A bridge arm parallel MMC parallel sub-bridge arm current sharing control method and device

Abstract

The present invention discloses a method and device for controlling the equal current of parallel sub-bridge arms of a parallel MMC bridge arm, comprising: obtaining the circulating current value between the parallel sub-bridge arms of sub-bridge arm 1 and sub-bridge arm 2; calculating the bridge arm modulation wave superposition amount by a damping coefficient based on the circulating current value between the parallel sub-bridge arms; distributing the bridge arm modulation wave superposition amount according to a preset distribution ratio, and obtaining the modulation wave superposition amount of sub-bridge arm 1 and the modulation wave superposition amount of sub-bridge arm 2 after amplitude limiting processing; combining the bridge arm modulation wave superposition amount to obtain the final modulation wave of sub-bridge arm 1 and the final modulation wave of sub-bridge arm 2, respectively, and then adjusting the output voltage of sub-bridge arm 1 and sub-bridge arm 2 to suppress the circulating current between the parallel sub-bridge arms. The bridge arm modulation wave superposition amount is obtained by obtaining the bridge arm currents of the two sub-bridge arms, and is distributed according to different preset distribution ratios of a specific device to obtain the final modulation wave of each sub-bridge arm, and then adjusting the sub-bridge arm output voltage to suppress the circulating current between the parallel sub-bridge arms.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible direct current transmission control, and in particular to a method and device for controlling current sharing of parallel sub-bridge arms of a parallel-bridge-arm MMC. Background Art

[0002] Flexible DC transmission technology based on modular multilevel converters (MMCs) has been widely adopted due to its advantages, including independent and flexible control of active and reactive power, no commutation failure, no need for reactive power compensation, and easy expansion. In recent years, with the implementation of demonstration projects and the growing demand for large-scale energy transmission in China, the demand for flexible DC transmission capacity has continued to increase. Since conventional UHVDC transmission lines are mostly ±800kV / 8000MW, building a ±800kV UHVDC grid and upgrading flexible DC systems to ±800kV / 8000MW has become necessary to better match existing or newly built conventional UHVDC lines. To meet this demand, system DC currents reach 5000A. Based on the conventional MMC topology and design, the peak current in the MMC bridge arm approaches 5500A. However, the highest specification of IGBT devices currently in use in China is only 4500V / 3000A, which is not suitable for such high current applications. This has, to a certain extent, hindered the promotion of flexible DC technology in the UHV and large-capacity sectors.

[0003] Given the current limitations of existing devices, developing a parallel-arm MMC (Multi-Channel Converter) is a viable compromise solution. This approach utilizes two sub-arms with identical structures and parameters in parallel to form one arm of the MMC. This reduces the current stress of a single sub-arm by half, allowing the use of existing 4500V / 3000A IGBTs to meet system requirements.

[0004] For the upper and lower bridge arms of each phase unit, although the two parallel sub-bridge arms have identical structures and parameter requirements, inevitable differences in component manufacturing can still lead to differences in the output voltages of the two sub-bridge arms, which in turn causes circulating currents between the parallel sub-bridge arms. This circulating current is determined by the differences between the sub-bridge arms and the bridge arm reactance values. When the differences are large, it cannot be ignored and can easily lead to prolonged overload or even overcurrent in individual sub-bridge arms, threatening the safe and stable operation of the equipment. Therefore, it is necessary to adopt measures to effectively suppress the circulating currents between the parallel sub-bridge arms. Summary of the Invention

[0005] The purpose of the embodiments of the present invention is to provide a method and device for controlling the equal current of the parallel sub-bridge arms of a parallel-bridge-arm MMC. The method obtains the bridge arm currents of the two sub-bridge arms and obtains the superposition of the bridge arm modulation waves. The superposition is distributed according to the preset distribution ratio of the specific device to obtain the final modulation waves of the two sub-bridge arms, and then adjusts the output voltage of the sub-bridge arms to suppress the circulating current between the parallel sub-bridge arms.

[0006] To solve the above technical problems, a first aspect of an embodiment of the present invention provides a method for controlling current sharing of parallel sub-bridge arms in a parallel-arm MMC. The upper bridge arm and the lower bridge arm of each phase in the parallel-arm MMC are each composed of a first sub-bridge arm and a second sub-bridge arm of the same structure connected in parallel, comprising the following steps:

[0007] Obtaining a circulating current value between the parallel sub-bridge arms of the first sub-bridge arm and the second sub-bridge arm;

[0008] Calculating the superposition amount of the bridge arm modulation wave by using the damping coefficient according to the circulating current value between the parallel sub-bridge arms;

[0009] The superposition amount of the modulated wave of the bridge arm is distributed according to a preset distribution ratio, and after amplitude limiting processing, the superposition amount of the modulated wave of the sub-bridge arm 1 and the superposition amount of the modulated wave of the sub-bridge arm 2 are obtained;

[0010] Combined with the original modulation wave of the bridge arm, the final modulation wave of the sub-bridge arm 1 and the final modulation wave of the sub-bridge arm 2 are obtained respectively, and then the output voltages of the sub-bridge arm 1 and the sub-bridge arm 2 are adjusted to suppress the circulating current between the parallel sub-bridge arms.

[0011] Furthermore, obtaining the circulating current value between the parallel sub-bridge arms of the first sub-bridge arm and the second sub-bridge arm includes:

[0012] Obtaining the bridge arm current of the sub-bridge arm 1;

[0013] Obtaining the bridge arm current of the second sub-bridge arm;

[0014] A half of the difference between the bridge arm current of the first sub-bridge arm and the bridge arm current of the second sub-bridge arm is calculated, that is, the circulating current value between the parallel sub-bridge arms.

[0015] Furthermore, the preset allocation ratio includes a first preset ratio value and a second preset ratio value, wherein the first preset ratio value is the ratio value of the superposition amount of the bridge arm modulation wave allocated to the sub-bridge arm 1, and the second preset ratio value is the ratio value of the superposition amount of the bridge arm modulation wave allocated to the sub-bridge arm 2;

[0016] The sum of the first preset ratio value and the second preset ratio value is 100%.

[0017] Furthermore, the combining of the original modulated waves of the bridge arms to obtain the final modulated wave of the sub-bridge arm 1 and the final modulated wave of the sub-bridge arm 2 respectively includes:

[0018] Adding the superposition amount of the bridge arm modulation wave and the superposition amount of the modulation wave of the sub-bridge arm 1 to obtain the final modulation wave of the sub-bridge arm 1;

[0019] The superposition amount of the modulated wave of the bridge arm is subtracted from the superposition amount of the modulated wave of the second sub-bridge arm to obtain the final modulated wave of the second sub-bridge arm.

[0020] Accordingly, a second aspect of an embodiment of the present invention provides a parallel-arm MMC sub-bridge arm current sharing control device, wherein the upper bridge arm and the lower bridge arm of each phase in the parallel-arm MMC are each composed of a sub-bridge arm 1 and a sub-bridge arm 2 of the same structure connected in parallel, including:

[0021] An acquisition module, configured to acquire a circulating current value between the parallel sub-bridge arms of the first sub-bridge arm and the second sub-bridge arm;

[0022] A calculation module, which is used to calculate the superposition amount of the bridge arm modulation wave according to the circulating current value between the parallel sub-bridge arms through the damping coefficient;

[0023] A distribution module, which is used to distribute the superposition amount of the modulated wave of the bridge arm according to a preset distribution ratio, and obtain the superposition amount of the modulated wave of the sub-bridge arm 1 and the superposition amount of the modulated wave of the sub-bridge arm 2 after limiting processing;

[0024] A control module is used to combine the original modulation wave of the bridge arm to obtain the final modulation wave of the sub-bridge arm 1 and the final modulation wave of the sub-bridge arm 2, respectively, and then adjust the output voltage of the sub-bridge arm 1 and the sub-bridge arm 2 to suppress the circulating current between the parallel sub-bridge arms.

[0025] Furthermore, the acquisition module includes: a first acquisition unit, a second acquisition unit and a first calculation unit;

[0026] The first acquisition unit is used to acquire the bridge arm current of the sub-bridge arm 1;

[0027] The second acquiring unit is used to acquire the bridge arm current of the second sub-bridge arm;

[0028] The first calculation unit is used to calculate half of the difference between the bridge arm current of the first sub-bridge arm and the bridge arm current of the second sub-bridge arm, that is, the circulating current value between the parallel sub-bridge arms.

[0029] Furthermore, the preset allocation ratio includes a first preset ratio value and a second preset ratio value, wherein the first preset ratio value is the ratio value of the superposition amount of the bridge arm modulation wave allocated to the sub-bridge arm 1, and the second preset ratio value is the ratio value of the superposition amount of the bridge arm modulation wave allocated to the sub-bridge arm 2;

[0030] The sum of the first preset ratio value and the second preset ratio value is 100%.

[0031] Furthermore, the control module includes: a first superimposing unit, a second superimposing unit and a control unit;

[0032] The first superposition unit is used to add the original modulated wave of the bridge arm and the superposition amount of the modulated wave of the sub-bridge arm 1 to obtain the final modulated wave of the sub-bridge arm 1;

[0033] The second superposition unit is used to subtract the superposition amount of the original modulated wave of the bridge arm and the modulated wave of the second sub-bridge arm to obtain the final modulated wave of the second sub-bridge arm;

[0034] The control unit is used to adjust the output voltages of the first sub-bridge arm and the second sub-bridge arm to suppress the circulating current between the parallel sub-bridge arms.

[0035] Accordingly, a third aspect of an embodiment of the present invention provides an electronic device, comprising: at least one processor; and a memory connected to the at least one processor; wherein the memory stores instructions that can be executed by the one processor, and the instructions are executed by the one processor to enable the at least one processor to execute the above-mentioned bridge arm parallel MMC parallel sub-bridge arm current sharing control method.

[0036] Accordingly, a fourth aspect of an embodiment of the present invention provides a computer-readable storage medium having computer instructions stored thereon, which, when executed by a processor, implements the above-mentioned method for controlling current sharing of parallel sub-bridge arms of a parallel-bridge-arm MMC.

[0037] The above technical solutions of the embodiments of the present invention have the following beneficial technical effects:

[0038] By obtaining the bridge arm currents of the two sub-bridge arms, the superposition of the bridge arm modulation waves is obtained, and it is distributed according to the preset distribution ratio of the specific device to obtain the final modulation waves of the two sub-bridge arms, and then the output voltage of the sub-bridge arms is adjusted to suppress the circulating current between the parallel sub-bridge arms. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic diagram of the principle of the bridge arm parallel MMC in the prior art;

[0040] Figure 2 This is a flow chart of a method for controlling current sharing of parallel sub-bridge arms of a parallel-connected MMC bridge arm according to an embodiment of the present invention;

[0041] Figure 3 Schematic diagram of a method for controlling current sharing of parallel sub-bridge arms of a parallel-bridge-arm MMC provided by an embodiment of the present invention;

[0042] Figure 4 This is a block diagram of a module of a bridge arm parallel MMC parallel sub-bridge arm current sharing control device provided by an embodiment of the present invention;

[0043] Figure 5 This is a block diagram of an acquisition module provided by an embodiment of the present invention;

[0044] Figure 6 This is a block diagram of a control module provided by an embodiment of the present invention.

[0045] Reference numerals:

[0046] 1. Acquisition module, 11. First acquisition unit, 12. Second acquisition unit, 13. First calculation unit, 2. Calculation module, 3. Allocation module, 4. Control module, 41. First superposition unit, 42. Second superposition unit, 43. Control unit. DETAILED DESCRIPTION

[0047] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present invention.

[0048] Figure 1 It is a schematic diagram of the principle of the bridge arm parallel MMC in the prior art.

[0049] Please refer to Figure 1 In the parallel-arm MMC, the upper and lower bridge arms of each phase are composed of two identical sub-bridge arms in parallel. Each sub-bridge arm contains multiple cascaded sub-modules and bridge arm reactors. The sub-module topologies include half-bridge sub-modules and full-bridge sub-modules.

[0050] Figure 2 This is a flow chart of a method for controlling current sharing of parallel sub-bridge arms of a parallel-bridge-arm MMC provided by an embodiment of the present invention.

[0051] Figure 3 Schematic diagram of a method for controlling current sharing of parallel sub-bridge arms of a parallel-bridge-arm MMC provided in an embodiment of the present invention.

[0052] Please refer to Figure 2 and Figure 3 A first aspect of an embodiment of the present invention provides a method for controlling current sharing of parallel sub-bridge arms in a parallel-arm MMC, wherein the upper bridge arm and the lower bridge arm of each phase in the parallel-arm MMC are each composed of a first sub-bridge arm and a second sub-bridge arm having the same structure and parameters connected in parallel, comprising the following steps:

[0053] S100, obtaining the circulating current value i between the parallel sub-bridge arms 1 and 2 loop_arm12 .

[0054] S200, based on the circulating current value i between the parallel sub-bridge arms loop_arm12 , calculate the bridge arm modulation wave superposition △m through the damping coefficient Kr loop_arm12 .

[0055] S300: The bridge arm modulation wave superposition amount △m is calculated according to the preset distribution ratio. loop_arm12 After distribution and limiting processing, the modulation wave superposition △m of the sub-bridge arm 1 is obtained loop_arm1 and the modulation wave superposition of the second arm △m loop_arm2 .

[0056] S400, combined with the original modulation wave m of the bridge arm arm , and the final modulation wave m of the sub-bridge arm 1 is obtained respectively arm_1 The final modulation wave m of the second sub-bridge arm arm_2 , and then adjust the output voltage of sub-bridge arm 1 and sub-bridge arm 2 to suppress the circulating current between the parallel sub-bridge arms.

[0057] Furthermore, in step S100, the circulating current value between the parallel sub-bridge arms of the first sub-bridge arm and the second sub-bridge arm is obtained, which specifically includes the following steps:

[0058] S110, obtaining the bridge arm current i of the sub-bridge arm 1 arm_1 .

[0059] S120, obtaining the bridge arm current i of the second sub-bridge arm arm_2 .

[0060] S130, calculating the bridge arm current i of the sub-bridge arm 1 arm_1 and the bridge arm current i of the second sub-bridge arm arm_2 Half of the difference, that is, the circulating current value i between the parallel sub-bridge arms loop_arm12 .

[0061] Furthermore, in step S300, the preset allocation ratio includes a first preset ratio value and a second preset ratio value, wherein the first preset ratio value is the bridge arm modulation wave superposition amount Δm allocated to the sub-bridge arm 1. loop_arm12 The second preset proportional value is the proportional value of the bridge arm modulation wave superposition amount △mloop_arm12 allocated to the sub-bridge arm 2; the sum of the first preset proportional value and the second preset proportional value is 100%.

[0062] Specifically, the allocation according to the preset allocation ratio described in the above scheme can be half allocated to each of the two sub-bridge arms, that is, the two coefficients s1 and s2 are both 0.5, or one sub-bridge arm can be fully allocated and the other sub-bridge arm can be unallocated, that is, s1=1, s2=0, or s1=0, s2=1, depending on the difference between the two sub-bridge arms.

[0063] Furthermore, in step S400, the original modulation wave m of the bridge arm is combined with arm The final modulation wave m of the sub-bridge arm 1 is obtained respectively arm_1 The final modulation wave m of the second sub-bridge arm arm_2 ,include:

[0064] S410 adds the bridge arm modulation wave superposition amount m arm The superposition of the modulation wave with the sub-bridge arm 1 △m loop_arm1 Add together to get the final modulation wave m of sub-bridge arm 1 arm_1 ;

[0065] S420 adds the bridge arm modulation wave superposition amount m arm The superposition of the modulation wave of the second sub-bridge arm △m loop_arm2 Subtract and get the final modulation wave m of sub-bridge arm 2 arm_2 .

[0066] The above-mentioned bridge arm parallel MMC parallel sub-bridge arm current sharing control method obtains the bridge arm current of the two sub-bridge arms and then obtains the bridge arm modulation wave superposition △m loop_arm12 , and distribute it according to the preset distribution ratio of the specific device to obtain the final modulation wave of the two sub-bridge arms, and then adjust the output voltage of the sub-bridge arm to suppress the inter-sub-bridge arm circulation problem caused by the difference between the two parallel sub-bridge arms in the bridge arm parallel MMC, thereby improving the operation reliability of the bridge arm parallel MMC.

[0067] Figure 4 This is a block diagram of a module of a bridge arm parallel MMC parallel sub-bridge arm current sharing control device provided by an embodiment of the present invention.

[0068] Accordingly, please refer to Figure 4 The second aspect of an embodiment of the present invention provides a bridge arm parallel MMC parallel sub-bridge arm current sharing control device, in which the upper bridge arm and the lower bridge arm of each phase in the bridge arm parallel MMC are both composed of a sub-bridge arm 1 and a sub-bridge arm 2 with the same structure connected in parallel, including: an acquisition module 1, a calculation module 2, a distribution module 3 and a control module 4.

[0069] Specifically, the acquisition module 1 is used to obtain the circulating current value i between the parallel sub-bridge arms of the first sub-bridge arm and the second sub-bridge arm. loop_arm12 ; Calculation module 2 is used to calculate the circulating current value i between the parallel sub-bridge arms loop_arm12 , calculate the bridge arm modulation wave superposition △m through the damping coefficient Kr loop_arm12 ; Distribution module 3 is used to distribute the bridge arm modulation wave superposition amount △m according to the preset distribution ratio loop_arm12 After distribution and limiting processing, the modulation wave superposition △m of the sub-bridge arm 1 is obtained loop_arm1 and the modulation wave superposition of the second arm △m loop_arm2; Control module 4 is used to combine the original modulation wave m arm , and the final modulation wave m of the sub-bridge arm 1 is obtained respectively arm_1 The final modulation wave m of the second sub-bridge arm arm_2 , and then adjust the output voltage of sub-bridge arm 1 and sub-bridge arm 2 to suppress the circulating current between the parallel sub-bridge arms.

[0070] Figure 5 This is a block diagram of an acquisition module provided by an embodiment of the present invention.

[0071] For further information, please refer to Figure 5 The acquisition module 1 includes: a first acquisition unit 11, a second acquisition unit 12 and a first calculation unit 13. The first acquisition unit 11 is used to obtain the bridge arm current i of the sub-bridge arm 1. arm_1 The second acquisition unit 12 is used to obtain the bridge arm current i of the second sub-bridge arm arm_2 The first calculation unit 13 is used to calculate the bridge arm current i of the sub-bridge arm arm_1 and the bridge arm current i of the second sub-bridge arm arm_2 Half of the difference, that is, the circulating current value i between the parallel sub-bridge arms loop_arm12 .

[0072] Furthermore, the preset allocation ratio includes a first preset ratio value and a second preset ratio value, wherein the first preset ratio value is the bridge arm modulation wave superposition amount △m allocated to the sub-bridge arm 1 loop_arm12 The second preset proportional value is the bridge arm modulation wave superposition amount △m allocated to the sub-bridge arm 2. loop_arm12 The sum of the first preset ratio value and the second preset ratio value is 100%.

[0073] Specifically, the allocation according to the preset allocation ratio described in the above scheme can be half allocated to each of the two sub-bridge arms, that is, the two coefficients s1 and s2 are both 0.5, or one sub-bridge arm can be fully allocated and the other sub-bridge arm can be unallocated, that is, s1=1, s2=0, or s1=0, s2=1, depending on the difference between the two sub-bridge arms.

[0074] Figure 6 This is a block diagram of a control module provided by an embodiment of the present invention.

[0075] For further information, please refer to Figure 6 The control module 4 includes: a first superposition unit 41, a second superposition unit 42 and a control unit 43. The first superposition unit 41 is used to superpose the original modulated wave m of the bridge arm. arm The superposition of the modulation wave with the sub-bridge arm 1 △m loop_arm1 Add together to get the final modulation wave m of sub-bridge arm 1 arm_1 The second superposition unit 42 is used to bridge the original modulation wave m armThe superposition of the modulation wave of the second sub-bridge arm △m loop_arm2 Subtract and get the final modulation wave m of sub-bridge arm 2 arm_2 The control unit 43 is used to adjust the output voltage of the sub-bridge arm 1 and the sub-bridge arm 2 to suppress the circulating current between the parallel sub-bridge arms.

[0076] The above-mentioned bridge arm parallel MMC parallel sub-bridge arm current sharing control device obtains the bridge arm current of the two sub-bridge arms to obtain the superposition of the bridge arm modulation waves, and distributes them according to the preset distribution ratio of the specific device to obtain the final modulation waves of the two sub-bridge arms, and then adjusts the output voltage of the sub-bridge arm to suppress the inter-sub-bridge arm circulation problem caused by the difference between the two parallel sub-bridge arms of the bridge arm parallel MMC, thereby improving the operation reliability of the bridge arm parallel MMC.

[0077] Accordingly, a third aspect of an embodiment of the present invention provides an electronic device, comprising: at least one processor; and a memory connected to the at least one processor; wherein the memory stores instructions that can be executed by the one processor, and the instructions are executed by the one processor to enable the at least one processor to execute the above-mentioned bridge arm parallel MMC parallel sub-bridge arm current sharing control method.

[0078] Accordingly, a fourth aspect of an embodiment of the present invention provides a computer-readable storage medium having computer instructions stored thereon, which, when executed by a processor, implements the above-mentioned method for controlling current sharing of parallel sub-bridge arms of a parallel-bridge-arm MMC.

[0079] The embodiment of the present invention aims to protect a method and device for controlling the equal current of parallel sub-bridge arms of a parallel-connected MMC bridge arm, wherein the method includes the following steps: obtaining the circulating current value between the parallel sub-bridge arms of sub-bridge arm 1 and sub-bridge arm 2; calculating the bridge arm modulation wave superposition amount through the damping coefficient based on the circulating current value between the parallel sub-bridge arms; distributing the bridge arm modulation wave superposition amount according to a preset distribution ratio, and obtaining the modulation wave superposition amount of sub-bridge arm 1 and the modulation wave superposition amount of sub-bridge arm 2 after amplitude limiting processing; combining the bridge arm modulation wave superposition amount, obtaining the final modulation wave of sub-bridge arm 1 and the final modulation wave of sub-bridge arm 2 respectively, and then adjusting the output voltage of sub-bridge arm 1 and sub-bridge arm 2 to suppress the circulating current between the parallel sub-bridge arms. The above technical solution has the following effects:

[0080] By obtaining the bridge arm currents of the two sub-bridge arms and thus obtaining the superposition of the bridge arm modulation waves, and distributing them according to the preset distribution ratio of the specific device, the final modulation waves of the two sub-bridge arms are obtained, and then the output voltage of the sub-bridge arms is adjusted to suppress the inter-sub-bridge arm circulation problem caused by the difference between the two parallel sub-bridge arms in the bridge arm parallel MMC, thereby improving the operation reliability of the bridge arm parallel MMC.

[0081] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt 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.) that contain computer-usable program code.

[0082] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes 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 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 steps in the process. 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.

[0083] 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.

[0084] 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 The steps for the function specified in one or more boxes.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A method for controlling the current sharing of parallel sub-bridge arms of a parallel-connected MMC bridge arm, characterized in that: The upper bridge arm and the lower bridge arm of each phase in the bridge arm parallel MMC are both composed of a sub-bridge arm 1 and a sub-bridge arm 2 with the same structure and parameters connected in parallel, including the following steps: Obtaining a circulating current value between the parallel sub-bridge arms of the first sub-bridge arm and the second sub-bridge arm; Calculating the superposition amount of the bridge arm modulation wave by using the damping coefficient according to the circulating current value between the parallel sub-bridge arms; The superposition amount of the modulated wave of the bridge arm is distributed according to a preset distribution ratio, and after amplitude limiting processing, the superposition amount of the modulated wave of the sub-bridge arm 1 and the superposition amount of the modulated wave of the sub-bridge arm 2 are obtained; Combining the original modulation wave of the bridge arm, respectively obtaining the final modulation wave of the sub-bridge arm 1 and the final modulation wave of the sub-bridge arm 2, and then adjusting the output voltage of the sub-bridge arm 1 and the sub-bridge arm 2 to suppress the circulating current between the parallel sub-bridge arms; The preset allocation ratio includes a first preset ratio value and a second preset ratio value, wherein the first preset ratio value is the ratio value of the superposition amount of the bridge arm modulation wave allocated to the sub-bridge arm 1, and the second preset ratio value is the ratio value of the superposition amount of the bridge arm modulation wave allocated to the sub-bridge arm 2; The sum of the first preset ratio value and the second preset ratio value is 100%; The combining of the original modulated waves of the bridge arms to obtain the final modulated wave of the sub-bridge arm 1 and the final modulated wave of the sub-bridge arm 2 respectively includes: Adding the original modulated wave of the bridge arm and the superposition of the modulated wave of the sub-bridge arm 1 to obtain the final modulated wave of the sub-bridge arm 1; The original modulated wave of the bridge arm and the superposition of the modulated wave of the second sub-bridge arm are subtracted to obtain the final modulated wave of the second sub-bridge arm.

2. The method for controlling the current sharing of parallel sub-bridge arms of a parallel-connected MMC according to claim 1, characterized in that: The obtaining of the circulating current value between the parallel sub-bridge arms of the first sub-bridge arm and the second sub-bridge arm includes: Obtaining the bridge arm current of the sub-bridge arm 1; Obtaining the bridge arm current of the second sub-bridge arm; A half of the difference between the bridge arm current of the first sub-bridge arm and the bridge arm current of the second sub-bridge arm is calculated, that is, the circulating current value between the parallel sub-bridge arms.

3. A bridge arm parallel MMC parallel sub-bridge arm current sharing control device, characterized in that: In the parallel-arm MMC, the upper and lower arms of each phase are composed of a sub-arm 1 and a sub-arm 2 with the same structure and parameters connected in parallel, including: An acquisition module, configured to acquire a circulating current value between the parallel sub-bridge arms of the first sub-bridge arm and the second sub-bridge arm; A calculation module, which is used to calculate the superposition amount of the bridge arm modulation wave according to the circulating current value between the parallel sub-bridge arms through the damping coefficient; A distribution module, which is used to distribute the superposition amount of the modulated wave of the bridge arm according to a preset distribution ratio, and obtain the superposition amount of the modulated wave of the sub-bridge arm 1 and the superposition amount of the modulated wave of the sub-bridge arm 2 after limiting processing; a control module, which is used to combine the original modulation wave of the bridge arm to obtain the final modulation wave of the sub-bridge arm 1 and the final modulation wave of the sub-bridge arm 2, respectively, and then adjust the output voltage of the sub-bridge arm 1 and the sub-bridge arm 2 to suppress the circulating current between the parallel sub-bridge arms; The preset allocation ratio includes a first preset ratio value and a second preset ratio value, wherein the first preset ratio value is the ratio value of the superposition amount of the bridge arm modulation wave allocated to the sub-bridge arm 1, and the second preset ratio value is the ratio value of the superposition amount of the bridge arm modulation wave allocated to the sub-bridge arm 2; The sum of the first preset ratio value and the second preset ratio value is 100%; The control module includes: a first superimposing unit, a second superimposing unit and a control unit; The first superposition unit is configured to add the original modulated wave of the bridge arm and the superposition amount of the modulated wave of the sub-bridge arm 1 to obtain the final modulated wave of the sub-bridge arm 1; The second superposition unit is used to subtract the superposition amount of the original modulated wave of the bridge arm and the modulated wave of the second sub-bridge arm to obtain the final modulated wave of the second sub-bridge arm; The control unit is used to adjust the output voltages of the first sub-bridge arm and the second sub-bridge arm to suppress the circulating current between the parallel sub-bridge arms.

4. The bridge arm parallel MMC parallel sub-bridge arm current sharing control device according to claim 3, characterized in that: The acquisition module includes: a first acquisition unit, a second acquisition unit and a first calculation unit; The first acquisition unit is used to acquire the bridge arm current of the sub-bridge arm 1; The second acquiring unit is used to acquire the bridge arm current of the second sub-bridge arm; The first calculation unit is used to calculate half of the difference between the bridge arm current of the first sub-bridge arm and the bridge arm current of the second sub-bridge arm, that is, the circulating current value between the parallel sub-bridge arms.

5. An electronic device, characterized in that: include: at least one processor; And a memory connected to the at least one processor; wherein the memory stores instructions that can be executed by the one processor, and the instructions are executed by the one processor to enable the at least one processor to execute the bridge arm parallel MMC parallel sub-bridge arm current sharing control method according to claim 1 or 2.

6. A computer-readable storage medium, characterized in that Computer instructions are stored thereon, and when the instructions are executed by the processor, the method for controlling the equal current of the parallel-connected MMC sub-bridge arms of the bridge arm parallel type according to claim 1 or 2 is implemented.

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