WO2020258512A1 - 混合直流输电系统中mmc的启动方法和系统 - Google Patents

混合直流输电系统中mmc的启动方法和系统 Download PDF

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Publication number
WO2020258512A1
WO2020258512A1 PCT/CN2019/104256 CN2019104256W WO2020258512A1 WO 2020258512 A1 WO2020258512 A1 WO 2020258512A1 CN 2019104256 W CN2019104256 W CN 2019104256W WO 2020258512 A1 WO2020258512 A1 WO 2020258512A1
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Prior art keywords
mmc
module
full
bridge
voltage
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PCT/CN2019/104256
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English (en)
French (fr)
Inventor
栾洪洲
闻福岳
薛飞
张帆
黄金魁
曹均正
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中电普瑞电力工程有限公司
南瑞集团有限公司
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Publication of WO2020258512A1 publication Critical patent/WO2020258512A1/zh

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    • 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
    • H02M1/36—Means for starting or stopping converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

Definitions

  • This application relates to the technical field of flexible direct current transmission, and in particular to a method and system for starting MMC in a hybrid direct current transmission system.
  • MMC-HVDC Modular multilevel converter high voltage direct current transmission
  • VSC-HVDC voltage source converter high voltage direct current transmission
  • MMC modular multilevel converters
  • the full-bridge sub-module MMC with DC fault clearing capability.
  • the high-voltage DC transmission system based on the full-bridge sub-module MMC can quickly block or output negative after a DC line failure occurs. It cuts off the DC fault current without tripping the AC side circuit breaker. After the fault is removed, the system can quickly resume operation. Therefore, the full-bridge submodule MMC is more suitable for hybrid DC transmission systems based on long-distance overhead lines.
  • the number of power switching devices used in the full-bridge sub-module is twice that of the half-bridge sub-module, so the cost and loss are greatly increased.
  • the capacitor voltage of the full-bridge sub-module and the half-bridge sub-module are inconsistent after the uncontrolled charging is completed; For controllable charging, it may happen that the capacitance of the full-bridge sub-module reaches or exceeds the rated voltage and the capacitance of the half-bridge sub-module does not reach the rated voltage, and the startup cannot be completed.
  • the embodiment of the present application proposes a method and system for starting an MMC in a hybrid direct current transmission system, which can at least avoid the problem that the MMC cannot be started and completed.
  • the embodiment of the application provides a method for starting MMC in a hybrid direct current transmission system.
  • the hybrid direct current transmission system is composed of an alternating current system equivalent power source, an alternating current circuit breaker, a starting resistor, and an MMC connected in sequence. The two ends of the starting resistor are connected in parallel Starting the resistance bypass switch, the MMC is composed of a half-bridge sub-module and a full-bridge sub-module, and the method includes:
  • Controllable charging is performed on the MMC until the capacitor voltage of the half-bridge sub-module and the capacitor voltage of the full-bridge sub-module in the MMC both reach the startup rated voltage of the MMC.
  • the uncontrolled charging of the MMC until the capacitor voltage of the half-bridge sub-module in the MMC reaches the first preset voltage and the capacitor voltage of the full-bridge sub-module reaches the second preset voltage includes:
  • the operation ends when the capacitor voltage of the half-bridge sub-module in the MMC is charged to the first preset voltage and the capacitor voltage of the full-bridge sub-module in the MMC is charged to the second preset voltage.
  • the first preset voltage U F is determined as follows;
  • U M AC power line voltage peak value equivalent system N F is the number of full-bridge MMC submodule; N H is the number of sub-half-bridge module MMC.
  • controllable charging of the MMC until the capacitor voltage of the half-bridge sub-module and the capacitor voltage of the full-bridge sub-module in the MMC both reach the startup rated voltage of the MMC includes:
  • One end of the power switch tube T4 of the full-bridge sub-module in the MMC is connected to the negative voltage of the full-bridge sub-module, and the other end is connected to the negative electrode of the capacitor in the full-bridge sub-module.
  • the voltage equalization control charging is performed on the MMC until the capacitor voltage of the half-bridge sub-module and the capacitor voltage of the full-bridge sub-module in the MMC both reach the third preset voltage, including:
  • Step 2 Control the working state of the AC circuit breaker to be closed, the working state of the starting resistance bypass switch to be open, and the working state of the half-bridge submodule in the MMC to be locked;
  • Step 3 Select N 1 full bridge submodules from all the full bridge submodules of the MMC, and control the bypass of the N 1 full bridge submodules, and the remaining full bridge submodules are blocked;
  • the step 3 includes:
  • U M is the equivalent power line voltage peak value of the AC system
  • N F is the number of full-bridge sub-modules in MMC
  • N H is the number of half-bridge sub-modules in MMC
  • U is the third preset voltage
  • the full-bridge sub-module half-bridge of the MMC until the power switch tubes T4 of the full-bridge sub-module in the MMC are all turned on includes:
  • the working state of the AC circuit breaker is controlled to be closed, the working state of the starting resistance bypass switch is closed, the working state of the half-bridge sub-module in the MMC is locked, and the working state of the full-bridge sub-module in the MMC is atresia;
  • the overall turn-on charging of the MMC until the capacitor voltage of the half-bridge sub-module and the capacitor voltage of the full-bridge sub-module in the MMC both reach the startup rated voltage of the MMC includes:
  • Step 5 Control the working state of the AC circuit breaker to be closed and the working state of the starting resistance bypass switch to be closed;
  • Step 6 Select N 2 sub-modules from all the sub-modules of the MMC, and control the N 2 sub-modules to bypass, and the remaining sub-modules are blocked;
  • the step 6 includes:
  • U M is the equivalent power line voltage peak value of the AC system
  • N F is the number of full-bridge sub-modules in MMC
  • N H is the number of half-bridge sub-modules in MMC
  • U C is the start of the modular multi-level converter Rated voltage value
  • the MMC neutron modules Arrange the MMC neutron modules in descending order according to the capacitance voltage of the MMC neutron modules, and select the first N 2 submodules in the sequence; wherein, the MMC neutron modules include the full bridge submodule and the half Bridge submodule.
  • the embodiment of the present application also provides a starting system for MMC in a hybrid direct current transmission system.
  • the hybrid direct current transmission system consists of an alternating current system equivalent power source, an alternating current circuit breaker, a starting resistor, and an MMC connected in sequence, and both ends of the starting resistor Parallel start resistance bypass switch, the MMC is composed of a half-bridge sub-module and a full-bridge sub-module, the improvement lies in that the system includes:
  • the uncontrolled charging module is configured to uncontrollably charge the MMC until the capacitor voltage of the half-bridge sub-module in the MMC reaches a first preset voltage and the capacitor voltage of the full-bridge sub-module reaches a second preset voltage;
  • the controllable charging module is configured to controllably charge the MMC until the capacitor voltage of the half-bridge sub-module and the capacitor voltage of the full-bridge sub-module in the MMC both reach the startup rated voltage of the MMC.
  • the uncontrolled charging module is configured as:
  • the operation ends when the capacitor voltage of the half-bridge sub-module in the MMC is charged to the first preset voltage and the capacitor voltage of the full-bridge sub-module in the MMC is charged to the second preset voltage.
  • the first preset voltage U F is determined as follows ;
  • U M AC power line voltage peak value equivalent system N F is the number of full-bridge MMC submodule; N H is the number of sub-half-bridge module MMC.
  • controllable charging module includes:
  • a voltage equalization control charging unit configured to perform voltage equalization control charging on the MMC until the capacitor voltage of the half-bridge sub-module and the capacitor voltage of the full-bridge sub-module in the MMC both reach the third preset voltage;
  • the full-bridge sub-module half-bridge unit is configured to perform the full-bridge sub-module half-bridge on the MMC until the power switch tubes T4 of the full-bridge sub-module in the MMC are all turned on;
  • An overall alternate conduction charging unit configured to perform overall alternate conduction charging on the MMC until the capacitor voltage of the half-bridge sub-module and the capacitor voltage of the full-bridge sub-module in the MMC both reach the startup rated voltage of the MMC;
  • One end of the power switch tube T4 of the full-bridge sub-module in the MMC is connected to the negative voltage of the full-bridge sub-module, and the other end is connected to the negative electrode of the capacitor in the full-bridge sub-module.
  • the voltage equalization control charging unit is configured as:
  • Step 2 Control the working state of the AC circuit breaker to be closed, the working state of the starting resistance bypass switch to be open, and the working state of the half-bridge submodule in the MMC to be locked;
  • Step 3 Select N 1 full bridge submodules from all the full bridge submodules of the MMC, and control the bypass of the N 1 full bridge submodules, and the remaining full bridge submodules are blocked;
  • the voltage equalization control charging unit is further configured to: for the step 3:
  • U M is the equivalent power line voltage peak value of the AC system
  • N F is the number of full-bridge sub-modules in MMC
  • N H is the number of half-bridge sub-modules in MMC
  • U is the third preset voltage
  • the full-bridge sub-module and half-bridge unit is configured as:
  • the working state of the AC circuit breaker is controlled to be closed, the working state of the starting resistance bypass switch is closed, the working state of the half-bridge sub-module in the MMC is locked, and the working state of the full-bridge sub-module in the MMC is atresia;
  • the overall turn-on charging unit is configured as:
  • Step 5 Control the working state of the AC circuit breaker to be closed and the working state of the starting resistance bypass switch to be closed;
  • Step 6 Select N 2 sub-modules from all the sub-modules of the MMC, and control the N 2 sub-modules to bypass, and the remaining sub-modules are blocked;
  • the overall turn-on charging unit is further configured to: for the step 6:
  • U M is the equivalent power line voltage peak value of the AC system
  • N F is the number of full-bridge sub-modules in MMC
  • N H is the number of half-bridge sub-modules in MMC
  • U C is the start of the modular multi-level converter Rated voltage value
  • the MMC neutron modules Arrange the MMC neutron modules in descending order according to the capacitance voltage of the MMC neutron modules, and select the first N 2 submodules in the sequence; wherein, the MMC neutron modules include the full bridge submodule and the half Bridge submodule.
  • the technical solution provided by the embodiment of the application performs uncontrolled charging of the MMC until the capacitor voltage of the half-bridge sub-module in the MMC reaches the first preset voltage and the capacitor voltage of the full-bridge sub-module reaches the second preset voltage;
  • the MMC performs controllable charging until the capacitor voltage of the half-bridge sub-module and the capacitor voltage of the full-bridge sub-module in the MMC both reach the start-up rated voltage of the MMC; a voltage equalization control charging stage is added in the controllable charging stage to In this way, the capacitor voltages of the full-bridge sub-module and the half-bridge sub-module of the MMC tend to be the same, and then the full-bridge sub-modules are half-bridged and the overall alternate conduction charging is performed on the MMC in turn, so that the capacitor voltage of the MMC neutron sub-module reaches the rated voltage at the same time Value, reducing the error rate of MMC startup, at least avoiding the problem of failing to start MMC
  • Fig. 1 is a flowchart of a method for starting MMC in a hybrid DC transmission system in an embodiment of the application;
  • Figure 2 is a diagram of the network topology of the hybrid DC transmission system in an embodiment of the application
  • FIG. 3 is a diagram of the topology structure of the MMC network in an embodiment of the application.
  • FIG. 4 is a flow chart of a startup system of MMC in a hybrid direct current transmission system in an embodiment of the application;
  • Figures 5 (a) and (b) are schematic diagrams of the structure of a full-bridge sub-module and a half-bridge sub-module in an embodiment of the application.
  • the embodiment of the application provides a method for starting MMC in a hybrid direct current transmission system.
  • the hybrid direct current transmission system is composed of an alternating current system equivalent power source, an alternating current circuit breaker, a starting resistor, and an MMC connected in sequence.
  • the two ends of the starting resistor are connected in parallel
  • Starting the resistance bypass switch the MMC is composed of a half-bridge sub-module and a full-bridge sub-module, as shown in Figure 1, the method includes:
  • Step 101 Uncontrolled charging of the MMC until the capacitor voltage of the half-bridge sub-module in the MMC reaches a first preset voltage and the capacitor voltage of the full-bridge sub-module reaches a second preset voltage;
  • the number of half-bridge sub-modules and full-bridge sub-modules on each bridge arm of the MMC is the same.
  • Step 102 Controllably charge the MMC until the capacitor voltage of the half-bridge sub-module and the capacitor voltage of the full-bridge sub-module in the MMC both reach the startup rated voltage of the MMC;
  • startup is the basis for the normal operation of the flexible DC transmission system.
  • the essence of startup is that the active AC system charges the MMC sub-module capacitors uncontrollably and controllably through the startup resistor, and finally makes the sub-module capacitor voltage reach Rated value.
  • the initial state of the AC circuit breaker is open, the initial state of the starting resistance bypass switch is open, the initial state of the half-bridge submodule in the MMC is locked, and the full bridge submodule in the MMC The initial state is locked.
  • the initial state in the embodiment of the present application is a state in which the MMC in the embodiment of the present application neither performs controlled charging nor uncontrolled charging.
  • the state of at least one of the above four devices will change when the MMC performs controlled charging or uncontrolled charging. For details, see Follow-up related instructions.
  • the above four devices are equivalent to all being in the non-working state, preparing for the subsequent MMC to enter the controlled charging phase or the uncontrolled charging phase.
  • the network topology structure of the hybrid direct current transmission system is shown in FIG. 2.
  • U S equivalent to the AC system power source (comprising a U sa and U sb), AC_BRK AC circuit breaker, R is the startup resistor, R_BRK resistor bypass switch to start, U DC of the DC voltage mixed MMC.
  • the hybrid MMC in the embodiments of the present application refers to an MMC that includes both a half-bridge sub-module and a full-bridge sub-module, which will be referred to as MMC in the following.
  • each half-bridge sub-module in MMC is composed of insulated gate bipolar transistor (IGBT) power device T5, IGBT power device T6 and capacitor C2;
  • IGBT insulated gate bipolar transistor
  • each full-bridge sub-module in the MMC consists of an IGBT power device T1, an IGBT power device T2, an IGBT power device T3, an IGBT power device T4, and a capacitor C2.
  • Fig. 3 is a network topology structure diagram of a hybrid MMC in an embodiment of the application. 3, the full-bridge comprising N F N H submodule and a half bridge module. Among them, point 1 is the positive voltage of the full-bridge sub-module; point 2 is the negative voltage of the full-bridge sub-module. P is the positive pole of the power supply of the hybrid MMC, and N is the negative pole of the power supply of the hybrid MMC.
  • one end of the power switch tube T1 of the full-bridge sub-module in the MMC is connected to the positive voltage of the full-bridge sub-module, and the other end is connected to the positive electrode of the capacitor in the full-bridge sub-module
  • One end of the power switch tube T2 of the full-bridge sub-module in the MMC is connected to the negative voltage of the full-bridge sub-module, and the other end is connected to the positive electrode of the capacitor in the full-bridge sub-module
  • One end of the power switch tube T3 of the full-bridge sub-module in the MMC is connected to the positive voltage of the full-bridge sub-module, and the other end is connected to the negative electrode of the capacitor in the full-bridge sub-module
  • One end of the power switch tube T4 of the full-bridge sub-module in the MMC is connected to the negative voltage of the full-bridge sub-module, and the other end is connected to the negative electrode of the capacitor in the full-bridge sub-module.
  • the step 101 includes:
  • the operation ends when the capacitor voltage of the half-bridge sub-module in the MMC is charged to the first preset voltage and the capacitor voltage of the full-bridge sub-module in the MMC is charged to the second preset voltage.
  • the first preset voltage U F is determined by the following formula
  • U M AC power line voltage peak value equivalent system N F is the number of full-bridge MMC submodule; N H is the number of sub-half-bridge module MMC.
  • the arrow direction is the direction of current flow
  • the gray area is the area where current flows (current path area).
  • the capacitor voltage of the full-bridge sub-module in MMC is twice that of the half-bridge sub-module in MMC, and the capacitor voltage of the full-bridge sub-module in MMC is the same as that of the half-bridge sub-module in MMC.
  • the sum of the capacitor voltage is the peak value U M of the equivalent power line voltage of the AC system, namely:
  • the step 102 includes:
  • Step a Perform voltage equalization control charging on the MMC until the capacitor voltage of the half-bridge sub-module and the capacitor voltage of the full-bridge sub-module in the MMC both reach the third preset voltage;
  • Step b Perform the full-bridge sub-module half-bridge on the MMC until the power switch tubes T4 of the full-bridge sub-module in the MMC are all turned on;
  • Step c Perform overall turn-on charging of the MMC until the capacitor voltage of the half-bridge sub-module and the capacitor voltage of the full-bridge sub-module in the MMC both reach the startup rated voltage of the MMC;
  • One end of the power switch tube T4 of the full-bridge sub-module in the MMC is connected to the negative voltage of the full-bridge sub-module, and the other end is connected to the negative electrode of the capacitor in the full-bridge sub-module.
  • the step a includes:
  • Step 2 Control the working state of the AC circuit breaker to be closed, the working state of the starting resistance bypass switch to be open, and the working state of the half-bridge submodule in the MMC to be locked;
  • Step 3 Select part of the full-bridge sub-modules, such as N 1 full-bridge sub-modules, among all the full-bridge sub-modules of the MMC, and control the bypass of the N 1 full-bridge sub-modules, and the remaining full-bridge sub-modules are blocked;
  • the step 3 includes:
  • U M is the equivalent power line voltage peak value of the AC system
  • N F is the number of full-bridge sub-modules in MMC
  • N H is the number of half-bridge sub-modules in MMC
  • U is the third preset voltage
  • U C is the starting rated voltage of MMC.
  • each bridge arm selects from each bridge arm A full bridge sub-module bypass. As shown in Figure 3, it includes two bridge arms, an upper bridge arm and a lower bridge arm.
  • the upper full-bridge sub-modules and half-bridge sub-modules of the upper and lower bridge arms are symmetrically arranged.
  • the step b includes:
  • the working state of the AC circuit breaker is controlled to be closed, the working state of the starting resistance bypass switch is closed, the working state of the half-bridge sub-module in the MMC is locked, and the working state of the full-bridge sub-module in the MMC is atresia;
  • the N1 bypassed full-bridge sub-modules are first reset Switch to the locked state, and then turn on the power switch tube T4 of the full bridge submodule in MMC (as shown in Figure 3, the power switch tube T4 of the full bridge submodule in MMC is an IGBT power switch with a lower corner in the full bridge submodule) Device).
  • the half-bridge sub-module in the MMC has exactly the same characteristics as the full-bridge sub-module in the MMC, and the full-bridge sub-module in the MMC is now half-bridged.
  • the step c includes:
  • Step 5 Control the working state of the AC circuit breaker to be closed and the working state of the starting resistance bypass switch to be closed;
  • Step 6 Select N 2 sub-modules from all the sub-modules of the MMC, and control the N 2 sub-modules to bypass, and the remaining sub-modules are blocked;
  • the step 6 includes:
  • U M is the equivalent power line voltage peak value of the AC system
  • N F is the number of full-bridge sub-modules in MMC
  • N H is the number of half-bridge sub-modules in MMC
  • U C is the start of the modular multi-level converter Rated voltage value
  • the MMC neutron modules Arrange the MMC neutron modules in descending order according to the capacitance voltages of the MMC neutron modules, and select part of the submodules in the sequence as the previous N 2 submodules; wherein, the MMC neutron modules include the MMC full bridge Sub-module and half-bridge sub-module;
  • the embodiment of the present application provides a starting system for MMC in a hybrid direct current transmission system.
  • the hybrid direct current transmission system is composed of an alternating current system equivalent power source, an alternating current circuit breaker, a starting resistor, and an MMC connected in sequence.
  • the two ends of the starting resistor are connected in parallel
  • Starting the resistance bypass switch the MMC is composed of a half-bridge sub-module and a full-bridge sub-module, as shown in Figure 4, the system includes:
  • the uncontrolled charging module 41 is configured to uncontrollably charge the MMC until the capacitor voltage of the half-bridge sub-module in the MMC reaches a first preset voltage and the capacitor voltage of the full-bridge sub-module reaches a second preset voltage;
  • the controllable charging module 42 is configured to controllably charge the MMC until the capacitor voltage of the half-bridge sub-module and the capacitor voltage of the full-bridge sub-module in the MMC both reach the startup rated voltage of the MMC.
  • the initial state of the AC circuit breaker is open, the initial state of the starting resistance bypass switch is open, the initial state of the half-bridge submodule in the MMC is locked, and the full bridge submodule in the MMC The initial state is locked.
  • the uncontrolled charging module 41 is configured as:
  • the operation ends when the capacitor voltage of the half-bridge sub-module in the MMC is charged to the first preset voltage and the capacitor voltage of the full-bridge sub-module in the MMC is charged to the second preset voltage.
  • the first preset voltage U F is determined by the following formula
  • U M AC power line voltage peak value equivalent system N F is the number of full-bridge MMC submodule; N H is the number of sub-half-bridge module MMC.
  • controllable charging module 42 includes:
  • a voltage equalization control charging unit configured to perform voltage equalization control charging on the MMC until the capacitor voltage of the half-bridge sub-module and the capacitor voltage of the full-bridge sub-module in the MMC both reach the third preset voltage;
  • the full-bridge sub-module half-bridge unit is configured to perform the full-bridge sub-module half-bridge on the MMC until the power switch tubes T4 of the full-bridge sub-module in the MMC are all turned on;
  • An overall alternate conduction charging unit configured to perform overall alternate conduction charging on the MMC until the capacitor voltage of the half-bridge sub-module and the capacitor voltage of the full-bridge sub-module in the MMC both reach the startup rated voltage of the MMC;
  • One end of the power switch tube T4 of the full-bridge sub-module in the MMC is connected to the negative voltage of the full-bridge sub-module, and the other end is connected to the negative electrode of the capacitor in the full-bridge sub-module.
  • the voltage equalization control charging unit is configured as:
  • Step 2 Control the working state of the AC circuit breaker to be closed, the working state of the starting resistance bypass switch to be open, and the working state of the half-bridge submodule in the MMC to be locked;
  • Step 3 Select N 1 full bridge submodules from all the full bridge submodules of the MMC, and control the bypass of the N 1 full bridge submodules, and the remaining full bridge submodules are blocked;
  • the voltage equalization control charging unit is configured to, for the step 3:
  • U M is the equivalent power line voltage peak value of the AC system
  • N F is the number of full-bridge sub-modules in MMC
  • N H is the number of half-bridge sub-modules in MMC
  • U is the third preset voltage
  • the half-bridged unit of the full-bridge sub-module is configured as:
  • the working state of the AC circuit breaker is controlled to be closed, the working state of the starting resistance bypass switch is closed, the working state of the half-bridge sub-module in the MMC is locked, and the working state of the full-bridge sub-module in the MMC is atresia;
  • the overall turn-on charging unit is configured as:
  • Step 5 Control the working state of the AC circuit breaker to be closed and the working state of the starting resistance bypass switch to be closed;
  • Step 6 Select N 2 sub-modules from all the sub-modules of the MMC, and control the N 2 sub-modules to bypass, and the remaining sub-modules are blocked;
  • the overall turn-on charging unit is configured to: for the step 6:
  • U M is the equivalent power line voltage peak value of the AC system
  • N F is the number of full-bridge sub-modules in MMC
  • N H is the number of half-bridge sub-modules in MMC
  • U C is the start of the modular multi-level converter Rated voltage value
  • the MMC neutron modules Arrange the MMC neutron modules in descending order according to the capacitance voltage of the MMC neutron modules, and select the first N 2 submodules in the sequence; wherein, the MMC neutron modules include the full bridge submodule and the half Bridge submodule.
  • the MMC startup system in the hybrid DC transmission system provided by the embodiments of the present application belongs to the same inventive concept as the foregoing MMC startup method in the hybrid DC transmission system.
  • the description of the system please refer to the foregoing description of the method. The repetition will not be repeated here. .
  • the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, this application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.
  • a computer-usable storage media including but not limited to disk storage, CD-ROM, optical storage, etc.
  • These computer program instructions can also be stored in a computer-readable memory that can guide a computer or other programmable data processing equipment to work in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture including the instruction device.
  • the device implements the functions specified in one process or multiple processes in the flowchart and/or one block or multiple blocks in the block diagram.
  • These computer program instructions can also be loaded on a computer or other programmable data processing equipment, so that a series of operation steps are executed on the computer or other programmable equipment to produce computer-implemented processing, so as to execute on the computer or other programmable equipment.
  • the instructions provide steps for implementing functions specified in a flow or multiple flows in the flowchart and/or a block or multiple blocks in the block diagram.
  • this application may adopt the form of hardware embodiment, software embodiment, or a combination of software and hardware embodiments.
  • this application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, optical storage, etc.) containing computer-usable program codes.
  • These computer program instructions can also be stored in a computer-readable memory that can guide a computer or other programmable data processing equipment to work in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture including the instruction device.
  • the device implements the functions specified in one process or multiple processes in the flowchart and/or one block or multiple blocks in the block diagram.
  • These computer program instructions can also be loaded on a computer or other programmable data processing equipment, so that a series of operation steps are executed on the computer or other programmable equipment to produce computer-implemented processing, so as to execute on the computer or other programmable equipment.
  • the instructions provide steps for implementing functions specified in a flow or multiple flows in the flowchart and/or a block or multiple blocks in the block diagram.
  • the MMC is charged uncontrollably until the capacitor voltage of the half-bridge sub-module and the capacitor voltage of the full-bridge sub-module in the MMC reach the first preset voltage and the second preset voltage respectively; Controllable charging until the capacitor voltage of the half-bridge sub-module and the capacitor voltage of the full-bridge sub-module in the MMC both reach the start-up rated voltage of the MMC; a voltage equalization control charging stage is added in the controllable charging stage to achieve The capacitor voltages of the full-bridge sub-module and the half-bridge sub-module in the MMC tend to be the same, and then the full-bridge sub-modules are half-bridged and the overall alternate conduction charging is performed on the MMC in turn, so that the capacitor voltage of the MMC neutron sub-module reaches the rated value at the same time, reducing This reduces the error rate of MMC startup, and at least avoids the problem of failing to start MMC.

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Abstract

一种混合直流输电系统中MMC的启动方法和系统，包括：对所述MMC进行不控充电，直至MMC中半桥子模块的电容电压至第一预设电压、全桥子模块的电容电压至第二预设电压（步骤101）；对所述MMC进行可控充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到所述MMC的启动额定电压（步骤102）。

Description

混合直流输电系统中MMC的启动方法和系统
相关申请的交叉引用
本申请基于申请号为201910563520.6、申请日为2019年06月26日的中国专利申请提出，并要求该中国专利申请的优先权，该中国专利申请的内容在此以引入方式并入本申请。
技术领域
本申请涉及柔性直流输电技术领域，具体涉及一种混合直流输电系统中MMC的启动方法和系统。
背景技术
模块化多电平换流器高压直流输电(MMC-HVDC)以其独特的技术优势，已成为未来电压源换流器高压直流输电(VSC-HVDC)领域的发展趋势。
目前工程中模块化多电平换流器(Modular Multilevel Converter，MMC)大都采用半桥型子模块结构，但基于半桥子模块的MMC并不能通过换流器的自身动作来处理直流架空线故障，其原因在于半桥子模块拓扑结构中即使绝缘栅双极型晶体管(IGBT)关断，交流系统仍会通过IGBT反并联的二极管向故障点馈入电流，对于交流系统的影响相当于三相短路。在高电压大容量直流断路器技术并不成熟的情况下，直流线路故障电流的切断依赖于换流器闭锁并同时跳开交流侧断路器这样整个系统的重启恢复时间较长，通常为秒级，不利于交直流输电系统的暂态稳定。
针对半桥子模块MMC的不足，有学者提出了具有直流故障清除能力的基于全桥子模块的MMC，基于全桥子模块MMC的高压直流输电系统在发生直流线路故障后能够迅速闭锁或输出负压切断直流故障电流，而不需要跳开交流侧断路器，故障切除后系统能够迅速恢复运行，因此全桥子模 块MMC更加适用于基于远距离架空线路的混合直流输电系统。然而全桥子模块所用功率开关器件的个数是半桥子模块的2倍，因而成本和损耗大大增加。
为此又有学者提出采用半桥子模块和全桥子模块混合的MMC，以使得MMC在运行时既能减少成本和损耗，又能并具备直流故障清除能力。
但是，由于不控充电阶段MMC中全桥子模块和半桥子模块充电速率的差异，导致不控充电结束后，全桥子模块电容电压与半桥子模块电容电压不一致；此时对MMC再进行可控充电，可能会出现全桥子模块电容到达甚至超过额定电压而半桥子模块电容未到达额定电压的情况，无法完成启动。
发明内容
针对现有技术的不足，本申请实施例在于提出一种混合直流输电系统中MMC的启动方法和系统，至少可避免无法对MMC进行启动完成的问题。
本申请实施例采用下述技术方案实现的：
本申请实施例提供一种混合直流输电系统中MMC的启动方法，所述混合直流输电系统由依次连接的交流系统等效电源、交流断路器、启动电阻和MMC组成，所述启动电阻两端并联启动电阻旁路开关，所述MMC由半桥子模块和全桥子模块组成，所述方法包括：
对所述MMC进行不控充电，直至MMC中半桥子模块的电容电压至第一预设电压、全桥子模块的电容电压至第二预设电压；
对所述MMC进行可控充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到所述MMC的启动额定电压。
前述方案中，所述对所述MMC进行不控充电，直至MMC中半桥子模块的电容电压至第一预设电压、全桥子模块的电容电压至第二预设电压，包括：
控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为断开、所述MMC中半桥子模块的工作状态为闭锁、所述MMC中全桥子模块的工作状态为闭锁；
当MMC中半桥子模块的电容电压充至第一预设电压且MMC中全桥子模块的电容电压充至第二预设电压时结束操作。
前述方案中，按下式确定所述第一预设电压U F；
Figure PCTCN2019104256-appb-000001
按下式确定所述第二预设电压U H；
Figure PCTCN2019104256-appb-000002
上式中，U M为交流系统等效电源线电压峰值；N F为MMC中全桥子模块数目；N H为MMC中半桥子模块数目。
前述方案中，所述对所述MMC进行可控充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到所述MMC的启动额定电压，包括：
对所述MMC进行均压控制充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到第三预设电压；
对所述MMC进行全桥子模块半桥化，直至所述MMC中全桥子模块的功率开关管T4均导通；
对所述MMC进行整体轮换导通充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到所述MMC的启动额定电压；
所述MMC中全桥子模块的功率开关管T4一端与所述全桥子模块的电压负极连接，另一端与所述全桥子模块中电容负极连接。
前述方案中，所述对所述MMC进行均压控制充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到第三预设电压，包括：
步骤1：初始化所述MMC进行均压控制充电的时刻t＝0；
步骤2：控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为断开、所述MMC中半桥子模块的工作状态为闭锁；
步骤3：在所述MMC的全部全桥子模块中选择N 1个全桥子模块，并控制所述N 1个全桥子模块旁路，其余全桥子模块闭锁；
步骤4：判断所述MMC中半桥子模块的电容电压和全桥子模块的电容电压是否均达到第三预设电压，若是，则结束操作；否则，令t＝t+1，并返回步骤3。
前述方案中，所述步骤3包括：
按下式确定旁路的全桥子模块数目N 1：
Figure PCTCN2019104256-appb-000003
式中，U M为交流系统等效电源线电压峰值；N F为MMC中全桥子模块数目；N H为MMC中半桥子模块数目；U为第三预设电压；
按所述MMC中全桥子模块的电容电压大小，降序排列所述MMC中全桥子模块，在序列中选择前N 1个全桥子模块。
前述方案中，所述对所述MMC进行全桥子模块半桥化，直至所述MMC中全桥子模块的功率开关管T4均导通，包括：
控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为闭合、所述MMC中半桥子模块的工作状态为闭锁、所述MMC中全桥子模块的工作状态为闭锁；
当MMC中全桥子模块的功率开关管T4均导通时结束操作。
前述方案中，所述对所述MMC进行整体轮换导通充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到所述MMC的启动额定电压，包括：
步骤4：初始化所述MMC进行整体轮换导通充电的时刻m＝0；
步骤5：控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为闭合；
步骤6：在所述MMC的全部子模块中选择N 2个子模块，并控制所述N 2个子模块旁路，其余子模块闭锁；
步骤7：判断MMC中半桥子模块的电容电压和全桥子模块的电容电压是否均达到所述MMC的启动额定电压，若是，结束操作；否则，令m＝m+1，并返回步骤6。
前述方案中，所述步骤6包括：
按下式确定旁路的子模块数目N 2：
Figure PCTCN2019104256-appb-000004
式中，U M为交流系统等效电源线电压峰值；N F为MMC中全桥子模块数目；N H为MMC中半桥子模块数目，U C为模块化多电平换流器的启动额定电压值；
按所述MMC中子模块的电容电压大小，降序排列所述MMC中子模块，在序列中选择前N 2个子模块；其中，所述MMC中子模块包括所述MMC中全桥子模块和半桥子模块。
本申请实施例还提供一种混合直流输电系统中MMC的启动系统，所述混合直流输电系统由依次连接的交流系统等效电源、交流断路器、启动电阻和MMC组成，所述启动电阻两端并联启动电阻旁路开关，所述MMC由半桥子模块和全桥子模块组成，其改进之处在于，所述系统包括：
不控充电模块，配置为对所述MMC进行不控充电，直至MMC中半桥子模块的电容电压至第一预设电压、全桥子模块的电容电压至第二预设电压；
可控充电模块，配置为对所述MMC进行可控充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到所述MMC的启动额定 电压。
前述方案中，所述不控充电模块，配置为：
控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为断开、所述MMC中半桥子模块的工作状态为闭锁、所述MMC中全桥子模块的工作状态为闭锁；
当MMC中半桥子模块的电容电压充至第一预设电压且MMC中全桥子模块的电容电压充至第二预设电压时结束操作。
优选的，按下式确定所述第一预设电压U F；
Figure PCTCN2019104256-appb-000005
按下式确定所述第二预设电压U H；
Figure PCTCN2019104256-appb-000006
上式中，U M为交流系统等效电源线电压峰值；N F为MMC中全桥子模块数目；N H为MMC中半桥子模块数目。
前述方案中，所述可控充电模块，包括：
均压控制充电单元，配置为对所述MMC进行均压控制充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到第三预设电压；
全桥子模块半桥化单元，配置为对所述MMC进行全桥子模块半桥化，直至所述MMC中全桥子模块的功率开关管T4均导通；
整体轮换导通充电单元，配置为对所述MMC进行整体轮换导通充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到所述MMC的启动额定电压；
所述MMC中全桥子模块的功率开关管T4一端与所述全桥子模块的电压负极连接，另一端与所述全桥子模块中电容负极连接。
前述方案中，所述均压控制充电单元，配置为：
步骤1：初始化所述MMC进行均压控制充电的时刻t＝0；
步骤2：控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为断开、所述MMC中半桥子模块的工作状态为闭锁；
步骤3：在所述MMC的全部全桥子模块中选择N 1个全桥子模块，并控制所述N 1个全桥子模块旁路，其余全桥子模块闭锁；
步骤4：判断所述MMC中半桥子模块的电容电压和全桥子模块的电容电压是否均达到第三预设电压，若是，则结束操作；否则，令t＝t+1，并返回步骤3。
前述方案中，所述均压控制充电单元，还配置为：针对所述步骤3：
按下式确定旁路的全桥子模块数目N 1：
Figure PCTCN2019104256-appb-000007
式中，U M为交流系统等效电源线电压峰值；N F为MMC中全桥子模块数目；N H为MMC中半桥子模块数目；U为第三预设电压；
按所述MMC中全桥子模块的电容电压大小，降序排列所述MMC中全桥子模块，在序列中选择前N 1个全桥子模块。
前述方案中，所述全桥子模块半桥化单元，配置为：
控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为闭合、所述MMC中半桥子模块的工作状态为闭锁、所述MMC中全桥子模块的工作状态为闭锁；
当MMC中全桥子模块的功率开关管T4均导通时结束操作。
前述方案中，所述整体轮换导通充电单元，配置为：
步骤4：初始化所述MMC进行整体轮换导通充电的时刻m＝0；
步骤5：控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为闭合；
步骤6：在所述MMC的全部子模块中选择N 2个子模块，并控制所述N 2 个子模块旁路，其余子模块闭锁；
步骤7：判断MMC中半桥子模块的电容电压和全桥子模块的电容电压是否均达到所述MMC的启动额定电压，若是，结束操作；否则，令m＝m+1，并返回步骤6。
前述方案中，所述整体轮换导通充电单元，还配置为：针对所述步骤6：
按下式确定旁路的子模块数目N 2：
Figure PCTCN2019104256-appb-000008
式中，U M为交流系统等效电源线电压峰值；N F为MMC中全桥子模块数目；N H为MMC中半桥子模块数目，U C为模块化多电平换流器的启动额定电压值；
按所述MMC中子模块的电容电压大小，降序排列所述MMC中子模块，在序列中选择前N 2个子模块；其中，所述MMC中子模块包括所述MMC中全桥子模块和半桥子模块。
与最接近的现有技术相比，本申请实施例具有的有益效果：
本申请实施例提供的技术方案对所述MMC进行不控充电，直至MMC中半桥子模块的电容电压至第一预设电压、全桥子模块的电容电压至第二预设电压；对所述MMC进行可控充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到所述MMC的启动额定电压；在可控充电阶段增加了一个均压控制充电阶段，以此来实现MMC中全桥子模块和半桥子模块的电容电压趋于一致，然后依次对MMC进行全桥子模块半桥化和整体轮换导通充电，使MMC中子模块电容电压同时达到额定值，减少了MMC启动的失误率，至少避免了无法对MMC进行启动完成的问题。
附图说明
图1为本申请实施例中一种混合直流输电系统中MMC的启动方法流 程图；
图2为本申请实施例中混合直流输电系统网络拓扑结构图；
图3为本申请实施例中MMC网络拓扑结构图；
图4为本申请实施例中一种混合直流输电系统中MMC的启动系统流程图；
图5(a)、(b)为本申请实施例中全桥子模块、半桥子模块的构成示意图。
具体实施方式
下面结合附图对本申请的具体实施方式作进一步的详细说明。
为使本申请实施例的目的、技术方案和优点更加清楚，下面将结合本申请实施例中的附图，对本申请实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其它实施例，都属于本申请保护的范围。
本申请实施例提供一种混合直流输电系统中MMC的启动方法，所述混合直流输电系统由依次连接的交流系统等效电源、交流断路器、启动电阻和MMC组成，所述启动电阻两端并联启动电阻旁路开关，所述MMC由半桥子模块和全桥子模块组成，如图1所示，所述方法包括：
步骤101：对所述MMC进行不控充电，直至MMC中半桥子模块的电容电压至第一预设电压、全桥子模块的电容电压至第二预设电压；
在本申请实施例中，MMC的各桥臂上的半桥子模块和全桥子模块的数目一致。
步骤102：对所述MMC进行可控充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到所述MMC的启动额定电压；
在本申请实施例中，启动是柔性直流输电系统正常运行的基础，启动 的实质是有源交流系统通过启动电阻给MMC子模块电容进行不控充电和可控充电，最终使得子模块电容电压达到额定值。
其中，所述交流断路器的初始状态为断开，所述启动电阻旁路开关的初始状态为断开，所述MMC中半桥子模块的初始状态为闭锁，所述MMC中全桥子模块的初始状态为闭锁。可以理解，本申请实施例中的初始状态为本申请实施例中的MMC既未执行可控充电也未执行不控充电的状态。在MMC执行可控充电或者执行不控充电时以上四个器件(交流断路器、启动电阻旁路开关、半桥子模块和全桥子模块)中的至少一个器件的状态会发生变化，具体参见后续相关说明。在初始状态中以上四个器件相当于均处于未工作状态，为后续MMC进入可控充电阶段或不控充电阶段做准备。
在本申请实施例中，所述混合直流输电系统的网络拓扑结构如图2所示。其中，U S为交流系统等效电源(包括U sa和U sb)，AC_BRK为交流断路器，R为启动电阻，R_BRK为启动电阻旁路开关，U DC为混合MMC的直流电压。本领域技术人员应该理解，本申请实施例中的混合MMC指的是既包括半桥子模块，又包括全桥子模块的MMC，后续简称为MMC。
如图5(a)所示，MMC中每个半桥子模块由绝缘栅双极型晶体管(IGBT)功率器件T5、IGBT功率器件T6和电容C2组成；
如图5(b)所示，MMC中每个全桥子模块由IGBT功率器件T1、IGBT功率器件T2、IGBT功率器件T3、IGBT功率器件T4和电容C2组成。
图3为本申请实施例中的混合MMC的网络拓扑结构图。如图3所示，包括N F个全桥子模块和N H个半桥子模块。其中，点1为全桥子模块的电压正极；点2为全桥子模块的电压负极。P为混合MMC的电源正极，N为混合MMC的电源负极。
其中，所述MMC中全桥子模块的功率开关管T1一端与所述全桥子模块的电压正极连接，另一端与所述全桥子模块中电容正极连接
所述MMC中全桥子模块的功率开关管T2一端与所述全桥子模块的电压负极连接，另一端与所述全桥子模块中电容正极连接
所述MMC中全桥子模块的功率开关管T3一端与所述全桥子模块的电压正极连接，另一端与所述全桥子模块中电容负极连接
所述MMC中全桥子模块的功率开关管T4一端与所述全桥子模块的电压负极连接，另一端与所述全桥子模块中电容负极连接。
具体的，所述步骤101，包括：
控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为断开、所述MMC中半桥子模块的工作状态为闭锁、所述MMC中全桥子模块的工作状态为闭锁；
当MMC中半桥子模块的电容电压充至第一预设电压且MMC中全桥子模块的电容电压充至第二预设电压时结束操作。
具体的，按下式确定所述第一预设电压U F；
Figure PCTCN2019104256-appb-000009
按下式确定所述第二预设电压U H；
Figure PCTCN2019104256-appb-000010
上式中，U M为交流系统等效电源线电压峰值；N F为MMC中全桥子模块数目；N H为MMC中半桥子模块数目。
在本申请实施例中，如图3所示，箭头方向为电流流向方向，灰色区域为存在电流流通的区域(电流通路区域)。对于MMC中半桥子模块，只有当充电电流方向为正时才可进行充电。对于MMC中全桥子模块，不论充电电流方向为正时还是为负均可进行充电。故而在对MMC不控充电结束后，MMC中全桥子模块的电容电压为MMC中半桥子模块的电容电压的两倍，并且MMC中全桥子模块的电容电压和MMC中半桥子模块的电容电 压之和为交流系统等效电源线电压峰值U M，即：
U F×2N F+U H×N H＝U M
U F＝2U H
解得：
Figure PCTCN2019104256-appb-000011
Figure PCTCN2019104256-appb-000012
所述步骤102，包括：
步骤a：对所述MMC进行均压控制充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到第三预设电压；
步骤b：对所述MMC进行全桥子模块半桥化，直至所述MMC中全桥子模块的功率开关管T4均导通；
步骤c：对所述MMC进行整体轮换导通充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到所述MMC的启动额定电压；
所述MMC中全桥子模块的功率开关管T4一端与所述全桥子模块的电压负极连接，另一端与所述全桥子模块中电容负极连接。
具体的，所述步骤a，包括：
步骤1：初始化所述MMC进行均压控制充电的时刻t＝0；
步骤2：控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为断开、所述MMC中半桥子模块的工作状态为闭锁；
步骤3：在所述MMC的全部全桥子模块中选择部分全桥子模块如N 1个全桥子模块，并控制所述N 1个全桥子模块旁路，其余全桥子模块闭锁；
步骤4：判断所述MMC中半桥子模块的电容电压和全桥子模块的电容电压是否均达到第三预设电压，若是，则结束操作；否则，令t＝t+1，并返回步骤3。
所述步骤3包括：
按下式确定旁路的全桥子模块数目N 1：
Figure PCTCN2019104256-appb-000013
式中，U M为交流系统等效电源线电压峰值；N F为MMC中全桥子模块数目；N H为MMC中半桥子模块数目；U为第三预设电压；
在本申请实施例中，令MMC中全桥子模块电容电压等于MMC中全桥子模块电容电压，假设第三预设电压为U，则U需满足：
U F<U<U C
上式中，U C为MMC的启动额定电压。
则有：
U×2(N F-N 1)+U×N H＝U M
解得：
Figure PCTCN2019104256-appb-000014
按所述MMC中全桥子模块的电容电压大小，降序排列所述MMC中全桥子模块，在序列中选择前N 1个全桥子模块；
在本申请实施例中，若有X个桥臂，则在各桥臂中选择
Figure PCTCN2019104256-appb-000015
个全桥子模块旁路。如图3所示，包括二个桥臂，为上桥臂和下桥臂。上、下桥臂上全桥子模块和半桥子模块对称设置。
具体的，所述步骤b，包括：
控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为闭合、所述MMC中半桥子模块的工作状态为闭锁、所述MMC中全桥子模块的工作状态为闭锁；
当MMC中全桥子模块的功率开关管T4均导通时结束操作。
在本申请实施例中，当MMC中半桥子模块电容电压与MMC中全桥子 模块电容电压同时达到U(第三预设电压)后，首先将N1个被旁路的全桥子模块重新切换为闭锁状态，然后将MMC中全桥子模块的功率开关管T4导通(如图3所示，MMC中全桥子模块的功率开关管T4为全桥子模块中有下角的IGBT功率开关器件)，此时MMC中半桥子模块与MMC中全桥子模块具有完全相同的特性，此时实现了MMC中全桥子模块半桥化。
具体的，所述步骤c，包括：
步骤4：初始化所述MMC进行整体轮换导通充电的时刻m＝0；
步骤5：控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为闭合；
步骤6：在所述MMC的全部子模块中选择N 2个子模块，并控制所述N 2个子模块旁路，其余子模块闭锁；
步骤7：判断MMC中半桥子模块的电容电压和全桥子模块的电容电压是否均达到所述MMC的启动额定电压，若是，结束操作；否则，令m＝m+1，并返回步骤6。
作为一种实现方式，所述步骤6包括：
按下式确定旁路的子模块数目N 2：
Figure PCTCN2019104256-appb-000016
式中，U M为交流系统等效电源线电压峰值；N F为MMC中全桥子模块数目；N H为MMC中半桥子模块数目，U C为模块化多电平换流器的启动额定电压值；
按所述MMC中子模块的电容电压大小，降序排列所述MMC中子模块，在序列中选择部分子模块如前N 2个子模块；其中，所述MMC中子模块包括所述MMC中全桥子模块和半桥子模块；
在本申请实施例中，若有X个桥臂，则在各桥臂中选择
Figure PCTCN2019104256-appb-000017
个子模块旁 路。
在本申请实施例中，混合直流输电系统中MMC的启动控制操作由表一所示：
表一
Figure PCTCN2019104256-appb-000018
本申请实施例提供一种混合直流输电系统中MMC的启动系统，所述混合直流输电系统由依次连接的交流系统等效电源、交流断路器、启动电阻和MMC组成，所述启动电阻两端并联启动电阻旁路开关，所述MMC由半桥子模块和全桥子模块组成，如图4所示，所述系统包括：
不控充电模块41，配置为对所述MMC进行不控充电，直至MMC中半桥子模块的电容电压至第一预设电压、全桥子模块的电容电压至第二预设电压；
可控充电模块42，配置为对所述MMC进行可控充电，直至MMC中半 桥子模块的电容电压和全桥子模块的电容电压均达到所述MMC的启动额定电压。
其中，所述交流断路器的初始状态为断开，所述启动电阻旁路开关的初始状态为断开，所述MMC中半桥子模块的初始状态为闭锁，所述MMC中全桥子模块的初始状态为闭锁。
具体的，所述不控充电模块41，配置为：
控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为断开、所述MMC中半桥子模块的工作状态为闭锁、所述MMC中全桥子模块的工作状态为闭锁；
当MMC中半桥子模块的电容电压充至第一预设电压且MMC中全桥子模块的电容电压充至第二预设电压时结束操作。
具体的，按下式确定所述第一预设电压U F；
Figure PCTCN2019104256-appb-000019
按下式确定所述第二预设电压U H；
Figure PCTCN2019104256-appb-000020
上式中，U M为交流系统等效电源线电压峰值；N F为MMC中全桥子模块数目；N H为MMC中半桥子模块数目。
具体的，所述可控充电模块42，包括：
均压控制充电单元，配置为对所述MMC进行均压控制充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到第三预设电压；
全桥子模块半桥化单元，配置为对所述MMC进行全桥子模块半桥化，直至所述MMC中全桥子模块的功率开关管T4均导通；
整体轮换导通充电单元，配置为对所述MMC进行整体轮换导通充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到所述 MMC的启动额定电压；
所述MMC中全桥子模块的功率开关管T4一端与所述全桥子模块的电压负极连接，另一端与所述全桥子模块中电容负极连接。
具体的，所述均压控制充电单元，配置为：
步骤1：初始化所述MMC进行均压控制充电的时刻t＝0；
步骤2：控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为断开、所述MMC中半桥子模块的工作状态为闭锁；
步骤3：在所述MMC的全部全桥子模块中选择N 1个全桥子模块，并控制所述N 1个全桥子模块旁路，其余全桥子模块闭锁；
步骤4：判断所述MMC中半桥子模块的电容电压和全桥子模块的电容电压是否均达到第三预设电压，若是，则结束操作；否则，令t＝t+1，并返回步骤3。
具体的，所述均压控制充电单元，配置为，针对所述步骤3：
按下式确定旁路的全桥子模块数目N 1：
Figure PCTCN2019104256-appb-000021
式中，U M为交流系统等效电源线电压峰值；N F为MMC中全桥子模块数目；N H为MMC中半桥子模块数目；U为第三预设电压；
按所述MMC中全桥子模块的电容电压大小，降序排列所述MMC中全桥子模块，在序列中选择前N 1个全桥子模块。
具体的，所述全桥子模块半桥化单元，配置为：
控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为闭合、所述MMC中半桥子模块的工作状态为闭锁、所述MMC中全桥子模块的工作状态为闭锁；
当MMC中全桥子模块的功率开关管T均导通时结束操作。
具体的，所述整体轮换导通充电单元，配置为：
步骤4：初始化所述MMC进行整体轮换导通充电的时刻m＝0；
步骤5：控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为闭合；
步骤6：在所述MMC的全部子模块中选择N 2个子模块，并控制所述N 2个子模块旁路，其余子模块闭锁；
步骤7：判断MMC中半桥子模块的电容电压和全桥子模块的电容电压是否均达到所述MMC的启动额定电压，若是，结束操作；否则，令m＝m+1，并返回步骤6。
具体的，所述整体轮换导通充电单元，配置为：针对所述步骤6：
按下式确定旁路的子模块数目N 2：
Figure PCTCN2019104256-appb-000022
式中，U M为交流系统等效电源线电压峰值；N F为MMC中全桥子模块数目；N H为MMC中半桥子模块数目，U C为模块化多电平换流器的启动额定电压值；
按所述MMC中子模块的电容电压大小，降序排列所述MMC中子模块，在序列中选择前N 2个子模块；其中，所述MMC中子模块包括所述MMC中全桥子模块和半桥子模块。
本申请实施例提供的混合直流输电系统中MMC的启动系统与前述的混合直流输电系统中MMC的启动方法属于同一发明构思，对于系统的描述请参见前述对方法的描述，重复之处不再赘述。
本领域内的技术人员应明白，本申请的实施例可提供为方法、系统、或计算机程序产品。因此，本申请可采用完全硬件实施例、完全软件实施例、或结合软件和硬件方面的实施例的形式。而且，本申请可采用在一个或多个其中包含有计算机可用程序代码的计算机可用存储介质(包括但不限于磁盘存储器、CD-ROM、光学存储器等)上实施的计算机程序产品的 形式。
本申请是参照根据本申请实施例的方法、设备(系统)、和计算机程序产品的流程图和/或方框图来描述的。应理解可由计算机程序指令实现流程图和/或方框图中的每一流程和/或方框、以及流程图和/或方框图中的流程和/或方框的结合。可提供这些计算机程序指令到通用计算机、专用计算机、嵌入式处理机或其他可编程数据处理设备的处理器以产生一个机器，使得通过计算机或其他可编程数据处理设备的处理器执行的指令产生用于实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能的装置。
这些计算机程序指令也可存储在能引导计算机或其他可编程数据处理设备以特定方式工作的计算机可读存储器中，使得存储在该计算机可读存储器中的指令产生包括指令装置的制造品，该指令装置实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能。
这些计算机程序指令也可装载到计算机或其他可编程数据处理设备上，使得在计算机或其他可编程设备上执行一系列操作步骤以产生计算机实现的处理，从而在计算机或其他可编程设备上执行的指令提供用于实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能的步骤。
最后应当说明的是：以上实施例仅用以说明本申请的技术方案而非对其限制，尽管参照上述实施例对本申请进行了详细的说明，所属领域的普通技术人员应当理解：依然可以对本申请的具体实施方式进行修改或者等同替换，而未脱离本申请精神和范围的任何修改或者等同替换，其均应涵盖在本申请的权利要求保护范围之内。
本领域内的技术人员应明白，本申请的实施例可提供为方法、系统、或计算机程序产品。因此，本申请可采用硬件实施例、软件实施例、或结 合软件和硬件方面的实施例的形式。而且，本申请可采用在一个或多个其中包含有计算机可用程序代码的计算机可用存储介质(包括但不限于磁盘存储器和光学存储器等)上实施的计算机程序产品的形式。
本申请是参照根据本申请实施例的方法、设备(系统)、和计算机程序产品的流程图和/或方框图来描述的。应理解可由计算机程序指令实现流程图和/或方框图中的每一流程和/或方框、以及流程图和/或方框图中的流程和/或方框的结合。可提供这些计算机程序指令到通用计算机、专用计算机、嵌入式处理机或其他可编程数据处理设备的处理器以产生一个机器，使得通过计算机或其他可编程数据处理设备的处理器执行的指令产生用于实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能的装置。
这些计算机程序指令也可存储在能引导计算机或其他可编程数据处理设备以特定方式工作的计算机可读存储器中，使得存储在该计算机可读存储器中的指令产生包括指令装置的制造品，该指令装置实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能。
这些计算机程序指令也可装载到计算机或其他可编程数据处理设备上，使得在计算机或其他可编程设备上执行一系列操作步骤以产生计算机实现的处理，从而在计算机或其他可编程设备上执行的指令提供用于实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能的步骤。
以上所述，仅为本申请的较佳实施例而已，并非用于限定本申请的保护范围。
工业实用性
本申请实施例中，对MMC进行不控充电，直至MMC中半桥子模块的 电容电压和全桥子模块的电容电压分别至第一预设电压和第二预设电压；对所述MMC进行可控充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到所述MMC的启动额定电压；在可控充电阶段增加了一个均压控制充电阶段，以此来实现MMC中全桥子模块和半桥子模块的电容电压趋于一致，然后依次对MMC进行全桥子模块半桥化和整体轮换导通充电，使MMC中子模块电容电压同时达到额定值，减少了MMC启动的失误率，至少避免了无法对MMC进行启动完成的问题。

Claims (18)

  1. 一种混合直流输电系统中MMC的启动方法，所述混合直流输电系统由依次连接的交流系统等效电源、交流断路器、启动电阻和MMC组成，所述启动电阻两端并联启动电阻旁路开关，所述MMC由半桥子模块和全桥子模块组成，所述方法包括：
    对所述MMC进行不控充电，直至MMC中半桥子模块的电容电压至第一预设电压、全桥子模块的电容电压至第二预设电压；
    对所述MMC进行可控充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到所述MMC的启动额定电压。
  2. 如权利要求1所述的方法，其中，所述对所述MMC进行不控充电，直至MMC中半桥子模块的电容电压至第一预设电压、全桥子模块的电容电压至第二预设电压，包括：
    控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为断开、所述MMC中半桥子模块的工作状态为闭锁、所述MMC中全桥子模块的工作状态为闭锁；
    当MMC中半桥子模块的电容电压充至第一预设电压且MMC中全桥子模块的电容电压充至第二预设电压时结束操作。
  3. 如权利要求1所述的方法，其中，所述第一预设电压U F为；
    Figure PCTCN2019104256-appb-100001
    所述第二预设电压U H为；
    Figure PCTCN2019104256-appb-100002
    上式中，U M为交流系统等效电源线电压峰值；N F为MMC中全桥子模块数目；N H为MMC中半桥子模块数目。
  4. 如权利要求1所述的方法，其中，所述对所述MMC进行可控充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到所述MMC的启动额定电压，包括：
    对所述MMC进行均压控制充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到第三预设电压；
    对所述MMC进行全桥子模块半桥化，直至所述MMC中全桥子模块的功率开关管T4均导通；
    对所述MMC进行整体轮换导通充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到所述MMC的启动额定电压；
    其中，所述MMC中全桥子模块的功率开关管T4一端与所述全桥子模块的电压负极连接，另一端与所述全桥子模块中电容负极连接。
  5. 如权利要求4所述的方法，其中，所述对所述MMC进行均压控制充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到第三预设电压，包括：
    步骤1：初始化所述MMC进行均压控制充电的时刻t＝0；
    步骤2：控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为断开、所述MMC中半桥子模块的工作状态为闭锁；
    步骤3：在所述MMC的全部全桥子模块中选择N 1个全桥子模块，并控制所述N 1个全桥子模块旁路，其余全桥子模块闭锁；
    步骤4：判断所述MMC中半桥子模块的电容电压和全桥子模块的电容电压是否均达到第三预设电压，若是，则结束操作；否则，令t＝t+1，并返回步骤3。
  6. 如权利要求5所述的方法，其中，所述步骤3包括：
    按下式确定旁路的全桥子模块数目N 1：
    Figure PCTCN2019104256-appb-100003
    式中，U M为交流系统等效电源线电压峰值；N F为MMC中全桥子模块数目；N H为MMC中半桥子模块数目；U为第三预设电压；
    按所述MMC中全桥子模块的电容电压大小，降序排列所述MMC中全桥子模块，在序列中选择前N 1个全桥子模块。
  7. 如权利要求4所述的方法，其中，所述对所述MMC进行全桥子模块半桥化，直至所述MMC中全桥子模块的功率开关管T4均导通，包括：
    控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为闭合、所述MMC中半桥子模块的工作状态为闭锁、所述MMC中全桥子模块的工作状态为闭锁；
    当MMC中全桥子模块的功率开关管T4均导通时结束操作。
  8. 如权利要求4所述的方法，其中，所述对所述MMC进行整体轮换导通充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到所述MMC的启动额定电压，包括：
    步骤4：初始化所述MMC进行整体轮换导通充电的时刻m＝0；
    步骤5：控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为闭合；
    步骤6：在所述MMC的全部子模块中选择N 2个子模块，并控制所述N 2个子模块旁路，其余子模块闭锁；
    步骤7：判断MMC中半桥子模块的电容电压和全桥子模块的电容电压是否均达到所述MMC的启动额定电压，若是，结束操作；否则，令m＝m+1，并返回步骤6。
  9. 如权利要求8所述的方法，其中，所述步骤6包括：
    按下式确定旁路的子模块数目N 2：
    Figure PCTCN2019104256-appb-100004
    式中，U M为交流系统等效电源线电压峰值；N F为MMC中全桥子模块 数目；N H为MMC中半桥子模块数目，U C为模块化多电平换流器的启动额定电压值；
    按所述MMC中子模块的电容电压大小，降序排列所述MMC中子模块，在序列中选择前N 2个子模块；其中，所述MMC中子模块包括所述MMC中全桥子模块和半桥子模块。
  10. 一种混合直流输电系统中MMC的启动系统，所述混合直流输电系统由依次连接的交流系统等效电源、交流断路器、启动电阻和MMC组成，所述启动电阻两端并联启动电阻旁路开关，所述MMC由半桥子模块和全桥子模块组成，所述系统包括：
    不控充电模块，配置为对所述MMC进行不控充电，直至MMC中半桥子模块的电容电压至第一预设电压、全桥子模块的电容电压至第二预设电压；
    可控充电模块，配置为对所述MMC进行可控充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到所述MMC的启动额定电压。
  11. 如权利要求10所述的系统，其中，所述不控充电模块，配置为：
    控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为断开、所述MMC中半桥子模块的工作状态为闭锁、所述MMC中全桥子模块的工作状态为闭锁；
    当MMC中半桥子模块的电容电压充至第一预设电压且MMC中全桥子模块的电容电压充至第二预设电压时结束操作。
  12. 如权利要求11所述的系统，其中，所述第一预设电压U F为；
    Figure PCTCN2019104256-appb-100005
    所述第二预设电压U H为；
    Figure PCTCN2019104256-appb-100006
    上式中，U M为交流系统等效电源线电压峰值；N F为MMC中全桥子模块数目；N H为MMC中半桥子模块数目。
  13. 如权利要求10所述的系统，其中，所述可控充电模块，包括：
    均压控制充电单元，配置为对所述MMC进行均压控制充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到第三预设电压；
    对所述MMC进行全桥子模块半桥化，直至所述MMC中全桥子模块的功率开关管T4均导通；
    对所述MMC进行整体轮换导通充电，直至MMC中半桥子模块的电容电压和全桥子模块的电容电压均达到所述MMC的启动额定电压；
    所述MMC中全桥子模块的功率开关管T4一端与所述全桥子模块的电压负极连接，另一端与所述全桥子模块中电容负极连接。
  14. 如权利要求13所述的系统，其中，所述均压控制充电单元，配置为：
    步骤1：初始化所述MMC进行均压控制充电的时刻t＝0；
    步骤2：控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为断开、所述MMC中半桥子模块的工作状态为闭锁；
    步骤3：在所述MMC的全部全桥子模块中选择N 1个全桥子模块，并控制所述N 1个全桥子模块旁路，其余全桥子模块闭锁；
    步骤4：判断所述MMC中半桥子模块的电容电压和全桥子模块的电容电压是否均达到第三预设电压，若是，则结束操作；否则，令t＝t+1，并返回步骤3。
  15. 如权利要求14所述的系统，其中，所述均压控制充电单元，还配置为：
    按下式确定旁路的全桥子模块数目N 1：
    Figure PCTCN2019104256-appb-100007
    式中，U M为交流系统等效电源线电压峰值；N F为MMC中全桥子模块数目；N H为MMC中半桥子模块数目；U为第三预设电压；
    按所述MMC中全桥子模块的电容电压大小，降序排列所述MMC中全桥子模块，在序列中选择前N 1个全桥子模块。
  16. 如权利要求13所述的系统，其中，所述全桥子模块半桥化单元，配置为：
    控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为闭合、所述MMC中半桥子模块的工作状态为闭锁、所述MMC中全桥子模块的工作状态为闭锁；
    当MMC中全桥子模块的功率开关管T4均导通时结束操作。
  17. 如权利要求13所述的系统，其中，所述整体轮换导通充电单元，配置为：
    步骤4：初始化所述MMC进行整体轮换导通充电的时刻m＝0；
    步骤5：控制所述交流断路器工作状态为闭合、所述启动电阻旁路开关的工作状态为闭合；
    步骤6：在所述MMC的全部子模块中选择N 2个子模块，并控制所述N 2个子模块旁路，其余子模块闭锁；
    步骤7：判断MMC中半桥子模块的电容电压和全桥子模块的电容电压是否均达到所述MMC的启动额定电压，若是，结束操作；否则，令m＝m+1，并返回步骤6。
  18. 如权利要求17所述的系统，其中，所述整体轮换导通充电单元，还配置为：按下式确定旁路的子模块数目N 2：
    Figure PCTCN2019104256-appb-100008
    式中，U M为交流系统等效电源线电压峰值；N F为MMC中全桥子模块数目；N H为MMC中半桥子模块数目，U C为模块化多电平换流器的启动额定电压值；
    按所述MMC中子模块的电容电压大小，降序排列所述MMC中子模块，在序列中选择前N 2个子模块；其中，所述MMC中子模块包括所述MMC中全桥子模块和半桥子模块。
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