WO2015143744A1 - 一种多端口直流-直流自耦变压器及其应用 - Google Patents
一种多端口直流-直流自耦变压器及其应用 Download PDFInfo
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- WO2015143744A1 WO2015143744A1 PCT/CN2014/075482 CN2014075482W WO2015143744A1 WO 2015143744 A1 WO2015143744 A1 WO 2015143744A1 CN 2014075482 W CN2014075482 W CN 2014075482W WO 2015143744 A1 WO2015143744 A1 WO 2015143744A1
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- autotransformer
- power
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- 238000006243 chemical reaction Methods 0.000 claims abstract description 27
- 230000005540 biological transmission Effects 0.000 claims abstract description 11
- 238000000034 method Methods 0.000 claims abstract description 11
- 230000007935 neutral effect Effects 0.000 claims description 6
- 238000010586 diagram Methods 0.000 description 15
- 238000005516 engineering process Methods 0.000 description 13
- 238000004088 simulation Methods 0.000 description 5
- 238000010168 coupling process Methods 0.000 description 3
- 238000005859 coupling reaction Methods 0.000 description 3
- 230000003247 decreasing effect Effects 0.000 description 3
- 238000010248 power generation Methods 0.000 description 3
- 230000002457 bidirectional effect Effects 0.000 description 2
- 230000005404 monopole Effects 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
- 238000011217 control strategy Methods 0.000 description 1
- 238000007728 cost analysis Methods 0.000 description 1
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Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
- H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
- H02M3/33584—Bidirectional converters
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J1/00—Circuit arrangements for dc mains or dc distribution networks
- H02J1/10—Parallel operation of dc sources
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- 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
-
- 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 interconnecting DC systems with different voltage levels.
- DC systems with different rated DC voltages require a DC-DC converter.
- DC microgrid is also one of the current technical hotspots.
- DC-DC converters are also needed to interconnect multiple DC microgrids with different DC voltages.
- a dc-dc multiport-converter-based solid-state by Sixifo Falcones et al. Transformer integrating distributed generation and storage " (IEEE Transactions on Power Electronics, 2013, 28(5), 2192 ⁇ 2203) discloses a multi-port DC-DC conversion technique using a multi-port high-frequency transformer, the technical details of each The DC system is connected to a port of the multi-port AC transformer on the AC side via a voltage source converter, and the multi-port AC transformer is used to match different output AC voltages of the respective voltage source converters to achieve different voltage levels of the interconnection. The purpose of the DC system.
- a significant common feature of the above-described multi-port DC-DC conversion technology using LCL circuits and the multi-port DC-DC conversion technology using multi-port high-frequency transformers is that there is no direct interconnection between the DC sides of the interconnected DC systems, for which multi-port DC -
- the DC conversion technology does not make full use of the DC voltage already existing in each DC system. All the transmitted power has to undergo DC-AC-DC conversion.
- the total capacity of the converter required is twice the interconnection capacity, bringing the inverter. High cost, high cost of AC link, and large running loss.
- the present invention provides a multi-port DC-DC autotransformer, Make full use of the DC voltage already existing in each DC system, and perform a certain degree of direct electrical interconnection on the DC system on the DC side, so that most of the power transmitted between the DC systems can be converted without DC-AC-DC conversion. Directly through each straight The electrical interconnection between the streaming systems is transmitted.
- the negative electrode of the first inverter is connected to the positive electrode of the second inverter, the negative electrode of the second inverter is connected to the positive electrode of the third inverter, and so on, and the positive electrode of the jth converter and the first
- the negative pole of the j-1 converter is connected, the cathode of the jth converter is connected to the anode of the j+1 converter, the anode of the 2N-1 converter and the cathode of the 2N-2 converter Connected, j is any positive integer between 2 and 2N-2;
- the anode of the first converter and the cathode of the second N-1 inverter are respectively connected to the positive and negative poles of the first DC system, and the anode of the first converter is connected.
- the negative pole of the 2N-2 inverter is respectively connected to the positive and negative poles of the second DC system, and so on, and the anode of the i-th converter and the cathode of the second N-i converter are respectively connected to the cathode of the ith DC system.
- the positive and negative poles are correspondingly connected, and the positive and negative poles of the Nth inverter are respectively connected with the positive and negative poles of the Nth DC system;
- the AC common point of the present invention is a common AC bus.
- the AC converters of the first to Nth inverters and the N+1th to the 2Nth inverters are close to the DC side.
- the ports are delta-connected to eliminate the neutral point imbalance of these inverters.
- the transformer of the N-th converter is close to the DC-side port and all converters can be star-shaped or close to the common AC bus side. Delta wiring.
- the ports of the first to N-1th inverters and the N+1th to the 2nd N-1th inverters near the common AC bus side are connected by delta wires to eliminate the inverters.
- the transformer of the Nth converter is close to the AC common bus
- the side ports and all 2N-1 inverters near the straight side can be wired with a star or delta connection.
- At least one of the 2N-1 inverters is used to control the AC voltage of the AC common bus, and the other converters are used to control the respective active powers, thereby implementing multi-port DC-DC auto-coupling.
- the stable operation of the transformer is used to control the AC voltage of the AC common bus, and the other converters are used to control the respective active powers, thereby implementing multi-port DC-DC auto-coupling.
- first to N-1th inverters and the (N+1)th to the 2nd N-1th inverters are connected to the AC bus through the phase reactance, and the phase reactance of each phase is triangulated to eliminate the commutation.
- the neutral point of the device is not balanced.
- any of the first DC system to the Nth DC system is formed by interconnecting one or more AC systems on the DC side after AC/DC conversion.
- any of the first DC system to the Nth DC system is formed by interconnecting one or more AC systems with AC/DC conversion and DC systems that output DC power on the DC side.
- AC common bus is also interconnected with an external AC grid.
- any of the first to the 2N-1th inverters is not connected to the common AC bus, but may be connected to the same or different AC grid.
- the rated DC voltages of the first inverter and the second N-1 inverter are designed as (E r E 2 )/2, and the rated DC voltages of the second converter and the second N-2 converter are designed as ( E 2 -E 3 )/2, and so on, the rated DC voltage of the i-th converter and the second N-i converter is designed as (Ei-E i+1 )/2, the rated DC of the Nth inverter
- the voltage is E N
- the above rated DC voltage is a design reference value.
- the multi-port DC-DC autotransformer can still be operated, and the E 1 ⁇ E N is the rated DC voltage of the first DC system to the Nth DC system, respectively, and E!>E 2 > .. E N , the rated DC voltage is the rated voltage of the high voltage DC port to the low voltage DC port.
- any one of the first DC system to the Nth DC system may be adopted.
- first to second inverters are preferably voltage source type inverters, so that any one of the first to the Nth DC systems can be bidirectionally connected to the multi-port DC.
- - DC autotransformer exchanges power.
- one or any of the first to the second N-1 inverters may adopt a thyristor-based phase-controlled converter or an uncontrolled rectifier bridge.
- the present invention also provides a design method for the rated capacity of each inverter of a multi-port DC-DC autotransformer, specifically for the second DC system to the Nth DC system to the multi-port DC-DC autotransformer
- the output power is P 2 ⁇ P N .
- the active power absorbed by the first DC system is (P 2 + . . . + P N )
- the second DC system to the Nth DC system output can be further calculated.
- the DC current is P 2 /E 2 ⁇ P N /E N
- the input current of the 1st DC system is (P 2 + . . . +PN)/EI, according to Kirchhoff's current law and the aforementioned multi-port DC-
- the topology of the DC autotransformer can calculate the DC current flowing from the first converter.
- the DC current flowing from the 2nd inverter is:
- the DC current flowing from the 3rd inverter is:
- the direct current flowing from the Nth inverter is the direct current flowing from the Nth inverter.
- the rectification power of the first converter can be obtained as
- the rectifier power of the converter is:
- the rectification power of the third converter is:
- the rectification power of the Nth inverter is
- Equation (11) to (12) P lmax to P Nmax represent the maximum output/input power of the first DC system to the Nth DC system, respectively. Substituting equations (11) and (12) into equation (6) can be obtained. Maximum of the 1st inverter Power is
- the maximum active power of the second to nth inverters cannot be obtained by the general expression, but needs to be obtained according to the specific P lmax ⁇ P Nmax and ⁇ , combined with the formulas (11) and (12).
- the maximum power of each inverter, the power to be obtained will be the rated power of each inverter, wherein the rated power of the 2N-1 inverter is the same as the rated power of the first inverter, 2nd - The rated power of the 2 inverters is the same as the power of the 2nd inverter, and so on.
- the rated power of the 2N-i converters is the same as the rated power of the ith inverter.
- the above rated power is the design reference value. In actual use, properly increasing or decreasing the rated power based on the above reference values can still enable multi-port DC-DC autotransformer operation.
- the present invention also provides a control method for a multi-port DC-DC autotransformer, specifically, at least one inverter is used for controlling an AC voltage of a common AC, and other converters are used for control and active power.
- a power related quantity such as DC power or DC voltage.
- the AC link inside the multi-port DC-DC autotransformer can be a single-phase AC circuit, a two-phase AC circuit, a three-phase AC circuit or a multi-phase AC. Circuit.
- the converter of the present invention has the following technical effects as compared with the prior art:
- the DC systems of different voltage levels are connected in series through a plurality of converters, which fully utilizes the DC voltage already existing in each interconnected DC system, which greatly reduces the rated voltage of each converter and reduces the cost.
- FIG. 1 is a schematic diagram showing the principle of a three-port DC-DC autotransformer according to an embodiment of the present invention
- FIG. 2 is a schematic diagram showing the principle of a four-port DC-DC autotransformer according to an embodiment of the present invention
- FIG. 3 is a schematic diagram showing the rated capacity design of each converter of a four-port DC-DC autotransformer according to an embodiment of the present invention
- FIG. 4 is a schematic diagram of a multi-port DC-DC conversion using an LCL circuit in the prior art
- FIG. 5 is a schematic diagram of DC-DC conversion using a multi-port high-frequency transformer in the prior art
- FIG. 6 is an embodiment of the present invention. Schematic diagram of the N-port DC-DC autotransformer
- Figure 7 is a schematic structural diagram of a four-port DC-DC autotransformer for each DC system with an asymmetric single-pole DC system;
- Figure 8 is a structural schematic view showing an embodiment of a thyristor-based phase-controlled inverter of a partial converter according to the present invention.
- Figure 9 is a structural schematic view showing another embodiment of a thyristor-based phase-controlled inverter of a partial converter according to the present invention.
- FIG. 10 is a schematic structural view of an embodiment of interconnecting an AC side of an inverter and an external AC system in the present invention
- FIG. 11 is a schematic structural view of an embodiment of an implementation of a DC system of the present invention.
- 12 is a schematic structural diagram of another embodiment of a DC system of the present invention.
- FIG. 13 is a schematic diagram of an AC voltage control according to an embodiment of the present invention.
- 16 is a simulation curve of output AC power of each converter of a four-port DC-DC autotransformer of the present invention
- Figure 17 is a simulation graph showing the sum of the absolute values of the output DC power of each DC system of the four-port DC-DC autotransformer of the present invention and the absolute value of the output AC power of each converter. ⁇ detailed description ⁇
- the multi-port DC-DC autotransformer provided by the embodiment of the invention is used for interconnecting DC systems with different rated DC voltages of three or more, and can solve the existing traditional multi-port DC using full-power DC-AC-DC conversion.
- the converters brought by DC converters have the disadvantages of high cost and large loss.
- the negative electrode is connected to the positive electrode of the second converter 2
- the negative electrode of the second converter 2 is connected to the positive electrode of the third converter 3
- the negative pole of the fourth inverter 4 is connected to the positive pole of the fifth inverter 5
- the anode of the first converter and the cathode of the fifth converter respectively correspond to the positive and negative poles of the first DC system.
- the positive pole of the second converter and the cathode of the fourth inverter are respectively connected to the positive and negative poles of the second DC system, and the positive and negative poles of the third converter are respectively connected to the third
- the positive and negative poles of the DC system are connected, and after the series connection of the DC sides is completed, the AC side of the first to fifth inverters 5 to 5 passes through a certain AC link 20 (for example, an AC transformer, a phase reactor, and an inductor).
- a capacitor-inductor circuit or the like is connected to the common AC bus 10.
- the inverters are preferably voltage source type inverters known in the art to enable each DC system to be multi-port DC-DC.
- the coupling transformer performs bidirectional power transmission.
- the negative electrode is connected to the positive electrode of the second converter 2
- the negative electrode of the second converter 2 is connected to the positive electrode of the third converter 3
- the cathode of the fourth converter 4 is connected to the anode of the fifth converter 5
- the cathode of the fifth converter 5 is connected to the anode of the sixth converter 6, and the cathode of the sixth converter 6
- the anode is connected to the anode of the seventh inverter 7, and the anode of the first converter and the cathode of the seventh converter are respectively connected to the positive and negative poles of the first DC system
- the anode of the second converter is
- the negative poles of the sixth inverter are respectively connected to the positive and negative poles of the second direct current system
- the positive and negative poles of the inverter are respectively connected with the positive and negative poles of the fourth DC system, and after the series connection of the DC side is completed, the first converter 1 A seventh inverter 7 is connected to the AC side of the AC bus 10 common link 20 (AC transformers, phase reactors, etc.) through a certain exchange.
- AC bus 10 common link 20 AC transformers, phase reactors, etc.
- the transformer connected to the three converters 3 and the fifth inverter 5 to the seventh inverter 7 can be connected to the DC side by means of a delta connection.
- FIG. 3 is a schematic diagram of the power flow analysis of the four-port DC-DC autotransformer of FIG. 2.
- the first to seventh inverters 7 to 7 are represented by corresponding numbers in boxes.
- the rated voltages of the first converter 7 and the seventh converter 7 are (E r E 2 )/2
- the second converter 2 and the sixth converter 6 The rated voltage can be taken as (E 2 -E 3 )/2
- the rated DC voltage of the third converter 5 and the fifth converter 5 can be taken as (E 3 -E 4 )/2
- the rated DC voltage of 4 can be taken as E 4
- the above rated DC voltage is only the reference value of the rated voltage design of each inverter.
- the actual operation can be increased or decreased as appropriate, and the multi-port DC-DC autotransformer can still operate.
- the DC power output of the fourth DC system 14, the third DC system 13 and the second DC system 12 in FIG. 3 is P 4 P 3 P 2 , respectively.
- the DC power input by the first DC system 11 is known. Is (P 4 + P 3 + P 2 ). Therefore, it can be calculated that the DC currents outputted by the fourth DC system 14 to the second DC system 12 are respectively P 4 /E 4 , ? 3 / and? 2 ⁇ 2 , and the DC input to the first DC system 11
- Kirchhoff's current law it can be determined that the direct currents flowing through the outputs of the first to fourth inverters 4 to 4 are:
- the rectified powers of the first to fourth inverters 4 to 4 can be determined as follows:
- Equation (35;) ⁇ (38) must meet the following conditions
- P 4max ⁇ P lmax respectively represent the maximum output/input DC power of the fourth DC system 14 to the first DC system 11, that is, the fourth DC system 14 ⁇ The absolute value of the rated output/input DC power of the first DC system 11.
- the rated DC voltages of the fourth DC system 14 to the first DC system 11 are respectively ⁇ 250kV ⁇ 320kV ⁇ 400kV ⁇ 500kV, that is, the values of E Ei are 500 640 800 1000, respectively.
- the value of E 4 E1 is substituted into (35) ⁇ (38):
- the rated power of the first converter 1 and the seventh converter 7 can be designed as 200MW
- the rated power of the second converter 2 and the sixth converter 6 can be designed to be 162MW
- the rated power of the third converter 5 and the fifth inverter 5 can be designed to be 111.125MW
- the fourth inverter The rated power of 4 can be designed to be 668.75 MW.
- the rated DC voltage and rated capacity of each of the inverters of this embodiment are summarized in Table 2.
- Figure 4 shows the "Multiport high power” of Dragan Jovcic et al. LCL DC hub for use in DC Transmission Grids " (IEEE on Power Delivery, 2014) proposed a multi-port DC-DC conversion technology based on LCL circuit.
- Figure 5 shows the "A dc-dc multiport-converter-based solid-state transformer integrating distributed generation and storage” of Sixifo Falcones et al. "Multi-port DC-DC conversion technology based on multi-port high frequency transformer” (IEEE Transactions on Power Electronics, 2013, 28(5), 2192 2203). Regardless of the scheme of FIG.
- the estimated cost per 1000 MW voltage source converter is 110 million euros according to the current international power grid conference (cost estimation is based on "DC fault performance and cost analysis of dc grids for connecting multiple offshore wind farms" (2013 IEEE Grenoble PowerTech, 1-6) estimates, for a 5000 MW four-port DC-DC converter, using conventional technology, the cost of the converter is 550 million euros, while using four-port DC-DC autotransformer technology, the converter The cost is only 178 million euros, and the cost savings are as high as 372 million euros.
- Figure 6 shows the topology diagram of the N-port DC-DC autotransformer.
- the N-port DC-DC autotransformer consists of 2N-1 inverters connected in series on the DC side, and connected in parallel to the AC side.
- the negative electrode of the first inverter is connected to the positive electrode of the second inverter
- the negative electrode of the second converter is connected to the positive electrode of the third inverter, and so on, the positive electrode of the jth converter and the j-th 1
- the negative pole of the converter is connected, the cathode of the jth converter is connected to the anode of the j+1 converter, and the anode of the 2N-1 converter is connected to the cathode of the 2N-2 converter.
- j is any positive integer between 2 and 2N-2; after the DC side of each of the above converters is sequentially connected in series, the positive pole of the first converter and the negative pole of the second N-1 inverter are respectively 1 The positive and negative poles of the DC system are connected, and the anode of the first converter and the cathode of the 2N-2 converter are respectively connected to the positive and negative poles of the second DC system, and so on, and the anode of the i-th converter And the negative pole of the 2N-i converter is respectively connected to the positive and negative poles of the ith DC system, and the positive and negative poles of the Nth inverter and the Nth DC system respectively Positive and negative Corresponding connection; After the DC side of each of the converters is connected to each DC system, the AC side of each converter is connected to a common point via a certain AC link, and the present invention is a common AC bus. .
- a feasible control strategy is to specify one or more inverters to control the AC voltage of the common AC bus and other converters to control the DC systems connected to each other. The active power transmitted.
- the 7 is a four-port DC-DC autotransformer connected to four asymmetric single-pole DC systems, including four inverters, the negative pole of the first converter 1 is connected to the anode of the second converter 2,
- the cathode of the second converter 2 is connected to the anode of the third converter 3
- the cathode of the third converter 3 is connected to the anode of the fourth converter 4
- the anode of the first converter 1 is DC.
- the line 30 is connected to the positive pole of the first DC system 11
- the anode of the second converter 2 is connected to the anode of the second DC system 12 via the DC line 30, and the anode of the third converter 3 is connected to the DC line 30.
- Line 30 is coupled to the cathode of fourth inverter 4 and is further coupled to ground 31, which may include power lines, cables, and corresponding DC inductors, etc., which are well known in the art.
- Figure 8 is a four-port DC-DC autotransformer embodiment in which the first inverter 1 and the seventh inverter 7 employ a phase-controlled inverter and the phase-controlled converter operates in a rectified state, this embodiment and the diagram
- the embodiment of 2 is basically the same, the only difference is that the first DC system 1 can only absorb DC power from the DC-DC autotransformer because the first converter 7 and the seventh converter 7 use a phase-controlled rectifier.
- a DC system 1 and a DC-DC autotransformer can only achieve one-way power transmission.
- Figure 9 is a four-port DC-DC autotransformer embodiment in which the first converter 1 and the seventh inverter 7 employ a phase-controlled inverter and the phase-controlled converter operates in an inverting state
- this embodiment is The embodiment of Fig. 2 is basically the same, the only difference is that the first DC system 1 can only output DC power to the DC-DC autotransformer because the first inverter 1 and the seventh inverter 7 use the phased inverter.
- the first DC system 1 and the DC-DC autotransformer can only achieve one-way power transmission.
- the AC terminals of the inverters are not necessarily connected to a common point.
- Figure 10 is an embodiment in which the AC side of the partial converter is not connected to the common AC bus but to other AC systems.
- the embodiment of Figure 10 is substantially identical to the embodiment of Figure 2, with the difference being that the second converter 2 and the The AC side of the six-converter 6 is not connected to the common AC bus 10 but to the AC system 40.
- the actual implementation of the present invention may be the AC side of one or more inverters and one or more external AC systems. 40 connected.
- FIG 11 is an implementation of the DC system of the present invention.
- the plurality of AC systems 40 are AC-DC-converted via the inverter 41 and then connected in parallel on the DC side via the DC line 30.
- FIG. 12 is still another implementation of the DC system of the present invention. After the AC system 40 is converted by the AC converter 40 through the AC-DC converter, the DC system 42 that outputs DC is itself passed through the DC line 30 on the DC side. Connected in parallel.
- FIG. 13 shows the block diagram of the common AC bus voltage control.
- U ⁇ f and U qref are the dq axis command values of the bus voltage, respectively.
- the unit is the standard, U dpu , IT, respectively, the dq axis voltage measured value, Idrrf,
- ⁇ is the 3-axis current command value, and specifies that the output direction is the positive direction of the current
- Lp U is the inductance value of the AC link
- M d is the inductance value of the AC link
- M q is the dq-axis modulation ratio
- the VCO is the voltage-controlled crystal oscillator.
- the trigger control of the flow device provides a reference angle
- f is the operating frequency of the AC link.
- Figure 14 shows the DC active power control block diagram.
- ⁇ and P dCTef are the DC power standard value and the DC power reference value respectively
- u is the instantaneous value of the common AC bus voltage
- the PLL is the phase locked loop.
- FIG. 15 shows the active power output from the fourth DC system to the first DC system from top to bottom. 0.1 second to 0.5 second, the output DC power command values of the fourth to second DC systems are increased from 0 to 700 MW, 1000 MW and -1300 MW, respectively, while the first DC system is used to balance the entire multi-port DC-DC.
- the active power of the autotransformer is not limited to a simulation example of a four-port DC-DC autotransformer.
- the active power output from each DC system can be controlled to reach the expected command value of 1.5 seconds to 1.9 seconds, and the output power command value of the third DC system is reduced from 1000MW to -1000MW and the fourth and second.
- the DC power command value of the DC system remains unchanged.
- the DC power outputted by the third DC system can be controlled to be reduced to -1000 MW (that is, the third DC system is changed from the output 1000 MW DC power to the DC-DC autotransformer).
- Absorbing 1000 MW of DC power) the active power of the output of the fourth DC system and the second DC system fluctuates slightly, but remains unchanged around its command value.
- the DC power output by a DC system after 1.5 seconds has changed from about -370 MW to about 1,650 MW.
- Figure 16 shows the AC power outputted by the first to seventh inverters. Since the fourth DC system to the first DC system in this embodiment are both symmetric bipolar DC systems, the first converter and the seventh converter The AC power output by the inverter is equal, the AC power output by the second converter and the sixth converter is equal, and the AC power output by the third converter and the fifth converter is equal.
- the DC power output from the fourth to the second DC system is 700 MW, 1000 MW and -1300 MW, respectively, according to the analysis method of the formula (31) to the formula (38), the first to fourth inverters can be obtained.
- the theoretical AC power values are -40 MW, -162 MW, -32.375 MW, and 468.75 MW, respectively.
- the AC power output from each converter during the period of 0.5 sec to 1.5 s in Fig. 16 corresponds to the above theoretical value.
- the present invention can greatly Reduce the capacity of the inverter used and reduce the capacity of the AC link used, thus greatly reducing the investment cost, reducing the power required to pass the DC-AC-DC two-stage AC-DC conversion, thereby greatly reducing the operation loss and reducing the running cost.
- the first to second N-1 inverters preferably use a voltage source type inverter to realize bidirectional flow of power.
- the voltage source type inverter is well known in the art and may have a two-level inverter. Three-level converters, modular multilevel converters and many other topologies.
- the total converter capacity required is only about 30% of the sum of the absolute values of the input/output DC power of each interconnected DC system, while the total commutation capacity required by conventional multi-port DC-DC converters For each interconnected DC system, about 100% of the sum of the absolute values of the input/output DC power, the present invention saves about 70% of the converter cost compared to the prior art.
- the present invention can also save the capacity of the AC transformer, phase reactance, etc. used.
- the present invention requires only about 30% of the interconnect power to undergo a two-stage DC-AC-DC conversion, while the conventional multi-port
- the 100% interconnection power of the DC-DC conversion technology needs to undergo DC-AC-DC conversion, so that the invention can greatly reduce the operation loss and reduce the operation cost.
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Abstract
一种多端口直流-直流自耦变压器,用于实现多个电压等级不同的直流***之间的互联传输,该自耦变压器包括2N-1个换流器,该2N-1个换流器在直流侧依次串联连接,并在交流侧连接到交流线路,且所述依次串联的所述2N-1个换流器中的第i个换流器的正极和第2N-i换流器的负极分别与第i个直流***的正负极对应连接;其中,N为直流***的个数,i为换流器的序号。进一步公开了上述自耦变压器中换流器的容量设计方法以及上述自耦变压器的控制方法。该自耦变压器可以使得各直流***之间传输的大部分功率可以无需经过直流-交流-直流变换,而是直接经过各直流***之间的电气互联进行传输,极大降低各换流器的额定电压和运行损耗,从而降低运行成本。
Description
一种多端口直流 -直流自耦变压器及其应用
【技术领域】
本发明属于电力***柔性输配电技术领域, 具体涉及一种直流-直流变 换器, 适用于互联多个电压等级不同的直流***。
【背景技术】
随着越来越多的风力发电, 太阳能发电等新能源发电接入电网以及直 流输电技术的发展, 将多条直流输电线路互联构成多端直流输电***以及 直流***从而解决大规模新能源发电的接入问题成为工业界广泛关注的技 术方案。 为了形成直流***, 各个区域直流***的互联是一个亟待解决的 问题。 由于各个区域直流***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***的额定直流电压不会完全一致。 为了互联多个
(大于等于 3个) 不同额定直流电压的直流***, 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, 互联多个不同额 定直流电压的直流微网也需要用到直流-直流变换器。
一种互联多个不同电压等级直流***的方案是利用多个两端口直流-直 流变换器将不同电压等级的直流***两两互联在一起。 但这种方案需要较 多的两端口直流-直流变换器, 成本高, 损耗大。 另一种方案是采用多端口 直流 -直流变换器技术。
现有技术中存在一种采用电感 -电容 -电感 (LCL)电路的多端口直流-直 流变换技术, 该方案中, 每个直流***直流侧与各自的换流器直流侧连接 在一起,每个换流器的交流侧经电感 -电容 (LC)电路连接到交流公共母线上。 该方案中,每个 LC电路的电感和电容的取值经过特殊设计从而能确保不同 电压等级的直流***不需要变压器也能直接互联在一起。
Sixifo Falcones 等人的 " A dc-dc multiport-converter-based solid-state
transformer integrating distributed generation and storage " (IEEE Transactions on Power Electronics, 2013, 28(5), 2192~2203)披露了一种采用多端口高频变 压器的多端口直流-直流变换技术, 其技术细节为每个直流***经电压源型 换流器在交流侧与多端***流变压器的某个端口连接在一起, 多端***流 变压器用于匹配各电压源型换流器的不同输出交流电压从而达到互联不同 电压等级直流***的目的。
上述采用 LCL 电路的多端口直流-直流变换技术以及采用多端口高频 变压器的多端口直流 -直流变换技术的一个显著共同点是各互联的直流*** 直流侧没有直接的互联, 为此多端口直流 -直流变换技术没有充分利用各个 直流***已经存在的直流电压,所有传输的功率都要经过直流-交流-直流变 换, 所需要的换流器总容量为互联容量的两倍, 带来换流器成本高, 交流 链路成本高, 运行损耗大的缺陷。
本申请的发明人在先申请的发明专利 CN201410024869.X 中提出了一 种立体式直流 -直流变换器技术, 该技术通过将三个换流器串联, 能充分利 用低电压直流***已经存在的直流电压从而可以极大地降低所使用的总的 换流器, 降低交流链路成本, 降低运行损耗,
但 201410024869X中的方案只能连接两个电压等级不同的直流***, 其并没有提出相应的方案以连接 3个及 3个以上的电压等级不同的直流系 统, 也没有指明如何设计含 3个以上换流器的立体式直流-直流变换器中各 个换流器的额定电压和额定功率。
【发明内容】
为了改进上述传统多端口直流-直流变换器存在的缺点, 降低多端口直 流-直流变换器总的变流容量从而降低成本, 降低损耗, 本提供了一种多端 口直流 -直流自耦变压器, 其充分利用了各直流***已经存在的直流电压, 在直流侧对各直流***进行一定程度的直接电气互联, 使得各直流***之 间传输的大部分功率可以无需经过直流 -交流 -直流变换,而是直接经过各直
流***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:
一种多端口直流 -直流自耦变压器, 用于实现 N个直流***之间的互联 传输 (N≥3), 其特征在于, 该直流 -直流自耦变压器由 2N-1个换流器在直流 侧依次串联, 在交流侧并联连接到一点, 其中,
所述第 1换流器的负极与第 2换流器的正极相连接, 第 2换流器的负 极与第 3换流器的正极相连接, 依次类推, 第 j换流器的正极与第 j-1换流 器的负极相连接,第 j换流器的负极与第 j+1换流器的正极相连接,第 2N-1 换流器的正极与第 2N-2换流器的负极相连接, j为介于 2和 2N-2之间的 任意正整数;
完成上述各换流器的直流侧依次串联后, 第 1换流器的正极和第 2N-1 换流器的负极分别与第 1直流***的正负极对应连接, 第 1换流器的正极 和第 2N-2换流器的负极分别与第 2直流***的正负极对应连接,依次类推, 第 i换流器的正极和第 2N-i换流器的负极分别与第 i直流***的正负极对应 连接, 第 N换流器的正负极分别和第 N直流***的正负极对应连接;
完成上述各换流器的直流侧与各直流***对应连接后, 各换流器的交 流侧经过一定的交流链路连接在一公共点, 本发明记此交流公共点为公共 交流母线。
更进一步地, 当交流链路采用交流变压器时, 所述第 1换流器〜第 N-1 换流器以及第 N+1换流器至第 2N-1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, 以消除这些换流器的中性点不平衡问题, 所述第 N 换流器的变压器靠近直流侧的端口以及所有换流器靠近公共交流母线侧可 以采用星形或三角形接线。
更进一步地, 所述第 1〜第 N-1换流器以及第 N+1〜第 2N-1换流器的 交流变压器靠近公共交流母线侧的端口采用三角形接线方式, 以消除这些 换流器的中性点不平衡问题, 所述第 N换流器的变压器靠近交流公共母线
侧的端口以及所有 2N- 1个换流器靠近直侧的端口可以采用星形或三角形接 线。
更进一步地, 所述 2N-1个换流器中至少一个换流器用于控制交流公共 母线的交流电压而其他换流器则用于控制各自的有功功率, 从而实现多端 口直流 -直流自耦变压器的稳定运行。
更进一步地, 所述第 1〜第 N-1换流器以及第 N+1〜第 2N-1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这些换流 器的中性点不平衡。
更进一步地, 所述任意第 1直流***〜第 N直流***是一个或多个交 流***经过交流 /直流变换后在直流侧互联构成的。
更进一步地, 所述任意第 1直流***〜第 N直流***是一个或多个交 流***经过交流 /直流变换后与本身即输出直流电的直流***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, 所述任意第 1换流器〜第 2N-1换流器的交流侧不与公共 交流母线连接, 而是可以连接到相同或不同的交流电网上。
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 1换流器和第 2N-1换流器的额定直流电压设计为 (ErE2)/2,第 2 换流器和第 2N-2 换流器的额定直流电压设计为 (E2-E3)/2, 依次类推, 第 i 换流器和第 2N-i换流器的额定直流电压设计为 (Ei-Ei+1)/2, 第 N换流器的额 定直流电压为 EN, 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多端口直流 -直流自耦变压器运 行, 所述 E1〜EN分别为第 1直流***〜第 N直流***的额定直流电压, 且 E!>E2> .. EN,所述的额定直流电压为高电压直流端口对低电压直流端口的 额定电压。
更进一步地, 所述第 1直流***〜第 N直流***的任意一个可以采用
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 1换流器〜第 2N-1换流器优选为电压源型换流器, 从而使得第 1直流***〜第 N直流***的任意一个都可以双向地与多端口 直流-直流自耦变压器交换功率。
更进一步地, 所述第 1换流器〜第 2N-1换流器的一个或任意一个可以 采用基于晶闸管的相控换流器或者不控整流桥。
更进一步地, 本发明还提供了一种多端口直流-直流自耦变压器各换流 器额定容量的设计方法, 具体为记第 2直流***〜第 N直流***向多端口 直流-直流自耦变压器输出的功率为 P2~PN, 根据功率守恒原理, 第 1直流 ***吸收的有功功率为 (P2+ . . . +PN), 进一步可以计算得第 2直流***〜第 N 直流***输出的直流电流为 P2/E2〜PN/EN, 第 1 直流***的输入电流为 (P2+ . . . +PN)/EI, 根据基尔霍夫电流定律以及前述多端口直流 -直流自耦变压 器的拓扑, 可以计算得到从第 1换流器流出的直流电流为
依次类推, 第 i换流器的整流功率为 ρ = (
上述公式 (6)-(10)满足以下条件
-P 2 max <一 p 2 <— p丄 2 max
(11)
-P N max <— p N <— p N max
(12)
式 (11)~(12)中, Plmax〜PNmax分别表示第 1直流***〜第 N直流***的 最大输出 /输入功率, 将式 (11)和 (12)代入式 (6)可以求得第 1 换流器的最大
功率为
p _ i o \ VSC l,max _ 、丄
第 2换流器〜第 N换流器的最大有功功率无法得到通用表达式, 而是 需要根据各具体的 Plmax〜PNmax以及 Ε^ΕΝ, 结合公式 (11)和 (12), 求得每 个换流器的最大功率, 所求取的功率将作为各个换流器的额定功率, 其中 第 2N-1个换流器的额定功率与第 1个换流器的额定功率相同, 第 2Ν-2个 换流器额定功率与第 2个换流器功率相同, 依次类推, 第 2N-i个换流器的 额定功率与第 i个换流器额定功率相同, 以上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功率仍能使多端口直 流 -直流自耦变压器运行
更进一步地, 本发明还提供了一种多端口直流-直流自耦变压器的控制 方法, 具体为, 至少 1 个换流器用于控制公共交流的交流电压, 其他换流 器则用于控制与有功功率相关的量, 如直流功率或直流电压。
更进一步地, 根据多端口直流-直流自耦变压器的容量大小, 多端口直 流-直流自耦变压器内部的交流链路可以采用单相交流电路,两相交流电路, 三相交流电路或多相交流电路。
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 ) 通过多个换流器将不同电压等级的直流***串联联接在一起, 充 分利用了各互联直流***已经存在的直流电压, 大大降低了各换流器的额 定电压从而降低了成本。
( 2 )本发明所使用的换流器容量总和大大小于传统的多端口直流 -直流 变换器, 本发明可以大大地节省换流器成本。
( 3 )本发明各直流***间互联的功率大部分会经过各直流***之间的 直接电气联系进行传输,大大减少了需要经过直流 -交流 -直流两级变换的功 率, 从而大大降低了运行损耗从而大大降低了运行成本, 而传统多端口直
流 -直流变换器所有互联功率都需要经过两级直流 -交流 -直流变换, 运行损 耗 [¾。
(4) 本发明各互联直流***只有一部分互联功率需要经过直流-交流- 直流两级变换从而可以大大降低交流链路成本, 而传统多端口直流-直流变 换器所有互联功率都需要经过直流-交流-直流两级变换,相应交流链路容量 为互联功率的 2倍。
【附图说明】
图 1是按照本发明一个实施例的三端口直流 -直流自耦变压器的原理结 构图;
图 2是按照本发明一个实施例的四端口直流 -直流自耦变压器的原理结 构图;
图 3是按照本发明一个实施例的四端口直流 -直流自耦变压器各换流器 额定容量设计示意图;
图 4是现有技术中的采用 LCL电路的多端口直流 -直流变换示意图; 图 5是现有技术中的采用多端口高频变压器的直流 -直流变换示意图; 图 6是按照本发明一个实施例的 N端口直流 -直流自耦变压器的原理结 构图;
图 7是各直流***为不对称单极直流***的四端口直流-直流自耦变压 器原理结构图;
图 8是本发明中部分换流器采用基于晶闸管的相控换流器的一个实施 例的结构示意图;
图 9是本发明中部分换流器采用基于晶闸管的相控换流器的另一个实 施例的结构示意图;
图 10是本发明中部分换流器交流侧与外部交流***互联的实施例的的 结构示意图;
图 11是本发明的直流***的一种实现方式的实施例的结构示意图;
图 12是本发明的直流***的又一种实现方式的实施例的结构示意图; 图 13是本发明实施例的交流电压控制原理图;
图 14是本发明实施例的直流功率控制原理图;
图 15 是本发明一个四端口直流-直流自耦变压器的各直流***输出直 流功率仿真曲线图;
图 16 是本发明一个四端口直流-直流自耦变压器的各换流器输出交流 功率仿真曲线图;
图 17 是本发明一个四端口直流-直流自耦变压器的各直流***输出直 流功率绝对值之和和各换流器输出交流功率绝对值之和的仿真曲线图。 【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多端口直流-直流自耦变压器用于用于互联大于等 于 3个额定直流电压不同的直流***, 能够解决现有的采用全功率直流-交 流 -直流变换的传统多端口直流-直流变换器所带来的换流器成本高,损耗大 的缺点。
图 1所示为一个三端口直流-直流自耦变压器 (N=3),其主要由 5个换流 器依次在直流侧串联而成 (2N-1=5),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的负极与第四换流器 4的正极相连接, 第四换流器 4的负极与第五 换流器 5的正极相连接, 同时第 1换流器的正极和第 5换流器的负极分别 和第 1直流***的正负极对应连接, 第 2换流器的正极和第 4换流器的负 极分别和第 2直流***的正负极对应连接,第 3换流器的正负极分别和第 3
直流***的正负极对应连接, 完成上述直流侧的串联后,第一换流器 1〜第 五换流器 5的交流侧通过一定的交流链路 20(例如交流变压器, 相电抗器, 电感-电容-电感电路等)连接到公共交流母线 10, 在本实施例中, 换流器优 选为本行业内公知的电压源型换流器以使得每个直流***能与多端口直流- 直流自耦变压器进行双向功率传输。
图 2所示为一个四端口直流-直流自耦变压器 (N=4),其主要由 7个换流 器依次在直流侧串联而成 (2N-1=7),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的负极与第四换流器 4的正极相连接, 第四换流器 4的负极与第五 换流器 5的正极相连接, 第五换流器 5的负极与第六换流器 6的正极相连 接, 第六换流器 6的负极与第七换流器 7的正极相连接, 同时第 1换流器 的正极和第 7换流器的负极分别和第 1直流***的正负极对应连接, 第 2 换流器的正极和第 6换流器的负极分别和第 2直流***的正负极对应连接, 第 3换流器的正极和第 5换流器的负极分别和第 3直流***的正负极对应 连接, 第 4换流器的正负极分别和第 4直流***的正负极对应连接, 完成 上述直流侧的串联后,第一换流器 1〜第七换流器 7的交流侧通过一定的交 流链路 20(交流变压器, 相电抗器等)连接到公共交流母线 10。
图 2中, 为了消除第一换流器 1〜第三换流器 3以及第五换流器 5〜第 七换流器 7的中性点不平衡问题,与第一换流器 1〜第三换流器 3及第五换 流器 5〜第七换流器 7连接的变压器靠近直流侧可以采用三角接线的方式。
图 3为对图 2的四端口直流-直流自耦变压器的潮流分析示意图, 为简 化绘图, 第一换流器 1〜第七换流器 7以方框内填相应数字表示。通过分析 图 2和图 3可以得出第一换流器 1和第七换流器 7的额定电压为 (ErE2)/2, 第 二换流器 2和第六换流器 6的额定电压可以取为 (E2-E3)/2,第三换流器 3和 第五换流器 5的额定直流电压可以取为 (E3-E4)/2,第四换流器 4的额定直流 电压可以取为 E4,上述额定直流电压只是各换流器额定电压设计的参考值,
实际运行时可适当增大或减小, 多端口直流-直流自耦变压器仍能运行。 记图 3中第四直流*** 14, 第三直流*** 13和第二直流*** 12输出 的直流功率分别为 P4 P3 P2, 根据功率平衡原则, 可知第一直流*** 11 输入的直流功率为 (P4+P3+P2)。 由此可以计算得第四直流*** 14〜第二直 流*** 12输出的直流电流分别为 P4/E4, ?3/ 和?2^2, 而输入到第一直流 *** 11的直流
根据基尔霍夫电流定律, 可以求得 流经第一换流器 1〜第四换流器 4的输出的直流电流分别为:
P4 + P, + P?
+ P3 + P2 p2 p3
AVSC4 (34)
E2 E3
由此可以求得第一换流器 1〜第四换流器 4的整流功率分别为:
式 (35;)〜 (38)需满足以下条件
P 4max <— p <— p 4max
3 max 3 3 max (39) p A 2max <— p A 2 <— p A 2max
< (p + p + P ) < p
lmax (40) 式 (39)~(40)中, P4max~P lmax分别表示第四直流*** 14〜第一直流*** 1 1的最大输出 /输入直流功率, 也即第四直流*** 14〜第一直流*** 11的 额定输出 /输入直流功率的绝对值。
例如一个具体实施例中,第四直流*** 14〜第一直流*** 11的额定直 流电压分别为 ±250kV ±320kV ±400kV ±500kV, 也即 E Ei的值分别 为 500 640 800 1000, 将此实施例下 E4 E1的值代入 (35)~(38)可得:
Ρ^2= 0.08(Ρ4 + Ρ3) - 0.02Ρ2 (42)
P^C3 = 0.07Ρ4 - 0.039375Ρ3 - 0.0175Ρ2 (43)
-Ρ 4 = 0.5Ρ4 + 0.28125Ρ3 + 0.125Ρ2 (44)
一个具体实施例 (各直流***额定直流电压和额定直流功率列于表 1中) 中 P4max=700MW P3 =1000MW P2max=1300MW P ax=2000MW, 将此 条件代入式 (41)~(44)并考虑式 (39)~式 (40)的约束可以求得。 PVSC1在 P4+P3+P2=Plmax=2000时取得最大值 200MW, PVSC2在 P4=700 P3=1000 P2=-1300时取得最大值 162MW, PVSC3在 P4=700 P3=-1000 P2=-1300时 取得最大值 111.125MW, PVC4在 P4=700 P3=1000 P2=300时取得最大 值 668.75MW。 为此第一换流器 1及第七换流器 7的额定功率可以设计为
200MW, 第二换流器 2及第六换流器 6的额定功率可设计为 162MW, 第 三换流器 3及第五换流器 5的额定功率可设计为 111.125MW, 第四换流器 4 的额定功率可设计为 668.75MW, 该实施例所采用的总的换流器容量为 200*2+162*2+111.125*2+668.75=1615MW。 该实施例各换流器的额定直流 电压和额定容量统计与表 2中。
表 1 某实施例中各直流***额定直流电压和额定直流功率绝对值
E4 E3 E2 Ei
±250 ±320 ±400 ±500
700 1000 1300 2000 表 2某实施例中各换流器的额定直流电压和额定功率
换流器编号 额定直流电压 (kV ) 额定功率 (MW)
第 1换流器 100 200
第 2换流器 80 162
第 3换流器 70 111.125 第 4换流器 500 668.75 第 5换流器 70 111.125 第 6换流器 80 162
第 7换流器 100 200
本发明总容量 1 1615
常规技术总容量 : 1 5000 为了对比本发明所提的多端口直流-直流自耦变压器与现有的多端口直 流-直流变换器的区别, 图 4给出了 Dragan Jovcic等人的 "Multiport high power LCL DC hub for use in DC Transmission Grids " (IEEE Transactions on
Power Delivery, 2014 )提出的一种基于 LCL电路的多端口直流 -直流变换技 术, 图 5给出了 Sixifo Falcones等人的 "A dc-dc multiport-converter-based solid-state transformer integrating distributed generation and storage" (IEEE Transactions on Power Electronics, 2013, 28(5), 2192 2203)所提及的基于多 端口高频变压器的多端口直流-直流变换技术。无论是图 4还是图 5的方案, 所有互联的功率都需要经过直流 -交流 -直流变换,为此对于上述四端口实施 例, 如果采用图 4 或者图 5 的方案, 所需要的总的换流器容量为 700+ 1000+ 1300+2000=5000MW, 远远高于本发明方案中所需要的 1615MW, 本发明所需要的总的换流器容量仅为现有技术的 32.3%。 按国际 大电网会议当前估算的每 1000MW电压源型换流器成本 1.1亿欧元 (成本估 算参考 Mohsen Taherbaneh等 "DC fault performance and cost analysis of dc grids for connecting multiple offshore wind farms " ( 2013 IEEE Grenoble PowerTech, 1-6) )的估计, 对于一个 5000MW的四端口直流-直流变换器, 采用常规技术, 换流器的成本为 5.5亿欧元, 而采用四端口直流-直流自耦 变压器技术,换流器的成本仅为 1.78亿欧元,节省的费用高达 3.72亿欧元。
图 6给出了 N端口直流 -直流自耦变压器的拓扑示意图, N端口直流- 直流自耦变压器由 2N-1个换流器在直流侧依次串联, 在交流侧并联连接到 一点构成, 所述第 1换流器的负极与第 2换流器的正极相连接, 第 2换流 器的负极与第 3换流器的正极相连接,依次类推,第 j换流器的正极与第 j-1 换流器的负极相连接, 第 j换流器的负极与第 j+1换流器的正极相连接, 第 2N-1换流器的正极与第 2N-2换流器的负极相连接, j为介于 2和 2N-2之 间的任意正整数; 完成上述各换流器的直流侧依次串联后, 第 1 换流器的 正极和第 2N-1换流器的负极分别与第 1直流***的正负极对应连接, 第 1 换流器的正极和第 2N-2换流器的负极分别与第 2直流***的正负极对应连 接,依次类推,第 i换流器的正极和第 2N-i换流器的负极分别与第 i直流系 统的正负极对应连接, 第 N换流器的正负极分别和第 N直流***的正负极
对应连接; 完成上述各换流器的直流侧与各直流***对应连接后, 各换流 器的交流侧经过一定的交流链路连接在一公共点, 本发明记此交流公共点 为公共交流母线。
为了使多端口直流 -直流自耦变能稳定运行, 一种可行的控制策略是指 定一个或多个换流器控制公共交流母线的交流电压而其他换流器用于控制 各自所连接的直流***所传输的有功功率。
图 7是连接四个不对称单极直流***的四端口直流 -直流自耦变压器, 包括四个换流器, 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 第四换流器 4的正极相连接, 同时第一换流器 1的正极经直流线路 30与第 一直流*** 11的正极相连接, 第二换流器 2的正极经直流线路 30与第二 直流*** 12的正极相连接, 第三换流器 3的正极经直流线路 30与第三直 流*** 13的正极相连接, 第四换流器 4的正极经直流线路 30与第四直流 *** 14的正极相连接, 第一直流*** 1〜第四直流*** 4的负极各自经直 流线路 30连接于第四换流器 4的负极, 并进一步连接至地 31, 所述直流线 路 30可以包括输电线, 电缆以及相应的直流电感等,此为行业内公知技术。
图 8是第一换流器 1和第七换流器 7采用相控换流器并且该相控换流 器工作在整流状态的四端口直流 -直流自耦变压器实施例, 该实施例与图 2 的实施例基本一致, 区别仅在于因为第一换流器 1和第七换流器 7采用相 控整流器使得第一直流*** 1 只能从该直流-直流自耦变压器吸收直流功 率, 第一直流*** 1与直流-直流自耦变压器只能实现单向的功率传输。
图 9是第一换流器 1和第七换流器 7采用相控换流器并且该相控换流 器工作在逆变状态的四端口直流 -直流自耦变压器实施例, 该实施例与图 2 的实施例基本一致, 区别仅在于因为第一换流器 1和第七换流器 7采用相 控逆变器使得第一直流*** 1 只能输出直流功率至直流 -直流自耦变压器, 第一直流*** 1与直流-直流自耦变压器只能实现单向的功率传输。
本申请中, 各换流器的交流端不是必须连在一个公共点上。 图 10是部 分换流器的交流侧不与公共交流母线连接而是与其他交流***连接的一个 实施例, 图 10实施例与图 2实施例基本一致, 区别在于第二换流器 2和第 六换流器 6的交流侧不与公共交流母线 10相连接而是与交流*** 40相连 接, 本发明实际实施时可以是一个或多个换流器的交流侧与一个或多个外 部交流*** 40相连接。
图 11是本发明所述直流***的一种实现方式, 由多个交流*** 40经 换流器 41通过交流-直流变换后, 在直流侧通过直流线路 30并联连接在一 起。
图 12是本发明所述直流***的又一种实现方式, 由多个交流*** 40 经换流器 41通过交流-直流变换后, 与本身即输出直流的直流*** 42在直 流侧通过直流线路 30并联连接在一起。
图 13所示为公共交流母线电压控制框图, 图中 U^f, Uqref分别为母线 电压的 dq轴指令值,单位为标幺, Udpu, IT,分别为 dq轴电压实测值, Idrrf,
^ 为3 轴电流指令值, 并且规定输出方向为电流正方向, LpU为交流链路 的电感标幺值, Md, Mq为 dq轴调制比, VCO为压控晶振, 用于给换流器 的触发控制提供参考角度, f为交流链路的运行频率。
图 14所示为直流有功功率控制框图,? ^及 PdCTef分别为直流功率标幺 值及直流功率参考值, u为公共交流母线电压瞬时值, PLL为锁相环。
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中搭建了四端口直流-直流自耦变压器的仿真算例, 该实施 例中各直流***的额定电压和额定直流功率列于表 1 中, 各换流器的额定 电压和额定功率列于表 2中。 图 15〜图 17为对应的仿真结果。 其中图 15 从上到下依次第四直流***〜第一直流***输出的有功功率。 0.1 秒〜 0.5 秒, 第四〜第二直流***的输出直流功率指令值分别从 0上升到 700MW, 1000MW以及 -1300MW, 而第一直流***则用于平衡整个多端口直流 -直流
自耦变压器的有功功率。 从图 15可以看出, 各直流***输出的有功功率可 以受控制地达到预期的指令值 1.5秒〜 1.9秒, 第三直流***的输出功率指 令值从 1000MW下降为 -1000MW而第四,第二直流***的直流功率指令值 仍维持不变。 从图 15的 1.5秒后的曲线可以看出, 第三直流***输出的直 流功率可以受控地将降至 -1000MW (即第三直流***从输出 1000MW直流 功率变为从直流-直流自耦变压器吸收 1000MW直流功率), 第四直流*** 和第二直流***输出的有功功率略有波动, 但仍维持在其指令值附近不变, 为了平衡整个多端口直流-直流自耦变压器的直流功率,第一直流***在 1.5 秒后输出的直流功率从 -370MW左右变为约 1650MW。
图 16给出了第一〜第七换流器输出的交流功率, 由于本实施例中第四 直流***〜第一直流***都为对称双极直流***, 因此第一换流器和第七 换流器输出的交流功率相等, 第二换流器和第六换流器输出的交流功率相 等, 第三换流器和第五换流器输出的交流功率相等。 当第四〜第二直流系 统输出的直流功率分别为 700MW, 1000MW和 -1300MW时,按照公式 (31)~ 公式 (38)的分析方法,可以求得第一换流器〜第四换流器输出的交流功率理 论值分别为 -40MW, -162MW, -32.375MW及 468.75MW, 图 16曲线 0.5 秒〜 1.5秒期间各换流器输出的交流功率与上述理论值对应。
图 17为各直流***输出 /输入直流功率绝对值之和以及各换流器输出 / 输入交流功率之和, 换流器功率之和远远小于实际传输的直流功率之和, 本发明可以大大地减少所使用换流器的容量和减少所使用交流链路的容量 从而大大地降低投资成本, 减少需要经过直流-交流-直流两级交-直变换的 功率从而大大地降低运行损耗, 减少运行成本。
本发明中第 1〜第 2N-1换流器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。
本发明的用于连接多个不同额定直流电压的直流***的直流-直流变换
器相比于传统的多端口直流-直流变换器, 优势在于:
( 1 )所需要的总的换流器容量仅为各互联直流***输入 /输出直流功率 绝对值的和的 30%左右, 而传统的多端口直流-直流变换器所需要的总的换 流容量为各互联直流***输入 /输出直流功率绝对值和的 100%左右,为此本 发明相比于现有技术, 节省约 70%的换流器成本。
(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, 以一个 5GW的四端口直流 -直流变换器为例, 本发明能节省 约 3.85亿欧元的成本, 而未来中国范围以及世界范围内需要互联的直流系 统容量高达数百 GW, 为此本发明的经济性相比于传统的多端口直流 -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。
(4) 由于本发明中各互联电网之间可以通过直接的电气连接传输大部 分有功功率,本发明仅需要约 30%的互联功率需要经过两级直流 -交流 -直流 变换, 而传统的多端口直流-直流变换技术 100%的互联功率需要经过直流- 交流 -直流变换, 为此本发明能极大地降低运行损耗从而降低运行成本。 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
1、一种多端口直流 -直流自耦变压器,用于实现三个以上的直流***之 间的互联传输, 其特征在于,
该自耦变压器包括 2N-1个换流器, 该 2N-1个换流器在直流侧依次串 联连接, 并在交流侧通过交流链路连接到交流线路;
且所述依次串联的所述 2N-1个换流器中的任意第 i个换流器的正极和 第 2N-i个换流器的负极分别与对应的第 i个直流***的正负极对应连接; 其中, N为直流***的个数, N 3, i为取不大于 N的自然数。
2、根据权利要求 1所述的一种多端口直流 -直流自耦变压器, 其中, 依 次串联的所述 2N-1个换流器中的除位于串联链路中间的第 N个换流器外的 其他 2N-2个换流器通过交流变压器连接到交流线路, 该 2N-2个交流变压 器的靠近直流侧的端口采用三角形接线方式, 以消除这些换流器的中性点 不平衡问题。
3、根据权利要求 1或 2所述的一种多端口直流 -直流自耦变压器,其中, 所述依次串联的所述 2N-1个换流器中的除位于串联链路中间的第 N个换流 器外的其他 2N-2个换流器的交流变压器的靠近交流线路侧的端口采用三角 形接线方式, 以消除这些换流器的中性点不平衡问题。
4、 根据权利要求 1-3 中任一项所述的一种多端口直流-直流自耦变压 器, 其中, 位于串联链路中间的第 N个换流器通过交流变压器连接到交流 线路, 该交流变压器靠近交流线路侧的端口以及所有 2N-1个换流器靠近直 侧的端口可以采用星形或三角形接线。
5、 根据权利要求 1-4 中任一项所述的一种多端口直流-直流自耦变压 器, 其中, 所述 2N-1个换流器中至少一个换流器用于控制交流线路的交流 电压而其他换流器则用于控制各自的有功功率, 从而实现多端口直流 -直流 自耦变压器的稳定运行。
6、 根据权利要求 1-5 中任一项所述的一种多端口直流-直流自耦变压
器, 其中, 依次串联的所述 2N-1个换流器中的一个或多个换流器通过相电 抗连接到交流线路, 每相相电抗采用三角接线方式以消除这些换流器的中 性点不平衡。
7、 根据权利要求 1-6 中任一项所述的一种多端口直流-直流自耦变压 器, 其中, 所述直流***中的任一个由一个或多个交流***经过交流 -直流 变换后在直流侧互联构成的; 或者由一个或多个交流***经过交流-直流变 换后与输出直流电的直流***在直流侧互联而形成的。
8、 根据权利要求 1-7 中任一项所述的一种多端口直流-直流自耦变压 器, 其中, 所述交流线路的一部分或全部可以与一个或多个外部交流电网 互联。
9、 根据权利要求 1-8 中任一项所述的一种多端口直流-直流自耦变压 器, 其中, 所述交流线路为交流公共母线, 各换流器的交流侧通过交流链 路连接到该公共母线。
10、 根据权利要求 1-8中任一项所述的一种多端口直流-直流自耦变压 器, 其中, 所述交流线路包括交流公共母线和外部交流***, 其中, 部分 换流器的交流侧与公共交流母线连接, 部分换流器的交流侧连接到所述外 部交流***上, 从而使得所述各换流器可以连接到相同或不同的交流电网 上。
11、根据权利要求 1-10中任一项所述的一种多端口直流-直流自耦变压 器, 其中, 各所述换流器可以采用对称双极, 对称单极, 不对称单极或不 对称双极结构。
12、根据权利要求 1-11中任一项所述的一种多端口直流-直流自耦变压 器, 其中, 所述换流器优选为电压源型换流器, 从而可使得任一直流*** 可以双向地与多端口直流 -直流自耦变压器交换功率, 或采用基于晶闸管的 相控换流器, 或采用不控整流桥。
13、根据权利要求 1-12中任一项所述的一种多端口直流-直流自耦变压
器其中, 所述交流链路可以采用单相, 两相, 三相或多相交流电路。
14、根据权利要求 1-13中任一项所述的一种多端口直流-直流自耦变压 器, 其中, 第 i个换流器及第 2N-i个换流器的额定直流电压取为 (Ei-Ei+1)/2, 第 N个换流器的额定直流电压取为 EN, 其中其中 、 Ei+1、 EN分别为第 i 个、 第 i+1个和第 N个直流***的额定直流电压。
15、权利要求 1-14中任一项所述的一种多端口直流 -直流自耦变压器的 各换流器额定容量的设计方法, 其特征在于, 包括:
式中, 为第 i个直流***向自耦变压器输出的功率, 为第 i个直流 ***的额定直流电压;
(2) 确定第 i个换流器的整流功率 Pvsa:
P. + · · · + Ρ.τ P.
pVSCi = (- -2 _ __J_2__ P i: i、、 *. E -E:
A
E1 E2 E; 2 其中,
-P l max <P l <P l max
一 P <(P +P H hP <P pimax表示第 i个 i流***的最大输出 /输入功率, 为第 i个 i流*** 的额定直流电压;
(3)根据上述直流电流和整流功率求得每个换流器的最大功率, 即作 为各个换流器的额定功率。
16、根据权利要求 15所述的一种多端口直流 -直流自耦变压器的各换流 器额定容量的设计方法, 其中, 依次串联的所述 2N-1个换流器中位于串联
链路中对称位置的两换流器的额定功率相等。
17、权利要求 1-14中任一项所述的一种多端口直流 -直流自耦变压器的 控制方法, 其特征在于, 其中的至少一个换流器用于控制公共交流的交流 电压, 其他换流器用于控制与有功功率相关的量。
18、根据权利要求 17所述的一种多端口直流 -直流自耦变压器的控制方 法, 其特征在于, 所述有功功率相关的量可以为直流功率和 /或直流电压。
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CN104600997B (zh) * | 2015-02-04 | 2017-02-22 | 国家电网公司 | 自耦式模块化多电平高压直流‑直流变压器及其控制方法 |
CN105048813B (zh) * | 2015-09-06 | 2017-09-12 | 华中科技大学 | 一种中频直流‑直流自耦变压器 |
CN105356757B (zh) * | 2015-11-19 | 2019-07-23 | 华中科技大学 | 一种单向直流-直流自耦变压器 |
CN105391321A (zh) * | 2015-12-16 | 2016-03-09 | 中国科学院上海应用物理研究所 | 一种超大电流源 |
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CN109039072B (zh) * | 2018-08-21 | 2020-09-08 | 南京南瑞继保电气有限公司 | 一种双极双向直流变换器及其控制方法和控制装置 |
CN112436739B (zh) * | 2020-12-10 | 2021-09-28 | 浙江大学 | 一种模块化组合式直流变压器及其控制方法 |
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