WO2017084120A1 - 单向直流-直流自耦变压器及其高低压侧故障隔离方法 - Google Patents

单向直流-直流自耦变压器及其高低压侧故障隔离方法 Download PDF

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WO2017084120A1
WO2017084120A1 PCT/CN2015/096386 CN2015096386W WO2017084120A1 WO 2017084120 A1 WO2017084120 A1 WO 2017084120A1 CN 2015096386 W CN2015096386 W CN 2015096386W WO 2017084120 A1 WO2017084120 A1 WO 2017084120A1
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Prior art keywords
voltage source
unidirectional
voltage
autotransformer
anode
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PCT/CN2015/096386
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English (en)
French (fr)
Inventor
林卫星
文劲宇
程时杰
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Huazhong University of Science and Technology
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Huazhong University of Science and Technology
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/10—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers
    • H02H7/12—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers
    • 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
    • H02M3/33507—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 with automatic control of the output voltage or current, e.g. flyback converters
    • H02M3/33523—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 with automatic control of the output voltage or current, e.g. flyback converters with galvanic isolation between input and output of both the power stage and the feedback loop
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/10—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; 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
    • 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

Definitions

  • the invention belongs to the technical field of power system transmission and distribution, and more particularly to a unidirectional DC-DC autotransformer for transmitting DC power from one DC system to another DC system in one direction.
  • DC-DC converters and DC-DC autotransformers are commonly used to achieve bidirectional power transfer between two DC grids.
  • the converters used are voltage source converters, resulting in high cost and high loss. cost.
  • power needs to be transmitted unidirectionally from one DC system to another. To this end, it is necessary to further optimize the design of a conventional DC-DC converter to reduce the cost.
  • the existing high-voltage high-power one-way DC-DC converter generally adopts a DC-AC-DC conversion technology, as shown in FIG. 1 , and the specific implementation manner thereof is to construct a voltage source converter and an uncontrolled rectifier, and the voltage source.
  • the DC converters of the type converter and the uncontrolled rectifier are respectively connected to the DC terminals of the first DC system and the second DC system to be interconnected (here, the rated DC voltage of the first DC system is lower than the rating of the second DC system) DC voltage), the AC terminals of the two inverters are interconnected by a certain AC circuit.
  • the DC power from a DC system will be first inverted by the voltage source converter to AC and then rectified by the uncontrolled rectifier to DC for transmission to another DC system.
  • the rated capacity of the voltage source type inverter and the uncontrolled rectifier used by the one-way DC-AC-DC conversion technology are equal to the rated transmission power.
  • the rated capacity of the AC link is also equal to the rated transmission power, so that there is a high investment cost of the inverter, and the cost of the AC link High and high operating loss defects.
  • the present invention provides a unidirectional DC-DC autotransformer which improves existing unidirectional DC-AC through optimized design of converters, rectifiers and AC links.
  • - DC converter technology has the advantages of large converter capacity, large AC link capacity and high running loss, achieving one-way transmission of DC power between two DC systems and the advantage of bidirectional DC fault isolation.
  • a unidirectional DC-DC autotransformer for unidirectionally transmitting DC from a second DC system of a high voltage level to a first DC system of a low voltage class.
  • the autotransformer comprises a first voltage source type converter, an uncontrolled rectifier and a second voltage source type converter, wherein
  • the anode of the first voltage source converter is coupled to the anode of the second DC system, and the anode of the first voltage source converter is coupled to the anode of the uncontrolled rectifier, and the anode and the second voltage of the rectifier are not controlled.
  • the anode of the source converter is coupled, the cathode of the second voltage source converter is coupled to the cathode of the second DC system, and the anode and cathode of the uncontrolled rectifier are respectively coupled to the anode of the first DC system.
  • the negative poles are coupled, and the alternating current sides of the first voltage source type inverter, the uncontrolled rectifier, and the second voltage source type converter are interconnected;
  • the DC power transmitted from the second DC system to the first DC system is controlled by controlling the AC voltage of the unidirectional DC-DC autotransformer by using a voltage source type converter.
  • the uncontrolled rectifier is further composed of a positive electrode subrectifier and a negative electrode subrectifier in series, wherein a negative electrode of the positive electrode subrectifier and a positive electrode of the negative electrode subrectifier are coupled, and the connection point is grounded.
  • the junction point of the positive electrode subrectifier and the negative pole subrectifier is also coupled to the neutral point of the first direct current system or the second direct current system via a metal return line, so that the direct current flows through the metal back during asymmetric operation.
  • the wires form a loop to prevent DC current from corroding the pipes on the DC line.
  • a unidirectional DC-DC autotransformer for interconnecting a positive polarity asymmetric monopole first DC system and a positive polarity asymmetric monopole second DC system. Transmitting DC power from a second DC system of a high voltage level to a first DC system of a low voltage level, wherein the autotransformer comprises a first voltage source converter and an uncontrolled rectifier, wherein
  • the positive pole of the first voltage source converter and the anode of the second DC system are connected, the anode of the first voltage source converter is connected with the anode of the uncontrolled rectifier, and the anode of the rectifier and the second DC system are not controlled.
  • the negative poles are coupled, and the positive and negative poles of the uncontrolled rectifier are respectively coupled to the positive and negative poles of the first direct current system, and the negative pole of the first direct current system, the negative pole of the second direct current system, and the negative pole of the uncontrolled rectifier Ground or ground through a metal return line;
  • the DC power transmitted from the second DC system to the first DC system is controlled by controlling the AC voltage of the unidirectional DC-DC autotransformer by using a voltage source type converter.
  • a unidirectional DC-DC autotransformer for interconnecting a negative polarity asymmetric monopole first DC system and a negative polarity asymmetric monopole second DC system. Transmitting DC power from a second DC system of a high voltage level to a first DC system of a low voltage level, wherein the autotransformer comprises an uncontrolled rectifier and a second voltage source converter, wherein
  • the anode of the uncontrolled rectifier is coupled to the anode of the second DC system, the anode of the uncontrolled rectifier is coupled to the anode of the second voltage source converter, and the cathode of the second voltage source converter and the second DC
  • the anodes of the system are coupled, and the anode and the cathode of the uncontrolled rectifier are respectively coupled to the anode and the cathode of the first DC system, and the anode of the first DC system, the anode of the second DC system, and the uncontrolled rectifier
  • the positive pole is grounded or grounded through a metal return line;
  • the DC power transmitted from the second DC system to the first DC system is controlled by controlling the AC voltage of the unidirectional DC-DC autotransformer by using a voltage source type converter.
  • the AC side of the uncontrolled rectifier and the voltage source converter is interconnected via a two or more winding AC transformer.
  • the AC sides of the uncontrolled rectifier and the voltage source converter are each coupled to an AC common bus or directly to an AC common bus via an AC transformer or phase reactor.
  • the alternating common bus is coupled to the external alternating current grid or the two or more windings
  • the AC transformer is connected to an external AC grid.
  • a high voltage side fault isolation method for a unidirectional DC-DC autotransformer characterized in that the voltage source type converter (including the first voltage source type change)
  • the sub-module of the voltage source converter is replaced with a sub-module capable of blocking the DC fault current,
  • the DC fault of the second DC system is isolated by blocking the trigger pulse of the voltage source type inverter full control power electronic device.
  • a low-voltage side fault isolation method for a unidirectional DC-DC autotransformer characterized in that, when a DC fault occurs in a first DC system, the voltage source type is blocked by blocking The trigger pulse of the fully controlled power electronics of the flow device isolates the DC fault of the first DC system,
  • the rated DC voltage of the voltage source type inverter is increased when the withstand voltage after the voltage source type inverter is blocked is lower than the rated voltage of the second DC system.
  • a unidirectional DC-DC autotransformer for unidirectionally transmitting DC power from a low voltage first DC system to a high voltage second DC system, wherein
  • the autotransformer includes a first uncontrolled rectifier, a voltage source converter, and a second uncontrolled rectifier, wherein
  • the anode of the first uncontrolled rectifier is coupled to the anode of the second DC system
  • the anode of the first uncontrolled rectifier is coupled to the anode of the voltage source converter
  • the positive pole of the controlled rectifier is connected
  • the negative pole of the second uncontrolled rectifier is connected with the negative pole of the second direct current system
  • the positive pole and the negative pole of the voltage source type converter are respectively connected with the positive pole and the negative pole of the first direct current system.
  • the DC power transmitted from the first DC system to the second DC system is controlled by controlling the AC voltage of the unidirectional DC-DC autotransformer by using a voltage source type inverter.
  • the voltage source type inverter is further composed of a positive electrode sub-converter and a negative electrode sub-converter connected in series, wherein a negative electrode of the positive-electrode sub-converter and a positive electrode of the negative-electrode sub-converter are coupled, and Join The grounding point is grounded, the positive pole of the positive pole sub-converter is connected with the negative pole of the first uncontrolled rectifier, and the negative pole of the negative pole sub-converter is connected with the positive pole of the second uncontrolled rectifier.
  • connection point of the positive and negative sub-converters is also coupled to the neutral point of the first direct current system or the second direct current system via a metal return line, so that the direct current during asymmetric operation
  • the metal return line forms a loop to avoid corrosion of the metal pipe on the direct current line by the direct current.
  • a unidirectional DC-DC autotransformer for interconnecting a positive polarity asymmetric monopole first DC system and a positive polarity asymmetric monopole second DC system. Transmitting DC power from a low voltage first DC system to a high voltage second DC system, the autotransformer comprising a first uncontrolled rectifier and a voltage source converter, wherein
  • the anode of the first uncontrolled rectifier is coupled to the anode of the first DC system
  • the anode of the first uncontrolled rectifier is coupled to the anode of the voltage source converter
  • the negative poles are coupled, and the positive and negative poles of the voltage source converter are respectively coupled to the anode and the cathode of the first direct current system, and the anode of the first direct current system, the cathode of the second direct current system, and the voltage source type
  • the negative pole of the inverter is grounded or grounded through a metal return line;
  • the DC power transmitted from the first DC system to the second DC system is controlled by controlling the AC voltage of the unidirectional DC-DC autotransformer by using a voltage source type inverter.
  • a unidirectional DC-DC autotransformer for interconnecting a negative polarity asymmetric monopole first DC system and a negative polarity asymmetric monopole second DC system. Directly transmitting DC power from the first DC system of the low voltage to the second DC system of the high voltage, the autotransformer comprising a voltage source type inverter and a second uncontrolled rectifier, wherein
  • the positive pole of the voltage source converter and the anode of the second DC system are connected, the cathode of the voltage source converter is connected with the anode of the second uncontrolled rectifier, and the cathode of the second uncontrolled rectifier and the second DC
  • the anodes of the system are coupled, and the anode and the cathode of the voltage source converter are respectively coupled to the anode and the cathode of the first DC system, and the anode of the first DC system, the anode of the second DC system, and the voltage
  • the anode of the source converter is directly grounded or grounded through a metal return line;
  • the DC power transmitted from the first DC system to the second DC system is controlled by controlling the AC voltage of the unidirectional DC-DC autotransformer by using a voltage source type inverter.
  • the AC side of the uncontrolled rectifier and the voltage source converter is interconnected via a two or more winding AC transformer.
  • the uncontrolled rectifier, the voltage source converter and the alternating current side are each coupled to an alternating current common bus via an alternating current transformer or phase reactor, or directly to the alternating current common bus.
  • the alternating current common bus is coupled to an external alternating current grid or the two-winding, multi-winding alternating current transformer is coupled to an external alternating current grid.
  • a high voltage side fault isolation method for the above DC-DC autotransformer characterized in that a DC circuit breaker is connected in series on the first uncontrolled rectifier and the second uncontrolled rectifier, when high voltage When a DC fault occurs on the side, the DC fault on the high voltage side can be isolated by breaking the DC circuit breaker.
  • a low-voltage side fault isolation method for the above-described DC-DC autotransformer characterized in that, when a DC fault occurs on the low voltage side, a trigger pulse of the blocking voltage source type converter is isolated Low-voltage side DC fault,
  • the first uncontrolled rectifier and the second uncontrolled rectifier may be additionally increased.
  • Rated DC voltage when the sum of the withstand voltages of the first uncontrolled rectifier and the second uncontrolled rectifier is lower than the rated DC voltage of the second DC system, the first uncontrolled rectifier and the second uncontrolled rectifier may be additionally increased.
  • Rated DC voltage when the sum of the withstand voltages of the first uncontrolled rectifier and the second uncontrolled rectifier is lower than the rated DC voltage of the second DC system, the first uncontrolled rectifier and the second uncontrolled rectifier may be additionally increased. Rated DC voltage.
  • the voltage source type converter can adopt various voltage source type converter topologies such as a modular multilevel converter, a two level converter, and a three level converter.
  • the uncontrolled rectifier can be formed by connecting a plurality of uncontrolled rectifiers in series, and reducing harmonics through a certain combination.
  • the AC side of the uncontrolled rectifier and the voltage source type converter can adopt a single-phase, two-phase, three-phase or multi-phase AC circuit.
  • the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:
  • the solution of the invention can reduce the rated power of the voltage source converter and the uncontrolled rectifier, reduce the power of the AC link, thereby reducing the investment cost and operation. loss;
  • FIG. 3 is a step-down type unidirectional DC-DC autotransformer according to another embodiment of the present invention, wherein the uncontrolled rectifier is formed by a series connection of a positive electrode subrectifier and a negative electrode subrectifier;
  • FIG. 4 is a step-down type unidirectional DC-DC autotransformer according to another embodiment of the present invention, wherein a junction point of a positive electrode subrectifier and a negative electrode subrectifier passes through a metal return line and a first direct current system and a second direct current system; Neutral point connection;
  • FIG. 5 is a step-down type unidirectional DC-DC autotransformer composed of a first voltage source type inverter and an uncontrolled rectifier according to another embodiment of the present invention
  • FIG. 6 is a step-down type unidirectional DC-DC autotransformer composed of an uncontrolled rectifier and a second voltage source type inverter according to another embodiment of the present invention
  • FIG. 8 is a boost type unidirectional DC-DC autotransformer according to another embodiment of the present invention, wherein a voltage source type inverter is obtained by connecting a positive electrode sub-converter and a negative electrode sub-converter in series;
  • FIG. 9 is a step-up type unidirectional DC-DC autotransformer according to another embodiment of the present invention, wherein a voltage source type inverter is obtained by connecting a positive electrode sub-converter and a negative electrode sub-converter in series, and two sub-converting currents The connection point of the device is connected to the neutral point of the first direct current system and the neutral point of the second direct current system via the metal return line;
  • FIG. 10 is a boost type unidirectional DC-DC autotransformer according to another embodiment of the present invention, wherein the AC common bus is divided into two segments and the two segments are not connected;
  • 11 is a step-up type unidirectional DC-DC autotransformer comprising a first uncontrolled rectifier and a voltage source converter according to another embodiment of the present invention
  • step-up type unidirectional DC-DC autotransformer comprising a voltage source type inverter and a second uncontrolled rectifier according to another embodiment of the present invention
  • FIG. 13 is a step-down type unidirectional DC-DC autotransformer according to another embodiment of the present invention, wherein The AC side of the first and second voltage source converters and the uncontrolled rectifier are interconnected by a three-winding AC transformer;
  • FIG. 14 is a step-down type unidirectional DC-DC autotransformer according to another embodiment of the present invention, wherein the AC sides of the first and second voltage source converters, the positive sub-rectifiers, and the negative sub-rectifiers pass through a four-winding AC transformer. Interconnected together;
  • 15 is a step-up type unidirectional DC-DC autotransformer according to another embodiment of the present invention, wherein an AC side of a first uncontrolled rectifier and a voltage source converter is interconnected via an AC transformer;
  • 16 is a step-down type unidirectional DC-DC autotransformer according to still another embodiment of the present invention, wherein a first voltage source type inverter and an AC side of an uncontrolled rectifier are interconnected by an alternating current transformer;
  • 17 is a step-down type unidirectional DC-DC autotransformer according to another embodiment of the present invention, wherein an AC side of the first and second voltage source converters is connected to an AC common bus via an AC transformer, and the AC of the rectifier is not controlled.
  • the lateral phase reactance is coupled to the alternating common bus;
  • 19 is a step-down type unidirectional DC-DC autotransformer according to another embodiment of the present invention, wherein a reactive power compensation and filtering device is also coupled to the AC common bus;
  • 20 is a step-up type unidirectional DC-DC autotransformer according to still another embodiment of the present invention, wherein an AC side of the voltage source type inverter is directly coupled to an AC common bus;
  • 21 is a step-up type unidirectional DC-DC autotransformer according to another embodiment of the present invention, wherein an AC side of a first uncontrolled rectifier and a second uncontrolled rectifier is directly coupled to an AC common bus;
  • 22 is a step-up type unidirectional DC-DC autotransformer according to another embodiment of the present invention, wherein the AC sides of the first and second uncontrolled rectifiers and the voltage source converter are directly coupled to the AC common bus;
  • Figure 23 is a view showing several typical topologies that can be employed in the voltage source type inverter of the present invention.
  • Figure 24 is a diagram showing several typical topologies that can be employed by the uncontrolled rectifier of the present invention.
  • Figure 26 is a detailed development of a step-down type unidirectional DC-DC autotransformer according to an embodiment of the present invention.
  • Figure 27 is a diagram showing the voltage source type converter used in the unidirectional DC-AC-DC converter of the prior art and the voltage source type commutation used in the unidirectional DC-DC autotransformer of one embodiment of the present invention. Comparison of the capacity of the device;
  • 29 is an AC power of a first voltage source type inverter and a non-controlled rectifier of a step-down type unidirectional DC-DC autotransformer of an embodiment of the present invention
  • 31 is a DC voltage value of a first DC system and a second DC system of a step-down type unidirectional DC-DC autotransformer according to an embodiment of the present invention
  • Figure 34 is a diagram showing a standard value of an AC voltage of a step-up type unidirectional DC-DC autotransformer according to another embodiment of the present invention.
  • 35 is a DC voltage value of a first DC system and a second DC system of a step-up type unidirectional DC-DC autotransformer according to another embodiment of the present invention.
  • the unidirectional DC-DC autotransformer provided by the embodiment of the invention is mainly used for transmitting DC power from one DC system to another DC system in one direction, and the remarkable technical performance is that the auto coupling technology is used. This reduces the total converter capacity used.
  • the autotransformer is mainly composed of a first voltage source type inverter 11
  • the uncontrolled rectifier 12 and the two voltage source converter 13 are connected in series, and the anode of the first voltage source converter 11 is connected to the anode of the second DC system 8 via the DC line 6 , and the first voltage source type
  • the negative pole of the inverter 11 is coupled to the anode of the uncontrolled rectifier 12, the anode of the uncontrolled rectifier 12 is coupled to the anode of the second voltage source converter 13, and the cathode of the second voltage source converter 13 is
  • the negative poles of the two DC systems 8 are connected, and the positive and negative poles of the uncontrolled rectifier 12 are also connected to the positive and negative poles of the first direct current system 7 via the direct current line 6, respectively, the first uncontrolled rectifier 11 and the voltage source type inverter 12 and the alternating current side of the second un
  • the uncontrolled rectifier 12 is in turn replaced with a positive sub-rectifier 12P and a negative sub-rectifier 12N, the negative pole of 12P and the positive pole of 12N are coupled and the coupling point is grounded.
  • the advantage of dividing the uncontrolled rectifier 12 into the positive sub-converter 12P and the negative sub-converter 12N is that if the first direct current system 7 and the second direct current system 8 are bipolar direct current systems, the first direct current system 7 or when the positive pole of the second DC system 8 fails, by isolating the first voltage source type inverter 11 and the positive electrode sub-rectifier 12P, only the anode sub-rectifier 12N and the second voltage source type converter 13 are maintained in operation.
  • the non-faulty part of the unidirectional DC-DC autotransformer can be kept in normal operation. Similarly, if the negative pole of the first DC system 7 or the negative pole of the second DC system 8 fails, the negative pole rectifier 12N and the first pass are isolated.
  • the step-down unidirectional DC-DC autotransformer DC neutral point passes through the metal return line 9 and the neutral of the first DC system 7 and the second DC system 8, respectively. Point joins.
  • the topology of FIG. 4 is basically the same as the topology of FIG. 3, and the advantage is that during asymmetric operation (only the first voltage source type converter 11 and the positive side sub-rectifier 12P are put into operation or only the anode sub-rectifier 12N and the second voltage source type commutating The device 13 is put into operation), and the direct current does not need to flow through the earth, but forms a loop through the metal return line 9 to avoid corrosion of the direct current to other civil equipment such as the metal line along the direct current line 6.
  • an autotransformer is used to interconnect the positive polarity asymmetric monopole first DC system 7 and the positive polarity asymmetric monopole second DC system 8, which includes only the first A voltage source type inverter 11 and a step-down type unidirectional DC-DC autotransformer that does not control the rectifier 12.
  • the anode of the first voltage source type inverter 11 is coupled to the anode of the second DC system 8
  • the cathode of the first voltage source type inverter 11 is coupled to the anode of the uncontrolled rectifier 12, and the anode and the cathode of the rectifier 12 are not controlled.
  • the negative poles of the two DC systems 8 are coupled, and the positive and negative poles of the uncontrolled rectifier 12 are respectively coupled to the positive and negative poles of the first direct current system 7, the negative pole of the first direct current system 7, the negative pole of the second direct current system 8, and
  • the negative pole of the controlled rectifier 12 is directly grounded or grounded through a metal return line 9, and the first voltage source type inverter 11 and the alternating current side of the uncontrolled rectifier 12 are respectively coupled to the alternating current common bus line 5 via the alternating current transformer 4.
  • an autotransformer is used to interconnect the negative polarity asymmetric monopole first DC system 7 and the negative polarity asymmetric monopole second DC system 8, which includes only the second A unidirectional DC-DC autotransformer for controlling the rectifier 12 and the second voltage source converter 13.
  • the anode of the uncontrolled rectifier 12 is coupled to the anode of the second DC system 8, and the anode of the uncontrolled rectifier 12 is coupled to the anode of the second voltage source converter 13, and the second voltage source converter 13 is
  • the anode and the cathode of the second DC system 8 are coupled, and the anode and the cathode of the uncontrolled rectifier 12 are respectively coupled to the anode and the cathode of the first DC system 7, the anode of the first DC system 7, and the cathode of the second DC system 8
  • the positive electrode and the positive electrode of the uncontrolled rectifier 12 are directly grounded or grounded via a metal return line 9, and the alternating current sides of the uncontrolled rectifier 12 and the second voltage source type inverter 13 are respectively coupled to the alternating current common bus 5 via the alternating current transformer 4.
  • Fig. 7 is a view showing the basic configuration of a step-up type unidirectional DC-DC autotransformer proposed in an embodiment of the present invention.
  • the unidirectional DC-DC autotransformer is mainly composed of a first uncontrolled rectifier 1, a voltage source converter 2 and a second uncontrolled rectifier 3 connected in series.
  • the anode of the first uncontrolled rectifier 1 is connected to the anode of the second DC system 8 via the DC line 6.
  • the cathode of the first uncontrolled rectifier 1 is connected to the anode of the voltage source converter 2, and the voltage source is switched.
  • the cathode of the second uncontrolled rectifier 3 is coupled to the cathode of the second uncontrolled rectifier 3, and the cathode of the second uncontrolled rectifier 3 is coupled to the cathode of the second DC system 8 via the DC line 6, the anode of the voltage source converter 2 and The negative pole is respectively connected to the DC line 6 A positive electrode and a negative electrode of a direct current system 7 are coupled.
  • the AC sides of the first uncontrolled rectifier 1, the voltage source converter 2 and the second uncontrolled rectifier 3 are respectively connected to the AC common bus 5 through the AC transformer 4, and the AC common bus 5 can be controlled by the voltage source converter 2
  • the AC voltage thus controls the DC voltage of the port of the first uncontrolled rectifier 1 and the second uncontrolled rectifier 3, thereby achieving the purpose of controlling the transmitted DC power.
  • the voltage source type inverter 2 can be further formed by a series connection of a positive electrode sub-converter 2P and a negative electrode sub-converter 2N, wherein a negative electrode of 2P and a positive electrode phase of 2N Connect and connect the joint to ground.
  • the advantage of dividing the voltage source converter 2 into the positive pole sub-converter 2P and the negative pole sub-converter 2N is that if the first direct current system 7 and the second direct current system 8 are bipolar direct current systems, when the first When the positive pole of the DC system 7 or the second DC system 8 fails, the first uncontrolled rectifier 1 and the positive subconverter 2P are isolated, and only the negative subconverter 2N and the second uncontrolled rectifier 3 are maintained in operation. The non-faulty part of the unidirectional DC-DC autotransformer can still be kept in normal operation. Similarly, if the negative pole of the first DC system 7 or the negative pole of the second DC system 8 fails, the negative pole inverter is isolated. The 2N and the second uncontrolled rectifier 3, only maintaining the first uncontrolled rectifier 1 and the positive subconverter 2P, can still cause the first DC system 7 of the non-faulty portion to transmit DC power to the second DC system 8.
  • the unidirectional DC-DC autotransformer DC neutral point is coupled to the neutral points of the first DC system 7 and the second DC system 8 via metal return lines 9, respectively.
  • the topology of Fig. 9 is basically the same as the topology of Fig. 8.
  • the advantage of this embodiment is that during asymmetric operation (only the first uncontrolled rectifier 1 and the positive subconverter 2P are put into operation or only the negative subconverter 2N and the second uncontrolled rectifier 3 put into operation), the DC current does not need to flow through the earth, but through the metal return line 9 constitutes a loop to avoid the corrosion of DC current to other civil equipment such as the metal line along the DC line 6.
  • FIG. 10 in one embodiment, it is substantially identical to FIG. 9, except that the AC common bus 5 is divided into two segments 5a and 5b, and there is no connection between 5a and 5b, and the first uncontrolled rectifier 1 and the positive electrode are
  • the AC side of the sub-converter 2P is coupled to 5a through a certain AC link
  • the AC side of the negative-pole sub-converter 2N and the second uncontrolled rectifier 3 are connected to 5b through a certain AC link
  • the advantages are 1 and 2P.
  • the sub-portion of the sub-portion and the sub-portion of 2N and 3 can be independently controlled so that the non-faulty portion is not affected when the positive or negative component fails.
  • an autotransformer is used to interconnect asymmetrical singles of positive polarity.
  • the pole first DC system 7 and the positive polarity asymmetric monopole second DC system 8 are unidirectional DC-DC autotransformers comprising only the first uncontrolled rectifier 1 and the voltage source converter 2.
  • the anode of the first uncontrolled rectifier 1 is coupled to the anode of the second DC system 8, the anode of the first uncontrolled rectifier 1 is coupled to the anode of the voltage source converter 2, and the anode of the voltage source converter 2 is
  • the negative poles of the two DC systems 8 are coupled, and the positive and negative poles of the voltage source converter 2 are respectively coupled to the positive and negative poles of the first DC system 7, the negative pole of the first DC system 7, and the second DC system 8
  • the negative electrode and the negative electrode of the voltage source type inverter 2 are directly grounded or grounded via a metal return line 9, and the alternating current sides of the first uncontrolled rectifier 1 and the voltage source type inverter 2 are respectively coupled to the alternating current common bus 5 via the alternating current transformer 4.
  • the autotransformer is a step-up type unidirectional DC-DC autotransformer including only the voltage source type converter 2 and the second uncontrolled rectifier 3 for interconnecting the negative polarity.
  • the positive pole of the voltage source converter 2 is coupled to the anode of the second DC system 8
  • the cathode of the voltage source converter 2 is coupled to the anode of the second uncontrolled rectifier 3
  • the anode of the second uncontrolled rectifier 3 is coupled.
  • the anode and the cathode of the second DC system 8 are coupled, and the anode and cathode of the voltage source converter 2 are respectively coupled to the anode and the cathode of the first DC system 7, and the anode and the second DC of the first DC system 7 are connected.
  • the anode of the system 8 and the anode of the voltage source converter 2 are directly grounded or grounded through the metal return line 9, and the alternating current sides of the voltage source converter 2 and the second uncontrolled rectifier 3 are respectively coupled to the alternating current via the alternating current transformer 4 Busbar 5.
  • FIG. 13 in one embodiment, it is substantially identical to the topology of the embodiment shown in FIG. 2, except that the first voltage source type inverter 11, the uncontrolled rectifier 12, and the second voltage source are the same in this embodiment.
  • the AC side of the converter 13 is interconnected via a three-winding transformer 9.
  • FIG. 14 in one embodiment, it is basically the same as the topology of the embodiment shown in FIG. 4, except that the first voltage source converter 11, the positive sub-rectifier 12P, and the negative sub-rectifier 12N are the same in this embodiment.
  • the AC side of the second voltage source type converter 13 is interconnected via a four-winding transformer 10.
  • FIG. 15 in one embodiment, it is substantially identical to the topology of the embodiment shown in FIG. 11, except that the AC side of the first uncontrolled rectifier 1 and the voltage source converter 2 in this embodiment passes through a The AC transformers 4 are interconnected.
  • FIG. 16 in one embodiment, it is substantially identical to the topology of the embodiment shown in FIG. The difference is that the first voltage source type inverter 11 and the alternating current side of the uncontrolled rectifier 12 are interconnected via an alternating current transformer 4 in this embodiment.
  • FIG. 17 in one embodiment, it is substantially identical to the topology of the embodiment shown in FIG. 2, with the difference that the uncontrolled rectifier 12 is coupled to the alternating common bus 5 via the phase reactor 15 in this embodiment.
  • FIG. 18 in one embodiment, it is substantially identical to the topology of the embodiment shown in FIG. 2, with the difference that the AC common bus 5 is also interconnected with the external communication system 14 in this embodiment.
  • FIG. 19 in one embodiment, it is substantially identical to the topology of the embodiment shown in FIG. 2, except that the AC common bus 5 is also coupled to the AC filter/AC reactive power compensation device 18 in this embodiment.
  • the harmonics of the rectifier 12 and the reactive power consumption are controlled.
  • FIG. 20 in one embodiment, it is substantially identical to the topology of the embodiment shown in FIG. 7, with the difference that the AC side of the voltage source converter 2 is directly coupled to the AC common bus 5 in this embodiment.
  • FIG. 21 in one embodiment, it is substantially identical to the topology of the embodiment shown in FIG. 7, with the difference that the AC side of the uncontrolled rectifier in this embodiment is directly coupled to the AC common bus 5.
  • FIG. 22 in one embodiment, it is substantially identical to the topology of the embodiment shown in FIG. 7, except that the first rectifier 1, the voltage source converter 2, and the second rectifier 3 are in communication in this embodiment.
  • the side is directly connected to the AC common bus.
  • the voltage source type inverter (2, 11 or 13) is a well-known AC-DC conversion circuit, which can adopt a two-level topology, a clamp-type multi-level topology, and a modularity. Multi-level topology, as well as many other well-known topologies.
  • the specific structure of the voltage source type converter can adopt a two-level topology as shown in FIG. 23(a), mainly consisting of six fully-controlled power electronic devices 50, a positive DC bus 16, and a negative electrode.
  • the DC busbar 17 is composed of a DC capacitor 52, and each of the two fully-controlled power electronic components 50 is connected in series to form a phase-commutated bridge arm.
  • each phase-commutated bridge arm is connected with the positive DC busbar 16 for each phase change.
  • the negative end of the bridge arm is connected with the negative DC bus 17, and the midpoint of each phase commutating bridge arm is respectively connected with the A phase AC terminal 51a, the B phase AC terminal 51b, the C phase AC terminal 51c, and the positive connection of the DC capacitor 52.
  • the positive DC bus 16 and the negative pole of the DC capacitor 52 are coupled to the negative DC bus 17.
  • a plurality of fully controlled power electronic devices 50 can be connected in series to form a fully controlled power electronic device 50.
  • the specific structure of the voltage source converter can also adopt the three-level topology as shown in Fig. 23(b), mainly consisting of 12 fully-controlled power electronic devices 50, 6 clamp diodes 53, and a positive DC bus 16
  • the negative DC bus 17, the positive DC capacitor 52a and the negative DC capacitor 52b are formed.
  • Each two fully-controlled power electronic devices 50 are connected in series to form a 'half bridge arm', and each two 'half bridge arms' are connected in series to form a
  • the phase shifting bridge arm, the midpoint of each 'half bridge arm' is coupled to the neutral point 57 via a clamping diode 53.
  • the neutral point 57 can be a grounding point or a common coupling point, and each phase is commutated, as needed.
  • the positive end of the bridge arm is connected with the positive DC bus 16
  • the negative end of each phase commutating bridge arm is connected with the negative DC bus 17
  • the midpoint of each phase commutating bridge arm is respectively communicated with the A phase AC end 51 a, B phase.
  • the terminal 51b and the C-phase AC terminal 51c are coupled, the positive terminal of the positive DC capacitor 52a is coupled to the positive DC bus 6, the negative terminal of the positive DC capacitor 52a is connected to the neutral point 57, and the positive terminal of the negative DC capacitor 52b is connected to the neutral point 57.
  • each of the fully controlled power electronic devices 50 can be formed by connecting a plurality of fully controlled power electronic devices in series, and each of the clamping diodes 53 can be connected in series by a plurality of clamping diodes. to make.
  • the specific structure of the voltage source converter can also adopt a modular multi-level topology as shown in FIG. 23(c), which mainly includes six half-bridge arms 55, and each two half-bridge arms 55 are connected in series to form one phase bridge arm.
  • the midpoint of each phase commutating bridge arm is respectively connected with the A phase AC terminal 51a, the B phase AC terminal 51b, and the C phase AC terminal 51c.
  • the positive and negative ends of each phase bridge arm are respectively connected to the positive DC bus 16 and the negative DC.
  • the bus bars 17 are connected, and each of the half bridge arms is connected in series by a plurality of submodules 54 and then the smooth wave reactors 56 are connected in series.
  • Each submodule can adopt a half bridge submodule, a full bridge submodule, a clamp double submodule,
  • a variety of well-known sub-module topologies such as self-blocking sub-modules, the half-bridge sub-module topology is given at the bottom of Figure 20(c), and each half-bridge sub-module consists of two fully-controlled power electronic devices 50 and one sub-module capacitor. 52 composition.
  • the uncontrolled rectifier (1, 3 or 12) is a well-known AC-DC conversion circuit, and the uncontrolled rectifier is mainly composed of a diode through a certain connection.
  • Fig. 24(a) illustrates a topology of an uncontrolled rectifier, which is mainly composed of six diodes 21, a positive DC bus 16, and a negative DC bus 17, and each two diodes 21 are connected in series to form a phase commutating bridge arm.
  • the positive end of the phase change bridge arm is coupled with the positive DC bus 16
  • the negative end of each phase commutating bridge arm is coupled with the negative DC bus 17
  • the midpoint of each phase commutating bridge arm is respectively connected with the A phase AC end 51 a , B intersect
  • the current terminal 51b and the C-phase AC terminal 51c are coupled.
  • each diode 21 may be formed by a plurality of diodes 21 connected in series.
  • 24(b) is substantially identical to FIG. 24(a) except that a DC capacitor 52 is coupled between the positive DC bus 16 and the negative DC bus 17.
  • Fig. 24(c) illustrates another topology of the uncontrolled rectifier, which is mainly formed by connecting the positive electrode sub-rectifier 22a and the negative electrode sub-rectifier 22b in series, and the alternating current sides of 22a and 22b are respectively connected via a triangle/star connection and a star.
  • /Star-connected AC transformers are connected together to reduce the harmonics of the DC side of the rectifier.
  • the DC side of the controller can also be connected in parallel with DC capacitors to reduce the DC side harmonics, and the rectifier is not controlled.
  • the side can also be connected in parallel with a reactive power compensation device or an alternating current filter.
  • Figure 25 shows the unfolded topology of the step-up unidirectional DC-DC autotransformer shown in Figure 7, and Figure 25 is basically the same as Figure 7, except that the first uncontrolled rectifier 1, the voltage source converter 2 and The second uncontrolled rectifier 3 is drawn in the form of a detailed circuit topology in which a DC breaker 18 is connected in series with the first uncontrolled rectifier 1 and the second uncontrolled rectifier 3, and the AC side of the voltage source converter 2 is directly coupled to The common busbar 5 is exchanged.
  • each bridge arm of the voltage source converter 2 is illustrated by a half bridge module.
  • Figure 26 shows the unfolded topology of the step-down unidirectional DC-DC autotransformer corresponding to Figure 2.
  • 26 is substantially identical to FIG. 2, except that the first voltage source type converter 11, the uncontrolled rectifier 12, and the second voltage source type inverter 13 are drawn into a detailed circuit topology form, wherein the first voltage source type is changed.
  • Each of the bridges of the flow device 11 and the second voltage source type inverter 13 is formed by a series connection of a half bridge module 54 and a self-blocking submodule 44. For simplified drawing, only one half bridge is drawn for each bridge arm.
  • the voltage source type converter included in the unidirectional DC-DC autotransformer can be used to control the internal AC voltage of the unidirectional DC-DC autotransformer to control the unidirectional DC-DC autotransformer.
  • the DC voltage rectified by the rectifier is not controlled, and then the DC power transmitted by the unidirectional DC-DC autotransformer is controlled to realize the control of the DC power transmitted by the unidirectional DC-DC autotransformer.
  • the DC power control process for a buck unidirectional DC-DC autotransformer is described below. Take the step-down unidirectional DC autotransformer shown in Figure 2 as an example, where E 1 is the DC voltage of the first DC system, and V dc1 ⁇ V dc3 are the first voltage source converters 11, respectively, and the rectifier is not controlled.
  • E dc is the high voltage DC port voltage of the step-down type unidirectional DC-DC autotransformer
  • E 2 is the DC voltage of the second DC system 8
  • v ac To exchange the AC voltage of the common bus 5
  • i dc1 is the DC current input to the first DC system 7
  • i dc2 is the DC current output by the second DC system 8
  • i DIO2 is the DC current of the uncontrolled rectifier.
  • V dc2 By increasing the amplitude of v ac , the value of V dc2 can be increased, thereby increasing the difference between V dc2 and E 1 , thereby increasing i dc1 and increasing the output of the second DC system 8 to the first DC system 7 .
  • DC power
  • a boost type unidirectional DC-DC autotransformer its DC power control process is described below.
  • E 1 is the DC voltage of the first DC system
  • V dc1 ⁇ V dc3 are the first uncontrolled rectifier 1, respectively, and the voltage source converter 2 and the second uncontrolled rectifier 3 port DC voltage
  • E dc is the boost type unidirectional DC-DC variable high voltage DC port voltage
  • E 2 is the DC voltage of the second DC system 8
  • v ac is the AC common bus 5
  • the AC voltage, i dc1 is the DC current output by the first DC system 7, i dc2 is the DC current absorbed by the second DC system 8, and i VSC2 is the DC current of the second voltage source converter.
  • Control i.e., can be improved by improving v ac amplitude value V dc1 and V dc2, thereby increasing the value of E dc, to increase the difference between E 2 and E dc thereby improving the object i dc2, i dc2 increase after
  • the DC power transmitted from the first DC system 7 to the second DC system 8 can be increased.
  • the first voltage source type inverter 11 and the second voltage source type converter 13 use a modular multilevel converter (MMC) structure by replacing part of the sub-modules of the first voltage source type inverter 11 and the second voltage source type converter 13 with sub-modules capable of blocking DC fault current, such as full bridge sub-modules, clamps
  • MMC modular multilevel converter
  • the DC voltage of the second DC system 8 is applied to the first voltage source converter 11 and the second voltage source converter 13, if the first voltage source type The rated withstand voltage of the inverter 11 and the second voltage source type inverter 13 is insufficient, by additionally connecting half of each of the bridge arms of the first voltage source type inverter 11 and the second voltage source type inverter 13
  • the bridge module can reach the first block The purpose of DC system 7 DC fault.
  • a DC circuit breaker may be connected in series between the first uncontrolled rectifier 1 and the second uncontrolled rectifier 3, and the second DC system 8 generates DC
  • the purpose of cutting off the DC fault path is achieved by breaking the DC breaker.
  • the DC power transmitted by the first DC system 7 to the second DC system 8 is P N . If you ignore the loss, you can calculate i dc1 and i dc2 as
  • the direct current flowing through the second voltage source type converter 2 is
  • the rated power of the second voltage source type converter 2 can be further obtained as follows:
  • the rated power of the first uncontrolled rectifier 1 and the second uncontrolled rectifier 3 can be calculated as
  • the inverter capacity of the voltage source converter is always P N
  • the inverter capacity of the uncontrolled rectifier is always P N
  • Figure 27 compares the capacity of a conventional DC-AC-DC converter technology with a unidirectional DC-DC autotransformer technology using a voltage source converter, where the 'DC-AC_DC' curve represents conventional DC-AC-DC technology.
  • 'Unidirectional DC AUTO' stands for unidirectional DC-DC autotransformer technology
  • 'PVSC/PN' stands for the ratio of the rated power of the voltage source converter to the rated transmission DC power. It can be seen that the voltage source type converter used in the unidirectional DC-DC autotransformer technology is always smaller than the converter capacity used in the conventional DC-AC-DC conversion technology when the ratio k ⁇ 5, so that it can be greatly Reduce investment costs and operating losses.
  • the present invention builds a simulation example of a step-up and step-down unidirectional DC-DC autotransformer on the internationally recognized software PSCAD/EMTDC, an example
  • the applied disturbance is that the DC power command value increases from 0 to 1000 MW from 0.2 s to 0.5 s, and the DC power command value decreases from 1000 MW to 0 in 2.0 s to 2.2 s, and the DC power increases from 0 to 3.0 s to 3.2 s.
  • the 4.0 s first DC system 7 applies a pole-to-pole DC fault with a duration of 0.1 s, and at 6.0 s the second DC system 8 applies a pole-to-pole DC permanent fault.
  • P dcref is a DC power command value transmitted by the second DC system 8 to the first DC system 7
  • P dc is a measured DC power value. It can be known that the measured value of the DC power can well track the DC power command value.
  • Figure 30 shows the standard value of the AC voltage of the unidirectional DC-DC autotransformer. It can be seen that when the DC power rises, the AC voltage rises and when the DC power decreases, the AC voltage drops.
  • the boost type unidirectional DC auto-coupling has bidirectional DC fault isolation capability.
  • the applied disturbance is a DC power command value of 0.2 s to 0.5 s rising from 0 to 1000 MW. 1.5s ⁇ 1.7s DC power command value decreased from 1000MW to 0, 3.0s ⁇ 3.2s DC power further increased from 0 to 1000MW, 4.0s first DC system 7 applied a duration of 0.1s pole-to-pole DC fault, 5.0 The second DC system 8 applies a pole-to-pole DC permanent fault when s.
  • P dcref is the DC power command value transmitted by the first DC system 7 to the second DC system 8
  • Pdc is the measured DC power value. It can be seen that the measured value of the DC power can well track the DC power command value.
  • P DIO1 is the AC power rectified by the first uncontrolled rectifier 1
  • P VSC2 is the AC power of the inverter of the second voltage source converter 2, as shown in Fig. 32 and Fig. 33, the unidirectional DC-DC auto coupling
  • the AC power in the transformer is much lower than the DC power.
  • Figure 34 shows the standard value of the AC voltage of the unidirectional DC-DC autotransformer. It can be seen that when the DC power rises, the AC voltage rises and when the DC power decreases, the AC voltage drops.
  • 35 is a DC voltage waveform of the first DC system 7 and the second DC system 8. It can be seen that, in 4.0 s, when the DC fault occurs in the first DC system 7, E 1 is reduced to 0, and E 2 remains substantially unchanged, 5.0. When the DC fault occurs in the second DC system 8, E 2 is reduced to 0, and E1 remains basically unchanged. That is, the boost type unidirectional DC auto-coupling has bidirectional DC fault isolation capability.

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Abstract

一种单向直流-直流自耦变压器，用于单向地在两个直流系统间传输直流功率。通过对换流器、整流器和交流链路的优化设计，改进现有单向直流-交流-直流变换技术存在的换流器容量大、交流链路容量大、运行损耗高的缺陷。通过利用电压源型换流器（11，13）控制单向直流-直流自耦变压器的交流电压，从而实现控制从低电压的第一直流系统（7）向高电压的第二直流系统（8）传输的直流功率、或者从高电压的第二直流系统向低电压的第一直流系统传输的直流功率，同时具有双向直流故障隔离能力。还提供了相应的高、低压侧直流故障隔离方法。

Description

[根据细则37.2由ISA制定的发明名称]　单向直流-直流自耦变压器及其高低压侧故障隔离方法 【技术领域】
本发明属于电力系统输配电技术领域，更具体地，涉及一种单向直流-直流自耦变压器，用于单向第从一个直流系统向另一个直流系统传输直流功率。
【背景技术】
随着模块化多电平换流器的发展，利用模块化多电平换流器构成直流电网是电力工业界近年来备受关注的一个热点。各个区域直流电网的互联是一个亟待解决的问题。由于各个区域直流电网功能不同，所采用的技术不同，所建设的年代不同，各个区域直流电网的额定直流电压不会完全一致。为了互联不同电压等级的直流电网，需要采用直流-直流变换器。
直流-直流变换器以及直流-直流自耦变压器通常用于实现两个直流电网之间的功率双向传输，所采用的换流器为电压源型换流器从而带来了成本高、损耗高的代价。在风电经直流组网等某些典型应用场合，功率只需要单向地从一个直流系统向另一个直流系统传输。为此，需要进一步优化设计常规的直流-直流变换器从而降低成本。
现有的高压大功率单向直流-直流变换器一般采用直流-交流-直流变换技术，如图1所示，其具体实施方式为建设一个电压源型换流器与一个不控整流器，电压源型换流器和不控整流器的直流端分别与待互联的第一直流系统和第二直流系统的直流端联接(此处记第一直流系统的额定直流电压低于第二直流系统的额定直流电压)，两个换流器的交流端通过一定的交流电路互联在一起。来自一个直流系统的直流功率将先由电压源型换流器逆变为交流电再经过不控整流器整流为直流电传输到另一个直流系统。可知，由于所有传输的直流功率都需要经过两级交流/直流变换，该单向直流-交流-直流变换技术所使用的电压源型换流器与不控整流器的额定容量都与额定传输功率相等，交流链路的额定容量也与额定传输功率相等，从而存在换流器投资成本高，交流链路成本 高、运行损耗大的缺陷。
【发明内容】
针对现有技术的以上缺陷或改进需求，本发明提供了一种单向直流-直流自耦变压器，其通过对换流器、整流器以及交流链路的优化设计，改进现有单向直流-交流-直流变换技术存在的换流器容量大、交流链路容量大、运行损耗高的缺陷，实现对两直流系统间直流功率的单向传输，同时具有双向直流故障隔离能力的优点。
为实现上述目的，按照本发明的一个方面，提供了一种单向直流-直流自耦变压器，用于从高电压等级的第二直流系统向低电压等级的第一直流系统单向传输直流功率，其特征在于，该自耦变压器包括第一电压源型换流器、不控整流器和第二电压源型换流器，其中，
所述第一电压源型换流器的正极和第二直流系统的正极相联接，第一电压源型换流器的负极和不控整流器的正极相联接，不控整流器的负极和第二电压源型换流器的正极相联接，第二电压源型换流器的负极和第二直流系统的负极相联接，同时所述不控整流器的正极和负极分别与第一直流系统的正极和负极相联接，且所述第一电压源型换流器、不控整流器和第二电压源型换流器的交流侧互联在一起；
通过利用电压源型换流器控制单向直流-直流自耦变压器的交流电压从而实现控制从第二直流系统向第一直流系统传输的直流功率。
优选地，所述不控整流器进一步地由正极子整流器和负极子整流器串联组成，其中所述正极子整流器的负极和负极子整流器的正极相联接，且联接点处接地。
优选地，所述正极子整流器和负极子整流器的联接点还经过金属回线与第一直流系统或第二直流系统的中性点相联接，使得在不对称运行时直流电流经过该金属回线构成回路从而避免直流电流对直流线路上管道的腐蚀。
按照本发明的另一方面，提供了一种单向直流-直流自耦变压器，用于互联正极性的不对称单极第一直流系统和正极性的不对称单极第二直流系统，实现 从高电压等级的第二直流系统向低电压等级的第一直流系统单向传输直流功率，其特征在于，该自耦变压器包括第一电压源型换流器和不控整流器，其中，
所述第一电压源型换流器的正极和第二直流系统正极相联接，第一电压源型换流器的负极和不控整流器的正极相联接，不控整流器的负极和第二直流系统的负极相联接，同时所述不控整流器的正极和负极分别与第一直流系统的正极和负极相联接，且第一直流系统的负极、第二直流系统的负极以及不控整流器的负极接地或者通过金属回线接地；
通过利用电压源型换流器控制单向直流-直流自耦变压器的交流电压从而实现控制从第二直流系统向第一直流系统传输的直流功率。
按照本发明的又一方面，提供了一种单向直流-直流自耦变压器，用于互联负极性的不对称单极第一直流系统和负极性的不对称单极第二直流系统，实现从高电压等级的第二直流系统向低电压等级的第一直流系统单向传输直流功率，其特征在于，该自耦变压器包括不控整流器和第二电压源型换流器，其中，
所述不控整流器的正极和第二直流系统的正极相联接，不控整流器的负极和第二电压源型换流器的正极相联接，第二电压源型换流器的负极和第二直流系统的负极相联接，同时所述不控整流器的正极和负极分别与第一直流系统的正极和负极相联接，且上述第一直流系统的正极、第二直流系统的正极以及不控整流器的正极接地或者通过金属回线接地；
通过利用电压源型换流器控制单向直流-直流自耦变压器的交流电压从而实现控制从第二直流系统向第一直流系统传输的直流功率。
优选地，不控整流器和电压源型换流器的交流侧经过一个两绕组或多绕组的交流变压器互联在一起。
优选地，不控整流器和电压源型换流器的交流侧各经过交流变压器或相电抗器联接至一交流公共母线或者直接联接至一交流公共母线。
优选地，交流公共母线与外部交流电网相联接或者所述两绕组或多绕组的 交流变压器与外部交流电网相联接。
按照本发明的另一个方面，提供了一种单向直流-直流自耦变压器的高压侧故障隔离方法，其特征为，在所述电压源型换流器(包括所述第一电压源型换流器和第二电压源型换流器)采用模块化多电平换流器拓扑时，将所述电压源型换流器的部分子模块替换为可阻断直流故障电流的子模块，第二直流系统发生直流故障时，通过闭锁所述电压源型换流器全控电力电子器件的触发脉冲隔离第二直流系统的直流故障。
按照本发明的另一个方面，提供了一种单向直流-直流自耦变压器的低压侧故障隔离方法，其特征为，在第一直流系统发生直流故障时，通过闭锁所述电压源型换流器的全控电力电子器件的触发脉冲从而隔离第一直流系统的直流故障，
优选地，在所述电压源型换流器闭锁后的耐压低于第二直流系统的额定电压时，增大所述电压源型换流器的额定直流电压。
按照本发明的又一个方面，提供了一种单向直流-直流自耦变压器，用于从低电压的第一直流系统向高电压的第二直流系统单向传输直流功率，其特征在于，该自耦变压器包括第一不控整流器、电压源型换流器和第二不控整流器，其中，
所述第一不控整流器的正极和第二直流系统的正极相联接，第一不控整流器的负极和电压源型换流器的正极相联接，电压源型换流器的负极和第二不控整流器的正极相联接，第二不控整流器的负极和第二直流系统的负极相联接，同时所述电压源型换流器的正极和负极分别与第一直流系统的正极和负极相联接，且所述第一不控整流器、电压源型换流器和第二不控整流器的交流侧互联在一起；
通过利用电压源型换流器控制单向直流-直流自耦变压器的交流电压从而实现控制从第一直流系统向第二直流系统传输的直流功率。
优选地，所述电压源型换流器进一步地由正极子换流器和负极子换流器串联组成，其中所述正极子换流器的负极和负极子换流器的正极相联接，且联接 点处接地，正极子换流器正极与第一不控整流器负极联接，负极子换流器的负极与第二不控整流器正极联接。
优选地，所述正极子换流器和负极子换流器的联接点还经过金属回线与第一直流系统或第二直流系统的中性点相联接，使得在不对称运行时直流电流经过该金属回线构成回路从而避免直流电流对直流线路上金属管道的腐蚀。
按照本发明的另一方面，提供了一种单向直流-直流自耦变压器，用于互联正极性的不对称单极第一直流系统和正极性的不对称单极第二直流系统，实现从低电压的第一直流系统向高电压的第二直流系统单向传输直流功率，该自耦变压器包括第一不控整流器和电压源型换流器，其中，
所述第一不控整流器的正极和第一直流系统正极相联接，第一不控整流器的负极和电压源型换流器的正极相联接，电压源型换流器负极和第二直流系统的负极相联接，同时所述电压源型换流器的正极和负极分别与第一直流系统的正极和负极相联接，且第一直流系统的负极、第二直流系统负极和电压源型换流器的负极接地或经过金属回线接地；
通过利用电压源型换流器控制单向直流-直流自耦变压器的交流电压从而实现控制从第一直流系统向第二直流系统传输的直流功率。
按照本发明的又一方面，提供了一种单向直流-直流自耦变压器，用于互联负极性的不对称单极第一直流系统和负极性的不对称单极第二直流系统，实现从低电压的所述第一直流系统向高电压的所述第二直流系统单向传输直流功率，该自耦变压器包括电压源型换流器和第二不控整流器，其中，
所述电压源型换流器的正极和第二直流系统的正极相联接，电压源型换流器的负极和第二不控整流器的正极相联接，第二不控整流器的负极和第二直流系统的负极相联接，同时所述电压源型换流器的正极和负极分别与第一直流系统的正极和负极相联接，且第一直流系统的正极、第二直流系统的正极以及电压源型换流器的正极直接接地或者经过金属回线接地；
通过利用电压源型换流器控制单向直流-直流自耦变压器的交流电压从而实现控制从第一直流系统向第二直流系统传输的直流功率。
优选地，不控整流器和电压源型换流器的交流侧经过一个两绕组或多绕组的交流变压器互联在一起。
优选地，不控整流器、电压源型换流器和的交流侧各经过交流变压器或相电抗器联接至一交流公共母线，或者直接联接至交流公共母线。
优选地，交流公共母线与外部交流电网相联接或者所述两绕组、多绕组的交流变压器与外部交流电网相联接。
按照本发明的另一个方面，提供了一种上述直流-直流自耦变压器的高压侧故障隔离方法，其特征为，在第一不控整流器和第二不控整流器上串联直流断路器，当高压侧发生直流故障时，通过开断所述直流断路器即可隔离高压侧直流故障。
按照本发明的另一个方面，提供了一种上述直流-直流自耦变压器的低压侧故障隔离方法，其特征为，在低压侧发生直流故障时，闭锁电压源型换流器的触发脉冲从而隔离低压侧直流故障，
优选地，在所述第一不控整流器和第二不控整流器闭锁后的耐压之和低于第二直流系统的额定直流电压时，可额外提高第一不控整流器和第二不控整流器的额定直流电压。
优选地，所述的电压源型换流器可以采用模块化多电平换流器、两电平换流器、三电平换流器等各种电压源型换流器拓扑。
优选地，所述的不控整流器可以采用多个不控整流器串联而成，并经过一定的组合降低谐波。
优选地，所述的不控整流器、电压源型换流器的交流侧可以采用单相、两相、三相或多相交流电路。总体而言，通过本发明所构思的以上技术方案与现有技术相比，能够取得下列有益效果：
(1)相比于常规的单向直流-交流-直流变换技术，本发明的方案可以降低电压源型换流器和不控整流器的额定功率，降低交流链路的功率从而降低投资成本和运行损耗；
(2)相比于常规的直流-直流自耦变压器，通过将直流-直流自耦变压器中 的部分换流器替换为不控整流器，降低了单向直流-直流自耦变压器的换流器成本，降低了控制复杂度并达到了功率单向传输的目的。
【附图说明】
图1是现有技术中的单向直流-直流变换器拓扑；
图2是本发明一个实施例的降压型单向直流-直流自耦变压器；
图3是本发明另一个实施例的降压型单向直流-直流自耦变压器，其中不控整流器由正极子整流器和负极子整流器串联而成；
图4是本发明另一个实施例的降压型单向直流-直流自耦变压器，其中正极子整流器和负极子整流器的联接点处经过金属回线与第一直流系统和第二直流系统的中性点相联接；
图5是本发明另一个实施例的由第一电压源型换流器和不控整流器构成的降压型单向直流-直流自耦变压器；
图6是本发明另一个实施例的由不控整流器和第二电压源型换流器构成的降压型单向直流-直流自耦变压器；
图7是本发明一个实施例的升压型单向直流-直流自耦变压器；
图8是本发明另一个实施例的升压型单向直流-直流自耦变压器，其中电压源型换流器由正极子换流器和负极子换流器串联而得；
图9是本发明另一个实施例的升压型单向直流-直流自耦变压器，其中电压源型换流器由正极子换流器和负极子换流器串联而得，且两个子换流器的联接点经过金属回线与第一直流系统的中性点和第二直流系统的中性点相联接；
图10是本发明另一个实施例的升压型单向直流-直流自耦变压器，其中交流公共母线分为两段且两段不联接；
图11是本发明另一个实施例的由第一不控整流器和电压源型换流器构成的升压型单向直流-直流自耦变压器；
图12是本发明另一个实施例的由电压源型换流器和第二不控整流器构成的升压型单向直流-直流自耦变压器；
图13是本发明另一个实施例的降压型单向直流-直流自耦变压器，其中第 一、二电压源型换流器和不控整流器的交流侧经过一个三绕组交流变压器互联在一起；
图14是本发明另一个实施例的降压型单向直流-直流自耦变压器，其中第一、二电压源型换流器、正极子整流器和负极子整流器的交流侧经过一个四绕组交流变压器互联在一起；
图15是本发明另一个实施例的升压型单向直流-直流自耦变压器，其中第一不控整流器和电压源型换流器的交流侧经过一个交流变压器互联在一起；
图16是本发明又一个实施例的降压型单向直流-直流自耦变压器，其中第一电压源型换流器和不控整流器的交流侧经过一个交流变压器互联在一起；
图17是本发明另一个实施例的降压型单向直流-直流自耦变压器，其中第一、二电压源型换流器的交流侧经交流变压器联接至交流公共母线，不控整流器的交流侧经相电抗联接至交流公共母线；
图18是本发明另一个实施例的降压型单向直流-直流自耦变压器，其中交流公共母线还与外部交流系统互联在一起；
图19是本发明另一个实施例的降压型单向直流-直流自耦变压器，其中交流公共母线上还联接了无功补偿和滤波装置；
图20是本发明又一个实施例的升压型单向直流-直流自耦变压器，其中电压源型换流器的交流侧直接联接至交流公共母线；
图21是本发明另一个实施例的升压型单向直流-直流自耦变压器，其中第一不控整流器和第二不控整流器的交流侧直接联接至交流公共母线；
图22是本发明另一个实施例的升压型单向直流-直流自耦变压器，其中第一、二不控整流器和电压源型换流器的交流侧直接联接至交流公共母线；
图23是本发明中的电压源型换流器可以采用的几种典型拓扑；
图24是本发明中的不控整流器可以采用的几种典型拓扑；
图25是本发明一个实施例的升压型单向直流-直流自耦变压器的详细展开拓扑；
图26是本发明一个实施例的降压型单向直流-直流自耦变压器的详细展开 拓扑；
图27是现有技术中的单向直流-交流-直流变换器所使用的电压源型换流器容量与本发明一个实施例的单向直流-直流自耦变压器所使用的电压源型换流器容量的对比图；
图28是仿真测试的本发明一个实施例的降压型单向直流-直流自耦变压器的直流功率指令值和直流功率实测值；
图29是仿真测试的本发明一个实施例的降压型单向直流-直流自耦变压器的第一电压源型换流器和不控整流器的交流功率；
图30是仿真测试的本发明一个实施例的降压型单向直流-直流自耦变压器交流电压的标幺值；
图31是仿真测试的本发明一个实施例的降压型单向直流-直流自耦变压器第一直流系统和第二直流系统直流电压值；
图32是仿真测试的本发明另一个实施例的升压型单向直流-直流自耦变压器的直流功率指令值和直流功率实测值；
图33是仿真测试的本发明另一个实施例的升压型单向直流-直流自耦变压器的第一不控整流器和电压源型换流器的交流功率；
图34是仿真测试的本发明另一个实施例的升压型单向直流-直流自耦变压器交流电压的标幺值；
图35是仿真测试的本发明另一个实施例的升压型单向直流-直流自耦变压器第一直流系统和第二直流系统直流电压值。
【具体实施方式】
为了使本发明的目的、技术方案及优点更加清楚明白，以下结合附图及实施例，对本发明进行进一步详细说明。应当理解，此处所描述的具体实施例仅仅用以解释本发明，并不用于限定本发明。此外，下面所描述的本发明各个实施方式中所涉及到的技术特征只要彼此之间未构成冲突就可以相互组合。
本发明实施例提供的单向直流-直流自耦变压器主要用于单向地从一个直流系统向另一个直流系统传输直流功率，其显著的技术性表现在于使用了自耦技 术从而降低了所使用的总的换流器容量。
图2为按照本发明另一实施例所提出的降压型单向直流-直流自耦变压器的基本结构图，如图2所示，该自耦变压器主要由第一电压源型换流器11、不控整流器12和二电压源型换流器13依次串联而成，第一电压源型换流器11的正极经直流线路6与第二直流系统8的正极相联接，第一电压源型换流器11的负极与不控整流器12的正极相联接，不控整流器12的负极与第二电压源型换流器13的正极相联接，第二电压源型换流器13的负极与第二直流系统8的负极相联接，不控整流器12的正极和负极还分别经直流线路6与第一直流系统7的正极和负极相联接，第一不控整流器11、电压源型换流器12和第二不控整流器13的交流侧分别通过交流变压器4联接至交流公共母线5，通过由第一电压源型换流器11以及第二电压源型换流器13控制交流公共母线5的交流电压即可控制不控整流器12的整流电压从而控制向第一直流系统7传输的直流功率。
如图3所示，在一个实施例中，不控整流器12又可替换为正极子整流器12P和负极子整流器12N，12P的负极和12N的正极相联接且联接点接地。将不控整流器12划分为正极子换流器12P和负极子换流器12N的好处在于，若第一直流系统7和第二直流系统8为双极性直流系统，当第一直流系统7或第二直流系统8的正极发生故障时，通过隔离第一电压源型换流器11和正极子整流器12P，仅维持负极子整流器12N和第二电压源型换流器13处于运行状态仍能使单向直流-直流自耦变压器的非故障部分保持正常运行，同理地若第一直流系统7的负极或第二直流系统8的负极发生故障时，通过隔离负极子整流器12N和第二电压源型换流器13，仅保持第一电压源型换流器11和正极子整流器12P运行仍可以使得非故障部分的第一直流系统7和第二直流系统8维持功率传输能力。
如图4所示，在一个实施例中，该降压型单向直流-直流自耦变压器直流中性点经金属回线9分别与第一直流系统7和第二直流系统8的中性点相联接。图4拓扑与图3拓扑基本一致，优点在于不对称运行时(仅第一电压源型换流器11和正极子整流器12P投入运行或仅负极子整流器12N和第二电压源型换流 器13投入运行)，直流电流无需流经大地，而是经过金属回线9构成回路从而避免了直流电流对直流线路6沿线金属管道等其他民用设备的腐蚀。
如图5所示，在一个实施例中，自耦变压器用于互联正极性的不对称单极第一直流系统7和正极性的不对称单极第二直流系统8，其为仅包含第一电压源型换流器11和不控整流器12的降压型单向直流-直流自耦变压器。第一电压源型换流器11的正极和第二直流系统8的正极相联接，第一电压源型换流器11的负极和不控整流器12的正极相联接，不控整流器12负极和第二直流系统8的负极相联接，不控整流器12的正极和负极分别与第一直流系统7的正极和负极相联接，第一直流系统7的负极、第二直流系统8的负极以及不控整流器12的负极直接接地或者通过金属回线9接地，第一电压源型换流器11和不控整流器12的交流侧分别经交流变压器4联接至交流公共母线5。
如图6所示，在一个实施例中，自耦变压器用于互联负极性不对称单极第一直流系统7和负极性不对称单极第二直流系统8，其为仅包含第二不控整流器12和第二电压源型换流器13的单向直流-直流自耦变压器。其中，不控整流器12的正极和第二直流系统8的正极相联接，不控整流器12的负极和第二电压源型换流器13的正极相联接，第二电压源型换流器13的负极和第二直流系统8的负极相联接，不控整流器12的正极和负极分别与第一直流系统7的正极和负极相联接，第一直流系统7的正极、第二直流系统8的正极以及不控整流器12的正极直接接地或者经过金属回线9接地，不控整流器12和第二电压源型换流器13的交流侧分别经交流变压器4联接至交流公共母线5。
图7是本发明一个实施例中所提出的升压型单向直流-直流自耦变压器的基本结构图。如图2所示，该单向直流-直流自耦变压器主要由第一不控整流器1、电压源型换流器2和第二不控整流器3依次串联而成。其中，第一不控整流器1的正极经直流线路6与第二直流系统8的正极相联接，第一不控整流器1的负极与电压源型换流器2的正极相联接，电压源型换流器2的负极与第二不控整流器3的正极相联接，第二不控整流器3的负极经直流线路6与第二直流系统8的负极相联接，电压源型换流器2的正极和负极经直流线路6分别与第 一直流系统7的正极和负极相联接。第一不控整流器1、电压源型换流器2和第二不控整流器3的交流侧分别通过交流变压器4联接至交流公共母线5，通过电压源型换流器2可以控制交流公共母线5的交流电压从而控制第一不控整流器1和第二不控整流器3的端口直流电压，进而达到控制所传输直流功率的目的。
如图8所示，在本发明的一个实施例中，电压源型换流器2又可由正极子换流器2P和负极子换流器2N串联而成，其中2P的负极和2N的正极相联接且联接点接地。将电压源型换流器2划分为正极子换流器2P和负极子换流器2N的好处在于，若第一直流系统7和第二直流系统8为双极性直流系统，当第一直流系统7或第二直流系统8的正极发生故障时，通过隔离第一不控整流器1和正极子换流器2P，仅维持负极子换流器2N和第二不控整流器3处于运行状态仍能使单向直流-直流自耦变压器的非故障部分保持正常运行，同理地若第一直流系统7的负极或第二直流系统8的负极发生故障时，通过隔离负极子换流器2N和第二不控整流器3，仅保持第一不控整流器1和正极子换流器2P运行仍可以使得非故障部分的第一直流系统7向第二直流系统8传输直流功率。
如图9所示，在一个实施例中，单向直流-直流自耦变压器直流中性点经金属回线9分别与第一直流系统7和第二直流系统8的中性点相联接。图9拓扑与图8拓扑基本一致，该实施例优点在于不对称运行时(仅第一不控整流器1和正极子换流器2P投入运行或仅负极子换流器2N和第二不控整流器3投入运行)，直流电流无需流经大地，而是经过金属回线9构成回路从而避免了直流电流对直流线路6沿线金属管道等其他民用设备的腐蚀。
如图10所示，在一个实施例中，其与图9基本一致，区别在于交流公共母线5划分为5a和5b两段，且5a和5b之间无联接，第一不控整流器1和正极子换流器2P的交流侧通过一定的交流链路联接于5a，负极子换流器2N以及第二不控整流器3的交流侧通过一定的交流链路联接于5b，其优点在于1和2P构成的子部分以及2N和3构成的子部分可以独立控制从而正极或者负极的部件发生故障时，非故障部分不受影响。
如图11所示，在一个实施例中，自耦变压器用于互联正极性的不对称单 极第一直流系统7和正极性不对称单极第二直流系统8，其为仅包含第一不控整流器1和电压源型换流器2的单向直流-直流自耦变压器。第一不控整流器1的正极和第二直流系统8的正极相联接，第一不控整流器1的负极和电压源型换流器2的正极相联接，电压源型换流器2负极和第二直流系统8的负极相联接，电压源型换流器2的正极和负极分别与第一直流系统7的正极和负极相联接，第一直流系统7的负极、第二直流系统8的负极以及电压源型换流器2的负极直接接地或经过金属回线9接地，第一不控整流器1和电压源型换流器2的交流侧分别经交流变压器4联接至交流公共母线5。
如图12所示，在一个实施例中，自耦变压器为仅包含电压源型换流器2和第二不控整流器3的升压型单向直流-直流自耦变压器，用于互联负极性不对称单极第一直流系统7和负极性不对称单极第二直流系统8。其中，电压源型换流器2的正极和第二直流系统8的正极相联接，电压源型换流器2的负极和第二不控整流器3的正极相联接，第二不控整流器3的负极和第二直流系统8的负极相联接，电压源型换流器2的正极和负极分别与第一直流系统7的正极和负极相联接，第一直流系统7的正极、第二直流系统8的正极以及电压源型换流器2的正极直接接地或者通过金属回线9接地，电压源型换流器2和第二不控整流器3的交流侧分别经交流变压器4联接至交流公共母线5。
如图13所示，在一个实施例中，其与图2所示实施例的拓扑基本一致，区别在于该实施例中第一电压源型换流器11、不控整流器12和第二电压源型换流器13的交流侧经三绕组变压器9互联在一起。
如图14所示，在一个实施例中，其与图4所示实施例的拓扑基本一致，区别在于该实施例中第一电压源型换流器11、正极子整流器12P、负极子整流器12N和第二电压源型换流器13的交流侧经四绕组变压器10互联在一起。
如图15所示，在一个实施例中，其与图11所示实施例的拓扑基本一致，区别在于该实施例中第一不控整流器1和电压源型换流器2的交流侧经过一个交流变压器4互联在一起。
如图16所示，在一个实施例中，其与图5所示实施例的拓扑基本一致， 区别在于该实施例中第一电压源型换流器11和不控整流器12的交流侧经过一个交流变压器4互联在一起。
如图17所示，在一个实施例中，其与图2所示实施例的拓扑基本一致，区别在于该实施例中不控整流器12经过相电抗器15联接至交流公共母线5。
如图18所示，在一个实施例中，其与图2所示实施例的拓扑基本一致，区别在于该实施例中交流公共母线5还与外部交流系统14互联在一起。
如图19所示，在一个实施例中，其与图2所示实施例的拓扑基本一致，区别在于该实施例中交流公共母线5上还联接了交流滤波/交流无功补偿装置18从而减小不控整流器12的谐波以及无功消耗。
如图20所示，在一个实施例中，其与图7所示实施例的拓扑基本一致，区别在于该实施例中电压源型换流器2的交流侧直接联接至交流公共母线5。
如图21所示，在一个实施例中，其与图7所示实施例的拓扑基本一致，区别在于该实施例中不控整流器的交流侧直接联接至交流公共母线5。
如图22所示，在一个实施例中，其与图7所示实施例的拓扑基本一致，区别在于该实施例中第一整流器1，电压源型换流器2以及第二整流器3的交流侧直接联接至交流公共母线。
在本发明中，所述电压源型换流器(2、11或13)是一种公知的交流-直流变换电路，可以采用两电平型拓扑结构，钳位型多电平拓扑，模块化多电平型拓扑，以及其他多种公知的拓扑结构。如图23所示，电压源型换流器的具体结构可以采用如图23(a)所示的两电平拓扑结构，主要由6个全控型电力电子器件50，正极直流母线16，负极直流母线17，直流电容52组成，每两个全控型电力电子器件50串联联接后构成一相换流桥臂，每相换流桥臂的正端与正极直流母线16相联接，每相换流桥臂的负端与负极直流母线17相联接，每相换流桥臂的中点分别与A相交流端51a，B相交流端51b，C相交流端51c联接，直流电容52的正极联接正极直流母线16，直流电容52的负极联接负极直流母线17，为了提高电压源型换流器的额定电压，可以将多个全控型电力电子器件50串联构成一个全控型电力电子器件50。
电压源型换流器的具体结构还可以采用如图23(b)所示的三电平拓扑结构，主要由12个全控型电力电子器件50，6个钳位二极管53，正极直流母线16，负极直流母线17，正极直流电容52a和负极直流电容52b组成，每两个全控型电力电子器件50串联联接后构成一个‘半桥臂’，每两个‘半桥臂’串联后构成一相换流桥臂，每个‘半桥臂’的中点经钳位二极管53与中性点57相联接，根据需要，中性点57可以为接地点或者一个公共联接点，每相换流桥臂的正端与正极直流母线16相联接，每相换流桥臂的负端与负极直流母线17相联接，每相换流桥臂的中点分别与A相交流端51a，B相交流端51b，C相交流端51c联接，正极直流电容52a的正端联接正极直流母线6，正极直流电容52a的负端接中性点57，负极直流电容52b的正端接中性点57，负极直流电容52b的负端与负极直流母线17相联接，为了提高电压源型换流器的额定电压，每个全控型电力电子器件50可以由多个全控型电力电子器件串联而成，每个钳位二极管53可以由多个钳位二极管串联而成。
电压源型换流器的具体结构还可以采用如图23(c)所示的模块化多电平拓扑结构，主要包括6个半桥臂55，每两个半桥臂55串联成一相桥臂，每相换流桥臂的中点分别与A相交流端51a，B相交流端51b，C相交流端51c联接，每相桥臂的正端和负端分别与正极直流母线16，负极直流母线17相联接，每个半桥臂由多个子模块54依次串联后再和平波电抗器56串联而成，每个子模块可以采用半桥子模块、全桥子模块、箝位双型子模块、自阻子模块等各种已公知的子模块拓扑，图20(c)底部给出了半桥子模块拓扑，每个半桥子模块由两个全控型电力电子器件50和一个子模块电容52构成。
在本发明中，所述不控整流器(1、3或12)是一种公知的交流-直流变换电路，不控整流器主要由二极管通过一定的联接构成。
图24(a)示例了不控整流器的一种拓扑结构，主要由6个二极管21，正极直流母线16，负极直流母线17组成，每两个二极管21串联后构成一相换流桥臂，每相换流桥臂的正端与正极直流母线16相联接，每相换流桥臂的负端与负极直流母线17相联接，每相换流桥臂的中点分别与A相交流端51a，B相交 流端51b，C相交流端51c联接，为了提高不控整流器的额定电压，每个二极管21可以由多个二极管21串联构成。
图24(b)与图24(a)基本一致，区别在于正极直流母线16和负极直流母线17之间联接了直流电容52。
图24(c)示例了不控整流器的另一种拓扑结构，其主要由正极子整流器22a和负极子整流器22b串联而成，22a和22b的交流侧分别经一个三角形/星形联接和星形/星形联接的交流变压器联接在一起从而减小不控整流器直流侧的谐波，根据需要，不控整器的直流侧还可以并联联接直流电容从而降低直流侧谐波，不控整流器的交流侧还可以并联联接无功补偿装置或者交流滤波器。
图25给出了图7所示升压型单向直流-直流自耦变压器的展开拓扑，图25与图7基本一致，区别在于将第一不控整流器1、电压源型换流器2和第二不控整流器3绘制成了详细电路拓扑形式，在第一不控整流器1和第二不控整流器3上串联了直流断路器18，并且电压源型换流器2的交流侧直接联接至交流公共母线5，为简化绘图，电压源型换流器2的每个桥臂以一个半桥子模块示意。
图26给出了与图2对应的降压型单向直流-直流自耦变压器的展开拓扑。图26与图2基本一致，区别在于将第一电压源型换流器11、不控整流器12和第二电压源型换流器13绘制成了详细电路拓扑形式，其中第一电压源型换流器11和第二电压源型换流器13的每个桥臂由半桥子模块54和自阻型子模块44串联而成，为简化绘图，每个桥臂只绘出了一个半桥子模块54和一个自阻型子模块44，同时图26中，不控整流器12的交流侧直接联接至交流公共母线5。
上述各实施例中，可利用单向直流-直流自耦变压器所包含的电压源型换流器控制单向直流-直流自耦变压器的内部交流电压从而控制单向直流-直流自耦变压器所包含的不控整流器整流后的直流电压，进而控制单向直流-直流自耦变压器传输的直流功率，实现对单向直流-直流自耦变压器所传输直流功率的控制。
在一个实施例中，对于降压型单向直流-直流自耦变压器，其直流功率控制过程描述如下。以图2所示降压型单向直流自耦变压器为例，其中E1为第一直 流系统的直流电压，Vdc1～Vdc3分别为第一电压源型换流器11，不控整流器12和第二电压源型换流器13的端口直流电压，Edc为降压型单向直流-直流自耦变压器的高压直流端口电压，E2为第二直流系统8的直流电压，vac为交流公共母线5的交流电压，idc1为输入到第一直流系统7的直流电流，idc2为第二直流系统8输出的直流电流，iDIO2为不控整流器的直流电流。控制中，通过提高vac的幅值即可以提高Vdc2的值，从而提高Vdc2与E1之间的差值，从而提高idc1，提高第二直流系统8向第一直流系统7输出的直流功率。
在一个实施例中，对于升压型单向直流-直流自耦变压器，其直流功率控制过程描述如下。以图7所示升压型单向直流自耦变压器为例，其中E1为第一直流系统的直流电压，Vdc1～Vdc3分别为第一不控整流器1，电压源型换流器2和第二不控整流器3的端口直流电压，Edc为升压型单向直流-直流变的高压直流端口电压，E2为第二直流系统8的直流电压，vac为交流公共母线5的交流电压，idc1为第一直流系统7输出的直流电流，idc2为第二直流系统8吸收的直流电流，iVSC2为第二电压源型换流器的直流电流。控制中，通过提高vac的幅值即可以提高Vdc1和Vdc2的值，从而提高Edc的值，达到提高Edc与E2的差值从而提高idc2的目的，idc2提高后即可提高从第一直流系统7向第二直流系统8传输的直流功率。
对于图2～图6所对应实施例的降压型单向直流自耦变压器，若第一电压源型换流器11和第二电压源型换流器13采用模块化多电平换流器(MMC)结构，通过将第一电压源型换流器11和第二电压源型换流器13的部分子模块替换为可阻断直流故障电流的子模块，如全桥子模块、箝位双子模块、自阻型子模块等，当第二直流系统8发生直流故障时，通过阻断第一电压源型换流器11和第二电压源型换流器13的触发脉冲达到隔离第二直流系统8直流故障的目的。当第一直流系统7发生直流故障时，第二直流系统8的直流电压将施加在第一电压源型换流器11和第二电压源型换流器13上，若第一电压源型换流器11和第二电压源型换流器13的额定耐压不够，通过在第一电压源型换流器11和第二电压源型换流器13的每个桥臂上额外串联半桥子模块可以达到阻断第一 直流系统7直流故障的目的。
对于图7～图12所示的升压型单向直流自耦变压器，第二直流系统8发生直流故障时，第一直流系统7将通过第一不控整流器1、第二不控整流器3向第二直流系统8的直流故障点提供短路电流，为了阻断此故障电流通路，可以在第一不控整流器1和第二不控整流器3上串联直流断路器，第二直流系统8发生直流故障时，通过开断直流断路器达到切断直流故障通路的目的。
对于图7～图12所示的升压型单向直流自耦变压器，第一直流系统7发生直流故障时，第二直流系统8的直流电压将施加在第一不控整流器1和第二不控整流器3上，当第一不控整流器1和第二不控整流器3的耐压不够时，通过提高第一不控整流器1和第二不控整流器3的耐压达到隔离第一直流系统7直流故障的目的。
在一个实施例中，例如对于图7所示的升压型单向直流自耦变压器，记第一直流系统7向第二直流系统8传输的直流功率为PN。如果忽略损耗，可计算得idc1、idc2为，
Figure PCTCN2015096386-appb-000001
流经第二电压源型换流器2的直流电流为
Figure PCTCN2015096386-appb-000002
可进一步得到第二电压源型换流器2的额定功率为：
Figure PCTCN2015096386-appb-000003
同理第可以计算得到第一不控整流器1和第二不控整流器3的额定功率为
Figure PCTCN2015096386-appb-000004
记直流电压变比为k＝E2/E1(k≥1)，式(3)和(4)可进一步化简为：
Figure PCTCN2015096386-appb-000005
Figure PCTCN2015096386-appb-000006
对于图1所示的常规DC-AC-DC型单向直流-直流变换器，其电压源型换流器的换流器容量始终为PN，其不控整流器的换流器容量也始终为PN。图27对比了常规直流-交流-直流变换技术与单向直流-直流自耦变压器技术所使用的电压源型换流器的容量，其中‘DC-AC_DC’曲线代表常规DC-AC-DC技术，‘Unidirectional DC AUTO’代表单向直流-直流自耦变压器技术，‘PVSC/PN’代表电压源型换流器额定功率与额定传输直流功率的比值。可知，在变比k≤5时，单向直流-直流自耦变压器技术所使用的电压源型换流器容量始终小于常规直流-交流-直流变换技术所使用的换流器容量，从而可以大大降低投资成本和运行损耗。
为了对单向直流-直流自耦变压器进行技术可行性验证，本发明在国际公认软件PSCAD/EMTDC上搭建了升压型和降压型单向直流-直流自耦变压器的仿真算例，算例中，第一直流系统7和第二直流系统8的额定直流电压分别为±320kV和±500kV(即E1＝640kV，E2＝1000kV)，额定传输的直流功率为1000MW。
图28-图31为一个实施例中降压型单向直流-直流自耦变压器的仿真结果。优选地，所施加的扰动为，0.2s～0.5s直流功率指令值从0上升为1000MW，2.0s～2.2s直流功率指令值从1000MW下降为0，3.0s～3.2s直流功率进一步从0上升为1000MW，4.0s第一直流系统7施加持续时间0.1s的极对极直流故障，6.0s时第二直流系统8施加极对极直流永久故障。
图28中Pdcref为第二直流系统8向第一直流系统7传输的直流功率指令值，Pdc为实测的直流功率值，可知直流功率实测值能良好地跟踪直流功率指令值。
图29中PVSC1为第一电压源型换流器11逆变的交流功率，PDIO2为不控整流器12整流的交流功率，对比图28和图29可知，单向直流-直流自耦变压器 中的交流功率远远低于直流功率。
图30为单向直流-直流自耦变压器交流电压的标幺值，可知，直流功率上升时，交流电压上升，直流功率下降时，交流电压下降。
图31为第一直流系统7和第二直流系统8的直流电压波形，可知，4.0s，第一直流系统7发生直流故障时，E1降为0，E2基本保持不变，6.0s第二直流系统8发生直流故障时，E2降为0，E1基本保持不变，即升压型单向直流自耦变具备双向直流故障隔离能力。
图32～图35为一个实施例中的升压型单向直流-直流自耦变压器的仿真结果，优选地，所施加的扰动为，0.2s～0.5s直流功率指令值从0上升为1000MW，1.5s～1.7s直流功率指令值从1000MW下降为0，3.0s～3.2s直流功率进一步从0上升为1000MW，4.0s第一直流系统7施加持续时间0.1s的极对极直流故障，5.0s时第二直流系统8施加极对极直流永久故障。
图32中Pdcref为第一直流系统7向第二直流系统8传输的直流功率指令值，Pdc为实测的直流功率值，可知直流功率实测值能良好地跟踪直流功率指令值。
图33中PDIO1为第一不控整流器1整流的交流功率，PVSC2为第二电压源型换流器2逆变的交流功率，对比图32和图33可知，单向直流-直流自耦变压器中的交流功率远远低于直流功率。
图34为单向直流-直流自耦变压器交流电压的标幺值，可知，直流功率上升时，交流电压上升，直流功率下降时，交流电压下降。
图35为第一直流系统7和第二直流系统8的直流电压波形，可知，4.0s，第一直流系统7发生直流故障时，E1降为0，E2基本保持不变，5.0s第二直流系统8发生直流故障时，E2降为0，E1基本保持不变，即升压型单向直流自耦变具备双向直流故障隔离能力。
本领域的技术人员容易理解，以上所述仅为本发明的较佳实施例而已，并不用以限制本发明，凡在本发明的精神和原则之内所作的任何修改、等同替换和改进等，均应包含在本发明的保护范围之内。

Claims (31)

  1. 一种单向直流-直流自耦变压器，用于从高电压等级的第二直流系统向低电压等级的第一直流系统单向传输直流功率，其特征在于，该自耦变压器包括第一电压源型换流器、不控整流器和第二电压源型换流器，其中，
    所述第一电压源型换流器的正极和第二直流系统的正极相联接，第一电压源型换流器的负极和不控整流器的正极相联接，不控整流器的负极和第二电压源型换流器的正极相联接，第二电压源型换流器的负极和第二直流系统的负极相联接，同时所述不控整流器的正极和负极分别与第一直流系统的正极和负极相联接，且所述第一电压源型换流器、不控整流器和第二电压源型换流器的交流侧互联在一起；
    通过利用两电压源型换流器控制单向直流-直流自耦变压器的交流电压从而实现控制从第二直流系统向第一直流系统传输的直流功率。
  2. 一种单向直流-直流自耦变压器，用于互联正极性的不对称单极第一直流系统和正极性的不对称单极第二直流系统，实现从高电压等级的第二直流系统向低电压等级的第一直流系统单向传输直流功率，其特征在于，该自耦变压器包括第一电压源型换流器和不控整流器，其中，
    所述第一电压源型换流器的正极和第二直流系统正极相联接，第一电压源型换流器的负极和不控整流器的正极相联接，不控整流器的负极和第二直流系统的负极相联接，同时所述不控整流器的正极和负极分别与第一直流系统的正极和负极相联接，且第一直流系统的负极、第二直流系统的负极以及不控整流器的负极接地或者通过金属回线接地；
    通过利用电压源型换流器控制单向直流-直流自耦变压器的交流电压从而实现控制从第二直流系统向第一直流系统传输的直流功率。
  3. 一种单向直流-直流自耦变压器，用于互联负极性的不对称单极第 一直流系统和负极性的不对称单极第二直流系统，实现从高电压等级的第二直流系统向低电压等级的第一直流系统单向传输直流功率，其特征在于，该自耦变压器包括不控整流器和第二电压源型换流器，其中，
    所述不控整流器的正极和第二直流系统的正极相联接，不控整流器的负极和第二电压源型换流器的正极相联接，第二电压源型换流器的负极和第二直流系统的负极相联接，同时所述不控整流器的正极和负极分别与第一直流系统的正极和负极相联接，且上述第一直流系统的正极、第二直流系统的正极以及不控整流器的正极接地或者通过金属回线接地；
    通过利用电压源型换流器控制单向直流-直流自耦变压器的交流电压从而实现控制从第二直流系统向第一直流系统传输的直流功率。
  4. 根据权利要求1所述的单向直流-直流自耦变压器，其中，所述不控整流器进一步地由正极子整流器和负极子整流器串联组成，其中所述正极子整流器的负极和负极子整流器的正极相联接，且联接点处接地。
  5. 根据权利要求4所述的单向直流-直流自耦变压器，其中，所述正极子整流器和负极子整流器的联接点还经过金属回线与第一直流系统或第二直流系统的中性点相联接，使得在不对称运行时直流电流经过该金属回线构成回路从而避免直流电流对直流线路上金属管道的腐蚀。
  6. 根据权利要求4或5所述的单向直流-直流自耦变压器，其中，所述第一电压源型换流器的交流侧和正极子整流器的交流侧互联在一起，所述负极子整流器的交流侧和第二电压源型换流器的交流侧互联在一起，两互联的交流联接之间无电气联接。
  7. 根据权利要求1—6中任一项所述的单向直流-直流自耦变压器，其中，所述不控整流器和电压源型换流器的交流侧经过一个两绕组或多绕组的交流变压器互联在一起。
  8. 根据权利要求1—6中任一项所述的单向直流-直流自耦变压器，其中，所述不控整流器和电压源型换流器的交流侧各经过交流变压器或相电 抗器联接至一交流公共母线，或者直接联接至一交流公共母线。
  9. 根据权利要求7或8所述的单向直流-直流自耦变压器，其中，交流公共母线与外部交流电网相联接或者所述两绕组或多绕组的交流变压器与外部交流电网相联接。
  10. 根据权利要求1—9中任一项所述的单向直流-直流自耦变压器，其特征在于，所述电压源型换流器采用模块化多电平换流器拓扑时，其每个桥臂的部分子模块为具备阻断直流故障电流能力的子模块，从而在第二直流系统发生直流故障时可为单向直流-直流自耦变压器提供直流故障隔离。
  11. 根据权利要求1—10中任一项所述的单向直流-直流自耦变压器，其特征在于，当所述电压源型换流器的额定直流电压不够时，在电压源型换流器的每个桥臂上额外串联半桥子模块从而增加所述电压源型换流器的耐压，使得在第一直流系统发生直流故障时可为单向直流-直流自耦变压器提供直流故障隔离，同时使得电压源型换流器不因为承载过电压而损毁。
  12. 一种权利要求1—11中任一项所述的单向直流-直流自耦变压器的高压侧故障隔离方法，其特征为，在所述电压源型换流器采用模块化多电平换流器拓扑时，将所述电压源型换流器的部分子模块替换为可阻断直流故障电流的子模块，使得在所述第二直流系统发生直流故障时，通过闭锁电压源型换流器的全控电力电子器件的触发脉冲隔离第二直流系统的直流故障。
  13. 一种权利要求1—12中任一项所述的直流-直流自耦变压器的低压侧故障隔离方法，其特征为，在第一直流系统发生直流故障时，通过闭锁所述电压源型换流器的全控电流电子器件的触发脉冲，从而隔离第一直流系统的直流故障。
  14. 根据权利要求13所述的低压侧故障隔离方法，其中，在所述电压源型换流器闭锁后的反向耐压之和低于第二直流系统的额定直流电压时，增大所述电压源型换流器的额定直流电压。
  15. 一种单向直流-直流自耦变压器，用于从低电压的第一直流系统向高电压的第二直流系统单向传输直流功率，其特征在于，该自耦变压器包括第一不控整流器、电压源型换流器和第二不控整流器，其中，
    所述第一不控整流器的正极和第二直流系统的正极相联接，第一不控整流器的负极和电压源型换流器的正极相联接，电压源型换流器的负极和第二不控整流器的正极相联接，第二不控整流器的负极和第二直流系统的负极相联接，同时所述电压源型换流器的正极和负极分别与第一直流系统的正极和负极相联接，且所述第一不控整流器、电压源型换流器和第二不控整流器的交流侧互联在一起；
    通过利用电压源型换流器控制单向直流-直流自耦变压器的交流电压从而实现控制从第一直流系统向第二直流系统传输的直流功率。
  16. 一种单向直流-直流自耦变压器，用于互联正极性的不对称单极第一直流系统和正极性的不对称单极第二直流系统，实现从低电压的所述第一直流系统向高电压的所述第二直流系统单向传输直流功率，该自耦变压器包括第一不控整流器和电压源型换流器，其中，
    所述第一不控整流器的正极和直流系统正极相联接，第一不控整流器的负极和电压源型换流器的正极相联接，电压源型换流器负极和第二直流系统的负极相联接，同时所述电压源型换流器的正极和负极分别与第一直流系统的正极和负极相联接，且第一直流系统的负极、第二直流系统负极和电压源型换流器的负极接地或经过金属回线接地；
    通过利用电压源型换流器控制单向直流-直流自耦变压器的交流电压从而实现控制从第一直流系统向第二直流系统传输的直流功率。
  17. 一种单向直流-直流自耦变压器，用于互联负极性的不对称单极第一直流系统和负极性的不对称单极第二直流系统，实现从低电压的所述第一直流系统向高电压的所述第二直流系统单向传输直流功率，该自耦变压器包括电压源型换流器和第二不控整流器，其中，
    所述电压源型换流器的正极和第二直流系统的正极相联接，电压源型换流器的负极和第二不控整流器的正极相联接，第二不控整流器的负极和第二直流系统的负极相联接，同时所述第电压源型换流器的正极和负极分别与第一直流系统的正极和负极相联接，且第一直流系统的正极、第二直流系统的正极以及电压源型换流器的正极直接接地或者经过金属回线接地；
    通过利用电压源型换流器控制单向直流-直流自耦变压器的交流电压从而实现控制从第一直流系统向第二直流系统传输的直流功率。
  18. 根据权利要求15所述的单向直流-直流自耦变压器，其中，所述电压源型换流器进一步地由正极子换流器和负极子换流器串联组成，其中所述正极子换流器的负极和负极子换流器的正极相联接，且联接点处接地。
  19. 根据权利要求18所述的单向直流-直流自耦变压器，其中，所述正极子换流器和负极子换流器的联接点还经过金属回线与第一直流系统或第二直流系统的中性点相联接，使得在不对称运行时直流电流经过该金属回线构成回路从而避免直流电流对直流线路上金属管道的腐蚀。
  20. 根据权利要求18或19所述的单向直流-直流自耦变压器，其中，所述第一不控整流器的交流侧和正极子换流器的交流侧互联在一起，所述负极子换流器的交流侧和第二不控整流器的交流侧互联在一起，两互联的交流联接之间无电气联接。
  21. 根据权利要求15—20中任一项所述的单向直流-直流自耦变压器，其中，所述不控整流器和电压源型换流器的交流侧经过一个两绕组或多绕组的交流变压器互联在一起。
  22. 根据权利要求15—20中任一项所述的单向直流-直流自耦变压器，其中，所述不控整流器和电压源型换流器的交流侧各经过交流变压器或相电抗器联接至一交流公共母线，或者直接联接至一交流公共母线。
  23. 根据权利要求21或22所述的单向直流-直流自耦变压器，其中，交流公共母线与外部交流电网相联接或者所述两绕组或多绕组的交流变压器与外部交流电网相联接。
  24. 根据权利要求15-23中任一项所述的单向直流-直流自耦变压器，其特征在于，在所述不控整流器上串联了直流断路器，从而可在第二直流系统发生直流故障时为单向直流-直流自耦变压器提供直流故障隔离。
  25. 根据权利要求15-24中任一项所述的单向直流-直流自耦变压器，其特征在于，在所述不控整流器闭锁后的反向耐压之和低于第二直流系统的直流电压时，可额外增加所述不控整流器的额定直流电压，从而在第一直流系统发生直流故障时为单向直流-直流自耦变压器提供直流故障隔离，同时使得所述不控整流器不因为承载过电压而损毁。
  26. 一种权利要求15-25中任一项所述的单向直流-直流自耦变压器的高压侧故障隔离方法，其特征为，在所述不控整流器上串联直流断路器，当高压侧发生直流故障时，通过开断所述直流断路器来隔离高压侧直流故障。
  27. 一种权利要求15-26中任一项所述的单向直流-直流自耦变压器的低压侧故障隔离方法，其特征为，在低压侧发生直流故障时，闭锁电压源型换流器的触发脉冲隔离低压侧直流故障。
  28. 根据权利要求27所述的直流-直流自耦变压器的低压侧故障隔离方法，其中，在所述不控整流器的反向耐压不够时，可额外提高不控整流器的额定直流电压。
  29. 根据权利要求1-28中任一项所述的单向直流-直流自耦变压器，其特征在于，所述的电压源型换流器可以采用模块化多电平换流器、两电平换流器、三电平换流器等各种电压源型换流器拓扑。
  30. 根据权利要求1-29中任一项所述的单向直流-直流自耦变压器，其特征在于，所述的不控整流器可以采用多个不控整流器串联而成，并经过 一定的组合降低谐波。
  31. 根据权利要求1—30中任一项所述的单向直流-直流自耦变压器，其特征在于，所述的不控整流器、电压源型换流器的交流侧可以采用单相、两相、三相或多相交流电路。
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