Bridge arm current suppression method and device of flexible direct current power transmission system

Abstract

The invention discloses a bridge arm current suppression method and device for a flexible direct-current power transmission system. The method comprises the following steps: acquiring bridge arm current values of all phases in the flexible direct-current power transmission system and a voltage average value of each phase of sub-module in real time; when an unbalanced fault occurs in the flexible direct current power transmission system or the fault is recovered, according to the maximum bridge arm current value in the bridge arm current values of all phases, dynamically adjusting the virtual impedance value added into the controller of the virtual impedance; the virtual impedance value is in positive correlation with the bridge arm current value, and the larger the bridge arm current value is, the larger the virtual impedance value is; performing balance control on the sub-module voltage according to the average value of the sub-module voltage of each phase; and carrying out cooperative suppression on the bridge arm current based on the dynamically adjusted virtual impedance value and the sub-module voltage after balance control. According to the invention, the impact of the bridge arm current during an unbalanced fault can be reduced, the limitation of single control in the prior art is solved, and the suppression effect of the bridge arm current is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible direct current transmission of electric 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 recited in the claims. No admission is made that the description herein is prior art by inclusion in this section.

[0003] The flexible DC transmission system adopts a voltage source converter, which can achieve independent control of active and reactive power, while avoiding the commutation failure problem of conventional DC systems. The modular multilevel converter adopts modular design and nearest level approximation modulation, which reduces the harmonic content and switching loss, and is widely used in high-voltage DC transmission systems. However, it was found in the simulation that when a two-phase unbalanced fault occurs in the flexible DC transmission system under the DC voltage control mode at the sending end, a large bridge arm current is generated due to the sudden change of the system voltage. The suppression effect of the bridge arm current in the existing technology is very limited and cannot meet the actual needs. Summary of the invention

[0004] The embodiment of the present invention provides a bridge arm current suppression method of 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 method includes:

[0005] Obtain the bridge arm current value 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 or fault recovery occurs in the flexible DC transmission system, 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;

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

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

[0009] The embodiment of the present invention further provides a bridge arm current suppression device of 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] A bridge arm current value and each-phase submodule voltage average value acquisition module is used to 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;

[0011] The virtual impedance value dynamic adjustment module is used to dynamically adjust 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 when an unbalanced fault occurs in the flexible DC transmission system or the fault is restored; 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;

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

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

[0014] An embodiment of the present invention also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the above-mentioned bridge arm current suppression method of the flexible direct current transmission system when executing the computer program.

[0015] An embodiment of the present invention further provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the bridge arm current suppression method of the above-mentioned 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 bridge arm current suppression method 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 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 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. 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 synergy of the virtual impedance and the voltage balancing control, solves the limitations of the single control in the prior art, and thus improves 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 use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0019] Figure 1 Flow chart of a bridge arm current suppression method of a flexible DC transmission system according to an embodiment of the present invention;

[0020] Figure 2 A 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 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 It is a schematic diagram of suppressing the 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 of a flexible DC transmission system in an embodiment of the present invention. DETAILED DESCRIPTION

[0025] To make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the embodiments of the present invention are further described in detail below in conjunction with 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 the technical solution of this application comply with the relevant provisions of national laws and regulations.

[0027] Figure 1 Flow chart of a bridge arm current suppression method of a flexible direct current transmission system according to an embodiment of the present invention, the method comprising:

[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 direct current transmission system;

[0029] Step 102, when an unbalanced fault occurs in the flexible direct current transmission system or the fault is restored, dynamically adjust 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 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 balanced control on the submodule voltages according to the average voltage of each phase submodule;

[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 restored, the voltage at the midpoint of the upper bridge arm and the lower bridge arm will suddenly change, the capacitors in the upper bridge arm and the lower bridge arm will be charged and discharged respectively, and the bridge arm current will increase rapidly. In order to solve the above problems, the present invention proposes the following when an unbalanced fault occurs or a fault is restored 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] According to the maximum bridge arm current value among the bridge arm current values ​​of all phases, 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 FIG. 1 is a schematic diagram showing a method of suppressing the bridge arm current by virtual impedance in an embodiment of the present invention.dcref 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, 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. As the bridge arm current increases, the larger the virtual impedance required can better reduce the bridge arm current impact, where R1 <R2<R3<R4。

[0040] Figure 3 The flowchart of calculating the d-axis reference wave and the q-axis reference wave after adding the virtual impedance in an embodiment of the present invention, in one embodiment, 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, includes:

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

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

[0043] In one embodiment, the d-axis reference wave and the q-axis reference wave after adding the virtual impedance are calculated respectively 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 The flowchart of obtaining the reference wave of the upper bridge arm and the lower bridge arm after balanced control in an embodiment of the present invention, in one embodiment, the submodule voltage is balanced controlled according to the average value of the submodule voltage of each phase, including:

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

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

[0050] Step 403 , balance control is performed 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 balance 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 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 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. In order to further suppress the bridge arm current, balanced control of the interphase submodule voltage is added to reduce the charging and discharging of the capacitor when the voltage at the midpoint of the upper bridge arm and the lower bridge arm suddenly changes, thereby achieving the purpose of reducing the bridge arm impact current.

[0055] In a specific embodiment, Figure 4 As shown, phase A is taken as an example to illustrate the voltage balancing control of the phase submodules. 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, based on the dynamically adjusted virtual impedance value and the balanced controlled submodule voltage, the bridge arm current is cooperatively suppressed, including:

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

[0059] In the embodiment of the present invention, an adaptive virtual impedance is first added to the controller, and the size of the virtual impedance is adaptively adjusted 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 voltage mutation at the midpoint of the upper bridge arm and the lower bridge arm is large when an unbalanced fault occurs or the fault is restored in the AC system, the current impact of the upper bridge arm or the lower bridge arm of the phase will also be large. In order to further suppress the impact of the bridge arm current, the inter-phase sub-module voltage balancing control is added to reduce the voltage mutation at the midpoint of the upper bridge arm and the lower bridge arm, thereby further reducing the impact of the bridge arm current.

[0060] The present invention also provides a bridge arm current suppression device for a flexible DC power transmission system in an embodiment, as described in the following embodiment. Since the principle of the problem solved by the device is similar to the bridge arm current suppression method for a flexible DC power transmission system, the implementation of the device can refer to the implementation of the bridge arm current suppression method for a flexible DC power transmission system, and the repeated parts will not be repeated.

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

[0062] The bridge arm current value and each phase submodule voltage average value acquisition module 601 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;

[0063] The virtual impedance value dynamic adjustment module 602 is used to dynamically adjust 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 when an unbalanced fault occurs in the flexible direct current transmission system or the fault is restored; 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 inter-phase submodule voltage balancing control module 603 is used to balance the submodule voltage according to the average value of the submodule voltage of each phase;

[0064] The bridge arm current cooperative suppression module 604 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.

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

[0066] According to the maximum bridge arm current value among the bridge arm current values ​​of all phases, 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 used to:

[0070] Obtaining the d-axis reference wave and the 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 respectively 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 used to:

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

[0077] The PI regulator is used to obtain the reference wave superposition of the upper bridge arm and the lower bridge arm 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 interphase submodule 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 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 used to:

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

[0084] An embodiment of the present invention also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the above-mentioned bridge arm current suppression method of the flexible direct current transmission system when executing the computer program.

[0085] An embodiment of the present invention further provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the bridge arm current suppression method of the above-mentioned 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 bridge arm current suppression method 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 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 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. 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 synergy of the virtual impedance and the voltage balancing control, solves the limitations of the single control in the prior art, and thus improves the suppression effect of the bridge arm current.

[0088] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. 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 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 flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, 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 generate 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 flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that specifies the functions of a block or multiple blocks.

[0090] These computer program instructions may also be stored in a computer readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture including an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A 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 operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified 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: Obtain the bridge arm current value of all phases and the average voltage of each phase submodule in the flexible DC transmission system in real time; When an unbalanced fault or fault recovery occurs in the flexible DC transmission system, 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; According to the average voltage of each phase submodule, the submodule voltage is balanced and controlled; Based on the dynamically adjusted virtual impedance value and the balanced controlled submodule voltage, the bridge arm current is cooperatively suppressed.

2. The method according to claim 1, characterized in that According to the maximum bridge arm current value among the bridge arm current values ​​of all phases, the virtual impedance value in the controller adding the virtual impedance is dynamically adjusted, including: According to the maximum bridge arm current value among the bridge arm current values ​​of all phases, the virtual impedance value is adjusted in sections according to the following threshold rules: 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.

3. The method according to claim 2, characterized in that 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: Obtaining the d-axis reference wave and the q-axis reference wave of the controller without adding virtual impedance; 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.

4. The method according to claim 3, characterized in that The d-axis reference wave and q-axis reference wave after adding virtual impedance are calculated according to the following formulas: 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.

5. The method according to claim 3, characterized in that According to the average voltage of each phase submodule, the submodule voltage is balanced and controlled, including: Obtain reference waves of the upper bridge arm and the lower bridge arm respectively; The PI regulator is used to obtain the reference wave superposition of the upper bridge arm and the lower bridge arm according to the average voltage of each phase submodule; 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 interphase submodule voltages are balanced controlled to obtain the reference waves of the upper bridge arm and the lower bridge arm after balanced control.

6. The method according to claim 5, characterized in that Calculate the reference wave after equalization control 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 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.

7. The method according to claim 5, characterized in that Based on the dynamically adjusted virtual impedance value and the balanced controlled submodule voltage, the bridge arm current is cooperatively suppressed, including: According to the reference waves of the upper bridge arm and the lower bridge arm after balanced control, the d-axis reference wave and the q-axis reference wave after adding virtual impedance, the bridge arm current is cooperatively suppressed.

8. A bridge arm current suppression device for a flexible DC transmission system, characterized in that: include: A bridge arm current value and each-phase submodule voltage average value acquisition module is used to 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; The virtual impedance value dynamic adjustment module is used to dynamically adjust 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 when an unbalanced fault occurs in the flexible DC transmission system or the fault is restored; 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 inter-phase submodule voltage balancing control module is used to balance the submodule voltage according to the average value of each phase submodule voltage; 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.

9. The device according to claim 8, characterized in that The virtual impedance value dynamic adjustment module is specifically used for: According to the maximum bridge arm current value among the bridge arm current values ​​of all phases, the virtual impedance value is adjusted in sections according to the following threshold rules: 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.

10. The device according to claim 9, characterized in that The virtual impedance value dynamic adjustment module is also used for: Obtaining the d-axis reference wave and the q-axis reference wave of the controller without adding virtual impedance; 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.

11. The device according to claim 10, characterized in that The d-axis reference wave and q-axis reference wave after adding virtual impedance are calculated according to the following formulas: 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.

12. The device according to claim 10, characterized in that The inter-phase sub-module voltage balancing control module is specifically used for: Obtain reference waves of the upper bridge arm and the lower bridge arm respectively; The PI regulator is used to obtain the reference wave superposition of the upper bridge arm and the lower bridge arm according to the average voltage of each phase submodule; 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 interphase submodule voltages are balanced controlled to obtain the reference waves of the upper bridge arm and the lower bridge arm after balanced control.

13. The device according to claim 12, characterized in that Calculate the reference wave after equalization control 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 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.

14. The device according to claim 12, characterized in that The bridge arm current cooperative suppression module is specifically used for: According to the reference waves of the upper bridge arm and the lower bridge arm after balanced control, the d-axis reference wave and the q-axis reference wave after adding virtual impedance, the bridge arm current is cooperatively 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, the method according to any one of claims 1 to 7 is implemented.

16. 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 7 is implemented.

17. 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 7 is implemented.

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