Bridge arm voltage equalization control method and system for sparse modular multilevel converter

Abstract

The present application belongs to the field of sparse modular multilevel converter, and discloses a kind of bridge arm voltage sharing control method and system of sparse modular multilevel converter, by collecting the average capacitor voltage of all bridge arms and constructing matrix, by double side common difference mode conversion decoupling, all degrees of freedom components including the voltage difference component between all bridge arms are obtained, and then corresponding zero sequence voltage instruction is generated based on each difference component, and by inner loop controller, it is integrated into modulation wave to drive converter.This method maps the bridge arm capacitor voltage to the decoupled degree of freedom space through mathematical transformation, so that each bridge arm voltage difference component can independently generate control instruction, thereby achieving complete coverage and independent regulation of all difference components.Using this method, effective equalization control of all bridge arm voltage difference components is realized, the voltage sharing effect is improved, and the robustness of the system to grid frequency fluctuations is enhanced through online self-adaptation, better adapting to the actual operating conditions of power system.

Description

Technical Field

[0001] This invention belongs to the technical field of sparse modular multilevel converters, and particularly relates to a method and system for voltage equalization control between bridge arms of a sparse modular multilevel converter. Background Technology

[0002] Frequency division transmission technology is suitable for applications such as long-distance, high-capacity power transmission and large-scale renewable energy grid connection, and is an important research direction in the current power transmission field. As the core energy conversion device in a frequency division transmission system, the AC converter's topology and operating performance directly affect the system's economy and operational reliability. The Sparse Modular Multilevel Converter (SMMC), a novel AC converter topology based on sinusoidal half-wave frequency conversion, was first proposed in 2016. This topology requires fewer power devices, has high power density, and possesses significant cost advantages; simultaneously, more than half of its power devices operate in soft-switching mode, resulting in lower operating losses, and it has broad application prospects in frequency division transmission systems.

[0003] Currently, research on SMMC is still in its early stages, with limited research results on its control strategies, especially a lack of mature and comprehensive voltage equalization control schemes for inter-arm capacitors. Existing bridge arm voltage equalization control strategies based on third harmonic injection obtain the phase reference value of the third harmonic through offline calculation, and use the overall voltage difference between the three half-bridge arms and the three full-bridge arms as the control command value to achieve voltage equalization regulation between the arms. However, this scheme has obvious technical defects: First, it does not cover all bridge arm voltage difference degree-of-freedom components. SMMC contains a total of 6 bridge arms, corresponding to 6 bridge arm capacitor voltage degree-of-freedom components, one of which is the average capacitor voltage component of all bridge arms, and the remaining 5 are the capacitor voltage difference components between bridge arms. This strategy can only achieve control of 1 difference degree-of-freedom component between the half-bridge arm group and the full-bridge arm group, and cannot effectively regulate the other 4 difference degree-of-freedom components, resulting in poor actual voltage equalization control effect. Second, the robustness of this control system is poor. Its third harmonic phase reference value is the result of offline calculation for a specific grid frequency, while the grid frequency fluctuates in real time during actual power system operation. Under fault conditions, the frequency will deviate significantly from the rated value. At this time, the offline calculated phase is no longer the optimal phase, and the expected bridge arm voltage equalization control effect cannot be achieved.

[0004] It is evident that the existing SMMC inter-arm voltage equalization control technology based on third harmonic injection has several drawbacks. First, it has incomplete control degree of freedom coverage and cannot effectively regulate all arm voltage difference components, resulting in limited actual voltage equalization control performance. Second, it has defects such as control parameters relying on offline calculation and weak grid frequency adaptability, resulting in insufficient system robustness and difficulty in adapting to the complex and ever-changing actual operating conditions of the power system. Summary of the Invention

[0005] This invention provides a method for inter-arm voltage equalization control of sparse modular multilevel converters (SMMCs). This method can effectively solve the problems of incomplete control degree of freedom coverage, inability to effectively regulate all arm voltage difference components, reliance on offline calculation of control parameters, weak grid frequency adaptability, and insufficient system robustness of existing inter-arm voltage equalization control technology based on third harmonic injection. It can adapt to the complex and ever-changing actual operating conditions of power systems.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for voltage equalization control between bridge arms of a sparse modular multilevel converter includes: The average capacitor voltage of all arms of the sparse modular multilevel converter is collected to construct the average capacitor voltage matrix of the arms. By performing a two-sided common-mode transformation on the average capacitor voltage matrix of the bridge arm, the complete voltage degree-of-freedom components of the sparse modular multilevel converter are obtained. Based on the voltage difference component between the capacitors of each bridge arm in the voltage degree of freedom component of the bridge arm, the corresponding zero-sequence voltage command value is generated respectively. Each zero-sequence voltage command value is input into the inner loop controller, which, combined with the grid-side control command, generates the final modulation wave and sends it to the sparse modular multilevel converter to achieve balanced control of the capacitor voltage between bridge arms.

[0007] Furthermore, the bridge arm voltage degree of freedom components include the average capacitor voltage component of all bridge arm modules, and the capacitor voltage difference component between the five bridge arms. The two-sided common-mode transformation decouples all bridge arm voltage degrees of freedom by performing common-mode and differential-mode calculations on both sides of the average capacitor voltage matrix of the bridge arms. The specific formula is as follows:

[0008] In the formula, The average capacitor voltage component of all bridge arm modules of the sparse modular multilevel converter; , , , , The voltage difference components between the capacitors of the five arms of the sparse modular multilevel converter are respectively considered. This is the average capacitor voltage matrix of the bridge arm; in, ; .

[0009] Furthermore, the generation of corresponding zero-sequence voltage command values ​​based on the inter-arm capacitor voltage difference components in the arm voltage degree of freedom components includes: For each inter-arm capacitor voltage difference component, a proportional-integral controller is used for closed-loop regulation. At the same time, the system current components on both sides of the sparse modular multilevel converter and the expansion module switching function are introduced for dynamic gain adjustment to generate the zero-sequence voltage command value of the corresponding inter-arm capacitor voltage difference component.

[0010] Furthermore, the switching function of the unfolding module is the switching function of the half-bridge unfolding module; Each phase unit of the sparse modular multilevel converter is equipped with a half-bridge expansion module and a full-bridge expansion module; both types of expansion modules are composed of several fully controlled devices, which are used to periodically flip the AC half-wave positive voltage output by the bridge arm to output a sinusoidal voltage with alternating positive and negative values.

[0011] Furthermore, the system current components on both sides of the sparse modular multilevel converter are the α component of the grid-side system current, the β component of the grid-side system current, the α component of the valve-side system current, and the β component of the valve-side system current, respectively.

[0012] Furthermore, the specific formula for generating the zero-sequence voltage command value corresponding to the voltage difference component between the bridge arms capacitors is as follows:

[0013]

[0014] In the formula, kp XY , k IXY For the proportional-integral controller, the proportional gain and integral gain are... ; i sα , i sβ , i lα , i lβ These represent the currents of the systems on both sides of the sparse modular multilevel converter. α , β Quantity;s Z This is the switching function for the half-bridge expansion module. a, b, and c are the grid-side three-phase deployment modules; r, s, and t are the valve-side three-phase deployment modules. and , respectively, are the zero-sequence voltage command values ​​on the valve side and the grid side; s is the Laplace operator.

[0015] Furthermore, in the step of inputting each zero-sequence voltage command value into the inner loop controller, combining it with the grid-side control command to generate the final modulation wave and sending it to the sparse modular multilevel converter, the inner loop controller superimposes and fuses the zero-sequence voltage command value with the grid-side control command to generate the modulation wave signal corresponding to each bridge arm sub-module, and sends the modulation wave signal to the half-bridge sub-module and the full-bridge sub-module, and controls the bridge arm output voltage by adjusting the number of sub-modules put into operation.

[0016] A bridge arm voltage equalization control system for a sparse modular multilevel converter includes: The acquisition module is used to acquire the average capacitor voltage of all arms of the sparse modular multilevel converter and construct the average capacitor voltage matrix of the arms. The decoupling module is used to perform a two-sided common-mode transformation on the average capacitor voltage matrix of the bridge arm, and decouple to obtain all the voltage degree-of-freedom components of the sparse modular multilevel converter. The generation module is used to generate corresponding zero-sequence voltage command values ​​based on the difference components of capacitor voltage between each bridge arm in the bridge arm voltage degree of freedom components. The fusion module is used to input the zero-sequence voltage command values ​​into the inner loop controller, combine them with the grid-side control commands to generate the final modulation wave and send it to the sparse modular multilevel converter to achieve balanced control of the capacitor voltage between bridge arms.

[0017] Furthermore, including: Memory, used to store computer programs; A processor is used to implement the above-described sparse modular multilevel converter arm voltage equalization control method when executing the computer program.

[0018] A computer-readable storage medium storing a computer program, which, when executed by a processor, is used to implement the above-described method for equalizing voltage between bridge arms of a sparse modular multilevel converter.

[0019] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for inter-arm voltage equalization control in a sparse modular multilevel converter. By collecting the average capacitor voltage of all arms and constructing a matrix, and then decoupling through a two-sided common-mode transform, all degrees of freedom components, including the voltage difference components between all arms, are obtained. Based on each difference component, a corresponding zero-sequence voltage command is generated, and these commands are integrated into a modulated wave to drive the converter via an inner-loop controller. This method maps the arm capacitor voltage to the decoupled degree-of-freedom space through mathematical transformation, enabling each inter-arm voltage difference component to independently generate control commands, thus achieving complete coverage and independent control of all difference components. Furthermore, this method generates control commands online, without relying on offline calculated fixed phase parameters. This method achieves effective equalization control of all arm voltage difference components, improves voltage equalization performance, and enhances the system's robustness to grid frequency fluctuations through online adaptive control, better adapting to actual power system operating conditions. Attached Figure Description

[0020] Figure 1 The SMMC circuit topology diagram provided for embodiments of the present invention; Figure 2 This is a block diagram of the SMMC bridge arm voltage equalization control based on two-sided common differential mode transformation provided in an embodiment of the present invention; Figure 3 The SMMC control system architecture provided in the embodiments of the present invention; Figure 4 The core flowchart of a bridge arm voltage equalization control method for a sparse modular multilevel converter provided in this embodiment of the invention; Figure 5 This is a schematic diagram of the structure of a bridge arm equalization control system for a sparse modular multilevel converter provided in an embodiment of the present invention. Detailed Implementation

[0021] To further understand the content of this invention, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments are merely illustrative and not limiting of the invention.

[0022] As mentioned in the background section, the SMMC arm-to-arm voltage equalization control based on third harmonic injection has the following drawbacks: First, the strategy fails to control all voltage difference degrees of freedom components across all bridge arms, resulting in poor actual control performance. The SMMC has six bridge arms, representing six voltage degrees of freedom components. One degree of freedom is the average capacitor voltage across all bridge arms, while the remaining five are the voltage difference components between the bridge arms. This strategy uses the voltage difference between all half-bridge arms and all full-bridge arms as the command value, only achieving voltage equalization control between these two groups—that is, controlling one degree of difference component—while neglecting to control the remaining four.

[0023] Second, the control system has poor robustness. The phase of the third harmonic in this strategy is calculated offline in advance for a specific grid frequency. In actual power system applications, the grid frequency is constantly changing, especially when a fault occurs, the frequency deviates significantly from its rated value. The offline calculated phase is no longer the optimal phase, and the expected voltage equalization control effect between bridge arms cannot be achieved.

[0024] To address the aforementioned issues, this embodiment provides a method for equalizing voltage between the arms of a sparse modular multilevel converter (SMMC). This method enables effective control of the voltage difference degrees of freedom components of all five arms of the SMMC and enhances the robustness of the control system by utilizing online feedback and dynamic gain control.

[0025] For example, such as Figure 4 As shown, a method for voltage equalization control between bridge arms of a sparse modular multilevel converter includes: The average capacitor voltage of all arms of the sparse modular multilevel converter is collected to construct the average capacitor voltage matrix of the arms. By performing a two-sided common-mode transformation on the average capacitor voltage matrix of the bridge arm, the complete voltage degree-of-freedom components of the sparse modular multilevel converter are obtained. Based on the voltage difference component between the capacitors of each bridge arm in the voltage degree of freedom component of the bridge arm, the corresponding zero-sequence voltage command value is generated respectively. Each zero-sequence voltage command value is input into the inner loop controller, which, combined with the grid-side control command, generates the final modulation wave and sends it to the sparse modular multilevel converter to achieve balanced control of the capacitor voltage between bridge arms.

[0026] The pressure equalization control method provided in this embodiment will be further explained below with reference to the accompanying drawings: For example, this embodiment provides a method for voltage equalization control between bridge arms of a sparse modular multilevel converter (SMMC), such as... Figure 1 As shown, the MMC consists of three phase units and one three-phase isolation transformer. Each phase unit can be structurally divided into three parts: Half bridge arm (HBA): It consists of several half bridge submodules (HBSM). The output voltage of the bridge arm is adjusted by controlling the number of submodules connected, thereby generating a positive half-wave AC voltage with a specific amplitude and frequency. Full bridge arm (FBA): It consists of several full bridge submodules (FBSM) and bridge arm inductors. Its output voltage and the half-bridge arm voltage together generate a positive half-wave AC voltage with a specific amplitude and frequency. The function of the bridge arm inductor is to suppress circulating current. Half-bridge unfolder (HBU) and full-bridge unfolder (FBU): Composed of several fully controllable devices, they periodically flip the half-wave positive voltage generated by the bridge arm to obtain an alternating positive and negative sine wave.

[0027] Furthermore, the specific steps of the inter-arm voltage equalization control method for sparse modular multilevel converters are as follows: Step 1: Sample the average capacitor voltage of the 6 arms of the SMMC to obtain the average capacitor voltage matrix of the arms: (1) Step 2: Through two-sided common-mode transformation, obtain the six arm voltage degrees of freedom components of the SMMC: (2) In the formula, The average capacitor voltage component of all bridge arm modules of the sparse modular multilevel converter; , , , , The voltage difference components between the capacitors of the five arms of the sparse modular multilevel converter are respectively considered. This is the average capacitor voltage matrix of the bridge arm.

[0028] in: (3) (4) Step 3: For each capacitor voltage difference component, the following control strategy is adopted to generate the corresponding zero-sequence voltage command value: (5) (6) In the formula, kp XY , k IXY For the proportional-integral controller, the proportional gain and integral gain are... ; isα , i sβ , i lα , i lβ These represent the currents of the systems on both sides of the sparse modular multilevel converter. α , β Quantity; s Z This is the switching function for the half-bridge expansion module. a, b, and c are the grid-side three-phase deployment modules; r, s, and t are the valve-side three-phase deployment modules. and , respectively, are the zero-sequence voltage command values ​​on the valve side and the grid side; s is the Laplace operator.

[0029] Step 4: Input the obtained zero-sequence voltage command value into the inner loop controller, and generate a modulation wave together with the grid-side control and send it to the SMMC.

[0030] For example, such as Figure 5 As shown, this embodiment also provides a bridge arm voltage equalization control system for a sparse modular multilevel converter, including: The acquisition module is used to acquire the average capacitor voltage of all arms of the sparse modular multilevel converter and construct the average capacitor voltage matrix of the arms. The decoupling module is used to perform a two-sided common-mode transformation on the average capacitor voltage matrix of the bridge arm, and decouple to obtain all the voltage degree-of-freedom components of the sparse modular multilevel converter. The generation module is used to generate corresponding zero-sequence voltage command values ​​based on the difference components of capacitor voltage between each bridge arm in the bridge arm voltage degree of freedom components. The fusion module is used to input the zero-sequence voltage command values ​​into the inner loop controller, combine them with the grid-side control commands to generate the final modulation wave and send it to the sparse modular multilevel converter to achieve balanced control of the capacitor voltage between bridge arms.

[0031] The present invention also provides a bridge arm voltage equalization control device for a sparse modular multilevel converter, comprising: a memory for storing a computer program; and a processor for executing the computer program to implement the steps of the bridge arm voltage equalization control method of the sparse modular multilevel converter.

[0032] The present invention also provides a computer program product, including a computer program / instruction that, when executed by a processor, implements the steps of the bridge arm equalization control method of the sparse modular multilevel converter.

[0033] When the processor executes the computer program, it implements the steps of the above-mentioned sparse modular multilevel converter arm voltage equalization control, for example: collecting the average capacitor voltage of all arms of the sparse modular multilevel converter and constructing an arm average capacitor voltage matrix. By performing a two-sided common-mode transformation on the average capacitor voltage matrix of the bridge arm, the complete voltage degree-of-freedom components of the sparse modular multilevel converter are obtained. Based on the voltage difference component between the capacitors of each bridge arm in the voltage degree of freedom component of the bridge arm, the corresponding zero-sequence voltage command value is generated respectively. Each zero-sequence voltage command value is input into the inner loop controller, which, combined with the grid-side control command, generates the final modulation wave and sends it to the sparse modular multilevel converter to achieve balanced control of the capacitor voltage between bridge arms.

[0034] For example, the computer program can be divided into one or more modules / units, which are stored in the memory and executed by the processor to complete the present invention. The one or more modules / units can be a series of computer program instruction segments capable of performing preset functions, wherein the instruction segments describe the execution process of the computer program in the inter-arm voltage equalization control device of the sparse modular multilevel converter. For example, the computer program can be divided into an acquisition module, a decoupling module, a generation module, and a fusion module; the specific functions are as follows: the acquisition module is used to acquire the average capacitor voltage of all arms of the sparse modular multilevel converter and construct the average capacitor voltage matrix of the arms; the decoupling module is used to perform a two-sided common-mode transformation on the average capacitor voltage matrix of the arms to decouple and obtain all the voltage degree-of-freedom components of the sparse modular multilevel converter; the generation module is used to generate corresponding zero-sequence voltage command values ​​based on the capacitor voltage difference components between the arms in the voltage degree-of-freedom components of the arms; the fusion module is used to input each zero-sequence voltage command value into the inner loop controller, combine it with the grid-side control command to generate the final modulation wave and send it to the sparse modular multilevel converter to achieve balanced control of the capacitor voltage between the arms.

[0035] The inter-arm voltage equalization control device of the sparse modular multilevel converter can be a computing device such as a desktop computer, laptop, handheld computer, or cloud server. The inter-arm voltage equalization control device of the sparse modular multilevel converter may include, but is not limited to, processors and memory. Those skilled in the art will understand that the above are examples of inter-arm voltage equalization control devices for sparse modular multilevel converters and do not constitute a limitation on the inter-arm voltage equalization control device of sparse modular multilevel converters. It may include more components than described above, or combine certain components, or different components. For example, the inter-arm voltage equalization control device of the sparse modular multilevel converter may also include input / output devices, network access devices, buses, etc.

[0036] The processor can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor, or any conventional processor. This processor is the control center for the inter-arm voltage equalization control of the sparse modular multilevel converter, connecting various parts of the inter-arm voltage equalization control equipment of the entire sparse modular multilevel converter via various interfaces and lines.

[0037] The memory can be used to store the computer program and / or module. The processor implements various functions of the bridge arm equalization control device of the sparse modular multilevel converter by running or executing the computer program and / or module stored in the memory and calling the data stored in the memory.

[0038] The memory may primarily include a program storage area and a data storage area. The program storage area may store the operating system and at least one application program required for a function (such as sound playback, image playback, etc.). The data storage area may store data created based on the use of the mobile phone (such as audio data, phonebook, etc.). Furthermore, the memory may include high-speed random access memory and non-volatile memory, such as hard disks, RAM, plug-in hard disks, smart media cards (SMC), secure digital cards (SD cards), flash cards, at least one disk storage device, flash memory device, or other volatile solid-state storage devices.

[0039] The present invention also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the bridge arm equalization control method for a sparse modular multilevel converter.

[0040] If the modules / units integrated in the inter-arm voltage equalization control system of the sparse modular multilevel converter are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium.

[0041] Based on this understanding, the present invention can implement all or part of the processes in the above-described inter-arm voltage equalization control method for sparse modular multilevel converters, or it can be accomplished by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium. When executed by a processor, the computer program can implement the steps of the above-described inter-arm voltage equalization control method for sparse modular multilevel converters. The computer program includes computer program code, which can be in the form of source code, object code, executable file, or a preset intermediate form, etc.

[0042] The computer-readable storage medium may include: any entity or device capable of carrying the computer program code, recording media, USB flash drive, portable hard drive, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signal, telecommunication signal, and software distribution medium, etc.

[0043] It should be noted that the content contained in the computer-readable storage medium may be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, the computer-readable storage medium does not include electrical carrier signals and telecommunication signals.

[0044] Compared to existing voltage equalization control measures, this invention provides a voltage equalization control method and system for sparse modular multilevel converters (SMMCs). Specifically, it offers a voltage equalization control strategy for SMMCs based on dual-sided common-mode converters, achieving effective control of all five degrees of freedom of voltage difference components in the SMMC arms. Furthermore, it utilizes online feedback and dynamic gain control to enhance the robustness of the control system, offering the following advantages: First, based on the two-sided common-mode transformation, all degrees of freedom of the SMMC arm voltage were extracted. In particular, all five voltage difference components between the SMMC arm capacitors were extracted. Control of all differential degree-of-freedom components was achieved, resulting in a significant improvement in control performance.

[0045] Secondly, the robustness of the control system is improved by utilizing online feedback control technology. This method does not require offline calculation in advance. Instead, it dynamically feeds back the zero-sequence voltage injection command value based on all extracted differential degree-of-freedom components through the proportional-integral controller and the actual operating state of the SMMC, thus possessing adaptive capability to grid-side frequency changes and improving robustness.

[0046] The above embodiments are merely one of the implementation methods for achieving the technical solution of the present invention. The scope of protection claimed by the present invention is not limited to this embodiment, but also includes any variations, substitutions and other implementation methods that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention.

[0047] 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, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for voltage equalization control between bridge arms of a sparse modular multilevel converter, characterized in that, include: The average capacitor voltage of all arms of the sparse modular multilevel converter is collected to construct the average capacitor voltage matrix of the arms. By performing a two-sided common-mode transformation on the average capacitor voltage matrix of the bridge arm, the complete voltage degree-of-freedom components of the sparse modular multilevel converter are obtained. Based on the voltage difference component between the capacitors of each bridge arm in the voltage degree of freedom component of the bridge arm, the corresponding zero-sequence voltage command value is generated respectively. Each zero-sequence voltage command value is input into the inner loop controller, which, combined with the grid-side control command, generates the final modulation wave and sends it to the sparse modular multilevel converter to achieve balanced control of the capacitor voltage between bridge arms.

2. The method for inter-arm voltage equalization control of a sparse modular multilevel converter according to claim 1, characterized in that, The bridge arm voltage degree of freedom components include the average capacitor voltage component of all bridge arm modules, and the capacitor voltage difference component between the five bridge arms. The two-sided common-mode transformation decouples all bridge arm voltage degrees of freedom by performing common-mode and differential-mode calculations on both sides of the average capacitor voltage matrix of the bridge arms. The specific formula is as follows: In the formula, The average capacitor voltage component of all bridge arm modules of the sparse modular multilevel converter; , , , , The voltage difference components between the capacitors of the five arms of the sparse modular multilevel converter are respectively considered. This is the average capacitor voltage matrix of the bridge arm; in, ; .

3. The method for inter-arm voltage equalization control of a sparse modular multilevel converter according to claim 1, characterized in that, The method for generating corresponding zero-sequence voltage command values ​​based on the inter-arm capacitor voltage difference components in the arm voltage degree of freedom components includes: For each inter-arm capacitor voltage difference component, a proportional-integral controller is used for closed-loop regulation. At the same time, the system current components on both sides of the sparse modular multilevel converter and the expansion module switching function are introduced for dynamic gain adjustment to generate the zero-sequence voltage command value of the corresponding inter-arm capacitor voltage difference component.

4. The method for voltage equalization control between bridge arms of a sparse modular multilevel converter according to claim 3, characterized in that, The switching function of the expansion module is the switching function of the half-bridge expansion module; Each phase unit of the sparse modular multilevel converter is equipped with a half-bridge expansion module and a full-bridge expansion module; both types of expansion modules are composed of several fully controlled devices, which are used to periodically flip the AC half-wave positive voltage output by the bridge arm to output a sinusoidal voltage with alternating positive and negative values.

5. The method for inter-arm voltage equalization control of a sparse modular multilevel converter according to claim 3, characterized in that, The system current components on both sides of the sparse modular multilevel converter are the α component of the grid-side system current, the β component of the grid-side system current, the α component of the valve-side system current, and the β component of the valve-side system current, respectively.

6. The method for inter-arm voltage equalization control of a sparse modular multilevel converter according to claim 3, characterized in that, The formula for generating the zero-sequence voltage command value corresponding to the voltage difference component between the bridge arms capacitors is as follows: In the formula, kp XY , k IXY For the proportional-integral controller, the proportional gain and integral gain are... ; i sα , i sβ , i lα , i lβ These represent the currents of the systems on both sides of the sparse modular multilevel converter. α , β Quantity; s Z This is the switching function for the half-bridge expansion module. a, b, and c are the grid-side three-phase deployment modules; r, s, and t are the valve-side three-phase deployment modules. and These are the zero-sequence voltage command values ​​for the valve side and the grid side, respectively. s is the Laplace operator.

7. The method for inter-arm voltage equalization control of a sparse modular multilevel converter according to claim 1, characterized in that, In the step of inputting each zero-sequence voltage command value into the inner loop controller, combining it with the grid-side control command to generate the final modulation wave and sending it to the sparse modular multilevel converter, the inner loop controller superimposes and fuses the zero-sequence voltage command value with the grid-side control command to generate the modulation wave signal corresponding to each bridge arm sub-module, and sends the modulation wave signal to the half-bridge sub-module and the full-bridge sub-module, and controls the bridge arm output voltage by adjusting the number of sub-modules put into operation.

8. A bridge arm voltage equalization control system for a sparse modular multilevel converter, characterized in that, include: The acquisition module is used to acquire the average capacitor voltage of all arms of the sparse modular multilevel converter and construct the average capacitor voltage matrix of the arms. The decoupling module is used to perform a two-sided common-mode transformation on the average capacitor voltage matrix of the bridge arm, and decouple to obtain all the voltage degree-of-freedom components of the sparse modular multilevel converter. The generation module is used to generate corresponding zero-sequence voltage command values ​​based on the difference components of capacitor voltage between each bridge arm in the bridge arm voltage degree of freedom components. The fusion module is used to input the zero-sequence voltage command values ​​into the inner loop controller, combine them with the grid-side control commands to generate the final modulation wave and send it to the sparse modular multilevel converter to achieve balanced control of the capacitor voltage between bridge arms.

9. A voltage equalization control device between bridge arms of a sparse modular multilevel converter, characterized in that, include: Memory, used to store computer programs; A processor, configured to implement the bridge arm equalization control method of the sparse modular multilevel converter according to any one of claims 1-7 when executing the computer program.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it is used to implement the bridge arm equalization control method of the sparse modular multilevel converter according to any one of claims 1-7.

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