WO2015014123A1 - 一种立体式直流-直流变换器与网间联络器 - Google Patents

一种立体式直流-直流变换器与网间联络器 Download PDF

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Publication number
WO2015014123A1
WO2015014123A1 PCT/CN2014/072498 CN2014072498W WO2015014123A1 WO 2015014123 A1 WO2015014123 A1 WO 2015014123A1 CN 2014072498 W CN2014072498 W CN 2014072498W WO 2015014123 A1 WO2015014123 A1 WO 2015014123A1
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Prior art keywords
converter
grid
dimensional
rated
voltage
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PCT/CN2014/072498
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English (en)
French (fr)
Inventor
林卫星
文劲宇
程时杰
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华中科技大学
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Application filed by 华中科技大学 filed Critical 华中科技大学
Priority to US14/412,002 priority Critical patent/US9755523B2/en
Priority to EP14833033.5A priority patent/EP2975721A4/en
Publication of WO2015014123A1 publication Critical patent/WO2015014123A1/zh

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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
    • H02M3/33507—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
    • 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
    • H02J1/102—Parallel operation of dc sources being switching converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/66—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal
    • H02M7/68—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters
    • H02M7/72—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/75—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means
    • H02M7/757—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only
    • H02M7/7575—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only for high voltage direct transmission link
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/66—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal
    • H02M7/68—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters
    • H02M7/72—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/79—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/797—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • 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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0095—Hybrid converter topologies, e.g. NPC mixed with flying capacitor, thyristor converter mixed with MMC or charge pump mixed with buck
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/4835—Converters with outputs that each can have more than two voltages levels comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/49—Combination of the output voltage waveforms of a plurality of converters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

Definitions

  • the invention belongs to the technical field of flexible transmission and distribution of power systems, and particularly relates to a DC-DC converter, which is suitable for interconnection of DC grids in various regions.
  • the traditional DC-DC converters generally use DC/AC/DC two-stage AC/DC conversion topology (Wang Peibo et al.) to improve the voltage stability of the renewable energy generation system.
  • Converter Research (Journal of North China Electric Power University, 2009, 36 (5), 22 ⁇
  • the specific embodiment is to construct two converters, the DC ends of the two converters are respectively connected to the first DC grid and the second DC grid to be interconnected (here, the rated DC voltage of the first DC grid is lower than the second DC grid)
  • the DC terminal of the rated DC voltage of the network is connected, and the AC terminals of the two inverters are interconnected by a certain AC circuit.
  • the converter performs DC/AC conversion to invert the DC power of the first DC grid to AC power
  • the inverter 2 performs AC/DC conversion to re-rect the power converted by the first DC grid to DC feed.
  • To the second DC grid To the second DC grid.
  • a notable feature of the above-mentioned conventional DC-DC converters is that there is no direct electrical interconnection between the DC terminals of the two converters, so there is no direct electrical interconnection between the two DC grids, and the two DC grids pass through the intermediate exchange.
  • the circuits are interconnected. So, first of all, this DC-DC
  • the rated DC voltage of the converter 1 and the converter 2 of the converter are equal to the rated DC voltages of the first DC grid and the second DC grid, respectively, so that the inverter 2 does not fully utilize the DC voltage already existing in the first DC grid. Inverter 2 has a high rated DC voltage, resulting in high cost.
  • the rated power of the converter 1 and the inverter 2 used in the above conventional DC-DC converter is equal to the interconnection power between the first DC grid and the second DC grid, and the sum of the converter capacities is the first DC.
  • the power interconnected by the converter needs to undergo two levels of full AC/DC (or DC/AC) conversion, power loss.
  • the sum of the capacity of the interconnected AC circuit is twice the interconnect power, and the investment in interconnecting AC circuit transformers, phase reactance, etc. is large.
  • the present invention provides a three-dimensional DC-DC converter, which fully utilizes the first The already existing DC voltage of the DC grid, on the DC side, a certain degree of direct electrical interconnection between the first DC grid and the second DC grid, so that part of the power transmitted between the first DC grid and the second DC grid can be transmitted without DC/ The AC/DC conversion is transmitted directly through the electrical interconnection between the first DC grid and the second DC grid.
  • a stereo DC-DC converter for interconnecting transmission between two DC power grids characterized in that the converter comprises a first converter a second converter and a third converter, wherein a positive pole of the first converter is connected to a positive pole of the second DC grid, and a cathode of the first converter and a second converter
  • the positive pole is connected
  • the cathode of the second converter is connected to the anode of the third converter
  • the cathode of the third converter is connected to the cathode of the second DC grid
  • the anode of the second converter is simultaneously a positive pole of the first direct current grid is connected, and a cathode of the second converter At the same time, it is connected to the negative pole of the first DC grid.
  • the AC side of the first converter, the second converter and the third converter are interconnected on the AC side through a transformer branch or a phase reactance branch, and the interconnection point of the AC side is AC bus bar.
  • the ports of the first converter and the third converter of the alternating current transformer near the direct current side adopt a delta connection manner to eliminate the neutral point imbalance problem of the first converter and the third converter.
  • the transformer of the second converter is close to the port on the DC side and the ports of the first converter and the third converter near the side of the AC bus can be connected in a star or delta connection.
  • first converter and the third converter are used to control respective active powers
  • the second converter is used to control the AC voltage of the AC common bus, thereby realizing stable operation of the stereo DC-DC converter.
  • first converter and the third converter are used for controlling an AC voltage of an AC common bus
  • the second converter is configured to control interconnection power between the first DC grid and the second DC grid, thereby realizing Stable operation of the three-dimensional DC-DC converter.
  • first converter and the third converter are connected to the AC bus through the phase reactance, and the phase reactance of each phase adopts a delta connection to eliminate the first converter, and the third converter neutral point unbalanced.
  • first DC power grid and the second DC power grid are formed by interconnecting one or more AC systems on the DC side after AC/DC conversion.
  • first DC power grid and the second DC power grid are formed by interconnecting one or more AC systems with an AC system that outputs DC power on the DC side after AC/DC conversion.
  • AC common bus is also interconnected with an external AC grid.
  • first converter, the second converter and the third converter are respectively connected to different AC grids.
  • the first The rated DC voltage of the converter and the third converter is designed to be 1/2 of the difference between the rated DC voltage of the second DC grid and the first DC grid, the rated DC voltage of the second converter and the first DC grid
  • the rated DC voltage is equal
  • the rated power of the first converter and the third converter is 0.5*P*(1-E1/E2)
  • the rated power of the second converter is P*(1) -E1/E2), where P is the rated exchange power between the first DC grid and the second DC grid
  • E1 is the rated DC voltage of the first DC grid (rated anode to cathode voltage)
  • E2 is the second DC grid Rated DC voltage
  • the above rated DC voltage and rated power are design reference values. In actual use, appropriately increasing or decreasing the rated value based on the above reference value can still make the DC-DC converter operate.
  • the rated DC voltage of the second converter Equal to the rated DC voltage of the first DC grid
  • the rated DC voltage of the first converter and the third converter is half of the difference between the rated DC voltage of the second DC grid and the rated DC voltage of the first DC grid
  • the first commutation The rated power of the second converter and the third converter can be designed as needed.
  • the above rated DC voltage is the design reference value. In actual use, the rated value is increased or decreased according to the above reference value. Enables the DC-DC converter to operate.
  • first DC grid and the second DC grid may adopt various structures such as a symmetric bipolar, a symmetrical monopole, an asymmetric monopole, and an asymmetric bipolar.
  • the first converter and the third converter adopt a thyristor-based phase-controlled converter technology, and the second converter still uses a voltage source type inverter, and when the topology is used, the DC The power can only be transmitted from the first DC grid to the second DC grid in one direction or from the second DC grid to the first DC grid in a single phase.
  • the present invention also provides a DC-DC converter that optimizes the installation position of the DC circuit breaker, characterized in that a first line is connected in series between the negative pole of the first converter and the anode of the second converter.
  • a DC circuit breaker, a second DC circuit breaker is connected in series between the negative pole of the second converter and the anode of the third converter, and the DC circuit breaker is installed in the above position, and is sent in the second DC grid
  • the first DC grid does not provide a fault current to the second DC grid.
  • the first DC breaker and the second DC converter are combined with the first converter and the third converter.
  • the inverters are connected in series to share the voltage of the second DC grid, so that the first converter and the third converter are not burned due to overvoltage.
  • the rated DC voltages of the first DC circuit breaker and the second DC circuit breaker are designed to be half of the rated DC voltage of the second converter, and the rated current design of the first DC circuit breaker and the second DC circuit breaker
  • the above design values are reference values, and can be appropriately increased or decreased according to the reference value in actual use.
  • the present invention further provides a method for protecting a DC-DC converter in a DC fault when a DC fault occurs in the second DC power grid, specifically, when the DC fault occurs in the second DC power grid, the first converter is blocked.
  • a trigger pulse of the fully-controlled power electronic device (or thyristor) of the second converter and the third converter, thereby cutting off the first converter, and the second converter and the third converter pass respective control Type power electronic device (or thyristor) provides a path of DC fault current to the fault point of the second DC grid, and at the same time, disconnects the first DC breaker and the second DC breaker to cut off the first DC grid through the first exchange
  • the diodes of the current transformer and the third converter provide a path for DC fault current to the second DC grid fault point.
  • the present invention further provides a method for protecting a three-dimensional DC-DC converter in a DC fault of a first DC power grid, specifically, when detecting a DC fault in the first DC power grid, blocking the first converter a trigger pulse of the fully-controlled power electronic device (or thyristor) of the second converter and the third converter, thereby cutting off the first converter, and the second converter and the third converter pass respective electric power
  • the controlled power electronic device (or thyristor) provides a DC fault current to the first DC grid fault point, and at the same time, opens the first DC breaker and the second DC breaker so that the voltage of the second DC grid is applied to a series circuit formed by an inverter, a first DC circuit breaker, a second DC circuit breaker and a third converter, preventing the first converter and the third converter from directly accommodating the DC of the second DC grid An overvoltage occurs due to the voltage, and the first converter and the third converter are burned.
  • the converter of the present invention has the following technical effects as compared with the prior art:
  • the sum of the capacities of the inverters required for the first to third converters of the present invention is 2P*(1-E1/E2), and the sum of the inverter capacities used in the conventional DC-DC converter is 2P, that is, twice the communication power between the networks, the sum of the inverter capacities used in the present invention is smaller than that of the conventional DC-DC converter, and the present invention can greatly save the converter cost.
  • the power interconnected by the converter of the present invention is only P*(1-E1/E2) interconnect power needs to be converted by two-stage AC/DC (or DC/AC), and the remaining interconnect power of ⁇ * ⁇ 1/ ⁇ 2 It can be directly transmitted through the electrical interconnection between the first DC grid and the second DC grid, and all interconnected power ports of the conventional DC-DC converter need to undergo a two-stage AC/DC (or DC/AC) conversion.
  • the power loss of the converter is lower than that of the conventional DC-DC converter, which greatly reduces the running cost.
  • the total capacity of the interconnected AC circuit in the present invention is 2 ⁇ *(1- ⁇ 1/ ⁇ 2), and the total capacity of the conventional DC-DC converter interconnecting AC circuit is 2 ⁇ , so that the present invention can greatly save the interconnected AC circuit. cost.
  • FIG. 1 is a schematic structural diagram of a three-dimensional DC-DC converter according to an embodiment of the present invention
  • FIG. 2 is a schematic diagram of a topology of a DC-DC converter in the prior art
  • FIG. 3 is a topological schematic diagram of a first inverter and a third inverter connected to an alternating current common bus through a phase connection of a delta connection according to another embodiment of the present invention
  • 4 is a schematic diagram of an AC common busbar connected to an AC power grid according to still another embodiment of the present invention
  • FIG. 5 is a schematic diagram of a first DC power grid interconnected by multiple AC power grids after AC/DC conversion on a DC side according to still another embodiment of the present invention; DC grid;
  • FIG. 6 is a DC power grid formed by further paralleling a DC grid between a DC grid and a DC grid by a plurality of AC grids after AC/DC conversion according to a fifth embodiment of the present invention
  • FIG. 7 is a first converter according to a sixth embodiment of the present invention, where the second converter and the third converter are respectively disconnected from the AC power grid;
  • the third converter adopts a phase-controlled inverter, and the second converter still uses a voltage source type inverter, and the power can only be unidirectionally a DC power grid flows to the second DC power grid to transmit power;
  • FIG. 9 is a first converter according to an eighth embodiment of the present invention, the third converter adopts a phase-controlled inverter, and the second converter still uses a voltage source type inverter, and the power can only be unidirectionally from the first The two DC power grids transmit power to the first DC power grid;
  • the third converter uses a voltage source type inverter
  • the second converter uses a phase-controlled inverter, and the power can only be unidirectionally from the first
  • the DC power grid flows to the second DC power grid to transmit power
  • 11 is a first converter according to a tenth embodiment of the present invention, wherein the third converter adopts an uncontrolled rectifier bridge, and the second converter uses a voltage source type inverter;
  • FIG. 12 is a first DC circuit breaker connected in series between a first converter negative pole and a second converter positive pole according to an eleventh embodiment of the present invention, between a second converter negative pole and a third converter positive pole a second DC circuit breaker is connected in series;
  • Figure 13 is a verification of the present invention built in the industry common simulation software PSCAD/EMTDC
  • the three-dimensional DC-DC converter provided by the embodiment of the present invention is used for interconnecting two DC power grids with different rated DC voltages, which can solve the current commutation caused by the conventional DC-DC converter with DC/AC/DC conversion.
  • the three-dimensional DC-DC converter is composed of a first converter 1, a second converter 2 and a third inverter 3, and the anode of the first converter 1 passes through a DC line 6 and a second
  • the anode of the DC power grid 9 is connected, the cathode of the first converter 1 is connected to the anode of the second converter 2, and the cathode of the second converter 2 is connected to the anode of the third converter 3, and the third The anode of the converter 3 is connected to the cathode of the second DC grid 9 via the DC line 6.
  • the anode and cathode of the second converter 2 are also connected to the anode and cathode of the first DC grid 8 via the DC line 6, respectively.
  • the AC terminal of the first converter 1 is connected to the AC common master 7 via a transformer 4, the AC terminal of the second converter 2 is connected to the AC common bus 7 via a transformer 5, and the AC terminal of the third converter 3 is passed through a transformer 4.
  • the inverter can be optionally configured with a voltage source type inverter known in the art to achieve bidirectional flow of power.
  • the first DC grid 8 and the second DC grid 9 are preferably both bipolar symmetrical DC systems, for which the transformer 4 is in a star/delta connection to eliminate the first converter 1 and
  • the neutral point imbalance problem of the third converter 3 the transformer 5 can be in the form of any wiring of a star/star connection or a star/delta connection.
  • a preferred control method is to cause the second converter 2 to control the AC voltage of the AC common bus 7, and the first converter 1 and the third converter 3 are Used to control the active power of the respective transmission.
  • the design of the rated DC voltage and rated power of the first converter 1, the second converter 2 and the third converter 3 are analyzed below. Recording the rated DC voltage of the first DC grid 8 and the second DC grid 9 They are El and E2 respectively, where the rated DC voltage refers to the rated positive to negative voltage, and the measured points of E1 and E2 are shown in Figure 1.
  • the DC current output from the first DC grid 8 is il, and the DC current input from the second DC grid 9 is DC.
  • the total capacity of the three inverters is 2*(1-E1/E2)*P.
  • the total capacity of the three converters is always less than 2* ⁇ , and the closer El and ⁇ 2 are The smaller the total capacity of the three inverters.
  • Equal to P which is equal to the rated switching power of the first DC grid 8 and the second DC grid 9, and the conventional DC-DC converter using the DC/AC/DC converter requires a total commutation capacity of 2*P.
  • the cost is much higher than the stereo DC-DC converter.
  • Figure 2 shows a conventional conventional DC-DC converter topology.
  • the conventional DC-DC converter is interconnected by the inverter 10 and the inverter 11 through the internal AC circuit 12.
  • Fig. 1 and Fig. 2 we can obtain the following differences:
  • the two DC grids are 9-phase connected, wherein the internal AC circuit 12 employs an AC transformer 19 to connect the AC circuit between the inverter 10 and the inverter 11, and the connection formed by the AC transformer 16 is referred to as magnetic coupling rather than direct electrical connection.
  • the first DC grid 8 in the three-dimensional DC-DC converter transmits power to the second DC grid 9 except for the AC circuit formed by 4, 5, 7 It is also possible to transmit power through the direct electrical connection of the first converter 1 and the third converter 3, for which the total converter capacity used for the three-dimensional DC-DC converter is smaller than the first DC grid and the second
  • the interconnect power between DC grids is twice that of a conventional DC-DC converter, and the total converter capacity required for a conventional DC-DC converter is always twice the interconnect power.
  • FIG. 3 shows another embodiment of the present invention.
  • FIG. 3 is similar to FIG. 1 except that the first inverter 1 and the third inverter 3 are not connected to the common common bus 7 via a transformer, but through a triangle.
  • the connected phase reactance 13 and the conventional phase reactance 16 are then connected to the alternating common busbar 7. Since the phase reactance cannot realize the boost/buck function of the AC voltage, the embodiment of FIG. 3 requires that the AC voltage of the AC common bus 7 is substantially the same as the AC voltage output by the first converter 1 and the third converter 3, but The output AC voltage amplitude of the second converter 2 does not necessarily coincide with the amplitude of the AC voltage output by the first converter 1 and the third converter 3, so in the scheme of FIG.
  • the second converter 2 Still connected to the common bus 7 through the transformer 5, so that the amplitude of the output AC voltage of the second converter 2 is passed through the boost/buck function of the transformer 5 and the first converter 1 and the third converter 3
  • the AC voltage amplitude is the same.
  • Fig. 4 shows a further embodiment of the invention.
  • Fig. 4 is substantially similar to Fig. 1, with the difference that the AC common busbar 7 is also connected to the AC grid 14.
  • FIG. 5 shows still another embodiment of the present invention.
  • FIG. 5 is substantially similar to FIG. 4, with the difference that FIG. 5 shows an implementation of the first DC grid, that is, a plurality of AC grids 14 via the inverter 15 After AC/DC conversion, they are interconnected on the DC side.
  • the first DC grid that is, a plurality of AC grids 14 via the inverter 15 After AC/DC conversion, they are interconnected on the DC side.
  • Figure 6 shows a further embodiment of the invention in which the first DC grid 8 is interconnected by a plurality of different AC grids 14 via an AC/DC converter of the converter 15 and then interconnected with the DC grid 18 on the DC side.
  • the second DC grid 9 can be constructed in a similar manner.
  • Fig. 7 shows a further embodiment of the invention, in which the alternating currents of the first converter 1, the second converter 2 and the third converter 3 are connected to different alternating current grids 14, respectively.
  • Figure 8 shows a further embodiment of the invention, in which the first converter 1 and the third converter 3 use a phase-controlled converter instead of a voltage source converter, in this embodiment, the power It can only flow to the second DC grid 9 through the first DC grid 8 and is suitable for the interconnection of two DC grids that only require one-way power exchange, since the rated voltage of the phase-controlled converter is currently much higher than that of the voltage source type. The rated voltage of the device, and the cost of the phase-controlled converter of the same rated power and the same rated voltage is lower than that of the voltage source converter.
  • the power can be transmitted from the first DC grid 8 to the lower cost at a lower cost.
  • the second DC grid 9 the phase-controlled converter is a thyristor-based converter, the technical details of which are well-known in the industry, and are not described herein.
  • FIG. 9 shows still another embodiment of the present invention, which is similar to FIG. 8 except that the wiring of the first converter 1 and the third inverter 3 is the same as that of the first converter 1 of FIG. In contrast to the wiring of the third converter 3, in the embodiment of Fig. 9, the power can only be transmitted unidirectionally from the second DC grid 9 to the first DC grid 8.
  • Figure 10 shows a further embodiment of the invention, which is similar to Figure 8, except that the first converter 1 and the third converter 3 employ a voltage source converter and a second converter. 2 Use a phased inverter.
  • FIG 11 shows still another embodiment of the present invention, wherein the second converter 2 uses a voltage source type inverter, and the first converter 1 and the third converter 3 adopt an uncontrolled rectifier bridge, which is not controlled.
  • the rectifier bridge is common knowledge in the industry, and its technical details are not described.
  • the advantage of this embodiment is that the cost of the first converter 1 and the third converter 3 can be greatly saved and the first converter 1 and the third can be improved.
  • the reliability of the inverter 3 is disadvantageous in that the control performance is poor.
  • Figure 12 shows a further embodiment of the invention in which a first DC breaker 20 is connected in series between the cathode of the first converter 1 and the anode of the second converter 2, the second converter 2 A second DC circuit breaker 25 is connected in series between the negative electrode and the positive electrode of the third converter 3.
  • the first converter 1, the second converter 2 and the third converter 3 employ a half bridge type modular multilevel converter.
  • the half bridge type modular multilevel converter is a voltage source type inverter known in the art, and its technical details will not be described again.
  • the technology for DC circuit breakers can be referred to (JtjRGEN HAFNER, BJORN JACOBSON "Proactive Hybrid HVDC Breakers - A key innovation for reliable HVDC grids", CIGRE 2011 Bologna Symp., Bologna, Italy, paper 264, Sep. 2011. ).
  • the embodiment of the invention indicates the optimal installation position of the DC circuit breaker, that is, the first DC circuit breaker 20 is installed between the first converter 1 and the second inverter 2, and the second DC circuit breaker 25 is installed at the Between the two converters 2 and the third converter.
  • the first change can be prevented by blocking the trigger pulses of the fully-controlled power electronics 26 of the first converter 1, the second converter 2 and the third converter 3
  • the streamer 1, the second converter 2 and the third converter 3 provide a DC fault current to the fault point of the second DC grid 9 through the respective fully-controlled power electronics 26, while simultaneously breaking the first straight
  • the flow breaker 20 and the second DC breaker 25 thereby shut off the first DC grid to provide a path for DC fault current to the second DC grid fault point through the diodes 27 of the first converter 1 and the third converter 3.
  • the first change can be prevented by blocking the trigger pulses of the fully-controlled power electronics 26 of the first converter 1, the second converter 2 and the third converter 3
  • the flow converter 1, the second inverter 2 and the third inverter 3 provide a DC fault current to the fault point of the first DC grid 8 through the respective fully-controlled power electronics 26, and at the same time, break the first straight
  • the flow breaker 20 and the second DC breaker 25 thereby cause the voltage of the second DC grid to be applied to the first converter 1, the first DC breaker 20, the second DC breaker 25 and the third inverter 3
  • the first converter 3 and the third converter 3 are prevented from overvoltage due to the DC voltage of the second DC grid 9 alone, and the first converter 1 and the third converter 3 are burned.
  • the rated DC current of the circuit breaker 25 is designed as (P/E1-P/E2).
  • the first converter 1 and the third converter 3 are The voltages that can be withstood by the respective fully-controlled power electronics are (E2-E1) /2, and the rated voltage of the second DC grid 9 is E2, in order to ensure the first converter 1 and the third converter 3
  • E1 the voltages that can be withstood by the respective fully-controlled power electronics
  • E2 the rated voltage of the second DC grid 9
  • the rated voltage of the first DC breaker 20 and the second DC breaker 25 is recommended to be El/2.
  • the first DC circuit breaker 20 and the second DC circuit breaker 25 only need to have the ability to break the DC fault current when the DC fault occurs in the second DC grid, the first DC breaker 20 and the second DC breaker 25 are recommended.
  • the one-way circuit breaker shown in Fig. 12 is selected to reduce the cost of the circuit breaker.
  • the one-way circuit breaker only needs to cut off the DC fault current supplied by the first DC grid 8 to the second DC grid 9 when the DC fault occurs in the second DC grid 9 , and when the DC fault occurs in the first DC grid 8 , the first lock is achieved.
  • the first inverter 1 in FIG. 12 the one or two inverters of the second converter 2 or the third converter 3 use a phase-controlled converter or an uncontrolled rectifier bridge, the positional configuration of FIG.
  • the first DC circuit breaker 20 and the second DC circuit breaker 25 can still realize that when the DC fault occurs in the second DC power grid 9, the first inverter 1 and the third inverter 3 are prevented from flowing through the overcurrent and burned.
  • FIG. 13 is built in the international general electromagnetic transient simulation software PSCAD/ETMDC, and the rated DC voltage of the first DC grid 8 is ⁇ 320 kV, and the second DC grid 9 The rated DC voltage is ⁇ 640kV and the interconnection power between the two DC grids is 2000MW.
  • Figure 14 shows the corresponding simulation results. At 0.2 to 0.7 seconds, the power delivered by the second DC grid 9 to the first DC grid 8 is increased from 0 MW to 2000 MW, and power reversal occurs at 1.0 second, and 2000 MW of power is delivered from the first DC grid 8 to the second DC grid 9.
  • Figure 14 shows that the present invention enables power transfer of two interconnected DC grids.
  • Figure 13 also shows The absolute values of the active power transmitted by the first converter 1 (VSC1), the second converter 2 (VSC2) and the third converter 3 (VSC3) at steady state are 499.7 MW, 999.5 MW and 499.7, respectively. MW.
  • VSC1 the first converter 1
  • VSC2 the second converter 2
  • VSC3 the third converter 3
  • the sum of the power of the three converters is about 2000 MW, which is equal to the interconnection power, while the conventional DC-DC converter requires a total of 4000 MW of converters.
  • the first converter 1, the second converter 2 and the third converter 3 preferably use a voltage source type converter to achieve bidirectional flow of power, and the voltage source type converter is well known in the art. It can have multiple topologies such as two-level inverters, three-level inverters, and modular multi-level inverters.
  • the total converter capacity required is less than 2 times the interconnect power, while the conventional DC-DC converter requires a total commutation capacity of 2 times the interconnect power, so the present invention is compared to the present There are techniques that can greatly reduce the capacity of the converters required.
  • the cost per inverter of 1 GW is 110 million Euros.
  • a typical ⁇ 320kV DC grid and a ⁇ 640kV DC grid are interconnected.
  • Each connected DC power is 1GW.
  • the DC-DC converter can save 1GW of converter capacity, and the current DC grid capacity in China and worldwide needs to be hundreds of GW, so the economics of the invention.
  • the traditional DC-DC converter is quite obvious.

Abstract

一种立体式直流-直流变换器，用于实现两直流电网之间的互联传输，其中该变换器包括第一换流器（1）、第二换流器（2）和第三换流器（3）,其中，所述第一换流器（1）的正极与第二直流电网（9）的正极相连接，所述第一换流器（1）的负极与第二换流器（2）的正极相连接，第二换流器（2）的负极与第三换流器（3）的正极相连接，第三换流器（3）的负极与第二直流电网（9）的负极相连接，所述第二换流器（2）的正极同时和第一直流电网（8）的正极相连接，所述第二换流器（2）的负极同时和第一直流电网（8）的负极相连接；该直流-直流变换器充分利用了第一直流电网（8）已经存在的直流电压，相比于常规的直流/交流/直流形式的直流-直流变换器，其可以大大减少所使用的总的换流器容量从而减小成本和损耗。

Description

一种立体式直流 -直流变换器与网间联络器
【技术领域】
本发明属于电力系统柔性输配电技术领域， 具体涉及一种直流-直流变 换器， 适用于各个区域直流电网的互联。
【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。 为了互联不同额定直流电压的直流电网， 需要采用直流-直流变换器。 在配电网层面， 直流微网也是目前的技术热点之一， 互联不同额定直流电 压的直流微网也需要用到直流-直流变换器。
在输电网层面上，传统的直流 -直流变换器一般采用直流 /交流 /直流两级 交 /直变换的拓扑 （王培波等 "用于提高可再生能源发电系统电压稳定性的 双向 DC/AC/DC变换器研究" （华北电力大学学报， 2009， 36 (5 ) ， 22〜
26) ) 。 其具体实施方式为建设两个换流器， 两个换流器的直流端分别与 待互联的第一直流电网和第二直流电网 （此处记第一直流电网的额定直流 电压低于第二直流电网的额定直流电压） 的直流端连接， 两个换流器的交 流端通过一定的交流电路互联在一起。 换流器一进行直流 /交流变换从而把 第一直流电网的直流电逆变为交流电， 换流器二再进行交流 /直流变换从而 把第一直流电网逆变后的电能再重新整流成直流电馈入到第二直流电网。
上述传统的直流 -直流变换器的一个显著特点是两个换流器的直流端没 有直接的电气互联， 因此两个直流电网之间没有直接的电气互联， 两个直 流电网是通过了中间的交流电路互联在一起。 这样， 首先， 这种直流 -直流 变换器的换流器一和换流器二的额定直流电压分别与第一直流电网和第二 直流电网的额定直流电压相等， 使得换流器二没有充分利用第一直流电网 已经存在的直流电压， 换流器二的额定直流电压高从而导致成本高。 其次， 上述传统直流 -直流变换器的所采用换流器一与换流器二的额定功率与第一 直流电网和第二直流电网之间的互联功率相等， 换流器容量总和为第一直 流电网和第二直流电网之间的互联功率的 2倍， 导致换流器成本高； 再次， 该变换器所互联的功率需要经过两级全额交流 /直流 （或直流 /交流） 变换， 功率损耗大； 另外， 互联交流电路的容量总和为互联功率的两倍， 互联交 流电路变压器， 相电抗等的投资大。
【发明内容】
为了改进上述传统直流 -直流变换器存在的缺点，降低直流 -直流变换器 总的变流容量从而降低成本， 降低损耗， 本发明提供了一种立体式直流-直 流变换器， 其充分利用第一直流电网已经存在的直流电压， 在直流侧对第 一直流电网和第二直流电网进行一定程度的直接电气互联， 使得第一直流 电网和第二直流电网之间传输的部分功率可以无需经过直流 /交流 /直流变 换， 而是直接经过第一直流电网和第二直流电网之间的电气互联进行传输。 为实现本发明的上述目的， 采用的具体技术方案如下： 一种立体式直流-直流变换器， 用于实现两直流电网之间的互联传输， 其特征在于， 该变换器包括第一换流器、 第二换流器和第三换流器， 其中， 所述第一换流器的正极与第二直流电网的正极相连接， 所述第一换流 器的负极与第二换流器的正极相连接， 第二换流器的负极与第三换流器的 正极相连接， 第三换流器的负极与第二直流电网的负极相连接， 所述第二 换流器的正极同时和第一直流电网的正极相连接， 所述第二换流器的负极 同时和第一直流电网的负极相连接。
更进一步地， 所述第一换流器， 第二换流器和第三换流器的交流侧通 过变压器支路或相电抗支路在交流侧互联在一起， 该交流侧的互联点为交 流母线。
更进一步地， 所述第一换流器和第三换流器的交流变压器靠近直流侧 的端口采用三角形接线方式， 以消除第一换流器和第三换流器中性点不平 衡问题， 所述第二换流器的变压器靠近直流侧的端口以及第一换流器和第 三换流器靠近交流母线侧的端口可以采用星形或三角形接线。
更进一步地， 所述第一换流器和第三换流器用于控制各自的有功功率 而第二换流器用于控制交流公共母线的交流电压， 从而实现立体式直流-直 流变换器的稳定运行。
更进一步地， 所述第一换流器和第三换流器用于控制交流公共母线的 交流电压， 第二换流器用于控制第一直流电网和第二直流电网之间的互联 功率， 从而实现立体式直流 -直流变换器的稳定运行。
更进一步地， 所述第一换流器和第三换流器通过相电抗连接到交流母 线， 每相相电抗采用三角接线方式以消除该第一换流器， 第三换流器中性 点不平衡。
更进一步地， 所述第一直流电网以及第二直流电网是一个或多个交流 系统经过交流 /直流变换后在直流侧互联构成的。
更进一步地， 所述第一直流电网以及第二直流电网是一个或多个交流 系统经过交流 /直流变换后与本身即输出直流电的直流系统在直流侧互联而 形成的。
更进一步地， 所述交流公共母线与外部交流电网还有互联。
更进一步地， 所述第一换流器， 第二换流器和第三换流器分别连接到 不同的交流电网上。
更进一步地， 当交流公共母线不再与外部交流电网连接时， 所述第一 换流器和第三换流器的额定直流电压设计为第二直流电网和第一直流电网 额定直流电压之差的 1/2， 所述第二换流器的额定直流电压与第一直流电网 的额定直流电压相等， 所述第一换流器和第三换流器的额定功率为 0.5*P*(1-E1/E2), 所述第二换流器的额定功率为 P*(1-E1/E2)， 其中 P为第 一直流电网和第二直流电网之间的额定交换功率， E1为第一直流电网的额 定直流电压 （额定正极对负极电压） ， E2为第二直流电网的额定直流电压
(额定正极对负极电压） ， 以上额定直流电压和额定功率为设计参考值， 实际使用时在上述参考值的基础上适当增大或减小额定值仍能使直流 -直流 变换器运行。
更进一步地， 当交流公共母线与外部交流电网连接， 或者第一换流器， 第二换流器和第三换流器分别与不同的交流电网互联时， 第二换流器的额 定直流电压与第一直流电网额定直流电压相等， 第一换流器和第三换流器 的额定直流电压为第二直流电网额定直流电压与第一直流电网额定直流电 压的差的一半， 第一换流器， 第二换流器和第三换流器的额定功率可以任 意按需要设计， 以上额定直流电压为设计参考值， 实际使用时在上述参考 值的基础上适当增大或减小额定值仍能使直流 -直流变换器运行。
更进一步地， 所述第一直流电网和第二直流电网可以采用对称双极， 对称单极， 不对称单极， 不对称双极等多种结构。
更进一步地， 所述第一换流器和第三换流器采用基于晶闸管的相控换 流技术， 所述第二换流器仍采用电压源型换流器， 采用此种拓扑时， 直流 功率只能单向第从第一直流电网输送至第二直流电网或单相地从第二直流 电网输送至第一直流电网。
更进一步地， 本发明还提供了一种优化了直流断路器安装位置的直流- 直流变换器， 其特征为在第一换流器的负极与第二换流器的正极之间串联 一个第一直流断路器， 在第二换流器的负极与第三换流器的正极之间串联 一个第二直流断路器， 直流断路器安装在上述位置后， 在第二直流电网发 生直流故障时， 第一直流电网不会给第二直流电网提供故障电流， 第一直 流电网发生直流故障时， 第一直流断路器和第二直流器会与第一换流器和 第三换流器串联在一起后共同承担第二直流电网的电压， 从而不至于使第 一换流器和第三换流器因为过电压而烧毁。
更进一步地， 第一直流断路器和第二直流断路器的额定直流电压设计 为第二换流器的额定直流电压的一半， 第一直流断路器和第二直流断路器 的额定电流设计为 P/E1-P/E2, 以上设计值为参考值， 实际使用时可依此参 考值适当增大或减小。
更进一步地， 本发明还提供了一种立体式直流-直流变换器在第二直流 电网发生直流故障时的保护方法， 具体为检测到第二直流电网发生直流故 障时，闭锁第一换流器，第二换流器和第三换流器的全控型电力电子器件 (或 晶闸管)的触发脉冲从而切断第一换流器， 第二换流器和第三换流器通过各 自的全控型电力电子器件 （或晶闸管） 给第二直流电网故障点提供直流故 障电流的通路， 与此同时， 开断第一直流断路器和第二直流断路器从而切 断第一直流电网通过第一换流器和第三换流器的二极管给第二直流电网故 障点提供直流故障电流的通路。
更进一步地， 本发明还提供了一种立体式直流-直流变换器在第一直流 电网发生直流故障时的保护方法， 具体为检测到第一直流电网发生直流故 障时， 闭锁第一换流器， 第二换流器和第三换流器的全控型电力电子器件 (或晶闸管） 的触发脉冲从而切断第一换流器， 第二换流器和第三换流器 通过各自的电全控型电力电子器件 （或晶闸管） 给第一直流电网故障点提 供直流故障电流， 与此同时， 开断第一直流断路器和第二直流断路器从而 使得第二直流电网的电压施加在第一换流器， 第一直流断路器， 第二直流 断路器和第三换流器构成的串联回路上， 防止第一换流器和第三换流器因 单独承担第二直流电网的直流电压而发生过电压， 烧毁第一换流器和第三 换流器。 总体而言， 本发明的变换器相对于现有技术， 具有如下技术效果：
( 1 )无需单独建设传统直流-直流变换器里的与第二直流电网额定直流 电压相等的换流器二， 而是通过低额定直流电压的第一换流器， 第一直流 电网和第三换流器串联后， 实现换流器二的功能， 由于串联了第一直流电 网， 本发明充分利用了第一直流电网已经存在的直流电压从而降低了第一 换流器和第三换流器的额定直流电压， 降低了成本。
(2 ) 本发明第一换流器至第三换流器所需要的换流器的容量总和为 2P*(1-E1/E2), 而传统直流-直流变换器所用换流器容量总和为 2P, 即网间 联络功率的 2倍， 本发明所使用的换流器容量总和小于传统直流-直流变换 器， 本发明可以大大地节省换流器成本。
(3 )本发明的变换器所互联的功率只有 P*(1-E1/E2)的互联功率需要经 过两级交流 /直流（或直流 /交流）变换， 剩余的 Ρ*Ε1/Ε2的互联功率可以直 接经过第一直流电网和第二直流电网之间的电气互联进行传输， 而传统直 流-直流变换器所有互联的功率 Ρ都需要经过两级交流 /直流（或直流 /交流) 变换， 为此该变换器的功率损耗低于传统直流 -直流变换器的功率损耗， 大 大降低了运行成本。
(4)本发明中互联交流电路的总的容量为 2Ρ*(1-Ε1/Ε2)， 而传统直流- 直流变换器互联交流电路的总容量为 2Ρ, 为此本发明能大大节省互联交流 电路成本。
【附图说明】
图 1 是按照本发明一个实施例的立体式直流-直流变换器的原理结构 图；
图 2是现有技术中直流 -直流变换器拓扑示意图；
图 3是本发明另一实施例中第一换流器和第三换流器通过三角形连接 的相电抗连接至交流公共母线的拓扑示意图； 图 4是本发明又一个实施例的交流公共母线连接交流电网的示意图； 图 5 是本发明再一实施例的第一直流电网由多个交流电网经交流 /直 流变换后在直流侧互联构成的直流电网；
图 6 是本发明第五实施例的第一直流电网由多个交流电网经交流 /直 流变换后在直流侧与直流电网进一步并联构成的直流电网；
图 7 是本发明第六实施例的第一换流器， 第二换流器， 第三换流器分 别接不通交流电网；
图 8是本发明第七实施例的第一换流器，第三换流器采用相控换流器， 第二换流器仍采用电压源型换流器， 功率只能单向地从第一直流电网流向 第二直流电网传输功率；
图 9是本发明第八实施例的第一换流器，第三换流器采用相控换流器， 第二换流器仍采用电压源型换流器， 功率只能单向地从第二直流电网流向 第一直流电网传输功率；
图 10是本发明第九实施例的第一换流器，第三换流器采用电压源型换 流器， 第二换流器采用相控换流器， 功率只能单向地从第一直流电网流向 第二直流电网传输功率；
图 11 是本发明第十实施例的第一换流器， 第三换流器采用不控整流 桥， 第二换流器采用电压源型换流器；
图 12 是本发明第十一实施例的第一换流器负极和第二换流器正极之 间串联了第一直流断路器， 第二换流器负极和第三换流器正极之间串联了 第二直流断路器；
图 13是在行业内通用仿真软件 PSCAD/EMTDC中搭建的验证本发明
【具体实鮮式】 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立体式直流-直流变换器用于互联两个额定直流电 压不同的直流电网， 能够解决现有的采用直流 /交流 /直流变换的传统直流- 直流变换器所带来的换流器成本高， 损耗大的缺点。
如图 1所示， 立体式直流 -直流变换器由第一换流器 1， 第二换流器 2 和第三换流器 3，第一换流器 1的正极通过直流线路 6与第二直流电网 9的 正极相连接， 第一换流器 1的负极与第二换流器 2的正极相连接， 第 2换 流器 2的负极与第三换流器 3的正极相连接， 第三换流器 3的负极通过直 流线路 6与第二直流电网 9的负极相连接， 第二换流器 2的正极和负极还 通过直流线路 6分别与第一直流电网 8的正极和负极相连接，第一换流器 1 的交流端通过变压器 4与交流公共母校 7连接， 第二换流器 2的交流端通 过变压器 5与交流公共母线 7连接， 第三换流器 3的交流端通过变压器 4 与交流公共母线 7相连接。 本实施例中， 换流器可选采用本行业内公知的 电压源型换流器以实现功率的双向流动。
在图 1所示实施例中， 第一直流电网 8和第二直流电网 9优选都为双 极对称的直流系统， 为此变压器 4采用星形 /三角形接线方式以消除第一换 流器 1和第三换流器 3的中性点不平衡问题， 变压器 5可以采用星形 /星形 接线或星形 /三角形接线的任意接线形式。 为了使图 1所示的实施例能正常 工作， 一种优选的控制方式为使第二换流器 2控制交流公共母线 7的交流 电压， 第一换流器 1和第三换流器 3则用于控制各自传输的有功功率。
以下分析第一换流器 1，第二换流器 2和第三换流器 3的额定直流电压 与额定功率的设计。 记第一直流电网 8和第二直流电网 9的额定直流电压 分别为 El和 E2， 其中额定直流电压指额定正极对负极电压， E1和 E2的 量测点见图 1， 记第一直流电网 8输出的直流电流为 il， 第二直流电网 9 输入的直流电流为 i2， 第一直流电网 8与第二直流电网 9之间交换的功率 为 ^ 根据本领域公知知识， 可以求得 il=P/El, i2=P/E2, 进一步求得， 第 二换流器 2的额定功率为 El*(il-i2)=(l-El/E2)*P， 而第一换流器 1和第三 换流器 3的额定功率为 (E2-El)/2*i2=0.5*P*(l-El/E2)。三个换流器的总容量 为 2*(1-E1/E2)*P。 通过上述计算第一换流器 1， 第二换流器 2和第三换流 器 3的额定功率，可以发现三个换流器的总容量始终小于 2*Ρ， 当 El与 Ε2 越接近时， 三个换流器的总容量越小。 假设第一直流电网 8 的额定直流电 压为 ±320kV， 即 El=640kV， 第二直流电网 9的额定直流电压为 ±640kV， 即 E2=1280kV， 可以求得三个换流器的总换流容量等于 P, 与第一直流电 网 8和第二直流电网 9的额定交换功率相等， 而传统的采用直流 /交流 /直流 变换的直流-直流变换器所需要的总的换流容量为 2*P， 成本大大高于立体 式直流-直流变换器。
为了对比本发明与现有技术的不同， 图 2给出了现有的传统直流 -直流 变换器拓扑。 该传统直流-直流变换器由换流器 10和换流器 11通过内部交 流电路 12互联而成， 对比图 1和图 2我们可以得到如下差别：
1 )立体式直流-直流变换器的第一直流电网 8与第二直流电网 9之间有 直接的电气互联， 即第一直流电网 8 的正极和负极分别通过通过第一换流 器 1和第三换流器 3与第二直流电网 9的正极和负极相连接； 而传统直流- 直流变换器的第一直流电网 8和第二直流电网 9之间没有直接的电气互联， 在传统直流-直流变换器中，第一直流电网 8需要通过换流器 10将直流电逆 变为交流电， 经内部交流电路 12传输至换流器 11 的交流侧， 再经由换流 器 11经过交流 /直流变换与第二直流电网 9相连接， 其中内部交流电路 12 采用了交流变压器 19连接换流器 10和换流器 11之间的交流电路， 通过交 流变压器 16形成的联接称为磁耦合而非直接电气连接。 2) 由于立体式直流-直流变换器采用了上述改进拓扑， 立体式直流-直 流变换器中第一直流电网 8除了通过 4， 5， 7构成的交流电路向第二直流 电网 9传输功率外， 还可以通过第一换流器 1和第三换流器 3的直接电气 连接部分传输功率， 为此立体式直流-直流变换器所采用的总的变流器容量 小于第一直流电网和第二直流电网之间的互联功率的 2倍， 而传统直流-直 流变换器所需的变流器总容量始终为互联功率的 2倍。
图 3 给出了本发明的另一种实施方式， 图 3 与图 1 类似， 区别在于 第一换流器 1和第三换流器 3不是通过变压器与交流公共母线 7连接， 而 是通过三角形连接的相电抗 13和常规相电抗 16再与交流公共母线 7连接。 由于相电抗无法实现交流电压的升压 /降压功能， 因此图 3实施方式要求交 流公共母线 7的交流电压与第一换流器 1和第三换流器 3输出的交流电压 基本一致， 但第二换流器 2 的输出交流电压幅值并不一定与第一换流器 1 和第三换流器 3输出的交流电压幅值一致， 为此图 3方案中， 第二换流器 2仍通过变压器 5与公共母线 7相连，从而使得第二换流器 2的输出交流电 压的幅值经变压器 5的升压 /降压功能后与第一换流器 1和第三换流器 3的 交流电压幅值一致。
图 4给出了本发明的又一种实施方式， 图 4与图 1基本类似， 区别在 于交流公共母线 7还与交流电网 14相连接。
图 5给出了本发明的又一种实施方式， 图 5与图 4基本类似， 区别在 于图 5给出了第一直流电网的一种实现方式，即多个交流电网 14经换流器 15进行交流 /直流变换后， 在直流侧互联而成。
图 6 给出了本发明的又一种实施方式， 其中第一直流电网 8由多个不 同的交流电网 14经过换流器 15的交流 /直流变换后再与直流电网 18在直流 侧互联而成， 第二直流电网 9可以采用类似的构成方式。
图 7给出了本发明的又一种实施方式， 图 7中第一换流器 1， 第二换 流器 2和第三换流器 3的交流侧分别与不同的交流电网 14连接。 图 8给出了本发明的又一种实施方式， 其中第一换流器 1和第三换流 器 3采用相控换流器而非电压源型换流器， 这种实施方式中， 功率只能通 过第一直流电网 8向第二直流电网 9流动， 适用于只需要单向功率交换的 两个直流电网的互联， 由于相控换流器的额定电压目前远高于电压源型换 流器的额定电压， 且相同额定功率和相同额定电压的相控换流器成本低于 电压源型换流器， 为此图 8可以通过较低成本将实现将功率从第一直流电 网 8传输给第二直流电网 9， 所述相控换流器是一种基于晶闸管的换流器， 其技术细节为行业公知技术， 不赘述。
图 9给出了本发明的又一种实施方式， 该实施方式与图 8类似， 区别 在于第一换流器 1和第三换流器 3的接线方式与图 8中第一换流器 1和第 三换流器 3的接线方式相反， 图 9实施例中功率只能单向第从第二直流电 网 9向第一直流电网 8传输。
图 10给出了本发明的又一种实施方式， 该实施方式与图 8类似， 区 别在于第一换流器 1和第三换流器 3采用电压源型换流器而第二换流器 2 采用相控换流器。
图 11给出了本发明的又一种实施方式，其中第二换流器 2采用电压源 型换流器， 第一换流器 1和第三换流器 3采用不控整流桥， 不控整流桥是 本行业内公知常识， 其技术细节不赘述， 该实施方式的优点在于可以大大 节省第一换流器 1和第三换流器 3的成本并提高第一换流器 1和第三换流 器 3的可靠性， 缺点在于控制性能较差。
图 12给出了本发明的又一种实施方式，其中第一换流器 1的负极和第 二换流器 2的正极之间串联了第一直流断路器 20， 第二换流器 2的负极和 第三换流器 3的正极之间串联了第二直流断路器 25。 第一换流器 1， 第二 换流器 2和第三换流器 3采用半桥型的模块化多电平换流器。 半桥型的模 块化多电平换流器是本行业公知的一种电压源型换流器， 其技术细节不再 赘述。 关于直流断路器的技术可以参考 （JtjRGEN HAFNER, BJORN JACOBSON "Proactive Hybrid HVDC Breakers - A key innovation for reliable HVDC grids", CIGRE 2011 Bologna Symp., Bologna, Italy, paper 264, Sep. 2011. )。本发明实施例指出了直流断路器的最佳安装位置， 即第一直流断路 器 20安装在第一换流器 1和第二换流器 2之间， 第二直流断路器 25安装 在第二换流器 2和第 3换流器之间。 当第二直流电网 9发生直流故障时， 可以通过闭锁第一换流器 1，第二换流器 2和第三换流器 3的全控型电力电 子器件 26的触发脉冲从而防止第一换流器 1， 第二换流器 2和第三换流器 3通过各自的全控型电力电子器件 26给第二直流电网 9的故障点提供直流 故障电流， 与此同时， 开断第一直流断路器 20和第二直流断路器 25从而 切断第一直流电网通过第一换流器 1和第三换流器 3的二极管 27给第二直 流电网故障点提供直流故障电流的通路。
当第一直流电网 8发生直流故障时， 可以通过闭锁第一换流器 1， 第二 换流器 2和第三换流器 3的全控型电力电子器件 26的触发脉冲从而防止第 一换流器 1，第二换流器 2和第三换流器 3通过各自的全控型电力电子器件 26给第一直流电网 8的故障点提供直流故障电流， 与此同时， 开断第一直 流断路器 20和第二直流断路器 25从而使得第二直流电网的电压施加在第 一换流器 1， 第一直流断路器 20， 第二直流断路器 25和第三换流器 3构成 的串联回路上， 防止第一换流器 1和第三换流器 3因为单独承担第二直流 电网 9的直流电压而发生过电压， 烧毁第一换流器 1和第三换流器 3。
由以上分析可知， 若第一直流断路器 20和第二直流断路器 25安装在 图 12所示的位置就可以保证无论是第一直流电网 8还是第二直流电网 9发 生直流故障， 立体式直流 -直流变换器都不会因为过电压或过电流而损毁。
图 12中第一直流断路器 20和第二直流断路器 25流过的额定电流为 il-i2=(P/El-P/E2)， 为此第一直流断路器 20和第二直流断路器 25的额定直 流电流设计为 (P/E1-P/E2)。
当第一直流电网 8发生直流故障时， 第一换流器 1和第三换流器 3在 各自的全控型电力电子器件闭锁后所能承受的电压为 （E2-E1 ) /2， 而第二 直流电网 9的额定电压为 E2, 为了保证第一换流器 1和第三换流器 3在第 二直流电网 9发生直流故障时不会因为过电压而烧毁， 第一直流断路器 20 和第二直流断路器 25的额定电压推荐值为 El/2。
由于第一直流断路器 20和第二直流断路器 25只需在第二直流电网发 生直流故障时具有开断直流故障电流的能力因此第一直流断路器 20和第二 直流断路器 25推荐选择为图 12所示的单向断路器从而减小断路器的成本。 该单向断路器只需要切断第二直流电网 9发生直流故障时，第一直流电网 8 给第二直流电网 9提供的直流故障电流， 当第一直流电网 8发生直流故障 时， 通过闭锁第一换流器 1和第三换流器 3的全控型电力电子器件 26的触 发脉冲， 第一直流断路器 20和第二直流断路器 25上不会流经故障电流， 为此第一直流断路器 20和第二直流断路器 25无需具备开断方向为从第二 直流电网 9流向第一直流电网 8的故障电流的能力。
若图 12中的第一换流器 1， 第二换流器 2或第三换流器 3的一个或两 个换流器采用相控换流器或不控整流桥，图 12的位置配置第一直流断路器 20和第二直流断路器 25仍可以实现在第二直流电网 9发生直流故障时，使 得第一换流器 1和第三换流器 3免于流过过电流而烧毁，在第一直流电网 8 发生直流故障时， 为第二换流器 2提供过电压保护。 为了验证本发明的技术可行性， 在国际通用电磁暂态仿真软件 PSCAD/ETMDC中搭建了图 13所示的仿真算例， 第一直流电网 8的额定 直流电压为 ±320kV， 第二直流电网 9的额定直流电压为 ±640kV， 两个直流 电网之间的互联功率为 2000MW。 图 14为对应的仿真结果。 0.2~0.7秒时， 第二直流电网 9向第一直流电网 8输送的功率从 0MW上升到 2000MW, 1.0秒时发生功率反转， 由第一直流电网 8向第二直流电网 9输送 2000MW 功率。 图 14表明本发明能实现两个互联直流电网的功率传输。 图 13还表 明， 第一换流器 1 (VSC1 ), 第二换流器 2 (VSC2)和第三换流器 3 (VSC3 ) 稳态时传输的有功功率的绝对值分别为 499.7MW, 999.5MW和 499.7MW。 为此三个换流器的功率总和约为 2000MW, 与互联功率相等， 而传统直流- 直流变换器则需要总共 4000MW的换流器。
本发明中第一换流器 1，第二换流器 2和第三换流器 3优选采用电压源 型换流器以实现功率的双向流动， 电压源型换流器是本领域的公知知识， 可以有两电平换流器， 三电平换流器， 模块化多电平换流器等多种拓扑结 构。
本发明的用于连接两个不同额定直流电压的直流电网的直流-直流变换 器相比于传统的直流-直流变换器， 优势在于：
( 1 ) 所需要的总的换流器容量小于 2倍的互联功率， 而传统的直流- 直流变换器所需要的总的换流容量为互联功率的 2倍， 为此本发明相比于 现有技术， 能大大地减小所需要的换流器的容量。
(2) 按照国际大电网会议组织公布的数据， 每 1GW的换流器的成本 为 1.1亿欧元， 以互联典型的 ±320kV直流电网和 ±640kV直流电网为例， 每 互联 1GW的直流功率， 立体式直流 -直流变换器相比于传统直流-直流变换 器能节省 1GW的变流器容量，而未来中国范围以及世界范围内需要互联的 直流电网容量高达数百 GW, 为此本发明的经济性相比于传统的直流 -直流 变换器是相当明显的。
(3 )由于本发明所采用的总的换流器容量少于传统直流-直流变换器所 采用换流器容量， 本发明也能节省所采用的交流变压器， 相电抗等的容量。 以上所述仅为本领域的技术人员容易理解的本发明的较佳实施例而 已， 并不用以限制本发明， 凡在本发明的精神和原则之内所作的任何修改、 等同替换和改进等， 均应包含在本发明的保护范围之内。

Claims

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1、 一种立体式直流-直流变换器， 用于实现两直流电网 （8， 9)之间的 互联传输， 其特征在于， 该变换器包括第一换流器 （1)、 第二换流器 （2) 和第三换流器 （3)， 其中， 所述第一换流器 （1) 的正极与第二直流电网 （9) 的正极相连接， 所 述第一换流器 （1) 的负极与第二换流器 （2) 的正极相连接， 第二换流器 (2) 的负极与第三换流器 （3) 的正极相连接， 第三换流器 （3) 的负极与 第二直流电网 （9) 的负极相连接， 所述第二换流器 （2) 的正极同时和第 一直流电网 （8) 的正极相连接， 所述第二换流器 （2) 的负极同时和第一 直流电网 （8) 的负极相连接。
2、根据权利要求 1所述的一种立体式直流-直流变换器， 其中， 所述第 一换流器 （1) 和第三换流器 （3) 的交流侧通过变压器支路与交流电网连 接， 所述第二换流器 （2) 通过变压器支路或相电抗支路与交流电网连接， 或者所述第一换流器 （1) 和第三换流器 （3) 的交流侧均通过相电抗支路 与交流电网连接， 而第二换流器 （2) 通过变压器支路与交流电网连接。
3、根据权利要求 2所述的一种立体式直流-直流变换器， 其中， 所述第 一换流器 （1)、 第二换流器 （2) 和第三换流器 （3) 的交流侧通过一公共 的交流母线 （7) 互联在一起， 或各自分别连接到不同的交流电网上。
4、根据权利要求 2或 3所述的一种立体式直流-直流变换器， 其中， 所 述第一换流器 （1) 和第三换流器 （3) 的变压器支路 （4， 5) 上的交流变 压器靠近直流侧的端口采用三角形接线方式， 以消除第一换流器 （1) 和第 三换流器 （3) 中性点不平衡问， 所述第二换流器 （2) 的变压器支路 （4， 5) 上的变压器靠近直流侧的端口以及第一换流器 （1) 和第三换流器 （3) 靠近交流侧的端口采用星形或三角形接线。
5、根据权利要求 2-4中任一项所述的一种立体式直流-直流变换器， 其 中， 所述第一换流器 （1 ) 和第三换流器 （3 ) 的相电抗支路 （13， 16) 上 的每相相电抗采用三角接线方式以消除该第一换流器（ 1 )和第三换流器（3 ) 中性点不平衡。
6、根据权利要求 1-5中任一项所述的一种立体式直流-直流变换器， 其 中， 所述第一换流器 （1 )， 第二换流器 （2) 和第三换流器 （3 ) 采用电压 源型换流器、 相控换流器或不控整流桥。
7、根据权利要求 1-5中任一项所述的一种立体式直流-直流变换器， 其 中， 所述第一换流器 （1 ) 和第三换流器 （3 ) 采用基于晶闸管的相控换流 器， 使得功率只能在两直流电网 （8， 9) 之间单向流动， 实现单向功率交 换的两个直流电网的互联。
8、根据权利要求 1-7中任一项所述的一种立体式直流-直流变换器， 其 中， 所述第一换流器 （1 ) 的负极和第二换流器 （2) 的正极之间串联了第 一直流断路器 （20)， 第二换流器 （2) 的负极和第三换流器 （3 ) 的正极之 间串联了第二直流断路器 （25 )， 可以保证所述在第一直流电网 （8) 和 /或 第二直流电网（9)发生直流故障时， 立体式直流 -直流变换器不会因为过电 压或过电流而损毁。
9、根据权利要求 8所述的一种立体式直流-直流变换器， 其中， 通过闭 锁第一换流器 （1 ) ， 第二换流器 （2) 和第三换流器 （3 ) 的全控型电力电 子器件或晶闸管的触发脉冲以切断第一换流器 （1 ) ， 第二换流器 （2) 和 第三换流器 （3 ) 通过各自的全控型电力电子器件 （26) 或晶闸管给第二直 流电网 （9) 故障点提供直流故障电流的通路， 同时开断所述第一直流断路 器 （20) 和第二直流断路器 （25 ) 以切断第一直流电网 （8) 通过第一换流 器 （1 ) 和第三换流器 （3 ) 的二极管给第二直流电网 （9) 故障点提供直流 故障电流的通路， 从而实现在第二直流电网 （9) 发生直流故障时对变换器 的保护。
10、 根据权利要求 8或 9所述的一种立体式直流-直流变换器， 其中， 通过闭锁所述第一换流器 （1) 、 第二换流器 （2) 和第三换流器 （3) 的全 控型电力电子器件（26)或晶闸管的触发脉冲从而切断该第一换流器（1)、 第二换流器（2)和第三换流器（3)通过各自的电全控型电力电子器件（26) 或晶闸管给第一直流电网 （8) 故障点提供直流故障电流， 同时， 开断第一 直流断路器 （20) 和第二直流断路器 （25) 从而使得第二直流电网 （9) 的 电压施加在第一换流器（1)、第一直流断路器（20)、第二直流断路器（25) 和第三换流器 （3) 构成的串联回路上， 防止第一换流器 （1) 和第三换流 器 （3) 因单独承担第二直流电网 （9) 的直流电压而发生过电压， 烧毁第 一换流器 （1) 和第三换流器 （3)， 实现在第一直流电网 （8) 发生直流故 障时对变换器的保护。
11、 根据权利要求 8-10中任一项所述的一种立体式直流-直流变换器， 其中， 所述第一直流断路器 （20) 和第二直流断路器 （25) 的额定直流电 压为第二换流器 （2) 的额定直流电压的一半， 第一直流断路器 （20) 和第 二直流断路器（25) 的额定电流为 P/E1-P/E2, 其中 P为第一直流电网 （8) 和第二直流电网 （9) 之间的额定交换功率， E1为第一直流电网 （8) 的额 定直流电压， E2为第二直流电网 （9) 的额定直流电压。
12、 根据权利要求 1-11中任一项所述的一种立体式直流-直流变换器， 其中， 所述第一换流器 （1) 和第三换流器 （3) 用于控制各自的有功功率 而第二换流器 （2) 用于控制与其连接的交流电网的交流电压， 从而实现立 体式直流 -直流变换器的稳定运行。
13、 根据权利要求 1-12中任一项所述的一种立体式直流-直流变换器， 其中， 所述第一换流器 （1) 和第三换流器 （3) 用于控制与其连接的交流 电网的交流电压， 第二换流器 （2) 用于控制第一直流电网 （8) 和第二直 流电网（9)之间的互联功率，从而实现立体式直流 -直流变换器的稳定运行。
14、 根据权利要求 1-13中任一项所述的一种立体式直流-直流变换器， 其中， 所述第一直流电网 （8 ) 和 /或第二直流电网 （9) 是一个或多个交流 系统经过交流 /直流变换后在直流侧互联构成。
15、 根据权利要求 1-13中任一项所述的一种立体式直流-直流变换器， 其中， 所述第一直流电网 （8 ) 和 /或第二直流电网 （9) 是一个或多个交流 系统经过交流 /直流变换后与本身即输出直流电的直流系统在直流侧互联而 形成的。
16、 根据权利要求 1-15中任一项所述的一种立体式直流-直流变换器， 其中， 所述第一直流电网或第二直流电网可以采用对称双极， 对称单极， 不对称单极或不对称双极结构。
17、 根据权利要求 1-16中任一项所述的一种立体式直流-直流变换器， 其中， 所述第一换流器 （1 ) 和第三换流器 （3 ) 的额定直流电压为第二直 流电网 （9) 和第一直流电网 （8) 额定直流电压之差的 1/2， 所述第二换流 器 （2) 的额定直流电压与第一直流电网 （8) 的额定直流电压相等。
18、 根据权利要求 1-17中任一项所述的一种立体式直流-直流变换器， 其中，所述第一换流器（ 1 )和第三换流器（3 )的额定功率为 0.5*Ρ*(1-Ε1/Ε2)， 所述第二换流器 （2) 的额定功率为 Ρ*(1-Ε1/Ε2)， 其中 Ρ为第一直流电网
(8 ) 和第二直流电网 （9) 之间的额定交换功率， E1为第一直流电网 （8) 的额定直流电压， Ε2为第二直流电网 （9) 的额定直流电压。
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CN103762582A (zh) 2014-04-30
CN103762582B (zh) 2016-04-13

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