Submodule based on series connection of double capacitors, control method and high-voltage voltage source converter

Abstract

The invention relates to a submodule based on series connection of double capacitors, a control method and a high-voltage voltage source converter. The submodule comprises a switch branch composed of a first switch module, a second switch module, a third switch module and a fourth switch module which are sequentially connected in series, a first capacitor, a second capacitor, a solid-state overcurrent protection branch and a fault clearing branch. The first capacitor and the second capacitor are connected in series and then connected in parallel with the switch branch. A connection point between the first switch module and the second switch module, one end of the solid-state overcurrent protection branch and one end of the fault clearing branch are connected in sequence to form an anode of the sub-module; and a connection point between the third switch module and the fourth switch module, the other end of the solid-state overcurrent protection branch and the other end of the fault clearing branch are connected in sequence to form a cathode of the sub-module. The use number and cost of devices in the sub-modules are reduced, the total use number of the sub-modules is reduced, and then the size and weight of the converter are reduced.

Description

Technical Field

[0001] This invention belongs to the field of high voltage direct current transmission technology, specifically relating to a sub-module based on dual capacitor series connection and control method and a high voltage source converter. 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 containing several cascaded sub-modules (SMs) and arm inductors. By connecting or bypassing these sub-modules, a multilevel output voltage is synthesized to approximate a sine wave, significantly reducing harmonic content and filter requirements. Its topology evolution has consistently focused on economic efficiency, reliability, and fault protection.

[0003] Currently, the mainstream modular multilevel converters mainly include three topologies: half-bridge submodule (HBSM), full-bridge submodule (FBSM), and hybrid submodule. The half-bridge submodule consists of two IGBTs and a single capacitor, capable of outputting only positive or zero voltage. It has a simple structure and the lowest cost, and is currently used in most projects. However, its inherent drawback is the lack of DC fault ride-through capability, requiring external circuit breakers to clear faults. The full-bridge submodule consists of four IGBTs and a capacitor, capable of outputting positive, negative, and zero levels. Under fault conditions, it can reverse-connect a negative voltage through the capacitor to block the fault current, achieving DC fault self-clearing. However, the increased number of components leads to higher costs, higher operating losses, and increased control complexity, making it difficult to apply on a large scale. To balance economy and fault clearing capability, a hybrid topology combining HBSM and FBSM in series is proposed, improving fault ride-through capability by optimizing the proportion of full-bridge submodules. However, in the only two high-voltage flexible DC transmission projects based on this type of topology currently in operation in China, the proportion of full-bridge submodules is as high as 60%~70%, resulting in high project costs.

[0004] The main technical bottlenecks of modular multilevel converters (MMCs) lie in two aspects: ① The urgent need to improve converter power density and achieve lightweight design. Especially in offshore wind power flexible DC transmission scenarios, the limited space of the offshore converter platform imposes stringent requirements on the size of the converter valves. Furthermore, high-voltage flexible DC projects use thousands of sub-modules. Each sub-module, in addition to IGBTs and freewheeling diodes, includes capacitors, bypass switches and bypass thyristors, press-fit end plates and disc springs for the sub-module press-fit structure, additional drive devices, and central control boards, resulting in a large, bulky converter station with low power density. ② The contradiction between economic efficiency and performance improvement: Under fault conditions, the IGBT devices in the sub-modules will withstand large overcurrents. The overcurrent tolerance and protection of the sub-modules directly affect the reliable operation of the entire project. HBSMs are low-cost but lack fault clearing capabilities, FBSMs can achieve fault clearing but are too expensive, and the high proportion of full-bridge sub-modules in hybrid topologies is uneconomical.

[0005] European patent DE101030T2A1 proposes a modular multilevel converter (MMC) topology that extends the three-level circuit to any number of levels by connecting multiple distributed energy storage submodules in series. However, the half-bridge submodule in this topology lacks fault overcurrent and bypass protection. European patent DE102011004D28B4 proposes a method for fault bypassing of an MMC submodule. This topology uses a bypass switch connected in parallel at the submodule port, but it is based on a half-bridge submodule structure and lacks fault overcurrent protection. US patent US2010 / 0066174A1 discloses a submodule topology with overcurrent protection. This topology uses an additional freewheeling diode connected in parallel at the submodule port. Although most of the short-circuit current flows through this additional parallel diode during a fault, this submodule lacks bypass protection. Chinese patent CN2091T40D1U proposes a three-level hybrid clamped inverter circuit. This topology achieves voltage equalization of the voltage divider capacitors in a three-level inverter by anti-connecting two sets of switching transistors S5 and S6 between the midpoint O and connection point A of the three-level midpoint clamped inverter circuit, along with a balancing resistor R. However, this topology has a large number of components and high losses due to the addition of two anti-connected switching transistors and the balancing resistor R. Chinese patent CN120200469A discloses a fault handling method for an MMC half-bridge submodule. It determines the submodule's fault state by connecting an equivalent resistance in series with the capacitors of each submodule and monitoring the change in the equivalent resistance value in real time. However, the series resistance in this method affects the charging and discharging speed of the submodule capacitors. Summary of the Invention

[0006] To overcome the problems existing in the above-mentioned related technologies, the present invention provides a sub-module based on dual capacitor series connection, a control method, and a high-voltage voltage source converter.

[0007] According to a first aspect of the present invention, a sub-module based on dual capacitors connected in series is provided, comprising: a switch branch consisting of a first switch module, a second switch module, a third switch module and a fourth switch module connected in series in sequence, and a first capacitor C1, a second capacitor C2, a solid-state overcurrent protection branch S and a fault clearing branch K; The first capacitor C1 and the second capacitor C2 are connected in series and then connected in parallel with the switch branch; The connection point between the first switch module and the second switch module, one end of the solid-state overcurrent protection branch S, and one end of the fault clearing branch K are connected in sequence to form the positive electrode 25 of the sub-module; The connection point between the third and fourth switch modules, the other end of the solid-state overcurrent protection branch S, and the other end of the fault clearing branch K are connected in sequence to form the negative terminal 45 of the sub-module.

[0008] Preferably, the first switching module includes: a first switch T1 and a first diode D1 connected in antiparallel to it; The second switching module includes: a second switch T2 and a second diode D2 connected in antiparallel to it; The third switch module includes: a third switch T3 and a third diode D3 connected in antiparallel to it; The fourth switch module includes: a fourth switch T4 and a fourth diode D4 connected in antiparallel to it.

[0009] Preferably, the inflow terminal of the conduction current of the first switch T1 is connected to the negative terminal of the first diode D1, and the outflow terminal of the conduction current of the first switch T1 is connected to the positive terminal of the first diode D1. The inflow terminal of the conduction current of the second switch T2 is connected to the negative terminal of the second diode D2, and the outflow terminal of the conduction current of the second switch T2 is connected to the positive terminal of the second diode D2. The inflow terminal of the conduction current of the third switch T3 is connected to the negative terminal of the third diode D3, and the outflow terminal of the conduction current of the third switch T3 is connected to the positive terminal of the third diode D3. The inflow terminal of the conduction current of the fourth switch T4 is connected to the negative terminal of the fourth diode D4, and the outflow terminal of the conduction current of the fourth switch T4 is connected to the positive terminal of the fourth diode D4. The second connection point is connected to the third connection point, the fourth connection point is connected to the fifth connection point, and the sixth connection point is connected to the seventh connection point; The second connection point is the connection point between the outflow terminal of the conduction current of the first switch T1 and the positive terminal of the first diode D1; the third connection point is the connection point between the inflow terminal of the conduction current of the second switch T2 and the negative terminal of the second diode D2; the fourth connection point is the connection point between the outflow terminal of the conduction current of the second switch T2 and the positive terminal of the second diode D2; the fifth connection point is the connection point between the inflow terminal of the conduction current of the third switch T3 and the negative terminal of the third diode D3; the sixth connection point is the connection point between the outflow terminal of the conduction current of the third switch T3 and the positive terminal of the third diode D3; and the seventh connection point is the connection point between the inflow terminal of the conduction current of the fourth switch T4 and the negative terminal of the fourth diode D4.

[0010] Preferably, one end of the first capacitor C1 is connected to the first connection point, and the other end is connected to one end of the second capacitor C2; The other end of the second capacitor C2 is connected to the eighth connection point; The connection point between the other end of the first capacitor C1 and one end of the second capacitor C2 is connected to the connection point between the fourth connection point and the fifth connection point; Wherein, the first connection point is the connection point between the inflow end of the conduction current of the first switch T1 and the negative terminal of the first diode D1, and the eighth connection point is the connection point between the outflow end of the conduction current of the fourth switch T4 and the positive terminal of the fourth diode D4.

[0011] Preferably, one end of the solid-state overcurrent protection branch S is connected to the connection point between the second connection point and the third connection point; The other end of the solid-state overcurrent protection branch S is connected to the connection point between the sixth connection point and the seventh connection point.

[0012] Preferably, the anti-parallel connection method of each switch and its corresponding diode in each switch module is: the diode and its corresponding switch are externally anti-parallel connected, or the anti-parallel diode is embedded inside the switch.

[0013] Preferably, the first switch T1, the second switch T2, the third switch T3 and the fourth switch T4 are all controllable semiconductor switching devices; The controllable semiconductor switching device is an insulated gate bipolar transistor, an integrated gate commutated thyristor, a gate turn-off thyristor, or an electron injection enhancement gate transistor.

[0014] Preferably, the solid-state overcurrent protection branch S is a controllable semiconductor switching device; The controllable semiconductor switching device is a thyristor, an insulated gate bipolar transistor, an integrated gate commutated thyristor, a gate turn-off thyristor, or an electron injection enhancement gate transistor.

[0015] Preferably, the fault clearing branch K is a mechanical switch; The mechanical switch is an electromechanical switch, a pneumatic switch, or a hydraulic switch.

[0016] According to a second aspect of the present invention, a control method for a submodule based on a dual-capacitor series connection is provided, applicable to the said dual-capacitor series connection submodule, comprising: When the submodule is running normally, the current flow path of the three-phase power supply in the submodule is controlled by controlling the switching state of each switch in each switching module, thereby controlling the output voltage of the submodule. When a submodule fails, the submodule is protected by controlling the switching status of each switch in each switching module, as well as the switching status of the solid-state overcurrent protection branch S or the fault clearing branch K.

[0017] Preferably, when the submodule is operating normally, the current flow path of the three-phase power supply in the submodule is controlled by controlling the switching state of each switch in each switching module, thereby controlling the output voltage of the submodule, including: When the submodule is operating normally and the three-phase power supply current is positive, the first switch T1 and the third switch T3 are turned on, while the second switch T2 and the fourth switch T4 are turned off. The positive current flows sequentially through the first diode D1, the first capacitor C1, and the second switch T2 to charge the first capacitor C1. The output voltage of the submodule is U. C1 ; When the submodule is operating normally and the three-phase power supply current is negative, the first switch T1 and the third switch T3 are turned on, while the second switch T2 and the fourth switch T4 are turned off. The negative current flows sequentially through the third diode D3, the first capacitor C1, and the first switch T1, causing the first capacitor C1 to discharge. The output voltage of the submodule is U. C1 ; Among them, U C1 This is the voltage across the first capacitor C1.

[0018] Preferably, when the submodule is operating normally, controlling the switching state of each switch in each switching module to control the current flow path of the three-phase power supply in the submodule, thereby controlling the output voltage of the submodule, further includes: When the submodule is operating normally and the three-phase power supply current is positive, the second switch T2 and the fourth switch T4 are turned on, while the first switch T1 and the third switch T3 are turned off. The positive current flows sequentially through the second switch T2, the second capacitor C2, and the fourth diode D4, charging the second capacitor C2. The output voltage of the submodule is U. C2 ; When the submodule is operating normally and the three-phase power supply current is negative, the second switch T2 and the fourth switch T4 are turned on, while the first switch T1 and the third switch T3 are turned off. The negative current flows sequentially through the fourth switch T4, the second capacitor C2, and the second diode D2, causing the second capacitor C2 to discharge. The output voltage of the submodule is U. C2 ; Among them, U C2 This is the voltage across the second capacitor C2.

[0019] Preferably, when the submodule is operating normally, controlling the switching state of each switch in each switching module to control the current flow path of the three-phase power supply in the submodule, thereby controlling the output voltage of the submodule, further includes: When the submodule is operating normally and the three-phase power supply current is positive, the first switch T1 and the fourth switch T4 are turned on, while the second switch T2 and the third switch T3 are turned off. The positive current flows sequentially through the first diode D1, the first capacitor C1, the second capacitor C2, and the fourth diode D4, causing the first capacitor C1 and the second capacitor C2 to be charged in series. The output voltage of the submodule is U. C1 +U C2 ; When the submodule is operating normally and the three-phase power supply current is negative, the first switch T1 and the fourth switch T4 are turned on, while the second switch T2 and the third switch T3 are turned off. The negative current flows sequentially through the fourth switch T4, the second capacitor C2, the first capacitor C1, and the first switch T1, causing the second capacitor C2 and the first capacitor C1 to discharge in series. The output voltage of the submodule is U. C1 +U C2 ; Among them, U C1 U is the voltage across the first capacitor C1. C2 This is the voltage across the second capacitor C2.

[0020] Preferably, when the submodule is operating normally, controlling the switching state of each switch in each switching module to control the current flow path of the three-phase power supply in the submodule, thereby controlling the output voltage of the submodule, further includes: When the submodule is operating normally and the current of the three-phase power supply is positive, the second switch T2 and the third switch T3 are turned on, the first switch T1 and the fourth switch T4 are turned off, and the positive current flows through the second switch T2 and the third switch T3 in sequence, so that the first capacitor C1 and the second capacitor C2 are bypassed, and the output voltage of the submodule is 0. When the submodule is operating normally and the current of the three-phase power supply is negative, the second switch T2 and the third switch T3 are turned on, and the first switch T1 and the fourth switch T4 are turned off. The negative current flows through the second switch T2 and the third switch T3 in sequence, so that the first capacitor C1 and the second capacitor C2 are bypassed, and the output voltage of the submodule is 0.

[0021] Preferably, when a submodule fails, the submodule is protected by controlling the switching state of each switch in each switching module, and by controlling the switching state of the solid-state overcurrent protection branch S or the fault clearing branch K, including: When a short circuit fault occurs in the submodule and the short circuit current exceeds the current withstand capability of each switch in each switch module, the first switch T1, the second switch T2, the third switch T3 and the fourth switch T4 are turned off, and the solid-state overcurrent protection branch S is turned on so that the negative current flows through the solid-state overcurrent protection branch S to provide overcurrent protection for the submodule. When the submodule is in a fault-locked state, the first switch T1, the second switch T2, the third switch T3 and the fourth switch T4 are turned off, and the fault clearing branch K is closed, so that both positive and negative currents flow through the fault clearing branch K, thereby disconnecting the submodule and providing fault protection for the submodule.

[0022] According to a first aspect of the present invention, a high-voltage voltage source converter is provided, comprising: an A-phase unit 7, a B-phase unit 8, and a C-phase unit 9 connected in parallel; each phase unit is composed of an upper bridge arm and a lower bridge arm connected in series; each bridge arm includes at least two of the aforementioned sub-modules based on dual-capacitor series connection. The ends of the upper bridge arms of phase A unit 7, phase B unit 8 and phase C unit 9 that are furthest from their corresponding lower bridge arms are all connected to the positive terminal 100 of the DC bus, and the ends of the lower bridge arms of phase A unit 7, phase B unit 8 and phase C unit 9 that are furthest from their corresponding upper bridge arms are all connected to the negative terminal 200 of the DC bus. The connection point between the upper and lower bridge arms of the A-phase unit 7 is phase a 300 of the three-phase power supply. The connection point between the upper and lower bridge arms of the B-phase unit 8 is the b-phase 400 of the three-phase power supply. The connection point between the upper and lower bridge arms of the C-phase unit 9 is the C-phase 500 of the three-phase power supply.

[0023] Preferably, the upper bridge arm 1 of the A-phase unit 7 includes: at least two sub-modules, a bridge arm resistor 71, and a bridge arm inductor 72 connected in series. The lower bridge arm 4 of the A-phase unit 7 includes: at least two sub-modules, a bridge arm resistor 74, and a bridge arm inductor 73 connected in series. The bridge arm inductor 72 is connected to the bridge arm inductor 73, and the connection point between the bridge arm inductor 72 and the bridge arm inductor 73 is phase a 300 of the three-phase power supply. The sub-module of the upper bridge arm 1 that is far from the lower bridge arm 4 is connected to the positive terminal 100 of the DC bus, and the sub-module of the lower bridge arm 4 that is far from the upper bridge arm 1 is connected to the negative terminal 200 of the DC bus.

[0024] Preferably, the upper bridge arm 2 of the B-phase unit 8 includes: at least two sub-modules, a bridge arm resistor 81, and a bridge arm inductor 82 connected in series. The lower bridge arm 5 of the B-phase unit 8 includes: at least two sub-modules, a bridge arm resistor 84, and a bridge arm inductor 83 connected in series. The bridge arm inductor 82 is connected to the bridge arm inductor 83, and the connection point between the bridge arm inductor 82 and the bridge arm inductor 83 is phase b 400 of the three-phase power supply. The sub-module of the upper bridge arm 2 that is away from the lower bridge arm 5 is connected to the positive terminal 100 of the DC bus, and the sub-module of the lower bridge arm 5 that is away from the upper bridge arm 2 is connected to the negative terminal 200 of the DC bus.

[0025] Preferably, the upper bridge arm 3 of the C-phase unit 9 includes: at least two sub-modules, a bridge arm resistor 91, and a bridge arm inductor 92 connected in series. The lower bridge arm 6 of the C-phase unit 9 includes: at least two sub-modules, a bridge arm resistor 94, and a bridge arm inductor 93 connected in series. The bridge arm inductor 92 is connected to the bridge arm inductor 93, and the connection point between the bridge arm inductor 92 and the bridge arm inductor 93 is the c phase 500 of the three-phase power supply. The sub-module of the upper bridge arm 3 that is away from the lower bridge arm 6 is connected to the positive terminal 100 of the DC bus, and the sub-module of the lower bridge arm 6 that is away from the upper bridge arm 3 is connected to the negative terminal 200 of the DC bus.

[0026] According to a fourth aspect of the present invention, an electronic device is provided, comprising: at least one processor and a 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, the control method based on the dual-capacitor series submodule is implemented.

[0027] According to a fifth aspect of the present invention, a readable storage medium is provided having an executable program stored thereon, wherein when the executable program is executed, the control method for the submodule based on dual capacitors in series is implemented.

[0028] The technical solution provided by this invention has the following beneficial effects: This invention provides a submodule and control method based on a dual-capacitor series connection, and a high-voltage voltage source converter. The submodule based on the dual-capacitor series connection includes: a switching branch consisting of a first switching module, a second switching module, a third switching module, and a fourth switching module connected in series; a first capacitor C1; a second capacitor C2; a solid-state overcurrent protection branch S; and a fault clearing branch K. The first capacitor C1 and the second capacitor C2 are connected in series and then in parallel with the switching branch. The connection point between the first and second switching modules, one end of the solid-state overcurrent protection branch S, and one end of the fault clearing branch K are connected in sequence to form the positive terminal 25 of the submodule. The connection point between the third and fourth switching modules, the other end of the solid-state overcurrent protection branch S, and the other end of the fault clearing branch K are connected in sequence to form the negative terminal 45 of the submodule. The technical solution provided by this invention reduces the number and cost of components used in the submodule, reduces the total number of submodules used in the converter, and thus reduces the size and weight of the converter, achieving a lightweight and high power density converter.

[0029] The control method for a submodule based on a dual-capacitor series connection provided by this invention includes: when the submodule is operating normally, controlling the switching state of each switch in each switching module to control the current flow path of the three-phase power supply in the submodule, thereby controlling the output voltage of the submodule; when the submodule fails, protecting the submodule by controlling the switching state of each switch in each switching module, as well as controlling the switching state of the solid-state overcurrent protection branch S or the fault clearing branch K. The submodule provided by this invention has ten switching states, increasing control redundancy. Furthermore, it achieves overcurrent protection and fault clearing for the submodule, and balances the voltage of the two capacitors through a self-clamping function, giving the submodule high reliability. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of a submodule based on dual capacitors connected in series, provided in an embodiment of the present invention. Figure 2This is a three-dimensional engineering structure diagram of a submodule based on dual capacitors connected in series, provided in an embodiment of the present invention. Figure 3 This is an exploded view of the engineering structure of a submodule based on dual capacitors connected in series, provided in an embodiment of the present invention. Figure 4 This is an exploded view of the engineering structure of a submodule based on dual capacitors connected in series, provided in an embodiment of the present invention. Figure 5 This is a three-dimensional diagram of the engineering structure of two existing cascaded half-bridge sub-modules provided in an embodiment of the present invention; Figure 6 This is a flowchart of a control method for a submodule based on dual capacitors connected in series, provided by an embodiment of the present invention. Figure 7 This is a schematic diagram of the charging of the first capacitor C1 provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of the discharge of the first capacitor C1 provided in an embodiment of the present invention; Figure 9 This is a schematic diagram of the charging of the second capacitor C2 provided in an embodiment of the present invention; Figure 10 This is a schematic diagram of the discharge of the second capacitor C2 provided in an embodiment of the present invention; Figure 11 This is a schematic diagram of the first capacitor C1 and the second capacitor C2 being charged in series according to an embodiment of the present invention; Figure 12 This is a schematic diagram of the first capacitor C1 and the second capacitor C2 being discharged in series according to an embodiment of the present invention; Figure 13 This is a schematic diagram of a forward capacitor bypass provided in an embodiment of the present invention; Figure 14 This is a schematic diagram of a current-negative capacitor bypass provided in an embodiment of the present invention; Figure 15 This is a schematic diagram of the trigger solid-state overcurrent protection branch S provided in an embodiment of the present invention; Figure 16 This is a schematic diagram of the trigger fault clearing branch K provided in an embodiment of the present invention; Figure 17 This is a schematic diagram of the structure of a high-voltage voltage source converter provided in an embodiment of the present invention; Figure 18 This is a schematic diagram of the AC output voltage and bridge arm current provided in an embodiment of the present invention; Figure 19 This is a schematic diagram of NLM level calculation provided in an embodiment of the present invention; Figure 20 This is a schematic diagram of the capacitor voltage difference distribution of the upper bridge arm submodule of phase A provided in an embodiment of the present invention; Figure 21 This is a schematic diagram of the voltage waveform of the submodule capacitor C1 provided in an embodiment of the present invention; Figure 22 This is a schematic diagram of the voltage waveform of the submodule capacitor C2 provided in an embodiment of the present invention; Figure 23 This is a structural block diagram of an electronic device provided in an embodiment of the present invention; In the diagram, C1 - first capacitor, C2 - second capacitor, S - solid-state overcurrent protection branch, K - fault clearing branch, 25 - positive terminal of submodule, 45 - negative terminal of submodule, T1 - first switch, T2 - second switch, T3 - third switch, T4 - fourth switch, D1 - first diode, D2 - second diode, D3 - third diode, D4 ​​- fourth diode, 7 - phase A unit, 8 - phase B unit, 9 - Phase C unit, 100 - Positive terminal of DC bus, 200 - Negative terminal of DC bus, 300 - Phase A of three-phase power supply, 400 - Phase B of three-phase power supply, 500 - Phase C of three-phase power supply, 1 - Upper bridge arm of Phase A unit 7, 2 - Upper bridge arm of Phase B unit 8, 3 - Upper bridge arm of Phase C unit 9, 4 - Lower bridge arm of Phase A unit 7, 5 - Lower bridge arm of Phase B unit 8, 6 - Lower bridge arm of Phase C unit 9, 71 - Bridge arm resistor, 72 - Bridge arm inductor, 73 - Bridge arm inductor, 74 - Bridge arm resistor, 81 - Bridge arm resistor, 82 - Bridge arm inductor, 83 - Bridge arm inductor, 84 - Bridge arm resistor, 91 - Bridge arm resistor, 92 - Bridge arm inductor, 93 - Bridge arm inductor, 94 - Bridge arm resistor, 101 - Submodule, 102 - Submodule 103-Submodule, 104-Submodule, 105-Submodule, 106-Submodule, 111-Submodule, 112-Submodule, 113-Submodule, 114-Submodule, 115-Submodule, 116-Submodule, 121-Submodule, 122-Submodule, 123-Submodule, 124-Submodule, 125-Submodule, 126-Submodule, 11-Board box, 12-IGBT busbar, 13-Heat sink, 14-Bypass switch, 15-Disc spring assembly, 16-Pressure fitting bracket assembly, 17-Pressure fitting end plate, 18-Capacitor, 19-IGBT, 31-Pressure fitting end plate A, 32-Pressure fitting end plate B, 33-Pressure fitting bracket A, 34-Pressure fitting bracket B, 35-Thyristor assembly. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the following embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0033] Example 1 The development of flexible direct current (HVDC) transmission technology began in the 1990s. Currently, the main converter stations for flexible HVDC transmission are of three types: two-level, three-level, and modular multilevel. As of 2009, flexible HVDC converter stations primarily used two-level and three-level converters. However, applying these two types of converters to high-voltage direct current (HVDC) transmission presents several technical challenges: (1) Difficulty in equalizing voltage of switching devices: Due to the limited voltage withstand level of individual power electronic devices (only a few kV), the two-level and three-level topologies must be connected in series with a large number of power electronic devices to be applied to high-voltage fields of hundreds or even thousands of kilovolts. In order to avoid uneven voltage distribution of each power electronic device leading to overvoltage breakdown of some devices and subsequent chain failures, strict and precise voltage equalization control must be adopted. (2) High switching frequency and large system loss: Two-level and three-level converters use pulse width modulation (PWM) technology, and the device operating frequency is 1k~2k Hz. Therefore, the switching loss of the system is relatively large. According to statistics, the power loss of a two-level flexible DC converter station is about 3% of the rated power, and the power loss of a three-level flexible DC converter station is about 1.7% of the rated power, both of which are much higher than the power loss of traditional DC transmission (about 0.8%).

[0034] (3) Poor DC fault tolerance. During a DC bipolar short circuit, the DC side capacitor discharges rapidly through the short circuit point of the DC line, and the transmitted power drops rapidly to 0. After the trigger pulse of the power electronic device is blocked, the AC line forms a freewheeling circuit through the anti-parallel diode, which is equivalent to a three-phase AC short circuit, posing a huge threat to the AC system.

[0035] The concept of Modular Converter (MC) was first proposed by German scholars R. Marquardt and A. Lesnicar around 2003, and it has attracted widespread attention from industry and academia, gradually being recognized as one of the key technologies for next-generation flexible DC transmission converters. Like two-level and three-level converters, the MMC is also a voltage source converter; however, unlike two-level and three-level converters, the MMC adopts a modular structure, distributing the DC-side capacitors into each sub-module, thus providing a degree of internal controllability.

[0036] The Modular Multilevel Converter (MMC) topology uses sub-modules connected in series, avoiding direct series connection of components. This effectively solves the problems of voltage equalization difficulties in switching devices, high switching frequencies, and large system losses inherent in two-level and three-level converters. Therefore, all flexible DC transmission projects since 2010 have adopted modular multilevel converters. Furthermore, to better address DC faults and expand the application areas of flexible DC transmission technology, various new types of multilevel converters with modular topologies have received widespread attention and research from academia and industry, resulting in a series of research achievements. Table 1 shows the status of flexible DC projects under construction / operation in China. Table 2 shows the status of offshore wind power flexible DC transmission projects already in operation in Europe.

[0037] Table 1. Status of Flexible DC Transmission Projects Under Construction / Commissioned

[0038] Table 2. Operational Status of Flexible DC Transmission Projects for Offshore Wind Power in Europe

[0039] As shown in Tables 1 and 2 above, flexible DC transmission is developing towards higher voltage and larger capacity, but it includes thousands of sub-modules, resulting in existing converter stations being large, bulky, with low power density and high cost. There is an urgent need to explore lightweight, compact, and economical topologies.

[0040] Furthermore, there are three common types of MMC submodules: half-bridge submodules, full-bridge submodules, and clamped dual submodules. Under normal operation, the three types of submodules operate on similar principles. During a DC fault, the half-bridge submodule cannot lock the MMC, and short-circuit current will flow through the bridge arm submodule. While the full-bridge submodule and clamped dual module can effectively lock the MMC and limit short-circuit current, the latter two types require additional insulated-gate bipolar transistors (IGBTs) and diodes, resulting in lower economic efficiency, higher losses, and higher maintenance costs.

[0041] Addressing the technical bottlenecks in existing MMC (Multi-Module Converter) systems and their engineering applications, particularly in scenarios like offshore wind power flexible direct transmission projects where converter stations face stringent requirements in terms of size, weight, and economic efficiency, this invention provides a submodule based on a dual-capacitor series connection, such as... Figure 1 As shown, it includes: a switch branch consisting of a first switch module, a second switch module, a third switch module and a fourth switch module connected in series, as well as a first capacitor C1, a second capacitor C2, a solid-state overcurrent protection branch S and a fault clearing branch K. The first capacitor C1 and the second capacitor C2 are connected in series and then connected in parallel with the switch branch. The connection point between the first switch module and the second switch module, one end of the solid-state overcurrent protection branch S, and one end of the fault clearing branch K are connected in sequence to form the positive terminal 25 of the sub-module. The connection point between the third and fourth switch modules, the other end of the solid-state overcurrent protection branch S, and the other end of the fault clearing branch K are connected in sequence to form the negative terminal 45 of the submodule.

[0042] The first switch module, the second switch module, the third switch module, and the fourth switch module have the same structure. Each switch module consists of a switch and a diode connected in antiparallel to it. Furthermore, the first switch module includes: a first switch T1 and a first diode D1 connected in antiparallel to it. The second switching module includes: a second switch T2 and a second diode D2 connected in antiparallel to it; The third switch module includes: a third switch T3 and a third diode D3 connected in anti-parallel to it; The fourth switch module includes: a fourth switch T4 and a fourth diode D4 connected in antiparallel to it.

[0043] Furthermore, the inflow terminal of the conduction current of the first switch T1 is connected to the negative terminal of the first diode D1, and the outflow terminal of the conduction current of the first switch T1 is connected to the positive terminal of the first diode D1. The inflow terminal of the conduction current of the second switch T2 is connected to the negative terminal of the second diode D2, and the outflow terminal of the conduction current of the second switch T2 is connected to the positive terminal of the second diode D2. The inflow terminal of the conduction current of the third switch T3 is connected to the negative terminal of the third diode D3, and the outflow terminal of the conduction current of the third switch T3 is connected to the positive terminal of the third diode D3. The inflow terminal of the conduction current of the fourth switch T4 is connected to the negative terminal of the fourth diode D4, and the outflow terminal of the conduction current of the fourth switch T4 is connected to the positive terminal of the fourth diode D4. The second connection point is connected to the third connection point, the fourth connection point is connected to the fifth connection point, and the sixth connection point is connected to the seventh connection point; The second connection point is the connection point between the outflow terminal of the conduction current of the first switch T1 and the positive terminal of the first diode D1; the third connection point is the connection point between the inflow terminal of the conduction current of the second switch T2 and the negative terminal of the second diode D2; the fourth connection point is the connection point between the outflow terminal of the conduction current of the second switch T2 and the positive terminal of the second diode D2; the fifth connection point is the connection point between the inflow terminal of the conduction current of the third switch T3 and the negative terminal of the third diode D3; the sixth connection point is the connection point between the outflow terminal of the conduction current of the third switch T3 and the positive terminal of the third diode D3; and the seventh connection point is the connection point between the inflow terminal of the conduction current of the fourth switch T4 and the negative terminal of the fourth diode D4.

[0044] It is understandable that when each switch in each switching module is an IGBT, the inlet of the IGBT's conduction current is the collector, and the outlet of the IGBT's conduction current is the emitter.

[0045] Furthermore, one end of the first capacitor C1 is connected to the first connection point, and the other end is connected to one end of the second capacitor C2; The other end of the second capacitor C2 is connected to the eighth connection point; The connection point between the other end of the first capacitor C1 and one end of the second capacitor C2 is connected to the connection point between the fourth connection point and the fifth connection point; The first connection point is the connection point between the inflow end of the conduction current of the first switch T1 and the negative terminal of the first diode D1, and the eighth connection point is the connection point between the outflow end of the conduction current of the fourth switch T4 and the positive terminal of the fourth diode D4.

[0046] It should be noted that the connection point between the other end of the first capacitor C1 and one end of the second capacitor C2, as well as the connection point between the fourth and fifth connection points, are the neutral connection points of the submodule. These neutral connection points, being capacitor neutral points, enable automatic clamping and voltage equalization of the two capacitors within the submodule, overcoming the problem of complex voltage equalization control caused by the independence of the two capacitors in a cascaded submodule structure.

[0047] Furthermore, one end of the solid-state overcurrent protection branch S is connected to the connection point between the second connection point and the third connection point; The other end of the solid-state overcurrent protection branch S is connected to the connection point between the sixth connection point and the seventh connection point.

[0048] Furthermore, the anti-parallel connection method of each switch and its corresponding diode in each switch module can be, but is not limited to: external anti-parallel connection of the diode and its corresponding switch, or internal anti-parallel diode embedded in the switch, or other forms that form an anti-parallel diode with the switch.

[0049] Furthermore, the first switch T1, the second switch T2, the third switch T3, and the fourth switch T4 are all controllable semiconductor switching devices; Controllable semiconductor switching devices include insulated gate bipolar transistors (IGBTs), integrated gate commutated thyristors (IGCTs), gate turn-off thyristors (GTOs), or electron injection enhancement gate transistors (IEGTs).

[0050] Furthermore, the solid-state overcurrent protection branch S is a controllable semiconductor switching device; Controllable semiconductor switching devices include thyristors, insulated gate bipolar transistors (IGBTs), integrated gate commutated thyristors (IGCTs), gate turn-off thyristors (GTOs), or electron injection enhancement gate transistors (IEGTs).

[0051] Furthermore, the fault clearing branch K is a mechanical switch; Mechanical switches can be electromechanical switches, pneumatic switches, or hydraulic switches.

[0052] To further illustrate the significant advantages of the dual-capacitor series-connected submodule in reducing the number of components, converter size and weight, and economic efficiency, this invention also provides practical application diagrams of the dual-capacitor series-connected submodule, such as... Figures 2-4 As shown, taking IGBTs as the switches and thyristors as the solid-state overcurrent protection branch S in each switching module as an example. In the actual application of the sub-module of this application, the structural components include a board box 11, an IGBT busbar 12, a heat sink 13, a bypass switch 14, a disc spring assembly 15, a press-fit body support assembly 16 (including press-fit body support A 33 and press-fit body support B 34), a press-fit end plate 17, two capacitors 18, four IGBTs 19, two press-fit end plates A31 and B32, and a thyristor assembly 35. In addition, as Figure 5 As shown, the existing two half-bridge modules are mostly connected in direct series. The structural components include two board boxes 11 and two IGBT busbars 12, two bypass switches 14 and two thyristor assemblies 35, two sets of disc spring assemblies 15 and two sets of press-fit end plates 17, and a large space between the two capacitors 18, which leads to the problem of large size in actual applications of large-scale projects.

[0053] Depend on Figure 2 The diagram shown is a three-dimensional engineering structure diagram of the sub-module provided by the present invention, compared to... Figure 5As shown in the three-dimensional diagram of the actual engineering structure of the two half-bridge sub-modules connected in series, the sub-modules provided by the present invention can reduce one board box 11, IGBT busbar 12, bypass switch 14 and thyristor assembly 35, reduce one set of press-fit end plate and disc spring assembly 15, and reduce the space between two capacitors 18, thereby reducing the volume and weight of the converter, increasing the power density of the converter, and achieving a dual reduction in volume and cost. It overcomes the inherent drawbacks of the existing technology of long connection lines and large stray inductance of two half-bridge sub-modules cascaded together.

[0054] The number of sub-modules in the entire project has been reduced, and the corresponding number of optical fibers, central control units, and power supplies has been reduced by half. In large-scale offshore wind power flexible DC transmission scenarios, hundreds or even tens of thousands of half-bridge sub-modules may be required. However, by using the sub-modules of this invention, the number of cascaded sub-modules in a single bridge arm can be reduced by half at the same voltage level. This reduces the number of components used and the cost, reduces the size and weight of the converter, and achieves a lightweight converter with high power density. It also overcomes the stringent requirements on the size and weight of high-voltage flexible DC converter valves in the confined space of offshore platforms.

[0055] Example 2 This invention also provides a control method for a submodule based on a dual-capacitor series connection, applicable to the aforementioned dual-capacitor series connection submodule, such as... Figure 6 As shown, it includes: Step 11: When the submodule is running normally, the current flow path of the three-phase power supply in the submodule is controlled by controlling the switching state of each switch in each switching module, thereby controlling the output voltage of the submodule; Step 12: When a submodule fails, the submodule is protected by controlling the switching status of each switch in each switching module, as well as the switching status of the solid-state overcurrent protection branch S or the fault clearing branch K.

[0056] Further, step 11 includes: like Figure 7 As shown, step 111: When the submodule is operating normally and the current of the three-phase power supply is positive, control the first switch T1 and the third switch T3 to conduct, and control the second switch T2 and the fourth switch T4 to turn off. The positive current flows sequentially through the first diode D1, the first capacitor C1, and the second switch T2 to charge the first capacitor C1. The output voltage of the submodule is U. C1 ; like Figure 8 As shown, step 112: When the submodule is operating normally and the current of the three-phase power supply is negative, control the first switch T1 and the third switch T3 to conduct, and the second switch T2 and the fourth switch T4 to turn off. The negative current flows sequentially through the third diode D3, the first capacitor C1, and the first switch T1, so that the first capacitor C1 discharges. The output voltage of the submodule is U. C1; Among them, U C1 This is the voltage across the first capacitor C1.

[0057] Furthermore, step 11 also includes: like Figure 9 As shown, step 113: When the submodule is operating normally and the three-phase power supply current is positive, control the second switch T2 and the fourth switch T4 to conduct, and control the first switch T1 and the third switch T3 to turn off. The positive current flows sequentially through the second switch T2, the second capacitor C2, and the fourth diode D4 to charge the second capacitor C2. The output voltage of the submodule is U. C2 ; like Figure 10 As shown, step 114: When the submodule is operating normally and the current of the three-phase power supply is negative, control the second switch T2 and the fourth switch T4 to conduct, and control the first switch T1 and the third switch T3 to turn off. The negative current flows sequentially through the fourth switch T4, the second capacitor C2, and the second diode D2, so that the second capacitor C2 discharges. The output voltage of the submodule is U. C2 ; Among them, U C2 This is the voltage across the second capacitor C2.

[0058] Furthermore, step 11 also includes: like Figure 11 As shown, step 115: When the submodule is operating normally and the current of the three-phase power supply is positive, control the first switch T1 and the fourth switch T4 to turn on, and the second switch T2 and the third switch T3 to turn off. The positive current flows sequentially through the first diode D1, the first capacitor C1, the second capacitor C2, and the fourth diode D4, so that the first capacitor C1 and the second capacitor C2 are charged in series. The output voltage of the submodule is U. C1 +U C2 ; like Figure 12 As shown, step 116: When the submodule is operating normally and the current of the three-phase power supply is negative, control the first switch T1 and the fourth switch T4 to turn on, and the second switch T2 and the third switch T3 to turn off. The negative current flows sequentially through the fourth switch T4, the second capacitor C2, the first capacitor C1, and the first switch T1, so that the second capacitor C2 and the first capacitor C1 discharge in series. The output voltage of the submodule is U. C1 +U C2 ; Among them, U C1 U is the voltage across the first capacitor C1. C2 This is the voltage across the second capacitor C2.

[0059] Furthermore, step 11 also includes: like Figure 13As shown, step 117: When the submodule is running normally and the current of the three-phase power supply is positive, control the second switch T2 and the third switch T3 to be turned on, and the first switch T1 and the fourth switch T4 to be turned off. The positive current flows through the second switch T2 and the third switch T3 in sequence, so that the first capacitor C1 and the second capacitor C2 are bypassed, and the output voltage of the submodule is 0. like Figure 14 As shown, in step 118: when the submodule is operating normally and the current of the three-phase power supply is negative, control the second switch T2 and the third switch T3 to turn on, and control the first switch T1 and the fourth switch T4 to turn off. The negative current flows through the second switch T2 and the third switch T3 in sequence, so that the first capacitor C1 and the second capacitor C2 are bypassed, and the output voltage of the submodule is 0.

[0060] Further, step 12 includes: like Figure 15 As shown, step 121: When a short circuit fault occurs in the submodule and the short circuit current exceeds the current withstand capability of each switch in each switch module, control the first switch T1, the second switch T2, the third switch T3 and the fourth switch T4 to turn off, and turn on the solid-state overcurrent protection branch S so that the negative current flows through the solid-state overcurrent protection branch S to provide overcurrent protection for the submodule. like Figure 16 As shown, step 122: When the submodule is in a fault-locked condition, control the first switch T1, the second switch T2, the third switch T3 and the fourth switch T4 to turn off, and close the fault clearing branch K so that both positive current and negative current flow through the fault clearing branch K, thereby disconnecting the submodule and thus providing fault protection for the submodule.

[0061] The submodule based on dual capacitors in series provided by this invention offers a high-power-density, lightweight MMC topology with overcurrent tolerance, significantly improving the overall performance and cost optimization for engineering applications.

[0062] This invention reduces the number of cascaded submodules in a single bridge arm while maintaining the same voltage level by increasing the voltage level of individual submodules. While achieving fault bypass and overcurrent protection, compared to conventional two half-bridge submodules connected in series, the proposed voltage source converter submodule structure based on a flexible and controllable dual-capacitor submodule eliminates a bypass switch and thyristors, and also reduces the number of hardware components such as the press-fit terminal plates and disc springs, additional drive devices, and central control boards in the submodule press-fit structure. This significantly reduces the size and weight of the converter station while ensuring stable and reliable power transmission, saving on the amount of optical fiber, central control, and power supply required for the entire project. Therefore, this invention has significant advantages in reducing the number of components, the size and weight of the converter station, and economic efficiency, and significantly improves the power density of the converter station.

[0063] Example 3 The present invention also provides a high-voltage voltage source converter, such as... Figure 17 As shown, it includes: A-phase unit 7, B-phase unit 8 and C-phase unit 9 connected in parallel; each phase unit is composed of an upper bridge arm and a lower bridge arm connected in series; each bridge arm includes at least two of the above-mentioned sub-modules based on dual capacitor series connection. The ends of the upper bridge arms of phase A unit 7, phase B unit 8 and phase C unit 9 that are furthest from their corresponding lower bridge arms are all connected to the positive terminal 100 of the DC bus. The ends of the lower bridge arms of phase A unit 7, phase B unit 8 and phase C unit 9 that are furthest from their corresponding upper bridge arms are all connected to the negative terminal 200 of the DC bus. The connection point between the upper and lower bridge arms of phase A unit 7 is phase a 300 of the three-phase power supply. The connection point between the upper and lower bridge arms of phase B unit 8 is phase B 400 of the three-phase power supply. The connection point between the upper and lower bridge arms of C-phase unit 9 is the C-phase 500 of the three-phase power supply.

[0064] Furthermore, the upper arm 1 of phase A unit 7 includes: at least two sub-modules, an arm resistor 71, and an arm inductor 72 connected in series. The lower bridge arm 4 of phase A unit 7 includes: at least two sub-modules connected in series, a bridge arm resistor 74 and a bridge arm inductor 73; Bridge arm inductor 72 is connected to bridge arm inductor 73, and the connection point between bridge arm inductor 72 and bridge arm inductor 73 is phase a 300 of the three-phase power supply. The submodule in upper bridge arm 1 that is furthest from lower bridge arm 4 is connected to the positive terminal 100 of the DC bus, and the submodule in lower bridge arm 4 that is furthest from upper bridge arm 1 is connected to the negative terminal 200 of the DC bus.

[0065] Furthermore, the upper arm 2 of phase B unit 8 includes: at least two sub-modules, an arm resistor 81, and an arm inductor 82 connected in series. The lower bridge arm 5 of phase B unit 8 includes: at least two sub-modules connected in series, a bridge arm resistor 84 and a bridge arm inductor 83; Bridge arm inductor 82 is connected to bridge arm inductor 83, and the connection point between bridge arm inductor 82 and bridge arm inductor 83 is phase b 400 of the three-phase power supply; The submodule in upper bridge arm 2 that is farthest from lower bridge arm 5 is connected to the positive terminal 100 of the DC bus, and the submodule in lower bridge arm 5 that is farthest from upper bridge arm 2 is connected to the negative terminal 200 of the DC bus.

[0066] Furthermore, the upper bridge arm 3 of the C-phase unit 9 includes: at least two sub-modules, a bridge arm resistor 91, and a bridge arm inductor 92 connected in series. The lower arm 6 of the C-phase unit 9 includes: at least two sub-modules connected in series, an arm resistor 94, and an arm inductor 93.

[0067] Bridge arm inductor 92 is connected to bridge arm inductor 93, and the connection point between bridge arm inductor 92 and bridge arm inductor 93 is the c phase 500 of the three-phase power supply. The submodule in upper bridge arm 3 that is furthest from lower bridge arm 6 is connected to the positive terminal 100 of the DC bus, and the submodule in lower bridge arm 6 that is furthest from upper bridge arm 3 is connected to the negative terminal 200 of the DC bus.

[0068] To further illustrate the high-voltage voltage source converter including a submodule based on dual capacitors in series, this invention provides a simulation example with the following simulation parameters: DC bus voltage. U dc The voltage is 11kV, the modulation index is 0.91, the AC peak voltage is 10kV, the number of bridge arm sub-modules is 100 (50 for each upper and lower bridge arm), and the control cycle is 10. μ s. The analysis results of this example take phase A as an example. The AC output voltage and bridge arm current, the number of NLM calculated levels, the distribution of the voltage difference between the upper bridge arm submodule capacitors, and the waveforms of the submodule capacitor voltages C1 and C2 are as follows: Figures 18-22 As shown.

[0069] The simulation results show that the proposed high-voltage voltage source converter, which includes a sub-module based on dual capacitors in series, works well and can achieve an ideal output waveform and a balance between capacitor voltage and bridge arm energy.

[0070] To further illustrate how a high-voltage source converter incorporating a dual-capacitor series-connected submodule reduces the number of components and cost, decreases converter size and weight, and achieves a lightweight and high power density converter, this invention compares it with the half-bridge submodules used in existing engineering projects. These projects use half-bridge submodules, with each bridge arm containing 288 submodules, totaling 1728 half-bridge submodules across six bridge arms. Here, based on the same engineering capacity under Borwin6 conditions, a comparison is made between two half-bridge submodules and the dual-capacitor series-connected submodule of this invention. The results are shown in Table 3.

[0071] Table 3. Comparison of Borwin6 projects using traditional half-bridge submodules and the topology of this invention.

[0072] In the table above, the bypass thyristor, bypass switch, central control board, power board, and optical fiber are calculated according to their respective unit prices. Compared with the traditional half-bridge topology, the cost of the sub-module based on dual capacitor series of the present invention is reduced by a total of RMB 184.3 million.

[0073] In summary, the comparative analysis shows that the topology of the present invention has significant advantages in reducing the number of devices, converter size and weight, and economy when applied to actual high-voltage flexible DC projects.

[0074] This invention proposes a submodule based on a dual-capacitor series connection, which is a flexible and controllable dual-capacitor energy unit. The flexible DC converter valve device (i.e., a high-voltage voltage source converter) developed based on this submodule topology is a core component for constructing a high-voltage DC transmission backbone network. It can meet the stringent requirements for the size and weight of high-voltage flexible DC converter valves in the confined space of offshore platforms in large-scale offshore wind power flexible DC transmission scenarios. Therefore, it has significant advantages in reducing the number of components, converter size and weight, and economic efficiency, with the following effects: (1) Reduced number of sub-modules: Compared with half-bridge sub-modules, the sub-modules of the present invention reduce the number of cascaded sub-modules in a single bridge arm at the same voltage level by increasing the number of voltage levels of a single sub-module; (2) Reduced number of components and cost: Compared with two half-bridge sub-modules connected in series, the sub-module of the present invention can reduce the number of at least one set of bypass thyristors and bypass switches, achieving a double reduction in volume and cost; (3) The volume and weight of the converter have been reduced, achieving a lightweight converter and high power density: Each sub-module press-fit structure reduces one set of press-fit end plate and disc spring, which can reduce the volume and weight of the converter and improve the power density of the converter; in addition, the number of sub-modules in the whole project has been reduced, and the corresponding number of optical fibers, central control and power supply has been reduced by half. (4) Increased control redundancy: In terms of modulation switching logic, compared with the three switching states of the half-bridge submodule, the submodule of this invention has more switching states and higher redundancy based on the original nearest level modulation capacitor voltage sorting algorithm; (5) Achieve overcurrent protection and high reliability: The sub-module of the present invention can achieve overcurrent protection through the solid-state overcurrent protection branch; under the fault lockout condition of the sub-module, the faulty sub-module is bypassed through the fault clearing branch, thus realizing the reliable removal of the faulty sub-module; (6) The self-equalizing voltage function of the two capacitors in the sub-module is realized: Compared with the independent capacitor voltages of the two series half-bridge sub-modules, the sub-module of the present invention has a neutral connection point, which can realize the equalization of the voltages of the two capacitors through the self-clamping function.

[0075] It is understood that the same or similar parts in the above embodiments can be referred to each other, and the contents not described in detail in some embodiments can be referred to the same or similar contents in other embodiments.

[0076] Example 4 like Figure 23As 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.

[0077] 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 the control method based on a submodule with two capacitors in series in the above embodiments.

[0078] Example 5 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 control method based on a dual-capacitor series-connected submodule in the above embodiments.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A submodule based on two capacitors connected in series, characterized in that, include: A switch branch consisting of a first switch module, a second switch module, a third switch module and a fourth switch module connected in series, as well as a first capacitor (C1), a second capacitor (C2), a solid-state overcurrent protection branch (S) and a fault clearing branch (K); The first capacitor (C1) and the second capacitor (C2) are connected in series and then connected in parallel with the switch branch; The connection point between the first switch module and the second switch module, one end of the solid-state overcurrent protection branch (S) and one end of the fault clearing branch (K) are connected in sequence to form the positive electrode (25) of the sub-module; The connection point between the third switch module and the fourth switch module, the other end of the solid-state overcurrent protection branch (S), and the other end of the fault clearing branch (K) are connected in sequence to form the negative electrode (45) of the submodule.

2. The submodule based on dual-capacitor series connection according to claim 1, characterized in that, The first switching module includes: a first switch (T1) and a first diode (D1) connected in antiparallel to it; The second switching module includes: a second switch (T2) and a second diode (D2) connected in antiparallel to it; The third switch module includes: a third switch (T3) and a third diode (D3) connected in antiparallel to it; The fourth switch module includes: a fourth switch (T4) and a fourth diode (D4) connected in antiparallel to it.

3. The submodule based on dual-capacitor series connection according to claim 2, characterized in that, The inflow terminal of the first switch (T1) is connected to the negative terminal of the first diode (D1), and the outflow terminal of the first switch (T1) is connected to the positive terminal of the first diode (D1). The inlet of the conducting current of the second switch (T2) is connected to the negative terminal of the second diode (D2), and the outlet of the conducting current of the second switch (T2) is connected to the positive terminal of the second diode (D2). The inflow terminal of the conduction current of the third switch (T3) is connected to the negative terminal of the third diode (D3), and the outflow terminal of the conduction current of the third switch (T3) is connected to the positive terminal of the third diode (D3). The inflow terminal of the conduction current of the fourth switch (T4) is connected to the negative terminal of the fourth diode (D4), and the outflow terminal of the conduction current of the fourth switch (T4) is connected to the positive terminal of the fourth diode (D4). The second connection point is connected to the third connection point, the fourth connection point is connected to the fifth connection point, and the sixth connection point is connected to the seventh connection point; The second connection point is the connection point between the outflow terminal of the conducting current of the first switch (T1) and the positive terminal of the first diode (D1); the third connection point is the connection point between the inflow terminal of the conducting current of the second switch (T2) and the negative terminal of the second diode (D2); the fourth connection point is the connection point between the outflow terminal of the conducting current of the second switch (T2) and the positive terminal of the second diode (D2); the fifth connection point is the connection point between the inflow terminal of the conducting current of the third switch (T3) and the negative terminal of the third diode (D3); the sixth connection point is the connection point between the outflow terminal of the conducting current of the third switch (T3) and the positive terminal of the third diode (D3); and the seventh connection point is the connection point between the inflow terminal of the conducting current of the fourth switch (T4) and the negative terminal of the fourth diode (D4).

4. The submodule based on dual-capacitor series connection according to claim 3, characterized in that, One end of the first capacitor (C1) is connected to the first connection point, and the other end is connected to one end of the second capacitor (C2); The other end of the second capacitor (C2) is connected to the eighth connection point; The connection point between the other end of the first capacitor (C1) and one end of the second capacitor (C2) is connected to the connection point between the fourth connection point and the fifth connection point; The first connection point is the connection point between the inflow end of the conduction current of the first switch (T1) and the negative terminal of the first diode (D1), and the eighth connection point is the connection point between the outflow end of the conduction current of the fourth switch (T4) and the positive terminal of the fourth diode (D4).

5. The submodule based on dual-capacitor series connection according to claim 3, characterized in that, One end of the solid-state overcurrent protection branch (S) is connected to the connection point between the second connection point and the third connection point; The other end of the solid-state overcurrent protection branch (S) is connected to the connection point between the sixth connection point and the seventh connection point.

6. The submodule based on dual-capacitor series connection according to claim 2, characterized in that, The anti-parallel connection method of each switch and its corresponding diode in each switch module is as follows: the diode and its corresponding switch are externally anti-parallel connected, or the anti-parallel diode is embedded inside the switch.

7. The submodule based on dual-capacitor series connection according to claim 2, characterized in that, The first switch (T1), the second switch (T2), the third switch (T3), and the fourth switch (T4) are all controllable semiconductor switching devices; The controllable semiconductor switching device is an insulated gate bipolar transistor, an integrated gate commutated thyristor, a gate turn-off thyristor, or an electron injection enhancement gate transistor.

8. The submodule based on dual-capacitor series connection according to claim 1, characterized in that, The solid-state overcurrent protection branch (S) is a controllable semiconductor switching device; The controllable semiconductor switching device is a thyristor, an insulated gate bipolar transistor, an integrated gate commutated thyristor, a gate turn-off thyristor, or an electron injection enhancement gate transistor.

9. The submodule based on dual-capacitor series connection according to claim 1, characterized in that, The fault clearing branch (K) is a mechanical switch; The mechanical switch can be an electromechanical switch, a pneumatic switch, or a hydraulic switch.

10. A control method for a submodule based on a dual-capacitor series connection, applicable to the dual-capacitor series connection submodule as described in any one of claims 1-9, characterized in that, include: When the submodule is running normally, the current flow path of the three-phase power supply in the submodule is controlled by controlling the switching state of each switch in each switching module, thereby controlling the output voltage of the submodule. When a submodule fails, the submodule is protected by controlling the switching status of each switch in each switching module, as well as the switching status of the solid-state overcurrent protection branch (S) or the fault clearing branch (K).

11. The method according to claim 10, characterized in that, When the submodule is operating normally, the current flow path of the three-phase power supply in the submodule is controlled by controlling the switching state of each switch in each switching module, thereby controlling the output voltage of the submodule, including: When the submodule is operating normally and the three-phase power supply current is positive, the first switch (T1) and the third switch (T3) are turned on, while the second switch (T2) and the fourth switch (T4) are turned off. The positive current flows sequentially through the first diode (D1), the first capacitor (C1), and the second switch (T2) to charge the first capacitor (C1). The output voltage of the submodule is U. C1 ; When the submodule is operating normally and the three-phase power supply current is negative, the first switch (T1) and the third switch (T3) are turned on, while the second switch (T2) and the fourth switch (T4) are turned off. The negative current flows sequentially through the third diode (D3), the first capacitor (C1), and the first switch (T1) to discharge the first capacitor (C1). The output voltage of the submodule is U. C1 ; Among them, U C1 This is the voltage across the first capacitor (C1).

12. The method according to claim 10, characterized in that, When the submodule is operating normally, the current flow path of the three-phase power supply in the submodule is controlled by controlling the switching state of each switch in each switching module, thereby controlling the output voltage of the submodule. This also includes: When the submodule is operating normally and the three-phase power supply current is positive, the second switch (T2) and the fourth switch (T4) are turned on, while the first switch (T1) and the third switch (T3) are turned off. The positive current flows sequentially through the second switch (T2), the second capacitor (C2), and the fourth diode (D4) to charge the second capacitor (C2). The output voltage of the submodule is U. C2 ; When the submodule is operating normally and the three-phase power supply current is negative, the second switch (T2) and the fourth switch (T4) are turned on, while the first switch (T1) and the third switch (T3) are turned off. The negative current flows sequentially through the fourth switch (T4), the second capacitor (C2), and the second diode (D2) to discharge the second capacitor (C2). The output voltage of the submodule is U. C2 ; Among them, U C2 This is the voltage across the second capacitor (C2).

13. The method according to claim 10, characterized in that, When the submodule is operating normally, the current flow path of the three-phase power supply in the submodule is controlled by controlling the switching state of each switch in each switching module, thereby controlling the output voltage of the submodule. This also includes: When the submodule is operating normally and the three-phase power supply current is positive, the first switch (T1) and the fourth switch (T4) are turned on, while the second switch (T2) and the third switch (T3) are turned off. The positive current flows sequentially through the first diode (D1), the first capacitor (C1), the second capacitor (C2), and the fourth diode (D4), causing the first capacitor (C1) and the second capacitor (C2) to be charged in series. The output voltage of the submodule is U. C1 +U C2 ; When the submodule is operating normally and the three-phase power supply current is negative, the first switch (T1) and the fourth switch (T4) are turned on, while the second switch (T2) and the third switch (T3) are turned off. The negative current flows sequentially through the fourth switch (T4), the second capacitor (C2), the first capacitor (C1), and the first switch (T1), causing the second capacitor (C2) and the first capacitor (C1) to discharge in series. The output voltage of the submodule is U. C1 +U C2 ; Among them, U C1 U is the voltage across the first capacitor (C1). C2 This is the voltage across the second capacitor (C2).

14. The method according to claim 10, characterized in that, When the submodule is operating normally, the current flow path of the three-phase power supply in the submodule is controlled by controlling the switching state of each switch in each switching module, thereby controlling the output voltage of the submodule. This also includes: When the submodule is operating normally and the current of the three-phase power supply is positive, the second switch (T2) and the third switch (T3) are turned on, and the first switch (T1) and the fourth switch (T4) are turned off. The positive current flows through the second switch (T2) and the third switch (T3) in sequence, so that the first capacitor (C1) and the second capacitor (C2) are bypassed, and the output voltage of the submodule is 0. When the submodule is operating normally and the current of the three-phase power supply is negative, the second switch (T2) and the third switch (T3) are turned on, and the first switch (T1) and the fourth switch (T4) are turned off. The negative current flows through the second switch (T2) and the third switch (T3) in sequence, so that the first capacitor (C1) and the second capacitor (C2) are bypassed, and the output voltage of the submodule is 0.

15. The method according to claim 10, characterized in that, When a submodule fails, the submodule is protected by controlling the switching states of each switch in each switching module, as well as the switching states of the solid-state overcurrent protection branch (S) or fault clearing branch (K), including: When a short circuit fault occurs in the submodule and the short circuit current exceeds the current withstand capability of each switch in each switch module, the first switch (T1), the second switch (T2), the third switch (T3) and the fourth switch (T4) are turned off, and the solid-state overcurrent protection branch (S) is turned on so that the negative current flows through the solid-state overcurrent protection branch (S) to provide overcurrent protection for the submodule. When the submodule is in a fault-locked state, the first switch (T1), the second switch (T2), the third switch (T3) and the fourth switch (T4) are turned off, and the fault clearing branch (K) is closed, so that both positive and negative currents flow through the fault clearing branch (K), thereby disconnecting the submodule and providing fault protection for the submodule.

16. A high-voltage voltage source converter, characterized in that, include: A phase unit (7), B phase unit (8) and C phase unit (9) are connected in parallel; each phase unit is composed of an upper bridge arm and a lower bridge arm connected in series; each bridge arm includes at least two sub-modules based on dual capacitor series as described in any one of claims 1-9; The upper arm of the A-phase unit (7), B-phase unit (8) and C-phase unit (9) is connected to the positive terminal (100) of the DC bus, and the lower arm of the A-phase unit (7), B-phase unit (8) and C-phase unit (9) is connected to the negative terminal (200) of the DC bus. The connection point between the upper and lower bridge arms of the A-phase unit (7) is phase a (300) of the three-phase power supply; The connection point between the upper and lower bridge arms of the B-phase unit (8) is the B-phase (400) of the three-phase power supply; The connection point between the upper and lower bridge arms of the C-phase unit (9) is the C-phase (500) of the three-phase power supply.

17. The high-voltage voltage source converter according to claim 16, characterized in that, The upper bridge arm (1) of the A phase unit (7) includes: at least two sub-modules connected in series, a bridge arm resistor (71) and a bridge arm inductor (72); The lower bridge arm (4) of the A-phase unit (7) includes: at least two sub-modules connected in series, a bridge arm resistor (74) and a bridge arm inductor (73); The bridge arm inductor (72) is connected to the bridge arm inductor (73), and the connection point between the bridge arm inductor (72) and the bridge arm inductor (73) is phase a (300) of the three-phase power supply; The sub-module of the upper bridge arm (1) that is away from the lower bridge arm (4) is connected to the positive terminal (100) of the DC bus, and the sub-module of the lower bridge arm (4) that is away from the upper bridge arm (1) is connected to the negative terminal (200) of the DC bus.

18. The high-voltage voltage source converter according to claim 16, characterized in that, The upper bridge arm (2) of the B-phase unit (8) includes: at least two sub-modules, a bridge arm resistor (81) and a bridge arm inductor (82) connected in series in sequence; The lower bridge arm (5) of the B-phase unit (8) includes: at least two sub-modules connected in series, a bridge arm resistor (84) and a bridge arm inductor (83); The bridge arm inductor (82) is connected to the bridge arm inductor (83), and the connection point between the bridge arm inductor (82) and the bridge arm inductor (83) is phase b (400) of the three-phase power supply; The sub-module of the upper bridge arm (2) that is away from the lower bridge arm (5) is connected to the positive terminal (100) of the DC bus, and the sub-module of the lower bridge arm (5) that is away from the upper bridge arm (2) is connected to the negative terminal (200) of the DC bus.

19. The high-voltage voltage source converter according to claim 16, characterized in that, The upper bridge arm (3) of the C-phase unit (9) includes: at least two sub-modules connected in series, a bridge arm resistor (91) and a bridge arm inductor (92); The lower bridge arm (6) of the C-phase unit (9) includes: at least two sub-modules connected in series, a bridge arm resistor (94) and a bridge arm inductor (93); The bridge arm inductor (92) is connected to the bridge arm inductor (93), and the connection point between the bridge arm inductor (92) and the bridge arm inductor (93) is the c phase (500) of the three-phase power supply; The sub-module of the upper bridge arm (3) that is away from the lower bridge arm (6) is connected to the positive terminal (100) of the DC bus, and the sub-module of the lower bridge arm (6) that is away from the upper bridge arm (3) is connected to the negative terminal (200) of the DC bus.

20. 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 control method based on a dual-capacitor series submodule as described in any one of claims 10 to 15 is implemented.

21. A readable storage medium, characterized in that, It contains an executable program, which, when executed, implements the control method for a submodule based on dual capacitors in series as described in any one of claims 10 to 15.

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