WO2013013858A1 - An apparatus for controlling the electric power transmission in a hvdc power transmission system - Google Patents

An apparatus for controlling the electric power transmission in a hvdc power transmission system Download PDF

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Publication number
WO2013013858A1
WO2013013858A1 PCT/EP2012/059885 EP2012059885W WO2013013858A1 WO 2013013858 A1 WO2013013858 A1 WO 2013013858A1 EP 2012059885 W EP2012059885 W EP 2012059885W WO 2013013858 A1 WO2013013858 A1 WO 2013013858A1
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WO
WIPO (PCT)
Prior art keywords
converter
electric power
hvdc
power source
direct current
Prior art date
Application number
PCT/EP2012/059885
Other languages
French (fr)
Inventor
Dimitris GIANNOCCARO
Sasitharan Subramanian
Soubhik AUDDY
Subhasish Mukherjee
Original Assignee
Abb Technology Ltd
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Filing date
Publication date
Application filed by Abb Technology Ltd filed Critical Abb Technology Ltd
Publication of WO2013013858A1 publication Critical patent/WO2013013858A1/en

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Classifications

    • 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
    • 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
    • H02M3/33569—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 having several active switching elements
    • H02M3/33576—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 having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
    • H02M3/33584—Bidirectional 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
    • H02J1/00—Circuit arrangements for dc mains or dc distribution networks
    • H02J1/10—Parallel operation of dc sources
    • 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
    • H02M1/0074—Plural converter units whose inputs 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
    • H02M1/0067—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
    • 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 present invention relates to an apparatus for controlling the electric power transmission in a high voltage direct current, HVDC, power transmission system comprising at least one HVDC transmission or distribution line for carrying direct current, DC, the apparatus being arranged to control the direct current of the HVDC transmission or distribution line by introducing a DC voltage in series with the HVDC transmission or distribution line.
  • the present invention relates to a HVDC power transmission system comprising at least one HVDC transmission or distribution line for carrying direct current, and a plurality of converter stations connected to the at least one HVDC transmission or distribution line, each of the converter stations being arranged to convert alternating current, AC, to direct current for input to the at least one HVDC transmission or distribution line, and/or di- rect current to alternating current, the system comprising at least one apparatus of the above-mentioned sort.
  • a HVDC power distribution network or a HVDC power transmission system uses direct current for the transmission of electrical power, in contrast to the more common AC systems.
  • HVDC systems may be less expensive and may suffer lower electrical losses.
  • a HVDC power transmission system comprises at least one long-distance HVDC link or cable for carrying direct current a long distance, e.g. under sea, and converter stations for converting alternating current to direct current for input to the HVDC power transmission system and converter stations for converting direct current back to alternating current.
  • US-B2-6,788,033 and US-A-5, 734,258 disclose DC to DC conversion and relate to stationary or portable systems powered by a DC battery, and to electric vehicles.
  • US-B2-6, 914,420 describes a power converter for converting power be- tween a first and a second voltage, and relates to electric vehicles.
  • US-B2-7, 518,266 discloses an AC power transmission system, where a DC transmission ring is used, utilizing controllable AC-DC converters in a multi-in- feed/out-feed arrangement.
  • US 3,694,728 describes a HVDC mesh-operated network comprising several interconnected stations for effecting an exchange of power by means of converters located at the stations and which are connected to AC networks.
  • WO 2010/1 15452 discloses a meshed HVDC power transmission network comprising at least three HVDC converter stations interconnected in a first closed path by at least three transmission lines.
  • DE 1513827 discloses an apparatus for influencing the current distribution in a HVDC network.
  • EP 2 293 407 describes a direct current power transmission and distribu- tion system suitable for subsea electrical loads.
  • each of the converter stations may be controlled, e.g. by controlling the DC voltage of each converter station.
  • the inventors of the present invention have found that the DC voltage control of the converter stations may not be sufficient in order to avoid or reduce load-flow congestion of the system.
  • the object of the present invention is to improve the electric power transmission in a HVDC power transmission system. It is also an object of the present invention to provide an improved control of the electric power transmission in a HVDC power transmission system. A further object of the present invention is to avoid, reduce or prevent load-flow congestion in the system. Another object of the present invention is to provide an improved HVDC power transmission system.
  • an apparatus for controlling the electric power transmission in a high voltage direct current, HVDC, power transmission system comprising at least one HVDC transmission or distribution line for carrying direct current, DC
  • the apparatus being arranged to control the direct current of the HVDC transmission or distribution line by introducing a DC voltage in series with the HVDC transmission or distribution line
  • the apparatus comprises a plurality of electric power source sections connectable to an electric power source
  • the apparatus comprises a plurality of DC-to-DC converter units, each DC-to-DC converter unit of the plurality of DC-to-DC converter units comprising a first DC side for output and/or input of direct current and a second DC side for output and/or input of direct current, wherein each DC-to-DC converter unit of the plurality of DC-to-DC converter units is connectable via its first DC side to the HVDC transmission or distribution line, and wherein each DC-to-DC converter unit of the plurality of DC-to-DC converter units is connected via
  • the electric power transmission in a HVDC power transmission system and the control thereof are efficiently improved, and load-flow congestion in the system may be avoided, reduced or prevented.
  • the apparatus of the present invention is especially advantageous and ef- ficient for a HVDC power transmission system of the sort shown in Fig. 1 , which may be called a DC grid concept, where the system comprises several HVDC transmission or distribution lines for carrying direct current and several converter stations connected to the HVDC transmission or distribution lines.
  • the apparatus of the present invention is especially advantageous when the control of DC voltage of the converter stations, or the control of shunt connected converter DC voltages of a DC grid, is not sufficient.
  • the direct current of the HVDC transmission or distribution line, to which the apparatus is connected can be increased or reduced in order to control the power transmission.
  • the direct current control is attained by means of the apparatus' in- traduction, or injection, of a DC voltage in series with the HVDC transmission or distribution line.
  • the injected DC voltage produces a fictive resistance, AR in j.
  • the fictive resistance provides an active power extraction or output from the HVDC transmission or distribution line when the fictive resistance corresponds to an increase in resistance, i.e. a positive AR in j, (since a resistance consumes pow- er/energy), or an active power input to the HVDC transmission or distribution line when the fictive resistance corresponds to a decrease in resistance, i.e. a negative ARinj.
  • a positive AR lnj is produced when the apparatus introduces a positive DC voltage in series with the HVDC transmission or distribution line
  • a negative ARinj is produced when the apparatus introduces a negative DC voltage in series with the HVDC transmission or distribution line.
  • the load of the HVDC transmission or distribution line, to which the apparatus is connected may be reduced or increased.
  • the apparatus' active power extraction or output from the HVDC transmission or distribution line results in a decrease in direct current of the line
  • the apparatus' active power input to the HVDC transmission or distribution line results in an increase in direct current of the line.
  • the apparatus of the present invention is arranged to regulate the voltage at its output to control the current flow in the HVDC transmission or distribution line.
  • the apparatus may comprise the electric power source.
  • the apparatus according to the present invention is arranged to control the direct current of the HVDC transmission or distribution line by introducing a fictive resistance in series with the HVDC transmission or distribution line by introducing a DC voltage in series with the HVDC transmission or distribution line.
  • the individual DC-to- DC converter units can be designed with lower rating power semiconductor switches, e.g. with lower rating IGBTs, which results in better utilization of the power semiconductor switches.
  • Each DC-to-DC converter unit may introduce a DC voltage in series with the HVDC transmission or distribution line, which is a contribution to the total DC voltage introduced in series with the HVDC transmission or distribution line by the apparatus. If some of the plurality of DC-to-DC converter units are impaired, it is possible continue to operate the apparatus by means of the faultless DC-to-DC converter units. Thus, the redundancy and reliability of the apparatus are improved.
  • the direct current in a HVDC power transmission system may reverse, and therefore, voltage polarity reversal for maintained fictive resistance is required, which is also attained by means of the apparatus of the present invention. Further, the apparatus of the present invention has the capability to operate in all four quadrants.
  • the various components of the apparatus of the present invention may be electrically connected, or connectable, to one another or to other units, e.g. via electrical conductors, e.g. busbars or DC lines, and/or may be indirectly connected, or connectable, e.g. electrically or inductively, via additional intermediate electric equipment or units located and connected/connectable between the components, e.g. a transformer, another converter etc.
  • Each DC-to-DC converter unit of the plurality of DC-to-DC converter units may be connected, via its second DC side, to one of the plurality of electric power source sections, or to two or more of the plurality of electric power source sections.
  • the DC-to-DC converter units of the plurality of DC-to-DC converter units are connected, via respective second DC side, to different electric power source sections of the plurality of electric power source sections.
  • the electric power transmission in a HVDC power transmis- sion system and the control thereof are further improved.
  • a plurality of the first DC sides of the plurality of DC- to-DC converter units are connected in series with one another.
  • a plurality of the first DC sides of the plurality of DC- to-DC converter units are connected in parallel with one another.
  • a plurality of the second DC sides of the plurality of DC-to-DC converter units are connected in series with one another.
  • a plurality of the second DC sides of the plurality of DC-to-DC converter units are connected in parallel with one another.
  • the redundancy and reliability of the apparatus are further improved.
  • Some of the first DC sides of the plurality of DC-to-DC converter units may be connected in series with one another, whereas the other first DC sides of the plurality of DC-to-DC converter units may be connected in parallel with one another.
  • the same may apply to the second DC sides of the plurality of DC-to-DC con- verter units. Combinations of series and parallel connections of the first and second DC sides, respectively, of the plurality of DC-to-DC converter units are thus possible.
  • each electric power source section of the plurality of electric power source sections is arranged to be connected to an electric power source comprising a DC source.
  • an electric power source comprising a DC source.
  • active power should be absorbed by the DC source, and to effect or introduce a negative fictive resistance, -AR m j, active power should be injected by and from the DC source.
  • the electric power transmis- sion in a HVDC power transmission system and the control thereof are further i mproved.
  • each electric power source section of the plurality of electric power source sections is arranged to be connected to an electric power source comprising a DC source that comprises an electric battery.
  • the DC source may comprise a capacitor.
  • the inventors of the present invention have found that the use of an electric battery for the DC source efficiently improves the electric power transmission in a HVDC power transmission system and the control thereof.
  • other suitable DC sources may be used.
  • the DC source may for exam- pie comprise photovoltaic cells and/or flywheels etc.
  • each electric power source section of the plurality of electric power source sections is arranged to be connected to an electric power source comprising a DC source that is part of a HVDC power transmission system.
  • an electric power source comprising a DC source that is part of a HVDC power transmission system.
  • each electric power source section of the plurality of electric power source sections is arranged to be connected to an electric power source comprising a DC source that comprises at least one cascaded cell.
  • the inventors of the present invention have found that the use of a cascaded cell for the DC source efficiently improves the electric power transmission in a HVDC power transmission system and the control thereof.
  • the at least one cascaded cell may be arranged to be part of a converter station included in the HVDC power transmission system, the converter station being arranged to convert alternating current to direct current, for input to the HVDC transmission line, and/or direct current to alternating current.
  • Each electric power source section of the plurality of electric power source sections may be arranged to be connected to an electric power source comprising a DC source that comprises a plurality of cascaded cells.
  • the inventors of the present invention have found that the use of several cascaded cells efficiently improves the flexibility and efficiency of the electric power transmission in a HVDC power transmission system and the control thereof.
  • Each cascaded cell may be a cascaded half-bridge cell (also called Cascaded Two-Level, CTL, cell).
  • Each cascaded cell may be a cascaded full-bridge cell.
  • a cascaded half-bridge cell and a cascaded full-bridge cell per se and their structure are well known to the person skilled in the art and therefore not disclosed or discussed in more detail.
  • the plurality of cascaded cells may comprise a plural- ity of half-bridge cells, or a plurality of cascaded full-bridge cells, or a mixture thereof.
  • the plurality of cascaded cells may be arranged to be part of a converter station included in the HVDC power transmission system.
  • the converter station may also comprise a mixture of cascaded half-bridge cells and cascaded full- bridge cells.
  • the plurality of cascaded cells may be interconnected to one another.
  • each electric power source section of the plurality of electric power source sections comprises a capacitor.
  • an electric power source e.g. an electric power source comprising a DC source
  • each electric power source section of the plurality of electric power source sections comprises a section converter for converting alternating current, AC, to direct current and/or direct current to alternating current, the sec- tion converter having an AC side for output and/or input of alternating current and a DC side for output and/or input of direct current, wherein each electric power source section of the plurality of electric power source sections is arranged to be connected, via the AC side of the section converter, to an electric power source comprising an AC source, and wherein each DC-to-DC converter unit of the plurality of DC-to-DC converter units is connected via its second DC side to the DC side of the section converter of at least one of the plurality of electric power source sections.
  • active power should be absorbed by the AC source, and to effect or introduce a negative fictive resistance, -AF? /ny , active power should be injected by and from the AC source.
  • active power transmission in a HVDC power transmission system and the control thereof are further improved.
  • each electric power source section of the plurality of electric power source sections is arranged to be connected, via the AC side of the section converter, to an electric power source comprising an AC source that comprises an AC grid.
  • the inventors of the present invention have found that the use of an AC grid for the AC source efficiently improves the electric power transmission in a HVDC power transmission system and the control thereof.
  • oth- er suitable AC sources are possible.
  • each DC-to-DC converter unit comprises a first converter for converting alternating current, AC, to direct current and/or direct current to alternating current, and a second converter for converting direct current to alter- nating current and/or alternating current to direct current, each of the first and second converters having an AC side for output and/or input of alternating current, wherein the first converter comprises the first DC side of the DC-to-DC converter unit, wherein the second converter comprises the second DC side of the DC-to-DC converter unit, and wherein the AC side of the second converter is connected to the AC side of the first converter.
  • each DC-to-DC converter unit comprises a transformer connected between the first and second converters, and each of the first and second converters is connectable via its AC side to the transformer.
  • the transformer may also take part in fulfilling the voltage requirements of the apparatus.
  • the transformer may be an electric power transformer.
  • the transformer may be in the form of a high or medium frequency transformer.
  • the transformer used can be of a higher frequency which will reduce the size of overall magnetics in the apparatus.
  • the insulation requirement will also be reduced for the individual transformer, which makes the transformer design less complex.
  • the transformer is arranged to isolate the first converter from the electric power source section.
  • the HVDC transmission or distribution line, to which the apparatus is connected is also efficiently isolated from the electric power source section and from the electric power source.
  • the second converter comprises four pairs of electronic switches.
  • the electronic switches may be connected to one another.
  • the inventors of the present invention have found that this structure of the second con- verter further improves the flexibility and efficiency of the electric power transmission in a HVDC power transmission system and the control thereof.
  • the second converter comprises four pairs of electronic control devices, each pair of electronic control devices comprising an elec- tronic switch and a diode.
  • the inventors of the present invention have found that this structure of the second converter further improves the flexibility and efficiency of the electric power transmission in a HVDC power transmission system and the control thereof.
  • the first converter comprises a full-bridge converter. The inventors of the present invention have found that this structure of the first converter further improves the flexibility and efficiency of the electric power transmission in a HVDC power transmission system and the control thereof.
  • the first converter may comprise a full-bridge converter with a bypass switch.
  • the first converter comprises four pairs of electronic switches.
  • the electronic switches may be connected to one another.
  • the in- ventors of the present invention have found that this structure of the first converter further improves the flexibility and efficiency of the electric power transmission in a HVDC power transmission system and the control thereof.
  • the first converter may also comprise a fifth pair of electronic switches.
  • the fifth pair of electronic switches may be connected in parallel with the four pairs of electronic switches.
  • the first converter comprises filter means for smoothing out the voltage and current ripple caused by the switching of the electronic switches.
  • the filter means may be connected to the electronic switches. By smoothing out the voltage and current ripple, a further improved control of the electric power transmission is attained.
  • the filter means, or filter components may comprise a capacitor and an inductor. The capacitor may be connected in parallel with the electronic switches. The inductor may be connected in series with the electronic switches.
  • electronic switch comprises a power semiconductor switch.
  • Each power semiconductor switch may comprise an Insulated Gate Bipolar Transistor, IGBT, or a Bi-Mode Insulated Gate Transistor, BiGT, or any other suit- able power semiconductor switch.
  • each power semiconductor switch may comprise a thyristor, e.g. a gate turn-off thyristor, GTO, an Integrated Gate- Commutated Thyristor, IGCT, or a Forced Commutated Thyristor.
  • GTO gate turn-off thyristor
  • IGCT Integrated Gate- Commutated Thyristor
  • Forced Commutated Thyristor e.g. a Forced Commutated Thyristor
  • other suitable thyristors may also be used.
  • the inventors of the present invention have found that these structures of first converter and/or the second converter further improves the flexibility and efficiency of the electric power transmission in a HVDC power transmission system and the control thereof.
  • the first converter is connectable in series with the HVDC transmission or distribution line.
  • the apparatus comprises control means for controlling the apparatus, wherein the control means are arranged to control the apparatus to introduce a positive DC voltage in series with the HVDC transmission or distribution line for reducing the direct current of the HVDC transmission or distribution line, and wherein the control means are arranged to control the apparatus to introduce a negative DC voltage in series with the HVDC transmission or distribution line for increasing the direct current of the HVDC transmission or distribution line.
  • the control means may be in form of a control unit and may be connectable to the HVDC power transmission system, e.g. to the HVDC transmission or distribution line.
  • the control means may comprise a computer and/or a CPU.
  • the control means may be arranged to control the apparatus to introduce a positive fictive resistance in series with the HVDC transmission or distribution line by introducing a positive DC voltage in series with the HVDC transmission or distribution line for reducing the direct current of the HVDC transmission or distribution line
  • the control means may be arranged to control the apparatus to introduce a negative fictive resistance in series with the HVDC transmission or distribution line by introducing a negative DC volt- age in series with the HVDC transmission or distribution line for increasing the direct current of the HVDC transmission or distribution line.
  • the apparatus comprises measuring means for measuring the DC load flow congestion of the HVDC power transmission system, and the measuring means are arranged to communicate with the control means.
  • the measuring means may be arranged to measure the direct current or direct voltage of the HVDC line, and the measuring means per se may have a structure known the person skilled in the art.
  • the measuring means, or measuring equipment may comprise conventional sensors, e.g. sensors for measuring direct current or direct voltage.
  • the apparatus is adapted for four quadrant operation.
  • the apparatus may be adapted for one quadrant operation, two quadrant operation or three quadrant operation, where the quadrant operation/-s may be any of the first to fourth quadrant operations.
  • the one, two or three quadrant operation may be attained by replacing suitable IGBT/IGBTs with diode/diodes of a four quadrant converter.
  • a bypass switch connectable to the HVDC transmission or distribution line and connected in parallel with the apparatus may be provided. When closed, the bypass switch is arranged to conduct the direct current of the HVDC transmission or distribution line to electrically bypass the apparatus. By the bypass switch, the apparatus may be bypassed during fault conditions, whereby the electric power transmission in a HVDC power transmission system and the control thereof are further improved.
  • a high voltage direct current, HVDC, power transmission system comprising at least one HVDC transmission or distribution line for carrying direct cur- rent, DC, and a plurality of converter stations connected to the at least one HVDC transmission or distribution line, each of the converter stations being arranged to convert alternating current, AC, to direct current for input to the at least one HVDC transmission or distribution line, and/or direct current to alternating current
  • the system comprises at least one apparatus as claimed in any of the claims 1 - 25 for controlling the electric power transmission in the system, and/or at least one apparatus according to any of the above-mentioned embodiments of the apparatus.
  • the at least one HVDC transmission or distribution line may be one or a plurality of HVDC transmission or distribution lines
  • the system comprises a plurality of HVDC transmission or distribution lines.
  • a plurality of HVDC transmission or distribution lines or converter stations may be two or more HVDC transmission or distribution lines or converter stations, respectively.
  • the at least one apparatus may be one or a plurality of apparatuses, e.g. two or more apparatuses.
  • a plurality of apparatuses may be connected to the same HVDC transmission or distribution line, or to different HVDC transmission or distribution lines. For example, two apparatuses adapted for two quadrant opera- tion may be connected to the same HVDC transmission or distribution line to attain four quadrant operation.
  • the system comprises at least three converter stations.
  • the system comprises at least four con- verter stations, or at least five converter stations.
  • the at least one HVDC transmission or distribution line comprises at least one long-distance HVDC link or cable.
  • the HVDC transmission or distribution lines may comprise at least two long-distance HVDC links or cables.
  • High Voltage may be about 1 -1 .5 kV and above. However, for HVDC applications and systems, High Voltage may be about 320 kV and above, e.g. 500 kV, 800 kV or 1000 kV, and above.
  • the apparatus and/or the system according to the present invention are advantageously adapted for the above-men- tioned HVDC voltage levels and above.
  • the voltage rating of the apparatus may be 1 -5 % of the HVDC transmission or distribution line voltage.
  • Fig. 1 is a schematic block diagram illustrating aspects of the HVDC power transmission system and aspects of the apparatus according to the present invention
  • Fig. 2A is schematic block diagram illustrating a first embodiment of a converter station shown in Fig. 1 ;
  • Fig. 2B is schematic block diagram illustrating a second embodiment of a converter station shown in Fig. 1 ;
  • Fig. 3A is a schematic block diagram illustrating a first embodiment of the apparatus according to the present invention.
  • Fig. 3B is a schematic block diagram illustrating a second embodiment of the apparatus according to the present invention.
  • Fig 4 is a schematic diagram illustrating an embodiment of a DC
  • Fig. 5 is a schematic diagram illustrating a first embodiment and aspects of the DC-to-DC converter unit of the apparatuses shown in Figs 3A and 3B in more detail;
  • Fig. 6 is a schematic diagram illustrating a second embodiment and aspects of the DC-to-DC converter unit of the apparatuses shown in Figs 3A and 3B;
  • Fig. 7 is a schematic diagram illustrating a third embodiment and aspects of the DC-to-DC converter unit of the apparatuses shown in Figs 3A and 3B;
  • Figs. 8A and 8B are schematic diagrams illustrating alternative electronic control devices
  • Fig. 9 is a schematic block diagram illustrating a third embodiment of the apparatus according to the present invention.
  • Fig. 10A is exemplary half-bridge topology for the section converter of the electric power source section of Fig. 9;
  • Fig. 10B is exemplary full-bridge topology for the section converter of the electric power source section of Fig. 9. Detailed Description of Preferred Embodiments Abbreviations
  • Fig.1 schematically shows aspects of the HVDC power transmission system and aspects of the apparatus 202; 212; 908 according to the present inven- tion.
  • the HVDC power transmission system comprises at least one HVDC transmission or distribution line for carrying direct current, hereinafter called HVDC line, e.g. a plurality of HVDC lines 102, 104, 106, 108, 1 10, 1 12, 1 14 for carrying direct current.
  • the HVDC lines may e.g. comprise HVDC cables, busbars, or other DC conductors.
  • the HVDC lines 102, 104, 106, 108, 1 10, 1 12, 1 14 may comprise at least one long-distance HVDC link.
  • the HVDC power transmission system comprises a plurality of converter stations 1 16, 1 18, 120, 122, 124 electrically connected to the HVDC lines 102, 104, 106, 108, 1 10, 1 12, 1 14. In Fig. 1 , five converter stations 1 16, 1 18, 120, 122, 124 are provided, but there may be more or fewer converter stations.
  • the HVDC power transmission system may e.g. comprise two, at least three, or at least four converter stations, or at least five converter stations.
  • Each of the converter stations 1 16, 1 18, 120, 122, 124 may be ar- ranged to convert alternating current to direct current for input to the HVDC lines 102, 104, 106, 108, 1 10, 1 12, 1 14 and convert direct current to alternating current for input to neighbouring AC systems.
  • Each converter station 1 16, 1 18, 120, 122, 124 may be electrically connected to a conventional transformer 126, 128, 130, 132, 134, which may be an electric power transformer, in conventional ways known to the skilled person. Transformers and their function are well known to the person skilled in the art and therefore not discussed in more detail.
  • Each converter station 1 16, 1 18, 120, 122, 124 which may be called a DC Grid converter station, may have asymmetrical monopoles with separate convert- ers for positive and negative polarity, as illustrated in Fig. 2A.
  • each converter station 1 16, 1 18, 120, 122, 124 may be in the form of a symmetrical monopolar converter, as illustrated in Fig. 2B.
  • the alternatives of Figs. 2A and 2B may also be combined in the same system.
  • the apparatus 202; 212; 908 according to the present invention is ar- ranged to be electrically connected to the HVDC system, e.g. by being connected between positions A and B as illustrated in Fig. 1 .
  • the apparatus 202 may e.g. be connected to any of the other HVDC lines.
  • R n beaut e of the HVDC line 102 in Fig. 1 illustrates the resistance of the HVDC line 102, and be in Fig. 1 is the direct current through the HVDC line 102, i.e. the direct current carried by the HVDC line 102.
  • the HVDC power transmission system may be adapted for single phase power or multi-phase power, e.g.
  • the HVDC power transmission system comprises an embodiment of the apparatus 202; 212; 908 for controlling the electric power transmission in the system according to the present invention, and aspects of the apparatus 202; 212; 908 will hereinafter be disclosed.
  • a bypass switch 136 may be provided and may be electrically connectable to the HVDC line 102 to which the apparatus 202; 212; 908 and may be connected in parallel with the apparatus 202; 212; 908.
  • the bypass switch 136 When the bypass switch 136 is closed, it is arranged to conduct the direct current of HVDC line 102 to electrically bypass the apparatus 202; 212; 908.
  • the apparatus 202 By the bypass switch 1 36, the apparatus 202 may be bypassed during fault conditions.
  • Fig. 3A schematically shows a first embodiment of the apparatus 202 according to the present invention for controlling the electric power transmission in a HVDC power transmission system, e.g. as shown in Fig.
  • the apparatus 202 comprises a plurality of electric power source sections 204 connectable to an elec- trie power source 316.
  • the apparatus 202 comprises plurality of DC-to-DC converter units 302; 602; 902.
  • Each DC-to-DC converter unit 302 of the plurality of DC-to-DC converter units 302 comprises a first DC side 206 for output and/or input of direct current and a second DC side 208 for output and/or input of direct current.
  • Each DC-to-DC converter unit 302 of the plurality of DC-to-DC converter units is connectable via its first DC side 206 to the HVDC line 102, and each DC-to-DC converter unit 302 of the plurality of DC-to-DC converter units is connected via its second DC side 208 to at least one of the plurality of electric power source sections 204, e.g. to one of the plurality of electric power source sections 204.
  • the DC-to-DC converter units 302 of the plurality of DC-to-DC converter units may be connected, via respective second DC side 208, to different electric power source sections 204 of the plurality of electric power source sections 204.
  • the first DC sides 206 of the plurality of DC-to-DC converter units 302 may be connected in series with one another.
  • Each DC-to-DC converter unit 302 may comprise a first converter 304 for converting alternating current to direct current and/or direct current to alternating current, and a second converter 306 for converting direct current to alternating current and/or alternating current to direct current.
  • Each of the first and second converters 304, 306 has an AC side 308, 310 for output and/or input of alternating current.
  • the first converter 304 comprises the first DC side 206 of the DC-to-DC con- verter unit 302, and the second converter 306 comprises the second DC side 208 of the DC-to-DC converter unit 302.
  • the AC side 310 of the second converter 306 is connected to the AC side 308 of the first converter 304.
  • the first converter 304 may be electrically connectable via the DC side 206 to the HVDC line 102, and the first converter 304 may be electrically connectable in series with the HVDC line 102.
  • the AC side 308 of the first converter 304 is arranged to provide alternating current to the AC side 310 of the second converter 306, and vice versa.
  • Each DC- to-DC converter unit 302 may comprise an transformer 318 connected between the first and second converters 304, 306, each of the first and second converters 304, 306 being connectable via its AC side 308, 310 to the transformer 318.
  • Each DC-to-DC converter unit 302, and each of the converters 304, 306 included therein, may be of soft switched type, e.g. ZCS, or ZVS.
  • Each transformer may be an electric power transformer.
  • Each transformer 318 may be a high or medium frequency transformer, and the second converter 306 may be arranged to convert DC voltage to high or medium frequency AC voltage.
  • the transformer 318 may be arranged to isolate the first converter 304 from the electric power source section 204, and may thus also be arranged to isolate the HVDC line 102 from the electric power source section 204, and from the electric power source 316.
  • Each electric power source section 204 may comprise a section capacitor 21 0 to which the DC-to-DC converter unit 302 and the second converter 306 are electrically connectable via the second DC side 208.
  • the apparatus 202 is arranged to control the direct current of the HVDC line 102 by introducing a DC voltage V AB in series with the HVDC line 102.
  • the apparatus 202 may comprise control means 324, e.g. a computer or CPU, for con- trolling the apparatus and its various components.
  • the control means 324 may be arranged to control the apparatus 302 to introduce a positive DC voltage, V AB > 0, in series with the HVDC line 102 for reducing the direct current, i.e.
  • Each of DC-to-DC converter units 302 may be arranged to introduce a DC voltage in series with the HVDC line 102, and each of DC-to-DC converter units 302 may thus take part in the control of the direct current of the HVDC line 102.
  • the number of DC-to-DC converter units 302 may be two or more.
  • Fig. 3B schematically shows a second embodiment of the apparatus 212 according to the present invention.
  • the apparatus 212 of Fig. 3B essentially corresponds to the embodiment of Fig. 3A except for the connection of the first DC sides 206 of the plurality of DC-to-DC converter units 302.
  • the first DC sides 206 of the plurality of DC-to-DC converter units 302; 602; 902 are connected in parallel with one another.
  • the electric power source 316 to which the plurality of electric power source sections 204 is arranged to be connected, may comprise a DC source 214.
  • the DC source 214 may comprise an electric battery, or the DC source 214 may be part of a HVDC power transmission system, or HVDC grid, or any other available DC source.
  • An electric battery and a HVDC power transmission system are well known to the skilled person and therefore not discussed in more detail.
  • the electric power source 316, to which the plurality of electric power source sections 204 is arranged to be connected may comprise a DC source 214 that comprises at least one cascaded cell 326, e.g. a cascaded half- bridge cell, or a cascaded full-bridge cell.
  • the at least one cascaded half-bridge cell 326 may be arranged to be part of a converter station 1 16 included in the HVDC power transmission system.
  • the DC source 214 may comprise a plurality of cascaded cells 326, e.g. cascaded half-bridge cells, or cascaded full-bridge cells, or a mixture thereof.
  • the plurality of cascaded cells 326 may be arranged to be part of a converter station 1 16 included in the HVDC power transmission system.
  • the electric power source 316 may comprise a power source capacitor 320 (see Fig. 4) to which the electric power source sections 204 may be electrically con- nectable.
  • the apparatus may 202 comprise the electric power source.
  • the second converter 306 of the DC-to-DC converter unit 302 may comprise four pairs 402, 404, 406, 408, also indicated as Ss/S's, Se/S' 6 , S 7 /S' 7 , Ss/S's in Fig. 4, of electrically in- terconnected electronic switches 410, 412.
  • the first converter 304 of the DC-to- DC converter unit 302 may comprise a full-bridge converter.
  • the first converter 304 may comprise four pairs 414, 416, 418, 420, also indicated as S/S'r, S ⁇ S' 2 , S3/S' 3 , S /S'4 in Fig. 4, of electrically interconnected electronic switches 422, 424.
  • the first converter 304 may also comprise a fifth pair 430 of electronic switches 431 , 433, also indicated as S A B S'AB in Fig. 4.
  • the fifth pair 430 of electronic switches may be electrically connected in parallel with the four pairs 414, 416, 418, 420 of electronic switches.
  • the fifth pair 430 of electronic switches may be used to give a path to the direct current when the first converter 304 is bypassed to give zero voltage.
  • the first converter 304 may comprise filter means 426, 428, connected to the electronic switches 422, 424, for smoothing out the voltage and current ripple caused by the switching of the electronic switches 422, 424.
  • the filter means may comprise a capacitor 426, also indicated as C ⁇ in Fig. 4, and an inductor 428, also indicated as L f , .
  • the capacitor 426 may be connected in parallel with the electronic switches 422, 424.
  • the inductor 428 may be electrically con- nected in series with the electronic switches 422, 424.
  • the capacitor 426 may be connected in parallel with the fifth pair 430 of electronic switches.
  • the DC-to-DC converter unit 302 may also comprise a second inductor 440 connected as indicated in Fig. 5.
  • the filter inductor 428 may be connected in series with the first converter
  • DC terminal with a first end connected to the common point of 414, 418 and 430, and with a second end connected to the filter capacitor 426.
  • the other end of the filter capacitor 426 may be connected to the common point of 420, 416 and 430.
  • This connection may also be reversed, i.e. the first end of the filter inductor 428 may be connected to the common point of 420, 416 and 430, and the second end of the filter inductor 428 may be connected to the filter capacitor 426.
  • the other end of the filter capacitor 426 may be connected to the common point of 414, 418 and 430.
  • the four quadrant operation of the apparatus may be supported by bi- directional valves.
  • the injected voltage V AB may be regulated to a desired value or level in an efficient way. PWM switching per se is well known to the skilled person and is thus not discussed in further detail.
  • the power requirement of first converter 304 is supplied from the second converter 306 via the transformer 318.
  • the second converter 306 may comprise at least two legs which convert direct current to alternating current and/or vice-versa. To effect or introduce a positive fictive resistance, +AR in j, active power should be absorbed by the DC source, and to effect or introduce a negative fictive resistance, -Af?/ ny , active power should be injected by and from the DC source.
  • Fig. 6 schematically shows a second embodiment and aspects of the DC- to-DC converter unit 602 of the embodiments of the apparatus shown in Figs 3A and 3B.
  • the first converter 604 of this embodiment corresponds to the first converter 304 of the first embodiment of Fig. 5, and is thus not further discussed.
  • the second converter 606 of the second embodiment is different from the second converter of Fig. 5 and may comprise four pairs 702, 704, 706, 708, al- so indicated as S5 D5, Se/D 6 , S7/D7, Ss/D 8 in Fig. 6, of electrically interconnected electronic control devices 710, 712.
  • Each pair of electronic control devices 710, 712 may comprise an electronic switch 710 and a diode 712.
  • the DC-to-DC converter unit 602 may comprise a transformer 718 connected between the first and second converters 604, 606.
  • the transformer 718 may be an electric power transformer.
  • the transformer 718 may be a high or medium frequency transformer.
  • Fig. 7 schematically shows a third embodiment and aspects of the DC-to- DC converter unit 902 of the embodiments of the apparatus shown in Figs 3A and 3B.
  • the second converter 906 of the third embodiment may comprise four pairs 802, 804, 806, 808, also indicated as S ⁇ S' 5 , Se/S'e, S 7 /S' 7 , Ss S's in Fig. 10, of electrically interconnected electronic switches 810, 812.
  • the first converter 904 may comprise four pairs 814, 816, 819, 820, also indicated as S S'f, S ⁇ S' 2, Ss/S's , S /S' 4 in Fig. 10, of electrically interconnected electronic switches 822, 824.
  • the first converter 904 may also comprise a fifth pair 830 of electronic switches 831 , 833, also indicated as S A B/S'AB-
  • the first converter 904 of the third embodiment may comprise filter means 826, 828, connected to the electronic switches 822, 824, for smoothing out the voltage and current ripple caused by the switching of the electronic switches 822, 824.
  • the filter means may comprise a capacitor 826, also indicated as C ⁇ in Fig. 7, and an inductor 828, also indicated as L f .
  • the components of the third embodiment of the DC-to-DC converter unit 902 are differently interconnected in relation to the first embodiment of Fig. 5, as illustrated in Fig. 7.
  • the DC-to-DC converter unit 902 of Fig. 7 may comprise a transformer 818 connected between the first and second converters 904, 906.
  • the transformer 818 may be an electric power transformer.
  • the transformer 818 may be a high or medium frequency transformer.
  • the second and third embodiments of the DC-to-DC converter unit 602; 902 of Figs. 6 and 7 may comprise any of the additional features mentioned in connection with Fig. 5.
  • the above-mentioned apparatuses 202, 212 may comprise a plurality of
  • Other configurations of the DC-to-DC converter units may also be possible.
  • a pair of anti-parallel power semiconductor switches e.g. IGBT
  • a pair of anti-series power semiconductor switches e.g. IGBT or BIGT
  • the advantage of the anti-series connection is that reverse blocking power semiconductor switches are not required.
  • Figs. 9 and 10A-B schematically shows aspects of a third embodiment of the apparatus 908 according to the present invention.
  • the apparatus 908 of Fig. 9 comprises a plurality of electric power source sections 910.
  • Each electric power source section 910 of the plurality of electric power source sections 910 may com- prise a section converter 912 for converting alternating current, AC, to direct current and/or direct current to alternating current.
  • the section converter 912 has an AC side 914 for output and/or input of alternating current and a DC side 916 for output and/or input of direct current.
  • each electric power source section 910 of the plurality of electric power source sections is arranged to be connected, via the AC side 914 of the section converter 912, to an electric power source 316 comprising an AC source 920.
  • the AC source 920 may comprise an AC grid, or any other suitable AC source.
  • the apparatus 908 comprises a plurality of DC-to- DC converter units 302; 602; 902, which can be of any sort described above, or a mixture thereof.
  • the first DC sides 206 of the plurality of DC-to-DC converter units 302 may be connected in parallel with one another as illustrated in Fig. 9, or in series with one another as shown in Fig. 3A.
  • Each DC-to-DC converter unit 302 of the plurality of DC-to-DC converter units may be connected via its second DC side 208 to the DC side 916 of the section converter 912 of at least one of the plurality of electric power source sections 910.
  • the apparatus 908 shown in Fig. 9 is suit- able for a single phase AC source.
  • each phase leg may be similar to the apparatus 908 of Fig. 9.
  • the apparatus 908 of Fig. 9 may be provided for any source where point R in Fig. 9 is connectable to the AC source and G n may be connected to a neutral point.
  • An inductor may be connected in series with each phase before the section converter 912.
  • Each section converter 912 may be of soft switched type to reduce losses, e.g. ZCS, or ZVS.
  • Each section converter 912 may be configured as illustrated in Fig 1 0A or in Fig. 10B, or in any other suitable manner.
  • the apparatus 908 may comprise a mixture of the section converters shown in Figs. 10A and 10B.
  • FIG. 10A illustrates an exemplary half-bridge topology for the section converter 912 of the electric power source section
  • Fig. 10B illustrates an exemplary full-bridge topology for the section converter 912 of the electric power source section.
  • the full-bridge topology of Fig. 10B may comprise the same pairs 702, 704, 706, 708 of electrically interconnected electronic control devices 710, 712 as the second converter 606 of Fig. 6.
  • the apparatus 202, 212, 908 may be connectable to the HVDC line 102, by connecting position P 1 to position A in Fig. 1 , and by connecting position Q n to position B in Fig. 1 .
  • Each of the above-mentioned electronic switches may comprise a power semiconductor switch, e.g. an IGBT, a BIGT or any other suitable power semiconductor switch.
  • each of the above-mentioned electronic switches may comprise a thyristor, e.g. a GTO, an IGCT, or a Forced Commutated Thyristor.
  • the invention shall not be considered limited to the embodiments illustrated, but can be modified and altered in many ways by one skilled in the art, without departing from the scope the appended claims.
  • the disclosed embodiments may be combined in various possible ways, and additional electric equipment, devices or units may be connected to and between the components of the embodiments.
  • One and the same apparatus may e.g. comprise DC-to-DC converter units of different configurations, e.g. a mixture of the DC-to-DC converter units as disclosed above.

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Abstract

An apparatus (202; 212; 908) for controlling the electric power transmission in a high voltage direct current, HVDC, power transmission system comprising at least one HVDC transmission or distribution line (102, 104, 106, 108, 110, 112, 114) for carrying direct current, DC, the apparatus being arranged to control the direct current of the HVDC transmission or distribution line by introducing a DC voltage in series with the HVDC transmission or distribution line, wherein the apparatus comprises a plurality of electric power source sections (204; 910) connectable to an electric power source (316), and a plurality of DC-to-DC converter units (302; 602; 902). Each DC-to-DC converter unit of the plurality of DC-to-DC converter units comprises a first DC side (206) for output and/or input of direct current and a second DC side (208) for output and/or input of direct current. Each DC-to-DC converter unit of the plurality of DC-to-DC converter units is connectable via its first DC side to the HVDC transmission or distribution line, and each DC-to-DC converter unit of the plurality of DC-to-DC converter units is connected via its second DC side to at least one of the plurality of electric power source sections. A HVDC power transmission system comprising at least one apparatus (202; 212; 908) of the above-mentioned sort.

Description

AN APPARATUS FOR CONTROLLING THE ELECTRIC POWER
TRANSMISSION IN A HVDC POWER TRANSMISSION SYSTEM
Technical Field
The present invention relates to an apparatus for controlling the electric power transmission in a high voltage direct current, HVDC, power transmission system comprising at least one HVDC transmission or distribution line for carrying direct current, DC, the apparatus being arranged to control the direct current of the HVDC transmission or distribution line by introducing a DC voltage in series with the HVDC transmission or distribution line. Further, the present invention relates to a HVDC power transmission system comprising at least one HVDC transmission or distribution line for carrying direct current, and a plurality of converter stations connected to the at least one HVDC transmission or distribution line, each of the converter stations being arranged to convert alternating current, AC, to direct current for input to the at least one HVDC transmission or distribution line, and/or di- rect current to alternating current, the system comprising at least one apparatus of the above-mentioned sort.
Background of the Invention
A HVDC power distribution network or a HVDC power transmission system uses direct current for the transmission of electrical power, in contrast to the more common AC systems. For long-distance transmission or distribution, HVDC systems may be less expensive and may suffer lower electrical losses. In general, a HVDC power transmission system comprises at least one long-distance HVDC link or cable for carrying direct current a long distance, e.g. under sea, and converter stations for converting alternating current to direct current for input to the HVDC power transmission system and converter stations for converting direct current back to alternating current.
US-B2-6,788,033 and US-A-5, 734,258 disclose DC to DC conversion and relate to stationary or portable systems powered by a DC battery, and to electric vehicles. US-B2-6, 914,420 describes a power converter for converting power be- tween a first and a second voltage, and relates to electric vehicles.
US-B2-7, 518,266 discloses an AC power transmission system, where a DC transmission ring is used, utilizing controllable AC-DC converters in a multi-in- feed/out-feed arrangement. US 3,694,728 describes a HVDC mesh-operated network comprising several interconnected stations for effecting an exchange of power by means of converters located at the stations and which are connected to AC networks.
WO 2010/1 15452 discloses a meshed HVDC power transmission network comprising at least three HVDC converter stations interconnected in a first closed path by at least three transmission lines.
DE 1513827 discloses an apparatus for influencing the current distribution in a HVDC network.
EP 2 293 407 describes a direct current power transmission and distribu- tion system suitable for subsea electrical loads.
The Object of the Invention
To control the electric power transmission in a HVDC power transmission system comprising at least one HVDC line and a plurality of converter stations for converting between alternating current and direct current in order to avoid or re- duce DC load-flow congestion in the system, each of the converter stations may be controlled, e.g. by controlling the DC voltage of each converter station. However, the inventors of the present invention have found that the DC voltage control of the converter stations may not be sufficient in order to avoid or reduce load-flow congestion of the system.
The object of the present invention is to improve the electric power transmission in a HVDC power transmission system. It is also an object of the present invention to provide an improved control of the electric power transmission in a HVDC power transmission system. A further object of the present invention is to avoid, reduce or prevent load-flow congestion in the system. Another object of the present invention is to provide an improved HVDC power transmission system.
Summary of the Invention
The above-mentioned objects of the present invention are attained by providing an apparatus for controlling the electric power transmission in a high voltage direct current, HVDC, power transmission system comprising at least one HVDC transmission or distribution line for carrying direct current, DC, the apparatus being arranged to control the direct current of the HVDC transmission or distribution line by introducing a DC voltage in series with the HVDC transmission or distribution line, wherein the apparatus comprises a plurality of electric power source sections connectable to an electric power source, wherein the apparatus comprises a plurality of DC-to-DC converter units, each DC-to-DC converter unit of the plurality of DC-to-DC converter units comprising a first DC side for output and/or input of direct current and a second DC side for output and/or input of direct current, wherein each DC-to-DC converter unit of the plurality of DC-to-DC converter units is connectable via its first DC side to the HVDC transmission or distribution line, and wherein each DC-to-DC converter unit of the plurality of DC-to-DC converter units is connected via its second DC side to at least one of the plurality of electric power source sections.
By means of the innovative apparatus of the present invention, the electric power transmission in a HVDC power transmission system and the control thereof are efficiently improved, and load-flow congestion in the system may be avoided, reduced or prevented.
The apparatus of the present invention is especially advantageous and ef- ficient for a HVDC power transmission system of the sort shown in Fig. 1 , which may be called a DC grid concept, where the system comprises several HVDC transmission or distribution lines for carrying direct current and several converter stations connected to the HVDC transmission or distribution lines. The apparatus of the present invention is especially advantageous when the control of DC voltage of the converter stations, or the control of shunt connected converter DC voltages of a DC grid, is not sufficient. By means of the apparatus of the present invention, the direct current of the HVDC transmission or distribution line, to which the apparatus is connected, can be increased or reduced in order to control the power transmission. The direct current control is attained by means of the apparatus' in- traduction, or injection, of a DC voltage in series with the HVDC transmission or distribution line. The injected DC voltage produces a fictive resistance, ARinj. The fictive resistance provides an active power extraction or output from the HVDC transmission or distribution line when the fictive resistance corresponds to an increase in resistance, i.e. a positive ARinj, (since a resistance consumes pow- er/energy), or an active power input to the HVDC transmission or distribution line when the fictive resistance corresponds to a decrease in resistance, i.e. a negative ARinj. A positive ARlnj is produced when the apparatus introduces a positive DC voltage in series with the HVDC transmission or distribution line, and a negative ARinj is produced when the apparatus introduces a negative DC voltage in series with the HVDC transmission or distribution line. Thus, by means of the apparatus of the present invention, the load of the HVDC transmission or distribution line, to which the apparatus is connected, may be reduced or increased. The apparatus' active power extraction or output from the HVDC transmission or distribution line results in a decrease in direct current of the line, and the apparatus' active power input to the HVDC transmission or distribution line results in an increase in direct current of the line. By the increase and decrease in direct current of HVDC transmission or distribution line, the power transmission is controlled and load-flow congestion may be avoided, reduced or prevented. Thus, the apparatus of the present invention is arranged to regulate the voltage at its output to control the current flow in the HVDC transmission or distribution line. The apparatus may comprise the electric power source.
In alternative words, the apparatus according to the present invention is arranged to control the direct current of the HVDC transmission or distribution line by introducing a fictive resistance in series with the HVDC transmission or distribution line by introducing a DC voltage in series with the HVDC transmission or distribution line.
By means of the apparatus of the present invention, the individual DC-to- DC converter units can be designed with lower rating power semiconductor switches, e.g. with lower rating IGBTs, which results in better utilization of the power semiconductor switches. Each DC-to-DC converter unit may introduce a DC voltage in series with the HVDC transmission or distribution line, which is a contribution to the total DC voltage introduced in series with the HVDC transmission or distribution line by the apparatus. If some of the plurality of DC-to-DC converter units are impaired, it is possible continue to operate the apparatus by means of the faultless DC-to-DC converter units. Thus, the redundancy and reliability of the apparatus are improved.
The direct current in a HVDC power transmission system, e.g. a DC grid system, may reverse, and therefore, voltage polarity reversal for maintained fictive resistance is required, which is also attained by means of the apparatus of the present invention. Further, the apparatus of the present invention has the capability to operate in all four quadrants.
The various components of the apparatus of the present invention, which are connected or connectable to one another or to other units, may be electrically connected, or connectable, to one another or to other units, e.g. via electrical conductors, e.g. busbars or DC lines, and/or may be indirectly connected, or connectable, e.g. electrically or inductively, via additional intermediate electric equipment or units located and connected/connectable between the components, e.g. a transformer, another converter etc.
Each DC-to-DC converter unit of the plurality of DC-to-DC converter units may be connected, via its second DC side, to one of the plurality of electric power source sections, or to two or more of the plurality of electric power source sections.
According to an advantageous embodiment of the apparatus according to the present invention, the DC-to-DC converter units of the plurality of DC-to-DC converter units are connected, via respective second DC side, to different electric power source sections of the plurality of electric power source sections. By means of this embodiment, the electric power transmission in a HVDC power transmis- sion system and the control thereof are further improved.
According to a further advantageous embodiment of the apparatus according to the present invention, a plurality of the first DC sides of the plurality of DC- to-DC converter units are connected in series with one another. By means of this embodiment, the redundancy and reliability of the apparatus are further improved.
According to another advantageous embodiment of the apparatus according to the present invention, a plurality of the first DC sides of the plurality of DC- to-DC converter units are connected in parallel with one another. By means of this embodiment, the redundancy and reliability of the apparatus are further improved.
According to a further advantageous embodiment of the apparatus accord- ing to the present invention, a plurality of the second DC sides of the plurality of DC-to-DC converter units are connected in series with one another. By means of this embodiment, the redundancy and reliability of the apparatus are further improved.
According to another advantageous embodiment of the apparatus accord- ing to the present invention, a plurality of the second DC sides of the plurality of DC-to-DC converter units are connected in parallel with one another. By means of this embodiment, the redundancy and reliability of the apparatus are further improved. Some of the first DC sides of the plurality of DC-to-DC converter units may be connected in series with one another, whereas the other first DC sides of the plurality of DC-to-DC converter units may be connected in parallel with one another. The same may apply to the second DC sides of the plurality of DC-to-DC con- verter units. Combinations of series and parallel connections of the first and second DC sides, respectively, of the plurality of DC-to-DC converter units are thus possible.
According to yet another advantageous embodiment of the apparatus according to the present invention, each electric power source section of the plurality of electric power source sections is arranged to be connected to an electric power source comprising a DC source. To effect or introduce a positive fictive resistance, +ARinj, active power should be absorbed by the DC source, and to effect or introduce a negative fictive resistance, -ARmj, active power should be injected by and from the DC source. By means of this embodiment, the electric power transmis- sion in a HVDC power transmission system and the control thereof are further i mproved.
According to still another advantageous embodiment of the apparatus according to the present invention, each electric power source section of the plurality of electric power source sections is arranged to be connected to an electric power source comprising a DC source that comprises an electric battery. The DC source may comprise a capacitor. The inventors of the present invention have found that the use of an electric battery for the DC source efficiently improves the electric power transmission in a HVDC power transmission system and the control thereof. However, other suitable DC sources may be used. The DC source may for exam- pie comprise photovoltaic cells and/or flywheels etc.
According to an advantageous embodiment of the apparatus according to the present invention, each electric power source section of the plurality of electric power source sections is arranged to be connected to an electric power source comprising a DC source that is part of a HVDC power transmission system. The inventors of the present invention have found that the use of a DC source being part of a HVDC power transmission system provides efficient electric power transmission in a HVDC power transmission system and an efficient control thereof.
According to a further advantageous embodiment of the apparatus according to the present invention, each electric power source section of the plurality of electric power source sections is arranged to be connected to an electric power source comprising a DC source that comprises at least one cascaded cell. The inventors of the present invention have found that the use of a cascaded cell for the DC source efficiently improves the electric power transmission in a HVDC power transmission system and the control thereof. The at least one cascaded cell may be arranged to be part of a converter station included in the HVDC power transmission system, the converter station being arranged to convert alternating current to direct current, for input to the HVDC transmission line, and/or direct current to alternating current. Each electric power source section of the plurality of electric power source sections may be arranged to be connected to an electric power source comprising a DC source that comprises a plurality of cascaded cells. The inventors of the present invention have found that the use of several cascaded cells efficiently improves the flexibility and efficiency of the electric power transmission in a HVDC power transmission system and the control thereof.
Each cascaded cell may be a cascaded half-bridge cell (also called Cascaded Two-Level, CTL, cell). Each cascaded cell may be a cascaded full-bridge cell. A cascaded half-bridge cell and a cascaded full-bridge cell per se and their structure are well known to the person skilled in the art and therefore not disclosed or discussed in more detail. The plurality of cascaded cells may comprise a plural- ity of half-bridge cells, or a plurality of cascaded full-bridge cells, or a mixture thereof. The plurality of cascaded cells may be arranged to be part of a converter station included in the HVDC power transmission system. The converter station may also comprise a mixture of cascaded half-bridge cells and cascaded full- bridge cells. The plurality of cascaded cells may be interconnected to one another.
According to yet another advantageous embodiment of the apparatus according to the present invention, each electric power source section of the plurality of electric power source sections comprises a capacitor. The inventors have found that an electric power source, e.g. an electric power source comprising a DC source, may be advantageously divided into a plurality of electric power source sections by means of a capacitor provided in each electric power source section.
According to an advantageous embodiment of the apparatus according to the present invention, each electric power source section of the plurality of electric power source sections comprises a section converter for converting alternating current, AC, to direct current and/or direct current to alternating current, the sec- tion converter having an AC side for output and/or input of alternating current and a DC side for output and/or input of direct current, wherein each electric power source section of the plurality of electric power source sections is arranged to be connected, via the AC side of the section converter, to an electric power source comprising an AC source, and wherein each DC-to-DC converter unit of the plurality of DC-to-DC converter units is connected via its second DC side to the DC side of the section converter of at least one of the plurality of electric power source sections. To effect or introduce a positive fictive resistance, +ARinj, active power should be absorbed by the AC source, and to effect or introduce a negative fictive resistance, -AF?/ny, active power should be injected by and from the AC source. By means of this embodiment, the electric power transmission in a HVDC power transmission system and the control thereof are further improved.
According to a further advantageous embodiment of the apparatus according to the present invention, each electric power source section of the plurality of electric power source sections is arranged to be connected, via the AC side of the section converter, to an electric power source comprising an AC source that comprises an AC grid. The inventors of the present invention have found that the use of an AC grid for the AC source efficiently improves the electric power transmission in a HVDC power transmission system and the control thereof. However, oth- er suitable AC sources are possible.
According to another advantageous embodiment of the apparatus according to the present invention, each DC-to-DC converter unit comprises a first converter for converting alternating current, AC, to direct current and/or direct current to alternating current, and a second converter for converting direct current to alter- nating current and/or alternating current to direct current, each of the first and second converters having an AC side for output and/or input of alternating current, wherein the first converter comprises the first DC side of the DC-to-DC converter unit, wherein the second converter comprises the second DC side of the DC-to-DC converter unit, and wherein the AC side of the second converter is connected to the AC side of the first converter. By means of this embodiment, the electric power transmission in a HVDC power transmission system and the control thereof are further improved. The AC side of the second converter may be arranged to provide, directly or indirectly, alternating current to the AC side of the first converter, and/or vice versa. According to yet another advantageous embodiment of the apparatus according to the present invention, each DC-to-DC converter unit comprises a transformer connected between the first and second converters, and each of the first and second converters is connectable via its AC side to the transformer. By means of the transformer, the flexibility and efficiency of the electric power transmission in a HVDC power transmission system and the control thereof are further improved. The transformer may also take part in fulfilling the voltage requirements of the apparatus. The transformer may be an electric power transformer. The transformer may be in the form of a high or medium frequency transformer. Thus, by means of the configuration of this embodiment, the transformer used can be of a higher frequency which will reduce the size of overall magnetics in the apparatus. By means of the configuration of this embodiment, the insulation requirement will also be reduced for the individual transformer, which makes the transformer design less complex.
According to still another advantageous embodiment of the apparatus according to the present invention, the transformer is arranged to isolate the first converter from the electric power source section. By means of this embodiment, the HVDC transmission or distribution line, to which the apparatus is connected, is also efficiently isolated from the electric power source section and from the electric power source.
According to a further advantageous embodiment of the apparatus according to the present invention, the second converter comprises four pairs of electronic switches. The electronic switches may be connected to one another. The inventors of the present invention have found that this structure of the second con- verter further improves the flexibility and efficiency of the electric power transmission in a HVDC power transmission system and the control thereof.
According to another advantageous embodiment of the apparatus according to the present invention, the second converter comprises four pairs of electronic control devices, each pair of electronic control devices comprising an elec- tronic switch and a diode. The inventors of the present invention have found that this structure of the second converter further improves the flexibility and efficiency of the electric power transmission in a HVDC power transmission system and the control thereof. According to yet another advantageous embodiment of the apparatus according to the present invention, the first converter comprises a full-bridge converter. The inventors of the present invention have found that this structure of the first converter further improves the flexibility and efficiency of the electric power transmission in a HVDC power transmission system and the control thereof. The first converter may comprise a full-bridge converter with a bypass switch.
According to still another advantageous embodiment of the apparatus according to the present invention, the first converter comprises four pairs of electronic switches. The electronic switches may be connected to one another. The in- ventors of the present invention have found that this structure of the first converter further improves the flexibility and efficiency of the electric power transmission in a HVDC power transmission system and the control thereof. Advantageously, the first converter may also comprise a fifth pair of electronic switches. The fifth pair of electronic switches may be connected in parallel with the four pairs of electronic switches.
According to an advantageous embodiment of the apparatus according to the present invention, the first converter comprises filter means for smoothing out the voltage and current ripple caused by the switching of the electronic switches. The filter means may be connected to the electronic switches. By smoothing out the voltage and current ripple, a further improved control of the electric power transmission is attained. The filter means, or filter components, may comprise a capacitor and an inductor. The capacitor may be connected in parallel with the electronic switches. The inductor may be connected in series with the electronic switches. By the above-mentioned embodiments of the filter means, a further im- proved control of the power transmission is provided.
According to a further advantageous embodiment of the apparatus according to the present invention, electronic switch comprises a power semiconductor switch. Each power semiconductor switch may comprise an Insulated Gate Bipolar Transistor, IGBT, or a Bi-Mode Insulated Gate Transistor, BiGT, or any other suit- able power semiconductor switch. Alternatively, each power semiconductor switch may comprise a thyristor, e.g. a gate turn-off thyristor, GTO, an Integrated Gate- Commutated Thyristor, IGCT, or a Forced Commutated Thyristor. However, other suitable thyristors may also be used. The inventors of the present invention have found that these structures of first converter and/or the second converter further improves the flexibility and efficiency of the electric power transmission in a HVDC power transmission system and the control thereof.
According to another advantageous embodiment of the apparatus according to the present invention, the first converter is connectable in series with the HVDC transmission or distribution line.
According to an advantageous embodiment of the apparatus according to the present invention, the apparatus comprises control means for controlling the apparatus, wherein the control means are arranged to control the apparatus to introduce a positive DC voltage in series with the HVDC transmission or distribution line for reducing the direct current of the HVDC transmission or distribution line, and wherein the control means are arranged to control the apparatus to introduce a negative DC voltage in series with the HVDC transmission or distribution line for increasing the direct current of the HVDC transmission or distribution line. By the control means of this embodiment, the current flow in the HVDC transmission or distribution line is efficiently controlled. The control means may be in form of a control unit and may be connectable to the HVDC power transmission system, e.g. to the HVDC transmission or distribution line. The control means may comprise a computer and/or a CPU. In alternative words, the control means may be arranged to control the apparatus to introduce a positive fictive resistance in series with the HVDC transmission or distribution line by introducing a positive DC voltage in series with the HVDC transmission or distribution line for reducing the direct current of the HVDC transmission or distribution line, and the control means may be arranged to control the apparatus to introduce a negative fictive resistance in series with the HVDC transmission or distribution line by introducing a negative DC volt- age in series with the HVDC transmission or distribution line for increasing the direct current of the HVDC transmission or distribution line.
According to a further advantageous embodiment of the apparatus according to the present invention, the apparatus comprises measuring means for measuring the DC load flow congestion of the HVDC power transmission system, and the measuring means are arranged to communicate with the control means. The measuring means may be arranged to measure the direct current or direct voltage of the HVDC line, and the measuring means per se may have a structure known the person skilled in the art. The measuring means, or measuring equipment, may comprise conventional sensors, e.g. sensors for measuring direct current or direct voltage.
According to another advantageous embodiment of the apparatus according to the present invention, the apparatus is adapted for four quadrant operation. Advantageously, the apparatus may be adapted for one quadrant operation, two quadrant operation or three quadrant operation, where the quadrant operation/-s may be any of the first to fourth quadrant operations. The one, two or three quadrant operation may be attained by replacing suitable IGBT/IGBTs with diode/diodes of a four quadrant converter.
A bypass switch connectable to the HVDC transmission or distribution line and connected in parallel with the apparatus may be provided. When closed, the bypass switch is arranged to conduct the direct current of the HVDC transmission or distribution line to electrically bypass the apparatus. By the bypass switch, the apparatus may be bypassed during fault conditions, whereby the electric power transmission in a HVDC power transmission system and the control thereof are further improved.
The above-mentioned objects of the present invention are also attained by providing a high voltage direct current, HVDC, power transmission system comprising at least one HVDC transmission or distribution line for carrying direct cur- rent, DC, and a plurality of converter stations connected to the at least one HVDC transmission or distribution line, each of the converter stations being arranged to convert alternating current, AC, to direct current for input to the at least one HVDC transmission or distribution line, and/or direct current to alternating current, wherein the system comprises at least one apparatus as claimed in any of the claims 1 - 25 for controlling the electric power transmission in the system, and/or at least one apparatus according to any of the above-mentioned embodiments of the apparatus. Positive technical effects of the HVDC power transmission system according to the present invention, and its embodiments, correspond to the above- mentioned technical effects mentioned in connection with the apparatus according to the present invention, and its embodiments. The at least one HVDC transmission or distribution line may be one or a plurality of HVDC transmission or distribution lines According to an advantageous embodiment of the HVDC power transmission system according to the present invention, the system comprises a plurality of HVDC transmission or distribution lines.
A plurality of HVDC transmission or distribution lines or converter stations may be two or more HVDC transmission or distribution lines or converter stations, respectively. The at least one apparatus may be one or a plurality of apparatuses, e.g. two or more apparatuses. A plurality of apparatuses may be connected to the same HVDC transmission or distribution line, or to different HVDC transmission or distribution lines. For example, two apparatuses adapted for two quadrant opera- tion may be connected to the same HVDC transmission or distribution line to attain four quadrant operation.
According to an advantageous embodiment of the HVDC power transmission system according to the present invention, the system comprises at least three converter stations. Advantageously, the system comprises at least four con- verter stations, or at least five converter stations.
According to a further advantageous embodiment of the HVDC power transmission system according to the present invention, the at least one HVDC transmission or distribution line comprises at least one long-distance HVDC link or cable. Advantageously, the HVDC transmission or distribution lines may comprise at least two long-distance HVDC links or cables.
In general, High Voltage may be about 1 -1 .5 kV and above. However, for HVDC applications and systems, High Voltage may be about 320 kV and above, e.g. 500 kV, 800 kV or 1000 kV, and above. The apparatus and/or the system according to the present invention are advantageously adapted for the above-men- tioned HVDC voltage levels and above. The voltage rating of the apparatus may be 1 -5 % of the HVDC transmission or distribution line voltage.
The above-mentioned embodiments and features of the apparatus and the HVDC power transmission system, respectively, according to the present invention may be combined in various possible ways providing further advantageous em- bodiments.
Further advantageous embodiments of the apparatus and the HVDC power transmission system, respectively, according to the present invention and further advantages with the present invention emerge from the detailed description of embodiments. Brief Description of the Drawings
The present invention will now be described, for exemplary purposes, in more detail by way of embodiments and with reference to the enclosed drawings, in which:
Fig. 1 is a schematic block diagram illustrating aspects of the HVDC power transmission system and aspects of the apparatus according to the present invention;
Fig. 2A is schematic block diagram illustrating a first embodiment of a converter station shown in Fig. 1 ;
Fig. 2B is schematic block diagram illustrating a second embodiment of a converter station shown in Fig. 1 ;
Fig. 3A is a schematic block diagram illustrating a first embodiment of the apparatus according to the present invention;
Fig. 3B is a schematic block diagram illustrating a second embodiment of the apparatus according to the present invention;
Fig 4 is a schematic diagram illustrating an embodiment of a DC
source in more detail;
Fig. 5 is a schematic diagram illustrating a first embodiment and aspects of the DC-to-DC converter unit of the apparatuses shown in Figs 3A and 3B in more detail;
Fig. 6 is a schematic diagram illustrating a second embodiment and aspects of the DC-to-DC converter unit of the apparatuses shown in Figs 3A and 3B;
Fig. 7 is a schematic diagram illustrating a third embodiment and aspects of the DC-to-DC converter unit of the apparatuses shown in Figs 3A and 3B;
Figs. 8A and 8B are schematic diagrams illustrating alternative electronic control devices;
Fig. 9 is a schematic block diagram illustrating a third embodiment of the apparatus according to the present invention;
Fig. 10A is exemplary half-bridge topology for the section converter of the electric power source section of Fig. 9; and
Fig. 10B is exemplary full-bridge topology for the section converter of the electric power source section of Fig. 9. Detailed Description of Preferred Embodiments Abbreviations
Alternating Current AC
Bi-Mode Insulated Gate Transistor BiGT
Direct Current DC
Central Processing Unit CPU
Gate Turn-Off thyristor GTO
High Voltage Direct Current HVDC
Insulated Gate Bipolar Transistor IGBT
Integrated Gate-Commutated Thyristor IGCT
Pulse Width Modulation PWM
Zero Current Switch ZCS
Zero Voltage Switch ZVS
Fig.1 schematically shows aspects of the HVDC power transmission system and aspects of the apparatus 202; 212; 908 according to the present inven- tion. The HVDC power transmission system comprises at least one HVDC transmission or distribution line for carrying direct current, hereinafter called HVDC line, e.g. a plurality of HVDC lines 102, 104, 106, 108, 1 10, 1 12, 1 14 for carrying direct current. The HVDC lines may e.g. comprise HVDC cables, busbars, or other DC conductors. The HVDC lines 102, 104, 106, 108, 1 10, 1 12, 1 14 may comprise at least one long-distance HVDC link. In Fig. 1 , a first and second long-distance HVDC link 102, 108 are provided. HVDC lines and links are well known to the skilled person and thus not discussed in further detail. The HVDC power transmission system comprises a plurality of converter stations 1 16, 1 18, 120, 122, 124 electrically connected to the HVDC lines 102, 104, 106, 108, 1 10, 1 12, 1 14. In Fig. 1 , five converter stations 1 16, 1 18, 120, 122, 124 are provided, but there may be more or fewer converter stations. The HVDC power transmission system may e.g. comprise two, at least three, or at least four converter stations, or at least five converter stations. Each of the converter stations 1 16, 1 18, 120, 122, 124 may be ar- ranged to convert alternating current to direct current for input to the HVDC lines 102, 104, 106, 108, 1 10, 1 12, 1 14 and convert direct current to alternating current for input to neighbouring AC systems. Each converter station 1 16, 1 18, 120, 122, 124 may be electrically connected to a conventional transformer 126, 128, 130, 132, 134, which may be an electric power transformer, in conventional ways known to the skilled person. Transformers and their function are well known to the person skilled in the art and therefore not discussed in more detail.
Each converter station 1 16, 1 18, 120, 122, 124, which may be called a DC Grid converter station, may have asymmetrical monopoles with separate convert- ers for positive and negative polarity, as illustrated in Fig. 2A. Alternatively, each converter station 1 16, 1 18, 120, 122, 124 may be in the form of a symmetrical monopolar converter, as illustrated in Fig. 2B. The alternatives of Figs. 2A and 2B may also be combined in the same system.
The apparatus 202; 212; 908 according to the present invention is ar- ranged to be electrically connected to the HVDC system, e.g. by being connected between positions A and B as illustrated in Fig. 1 . However, other locations and connections points are possible. The apparatus 202 may e.g. be connected to any of the other HVDC lines. Rn„e of the HVDC line 102 in Fig. 1 illustrates the resistance of the HVDC line 102, and be in Fig. 1 is the direct current through the HVDC line 102, i.e. the direct current carried by the HVDC line 102. The HVDC power transmission system may be adapted for single phase power or multi-phase power, e.g. three-phase power, and the components of the system and the apparatus 202; 212; 908 may be configured accordingly in ways known to the skilled person. The HVDC power transmission system comprises an embodiment of the apparatus 202; 212; 908 for controlling the electric power transmission in the system according to the present invention, and aspects of the apparatus 202; 212; 908 will hereinafter be disclosed.
A bypass switch 136 (see Fig. 1 ) may be provided and may be electrically connectable to the HVDC line 102 to which the apparatus 202; 212; 908 and may be connected in parallel with the apparatus 202; 212; 908. When the bypass switch 136 is closed, it is arranged to conduct the direct current of HVDC line 102 to electrically bypass the apparatus 202; 212; 908. By the bypass switch 1 36, the apparatus 202 may be bypassed during fault conditions. Fig. 3A schematically shows a first embodiment of the apparatus 202 according to the present invention for controlling the electric power transmission in a HVDC power transmission system, e.g. as shown in Fig. 1 The apparatus 202 comprises a plurality of electric power source sections 204 connectable to an elec- trie power source 316. The apparatus 202 comprises plurality of DC-to-DC converter units 302; 602; 902. Each DC-to-DC converter unit 302 of the plurality of DC-to-DC converter units 302 comprises a first DC side 206 for output and/or input of direct current and a second DC side 208 for output and/or input of direct current. Each DC-to-DC converter unit 302 of the plurality of DC-to-DC converter units is connectable via its first DC side 206 to the HVDC line 102, and each DC-to-DC converter unit 302 of the plurality of DC-to-DC converter units is connected via its second DC side 208 to at least one of the plurality of electric power source sections 204, e.g. to one of the plurality of electric power source sections 204. The DC-to-DC converter units 302 of the plurality of DC-to-DC converter units may be connected, via respective second DC side 208, to different electric power source sections 204 of the plurality of electric power source sections 204. As shown in Fig. 3A, the first DC sides 206 of the plurality of DC-to-DC converter units 302 may be connected in series with one another.
Each DC-to-DC converter unit 302 may comprise a first converter 304 for converting alternating current to direct current and/or direct current to alternating current, and a second converter 306 for converting direct current to alternating current and/or alternating current to direct current. Each of the first and second converters 304, 306 has an AC side 308, 310 for output and/or input of alternating current. The first converter 304 comprises the first DC side 206 of the DC-to-DC con- verter unit 302, and the second converter 306 comprises the second DC side 208 of the DC-to-DC converter unit 302. The AC side 310 of the second converter 306 is connected to the AC side 308 of the first converter 304. The first converter 304 may be electrically connectable via the DC side 206 to the HVDC line 102, and the first converter 304 may be electrically connectable in series with the HVDC line 102. The AC side 308 of the first converter 304 is arranged to provide alternating current to the AC side 310 of the second converter 306, and vice versa. Each DC- to-DC converter unit 302 may comprise an transformer 318 connected between the first and second converters 304, 306, each of the first and second converters 304, 306 being connectable via its AC side 308, 310 to the transformer 318. Each DC-to-DC converter unit 302, and each of the converters 304, 306 included therein, may be of soft switched type, e.g. ZCS, or ZVS.
Each transformer may be an electric power transformer. Each transformer 318 may be a high or medium frequency transformer, and the second converter 306 may be arranged to convert DC voltage to high or medium frequency AC voltage. The transformer 318 may be arranged to isolate the first converter 304 from the electric power source section 204, and may thus also be arranged to isolate the HVDC line 102 from the electric power source section 204, and from the electric power source 316. Each electric power source section 204 may comprise a section capacitor 21 0 to which the DC-to-DC converter unit 302 and the second converter 306 are electrically connectable via the second DC side 208.
The apparatus 202 is arranged to control the direct current of the HVDC line 102 by introducing a DC voltage VAB in series with the HVDC line 102. The apparatus 202 may comprise control means 324, e.g. a computer or CPU, for con- trolling the apparatus and its various components. The control means 324 may be arranged to control the apparatus 302 to introduce a positive DC voltage, VAB> 0, in series with the HVDC line 102 for reducing the direct current, i.e. he, of the HVDC line 102, and the control means 324 are arranged to control the apparatus 302 to introduce a negative DC voltage, VAB< 0, in series with the HVDC line 102 for increasing direct current \Dc of the HVDC line 102. The above-mentioned fictive resistance ARinj may be defined by the following expression: ARlnj = VABI foe- Each of DC-to-DC converter units 302 may be arranged to introduce a DC voltage in series with the HVDC line 102, and each of DC-to-DC converter units 302 may thus take part in the control of the direct current of the HVDC line 102. The number of DC-to-DC converter units 302 may be two or more.
Fig. 3B schematically shows a second embodiment of the apparatus 212 according to the present invention. The apparatus 212 of Fig. 3B essentially corresponds to the embodiment of Fig. 3A except for the connection of the first DC sides 206 of the plurality of DC-to-DC converter units 302. In Fig. 3B, the first DC sides 206 of the plurality of DC-to-DC converter units 302; 602; 902 are connected in parallel with one another.
The electric power source 316, to which the plurality of electric power source sections 204 is arranged to be connected, may comprise a DC source 214. The DC source 214 may comprise an electric battery, or the DC source 214 may be part of a HVDC power transmission system, or HVDC grid, or any other available DC source. An electric battery and a HVDC power transmission system are well known to the skilled person and therefore not discussed in more detail. With reference to Fig. 4, the electric power source 316, to which the plurality of electric power source sections 204 is arranged to be connected, may comprise a DC source 214 that comprises at least one cascaded cell 326, e.g. a cascaded half- bridge cell, or a cascaded full-bridge cell. The at least one cascaded half-bridge cell 326 may be arranged to be part of a converter station 1 16 included in the HVDC power transmission system. The DC source 214 may comprise a plurality of cascaded cells 326, e.g. cascaded half-bridge cells, or cascaded full-bridge cells, or a mixture thereof. The plurality of cascaded cells 326 may be arranged to be part of a converter station 1 16 included in the HVDC power transmission system. The electric power source 316 may comprise a power source capacitor 320 (see Fig. 4) to which the electric power source sections 204 may be electrically con- nectable. The apparatus may 202 comprise the electric power source.
With reference to Fig. 5, a first embodiment of the DC-to-DC converter unit 302 of Figs. 3A and 3B is schematically illustrated in more detail. The second converter 306 of the DC-to-DC converter unit 302 may comprise four pairs 402, 404, 406, 408, also indicated as Ss/S's, Se/S'6, S7/S'7, Ss/S's in Fig. 4, of electrically in- terconnected electronic switches 410, 412. The first converter 304 of the DC-to- DC converter unit 302 may comprise a full-bridge converter. The first converter 304 may comprise four pairs 414, 416, 418, 420, also indicated as S/S'r, S^S'2, S3/S'3, S /S'4 in Fig. 4, of electrically interconnected electronic switches 422, 424. The first converter 304 may also comprise a fifth pair 430 of electronic switches 431 , 433, also indicated as SAB S'AB in Fig. 4. The fifth pair 430 of electronic switches may be electrically connected in parallel with the four pairs 414, 416, 418, 420 of electronic switches. The fifth pair 430 of electronic switches may be used to give a path to the direct current when the first converter 304 is bypassed to give zero voltage. The first converter 304 may comprise filter means 426, 428, connected to the electronic switches 422, 424, for smoothing out the voltage and current ripple caused by the switching of the electronic switches 422, 424. The filter means may comprise a capacitor 426, also indicated as C^ in Fig. 4, and an inductor 428, also indicated as Lf, . The capacitor 426 may be connected in parallel with the electronic switches 422, 424. The inductor 428 may be electrically con- nected in series with the electronic switches 422, 424. The capacitor 426 may be connected in parallel with the fifth pair 430 of electronic switches. The DC-to-DC converter unit 302 may also comprise a second inductor 440 connected as indicated in Fig. 5.
The filter inductor 428 may be connected in series with the first converter
DC terminal with a first end connected to the common point of 414, 418 and 430, and with a second end connected to the filter capacitor 426. The other end of the filter capacitor 426 may be connected to the common point of 420, 416 and 430. This connection may also be reversed, i.e. the first end of the filter inductor 428 may be connected to the common point of 420, 416 and 430, and the second end of the filter inductor 428 may be connected to the filter capacitor 426. The other end of the filter capacitor 426 may be connected to the common point of 414, 418 and 430.
The four quadrant operation of the apparatus may be supported by bi- directional valves. By introducing PWM switching, the injected voltage VAB may be regulated to a desired value or level in an efficient way. PWM switching per se is well known to the skilled person and is thus not discussed in further detail. The power requirement of first converter 304 is supplied from the second converter 306 via the transformer 318. The second converter 306 may comprise at least two legs which convert direct current to alternating current and/or vice-versa. To effect or introduce a positive fictive resistance, +ARinj, active power should be absorbed by the DC source, and to effect or introduce a negative fictive resistance, -Af?/ny, active power should be injected by and from the DC source.
Fig. 6 schematically shows a second embodiment and aspects of the DC- to-DC converter unit 602 of the embodiments of the apparatus shown in Figs 3A and 3B. The first converter 604 of this embodiment corresponds to the first converter 304 of the first embodiment of Fig. 5, and is thus not further discussed. However, the second converter 606 of the second embodiment is different from the second converter of Fig. 5 and may comprise four pairs 702, 704, 706, 708, al- so indicated as S5 D5, Se/D6, S7/D7, Ss/D8 in Fig. 6, of electrically interconnected electronic control devices 710, 712. Each pair of electronic control devices 710, 712 may comprise an electronic switch 710 and a diode 712. The DC-to-DC converter unit 602 may comprise a transformer 718 connected between the first and second converters 604, 606. The transformer 718 may be an electric power transformer. The transformer 718 may be a high or medium frequency transformer.
Fig. 7 schematically shows a third embodiment and aspects of the DC-to- DC converter unit 902 of the embodiments of the apparatus shown in Figs 3A and 3B. The second converter 906 of the third embodiment may comprise four pairs 802, 804, 806, 808, also indicated as S^S'5, Se/S'e, S7/S'7, Ss S's in Fig. 10, of electrically interconnected electronic switches 810, 812. The first converter 904 may comprise four pairs 814, 816, 819, 820, also indicated as S S'f, S^S'2, Ss/S's, S /S'4 in Fig. 10, of electrically interconnected electronic switches 822, 824. The first converter 904 may also comprise a fifth pair 830 of electronic switches 831 , 833, also indicated as SAB/S'AB- The first converter 904 of the third embodiment may comprise filter means 826, 828, connected to the electronic switches 822, 824, for smoothing out the voltage and current ripple caused by the switching of the electronic switches 822, 824. The filter means may comprise a capacitor 826, also indicated as C^ in Fig. 7, and an inductor 828, also indicated as Lf. The components of the third embodiment of the DC-to-DC converter unit 902 are differently interconnected in relation to the first embodiment of Fig. 5, as illustrated in Fig. 7. The DC-to-DC converter unit 902 of Fig. 7 may comprise a transformer 818 connected between the first and second converters 904, 906. The transformer 818 may be an electric power transformer. The transformer 818 may be a high or medium frequency transformer.
The second and third embodiments of the DC-to-DC converter unit 602; 902 of Figs. 6 and 7 may comprise any of the additional features mentioned in connection with Fig. 5.
The above-mentioned apparatuses 202, 212 may comprise a plurality of
DC-to-DC converter units 302; 602; 902 of any sort described above, or a mixture thereof. Other configurations of the DC-to-DC converter units may also be possible.
Instead of a pair of anti-parallel power semiconductor switches, e.g. IGBT, used in the embodiments described above, a pair of anti-series power semiconductor switches, e.g. IGBT or BIGT, as shown in Figs. 8A and 8B may be used. The advantage of the anti-series connection is that reverse blocking power semiconductor switches are not required. Figs. 9 and 10A-B schematically shows aspects of a third embodiment of the apparatus 908 according to the present invention. The apparatus 908 of Fig. 9 comprises a plurality of electric power source sections 910. Each electric power source section 910 of the plurality of electric power source sections 910 may com- prise a section converter 912 for converting alternating current, AC, to direct current and/or direct current to alternating current. The section converter 912 has an AC side 914 for output and/or input of alternating current and a DC side 916 for output and/or input of direct current. In Fig. 9, each electric power source section 910 of the plurality of electric power source sections is arranged to be connected, via the AC side 914 of the section converter 912, to an electric power source 316 comprising an AC source 920. The AC source 920 may comprise an AC grid, or any other suitable AC source. The apparatus 908 comprises a plurality of DC-to- DC converter units 302; 602; 902, which can be of any sort described above, or a mixture thereof. The first DC sides 206 of the plurality of DC-to-DC converter units 302 may be connected in parallel with one another as illustrated in Fig. 9, or in series with one another as shown in Fig. 3A. Each DC-to-DC converter unit 302 of the plurality of DC-to-DC converter units may be connected via its second DC side 208 to the DC side 916 of the section converter 912 of at least one of the plurality of electric power source sections 910. The apparatus 908 shown in Fig. 9 is suit- able for a single phase AC source. For multi-phase source/supply, each phase leg may be similar to the apparatus 908 of Fig. 9. For a three-phase AC source, the apparatus 908 of Fig. 9 may be provided for any source where point R in Fig. 9 is connectable to the AC source and Gn may be connected to a neutral point. An inductor may be connected in series with each phase before the section converter 912. Each section converter 912 may be of soft switched type to reduce losses, e.g. ZCS, or ZVS. Each section converter 912 may be configured as illustrated in Fig 1 0A or in Fig. 10B, or in any other suitable manner. The apparatus 908 may comprise a mixture of the section converters shown in Figs. 10A and 10B. Fig. 10A illustrates an exemplary half-bridge topology for the section converter 912 of the electric power source section, and Fig. 10B illustrates an exemplary full-bridge topology for the section converter 912 of the electric power source section. The full-bridge topology of Fig. 10B may comprise the same pairs 702, 704, 706, 708 of electrically interconnected electronic control devices 710, 712 as the second converter 606 of Fig. 6. With reference to Figs. 1 , 3A-B and 9, the apparatus 202, 212, 908 may be connectable to the HVDC line 102, by connecting position P1 to position A in Fig. 1 , and by connecting position Qn to position B in Fig. 1 .
Each of the above-mentioned electronic switches may comprise a power semiconductor switch, e.g. an IGBT, a BIGT or any other suitable power semiconductor switch. Alternatively, each of the above-mentioned electronic switches may comprise a thyristor, e.g. a GTO, an IGCT, or a Forced Commutated Thyristor.
The invention shall not be considered limited to the embodiments illustrated, but can be modified and altered in many ways by one skilled in the art, without departing from the scope the appended claims. For example, the disclosed embodiments may be combined in various possible ways, and additional electric equipment, devices or units may be connected to and between the components of the embodiments. One and the same apparatus may e.g. comprise DC-to-DC converter units of different configurations, e.g. a mixture of the DC-to-DC converter units as disclosed above.

Claims

1 . An apparatus (202; 212; 908) for controlling the electric power transmission in a high voltage direct current, HVDC, power transmission system compris- ing at least one HVDC transmission or distribution line (102, 104, 106, 108, 1 10, 1 12, 1 14) for carrying direct current, DC, the apparatus being arranged to control the direct current of the HVDC transmission or distribution line by introducing a DC voltage in series with the HVDC transmission or distribution line, characterized in that the apparatus comprises a plurality of electric power source sections (204; 910) connectable to an electric power source (316), in that the apparatus comprises a plurality of DC-to-DC converter units (302; 602; 902), each DC-to-DC converter unit of the plurality of DC-to-DC converter units comprising a first DC side (206) for output and/or input of direct current and a second DC side (208) for output and/or input of direct current, in that each DC-to-DC converter unit of the plurality of DC-to-DC converter units is connectable via its first DC side to the HVDC transmission or distribution line, and in that each DC-to-DC converter unit of the plurality of DC-to-DC converter units is connected via its second DC side to at least one of the plurality of electric power source sections.
2. An apparatus according to claim 1 , characterized in that the DC-to-DC converter units (302; 602; 902) of the plurality of DC-to-DC converter units are connected, via respective second DC side, to different electric power source sections (204; 910) of the plurality of electric power source sections.
3. An apparatus according to claim 1 or 2, characterized in that a plurality of the first DC sides (206) of the plurality of DC-to-DC converter units (302) are connected in series with one another.
4. An apparatus according to any of the claims 1 to 3, characterized in that a plurality of the first DC sides (206) of the plurality of DC-to-DC converter units (302) are connected in parallel with one another.
5. An apparatus according to any of the claims 1 to 4, characterized in that a plurality of the second DC sides (208) of the plurality of DC-to-DC converter units (302) are connected in series with one another.
6. An apparatus according to any of the claims 1 to 5, characterized in that a plurality of the second DC sides (208) of the plurality of DC-to-DC converter units (302) are connected in parallel with one another.
7. An apparatus according to any of the claims 1 to 6, characterized in that each electric power source section (204) of the plurality of electric power source sections is arranged to be connected to an electric power source (316) comprising a DC source (214).
8. An apparatus according to claim 7, characterized in that each electric power source section (204) of the plurality of electric power source sections is arranged to be connected to an electric power source (316) comprising a DC source (214) that comprises an electric battery.
9. An apparatus according to claim 7, characterized in that each electric power source section (204) of the plurality of electric power source sections is arranged to be connected to an electric power source (316) comprising a DC source (214) that is part of a HVDC power transmission system.
10. An apparatus according to claim 7, characterized in that each electric power source section (204) of the plurality of electric power source sections is arranged to be connected to an electric power source (316) comprising a DC source (214) that comprises at least one cascaded cell (326).
1 1 . An apparatus according to any of the claims 1 to 10, characterized in that each electric power source section (204) of the plurality of electric power source sections comprises a capacitor (210).
12. An apparatus according to any of the claims 1 to 6, characterized in that each electric power source section (910) of the plurality of electric power source sections comprises a section converter (912) for converting alternating current, AC, to direct current and/or direct current to alternating current, the section converter having an AC side (914) for output and/or input of alternating current and a DC side (916) for output and/or input of direct current, in that each electric power source section of the plurality of electric power source sections is arranged to be connected, via the AC side of the section converter, to an electric power source (316) comprising an AC source (920), and in that each DC-to-DC converter unit (302; 602; 902) of the plurality of DC-to-DC converter units is connected via its second DC side (208) to the DC side of the section converter of at least one of the plurality of electric power source sections.
13. An apparatus according to claim 12, characterized in that each electric power source section (910) of the plurality of electric power source sections is arranged to be connected, via the AC side (914) of the section converter (912), to an electric power source (316) comprising an AC source (920) that comprises an AC grid.
14. An apparatus according to any of the claims 1 to 13, characterized in that each DC-to-DC converter unit (302; 602; 902) comprises a first converter (304; 604; 904) for converting alternating current, AC, to direct current and/or direct current to alternating current, and a second converter (306; 606; 906) for converting direct current to alternating current and/or alternating current to direct current, each of the first and second converters having an AC side (308, 310) for output and/or input of alternating current, in that the first converter comprises the first DC side (206) of the DC-to-DC converter unit, in that the second converter comprises the second DC side (208) of the DC-to-DC converter unit, and in that the AC side (310) of the second converter is connected to the AC side (308) of the first converter.
15. An apparatus according to claim 14, characterized in that each DC-to- DC converter unit (302; 602; 902) comprises a transformer (318; 718; 818) connected between the first and second converters (304, 306 ; 604, 606; 904, 906), and in that each of the first and second converters is connectable via its AC side (308, 310) to the transformer.
16. An apparatus according to claim 1 5, characterized in that the transformer (318; 718; 818) is arranged to isolate the first converter (304; 604; 904) from the electric power source section.
17. An apparatus according to any of the claims 14 to 16, characterized in that the second converter (306) comprises four pairs (402, 404, 406, 408) of electronic switches (410, 412).
18. An apparatus according to any of the claims 14 to 17, characterized in that the second converter (606) comprises four pairs (702, 704, 706, 708) of electronic control devices (710, 712), each pair of electronic control devices comprising an electronic switch (710) and a diode (712).
19. An apparatus according to any of the claims 14 to 18, characterized in that the first converter (304) comprises a full-bridge converter.
20. An apparatus according to any of the claims 14 to 19, characterized in that the first converter (304) comprises four pairs (414, 416, 418, 420) of electronic switches (422, 424).
21 . An apparatus according to claim 20, characterized in that the first converter (304) comprises a fifth pair (430) of electronic switches (431 , 433).
22. An apparatus according to claim 20 or 21 , characterized in that the first converter (304) comprises filter means (426, 428) for smoothing out the voltage and current ripple caused by the switching of the electronic switches (422, 424).
23. An apparatus according to claim 17, 18, 20, 21 , or 22, characterized in that each electronic switch (410, 422, 424; 710; 810, 812) comprises a power semiconductor switch.
24. An apparatus according to any of the claims 14 to 23, characterized in that the first converter (304; 604; 904) is connectable in series with the HVDC transmission or distribution line (102).
25. An apparatus according to any of the claims 1 to 24, characterized in that the apparatus (202; 212; 908) comprises control means (324) for controlling the apparatus, in that the control means are arranged to control the apparatus to introduce a positive DC voltage in series with the HVDC transmission or distribution line (102) for reducing the direct current of the HVDC transmission or distribu- tion line, and in that the control means are arranged to control the apparatus to introduce a negative DC voltage in series with the HVDC transmission or distribution line for increasing the direct current of the HVDC transmission or distribution line.
26. A high voltage direct current, HVDC, power transmission system compris- ing at least one HVDC transmission or distribution line (102, 104, 106, 108, 1 10,
1 12, 1 14) for carrying direct current, DC, and a plurality of converter stations (1 16, 1 18, 120, 122, 1 24) connected to the at least one HVDC transmission or distribution line, each of the converter stations being arranged to convert alternating current, AC, to direct current for input to the at least one HVDC transmission or distri- bution line, and/or direct current to alternating current, wherein the system comprises at least one apparatus (202; 212; 908) as claimed in any of the claims 1 -25 for controlling the electric power transmission in the system.
27. A HVDC power transmission system according to claim 26, character- ized in that the system comprises a plurality of HVDC transmission or distribution lines (102, 104, 106, 108, 1 10, 1 12, 1 14).
28. A HVDC power transmission system according to claim 26 or 27, characterized in that the system comprises at least three converter stations (1 16, 1 18, 120, 122, 124), or at least four converter stations (1 16, 1 18, 120, 122, 124).
29. A HVDC power transmission system according to any of the claims 26 to 28, characterized in that the at least one HVDC transmission or distribution line (102, 104, 106, 108, 1 10, 1 12, 1 14) comprises at least one long-distance HVDC link (102, 108).
PCT/EP2012/059885 2011-07-22 2012-05-25 An apparatus for controlling the electric power transmission in a hvdc power transmission system WO2013013858A1 (en)

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2017163508A1 (en) 2016-03-22 2017-09-28 三菱電機株式会社 Electric power conversion device
WO2019016449A1 (en) 2017-07-20 2019-01-24 Supergrid Institute Power flow control device for controlling the distribution of currents in a mesh network
FR3083019A1 (en) * 2018-06-25 2019-12-27 Supergrid Institute SYSTEM COMPRISING A POWER FLOW CONTROL DEVICE USED FOR CONTROLLING THE DISTRIBUTION OF CURRENTS IN A MESH NETWORK AND MEANS FOR PROTECTING SAID DEVICE
WO2020045759A1 (en) * 2018-08-30 2020-03-05 엘지이노텍 주식회사 Dc-dc converter for photovoltaic-linked energy storage system and control method therefor
WO2020136179A1 (en) 2018-12-28 2020-07-02 Supergrid Institute System incorporating a solution for reconfiguring connections of a device for controlling power flow in a mesh network
US11043901B2 (en) * 2019-11-15 2021-06-22 National Taiwan University Of Science And Technology Full bridge converter having wide output voltage range

Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1513827A1 (en) 1966-02-26 1969-09-18 Siemens Ag Arrangement for influencing the current distribution in maximum voltage direct current networks
US3694728A (en) 1970-03-25 1972-09-26 Bbc Brown Boveri & Cie Circuit arrangement for altering current distribution in mesh-operated high voltage direct current transmission networks
US5734258A (en) 1996-06-03 1998-03-31 General Electric Company Bidirectional buck boost converter
US6788033B2 (en) 2002-08-08 2004-09-07 Vlt, Inc. Buck-boost DC-DC switching power conversion
US6914420B2 (en) 2001-06-09 2005-07-05 3D Instruments Limited Power converter and method for power conversion
US7518266B2 (en) 2006-11-01 2009-04-14 Electric Power Research Institute, Inc. Method and apparatus for improving AC transmission system dispatchability, system stability, and power flow controllability using DC transmission systems
WO2010115452A1 (en) 2009-04-06 2010-10-14 Abb Technology Ag Power flow control in a meshed hvdc power transmission network
EP2293407A1 (en) 2009-09-08 2011-03-09 Converteam Technology Ltd Power transmission and distribution systems
EP2341594A1 (en) * 2009-12-29 2011-07-06 Converteam Technology Ltd Power collection and transmission systems
WO2012037966A1 (en) * 2010-09-21 2012-03-29 Abb Technology Ag An apparatus for controlling the electric power transmission in a hvdc power transmission system

Patent Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1513827A1 (en) 1966-02-26 1969-09-18 Siemens Ag Arrangement for influencing the current distribution in maximum voltage direct current networks
US3694728A (en) 1970-03-25 1972-09-26 Bbc Brown Boveri & Cie Circuit arrangement for altering current distribution in mesh-operated high voltage direct current transmission networks
US5734258A (en) 1996-06-03 1998-03-31 General Electric Company Bidirectional buck boost converter
US6914420B2 (en) 2001-06-09 2005-07-05 3D Instruments Limited Power converter and method for power conversion
US6788033B2 (en) 2002-08-08 2004-09-07 Vlt, Inc. Buck-boost DC-DC switching power conversion
US7518266B2 (en) 2006-11-01 2009-04-14 Electric Power Research Institute, Inc. Method and apparatus for improving AC transmission system dispatchability, system stability, and power flow controllability using DC transmission systems
WO2010115452A1 (en) 2009-04-06 2010-10-14 Abb Technology Ag Power flow control in a meshed hvdc power transmission network
EP2293407A1 (en) 2009-09-08 2011-03-09 Converteam Technology Ltd Power transmission and distribution systems
EP2341594A1 (en) * 2009-12-29 2011-07-06 Converteam Technology Ltd Power collection and transmission systems
WO2012037966A1 (en) * 2010-09-21 2012-03-29 Abb Technology Ag An apparatus for controlling the electric power transmission in a hvdc power transmission system

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2017163508A1 (en) 2016-03-22 2017-09-28 三菱電機株式会社 Electric power conversion device
EP3435531A4 (en) * 2016-03-22 2019-05-01 Mitsubishi Electric Corporation Electric power conversion device
US10998824B2 (en) 2016-03-22 2021-05-04 Mitsubishi Electric Corporation Electric power conversion device
WO2019016449A1 (en) 2017-07-20 2019-01-24 Supergrid Institute Power flow control device for controlling the distribution of currents in a mesh network
US11121549B2 (en) 2017-07-20 2021-09-14 Supergrid Institute Power flow control device for controlling the distribution of currents in a mesh network
FR3083019A1 (en) * 2018-06-25 2019-12-27 Supergrid Institute SYSTEM COMPRISING A POWER FLOW CONTROL DEVICE USED FOR CONTROLLING THE DISTRIBUTION OF CURRENTS IN A MESH NETWORK AND MEANS FOR PROTECTING SAID DEVICE
WO2020002266A1 (en) 2018-06-25 2020-01-02 Supergrid Institute System comprising a power flow control device used to control the distribution of currents in a grid network and means for protecting said device
WO2020045759A1 (en) * 2018-08-30 2020-03-05 엘지이노텍 주식회사 Dc-dc converter for photovoltaic-linked energy storage system and control method therefor
US11418116B2 (en) 2018-08-30 2022-08-16 Lg Innotek Co., Ltd. DC-DC converter for photovoltaic-linked energy storage system and control method therefor
WO2020136179A1 (en) 2018-12-28 2020-07-02 Supergrid Institute System incorporating a solution for reconfiguring connections of a device for controlling power flow in a mesh network
FR3091424A1 (en) 2018-12-28 2020-07-03 Supergrid Institute System integrating a connection reconfiguration solution for a power flow control device in a mesh network
US11043901B2 (en) * 2019-11-15 2021-06-22 National Taiwan University Of Science And Technology Full bridge converter having wide output voltage range

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