WO2014071598A1 - A step-up dc autotransformer for hvdc and a system thereof - Google Patents

A step-up dc autotransformer for hvdc and a system thereof Download PDF

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Publication number
WO2014071598A1
WO2014071598A1 PCT/CN2012/084350 CN2012084350W WO2014071598A1 WO 2014071598 A1 WO2014071598 A1 WO 2014071598A1 CN 2012084350 W CN2012084350 W CN 2012084350W WO 2014071598 A1 WO2014071598 A1 WO 2014071598A1
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WO
WIPO (PCT)
Prior art keywords
converter
transformer
phase
autotransformer
converters
Prior art date
Application number
PCT/CN2012/084350
Other languages
French (fr)
Inventor
Dawei YAO
Xiaobo Yang
Chunming YUAN
Original Assignee
Abb Technology Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Abb Technology Ltd. filed Critical Abb Technology Ltd.
Priority to PCT/CN2012/084350 priority Critical patent/WO2014071598A1/en
Publication of WO2014071598A1 publication Critical patent/WO2014071598A1/en

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/66—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal
    • H02M7/68—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters
    • H02M7/72—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/75—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with 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
    • H02M7/757—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with 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
    • H02M7/7575—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with 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 for high voltage direct transmission 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
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/49—Combination of the output voltage waveforms of a plurality of converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0083—Converters characterised by their input or output configuration
    • H02M1/0093—Converters characterised by their input or output configuration wherein the output is created by adding a regulated voltage to or subtracting it from an unregulated input
    • 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
    • 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 relates to the technical field of HVDC applications as a step-up DC autotransformer for HVDC and a system thereof.
  • DC to DC converter with commutating transformer (US5311418A, Magnus Lalander) needs local AC grid for active and reactive power exchange; or "Step-up DC-DC converter for megawatt size applications” (D. Jovcic, IET Power Electronics, Vol. 2, issue 6, 2009: pp 675-685) is not verified for GW level application.
  • Step-up DC-DC converter for megawatt size applications D. Jovcic, IET Power Electronics, Vol. 2, issue 6, 2009: pp 675-685
  • both the prior arts use the full power converter, that's to say, each converter has the same capacity as the transmission capacity. Hence such DC/DC converter is of high cost.
  • DC-DC converter provided with an AC link (US4462070, Katsuji lida) is designed as alternative solution of low voltage chopper converter, but with only 1200V input level and the topology comprises single phase inverters and cannot be used for high voltage high power HVDC transmission system. Further, the current inverter in US4462070 needs controlled rectifiers with forced turn off capacity, such as transistor, GTO or thyristor with forced turn off circuit, and additional smoothing reactor and capacitors are necessary to realize its control function.
  • forced turn off capacity such as transistor, GTO or thyristor with forced turn off circuit
  • the present invention proposes a step-up DC autotransformer for HVDC and a system thereof, where the power capacity of each converter and transformer is only part of the transmitted power in case of low cost and high performance.
  • the monopoiar topology of the DC autotransformer comprises: a first AC/DC converter, a second AC/DC converter operated as a rectifier and AC transformer with at least two windings; in which the first AC/DC converter can be a converter with three-phase or multi-phase; the second AC/DC converter can be a voltage source converter, line commutated converter or diode rectifier with single-phase, three-phase or multi-phase; the AC transformer can be composed of a transformer or a number of transformers with single-phase, three-phase or multi-phase; the DC side of the first AC/DC converter is connected between a low DC voltage line and a neutral bus; the DC side of the second AC/DC converter is connected between a high DC voltage line and the low DC voltage line; and the AC sides of the first AC/DC converter and second AC/DC converter are connected via the AC transformer.
  • the AC transformer are a number of AC transformers; in which the AC side of each the first and second AC/DC converter is connected to one side of each the a number of AC transformers; and the other side of each the a number of AC transformers is connected together with an AC bus.
  • an additional winding is installed in the AC transformer.
  • the other side of a number of AC transformers or the additional winding of the AC transformer is connected to AC system; and the AC system can be local AC network, energy storage system, StatCom or condenser.
  • AC/DC converter is a voltage source converter operated as an inverter; and the second AC/DC converter can be a voltage source converter, a line commutated converter or a diode rectifier.
  • the first AC/DC converter can be a voltage source converter or a line commutated converter operated as an inverter; and the second AC/DC converter is a voltage source converter, a line commutated converter or a diode rectifier.
  • the first AC/DC converter is a line commutated converter; and the second AC/DC converter is a voltage source converter.
  • both the first and second AC/DC converters are tiltage source converters with single-phase, three-phase or multi-phase.
  • both the first and second AC/DC converters are line commutated converters with singie-phase, three-phase or multi-phase.
  • the AC bus can exchange the power bi-directionally between the first and second AC/DC converter by the controlling the rectified power and inverted power of the first and second AC/DC converter.
  • the bipolar topology of the DC autotransformer comprises: a first pole comprising a first AC/DC converter, a second AC/DC converter operated as a rectifier and first AC transformer with at least two windings; a second pole comprising a third AC/DC converter, a fourth AC/DC converter operated as a rectifier and second AC transformer with at least two windings; and a neutral bus; in which each the first, second, third and fourth AC/DC converters can be converter with single-phase, three-phase or multi-phase; each the first and second AC transformers can be composed of an AC transformer or a number of AC transformers with single-phase, three-phase or multi-phase; the DC side of the first AC/DC converter is connected between a first low DC voltage line and the neutral bus; the DC side of the second AC/DC converter is connected between a first high DC voltage line and the first low DC voltage line; and the AC sides of the first AC/
  • each the first AC transformer and the second AC transformer is composed of a number of AC transformers; in which each the AC side of the first and second AC/DC converter is connected to one side of the a number of AC transformers; and the other side of each the a number of AC transformers is connected together with an AC bus.
  • an additional winding is installed in the first AC transformer; and besides the windings connected to the AC sides of the third and fourth AC/DC converters, an additional winding is installed in the second AC transformer.
  • the other side of the a number of AC transformers or the additional winding of the AC transformers is connected to AC system; and the AC system can be local AC network, energy storage system, StatCom or condenser.
  • both the first and third AC/DC converters are voltage source converters operated as inverters, and each the second and fourth AC/DC converters is operated as rectifier and can be voltage source converter, line com mutated converter or diode rectifier.
  • both the first and third AC/DC converters are voltage source converters or line commutated converters; and both the second and fourth AC/DC converters can be voltage source converter, line commutated converter or diode rectifier.
  • both the first and third AC/DC converters are line commutated converter
  • both the second and fourth AC/DC converters are voltage source converter
  • all the first, second, third and fourth AC/DC converters are voltage source converters with single-phase, three-phase or multi-phase.
  • all the first, second, third and fourth AC/DC converters are line commutated converters.
  • the AC bus can exchange the power bi-directionaliy between the first pole and second pole by controlling the rectified power or inverted power of the first, second, third and/or fourth AC/DC converter.
  • the currents of the first AC/DC converter and the third AC/DC converter are equal to avoid unbalanced current through earth via the neutral bus.
  • the line commutated converter can be replaced by a capacitor commutated converter.
  • the high DC voltage line and low DC voltage line are connected to different DC systems with different voltage levels.
  • the DC transformer comprises: a first AC/DC converter used as an inverter, a second AC/DC converter used as a rectifier and an AC transformer; in which the first AC/DC converter is voltage source converter; the second AC/DC converter is line commutated converter; the DC side of the first AC/DC converter is connected between a high DC voltage line and a neutral bus; the DC side of the second AC/DC converter is connected between a low DC voltage line and a neutral bus; and the AC sides of the first AC/DC converter and second AC/DC converter are connected via the AC transformer.
  • an additional winding is installed in the AC transformer which can be an AC transformer with single-phase, three-phase or multi-phase; the additional winding of the AC transformer is connected to AC system; and the AC system can be local AC network, energy storage system, StatCom or condenser.
  • it provides a system comprising at least one of the step-up DC autotransformer or transformer above mentioned.
  • Embodiments of the present invention provide a step-up DC autotransformer for HVDC and a system thereof, which facilitates the development of HVDC applications at high altitude area where the lower DC voltage level is desired to decrease insulation cost.
  • the lower DC voltage will be stepped up at low altitude area to realize high power and long distance transmission.
  • Figs.1a-1g individually illustrate a monopolar topology of a step-up DC autotransformer for HVDC according to an embodiment of the present invention
  • Fig.2 illustrates a monopolar topology of a step-up DC autotransformer for HVDC according to another embodiment of the present invention
  • Figs.3a-3j individually illustrate a monopolar topology of a step-up DC autotransformer for HVDC according to another embodiment of the present invention
  • Figs.4a-4e individually illustrate a bipolar topology of a step-up DC autotransformer for HVDC according to another embodiment of the present invention
  • Figs.5a-5g individually illustrate a bipolar topology of a step-up DC autotransformer for HVDC according to another embodiment of the present invention
  • Fig.6 illustrates a monopolar topology of a full-power step-up DC autotransformer for HVDC according to another embodiment of the present invention.
  • the nominal power flow direction of the step-up DC autotransformer is from low DC voltage side to high DC voltage side in terms of absolute voltage value. Therefore, the direction of reversed power flow is from high DC voltage side to low DC voltage side.
  • VSC voltage source converter
  • LCC thyristor based line commutated converter
  • AC transformer technology AC transformer technology
  • the topology of VSC can be two-level converter, multi-level converter (MLC), modular multi-!evel converter (MMC), cascaded two-level converter (CTL) or alternating arm multi-level converter (AMMC) and so forth. All VSC topologies employ fully controllable semiconductor devices, such as IGBT, IGCT, iEGT, GTO, MOSFET and so forth.
  • the LCC topology can be a single phase converter, a 6 pulse converter, a 12-puise converter and so forth.
  • VSC or LCC can be realized by other various topologies.
  • the converter either AC/DC VSC or AC/DC LCC, can be operated at rectifier mode (power flows from AC side to DC side) or inverter mode (power flows from DC side to AC side), according to function requirement.
  • the frequency of the AC transformer in the invention may be not limited to be 50 or 60Hz.
  • the frequency can be optimally designed based on the comprehensive consideration on the cost, efficiency, weight and footprint etc.
  • the size of reactive power compensation equipment for LCC is decreased significantly, as the reactive power can be provided by VSC.
  • the AC transformer in the invention is also not limited to be a three-phase transformer, the descriptions of winding of the AC transformer below can be single phase winding, three phase winding or any other winding types to form a multiphase AC transformer.
  • Fig.1a illustrates a monopole topology of a step-up DC autotransformer for HVDC according to an embodiment of the present invention.
  • the step-up DC autotransformer for HVDC is a monopolar topology, which comprises a first AC/DC converter VSC 1 used as an inverter, a second AC/DC converter LCC 2 used as a rectifier, and a three-winding AC transformer 3; in which DC side of VSC 1 is connected between a low DC voltage line and a neutral bus; the DC side of LCC 2 is connected between a high DC voltage line and the low DC voltage line; and the AC sides of the VSC 1 and LCC 2 are connected via the AC transformer 3, in which one winding is connected to the AC side of the VSC 1 , and the other two windings are connected to the AC side of the LCC 2.
  • the DC autotransformer is a cascaded type which consisted of VSC and/or LCC and an AC transformer which frequency can be designed optimally.
  • the power capacity of each converter or transformer is only part of the transmitted power, which depends on the DC/DC step-up ratio. Therefore the cost and footprint are low with high performance.
  • Fig.1b illustrates a monopolar topology of a step-up DC autotransformer for HVDC according to an embodiment of the present invention.
  • the step-up DC autotransformer for HVDC is a monopolar topology, which comprises a VSC 1 used as an inverter, a LCC 2 used as a rectifier and a two-winding AC transformer 3; in which DC side of VSC 1 is connected between a low DC voltage line and a neutral bus; the DC side of LCC 2 is connected between a high DC voltage line and the low DC voltage line; and the AC sides of the VSC 1 and LCC 2 are connected via the AC transformer 3, in which one winding is connected to the AC side of the VSC 1 , and the other winding is connected to the AC side of the LCC 2.
  • Fig.1c illustrates a monopolar topology of a step-up DC autotransformer for HVDC according to an embodiment of the present invention.
  • the step-up DC autotransformer for HVDC is configured to realize a bi-directional power flow; converter 1 and converter 2 are both VSC converters.
  • the VSC 1 is used as an inverter, and VSC 2 is used as a rectifier in the step-up DC autotransformer for HVDC.
  • DC current direction of VSC 1 and VSC 2 are changed, conversion mode of VSC 1 is changed to rectifier and conversion mode of VSC 2 is changed to inverter.
  • Other components and connection are similar to those in Fig.1b, and will not be repeatedly described.
  • Fig.ld illustrates a monopolar topology of a step-up DC autotransformerfor HVDC according to an embodiment of the present invention.
  • the step-up DC autotransformer for HVDC is a monopolar topology, which comprises a VSC 1 used as an inverter, a diode rectifier 2 and a two-winding AC transformer 3; in which DC side of VSC 1 is connected between a low DC voltage line and a neutral bus; the DC side of diode rectifier 2 is connected between a high DC voltage line and the low DC voltage line; and the AC sides of the VSC 1 and diode rectifier 2 are connected via the AC transformer 3, in which one winding is connected to the AC side of the VSC 1 , and the other winding is connected to the AC side of the diode rectifier 2.
  • Fig.1 e illustrates a monopolar topology of a step-up DC autotransformer for
  • HVDC according to an embodiment of the present invention.
  • the step-up DC autotransformer for HVDC is a monopolar topology, which comprises a LCC 1 used as an inverter, a VSC 2 used as a rectifier and a two-winding AC transformer 3; in which DC side of LCC 1 is connected between a low DC voltage line and a neutral bus; the DC side of VSC 2 is connected between a high DC voltage line and the low DC voltage line; and the AC sides of the LCC 1 and VSC 2 are connected via the AC transformer 3, in which one winding is connected to the AC side of the LCC 1 , and the other winding is connected to the AC side of the VSC 2.
  • Fig.lf illustrates a monopolar topology of a step-up DC autotransformer for
  • HVDC according to an embodiment of the present invention.
  • the step-up DC autotransformer for HVDC is a monopolar topology, which comprises a first AC/DC converter LCC 1 used as an inverter, a second AC/DC converter VSC 2 used as a rectifier, and a three-winding AC transformer 3; in which DC side of LCC 1 is connected between a low DC voltage line and a neutral bus; the DC side of VSC 2 is connected between a high DC voltage line and the low DC voltage line; and the AC sides of the LCC 1 and VSC 2 are connected via the AC transformer 3, in which two windings are connected to the AC side of the LCC 1 , and the other one winding is connected to the AC side of the VSC 2.
  • Fig.lg illustrates a monopolar topology of a step-up DC autotransformerfor HVDC according to an embodiment of the present invention.
  • the step-up DC autotransformer for HVDC is a monopolar topology, which comprises a VSC 1 used as an inverter, a LCC 2 used as a rectifier and three single phase AC transformers 3; in which DC side of VSC 1 is connected between a low DC voltage line and a neutral bus; the DC side of LCC 2 is connected between a high DC voltage line and the low DC voltage line; and the AC sides of the VSC 1 and LCC 2 are connected via the three AC transformers 3, in which one side of those AC transformers is connected to VSC 1 and the other side of those AC transformers is connected to LCC 2.
  • Fig.2 illustrates a monopolar topology of a step-up DC autotransformer for HVDC according to another embodiment of the present invention.
  • the step-up DC autotransformer for HVDC is a monopolar topology which comprises a VSC 1 used as an inverter and a LCC 2 used as a rectifier, three AC transformers 3 and an AC bus 4.
  • the DC side of the VSC 1 is connected between a low DC voltage line and a neutral bus;
  • the DC side of the LCC 2 is connected between a high DC voltage line and the low DC voltage line;
  • one side of all AC transformers 3 are connected to the AC sides of the VSC 1 and LCC 2, and the other side of all AC transformers 3 are connected to the AC bus 4.
  • Figs.3a-3f individually illustrate a topology of a step-up DC autotransformer for HVDC according to an embodiment of the present invention.
  • Each DC autotransformer topology shown in Figs.3a-3f is similar to the respective topology shown in Figs.1a-1f except that an additional winding is added into the AC transformer 3.
  • the additional winding of AC transformer 3 can be connected to an AC system, for example a local AC network, an energy storage system, a StatCom or a condenser.
  • Fig.3g illustrates a monopolar topology of a step-up DC autotransformerfor HVDC according to another embodiment of the present invention.
  • the step-up DC autotransformer for HVDC is a monopoiar topology which comprises a VSC 1 used as an inverter and a LCC 2 used as a rectifier, three AC transformers 3 and an AC bus 4.
  • the DC side of the VSC 1 is connected between a low DC voltage line and a neutral bus;
  • the DC side of the LCC 2 is connected between a high DC voltage line and the low DC voltage line;
  • one side of the all three AC transformers are connected to the AC sides of VSC 1 and LCC 2, and the other sides of AC transformers are connected to the AC bus 4.
  • the AC bus 4 can be either a standalone AC bus or connected to an AC system, for example a local AC network, an energy storage system, a StatCom or a condenser.
  • Fig.3h illustrates a monopolar topology of a step-up DC autotransformer for HVDC according to another embodiment of the present invention.
  • another step-up DC autotransformer for HVDC is configured to realize a bi-directional power flow, which comprises two LCC converters LCC 1 and LCC 2, and a three-winding AC transformer 3, in which DC side of LCC 1 is connected between a neutral bus and a low DC voltage line; the DC side of LCC 2 is connected between a high DC voltage line and the low DC voltage line; and the AC sides of the LCC 1 and LCC 2 are connected via the AC transformer 3, in which the first winding is connected to the AC side of the LCC 1 , the second winding is connected to the AC side of the LCC 2, and the third winding is connected to an AC system, for example a local AC network, an energy storage system, a StatCom or a condenser.
  • an AC system for example a local AC network, an energy storage system, a StatCom or a condenser.
  • the LCC 1 is used as an inverter, and LCC 2 is used as a rectifier in the step-up DC autotransformer.
  • DC voltage polarity of both LCC 1 and LCC 2 are changed: operation mode of LCC 1 is changed to rectifier and operation mode of LCC 2 is changed to inverter.
  • Fig.3i illustrates a monopolar topology of a step-up autotransformer for HVDC according to another embodiment of the present invention.
  • FIG.3i another step-down DC autotransformer for HVDC is configured to realize a bi-directional power flow.
  • the topology shown in Fig. 3i is similar to that shown in Fig. 3g except that the connection direction of LCC 1 is reversed.
  • both LCC 1 and LCC 2 are operated as rectifiers in the step-down DC autotransformer.
  • DC voltage polarity of both LCC 1 and LCC 2 are changed; operation modes of LCC 1 and LCC 2 are changed to inverter.
  • FIG.3j another step-down DC autotransformer for HVDC is configured to realize a bi-directional power flow.
  • the topology shown in Fig. 3j is similar to that shown in Fig. 3c except that the VSC 1 is replaced by LCC 1 .
  • Fig.4a illustrates a bipolar topology of a step-up DC autotransformer for HVDC according to another embodiment of the present invention.
  • the bipolar topology of a step-up DC autotransformer for HVDC comprises: a first pole comprising a VSC 1 operated as an inverter, a LCC 2 operated as a rectifier and a first AC transformer 3 and a second pole comprising another VSC 10perated as an inverter, another LCC 2' operated as a rectifier and a second AC transformer 3'; in which the DC side of VSC 1 is connected between a first low DC voltage line (Low DC voltage Pole 1 , U d ci + ) and a neutral bus; the DC side of LCC 2 is connected between a first high DC voltage line (High DC voltage Pole 1 , U d0 2+) and the first low DC voltage line; and the AC sides of VSC 1 and LCC 2 are connected via the first AC transformer 3; and the DC side of VSC V is connected between a second low DC voltage line (Low DC voltage Pole 2, Ud C i-) and the neutral bus; the DC side of LCC 2'
  • both the first and second AC transformers (3, 3') are three-winding transformers, in which one winding of the first AC transformer 3 is connected to the AC side of the first VSC 1 , the other two windings are connected to the AC side of the first LCC 2; and one winding of the second AC transformer 3' is connected to the AC side of VSC 1 ', the other two windings are connected to the AC side of LCC 2'.
  • Fig.4b illustrates a bipolar topology of a step-up DC autotransformer for
  • HVDC according to another embodiment of the present invention.
  • Fig.4b is similar to Fig.4a except that the first and second AC transformers (3, 3') are two-winding transformers. One winding of the first AC transformer 3 is connected to the AC side of the first VSC 1 , the other winding is connected to the AC side of the first LCC 2; and one winding of the second AC transformer 3 1 is connected to the AC side of the second VSC 1 ', the other winding , is connected to the AC side of the second LCC 2'.
  • Fig.4c illustrates a bipolar topology of a step-up DC autotransformer for
  • HVDC according to another embodiment of the present invention.
  • the step-up DC autotransformer for HVDC is configured to realize a bi-directiona! power flow; in detail, all the first, second third and fourth converters are VSCs (1 , 1', 2, 2').
  • the DC side of VSC 1 is connected between a first iow DC voltage line (Low DC voltage Pole 1 , U dc +) and a neutral bus;
  • the DC side of VSC 2 is connected between a first high DC voltage line (High DC voltage Pole 1 , U dC 2+) and the first low DC voltage line; and the AC sides of VSC 1 and VSC 2 are connected via the first AC transformer 3;
  • the DC side of VSC V is connected between a second low DC voltage line (Low DC voltage Pole 2, U dc i-) and the neutral bus;
  • the DC side of VSC 2' is connected between a second high DC voltage line (High DC voltage pole 2, U dc2 -) and the second low DC voltage line U dc i-; and the AC sides of VSC 1 ' and VSC 2' are connected via the second converter transformer 3'.
  • conversion mode VSC 1 and VSC 1 ' are inverters and conversion mode of VSC 2 and VSC 2' are rectifiers.
  • DC current direction of all converters (1 , 1 ', 2, 2') is changed, conversion mode of VSC 1 and VSC 1 ' is changed to rectifier and conversion mode of VSC 2 and VSC 2' is changed to inverter.
  • Fig.4d illustrates a bipolar topology of a step-up DC autotransformer for
  • HVDC according to another embodiment of the present invention.
  • the bipolar topology of a step-up DC autotransformer for HVDC comprises: a first pole comprising a LCC 1 operated as inverter, a VSC 2 operated as rectifier and a first AC transformer 3 and a second pole comprising another LCC V operated as inverter, another VSC 2' operated as rectifier and a second AC transformer 3'; in which the DC side of LCC 1 is connected between a first low DC voltage line (Low DC voltage Pole 1 , U dc i+) and a neutral bus; the DC side of VSC 2 is connected between a first high DC voltage line (High DC voltage Pole 1 , Udc2+) and the first low DC voltage line; and the AC sides of LCC 1 and VSC 2 are connected via the first AC transformer 3; and the DC side of LCC V is connected between a second low DC voltage line (Low DC voltage Pole 2, U dc i-) and the neutral bus; the DC side of VSC 2' is connected between a second high DC
  • both the first and second AC transformers (3, 3') are three-winding transformers, in which one winding of the first AC transformer 3 is connected to the AC side of the first VSC 2, the other two windings are connected to the AC side of the first LCC 1 ; and one winding of the second AC transformer 3' is connected to the AC side of VSC 2', the other two windings are connected to the AC side of LCC 1 '.
  • Fig.4e illustrates a bipolar topology of a step-up DC autotransformer for
  • HVDC according to another embodiment of the present invention.
  • the bipolar topology of step-up DC autotransformer for HVDC comprises: first pole comprising a VSC 1 operated as an inverter, a LCC 2 operated as a rectifier and a first AC transformer 3 and a second pole comprising a VSC 1' operated as an inverter, a LCC 2' operated as a rectifier and a second AC transformer 3', and a common AC bus 4; in which the DC side of VSC 1 is connected between a first low DC voltage line (Low DC voltage Pole 1 , U dd + ) and a neutral bus; the DC side of LCC 2 is connected between a first high DC voltage line (High DC voltage Pole 1 , U dC 2 + ) and the first low DC voltage line; one side of the all three AC transformers 3 are connected to the AC sides of the VSC 1 and LCC 2, and the other side of AC transformers 3 are connected to the common AC bus 4; and the DC side of VSC 1 ' is connected between a second low DC
  • Fig.5a, Fig.5b, Fig.5c and Fig.5d individually illustrates a bipolar topology of a step-up DC autotransformer for HVDC according to an embodiment of the present invention
  • Fig.5d is similar to the respective topology shown in Fig.4a, Fig.4b, Fig.4c and Fig.4d except that an additional winding is added into the AC transformer 3.
  • the additional winding of AC transformer 3 can be connected to an AC system, for example a local AC network, an energy storage system, a StatCom or a condenser.
  • Fig.5e illustrates a bipolar topology of a step-up DC autotransformer for HVDC according to another embodiment of the present invention.
  • the step-up DC autotransformer for HVDC comprises: a first pole comprising a LCC 1 operated as an inverter, a LCC 2 operated as a rectifier and a first AC transformer 3 and a second pole comprising a LCC V operated as an inverter, a LCC 2' operated as a rectifier and a second AC transformer 3'; in which the DC side of LCC 1 is connected between a first low DC voltage line (Low DC voltage Pole 1 , Udc1+) and a neutral bus; the DC side of LCC 2 is connected between the first high DC voltage line (High DC voltage Pole 1 , Udc2+) and the first low DC voltage line; and the AC sides of LCC 1 and LCC 2 are connected via the first AC transformer 3, in which the first winding is connected to the AC side of the LCC 1 , the second winding is connected to the AC side of the LCC 2, and the third winding is connected to an AC system, for example a local AC network, an energy storage
  • the DC side of LCC V is connected between a second low DC voltage line (Low DC voltage Pole 2, Udc1-) and a neutral bus; the DC side of LCC 2' is connected between the second low DC voltage line (Low DC voltage Pole 2, Udc1-) and the a second high DC voltage line (High DC voltage Pole 2, Udc2-); and the AC sides of LCC V and LCC 2' are connected via the second AC transformer 3', in which the first winding is connected to the AC side of the LCC 1 ', the second winding is connected to the AC side of the LCC 2', and the third winding is connected to an AC system, for example a local AC network, an energy storage system, a StatCom or a condenser.
  • an AC system for example a local AC network, an energy storage system, a StatCom or a condenser.
  • LCC 1 and LCC 1 ' are used as inverters, and LCC 2 and LCC 2' are used as rectifiers in the step-down DC autotransformer.
  • DC voltage polarity of both LCC 1 , LCC 1 ⁇ LCC 2 and LCC 2' are changed: operation mode of LCC 1 and LCC 1' is changed to rectifier and operation mode of LCC 2 and LCC 2' is changed to inverter.
  • Fig.5f illustrates a bipolar topology of a step-up DC autotransformer for HVDC according to another embodiment of the present invention.
  • FIG.Sf another step-down DC autotransformer for HVDC is configured to realize bi-directional power flow.
  • the topology shown in Fig. 5f is similar to that shown in Fig. 5e except that the connection direction of LCC 1 and LCC 1 ' are reversed.
  • LCC 1 , LCC1', LCC 2 and LCC 2 are operated as rectifiers in the step-up DC autotransformer.
  • DC voltage polarity of LCC 1 , LCC 1 ', LCC 2 and LCC 2' are changed; operation modes of LCC 1 , LCC 1', LCC2 and LCC 2 are changed to inverters.
  • Fig.5g illustrates a bipolar topology of a step-up DC autotransformer for HVDC according to another embodiment of the present invention.
  • FIG.5g another step-down DC autotransformer for HVDC is configured to realize bi-directional power flow.
  • the topoiogy shown in Fig. 5g is similar to that shown in Fig. 5c except that the VSC 1 and VSC V are replaced by LCC 1 and LCC 1 ' respectively.
  • Fig.6 illustrates a monopolar topology of a full-power step-up DC autotransformer for HVDC according to another embodiment of the present invention.
  • the DC autotransformer comprises: a VSC 1 used as an inverter, a LCC 2 used as a rectifier and an AC transformer 3; in which the DC side of VSC 1 is connected between a low DC voltage line and a neutral bus; the DC side of LCC 2 is connected between a high DC voltage line and a neutral bus; and the AC sides of the VSC 1 and LCC 2 are connected via the AC transformer 3.
  • the AC transformer 3 is a two-winding transformer, in which one winding is connected to the AC side of the VSC 1 , and the other winding is connected to the AC side of the LCC 2.
  • any converter is a LCC and operates as a rectifier, it can be replaced by a diode rectifier.

Abstract

A step-up DC autotransformer for HVDC and a system thereof are provided. The monopolar topology of the DC autotransformer comprises a first AC/DC voltage source converter (1), a second AC/DC line commutated converter used as a rectifier (2) and an AC transformer (3). The DC side of the inverter is connected between a low DC voltage line and a neutral bus. The DC side of the rectifier is connected between a high DC voltage line and the low DC voltage line. The AC sides of the inverter and rectifier are connected via the AC transformer. The step-up DC autotransformer also can be a bipolar topology. For the proposed solutions, the power capacity of each converter or AC transformer is only part of the transmitted power, which depends on the DC/DC step-up ratio. Therefore the cost and footprint is low but high performance.

Description

A Step-up DC Autotransformer for HVDC and a System Thereof
FIELD OF THE INVENTION
The invention relates to the technical field of HVDC applications as a step-up DC autotransformer for HVDC and a system thereof.
BACKGROUND OF THE INVENTION
DC/DC transformer would become a fundamental component for HVDC applications in the future. Actually there is no essentially practical DC/DC transformer solution for HVDC system.
There is potential requirement for DC/DC transformer. One application is to step up DC voltage of one HVDC line with lower voltage level in high altitude area to a higher voltage level (say from 400kV to 800kV) in low altitude area for power transmission by another HVDC line. Existing solutions for DC/DC transformer, for example prior arts: "HVDC
DC to DC converter with commutating transformer" (US5311418A, Magnus Lalander) needs local AC grid for active and reactive power exchange; or "Step-up DC-DC converter for megawatt size applications" (D. Jovcic, IET Power Electronics, Vol. 2, issue 6, 2009: pp 675-685) is not verified for GW level application. Besides, both the prior arts use the full power converter, that's to say, each converter has the same capacity as the transmission capacity. Hence such DC/DC converter is of high cost. Another example: "DC-DC converter provided with an AC link" (US4462070, Katsuji lida) is designed as alternative solution of low voltage chopper converter, but with only 1200V input level and the topology comprises single phase inverters and cannot be used for high voltage high power HVDC transmission system. Further, the current inverter in US4462070 needs controlled rectifiers with forced turn off capacity, such as transistor, GTO or thyristor with forced turn off circuit, and additional smoothing reactor and capacitors are necessary to realize its control function.
Due to the above mentioned problems, a simple and low cost solution for DC voltage conversion is proposed in the present invention and mainly used for boosting of DC voltage in a HVDC system.
SUMMARY OF THE INVENTION
To overcome the problems mentioned above, the present invention proposes a step-up DC autotransformer for HVDC and a system thereof, where the power capacity of each converter and transformer is only part of the transmitted power in case of low cost and high performance.
According to an aspect of the present invention, it provides a step-up DC autotransformer for HVDC. The monopoiar topology of the DC autotransformer comprises: a first AC/DC converter, a second AC/DC converter operated as a rectifier and AC transformer with at least two windings; in which the first AC/DC converter can be a converter with three-phase or multi-phase; the second AC/DC converter can be a voltage source converter, line commutated converter or diode rectifier with single-phase, three-phase or multi-phase; the AC transformer can be composed of a transformer or a number of transformers with single-phase, three-phase or multi-phase; the DC side of the first AC/DC converter is connected between a low DC voltage line and a neutral bus; the DC side of the second AC/DC converter is connected between a high DC voltage line and the low DC voltage line; and the AC sides of the first AC/DC converter and second AC/DC converter are connected via the AC transformer.
According to a preferred embodiment of the present invention, the AC transformer are a number of AC transformers; in which the AC side of each the first and second AC/DC converter is connected to one side of each the a number of AC transformers; and the other side of each the a number of AC transformers is connected together with an AC bus.
According to a preferred embodiment of the present invention, besides the windings connected to the AC sides of the first AC/DC converter and the second AC/DC converter, an additional winding is installed in the AC transformer. According to a preferred embodiment of the present invention, the other side of a number of AC transformers or the additional winding of the AC transformer is connected to AC system; and the AC system can be local AC network, energy storage system, StatCom or condenser.
According to a preferred embodiment of the present invention, the first
AC/DC converter is a voltage source converter operated as an inverter; and the second AC/DC converter can be a voltage source converter, a line commutated converter or a diode rectifier.
According to a preferred embodiment of the present invention, the first AC/DC converter can be a voltage source converter or a line commutated converter operated as an inverter; and the second AC/DC converter is a voltage source converter, a line commutated converter or a diode rectifier.
According to a preferred embodiment of the present invention, the first AC/DC converter is a line commutated converter; and the second AC/DC converter is a voltage source converter.
According to a preferred embodiment of the present invention, both the first and second AC/DC converters are voitage source converters with single-phase, three-phase or multi-phase.
According to a preferred embodiment of the present invention, both the first and second AC/DC converters are line commutated converters with singie-phase, three-phase or multi-phase.
According to a preferred embodiment of the present invention, the AC bus can exchange the power bi-directionally between the first and second AC/DC converter by the controlling the rectified power and inverted power of the first and second AC/DC converter.
According to the other aspect of the present invention, it provides a step-up DC autotransformer for HVDC. The bipolar topology of the DC autotransformer comprises: a first pole comprising a first AC/DC converter, a second AC/DC converter operated as a rectifier and first AC transformer with at least two windings; a second pole comprising a third AC/DC converter, a fourth AC/DC converter operated as a rectifier and second AC transformer with at least two windings; and a neutral bus; in which each the first, second, third and fourth AC/DC converters can be converter with single-phase, three-phase or multi-phase; each the first and second AC transformers can be composed of an AC transformer or a number of AC transformers with single-phase, three-phase or multi-phase; the DC side of the first AC/DC converter is connected between a first low DC voltage line and the neutral bus; the DC side of the second AC/DC converter is connected between a first high DC voltage line and the first low DC voltage line; and the AC sides of the first AC/DC converter and second AC/DC converter are connected via the first AC transformer; and the DC side of the third AC/DC converter is connected between a second low DC voltage line and the neutral bus; the DC side of the fourth AC/DC converter is connected between a second high DC voltage line and the second low DC voltage line; and the AC sides of the third AC/DC converter and the fourth AC/DC converter are connected via the second AC transformer.
According to a preferred embodiment of the present invention, each the first AC transformer and the second AC transformer is composed of a number of AC transformers; in which each the AC side of the first and second AC/DC converter is connected to one side of the a number of AC transformers; and the other side of each the a number of AC transformers is connected together with an AC bus.
According to a preferred embodiment of the present invention, besides the windings connected to the AC sides of the first and second AC/DC converters, an additional winding is installed in the first AC transformer; and besides the windings connected to the AC sides of the third and fourth AC/DC converters, an additional winding is installed in the second AC transformer.
According to a preferred embodiment of the present invention, the other side of the a number of AC transformers or the additional winding of the AC transformers is connected to AC system; and the AC system can be local AC network, energy storage system, StatCom or condenser.
According to a preferred embodiment of the present invention, both the first and third AC/DC converters are voltage source converters operated as inverters, and each the second and fourth AC/DC converters is operated as rectifier and can be voltage source converter, line com mutated converter or diode rectifier.
According to a preferred embodiment of the present invention, both the first and third AC/DC converters are voltage source converters or line commutated converters; and both the second and fourth AC/DC converters can be voltage source converter, line commutated converter or diode rectifier.
According to a preferred embodiment of the present invention, both the first and third AC/DC converters are line commutated converter, and both the second and fourth AC/DC converters are voltage source converter.
According to a preferred embodiment of the present invention, all the first, second, third and fourth AC/DC converters are voltage source converters with single-phase, three-phase or multi-phase.
According to a preferred embodiment of the present invention, all the first, second, third and fourth AC/DC converters are line commutated converters.
According to a preferred embodiment of the present invention, the AC bus can exchange the power bi-directionaliy between the first pole and second pole by controlling the rectified power or inverted power of the first, second, third and/or fourth AC/DC converter.
According to a preferred embodiment of the present invention, the currents of the first AC/DC converter and the third AC/DC converter are equal to avoid unbalanced current through earth via the neutral bus.
According to a preferred embodiment of the present invention, the line commutated converter can be replaced by a capacitor commutated converter.
According to a preferred embodiment of the present invention, the high DC voltage line and low DC voltage line are connected to different DC systems with different voltage levels.
According to another aspect of the present invention, it provides a step-up
DC transformer for HVDC. The DC transformer comprises: a first AC/DC converter used as an inverter, a second AC/DC converter used as a rectifier and an AC transformer; in which the first AC/DC converter is voltage source converter; the second AC/DC converter is line commutated converter; the DC side of the first AC/DC converter is connected between a high DC voltage line and a neutral bus; the DC side of the second AC/DC converter is connected between a low DC voltage line and a neutral bus; and the AC sides of the first AC/DC converter and second AC/DC converter are connected via the AC transformer.
According to a preferred embodiment of the present invention, besides the windings connected to the AC sides of the first AC/DC converter and the second AC/DC converter, an additional winding is installed in the AC transformer which can be an AC transformer with single-phase, three-phase or multi-phase; the additional winding of the AC transformer is connected to AC system; and the AC system can be local AC network, energy storage system, StatCom or condenser.
According to another aspect of the present invention, it provides a system comprising at least one of the step-up DC autotransformer or transformer above mentioned.
Embodiments of the present invention provide a step-up DC autotransformer for HVDC and a system thereof, which facilitates the development of HVDC applications at high altitude area where the lower DC voltage level is desired to decrease insulation cost. With the proposed invention, the lower DC voltage will be stepped up at low altitude area to realize high power and long distance transmission.
BRIEF DESCRIPTION OF THE DRAWINGS
The subject matter of the invention will be explained in more details in the following description with reference to preferred exemplary embodiments which are illustrated in the drawings, in which:
Figs.1a-1g individually illustrate a monopolar topology of a step-up DC autotransformer for HVDC according to an embodiment of the present invention;
Fig.2 illustrates a monopolar topology of a step-up DC autotransformer for HVDC according to another embodiment of the present invention;
Figs.3a-3j individually illustrate a monopolar topology of a step-up DC autotransformer for HVDC according to another embodiment of the present invention;
Figs.4a-4e individually illustrate a bipolar topology of a step-up DC autotransformer for HVDC according to another embodiment of the present invention;
Figs.5a-5g individually illustrate a bipolar topology of a step-up DC autotransformer for HVDC according to another embodiment of the present invention;
Fig.6 illustrates a monopolar topology of a full-power step-up DC autotransformer for HVDC according to another embodiment of the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Exemplary embodiments of the present invention are described in conjunction with the accompanying drawings hereinafter. For the sake of clarity and conciseness, not all the features of actual implementations are described in the specification.
It is defined that the nominal power flow direction of the step-up DC autotransformer is from low DC voltage side to high DC voltage side in terms of absolute voltage value. Therefore, the direction of reversed power flow is from high DC voltage side to low DC voltage side.
Fully controlled semiconductor based voltage source converter (VSC) technology or thyristor based line commutated converter (LCC) technology and AC transformer technology will be employed in this invention. The topology of VSC can be two-level converter, multi-level converter (MLC), modular multi-!evel converter (MMC), cascaded two-level converter (CTL) or alternating arm multi-level converter (AMMC) and so forth. All VSC topologies employ fully controllable semiconductor devices, such as IGBT, IGCT, iEGT, GTO, MOSFET and so forth. The LCC topology can be a single phase converter, a 6 pulse converter, a 12-puise converter and so forth. It's obvious to the person skilled in art that VSC or LCC can be realized by other various topologies. The converter, either AC/DC VSC or AC/DC LCC, can be operated at rectifier mode (power flows from AC side to DC side) or inverter mode (power flows from DC side to AC side), according to function requirement.
It shall be noted that the frequency of the AC transformer in the invention may be not limited to be 50 or 60Hz. For some embodiments, the frequency can be optimally designed based on the comprehensive consideration on the cost, efficiency, weight and footprint etc. The size of reactive power compensation equipment for LCC is decreased significantly, as the reactive power can be provided by VSC. Besides, the AC transformer in the invention is also not limited to be a three-phase transformer, the descriptions of winding of the AC transformer below can be single phase winding, three phase winding or any other winding types to form a multiphase AC transformer.
Fig.1a illustrates a monopole topology of a step-up DC autotransformer for HVDC according to an embodiment of the present invention.
As shown in Fig.1 a, the step-up DC autotransformer for HVDC is a monopolar topology, which comprises a first AC/DC converter VSC 1 used as an inverter, a second AC/DC converter LCC 2 used as a rectifier, and a three-winding AC transformer 3; in which DC side of VSC 1 is connected between a low DC voltage line and a neutral bus; the DC side of LCC 2 is connected between a high DC voltage line and the low DC voltage line; and the AC sides of the VSC 1 and LCC 2 are connected via the AC transformer 3, in which one winding is connected to the AC side of the VSC 1 , and the other two windings are connected to the AC side of the LCC 2.
Such a simple and low cost solution of the DC autotransformer shown in Fig.1 a can be used for HVDC voltage step-up in the case of unidirectional power flow.
It's obvious to the person skilled in art that the DC autotransformer is a cascaded type which consisted of VSC and/or LCC and an AC transformer which frequency can be designed optimally. Especially, the power capacity of each converter or transformer is only part of the transmitted power, which depends on the DC/DC step-up ratio. Therefore the cost and footprint are low with high performance.
Fig.1b illustrates a monopolar topology of a step-up DC autotransformer for HVDC according to an embodiment of the present invention.
As shown in Fig.1b, the step-up DC autotransformer for HVDC is a monopolar topology, which comprises a VSC 1 used as an inverter, a LCC 2 used as a rectifier and a two-winding AC transformer 3; in which DC side of VSC 1 is connected between a low DC voltage line and a neutral bus; the DC side of LCC 2 is connected between a high DC voltage line and the low DC voltage line; and the AC sides of the VSC 1 and LCC 2 are connected via the AC transformer 3, in which one winding is connected to the AC side of the VSC 1 , and the other winding is connected to the AC side of the LCC 2.
Fig.1c illustrates a monopolar topology of a step-up DC autotransformer for HVDC according to an embodiment of the present invention.
As shown in Fig.1c, the step-up DC autotransformer for HVDC is configured to realize a bi-directional power flow; converter 1 and converter 2 are both VSC converters. For nominal power flow operation, the VSC 1 is used as an inverter, and VSC 2 is used as a rectifier in the step-up DC autotransformer for HVDC. For power flow reverse operation, DC current direction of VSC 1 and VSC 2 are changed, conversion mode of VSC 1 is changed to rectifier and conversion mode of VSC 2 is changed to inverter. Other components and connection are similar to those in Fig.1b, and will not be repeatedly described.
Fig.ld illustrates a monopolar topology of a step-up DC autotransformerfor HVDC according to an embodiment of the present invention.
As shown in Fig.ld, the step-up DC autotransformer for HVDC is a monopolar topology, which comprises a VSC 1 used as an inverter, a diode rectifier 2 and a two-winding AC transformer 3; in which DC side of VSC 1 is connected between a low DC voltage line and a neutral bus; the DC side of diode rectifier 2 is connected between a high DC voltage line and the low DC voltage line; and the AC sides of the VSC 1 and diode rectifier 2 are connected via the AC transformer 3, in which one winding is connected to the AC side of the VSC 1 , and the other winding is connected to the AC side of the diode rectifier 2.
Fig.1 e illustrates a monopolar topology of a step-up DC autotransformer for
HVDC according to an embodiment of the present invention.
As shown in Fig.le, the step-up DC autotransformer for HVDC is a monopolar topology, which comprises a LCC 1 used as an inverter, a VSC 2 used as a rectifier and a two-winding AC transformer 3; in which DC side of LCC 1 is connected between a low DC voltage line and a neutral bus; the DC side of VSC 2 is connected between a high DC voltage line and the low DC voltage line; and the AC sides of the LCC 1 and VSC 2 are connected via the AC transformer 3, in which one winding is connected to the AC side of the LCC 1 , and the other winding is connected to the AC side of the VSC 2.
Fig.lf illustrates a monopolar topology of a step-up DC autotransformer for
HVDC according to an embodiment of the present invention.
As shown in Fig.lf, the step-up DC autotransformer for HVDC is a monopolar topology, which comprises a first AC/DC converter LCC 1 used as an inverter, a second AC/DC converter VSC 2 used as a rectifier, and a three-winding AC transformer 3; in which DC side of LCC 1 is connected between a low DC voltage line and a neutral bus; the DC side of VSC 2 is connected between a high DC voltage line and the low DC voltage line; and the AC sides of the LCC 1 and VSC 2 are connected via the AC transformer 3, in which two windings are connected to the AC side of the LCC 1 , and the other one winding is connected to the AC side of the VSC 2. Fig.lg illustrates a monopolar topology of a step-up DC autotransformerfor HVDC according to an embodiment of the present invention.
As shown in Fig.lg, the step-up DC autotransformer for HVDC is a monopolar topology, which comprises a VSC 1 used as an inverter, a LCC 2 used as a rectifier and three single phase AC transformers 3; in which DC side of VSC 1 is connected between a low DC voltage line and a neutral bus; the DC side of LCC 2 is connected between a high DC voltage line and the low DC voltage line; and the AC sides of the VSC 1 and LCC 2 are connected via the three AC transformers 3, in which one side of those AC transformers is connected to VSC 1 and the other side of those AC transformers is connected to LCC 2.
Fig.2 illustrates a monopolar topology of a step-up DC autotransformer for HVDC according to another embodiment of the present invention.
As shown in Fig.2, the step-up DC autotransformer for HVDC is a monopolar topology which comprises a VSC 1 used as an inverter and a LCC 2 used as a rectifier, three AC transformers 3 and an AC bus 4. The DC side of the VSC 1 is connected between a low DC voltage line and a neutral bus; the DC side of the LCC 2 is connected between a high DC voltage line and the low DC voltage line; one side of all AC transformers 3 are connected to the AC sides of the VSC 1 and LCC 2, and the other side of all AC transformers 3 are connected to the AC bus 4.
Figs.3a-3f individually illustrate a topology of a step-up DC autotransformer for HVDC according to an embodiment of the present invention.
Each DC autotransformer topology shown in Figs.3a-3f is similar to the respective topology shown in Figs.1a-1f except that an additional winding is added into the AC transformer 3. The additional winding of AC transformer 3 can be connected to an AC system, for example a local AC network, an energy storage system, a StatCom or a condenser.
As shown in Figs.3a-3f, various power flow direction can be realized with these topologies.
Fig.3g illustrates a monopolar topology of a step-up DC autotransformerfor HVDC according to another embodiment of the present invention.
As shown in Fig.3g, the step-up DC autotransformer for HVDC is a monopoiar topology which comprises a VSC 1 used as an inverter and a LCC 2 used as a rectifier, three AC transformers 3 and an AC bus 4. The DC side of the VSC 1 is connected between a low DC voltage line and a neutral bus; the DC side of the LCC 2 is connected between a high DC voltage line and the low DC voltage line; one side of the all three AC transformers are connected to the AC sides of VSC 1 and LCC 2, and the other sides of AC transformers are connected to the AC bus 4. The AC bus 4 can be either a standalone AC bus or connected to an AC system, for example a local AC network, an energy storage system, a StatCom or a condenser.
As shown in Fig.3g, various power flow direction can be realized with this topology.
Fig.3h illustrates a monopolar topology of a step-up DC autotransformer for HVDC according to another embodiment of the present invention.
As shown in Fig.Sh, another step-up DC autotransformer for HVDC is configured to realize a bi-directional power flow, which comprises two LCC converters LCC 1 and LCC 2, and a three-winding AC transformer 3, in which DC side of LCC 1 is connected between a neutral bus and a low DC voltage line; the DC side of LCC 2 is connected between a high DC voltage line and the low DC voltage line; and the AC sides of the LCC 1 and LCC 2 are connected via the AC transformer 3, in which the first winding is connected to the AC side of the LCC 1 , the second winding is connected to the AC side of the LCC 2, and the third winding is connected to an AC system, for example a local AC network, an energy storage system, a StatCom or a condenser.
For nominal power flow operation, the LCC 1 is used as an inverter, and LCC 2 is used as a rectifier in the step-up DC autotransformer. For power flow reverse operation, DC voltage polarity of both LCC 1 and LCC 2 are changed: operation mode of LCC 1 is changed to rectifier and operation mode of LCC 2 is changed to inverter.
Fig.3i illustrates a monopolar topology of a step-up autotransformer for HVDC according to another embodiment of the present invention.
As shown in Fig.3i, another step-down DC autotransformer for HVDC is configured to realize a bi-directional power flow. The topology shown in Fig. 3i is similar to that shown in Fig. 3g except that the connection direction of LCC 1 is reversed.
For nominal power flow operation, both LCC 1 and LCC 2 are operated as rectifiers in the step-down DC autotransformer. For power flow reverse operation, DC voltage polarity of both LCC 1 and LCC 2 are changed; operation modes of LCC 1 and LCC 2 are changed to inverter.
As shown in Fig.3j, another step-down DC autotransformer for HVDC is configured to realize a bi-directional power flow. The topology shown in Fig. 3j is similar to that shown in Fig. 3c except that the VSC 1 is replaced by LCC 1 .
Fig.4a illustrates a bipolar topology of a step-up DC autotransformer for HVDC according to another embodiment of the present invention.
As shown in Fig.4a, the bipolar topology of a step-up DC autotransformer for HVDC comprises: a first pole comprising a VSC 1 operated as an inverter, a LCC 2 operated as a rectifier and a first AC transformer 3 and a second pole comprising another VSC 10perated as an inverter, another LCC 2' operated as a rectifier and a second AC transformer 3'; in which the DC side of VSC 1 is connected between a first low DC voltage line (Low DC voltage Pole 1 , Udci+) and a neutral bus; the DC side of LCC 2 is connected between a first high DC voltage line (High DC voltage Pole 1 , Ud02+) and the first low DC voltage line; and the AC sides of VSC 1 and LCC 2 are connected via the first AC transformer 3; and the DC side of VSC V is connected between a second low DC voltage line (Low DC voltage Pole 2, UdCi-) and the neutral bus; the DC side of LCC 2' is connected between a second high DC voltage line (High DC voltage pole 2, UdC2-) and the second low DC voltage line Udc -; and the AC sides of VSC 1' and LCC 2' are connected via the second converter transformer 3'.
According to a preferred embodiment of the present invention, both the first and second AC transformers (3, 3') are three-winding transformers, in which one winding of the first AC transformer 3 is connected to the AC side of the first VSC 1 , the other two windings are connected to the AC side of the first LCC 2; and one winding of the second AC transformer 3' is connected to the AC side of VSC 1 ', the other two windings are connected to the AC side of LCC 2'. Fig.4b illustrates a bipolar topology of a step-up DC autotransformer for
HVDC according to another embodiment of the present invention.
Fig.4b is similar to Fig.4a except that the first and second AC transformers (3, 3') are two-winding transformers. One winding of the first AC transformer 3 is connected to the AC side of the first VSC 1 , the other winding is connected to the AC side of the first LCC 2; and one winding of the second AC transformer 31 is connected to the AC side of the second VSC 1 ', the other winding , is connected to the AC side of the second LCC 2'. Fig.4c illustrates a bipolar topology of a step-up DC autotransformer for
HVDC according to another embodiment of the present invention.
As shown in Fig.4c, the step-up DC autotransformer for HVDC is configured to realize a bi-directiona! power flow; in detail, all the first, second third and fourth converters are VSCs (1 , 1', 2, 2'). The DC side of VSC 1 is connected between a first iow DC voltage line (Low DC voltage Pole 1 , Udc +) and a neutral bus; the DC side of VSC 2 is connected between a first high DC voltage line (High DC voltage Pole 1 , UdC2+) and the first low DC voltage line; and the AC sides of VSC 1 and VSC 2 are connected via the first AC transformer 3; and the DC side of VSC V is connected between a second low DC voltage line (Low DC voltage Pole 2, Udci-) and the neutral bus; the DC side of VSC 2' is connected between a second high DC voltage line (High DC voltage pole 2, Udc2-) and the second low DC voltage line Udci-; and the AC sides of VSC 1 ' and VSC 2' are connected via the second converter transformer 3'.
For nominal power flow operation, conversion mode VSC 1 and VSC 1 ' are inverters and conversion mode of VSC 2 and VSC 2' are rectifiers. For power flow reverse operation, DC current direction of all converters (1 , 1 ', 2, 2') is changed, conversion mode of VSC 1 and VSC 1 ' is changed to rectifier and conversion mode of VSC 2 and VSC 2' is changed to inverter. Fig.4d illustrates a bipolar topology of a step-up DC autotransformer for
HVDC according to another embodiment of the present invention.
As shown in Fig.4d, the bipolar topology of a step-up DC autotransformer for HVDC comprises: a first pole comprising a LCC 1 operated as inverter, a VSC 2 operated as rectifier and a first AC transformer 3 and a second pole comprising another LCC V operated as inverter, another VSC 2' operated as rectifier and a second AC transformer 3'; in which the DC side of LCC 1 is connected between a first low DC voltage line (Low DC voltage Pole 1 , Udci+) and a neutral bus; the DC side of VSC 2 is connected between a first high DC voltage line (High DC voltage Pole 1 , Udc2+) and the first low DC voltage line; and the AC sides of LCC 1 and VSC 2 are connected via the first AC transformer 3; and the DC side of LCC V is connected between a second low DC voltage line (Low DC voltage Pole 2, Udci-) and the neutral bus; the DC side of VSC 2' is connected between a second high DC voltage line (High DC voltage pole 2, UdC2-) and the second low DC voltage line Udd-; and the AC sides of LCC 1 ' and VSC 2' are connected via the second converter transformer 3'.
According to a preferred embodiment of the present invention, both the first and second AC transformers (3, 3') are three-winding transformers, in which one winding of the first AC transformer 3 is connected to the AC side of the first VSC 2, the other two windings are connected to the AC side of the first LCC 1 ; and one winding of the second AC transformer 3' is connected to the AC side of VSC 2', the other two windings are connected to the AC side of LCC 1 '. Fig.4e illustrates a bipolar topology of a step-up DC autotransformer for
HVDC according to another embodiment of the present invention.
As shown in Fig.4e, the bipolar topology of step-up DC autotransformer for HVDC comprises: first pole comprising a VSC 1 operated as an inverter, a LCC 2 operated as a rectifier and a first AC transformer 3 and a second pole comprising a VSC 1' operated as an inverter, a LCC 2' operated as a rectifier and a second AC transformer 3', and a common AC bus 4; in which the DC side of VSC 1 is connected between a first low DC voltage line (Low DC voltage Pole 1 , Udd +) and a neutral bus; the DC side of LCC 2 is connected between a first high DC voltage line (High DC voltage Pole 1 , UdC2+) and the first low DC voltage line; one side of the all three AC transformers 3 are connected to the AC sides of the VSC 1 and LCC 2, and the other side of AC transformers 3 are connected to the common AC bus 4; and the DC side of VSC 1 ' is connected between a second low DC voltage line (Low DC voltage Pole 2, Udc1-) and the neutral bus; the DC side of LCC 2' is connected between a second high DC voltage line (High DC voltage pole 2, UdC2-) and the second low DC voltage line Udd-; one side of the all three AC transformers 3' are connected to the AC sides of the VSC V and LCC 2', and the other side of AC transformers 3 are connected to the common AC bus 4. The AC bus 4 can be either a standalone bus, or connected to an AC system, for example a local AC network, an energy storage system, a StatCom or a condenser.
Fig.5a, Fig.5b, Fig.5c and Fig.5d individually illustrates a bipolar topology of a step-up DC autotransformer for HVDC according to an embodiment of the present invention;
Each DC autotransformer topology shown in Fig.5a, Fig.5b, Fig.5c and
Fig.5d is similar to the respective topology shown in Fig.4a, Fig.4b, Fig.4c and Fig.4d except that an additional winding is added into the AC transformer 3. The additional winding of AC transformer 3 can be connected to an AC system, for example a local AC network, an energy storage system, a StatCom or a condenser.
As shown in Fig.5a, Fig.5b, Fig.5c and Fig.5d, various power flow direction can be realized with these topologies.
Fig.5e illustrates a bipolar topology of a step-up DC autotransformer for HVDC according to another embodiment of the present invention.
As shown in Fig.5e, the step-up DC autotransformer for HVDC comprises: a first pole comprising a LCC 1 operated as an inverter, a LCC 2 operated as a rectifier and a first AC transformer 3 and a second pole comprising a LCC V operated as an inverter, a LCC 2' operated as a rectifier and a second AC transformer 3'; in which the DC side of LCC 1 is connected between a first low DC voltage line (Low DC voltage Pole 1 , Udc1+) and a neutral bus; the DC side of LCC 2 is connected between the first high DC voltage line (High DC voltage Pole 1 , Udc2+) and the first low DC voltage line; and the AC sides of LCC 1 and LCC 2 are connected via the first AC transformer 3, in which the first winding is connected to the AC side of the LCC 1 , the second winding is connected to the AC side of the LCC 2, and the third winding is connected to an AC system, for example a local AC network, an energy storage system, a StatCom or a condenser. The DC side of LCC V is connected between a second low DC voltage line (Low DC voltage Pole 2, Udc1-) and a neutral bus; the DC side of LCC 2' is connected between the second low DC voltage line (Low DC voltage Pole 2, Udc1-) and the a second high DC voltage line (High DC voltage Pole 2, Udc2-); and the AC sides of LCC V and LCC 2' are connected via the second AC transformer 3', in which the first winding is connected to the AC side of the LCC 1 ', the second winding is connected to the AC side of the LCC 2', and the third winding is connected to an AC system, for example a local AC network, an energy storage system, a StatCom or a condenser. For nominal power flow operation, the LCC 1 and LCC 1 ' are used as inverters, and LCC 2 and LCC 2' are used as rectifiers in the step-down DC autotransformer. For power flow reverse operation, DC voltage polarity of both LCC 1 , LCC 1\ LCC 2 and LCC 2' are changed: operation mode of LCC 1 and LCC 1' is changed to rectifier and operation mode of LCC 2 and LCC 2' is changed to inverter.
As shown in Fig.5e, various power flow direction can be realized with the topology.
Fig.5f illustrates a bipolar topology of a step-up DC autotransformer for HVDC according to another embodiment of the present invention.
As shown in Fig.Sf, another step-down DC autotransformer for HVDC is configured to realize bi-directional power flow. The topology shown in Fig. 5f is similar to that shown in Fig. 5e except that the connection direction of LCC 1 and LCC 1 ' are reversed.
For nominal power flow operation, LCC 1 , LCC1', LCC 2 and LCC 2 are operated as rectifiers in the step-up DC autotransformer. For power f!ow reverse operation, DC voltage polarity of LCC 1 , LCC 1 ', LCC 2 and LCC 2' are changed; operation modes of LCC 1 , LCC 1', LCC2 and LCC 2 are changed to inverters.
As shown in Fig.5f, various power flow direction can be realized with the topology.
Fig.5g illustrates a bipolar topology of a step-up DC autotransformer for HVDC according to another embodiment of the present invention.
As shown in Fig.5g, another step-down DC autotransformer for HVDC is configured to realize bi-directional power flow. The topoiogy shown in Fig. 5g is similar to that shown in Fig. 5c except that the VSC 1 and VSC V are replaced by LCC 1 and LCC 1 ' respectively.
Fig.6 illustrates a monopolar topology of a full-power step-up DC autotransformer for HVDC according to another embodiment of the present invention.
As shown in Fig.6, a ful!-power step-up DC autotransformer for HVDC is provided. The DC autotransformer comprises: a VSC 1 used as an inverter, a LCC 2 used as a rectifier and an AC transformer 3; in which the DC side of VSC 1 is connected between a low DC voltage line and a neutral bus; the DC side of LCC 2 is connected between a high DC voltage line and a neutral bus; and the AC sides of the VSC 1 and LCC 2 are connected via the AC transformer 3. The AC transformer 3 is a two-winding transformer, in which one winding is connected to the AC side of the VSC 1 , and the other winding is connected to the AC side of the LCC 2.
It shall be noted that the proposed solution in Fig. 6 employs full power converters, which means in spite of the DC/DC ratio, the capacity of each converter as well as converter transformer is always the same as power to be transmitted. In ail the solutions proposed above, if any converter is a LCC, it can be replaced by CCC (Capacitor Commutated Converter) or a fully controlled semiconductor based current source converter (CSC).
In all the solutions proposed above, if any converter is a LCC and operates as a rectifier, it can be replaced by a diode rectifier.
According to another aspect of the present invention, it provides a system comprising at least one of the DC autotransformer above embodiments mentioned.
Though the present invention has been described on the basis of some preferred embodiments, those skilled in the art should appreciate that those embodiments should by no means limit the scope of the present invention. Without departing from the spirit and concept of the present invention, any variations and modifications to the embodiments should be within the apprehension of those with ordinary knowledge and skills in the art, and therefore fall in the scope of the present invention which is defined by the accompanied claims.

Claims

1. A step-up DC autotransformer for HVDC, wherein the monopolar topology of said DC autotransformer comprises:
a first AC/DC converter, a second AC/DC converter operated as a rectifier and AC transformer with at least two windings;
in which
said first AC/DC converter can be a converter with three-phase or multi-phase;
said second AC/DC converter can be a voltage source converter, line com mutated converter or diode rectifier with single-phase, three-phase or multi-phase;
said AC transformer can be composed of a transformer or a number of transformers with single-phase, three-phase or multi-phase;
the DC side of said first AC/DC converter is connected between a low DC voltage line and a neutral bus;
the DC side of said second AC/DC converter is connected between a high DC voltage line and said low DC voltage line; and
the AC sides of said first AC/DC converter and second AC/DC converter are connected via said AC transformer.
2. The step-up DC autotransformer according to Claim 1 , wherein said AC transformer are a number of AC transformers; in which
said AC side of each said first and second AC/DC converter is connected to one side of each said a number of AC transformers; and
each the other side of said a number of AC transformers is connected together with an AC bus.
3. The step-up DC autotransformer according to Claim 1 , wherein besides the windings connected to said AC sides of said first AC/DC converter and said second AC/DC converter, an additional winding is installed in said AC transformer.
4. The step-up DC autotransformer according to Claim 2 or 3, wherein said other side of said a number of AC transformers or said additional winding of said AC transformer is connected to AC system; and
said AC system can be local AC network, energy storage system, StatCom or condenser.
5. The step-up DC autotransformer according to Claim 1 or 2, wherein
said first AC/DC converter is a voltage source converter operated as an inverter; and
said second AC/DC converter can be a voltage source converter, a line commutated converter or a diode rectifier.
6. The step-up DC autotransformer according to Claim 4, wherein
said first AC/DC converter can be a voltage source converter or a line commutated converter operated as an inverter; and
said second AC/DC converter is a voltage source converter, a line commutated converter or a diode rectifier.
7. The step-up DC autotransformer according to Claim 1 or 2, wherein
said first AC/DC converter is a line commutated converter; and
said second AC/DC converter is a voltage source converter.
8. The step-up DC autotransformer according to any one of Claims 1-4, wherein both said first and second AC/DC converters are voltage source converters with single-phase, three-phase or multi-phase.
9. The step-up DC autotransformer according to Claim 4, wherein both said first and second AC/DC converters are line commutated converters with single-phase, three-phase or multi-phase.
10. The step-up DC autotransformer according to any one of Claims 4-9, wherein said AC bus can exchange the power bi-directionally between said first and second AC/DC converter by the controlling the rectified power and inverted power of said first and second AC/DC converter.
11. A step-up DC autotransformer for HVDC, wherein the bipolar topology of said DC autotransformer comprises:
a first pole comprising a first AC/DC converter, a second AC/DC converter operated as a rectifier and first AC transformer with at least two windings;
a second pole comprising a third AC/DC converter, a fourth AC/DC converter operated as a rectifier and second AC transformer with at least two windings; and a neutral bus;
in which
each said first, second, third and fourth AC/DC converters can be converter with single-phase, three-phase or multi-phase;
each said first and second AC transformers can be composed of an AC transformer or a number of AC transformers with single-phase, three-phase or multi-phase;
the DC side of said first AC/DC converter is connected between a first low DC voltage line and said neutral bus; the DC side of said second AC/DC converter is connected between a first high DC voltage line and said first low DC voltage line; and the AC sides of said first AC/DC converter and second AC/DC converter are connected via said first AC transformer; and
the DC side of said third AC/DC converter is connected between a second low DC voltage line and said neutral bus; the DC side of said fourth AC/DC converter is connected between a second high DC voltage line and said second low DC voltage line; and the AC sides of said third AC/DC converter and said fourth AC/DC converter are connected via said second AC transformer.
12. The step-up DC autotransformer according to Claim 11 , wherein each said first AC transformer and said second AC transformer is composed of a number of AC transformers; in which
each said AC side of said first and second AC/DC converter is connected to one side of said a number of AC transformers; and
each other side of said a number of AC transformers is connected together with an AC bus.
13. The step-up DC autotransformer according to Claim 11 , wherein
besides the windings connected to said AC sides of said first and second AC/DC converters, an additional winding is installed in said first AC transformer; and
besides the windings connected to said AC sides of said third and fourth AC/DC converters, an additional winding is installed in said second AC transformer.
14. The step-up DC autotransformer according to Claim 12 or 13, wherein said other side of said a number of AC transformers or said additional winding of said AC transformers is connected to AC system; and
said AC system can be local AC network, energy storage system, StatCom or condenser.
15. The step-up DC autotransformer according to Claim 11 or 12, wherein both said first and third AC/DC converters are voltage source converters operated as inverters; and
each said second and fourth AC/DC converters is operated as rectifier, which can be voltage source converter, line commutated converter or diode rectifier.
16. The step-up DC autotransformer according to Claim 14, wherein
both said first and third AC/DC converters are voltage source converters or line commutated converters; and
both said second and fourth AC/DC converters can be voltage source converter, line commutated converter or diode rectifier.
17. The step-up DC autotransformer according to Claim 11 or 12, wherein both said first and third AC/DC converters are line commutated converter; and
both said second and fourth AC/DC converters are voltage source converter.
18. The step-up DC autotransformer according to any one of Claims 11-14, wherein ail said first, second, third and fourth AC/DC converters are voltage source converters with single-phase, three-phase or multi-phase.
19. The step-up DC autotransformer according to Claim 14, wherein all said first, second, third and fourth AC/DC converters are line com mutated converters.
20. The step-up DC autotransformer according to any one of Claims 14-19, wherein said AC bus can exchange the power bi-directionally between said first pole and second pole by controlling the rectified power or inverted power of said first, second, third and/or fourth AC/DC converter.
21. The step-up DC autotransformer according to any one of Claims 11-20, wherein the currents of said first AC/DC converter and said third AC/DC converter are equal to avoid unbalanced current through earth via said neutral bus.
22. The step-up DC autotransformer according to any one of Claims 5, 6, 15 and 16, wherein said line commutated converter can be replaced by a capacitor commutated converter.
23. The step-up DC autotransformer according to any one of Claims 1 , 11 and 22, wherein said high DC voltage line and low DC voltage line are connected to different DC systems with different voltage levels.
24. A step-up DC transformer for HVDC, wherein said DC transformer comprises:
a first AC/DC converter used as an inverter, a second AC/DC converter used as a rectifier and an AC transformer;
in which
said first AC/DC converter is voltage source converter;
said second AC/DC converter is line commutated converter;
the DC side of said first AC/DC converter is connected between a high DC voltage line and a neutral bus;
the DC side of said second AC/DC converter is connected between a iow DC voltage line and a neutral bus; and
the AC sides of said first AC/DC converter and second AC/DC converter are connected via said AC transformer.
25. The step-up DC transformer according to Claim 24, wherein besides the windings connected to said AC sides of said first AC/DC converter and said second AC/DC converter, an additional winding is installed in said AC transformer which can be an AC transformer with single-phase, three-phase or multi-phase;
said additional winding of said AC transformer is connected to AC system; and
said AC system can be local AC network, energy storage system, StatCom or condenser.
26. A system, wherein said system comprises at least one of said step-up DC autotransformer or transformer according to any one of above ciaims.
PCT/CN2012/084350 2012-11-09 2012-11-09 A step-up dc autotransformer for hvdc and a system thereof WO2014071598A1 (en)

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Publication number Priority date Publication date Assignee Title
WO2017084120A1 (en) * 2015-11-19 2017-05-26 华中科技大学 Unidirectional direct current-direct current autotransformer, and high-low voltage side fault isolation method therefor
CN108736506A (en) * 2018-08-02 2018-11-02 南方电网科学研究院有限责任公司 A kind of HVDC transmission system
WO2020108739A1 (en) * 2018-11-27 2020-06-04 Siemens Aktiengesellschaft Device for transforming a direct current voltage

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CN102185480A (en) * 2011-04-13 2011-09-14 中电普瑞科技有限公司 Bidirectional isolation direct-current converter

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JP2000050403A (en) * 1998-08-03 2000-02-18 Denso Corp Power source unit for hybrid electric automobile
CN1503444A (en) * 2002-11-22 2004-06-09 株洲电力机车研究所 DC boosting conversion circuit
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Publication number Priority date Publication date Assignee Title
WO2017084120A1 (en) * 2015-11-19 2017-05-26 华中科技大学 Unidirectional direct current-direct current autotransformer, and high-low voltage side fault isolation method therefor
CN108736506A (en) * 2018-08-02 2018-11-02 南方电网科学研究院有限责任公司 A kind of HVDC transmission system
CN108736506B (en) * 2018-08-02 2023-12-01 南方电网科学研究院有限责任公司 High-voltage direct-current transmission system
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