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WO2015180204A1 - 用于模块化多电平换流器的子模块拓扑及其应用 - Google Patents

用于模块化多电平换流器的子模块拓扑及其应用 Download PDF

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Publication number
WO2015180204A1
WO2015180204A1 PCT/CN2014/079502 CN2014079502W WO2015180204A1 WO 2015180204 A1 WO2015180204 A1 WO 2015180204A1 CN 2014079502 W CN2014079502 W CN 2014079502W WO 2015180204 A1 WO2015180204 A1 WO 2015180204A1
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WO
WIPO (PCT)
Prior art keywords
switch module
module
sub
fault
submodule
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/CN2014/079502
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English (en)
French (fr)
Inventor
林卫星
向往
文劲宇
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Huazhong University of Science and Technology
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Huazhong University of Science and Technology
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Priority to US15/028,359 priority Critical patent/US20160268915A1/en
Priority to EP14893132.2A priority patent/EP3041127A4/en
Publication of WO2015180204A1 publication Critical patent/WO2015180204A1/zh
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output
    • H02M7/42—Conversion of DC power input into AC power output without possibility of reversal
    • H02M7/44—Conversion of DC power input into AC power output without possibility of reversal by static converters
    • H02M7/48—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M5/00—Conversion of AC power input into AC power output, e.g. for change of voltage, for change of frequency, for change of number of phases
    • H02M5/40—Conversion of AC power input into AC power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into DC
    • H02M5/42—Conversion of AC power input into AC power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into DC by static converters
    • H02M5/44—Conversion of AC power input into AC power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into DC by static converters using discharge tubes or semiconductor devices to convert the intermediate DC into AC
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output
    • H02M7/42—Conversion of DC power input into AC power output without possibility of reversal
    • H02M7/44—Conversion of DC power input into AC power output without possibility of reversal by static converters
    • H02M7/48—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/4835—Converters with outputs that each can have more than two voltages levels comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output
    • H02M7/42—Conversion of DC power input into AC power output without possibility of reversal
    • H02M7/44—Conversion of DC power input into AC power output without possibility of reversal by static converters
    • H02M7/48—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/49—Combination of the output voltage waveforms of a plurality of converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output
    • H02M7/42—Conversion of DC power input into AC power output without possibility of reversal
    • H02M7/44—Conversion of DC power input into AC power output without possibility of reversal by static converters
    • H02M7/48—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters

Definitions

  • the invention belongs to the technical field of power system transmission and distribution, and more particularly relates to a novel sub-module topology of a modular multi-level converter and a hybrid inverter composed of a novel sub-module topology and a half-bridge sub-module topology. Topology.
  • HVDC high-voltage direct current
  • MTDC multi-terminal direct current transmission
  • DC grid technology which can achieve multi-supply power supply and multi-drop power receiving, have received strong attention.
  • converter technology is one of its key technologies.
  • the inverter converts alternating current into direct current or converts direct current into alternating current to realize AC-DC/DC-AC energy transmission.
  • the technologies that can be used for AC-DC/DC-AC conversion are mainly phase-controlled converters based on crystal tubes and voltage source converters based on fully-controlled power electronics.
  • the phase-controlled converter requires an external AC voltage source to provide a commutation voltage during operation, and a cascade commutation failure in a multi-terminal DC transmission system based on a phase-controlled converter causes a system collapse.
  • the voltage source converter based on fully-controlled power electronic components can realize independent decoupling control of active and reactive power, can supply power to weak grids or islands, and easily form a multi-terminal DC system, improving system stability and transmission capacity. Other aspects have great advantages.
  • voltage source type HVDC transmission has been widely used in the field of renewable energy access, and has achieved tremendous development.
  • MMC multilevel converter technology
  • the package, the switching device is subjected to less electrical stress, low switching loss, etc., and can realize high-voltage and high-power level power transmission.
  • Modular multilevel converters are generally classified into three types: half bridge type, full bridge type and clamp double type according to the sub-module topology.
  • the modular multilevel converter based on the half-bridge sub-module is the most commonly used converter technology among the three types, and has been deeply researched and widely applied by academia and industry.
  • DC-side faults are a serious type of fault that must be considered in engineering design operations. They have an important impact on equipment parameters, control strategies and protection configurations.
  • AC side equipment such as AC circuit breakers, AC fuses, etc., but the method has a slow response speed, a complicated restart operation timing, and a long system recovery time.
  • the effective solution is to use the converter's own control to achieve self-clearing of the DC-side fault, without the need for mechanical equipment action, and the system recovery speed is fast.
  • modular multi-level converter technology with the function of blocking DC fault current has received more and more attention.
  • Full-bridge and clamp-type MMCs have the ability to isolate DC faults due to the special structure of the submodules they use. However, in order to achieve the function of isolating DC faults, the full-bridge and clamp dual-mode MMCs use more fully-controlled power electronics. Under the same voltage and power level output conditions, the full-bridge MMC doubles the number of fully-controlled power electronic components compared to the half-bridge MMC, which greatly increases the cost of the MMC; a sub-module of the clamped dual-mode MMC It contains two capacitors, which increases the number of fully-controlled power electronic components by 25% compared with the half-bridge MMC, but increases the control complexity of the system and the sub-module packaging, industrial design difficulty, and reduces the reliability of the system.
  • the present invention provides a sub-module topology for blocking a DC fault current function for a modular multi-level converter, which has a blocking DC as compared with the prior art.
  • the sub-module of fault current has the advantages of reducing the number of fully-controlled power electronic devices in the sub-module and reducing the difficulty of the process realization of the sub-modules. These sub-modules can be used to form a modular multi-level commutation with isolated DC fault function. Device.
  • a submodule topology for use in a modular multilevel converter wherein the submodule topology includes:
  • a first switch module and a second switch module connected in series, wherein a negative end of the first switch module is connected to a positive end of the second switch module, wherein the switch module is formed by a fully controlled device and a diode connected in anti-parallel And a DC capacitor having a positive terminal and a negative electrode connected to a positive terminal of the first switching module and a negative terminal of the second switching module, respectively;
  • the method further includes a third switch module electrically connected to the first switch module and the second switch module, so that the full-control device of the third switch module always applies a trigger pulse during normal operation, and is always in a conductive state.
  • the DC fault current is blocked by blocking the trigger pulse of the third switch module.
  • the negative end of the third switch module is connected to the negative end of the second switch module, and the positive end of the third switch module is used as the output negative end of the submodule, the first switch module and the second switch module.
  • the connection point serves as the output positive end of the submodule.
  • a fourth diode is further included, the anode of which is connected to the positive terminal of the third switching module, and the cathode is connected to the anode of the DC capacitor.
  • the positive end of the third switch module is connected to the connection point of the first switch module and the second switch module, the negative end of the third switch module serves as the output positive end of the submodule, and the second switch module is negative The end serves as the output negative end of the sub-module.
  • the negative end of the third switch module is connected with the connection point of the first switch module and the second switch module, and the positive end of the third switch module is used as the output negative end of the submodule, and the first switch module is positive The end serves as the output positive end of the submodule.
  • the positive end of the third switch module is connected to the positive end of the first switch module, the negative end of the third switch module is used as the output positive end of the submodule, and the connection between the first switch module and the second switch module The point is the output negative end of the sub-module.
  • a fourth diode is further included, the anode of which is connected to the negative terminal of the DC capacitor, and the cathode Connected to the negative terminal of the third switch module.
  • the fully controlled device may be an insulated gate bipolar transistor (IGBT), an integrated gate commutated thyristor (IGCT) or a gate turn-off thyristor (GTO).
  • IGBT insulated gate bipolar transistor
  • IGCT integrated gate commutated thyristor
  • GTO gate turn-off thyristor
  • a modular multilevel converter comprising one or more phase units, each phase unit comprising an upper and a lower arm connected in series, and an upper bridge
  • the arm and the lower arm respectively correspond to the bridge arm inductances in series, wherein the negative ends of the upper arm and the lower arm are respectively connected with the positive and negative poles of the DC bus, and the upper and lower ends of the upper arm of each phase unit are
  • the connection point of the positive end of the bridge arm serves as the A, B, C three-phase output terminal lead-out point
  • the upper bridge arm or the lower bridge arm is formed by serially connecting a plurality of the above-mentioned sub-modules.
  • a modular multilevel converter comprising one or more phase units, each phase unit comprising an upper and a lower arm connected in series, and an upper bridge
  • the arm and the lower arm respectively correspond to the bridge arm inductances in series, wherein the negative ends of the upper arm and the lower arm are respectively connected with the positive and negative poles of the DC bus, and the upper and lower ends of the upper arm of each phase unit are
  • the connection point of the positive end of the bridge arm serves as the lead-out point of the A, B, C three-phase output terminal, and the upper arm or the lower arm is mixed and connected in series with one or more of the above-mentioned sub-module topologies and one or more half-bridge sub-modules. to make.
  • the number of the above-mentioned sub-modules in the upper or lower arm is the same as the topology of the half-bridge sub-module.
  • a method for blocking a DC fault current by using the modular multilevel converter described above is used to block the DC fault current in the event of a DC fault, characterized in that the method Specifically, when a DC fault occurs, the trigger pulse of the third switch module of the sub-module topology is blocked, and the path of the fault current provided by the AC side to the DC side is disconnected.
  • the DC fault is judged by detecting whether the DC current value exceeds the limit or detecting whether the DC current rising rate is exceeded or not.
  • the DC fault is a permanent fault on the DC side
  • the specific process of blocking the DC fault current is: first blocking all the trigger pulses of the full control device to isolate the DC fault, and then turning off the AC side circuit breaker, Wait for the DC side fault to clear and then recharge the operation.
  • the DC fault is a temporary fault on the DC side
  • the specific process of blocking the DC fault current is: first blocking all the trigger pulses of the full control device to isolate the DC fault, and after the DC arc is extinguished, unlock each The trigger pulse of the full-control device of the third switch module in the sub-module is charged by the AC side to the DC line, and finally the remaining fully-controlled devices are unlocked to re-enter steady-state operation.
  • the number of fully controlled power electronic devices can be greatly reduced, and only about 25% of the total control can be added to the existing half bridge type MMC.
  • the type of power electronics allows the hybrid inverter to have the function of isolating DC fault current.
  • the submodule is formed by three switch modules, a DC capacitor, a positive output of the submodule, and a negative end of the output of the submodule through a certain electrical connection, wherein
  • Each switch module consists of a fully controlled device and a diode in anti-parallel.
  • the connection between the collector of the fully-controlled device and the cathode of the diode is the positive terminal of the switch module, and the connection between the emitter of the fully-controlled device and the anode of the diode is the negative terminal of the switch module.
  • the first switch module and the second switch module are sequentially connected in series, and the negative end of the first switch module is connected to the positive end of the second switch module; the positive pole of the DC capacitor positive electrode and the DC capacitor are respectively positive with the first switch module
  • the terminal is connected to the negative terminal of the second switch module; thereby completing the connection of the DC capacitor, the first switch module and the second switch module. If the sub-module output positive terminal and the sub-module output negative terminal are respectively connected with the first, the second switch module connection point and the negative terminal of the second switch module, a typical half-bridge sub-module topology is formed, and the topology does not have The ability to block DC fault currents.
  • the negative terminal of the third switch module is connected to the negative terminal of the second switch module, and the sub-module output positive terminal and the sub-module output negative terminal are respectively respectively The connection point of the second switch module and the positive end of the third switch module are connected.
  • the full-control device of the third switch module always applies the trigger pulse, and is always in the on state, so that the invention is no different from the conventional half-bridge module in normal operation, and the third switch module is blocked when the DC fault occurs.
  • the trigger pulse is used to achieve the purpose of blocking the DC fault current.
  • the positive end of the third switch module may be connected to the connection point of the first and second switch modules, and the positive end of the submodule output and the sub-module are respectively taken from the negative end of the third switch module and the negative pole of the DC capacitor.
  • the negative terminal of the third switch module is connected to the connection point of the first and second switch modules, and the positive terminal output of the submodule is respectively taken from the positive terminal of the DC capacitor and the positive terminal of the third switch module. And the submodule outputs the negative terminal.
  • the positive terminal of the third switch module and the positive pole of the DC capacitor may be connected, and the positive terminal and the submodule of the submodule output are respectively taken from the negative end of the third switch module and the connection point of the first and second switch modules.
  • Output negative the DC fault current can be blocked by blocking the trigger pulse of the third switch module in the event of a DC fault, but the modular multilevel converter blocks all thirds when the level is high. Switch module trigger pulse The simultaneity requirement is high, otherwise the third switch module in the sub-module is blocked due to different latching, and the full-control device in the third switch module of a certain sub-module that is first latched is subjected to the full AC voltage and is burned, in order to reduce the trigger. Simultaneous requirements can be overcome by adding a fourth diode. .
  • the anode of the fourth diode may be connected to the positive terminal of the third switching module, and the cathode of the fourth diode is connected to the anode of the DC capacitor.
  • the newly added fourth diode does not affect the normal operation of the new sub-module; after the DC-side fault occurs, if the fault current flows from the positive output of the sub-module, the fault current flows from the anti-parallel diode of the first switch module.
  • the full-control device of the third switch module withstands a voltage drop of almost 0; if the fault current flows from the negative output of the sub-module, the fault current flows through the fourth The pole tube, the DC capacitor, and the anti-parallel diode of the second switch module circulate, and the voltage of the fully-controlled device of the third switch module is clamped to the capacitor voltage; neither of the two conditions causes the third switch module to be fully controlled.
  • the type of device is subjected to the latching of the lock and the entire AC voltage is burned, thereby reducing the requirement of triggering simultaneity.
  • the fourth diode is added, the anode thereof can also be connected to the negative terminal of the DC capacitor, and the cathode of the fourth diode is connected to the negative terminal of the third switch module, so as to achieve the requirement of reducing the triggering simultaneity. .
  • one connection mode of each phase unit is that one end of the upper arm inductance is connected to the positive DC bus, and the other end of the upper arm inductance is connected to the positive end of the upper arm, and the negative end of the upper arm and the lower arm
  • the positive terminal is connected
  • the negative end of the lower arm is connected to one end of the lower arm inductance
  • the other end of the lower arm inductance is connected to the negative DC bus.
  • the negative end of the upper arm of each phase unit is connected to the positive end of the lower arm.
  • Point A, B, C three-phase output terminals at the point.
  • Another connection method of each phase unit is that the positive end of the upper arm is connected to the positive DC bus, the negative end of the upper arm is connected to one end of the upper arm inductance, and the other end of the upper arm inductance is connected to the lower arm.
  • One end of the inductor is connected, the other end of the lower arm inductor is connected to the positive end of the lower arm, the negative end of the lower arm is connected to the negative DC bus, and the upper arm inductance of each phase unit is connected to the lower arm inductance
  • the A, B, C three-phase output terminals are led out.
  • modular multilevel converter described above may comprise one or more phase units to form a one or more phase modular multilevel converter.
  • the present invention also provides a hybrid inverter composed of the above sub-module and a conventional half-bridge sub-module, the technical details of which are the above-mentioned modular multi-level converter composed of the above sub-modules A portion of the sub-modules of each of the bridge arms are replaced with conventional half-bridge sub-modules to reduce the number of sub-modules employed to reduce inverter cost.
  • the ratio of the conventional half bridge submodule included in each leg of the hybrid inverter to the above submodule is 1:1 to reduce the number of fully controlled devices added to block DC fault current.
  • press The 1:1 ratio allows the hybrid inverter to have the ability to block DC fault currents by simply adding 25% of the full-controlled device to the conventional half-bridge submodule MMC.
  • the present invention also provides a method for blocking a DC fault current by using a modular multilevel converter or a hybrid modular multilevel converter constructed by the above submodule, and blocking by a DC fault.
  • the trigger pulse of the third switch module of the new sub-module can disconnect the AC side from the DC side to provide a fault current path to block the DC fault current.
  • the single-phase, three-phase or multi-phase modular multilevel converter composed of the novel sub-module topology proposed by the solution of the present invention isolates the DC fault by the following isolation step after the DC side fails.
  • isolation step 1 Determine whether the DC current fault occurs by detecting whether the DC current value exceeds the limit, or whether the DC current rising rate is exceeded. In isolation step 2, it is determined that a DC fault occurs, then the lock is blocked. All fully-controlled power electronic devices trigger pulses to isolate DC faults. Step 3: Turn off the AC-side circuit breaker. After the DC-side fault is cleared, the system is recharged.
  • isolation step 1 Determine whether the DC side fault occurs by detecting whether the DC current value exceeds the limit, or whether the DC current rising rate is exceeded. Isolation step 2, if it is determined that a DC fault has occurred, Block all the full-control power electronic device trigger pulses to isolate the DC fault; Isolation step 3, after the DC arc is extinguished, unlock the full-control power electronic device trigger pulse of the third switch module in each sub-module, DC from the AC side Line charging; Isolation step 4, unlock the remaining fully-controlled power electronics, resume control, and the system re-enters steady-state operation.
  • the novel sub-module topology provided by the present invention can implement the isolated DC fault function, and is compared with the full-bridge sub-module, Clamped dual-type sub-modules and diode-clamped sub-modules reduce the number of switching devices and switching losses in sub-modules, reducing the difficulty of structural design and industrial applications.
  • 1 is a topological structural view of a conventional half bridge type submodule
  • FIG. 2 is a topological structural view of a conventional full bridge type submodule
  • Figure 3 is a topological view of a conventional clamped dual-type sub-module
  • Figure 4 is a topological structure diagram of a diode clamp type sub-module
  • Figure 5 is a topological structural view of a first embodiment of the sub-module of the present invention.
  • Figure 6 is a topological view of a second embodiment of the sub-module of the present invention
  • Figure 7 is a topological structural view of a third embodiment of the submodule of the present invention
  • Figure 8 is a topological view of a fourth embodiment of the sub-module of the present invention.
  • Figure 9 is a topological structural view of a fifth embodiment of the submodule of the present invention.
  • Figure 10 is a topological structural view of a sixth embodiment of the submodule of the present invention.
  • Figure 11 is a first three-phase modular multilevel converter topology constructed by the sub-modules (first to sixth embodiments) of the present invention.
  • Figure 12 is a second three-phase modular multi-level converter topology constructed by the sub-modules (first to sixth embodiments) of the present invention.
  • FIG. 13 is a schematic structural diagram of a three-phase hybrid modular multilevel converter composed of various embodiments of a submodule and a half bridge submodule according to an embodiment of the present invention
  • Figure 14 is a schematic diagram of a three-phase 9-level modular multilevel converter composed of a novel sub-module;
  • Figure 15 is a simplified analysis circuit diagram of the modular multilevel converter shown in Figure 14.
  • 16 is an equivalent circuit diagram of a three-phase modular multilevel converter provided by an embodiment of the present invention at an instant of IGBT latching after a fault;
  • 17 is a simulation waveform diagram of a sub-module capacitance voltage value of a three-phase 9-level modular multilevel converter according to an embodiment of the present invention.
  • Figure 18 is a diagram showing the simulation waveform of the upper arm current value of the three-phase 9-level modular multilevel converter according to the embodiment of the present invention.
  • the novel sub-module topology provided by the embodiments of the present invention is mainly used for constructing a novel modular multi-level converter, so that the new modular multi-level converter is used for DC transmission at both ends, multi-terminal DC transmission, and DC power grid, which is remarkable
  • the technical performance is that compared to the conventional half-bridge modular multilevel converter without blocking DC fault current capability, only a 25% increase in fully-controlled devices can be used to enable the new modular multi-level.
  • the inverter has the ability to block the DC fault current. Compared with the full-bridge sub-module and the clamped double-sub-module type, the number of sub-modules and switching loss are reduced, which is more conducive to engineering design and implementation.
  • Figure 1 shows the well-known conventional half-bridge sub-module topology.
  • the inverter When a DC fault occurs, the inverter is connected.
  • the flow system will supply DC fault current through the lower diode D2, which makes the DC arc difficult to extinguish, and makes the AC system short-circuited.
  • D2 flows through a large fault current and may be burned.
  • the AC side switch needs to be disconnected to cut off the DC fault. The current, which greatly delays the time it takes for the system to resume power.
  • FIG 2 shows the well-known full-bridge sub-module topology. This topology has the ability to block DC fault current. However, as can be seen from Figure 1 and Figure 2, the number of switching devices used in the full-bridge sub-module topology is The cost of the half bridge module is doubled.
  • the clamped dual sub-module topology will block all fully-controlled devices in the event of a DC-side fault.
  • the clamped dual-submodule has two discharge paths at the time of the fault, but due to the DC capacitor voltage at the two paths. And greater than the AC system line voltage amplitude, will cause the diode to be reversely blocked, thereby isolating the DC fault.
  • the clamped dual sub-module type uses more semiconductor devices, which increases the difficulty of process design.
  • the energy stored in the DC network is mainly absorbed by the sub-module capacitance. If the energy is too large, the sub-module capacitor voltage increases greatly. The resulting overvoltage problem may burn the semiconductor device.
  • the diode-clamped sub-module topology shown in Figure 4 uses three IGBT devices, two DC capacitors, and diode clamps to isolate DC faults. However, this topology uses two capacitors, increasing the size and design cost of the sub-modules.
  • FIG. 5 is a first embodiment of a submodule according to the present invention.
  • the new submodule is composed of three switch modules 1 to 3, a DC capacitor 4, a submodule output positive terminal 5, and a submodule output negative terminal 6.
  • Each switch module is formed by anti-parallel connection of fully controlled devices (Tl, T2, T3) and diodes (Dl, D2, D3).
  • connection between the fully-controlled device and the diode cathode is the positive terminal of the switch module
  • connection between the fully-controlled device and the diode anode is the negative terminal of the switch module.
  • the positive terminal and the negative terminal of the DC capacitor 4 are respectively connected to the positive terminal of the first switch module 1 and the negative terminal of the second switch module 2, and the negative terminal of the first switch module 1 is connected to the positive terminal of the second switch module 2, thereby
  • the DC capacitor 4 is connected, and the connection between the first switch module 1 and the second switch module 2 is output from the connection point of the first and second switch modules and the negative terminal of the second switch module 2 to the positive terminal 5 and the submodule.
  • Output negative terminal 6, which constitutes a typical half-bridge sub-module topology that is fully consistent with Figure 1, which does not have the ability to block DC fault currents.
  • the negative terminal of the third switch module 3 is connected to the negative terminal of the second switch module 2, and the sub-module is further outputted to the positive terminal 5 and the sub-module.
  • the module output negative terminal 6 is connected to the connection point of the first switch module 1, the second switch module 2 and the positive terminal of the third switch module 3, respectively.
  • the trigger pulse is always applied to the full control device of the third switch module 3 during normal operation, so that the embodiment of the present invention is no different from the conventional half bridge module in normal operation, and triggers by blocking the third switch module 3 when a DC fault occurs. Pulse can To block the flow path of DC fault current.
  • Figure 6 shows a second embodiment of the sub-module of the present invention, which differs from the first embodiment only in that the positive end of the third switch module 3 is connected to the negative end of the first switch module 1, from the third The negative terminal of the switch module 3 and the negative terminal of the DC capacitor 4 (the negative terminal of the second switch module 2) respectively lead to the submodule output positive terminal 5 and the submodule output negative terminal 6.
  • FIG. 7 is a third embodiment of the submodule of the present invention, which differs from the first embodiment only in that the negative end of the third switch module 3 and the negative end of the first switch module 1 (the connection point is also A switch module 1 is connected to a connection point of the second switch module 2, and a positive output terminal 5 and a sub-module are respectively extracted from a positive pole of the DC capacitor 4 (a positive pole of the first switch module 1) and a positive terminal of the third switch module 3, respectively.
  • the module outputs a negative terminal 6.
  • the sub-module output positive terminal 5 and the sub-module output negative terminal 6 are respectively led from the negative terminal of the third switching module 3 and the negative terminal of the first switching module 1.
  • the modular multi-level inverter composed of the above four schemes has a high requirement for the triggering pulse of the fully-controlled device in the third switching module 3 of each bridge arm after the failure of the DC side. Otherwise, the third switch module 3 in the sub-module is not locked at the same time, so that the full-control device in the third switch module 3 of a certain sub-module that is first latched is subjected to the full AC voltage and is burned, in order to reduce the triggering simultaneity. It is required that the present invention can be better applied to a modular multilevel converter of a high level, and a fourth diode can be further added to constitute a new embodiment.
  • Figure 9 is a fifth embodiment of the sub-module of the present invention, which differs from the first embodiment only in that a fourth diode 7 is added, the anode of the diode 7 and the positive terminal of the third switching module 3 Connected, the cathode of the diode 7 is connected to the anode of the DC capacitor 4 (the anode of the first switching module 1).
  • the newly added diode 7 does not affect the normal operation of the sub-module; after the DC-side fault occurs, if the fault current flows from the positive terminal 5 of the sub-module, the fault current flows through the anti-parallel diode of the first switch module, and then through the direct current
  • the capacitor 4 is further circulated from the anti-parallel diode of the third switch module 3, and the full-control device of the third switch module is subjected to a voltage drop of almost 0; if the fault current flows from the negative terminal 6 of the sub-module, the fault current flows through the diode 7
  • the DC capacitor 4 and the anti-parallel diode of the second switch module 2 are circulated, and the voltage of the fully-controlled device in the third switch module 3 is clamped to the capacitor voltage; neither of the two causes the third switch module 3 to be
  • the fully-controlled device suffers from the fact that the entire AC voltage is burned due to the triggering of the latch at the same time, thereby reducing the requirement of triggering simultan
  • Figure 10 is a sixth embodiment of the sub-module of the present invention, which differs from the fourth embodiment only in that a diode 7 is added, the anode of the diode 7 is connected to the negative terminal of the DC capacitor 4, and the cathode of the diode is The negative ends of the third switch module 3 are connected.
  • FIG 11 shows a three-phase modular multilevel converter extension consisting of the above sub-modules proposed by the present invention.
  • the new three-phase modular multilevel converter comprises three phase units 11, each phase unit being connected in series by an upper arm 12, an upper arm inductance 13, a lower arm inductance 14, and a lower arm 15 in sequence.
  • Each bridge arm is sequentially connected in series by N sub-modules, the positive end of each phase unit 11 is connected to the positive DC bus 16 , and the negative end of the phase unit 11 is connected to the DC negative bus 17 , from each upper bridge
  • the arm inductance and the connection point of the lower arm inductance lead to the AC output terminals 8 to 10, respectively.
  • the specific connection of each bridge arm is shown on the left side of Figure 11.
  • Figure 12 is a diagram showing another implementation of a novel three-phase modular multilevel converter constructed by the improved novel sub-module proposed by the present invention.
  • the topology is basically similar to that of Figure 11, except that each phase is formed.
  • the connection between the bridge arm and the bridge arm inductance is different.
  • the novel three-phase modular multilevel converter comprises three phase units 11, each phase unit being formed by connecting the upper arm inductance 13, the upper arm 12, the lower arm 15, and the lower arm inductor 14 in series.
  • the AC output terminals 8 to 10 are respectively taken out from the connection points of the upper arm and the lower arm.
  • the implementation of other components of the solution is completely identical to that of FIG. 11 and will not be described again.
  • each new modular multilevel converter can be composed of one or more phase units to form a one-phase or multi-phase new modular multi-module.
  • the level converter is not limited to the number of phase units described in the embodiment of Figs. 11 and 12.
  • Figure 13 shows a hybrid inverter with a new sub-module improved topology and a conventional half-bridge sub-module.
  • the topology of Figure 13 is basically the same as the topology of Figure 11, except that each bridge arm 12, 15 consists of several new types.
  • the sub-module and the conventional half-bridge sub-module are mixed and connected in series, wherein the serial order of the new sub-module and the conventional half-bridge sub-module is arbitrary.
  • the novel sub-module described above may be any one of the above-described first to sixth embodiments.
  • FIG. 14 is a schematic diagram of simulation of a three-phase 9-level modular multilevel converter composed of a novel submodule according to an embodiment of the present invention. For the convenience of analysis, one phase of Fig. 14 is taken out for analysis, and eight new sub-modules of the upper and lower arms are respectively equivalent to one sub-module, as shown in Fig. 15.
  • the capacitors 22 and 28 are the equivalent series capacitance values of the upper and lower arms, and the capacitor voltages are the sum of the capacitor voltages of the upper arm and the lower arm submodule, respectively.
  • a DC-side pole-to-pole short-circuit fault 29 occurs, the fully-controlled device in the switch modules 19, 20, 21, 24, 25, 26 will be blocked. Assuming that the fault current flows from the AC side to the DC side, the upper arm is blocked by the IGBT, and the fault current can only flow through the diode 23, the capacitor 22, and the anti-parallel diode in the switch module 20, but the sum of the capacitor voltages of the upper arm is maintained at the DC voltage.
  • the diode is subjected to back pressure and cannot be turned on, and the upper arm has no conductive path; the fault current of the lower arm can only pass through the switch modules 24, 26 Anti-parallel diode and capacitor 27
  • the conductive path is formed, but since the sum of the capacitor voltages of the lower arm is maintained near the DC voltage [ ⁇ , and the amplitude of the phase voltage of the AC side is less than [ ⁇ , the diode is subjected to the back pressure and cannot be turned on, and the lower arm has no conductive path.
  • the possible path of the upper arm fault current is the capacitor 22 and the anti-parallel diode in the switch modules 19, 21, but the sum of the upper arm capacitor voltages is maintained near the DC voltage [ ⁇ , diode Withstand back pressure and cannot conduct, the upper arm has no conductive path; the possible fault current path of the lower arm is the anti-parallel diode, the capacitor 27 and the diode 28 in the switch module 24, but the sum of the capacitor voltages of the lower arm is maintained.
  • the AC power source 30 cannot provide a short-circuit current to the fault point, thereby achieving isolation of the DC fault.
  • each phase bridge arm requires only N/2 new sub-modules to achieve isolated DC fault function.
  • the ratio of the number of new sub-modules used to each bridge arm to the conventional half-bridge sub-module is preferably 1:1.
  • each device uses a detailed model from the PSCAD/EMTDC standard model library.
  • the rated capacity of the system is 1000 MVA
  • the rated AC voltage is 230kV
  • the DC voltage is ⁇ 200kV
  • the sub-module capacitance is 300 ( ⁇ F
  • the bridge arm inductance is 0.0154H
  • the upper and lower arms are 8 sub-modules.
  • the corresponding simulation results are shown in Fig. 17 and Fig. 18.
  • Fig. 17 shows the submodule capacitance voltage value
  • Fig. 18 shows the DC current value.
  • the simulation time Is the system has a permanent pole-to-pole DC short-circuit fault at the DC-side outlet of the inverter.
  • FIG. 17 and FIG. 18 are mainly used for the principle verification of the novel sub-module proposed by the present invention.
  • the rated voltage of the sub-module is 50 kV.
  • the principles verified in Figures 17 and 18 can be generalized to any level MMC in practice.
  • the hybrid inverter topology proposed by the example of the present invention has an isolated DC fault function, which only increases the number of sub-modules by 25% compared to a known half-bridge MMC that does not have a DC fault current. Compared with the existing MMC with the ability to block DC fault current, no additional damping resistor is needed, which reduces the cost and the difficulty of industrial design, and has considerable industrial application value.

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Abstract

一种用于模块化多电平换流器中的子模块拓扑结构、包括该子模块的换流器及其应用，所述子模块拓扑结构包括：相互串联的第一开关模块（1）和第二开关模块（2），其中第一开关模块（1）的负端与第二开关模块（2）的正端相连接，开关模块（1、2、3）由一个全控型器件和一个二极管反并联而成；直流电容（4），其正极和负极分别与第一开关模块（1）的正端和第二开关模块（2）的负端相连接；还包括第三开关模块（3），其与第一开关模块（1）和第二开关模块（2）电气连接，使得正常工作时该第三开关模块（3）的全控型器件一直施加触发脉冲从而一直处于导通状态，而发生直流故障时通过闭锁该第三开关模块（3）的触发脉冲实现阻断直流故障电流。该方案可以实现隔离直流故障功能，同时减少了子模块中开关器件的数量与开关损耗，降低了触发同时性的要求。

Description

用于模:^多电平换流器的子模 ^¾扑及其应用
【技术领域】
本发明属于电力系统输配电技术领域， 更具体地， 涉及一种模块化多电平换流器 新型子模块拓扑以及由新型子模块拓扑与半桥型子模块拓扑构成的混合型换流器拓 扑。
【背景技术】
目前， 高压直流输电 （HVDC) 技术在可再生能源并网领域得到了广泛的应用。 随 着高压直流输电技术的进一步发展， 能够实现多电源供电、 多落点受电的多端直流输 电 （MTDC) 技术与直流电网技术得到了强烈的关注。
无论是两端高压直流输电技术， 还是多端高压直流输电技术以及直流电网技术， 换流器技术都是其关键技术之一。 换流器将交流电变换成直流电或者将直流电变换成 交流电， 来实现交流 -直流 /直流 -交流的能量传输。 可用于交流 -直流 /直流 -交流变换的 技术主要有基于晶闹管的相控换流器和基于全控型电力电子器件的电压源型换流器两 种。 然而相控换流器在工作时需要外在交流电压源为其提供换相电压， 而且在基于相 控换流器的多端直流输电系统中容易发生连锁换相失败导致系统的崩溃。 基于全控型 电力电子器件的电压源型换流器能够实现有功和无功的独立解耦控制、 能向弱电网或 者孤岛供电、 且易于构成多端直流系统， 在提高系统的稳定性和输电能力等方面具有 很大优势。 近年来， 电压源型高压直流输电在可再生能源接入领域得到广泛应用， 取 得了巨大的发展。
然而随着新型可再生能源容量的不断增大， 高压直流输电系统需要传输的电能越 来越大， 预期到 2015年， 电压源型换流器的典型电压和功率为 ±320kV， 1000MW。 这 对电压源型换流器提出了很高的要求。 传统的两电平电压源型换流器由于受限于全控 型器件的功率等级， 不易实现高压大功率的电能传输。
随着电压源型换流器技术的进一步发展， 现有技术中出现了一种模块化多电平换 流器技术 （MMC) ， 其具有交流输出电压谐波畸变率很小， 模块化结构易于封装， 开 关器件承受更小的电气应力， 开关损耗低等优点， 并且能实现高压大功率等级的电能 传输。 模块化多电平换流器按照子模块拓扑结构的不同， 一般分为半桥型、 全桥型与 箝位双型三种类型。 基于半桥型子模块的模块化多电平换流器是三种类型中最常用的变流器技术， 得 到了学术界与工业界深入的研究与广泛的应用。 2010 年， 世界首条商业运行的 MMC-HVDC系统， 即美国 Trans Bay Cable工程采用的就是半桥型 MMC技术。 上海南 汇示范工程以及广东南澳 3端柔性直流输电工程是国内已经投入运行的 MMC工程； 浙 江舟山的 5端柔性直流输电工程正在建设中， 厦门 2端柔性直流输电工程也处于规划 中。 这些工程均采用的是基于半桥型子模块的 MMC技术。
这些 MMC-HVDC 工程大多采用低故障率的直流电缆线路， 以减少直流故障发生 概率， 但造价昂贵、 经济效益差。 在多端直流输电系统以及直流电网中， 直流侧故障 是工程设计运行必须考虑的一种严重故障类型， 其对设备参数、 控制策略和保护配置 具有重要影响， 然而由于没有成熟的直流断路器设备， 只能通过利用交流侧设备如交 流断路器、 交流熔断器等切断与交流系统的连接， 但该方法响应速度较慢、 重启动配 合动作时序复杂、 系统恢复时间较长。 有效的解决方案是利用换流器自身控制实现直 流侧故障的自清除， 无需机械设备动作， 系统恢复速度快。 随着架空线传输直流电、 三极直流输电技术等的提出， 具有阻断直流故障电流功能的模块化多电平换流器技术 越来越受到重视。
全桥型与箝位双型 MMC由于它们所采用的子模块结构特殊， 具有隔离直流故障的 能力。 但是全桥型与箝位双型 MMC为了实现隔离直流故障的功能， 采用了更多的全控 型电力电子器件。 在相同电压、 功率等级输出条件下， 全桥 MMC比半桥型 MMC增加 了一倍的全控型电力电子器件的数量， 这很大地增加了 MMC的成本； 箝位双型 MMC 的一个子模块中包含两个电容， 比半桥型 MMC 增加了 25%的全控型电力电子器件数 量， 但增加了系统的控制复杂度与子模块封装、 工业设计难度， 降低了系统的可靠 性。
针对具有直流故障隔离功能的换流器中全控型电力电子器件数量过多的问题， 目 前存在一种方式是将箝位双子模块型与半桥型子模块进行串联构成混合型模块化多电 平换流器。 这种混合型换流器在发生直流侧故障后能有效隔离直流故障， 同时全控型 电力电子器件的数量只比半桥型 MMC增加了 17.5%。 但是这种混合型换流器在发生直 流侧故障后， 箝位双子模块型电容会一直处于充电状态， 造成电容电压过大， 必须在 箝位双子模块型中加入阻尼电阻来耗散掉多余的能量， 额外的阻尼电阻会加大子模块 的体积， 散热器， 重量等， 从而加大子模块的制造成本与工艺设计难度， 提高子模块 成本。 【发明内容】
针对现有技术的以上缺陷或改进需求， 本发明提供一种用于模块化多电平换流器 的具有阻断直流故障电流功能的子模块拓扑结构， 相比于现有的具备阻断直流故障电 流的子模块， 其具有减少子模块中全控型电力电子器件的数量， 降低子模块的工艺实 现难度的优点， 使用这些子模块可以构成具备隔离直流故障功能的模块化多电平换流 器。
按照本发明的一个方面， 提供一种用于模块化多电平换流器中的子模块拓扑结构， 其中， 该子模块拓扑结构包括：
相互串联的第一开关模块和第二开关模块，其中第一开关模块的负端与第二开关模 块的正端相连接， 其中所述开关模块由一个全控型器件和一个二极管反并联而成； 以及 直流电容， 其正极和负极分别与第一开关模块的正端和第二开关模块的负端相连 接；
其特征在于， 还包括第三开关模块， 其与上述第一开关模块和第二开关模块电气连 接， 使得正常工作时该第三开关模块的全控型器件一直施加触发脉冲从而一直处于导通 状态， 而发生直流故障时通过闭锁该第三开关模块的触发脉冲实现阻断直流故障电流。
作为本发明的改进， 所述第三开关模块负端与第二开关模块的负端相连接， 第三开 关模块正端作为所述子模块的输出负端，第一开关模块和第二开关模块的连接点作为子 模块的输出正端。
作为本发明的改进，还包括一个第四二极管， 其阳极与第三开关模块的正端相连， 阴极与直流电容的正极相连。
作为本发明的改进，所述第三开关模块正端与第一开关模块和第二开关模块的连接 点连接， 第三开关模块负端作为所述子模块的输出正端， 第二开关模块负端作为所述子 模块的输出负端。
作为本发明的改进，所述第三开关模块负端与第一开关模块和第二开关模块的连接 点连接， 第三开关模块正端作为所述子模块的输出负端， 第一开关模块正端作为所述子 模块的输出正端。
作为本发明的改进， 所述第三开关模块正端与第一开关模块正端连接， 第三开关模 块负端作为所述子模块的输出正端，第一开关模块和第二开关模块的连接点作为所述子 模块的输出负端。
作为本发明的改进，还包括一个第四二极管， 其阳极与直流电容的负端相连， 阴极 与第三开关模块的负端相连。
作为本发明的改进， 所述全控型器件可以是绝缘门极双极型晶体管 （IGBT) 、 集 成门极换流晶闸管 （IGCT) 或门极可关断晶闸管 （GTO) 。
按照本发明的另一方面，提供一种模块化多电平换流器，其包括一个或多个相单元， 每个相单元包括串联连接的上桥臂和下桥臂， 以及与该上桥臂和下桥臂分别对应串联的 桥臂电感， 其中， 上桥臂正端和下桥臂的负端分别与直流母线的正极和负极相连接， 每 个相单元的上桥臂负端和下桥臂正端的连接点处作为 A， B， C三相输出端子引出点， 上桥臂或下桥臂由多个上述子模块拓扑依次串联而成。
按照本发明的又一方面，提供一种模块化多电平换流器，其包括一个或多个相单元， 每个相单元包括串联连接的上桥臂和下桥臂， 以及与该上桥臂和下桥臂分别对应串联的 桥臂电感， 其中， 上桥臂正端和下桥臂的负端分别与直流母线的正极和负极相连接， 每 个相单元的上桥臂负端和下桥臂正端的连接点处作为 A， B， C三相输出端子引出点， 上桥臂或下桥臂由一个或多个上述子模块拓扑与一个或多个半桥型子模块拓扑混合串 联而成。
作为本发明的改进，所述上桥臂或下桥臂中的上述子模块拓扑个数与半桥型子模块 拓扑相同。
按照本发明的再一方面，通过一种利用上述模块化多电平换流器进行阻断直流故障 电流的方法，用于在发生直流故障时阻断该直流故障电流，其特征在于，该方法具体为， 在发生直流故障时， 闭锁所述子模块拓扑的第三开关模块的触发脉冲， 即可断开交流侧 向直流侧提供故障电流的通路。
作为本发明的改进，所述直流故障通过检测直流电流值是否越限， 或检测直流电流 上升速率是否越限等操作判断进行判断。
作为本发明的改进， 所述直流故障为直流侧永久性故障， 其阻断直流故障电流具体 过程为： 首先闭锁所有的全控型器件触发脉冲从而隔离直流故障， 然后关断交流侧断路 器， 以待直流侧故障清除后重新充电运行。
作为本发明的改进， 所述直流故障为直流侧暂时性故障， 其阻断直流故障电流具体 过程为： 首先闭锁所有的全控型器件触发脉冲从而隔离直流故障， 待直流电弧熄灭后， 解锁每个子模块中第三开关模块的全控型器件的触发脉冲， 由交流侧给直流线路充电， 最后解锁其余的全控型器件， 以重新进入稳态运行。 本发明的混合型模块化多电平换流器中， 可以很大程度地减少全控型电力电子器 件的数量， 只需在现有的半桥型 MMC的基础上增加约 25%的全控型电力电子器件就可 以使得混合型换流器具有隔离直流故障电流的功能。
本发明的模块化多电平换流器子模块拓扑结构中， 该子模块由三个开关模块， 一 个直流电容， 子模块输出正端以及子模块输出负端通过一定的电气连接而成， 其中每 个开关模块由一个全控型器件和一个二极管反并联而成。 记全控型器件集电极与二极 管阴极的连接处为开关模块的正端， 全控型器件发射极与二极管阳极的连接处为开关 模块的负端。
本发明中，第一开关模块与第二开关模块依次串联， 第一开关模块的负端与第二开 关模块的正端相连接； 直流电容正极和直流电容的负极分别与第一开关模块的正端和 第二开关模块的负端相连接； 从而完成直流电容、 第一开关模块和第二开关模块的连 接。若分别将子模块输出正端和子模块输出负端与第一， 第二开关模块的连接点和第二 开关模块的负端相连接， 则构成了典型的半桥子模块拓扑， 该拓扑不具备阻断直流故 障电流的能力。
本发明中为使子模块具有阻断直流故障电流的能力， 将第三开关模块的负端与第 二开关模块的负端相连接， 并进一步地将子模块输出正端和子模块输出负端分别与第 第二开关模块的连接点和第三开关模块的正端相连接。 正常工作时第三开关模块 的全控型器件一直施加触发脉冲， 一直处于导通状态， 使得本发明在正常运行时与常 规半桥子模块无异， 发生直流故障时通过闭锁第三开关模块的触发脉冲来达到阻断直 流故障电流的目的。
本发明中，还可以将第三开关模块的正端与第一， 第二开关模块的连接点相连接， 从第三开关模块的负端与直流电容的负极分别引出子模块输出正端及子模块输出负 本发明中，还可以将第三开关模块的负端与第一， 二开关模块的连接点相连接， 从 直流电容的正极与第三开关模块的正端分别引出子模块输出正端和子模块输出负端。
本发明中，还可以将第三开关模块的正端和直流电容正极相连接， 从第三开关模块 的负端和第一， 第二开关模块的连接点处分别引出子模块输出正端和子模块输出负 本发明中，在发生直流故障时通过闭锁第三开关模块的触发脉冲就可以阻断直流故 障电流， 但模块化多电平换流器在电平数较高时， 对闭锁所有第三开关模块触发脉冲 的同时性要求高， 否则子模块中的第三开关模块由于不同时闭锁而导致先闭锁的某个 子模块的第三开关模块中的全控型器件承受全部的交流电压而被烧毁， 为了降低触发 同时性的要求， 可以通过增加一个第四二极管， 从而克服上述缺陷。 。
具体地，第四二极管的阳极可以与第三开关模块的正端相连， 第四二极管的阴极与 直流电容的正极相连。 新增加的第四二极管不会影响新型子模块的正常运行； 在发生 直流侧故障后， 如果故障电流从子模块输出正端流入， 则故障电流从第一开关模块的 反并联二极管后， 经由直流电容再经第三开关模块的反并联二极管流出， 第三开关模 块的全控型器件承受压降几乎为 0; 若故障电流从子模块输出负端流入， 则故障电流流 经由第四二极管、 直流电容、 和第二开关模块的反并联二极管流通， 第三开关模块的 全控型器件承受的电压被箝制在电容电压； 这两种情况均不会导致第三开关模块中全 控型器件由于不同时触发闭锁而承受全部交流电压被烧毁， 从而减少了触发同时性的 要求。
另外，增加的第四二极管， 其阳极还可以与直流电容的负端相连， 第四二极管的阴 极与第三开关模块的负端相连， 也可以达到降低触发同时性的要求的目的。
本发明中，每个相单元的一种连接方式是上桥臂电感的一端连接正极直流母线， 上 桥臂电感的另一端与上桥臂正端相连接， 上桥臂负端与下桥臂正端相连接， 下桥臂负 端与下桥臂电感的一端连接， 下桥臂电感的另一端与负极直流母线相连接， 每个相单 元的上桥臂负端和下桥臂正端连接点处引出 A， B， C三相输出端子。
每个相单元的另一种连接方式是上桥臂的正端与正极直流母线连接， 上桥臂的负 端与上桥臂电感的一端相连接， 上桥臂电感的另一端与下桥臂电感的一端连接， 下桥 臂电感的另一端与下桥臂的正端相连接， 下桥臂的负端与负极直流母线相连接， 每个 相单元的上桥臂电感与下桥臂电感连接处引出 A， B， C三相输出端子。
更进一步地， 上述模块化多电平换流器可以包含一个或多个相单元从而构成一相 或多相模块化多电平换流器。
更进一步地， 本发明还提供了一种由上述子模块与常规半桥子模块构成的混合型 换流器， 其技术细节为将上述由上述子模块构成的模块化多电平换流器的每个桥臂的 一部分上述子模块用常规的半桥型子模块替代从而减少所采用的上述子模块的数量以 减少换流器成本。
更进一步地， 混合型换流器的每个桥臂所包含的常规半桥子模块与上述子模块的 比例为 1 : 1 从而减少为了达到阻断直流故障电流而额外增加的全控型器件数量， 按 1： 1的比例， 只需相比常规半桥型子模块 MMC增加 25%的全控型器件就可以使得混合 型换流器具备阻断直流故障电流的能力。
更进一步地， 本发明还提供了一种利用上述子模块构成的模块化多电平换流器或 混合型模块化多电平换流器的阻断直流故障电流方法， 发生直流故障时通过闭锁新型 子模块的第三开关模块的触发脉冲即可断开交流侧向直流侧提供故障电流的通路从而 阻断直流故障电流。
更进一步地， 本发明方案提出的由新型子模块拓扑构成的单相、 三相或多相模块 化多电平换流器在直流侧发生故障后， 通过以下隔离步骤隔离直流故障。
针对直流侧永久性故障， 隔离步骤 1 : 通过检测直流电流值是否越限， 或检测直流 电流上升速率是否越限等操作判断是否发生直流侧故障； 隔离步骤 2， 已判断发生直流 故障， 则闭锁所有的全控型电力电子器件触发脉冲从而隔离直流故障； 步骤 3， 关断交 流侧断路器， 待直流侧故障清除后， 系统再重新充电运行。
针对直流侧暂时性故障， 隔离步骤 1 : 通过检测直流电流值是否越限， 或检测直流 电流上升速率是否越限等操作判断是否发生直流侧故障； 隔离步骤 2， 若已判断发生直 流故障， 则闭锁所有的全控型电力电子器件触发脉冲从而隔离直流故障； 隔离步骤 3， 待直流电弧熄灭后， 解锁每个子模块中第三开关模块的全控型电力电子器件触发脉 冲， 由交流侧给直流线路充电； 隔离步骤 4， 解锁其余的全控型电力电子器件， 恢复控 制， 系统重新进入稳态运行。
总体而言， 通过本发明所构思的以上技术方案与现有技术相比， 具有以下有益效 果： 本发明提供的新型子模块拓扑可以实现隔离直流故障功能， 且相比于全桥型子模 块、 箝位双型子模块与二极管箝位型子模块， 减少了子模块中开关器件的数量与开关 损耗， 降低了结构设计与工业应用的难度。
【附图说明】
图 1是常规的半桥型子模块的拓扑结构图；
图 2是常规的全桥型子模块的拓扑结构图；
图 3是常规的箝位双型子模块的拓扑结构图；
图 4是二极管箝位型子模块拓扑结构图；
图 5是本发明子模块的第一实施例的拓扑结构图；
图 6是本发明子模块的第二实施例的拓扑结构图； 图 7是本发明子模块的第三实施例的拓扑结构图；
图 8是本发明子模块的第四实施例的拓扑结构图；
图 9是本发明子模块的第五实施例的拓扑结构图；
图 10是本发明子模块的第六实施例的拓扑结构图；
图 11是由本发明子模块 （第一实施例至第六实施例） 构成的第一种三相模块化多 电平换流器拓扑；
图 12是由本发明子模块 （第一实施例至第六实施例） 构成的第二种三相模块化多 电平换流器拓扑；
图 13是本发明实施例提供的由子模块多种实施例和半桥型子模块构成的三相混合 型模块化多电平换流器结构示意图；
图 14是由新型子模块构成的三相 9电平的模块化多电平换流器仿真示意图； 图 15是图 14所示的模块化多电平换流器简化分析电路图
图 16是本发明实施例提供的三相模块化多电平换流器在故障后 IGBT闭锁瞬间的 等值电路图；
图 17是本发明实施例提供的三相 9电平模块化多电平换流器的子模块电容电压值 的仿真波形图；
图 18是本发明实施例提供的三相 9电平模块化多电平换流器的上桥臂电流值的仿 真波形图。
【具体实肺式】
为了使本发明的目的、 技术方案及优点更加清楚明白， 以下结合附图及实施例， 对本发明进行进一步详细说明。 应当理解， 此处所描述的具体实施例仅仅用以解释本 发明， 并不用于限定本发明。 此外， 下面所描述的本发明各个实施方式中所涉及到的 技术特征只要彼此之间未构成冲突就可以相互组合。
本发明实施例提供的新型子模块拓扑主要用于构造新型模块化多电平换流器， 使 得新型模块化多电平换流器用于两端直流输电， 多端直流输电以及直流电网中， 其显 著的技术性表现在相比于常规的不具备阻断直流故障电流能力的半桥型模块化多电平 换流器， 只需要增加 25%的全控型器件就可以使得新型的模块化多电平换流器具备阻 断直流故障电流的能力， 相比于全桥型子模块与箝位双子模块型减少了子模块数量与 开关损耗， 更利于工程设计与实现。
图 1 所示已公知的常规半桥型子模块拓扑， 发生直流故障时， 换流器所连接的交 流系统将通过下部二极管 D2给直流故障电流供电从而使得直流电弧难以熄灭， 并使交 流系统处于短路状态， D2 流经较大的故障电流有可能被烧毁， 需要断开交流侧开关以 切断直流故障电流， 从而大大延迟了系统恢复供电的时间。
如图 2 所示为已公知的全桥子模块拓扑， 该拓扑具备阻断直流故障电流的能力， 但对比图 1和图 2可以明显看出， 全桥子模块拓扑所采用的开关器件数量为半桥子模 块的 2倍， 成本大大增加。
如图 3 所示的箝位双子模块拓扑， 在发生直流侧故障时， 将闭锁所有全控型器 件， 箝位双子模块在故障时刻存在两条放电通路， 但由于两条通路下直流电容电压之 和大于交流系统线电压幅值， 将导致二极管被反向阻断， 从而隔离直流故障。 但是箝 位双子模块型采用了更多的半导体器件， 增加了工艺设计的难度； 同时由于闭锁后， 直流网络储存的能量主要由子模块电容吸收， 如果能量过大会引起子模块电容电压增 加幅度大， 引起的过电压问题可能烧毁半导体器件。
图 4所示的二极管箝位型子模块拓扑， 该结构采用了三个 IGBT器件、 两个直流电 容器， 利用二极管箝位来实现直流故障的隔离。 但该拓扑采用了两个电容器， 增加了 子模块的体积与设计成本。
图 5 为本发明所提出的子模块的第一实施例， 该新型子模块由三个开关模块 1〜 3， 一个直流电容 4， 子模块输出正端 5和子模块输出负端 6构成。 每个开关模块由全控 型器件 (Tl, T2, T3)和二极管 (Dl, D2, D3)反向并联而成。
记全控型器件与二极管阴极的连接处为开关模块的正端， 全控型器件与二极管阳 极的连接处为开关模块的负端。 直流电容 4的正极和负极分别与第一开关模块 1的正端 和第二开关模块 2的负端相连接， 第一开关模块 1的负端与第二开关模块 2的正端相连 接， 从而完成直流电容 4， 第一开关模块 1和第二开关模块 2的连接， 若分别从第一， 第二开关模块的连接点以及第二开关模块 2的负端引出子模块输出正端 5和子模块输出 负端 6， 则构成了与图 1完全一致的典型的半桥子模块拓扑， 该拓扑不具备阻断直流故 障电流的能力。
为使子模块具有阻断直流故障电流的能力， 本实施例中， 将第三开关模块 3的负端 与第二开关模块 2的负端相连接， 并进一步地将子模块输出正端 5和子模块输出负端 6 分别与第一开关模块 1， 第二开关模块 2的连接点和第三开关模块 3的正端相连接。 正 常工作时会一直给第三开关模块 3的全控型器件施加触发脉冲使得本发明实施例在正常 运行时与常规半桥子模块无异， 发生直流故障时通过闭锁第三开关模块 3的触发脉冲可 以阻断直流故障电流的通流途径。
图 6 所示为本发明子模块的第二实施例， 其与第一实施例不同之处仅在于， 第三 开关模块 3的正端与第一开关模块 1的负端相连接， 从第三开关模块 3的负端与直流电 容 4的负极 (第二开关模块 2的负端)分别引出子模块输出正端 5及子模块输出负端 6。
图 7 为本发明子模块的第三的实施例， 其与第一实施例不同之处仅在于， 第三开 关模块 3的负端与第一开关模块 1的负端（该连接点也为第一开关模块 1与第二开关模 块 2的连接点）相连接， 从直流电容 4的正极（第一开关模块 1的正极） 与第三开关模 块 3的正端分别引出子模块输出正端 5和子模块输出负端 6。
图 8 为本发明子模块的第四实施例， 其与第一实施例不同之处仅在于， 第三开关 模块 3的正端和直流电容 4的正极（第一开关模块 1的正极）相连接， 从第三开关模块 3的负端和第一开关模块 1的负端分别引出子模块输出正端 5和子模块输出负端 6。
上述四种方案构成的模块化多电平换流器在直流侧发生故障后， 对闭锁每个桥臂 的第三开关模块 3中全控型器件的触发脉冲同时性要求很高。 否则子模块中的第三开关 模块 3由于不同时闭锁而导致先闭锁的某个子模块的第三开关模块 3中的全控型器件承 受全部的交流电压而被烧毁， 为减小触发同时性的要求， 使本发明能更好地应用于高 电平数的模块化多电平换流器， 可以进一步增加一个第四二极管构成新的实施方案。 图 9为本发明子模块的的第五实施例， 其与第一实施例不同之处仅在于， 增加了一个第四 二极管 7， 该二极管 7的阳极与第三开关模块 3的正端相连， 将二极管 7的阴极与直流 电容 4的正极 （第一开关模块 1的正极） 相连。
新增加的二极管 7不影响子模块的正常运行； 在发生直流侧故障后， 若故障电流从 子模块输出正端 5流入， 则故障电流流经第一开关模块一的反并联二极管后， 经由直流 电容 4再从第三开关模块 3的反并联二极管流通， 第三开关模块的全控型器件承受压降 几乎为 0; 若故障电流从子模块输出负端 6流入， 则故障电流流经二极管 7、 直流电容 4、 第二开关模块 2的反并联二极管流通， 第三开关模块 3中的全控型器件承受的电压 被箝制在电容电压； 这两种情况均不会导致第三开关模块 3中全控型器件由于不同时触 发闭锁而承受全部交流电压被烧毁， 从而减少了触发同时性的要求。
图 10 为本发明子模块的第六实施例， 其与第四实施例不同之处仅在于， 增加一个 二极管 7， 该二极管 7的阳极与直流电容 4的负端相连， 将该二极管的阴极与第三开关 模块 3的负端相连。
图 11 所示为由本发明所提出的由上述子模块构成的三相模块化多电平换流器拓 扑， 该新型三相模块化多电平换流器包括三个相单元 11， 每个相单元由上桥臂 12， 上 桥臂电感 13， 下桥臂电感 14， 下桥臂 15依次串联而成， 每个桥臂由 N个子模块依次串 联而成， 每个相单元 11的正端与正极直流母线 16相连接， 相单元 11的负端与直流负 极母线 17相连接， 从每个上桥臂电感， 下桥臂电感的连接点处分别引出交流输出端子 8〜10。 每个桥臂的具体连接方式示于图 11左侧。
图 12所示为由本发明所提出的新型子模块改进型构成的新型三相模块化多电平换 流器的另一种实现方式， 该拓扑与图 11基本类似， 区别仅在于构成每个相单元的桥臂 与桥臂电感的连接先后次序不同。 该新型三相模块化多电平换流器包括三个相单元 11， 每个相单元由上桥臂电感 13， 上桥臂 12， 下桥臂 15， 下桥臂电感 14依次串联而 成， 从每个上桥臂， 下桥臂的连接点处分别引出交流输出端子 8〜10， 该方案其他部件 实现形式与图 11完全一致， 不再赘述。
本发明中，根据新型模块化多电平换流器传输功率的大小， 每个新型模块化多电平 换流器可以由一个或多个相单元组成从而构成一相或多相新型模块化多电平换流器， 并 不限定于图 11和图 12实施例所述的相单元数量。
图 13 为由新型子模块改进型拓扑和常规半桥型子模块混合而成的混合型换流器， 图 13拓扑与图 11拓扑基本一致， 区别在于每个桥臂 12， 15由多个新型子模块和常规 半桥型子模块混合串联而成， 其中新型子模块和常规半桥子模块的串联次序任意。 所 述的新型子模块可以是上述实施例一至实施例六中的任何一种。
每个桥臂所使用的新型子模块与常规半桥子模块的数量比例优选值为 1 : 1， 这样 在发生直流故障时通过闭锁所有新型子模块的触发脉冲可以阻断直流故障电流同时又 因为选择了足够数量的新型子模块， 新型子模块的第三开关模块 3不会因为承载过电压 而烧毁。 图 14为本发明实施例提出的由新型子模块构成的三相 9电平模块化多电平换 流器仿真示意图。 为分析方便， 取出图 14的一相来进行分析， 并将上下桥臂 8个新型 子模块分别等效为一个子模块， 如图 15所示。 电容 22、 28为上下桥臂的等效串联电 容值， 电容电压分别是上桥臂、 下桥臂子模块电容电压之和。 当发生直流侧极对极短 路故障 29后， 将闭锁开关模块 19、 20、 21、 24、 25、 26中的全控型器件。 假设故障电 流从交流侧流向直流侧， 上桥臂由于 IGBT 闭锁， 故障电流只能通过二极管 23、 电容 22和开关模块 20中的反并联二极管流通， 但上桥臂电容电压之和维持在直流电压 Udc 附近， 而交流侧相电压幅值是小于 [^的， 二极管承受反压而无法导通， 上桥臂没有导 电通路； 下桥臂的故障电流也只能通过开关模块 24、 26中的反并联二极管和电容 27构 成导电通路， 但是由于下桥臂电容电压之和维持在直流电压 [^附近， 而交流侧相电压 幅值是小于 [^的， 二极管承受反压而无法导通， 下桥臂没有导电通路。
假设故障电流从直流侧流向交流侧， 上桥臂故障电流的可能路径为电容 22和开关 模块 19、 21 中的反并联二极管， 但上桥臂电容电压之和维持在直流电压 [^附近， 二 极管承受反压而无法导通， 上桥臂没有导电通路； 下桥臂的可能故障电流路径为开关 模块 24、 中的反并联二极管、 电容 27和二极管 28， 但是由于下桥臂电容电压之和维持 在直流电压 [^附近， 二极管承受反压而无法导通， 下桥臂没有导电通路。 从而交流电 源 30无法向故障点提供短路电流， 实现了直流故障的隔离。
在发生直流侧故障后， 换流器在闭锁瞬间的等值电路如图 16所示。 取 [/m为三相 电源相电压幅值 （即相对地的电压最大值） ， ^为子模块额定电容电压， N为每个桥臂 上子模块的个数， 为桥臂子模块电容电压之和， Uarm=Nnjc。 为了达到隔离直流侧 故障功能， 需要满足下式：
(1) 取换流器电压调制比为 则:
Figure imgf000014_0001
在换流器正常运行时， 必须满足调制比 < 1， 从而：
(3) 然而直流侧电压 [^为 N个子模块额定电容电压之和， 即
1 1 N
-U , = -* NU =— *U (4)
2 2 c 2
由式 （1 ) 与式 （4) 可知， 每相桥臂只需要 N/2个新型子模块就可以达到隔离直流 故障功能。 为此图 13所示的混合型换流器中， 每个桥臂所使用的新型子模块与常规半 桥子模块的数量比例优选值为 1 : 1。
为验证本发明的技术可行性， 利用国际通用直流输电仿真软件 PSCAD/EMTDC搭 建了与对应的仿真算例进行仿真验证。
仿真算例中， 各个器件都采用 PSCAD/EMTDC标准模型库中的详细模型。 系统额 定容量为 1000 MVA , 额定交流电压为 230kV， 直流电压为 ±200kV,子模块电容为 300(^F， 桥臂电感为 0.0154H, 上下桥臂各 8个子模块。 相应仿真结果如图 17和图 18所示， 图 17为子模块电容电压值， 图 18为直流电 流值。 仿真时间 Is 时， 系统在换流器直流侧出口处发生永久性极对极直流短路故障。 从图 17可以看出， 在发生短路故障， 全控型器件触发脉冲被闭锁后， 子模块电容电压 值几乎维持在额定电压值附近； 从图 18可以看出在发生直流侧短路故障后， 直流故障 电流立即下降至 0， 能有效隔离直流故障。
需要指出的是， 图 17和图 18主要用于对本发明所提出的新型子模块进行原理性 验证， 子模块的额定电压值为 50kV。 图 17和图 18所验证的原理可以推广应用到实际 中的任意电平数 MMC。
本发明实例提出的混合型换流器拓扑， 具备隔离直流故障功能， 相比于不具备阻 断直流故障电流的公知半桥型 MMC仅仅增加了 25%的子模块数量。 相比于已有的具有 阻断直流故障电流能力的 MMC， 不需要额外的阻尼电阻， 减少了成本、 降低了工业设 计的难度， 具有相当大的工业应用价值。
本领域的技术人员容易理解， 以上所述仅为本发明的较佳实施例而已， 并不用以 限制本发明， 凡在本发明的精神和原则之内所作的任何修改、 等同替换和改进等， 均 应包含在本发明的保护范围之内。

Claims

m
1、 一种用于模块化多电平换流器中的子模块拓扑结构， 其中， 该子模块拓扑结构 包括：
相互串联的第一开关模块 （1) 和第二开关模块 （2) ， 其中第一开关模块 （1) 的 负端与第二开关模块 （2) 的正端相连接；
直流电容（4)，其正极和负极分别与第一开关模块（1)的正端和第二开关模块（2) 的负端相连接；
其特征在于， 还包括第三开关模块 （3) ， 其与上述第一开关模块 （1) 和第二开关 模块 （2) 电气连接， 使得正常工作时该第三开关模块 （3) 的全控型器件一直施加触发 脉冲从而一直处于导通状态， 而发生直流故障时通过闭锁该第三开关模块 （3) 的触发 脉冲实现阻断直流故障电流， 其中， 所述各开关模块 （1、 2、 3) 均由一个全控型器件 和一个二极管反并联而成。
2、 根据权利要求 1所述的用于模块化多电平换流器中的子模块拓扑结构， 其中， 所述第三开关模块 （3) 负端与第二开关模块 （2) 的负端相连接， 第三开关模块 （3) 正端作为所述子模块的输出负端 （6) ， 第一开关模块和第二开关模块的连接点作为子 模块的输出正端 （5) 。
3、 根据权利要求 2所述的用于模块化多电平换流器中的子模块拓扑结构， 其中， 还包括一个第四二极管 （7) ， 其阳极与第三开关模块 （3) 的正端相连， 阴极与直流电 容（4) 的正极相连， 以减小所述第三开关模块 （3) 的全控型器件的触发脉冲同时性要 求。
4、 根据权利要求 1所述的用于模块化多电平换流器中的子模块拓扑结构， 其中， 所述第三开关模块 （3) 正端与第一开关模块 （1) 和第二开关模块 （2) 的连接点连接， 第三开关模块 （3) 负端作为所述子模块的输出正端 （5) ， 第二开关模块 （2) 负端作 为所述子模块的输出负端 （6) 。
5、 根据权利要求 1所述的用于模块化多电平换流器中的子模块拓扑结构， 其中， 所述第三开关模块 （3) 负端与第一开关模块 （1) 和第二开关模块 （2) 的连接点连接， 第三开关模块 （3) 正端作为所述子模块的输出负端 （6) ， 第一开关模块 （1) 正端作 为所述子模块的输出正端 （5) 。
6、 根据权利要求 1所述的用于模块化多电平换流器中的子模块拓扑结构， 其中， 所述第三开关模块 （3) 正端与第一开关模块 （1) 正端连接， 第三开关模块 （3) 负端 作为所述子模块的输出正端 （5 ) ， 第一开关模块 （1 ) 和第二开关模块 （2) 的连接点 作为所述子模块的输出负端 （6) 。
7、 根据权利要求 6所述的用于模块化多电平换流器中的子模块拓扑结构， 其中， 还包括一个第四二极管 （7) ， 其阳极与直流电容 （4) 的负端相连， 阴极与第三开关模 块（3 ) 的负端相连， 以减小所述第三开关模块 （3 ) 的全控型器件的触发脉冲同时性要 求。
8、 根据权利要求 1-7 中任一项所述的用于模块化多电平换流器中的子模块拓扑结 构， 其中， 所述全控型器件可以是绝缘门极双极型晶体管 （IGBT) 、 集成门极换流晶 闸管 （IGCT) 或门极可关断晶闸管 （GTO) 。
9、 一种模块化多电平换流器， 其包括一个或多个相单元 （11 ) ， 每个相单元 （11 ) 包括串联连接的上桥臂 （12) 和下桥臂 （15 ) ， 以及与该上桥臂 （12) 和下桥臂 （15 ) 分别对应串联的桥臂电感 （13、 14) ， 其中， 上桥臂 （12) 正端和下桥臂 （15 ) 的负端 分别与直流母线的正极 （16) 和负极 （17) 相连接， 每个相单元 （11 ) 的上桥臂 （12) 负端和下桥臂 （15 ) 正端的连接点处作为 A， B， C三相输出端子引出点， 上桥臂 （12) 或下桥臂 （15 ) 由一个或多个上述权利要求 1-8中任一项或多项所述的子模块拓扑串联 而形成。
10、 一种混合型模块化多电平换流器， 其包括一个或多个相单元 （11 ) ， 每个相单 元包括串联连接的上桥臂 （12)和下桥臂（15 ) ， 以及与该上桥臂（12)和下桥臂（15 ) 分别对应串联的桥臂电感 （13、 14) ， 其中， 上桥臂 （12) 正端和下桥臂 （15 ) 的负端 分别与直流母线的正极 （16) 和负极 （17) 相连接， 每个相单元 （11 ) 的上桥臂 （12) 负端和下桥臂 （15 ) 正端的连接点处作为 A， B， C三相输出端子引出点， 上桥臂 （12) 或下桥臂 （15 ) 由一个或多个上述权利要求 1-8中任一项所述的子模块拓扑与一个或多 个半桥型子模块拓扑混合串联而成。
11、 根据权利要求 10所述的一种模块化多电平换流器， 其中， 所述上桥臂 （12) 或下桥臂 （15 ) 中的上述子模块拓扑个数与半桥型子模块拓扑相同。
12、 一种利用上述权利要求 9-11 中任一项所述的模块化多电平换流器进行阻断直 流故障电流的方法， 用于在发生直流故障时阻断该直流故障电流， 其特征在于， 该方法 具体为， 在发生直流故障时， 闭锁所述子模块拓扑的第三开关模块 （3 ) 的触发脉冲， 即可断开交流侧向直流侧提供故障电流的通路。
13、 根据权利要求 12所述的方法， 其中， 所述直流故障通过检测直流电流值是否 越限， 或检测直流电流上升速率是否越限进行判断。
14、根据权利要求 12或 13所述的方法，其中，所述直流故障为直流侧永久性故障， 其阻断直流故障电流具体过程为： 首先闭锁所有的全控型器件触发脉冲从而隔离直流故 障， 然后开断交流侧断路器， 以待直流侧故障清除后重新充电运行。
15、根据权利要求 12或 13所述的方法，其中，所述直流故障为直流侧暂时性故障， 其阻断直流故障电流具体过程为： 首先闭锁所有的全控型器件触发脉冲从而隔离直流故 障， 待直流电弧熄灭后， 解锁每个子模块中第三开关模块的全控型器件的触发脉冲， 由交流侧给直流线路充电， 最后解锁其余的全控型器件， 以重新进入稳态运行。
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