Overvoltage suppression method, device and equipment after transient operation of MMC (Modular Multilevel Converter), and storage medium

Abstract

The invention discloses an overvoltage suppression method, device and equipment after MMC transient operation and a storage medium, and belongs to the technical field of power electronic converters, the overvoltage suppression method and device are applied to a system formed by a modular multilevel converter MMC, the system comprises the MMC, a converter control module and a valve control module, the MMC comprises a plurality of sub-modules, the suppression method is operated in the converter control module, and the valve control module is used for controlling the MMC to operate in the converter control module. The suppression method comprises the following steps: acquiring a real-time value of an average voltage of a sub-module and a voltage calculation value of the sub-module; determining a preset additional coefficient based on the real-time value of the average voltage of the sub-module and the voltage calculation value of the sub-module; determining an overvoltage active suppression strategy based on a preset additional coefficient, the AC reference wave of the MMC and the DC bias; and when the real-time value of the average voltage of the sub-modules is greater than a preset threshold value, inputting an overvoltage active suppression strategy to carry out overvoltage suppression. According to the invention, AC and DC overvoltage suppression after transient operation of the MMC is realized, and the operation requirement of the MMC is met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power electronic converters, and particularly relates to a MMC post-transient operation overvoltage suppression method, device, equipment and storage medium. BACKGROUND

[0002] The traditional method for suppressing overvoltage after transient operation of a modular multilevel converter is to limit the power recovery speed when networking and limit the energy consumption resistor exit speed when islanding, which is not conducive to the rapid recovery of power after transient operation. Therefore, there is an urgent need for a simple and effective method and device for suppressing overvoltage after transient operation without affecting power recovery, to meet the operation needs of the modular multilevel converter. SUMMARY

[0003] The application develops a MMC post-transient operation overvoltage suppression method, aiming to realize the suppression of AC and DC overvoltage after transient operation of a modular multilevel converter, and meet the operation needs of the modular multilevel converter.

[0004] Technical scheme: The embodiment of the application provides a MMC post-transient operation overvoltage suppression method, applied to a system composed of a modular multilevel converter (MMC), the system comprising an MMC, a converter control module and a valve control module, the MMC comprising a plurality of sub-modules, the suppression method running in the converter control module, and the suppression method comprising the following steps:

[0005] obtaining a real-time value of an average voltage of the sub-modules of the MMC and a sub-module voltage calculation value used by the valve control module to calculate the number of sub-modules;

[0006] determining a preset additional coefficient based on the real-time value of the average voltage of the sub-modules and the sub-module voltage calculation value;

[0007] determining an overvoltage active suppression strategy based on the preset additional coefficient, an AC reference wave and a DC bias of the MMC;

[0008] when the real-time value of the average voltage of the sub-modules of the MMC is greater than a preset threshold, the overvoltage active suppression strategy is put into operation for overvoltage suppression.

[0009] In some embodiments, the real-time value of the average voltage of the sub-modules is obtained, comprising:

[0010] the valve control module obtains the sum of the real-time values of the voltages of all normally operating sub-modules in the MMC, and determines the quotient of the sum of the real-time values of the voltages of all normally operating sub-modules in the MMC and the number of all normally operating sub-modules in the MMC as the real-time value of the average voltage of the sub-modules.

[0011] In some embodiments, when the valve control module calculates the number of conducting submodules using a fixed rated voltage, obtaining the calculated voltage value of the submodule includes:

[0012] The fixed rated voltage of the valve control module is determined as the calculated voltage value of the submodule.

[0013] When the valve control module uses a variable rated voltage to calculate the number of conducting submodules, it obtains the calculated voltage value of the submodule, including:

[0014] Based on the number of faulty submodules in the bridge arm with the most faults in the MMC, the variable rated voltage of the valve control module is dynamically adjusted, and the dynamically adjusted variable rated voltage of the valve control module is determined as the calculated voltage value of the submodule.

[0015] In some embodiments, the preset additional coefficients include a preset AC reference waveform coefficient and a preset DC bias coefficient. The preset AC reference waveform coefficient is the result obtained by dividing the calculated value of the submodule voltage by the real-time value of the average voltage of the submodule. The preset DC bias coefficient is the result obtained by dividing the calculated value of the submodule voltage by the minimum value among the real-time value of the average voltage of the submodule, the margin coefficient, and the overvoltage limit value of the real-time value of the average voltage of the submodule of the MMC.

[0016] In some embodiments, the step of determining an active overvoltage suppression strategy includes:

[0017] The preset AC reference waveform coefficient is adjusted using the calculated submodule voltage value and the real-time value of the average submodule voltage, and the preset DC bias coefficient is adjusted using the calculated submodule voltage value, the real-time value of the average submodule voltage, and the submodule overvoltage limit value of the MMC.

[0018] Depending on the overvoltage suppression requirements, one can choose to multiply only the preset AC reference waveform coefficient with the AC reference waveform of the MMC; or choose to multiply the preset AC reference waveform coefficient with the AC reference waveform of the MMC, and simultaneously multiply the preset DC bias coefficient with the DC bias of the MMC, to obtain the active overvoltage suppression strategy.

[0019] Accordingly, the overvoltage suppression device after transient operation of an MMC described in this application embodiment is applied to a system composed of a modular multilevel converter (MMC). The system includes an MMC, a converter control module, and a valve control module. The MMC includes several sub-modules. The suppression device operates within the converter control module. The device includes:

[0020] The acquisition unit is used to acquire the real-time value of the average voltage of the submodule and the parameters required for calculating the voltage of the submodule;

[0021] The valve control unit is used to calculate the real-time value of the average voltage of the submodule and the calculated value of the voltage of the submodule;

[0022] The overvoltage active suppression unit is used to determine a preset additional coefficient based on the real-time value of the average voltage of the submodule and the calculated value of the voltage of the submodule, and to determine an overvoltage active suppression strategy based on the preset additional coefficient, the AC reference wave of the MMC and the DC bias.

[0023] The judgment unit is used to determine the relationship between the real-time value of the average voltage of the submodule and a preset threshold, and to determine whether to activate the overvoltage active suppression strategy to suppress overvoltage when the real-time value of the average voltage of the submodule is greater than the preset threshold.

[0024] In some embodiments, obtaining the real-time value of the average voltage of the submodule includes:

[0025] The valve control unit calculates the sum of the real-time voltage values ​​of all normally functioning sub-modules in the MMC, and then uses the quotient of the sum of the real-time voltage values ​​of all normally functioning sub-modules in the MMC and the number of normally functioning sub-modules in the MMC to obtain the real-time average voltage value of the sub-module.

[0026] In some embodiments, when the valve control unit calculates the number of conducting submodules using a fixed rated voltage, obtaining the calculated voltage value of the submodule includes:

[0027] The fixed rated voltage of the valve control unit is determined as the calculated voltage value of the submodule.

[0028] In some embodiments, when the valve control unit uses a variable rated voltage to calculate the number of conducting submodules, obtaining the calculated voltage value of the submodule includes:

[0029] Based on the number of faulty submodules in the bridge arm with the most faults collected by the acquisition unit, the variable rated voltage of the valve control unit is dynamically adjusted, and the dynamically adjusted variable rated voltage of the valve control unit is determined as the calculated voltage value of the submodule.

[0030] Accordingly, an electronic device according to an embodiment of this application includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the steps of the overvoltage suppression method after MMC transient operation as described above.

[0031] Accordingly, the computer-readable storage medium described in the embodiments of this application stores a computer program thereon, which, when executed by a processor, implements the steps of the overvoltage suppression method after transient operation of MMC as described above.

[0032] Beneficial Effects: Compared with the prior art, the overvoltage suppression method, apparatus, device, and storage medium provided in this application embodiment for MMC transient operation includes: obtaining the real-time value of the average voltage of the MMC sub-modules and the calculated value of the sub-module voltage obtained by the valve control module; determining a preset additional coefficient based on the real-time value and the calculated value of the sub-module average voltage; determining an active overvoltage suppression strategy based on the preset additional coefficient, the AC reference waveform and DC bias of the MMC; and implementing the active overvoltage suppression strategy when the real-time value of the average voltage of the MMC sub-modules exceeds a preset threshold. Specifically, by multiplying the AC reference waveform and DC bias of the MMC by a preset coefficient, the reference waveform of the MMC is suppressed by the preset coefficient, preventing AC voltage overvoltage. Therefore, it is possible to suppress AC and DC overvoltages after MMC transient operation, ensuring the stable operation of the MMC. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is an overall flowchart of the active suppression method for AC / DC overvoltage after transient operation of a modular multilevel converter provided in an embodiment of the present invention;

[0035] Figure 2 A detailed flowchart of the active suppression method for AC / DC overvoltage after transient operation of a modular multilevel converter provided in this embodiment of the invention;

[0036] Figure 3 A schematic diagram illustrating the principle of the active suppression method for AC / DC overvoltage after transient operation of a modular multilevel converter provided in an embodiment of the present invention;

[0037] Figure 4 This is a structural block diagram of the active AC / DC overvoltage suppression device for transient operation of a modular multilevel converter provided in an embodiment of the present invention.

[0038] Figure 5 This is a schematic diagram of the structure of an electronic device according to an embodiment of this application.

[0039] Reference numerals: 301-Acquisition unit; 302-Valve control unit; 303-Judgment unit; 304-Overvoltage active suppression unit. Detailed Implementation

[0040] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0041] It should be understood that although the terms first, second, etc., may be used herein to describe various components, these components should not be limited by these terms. These terms are used to distinguish one component from another. Therefore, the first component discussed below may be referred to as the second component without departing from the teachings of this application. As used herein, the term "and / or" includes all combinations of any and more of the associated listed items.

[0042] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of exemplary embodiments and may not be to scale. The modules or processes shown in the drawings are not necessarily essential for implementing this application and therefore should not be used to limit the scope of protection of this application.

[0043] A Modular Multilevel Converter (MMC) is composed of multiple cascaded sub-modules (SMs) with identical structures. The sub-modules can be categorized into three types: half-H-bridge, full-H-bridge, and double-clamped. By employing a modular design and nearest-level modulation (NLM), the MMC reduces harmonic content and switching losses, and is widely used in high-voltage direct current transmission, static var compensators (SVCs), DC-connected energy storage, and low-frequency power transmission.

[0044] Transient operation refers to the instantaneous response and dynamic behavior of a power system when sudden events, faults, or changes occur. These events include short-circuit faults, valve group activation / deactivation, switch operations, load changes, generator starting or shutdown, etc. During transient operation, parameters such as system voltage, current, and power may undergo instantaneous changes.

[0045] Traditional methods for suppressing overvoltage after transient operation of modular multilevel converters (MMCs) involve limiting the power recovery speed when connected to the grid and limiting the disconnection speed of energy-consuming resistors when isolated. These methods are not conducive to rapid power recovery after transient operation. Therefore, there is an urgent need for a simple and effective method and device to suppress overvoltage after transient operation without affecting power recovery, so as to meet the operational requirements of MMCs.

[0046] In view of this, this application provides an overvoltage suppression method after transient operation of an MMC, which is applied to a system composed of a modular multilevel converter (MMC). The method multiplies the AC reference wave and DC bias of the MMC by a preset coefficient, thereby suppressing the AC and DC overvoltages after transient operation of the MMC and ensuring the stable operation of the MMC, thus solving at least part of the above-mentioned technical problems.

[0047] In some embodiments, the system composed of modular multilevel converters (MMCs) can be a flexible DC transmission system, which includes, but is not limited to, flexible DC grids, offshore wind power, and ultra-high voltage DC transmission.

[0048] Please see Figure 1 and Figure 2 , Figure 1 This illustration shows the overall flow of the overvoltage suppression method after transient operation of MMC according to an embodiment of this application. Figure 2 The illustration shows the specific flow of the overvoltage suppression method after transient operation of the MMC according to an embodiment of this application. The system composed of a modular multilevel converter (MMC) includes the MMC, a converter control module, and a valve control module. The MMC includes several sub-modules. The suppression method operates in the converter control module. The overvoltage suppression method after transient operation of the MMC includes the following steps:

[0049] Step 101: Obtain the real-time value of the average voltage Uv of the MMC submodule. avg The valve control module is used to calculate the submodule voltage Uv value for determining the number of submodules. avgcal .

[0050] Among them, the submodule voltage calculation value Uv avgcal It is obtained from the valve control module by the converter control module.

[0051] In some embodiments, the real-time value Uv of the average voltage of the MMC submodules is obtained through the valve control module. avg The specific methods are as follows:

[0052] The valve control module obtains the sum of the real-time voltage values ​​Uv of all normally functioning sub-modules of the MMC. SUM And sum the real-time voltage values ​​Uv of all normally functioning submodules in the MMC. SUM The number N of all normally functioning submodules in MMC v The quotient is determined as the real-time value of the average voltage of the MMC submodules, i.e.

[0053]

[0054] In some embodiments, the calculated submodule voltage value Uv can be obtained through method b1.avgcal :

[0055] Based on the valve control module using a fixed rated voltage Uv avgN Calculate the number of sub-modules to be deployed in the bridge arm. Method b1 involves setting the fixed rated voltage Uv of the valve control module. avgN The calculated voltage value Uv for the submodule was determined. avgcal That is, UV. avgcal =Uv avgN .

[0056] In some embodiments, the calculated submodule voltage value Uv can be obtained through method b2. avgcal :

[0057] Based on the valve control module, a variable rated voltage Uv is used. avgNC Calculate the number of submodules deployed in the bridge arm. Method b2 is based on the number of faulty submodules Ns in the bridge arm with the most faulty submodules in the MMC. m_bad The variable rated voltage Uv of the dynamic adjustment valve control module avgNC The dynamically adjusted UV avgNC The calculated voltage value Uv for the submodule is determined. avgcal .

[0058] Among them, UV avgcal satisfy U dcN For the modular multilevel converter, the DC rated voltage is N. sm This represents the total number of submodules in a single bridge arm.

[0059] Step 102: Based on the real-time value Uv of the submodule average voltage avg Calculated voltage value Uv of sub-module avgcal Determine the preset additional coefficient.

[0060] Specifically, the preset additional coefficients include the preset AC reference wave coefficient k. Mac and preset DC bias coefficient k Mdc Preset AC reference wave coefficient k Mac The calculated voltage value Uv for the submodule avgcal Divide by the real-time value of the average voltage of the submodule, Uv avg The result obtained is Preset DC bias coefficient k Mdc The calculated voltage value Uv for the submodule avgcal Divide by the real-time value of the average voltage of the submodule, Uv avg Margin coefficient k u The overvoltage limit Uv of the real-time average voltage of the submodule over The result obtained by finding the minimum value among the three is...

[0061]

[0062] Wherein, the margin coefficient k u Satisfying k u ≤1. Overvoltage limit Uv of the real-time average voltage of the submodule. over It can be determined based on AC overvoltage limits and DC overvoltage limits.

[0063] Step 103: Determine the active overvoltage suppression strategy based on the preset additional coefficients, the AC reference waveform of MMC, and the DC bias.

[0064] Among them, such as Figure 3 As shown, the AC reference wave of the MMC is the AC reference wave U output by the modular multilevel conventional control strategy. ref The DC bias of the MMC is a modular multi-level conventional control strategy that outputs DC bias U. dvbia .

[0065] In some embodiments, an active overvoltage suppression strategy can be determined through the following steps:

[0066] Step 1: Calculate the value Uv using the submodule voltage. avgcal Real-time value of average voltage Uv of submodule avg Dynamically adjust the preset AC reference wave coefficient k Mac Calculate the value Uv using the submodule voltage. avgcal Real-time value of average voltage Uv of submodule avg The overvoltage limit Uv of the real-time average voltage of the submodule over Dynamically adjust the preset DC bias coefficient k Mdc ;

[0067] Step 2, preset the AC reference wave coefficient k Mac AC reference wave with MMC (i.e., U) ref Multiplying these together yields the active overvoltage suppression strategy.

[0068] In some embodiments, an active overvoltage suppression strategy can be determined through the following steps:

[0069] Step 1: Calculate the value Uv using the submodule voltage. avgcal Real-time value of average voltage Uv of submodule avg Dynamically adjust the preset AC reference wave coefficient k Mac Calculate the value Uv using the submodule voltage. avgcal Real-time value of average voltage Uv of submodule avg The overvoltage limit Uv of the real-time average voltage of the submodule over Dynamically adjust the preset DC bias coefficient k Mdc ;

[0070] Step 2, preset the AC reference wave coefficient k Mac AC reference wave with MMC (i.e., U) ref Multiply by the preset DC bias coefficient k Mdc DC bias of MMC (i.e., U) dvbia Multiplying these together yields the active overvoltage suppression strategy.

[0071] Step 104: When the real-time value of the average voltage of the MMC submodules is greater than the preset threshold, the overvoltage active suppression strategy is activated to suppress overvoltage.

[0072] The preset threshold is a fixed value Uv. t constant value Uv t Select a value Uv that is 1.05-1.3 times the calculated submodule voltage. avgcal constant value Uv t It can be adjusted according to the simulated AC overvoltage conditions.

[0073] In some embodiments, the method for determining the exit from the active overvoltage suppression strategy is as follows:

[0074] Real-time value of average voltage Uv of submodule avg Less than a fixed value Uv avgtui After a period of time, the overvoltage active suppression strategy is discontinued. That is, the preset AC reference waveform coefficient k... Mac The reference wave (i.e., U) that is not connected to the MMC ref Multiply by the preset DC bias coefficient k Mdc Not with DC bias of MMC (i.e., U) dvbia Multiplying these values ​​together results in the exit of the active overvoltage suppression strategy.

[0075] Among them, the constant value Uv avgtui Less than or equal to a fixed value Uv t .

[0076] It should be noted that the time period can be 0 or a period of less than or equal to 1 ms. When set to less than or equal to 1 ms, the purpose is to prevent the impact of short-term fluctuations in the submodule capacitor voltage. When not 0, it can be set to 1 ms or less than 1 ms, as long as it achieves the anti-jitter effect.

[0077] Specifically, when the real-time value of the average voltage of the submodule is Uv avg Less than the submodule overvoltage danger value Uv avgdan At this time, the preset AC reference wave coefficient does not need to be multiplied with the AC reference wave of the MMC, and the preset DC bias coefficient does not need to be multiplied with the DC bias of the MMC.

[0078] Among them, UV avgdan The submodule voltage calculation value Uv can be obtained. avgcalOvervoltage limit Uv of the real-time value of the average voltage of the submodule over The value between, i.e., Uv avgcal <Uv avgdan ≤Uv over .

[0079] In some embodiments, when the overvoltage active suppression strategy is not engaged or disengaged, the AC reference waveform and DC bias are not multiplied by an additional coefficient, i.e., they are switched to being multiplied by 1, such as... Figure 3 Set CHOOSE to 0.

[0080] Accordingly, this application also provides an overvoltage suppression device after transient operation of MMC. Please refer to [link to relevant documentation]. Figure 4 , Figure 4 This illustration shows a structural block diagram of the active AC / DC overvoltage suppression device after transient operation of an MMC, according to an embodiment of this application. The active AC / DC overvoltage suppression device after transient operation of an MMC provided in this application embodiment is applied to a system composed of a modular multilevel converter (MMC). This system includes a MMC, a converter control module, and a valve control module. The MMC includes several sub-modules. The suppression device operates within the converter control module, and the device includes:

[0081] The acquisition unit 301 is used to acquire the real-time value of the average voltage of the submodule and the parameters required for calculating the voltage of the submodule.

[0082] Valve control unit 302 is used to calculate the real-time value of the average voltage of the submodule and the calculated value of the submodule voltage;

[0083] The overvoltage active suppression unit 304 is used to determine a preset additional coefficient based on the real-time value of the average voltage of the submodule and the calculated value of the voltage of the submodule, and to determine an overvoltage active suppression strategy based on the preset additional coefficient, the AC reference wave of the MMC and the DC bias.

[0084] The judgment unit 303 is used to determine the relationship between the real-time value of the average voltage of the submodule and the preset threshold, and to determine whether to activate the overvoltage active suppression strategy to suppress overvoltage when the real-time value of the average voltage of the submodule is greater than the preset threshold.

[0085] It should be noted that the acquisition unit 301 acquires the voltage of all submodules in the MMC and the number of faulty submodules in each bridge arm, and transmits this data to the valve control unit 302. The valve control unit 302 then calculates the real-time value Uv of the average voltage of the submodules. avg Calculated voltage value Uv of sub-module avgcal The valve control unit 302 calculates the real-time value Uv of the average voltage of the submodule. avg Calculated voltage value Uv of sub-module avgcal It is sent to the judgment unit 303 and the overvoltage active suppression unit 304.

[0086] The judgment unit 303 determines whether to activate or deactivate the active overvoltage suppression strategy.

[0087] The overvoltage active suppression unit 304 calculates the preset AC reference waveform coefficient k based on the received information. Mac and preset DC bias coefficient k Mdc The valve control unit 302 receives the k calculated by the overvoltage active suppression unit 304. Mac and k Mdc Combined with the AC reference wave of MMC (i.e., U) ref ) and DC bias of MMC (i.e., U dvbia Thus, an active overvoltage suppression strategy was obtained.

[0088] Accordingly, this application also provides an electronic device, please refer to... Figure 5 , Figure 5 A structural diagram of an electronic device according to an embodiment of this application is shown. The electronic device includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the steps of the above-described overvoltage suppression method after MMC transient operation. Since the overvoltage suppression method after MMC transient operation has been described in detail above, it will not be repeated here.

[0089] Accordingly, embodiments of this application also provide a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the steps of the above-described overvoltage suppression method after MMC transient operation. Since the overvoltage suppression method after MMC transient operation has been described in detail above, it will not be repeated here.

[0090] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0091] The above provides a detailed description of the overvoltage suppression method, apparatus, device, and storage medium after transient operation of MMC provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for suppressing overvoltage after transient operation of an MMC, characterized in that, A system composed of a modular multilevel converter (MMC) is applied, the system including the MMC, a converter control module, and a valve control module. The MMC includes several sub-modules. The suppression method operates in the converter control module, and the suppression method includes the following steps: Obtain the real-time value of the average voltage of the sub-modules of the MMC and the calculated value of the sub-module voltage used by the valve control module to calculate the number of sub-modules; Based on the real-time value of the average voltage of the submodule and the calculated value of the voltage of the submodule, a preset additional coefficient is determined; Based on the preset additional coefficients, the AC reference waveform of the MMC, and the DC bias, an active overvoltage suppression strategy is determined. When the real-time value of the average voltage of the sub-modules of the MMC is greater than a preset threshold, the overvoltage active suppression strategy is activated to suppress overvoltage.

2. The overvoltage suppression method after transient operation of MMC according to claim 1, characterized in that, Obtaining the real-time value of the average voltage of the submodule includes: The valve control module obtains the sum of the real-time voltage values ​​of all normally functioning sub-modules in the MMC, and determines the real-time average voltage value of the sub-module by dividing the sum of the real-time voltage values ​​of all normally functioning sub-modules in the MMC by the number of normally functioning sub-modules in the MMC.

3. The overvoltage suppression method after transient operation of MMC according to claim 1, characterized in that, When the valve control module calculates the number of sub-modules to be turned on using a fixed rated voltage, it obtains the calculated voltage value of the sub-module, including: The fixed rated voltage of the valve control module is determined as the calculated voltage value of the submodule.

4. The overvoltage suppression method after transient operation of MMC according to claim 1, characterized in that, When the valve control module uses a variable rated voltage to calculate the number of conducting submodules, it obtains the calculated voltage value of the submodule, including: Based on the number of faulty submodules in the bridge arm with the most faults in the MMC, the variable rated voltage of the valve control module is dynamically adjusted, and the dynamically adjusted variable rated voltage of the valve control module is determined as the calculated voltage value of the submodule.

5. The overvoltage suppression method after transient operation of MMC according to claim 1, characterized in that, The preset additional coefficients include a preset AC reference wave coefficient and a preset DC bias coefficient. The preset AC reference wave coefficient is the result obtained by dividing the calculated value of the submodule voltage by the real-time value of the average voltage of the submodule. The preset DC bias coefficient is the result obtained by dividing the calculated value of the submodule voltage by the minimum value among the real-time value of the average voltage of the submodule, the margin coefficient, and the overvoltage limit value of the real-time value of the average voltage of the submodule of the MMC.

6. The overvoltage suppression method after transient operation of MMC according to claim 5, characterized in that, The steps for determining an active overvoltage suppression strategy include: The preset AC reference waveform coefficient is adjusted using the calculated submodule voltage value and the real-time value of the average submodule voltage, and the preset DC bias coefficient is adjusted using the calculated submodule voltage value, the real-time value of the average submodule voltage, and the submodule overvoltage limit value of the MMC. Depending on the overvoltage suppression requirements, one can choose to multiply only the preset AC reference waveform coefficient with the AC reference waveform of the MMC; or choose to multiply the preset AC reference waveform coefficient with the AC reference waveform of the MMC, and simultaneously multiply the preset DC bias coefficient with the DC bias of the MMC, to obtain the active overvoltage suppression strategy.

7. An overvoltage suppression device after transient operation of an MMC, characterized in that, A system is applied to a modular multilevel converter (MMC) system, the system including an MMC, a converter control module, and a valve control module. The MMC includes several sub-modules. The suppression device operates within the converter control module, and the device includes: The acquisition unit (301) is used to acquire the real-time value of the average voltage of the submodule and the parameters required for calculating the voltage of the submodule; Valve control unit (302) is used to calculate the real-time value of the average voltage of the submodule and the calculated value of the voltage of the submodule; The overvoltage active suppression unit (304) is used to determine a preset additional coefficient based on the real-time value of the average voltage of the submodule and the calculated value of the voltage of the submodule, and to determine an overvoltage active suppression strategy based on the preset additional coefficient, the AC reference wave of the MMC and the DC bias. The judgment unit (303) is used to determine the relationship between the real-time value of the average voltage of the submodule and the preset threshold, and to determine whether to activate the overvoltage active suppression strategy to suppress overvoltage when the real-time value of the average voltage of the submodule is greater than the preset threshold.

8. The overvoltage suppression device after transient operation of MMC according to claim 7, characterized in that, Obtaining the real-time value of the average voltage of the submodule includes: The valve control unit (302) calculates the sum of the real-time voltage values ​​of all normally functioning sub-modules in the MMC, and determines the real-time average voltage value of the sub-module by dividing the sum of the real-time voltage values ​​of all normally functioning sub-modules in the MMC by the number of normally functioning sub-modules in the MMC.

9. The overvoltage suppression device after transient operation of MMC according to claim 7, characterized in that, When the valve control unit (302) calculates the number of conducting submodules using a fixed rated voltage, it obtains the calculated voltage value of the submodule, including: The fixed rated voltage of the valve control unit (302) is determined as the calculated voltage value of the submodule.

10. The overvoltage suppression device after transient operation of MMC according to claim 7, characterized in that, When the valve control unit (302) uses a variable rated voltage to calculate the number of conducting submodules, it obtains the calculated voltage value of the submodule, including: Based on the number of faulty submodules in the bridge arm with the most faults collected by the acquisition unit (301) in the MMC, the variable rated voltage of the valve control unit (302) is dynamically adjusted, and the dynamically adjusted variable rated voltage of the valve control unit (302) is determined as the calculated voltage value of the submodule.

11. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the overvoltage suppression method after transient operation of MMC as described in any one of claims 1-6.

12. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the overvoltage suppression method after transient operation of MMC as described in any one of claims 1-6.

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