Voltage-sharing control method and system for sub-modules of modular multilevel converter

Abstract

The invention provides a voltage-sharing control method and system for sub-modules of a modular multilevel converter, and the method comprises the steps: judging the number of to-be-acted sub-modules and the increase and decrease states of the input sub-modules based on the total number of the sub-modules needing to be input in the current simulation step length of the converter and the number of the input sub-modules in the previous simulation step length; based on the number of sub-modules to be operated, the increasing and decreasing state of the input sub-modules and the charging and discharging state of a bridge arm in the converter, according to the respective capacitor voltage sequence of the input sub-modules and the bypass sub-modules before switching, carrying out preliminary switching on the sub-modules; if the capacitor voltage input into the sub-module exceeds a voltage fluctuation threshold value after preliminary switching, switching in turn according to the capacitor voltage; on the basis of the state of the sub-module in the converter after alternating switching, updating the on-off state of the sub-module; compared with a method of fixed rotation logarithm, the problem of unnecessary rotation is solved, and dynamic switching is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of power transmission and distribution of electric power systems, and in particular to a method and system for controlling voltage sharing of submodules of a modular multi-level converter. Background Art

[0002] Modular multilevel converters are composed of identical submodules connected in series, and have shown extremely important engineering application prospects. Based on this topology, a variety of converters are proposed, including but not limited to modular multilevel matrix converters (M3C) and traditional MMC (Modular Multilevel Converter). With the continuous improvement of capacity and voltage levels, the number of submodules in high-voltage and large-capacity M3C and MMC systems has increased rapidly, resulting in increasingly prominent operating loss problems in modular multilevel converters.

[0003] At present, the nearest level modulation (NLM) and sorting voltage balancing control strategy are widely used for the topology of modular multi-level converters to achieve voltage balancing control of the converter. The voltage balancing control strategy based on complete sorting and overall input is widely accepted by the industry due to its simplicity. This control strategy can well achieve the lowest voltage of the charging capacitor and the highest voltage of the discharging capacitor at any simulation step by sorting the capacitor voltage and re-investing the module at each simulation step, thereby averaging the sub-module capacitor voltage.

[0004] However, due to the uninterrupted full re-sequencing of this control strategy, the small voltage difference between the capacitors causes the module to repeatedly operate in a very short time, which increases the switching frequency in the sub-module and increases the operating loss of the modular multi-level converter. In response to the above problems, existing studies have proposed that in the process of capacitor voltage sequencing and module re-engagement at each simulation step, the rotation logarithm of the sub-modules that are fixed and bypassed is reduced compared to the full re-engagement in the traditional method. The rotation logarithm reduces the switching frequency, but in the actual operation process, there are situations where the capacitor voltage difference of the sub-module is very small and does not need to be re-engaged. Therefore, the method of fixing the rotation logarithm still has the problem of unnecessary rotation, which increases unnecessary operating losses, and there is still a large room for optimization of the switching frequency and capacitor voltage fluctuation range. Summary of the invention

[0005] In order to overcome the above-mentioned deficiencies of the prior art, the present invention proposes a voltage sharing control method for a modular multi-level converter submodule, comprising:

[0006] Based on the total number of sub-modules that need to be put into operation in the current simulation step of the converter and the number of sub-modules put into operation in the previous simulation step, the number of sub-modules to be operated in the current simulation step and the increase or decrease status of the sub-modules put into operation are determined;

[0007] Based on the number of submodules to be operated, the increase and decrease status of the submodules put into operation, and the charge and discharge status of the bridge arm in the converter, the submodules in the converter are preliminarily switched in accordance with the respective capacitor voltage sequence of the submodules put into operation and the bypass submodules before switching in the current simulation step;

[0008] If the capacitor voltage of a submodule after the initial switching exceeds the voltage fluctuation threshold, the submodule and the bypass submodule after the initial switching are switched in rotation according to the capacitor voltage;

[0009] The switch state of the submodule is updated based on the state of the submodule in the converter after the rotation switching.

[0010] Optionally, based on the number of submodules to be operated, the increase and decrease status of the put-in submodules, and the charge and discharge status of the bridge arm in the converter, the submodules in the converter are preliminarily switched according to the capacitor voltage sequence of the put-in submodules and the bypass submodules before the current simulation step is switched, including:

[0011] When the increase or decrease state of the submodules put into operation at the current simulation step length is the state of adding submodules put into operation, the state of the submodules put into operation before switching is kept unchanged, and based on the number of submodules to be operated and the charge and discharge state of the bridge arm, the bypass submodules are put into operation according to the order of the capacitor voltage of the bypass submodules before switching;

[0012] When the increase or decrease state of the sub-modules put into operation in the current simulation step is the state of reducing the sub-modules put into operation, the state of the bypass sub-module before switching is kept unchanged, and based on the number of sub-modules to be acted on and the charge and discharge state of the bridge arm, the sub-modules put into operation are removed in the order of the capacitor voltage of the sub-modules put into operation before switching.

[0013] Optionally, the switching on of the bypass submodules according to the order of the capacitor voltages of the bypass submodules before switching on based on the number of the submodules to be operated and the charge and discharge state of the bridge arm includes:

[0014] If the bridge arm is in a charging state, based on the number of the submodules to be operated, the bypass submodules are switched on in the order of the capacitor voltages of the bypass submodules before switching on from low to high;

[0015] If the bridge arm is in a discharge state, based on the number of the submodules to be operated, the bypass submodules are switched on in a descending order of the capacitor voltages of the bypass submodules before switching on.

[0016] Optionally, the switching on submodules according to the capacitor voltage sequence of the switched on submodules before switching on based on the number of the submodules to be operated and the charge and discharge state of the bridge arm comprises:

[0017] If the bridge arm is in a discharge state, based on the number of submodules to be operated, the submodules to be switched on are switched off in the order of the capacitor voltages of the submodules before switching on from low to high;

[0018] If the bridge arm is in a charging state, based on the number of the submodules to be operated, the submodules are cut off in descending order of the capacitor voltages of the submodules before switching on.

[0019] Optionally, the determining the number of submodules to be acted on in the current simulation step and the increase or decrease status of the submodules put into operation based on the total number of submodules required to be put into operation in the current simulation step of the converter and the number of submodules put into operation in the previous simulation step includes:

[0020] Determine whether the total number of submodules required to be put into operation in the current simulation step of the converter is equal to the number of submodules put into operation in the previous simulation step;

[0021] If they are equal, the switch state of the submodule is updated according to the capacitor voltage difference and capacitor voltage order of the submodule in the current simulation step;

[0022] If they are not equal, the number of sub-modules to be acted on in the current simulation step and the increase or decrease status of the invested sub-modules are determined.

[0023] Optionally, the determining of the number of submodules to be acted upon in the current simulation step and the increase or decrease status of the invested submodules includes:

[0024] According to the difference between the total number of sub-modules required to be put into operation in the current simulation step of the converter and the number of sub-modules put into operation in the previous simulation step, the number of sub-modules to be acted on in the current simulation step is obtained;

[0025] The total number of sub-modules that need to be invested is recorded as N1, and the number of sub-modules invested in the previous simulation step is recorded as N0;

[0026] If N1>N0 and N0≥0, the increase / decrease state of the input submodule of the current step length is determined to be the increase input submodule state; if N1>N0 and N1≤0, the increase / decrease state of the input submodule of the current step length is determined to be the decrease input submodule state;

[0027] If N1<N0 and N1≥0, the increase / decrease state of the input submodule of the current step length is determined to be a decrease input submodule state; if N1<N0 and N0≤0, the increase / decrease state of the input submodule of the current step length is determined to be an increase input submodule state.

[0028] Optionally, updating the switch state of the submodule according to the capacitor voltage difference and capacitor voltage order of the submodule in the current simulation step includes:

[0029] If the capacitor voltage difference of the submodule in the current simulation step is less than the capacitor voltage difference threshold, the submodule in the current simulation step is not switched; based on the submodule and bypass submodule in the previous simulation step, a trigger signal is generated to update the switch state of each submodule in the converter under the current simulation step;

[0030] If the capacitor voltage difference of the submodules in the current simulation step is not less than the capacitor voltage difference threshold, the capacitor voltage of the submodules in the current simulation step is fully sorted; the submodules in the current simulation step are switched based on the submodule sequence after the capacitor voltage is fully sorted; a trigger signal is generated based on the state of the submodule after the switching is completed, and the switch state of each submodule in the converter under the current simulation step is updated.

[0031] Optionally, the voltage fluctuation threshold includes an upper threshold and a lower threshold of the voltage fluctuation;

[0032] If the capacitor voltage of the input submodule exceeds the voltage fluctuation threshold after the preliminary switching, the input submodule and the bypass submodule after the preliminary switching are switched in rotation according to the capacitor voltage, including:

[0033] When the bridge arm is in a charging state, if after the initial switching, there is an input submodule whose capacitor voltage is higher than the upper limit threshold, and there is a bypass submodule whose capacitor voltage is not higher than the upper limit threshold and is not put into operation, then based on the principle that the input submodule with the highest capacitor voltage corresponds to the bypass submodule with the lowest capacitor voltage, the input submodule and the bypass submodule after the initial switching are rotated; until there is no input submodule higher than the upper limit threshold or bypass submodule with a voltage not higher than the upper limit threshold, the rotation switching is stopped;

[0034] When the bridge arm is in a discharge state, if after the initial switching, there is an input submodule whose capacitor voltage is lower than the lower threshold value, and there is a bypass submodule whose capacitor voltage is not lower than the lower threshold value and is not put into operation, then based on the principle that the input submodule with the highest capacitor voltage corresponds to the bypass submodule with the lowest capacitor voltage, the input submodule and the bypass submodule after the initial switching are rotated; until there is no input submodule whose voltage is lower than the lower threshold value or no bypass submodule whose voltage is not lower than the lower threshold value, the rotation switching is stopped.

[0035] Optionally, updating the switch state of the submodule based on the state of the submodule in the converter after the rotation switching includes:

[0036] A trigger signal is generated based on the switched-on submodule and the bypass submodule, and the switch states of the submodules in the converter under the current simulation step are updated.

[0037] Optionally, after updating the switch state of the submodule based on the state of the submodule in the converter after the rotation switching, the method further includes:

[0038] Converting the binary trigger signals of the input submodule and the bypass submodule into decimal numbers for indicating the states of the input submodule and the bypass submodule;

[0039] The decimal number is stored.

[0040] Optionally, the total number of submodules required to be invested in the current simulation step of the converter is obtained according to the following steps:

[0041] Obtain the modulation wave voltage of the bridge arm in the current simulation step of the converter;

[0042] Based on the modulation wave voltage of the bridge arm and the nearest level approximation modulation method, the total number of sub-modules required to be invested in the current simulation step of the converter is obtained.

[0043] Based on the same inventive concept, the present invention proposes a voltage sharing control system for a modular multi-level converter submodule, comprising:

[0044] The submodule analysis subsystem to be acted upon is used to determine the number of submodules to be acted upon in the current simulation step and the increase or decrease status of the submodules put into operation based on the total number of submodules to be put into operation in the current simulation step of the converter and the number of submodules put into operation in the previous simulation step;

[0045] A sequential switching subsystem, for performing preliminary switching of the submodules in the converter based on the number of submodules to be operated, the increase and decrease status of the submodules put into operation, and the charge and discharge status of the bridge arm in the converter, according to the respective capacitor voltage sequence of the submodules put into operation and the bypass submodule before switching at the current simulation step;

[0046] Optimizing the rotation subsystem, if the capacitor voltage of the submodule after the initial switching exceeds the voltage fluctuation threshold, the submodule and the bypass submodule after the initial switching are switched in rotation according to the capacitor voltage;

[0047] The submodule status update subsystem is used to update the switch status of the submodule based on the status of the submodule in the converter after the rotation switching.

[0048] Optionally, the sequential switching subsystem includes:

[0049] The submodule input unit, when the input submodule increase / decrease state of the current simulation step is the state of adding the input submodule, keeps the input submodule state before switching unchanged, and inputs the bypass submodule according to the bypass submodule capacitor voltage sequence before switching based on the number of the submodules to be operated and the charge / discharge state of the bridge arm;

[0050] The submodule removal unit keeps the bypass submodule state before switching on unchanged when the increase or decrease state of the submodules put into operation in the current simulation step is the state of reducing the submodules put into operation, and removes the submodules put into operation in the order of the capacitor voltage of the submodules put into operation before switching on, based on the number of submodules to be acted on and the charge and discharge state of the bridge arm.

[0051] Optionally, the submodule input unit is specifically used to:

[0052] If the bridge arm is in a charging state, based on the number of the submodules to be operated, the bypass submodules are switched on in the order of the capacitor voltages of the bypass submodules before switching on from low to high;

[0053] If the bridge arm is in a discharge state, based on the number of the submodules to be operated, the bypass submodules are switched on in a descending order of the capacitor voltages of the bypass submodules before switching on.

[0054] Optionally, the submodule removal unit is specifically used to:

[0055] If the bridge arm is in a discharge state, based on the number of submodules to be operated, the submodules to be switched on are switched off in the order of the capacitor voltages of the submodules before switching on from low to high;

[0056] If the bridge arm is in a charging state, based on the number of the submodules to be operated, the submodules are cut off in descending order of the capacitor voltages of the submodules before switching on.

[0057] Optionally, the sub-module analysis subsystem to be acted upon includes:

[0058] A preliminary judgment unit determines whether the total number of submodules required to be put into operation in the current simulation step of the converter is equal to the number of submodules put into operation in the previous simulation step;

[0059] Fully sorted rotation units, if the number is equal, then the switch states of the submodules are updated according to the capacitor voltage difference and capacitor voltage sorting of the submodules in the current simulation step;

[0060] The analysis unit for the submodules to be acted upon determines the number of submodules to be acted upon at the current simulation step and the increase or decrease status of the input submodules if the numbers are not equal.

[0061] Optionally, the submodule analysis unit to be acted upon is specifically used to:

[0062] The total number of sub-modules that need to be invested is recorded as N1, and the number of sub-modules invested in the previous simulation step is recorded as N0;

[0063] If N1>N0 and N0≥0, the increase / decrease state of the input submodule of the current step length is determined to be the increase input submodule state; if N1>N0 and N1≤0, the increase / decrease state of the input submodule of the current step length is determined to be the decrease input submodule state;

[0064] If N1<N0 and N1≥0, the increase / decrease state of the input submodule of the current step length is determined to be a decrease input submodule state; if N1<N0 and N0≤0, the increase / decrease state of the input submodule of the current step length is determined to be an increase input submodule state.

[0065] Optionally, the full sorting rotation unit is specifically used to:

[0066] If the capacitor voltage difference of the submodule in the current simulation step is less than the capacitor voltage difference threshold, the submodule in the current simulation step is not switched; based on the submodule and bypass submodule in the previous simulation step, a trigger signal is generated to update the switch state of each submodule in the converter under the current simulation step;

[0067] If the capacitor voltage difference of the submodules in the current simulation step is not less than the capacitor voltage difference threshold, the capacitor voltage of the submodules in the current simulation step is fully sorted; the submodules in the current simulation step are switched based on the submodule sequence after the capacitor voltage is fully sorted; a trigger signal is generated based on the state of the submodule after the switching is completed, and the switch state of each submodule in the converter under the current simulation step is updated.

[0068] Optionally, the optimization rotation subsystem is specifically used for:

[0069] When the bridge arm is in a charging state, if after the initial switching, there is an input submodule whose capacitor voltage is higher than the upper limit threshold, and there is a bypass submodule whose capacitor voltage is not higher than the upper limit threshold and is not put into operation, then based on the principle that the input submodule with the highest capacitor voltage corresponds to the bypass submodule with the lowest capacitor voltage, the input submodule and the bypass submodule after the initial switching are rotated; until there is no input submodule higher than the upper limit threshold or bypass submodule with a voltage not higher than the upper limit threshold, the rotation switching is stopped;

[0070] When the bridge arm is in a discharge state, if after the initial switching, there is an input submodule whose capacitor voltage is lower than the lower threshold value, and there is a bypass submodule whose capacitor voltage is not lower than the lower threshold value and is not put into operation, then based on the principle that the input submodule with the highest capacitor voltage corresponds to the bypass submodule with the lowest capacitor voltage, the input submodule and the bypass submodule after the initial switching are rotated; until there is no input submodule whose voltage is lower than the lower threshold value or no bypass submodule whose voltage is not lower than the lower threshold value, the rotation switching is stopped.

[0071] Optionally, the system further includes a storage subsystem, which is used for, after updating the switch state of the submodule in the converter based on the state of the submodule after the rotation switching:

[0072] Converting the binary trigger signals of the input submodule and the bypass submodule into decimal numbers for indicating the states of the input submodule and the bypass submodule;

[0073] The decimal number is stored.

[0074] In another aspect, the present application further provides an electronic device, comprising: at least one processor and a memory; the memory and the processor are connected via a bus;

[0075] The memory is used to store one or more programs;

[0076] When the one or more programs are executed by the at least one processor, the voltage sharing control method for sub-modules of a modular multi-level converter as described above is implemented.

[0077] On the other hand, the present application further provides a computer-readable storage medium having an execution program stored thereon, and when the execution program is executed, the voltage balancing control method for sub-modules of a modular multi-level converter as described above is implemented.

[0078] Compared with the closest prior art, the present invention has the following beneficial effects:

[0079] The present invention provides a method and system for controlling voltage balancing of submodules of a modular multilevel converter, comprising: judging the number of submodules to be acted on in the current simulation step of the converter and the number of submodules to be acted on in the previous simulation step based on the total number of submodules to be acted on in the current simulation step and the number of submodules to be acted on in the previous simulation step; performing preliminary switching of the submodules in the converter according to the capacitor voltage sequence of the acted submodules and the bypass submodules before the current simulation step is not switched based on the number of submodules to be acted on, the increase or decrease state of the acted submodules and the charge and discharge state of the bridge arm in the converter; if the capacitor voltage of the acted submodule exceeds the voltage fluctuation threshold after the preliminary switching, switching the acted submodules and the bypass submodules after the preliminary switching in rotation according to the capacitor voltage; and switching the acted submodules and the bypass submodules after the preliminary switching in rotation based on the capacitor voltage sequence after the rotation switching. The status of the submodule in the converter updates the switch status of the submodule; the present application sequentially switches the number of submodules put into operation in adjacent simulation steps and the capacitor voltage sequence of the submodules, thereby realizing voltage equalization control of the submodules during operation, and determining the current number of switched submodules according to the number of put into operation submodules. Compared with the method of fixed rotation logarithm, it overcomes the problem of unnecessary rotation and realizes dynamic switching; after sequential switching, it further determines whether there are submodules put into operation that exceed the voltage fluctuation threshold, and optimizes the rotation thereof, which can further reduce the voltage fluctuation range of the put into operation submodule; therefore, the present application greatly reduces the switching frequency while ensuring the minimum voltage fluctuation range, and the number of transistor switching actions in the submodule is averaged, which can effectively reduce losses and extend the service life of the converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] Figure 1 A schematic diagram of a process flow of a voltage balancing control method for a modular multi-level converter submodule provided by the present invention Figure 1 ;

[0081] Figure 2 A schematic diagram of a process flow of a voltage balancing control method for a modular multi-level converter submodule provided by the present invention Figure 2 ;

[0082] Figure 3 A test data diagram based on the pressure equalization control method provided by the present invention;

[0083] Figure 4 A schematic diagram of the structure of a voltage sharing control system of a modular multi-level converter submodule provided by the present invention;

[0084] Figure 5 The present invention provides a schematic structural diagram of an electronic device. DETAILED DESCRIPTION

[0085] The specific implementation modes of the present invention are further described in detail below with reference to the accompanying drawings.

[0086] Example 1

[0087] The present invention provides a method for controlling voltage sharing of a modular multi-level converter submodule, such as Figure 1 As shown, including:

[0088] S1. Based on the total number of sub-modules that need to be put into operation in the current simulation step of the converter and the number of sub-modules put into operation in the previous simulation step, determine the number of sub-modules to be operated in the current simulation step and the increase or decrease status of the sub-modules put into operation;

[0089] S2, based on the number of submodules to be operated, the increase and decrease status of the submodules put into operation, and the charge and discharge status of the bridge arm in the converter, the submodules in the converter are preliminarily switched in accordance with the capacitor voltage sequence of the submodules put into operation and the bypass submodules before switching in the current simulation step;

[0090] S3. If the capacitor voltage of a submodule after the initial switching exceeds the voltage fluctuation threshold, the submodule and the bypass submodule after the initial switching are switched in rotation according to the capacitor voltage;

[0091] S4. Update the switch state of the submodule based on the state of the submodule in the converter after the rotation switching.

[0092] Combination Figure 2 The flowchart of this scheme is described in detail.

[0093] In step S1, based on the total number of submodules required to be put into operation in the current simulation step of the converter and the number of submodules put into operation in the previous simulation step, the number of submodules to be operated in the current simulation step and the increase or decrease status of the submodules put into operation are determined.

[0094] S11. Obtain the modulation wave voltage of the bridge arm in the current simulation step of the converter; based on the modulation wave voltage of the bridge arm combined with the nearest level modulation method (NLM), obtain the total number of sub-modules that need to be invested in the current simulation step of the converter, recorded as N1, N1 is obtained through the modulation wave voltage, so there are positive and negative values.

[0095] S12, numbering the submodules according to the arrangement order of the submodules on the bridge arm of the converter; calling the submodule status of the previous simulation step, that is, obtaining the status of all submodules of the previous simulation step, and reading the number of submodules stored in the previous simulation step, recorded as N0.

[0096] S13, determining whether the total number of sub-modules required to be put into operation in the current simulation step of the converter is equal to the number of sub-modules put into operation in the previous simulation step.

[0097] S13-1, if they are equal N1=N0, then the switch state of the submodule is updated according to the capacitor voltage difference and capacitor voltage sequence of the submodule in the current simulation step, specifically:

[0098] A threshold value of the difference between the maximum capacitor voltage and the minimum capacitor voltage is specified, which is recorded as the capacitor voltage difference threshold value D;

[0099] If the capacitor voltage difference of the submodule in the current simulation step is less than the capacitor voltage difference threshold D, the submodule in the current simulation step will not be switched on and off, and the states of all submodules will remain unchanged; based on the submodule and bypass submodule in the previous simulation step, a trigger signal is generated to update the switch state of each submodule in the converter under the current simulation step;

[0100] If the capacitor voltage difference of the submodules in the current simulation step is not less than the capacitor voltage difference threshold, the capacitor voltage of the submodules in the current simulation step is fully sorted; the submodules in the current simulation step are switched based on the submodule sequence after the capacitor voltage is fully sorted; a trigger signal is generated based on the state of the submodule after the switching is completed, and the switch state of each submodule in the converter under the current simulation step is updated.

[0101] S13-2. If the total number of submodules required to be invested in the current simulation step is not equal to the number of submodules invested in the previous simulation step (N1≠N0), then determine the number of submodules to be acted on in the current step and the increase or decrease status of the invested submodules.

[0102] According to the difference between the total number of sub-modules required to be put into operation in the current simulation step of the converter and the number of sub-modules put into operation in the previous simulation step, the number of sub-modules to be acted on in the current simulation step is obtained;

[0103] If N1>N0 and N0≥0, the input submodule increase / decrease state of the current step length is determined to be the input submodule increase state;

[0104] If N1>N0 and N1≤0, the input submodule increase / decrease state of the current step length is determined to be the input submodule decrease state;

[0105] If N1<N0 and N1≥0, it is determined that the input submodule increase / decrease state of the current step length is the input submodule decrease state;

[0106] If N1<N0 and N0≤0, it is determined that the input submodule increase / decrease state of the current step length is the input submodule increase state.

[0107] In step S2, when the current simulation step is to increase the state of the submodule being put into operation, the state of the submodule being put into operation before switching is kept unchanged, and based on the number of submodules to be operated and the charge and discharge state of the bridge arm, the bypass submodule is put into operation according to the order of the capacitor voltage of the bypass submodule before switching;

[0108] Among them, if the bridge arm is in a charging state, based on the number of sub-modules to be operated, the bypass sub-modules are put into operation in an ascending order of the bypass sub-module capacitor voltages before being switched on; if the bridge arm is in a discharging state, based on the number of sub-modules to be operated, the bypass sub-modules are put into operation in an ascending order of the bypass sub-module capacitor voltages before being switched on.

[0109] When the current simulation step is to reduce the state of the put-in-submodule, the state of the bypass submodule before switching is kept unchanged, and based on the number of the submodules to be acted and the charge and discharge state of the bridge arm, the put-in-submodule is removed in the order of the capacitor voltage of the put-in-submodule before switching;

[0110] Among them, if the bridge arm is in a discharging state, based on the number of sub-modules to be operated, the sub-modules to be operated are removed in an ascending order of the capacitor voltages of the sub-modules before being switched on; if the bridge arm is in a charging state, based on the number of sub-modules to be operated, the sub-modules to be operated are removed in an ascending order of the capacitor voltages of the sub-modules before being switched on.

[0111] That is, by monitoring the switching changes of the sub-modules, the sub-modules that remain unchanged are determined according to the status of the sub-modules in the previous simulation step: if the number of sub-modules put into operation in the adjacent simulation step does not change, all modules will not operate; if it is necessary to increase the sub-modules put into operation, the sub-modules that have been put into operation will remain inoperable; if it is necessary to remove the sub-modules put into operation, the bypass state will be maintained and will not operate.

[0112] Specifically, by judging the current direction, voltage direction, and module number change of the bridge arm, there are eight switching states. Among them, the current direction and voltage direction are used to judge the charging and discharging state, and the positive and negative voltage and current positive and negative combinations have different charging and discharging states. That is, the order of removing the sub-modules and the order of putting the bypass sub-modules into operation are determined by the charging and discharging state of the bridge arm and the switching demand.

[0113] Determine the state of the previous simulation step of the submodule in the converter. If it is in the on-state, store its state, capacitor voltage Uon, and submodule number in the array of the on-submodule respectively; if it is in the bypass state, store its state, capacitor voltage Uoff, and submodule number in the array of the bypass module respectively;

[0114] The submodules put into operation are sorted according to the capacitor voltage of the current simulation step. In the present embodiment, the capacitor voltages are arranged in ascending order to obtain the capacitor voltage sequence of the submodules put into operation before the current simulation step is not switched on. The bypass submodules are sorted according to the capacitor voltage of the current simulation step. In the present embodiment, the capacitor voltages are arranged in ascending order to obtain the capacitor voltage sequence of the bypass submodules put into operation before the current simulation step is not switched on. The present invention is not limited to the capacitor voltage sequence from small to large, and other sorting methods may also be selected.

[0115] like Figure 2 As shown, when N1>N0 and N0≥0 is satisfied: if the bridge arm current Iarm≥0, it is in the forward charging state, the state of the put-in module is kept unchanged, and the module with the lowest capacitor voltage is selected from the bypass submodules and put into operation in sequence until the module number change is satisfied (the number of submodules to be acted on, if the module number change is satisfied, the submodule will not be put into operation / removed). Figure 2 Y in the formula indicates that the judgment condition is met, and N indicates that the judgment condition is not met;

[0116] When N1>N0 and N0≥0 is satisfied: if the bridge arm current Iarm<0, it is in the forward discharge state, the state of the put-in module is kept unchanged, and the modules with the highest capacitor voltage are selected from the bypass submodules and put in order until the number of modules is satisfied;

[0117] When N1>N0 and N1≤0: If the bridge arm current Iarm≥0, it is in reverse discharge state, and the bypass module state is kept unchanged. The modules with the lowest capacitor voltage are selected from the put-in modules and removed in sequence until the number of modules changes;

[0118] When N1>N0 and N1≤0: If the bridge arm current Iarm<0, it is in reverse charging state, and the bypass module state is kept unchanged. The modules with the highest capacitor voltage are selected from the put-in modules and removed in sequence until the number of modules is changed;

[0119] When N1<N0 and N1≥0: If the bridge arm current Iarm≥0, it is in the forward charging state, and the bypass module state is kept unchanged. The modules with the highest capacitor voltage are selected from the put-in modules and removed in sequence until the number of modules is changed;

[0120] When N1<N0 and N1≥0 is satisfied: if the bridge arm current Iarm<0, it is in the forward discharge state, the bypass module state is kept unchanged, and the modules with the lowest capacitor voltage are selected from the put-in modules and removed in sequence until the number of modules is satisfied;

[0121] When N1<N0 and N0≤0 is satisfied: if the bridge arm current Iarm≥0, it is in reverse discharge state, the state of the put-in module is kept unchanged, and the module with the highest capacitor voltage is selected from the bypass module and put into operation in sequence until the number of modules is satisfied;

[0122] When N1<N0 and N0≤0: if the bridge arm current Iarm<0, it is a reverse charging state, and the state of the put-in-power module remains unchanged. The modules with the lowest capacitor voltage are selected from the bypass modules and put into power in sequence until the number of modules changes.

[0123] At this point, the initial switching of the submodules in the converter is completed.

[0124] In step S3, if the capacitor voltage fluctuates too much, optimization rotation is performed. That is, if the capacitor voltage of a submodule after the initial switching exceeds the voltage fluctuation threshold, the submodule and bypass submodule after the initial switching are switched in rotation according to the capacitor voltage.

[0125] The voltage fluctuation threshold is specified to include an upper threshold LimitH and a lower threshold LimitL of the voltage fluctuation; and when the number of submodules put into operation in the converter is at least 1 and the number of bypass submodules is at least 1, optimization rotation is performed.

[0126] The charge and discharge state is judged by the direction of voltage and current, and the positive and negative directions are not subdivided here; when the bridge arm is in the charging state, in order to ensure that the capacitor voltage is not too high, the high-voltage submodule is rotated:

[0127] Search sequentially from the submodules with the highest capacitor voltage. If after the preliminary switching, there is an input submodule with a capacitor voltage higher than the upper limit threshold, and there is a bypass submodule with a capacitor voltage not higher than the upper limit threshold and not put into operation, then based on the principle that the input submodule with the highest capacitor voltage corresponds to the bypass submodule with the lowest capacitor voltage, the input submodules and bypass submodules after the preliminary switching are rotated (that is, if there is an input submodule with a capacitor voltage higher than LimitH, the bypass submodule is searched in the order of the lowest capacitor voltage, and if there is a bypass submodule with a capacitor voltage not higher than LimitH and not changed to the input state after the preliminary switching, the states of the two are rotated); until there is no input submodule higher than the upper limit threshold or bypass submodule not higher than the upper limit threshold, the rotation switching is stopped;

[0128] When the bridge arm is in the discharge state, in order to ensure that the capacitor voltage is not too low, the low voltage submodules are rotated:

[0129] The submodule with the lowest capacitor voltage is searched sequentially. If there is an input submodule with a capacitor voltage lower than the lower threshold after the preliminary switching, and there is a bypass submodule with a capacitor voltage not lower than the lower threshold and has not been put into operation, then based on the principle that the input submodule with the highest capacitor voltage corresponds to the bypass submodule with the lowest capacitor voltage, the input submodule and the bypass submodule after the preliminary switching are rotated (that is, if there is an input submodule with a capacitor voltage lower than LimitL, the bypass submodule with the highest capacitor voltage is searched sequentially, and if there is a bypass submodule with a capacitor voltage not lower than LimitL and has not changed to the input state, the two states are rotated); until there is no input submodule with a capacitor voltage lower than the lower threshold or no bypass submodule with a capacitor voltage not lower than the lower threshold, the rotation switching is stopped.

[0130] The core point of optimized rotation is to "replace as many as possible". If there are multiple sub-modules and bypass sub-modules that exceed the threshold, all of them will be rotated. If the number of sub-modules that exceed the upper threshold is greater than the number of bypass sub-modules that do not exceed the upper threshold, the excess part cannot be replaced, indicating that all sub-modules with lower voltages have been put into use and the optimal voltage balancing effect has been achieved.

[0131] In step S4, the switch state of the submodule is updated based on the state of the submodule in the converter after the rotation switching.

[0132] The states of the input submodule and the bypass submodule after the rotation switching, which are represented by decimal numbers, are converted into four-bit binary trigger signals for updating the switch states of the submodules in the converter.

[0133] In order to facilitate storage and call, the four-bit binary trigger signal is converted into a decimal number to represent the state of the input submodule and the bypass submodule; and is stored in the storage space for the control of the next simulation step. The four binary 0 / 1 control signals are converted into decimal numbers to reduce the storage capacity and avoid simulation software storage out of bounds when the number of submodules in the converter is large.

[0134] like Figure 3As shown, it is an experimental data diagram of voltage equalization control using this scheme, M3C (Modular Multilevel Matrix Converter) represents a modular multilevel matrix converter; the ordinate of the upper part is the DC voltage UCMau of the converter bridge arm, and the abscissa represents time sec, the ordinate of the lower part represents the switching frequency of the submodule on the bridge arm, and the abscissa represents time sec; T1au, T2au, T3au and T4au represent the switching frequencies in the four submodules respectively; at 6s, frequency optimization is put into operation, that is, the sequential switching in step S2, the switching frequency is greatly reduced, but the DC voltage fluctuation becomes larger compared to the full-sequence rotation, and the rotation is further optimized at 8s, that is, the rotation switching in step S3, which can reduce the voltage fluctuation to the full-sequence level, and the switching frequency is low.

[0135] In the present invention, the number of sub-modules put into operation in adjacent simulation steps and the capacitor voltage sequence of the sub-modules are sequentially switched, thereby realizing voltage equalization control of the sub-modules during operation, and determining the current number of switched sub-modules according to the number of sub-modules put into operation. Compared with the method of fixed rotation logarithm, the problem of unnecessary rotation is overcome and dynamic switching is realized; after the sequential switching, it is further determined whether there are sub-modules put into operation that exceed the voltage fluctuation threshold, and the rotation is optimized to further reduce the voltage fluctuation range of the sub-modules put into operation; therefore, the present application greatly reduces the switching frequency while ensuring the minimum voltage fluctuation range, and the number of transistor switching actions in the sub-module is averaged, which can effectively reduce the loss and extend the service life of the converter.

[0136] Example 2

[0137] Based on the same inventive concept, the present invention also provides a voltage sharing control system for a modular multi-level converter submodule, such as Figure 4 As shown, including:

[0138] The submodule analysis subsystem to be acted upon is used to determine the number of submodules to be acted upon in the current simulation step and the increase or decrease status of the submodules put into operation based on the total number of submodules to be put into operation in the current simulation step of the converter and the number of submodules put into operation in the previous simulation step;

[0139] A sequential switching subsystem, for performing preliminary switching of the submodules in the converter based on the number of submodules to be operated, the increase and decrease status of the submodules put into operation, and the charge and discharge status of the bridge arm in the converter, according to the respective capacitor voltage sequence of the submodules put into operation and the bypass submodule before switching at the current simulation step;

[0140] Optimizing the rotation subsystem, if the capacitor voltage of the submodule after the initial switching exceeds the voltage fluctuation threshold, the submodule and the bypass submodule after the initial switching are switched in rotation according to the capacitor voltage;

[0141] The submodule status update subsystem is used to update the switch status of the submodule based on the status of the submodule in the converter after the rotation switching.

[0142] In a possible implementation, the sequential switching subsystem includes:

[0143] The submodule input unit, when the input submodule increase / decrease state of the current simulation step is the state of adding the input submodule, keeps the input submodule state before switching unchanged, and inputs the bypass submodule according to the bypass submodule capacitor voltage sequence before switching based on the number of the submodules to be operated and the charge / discharge state of the bridge arm;

[0144] The submodule removal unit keeps the bypass submodule state before switching on unchanged when the increase or decrease state of the submodules put into operation in the current simulation step is the state of reducing the submodules put into operation, and removes the submodules put into operation in the order of the capacitor voltage of the submodules put into operation before switching on, based on the number of submodules to be acted on and the charge and discharge state of the bridge arm.

[0145] In a possible implementation, the submodule input unit is specifically used to:

[0146] If the bridge arm is in a charging state, based on the number of the submodules to be operated, the bypass submodules are switched on in the order of the capacitor voltages of the bypass submodules before switching on from low to high;

[0147] If the bridge arm is in a discharge state, based on the number of the submodules to be operated, the bypass submodules are switched on in a descending order of the capacitor voltages of the bypass submodules before switching on.

[0148] In a possible implementation, the submodule removal unit is specifically used to:

[0149] If the bridge arm is in a discharge state, based on the number of submodules to be operated, the submodules to be switched on are switched off in the order of the capacitor voltages of the submodules before switching on from low to high;

[0150] If the bridge arm is in a charging state, based on the number of the submodules to be operated, the submodules are cut off in descending order of the capacitor voltages of the submodules before switching on.

[0151] In a possible implementation, the above-mentioned sub-module analysis subsystem to be acted upon includes:

[0152] A preliminary judgment unit determines whether the total number of submodules required to be put into operation in the current simulation step of the converter is equal to the number of submodules put into operation in the previous simulation step;

[0153] The full sorting rotation unit, if the quantities are equal, updates the switching states of the sub-modules according to the capacitance voltage difference and the capacitance voltage sorting of the sub-modules in the current simulation step;

[0154] The sub-module to be actuated analysis unit, if the quantities are not equal, determines the number of sub-modules to be actuated in the current simulation step and the increase or decrease state of the inserted sub-modules.

[0155] In a possible implementation manner, the above-mentioned sub-module to be actuated analysis unit is specifically used for:

[0156] Denote the total number of sub-modules to be inserted as N1, and the number of inserted sub-modules in the previous simulation step as N0;

[0157] If N1 > N0 and N0 ≥ 0, determine that the increase or decrease state of the inserted sub-modules in the current step is the state of increasing the inserted sub-modules; if N1 > N0 and N1 ≤ 0, determine that the increase or decrease state of the inserted sub-modules in the current step is the state of decreasing the inserted sub-modules;

[0158] If N1 < N0 and N1 ≥ 0, determine that the increase or decrease state of the inserted sub-modules in the current step is the state of decreasing the inserted sub-modules; if N1 < N0 and N0 ≤ 0, determine that the increase or decrease state of the inserted sub-modules in the current step is the state of increasing the inserted sub-modules.

[0159] In a possible implementation manner, the above-mentioned full sorting rotation unit is specifically used for:

[0160] If the capacitance voltage difference of the sub-modules in the current simulation step is less than the capacitance voltage difference threshold, do not switch the sub-modules in the current simulation step; generate a trigger signal based on the inserted sub-modules and bypassed sub-modules in the previous simulation step, and update the switching states of each sub-module in the current simulation step of the converter;

[0161] If the capacitance voltage difference of the sub-modules in the current simulation step is not less than the capacitance voltage difference threshold, perform a full capacitance voltage sorting on the sub-modules in the current simulation step; switch the sub-modules in the current simulation step according to the order of the sub-modules after the full capacitance voltage sorting; generate a trigger signal based on the states of the sub-modules after the switching, and update the switching states of each sub-module in the current simulation step of the converter.

[0162] In a possible implementation manner, the above-mentioned optimized rotation subsystem is specifically used for:

[0163] When the bridge arm is in a charging state, if after the initial switching, there is an input submodule whose capacitor voltage is higher than the upper limit threshold, and there is a bypass submodule whose capacitor voltage is not higher than the upper limit threshold and is not put into operation, then based on the principle that the input submodule with the highest capacitor voltage corresponds to the bypass submodule with the lowest capacitor voltage, the input submodule and the bypass submodule after the initial switching are rotated; until there is no input submodule higher than the upper limit threshold or bypass submodule with a voltage not higher than the upper limit threshold, the rotation switching is stopped;

[0164] When the bridge arm is in a discharge state, if after the initial switching, there is an input submodule whose capacitor voltage is lower than the lower threshold value, and there is a bypass submodule whose capacitor voltage is not lower than the lower threshold value and is not put into operation, then based on the principle that the input submodule with the highest capacitor voltage corresponds to the bypass submodule with the lowest capacitor voltage, the input submodule and the bypass submodule after the initial switching are rotated; until there is no input submodule whose voltage is lower than the lower threshold value or no bypass submodule whose voltage is not lower than the lower threshold value, the rotation switching is stopped.

[0165] In a possible implementation, the system further includes a storage subsystem, which is used for, after updating the switch state of the submodule in the converter based on the state of the submodule after the rotation switching:

[0166] Converting the binary trigger signals of the input submodule and the bypass submodule into decimal numbers for indicating the states of the input submodule and the bypass submodule;

[0167] The decimal number is stored.

[0168] Example 3

[0169] like Figure 5 As shown, the present invention also provides an electronic device, which may be a computer device, a single-chip device, an intelligent mobile device, etc. The electronic device in this embodiment may include a processor, a memory, a transceiver component, etc. The memory, the processor, and the transceiver component are connected via a bus; the memory may be used to store an execution program, and an exemplary execution program may include instructions; the processor is used to execute the instructions stored in the memory. The memory may also be used to store data, which may be called and / or modified when the instructions are executed.

[0170] The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, and is specifically suitable for loading and executing one or more instructions in a storage medium to implement a corresponding method flow or a corresponding function, so as to implement the steps of a voltage balancing control method for a modular multilevel converter sub-module in the above-mentioned embodiment.

[0171] Example 4

[0172] Based on the same inventive concept, the present invention also provides a readable storage medium, specifically an electronic device readable storage medium (Memory), which is a memory device in an electronic device for storing programs and data. It can be understood that the storage medium here can include both a built-in storage medium in an electronic device and an extended storage medium supported by the electronic device. The storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by a processor are also stored in the storage space, and these instructions can be one or more execution programs (including program codes). It should be noted that the storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor loads and executes one or more instructions stored in the storage medium, which can implement the steps of a voltage balancing control method for a modular multi-level converter submodule in the above embodiment.

[0173] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0174] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0175] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0176] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0177] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit its protection scope. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that after reading the present invention, those skilled in the art can still make various changes, modifications or equivalent substitutions to the specific implementation methods of the application, but these changes, modifications or equivalent substitutions are all within the protection scope of the claims to be approved.

Claims

1. A method for controlling voltage sharing of submodules of a modular multilevel converter, characterized in that: include: Based on the total number of sub-modules that need to be put into operation in the current simulation step of the converter and the number of sub-modules put into operation in the previous simulation step, the number of sub-modules to be operated in the current simulation step and the increase or decrease status of the sub-modules put into operation are determined; Based on the number of submodules to be operated, the increase and decrease status of the submodules put into operation, and the charge and discharge status of the bridge arm in the converter, the submodules in the converter are preliminarily switched in accordance with the respective capacitor voltage sequence of the submodules put into operation and the bypass submodules before switching in the current simulation step; If the capacitor voltage of a submodule after the initial switching exceeds the voltage fluctuation threshold, the submodule and the bypass submodule after the initial switching are switched in rotation according to the capacitor voltage; The switch state of the submodule is updated based on the state of the submodule in the converter after the rotation switching.

2. The method according to claim 1, characterized in that Based on the number of submodules to be operated, the increase and decrease status of the submodules put into operation, and the charge and discharge status of the bridge arm in the converter, the submodules in the converter are preliminarily switched according to the capacitor voltage sequence of the submodules put into operation and the bypass submodule before switching at the current simulation step, including: When the increase or decrease state of the submodules put into operation at the current simulation step length is the state of adding submodules put into operation, the state of the submodules put into operation before switching is kept unchanged, and based on the number of submodules to be operated and the charge and discharge state of the bridge arm, the bypass submodules are put into operation according to the order of the capacitor voltage of the bypass submodules before switching; When the increase or decrease state of the sub-modules put into operation in the current simulation step is the state of reducing the sub-modules put into operation, the state of the bypass sub-module before switching is kept unchanged, and based on the number of sub-modules to be acted on and the charge and discharge state of the bridge arm, the sub-modules put into operation are removed in the order of the capacitor voltage of the sub-modules put into operation before switching.

3. The method according to claim 2, characterized in that The step of switching on the bypass submodules according to the order of the capacitor voltages of the bypass submodules before switching on based on the number of the submodules to be operated and the charge and discharge state of the bridge arm comprises: If the bridge arm is in a charging state, based on the number of the submodules to be operated, the bypass submodules are switched on in the order of the capacitor voltages of the bypass submodules before switching on from low to high; If the bridge arm is in a discharge state, based on the number of the submodules to be operated, the bypass submodules are switched on in a descending order of the capacitor voltages of the bypass submodules before switching on.

4. The method according to claim 2, characterized in that The method of removing the submodules in operation according to the order of the capacitor voltages of the submodules before switching on based on the number of the submodules to be operated and the charge and discharge state of the bridge arm comprises: If the bridge arm is in a discharge state, based on the number of submodules to be operated, the submodules to be switched on are switched off in the order of the capacitor voltages of the submodules before switching on from low to high; If the bridge arm is in a charging state, based on the number of the submodules to be operated, the submodules are cut off in descending order of the capacitor voltages of the submodules before switching on.

5. The method according to claim 1, characterized in that The method of judging the number of submodules to be acted on in the current simulation step and the increase or decrease status of the put-in submodules based on the total number of submodules required to be put into operation in the current simulation step of the converter and the number of put-in submodules in the previous simulation step, includes: Determine whether the total number of submodules required to be put into operation in the current simulation step of the converter is equal to the number of submodules put into operation in the previous simulation step; If they are equal, the switch state of the submodule is updated according to the capacitor voltage difference and capacitor voltage order of the submodule in the current simulation step; If they are not equal, the number of sub-modules to be acted on in the current simulation step and the increase or decrease status of the invested sub-modules are determined.

6. The method according to claim 5, characterized in that The step of determining the number of submodules to be acted upon in the current simulation step and the increase or decrease status of the input submodules includes: According to the difference between the total number of sub-modules required to be put into operation in the current simulation step of the converter and the number of sub-modules put into operation in the previous simulation step, the number of sub-modules to be acted on in the current simulation step is obtained; The total number of sub-modules that need to be invested is recorded as N1, and the number of sub-modules invested in the previous simulation step is recorded as N0; If N1>N0 and N0≥0, the increase / decrease state of the input submodule of the current step length is determined to be the increase input submodule state; if N1>N0 and N1≤0, the increase / decrease state of the input submodule of the current step length is determined to be the decrease input submodule state; If N1<N0 and N1≥0, the increase / decrease state of the input submodule of the current step length is determined to be the decrease input submodule state; if N1<N0 and N0≤0, the increase / decrease state of the input submodule of the current step length is determined to be the increase input submodule state.

7. The method according to claim 5, characterized in that The updating of the switch state of the submodule according to the capacitor voltage difference and capacitor voltage order of the submodule in the current simulation step includes: If the capacitor voltage difference of the submodule in the current simulation step is less than the capacitor voltage difference threshold, the submodule in the current simulation step is not switched; based on the submodule and bypass submodule in the previous simulation step, a trigger signal is generated to update the switch state of each submodule in the converter under the current simulation step; If the capacitor voltage difference of the submodules in the current simulation step is not less than the capacitor voltage difference threshold, the capacitor voltage of the submodules in the current simulation step is fully sorted; the submodules in the current simulation step are switched based on the submodule sequence after the capacitor voltage is fully sorted; a trigger signal is generated based on the state of the submodule after the switching is completed, and the switch state of each submodule in the converter under the current simulation step is updated.

8. The method according to claim 1, characterized in that The voltage fluctuation threshold includes an upper threshold and a lower threshold of the voltage fluctuation; If the capacitor voltage of the input submodule exceeds the voltage fluctuation threshold after the preliminary switching, the input submodule and the bypass submodule after the preliminary switching are switched in rotation according to the capacitor voltage, including: When the bridge arm is in a charging state, if after the initial switching, there is an input submodule whose capacitor voltage is higher than the upper limit threshold, and there is a bypass submodule whose capacitor voltage is not higher than the upper limit threshold and is not put into operation, then based on the principle that the input submodule with the highest capacitor voltage corresponds to the bypass submodule with the lowest capacitor voltage, the input submodule and the bypass submodule after the initial switching are rotated; until there is no input submodule higher than the upper limit threshold or bypass submodule with a voltage not higher than the upper limit threshold, the rotation switching is stopped; When the bridge arm is in a discharge state, if after the initial switching, there is an input submodule whose capacitor voltage is lower than the lower threshold value, and there is a bypass submodule whose capacitor voltage is not lower than the lower threshold value and is not put into operation, then based on the principle that the input submodule with the highest capacitor voltage corresponds to the bypass submodule with the lowest capacitor voltage, the input submodule and the bypass submodule after the initial switching are rotated; until there is no input submodule whose voltage is lower than the lower threshold value or no bypass submodule whose voltage is not lower than the lower threshold value, the rotation switching is stopped.

9. The method according to claim 1, characterized in that The updating of the switch state of the submodule based on the state of the submodule in the converter after the rotation switching includes: A trigger signal is generated based on the switched-on submodule and the bypass submodule, and the switch states of the submodules in the converter under the current simulation step are updated.

10. The method according to claim 1, characterized in that After updating the switch state of the submodule based on the state of the submodule in the converter after the rotation switching, the method further includes: Converting the binary trigger signals of the input submodule and the bypass submodule into decimal numbers for indicating the states of the input submodule and the bypass submodule; The decimal number is stored.

11. The method according to claim 1, characterized in that The total number of submodules required to be invested in the current simulation step of the converter is obtained according to the following steps: Obtain the modulation wave voltage of the bridge arm in the current simulation step of the converter; Based on the modulation wave voltage of the bridge arm and the nearest level approximation modulation method, the total number of sub-modules required to be invested in the current simulation step of the converter is obtained.

12. A voltage balancing control system for modular multilevel converter submodules, characterized in that: include: The submodule analysis subsystem to be acted upon is used to determine the number of submodules to be acted upon in the current simulation step and the increase or decrease status of the submodules put into operation based on the total number of submodules to be put into operation in the current simulation step of the converter and the number of submodules put into operation in the previous simulation step; A sequential switching subsystem, for performing preliminary switching of the submodules in the converter based on the number of submodules to be operated, the increase and decrease status of the submodules put into operation, and the charge and discharge status of the bridge arm in the converter, according to the respective capacitor voltage sequence of the submodules put into operation and the bypass submodule before switching at the current simulation step; Optimizing the rotation subsystem, if the capacitor voltage of the submodule after the initial switching exceeds the voltage fluctuation threshold, the submodule and the bypass submodule after the initial switching are switched in rotation according to the capacitor voltage; The submodule status update subsystem is used to update the switch status of the submodule based on the status of the submodule in the converter after the rotation switching.

13. The system of claim 12, wherein: The sequential switching subsystem comprises: The submodule input unit, when the input submodule increase / decrease state of the current simulation step is the state of adding the input submodule, keeps the input submodule state before switching unchanged, and inputs the bypass submodule according to the bypass submodule capacitor voltage sequence before switching based on the number of the submodules to be operated and the charge / discharge state of the bridge arm; The submodule removal unit keeps the bypass submodule state before switching on unchanged when the increase or decrease state of the submodules put into operation in the current simulation step is the state of reducing the submodules put into operation, and removes the submodules put into operation in the order of the capacitor voltage of the submodules put into operation before switching on, based on the number of submodules to be acted on and the charge and discharge state of the bridge arm.

14. The system of claim 13, wherein: The submodule input unit is specifically used for: If the bridge arm is in a charging state, based on the number of the submodules to be operated, the bypass submodules are switched on in the order of the capacitor voltages of the bypass submodules before switching on from low to high; If the bridge arm is in a discharge state, based on the number of the submodules to be operated, the bypass submodules are switched on in a descending order of the capacitor voltages of the bypass submodules before switching on.

15. The system of claim 13, wherein: The submodule removal unit is specifically used for: If the bridge arm is in a discharge state, based on the number of submodules to be operated, the submodules to be switched on are switched off in the order of the capacitor voltages of the submodules before switching on from low to high; If the bridge arm is in a charging state, based on the number of the submodules to be operated, the submodules are cut off in descending order of the capacitor voltages of the submodules before switching on.

16. The system of claim 12, wherein: The submodule analysis subsystem to be acted upon includes: A preliminary judgment unit determines whether the total number of submodules required to be put into operation in the current simulation step of the converter is equal to the number of submodules put into operation in the previous simulation step; Fully sorted rotation units, if the number is equal, then the switch states of the submodules are updated according to the capacitor voltage difference and capacitor voltage sorting of the submodules in the current simulation step; The analysis unit for the submodules to be acted upon determines the number of submodules to be acted upon at the current simulation step and the increase or decrease status of the input submodules if the numbers are not equal.

17. The system of claim 16, wherein: The submodule analysis unit to be acted upon is specifically used for: The total number of sub-modules that need to be invested is recorded as N1, and the number of sub-modules invested in the previous simulation step is recorded as N0; If N1>N0 and N0≥0, the increase / decrease state of the input submodule of the current step length is determined to be the increase input submodule state; if N1>N0 and N1≤0, the increase / decrease state of the input submodule of the current step length is determined to be the decrease input submodule state; If N1<N0 and N1≥0, the increase / decrease state of the input submodule of the current step length is determined to be the decrease input submodule state; if N1<N0 and N0≤0, the increase / decrease state of the input submodule of the current step length is determined to be the increase input submodule state.

18. The system of claim 16, wherein: The full sorting rotation unit is specifically used for: If the capacitor voltage difference of the submodule in the current simulation step is less than the capacitor voltage difference threshold, the submodule in the current simulation step will not be switched; Based on the trigger signal generated by the input submodule and the bypass submodule in the previous simulation step, the switch state of each submodule in the converter in the current simulation step is updated; If the capacitance voltage difference of the submodules in the current simulation step is not less than the capacitance voltage difference threshold, the capacitance voltage of the submodules in the current simulation step is fully sorted; Switching the submodules in the current simulation step is performed based on the submodule sequence after the capacitor voltage is fully sorted; A trigger signal is generated based on the state of the submodule after switching is completed, and the switch state of each submodule in the converter is updated under the current simulation step.

19. The system of claim 16, wherein: The optimized rotation subsystem is specifically used for: When the bridge arm is in a charging state, if after the initial switching, there is an input submodule whose capacitor voltage is higher than the upper limit threshold, and there is a bypass submodule whose capacitor voltage is not higher than the upper limit threshold and is not put into operation, then based on the principle that the input submodule with the highest capacitor voltage corresponds to the bypass submodule with the lowest capacitor voltage, the input submodule and the bypass submodule after the initial switching are rotated; until there is no input submodule higher than the upper limit threshold or bypass submodule with a voltage not higher than the upper limit threshold, the rotation switching is stopped; When the bridge arm is in a discharge state, if after the initial switching, there is an input submodule whose capacitor voltage is lower than the lower threshold value, and there is a bypass submodule whose capacitor voltage is not lower than the lower threshold value and is not put into operation, then based on the principle that the input submodule with the highest capacitor voltage corresponds to the bypass submodule with the lowest capacitor voltage, the input submodule and the bypass submodule after the initial switching are rotated; until there is no input submodule whose voltage is lower than the lower threshold value or no bypass submodule whose voltage is not lower than the lower threshold value, the rotation switching is stopped.

20. The system of claim 12, wherein: The system further includes a storage subsystem, which is used for updating the switch state of the submodule in the converter based on the state of the submodule in the converter after the rotation switching: Converting the binary trigger signals of the input submodule and the bypass submodule into decimal numbers for indicating the states of the input submodule and the bypass submodule; The decimal number is stored.

21. An electronic device, characterized in that: include: at least one processor and memory; The memory and the processor are connected via a bus; The memory is used to store one or more programs; When the one or more programs are executed by the at least one processor, a voltage sharing control method for a modular multilevel converter submodule according to any one of claims 1 to 11 is implemented.

22. A computing device readable storage medium, characterized in that: An execution program is stored thereon, and when the execution program is executed, a voltage sharing control method for a modular multilevel converter submodule according to any one of claims 1 to 11 is implemented.

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