WO2014187181A1 - 一种混合型换流器及风力发电系统 - Google Patents

一种混合型换流器及风力发电系统 Download PDF

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Publication number
WO2014187181A1
WO2014187181A1 PCT/CN2014/072492 CN2014072492W WO2014187181A1 WO 2014187181 A1 WO2014187181 A1 WO 2014187181A1 CN 2014072492 W CN2014072492 W CN 2014072492W WO 2014187181 A1 WO2014187181 A1 WO 2014187181A1
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Prior art keywords
phase
converter
controlled
inverter
voltage source
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Application number
PCT/CN2014/072492
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English (en)
French (fr)
Inventor
林卫星
文劲宇
王少荣
程时杰
Original Assignee
华中科技大学
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Filing date
Publication date
Application filed by 华中科技大学 filed Critical 华中科技大学
Priority to US14/411,801 priority Critical patent/US9502991B2/en
Priority to PCT/CN2014/072492 priority patent/WO2014187181A1/zh
Priority to EP14800428.6A priority patent/EP3001556B1/en
Publication of WO2014187181A1 publication Critical patent/WO2014187181A1/zh

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03D—WIND MOTORS
    • F03D9/00—Adaptations of wind motors for special use; Combinations of wind motors with apparatus driven thereby; Wind motors specially adapted for installation in particular locations
    • F03D9/20—Wind motors characterised by the driven apparatus
    • F03D9/25—Wind motors characterised by the driven apparatus the apparatus being an electrical generator
    • F03D9/255—Wind motors characterised by the driven apparatus the apparatus being an electrical generator connected to electrical distribution networks; Arrangements therefor
    • F03D9/257—Wind motors characterised by the driven apparatus the apparatus being an electrical generator connected to electrical distribution networks; Arrangements therefor the wind motor being part of a wind farm
    • 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
    • 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
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/145—Conversion of ac power input into dc 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 thyratron or thyristor type requiring extinguishing means
    • 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
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/145—Conversion of ac power input into dc 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 thyratron or thyristor type requiring extinguishing means
    • H02M7/155—Conversion of ac power input into dc 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 thyratron or thyristor type requiring extinguishing means using semiconductor devices only
    • H02M7/19—Conversion of ac power input into dc 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 thyratron or thyristor type requiring extinguishing means using semiconductor devices only arranged for operation in series, e.g. for voltage multiplication
    • 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
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/21—Conversion of ac power input into dc 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
    • 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
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/21—Conversion of ac power input into dc 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
    • H02M7/217—Conversion of ac power input into dc 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
    • H02M7/25—Conversion of ac power input into dc 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 arranged for operation in series, e.g. for multiplication of 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
    • H02M7/4835—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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
    • H02M1/0077—Plural converter units whose outputs are connected in series
    • 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
    • H02M1/0095—Hybrid converter topologies, e.g. NPC mixed with flying capacitor, thyristor converter mixed with MMC or charge pump mixed with buck
    • 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
    • H02M7/487—Neutral point clamped inverters
    • 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
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/72—Wind turbines with rotation axis in wind direction
    • 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
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/76—Power conversion electric or electronic aspects
    • 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

  • the invention belongs to the technical field of power system transmission and distribution, and more particularly to a hybrid converter and a wind power generation system.
  • the application of direct current transmission to wind power generation first requires the conversion of alternating current from the wind farm into direct current through an inverter.
  • the technologies that can be used for AC-DC conversion mainly include phase-controlled converters based on thyristors and voltage source converters based on fully-controlled devices. Since the phase-controlled converter requires an external AC voltage source to provide a commutation voltage for it, and the wind farm is a passive AC grid, it is difficult to establish an AC voltage depending on an independent wind turbine. The device is not suitable for converting wind power directly to direct current.
  • the voltage source converter can be used to transmit wind power, and the DC transmission system using multiple voltage source converters has been applied to transmit offshore wind power. However, there have been no reports of the application of voltage source converters to transmit inland wind power over long distances.
  • the main technical problem faced by the voltage source converter for long-distance transmission of inland wind power is that the rated voltage and rated power of the voltage source converter cannot meet the needs of transmitting inland wind power over long distances. It is expected that by 2015, the typical voltage and power of a voltage source converter will be ⁇ 320kV, 1000MW. At present, the voltage source converter is mainly used to transmit offshore wind power, and the transmission distance is about 100km. In the long-distance transmission of thousands of kilometers, if the DC voltage is low, the power transmitted by each DC transmission line is low, and the income from the transmission system is difficult to recover the investment in the construction of the transmission corridor. At the same time, after the DC voltage is reduced, the DC current required to deliver the same power increases, and the line loss also increases accordingly.
  • the phase-controlled converter is used in the long-distance DC transmission of the kilometer level.
  • the typical rated voltage is ⁇ 800kV. Obviously, the rated voltage of the voltage source converter is far from meeting the needs of long-distance large-scale transmission.
  • the present invention provides a hybrid inverter, the purpose of which is to connect a first phase-controlled converter, a second phase-controlled inverter and a voltage source-type converter in series. After being applied to transmission wind power generation, the voltage source type converter rated voltage and rated power are insufficient, and the phase-controlled inverter has no self-commutation function, which cannot be applied to the technical problem of the wind farm.
  • the invention provides a hybrid inverter, comprising a voltage source converter, a first phase change converter And a second phase-controlled inverter; a DC positive terminal of the voltage source converter is connected to a DC negative terminal of the first phase-controlled inverter, and a DC of the first phase-controlled inverter
  • the positive terminal is connected to the positive DC transmission line
  • the DC negative terminal of the voltage source converter is connected to the DC positive terminal of the second phase control inverter
  • the DC of the second phase control inverter is a negative terminal is connected to the negative DC power transmission line
  • an AC terminal of the voltage source type inverter, an AC terminal of the first phase control inverter, and an AC terminal of the second phase control inverter are used for Connect to the AC common bus.
  • the voltage source type inverter adopts a fully controlled type device, and the first phase controlled converter and the second phase controlled converter use a thyristor.
  • the voltage source type inverter is used for controlling an alternating current voltage of an alternating current common bus, and the alternating current voltage is applied to the first phase-controlled inverter and the second phase-controlled inverter as a first phase-controlled inverter.
  • the second phase-controlled inverter provides a commutation voltage such that the first phase-controlled inverter and the second phase-controlled inverter continue to operate normally when the conventional synchronous generator set maintains the alternating voltage of the alternating common bus.
  • first phase-controlled converter or the second phase-controlled converter is composed of a six-pulse phase-controlled converter bridge
  • the six-pulse phase-controlled converter bridge is a crystal-based converter Three-phase full-bridge AC-DC converter circuit for inter-tube.
  • first phase-controlled converter or the second phase-controlled converter is composed of a plurality of six-pulse phase-controlled converter bridges connected in series.
  • the voltage source converter is a three-phase full-bridge AC-DC conversion circuit based on a fully-controlled switching device, and can adopt a two-level topology or a three-level topology or modular multi-electricity. Flat topology.
  • the hybrid inverter further includes: a first bypass switch connected in parallel with the first phase-controlled inverter, and a second bypass switch connected in parallel with the second phase-controlled inverter
  • the first bypass switch is configured to bypass the first phase-controlled inverter during black start and power flow reversal
  • the second bypass switch is configured to bypass the first phase during black start and power flow reversal
  • the inverter is controlled so that the hybrid inverter has the functions of black start and power flow reversal.
  • the first bypass switch has the same structure as the second bypass switch;
  • the first bypass switch includes a mechanical switch and an anti-parallel thyristor pair in series with the mechanical switch.
  • the anti-parallel thyristor pair is formed by connecting a plurality of anti-parallel thyristors in series.
  • the first bypass switch or the second bypass switch is a DC circuit breaker.
  • the present invention also provides a wind power generation system, comprising: an alternating common bus, a first step-up transformer, a second step-up transformer, a third transformer, a fourth transformer, a hybrid inverter, and are respectively connected to the alternating current An AC filter unit and a reactive power compensation unit of the common bus; the input end of the first step-up transformer is used to connect the wind turbine, and the output end of the first step-up transformer is connected to the second step-up transformer through an AC transmission line.
  • An input end, an output end of the second step-up transformer is connected to the AC common bus through an AC transmission line;
  • the hybrid inverter includes a voltage source converter, a first phase-controlled inverter, and a second phase control
  • the DC positive terminal of the voltage source type inverter is connected to the DC negative terminal of the first phase control inverter, and the DC positive terminal of the first phase control inverter passes the first inductance a positive DC transmission line is connected, a DC negative end of the voltage source converter is connected to a DC positive end of the second phase control inverter, and a DC negative end of the second phase control inverter
  • the second inductor is connected to the negative DC power transmission line;
  • the AC terminal of the voltage source converter is connected to the AC common bus through the fourth transformer;
  • the AC terminal of the two-phase inverter is connected to the AC common bus through a third transformer.
  • the hybrid inverter further includes: a first bypass switch connected in parallel with the first phase-controlled inverter, and a second bypass switch connected in parallel with the second phase-controlled inverter
  • the first bypass switch is configured to bypass the first phase-controlled inverter during black start and power flow reversal
  • the second bypass switch is used to bypass the black start and the power flow reversal
  • the second phased inverter is described.
  • the first bypass switch has the same structure as the second bypass switch; the first bypass switch includes a mechanical switch and an anti-parallel thyristor pair in series with the mechanical switch.
  • the anti-parallel thyristor pair is formed by connecting a plurality of anti-parallel thyristors in series.
  • the first phase-controlled converter and the second phase-controlled inverter have the same structure; the first phase-controlled converter includes a phase-controlled converter bridge, and the six-pulse phase
  • the control converter bridge is a three-phase full-bridge AC-DC converter circuit based on a thyristor.
  • first phase-controlled converter and the second phase-controlled inverter have the same structure; the first phase-controlled inverter includes a plurality of phase-controlled converter bridges connected in series in series.
  • the hybrid converter provided by the invention applies the first phase-controlled converter, the second phase-controlled converter and the voltage source converter in series to transmit wind power generation, has self-commutation capability, and can directly connect the wind farm
  • the wind power can be converted into direct current and can be applied to the wind farm independently.
  • FIG. 1 is a schematic structural diagram of a hybrid inverter according to an embodiment of the present invention.
  • FIG. 2 is a schematic diagram of a basic topology of a hybrid inverter according to an embodiment of the present invention
  • FIG. 3 is a topology diagram of a phase-controlled converter bridge in a hybrid inverter according to an embodiment of the present invention
  • a schematic diagram of several topologies of a voltage source converter in a hybrid converter provided by the example (a) is a two-level topology, (b) is a three-level topology, and (c) is modular multi-power Flat topology
  • FIG. 5 is a schematic structural diagram of a wind power generation system according to an embodiment of the present invention.
  • FIG. 6 is a schematic diagram of a topology structure of a hybrid inverter including a bypass switch according to an embodiment of the present invention
  • FIG. 7 is a schematic structural diagram of a two-terminal direct current power transmission system composed of a hybrid inverter including a bypass switch according to an embodiment of the present invention
  • FIG. 8 is a simulation waveform of a two-terminal DC power transmission system composed of a hybrid inverter including a bypass switch according to an embodiment of the present invention; wherein (a) is an active power generated by a wind farm and a DC power sent by a rectifier station, (b) is the instantaneous value of the positive DC voltage of the rectifier station, (c) is the instantaneous value of the positive DC current of the rectifier station, and (d) is the effective value of the AC voltage of the AC bus of the rectifier station. [specific lung type]
  • the hybrid inverter provided by the embodiment of the invention is mainly applied to the field of wind power generation and direct access to the power system through the direct current transmission, and can solve the rated voltage of the voltage source type converter when used for long-distance large-scale transmission of inland wind power.
  • the rated power is too low to meet the long-distance large-scale transmission requirements and the phase-controlled converter cannot directly be applied to the transmission of wind power because it requires an external AC voltage source to provide a commutation voltage.
  • the hybrid inverter includes a voltage source type inverter 2 and a phase-controlled inverter 3 connected in series with the voltage source type inverter 2; wherein the voltage source type inverter 2 is used
  • the phased inverter 3 uses a thyristor
  • the phased inverter 3 includes a first phased inverter 3a and a second phased inverter 3b ; the first phased inverter 3a is connected to the direct current
  • the positive phase of the transmission line is connected to the anode of the direct current transmission line; the alternating current end of the voltage source type inverter 2, the alternating current end of the first phased inverter 3a and the second phased inverter 3b
  • the AC terminals are connected to the AC common bus 14 of the hybrid inverter through the intermediate connection circuit 12 and the intermediate connection circuit 13 (such as a transformer or a transformer in series with the filter branch), and the DC of the voltage source converter 2 is positive.
  • the terminal is connected to the DC negative terminal of the first phase-controlled inverter 3a, the DC positive terminal of the first phase-controlled inverter 3a is connected to the positive DC transmission line 8, and the DC-negative terminal of the voltage source converter 2 is The DC positive terminal of the second phase-controlled inverter 3b is connected, and the DC negative terminal and the negative DC of the second phase-controlled inverter 3b are connected.
  • the transmission lines 9 are connected.
  • the first phase-controlled inverter 3a and the second phase-controlled inverter 3b need to be supplied with an alternating voltage source to provide a commutation voltage, for which the first of the hybrid inverters 1
  • the phase-controlled inverter 3a and the second phase-controlled inverter 3b do not have self-commutation capability, and the voltage source type inverter 2 Thanks to the fully controlled device, it has a self-commutation function that can be used to establish the AC voltage on the AC side.
  • the AC source voltage of the AC common bus 14 can be controlled by the voltage source type inverter 2, and the AC voltage is applied to the first phase-controlled commutation through the intermediate connection circuit 12.
  • the second phase-controlled inverter 3b so that the first phase-controlled converter 3a and the second phase-controlled inverter 3b can work normally.
  • the hybrid converter 1 When no external AC voltage source is applied, the voltage source type inverter 2 and the first phase-controlled inverter 3a and the second phase-controlled inverter 3b can be combined by its own voltage source type inverter 2 and the second phase-controlled inverter 3b. Both the phase-controlled inverter 3a and the second phase-controlled inverter 3b can work normally, so that the entire hybrid inverter 1 can work normally without an external AC voltage source, so that the hybrid inverter 1 has Self-commutation capability.
  • the alternating current generated by the wind turbine is converted into direct current, and the voltage source converter 2 is used to control the alternating current of the alternating current bus 14.
  • the commutation voltage is such that the hybrid inverter 1 can still operate normally without the conventional synchronous genset maintaining the AC voltage of the AC common bus 14, so that the hybrid inverter 1 has self-commutation capability.
  • the first phase-controlled inverter 3a and the second phase-controlled inverter 3b can be realized by a six-pulse phase-controlled converter bridge 23.
  • the phase-controlled inverter can be controlled by a plurality of six-pulse phases.
  • the flow bridges 23 are connected in series.
  • the first phase-controlled inverter 3a and the second phase-controlled inverter 3b have the same structure; the first phase-controlled inverter 3a includes a phase-controlled converter bridge.
  • the first phase-controlled inverter 3a and the second phase-controlled inverter 3b may further include a plurality of phase-controlled converter bridges 23 connected in series in series.
  • the phase-controlled converter bridge 23 is a mature thyristor-based three-phase full-control AC-DC converter circuit.
  • Each phase-controlled converter bridge can be rated at 200kV, rated power up to 800MW, and multiple phase-controlled converters.
  • the flow bridge can be easily connected in series directly to further increase the rated voltage and rated power.
  • the first phase-controlled converter 3a and the second phase-controlled inverter 3b provided by the embodiments of the present invention are mature high-voltage and high-power AC-DC converters, and the advantage is that compared with the voltage source converter 2,
  • the first phase-controlled converter 3a and the second phase-controlled inverter 3b are rated for voltages up to ⁇ 800kV, 6400 MW, and are mature in technology.
  • the voltage source converter 2 can achieve the mature voltage rating of the technology, the rated power is up to ⁇ 320kV, about 1000MW.
  • the loss of the first phase-controlled inverter 3a and the second phase-controlled inverter 3b is about 0.35%, which is lower than the loss of the voltage source type converter 2 (minimum 0.5%).
  • the voltage source type inverter 2 of the same power has a cost which is about 20% higher than that of the first phase-controlled inverter 3a and the second phase-controlled inverter 3b.
  • the first phase-controlled converter 3a and the second phase-controlled converter 3b require a stable AC voltage source to provide a commutation voltage, and the wind farm is a passive AC grid, depending on an independent wind turbine. It is difficult to establish a stable AC voltage, and the phase-controlled inverter cannot be directly applied to convert wind power into DC power.
  • the phase-controlled converter 3 is an AC-DC conversion circuit, and the basic topology thereof is a six-pulse phase-controlled converter bridge 23 as shown in FIG. 3, mainly composed of six thyristors 5, and a positive pole.
  • each of the two thyristors 5 connected in series to form a phase commutating bridge arm the positive end of each phase commutating bridge arm is connected with the positive DC bus 6, the negative of each phase commutating arm
  • the terminal is connected to the negative DC bus 7
  • the midpoint of each phase commutating bridge arm is respectively connected with the A phase AC terminal 51a, the B phase AC terminal 51b, and the C phase AC terminal 51c, in order to increase the rated voltage of the phase control converter bridge 23
  • Each thyristor 5 can be formed by a plurality of thyristors 5 connected in series.
  • phase-controlled converter bridge operates at a frequency of 50 Hz or 60 Hz, and multiple thyristors 5 are directly connected in series, the trigger synchronization can still be guaranteed.
  • the phase-controlled converters are often connected in series by a plurality of phase-controlled converter bridges, so that the rated voltage after series connection, the rated power can reach ⁇ 800kV, 6400MW, and the technology is mature.
  • the voltage source converter 2 is also an AC-DC conversion circuit, which can adopt a two-level topology, a clamp-type multi-level topology, a modular multi-level topology, and the like. Topology. As shown in FIG. 4, the specific structure of the voltage source converter 2 can adopt a two-level topology as shown in FIG. 4(a), mainly composed of six full-control devices 50, a positive DC bus 6, and a negative DC.
  • the type devices 50 are connected in series to form a phase commutating bridge arm, and the positive end of each phase commutating bridge arm is connected with the positive DC bus 6 , and the negative end of each phase commutating bridge arm is connected with the negative DC bus 7 , each phase
  • the midpoint of the commutating bridge arm is respectively connected with the A phase AC terminal 51a, the B phase AC terminal 51b, and the C phase AC terminal 51c.
  • the positive terminal of the positive DC capacitor is connected to the positive DC bus 6 and the negative terminal of the positive DC capacitor is grounded 57.
  • the positive terminal of the DC capacitor is grounded 57, and the negative terminal of the negative DC capacitor is connected to the negative DC bus 7.
  • a plurality of fully controlled devices 50 need to be connected in series to form a full control type. Instead of connecting multiple voltage source converters in series, device 50.
  • the specific structure of the voltage source converter 2 can also adopt a three-level topology as shown in FIG. 4(b), mainly consisting of 12 full-control devices 50, 6 clamp diodes 53, and a positive DC bus 6.
  • the negative DC bus 7, the positive DC capacitor 52a, and the negative DC capacitor 52b are formed.
  • Each two fully controlled devices 50 are connected in series to form a 'half bridge arm', and each two 'half bridge arms' are connected in series to form a phase commutating flow.
  • the bridge arm, the midpoint of each 'half bridge arm' is connected to the ground 57 via a clamp diode 53.
  • each phase commutating bridge arm is connected to the positive DC bus 6 and the negative end of each phase commutating bridge arm Connected to the negative DC busbar 7, the midpoint of each phase commutating bridge arm is respectively connected with the A phase AC terminal 51a, the B phase AC terminal 51b, and the C phase AC terminal 51c, and the positive terminal of the positive DC capacitor is connected to the positive DC busbar 6,
  • the negative terminal of the positive DC capacitor is grounded 57
  • the positive terminal of the negative DC capacitor is grounded 57
  • the negative terminal of the negative DC capacitor is connected to the negative DC bus 7.
  • each fully controlled type Device 50 can be made up of multiple The control devices are connected in series, and each of the clamp diodes 53 may be connected in series by a plurality of clamp diodes instead of directly connecting the plurality of voltage source inverters 2 in series to increase the rated voltage of the voltage source type converter 2 .
  • the specific structure of the voltage source converter 2 can also adopt a modular multi-level topology as shown in FIG. 4(c), which mainly includes six half-bridge arms 55, and each two half-bridge arms 55 are connected in series to form one phase bridge.
  • the middle point of each phase commutating bridge arm is respectively connected with the A phase AC terminal 51a, the B phase AC terminal 51b, and the C phase AC terminal 51c.
  • the positive and negative ends of each phase bridge arm are respectively connected to the positive DC bus 6 and the negative pole.
  • the DC bus bars 7 are connected, and each of the half bridge arms has a plurality of submodules 54 connected in series, and then the smooth wave reactors 56 are connected in series.
  • Each submodule is composed of two fully controlled devices 50 and DC capacitors 55.
  • the fully-controlled device 50 connected in series increases the rated voltage of the two-level topology and the three-level topology by about ⁇ 300 kV by increasing the series-controlled full-control device 50, further improving the two-level topology and the three-level
  • the rated voltage of the topology is not technically feasible.
  • the two-level topology and the three-level topology work switching frequency are several kilohertz. It is necessary to ensure that many direct-connected full-control devices 50 are synchronously triggered at a frequency of several kilohertz, and the system reliability is low, and the two systems are simultaneously Flat and three-level topologies have high losses of about 1.6%.
  • the modular multi-level topology increases the voltage rating of the voltage source converter by indirectly connecting a plurality of fully controlled devices 50 in series by increasing the number of sub-modules 54 connected in series. Since the fully-controlled devices 50 are indirectly connected in series by the sub-module 54, the modular multi-level topology does not require the in-line series of fully-controlled devices 50 to be triggered synchronously, compared to a two-level topology and a three-level topology. Modular multi-level topologies require less synchronization for triggers, higher system reliability, and easier to further increase the voltage rating of modular multilevel converters.
  • the loss of a modular multi-level topology is lower than that of a two-level topology and a three-level topology with a loss of approximately 0.5%.
  • the existence of a modular multi-level topology also has a technical bottleneck in which the sub-module capacitance is difficult to increase after the serial sub-modules are increased. It is expected that the rated voltage of the modular multi-level topology will be around ⁇ 320kV by 2015, and a modular multi-level topology with higher voltage rating is under development with certain technical uncertainty.
  • the voltage source converter 2 in the hybrid inverter 1 recommends a modular multilevel topology.
  • the voltage source type inverter 2 provided by the embodiment of the invention has advantages over the first phase-controlled inverter 3a and the second phase-controlled inverter 3b in that it can be self-transformed, can be black-started, and has a small footprint.
  • Trend reversal There is no need to change the polarity of the voltage, and the disadvantage is that the loss and investment of the voltage source type converter 2 is higher than that of the first phase-controlled inverter 3a and the second phase-controlled inverter 3b.
  • the voltage source converter 2 mainly has multiple topologies such as a two-level inverter and a modular multi-level converter.
  • the loss rate of the two-level voltage source converter is about 1.6%, and the modularity is large.
  • the level-voltage source converter has a loss rate of approximately 0.5%.
  • the present invention also provides a wind power generation system including an alternating common bus 14, a first step-up transformer 18, a second step-up transformer 20, a third transformer 12, a fourth transformer 13, a hybrid inverter 1, and respectively
  • the AC filter unit 15 and the reactive power compensation unit 16 are connected to the AC common bus 14; the input end of the first step-up transformer 18 is used to connect the wind turbine 17 , and the output of the first step-up transformer 18 is connected to the AC power transmission line 19 to An input end of the second step-up transformer 20, an output end of the second step-up transformer 20 is connected to the AC common bus 14 through an AC power transmission line 21;
  • the hybrid inverter 1 includes a voltage source converter 2, Phase-controlled inverter 3a and second phase-controlled inverter 3b; DC positive terminal of voltage source converter 2 is connected to DC negative terminal of said first phase-controlled inverter 3a, first phase-controlled commutation
  • the DC positive terminal of the device 3a is connected to the positive DC transmission line 8 through the first inductor 10, and the DC
  • the DC negative terminal is connected to the negative DC power transmission line 9 through the second inductor 11; the AC terminal of the voltage source converter 2 is connected to the AC common bus 14 through the fourth transformer 13; the AC terminal of the first phase-controlled inverter 3a and The AC terminals of the second phase-controlled inverter 3b are connected to the AC common bus 14 via a third transformer 12, respectively.
  • Fig. 5 shows that the above-described hybrid inverter 1 having a self-commutation function is applied to a wind power generation system, and the first phase-controlled inverter 3a and the second phase-controlled inverter 3b of the hybrid inverter are respectively Three six-pulse phase-controlled converter bridges 23 with a rated voltage of 200kV are connected in series, and each six-pulse phase is controlled.
  • the rated voltage of the bridge is matched with the existing ⁇ 800kV phase-controlled converter technology.
  • the voltage source converter 2 is rated at ⁇ 200kV. It adopts a two-level topology and the rated voltage of the entire hybrid inverter.
  • the current phase of the first phase-controlled inverter 3a and the second phase-controlled inverter 3b and the voltage-source converter 2 are connected to the alternating current common busbars 14a-14c via the transformers 12, 13 respectively, ⁇ 800 kV, the wind turbine 17 through the respective first step-up transformers 18, the AC power transmission line 19 is collected in the wind farm, and the second step-up transformer 20 and the AC power transmission line 21 of the wind farm collection point are connected to the AC common bus lines 14a-14c, in order to compensate for the first
  • the reactive power consumed by the phase-controlled inverter 3a and the second phase-controlled inverter 3b and the harmonic current generated by the first phase-controlled inverter 3a and the second phase-controlled inverter 3b are filtered,
  • the AC common bus 14a-14c of the type converter 1 is provided with an AC filter unit 15 and a reactive power compensation unit 16, and the AC filter unit 15 and the reactive power compensation unit 16 are divided into a plurality of groups so that the active power can be transmitted according to the hybrid in
  • the size of the power is put into the appropriate number of AC filters Unit 15 and reactive compensation unit 16. Since the hybrid inverter 1 of FIG. 5 is only connected to the passive power grid of the wind farm 60 on the AC side and is not connected to the AC voltage source, the application shown in FIG. 5 requires the hybrid inverter 1 to have Self-commutation capability, otherwise the hybrid inverter 1 cannot be applied to transmit wind power. In order to make the hybrid inverter 1 have a self-commutation function as a whole, the voltage source type inverter 2 can be used to control the terminal voltage of the AC terminal of the hybrid inverter 1, and the terminal voltage is applied to the first phase through the AC bus 14.
  • the voltage source type inverter can be made by the combination of its own voltage source type inverter 2 and the first phase-controlled inverter 3a and the second phase-controlled inverter 3b when no external AC voltage source is applied. 2 and the first phase-controlled inverter 3a and the second phase-controlled inverter 3b can work normally, so that the entire hybrid inverter 1 can work normally without an external AC voltage source, so that the hybrid inverter 1 has self-commutation ability.
  • FIG. 6 shows a modified hybrid inverter 24, which has a modified hybrid inverter 24 phase.
  • An improvement over the hybrid inverter 1 is the first phase-controlled inverter 3a and the second phase-controlled commutation
  • the DC positive terminal and the DC negative terminal of the device 3b are connected in parallel with a bypass switch 25 formed by a series connection of a mechanical switch 4 and a pair of anti-parallel thyristors 5a, 5b, and the phase change is controlled by a bypass switch during black start and power flow reversal.
  • the shunt is shorted so that the hybrid inverter is only put into the voltage source type converter, and the voltage source type converter has the black start and the power flow reversal capability.
  • the advantage of adding the bypass switch 25 is that the hybrid inverter 1 can have the functions of black start and power flow reversal. Otherwise, if the hybrid inverter 1 does not have a black start function, when the hybrid inverter 1 is only connected to the wind farm 60, the wind farm 60 cannot be switched from the outage state to the running state. When the hybrid inverter 1 is connected to the wind farm 60 and connected to the local load, if the hybrid inverter 1 does not have the power flow reversal function, when the wind power is lower than the local load, the local load will be insufficiently supplied. problem.
  • the bypass switch 25 can be formed by connecting mechanical switches 4 and anti-parallel thyristors 5a, 5b in series, or a DC circuit breaker.
  • the anti-parallel thyristor pair may be composed of a pair of anti-parallel thyristors; in order to improve the withstand voltage level of the bypass switch, a plurality of anti-parallel thyristor pairs may also be connected in series.
  • the black start principle of the system is as follows: Taking the two-terminal DC power transmission system shown in FIG. 7 as an example, by closing the bypass mechanical switches 4, 34 and applying the anti-parallel thyristors 5a, 5b, 35a, 35b The trigger signal, the rectifying side phase-controlled converter bridge 3 and the inverter-side phase-controlled converter bridge 33 are all short-circuited by the bypass, and the rectifying-side hybrid inverter 1 and the inverter-side hybrid inverter 31 have only the voltage source.
  • the type inverters 2, 32 are put into operation, so that the direct current transmission system can realize the black start function according to the startup process of the two-terminal direct current transmission system based on the voltage source type inverter.
  • the principle of the power flow reversal of the system is as follows: Before the power flow is reversed, the phase-controlled inverters 3, 33 and the voltage source-type inverters 2, 32 are all in the commissioning state, the mechanical bypass switch 4, 34 disconnected, anti-parallel thyristors 5a, 5b, 35a, 35b are in a locked state. After receiving the power flow reversal command, the system moves the trigger angle of the rectifying-side phase-controlled inverter 3 to 120°-150°, so that the phase-controlled inverter 3 operates in the inverter state, because the phase-controlled inverter 3 33 is in the inverter state, and the DC voltage of the DC transmission lines 8, 9 is rapidly decreased.
  • phase-controlled inverters 3, 33 When the positive and negative of the phase-controlled inverters 3, 33 are detected, When the DC voltage seen by the flow port is lower than the withstand voltage of the anti-parallel thyristors 5a, 5b, 35a, 35b, the system closes the mechanical bypass switches 4, 34, and applies a trigger signal to the anti-parallel thyristors 5a, 5b, 35a, 35b, thereby being short.
  • the phase-controlled converters 3, 33 are connected to the voltage source type converters 2, 32 on both sides of the system, so that the system can realize partial power flow according to the operation mode of the two-terminal DC power transmission system based on the voltage source type converter. Reverse function.
  • a parallel connection between the DC positive terminal and the DC negative terminal of each of the first phase-controlled inverter 3a and the second phase-controlled inverter 3b may be employed.
  • the bypass switch 25 When the bypass switch 25 is connected, the bypass switch 25 is turned on during the black start and the power flow reversal to short the first phase-controlled inverter 3a and the second phase-controlled inverter 3b, so that the hybrid inverter 1 is only put into the voltage source.
  • the type inverter 2 is such that the hybrid inverter 1 has a black start and a power flow reversal capability, wherein a preferred arrangement of the bypass switch 25 is formed by connecting a conventional mechanical switch 4 and anti-parallel thyristors 5a, 5b in series.
  • the anti-parallel thyristors 5a, 5b may be formed by connecting a plurality of anti-parallel thyristors in series to increase the withstand voltage level of the bypass switch.
  • the number of the flow bridges 23 increases the rated voltages of the first phase-controlled inverter 3a and the second phase-controlled inverter 3b, thereby increasing the rated voltage of the hybrid inverter 1, and establishing a common current through the voltage source type inverter 2
  • the AC voltage of the bus bar 14 is applied to the first phase-controlled inverter 3a and the second phase-controlled inverter 3b via the intermediate connection circuit 12, for the first phase-controlled inverter 3a and the second phase-controlled converter
  • the flow device 3b provides a commutation voltage, so that the hybrid inverter 1 has self-commutation capability, and can directly connect the wind farm 60 to convert the alternating current generated by the wind farm 60 into direct current, and the scheme comprehensively utilizes the first phase-controlled invert
  • first phase-controlled inverter 3a and second phase-controlled inverter 3b requires an external AC voltage source to provide a commutation voltage for it, which cannot be directly applied to the transmission of wind power defects; (2) It is proposed that the first phase-controlled inverter 3a and the second phase-controlled inverter 3b and the voltage source-type inverter are connected in series with the inverter 1, and the voltage source-type inverter 2 is first.
  • the phase-controlled inverter 3a and the second phase-controlled inverter 3b provide a commutation voltage so that the hybrid inverter 1 has a self-commutation capability as a whole, and can be applied to passives that do not have a conventional synchronous generator to maintain the AC grid voltage.
  • the AC grid eg wind farm, pure load network
  • Figure 7 shows a DC transmission system with a rated voltage of ⁇ 800kV and a rated power of 4000MW.
  • the system mainly includes a rectification side hybrid inverter 1 and an inverter side hybrid inverter 31.
  • the common AC bus 14 of the hybrid inverter 1 is connected to the wind farm 60 and the local load 22, and the AC common bus 44 of the hybrid inverter 31 is connected to the receiving AC grid 47.
  • phased inverter 3 and the phased inverter 33 are respectively connected with the bypass switches 4, 5a, 5b and 34, 35a, 35b.
  • the voltage source type inverters 2, 32 have a rated voltage of ⁇ 200kV and a rated power of 1000MW.
  • Each phase-controlled inverter 3, 33 is formed by three six-pulse phase-controlled inverters 23 connected in series, each of which is six The pulsed phased inverter 23 has a rated DC voltage of 200 kV.
  • each converter uses the detailed switch model in the PSCAD/EMTDC standard model library.
  • multiple wind farms are modeled by an equal-capacity wind turbine, but the inverter is still used.
  • Detailed switch model modeling Since the primary device models of the simulation examples are all built from the detailed switch models in the standard model library, the results from the simulation experiments are highly reliable.
  • Figure 8 (a) shows the active power from the wind farm and the DC power delivered by the hybrid inverter 1.
  • Figure 8 (b) shows the positive DC voltage of the hybrid inverter 1
  • the time value, Figure 8 (c) is the instantaneous value of the positive DC current of the hybrid inverter 1
  • Figure 8 (d) is the RMS effective value of the AC bus 14 of the hybrid inverter 1.
  • the bypass switches 4, 5a, 5b, 34, 35a, 35b of the hybrid inverters 1, 31 on both sides are input, the phase-controlled inverters 3, 33 are short-circuited, and the system only inputs the voltage source.
  • Type converters 2, 32 the system performs a black start in accordance with the operating mode of a similar voltage source type DC transmission system.
  • the bypass switch was kept in the input state due to the low wind power. As shown in Figure 8 (a), during this period, the rectifier side DC voltage is about 220kV, which is higher than the DC voltage on the inverter side.
  • the system DC voltage does not contain the typical pulsation of the phase-controlled converter DC voltage.
  • Figure 8 (d) shows that the AC voltage of the wind farm is always maintained near the rated value, and the hybrid inverter 1 can still operate normally without the conventional synchronous generator maintaining the AC voltage.
  • the above simulation results show that the hybrid converter is directly applicable to the transmission of wind power is technically feasible.
  • the DC voltage of the system is about ⁇ 200kV (Fig. 8a), and the active power is about 600MW (Fig. 8b).
  • the DC voltage of the system is about ⁇ 800kV (Fig. 8a), and the active power is up to 3900MW (Fig. 8b).
  • the above simulation results prove that the invention can solve the rated voltage existing in the existing voltage source converter. And the rated power can not meet the technical requirements of large-scale long-distance transmission of wind power generation (thousands of kilometers of transmission distance).
  • the present invention provides a technically viable solution for large-scale wind power generation via DC long-distance transmission while other solutions or techniques are not feasible or have technical uncertainty and require higher costs.
  • the separate first phase-controlled inverter 3a and second phase-controlled inverter 3b have no self-commutation compared to the separate first phase-controlled inverter 3a and second phase-controlled inverter 3b
  • the capability, which cannot be independently applied to the wind farm, is not technically feasible for the separate first phase-controlled inverter 3a and the second phase-controlled inverter 3b to transmit wind power, and the hybrid inverter 1 of the present invention
  • the utility model has the self-commutation capability, can directly connect the wind farm to convert the wind power into the direct current power, and the invention is technically feasible for transmitting the wind power generation;
  • the voltage of the voltage source converter 2 will be about ⁇ 320kV by 2015, and the voltage source converter 2 with higher voltage rating is not mature, research and development There is technical uncertainty, and the rated voltage of the invention can reach ⁇ 800kV, and the technical components of each component are mature, which satisfies the requirement of the rated voltage of the large-scale long-distance transmission of wind power by DC.
  • the voltage source type converter 2 has a loss rate of at least about 0.5%, and the present invention has the capacity of the voltage source type inverter 2 and the total first phase-controlled inverter 3a and the second phase-controlled inverter 3b.
  • the number is taken as 2000 hours, and the power transmission system based on the voltage source type converter 2 of the same capacity is compared with the present invention (assuming future storage) In this technology, the annual transmission loss is estimated to be 28 million yuan.
  • the investment cost of the present invention compared to the same capacity of the power source-based converter 2 (supposed in the future) is about 3 billion yuan.

Abstract

一种混合型换流器及风力发电系统，该混合型换流器由基于晶闸管的相控换流器和基于全控型器件的电压源型换流器串联而成，包含一个电压源型换流器（2），连接在正极的相控换流器（3a）和连接在负极的相控换流器（3b），相控换流器（3a，3b）和电压源型换流器（2）都通过变压器与交流电网（47）相连接，电压源型换流器（2）的直流正端与相控换流器（3a）的直流负端相连接，相控换流器（3a）的直流正端与正极直流输电线路（8）相连接，电压源型换流器（2）的直流负端与相控换流器（3b）的直流正端相连接，相控换流器（3b）的直流负端与负极直流输电线路（9）相连接。所述混合型换流器具有自换相能力，可以直接连接风电场将风电转换为直流电，提高混合型换流器的额定电压和额定功率的同时且各个部件技术成熟，整个系统技术可靠性高。

Description

一种混合型换流器及风力发电系统
【技术领域】
本发明属于电力系统输配电技术领域， 更具体地， 涉及一种混合型换 流器及风力发电系统。
【背景技术】
自 2005年以来，世界范围内风电装机容量一直在迅猛增加， 2005-2011 年风电装机容量年均增速在 20%以上， 从 2011年后， 全球风电发展进入平 稳期， 每年新增的装机容量保持在 40GW左右。 但与风电快速发展相对应 的瓶颈是， 大部分风电基地位于偏远地区， 本地交流电网用电负荷低， 自 身消纳能力弱， 风能资源与负荷中心呈逆向分布， 决定了大部分风力发电 需要经过大规模远距离输电使其在负荷中心进行消纳。 直流输电是实现大 规模远距离输电的一种通用技术。
应用直流输电传输风力发电首先需要通过换流器将风电场发出的交流 电转换为直流电。 在直流输电领域， 可用于交流 -直流变换的技术主要有基 于晶闸管的相控换流器和基于全控型器件的电压源型换流器两种。 由于相 控换流器工作时需要外在交流电压源为其提供换相电压， 而风电场是无源 交流电网， 依赖一个个独立的风力发电机组难以建立起交流电压， 为此相 控换流器不适用于直接将风电转换为直流电。
电压源型换流器可应用于传输风力发电， 已有多回应用电压源型换流 器的直流输电系统应用于传输海上风电。 但目前尚未见到应用电压源型换 流器远距离传输内陆风电的报道。
电压源型换流器应用于远距离传输内陆风电面临的主要技术问题为电 压源型换流器的额定电压与额定功率无法满足远距离传输内陆风电的需 要。预期到 2015年，电压源型换流器的典型电压和功率为 ±320kV， 1000MW, 目前电压源型换流器主要应用于传输海上风电， 输电距离为 100km左右。 在数千千米的远距离输电中若直流电压偏低， 每回直流输电线路输送 的功率偏低， 从输电系统所得到的收益难以回收建设输电走廊的投资。 同 时直流电压降低后， 输送相同功率所要求的直流电流升高， 线路损耗也相 应地提高。 当输电距离长达数千千米时常常需要增大输电电压从而提高输 电功率和降低输电损耗。 目前千米级别的远距离直流输电中采用相控换流 器， 其典型额定电压为 ±800kV， 很明显， 电压源型换流器的额定电压远不 能满足长距离大规模输电的需要。
即使随着技术的发展，未来电压源型换流器可能达到 ±800kV额定电压。 由于电压源型换流器采用全控型器件， 单个全控型器件的额定功率远低于 单个晶闸管。 为了使电压源型换流器的额定电压达到远距离输电的要求， 需要将多个全控型器件串联 （直接或间接串联） 以提高电压源型换流器的 额定电压。 由于采用的全控型器件数量过多， 增大了系统复杂度， 降低了 系统可靠性， 同时电压源型换流器的功率仍不能满足远距离输送的要求。 为了使电压源型换流器的额定电压和额定功率都达到远距离输送的要求， 一种非常规的方案是采用多个低压大电流的全控型器件串联以提高电压源 型换流器的额定电压和额定功率。 采用这种方案后， 电压源型换流器所采 用的全控型器件数量将进一步增多， 进一步增大了系统复杂度， 降低系统 可靠性。
【发明内容】
针对现有技术的以上缺陷或改进需求， 本发明提供了一种混合型换流 器， 其目的在于将第一相控换流器、 第二相控换流器和电压源型换流器串 联后应用于传输风力发电， 由此解决了电压源型换流器额定电压、 额定功 率不够以及相控换流器没有自换相功能， 不能应用于风电场的技术问题。 本发明提供了一种混合型换流器， 包括电压源型换流器、 第一相控换 流器和第二相控换流器； 所述电压源型换流器的直流正端与所述第一相控 换流器的直流负端连接， 所述第一相控换流器的直流正端用于与正极直流 输电线路连接， 所述电压源型换流器的直流负端与所述第二相控换流器的 直流正端连接， 所述第二相控换流器的直流负端用于与负极直流输电线路 连接； 所述电压源型换流器的交流端、 所述第一相控换流器的交流端和所 述第二相控换流器的交流端用于与交流公共母线连接。
更进一步地， 所述电压源型换流器采用全控型器件， 所述第一相控换 流器和第二相控换流器采用晶闸管。
更进一步地， 所述电压源型换流器用于控制交流公共母线的交流电压， 该交流电压作用到第一相控换流器和第二相控换流器上为第一相控换流器 和第二相控换流器提供换相电压， 使得第一相控换流器和第二相控换流器 在没有常规同步发电机组维持交流公共母线的交流电压时仍正常工作。
更进一步地， 所述第一相控换流器或所述第二相控换流器由一个六脉 波相控换流桥组成， 所述六脉波相控换流桥是一种基于晶间管的三相全桥 交流-直流变换电路。
更进一步地， 所述第一相控换流器或所述第二相控换流器由多个六脉 波相控换流桥串联组成。
更进一步地， 所述电压源型换流器为一种基于全控型开关器件的三相 全桥交流-直流变换电路， 可以采用两电平拓扑结构或三电平拓扑结构或模 块化多电平拓扑结构。
更进一步地， 所述混合型换流器还包括： 与所述第一相控换流器并联 的第一旁路开关， 以及与所述第二相控换流器并联的第二旁路开关， 所述 第一旁路开关用于在黑启动以及潮流反转时旁路第一相控换流器， 所述第 二旁路开关用于在黑启动以及潮流反转时旁路第一相控换流器从而使得混 合型换流器具有黑启动和潮流反转的功能。
更进一步地， 所述第一旁路开关与所述第二旁路开关的结构相同； 所 述第一旁路开关包括机械开关以及与所述机械开关串联的反并联晶闸管 对。
更进一步地， 所述反并联晶闸管对为多个反并联的晶闸管串联而成。 更进一步地， 所述第一旁路开关或第二旁路开关为直流断路器。
本发明还提供了一种风力发电系统， 包括： 交流公共母线， 第一升压 变压器， 第二升压变压器， 第三变压器， 第四变压器， 混合型换流器， 以 及分别连接至所述交流公共母线的交流滤波单元和无功补偿单元； 所述第 一升压变压器的输入端用于连接风电机组， 所述第一升压变压器的输出端 通过交流输电线路连接至第二升压变压器的输入端， 第二升压变压器的输 出端通过交流输电线路连接至所述交流公共母线； 所述混合型换流器包括 电压源型换流器、 第一相控换流器和第二相控换流器； 所述电压源型换流 器的直流正端与所述第一相控换流器的直流负端连接， 所述第一相控换流 器的直流正端通过第一电感与正极直流输电线路连接， 所述电压源型换流 器的直流负端与所述第二相控换流器的直流正端连接， 所述第二相控换流 器的直流负端通过第二电感与负极直流输电线路连接； 所述电压源型换流 器的交流端通过所述第四变压器连接至交流公共母线； 所述第一相控换流 器的交流端和所述第二相控换流器的交流端分别通过第三变压器连接至交 流公共母线。
更进一步地， 所述混合型换流器还包括： 与所述第一相控换流器并联 的第一旁路开关， 以及与所述第二相控换流器并联的第二旁路开关； 所述 第一旁路开关用于在黑启动以及潮流反转时旁路所述第一相控换流器， 所 述第二旁路开关用于在黑启动以及潮流反转时旁路所述第二相控换流器。
更进一步地， 所述第一旁路开关与所述第二旁路开关的结构相同； 所 述第一旁路开关包括机械开关以及与所述机械开关串联的反并联晶闸管 对。
更进一步地， 所述反并联晶闸管对为多个反并联的晶闸管串联而成。 更进一步地， 所述第一相控换流器和所述第二相控换流器的结构相同； 所述第一相控换流器包括一个相控换流桥， 所述六脉波相控换流桥是一种 基于晶闸管的三相全桥交流-直流变换电路。
更进一步地， 所述第一相控换流器和所述第二相控换流器的结构相同； 所述第一相控换流器包括多个依次串联连接的相控换流桥。
本发明提供的混合换流器将第一相控换流器、 第二相控换流器和电压 源型换流器串联后应用于传输风力发电， 具有自换相能力， 可以直接连接 风电场将风电转换为直流电， 能独立地应用于风电场； 通过对现有成熟技 术的组合改进， 能同时提高混合型换流器的额定电压和额定功率， 且各个 部件技术成熟， 整个系统技术可靠性高。
【附图说明】
图 1是本发明实施例提供的混合型换流器的原理结构图；
图 2是本发明实施例提供的混合型换流器的基本拓扑结构示意图； 图 3是本发明实施例提供的混合型换流器中的相控换流桥的拓扑； 图 4是本发明实施例提供的混合型换流器中的电压源型换流器的几种 拓扑结构示意图； 其中 （a) 为两电平拓扑， （b ) 为三电平拓扑， （c) 为 模块化多电平拓扑；
图 5是本发明实施例提供的风力发电系统的结构示意图；
图 6是本发明实施例提供的包含旁路开关的混合型换流器的拓扑结构 示意图；
图 7是本发明实施例提供的由包含旁路开关的混合型换流器构成的两 端直流输电系统的结构示意图；
图 8是本发明实施例提供的由包含旁路开关的混合型换流器构成的两 端直流输电系统的仿真波形； 其中 （a) 为风电场发出的有功功率及整流站 送出的直流功率， （b ) 为整流站正极直流电压瞬时值， （c) 为整流站正 极直流电流瞬时值， （d ) 为整流站交流母线的交流电压有效值。 【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混合型换流器主要应用于风力发电经直流输电接 入至电力系统的领域， 能够解决电压源型换流器应用于远距离大规模传输 内陆风电时， 其额定电压， 额定功率偏低， 无法满足远距离大规模输电要 求以及相控换流器因为需要外在交流电压源提供换相电压而无法直接应用 于传输风力发电的问题。
如图 1和图 2所示， 混合型换流器包括电压源型换流器 2以及与电压 源型换流器 2串联连接的相控换流器 3;其中电压源型换流器 2采用全控型 器件， 相控换流器 3采用晶闸管， 相控换流器 3包括第一相控换流器 3a和 第二相控换流器 3b; 第一相控换流器 3a连接在直流输电线路正极； 第二相 控换流器 3b连接在直流输电线路负极； 电压源型换流器 2的交流端、 第一 相控换流器 3a的交流端和第二相控换流器 3b的交流端都通过中间连接电 路 12和中间连接电路 13 (如变压器或变压器与滤波支路串联等）与混合型 换流器的交流公共母线 14相连接， 电压源型换流器 2的直流正端与第一相 控换流器 3a的直流负端相连接，第一相控换流器 3a的直流正端与正极直流 输电线路 8相连接， 电压源型换流器 2的直流负端与第二相控换流器 3b的 直流正端相连接， 第二相控换流器 3b的直流负端与负极直流输电线路 9相 连接。
在本发明实施例中， 第一相控换流器 3a和第二相控换流器 3b工作时 需要外加交流电压源为其提供换相电压， 为此混合型换流器 1 中的第一相 控换流器 3a和第二相控换流器 3b不具备自换相能力， 电压源型换流器 2 由于采用了全控型器件， 具有自换相功能， 可以用于建立起交流侧的交流 电压。 为了使混合型换流器 1 整体具有自换相功能， 可以利用电压源型换 流器 2控制交流公共母线 14的交流电压，该交流电压通过中间连接电路 12 被施加在第一相控换流器 3a和第二相控换流器 3b上， 从而使得第一相控 换流器 3a和第二相控换流器 3b能正常工作， 通过上述控制层面的布局， 混合型换流器 1 在无外加交流电压源时， 通过其自身的电压源型换流器 2 和第一相控换流器 3a和第二相控换流器 3b的组合即可使得电压源型换流 器 2和第一相控换流器 3a和第二相控换流器 3b都能正常工作， 从而使得 整个混合型换流器 1 在无外加交流电压源时能正常工作， 使得混合型换流 器 1具备了自换相能力。
在本发明实施例中，为了使该混合型换流器 1能直接连接在风电场 60， 将风电机组发出的交流电转换为直流电， 电压源型换流器 2用于控制交流 公共母线 14的交流电压， 该交流电压经中间连接电路 12作用到第一相控 换流器 3a和第二相控换流器 3b上， 为第一相控换流器 3a和第二相控换流 器 3b提供换相电压从而使得该混合型换流器 1在没有常规同步发电机组维 持交流公共母线 14的交流电压时仍可以正常工作， 因此该混合型换流器 1 具有自换相能力。 第一相控换流器 3a和第二相控换流器 3b可以由一个六 脉波相控换流桥 23实现。 为了提高第一相控换流器 3a和第二相控换流器 3b的额定电压从而提高整个混合型换流器 1的额定电压， 相控换流器可以 由多个六脉波相控换流桥 23串联而成。
在本发明实施例中， 第一相控换流器 3a和第二相控换流器 3b的结构 相同；第一相控换流器 3a包括一个相控换流桥。第一相控换流器 3a和第二 相控换流器 3b还可以包括多个依次串联连接的相控换流桥 23。相控换流桥 23是一种技术成熟的基于晶闸管的三相全控交流-直流变换电路， 每个相控 换流桥的额定电压可达 200kV， 额定功率可达 800MW, 多个相控换流桥可 方便地直接串联， 进一步加大额定电压， 额定功率。 本发明实施例提供的第一相控换流器 3a和第二相控换流器 3b是技术 成熟的高压大功率交流-直流变换器， 相比于电压源型换流器 2， 其优点在 于第一相控换流器 3a 和第二相控换流器 3b 额定电压， 额定功率可达 ±800kV, 6400MW, 且技术成熟。 而电压源型换流器 2所能达到的技术成 熟的额定电压， 额定功率最高为 ±320kV， 1000MW左右。 第一相控换流器 3a和第二相控换流器 3b损耗约为 0.35% ,低于电压源型换流器 2的损耗 (最 低为 0.5% )。 同等功率的电压源型换流器 2其成本比第一相控换流器 3a和 第二相控换流器 3b高 20%左右。 但第一相控换流器 3a和第二相控换流器 3b工作时需要稳定的交流电压源为其提供换相电压， 而风电场是无源交流 电网， 依赖于一个个独立的风电机组难以建立稳定的交流电压， 为此相控 换流器无法直接应用于将风电转换为直流电。
在本发明实施例中， 相控换流器 3是一种交流-直流变换电路， 其基本 拓扑为如图 3所示的六脉波相控换流桥 23， 主要由 6个晶闸管 5， 正极直 流母线 6，负极直流母线 7，每两个晶闸管 5串联连接后构成一相换流桥臂， 每相换流桥臂的正端与正极直流母线 6相连接， 每相换流桥臂的负端与负 极直流母线 7相连接，每相换流桥臂的中点分别与 A相交流端 51a， B相交 流端 51b， C相交流端 51c连接， 为了提高相控换流桥 23的额定电压， 每 个晶闸管 5可以由多个晶闸管 5串联而成， 由于相控换流桥工作频率为 50 赫兹或 60赫兹， 多个晶闸管 5直接串联后， 触发同步性仍能得到保障， 直 流输电中所采用的相控换流器常由多个相控换流桥串联而成使得串联后额 定电压， 额定功率可达 ±800kV， 6400MW, 且技术成熟。
在本发明实施例中， 电压源型换流器 2也是一种交流-直流变换电路， 可以采用两电平型拓扑结构， 钳位型多电平拓扑， 模块化多电平型拓扑等 多种拓扑结构。如图 4所示， 电压源型换流器 2的具体结构可以采用如图 4 (a)所示的两电平拓扑结构， 主要由 6个全控型器件 50， 正极直流母线 6， 负极直流母线 7， 正极直流电容 52a， 负极直流电容 52b组成， 每两个全控 型器件 50串联连接后构成一相换流桥臂， 每相换流桥臂的正端与正极直流 母线 6相连接， 每相换流桥臂的负端与负极直流母线 7相连接， 每相换流 桥臂的中点分别与 A相交流端 51a， B相交流端 51b， C相交流端 51c连接， 正极直流电容的正端连接正极直流母线 6， 正极直流电容的负端接地 57， 负极直流电容的正端接地 57， 负极直流电容的负端与负极直流母线 7相连 接， 为了提高电压源型换流器 2的额定电压， 需要将多个全控型器件 50串 联构成一个全控型器件 50， 而不是将多个电压源型换流器直接串联。
电压源型换流器 2的具体结构还可以采用如图 4 (b) 所示的三电平拓 扑结构， 主要由 12个全控型器件 50， 6个钳位二极管 53， 正极直流母线 6， 负极直流母线 7， 正极直流电容 52a， 负极直流电容 52b组成， 每两个全控 型器件 50串联连接后构成一个 '半桥臂'，每两个 '半桥臂'串联后构成一相换 流桥臂， 每个'半桥臂'的中点经钳位二极管 53与地 57相连接， 每相换流桥 臂的正端与正极直流母线 6相连接，每相换流桥臂的负端与负极直流母线 7 相连接， 每相换流桥臂的中点分别与 A相交流端 51a， B相交流端 51b， C 相交流端 51c连接， 正极直流电容的正端连接正极直流母线 6， 正极直流电 容的负端接地 57， 负极直流电容的正端接地 57， 负极直流电容的负端与负 极直流母线 7相连接， 为了提高电压源型换流器 2的额定电压， 每个全控 型器件 50可以由多个全控型器件串联而成， 每个钳位二极管 53可以由多 个钳位二极管串联而成， 而不是将多个电压源型换流器 2直接串联以提高 电压源型换流器 2的额定电压。
电压源型换流器 2的具体结构还可以采用如图 4 (c) 所示的模块化多 电平拓扑结构，主要包括 6个半桥臂 55，每两个半桥臂 55串联成一相桥臂， 每相换流桥臂的中点分别与 A相交流端 51a， B相交流端 51b， C相交流端 51c连接， 每相桥臂的正端和负端分别与正极直流母线 6， 负极直流母线 7 相连接， 每个半桥臂有多个子模块 54依次串联后再和平波电抗器 56串联 而成， 每个子模块由两个全控型器件 50和直流电容 55构成。 上述三种电压源型换流器 2 的拓扑中， 为了提高两电平拓扑和三电平 拓扑的额定电压需要将多个全控型器件 50直接串联， 由于两电平拓扑和三 电平拓扑工作时需要以数千赫兹的频率同步地触发直接串联连接的全控型 器件 50， 当串联的全控型器件 50的数目达到一定程度后， 难以保证以数千 赫兹的频率同步地触发众多直接串联连接的全控型器件 50， 通过增加串联 的全控型器件 50 来提高两电平拓扑和三电平拓扑的额定电压只能做到 ±300kV左右， 进一步提高两电平拓扑和三电平拓扑的额定电压是技术不可 行的。 同时两电平拓扑和三电平拓扑工作开关频率为数千赫兹， 要保证众 多直接串联的全控型器件 50以数千赫兹的频率同步地触发技术难度大， 系 统可靠性低， 同时两电平拓扑和三电平拓扑的损耗很高， 约为 1.6%。
模块化多电平拓扑通过增加串联的子模块 54的数目间接地将多个全控 型器件 50 串联从而提高电压源型换流器的额定电压。 由于全控型器件 50 是通过子模块 54间接地串联在一起， 模块化多电平拓扑不要求间接串联的 全控型器件 50被同步触发， 相比于两电平拓扑和三电平拓扑， 模块化多电 平拓扑对触发的同步性要求更低， 系统可靠性更高， 同时也更容易进一步 提高模块化多电平换流器的额定电压。 由于不要求所有串联的全控型器件 50 以数千赫兹的频率被同步触发， 模块化多电平拓扑的损耗低于两电平拓 扑和三电平拓扑， 其损耗约为 0.5%。 但模块化多电平拓扑存在也存在着串 联的子模块增加后， 子模块电容均压困难的技术瓶颈。 预期到 2015年模块 化多电平拓扑的额定电压为 ±320kV左右， 更高额定电压的模块化多电平拓 扑正在研发中， 具有一定的技术不确定性。 模块化多电平拓扑的另一缺点 是所采用的全控型器件 50的数量约为同额定电压两电平拓扑和三电平拓扑 的 2倍， 系统投资大。 混合型换流器 1中的电压源型换流器 2推荐采用模 块化多电平拓扑。
本发明实施例提供的电压源型换流器 2相比于第一相控换流器 3a和第 二相控换流器 3b的优点在于可自换相、 可黑启动、 占地面积小、 潮流反转 时不需要改变电压极性， 缺点在于电压源型换流器 2 的损耗和投资高于第 一相控换流器 3a和第二相控换流器 3b。电压源型换流器 2主要有两电平换 流器和模块化多电平换流器等多种拓扑， 其中两电平电压源型换流器的损 耗率约为 1.6% , 模块化多电平电压源型换流器的损耗率约为 0.5%。
另外， 由于单个全控型器件的额定电压较低， 为了提高电压源型换流 器 2 的额定电压需要将多个全控型器件串联， 增大了系统复杂度， 降低了 系统可靠性。 为了同时提高电压源型换流器 2 的额定电压和额定电流， 则 需要串联更多的低压大电流全控型器件， 进一步增大了系统复杂性， 降低 了系统可靠性。
本发明还提供了一种风力发电系统， 包括交流公共母线 14， 第一升压 变压器 18， 第二升压变压器 20， 第三变压器 12， 第四变压器 13， 混合型 换流器 1，以及分别连接至交流公共母线 14的交流滤波单元 15和无功补偿 单元 16; 第一升压变压器 18的输入端用于连接风电机组 17， 第一升压变 压器 18的输出端通过交流输电线路 19连接至第二升压变压器 20的输入端， 第二升压变压器 20的输出端通过交流输电线路 21连接至所述交流公共母 线 14; 混合型换流器 1包括电压源型换流器 2、 第一相控换流器 3a和第二 相控换流器 3b; 电压源型换流器 2的直流正端与所述第一相控换流器 3a的 直流负端连接， 第一相控换流器 3a的直流正端通过第一电感 10与正极直 流输电线路 8连接， 电压源型换流器 2的直流负端与第二相控换流器 3b的 直流正端连接， 第二相控换流器 3b的直流负端通过第二电感 11与负极直 流输电线路 9连接； 电压源型换流器 2的交流端通过第四变压器 13连接至 交流公共母线 14; 第一相控换流器 3a的交流端和第二相控换流器 3b的交 流端分别通过第三变压器 12连接至交流公共母线 14。
图 5示出了上述具有自换相功能的混合型换流器 1应用于风力发电系 统中， 混合型换流器的第一相控换流器 3a和第二相控换流器 3b分别由三 个额定电压为 200kV的六脉波相控换流桥 23串联而成，每个六脉波相控换 流桥的额定电压是与现有的 ±800kV相控换流器技术相匹配的， 电压源型换 流器 2额定电压为 ±200kV， 采用两电平拓扑， 整个混合型换流器的额定电 压为 ±800kV， 第一相控换流器 3a和第二相控换流器 3b和电压源型换流器 2的交流侧分别经变压器 12， 13连接至交流公共母线 14a-14c上， 风电机 组 17通过各自的第一升压变压器 18， 风电场内汇集交流输电线路 19， 风 电场汇集点第二升压变压器 20和的交流输电线路 21连接至交流公共母线 14a- 14c上， 为了补偿第一相控换流器 3a和第二相控换流器 3b工作时消耗 的无功功率及滤除第一相控换流器 3a和第二相控换流器 3b产生的谐波电 流， 在混合型换流器 1的交流公共母线 14a-14c上装设了交流滤波单元 15 和无功补偿单元 16， 交流滤波单元 15和无功补偿单元 16分多组从而可以 根据混合型换流器 1输送有功功率的大小投入合适组数的交流滤波单元 15 和无功补偿单元 16。 由于图 5中混合型换流器 1在交流侧只连接了风电场 60这类无源电网而没有与交流电压源相连接， 为此图 5所示的应用场合要 求混合型换流器 1具有自换相能力， 否则该混合型换流器 1无法应用于传 输风电。 为了使混合型换流器 1 整体具有自换相功能， 可以利用电压源型 换流器 2控制混合型换流器 1交流端的端电压， 而该端电压通过交流母线 14被施加在第一相控换流器 3a和第二相控换流器 3b上， 从而使得第一相 控换流器 3a和第二相控换流器 3b能正常工作， 通过上述控制层面的布局， 混合型换流器 1 在无外加交流电压源时， 通过其自身的电压源型换流器 2 和第一相控换流器 3a和第二相控换流器 3b的组合即可使得电压源型换流 器 2和第一相控换流器 3a和第二相控换流器 3b都能正常工作， 从而使得 整个混合型换流器 1 在无外加交流电压源时能正常工作， 使得混合型换流 器 1具备了自换相能力。
在本发明实施例中， 为了使混合型换流器 1 具有黑启动和部分潮流反 转功能， 图 6示出了一种改进型混合型换流器 24， 该改进混合型换流器 24 相比于混合型换流器 1的改进之处在于第一相控换流器 3a和第二相控换流 器 3b 的直流正端和直流负端并联了由机械开关 4和一对反并联的晶闸管 5a, 5b串联而成的旁路开关 25， 黑启动以及潮流反转时通过旁路开关将相 控换流器短接从而使得混合型换流器只投入电压源型换流器， 而电压源型 换流器具有黑启动和潮流反转能力。
增加旁路开关 25后的好处在于可以使得混合型换流器 1具有黑启动和 潮流反转的功能。 否则， 如果混合型换流器 1 不具备黑启动功能， 当混合 型换流器 1只连接风电场 60时， 风电场 60无法从停运状态转入运行状态。 当混合型换流器 1除连接了风电场 60还连接了本地负荷时， 如果混合型换 流器 1 不具备潮流反转功能， 当风电功率低于本地负荷时， 本地负荷将出 现供电不足的问题。
旁路开关 25可以采用机械开关 4和反并联晶闸管对 5a， 5b串联而成， 也可以采用直流断路器。 其中反并联晶闸管对可以为一对反并联的晶闸管 组成； 为了提高旁路开关的耐压等级， 也可以由多个反并联晶闸管对串联 而成。
增加旁路开关 25后， 系统的黑启动原理如下： 以图 7所示的两端直流 输电系统为例， 通过闭合旁路机械开关 4， 34并给反并联晶闸管 5a， 5b, 35a, 35b施加触发信号， 整流侧相控换流桥 3和逆变侧相控换流桥 33都被 旁路短接， 整流侧混合型换流器 1和逆变侧混合型换流器 31都只有电压源 型换流器 2， 32投入运行， 从而使得直流输电系统可以按照基于电压源型 换流器的两端直流输电系统的启动过程实现黑启动的功能。
增加旁路开关 25后， 系统的潮流反转原理如下： 潮流反转前， 相控换 流器 3， 33和电压源型换流器 2， 32都处于投运状态， 机械旁路开关 4， 34 断开， 反并联晶闸管 5a， 5b, 35a, 35b处于闭锁状态。 系统接收到潮流反 转指令后， 将整流侧相控换流器 3的触发角移到 120°-150°， 从而使得相控 换流器 3运行在逆变状态， 由于相控换流器 3， 33都处于逆变状态， 直流 输电线路 8， 9的直流电压迅速降低， 当检测到相控换流器 3， 33的正负直 流端口见的直流电压低于反并联晶闸管 5a， 5b, 35a, 35b的耐压时， 系统 闭合机械旁路开关 4， 34， 并给反并联晶闸管 5a， 5b, 35a, 35b施加触发 信号，从而短接相控换流器 3， 33， 使得系统两侧只投入电压源型换流器 2， 32， 从而使得系统可以按照基于电压源型换流器的两端直流输电系统的运 行模式实现部分潮流反转功能。
为了使该混合型换流器 1 具有黑启动和潮流反转能力， 可以在每个第 一相控换流器 3a和第二相控换流器 3b的直流正端和直流负端之间并联连 接旁路开关 25，黑启动以及潮流反转时投入旁路开关 25从而短接第一相控 换流器 3a和第二相控换流器 3b，使得混合型换流器 1只投入电压源型换流 器 2， 从而使得混合型换流器 1具有黑启动和潮流反转能力， 其中旁路开关 25的一种优选方案是由常规机械开关 4和反并联晶闸管 5a， 5b串联而成， 其中反并联晶闸管 5a， 5b可以由多个反并联晶闸管对串联而成从而提高旁 路开关的耐压等级。
与现有技术相比， 本发明的新颖性和创造性体现在：
( 1 ) 提出了将第一相控换流器 3a和第二相控换流器 3b和电压源型换 流器 2 串联后应用于传输风力发电的方案， 从而可以通过增加串联的相控 换流桥 23的数量提高第一相控换流器 3a和第二相控换流器 3b的额定电压， 进而提高混合型换流器 1 的额定电压， 通过电压源型换流器 2建立交流公 共母线 14的交流电压， 该交流电压经中间连接电路 12作用到第一相控换 流器 3a和第二相控换流器 3b上， 为第一相控换流器 3a和第二相控换流器 3b提供换相电压， 从而使得混合型换流器 1具有自换相能力， 能直接连接 风电场 60将风电场 60发出的交流电转换为直流电， 该方案综合利用第一 相控换流器 3a和第二相控换流器 3b的高压大功率和电压源型换流器 2的 可自换相能直接应用于风电场的优点， 并弥补了电压源型换流器 2额定电 压， 额定功率偏低， 第一相控换流器 3a和第二相控换流器 3b需要外在交 流电压源为其提供换相电压， 无法直接应用于传输风力发电的缺陷； (2) 提出了将第一相控换流器 3a和第二相控换流器 3b和电压源型换 流器串联混合型换流器 1， 并通过电压源型换流器 2为第一相控换流器 3a 和第二相控换流器 3b提供换相电压从而使得该混合型换流器 1整体具有自 换相能力， 可以应用在没有常规同步发电机维持交流电网电压的无源交流 电网上 （如风电场， 纯负荷网络）；
(3 ) 提出了将第一相控换流器 3a和第二相控换流器 3b和电压源型换 流器 2串联混合型换流器， 并在第一相控换流器 3a和第二相控换流器 3b 的直流正端和直流负端间并联了旁路开关 25从而使得该混合型换流器具备 了黑启动和潮流反转的能力。
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搭建了与图 7对应的仿真算例进行仿真验证。 图 7是一个 额定电压 ±800kV， 额定功率 4000MW的两端直流输电系统。 该系统主要包 括整流侧混合型换流器 1和逆变侧混合型换流器 31。 混合型换流器 1的公 共交流母线 14连接有风电场 60和本地负荷 22，混合型换流器 31的交流公 共母线 44连接在受端交流电网 47上。 为了使该系统具有黑启动和潮流反 转的功能， 相控换流器 3和相控换流器 33的正负直流端口分别并联了旁路 开关 4， 5a, 5b和 34， 35a, 35b。电压源型换流器 2， 32的额定电压为 ±200kV， 额定功率 1000MW, 每个相控换流器 3， 33分别由三个六脉波相控换流器 23串联而成， 每个六脉波相控换流器 23的额定直流电压为 200kV。
仿真算例中， 各个换流器都采用 PSCAD/EMTDC标准模型库中的详细 开关模型， 为提高计算速度， 多个风电场用一台等容量的风力发电机组建 模， 但其变频器仍采用详细开关模型建模。 由于仿真算例的一次设备模型 全部都由标准模型库中的详细开关模型搭建， 仿真实验所得的结果是高度 可信的。
相应仿真结果如图 8所示。 图 8 (a) 为风电场发出的有功功率及混合 型换流器 1送出的直流功率， 图 8 (b) 为混合型换流器 1正极直流电压瞬 时值， 图 8 ( c ) 为混合型换流器 1正极直流电流瞬时值， 图 8 ( d ) 为混合 型换流器 1交流母线 14的交流电压有效值。
0s至 1.2s，两侧的混合型换流器 1， 31的旁路开关 4， 5a, 5b, 34， 35a, 35b投入， 相控换流器 3， 33被短接， 系统只投入电压源型换流器 2， 32， 系统按照类似电压源型直流输电系统的工作模式进行黑启动。 1.8s前由于风 电功率较低， 旁路开关一直保持在投入状态。 如图 8 (a) 所示， 此段时间 内， 整流侧直流电压约为 220kV， 高于逆变侧的直流电压。 且只有电压源 型换流器投入工作时， 系统直流电压不含有相控换流器直流电压典型的脉 动。 1.8s随着风电功率增大， 两侧旁路开关切除， 整流侧单极直流电压上升 至 +800kV左右， 并呈现出 LCC换流器直流电压的脉动特性， 同时直流电 流在 1.8s下降。 1.8s-3.4s， 风电功率增大至 3900MW, 直流系统输送的直 流功率也相应增大至 3900MW。
4.0s 投入本地负荷 600MW , 系统输送的直流功率相应地减小到 3300MW,如附图 8a所示。 4.5s至 6.05s风电功率从 3900MW减小至 200MW 左右， 直流系统输送的直流功率随之减小， 直流系统直流电流也随之减小。 5.7s左右系统检测到直流电流小于 10%额定电流， 旁路开关再一次投入， 整流侧和逆变侧都只投入电压源型换流器 2， 32。 6.05s后， 由于风电功率 小于整流站本地负荷，直流系统反向输送约 400MW功率给本地负荷，工作 在潮流反转状态。
图 8 ( d ) 表明风电场交流电压一直维持在额定值附近， 混合型换流器 1在没有常规同步发电机维持交流电压时仍能正常工作。
上述仿真结果表明混合型换流器直接应用于传输风电功率是技术可行 的。 在没有投入相控换流器而只投入电压源型换流器时， 系统的直流电压 约为 ±200kV (图 8a)， 有功功率约为 600MW (图 8b)， 投入相控换流器后， 系统的直流电压约为 ±800kV (图 8a)， 有功功率可达 3900MW (图 8b)， 上 述仿真结果证明本发明能够解决现有的电压源型换流器所存在的额定电压 和额定功率无法满足风力发电大规模远距离输送 （数千千米输电距离） 要 求的技术问题。
本发明为大规模风力发电经直流远距离输送提供了一种技术可行的方 案而其他方案或者技术不可行或者具有技术不确定性且需要更高的成本。
( 1 ) 与单独的第一相控换流器 3a和第二相控换流器 3b相比， 单独的 第一相控换流器 3a和第二相控换流器 3b 由于没有自换相能力， 不能独立 地应用于风电场， 单独的第一相控换流器 3a和第二相控换流器 3b应用于 传输风力发电是技术不可行的， 而本发明的混合型换流器 1 具有自换相能 力， 可以直接连接风电场将风电转换为直流电， 本发明应用于传输风力发 电是技术可行的；
(2) 与电压源型换流器 2相比， 预期到 2015年， 电压源型换流器 2 的电压约为 ±320kV， 更高额定电压的电压源型换流器 2技术不成熟， 研发 存在技术不确定性， 而本发明的额定电压可达 ±800kV， 且各部件技术成熟， 满足了风电经直流大规模远距离输送对额定电压的需求。
( 3 )强行将多个全控型器件直接或间接串联虽然可以提高电压源型换 流器 2 的额定电压， 但系统复杂性提高， 可靠性降低， 同时尽管额定电压 提高了， 额定功率仍不能满足大规模远距离输送要求， 而将更多数量的低 压大电流全控型器件串联从而同时提高电压源型换流器 2 的额定电压和额 定功率将进一步增大系统复杂性， 降低系统可靠性， 而本发明可以通过对 现有成熟技术的组合改进， 能同时提高混合型换流器 1 的额定电压和额定 功率且各个部件技术成熟， 整个系统技术可靠性高。
(4)电压源型换流器 2损耗率最低约为 0.5%,而本发明若电压源型换 流器 2与总的第一相控换流器 3a和第二相控换流器 3b容量比取 1 : 3则本 发明的损耗率为 0.35%*0.75+0.5%*0.25=0.39%， 低于电压源型换流器 2的 损耗率， 以 6400MW的输电线路为例， 且年利用小时数取为 2000小时， 采 用本发明相比于同容量的基于电压源型换流器 2 的输电系统 （假设未来存 在此技术） 每年节省的输电损耗估计为 2800万元。
(5 )仍以 6400MW输电线路为例，采用本发明相比于同容量的基于电 压源型换流器 2 的输电系统 （假设未来存在此技术） 节省的投资成本约为 30亿元。
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

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1、 一种混合型换流器， 其特征在于， 包括电压源型换流器 （2)、 第一 相控换流器 （3a) 和第二相控换流器 （3b );
所述电压源型换流器 （2) 的直流正端与所述第一相控换流器 （3a) 的 直流负端连接， 所述第一相控换流器 （3a) 的直流正端用于与正极直流输 电线路 （8 ) 连接， 所述电压源型换流器 （2) 的直流负端与所述第二相控 换流器 （3b ) 的直流正端连接， 所述第二相控换流器 （3b ) 的直流负端用 于与负极直流输电线路 （9 ) 连接；
所述电压源型换流器 （2) 的交流端、 所述第一相控换流器 （3a) 的交 流端和所述第二相控换流器 （3b ) 的交流端用于与交流公共母线 （14) 连
2、 如权利要求 1所述的混合型换流器， 其特征在于， 所述电压源型换 流器 （2) 用于控制交流公共母线 （14) 的交流电压， 该交流电压作用到第 一相控换流器（3a)和第二相控换流器（3b )上为第一相控换流器（3a)和 第二相控换流器 （3b ) 提供换相电压， 使得在没有常规同步发电机组维持 交流公共母线 （14) 的交流电压时仍正常工作。
3、 如权利要求 1或 2所述的混合型换流器， 其特征在于， 所述第一相 控换流器 （3a) 或所述第二相控换流器 （3b ) 由一个或多个串联的六脉波 相控换流桥组成， 所述六脉波相控换流桥为基于晶闸管的三相全桥交流-直 流变换电路。
4、 如权利要求 1或 2所述的混合型换流器， 其特征在于， 所述电压源 型换流器 （2) 为基于全控型开关器件的三相全桥交流-直流变换电路。
5、 如权利要求 1所述的混合型换流器， 其特征在于， 所述混合型换流 器还包括： 与所述第一相控换流器并联的第一旁路开关， 以及与所述第二 相控换流器并联的第二旁路开关； 所述第一旁路开关用于在黑启动以及潮 流反转时旁路第一相控换流器， 所述第二旁路开关用于在黑启动以及潮流 反转时旁路第二相控换流器， 使得混合型换流器具有黑启动和潮流反转的 功能。
6、 如权利要求 5所述的混合型换流器， 其特征在于， 所述第一旁路开 关与所述第二旁路开关的结构相同； 所述第一旁路开关包括机械开关 （4) 以及与所述机械开关串联的反并联晶闸管对 （5a， 5b
7、 如权利要求 6所述的混合型换流器， 其特征在于， 所述反并联晶闸 管对为多个反并联的晶闸管串联而成。
8、 一种风力发电系统， 包括： 交流公共母线 （14) ， 第一升压变压器 ( 18 ) ， 第二升压变压器 （20) ， 第三变压器 （12) ， 第四变压器 （13 ) ， 混合型换流器 （1 ) ， 以及分别连接至所述交流公共母线 （14) 的交流滤波 单元 （15 ) 和无功补偿单元 （16 ) ； 所述第一升压变压器 （18 ) 的输入端 用于连接风电机组 (17)， 所述第一升压变压器（18 ) 的输出端通过交流输电 线路 （19) 连接至第二升压变压器 （20) 的输入端， 第二升压变压器 （20) 的输出端通过交流输电线路 （21 ) 连接至所述交流公共母线 （14) ； 其特 征在于， 所述混合型换流器 （1 ) 包括电压源型换流器 （2) 、 第一相控换 流器 (3a) 和第二相控换流器 (3b) ；
所述电压源型换流器 （2) 的直流正端与所述第一相控换流器 （3a) 的 直流负端连接， 所述第一相控换流器 （3a) 的直流正端通过第一电感 （10) 与正极直流输电线路 （8 ) 连接， 所述电压源型换流器 （2) 的直流负端与 所述第二相控换流器 （3b ) 的直流正端连接， 所述第二相控换流器 （3b ) 的直流负端通过第二电感 （11 ) 与负极直流输电线路 （9) 连接；
所述电压源型换流器 （2) 的交流端通过所述第四变压器 （13 )连接至 交流公共母线 （14) ； 所述第一相控换流器 （3a) 的交流端和所述第二相 控换流器 （3b ) 的交流端分别通过第三变压器 （12) 连接至交流公共母线 ( 14) 。
9、 如权利要求 8所述的风力发电系统， 其特征在于， 所述混合型换流 器还包括： 与所述第一相控换流器并联的第一旁路开关， 以及与所述第二 相控换流器并联的第二旁路开关； 所述第一旁路开关用于在黑启动以及潮 流反转时旁路所述第一相控换流器， 所述第二旁路开关用于在黑启动以及 潮流反转时旁路所述第二相控换流器。
10、 如权利要求 9所述的风力发电系统， 其特征在于， 所述第一旁路 开关与所述第二旁路开关的结构相同；所述第一旁路开关包括机械开关（4) 以及与所述机械开关串联的反并联晶闸管对 （5a， 5b
11、 如权利要求 10所述的混合型换流器， 其特征在于， 所述反并联晶 闸管对为多个反并联的晶闸管串联而成。
12、 如权利要求 8-11任一项所述的风力发电系统， 其特征在于， 所述 第一相控换流器 （3a) 和所述第二相控换流器 （3b ) 的结构相同； 所述第 一相控换流器 （3a) 包括一个或多个串联的六脉波相控换流桥， 所述六脉 波相控换流桥为基于晶闸管的三相全桥交流或直流变换电路。
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