CN113726163B - Parallel network type transformer based on step-down type public direct-current voltage bus - Google Patents

Parallel network type transformer based on step-down type public direct-current voltage bus Download PDF

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Publication number
CN113726163B
CN113726163B CN202110956890.3A CN202110956890A CN113726163B CN 113726163 B CN113726163 B CN 113726163B CN 202110956890 A CN202110956890 A CN 202110956890A CN 113726163 B CN113726163 B CN 113726163B
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bridge
switching tube
direct current
bus
leg
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CN113726163A (en
Inventor
曾嵘
孙长平
赵彪
尹立坤
余占清
唐博进
安峰
潘海宁
白睿航
郭明珠
崔彬
周兴达
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Tsinghua University
China Three Gorges Corp
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Tsinghua University
China Three Gorges Corp
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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
    • 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
    • H02J1/00—Circuit arrangements for dc mains or dc distribution networks
    • H02J1/14—Balancing the load in a network
    • 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
    • H02J5/00—Circuit arrangements for transfer of electric power between ac networks and dc networks
    • 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
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Inverter Devices (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention provides a parallel network transformer based on a step-down type public direct current voltage bus, which comprises: the device comprises a medium-voltage direct current bus and two-end alternating current buses, wherein the two-end alternating current buses are connected into the medium-voltage direct current bus through an alternating current-direct current converter. The parallel network type transformer based on the step-down type public direct current voltage bus is oriented to a high-reliability power distribution application scene under the background of double high, and is low in cost, compact and high in efficiency; the invention realizes the application requirements of on-line interconnection, high-proportion distributed energy collection, high-capacity energy storage access and flexible interaction of source network charge storage of the medium-voltage alternating-current power distribution network.

Description

Parallel network type transformer based on step-down type public direct-current voltage bus
Technical Field
The invention belongs to the field of power electronics, and particularly relates to a parallel network transformer based on a step-down type public direct-current voltage bus.
Background
With the continuous development of power distribution networks, medium voltage power distribution networks are facing a series of development bottlenecks, mainly including: 1) The power consumption load of the power distribution network is rapidly increased, and the problems of overhigh distribution transformer load rate, unbalanced feeder load distribution and the like occur; 2) Statistics show that more than 80% of user power failures are caused by the power distribution network side, and short-time power failures are avoided during fault switching operation of the open-loop power distribution network subjected to power distribution automation transformation; 3) With the promotion of 'double carbon', the distributed energy and energy storage access requirements of the power distribution network are greatly increased, and the power distribution network has the characteristics of various operation modes, complex tidal current transfer and supply modes and the like.
The traditional alternating current power distribution system cannot quickly track and respond to the changes of distributed energy output and load due to the limitation of open-loop operation conditions, and cannot continuously and accurately regulate power flow, so that the deviation of system voltage becomes an increasingly prominent problem in power distribution network operation management. The introduction of direct current power distribution technology and the construction of an alternating current-direct current hybrid power distribution system based on a power electronic converter are important means for coping with the challenge. The alternating current-direct current hybrid power distribution system can fully exert the quick response characteristic of the power electronic device, greatly reduce the electric energy conversion links, and realize the quick, flexible, continuous and accurate power and voltage regulation and control of the power distribution network under the condition of strong uncertainty of the two ends of the source load.
After the traditional alternating-current power distribution network is connected with distributed energy sources such as photovoltaic and energy storage and direct-current loads, a large number of AC/DC conversion links are used, so that the system efficiency is low and the cost is high. Meanwhile, a low-voltage direct current bus can be added to the power distribution network through an AC/DC bidirectional converter to construct a direct current micro-grid, and a direct current load is connected into the direct current micro-grid, so that a plurality of electric energy conversion links are reduced. Furthermore, an AC/DC hybrid power distribution network using a multi-port Power Electronic Transformer (PET) as a hub is simultaneously connected with Medium Voltage AC (MVAC), medium Voltage DC (MVDC), low Voltage AC (LVAC) and Low Voltage DC (LVDC) 4 groups of buses, so that flexible regulation and control of power and voltage of each port, power quality management, energy interconnection and mutual fault isolation between ports can be realized. Therefore, the multi-port PET can play a key pivot role in an AC/DC hybrid power distribution network, and has very important theoretical significance and engineering practical value for research. However, the existing multi-port PET still has the problems of high cost, low efficiency and the like.
Disclosure of Invention
The invention provides a parallel network transformer based on a step-down type public direct current voltage bus.
The invention relates to a parallel network type transformer based on a step-down type public direct current voltage bus, which comprises the following components: a medium-voltage direct current bus, two-end alternating current buses,
wherein,,
the alternating current buses at the two ends are connected into the medium-voltage direct current bus through an alternating current-direct current converter.
Further, the method comprises the steps of,
the two-terminal ac bus includes a first two-terminal ac bus (MVACI) and a second two-terminal ac bus (MVACII).
Further, the method comprises the steps of,
the alternating current-direct current converter is a step-down voltage source alternating current-direct current converter.
Further, the method comprises the steps of,
the buck voltage source ac-dc converter has a dc bus voltage of 10kV,
the step-down voltage source ac-dc converter includes: a first phase input (A), a second phase input (B) and a third phase input (C) of a three-phase alternating current,
the first phase input end (A) is connected with the first end of the first half-bridge (a 1) and the second end of the second half-bridge (a 2), the second phase input end (B) is connected with the first end of the third half-bridge (B1) and the second end of the fourth half-bridge (B2), and the third phase input end (C) is connected with the first end of the fifth half-bridge (C1) and the second end of the sixth half-bridge (C2);
the first half bridge (a 1) to the sixth half bridge (c 2) comprise a first switching tube unit (S) and a full bridge module (M) which are connected in series, the first switching tube unit (S) comprises a first half bridge switching tube and a first half bridge diode which is antiparallel with the first half bridge switching tube, a first end of the first half bridge switching tube is connected with a cathode of the first half bridge diode to serve as a first end of the first switching tube unit (S), and a second end of the first half bridge switching tube is connected with an anode of the first half bridge diode to serve as a second end of the first switching tube unit (S);
the full-bridge module (M) is composed of two-phase four-leg, a full-bridge capacitor (cc) is connected in parallel between the two-phase four-leg, each leg is composed of a first leg switch tube and a freewheeling diode connected in anti-parallel with the first leg switch tube, the four-leg comprises a first leg (SS 1) to a fourth leg (SS 4), a first leg switch tube in the first leg (SS 1) and a first leg switch tube in the second leg (SS 2) are connected in series to form a first phase of the full-bridge module (M), wherein a second end of the first leg switch tube of the first leg (SS 1) is connected with a first end of the first leg switch tube of the second leg (SS 2) as a first end of the full-bridge module (M), and a first leg switch tube in the third leg (SS 3) and a first leg switch tube in the fourth leg (SS 4) are connected in series to form a second phase of the full-bridge module (M), and a first end of the first leg switch tube in the third leg (SS 3) is connected with a first end of the first leg switch tube in the fourth leg (SS 4) as a second end of the first leg switch tube in the fourth leg (SS 3) is connected with a first end of the first leg switch tube in the fourth leg switch tube (SS 4);
the first half bridge (a 1), the third half bridge (b 1) and the fifth half bridge (c 1), wherein the first end of the first switching tube unit (S) is used as the first end of the half bridge, the second end of the first switching tube unit (S) is connected with the first end of the full bridge module (M), the second end of the full bridge module (M) is used as the second end of the half bridge, and the second ends of the first half bridge (a 1), the third half bridge (b 1) and the fifth half bridge (c 1) are mutually connected to serve as the cathode (E1) or the cathode (E4) of the buck voltage source alternating current-direct current converter; the second half bridge (a 2), the fourth half bridge (b 2) and the sixth half bridge (c 2), wherein the second end of the first switching tube unit (S) is used as the second end of the half bridge, the first end of the first switching tube unit (S) is connected with the second end of the full bridge module (M), the first end of the full bridge module (M) is used as the first end of the half bridge, and the first ends of the second half bridge (a 2), the fourth half bridge (b 2) and the sixth half bridge (c 2) are mutually connected to serve as an anode (F1) or an anode (F4) of the buck voltage source alternating current-direct current converter;
a first capacitor cc1 is connected in parallel between the cathode E1 and the anode F1, and a fourth capacitor cc4 is connected in parallel between the cathode E4 and the anode F4.
Further, the method comprises the steps of,
the first half-bridge switching tube is a first insulated gate bipolar transistor, a first end of the first half-bridge switching tube is a collector electrode of the first insulated gate bipolar transistor, a second end of the first half-bridge switching tube is an emitter electrode of the first insulated gate bipolar transistor, or the first half-bridge switching tube is a first integrated gate commutated thyristor, the first end of the first half-bridge switching tube is an anode electrode of the first integrated gate commutated thyristor, and the second end of the first half-bridge switching tube is a cathode electrode of the first integrated gate commutated thyristor;
the first bridge arm switch tube is a second insulated gate bipolar transistor, the first end of the first bridge arm switch tube is a collector electrode of the second insulated gate bipolar transistor, the second end of the first bridge arm switch tube is an emitter electrode of the second insulated gate bipolar transistor, or the first bridge arm switch tube is a second integrated gate commutated thyristor, the first end of the first bridge arm switch tube is an anode electrode of the second integrated gate commutated thyristor, and the second end of the first bridge arm switch tube is a cathode electrode of the second integrated gate commutated thyristor.
Further, the method comprises the steps of,
the low-voltage direct current bus is also included.
Further, the method comprises the steps of,
the low-voltage direct current bus is a concentrated low-voltage direct current bus,
the centralized low-voltage direct current bus is connected into the medium-voltage direct current bus through a direct current transformer.
Further, the method comprises the steps of,
the direct current transformer is a direct current-direct current converter based on intermediate frequency isolation.
Further, the method comprises the steps of,
the direct current-direct current converter based on the intermediate frequency isolation comprises: the full-bridge inverter comprises a cascaded full-bridge inverter, an intermediate frequency isolation Transformer (TR) and a rectifier;
the first input end (BB) of the full-bridge inverter is used as the positive electrode input end of the direct current-direct current converter based on the medium frequency isolation, the second input end (AA) of the full-bridge inverter is used as the negative electrode input end of the direct current-direct current converter based on the medium frequency isolation, a full-bridge inverter capacitor is connected in parallel between the first input end (BB) and the second input end (AA), the full-bridge inverter comprises a first bridge arm and a second bridge arm, the first bridge arm is formed by connecting a first switching tube (S1) and a third switching tube (S3) in series, the second end of the first switching tube (S1) is connected with the first end of a third switching tube (S3), the second end of the second switching tube (S2) is connected with the first end of a first switching tube (S4) in parallel, the first switching tube (S1) to each of the fourth switching tubes (S4) is connected with the first end of the fourth switching tube (S4) in parallel, the second end of the fourth switching tube (S1) is connected with the first end of the fourth switching tube (S4) as the first end of the full-bridge inverter,
the homopolar end of the primary side of the intermediate frequency isolation Transformer (TR) is connected with the second end of the first switching tube (S1), and the heteropolar end is connected with the second end of the second switching tube (S2);
the rectifier comprises a third bridge arm and a fourth bridge arm, the third bridge arm comprises a seventh half-bridge (d 1) and an eighth half-bridge (d 2), the fourth bridge arm comprises a ninth half-bridge (e 1) and a tenth half-bridge (e 2), the seventh half-bridge d1 to the tenth half-bridge e2 have the same structure and each comprise at least two second switching tube units (SS) connected in series, and the second end of the previous second switching tube unit (SS) is connected with the first end of the next second switching tube unit (SS); -a first end of a first second switching tube unit (SS) of each of said seventh to tenth half-bridges (d 1) to (e 2) is taken as a first end of said each half-bridge; -a second end of a last second switching tube unit (SS) of each of said seventh to tenth half-bridges (d 1) to (e 2) is taken as a second end of said each half-bridge; a first end of the seventh half-bridge (d 1) is connected with a second end of the eighth half-bridge (d 2) to serve as a midpoint of the third bridge arm, and a first end of the ninth half-bridge (e 1) is connected with a second end of the tenth half-bridge (e 2) to serve as a midpoint of the fourth bridge arm;
the homopolar end of the secondary side of the intermediate frequency isolation transformer is connected with the middle point of the third bridge arm, the heteropolar end of the secondary side of the intermediate frequency isolation transformer is connected with the middle point of the fourth bridge arm, the second end of the seventh half bridge (d 1) is connected with the second end of the ninth half bridge (E1) to serve as a cathode (E2) of the direct current transformer, the first end of the eighth half bridge (d 2) is connected with the first end of the tenth half bridge (E1) to serve as an anode (F2) of the direct current transformer, and a rectifier capacitor (cc 2) is connected between the cathode (E2) and the anode (F2) in parallel;
the capacity of the intermediate frequency isolation transformer is MW level.
Further, the method comprises the steps of,
the first switch tube (S1) to the fourth switch tube (S4) are third insulated gate bipolar transistors, the first ends of the first switch tube (S1) to the fourth switch tube (S4) are collectors of the third insulated gate bipolar transistors, the second ends are emitters of the third insulated gate bipolar transistors,
or (b)
The first switching tube (S1) to the fourth switching tube (S4) are third integrated gate pole commutated thyristors, and the first end of the first switching tube (S1) to the fourth switching tube (S4) is the anode of the third integrated gate pole commutated thyristors, and the second end is the cathode of the third integrated gate pole commutated thyristors;
the second switching tube unit (SS) is formed by antiparallel connection of a fourth insulated gate bipolar transistor and a diode, the first end of the second switching tube unit (SS) is the collector electrode of the fourth insulated gate bipolar transistor, and the second end is the emitter electrode of the fourth insulated gate bipolar transistor;
or (b)
The second switching tube unit (SS) is formed by antiparallel connection of a fourth integrated gate commutated thyristor and a diode, the first end of the second switching tube unit (SS) is the anode of the fourth integrated gate commutated thyristor, and the second end of the second switching tube unit is the cathode of the fourth integrated gate commutated thyristor.
Further, the method comprises the steps of,
the energy storage is connected to the medium-voltage direct current bus by adopting a converter formed by connecting non-isolated half-bridge or full-bridge modules in series;
when more than one energy storage is carried out, different converters formed by connecting different non-isolated half-bridge or full-bridge modules in series are respectively connected between different energy storage, the converters formed by connecting the non-isolated half-bridge or full-bridge modules in series are connected in series to form a series converter structure, and then the series converter structure is connected into the medium-voltage direct-current bus, wherein an inductor is arranged at an outlet of the series converter structure.
Further, the method comprises the steps of,
the medium-voltage direct current bus comprises a negative electrode bus (M-) and a positive electrode bus (M+),
the cathodes of the converters connected in series with the non-isolated half-bridge or full-bridge modules are respectively connected to the negative bus (M-);
the anodes of the converters connected in series with the non-isolated half-bridge or full-bridge modules of the alternating current-direct current converter, the direct current transformer and the alternating current-direct current converter are respectively connected to the positive bus (M+), through switches.
The parallel network type transformer based on the step-down type public direct current voltage bus is oriented to a high-reliability power distribution application scene under the background of double high, and is low in cost, compact and high in efficiency; the invention realizes the application requirements of on-line interconnection, high-proportion distributed energy collection, high-capacity energy storage access and flexible interaction of source network charge storage of the medium-voltage alternating-current power distribution network.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 shows a basic structural schematic diagram of a parallel network transformer based on a buck-type common dc bus according to an embodiment of the present invention;
fig. 2 shows a topology structure diagram of a parallel network transformer based on a buck-type common dc bus according to an embodiment of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Fig. 1 shows a basic structure of a parallel-structured network type transformer based on a step-down type common dc bus according to the present invention. Fig. 2 shows the topology of the parallel network type transformer based on the buck type common direct current bus of the present invention.
As can be seen from fig. 1 and 2, the parallel network transformer based on the step-down common dc bus of the present invention comprises: MVDC bus, first two-terminal alternating current bus MVACI and second two-terminal alternating current bus MVACII, direct current bus is concentrated LVDC, energy storage for example. Wherein, MVDC bus totally has two: positive busbar m+ and negative busbar M-; the first two-end alternating current bus MVACI and the second two-end alternating current bus MVACII are connected in parallel between the positive electrode bus M+ and the negative electrode bus M-respectively through centralized LVDC and energy storage.
The first two-terminal alternating current bus MVACI and the second two-terminal alternating current bus MVACII are connected to the MVDC bus through a step-down voltage source Alternating Current (AC) -Direct Current (DC) converter CA or CD. Referring to fig. 2, the buck voltage source AC-DC converter CA or CD includes: a first phase input terminal A, a second phase input terminal B and a third phase input terminal C of the three-phase alternating current. The first phase input end A is connected with a first end of the first half-bridge a1 and a second end of the second half-bridge a 2; the second phase input end B is connected with the first end of the third half bridge B1 and the second end of the fourth half bridge B2; the third phase input terminal C connects the first terminal of the fifth half bridge C1 and the second terminal of the sixth half bridge C2. The first to sixth half-bridges a1 to c2 each include a first switching tube unit S and a full-bridge module M connected in series. The first switching tube unit S includes a first half-bridge switching tube and a first half-bridge diode connected in anti-parallel with the first half-bridge switching tube, where the first half-bridge switching tube may be a first Insulated Gate Bipolar Transistor (IGBT), a collector of the first half-bridge switching tube is connected to a cathode of the first half-bridge diode as a first end of the first switching tube unit S, an emitter of the first half-bridge switching tube is connected to an anode of the first half-bridge diode as a second end of the first switching tube unit S, and the first half-bridge switching tube may also be a first Integrated Gate Commutated Thyristor (IGCT) or other fully-controlled devices, and at this time, an anode of the first half-bridge switching tube is connected to a cathode of the first half-bridge diode as a first end of the first switching tube unit S, and a cathode of the first half-bridge switching tube is connected to an anode of the first half-bridge diode as a second end of the first switching tube unit S. The full-bridge module M is formed by two-phase four-leg (including a first leg SS1, a second leg SS2, a third leg SS3, and a fourth leg SS 4), and a full-bridge capacitor cc is connected in parallel between the two phases, each leg is formed by a first leg switching tube such as a second IGBT and a freewheeling diode connected in anti-parallel with the first leg switching tube, the second IGBT of the four legs is respectively an IGBT1 (which is the first leg switching tube in the first leg SS 1), an IGBT2 (which is the first leg switching tube in the second leg SS 2), an IGBT3 (which is the first leg switching tube in the third leg SS 3), and an IGBT4 (which is the first leg switching tube in the fourth leg SS 4), the IGBT1 and the IGBT2 are connected in series (the emitter of the IGBT1 is connected with the collector of the IGBT 2), the first phase of the full-bridge module M is formed by the first leg switching tube, the midpoint (the emitter of the IGBT3 is connected with the collector of the IGBT 4) of the full-bridge module M is the second phase, and the midpoint (the emitter of the IGBT3 is the second phase of the full-bridge module M is the second phase, and the midpoint of the full-bridge module M is the second end of the full-bridge module M is the second phase, and the full-bridge module M is similar to the first end of the first bridge switching tube. In the first half bridge a1, the third half bridge b1 and the fifth half bridge c1, the first end of the first switching tube unit S is used as the first end of the half bridge, the second end of the first switching tube unit S is connected with the first end of the full bridge module M, the second end of the full bridge module M is used as the second end of the half bridge, and the second ends of the first half bridge a1, the third half bridge b1 and the fifth half bridge c1 are mutually connected to serve as the cathode E1 (or E4) of the buck voltage source AC-DC converter CA (or CD). In the second half bridge a2, the fourth half bridge b2 and the sixth half bridge c2, the second end of the first switching tube unit S is used as the second end of the half bridge, the first end of the first switching tube unit S is connected with the second end of the full bridge module M, the first end of the full bridge module M is used as the first end of the half bridge, and the first ends of the second half bridge a2, the fourth half bridge b2 and the sixth half bridge c2 are mutually connected to be used as the anode F1 (or F4) of the buck voltage source AC-DC converter CA (or CD). A first capacitor cc1 is connected in parallel between the cathode E1 and the anode F1, and a fourth capacitor cc4 is connected in parallel between the cathode E4 and the anode F4. The step-down voltage source AC-DC converter preferably adopts a series full-bridge module on the alternating current side for realizing step-down, and can reduce harmonic content. The step-down voltage source AC-DC converter CA or CD has a DC bus voltage of 10 kV. The step-down voltage source AC-DC converter CA or CD is based on a step-down device direct-string, and can provide a direct-current voltage bus smaller than an alternating-current side voltage peak value, so that the number of direct-string devices and the system cost are reduced.
The centralized LVDC is connected to the MVDC bus through a direct current transformer CB, and the direct current transformer CB adopts a Direct Current (DC) -Direct Current (DC) converter based on intermediate frequency isolation. Referring to fig. 2, the intermediate frequency isolated DC-DC converter includes a cascaded full bridge inverter, an intermediate frequency isolation transformer TR, and a rectifier. The first input end BB of the full-bridge inverter is used as the positive electrode input end of the DC-DC converter, the second input end AA of the full-bridge inverter is used as the negative electrode input end of the DC-DC converter, and a full-bridge inverter capacitor is connected in parallel between the first input end BB and the second input end AA. The full-bridge inverter comprises a first bridge arm and a second bridge arm, wherein the first bridge arm is formed by connecting a first switching tube S1 and a third switching tube S3 in series, and a second end of the first switching tube S1 is connected with a first end of the third switching tube S3. The second bridge arm is formed by connecting a second switching tube S2 and a fourth switching tube S4 in series, and the second end of the second switching tube S2 is connected with the first end of the fourth switching tube S4. Each of the first to fourth switching transistors S1 to S4 is antiparallel with a diode. The first end of the first switching tube S1 is connected with the first end of the second switching tube S2 and serves as a first input end BB of the full-bridge inverter, and the second end of the third switching tube S3 is connected with the second end of the fourth switching tube S4 and serves as a second input end AA of the full-bridge inverter. The homopolar end of the primary side of the intermediate frequency isolation transformer is connected with a first bridge arm middle point (namely a second end of the first switching tube S1 or a first end of the third switching tube S3), the heteropolar end is connected with a second bridge arm middle point (namely a second end of the second switching tube S2 or a first end of the fourth switching tube S4), the first switching tube S1 to the fourth switching tube S4 can be a third IGBT, at this time, the first end of the first switching tube S1 to the fourth switching tube S4 is a collector of the third IGBT, the second end is an emitter of the third IGBT, the first switching tube S1 to the fourth switching tube S4 can also be a third IGCT, at this time, the first end of the first switching tube S1 to the fourth switching tube S4 is an anode of the third IGCT, and the second end is a cathode of the third IGBT. The rectifier comprises a third bridge arm and a fourth bridge arm, wherein the third bridge arm comprises a seventh half-bridge d1 and an eighth half-bridge d2, and the fourth bridge arm comprises a ninth half-bridge e1 and a tenth half-bridge e2. The seventh half bridge d1 to the tenth half bridge e2 have the same structure and comprise at least two second switching tube units SS connected in series, and the second end of the former second switching tube unit SS is connected with the first end of the next second switching tube unit SS; a first end of a first second switching tube unit SS of each of the seventh to tenth half-bridges d1 to e2 serves as a first end of the half-bridge; the second terminal of the last second switching tube unit SS of each of the seventh to tenth half-bridges d1 to e2 serves as the second terminal of the half-bridge. The second switching tube unit SS adopts a fourth IGBT and diode anti-parallel structure (the collector of the fourth IGBT is connected to the cathode of the diode, the emitter of the fourth IGBT is connected to the anode of the diode, at this time, the first end of the second switching tube unit SS is the collector of the fourth IGBT, and the second end is the emitter of the fourth IGBT), or adopts a fourth IGCT and diode anti-parallel structure (the anode of the fourth IGCT is connected to the cathode of the diode, and the cathode of the fourth IGCT is connected to the anode of the diode, at this time, the first end of the second switching tube unit SS is the anode of the fourth IGCT, and the second end is the cathode of the fourth IGCT). The first end of the seventh half bridge d1 is connected with the second end of the eighth half bridge d2 to serve as a midpoint of the third bridge arm, and the first end of the ninth half bridge e1 is connected with the second end of the tenth half bridge e2 to serve as a midpoint of the fourth bridge arm. The homopolar end of the secondary side of the intermediate frequency isolation transformer is connected with the midpoint of the third bridge arm, and the heteropolar end is connected with the midpoint of the fourth bridge arm. The second end of the seventh half-bridge d1 is connected with the second end of the ninth half-bridge E1 to serve as a cathode E2 of the direct-current transformer CB, the first end of the eighth half-bridge d2 is connected with the first end of the tenth half-bridge E1 to serve as an anode F2 of the direct-current transformer CB, and a rectifier capacitor cc2 is connected between the cathode E2 and the anode F2 in parallel. In the dc transformer CB, the MVDC side conversion section employs a plurality of second switching tube units SS directly connected in series. The capacity of the intermediate frequency isolation transformer is MW level. The DC-DC converter based on the intermediate frequency isolation is based on a device direct string, a device series technology is adopted to replace a module series technology, so that the system cost is reduced, and meanwhile, the alternating current side and the direct current side are mutually decoupled, namely, the number of alternating current transformers is not limited by the number of power modules.
The energy storage adopts a converter CC formed by connecting non-isolated half-bridge or full-bridge modules in series to be directly connected into the MVDC bus, when more than one energy storage is realized, different converters CC are respectively adopted among different energy storage, each converter CC is connected in series to form a series converter structure and then is connected into the MVDC bus, wherein an inductor is arranged at an outlet of the series converter structure. The conversion links and the access cost are greatly reduced. As shown in fig. 2, the non-isolated half bridge (or full bridge module) is composed of a switching tube unit composed of a switching tube such as an IGBT and a diode antiparallel thereto, and a parallel capacitor. The converter CC formed by connecting the non-isolated half-bridge or full-bridge modules in series realizes that a discrete module energy storage access technology is adopted to replace the traditional centralized access technology, so that the cost of the system is reduced, the power density is improved, the control system of the direct current collector of the converter CC formed by connecting the non-isolated half-bridge or full-bridge modules in series is simpler, and the voltage balance of each module can be independently controlled.
Each converter (including a buck voltage source AC-DC converter CA or CD, a direct current transformer CB, and a converter CC formed by connecting non-isolated half-bridge or full-bridge modules in series) is switched in or out of the MVDC bus through a parallel switch, specifically, the cathode E1 (or E4) of the buck voltage source AC-DC converter CA (or CD) is connected to the anode F1 (or F4) through a switch to the cathode bus M-and the anode bus m+; the cathode E2 and the anode F2 of the direct-current transformer CB are respectively connected to the negative bus M-and the positive bus M+ through switches; the cathode E3 and the anode F3 of the converter CC formed by connecting non-isolated half-bridge or full-bridge modules in series are respectively connected to the negative bus M-and the positive bus M+ through switches.
Most of the existing power electronic transformers are voltage source type boost topologies, for example: the DC bus voltage of the AC-DC converter connected with the 10kV AC bus is 20kV (+ -10 kV), and for the DC transformers of the Modular Multilevel Converter (MMC) and the double active bridge converter (DAB) connected in series and parallel, the module numbers of the DC transformers are designed according to the 20kV DC bus voltage. The AC/DC converter is designed by using 10kV direct current bus voltage, and the number of modules used at the same device level can be reduced by 50%. In addition, the existing power electronic transformers are all based on modular cascading modes, such as: the cascade H-bridge topology adopts a full-bridge subunit, and each module has 4 devices; half-bridge subunits are used in the MMC topology, and each module has 2 devices. In the invention, the AC-DC converter is designed by adopting devices in series, which is equivalent to adopting only 1 device per module, and the number of devices is greatly reduced.
The direct-current transformer adopts the device series connection to realize the complete decoupling of the medium-voltage direct-current chain and the alternating-current chain, and the isolation transformer does not need to follow the number of the power modules.
Meanwhile, in order to reduce the number of transformers, the capacity of the isolation transformer reaches MW level in the invention. In fact, unlike kW-level isolation transformers, for MW-level isolation transformers, limited by isolation and insulation levels, heat dissipation requirements, etc., increasing the switching frequency does not result in a reduction in volume, but rather greatly enhances skin and proximity effects, drastically reducing efficiency. Therefore, the isolation transformer adopts an intermediate frequency operation mode, and the efficiency is greatly improved when the power density of the system is improved. For a MW-level direct-current transformer connected to a 10kV step-down bus, only 1-2 isolation transformers are needed.
The parallel network type transformer based on the step-down type public direct current voltage bus is low in cost, compact and high in efficiency; the application requirements of flexible interaction of medium-voltage alternating-current distribution network on-line interconnection, high-proportion distributed energy collection, high-capacity energy storage access and 'source network load storage' are realized.
Although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. Parallel network-structured transformer based on step-down type public direct current voltage bus, which is characterized by comprising: a medium-voltage direct current bus, two-end alternating current buses,
wherein,,
the two ends of the alternating current buses are connected into the medium voltage direct current buses through alternating current-direct current converters;
the alternating current-direct current converter is a step-down voltage source alternating current-direct current converter;
the buck voltage source ac-dc converter has a dc bus voltage of 10kV,
the step-down voltage source ac-dc converter includes: a first phase input (A), a second phase input (B) and a third phase input (C) of a three-phase alternating current,
the first phase input end (A) is connected with the first end of the first half-bridge (a 1) and the second end of the second half-bridge (a 2), the second phase input end (B) is connected with the first end of the third half-bridge (B1) and the second end of the fourth half-bridge (B2), and the third phase input end (C) is connected with the first end of the fifth half-bridge (C1) and the second end of the sixth half-bridge (C2);
the first half bridge (a 1) to the sixth half bridge (c 2) comprise a first switching tube unit (S) and a full bridge module (M) which are connected in series, the first switching tube unit (S) comprises a first half bridge switching tube and a first half bridge diode which is antiparallel with the first half bridge switching tube, a first end of the first half bridge switching tube is connected with a cathode of the first half bridge diode to serve as a first end of the first switching tube unit (S), and a second end of the first half bridge switching tube is connected with an anode of the first half bridge diode to serve as a second end of the first switching tube unit (S);
the full-bridge module (M) is composed of two-phase four-leg, a full-bridge capacitor (cc) is connected in parallel between the two-phase four-leg, each leg is composed of a first leg switch tube and a freewheeling diode connected in anti-parallel with the first leg switch tube, the four-leg comprises a first leg (SS 1) to a fourth leg (SS 4), a first leg switch tube in the first leg (SS 1) and a first leg switch tube in the second leg (SS 2) are connected in series to form a first phase of the full-bridge module (M), wherein a second end of the first leg switch tube of the first leg (SS 1) is connected with a first end of the first leg switch tube of the second leg (SS 2) as a first end of the full-bridge module (M), and a first leg switch tube in the third leg (SS 3) and a first leg switch tube in the fourth leg (SS 4) are connected in series to form a second phase of the full-bridge module (M), and a first end of the first leg switch tube in the third leg (SS 3) is connected with a first end of the first leg switch tube in the fourth leg (SS 4) as a second end of the first leg switch tube in the fourth leg (SS 3) is connected with a first end of the first leg switch tube in the fourth leg switch tube (SS 4);
the first half bridge (a 1), the third half bridge (b 1) and the fifth half bridge (c 1), wherein the first end of the first switching tube unit (S) is used as the first end of the half bridge, the second end of the first switching tube unit (S) is connected with the first end of the full bridge module (M), the second end of the full bridge module (M) is used as the second end of the half bridge, and the second ends of the first half bridge (a 1), the third half bridge (b 1) and the fifth half bridge (c 1) are mutually connected to serve as the cathode (E1) or the cathode (E4) of the buck voltage source alternating current-direct current converter; the second half bridge (a 2), the fourth half bridge (b 2) and the sixth half bridge (c 2), wherein the second end of the first switching tube unit (S) is used as the second end of the half bridge, the first end of the first switching tube unit (S) is connected with the second end of the full bridge module (M), the first end of the full bridge module (M) is used as the first end of the half bridge, and the first ends of the second half bridge (a 2), the fourth half bridge (b 2) and the sixth half bridge (c 2) are mutually connected to serve as an anode (F1) or an anode (F4) of the buck voltage source alternating current-direct current converter;
the cathodes (E1, E4) and the anodes (F1 or F4) of the buck voltage source alternating current-direct current converter are connected in parallel with capacitors (cc 1, cc 4).
2. The parallel-structured network transformer based on a step-down common direct voltage bus as claimed in claim 1, wherein,
the two-terminal ac bus includes a first two-terminal ac bus (MVACI) and a second two-terminal ac bus (MVACII).
3. The parallel-structured network transformer based on a step-down common direct voltage bus as claimed in claim 1, wherein,
the first half-bridge switching tube is a first insulated gate bipolar transistor, a first end of the first half-bridge switching tube is a collector electrode of the first insulated gate bipolar transistor, a second end of the first half-bridge switching tube is an emitter electrode of the first insulated gate bipolar transistor, or the first half-bridge switching tube is a first integrated gate commutated thyristor, the first end of the first half-bridge switching tube is an anode electrode of the first integrated gate commutated thyristor, and the second end of the first half-bridge switching tube is a cathode electrode of the first integrated gate commutated thyristor;
the first bridge arm switch tube is a second insulated gate bipolar transistor, the first end of the first bridge arm switch tube is a collector electrode of the second insulated gate bipolar transistor, the second end of the first bridge arm switch tube is an emitter electrode of the second insulated gate bipolar transistor, or the first bridge arm switch tube is a second integrated gate commutated thyristor, the first end of the first bridge arm switch tube is an anode electrode of the second integrated gate commutated thyristor, and the second end of the first bridge arm switch tube is a cathode electrode of the second integrated gate commutated thyristor.
4. A parallel network transformer based on a step-down common DC voltage bus as claimed in any one of claims 1-3, wherein,
the low-voltage direct current bus is also included.
5. The parallel-structured network transformer based on a step-down common direct voltage bus as claimed in claim 4, wherein,
the low-voltage direct current bus is a concentrated low-voltage direct current bus,
the centralized low-voltage direct current bus is connected into the medium-voltage direct current bus through a direct current transformer.
6. The parallel-structured network transformer based on a step-down common direct voltage bus as claimed in claim 5, wherein,
the direct current transformer is a direct current-direct current converter based on intermediate frequency isolation.
7. The parallel-structured network transformer based on a step-down common direct voltage bus as claimed in claim 6, wherein,
the direct current-direct current converter based on the intermediate frequency isolation comprises: the full-bridge inverter comprises a cascaded full-bridge inverter, an intermediate frequency isolation Transformer (TR) and a rectifier;
the first input end (BB) of the full-bridge inverter is used as the positive electrode input end of the direct current-direct current converter based on the medium frequency isolation, the second input end (AA) of the full-bridge inverter is used as the negative electrode input end of the direct current-direct current converter based on the medium frequency isolation, a full-bridge inverter capacitor is connected in parallel between the first input end (BB) and the second input end (AA), the full-bridge inverter comprises a first bridge arm and a second bridge arm, the first bridge arm is formed by connecting a first switching tube (S1) and a third switching tube (S3) in series, the second end of the first switching tube (S1) is connected with the first end of a third switching tube (S3), the second end of the second switching tube (S2) is connected with the first end of a first switching tube (S4) in parallel, the first switching tube (S1) to each of the fourth switching tubes (S4) is connected with the first end of the fourth switching tube (S4) in parallel, the second end of the fourth switching tube (S1) is connected with the first end of the fourth switching tube (S4) as the first end of the full-bridge inverter,
the homopolar end of the primary side of the intermediate frequency isolation Transformer (TR) is connected with the second end of the first switching tube (S1), and the heteropolar end is connected with the second end of the second switching tube (S2);
the rectifier comprises a third bridge arm and a fourth bridge arm, the third bridge arm comprises a seventh half-bridge (d 1) and an eighth half-bridge (d 2), the fourth bridge arm comprises a ninth half-bridge (e 1) and a tenth half-bridge (e 2), the seventh half-bridge (d 1) to the tenth half-bridge (e 2) have the same structure and each comprise at least two second switching tube units (SS) connected in series, and the second end of the previous second switching tube unit (SS) is connected with the first end of the next second switching tube unit (SS); -a first end of a first second switching tube unit (SS) of each of said seventh to tenth half-bridges (d 1) to (e 2) is taken as a first end of said each half-bridge; -a second end of a last second switching tube unit (SS) of each of said seventh to tenth half-bridges (d 1) to (e 2) is taken as a second end of said each half-bridge; a first end of the seventh half-bridge (d 1) is connected with a second end of the eighth half-bridge (d 2) to serve as a midpoint of the third bridge arm, and a first end of the ninth half-bridge (e 1) is connected with a second end of the tenth half-bridge (e 2) to serve as a midpoint of the fourth bridge arm;
the secondary side of the intermediate frequency isolation transformer is connected with the middle point of the third bridge arm, the opposite polarity end is connected with the middle point of the fourth bridge arm, the second end of the seventh half-bridge (d 1) is connected with the second end of the ninth half-bridge (E1) to serve as a cathode (E2) of the direct current transformer, the first end of the eighth half-bridge (d 2) is connected with the first end of the tenth half-bridge (E2) to serve as an anode (F2) of the direct current transformer, and a rectifier capacitor (cc 2) is connected in parallel between the cathode (E2) and the anode (F2) of the direct current transformer;
the capacity of the intermediate frequency isolation transformer is MW level.
8. The parallel-structured network transformer based on a step-down common direct voltage bus as claimed in claim 7, wherein,
the first switch tube (S1) to the fourth switch tube (S4) are third insulated gate bipolar transistors, the first ends of the first switch tube (S1) to the fourth switch tube (S4) are collectors of the third insulated gate bipolar transistors, the second ends are emitters of the third insulated gate bipolar transistors,
or (b)
The first switching tube (S1) to the fourth switching tube (S4) are third integrated gate pole commutated thyristors, and the first end of the first switching tube (S1) to the fourth switching tube (S4) is the anode of the third integrated gate pole commutated thyristors, and the second end is the cathode of the third integrated gate pole commutated thyristors;
the second switching tube unit (SS) is formed by antiparallel connection of a fourth insulated gate bipolar transistor and a diode, the first end of the second switching tube unit (SS) is the collector electrode of the fourth insulated gate bipolar transistor, and the second end is the emitter electrode of the fourth insulated gate bipolar transistor;
or (b)
The second switching tube unit (SS) is formed by antiparallel connection of a fourth integrated gate commutated thyristor and a diode, the first end of the second switching tube unit (SS) is the anode of the fourth integrated gate commutated thyristor, and the second end of the second switching tube unit is the cathode of the fourth integrated gate commutated thyristor.
9. The parallel-structured network transformer based on a step-down common direct voltage bus as claimed in claim 8, wherein,
the energy storage is connected to the medium-voltage direct current bus by adopting a converter formed by connecting non-isolated half-bridge or full-bridge modules in series;
when more than one energy storage is carried out, different converters formed by connecting different non-isolated half-bridge or full-bridge modules in series are respectively connected between different energy storage, the converters formed by connecting the non-isolated half-bridge or full-bridge modules in series are connected in series to form a series converter structure, and then the series converter structure is connected into the medium-voltage direct-current bus, wherein an inductor is arranged at an outlet of the series converter structure.
10. The parallel-structured network transformer based on a step-down common direct voltage bus as claimed in claim 9, wherein,
the medium-voltage direct current bus comprises a negative electrode bus (M-) and a positive electrode bus (M+),
the cathodes of the converters connected in series with the non-isolated half-bridge or full-bridge modules are respectively connected to the negative bus (M-);
the anodes of the converters connected in series with the non-isolated half-bridge or full-bridge modules of the alternating current-direct current converter, the direct current transformer and the alternating current-direct current converter are respectively connected to the positive bus (M+), through switches.
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