A method and system for energy balancing control between bridge arms of a bridge arm multiplexing MMC

Abstract

This invention proposes a method and system for inter-arm energy balance control in AM-MMC (AM-MMC) with multiplexed arms. By analyzing the combination relationship between the equivalent and actual reference voltages of the AM-MMC arms, it introduces an equivalent lower arm voltage distribution coefficient when the phase unit operates in the lower arm multiplexing mode and an equivalent upper arm voltage distribution coefficient when the phase unit operates in the upper arm multiplexing mode. This is supplemented by an active and controlled inter-arm energy balance control system that adjusts the distribution of the reference wave in real time, significantly reducing the deviation between the capacitor voltage and rated value of each arm submodule. This invention effectively solves the problem of inter-arm energy imbalance in AM-MMC and is applicable to different operating conditions, further improving the dynamic performance and operational stability of AM-MMC.

Description

Technical Field

[0001] This invention belongs to the technical field of bridge arm reuse type MMC control, and particularly relates to a method and system for energy balance control between bridge arms of bridge arm reuse type MMC. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Modular multilevel converters (MMCs) have been widely used in flexible DC transmission due to their advantages such as high output voltage quality, easy expansion, and redundant fault-tolerant operation. However, with the continuous improvement of MMC voltage levels and capacities, the drawbacks of high cost and large size of MMC converter platforms are becoming increasingly prominent. Patent CN112152496A discloses an arm multiplexing MMC (AM-MMC) topology that can improve the utilization rate of submodules. By dividing the multiplexing arms to perform time-division multiplexing of some submodules, AM-MMC can reduce the number of submodules assembled by at least 25% compared with MMCs of the same voltage and capacity level, thereby achieving a lighter design.

[0004] Unlike the symmetrical electrical structure and control objectives of the upper and lower bridge arms in traditional MMC phase units, the three bridge arms in AM-MMC phase units do not have good symmetry in terms of electrical structure and control objectives. Therefore, AM-MMC may face the problem of energy imbalance between the bridge arms of the phase unit during normal operation, which will greatly affect the stable voltage waveform of the converter output, and thus affect the normal power transmission function and dynamic performance of the converter. Currently, various modulation methods that have been proposed or disclosed for AM-MMC cannot solve the problem of energy balance between the bridge arms of AM-MMC very well. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention provides a method and system for energy balance control between bridge arms of a bridge arm reuse type MMC, which effectively solves the problem of energy imbalance between bridge arms of AM-MMC and is applicable to different operating conditions, further improving the dynamic performance and operational stability of AM-MMC.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for energy balancing control between bridge arms of a bridge arm reuse type MMC, comprising:

[0008] Determine the reuse mode of the bridge arm reuse type MMC phase unit;

[0009] Based on the multiplexing mode, and combining the correspondence between the reference voltage of each bridge arm in the phase unit and the reference voltage of the equivalent bridge arm in the bridge arm multiplexing type MMC, the distribution of the reference voltage of each bridge arm in the phase unit under the corresponding multiplexing mode is independently controlled by the equivalent lower bridge arm voltage distribution coefficient when the phase unit is operating in the lower bridge arm multiplexing mode or the equivalent upper bridge arm voltage distribution coefficient when the phase unit is operating in the upper bridge arm multiplexing mode.

[0010] The equivalent upper arm voltage distribution coefficient and the equivalent lower arm voltage distribution coefficient are dynamically adjusted according to the deviation of the average capacitor voltage of different bridge arm submodules of the phase unit, thereby adjusting the distribution relationship of the equivalent bridge arm reference voltage in the three bridge arms and thus achieving energy balance among the bridge arms.

[0011] Secondly, the present invention provides an inter-arm energy balancing control system for an arm-reuse type MMC, comprising:

[0012] The reuse mode determination module is configured to determine the reuse mode of the bridge arm reuse type MMC phase unit;

[0013] The allocation module is configured to: based on the multiplexing mode, and combined with the correspondence between the reference voltage of each bridge arm in the phase unit and the reference voltage of the equivalent bridge arm in the bridge arm multiplexing type MMC, independently control the allocation of the reference voltage of each bridge arm in the phase unit under the corresponding multiplexing mode by means of the equivalent lower bridge arm voltage allocation coefficient when the phase unit is operating in the lower bridge arm multiplexing mode or the equivalent upper bridge arm voltage allocation coefficient when the phase unit is operating in the upper bridge arm multiplexing mode.

[0014] The energy balance control module is configured to dynamically adjust the equivalent upper arm voltage distribution coefficient and the equivalent lower arm voltage distribution coefficient according to the deviation of the average value of the capacitor voltage of different bridge arm submodules of the phase unit, thereby adjusting the distribution relationship of the equivalent bridge arm reference voltage in the three bridge arms and thus achieving energy balance between bridge arms.

[0015] Thirdly, the present invention provides an electronic device including a memory and a processor, and computer instructions stored in the memory and running on the processor, wherein the computer instructions, when executed by the processor, perform the method described in the first aspect.

[0016] Fourthly, the present invention provides a computer-readable storage medium for storing computer instructions, which, when executed by a processor, perform the method described in the first aspect.

[0017] The above one or more technical solutions have the following beneficial effects:

[0018] In this invention, by analyzing the combined relationship between the equivalent and actual bridge arm reference voltages of AM-MMC, an equivalent lower bridge arm voltage distribution coefficient is introduced when the phase unit operates in the lower bridge arm multiplexing mode and an equivalent upper bridge arm voltage distribution coefficient is introduced when the phase unit operates in the upper bridge arm multiplexing mode. An additional inter-bridge arm energy balance control actively and controllably adjusts the distribution of the reference wave in real time, significantly reducing the deviation between the capacitor voltage and rated value of each bridge arm submodule. This invention effectively solves the problem of inter-bridge arm energy imbalance in AM-MMC and is applicable to different operating conditions, further improving the dynamic performance and operational stability of AM-MMC.

[0019] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0021] Figure 1 This is a diagram of a three-phase AM-MMC topology.

[0022] Figure 2 This is a schematic diagram of the AM-MMC energy balance control process in Embodiment 1 of the present invention;

[0023] Figure 3 This is a schematic diagram of the allocation coefficient A value used in the general modulation system of Embodiment 1 of the present invention;

[0024] Figure 4 This is a schematic diagram of the steady-state bridge arm reference voltage before and after the additional energy equalization control stage in Embodiment 1 of the present invention;

[0025] Figure 5 This is a schematic diagram of the average capacitor voltage of the bridge arm submodule in Embodiment 1 of the present invention;

[0026] Figure 6 This is a schematic diagram of the DC component of the average capacitor voltage of the bridge arm submodule in Embodiment 1 of the present invention. Detailed Implementation

[0027] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0028] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations of the present invention.

[0029] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0030] Example 1

[0031] This embodiment discloses a method for energy balance control between bridge arms of a bridge arm reuse type MMC, including:

[0032] Determine the reuse mode of the bridge arm reuse type MMC phase unit;

[0033] Based on the multiplexing mode, and combining the correspondence between the reference voltage of each bridge arm in the phase unit and the reference voltage of the equivalent bridge arm in the bridge arm multiplexing type MMC, the distribution of the reference voltage of each bridge arm in the phase unit under the corresponding multiplexing mode is independently controlled by the equivalent lower bridge arm voltage distribution coefficient when the phase unit is operating in the lower bridge arm multiplexing mode or the equivalent upper bridge arm voltage distribution coefficient when the phase unit is operating in the upper bridge arm multiplexing mode.

[0034] The equivalent upper arm voltage distribution coefficient and the equivalent lower arm voltage distribution coefficient are dynamically adjusted based on the deviation of the average capacitor voltage of different bridge arm submodules of the phase unit. This adjusts the distribution relationship of the equivalent bridge arm reference voltage in the three bridge arms, thereby achieving energy balance among the bridge arms.

[0035] To more clearly illustrate this embodiment, the topology and basic working principle of AM-MMC will first be explained, such as... Figure 1 As shown, each phase unit of AM-MMC consists of an upper bridge arm, a multiplexed bridge arm, a lower bridge arm, two bridge arm inductors L, and two bridge arm switching switches K1 and K2. Each bridge arm contains N / 2 series sub-modules, where N can be calculated by the following formula:

[0036]

[0037] Among them, U dc U is the rated DC voltage. cN U is the rated voltage of the submodule capacitor. dc U cN All are determined by the system design parameters and scale.

[0038] The design concept of AM-MMC originates from the operating characteristics of traditional MMC. In a conventional MMC, each phase unit always has N sub-modules in operation. If the number of sub-modules in the upper bridge arm is small, the number of sub-modules in the lower bridge arm will be larger. In this case, some idle sub-modules in the upper bridge arm can be allocated to the lower bridge arm for modulation, thus reducing the number of sub-modules in the lower bridge arm. Similarly, if the number of sub-modules in the upper bridge arm is large, the number of sub-modules in the lower bridge arm will be small. In this case, some idle sub-modules in the lower bridge arm can be allocated to the upper bridge arm for modulation, thus reducing the number of sub-modules in the upper bridge arm. These idle sub-modules are used as multiplexed bridge arms, and the multiplexed bridge arms are time-division multiplexed according to the number of sub-modules required by the upper and lower bridge arms.

[0039] The following explanation uses the A-phase unit as an example to illustrate the operating principle of AM-MMC. Analogous to the upper and lower arm voltages of a conventional MMC, the voltage u between the positive terminal and the AC terminal of the upper arm of the AM-MMC is... epa This is called the equivalent upper arm voltage, which is the voltage u between the AC terminal and the negative terminal of the lower arm. ena This is called the equivalent lower bridge arm voltage. Ignoring the bridge arm inductance voltage drop, according to the voltage loop equation, we can obtain:

[0040]

[0041] As shown in equation (2), AM-MMC can convert the modulation of the AC output voltage into the modulation of the equivalent upper and lower bridge arm voltages. Under the control of the bridge arm switching switch, the multiplexed bridge arm can be connected in series with the upper and lower bridge arms to form composite upper and lower bridge arms, and the AM-MMC phase unit can operate in upper bridge arm multiplexing mode and lower bridge arm multiplexing mode, respectively. When K a1 Shutdown, K a2 When on, the upper bridge arm and the multiplexed bridge arm output in series, and the phase unit operates in the upper bridge arm multiplexing mode; when K a1 Conductivity, K a2 When turned off, the multiplexed bridge arm and the lower bridge arm are output in series, and the phase unit operates in the lower bridge arm multiplexing mode.

[0042] The general segmented bridge arm modulation method of AM-MMC is explained in detail below:

[0043] In MMC, the output voltages of the upper and lower bridge arms are symmetrical. Similarly, the equivalent output voltages of the upper and lower bridge arms in AM-MMC also exhibit corresponding symmetry, as do the reference voltages of the equivalent upper and lower bridge arms. and They can be represented as follows:

[0044]

[0045] Where m is the differential-mode reference voltage modulation ratio of the converter. The phase angle is the differential voltage.

[0046] The correspondence between the bridge arm reference voltage and the equivalent bridge arm reference voltage when the phase unit operates in different modes can be expressed as:

[0047]

[0048] in, and These are the reference voltages for the upper bridge arm, multiplexed bridge arm, and lower bridge arm in the phase unit, respectively.

[0049] Based on satisfying equations (4) and (5), the reference voltages of the equivalent upper and lower bridge arms can be allocated to the three bridge arms according to certain rules, and then the control sub-modules can be switched separately and independently to approximate the reference voltage wave. One of the innovations of this embodiment is that a general reference voltage allocation method is designed. This method can modify the allocation of reference voltage by adjusting the allocation coefficient, thereby increasing the control flexibility of the system.

[0050] Let A and C be DC voltage distribution coefficients, and B and D be AC ​​voltage distribution coefficients, then A + C = 1 and B + D = 1. When the phase unit operates in the lower arm multiplexing mode, the expression for the arm reference voltage is:

[0051]

[0052] When the phase unit operates in the upper arm multiplexing mode, the expression for the arm reference voltage is:

[0053]

[0054] As shown in equation (1), each arm of the AM-MMC contains N / 2 sub-modules, and the output voltage range of each arm during normal operation is [0, U]. dc / 2]. To ensure that the bridge arm reference voltage does not exceed the output voltage range, the distribution coefficients should satisfy A+B≤1, C+D≤1, and A, B, C, and D should all be within the range of [0,1]. Here, the modulation ratio m is not greater than 1.

[0055] Based on A+C=1 and B+D=1, we can further deduce that:

[0056]

[0057] Representing B, C, and D as A, the expressions for the reference voltages of the three bridge arms of the phase unit are as follows:

[0058]

[0059] In this context, "①" and "②" represent the phase unit operating in the lower arm multiplexing mode and the upper arm multiplexing mode, respectively, and the following formula is similar. It can be noted that after unifying all the allocation coefficients into variable A, the value of A not only determines the DC voltage allocation but also affects the AC voltage allocation. For ease of explanation and understanding, variable A will be specifically referred to as "symmetric allocation coefficient" in the subsequent instructions.

[0060] Equations (9) to (11) actually define a symmetrical general segmented bridge arm modulation method. The distribution relationship of the equivalent bridge arm voltage is consistent in different multiplexing modes, and the reference voltages of the upper and lower bridge arms are symmetrical. In fact, the distribution relationship of the multiplexed bridge arm and the lower bridge arm to the equivalent lower bridge arm voltage can be different from the distribution relationship of the multiplexed bridge arm and the upper bridge arm to the equivalent upper bridge arm voltage, thus obtaining a more general segmented bridge arm modulation expression, namely:

[0061]

[0062] Where x is the equivalent lower arm voltage distribution coefficient when the phase unit operates in the lower arm multiplexing mode, and y is the equivalent upper arm voltage distribution coefficient when the phase unit operates in the upper arm multiplexing mode, and 0≤x, y≤1.

[0063] The general split bridge arm modulation method determined by equations (12) to (14) has higher control flexibility. x and y can independently control the distribution relationship of the equivalent bridge arm voltage under different multiplexing modes. When x ≠ y, the reference voltages of the upper and lower bridge arms no longer have symmetry. When x = y, equations (9) to (11) are equivalent to equations (12) to (14).

[0064] AM-MMC consists of three phases and a total of nine arms. The phase units are equal in status, and the upper and lower arms of each phase unit are also equal in status. However, the multiplexed arms are not equal in status with the upper and lower arms. Therefore, AM-MMC has an energy balance problem among the arms. Split-arm modulation requires an additional energy balance control circuit to achieve a uniform distribution of phase unit energy among the three arms. Furthermore, when the parameters and status of the upper and lower arms of the multiplexed MMC are completely equal, the modulation method based on equations (9) to (11) can achieve energy balance; conversely, when the parameters and status of the upper and lower arms of the multiplexed MMC are not equal, the general split-arm modulation method shown in equations (12) to (14) must be used for energy balance.

[0065] In general, it is more common for the parameters and status of the upper and lower arms of a bridge-arm multiplexing type MMC to be completely equal. Therefore, the general segmented bridge arm modulation method determined by equations (9) to (11) is more practical and universal. As can be seen from equations (9) to (11), the symmetrical allocation coefficient A is the only controllable variable of the proposed general segmented bridge arm modulation. By adjusting the allocation coefficient, an energy balance control strategy between AM-MMC bridge arms is proposed, such as... Figure 2 As shown, taking phase A unit as an example, let u ca The average capacitor voltage of phase A submodule is expressed as follows:

[0066]

[0067] Among them, u cua u cma and u cda These are the average values ​​of the submodule capacitor voltages for the upper bridge arm, the multiplexed bridge arm, and the lower bridge arm, respectively. Since the upper and lower bridge arms are of equal status and symmetrical, u cua and u cda The DC components are equal. Choose u ca and u cma The difference between the DC components of the tracking object and the controlled object, respectively, is processed by a PI controller to obtain the adjustment amount ΔA of the symmetrical allocation coefficient A, where A = A0 + ΔA, and A0 is the initial value of the symmetrical allocation coefficient A. To ensure that the bridge arm reference voltage is within the range of the bridge arm output voltage, the value of A still needs to be between 0 and 1. After the energy balance control between the additional bridge arms, the split bridge arm modulation can actively and controllably adaptively adjust the allocation coefficient.

[0068] To verify the effectiveness of the proposed AM-MMC inter-arm energy balance control method, a single-ended AM-MMC system was built based on an electromagnetic transient simulation platform. The specific parameters of the system are shown in Table 1 below. The dynamic characteristics of AM-MMC before and after the addition of the inter-arm energy balance control method were verified by simulation. AM-MMC adopted the general segmented inter-arm modulation method corresponding to equations (9) to (11). At the beginning of the simulation, the symmetry allocation coefficient A was fixed at 0.5. After running for 4 seconds, the proposed inter-arm energy balance control method was applied to dynamically adjust the symmetry allocation coefficient A.

[0069] Table 1 AM-MMC Simulation Parameters

[0070]

[0071] Figure 3 The values ​​of the symmetric allocation coefficient A used by the modulation system before and after the energy equalization system is started are shown. After the additional energy equalization stage is activated for 4 seconds, the symmetric allocation coefficient A is adjusted from 0.5 to about 0.41 under the action of the control system. Figure 4 By comparing the steady-state bridge arm reference voltage of phase A unit before and after the additional energy equalization control stage, it can be seen that the reference voltage distribution results of the composite bridge arm are different under the effect of different distribution coefficients. Figure 5 The average value of the capacitor voltage in the bridge arm submodule is shown. After the additional energy balancing control is activated, the average capacitor voltage is controlled back to near the rated voltage, and the capacitor voltage fluctuation is correspondingly reduced. Figure 6 The extracted average DC component of the capacitor voltage shows that the additional energy balancing control loop effectively solves the problem of energy imbalance between bridge arms. The DC components of the capacitor voltage of the three bridge arms are adjusted to be consistent under the action of the control system.

[0072] This invention analyzes the combined relationship between the equivalent and actual bridge arm reference voltages of AM-MMC and designs a general segmented bridge arm modulation method. Based on the proposed modulation method, an active and controlled inter-arm energy balance control is added to actively and controllably adjust the distribution of the reference wave in real time, significantly reducing the deviation of the capacitor voltage and rated value of each bridge arm submodule. This invention effectively solves the problem of inter-arm energy imbalance in AM-MMC and is applicable to different operating conditions, further improving the dynamic performance and operational stability of AM-MMC.

[0073] Example 2

[0074] The purpose of this embodiment is to provide an inter-arm energy balancing control system for an arm-reuse type MMC, including:

[0075] The reuse mode determination module is configured to determine the reuse mode of the bridge arm reuse type MMC;

[0076] The allocation module is configured to: based on the multiplexing mode, and combined with the correspondence between the reference voltage of each bridge arm in the phase unit and the reference voltage of the equivalent bridge arm in the bridge arm multiplexing type MMC, independently control the allocation of the reference voltage of each bridge arm in the phase unit under the corresponding multiplexing mode by means of the equivalent lower bridge arm voltage allocation coefficient when the phase unit is operating in the lower bridge arm multiplexing mode or the equivalent upper bridge arm voltage allocation coefficient when the phase unit is operating in the upper bridge arm multiplexing mode.

[0077] The energy balance control module is configured to dynamically adjust the distribution of the reference voltage of the corresponding bridge arm according to the deviation of the average value of the capacitor voltage of different bridge arm submodules, so as to achieve energy balance between bridge arms.

[0078] In further embodiments, the following is also provided:

[0079] An electronic device includes a memory and a processor, as well as computer instructions stored in the memory and running on the processor. When executed by the processor, the computer instructions perform the method described in Embodiment 1. For brevity, further details are omitted here.

[0080] It should be understood that in this embodiment, the processor can be a central processing unit (CPU), or it can be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), 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, etc.

[0081] Memory may include read-only memory and random access memory, and provides instructions and data to the processor. A portion of memory may also include non-volatile random access memory. For example, memory may also store information about the device type.

[0082] A computer-readable storage medium for storing computer instructions, which, when executed by a processor, perform the method described in Embodiment 1.

[0083] The method in Embodiment 1 can be directly implemented by a hardware processor, or implemented by a combination of hardware and software modules within the processor. The software modules can reside in readily available storage media in the art, such as random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, or registers. This storage medium is located in memory; the processor reads information from the memory and, in conjunction with its hardware, completes the steps of the above method. To avoid repetition, a detailed description is not provided here.

[0084] A computer program product includes a computer program that, when executed by a processor, implements the method described in Embodiment 1.

[0085] The present invention also provides at least one computer program product tangibly stored on a non-transitory computer-readable storage medium. The computer program product includes computer-executable instructions, such as instructions included in program modules, which execute in a device on a target real or virtual processor to perform the processes / methods described above. Typically, program modules include routines, programs, libraries, objects, classes, components, data structures, etc., that perform specific tasks or implement specific abstract data types. In various embodiments, the functionality of program modules can be combined or divided among program modules as needed. The machine-executable instructions for the program modules can execute within a local or distributed device. In a distributed device, the program modules can reside in both local and remote storage media.

[0086] The computer program code used to implement the methods of the present invention may be written in one or more programming languages. This computer program code may be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing device, such that when executed by the computer or other programmable data processing device, the program code causes the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code may be executed entirely on a computer, partially on a computer, as a stand-alone software package, partially on a computer and partially on a remote computer, or entirely on a remote computer or server.

[0087] In the context of this invention, computer program code or related data may be carried by any suitable carrier to enable a device, apparatus, or processor to perform the various processes and operations described above. Examples of carriers include signals, computer-readable media, and the like. Examples of signals may include electrical, optical, radio, sound, or other forms of propagation signals, such as carrier waves, infrared signals, etc.

[0088] Those skilled in the art will recognize that the units and algorithm steps described in conjunction with the embodiments herein can be implemented in electronic hardware or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0089] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for energy balance control between bridge arms in a bridge arm reuse type MMC, characterized in that, include: Determine the reuse mode of the phase unit of the bridge arm reuse type MMC; take the voltage between the positive terminal and the AC terminal of the upper bridge arm of the bridge arm reuse type MMC as the equivalent upper bridge arm voltage, and take the voltage between the AC terminal and the negative terminal of the lower bridge arm of the bridge arm reuse type MMC as the equivalent lower bridge arm voltage. Based on the multiplexing mode, and considering the correspondence between the reference voltage of each arm in the phase unit and the reference voltage of the equivalent arm in the multiplexing MMC, the distribution of the reference voltage of each arm in the phase unit under the corresponding multiplexing mode is independently controlled by the equivalent lower arm voltage distribution coefficient when the phase unit operates in the lower arm multiplexing mode or the equivalent upper arm voltage distribution coefficient when the phase unit operates in the upper arm multiplexing mode; specifically: In this context, "①" and "②" represent the phase unit operating in the lower arm multiplexing mode and the phase unit operating in the upper arm multiplexing mode, respectively. U dc DC rated voltage, m The differential-mode reference voltage modulation ratio of the converter. φ u The phase angle of the differential mode voltage. x This is the equivalent lower arm voltage distribution coefficient when the phase unit operates in lower arm multiplexing mode. y This is the equivalent upper arm voltage distribution coefficient when the phase unit operates in the upper arm multiplexing mode; u ua , u ma and u da These are the reference voltages for the upper bridge arm, multiplexed bridge arm, and lower bridge arm in the phase unit, respectively. The equivalent upper arm voltage distribution coefficient and the equivalent lower arm voltage distribution coefficient are dynamically adjusted according to the deviation of the average value of the capacitor voltage of different bridge arm submodules of the phase unit, thereby adjusting the distribution relationship of the equivalent bridge arm reference voltage in the three bridge arms and thus achieving energy balance between bridge arms. The equivalent lower arm voltage distribution coefficient of the phase unit when operating in the lower arm multiplexing mode is greater than or equal to 0 and less than or equal to 1; the equivalent upper arm voltage distribution coefficient of the phase unit when operating in the upper arm multiplexing mode is greater than or equal to 0 and less than or equal to 1. When the parameters and positions of the upper and lower arms of a bridge arm multiplexing MMC are completely equivalent, a modulation method with symmetrical upper and lower arm reference voltages is adopted. In this case, the equivalent upper arm voltage distribution coefficient and the equivalent lower arm voltage distribution coefficient are consistent, collectively referred to as the symmetrical distribution coefficient. Adjusting the symmetrical distribution coefficient achieves energy balance between the bridge arms of the bridge arm multiplexing MMC. Specifically: Calculate the average value of the phase unit submodule capacitor voltage based on the average value of the submodule capacitor voltage of the upper bridge arm, the reused bridge arm, and the lower bridge arm; The difference between the average value of the capacitor voltage of the submodule of the multiplexed bridge arm and the DC component of the average value of the capacitor voltage of the phase unit submodule is passed through a PI controller to obtain the adjustment amount of the symmetric allocation coefficient. The reference voltages of the upper arm, multiplexed arm, and lower arm are adjusted based on the adjustment amount of the obtained symmetrical allocation coefficient, thereby modulating the output voltage of each arm.

2. The energy balance control method between bridge arms of a bridge arm reuse type MMC as described in claim 1, characterized in that, When the equivalent lower arm voltage distribution coefficient of the phase unit operating in the lower arm multiplexing mode is not equal to the equivalent upper arm voltage distribution coefficient of the phase unit operating in the upper arm multiplexing mode, the upper arm reference voltage and lower arm reference voltage of the multiplexed MMC are not symmetrical; when the equivalent lower arm voltage distribution coefficient of the phase unit operating in the lower arm multiplexing mode is equal to the equivalent upper arm voltage distribution coefficient of the phase unit operating in the upper arm multiplexing mode, the upper arm reference voltage and lower arm reference voltage of the multiplexed MMC are symmetrical.

3. The energy balance control method between bridge arms of a bridge arm reuse type MMC as described in claim 1, characterized in that, The sum of the adjustment amount of the symmetric allocation coefficient and the initial value of the symmetric allocation coefficient ranges from 0 to 1.

4. An inter-arm energy balancing control system for an arm-reuse type MMC, employing the inter-arm energy balancing control method for an arm-reuse type MMC as described in any one of claims 1-3, characterized in that, include: The reuse mode determination module is configured to determine the reuse mode of the bridge arm reuse type MMC phase unit; The allocation module is configured to: based on the multiplexing mode, and combined with the correspondence between the reference voltage of each bridge arm in the phase unit and the reference voltage of the equivalent bridge arm in the bridge arm multiplexing type MMC, independently control the allocation of the reference voltage of each bridge arm in the phase unit under the corresponding multiplexing mode by means of the equivalent lower bridge arm voltage allocation coefficient when the phase unit is operating in the lower bridge arm multiplexing mode or the equivalent upper bridge arm voltage allocation coefficient when the phase unit is operating in the upper bridge arm multiplexing mode. The energy balance control module is configured to dynamically adjust the equivalent upper arm voltage distribution coefficient and the equivalent lower arm voltage distribution coefficient according to the deviation of the average value of the capacitor voltage of different bridge arm submodules of the phase unit, thereby adjusting the distribution relationship of the equivalent bridge arm reference voltage in the three bridge arms and thus achieving energy balance between bridge arms.

5. An electronic device, characterized in that, It includes a memory and a processor, as well as computer instructions stored in the memory and running on the processor, which, when executed by the processor, perform the method according to any one of claims 1-3.

6. A computer-readable storage medium, characterized in that, Used to store computer instructions, which, when executed by a processor, perform the method described in any one of claims 1-3.

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