Bridge-arm current suppression method and apparatus for flexible direct-current transmission system

Abstract

Disclosed in the present invention are a bridge-arm current suppression method and apparatus for a flexible direct-current transmission system. The method comprises: acquiring in real time bridge-arm current values of all phases in a flexible direct-current transmission system, and the average sub-module voltage value of each phase; when the flexible direct-current transmission system undergoes an unbalancing fault or recovers from a fault, on the basis of the maximum bridge-arm current value from among the bridge-arm current values of all phases, dynamically adjusting a virtual impedance value in a controller that is provided with virtual impedance, wherein the virtual impedance value is positively correlated with the bridge-arm current value, and the greater the bridge-arm current value, the greater the virtual impedance value; on the basis of the average sub-module voltage value of each phase, performing equalization control over sub-module voltages; and on the basis of the dynamically adjusted virtual impedance value, and the sub-module voltages that have been subjected to equalization control, performing cooperative suppression on bridge-arm currents. The present invention can reduce the impact from bridge-arm currents when an unbalancing fault occurs, overcome the limitation of single control in the prior art, and improve the effect of suppressing the bridge-arm currents.

Description

Methods and devices for suppressing bridge arm current in flexible DC transmission systems Technical Field

[0001] This invention relates to the field of flexible DC transmission technology in power systems, and particularly to a method and apparatus for suppressing bridge arm current in flexible DC transmission systems. Background Technology

[0002] This section is intended to provide background or context for the embodiments of the invention set forth in the claims. The description herein is not an admission that it is prior art simply because it is included in this section.

[0003] Flexible DC transmission systems employ voltage source converters, enabling independent control of active and reactive power while avoiding commutation failure issues common in conventional DC systems. Modular multilevel converters, with their modular design and nearest-level approximation modulation, reduce harmonic content and switching losses, and are widely used in HVDC transmission systems. However, simulations have revealed that when a two-phase imbalance fault occurs in the sending-end controlled DC voltage mode of a flexible DC transmission system, the sudden change in system voltage leads to a large arm current. Existing technologies have limited effectiveness in suppressing this arm current, failing to meet practical requirements. Summary of the Invention

[0004] This invention provides a method for suppressing arm current in a flexible DC transmission system to address the problem of poor arm current suppression in the prior art when a two-phase imbalance fault occurs. The method includes:

[0005] Real-time acquisition of the arm current values ​​of all phases and the average voltage of each phase submodule in the flexible DC transmission system;

[0006] When an unbalanced fault occurs or a fault is recovered in the flexible DC transmission system, the virtual impedance value in the controller that adds 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 voltage of each sub-module is balanced based on the average voltage of each phase sub-module.

[0008] Based on the dynamically adjusted virtual impedance value and the submodule voltage after equalization control, the bridge arm current is suppressed in a coordinated manner.

[0009] This invention also provides a bridge arm current suppression device for a flexible DC transmission system to solve the problem of poor bridge arm current suppression effect when a two-phase imbalance fault occurs in the prior art. The device includes:

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

[0011] The virtual impedance value dynamic adjustment module is used to dynamically adjust the virtual impedance value in the controller based on the maximum bridge arm current value among all phase bridge arm current values ​​when an unbalanced fault occurs or a fault is recovered 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 phase-to-phase submodule voltage equalization control module is used to equalize the voltage of the submodules based on the average voltage of each phase submodule.

[0013] The bridge arm current collaborative suppression module is used to collaboratively suppress the bridge arm current based on the dynamically adjusted virtual impedance value and the submodule voltage after equalization control.

[0014] This invention also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the above-described method for suppressing the arm current of a flexible DC transmission system.

[0015] This invention also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described method for suppressing bridge arm current in a flexible DC transmission system.

[0016] This invention also provides a computer program product, which includes a computer program that, when executed by a processor, implements the above-described method for suppressing bridge arm current in a flexible DC transmission system.

[0017] In this embodiment of the invention, the arm current values ​​of all phases and the average voltage of each phase submodule in the flexible DC transmission system are acquired in real time. When an unbalanced fault occurs or the fault is recovered in the flexible DC transmission system, the virtual impedance value in the controller is dynamically adjusted based on the maximum arm current value among all phase arm current values. The virtual impedance value is positively correlated with the arm current value; the larger the arm current value, the larger the virtual impedance value. The submodule voltage is balanced based on the average voltage of each phase submodule. Based on the dynamically adjusted virtual impedance value and the balanced submodule voltage, the arm current is synergistically suppressed. In the above process, this embodiment of the invention reduces the impact of arm current during unbalanced faults by dynamically adjusting the synergistic effect of virtual impedance and voltage balancing control, overcoming the limitations of single control in the prior art, thereby improving the suppression effect of arm current. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. 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 effort. In the drawings:

[0019] Figure 1 is a flowchart of the arm current suppression method of the flexible DC transmission system in an embodiment of the present invention;

[0020] Figure 2 is a schematic diagram of suppressing bridge arm current through virtual impedance in an embodiment of the present invention;

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

[0022] Figure 4 is a flowchart of obtaining the reference waves of the upper and lower bridge arms after equalization control in an embodiment of the present invention.

[0023] Figure 5 is a schematic diagram of suppressing bridge arm current through phase-to-phase submodule voltage equalization control in an embodiment of the present invention;

[0024] Figure 6 is a schematic diagram of the bridge arm current suppression device of the flexible DC transmission system in an embodiment of the present invention. Embodiments of the present invention

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Here, the illustrative 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 all comply with the relevant provisions of national laws and regulations.

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

[0028] Step 101: Real-time acquisition of the bridge arm current value 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 or a fault is recovered in the flexible DC transmission system, the virtual impedance value in the controller that adds 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, and the larger the bridge arm current value, the larger the virtual impedance value.

[0030] Step 103: Perform voltage equalization control on the sub-modules based on the average voltage of each phase sub-module;

[0031] Step 104: Based on the dynamically adjusted virtual impedance value and the submodule voltage after equalization control, the bridge arm current is collaboratively suppressed. Each step is explained in detail below.

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

[0033] In a specific embodiment, during an unbalanced fault or fault recovery, a sudden voltage change occurs at the midpoint of the upper and lower bridge arms, causing the capacitors in the upper and lower bridge arms to charge and discharge respectively, resulting in a rapid increase in the bridge arm current. To address the above problems, this invention proposes the following solutions for unbalanced faults or fault recovery in flexible DC transmission systems:

[0034] In step 102, when an unbalanced fault occurs or a fault is recovered in the flexible DC transmission system, the virtual impedance value in the controller that adds 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.

[0035] In one embodiment, dynamically adjusting the virtual impedance value in the controller that incorporates the virtual impedance based on the maximum bridge arm current value among all phase bridge arm current values ​​includes:

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

[0037]

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

[0039] In a specific embodiment, Figure 2 shows a schematic diagram of suppressing bridge arm current through virtual impedance in an embodiment of the present invention. dcref U is the reference value for DC voltage. dc Q is the actual value of the DC voltage. refHere, R1 represents the reactive power reference value, Q represents the actual reactive power value, wL represents the fundamental angular frequency, and L represents the equivalent inductance on the AC side. An adaptive virtual impedance is added to the controller, adjusting its magnitude according to the bridge arm current. The larger the bridge arm current, the larger the virtual impedance, thus suppressing the bridge arm current surge. Since a larger bridge arm current requires a larger virtual impedance to better reduce the bridge arm current surge, R1... <R2<R3<R4。

[0040] Figure 3 is a flowchart illustrating the calculation of the d-axis reference wave and 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 that adds virtual impedance based on the maximum bridge arm current value among all phase bridge arm current values, the process includes:

[0041] Step 301: Obtain the d-axis reference wave and q-axis reference wave of the controller without virtual impedance;

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

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

[0044]

[0045] Among them, V dref V qref These are the d-axis and q-axis reference waveforms for the controller without virtual impedance, respectively. , These are the d-axis and q-axis reference waves after adding virtual impedance, respectively. d i q These are the d-axis current value and the q-axis current value, respectively, R x This is a virtual impedance.

[0046] In step 103, the voltage of the submodule is balanced based on the average voltage of each phase submodule.

[0047] Figure 4 is a flowchart illustrating the acquisition of reference waves for the upper and lower bridge arms after equalization control in an embodiment of the present invention. In one embodiment, equalization control of the sub-module voltage is performed based on the average voltage value of each phase sub-module, including:

[0048] Step 401: Obtain the reference waves for the upper and lower bridge arms respectively;

[0049] Step 402: Using a PI regulator, the reference wave superposition of the upper and lower bridge arms is obtained based on the average voltage of each phase submodule.

[0050] Step 403: Based on the reference waves of the upper and lower bridge arms and the superposition of the reference waves of the upper and lower bridge arms, perform equalization control on the voltage of the phase sub-modules to obtain the reference waves of the upper and lower bridge arms after equalization control.

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

[0052]

[0053] in, , These are the reference waves for the upper and lower bridge arms, respectively. , These are the superposition amounts of reference waves for the upper and lower bridge arms, respectively. , These are the reference waves for the upper and lower bridge arms after equalization control, respectively.

[0054] Figure 5 shows a schematic diagram of suppressing bridge arm current through phase-to-phase submodule voltage equalization control in an embodiment of the present invention. , These are the reference waves for the upper and lower bridge arms, respectively. , These are the superposition amounts of reference waves for the upper and lower bridge arms, respectively. , These are the reference waves for the upper and lower bridge arms after equalization control. To further suppress the bridge arm current, equalization control of the phase-to-phase submodule voltage is added to reduce the charging and discharging of the capacitors when the voltage changes at the midpoint of the upper and lower bridge arms, thereby reducing the bridge arm inrush current.

[0055] In a specific embodiment, as shown in Figure 4, the phase A submodule voltage balancing control is illustrated using this example. First, the total average value U of the six bridge arm voltages is calculated. cav The average voltage U of phase A cav_A The difference is calculated, and after passing through the PI regulator, the superposition amount of the bridge arm voltage reference wave duref is obtained. 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 to charge phase A and increase the average voltage of phase A. 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 decreased to discharge phase A and decrease the average voltage of phase A.

[0056] In step 104, the bridge arm current is synergistically suppressed based on the dynamically adjusted virtual impedance value and the submodule voltage after equalization control.

[0057] In one embodiment, the arm current is collaboratively suppressed based on the dynamically adjusted virtual impedance value and the submodule voltage after equalization control, including:

[0058] Based on the reference waves of the upper and lower bridge arms after equalization control, and the d-axis and q-axis reference waves after adding virtual impedance, the bridge arm current is synergistically suppressed.

[0059] In this embodiment of the invention, an adaptive virtual impedance is first added to the controller. The size of the virtual impedance is adaptively adjusted according to the magnitude of the bridge arm current. The larger the bridge arm current, the larger the virtual impedance, thereby suppressing the impact of the bridge arm current. Since the voltage change at the midpoint of the upper and lower bridge arms is large when an unbalanced fault occurs or a fault is recovered in the AC system, the current impact of the upper or lower bridge arm of that phase will also be large. To further suppress the bridge arm current impact, phase-to-phase submodule voltage equalization control is added to reduce the voltage change at the midpoint of the upper and lower bridge arms, thereby further reducing the impact of the bridge arm current.

[0060] This invention also provides a bridge arm current suppression device for a flexible DC transmission system, as described in the following embodiments. Since the principle by which this device solves the problem is similar to the bridge arm current suppression method for flexible DC transmission systems, the implementation of this device can refer to the implementation of the bridge arm current suppression method for flexible DC transmission systems; repeated details will not be elaborated further.

[0061] Figure 6 is a schematic diagram of the bridge arm current suppression device of the flexible DC transmission system in an embodiment of the present invention. The device includes:

[0062] The arm current value and average voltage of each phase submodule acquisition module 601 is used to acquire the arm current value and average voltage of each phase submodule of all phases in the flexible DC transmission system in real time.

[0063] The virtual impedance value dynamic adjustment module 602 is used to dynamically adjust the virtual impedance value in the controller added to the virtual impedance according to the maximum bridge arm current value among all phase bridge arm current values ​​when an unbalanced fault occurs or a fault is recovered 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 phase-to-phase submodule voltage equalization control module 603 is used to perform equalization control on the submodule voltage according to the average voltage of each phase submodule.

[0064] The bridge arm current collaborative suppression module 604 is used to collaboratively suppress the bridge arm current based on the dynamically adjusted virtual impedance value and the submodule voltage after equalization control.

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

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

[0067]

[0068] Where 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 a value between 1.2 times the rated value of the bridge arm current and the preset value of the bridge arm current protection. armMax R is the maximum current value in each bridge arm. x R1 is a virtual impedance and a preset resistance value.

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

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

[0071] Based on the d-axis reference wave, q-axis reference wave, and virtual impedance value, calculate the d-axis reference wave and q-axis reference wave after adding virtual impedance.

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

[0073]

[0074] Among them, V dref V qref These are the d-axis and q-axis reference waveforms for the controller without virtual impedance, respectively. , These are the d-axis and q-axis reference waves after adding virtual impedance, respectively. d i q These are the d-axis current value and the q-axis current value, respectively, R x This is a virtual impedance.

[0075] In one embodiment, the phase-to-phase submodule voltage equalization control module 603 is specifically used for:

[0076] The reference waves for the upper and lower bridge arms are obtained separately.

[0077] The reference wave superposition of the upper and lower bridge arms is obtained by using a PI regulator based on the average voltage of each phase submodule.

[0078] Based on the reference waves of the upper and lower bridge arms and the superposition of the reference waves of the upper and lower bridge arms, the voltage of the phase-to-phase submodules is balanced to obtain the reference waves of the upper and lower bridge arms after the balanced control.

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

[0080]

[0081] in, , These are the reference waves for the upper and lower bridge arms, respectively. , These are the superposition amounts of reference waves for the upper and lower bridge arms, respectively. , These are the reference waves for the upper and lower bridge arms after equalization control, respectively.

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

[0083] Based on the reference waves of the upper and lower bridge arms after equalization control, and the d-axis and q-axis reference waves after adding virtual impedance, the bridge arm current is synergistically suppressed.

[0084] This invention also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the above-described method for suppressing the arm current of a flexible DC transmission system.

[0085] This invention also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described method for suppressing bridge arm current in a flexible DC transmission system.

[0086] This invention also provides a computer program product, which includes a computer program that, when executed by a processor, implements the above-described method for suppressing bridge arm current in a flexible DC transmission system.

[0087] In this embodiment of the invention, the arm current values ​​of all phases and the average voltage of each phase submodule in the flexible DC transmission system are acquired in real time. When an unbalanced fault occurs or the fault is recovered in the flexible DC transmission system, the virtual impedance value in the controller is dynamically adjusted based on the maximum arm current value among all phase arm current values. The virtual impedance value is positively correlated with the arm current value; the larger the arm current value, the larger the virtual impedance value. The submodule voltage is balanced based on the average voltage of each phase submodule. Based on the dynamically adjusted virtual impedance value and the balanced submodule voltage, the arm current is synergistically suppressed. In the above process, this embodiment of the invention reduces the impact of arm current during unbalanced faults by dynamically adjusting the synergistic effect of virtual impedance and voltage balancing control, overcoming the limitations of single control in the prior art, thereby improving the suppression effect of arm current.

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

[0089] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations 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, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in one or more blocks of the flowchart illustrations and / or one or more blocks of the block diagrams.

[0090] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means that implement the functions specified in one or more flowcharts and / or one or more block diagrams.

[0091] These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, such that the instructions, which execute on the computer or other programmable apparatus, provide steps for implementing the functions specified in one or more flowcharts and / or one or more block diagrams.

[0092] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are 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 within the scope of protection of the present invention.

Claims

1. A method for suppressing arm current in a flexible DC transmission system, characterized in that, include: Real-time acquisition of the arm current values ​​of all phases and the average voltage of each phase submodule in the flexible DC transmission system; When an unbalanced fault occurs or a fault is recovered in the flexible DC transmission system, the virtual impedance value in the controller that adds 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 voltage of each sub-module is balanced based on the average voltage of each phase sub-module. Based on the dynamically adjusted virtual impedance value and the submodule voltage after equalization control, the bridge arm current is suppressed in a coordinated manner.

2. The method as described in claim 1, characterized in that, Based on the maximum bridge arm current value among all phase bridge arm current values, the virtual impedance value in the controller that incorporates the virtual impedance is dynamically adjusted, including: Based on the maximum bridge arm current value among all phase bridge arm current values, adjust the virtual impedance value in segments according to the following threshold rules: Where 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 a value between 1.2 times the rated value of the bridge arm current and the preset value of the bridge arm current protection. armMax R represents the maximum current value in each bridge arm. x R1 is a virtual impedance and a preset resistance value.

3. The method as described in claim 2, characterized in that, After dynamically adjusting the virtual impedance value in the controller based on the maximum bridge arm current value among all phase bridge arm current values, the following steps are included: Obtain the d-axis and q-axis reference waveforms of the controller without virtual impedance; Based on the d-axis reference wave, q-axis reference wave, and virtual impedance value, calculate the d-axis reference wave and q-axis reference wave after adding virtual impedance.

4. The method as described in claim 3, characterized in that, Calculate the d-axis and q-axis reference waves after adding virtual impedance using the following formulas: Among them, V dref V qref These are the d-axis and q-axis reference waveforms for the controller without virtual impedance, respectively. 、 These are the d-axis and q-axis reference waves after adding virtual impedance, respectively. d i q These are the d-axis current value and the q-axis current value, respectively, R x This is a virtual impedance.

5. The method as described in claim 3, characterized in that, Based on the average voltage of each phase submodule, the submodule voltage is balanced and controlled, including: The reference waves for the upper and lower bridge arms are obtained separately. The reference wave superposition of the upper and lower bridge arms is obtained by using a PI regulator based on the average voltage of each phase submodule. Based on the reference waves of the upper and lower bridge arms and the superposition of the reference waves of the upper and lower bridge arms, the voltage of the phase-to-phase submodules is balanced to obtain the reference waves of the upper and lower bridge arms after the balanced control.

6. The method as described in claim 5, characterized in that, Calculate the reference wave after equalization control using the following formula: in, 、 These are the reference waves for the upper and lower bridge arms, respectively. 、 These are the superposition amounts of reference waves for the upper and lower bridge arms, respectively. 、 These are the reference waves for the upper and lower bridge arms after equalization control, respectively.

7. The method as described in claim 5, characterized in that, Based on the dynamically adjusted virtual impedance value and the submodule voltage after equalization control, the bridge arm current is collaboratively suppressed, including: Based on the reference waves of the upper and lower bridge arms after equalization control, and the d-axis and q-axis reference waves after adding virtual impedance, the bridge arm current is synergistically suppressed.

8. A bridge arm current suppression device for a flexible DC transmission system, characterized in that, include: The arm current value and average voltage of each phase submodule acquisition module is used to acquire the arm current value and average voltage of each phase submodule of all phases in the flexible DC transmission system in real time. The virtual impedance value dynamic adjustment module is used to dynamically adjust the virtual impedance value in the controller based on the maximum bridge arm current value among all phase bridge arm current values ​​when an unbalanced fault occurs or a fault is recovered 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 phase-to-phase submodule voltage equalization control module is used to equalize the voltage of the submodules based on the average voltage of each phase submodule. The bridge arm current collaborative suppression module is used to collaboratively suppress the bridge arm current based on the dynamically adjusted virtual impedance value and the submodule voltage after equalization control.

9. The apparatus as claimed in claim 8, characterized in that, The virtual impedance dynamic adjustment module is specifically used for: Based on the maximum bridge arm current value among all phase bridge arm current values, adjust the virtual impedance value in segments according to the following threshold rules: Where 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 a value between 1.2 times the rated value of the bridge arm current and the preset value of the bridge arm current protection. armMax R represents the maximum current value in each bridge arm. x R1 is a virtual impedance and a preset resistance value.

10. The apparatus as claimed in claim 9, characterized in that, The virtual impedance dynamic adjustment module is also used for: Obtain the d-axis and q-axis reference waveforms of the controller without virtual impedance; Based on the d-axis reference wave, q-axis reference wave, and virtual impedance value, calculate the d-axis reference wave and q-axis reference wave after adding virtual impedance.

11. The apparatus as claimed in claim 10, characterized in that, Calculate the d-axis and q-axis reference waves after adding virtual impedance using the following formulas: Among them, V dref V qref These are the d-axis and q-axis reference waveforms for the controller without virtual impedance, respectively. 、 These are the d-axis and q-axis reference waves after adding virtual impedance, respectively. d i q These are the d-axis current value and the q-axis current value, respectively, R x This is a virtual impedance.

12. The apparatus as claimed in claim 10, characterized in that, The phase-to-phase submodule voltage equalization control module is specifically used for: The reference waves for the upper and lower bridge arms are obtained separately. The reference wave superposition of the upper and lower bridge arms is obtained by using a PI regulator based on the average voltage of each phase submodule. Based on the reference waves of the upper and lower bridge arms and the superposition of the reference waves of the upper and lower bridge arms, the voltage of the phase-to-phase submodules is balanced to obtain the reference waves of the upper and lower bridge arms after the balanced control.

13. The apparatus as claimed in claim 12, characterized in that, Calculate the reference wave after equalization control using the following formula: in, 、 These are the reference waves for the upper and lower bridge arms, respectively. 、 These are the superposition amounts of reference waves for the upper and lower bridge arms, respectively. 、 These are the reference waves for the upper and lower bridge arms after equalization control, respectively.

14. The apparatus as claimed in claim 12, characterized in that, The bridge arm current collaborative suppression module is specifically used for: Based on the reference waves of the upper and lower bridge arms after equalization control, and the d-axis and q-axis reference waves after adding virtual impedance, the bridge arm current is synergistically suppressed.

15. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the method of any one of claims 1 to 7.

16. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the method of any one of claims 1 to 7.

17. A computer program product, characterized in that, The computer program product includes a computer program that, when executed by a processor, implements the method of any one of claims 1 to 7.

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