A capacitor voltage equalization control method, system, device, and dielectric

Abstract

This invention provides a capacitor voltage equalization control method, system, device, and medium, comprising: acquiring the bridge arm current and DC voltage within the bridge arm at the current moment, and the capacitor voltage values ​​of each modular multilevel converter dual-capacitor three-level sub-module within the bridge arm; sorting the capacitor voltage values ​​of each sub-module to obtain a capacitor voltage value sequence; calculating the change in the number of voltage levels to be switched on the bridge arm at the next moment based on the DC voltage using a rounding algorithm; selecting capacitors to be switched from within the bridge arm based on the change in the number of voltage levels, the bridge arm current, and the capacitor voltage value sequence, and switching the operating mode of the sub-module containing the selected capacitor to control DC voltage equalization; the method proposed in this invention generates three voltage levels and multiple operating modes through dual capacitors in the sub-module topology, increasing the number of voltage levels of a single sub-module to reduce the number of cascaded sub-modules in a single bridge arm at the same voltage level.

Description

Technical Field

[0001] This invention relates to the field of high-voltage direct current transmission, specifically to a capacitor voltage equalization control method, system, device, and medium. Background Technology

[0002] Since its introduction by German scholar R. Marquardt in 2001, the Modular Multilevel Converter (MMC) has become a core component of flexible DC-DC (VSC-HVDC) and flexible AC-DC transmission systems due to its modular design, low harmonic content, high scalability, and redundancy tolerance. An MMC consists of six arms across three phases. Each arm contains several cascaded sub-modules (SMs) and arm inductors. Through a rational control strategy, sub-modules can be connected or bypassed. Based on the equalization of sub-module capacitor voltages, the synthesized multilevel output voltage of the arms approximates a sine wave, significantly reducing harmonic content and filter requirements. Therefore, equalization of sub-module capacitor voltages is a prerequisite for the normal operation of the MMC.

[0003] Traditional MMC submodule capacitor balancing control algorithms first monitor and sort the capacitor voltage values ​​of each submodule, then determine whether to switch on a submodule with a higher or lower capacitor voltage based on the direction of the arm current. However, this method is only applicable to traditional single-capacitor MMC converters. As flexible DC transmission technology moves towards lower cost and compactness, diode-clamped three-level submodule converters with dual capacitors, by increasing the number of levels in a single submodule, reduce the number of cascaded submodules per arm while maintaining the same voltage level. This demonstrates unique advantages in applications such as offshore wind power flexible DC transmission where the size, weight, and economy of the converter station are critical. However, a comprehensive capacitor voltage balancing control method is currently lacking for this type of topology. Therefore, a capacitor voltage balancing control method suitable for dual-capacitor three-level submodule MMCs is urgently needed. Summary of the Invention

[0004] To address the requirement of high-voltage, high-capacity MMCs for multi-level submodules, this invention proposes a capacitor voltage balancing control method and system suitable for dual-capacitor, three-level submodule MMCs. By increasing the number of levels in a single submodule, the number of cascaded submodules in a single bridge arm is reduced while maintaining the same voltage level. Then, the control strategy of this invention enables the rational activation or bypassing of submodules, achieving both near-sine wave approximation of the synthesized multi-level output voltage from the bridge arms, significantly reducing harmonic content and filter requirements, and enabling capacitor voltage balancing control between submodules and dynamic balancing control of the two capacitor voltages within a single submodule.

[0005] This invention proposes a capacitor voltage equalization control method, comprising:

[0006] Collect the bridge arm current and DC voltage within the bridge arm at the current moment, as well as the capacitor voltage values ​​of each modular multilevel converter dual-capacitor three-level sub-module within the bridge arm;

[0007] The capacitor voltage values ​​of each submodule are sorted to obtain a capacitor voltage value sequence;

[0008] The change in the number of voltage levels applied to the bridge arm at the next moment is calculated using a rounding algorithm based on the DC voltage.

[0009] Based on the changes in the voltage level, the bridge arm current, and the capacitor voltage value sequence, the capacitor to be switched from the bridge arm is selected, and the operating mode of the submodule containing the selected capacitor is switched to control DC voltage balance.

[0010] Preferably, the step of selecting the capacitor to be switched from within the bridge arm based on the change in the level number, the bridge arm current, and the capacitor voltage value sequence, and switching the operating mode of the submodule containing the selected capacitor, includes:

[0011] If the level change is greater than zero and the bridge arm current is greater than zero, then select the capacitor with the smallest level change in the capacitor voltage value sequence, and switch the operating mode of the sub-module where the capacitor is located to put the selected capacitor into operation.

[0012] If the level change is greater than zero and the bridge arm current is less than zero, then select the capacitor with the largest level change in the capacitor voltage value sequence, and switch the operating mode of the sub-module containing the capacitor to put the selected capacitor into operation.

[0013] If the level change is less than zero and the bridge arm current is greater than zero, then select the capacitor with the largest level change in the capacitor voltage value sequence, and switch the operating mode of the sub-module containing the capacitor to remove the selected capacitor.

[0014] If the level change is less than zero and the bridge arm current is less than zero, then select the capacitor with the smallest level change in the capacitor voltage value sequence, and switch the operating mode of the submodule containing the capacitor to remove the selected capacitor.

[0015] Preferably, if the level change is greater than zero and the bridge arm current is greater than zero, then the capacitor with the smallest level change in the capacitor voltage value sequence is selected, and the operating mode of the submodule containing the selected capacitor is switched to activate the selected capacitor, including:

[0016] If the change in the number of voltage levels is greater than zero and the bridge arm current is greater than zero, then select the capacitor with the smallest change in the number of voltage levels in the capacitor voltage value sequence.

[0017] Determine if two capacitors are selected in one or more sub-modules: If yes, switch the operating mode of the sub-module where both capacitors are selected from cut-off mode to two capacitors in series charging mode, and switch the operating mode of the sub-module containing the remaining capacitors from cut-off mode to single capacitor charging mode; if no, switch the operating mode of the sub-modules containing each capacitor from cut-off mode to single capacitor charging mode.

[0018] Preferably, if the level change is greater than zero and the bridge arm current is less than zero, then the capacitor with the largest level change in the capacitor voltage value sequence is selected, and the operating mode of the submodule containing the selected capacitor is switched to activate the selected capacitor, including:

[0019] If the change in voltage level is greater than zero and the bridge arm current is less than zero, then select the capacitor with the largest change in voltage level in the capacitor voltage value sequence.

[0020] Determine if two capacitors are selected in one or more sub-modules: If yes, switch the operating mode of the sub-module where both capacitors are selected from cut-off mode to two capacitors in series discharge mode, and switch the operating mode of the sub-module containing the remaining capacitors from cut-off mode to single capacitor discharge mode; if no, switch the operating mode of the sub-modules containing each capacitor from cut-off mode to single capacitor discharge mode.

[0021] Preferably, if the level change is less than zero and the bridge arm current is greater than zero, then the capacitor with the largest level change in the capacitor voltage value sequence is selected, and the operating mode of the submodule containing the selected capacitor is switched to remove the selected capacitor, including:

[0022] If the change in voltage level is less than zero and the bridge arm current is greater than zero, then select the capacitor with the largest change in voltage level in the capacitor voltage value sequence.

[0023] Determine if two capacitors are selected in one or more sub-modules: If yes, switch the operating mode of the sub-module where both capacitors are selected from the two capacitors in series charging mode to the capacitor bypass mode, and switch the operating mode of the sub-module containing the remaining capacitors from the single capacitor charging mode to the capacitor bypass mode; if no, switch the operating mode of the sub-module containing each capacitor from the single capacitor charging mode to the capacitor bypass mode.

[0024] Preferably, if the level change is less than zero and the bridge arm current is less than zero, then the capacitor with the smallest level change in the capacitor voltage value sequence is selected, and the operating mode of the submodule containing the selected capacitor is switched to remove the selected capacitor, including:

[0025] If the change in the number of voltage levels is less than zero and the bridge arm current is less than zero, then select the capacitor with the smallest change in the number of voltage levels in the capacitor voltage value sequence.

[0026] Determine if two capacitors are selected in one or more sub-modules: if so, switch the operating mode of the sub-module where both capacitors are selected from the two capacitors in series discharge mode to the capacitor bypass mode; if not, switch the operating mode of the sub-module containing each capacitor from the single capacitor discharge mode to the capacitor bypass mode.

[0027] Preferably, the step of calculating the change in the number of voltage levels applied to the bridge arm at the next moment using a rounding algorithm based on the DC voltage includes:

[0028] Based on the DC voltage, the AC voltage to be generated, and the voltage of a single capacitor in the submodule, the number of voltage levels to be applied at the next moment is calculated using a rounding algorithm.

[0029] The change in the number of voltage levels applied on the bridge arm at the next moment is obtained by subtracting the number of voltage levels already applied from the number of voltage levels that need to be applied at the next moment.

[0030] Preferably, the formula for calculating the number of levels to be applied in the next moment is as follows:

[0031]

[0032] In the formula, N xp This indicates the number of voltage levels that need to be applied in the next moment. U dc Indicates DC voltage. U d This represents the voltage of a single capacitor in the module. m cos( ωt ) represents the AC voltage to be generated, where m Indicates the amplitude of AC voltage. ω Represents angular frequency. t For time, round 0.5 (•) represents the floor function.

[0033] Based on the same inventive concept, this application also provides a capacitor voltage equalization control system, including: a data acquisition module, a sequence module, a level number change module, and a mode switching module;

[0034] The acquisition module is used to acquire the bridge arm current and DC voltage in the bridge arm at the current moment, as well as the capacitor voltage value of each modular multilevel converter dual-capacitor three-level sub-module in the bridge arm.

[0035] The sequence module is used to sort the capacitor voltage values ​​of each sub-module to obtain a capacitor voltage value sequence.

[0036] The level change module is used to calculate the level change of the bridge arm at the next moment based on the DC voltage using a rounding algorithm.

[0037] The mode switching module is used to select the capacitor to be switched from within the bridge arm according to the change in the level number, the bridge arm current and the capacitor voltage value sequence, and to switch the operating mode of the sub-module where the selected capacitor is located in order to control DC voltage balance.

[0038] Preferably, the mode switching module selects the capacitor to be switched from within the bridge arm based on the level change, bridge arm current, and capacitor voltage value sequence, and switches the operating mode of the sub-module containing the selected capacitor, including:

[0039] If the level change is greater than zero and the bridge arm current is greater than zero, then select the capacitor with the smallest level change in the capacitor voltage value sequence, and switch the operating mode of the sub-module where the capacitor is located to put the selected capacitor into operation.

[0040] If the level change is greater than zero and the bridge arm current is less than zero, then select the capacitor with the largest level change in the capacitor voltage value sequence, and switch the operating mode of the sub-module containing the capacitor to put the selected capacitor into operation.

[0041] If the level change is less than zero and the bridge arm current is greater than zero, then select the capacitor with the largest level change in the capacitor voltage value sequence, and switch the operating mode of the sub-module containing the capacitor to remove the selected capacitor.

[0042] If the level change is less than zero and the bridge arm current is less than zero, then select the capacitor with the smallest level change in the capacitor voltage value sequence, and switch the operating mode of the submodule containing the capacitor to remove the selected capacitor.

[0043] Preferably, if the level change is greater than zero and the bridge arm current is greater than zero, the mode switching module selects the capacitor with the smallest level change in the capacitor voltage value sequence, and switches the operating mode of the submodule containing the selected capacitor to engage the selected capacitor, including:

[0044] If the change in the number of voltage levels is greater than zero and the bridge arm current is greater than zero, then select the capacitor with the smallest change in the number of voltage levels in the capacitor voltage value sequence.

[0045] Determine if two capacitors are selected in one or more sub-modules: If yes, switch the operating mode of the sub-module where both capacitors are selected from cut-off mode to two capacitors in series charging mode, and switch the operating mode of the sub-module containing the remaining capacitors from cut-off mode to single capacitor charging mode; if no, switch the operating mode of the sub-modules containing each capacitor from cut-off mode to single capacitor charging mode.

[0046] Preferably, if the level change is greater than zero and the bridge arm current is less than zero, the mode switching module selects the capacitor with the largest level change in the capacitor voltage value sequence and switches the operating mode of the submodule containing the selected capacitor to engage the selected capacitor, including:

[0047] If the change in voltage level is greater than zero and the bridge arm current is less than zero, then select the capacitor with the largest change in voltage level in the capacitor voltage value sequence.

[0048] Determine if two capacitors are selected in one or more sub-modules: If yes, switch the operating mode of the sub-module where both capacitors are selected from cut-off mode to two capacitors in series discharge mode, and switch the operating mode of the sub-module containing the remaining capacitors from cut-off mode to single capacitor discharge mode; if no, switch the operating mode of the sub-modules containing each capacitor from cut-off mode to single capacitor discharge mode.

[0049] Preferably, if the level change is less than zero and the bridge arm current is greater than zero, the mode switching module selects the capacitor with the largest level change in the capacitor voltage value sequence and switches the operating mode of the submodule containing the selected capacitor to remove it, including:

[0050] If the change in voltage level is less than zero and the bridge arm current is greater than zero, then select the capacitor with the largest change in voltage level in the capacitor voltage value sequence.

[0051] Determine if two capacitors are selected in one or more sub-modules: If yes, switch the operating mode of the sub-module where both capacitors are selected from the two capacitors in series charging mode to the capacitor bypass mode, and switch the operating mode of the sub-module containing the remaining capacitors from the single capacitor charging mode to the capacitor bypass mode; if no, switch the operating mode of the sub-module containing each capacitor from the single capacitor charging mode to the capacitor bypass mode.

[0052] Preferably, if the level change is less than zero and the bridge arm current is less than zero, the mode switching module selects the capacitor with the smallest level change in the capacitor voltage value sequence, and switches the operating mode of the submodule containing the selected capacitor to remove it, including:

[0053] If the change in the number of voltage levels is less than zero and the bridge arm current is less than zero, then select the capacitor with the smallest change in the number of voltage levels in the capacitor voltage value sequence.

[0054] Determine if two capacitors are selected in one or more sub-modules: if so, switch the operating mode of the sub-module where both capacitors are selected from the two capacitors in series discharge mode to the capacitor bypass mode; if not, switch the operating mode of the sub-module containing each capacitor from the single capacitor discharge mode to the capacitor bypass mode.

[0055] Preferably, the level change module is specifically used for:

[0056] Based on the DC voltage, the AC voltage to be generated, and the voltage of a single capacitor in the submodule, the number of voltage levels to be applied at the next moment is calculated using a rounding algorithm.

[0057] The change in the number of voltage levels applied on the bridge arm at the next moment is obtained by subtracting the number of voltage levels already applied from the number of voltage levels that need to be applied at the next moment.

[0058] Preferably, the formula for calculating the number of levels to be applied in the next moment of the level change module is as follows:

[0059]

[0060] In the formula, N xp This indicates the number of voltage levels that need to be applied in the next moment. U dc Indicates DC voltage. U d This represents the voltage of a single capacitor in the module. m cos( ωt ) represents the AC voltage to be generated, where m Indicates the amplitude of AC voltage. ω Represents angular frequency. t For time, round 0.5 (•) represents the floor function.

[0061] Furthermore, this application also provides a computing device, comprising: at least one processor and a memory;

[0062] The memory is used to store one or more programs;

[0063] When the one or more programs are executed by the one or more processors, a capacitor voltage equalization control method as described above is implemented.

[0064] In another aspect, this application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed, implements a capacitor voltage equalization control method as described above.

[0065] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0066] This invention provides a capacitor voltage equalization control method, system, device, and medium, comprising: acquiring the bridge arm current and DC voltage within the bridge arm at the current moment, and the capacitor voltage values ​​of each modular multilevel converter (MMC) dual-capacitor three-level submodule within the bridge arm; sorting the capacitor voltage values ​​of each submodule to obtain a capacitor voltage value sequence; calculating the change in the number of voltage levels to be switched on the bridge arm at the next moment based on the DC voltage using a rounding algorithm; selecting capacitors to be switched from within the bridge arm based on the change in the number of voltage levels, the bridge arm current, and the capacitor voltage value sequence, and switching the operating mode of the submodule containing the selected capacitor to control DC voltage equalization; the capacitor voltage equalization control method proposed in this invention, applicable to dual-capacitor three-level submodules (MMC), increases the number of voltage levels in a single submodule by generating three voltage levels and multiple operating modes through dual capacitors in the submodule topology, thereby reducing the number of cascaded submodules in a single bridge arm at the same voltage level. Then, the control strategy of the present invention realizes the switching of the operating mode of the sub-module, which can not only make the bridge arm synthesized multi-level output voltage approximate a sine wave, significantly reduce the harmonic content and reduce the filter requirement, but also realize the equalization control of capacitor voltage between sub-modules and the dynamic equalization control of the two capacitor voltages of a single sub-module based on the redundant mode switching of the sub-module. Attached Figure Description

[0067] Figure 1 This is a schematic diagram of a capacitor voltage equalization control method provided by the present invention;

[0068] Figure 2 This is a schematic diagram of the dual-capacitor three-level submodule provided by the present invention;

[0069] Figure 3 This is a schematic diagram of the submodule modes and charging / discharging conditions provided by the present invention;

[0070] Figure 4 A schematic diagram of a capacitor voltage equalization control method for a dual-capacitor three-level submodule MMC provided by the present invention;

[0071] Figure 5 This is a schematic diagram of the compact three-level sub-module structure provided by the present invention;

[0072] Figure 6 This is a schematic diagram of the diode clamping submodule structure provided by the present invention;

[0073] Figure 7 A schematic diagram of a capacitor voltage equalization control system provided by the present invention;

[0074] Figure 8 This is a schematic diagram of an electronic device structure provided by the present invention. Detailed Implementation

[0075] To achieve stable capacitor voltage control in dual-capacitor three-level submodules, this invention proposes a capacitor voltage balancing control method, system, device, and medium suitable for dual-capacitor three-level submodules (MMC). Based on the different operating modes of the dual-capacitor three-level submodule, this invention employs a sorting algorithm to balance the capacitor voltage of the MMC submodules, effectively achieving balanced capacitor voltage control between submodules and dynamic balanced control of the two capacitor voltages within a single submodule.

[0076] Example 1:

[0077] A capacitor voltage equalization control method, such as Figure 1 As shown, it includes:

[0078] Step 1: Collect the bridge arm current and DC voltage in the bridge arm at the current moment, as well as the capacitor voltage value of each modular multilevel converter dual-capacitor three-level sub-module in the bridge arm;

[0079] Step 2: Sort the capacitor voltage values ​​of each submodule to obtain a capacitor voltage value sequence;

[0080] Step 3: Calculate the change in the number of voltage levels applied to the bridge arm at the next moment based on the DC voltage using a rounding algorithm;

[0081] Step 4: Based on the changes in the voltage level, the bridge arm current, and the capacitor voltage value sequence, select the capacitor to be switched from within the bridge arm, and switch the operating mode of the submodule where the selected capacitor is located to control DC voltage balance.

[0082] Step 1 specifically includes: acquiring the capacitor voltage values ​​of the N MMC sub-modules (i.e., modular multilevel converter dual-capacitor three-level sub-modules) within the bridge arm at the current moment. U ck ( k =1,2,3,…,N), and the bridge arm current values. i arm and DC voltage U dc ;

[0083] Step 2 specifically includes: checking the capacitor voltage values ​​of each MMC submodule within the bridge arm. U ck ( k Sort the numbers (e.g., 1, 2, 3, ..., N) in ascending or descending order. The bubble sort algorithm can be used for sorting.

[0084] Step 3 specifically includes:

[0085] 3-1: Each arm of the MMC generates N levels. The number of MMC levels that each arm of the MMC needs to activate at the next moment is calculated based on the rounding algorithm selected by the control system. Nxp or N xn ;in N xp This indicates the number of voltage levels that the upper bridge arm needs to be engaged. N xn This indicates the number of voltage levels that the lower bridge arm needs to be engaged. The control methods for both the upper and lower bridge arms are the same; the following explanation will use the upper bridge arm as an example. The formula for calculating the number of voltage levels to be engaged in the next moment is as follows:

[0086]

[0087] In the formula, N xp This indicates the number of voltage levels that need to be applied in the next moment. U dc Indicates DC voltage. U d This represents the voltage of a single capacitor in the module. m cos( ωt ) represents the AC voltage to be generated, where m Indicates the amplitude of AC voltage. ω Represents angular frequency. t For time, round 0.5 (•) represents the floor function.

[0088] 3-2: Calculate the change in the number of levels: ΔN = N xp -N xp0 ,in N xp0 This represents the current input level.

[0089] Step 4 specifically includes:

[0090] 4-1: Determine the changes in voltage levels and submodule input / output: If the voltage level change ΔN is greater than zero, a new submodule needs to be input; if the voltage level change ΔN is less than zero, a new submodule needs to be output; if the voltage level change ΔN is zero, the number of input / output submodules remains unchanged. The specific submodules to input or output are determined by the direction of the bridge arm current—either the submodule with the highest or lowest capacitor voltage. Proceed to the next step.

[0091] 4-2: Select according to the following method:

[0092] If the voltage level change ΔN is greater than zero, it means that more submodules need to be added. In this case, it is necessary to determine the positive or negative direction of the bridge arm current. If the bridge arm current is greater than zero (i.e., it is in a charging state), select the first |ΔN| capacitors with smaller voltages after sorting in step 2; if the bridge arm current is less than zero (i.e., it is in a discharging state), select the first |ΔN| capacitors with larger voltages after sorting in step 2.

[0093] If the voltage level change ΔN is less than zero, it means that more submodules need to be removed. In this case, it is necessary to determine the positive or negative direction of the bridge arm current. If the bridge arm current is greater than zero (i.e., it is in a charging state), select the first |ΔN| capacitors with larger voltages after sorting in step 2; if the bridge arm current is less than zero (i.e., it is in a discharging state), select the first |ΔN| capacitors with smaller voltages after sorting in step 2.

[0094] 4-3: Determining whether ΔN capacitors are in the same submodule:

[0095] After selecting the first |ΔN| capacitors after sorting by capacitor voltage, determine whether there are cases where two capacitors from m (m=1,…,|ΔN| / 2) sub-modules are selected.

[0096] 4-4: Submodule runtime mode selection:

[0097] ① If the voltage level change ΔN is greater than zero and the bridge arm current is greater than zero (i.e., it is in a charging state), the first |ΔN| operating modes with smaller capacitor voltages after sorting in step 4-2 are selected according to the following principles:

[0098] If two capacitors from m submodules are selected, the module is switched to mode 4 (two capacitors are charged in series), and the remaining submodules containing |ΔN|-2m capacitors are switched from the cut-off mode to mode 1 or mode 3 (single capacitor within the submodule is charged); if two capacitors from m submodules are not selected, the submodules containing |ΔN| capacitors are switched from the cut-off mode to mode 1 or mode 3 (single capacitor within the submodule is charged).

[0099] ② If the voltage level change ΔN is greater than zero and the bridge arm current is less than zero (i.e., in a discharge state), the top |ΔN| operating modes with the largest capacitor voltages after sorting in step 4-2 are selected according to the following principles:

[0100] If two capacitors from m submodules are selected, the module is switched to mode 8 (two capacitors are discharged in series), and the remaining submodules containing |ΔN|-2m capacitors are switched from the cut-off mode to mode 5 or mode 7 (single capacitor discharge within the submodule); if two capacitors from m submodules are not selected, the submodules containing |ΔN| capacitors are switched from the cut-off mode to mode 5 or mode 7 (single capacitor discharge within the submodule).

[0101] ③ If the voltage level change ΔN is less than zero and the bridge arm current is greater than zero (i.e., it is in a charging state), the top |ΔN| operating modes with higher capacitor voltages after sorting in step 4-2 are selected according to the following principles:

[0102] If two capacitors from m sub-modules are selected, then that module is switched to mode 2 (capacitor bypass), and the remaining sub-modules containing |ΔN|-2m capacitors are switched from the input mode to mode 2; if no two capacitors from m sub-modules are selected, then the sub-modules containing |ΔN| capacitors are switched from the input mode to mode 2.

[0103] ④ If the voltage level change ΔN is less than zero and the bridge arm current is less than zero (i.e., in a discharge state), the first |ΔN| operating modes with smaller capacitor voltages after sorting in step 6 are selected according to the following principles:

[0104] If two capacitors from m sub-modules are selected, then that module is switched to mode 6 (capacitor bypass), and the remaining sub-modules containing |ΔN|-2m capacitors are switched from the input mode to mode 6; if no two capacitors from m sub-modules are selected, then the sub-modules containing |ΔN| capacitors are switched from the input mode to mode 6.

[0105] After step 4, wait for the next control cycle and repeat steps 1-4.

[0106] The dual-capacitor three-level submodule used in this invention is as follows: Figure 2 As shown, one end of the first capacitor 20 is connected to the power conversion section 52, and the other end of the first capacitor 20 (i.e., C1) is connected to one end of the second capacitor 30 (i.e., C2). The other end of the second capacitor 30 is connected to the power conversion section 52. The intersection of the first capacitor 20 and the second capacitor 30 is connected to the power conversion section 52. The power conversion section 52 is connected to the positive terminal 25 and the negative terminal 45 of the MMC submodule, respectively.

[0107] The modes (i.e., operating modes) of the dual-capacitor three-level submodule used in this invention are as follows: Figure 3 As shown.

[0108] The modes are 1 to 8, namely: Mode 1: C1 charging, Mode 2: capacitor bypass, Mode 3: C2 charging, Mode 4: C1 and C2 connected in series charging, Mode 5: C1 discharging, Mode 6: capacitor bypass, Mode 7: C2 discharging, and Mode 8: C1 and C2 connected in series discharging.

[0109] C1 or C2 charges and discharges, generating U. c Level; capacitor bypass generates 0 level; C1 and C2 are connected in series for charging or discharging, generating 2U. c Level.

[0110] The capacitor voltage equalization control method for the dual-capacitor three-level submodule MMC provided by this invention is as follows: Figure 4 As shown.

[0111] The power conversion section of the dual-capacitor three-level sub-module used in this invention includes, but is not limited to, devices such as thyristors, diodes, insulated gate bipolar transistors (IGBTs), integrated gate commutated thyristors (IGCTs), gate turn-off thyristors (GTOs), or electron injection enhancement gate transistors (IEGTs).

[0112] The dual-capacitor three-level sub-module topology used in this invention includes, but is not limited to, compact three-level sub-modules, diode-clamped sub-modules, etc., where dual capacitors are connected in series to generate 0 and U. c 2U c A three-level topology. The compact three-level submodule is as follows: Figure 5 As shown, the diode clamping submodule is as follows: Figure 6 As shown, Figure 6 C1 and C2 are two capacitors in the diode clamping submodule, D1~D6 are diodes, and T1~T4 are transistors.

[0113] Example 2:

[0114] Based on the same inventive concept, this invention also provides a capacitor voltage equalization control system, such as... Figure 7 As shown, it includes:

[0115] Acquisition module, sequence module, level number change module, and mode switching module;

[0116] The acquisition module is used to acquire the bridge arm current and DC voltage in the bridge arm at the current moment, as well as the capacitor voltage value of each modular multilevel converter dual-capacitor three-level sub-module in the bridge arm.

[0117] The sequence module is used to sort the capacitor voltage values ​​of each sub-module to obtain a capacitor voltage value sequence.

[0118] The level change module is used to calculate the level change of the bridge arm at the next moment based on the DC voltage using a rounding algorithm.

[0119] The mode switching module is used to select the capacitor to be switched from within the bridge arm according to the change in the level number, the bridge arm current and the capacitor voltage value sequence, and to switch the operating mode of the sub-module where the selected capacitor is located in order to control DC voltage balance.

[0120] Preferably, the mode switching module selects the capacitor to be switched from within the bridge arm based on the level change, bridge arm current, and capacitor voltage value sequence, and switches the operating mode of the sub-module containing the selected capacitor, including:

[0121] If the level change is greater than zero and the bridge arm current is greater than zero, then select the capacitor with the smallest level change in the capacitor voltage value sequence, and switch the operating mode of the sub-module where the capacitor is located to put the selected capacitor into operation.

[0122] If the level change is greater than zero and the bridge arm current is less than zero, then select the capacitor with the largest level change in the capacitor voltage value sequence, and switch the operating mode of the sub-module containing the capacitor to put the selected capacitor into operation.

[0123] If the level change is less than zero and the bridge arm current is greater than zero, then select the capacitor with the largest level change in the capacitor voltage value sequence, and switch the operating mode of the sub-module containing the capacitor to remove the selected capacitor.

[0124] If the level change is less than zero and the bridge arm current is less than zero, then select the capacitor with the smallest level change in the capacitor voltage value sequence, and switch the operating mode of the submodule containing the capacitor to remove the selected capacitor.

[0125] Preferably, if the level change is greater than zero and the bridge arm current is greater than zero, the mode switching module selects the capacitor with the smallest level change in the capacitor voltage value sequence, and switches the operating mode of the submodule containing the selected capacitor to engage the selected capacitor, including:

[0126] If the change in the number of voltage levels is greater than zero and the bridge arm current is greater than zero, then select the capacitor with the smallest change in the number of voltage levels in the capacitor voltage value sequence.

[0127] Determine if two capacitors are selected in one or more sub-modules: If yes, switch the operating mode of the sub-module where both capacitors are selected from cut-off mode to two capacitors in series charging mode, and switch the operating mode of the sub-module containing the remaining capacitors from cut-off mode to single capacitor charging mode; if no, switch the operating mode of the sub-modules containing each capacitor from cut-off mode to single capacitor charging mode.

[0128] Preferably, if the level change is greater than zero and the bridge arm current is less than zero, the mode switching module selects the capacitor with the largest level change in the capacitor voltage value sequence and switches the operating mode of the submodule containing the selected capacitor to engage the selected capacitor, including:

[0129] If the change in voltage level is greater than zero and the bridge arm current is less than zero, then select the capacitor with the largest change in voltage level in the capacitor voltage value sequence.

[0130] Determine if two capacitors are selected in one or more sub-modules: If yes, switch the operating mode of the sub-module where both capacitors are selected from cut-off mode to two capacitors in series discharge mode, and switch the operating mode of the sub-module containing the remaining capacitors from cut-off mode to single capacitor discharge mode; if no, switch the operating mode of the sub-modules containing each capacitor from cut-off mode to single capacitor discharge mode.

[0131] Preferably, if the level change is less than zero and the bridge arm current is greater than zero, the mode switching module selects the capacitor with the largest level change in the capacitor voltage value sequence and switches the operating mode of the submodule containing the selected capacitor to remove it, including:

[0132] If the change in voltage level is less than zero and the bridge arm current is greater than zero, then select the capacitor with the largest change in voltage level in the capacitor voltage value sequence.

[0133] Determine if two capacitors are selected in one or more sub-modules: If yes, switch the operating mode of the sub-module where both capacitors are selected from the two capacitors in series charging mode to the capacitor bypass mode, and switch the operating mode of the sub-module containing the remaining capacitors from the single capacitor charging mode to the capacitor bypass mode; if no, switch the operating mode of the sub-module containing each capacitor from the single capacitor charging mode to the capacitor bypass mode.

[0134] Preferably, if the level change is less than zero and the bridge arm current is less than zero, the mode switching module selects the capacitor with the smallest level change in the capacitor voltage value sequence, and switches the operating mode of the submodule containing the selected capacitor to remove it, including:

[0135] If the change in the number of voltage levels is less than zero and the bridge arm current is less than zero, then select the capacitor with the smallest change in the number of voltage levels in the capacitor voltage value sequence.

[0136] Determine if two capacitors are selected in one or more sub-modules: if so, switch the operating mode of the sub-module where both capacitors are selected from the two capacitors in series discharge mode to the capacitor bypass mode; if not, switch the operating mode of the sub-module containing each capacitor from the single capacitor discharge mode to the capacitor bypass mode.

[0137] Preferably, the level change module is specifically used for:

[0138] Based on the DC voltage, the AC voltage to be generated, and the voltage of a single capacitor in the submodule, the number of voltage levels to be applied at the next moment is calculated using a rounding algorithm.

[0139] The change in the number of voltage levels applied on the bridge arm at the next moment is obtained by subtracting the number of voltage levels already applied from the number of voltage levels that need to be applied at the next moment.

[0140] Preferably, the formula for calculating the number of levels to be applied in the next moment of the level change module is as follows:

[0141]

[0142] In the formula, N xp This indicates the number of voltage levels that need to be applied in the next moment. U dc Indicates DC voltage. U d This represents the voltage of a single capacitor in the module. m cos( ωt ) represents the AC voltage to be generated, where m Indicates the amplitude of AC voltage. ω Represents angular frequency. t For time, round 0.5 (•) represents the floor function.

[0143] Example 3

[0144] like Figure 8 As shown, the present invention also provides an electronic device, which may be a computer device, a microcontroller device, a smart mobile device, etc. The electronic device in this embodiment may include a processor, a memory, a transceiver component, etc. The memory, processor, and transceiver component are connected via a bus; the memory can be used to store executable programs, and an exemplary executable program may include instructions; the processor is used to execute the instructions stored in the memory. The memory can also be used to store data, which can be accessed and / or modified when instructions are executed.

[0145] The processor may be a Central Processing Unit (CPU), or it may be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, and it is suitable for implementing one or more instructions. Specifically, it is suitable for loading and executing one or more instructions in the storage medium to implement the corresponding method flow or corresponding function, so as to implement the steps of a capacitor voltage equalization control method in the above embodiments.

[0146] Example 4

[0147] Based on the same inventive concept, this invention also provides a readable storage medium, specifically an electronic device readable storage medium (Memory). This readable storage medium is a memory device within an electronic device used to store programs and data. It is understood that the storage medium here can include both built-in storage media within the electronic device and extended storage media supported by the electronic device. The storage medium provides storage space, which stores the terminal's operating system. Furthermore, this storage space also stores one or more instructions suitable for loading and execution by a processor. These instructions can be one or more executable programs (including program code). It should be noted that the storage medium here can be high-speed RAM or non-volatile memory, such as at least one disk storage device. Loading and executing one or more instructions stored in the storage medium by the processor can implement the steps of a capacitor voltage equalization control method in the above embodiments.

[0148] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied 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.

[0149] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0150] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0151] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0152] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of the claims of the present invention pending approval.

Claims

1. A capacitor voltage equalization control method, characterized in that, include: Collect the bridge arm current and DC voltage within the bridge arm at the current moment, as well as the capacitor voltage values ​​of each modular multilevel converter dual-capacitor three-level sub-module within the bridge arm; The capacitor voltage values ​​of each submodule are sorted to obtain a capacitor voltage value sequence; The change in the number of voltage levels applied to the bridge arm at the next moment is calculated using a rounding algorithm based on the DC voltage. Based on the changes in the voltage level, the bridge arm current, and the capacitor voltage value sequence, the capacitor to be switched from the bridge arm is selected, and the operating mode of the submodule where the selected capacitor is located is switched to control DC voltage balance. The step of selecting a capacitor for switching from within the bridge arm based on the changes in the voltage level, the bridge arm current, and the capacitor voltage value sequence, and switching the operating mode of the submodule containing the selected capacitor, includes: If the level change is greater than zero and the bridge arm current is greater than zero, then select the capacitor with the smallest level change in the capacitor voltage value sequence, and switch the operating mode of the sub-module where the capacitor is located to put the selected capacitor into operation. If the level change is greater than zero and the bridge arm current is less than zero, then select the capacitor with the largest level change in the capacitor voltage value sequence, and switch the operating mode of the sub-module containing the capacitor to put the selected capacitor into operation. If the level change is less than zero and the bridge arm current is greater than zero, then select the capacitor with the largest level change in the capacitor voltage value sequence, and switch the operating mode of the sub-module containing the capacitor to remove the selected capacitor. If the level change is less than zero and the bridge arm current is less than zero, then select the capacitor with the smallest level change in the capacitor voltage value sequence, and switch the operating mode of the sub-module containing the capacitor to remove the selected capacitor. The calculation of the change in the number of voltage levels applied to the bridge arm at the next moment based on the rounding algorithm of the DC voltage includes: Based on the DC voltage, the AC voltage to be generated, and the voltage of a single capacitor in the submodule, the number of voltage levels to be applied at the next moment is calculated using a rounding algorithm. The change in the number of voltage levels applied on the bridge arm at the next moment is obtained by subtracting the number of voltage levels already applied from the number of voltage levels that need to be applied at the next moment. The formula for calculating the number of voltage levels to be applied in the next moment is as follows: In the formula, N xp This indicates the number of voltage levels that need to be applied in the next moment. U dc Indicates DC voltage. U d This represents the voltage of a single capacitor in the module. m cos( ωt ) represents the AC voltage to be generated, where m Indicates the amplitude of AC voltage. ω Represents angular frequency. t For time, round 0.5 (•) represents the floor function.

2. The method as described in claim 1, characterized in that, If the voltage level change is greater than zero and the bridge arm current is greater than zero, then the capacitor with the smallest voltage level change in the capacitor voltage value sequence is selected, and the operating mode of the submodule containing the selected capacitor is switched to activate the selected capacitor, including: If the change in the number of voltage levels is greater than zero and the bridge arm current is greater than zero, then select the capacitor with the smallest change in the number of voltage levels in the capacitor voltage value sequence. Determine if two capacitors are selected in one or more sub-modules: If yes, switch the operating mode of the sub-module where both capacitors are selected from cut-off mode to two capacitors in series charging mode, and switch the operating mode of the sub-module containing the remaining capacitors from cut-off mode to single capacitor charging mode; if no, switch the operating mode of the sub-modules containing each capacitor from cut-off mode to single capacitor charging mode.

3. The method as described in claim 1, characterized in that, If the voltage level change is greater than zero and the bridge arm current is less than zero, then the capacitor with the largest voltage level change in the capacitor voltage value sequence is selected, and the operating mode of the submodule containing the selected capacitor is switched to activate the selected capacitor, including: If the change in voltage level is greater than zero and the bridge arm current is less than zero, then select the capacitor with the largest change in voltage level in the capacitor voltage value sequence. Determine if two capacitors are selected in one or more sub-modules: If yes, switch the operating mode of the sub-module where both capacitors are selected from cut-off mode to two capacitors in series discharge mode, and switch the operating mode of the sub-module containing the remaining capacitors from cut-off mode to single capacitor discharge mode; if no, switch the operating mode of the sub-modules containing each capacitor from cut-off mode to single capacitor discharge mode.

4. The method as described in claim 1, characterized in that, If the voltage level change is less than zero and the bridge arm current is greater than zero, then the capacitor with the largest voltage level change in the capacitor voltage value sequence is selected, and the operating mode of the submodule containing the selected capacitor is switched to remove the selected capacitor, including: If the change in voltage level is less than zero and the bridge arm current is greater than zero, then select the capacitor with the largest change in voltage level in the capacitor voltage value sequence. Determine if two capacitors are selected in one or more sub-modules: If yes, switch the operating mode of the sub-module where both capacitors are selected from the two capacitors in series charging mode to the capacitor bypass mode, and switch the operating mode of the sub-module containing the remaining capacitors from the single capacitor charging mode to the capacitor bypass mode; if no, switch the operating mode of the sub-module containing each capacitor from the single capacitor charging mode to the capacitor bypass mode.

5. The method as described in claim 1, characterized in that, If the voltage level change is less than zero and the bridge arm current is less than zero, then the capacitor with the smallest voltage level change in the capacitor voltage value sequence is selected, and the operating mode of the submodule containing the selected capacitor is switched to remove the selected capacitor, including: If the change in the number of voltage levels is less than zero and the bridge arm current is less than zero, then select the capacitor with the smallest change in the number of voltage levels in the capacitor voltage value sequence. Determine if two capacitors are selected in one or more sub-modules: if so, switch the operating mode of the sub-module where both capacitors are selected from the two capacitors in series discharge mode to the capacitor bypass mode; if not, switch the operating mode of the sub-module containing each capacitor from the single capacitor discharge mode to the capacitor bypass mode.

6. A capacitor voltage equalization control system, characterized in that, include: Acquisition module, sequence module, level number change module, and mode switching module; The acquisition module is used to acquire the bridge arm current and DC voltage in the bridge arm at the current moment, as well as the capacitor voltage value of each modular multilevel converter dual-capacitor three-level sub-module in the bridge arm. The sequence module is used to sort the capacitor voltage values ​​of each sub-module to obtain a capacitor voltage value sequence. The level change module is used to calculate the level change of the bridge arm at the next moment based on the DC voltage using a rounding algorithm. The mode switching module is used to select the capacitor to be switched from the bridge arm according to the change of the level number, the bridge arm current and the capacitor voltage value sequence, and switch the operating mode of the sub-module where the selected capacitor is located in order to control the DC voltage balance. The mode switching module selects the capacitor to be switched from within the bridge arm based on the changes in the level number, the bridge arm current, and the capacitor voltage value sequence, and switches the operating mode of the submodule containing the selected capacitor, including: If the level change is greater than zero and the bridge arm current is greater than zero, then select the capacitor with the smallest level change in the capacitor voltage value sequence, and switch the operating mode of the sub-module where the capacitor is located to put the selected capacitor into operation. If the level change is greater than zero and the bridge arm current is less than zero, then select the capacitor with the largest level change in the capacitor voltage value sequence, and switch the operating mode of the sub-module containing the capacitor to put the selected capacitor into operation. If the level change is less than zero and the bridge arm current is greater than zero, then select the capacitor with the largest level change in the capacitor voltage value sequence, and switch the operating mode of the sub-module containing the capacitor to remove the selected capacitor. If the level change is less than zero and the bridge arm current is less than zero, then select the capacitor with the smallest level change in the capacitor voltage value sequence, and switch the operating mode of the sub-module containing the capacitor to remove the selected capacitor. The level change module is specifically used for: Based on the DC voltage, the AC voltage to be generated, and the voltage of a single capacitor in the submodule, the number of voltage levels to be applied at the next moment is calculated using a rounding algorithm. The change in the number of voltage levels applied on the bridge arm at the next moment is obtained by subtracting the number of voltage levels already applied from the number of voltage levels that need to be applied at the next moment. The formula for calculating the number of levels to be applied in the next moment of the level change module is as follows: In the formula, N xp This indicates the number of voltage levels that need to be applied in the next moment. U dc Indicates DC voltage. U d This represents the voltage of a single capacitor in the module. m cos( ωt ) represents the AC voltage to be generated, where m Indicates the amplitude of AC voltage. ω Represents angular frequency. t For time, round 0.5 (•) represents the floor function.

7. The system as described in claim 6, characterized in that, If the voltage level change is greater than zero and the bridge arm current is greater than zero, the mode switching module selects the capacitor with the smallest voltage level change in the capacitor voltage value sequence, and switches the operating mode of the submodule containing the selected capacitor to activate it, including: If the change in the number of voltage levels is greater than zero and the bridge arm current is greater than zero, then select the capacitor with the smallest change in the number of voltage levels in the capacitor voltage value sequence. Determine if two capacitors are selected in one or more sub-modules: If yes, switch the operating mode of the sub-module where both capacitors are selected from cut-off mode to two capacitors in series charging mode, and switch the operating mode of the sub-module containing the remaining capacitors from cut-off mode to single capacitor charging mode; if no, switch the operating mode of the sub-modules containing each capacitor from cut-off mode to single capacitor charging mode.

8. The system as described in claim 6, characterized in that, If the voltage level change is greater than zero and the bridge arm current is less than zero, the mode switching module selects the capacitor with the largest voltage level change in the capacitor voltage value sequence, and switches the operating mode of the sub-module containing the selected capacitor to activate it, including: If the change in voltage level is greater than zero and the bridge arm current is less than zero, then select the capacitor with the largest change in voltage level in the capacitor voltage value sequence. Determine if two capacitors are selected in one or more sub-modules: If yes, switch the operating mode of the sub-module where both capacitors are selected from cut-off mode to two capacitors in series discharge mode, and switch the operating mode of the sub-module containing the remaining capacitors from cut-off mode to single capacitor discharge mode; if no, switch the operating mode of the sub-modules containing each capacitor from cut-off mode to single capacitor discharge mode.

9. The system as described in claim 6, characterized in that, If the voltage level change is less than zero and the bridge arm current is greater than zero, the mode switching module selects the capacitor with the largest voltage level change in the capacitor voltage value sequence, and switches the operating mode of the submodule containing the selected capacitor to remove it, including: If the change in voltage level is less than zero and the bridge arm current is greater than zero, then select the capacitor with the largest change in voltage level in the capacitor voltage value sequence. Determine if two capacitors are selected in one or more sub-modules: If yes, switch the operating mode of the sub-module where both capacitors are selected from the two capacitors in series charging mode to the capacitor bypass mode, and switch the operating mode of the sub-module containing the remaining capacitors from the single capacitor charging mode to the capacitor bypass mode; if no, switch the operating mode of the sub-module containing each capacitor from the single capacitor charging mode to the capacitor bypass mode.

10. The system as described in claim 6, characterized in that, If the voltage level change is less than zero and the bridge arm current is less than zero, the mode switching module selects the capacitor with the smallest voltage level change in the capacitor voltage value sequence, and switches the operating mode of the submodule containing the selected capacitor to remove it, including: If the change in the number of voltage levels is less than zero and the bridge arm current is less than zero, then select the capacitor with the smallest change in the number of voltage levels in the capacitor voltage value sequence. Determine if two capacitors are selected in one or more sub-modules: if so, switch the operating mode of the sub-module where both capacitors are selected from the two capacitors in series discharge mode to the capacitor bypass mode; if not, switch the operating mode of the sub-module containing each capacitor from the single capacitor discharge mode to the capacitor bypass mode.

11. An electronic device, characterized in that, include: At least one processor and memory; The memory and 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, the capacitor voltage equalization control method as described in any one of claims 1 to 5 is implemented.

12. A computer-readable storage medium, characterized in that, It contains an execution program, which, when executed, implements the capacitor voltage equalization control method as described in any one of claims 1 to 5.

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