim 7, wherein The virtual impedance value dynamic adjustment module is also used to: Get the controller without adding virtual impedance d Axis reference wave and q Axis reference wave; according to d Axis reference wave, q Axis reference wave and virtual impedance value, respectively calculate the value after adding virtual impedance d Axis reference wave and q Axis reference wave.

9. The device according to claim 8, wherein Calculate the value after adding virtual impedance according to the following formulas d Axis reference wave and q Axis reference wave: in, V dref 、 V qref are the controllers without virtual impedance. d Axis reference wave and q Axis reference wave, 、 After adding virtual impedance d Axis reference wave and q Axis reference wave, i d 、i q They are d Shaft current value and q Shaft current value, R x is the virtual impedance.

10. The device according to claim 8, wherein The inter-phase sub-module voltage balancing control module is specifically used to: Obtain the reference waves of the upper bridge arm and the lower bridge arm respectively; The PI regulator is used to obtain the superposition of the reference waves of the upper bridge arm and the lower bridge arm according to the average voltage of each phase sub-module; According to the reference waves of the upper bridge arm and the lower bridge arm and the superposition of the reference waves of the upper bridge arm and the lower bridge arm, the inter-phase sub-module voltages are balanced controlled to obtain the reference waves of the upper bridge arm and the lower bridge arm after balanced control.

11. The device according to claim 10, wherein The reference wave after equalization control is calculated according to the following formula: in, 、 are the reference waves of the upper bridge arm and the lower bridge arm respectively, 、 are the reference wave superposition amounts of the upper bridge arm and the lower bridge arm respectively, 、 They are the reference waves of the upper bridge arm and the lower bridge arm after balanced control.

12. The device according to claim 10, wherein The bridge arm current cooperative suppression module is specifically used for: According to the reference wave of the upper bridge arm and the lower bridge arm after balanced control, the virtual impedance is added d Axis reference wave and q Axis reference wave, cooperatively suppressing the bridge arm current.

13. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the method according to any one of claims 1 to 6 is implemented.

14. A computer-readable storage medium, characterized in that The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method according to any one of claims 1 to 6 is implemented.

15. A computer program product, characterized in that The computer program product comprises a computer program, and when the computer program is executed by a processor, the method according to any one of claims 1 to 6 is implemented.

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