Novel MMC topology introducing super capacitor and control method thereof

Abstract

The invention relates to the technical field of power electronics, in particular to a novel MMC topology introducing a super capacitor and a control method thereof, and the method comprises the steps: collecting a grid-side voltage, and carrying out the dq conversion of the grid-side voltage, and obtaining a dq-axis voltage; reversely deducing a reference current value according to the dq-axis voltage, and obtaining a circulating current reference value according to the power reference value and the direct current side voltage; in each control period, state prediction is carried out on a plurality of candidate sub-module input quantity combinations, an output current prediction value at the next moment is obtained based on prediction, the prediction value is compared with a current reference value, and a combination with the minimum current error is selected as a candidate combination; calculating a circulating current value corresponding to each candidate combination, and selecting the circulating current value closest to the circulating current reference value as a final sub-module number; according to a set voltage priority sequence, common capacitor sub-modules are preferentially used, and sub-modules which specifically need to be switched are selected according to the principle that super-capacitor sub-modules are complementarily used when common sub-modules are insufficient.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronics, in particular to a new MMC topology with supercapacitors and a control method thereof. BACKGROUND

[0002] Large-scale grid connection of new energy power generation not only optimizes the primary energy structure of the power system, but also effectively reduces carbon emissions and promotes the development of clean electricity. With the increasing penetration of new energy power generation in the power system, power converters play an important role in power conversion and are widely used. Among them, the modular multilevel converter (MMC) is widely used in high-voltage direct current transmission, energy storage systems and high-power motor drive systems due to its modular design, easy expansion and fault tolerance.

[0003] However, energy fluctuations inevitably occur between the sub-modules of each bridge arm in the traditional MMC, resulting in unbalanced sub-module capacitor voltages and affecting the operation of the converter system. At the same time, due to the multi-variable control requirements of MMC, its control system is relatively complex, and the traditional model predictive control cannot avoid the problems of weight factor design and large amount of calculation.

[0004] The information disclosed in this BACKGROUND section is only intended to enhance the understanding of the general background of the application, and should not be considered as recognition or implicit admission in any form that this information constitutes prior art known to those skilled in the art. SUMMARY

[0005] The present application provides a new MMC topology with supercapacitors and a control method thereof, thereby effectively solving the problems in the background art.

[0006] To achieve the above purpose, the technical solution adopted by the present application is as follows: a new MMC topology with supercapacitors, comprising: An MMC main circuit, the MMC main circuit comprising three-phase six bridge arms, each bridge arm comprising N sub-modules; Among them, at least part of the sub-modules use supercapacitors as capacitors, forming supercapacitor sub-modules; In each bridge arm, the supercapacitor sub-modules and ordinary capacitor sub-modules are alternately combined, and are connected in series with a bridge arm inductor to form a single bridge arm circuit.

[0007] The present application also includes a control method for a new MMC topology with supercapacitors, which controls the MMC topology as described above, comprising the following steps: Receive and set the active / reactive power reference values ​​of the converter, collect the grid-side voltage, perform dq transformation on the grid-side voltage to obtain the dq-axis voltage; deduce the reference current value based on the dq-axis voltage, and obtain the circulating current reference value based on the power reference value and the DC-side voltage; Within each control cycle, the state prediction is performed on several candidate combinations of the number of sub-modules to be deployed. Based on the prediction, the predicted value of the output current at the next moment is obtained. The predicted value is compared with the current reference value, and the combination with the smallest current error is selected as the candidate combination. Calculate the circulation value corresponding to each candidate combination, and select the one whose circulation value is closest to the circulation reference value as the final number of sub-modules; Based on the charging and discharging direction of each bridge arm and the capacitor voltage value of each submodule, the specific submodule to be switched is selected according to the set voltage priority order and the principle of prioritizing the use of ordinary capacitor submodules and supplementing with supercapacitor submodules when ordinary submodules are insufficient.

[0008] Furthermore, in the process of introducing supercapacitors into at least some sub-modules of the MMC main circuit bridge arm to form a supercapacitor sub-module, ordinary capacitor sub-modules and supercapacitor sub-modules are arranged alternately in each bridge arm.

[0009] Furthermore, The process involves predicting the state of several candidate combinations of submodule deployment quantities. Based on this prediction, the output current prediction value for the next moment is obtained. In each control cycle, the submodule combination whose level differs from the previous cycle by less than 1 is considered, i.e., the number of upper and lower bridge arm submodules in the previous cycle is ( n p , n n If the number of sub-modules is considered in the next cycle, then the combination of sub-modules will be examined. n p , n n ), ( n p +1, n n -1), ( n p -1, n n +1) The effect on output current; The calculation of the circulating current value corresponding to each candidate combination, and the selection of the combination that makes the circulating current value closest to the circulating current reference value as the final number of sub-modules, involves adjusting the combination of sub-module numbers obtained in the current tracking stage. That is, the number of upper and lower bridge arm sub-modules in the previous cycle is ( n p , n n Then examine the combination of the number of submodules () np , n n ), ( n p +1, n n +1), ( n p -1, n n -1), calculate the ring current value under the combination.

[0010] Further, the principle of selecting the specific sub-module to be switched according to the set voltage priority order and preferentially using the ordinary capacitor sub-module and supplementarily using the super capacitor sub-module when the ordinary sub-module is insufficient comprises: When it is detected that the current direction of a bridge arm is to charge the capacitor of the sub-module, the capacitor voltage is sorted from low to high in the ordinary capacitor sub-module, and the ordinary capacitor sub-module with the lowest voltage and lower than the set capacitor voltage reference value is selected to be put into, and if the number of ordinary sub-modules is insufficient, the super capacitor sub-module is supplemented to be put into; When it is detected that the current direction of a bridge arm is to discharge the capacitor of the sub-module, the capacitor voltage is sorted from high to low in the ordinary capacitor sub-module, and the ordinary capacitor sub-module with the highest voltage and higher than the set capacitor voltage reference value is selected to be put into, and if the number of ordinary sub-modules is insufficient, the super capacitor sub-module is supplemented to be put into.

[0011] Further, it further comprises: at the initial moment, the number of bridge arm sub-modules put in is set to half of the total number of sub-modules, and then the final number of sub-modules is determined based on current tracking and ring current suppression hierarchical optimization.

[0012] The application also comprises a control system of a new MMC topology with super capacitors, which uses the method as described above, and the system comprises: An acquisition unit is used for receiving and setting active / reactive power reference values of a converter, acquiring grid-side voltage, obtaining dq-axis voltage by dq transformation of the grid-side voltage, backstepping reference current values according to the dq-axis voltage, and obtaining ring current reference values according to power reference values and DC-side voltage; A current tracking unit is used for state prediction of a plurality of candidate sub-module put-in number combinations in each control period, obtaining output current prediction values at the next moment based on the prediction, comparing the prediction values with current reference values, and selecting the combination with the minimum current error as a candidate combination; A ring current suppression unit is used for calculating ring current values corresponding to each candidate combination, and selecting the combination with the ring current value closest to the ring current reference value as the final number of sub-modules; The switching unit is used to select the specific submodule to be switched based on the charging and discharging direction of each bridge arm and the capacitor voltage value of each submodule, according to the set voltage priority order and the principle of giving priority to using ordinary capacitor submodules and supplementing with supercapacitor submodules when ordinary submodules are insufficient.

[0013] The present invention also includes a computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the method as described above.

[0014] The present invention also includes a storage medium having a computer program stored thereon, which, when executed by a processor, implements the method as described above.

[0015] The beneficial effects of this invention are as follows: When selecting specific sub-modules for switching, the charging and discharging state of the bridge arm and the capacitor voltage value of each sub-module are comprehensively considered. By charging the capacitors of sub-modules with lower voltage and discharging the capacitors of sub-modules with higher voltage, capacitor voltage balance is achieved. While ensuring the capacitor voltage balance of sub-modules, the control effect can be further improved and the system control failure caused by bridge arm voltage fluctuations can be reduced. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 MMC topology diagram for introducing supercapacitors; Figure 2 A flowchart of the control method for the novel topology; Figure 3 This is a schematic diagram of the structure of the computer device of the present invention. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0019] Example 1: like Figure 1 The above describes a novel MMC topology that incorporates supercapacitors, comprising: The MMC main circuit consists of three phases and six bridge arms, with each bridge arm comprising N sub-modules. At least part of the capacitors in the sub-modules are super capacitors, forming super capacitor sub-modules. In each bridge arm, the super capacitor sub-modules and the ordinary capacitor sub-modules are alternately combined, and the single bridge arm circuit is formed by the series connection of the bridge arm inductors.

[0020] As shown in Figure 2 A control method of a new MMC topology with super capacitors is used to control the MMC topology as described above, and includes the following steps: The active / reactive power reference value of the converter is received and set, the grid-side voltage is collected, and the dq-axis voltage is obtained by dq transformation of the grid-side voltage; the reference current value is back calculated according to the dq-axis voltage, and the circulating current reference value is obtained according to the power reference value and the DC-side voltage; In each control cycle, the state of a plurality of candidate sub-module input quantity combinations is predicted, the output current prediction value at the next moment is obtained based on the prediction, the prediction value is compared with the current reference value, and the combination with the minimum current error is selected as the candidate combination; The circulating current value corresponding to each candidate combination is calculated, and the combination that makes the circulating current value closest to the circulating current reference value is selected as the final sub-module quantity; According to the charge / discharge direction of each bridge arm and the capacitor voltage value of each sub-module, the specific sub-modules to be switched are selected according to the set voltage priority order and the principle of preferentially using ordinary capacitor sub-modules and supplementarily using super capacitor sub-modules when the ordinary sub-modules are insufficient.

[0021] In the embodiment, super capacitors are introduced into at least part of the sub-modules of the MMC main circuit bridge arm to form super capacitor sub-modules, and in each bridge arm, the ordinary capacitor sub-modules and the super capacitor sub-modules are alternately arranged.

[0022] The state of a plurality of candidate sub-module input quantity combinations is predicted, and the output current prediction value at the next moment is obtained based on the prediction, wherein each control cycle examines the sub-module combination that differs from the sub-module combination in the previous cycle by 1 or less, i.e., the sub-module quantity in the upper and lower bridge arms in the previous cycle is n p , n n ), then the influence of the sub-module quantity combination n p , n n ), ( n p +1, n n -1), ( n p -1, n n +1) on the output current is examined; Calculate the circulating current value corresponding to each candidate combination, and select the combination that makes the circulating current value closest to the circulating current reference value as the final number of submodules. Adjust the combination of submodule numbers obtained in the current tracking stage, that is, the number of upper and lower bridge arm submodules in the previous cycle is ( n p , n n Then examine the combination of the number of submodules () n p , n n ), ( n p +1, n n +1), ( n p -1, n n -1), calculate the circulation value under this combination.

[0023] The selection of specific submodules to be switched is based on the principle of prioritizing the use of ordinary capacitor submodules according to the set voltage priority order, and supplementing with supercapacitor submodules when ordinary submodules are insufficient. This includes: When it is detected that the current direction of a certain bridge arm is to charge the capacitor of the submodule, the capacitor voltages of the ordinary capacitor submodules are sorted from low to high first, and the ordinary capacitor submodule with the lowest voltage and lower than the set capacitor voltage reference value is selected for input. If the number of ordinary submodules is insufficient, supercapacitor submodules are added. When the current direction of a certain bridge arm is detected to cause the capacitor of the submodule to discharge, the capacitor voltages of the ordinary capacitor submodules are sorted from high to low first, and the ordinary capacitor submodule with the highest voltage and higher than the set capacitor voltage reference value is selected for activation. If the number of ordinary submodules is insufficient, supercapacitor submodules are added.

[0024] As a preferred embodiment of the above, the method further includes: setting the number of bridge arm sub-modules to half of the total number of sub-modules at the initial moment, and then determining the final number of sub-modules based on current tracking and circulating current suppression hierarchical optimization.

[0025] This embodiment also includes a control system for a novel MMC topology that incorporates supercapacitors. Using the method described above, the system includes: The acquisition unit is used to receive and set the active / reactive power reference values ​​of the converter, acquire the grid-side voltage, perform dq transformation on the grid-side voltage to obtain the dq-axis voltage, deduce the reference current value based on the dq-axis voltage, and obtain the circulating current reference value based on the power reference value and the DC-side voltage. The current tracking unit is used to predict the state of several candidate combinations of the number of sub-modules to be put into operation in each control cycle, obtain the predicted value of the output current at the next moment based on the prediction, compare the predicted value with the current reference value, and select the combination with the smallest current error as the candidate combination. The circulation suppression unit is used to calculate the circulation value corresponding to each candidate combination and select the one that makes the circulation value closest to the circulation reference value as the final number of sub-modules. The switching unit is used to select the specific submodule to be switched based on the charging and discharging direction of each bridge arm and the capacitor voltage value of each submodule, according to the set voltage priority order and the principle of giving priority to using ordinary capacitor submodules and supplementing with supercapacitor submodules when ordinary submodules are insufficient.

[0026] Example 2: The MMC topology diagram with supercapacitors designed in this embodiment is as follows: Figure 1 As shown. This converter topology introduces supercapacitors. The MMC main circuit includes three phases and six arms. Each arm consists of N sub-modules. Some sub-modules use supercapacitors as capacitors. In each arm, sub-modules composed of supercapacitors and sub-modules composed of ordinary capacitors are alternately combined, and the arm inductors are connected in series to form a single arm circuit.

[0027] The control strategy for the novel topology described in this embodiment first provides a power reference value for the converter. P ref , Q ref Simultaneously, the grid-side voltage is collected. u abc The dq-axis voltage is obtained by performing a dq transformation on the grid-side voltage. u dq The reference current value can be derived by using the dq axis power calculation formula. i ref Simultaneously, based on the power reference value and DC-side voltage, a circulating current reference value is obtained. Further, the system state is predicted, and different combinations of submodule numbers are selected to predict the converter output current value. The predicted value is compared with the current reference value, and the output current value closest to the predicted value is obtained. After current optimization, the number of submodules is further adjusted, and the output circulating current value under different combinations is calculated to obtain the submodule number combination with the circulating current value closest to the reference value. After obtaining the final number of submodules, specific submodules to be switched are selected based on the arm charging / discharging status and submodule voltage. When selecting specific submodules to be switched, the charging / discharging status of the arm and the capacitor voltage value of each submodule are comprehensively considered. By charging the capacitors of submodules with lower voltage and discharging the capacitors of submodules with higher voltage, capacitor voltage balance is achieved. While ensuring the capacitor voltage balance of submodules, the control effect can be further improved, and system control failures caused by arm voltage fluctuations can be reduced.

[0028] See Figure 2 The control strategy algorithm diagram shown sets the converter power reference value according to the actual needs or preset conditions of the system. After setting the power reference value, the required output current value is calculated using the grid-side voltage and the power reference value as the current reference value. At the same time, the circulating current reference value is calculated based on the power reference value and the DC-side voltage. Initially, the number of upper and lower bridge arm sub-modules is set to half of the total number. Then, the influence of adjacent voltage levels on the output current is examined, and the combination of sub-modules that minimizes the error between the output current and the reference current is selected. For example, the number of upper and lower bridge arm sub-modules in the previous cycle was ( n p , n n If the number of sub-modules is considered in the next cycle, then the combination of sub-modules will be examined. n p , n n ), ( n p +1, n n -1), ( n p -1, n n +1) The effect on output current; then the circulating current is suppressed, and the number of sub-modules is changed without changing the difference in the number of sub-modules engaged in the upper and lower bridge arms (i.e., without changing the output voltage of the bridge arms). For example, the number of sub-modules engaged in the upper and lower bridge arms in the previous cycle was ( n p , n n Then examine the combination of the number of submodules () n p , n n ), ( n p +1, n n +1), ( n p -1, n n-1), thus finding the combination of submodules with the lowest circulating current; during the modulation stage, the bridge arm current is first detected. When the bridge arm current direction is to charge the submodule capacitor, ordinary submodules are examined first. The ordinary submodule capacitor voltages are sorted from low to high. The submodule with the lowest voltage and a voltage value lower than the submodule capacitor voltage reference value is selected for charging. When the number of ordinary submodules is insufficient, submodules composed of supercapacitors are selected for charging. When the bridge arm current direction is to discharge the submodule capacitor, ordinary submodules are examined first. The ordinary submodule capacitor voltages are sorted from low to high. The submodule with the highest voltage and a voltage value higher than the submodule capacitor voltage reference value is selected for discharging. When the number of ordinary submodules is insufficient, submodules composed of supercapacitors are selected for discharging. This determines the submodules that need to be switched on and off, thus completing the control of the new converter system.

[0029] Please see Figure 3 The diagram shows a structural schematic of a computer device provided in an embodiment of this application. An embodiment of this application provides a computer device 400, including a processor 410 and a memory 420. The memory 420 stores a computer program executable by the processor 410. When the computer program is executed by the processor 410, it performs the method described above.

[0030] This application embodiment also provides a storage medium 430, on which a computer program is stored, and the computer program is executed by a processor 410 to perform the above method.

[0031] The storage medium 430 can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as Static Random Access Memory (SRAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), Erasable Programmable Read Only Memory (EPROM), Programmable Red-Only Memory (PROM), Read-Only Memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk.

[0032] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. "A plurality of" means two or more, unless otherwise explicitly specified.

[0033] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0034] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0035] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of the preferred embodiments of the invention includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as will be understood by those skilled in the art to which embodiments of the invention pertain.

[0036] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Alternatively, the computer-readable medium may be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in a computer memory.

[0037] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0038] Those skilled in the art will understand that all or part of the steps of the methods in the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, the program includes one or a combination of the steps of the method embodiments.

[0039] The storage medium mentioned above can be a read-only memory, a disk, or an optical disk, etc. Although embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A novel MMC topology incorporating supercapacitors, characterized in that, include: The MMC main circuit includes three phases and six bridge arms, and each bridge arm includes N sub-modules; At least some of the sub-modules use supercapacitors as capacitors, forming supercapacitor sub-modules; In each bridge arm, the supercapacitor submodule and the ordinary capacitor submodule are alternately combined, and the bridge arm inductor is connected in series to form a single bridge arm circuit.

2. A control method for a novel MMC topology incorporating supercapacitors, characterized in that, Controlling the MMC topology as described in claim 1 includes the following steps: Receive and set the active / reactive power reference values ​​of the converter, collect the grid-side voltage, perform dq transformation on the grid-side voltage to obtain the dq-axis voltage; deduce the reference current value based on the dq-axis voltage, and obtain the circulating current reference value based on the power reference value and the DC-side voltage; Within each control cycle, the state prediction is performed on several candidate combinations of the number of sub-modules to be deployed. Based on the prediction, the predicted value of the output current at the next moment is obtained. The predicted value is compared with the current reference value, and the combination with the smallest current error is selected as the candidate combination. Calculate the circulation value corresponding to each candidate combination, and select the one whose circulation value is closest to the circulation reference value as the final number of sub-modules; Based on the charging and discharging direction of each bridge arm and the capacitor voltage value of each submodule, the specific submodule to be switched is selected according to the set voltage priority order and the principle of prioritizing the use of ordinary capacitor submodules and supplementing with supercapacitor submodules when ordinary submodules are insufficient.

3. The control method for the novel MMC topology incorporating supercapacitors according to claim 2, characterized in that, In the process of introducing supercapacitors into at least some sub-modules of the MMC main circuit bridge arm to form a supercapacitor sub-module, ordinary capacitor sub-modules and supercapacitor sub-modules are arranged alternately in each bridge arm.

4. The control method for the novel MMC topology incorporating supercapacitors according to claim 2, characterized in that, The process involves predicting the state of several candidate combinations of submodule deployment quantities. Based on this prediction, the output current prediction value for the next moment is obtained. In each control cycle, the submodule combination whose level differs from the previous cycle by less than 1 is considered, i.e., the number of upper and lower bridge arm submodules in the previous cycle is ( n p , n n If the number of sub-modules is considered in the next cycle, then the combination of sub-modules will be examined. n p , n n ), ( n p +1, n n -1), ( n p -1, n n +1) The effect on output current; The calculation of the circulating current value corresponding to each candidate combination, and the selection of the combination that makes the circulating current value closest to the circulating current reference value as the final number of sub-modules, involves adjusting the combination of sub-module numbers obtained in the current tracking stage. That is, the number of upper and lower bridge arm sub-modules in the previous cycle is ( n p , n n Then examine the combination of the number of submodules () n p , n n ), ( n p +1, n n +1), ( n p -1, n n -1), calculate the circulation value under this combination.

5. The control method for the novel MMC topology incorporating supercapacitors according to claim 2, characterized in that, The selection of specific submodules to be switched according to the set voltage priority order and the principle of prioritizing the use of ordinary capacitor submodules and supplementing with supercapacitor submodules when ordinary submodules are insufficient includes: When it is detected that the current direction of a certain bridge arm is to charge the capacitor of the submodule, the capacitor voltages of the ordinary capacitor submodules are sorted from low to high first, and the ordinary capacitor submodule with the lowest voltage and lower than the set capacitor voltage reference value is selected for input. If the number of ordinary submodules is insufficient, supercapacitor submodules are added. When the current direction of a certain bridge arm is detected to cause the capacitor of the submodule to discharge, the capacitor voltages of the ordinary capacitor submodules are sorted from high to low first, and the ordinary capacitor submodule with the highest voltage and higher than the set capacitor voltage reference value is selected for activation. If the number of ordinary submodules is insufficient, supercapacitor submodules are added.

6. The control method for the novel MMC topology incorporating supercapacitors according to claim 2, characterized in that, Also includes: Initially, the number of bridge arm submodules is set to half of the total number of submodules. Then, the final number of submodules is determined based on hierarchical optimization of current tracking and circulating current suppression.

7. A control system for a novel MMC topology incorporating supercapacitors, characterized in that, Using the method as described in any one of claims 2 to 6, the system comprises: The acquisition unit is used to receive and set the active / reactive power reference values ​​of the converter, acquire the grid-side voltage, perform dq transformation on the grid-side voltage to obtain the dq-axis voltage, deduce the reference current value based on the dq-axis voltage, and obtain the circulating current reference value based on the power reference value and the DC-side voltage. The current tracking unit is used to predict the state of several candidate combinations of the number of sub-modules to be put into operation in each control cycle, obtain the predicted value of the output current at the next moment based on the prediction, compare the predicted value with the current reference value, and select the combination with the smallest current error as the candidate combination. The circulation suppression unit is used to calculate the circulation value corresponding to each candidate combination and select the one that makes the circulation value closest to the circulation reference value as the final number of sub-modules. The switching unit is used to select the specific submodule to be switched based on the charging and discharging direction of each bridge arm and the capacitor voltage value of each submodule, according to the set voltage priority order and the principle of giving priority to using ordinary capacitor submodules and supplementing with supercapacitor submodules when ordinary submodules are insufficient.

8. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the method as described in any one of claims 2-6.

9. A storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the method as described in any one of claims 2-6.

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