CN111245254A - Single-phase direct current port interconnected cascade multilevel converter - Google Patents

Single-phase direct current port interconnected cascade multilevel converter Download PDF

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Publication number
CN111245254A
CN111245254A CN202010042010.7A CN202010042010A CN111245254A CN 111245254 A CN111245254 A CN 111245254A CN 202010042010 A CN202010042010 A CN 202010042010A CN 111245254 A CN111245254 A CN 111245254A
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voltage source
phase
converter
port
group
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Inventor
李伟瑞
魏应冬
胡长江
李笑倩
张权利卿
陆超
袁志昌
马慧远
于希娟
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Tsinghua University
State Grid Beijing Electric Power Co Ltd
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Tsinghua University
State Grid Beijing Electric Power Co Ltd
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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
    • H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
    • H02M5/40—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc
    • H02M5/42—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters
    • H02M5/44—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac
    • H02M5/453—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M5/458—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M5/4585—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only having a rectifier with controlled elements
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60M—POWER SUPPLY LINES, AND DEVICES ALONG RAILS, FOR ELECTRICALLY- PROPELLED VEHICLES
    • B60M1/00—Power supply lines for contact with collector on vehicle
    • B60M1/12—Trolley lines; Accessories therefor
    • B60M1/13—Trolley wires
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60M—POWER SUPPLY LINES, AND DEVICES ALONG RAILS, FOR ELECTRICALLY- PROPELLED VEHICLES
    • B60M3/00—Feeding power to supply lines in contact with collector on vehicles; Arrangements for consuming regenerative power
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/487—Neutral point clamped inverters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0083—Converters characterised by their input or output configuration

Abstract

The invention provides a cascade multilevel converter with interconnected single-phase direct-current ports, which comprises a first single-phase double-winding transformer, two cascade multilevel voltage source type converter groups and a reactor group positioned at the alternating current side of any one or two converter groups; each cascade multilevel voltage source type converter group respectively comprises a plurality of single-phase voltage source converters, the alternating current side of the first cascade multilevel voltage source type converter group is connected to a single-phase power grid power supply through a first single-phase double-winding transformer, and the alternating current side of the second cascade multilevel voltage source type converter group is connected to another single-phase power grid power supply. And a direct current filter bank is also arranged between the direct current sides of the two-stage multi-level voltage source type converter bank. And a second single-phase double-winding transformer or an alternating current filter is arranged on the alternating current side of the second cascade multi-level voltage source type converter group and used for supplying power to a single-phase passive power grid. The invention has the characteristics of good harmonic characteristics of the alternating current ports at two sides, high operation efficiency in a full load range, low loss, high reliability of fault locking and redundant operation and the like.

Description

Single-phase direct current port interconnected cascade multilevel converter
Technical Field
The invention relates to a cascaded multilevel converter in a traction power supply system, in particular to a cascaded multilevel converter with single-phase direct-current ports interconnected.
Background
In a traction power supply system, the problems of unbalanced three-phase voltage, harmonic waves and low power factor caused by asymmetric load of traction power transformation exist. Meanwhile, the electric phase-splitting non-electric area exists in the traction substation and the subareas, so that the continuous and reliable current collection of the electric locomotive is influenced, the average speed of the locomotive is limited, and the driving accidents such as arc drawing, locomotive groveling and the like can be seriously caused.
By using the cascaded multilevel converter with the large-capacity single-phase direct-current ports interconnected, the comprehensive compensation of negative sequence, reactive power and harmonic waves can be realized on the traction side of the traction substation. Meanwhile, one or more cascaded multilevel converters with single-phase direct-current ports interconnected are arranged between an external three-phase power grid and a single-phase traction grid, decoupling and isolation of the external power grid and the traction grid can be achieved, the problem of electric energy quality of a traction substation is solved comprehensively, electric phase splitting of the traction grid is cancelled, and single-phase alternating-current power supply in a run-through mode is achieved.
As a core device for achieving the above technical purpose, a single-phase ac-dc-ac type back-to-back power electronic converter is required to have two-port electrical isolation capability, good harmonic characteristics of two ac ports at two sides, high full-load range operation efficiency, low loss, and strong fault locking and redundancy operation reliability.
The applicant of the invention successively provides two related granted patents, namely a single-phase unified power quality controller for electrified railway power supply (patent number ZL200710175253.2) and a unified power quality controller based on transformer series connection multiplexing and chain structure (patent number ZL200810119942.6), but the two related granted patents have certain defects. Wherein:
the single-phase multi-winding transformer adopted on one side of patent ZL200710175253.2 brings the following disadvantages: 1) the single-phase multi-winding transformer has the advantages of more complex processing technology, larger volume and weight and higher manufacturing cost, and the larger leakage reactance of the split transformer reduces the capacity utilization rate of the converter; 2) in order to obtain relatively good harmonic characteristics at the primary side port of the single-phase multi-winding transformer, phase shift control needs to be performed between the windings of the secondary sides, so that a large characteristic subharmonic circulating current is formed, the operation loss is increased, and the capacity utilization rate of a power electronic converter connected to the secondary side is further reduced.
One side of the invention patent ZL2008101199426 adopts not less than 2 single-phase transformers, each single-phase transformer is provided with a series-connection multiple transformer bank formed by not less than 2 secondary windings, and the electrical isolation and the electrical matching of alternating current ports on two sides of equipment are realized. The number of splits of a single multi-split transformer is reduced, so that the manufacturing difficulty of the multi-split transformer is reduced to a certain extent. Meanwhile, through the series connection of a plurality of transformers, the harmonic characteristic of the primary side port of the series-connected multiplex transformer is improved, and the characteristic subharmonic circulation between secondary windings is reduced. However, the series connection of multiple transformers introduces new problems: 1) because the excitation reactance values of all the transformers have inherent differences, when equipment breaks down and the on-load operation enters a pulse locking state, the difference of the induced voltages of the secondary windings of all the transformers is large, the direct-current voltages of all the secondary converters are possibly inconsistent, and the equipment is seriously damaged due to overvoltage. In order to suppress the inconsistency of the transformer, an additional damping circuit is required, so that the complexity and the cost of the circuit are increased, and the operation efficiency is reduced. 2) The total number of secondary windings of the series-connected multiple transformer bank is not substantially reduced, and is still the same as the total number of power units on one side of the converter, and the manufacturing cost and the protection cost of the multiple transformer bank are still high. When the equipment has fault redundant operation of N-1 or even N-2 units, the matching difficulty of control and protection between the transformer and the converter power unit is further increased, and the operation reliability is reduced.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a cascaded multilevel converter with single-phase direct-current ports interconnected, which avoids the problems caused by the adoption of a multi-split transformer or the multiple series connection of a plurality of transformers.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a cascaded multilevel converter with interconnected single-phase direct-current ports, which is characterized by comprising a first single-phase double-winding transformer, two cascaded multilevel voltage source type converter groups and a reactor group positioned at the alternating current side of any cascaded multilevel voltage source type converter group or two cascaded multilevel voltage source type converter groups, wherein the reactor group comprises a first single-phase double-winding transformer, a second single-phase double-winding transformer, a first voltage source type converter group and a second single-phase voltage source type converter group;
the first cascade multilevel voltage source type converter group comprises n first single-phase voltage source converters V which have the same structure and are sequentially connected in series 1i1, 2, …, n, a first single-phase voltage source converter V11Ac positive terminal and first single-phase voltage source converter V1nThe alternating current negative port of the converter group is respectively used as an alternating current positive port and an alternating current negative port of the first cascade multi-level voltage source type converter group; the second cascade multilevel voltage source type converter group comprises n second single-phase voltage source converters V which have the same structure and are sequentially connected in series2iSecond single-phase voltage source converter V21Ac positive port and second single-phase voltage source converter V2nThe AC negative port is respectively used as a second cascade multi-level voltage source type converter groupThe alternating current positive port and the alternating current negative port; corresponding first single-phase voltage source converter V1iAnd a second single-phase voltage source converter V2iThe homopolar direct current ports are connected; the alternating current port of the first cascade multilevel voltage source type converter group is connected to a single-phase power grid power supply M through the first single-phase double-winding transformer, and the alternating current port of the second cascade multilevel voltage source type converter group is connected to a single-phase power grid power supply N;
the reactor group comprises n reactors with the same structure; in the reactor group positioned at the AC side of the first cascade multilevel voltage source type converter group, the first reactor is connected with the first single-phase voltage source converter V11The other reactors are sequentially connected between two adjacent first single-phase voltage source converters; in the reactor group positioned at the AC side of the second cascade multilevel voltage source type converter group, the first reactor is connected with the second single-phase voltage source converter V21The other reactors are sequentially connected between two adjacent second single-phase voltage source converters;
the inductance values of all reactors in the reactor group are equal, and the sum of the series connection of the inductance values of all reactors is LxThe following formula is satisfied:
Figure BDA0002368090490000031
in the formula (I), the compound is shown in the specification,
KTis a constant, value range KT∈[0.04,0.4]；
VaIs rated voltage V between AC positive and negative ports of a cascade multi-level voltage source type converter group connected with a reactor groupa＝n×Ua，UaThe rated voltage effective value of each single-phase voltage source converter alternating current port in the cascade multilevel voltage source type converter group is obtained;
s is the rated apparent power capacity of the cascade multi-level voltage source type converter group connected with the reactor group, and S is nxVa×Ia，IaThe rated current effective value of each single-phase voltage source converter alternating current port in the cascade multilevel voltage source type converter group is obtained;
fnand the rated power of the single-phase power supply N is accessed to the alternating current port of the second cascade multi-level voltage source type converter group.
Furthermore, a direct current filter bank is arranged between the direct current sides of the two cascade multilevel voltage source type converter banks, and the direct current filter bank comprises n direct current filters F with the same structurei,D.C. filter Fi,One side port of the converter is connected in parallel with a first single-phase voltage source converter V1iAnd a second single-phase voltage source converter V2iD.c. positive port, d.c. filter FiThe other side port of the converter is connected in parallel with a first single-phase voltage source converter V1iAnd a second single-phase voltage source converter V2iA direct current negative port; each direct current filter is respectively formed by connecting a first filter inductor, a first filter capacitor and a first filter resistor in series.
Furthermore, a second single-phase double-winding transformer is arranged between the alternating current port of the second cascade multi-level voltage source type converter group and the single-phase power grid power supply N, and the rated apparent power capacity of the second single-phase double-winding transformer is S.
Further, the single-phase power grid source N is replaced by a single-phase passive power grid N ', an alternating current filter is connected in parallel between an alternating current port of the second cascade multilevel voltage source type converter group and the single-phase passive power grid N', and the alternating current filter is formed by connecting a second filter capacitor and a second filter resistor in series.
The invention has the characteristics and beneficial effects that:
the single-phase direct-current port interconnected cascaded multilevel converter provided by the invention avoids the problems caused by the adoption of a multi-split transformer or the multiple series connection of a plurality of transformers. And at most one single-phase double-winding transformer is adopted on one side, so that the volume and the manufacturing cost of the transformer are saved under the same power level, the protection difficulty of the transformer is simplified, and the single-phase double-winding transformer has better economic advantages. Good harmonic characteristics are obtained at the alternating current ports on the two sides, and the problems of loss increase and reduction of the capacity utilization rate of the converter caused by characteristic secondary circulation are solved. The problem of dynamic voltage sharing of the cascaded power units under the condition of large disturbance caused by the inconsistency of ferromagnetics of a plurality of series transformers under the condition of fault locking is solved.
According to different implementation modes of the invention, the power supply can be used for comprehensive control of the power quality of a traction substation or used as a power supply of a traction network, and through type single-phase alternating current power supply of the traction network is realized. The power supply circuit is particularly suitable for AC-DC-AC isolated power supply in the situation that the amplitude and the phase of input and output voltage are not greatly different. The single-phase double-winding transformer can be arranged at the single-phase alternating current ports at two sides of the device, so that the flexibility of adapting to the voltage grades of power supplies or loads of power networks at two sides is improved.
Drawings
Fig. 1 is a schematic structural diagram of a single-phase dc port-interconnected cascade multi-level converter 10 according to embodiment 1 of the present invention.
Fig. 2 is a schematic diagram of a topology structure of a two-level H-bridge type single-phase voltage source converter adopted in embodiment 1.
Fig. 3 is a schematic diagram of a topology structure of a midpoint-clamped three-level single-phase voltage source converter adopted in embodiment 1.
Fig. 4 is a schematic view of a topology structure of a flying capacitor three-level single-phase voltage source converter adopted in embodiment 1.
Fig. 5 is a schematic circular current diagram of an adjacent single-phase voltage source converter in embodiment 1 without a reactor.
Fig. 6 is a circular current equivalent diagram of a reactor additionally arranged between adjacent single-phase voltage source converters in embodiment 1.
Fig. 7 is a schematic structural diagram of a dc filter that can be selectively connected to the dc side of the single-phase voltage source converter in embodiment 1.
Fig. 8 is a schematic structural diagram of a single-phase dc port-interconnected cascade multi-level converter 20 according to embodiment 2 of the present invention.
Fig. 9 is a schematic structural diagram of a single-phase dc port-interconnected cascaded multi-level converter 30 according to embodiment 3 of the present invention.
Fig. 10 is a schematic structural diagram of a single-phase dc port interconnected cascaded multilevel converter 40 according to embodiment 4 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the detailed description and specific examples, while indicating the scope of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
For better understanding of the present invention, a specific technical solution of the single-phase dc port interconnected cascaded multilevel converter of the present invention is described in detail below.
The single-phase dc port interconnected cascade multi-level converter 10 according to embodiment 1 of the present invention may be used to connect different single-phase power grid power supplies M, N. Referring to fig. 1, the cascaded multi-level converter 10 includes: a single-phase double-winding transformer 1; two cascaded multi-level voltage source type converter groups (hereinafter referred to as "chained converter groups") 2 and 4 with the number of links being n; a reactor group (in the embodiment, reactor groups are arranged on both sides) positioned at the alternating current side of any one cascaded multilevel voltage source type converter group (2 or 4) or two cascaded multilevel voltage source type converter groups (2 and 4), and each reactor group is respectively composed of n reactors; and optionally a dc filter bank 3 of n dc filters.
The chain-type converter group 2 comprises n single-phase voltage source converters V with the same structure11，V12，…，V1i，…，V1nThe connection mode is as follows: first single-phase voltage source converter V11Ac positive port e11As an AC positive port of the chain-link converter group 2, a first single-phase voltage source converter V11Ac negative port f of11By means of reactors jXm2With a second single-phase voltage source converter V12Ac positive port e12Connected, further, the ith single-phase voltage source converter V1iAc negative port f of1iAre all passed through the reactor jXmiAnd the (i + 1) th single-phase voltage source converter V1(i+1)Ac positive port e1(i+1)Connection, i is a natural number and i is as much as [2, n ]](ii) a Variable current of nth single-phase voltage sourceDevice V1nAc negative port f of1nAs the negative ac port of the chain-link converter group 2.
The chain-type converter group 4 comprises n single-phase voltage source converters V with the same structure21，V22，…，V2i，…，V2nThe connection mode is as follows: first single-phase voltage source converter V21Ac positive port e21As the positive port of the chain-type converter group 4, the first single-phase voltage source converter V21Ac negative port f of21By means of reactors jXn2With a second single-phase voltage source converter V22Ac positive port e22Connected, further, the ith single-phase voltage source converter V2iAc negative port f of2iBy means of reactors jXniAnd the (i + 1) th single-phase voltage source converter V2(i+1)Ac positive port e2(i+1)Connecting; nth single-phase voltage source converter V2nAc negative port f of2nAs the negative ac port of the chain-link converter group 4.
The voltage source converter V11D of the direct current positive port11And voltage source converter V21D of the direct current positive port21Connected, voltage source converter V11D.c. negative port c11And voltage source converter V21D.c. negative port c21Connecting; further, the voltage source converter V1iD of the direct current positive port1iAnd voltage source converter V2iD of the direct current positive port2iConnected, voltage source converter V1iD.c. negative port c1iAnd voltage source converter V2iD.c. negative port c2iAre connected.
The primary side ports z and w of the single-phase double-winding transformer 1 are respectively connected to a single-phase power grid power supply M; the secondary side port z' of the single-phase double-winding transformer 1 passes through the reactor jXm1And the positive port e of the chain type converter group 211The secondary port w' of the single-phase double-winding transformer 1 is connected with the negative port f of the chain type converter group 21nAre connected.
AC positive port e of chain type converter group 421By reactor jXn1Is connected with an AC positive port x of a single-phase power grid power supply N and an AC negative port f of the chain type converter group 42nAnd is connected with an alternating current negative port y of a single-phase power grid power supply N. The ports x and y are used as one-side alternating current ports of the single-phase direct current back-to-back connected cascaded multi-level converter 10, and the primary side ports z and w of the single-phase double-winding transformer 1 are used as the other-side alternating current ports of the single-phase direct current back-to-back connected cascaded multi-level converter 10.
The rated direct current voltage of each single-phase voltage source converter is set to be UdThe rated voltage effective value of the AC port is UaThe rated current of the AC port has an effective value of IaThen the chain converter group 2 AC port e11、f1nAnd a chain-link converter group 4 AC port e21、f2nRated voltage V betweenaThe following formula is satisfied:
Va＝n×Ua(1)
the rated apparent power capacity of the single-phase double-winding transformer 1 and the cascade multilevel voltage source type converter groups 2 and 4 with the number of the links being n is S, then the following are provided:
S＝n×Va×Ia(2)
the effective value of the rated voltage of the single-phase power grid power supply M connected to the alternating-current ports z and w of the cascade multi-level converter 10 in the embodiment of the invention is VmRated frequency of fm(ii) a The rated voltage effective value of the AC port x, y connected to the single-phase power grid power supply N is VnRated frequency of fn. The cascaded multi-level converter 10 of the embodiment of the present invention should satisfy
Figure BDA0002368090490000051
And the rated voltage transformation ratio of the primary side ports z and w and the secondary side ports z 'and w' of the single-phase double-winding transformer 1 is Rm: 1, should satisfy:
Rm＝Vm/Va(3)
wherein R ismIs positive and real, and has a value range of 0.1, 10]In the meantime.
Each single-phase voltage source converter can adopt any one of a two-level H-bridge structure, a three-level midpoint clamping H-bridge structure, a three-level flying capacitor H-bridge structure and a cross-connected three-level H-bridge structure, and the topological structures of the single-phase voltage source converters are shown in figures 2, 3 and 4. The topological structure disclosed in the modern power electronics literature can be adopted, and the protection content of the invention is not included.
In the embodiment of the invention, the voltage source converter adopts a two-level H-bridge structure as shown in fig. 2, and comprises an insulated gate bipolar transistor (IGBT, hereinafter referred to as transistor) S1、S2、S3、S4Antiparallel diodes D connected in parallel to the IGBTs, respectively1、D2、D3、D4And a DC capacitor C1. The connection mode is as follows: transistor S1Collector of and transistor S3The collector electrode is connected with the direct current capacitor C through the direct current busbar1The positive terminal of the voltage source converter V is connected intoqi(when q is 1 or 2, and q is 1, it represents the voltage source converter V1iWhen q is 2, it represents the voltage source converter V2i) D of the direct current positive portqiTransistor S2And transistor S4The emitting electrodes are connected through a direct current bus bar and finally connected to a direct current capacitor C1Negative terminal of (2), the terminal is connected into a voltage source converter VqiD.c. negative port cqi. Transistor S1And transistor S2Is connected to node AiTransistor S3And transistor S4Is connected to node BiNode AiAnd BiBetween port voltage Ua, node AiDirect and voltage source converter VqiAc positive port eqiConnection, node BiAnd voltage source converter VqiAc negative port f ofqiAnd (4) connecting. Diode D1、D2、D3、D4Are respectively connected in reverse and parallel to the transistor S1、S2、S3And S4On the collector and emitter.
The embodiment of the invention provides a three-level midpoint clamping type H-bridge structureAs shown in fig. 3, includes an insulated gate bipolar transistor (IGBT, hereinafter referred to as "transistor") S1、S2、S3、S4、S5、S6、S7、S8Antiparallel diodes D connected in parallel to the transistors1、D2、D3、D4、D5、D6、D7、D8Series connection of DC capacitors C1And C2And a freewheel clamp diode VD1、VD2、VD3、VD4. The connection mode is as follows: in the left arm, transistor S1Collector of and transistor S5The collector electrode is connected with the direct current capacitor C through the direct current busbar1The positive terminal of the voltage source converter V is connected intoqi(when q is 1 or 2, and q is 1, it represents the voltage source converter V1iWhen q is 2, it represents the voltage source converter V2i) D of the direct current positive portqiTransistor S4And transistor S8The emitting electrodes are connected through a direct current bus bar and finally connected to a direct current capacitor C2Negative terminal of (2), the terminal is connected into a voltage source converter VqiD.c. negative port cqi. Transistor S1、S2、S3、S4Are connected in series from top to bottom, and the transistor S1And transistor S2Is connected to node C and transistor S2And transistor S3Is connected to node BiTransistor S3And transistor S4A collector connected to node E, and a freewheeling clamp diode VD1、VD2The midpoint after the series connection is O3Free-wheeling clamping diode VD1Negative pole of (1) connected to node C, freewheeling clamp diode VD2The positive electrode of (2) is connected to node E. The electrical connection of the right arm is identical to that of the left arm, and the transistor S5、S6、S7、S8Are connected in series from top to bottom, and the transistor S5And transistor S6Is connected to node D and transistor S6And transistor S7Is connected to node AiTransistor S7Emitter and S8Is connected to node F, and a freewheeling clamp diode VD3、VD4The midpoint after the series connection is O2Free-wheeling clamping diode VD3Negative pole of (D) is connected to a node (D), and a freewheeling clamp diode (VD)4The positive pole of (2) is connected to node F. DC capacitor C1、C2In series, the midpoint of which is O1Node O1、O2、O3Directly interconnected as reference ground of three levels, A of left and right bridge armsiAnd BiThe node output is the whole voltage source type converter VqiOutput node e ofqiAnd fqi。
The three-level flying capacitor H-bridge structure in the embodiment of the invention is shown in fig. 4, and the basic connection principle is similar to that of the three-level midpoint clamping H-bridge structure, except that the three-level flying capacitor H-bridge structure adopts a clamping capacitor VC1And VC2The two ends of the clamp capacitor are connected to the nodes C, E and D, F, respectively, and the remaining electrical connection forms are consistent with the three-level midpoint-clamped H-bridge structure.
Single-phase voltage source converter V of the cascaded multilevel converter 10 of the embodiment11，V12，…，V1i，…，V1nAnd V21、V21，V22，…，V2i，…，V2nThere will be a circulating current between them, the circulating current path between the single-phase voltage source 'back-to-back' converters is shown in fig. 5, in order to restrain the circulating current between the voltage source converters, the invention proposes to connect a reactor jXn in series between the cascaded converters1，jXn2，…，jXni，…，jXnnOr jXm1，jXm2，…，jXmi，…，jXmnThe connection mode is as follows: reactor jXn1Is connected with an alternating current port x and a reactor jXn1The other port of the voltage source converter is connected with a voltage source converter V21Ac positive port e21(ii) a Reactor jXniOne port of the voltage source converter is connected with a voltage source converter V2(i-1)Ac negative port f of2(i-1)The other port is connected with a voltage source converter V2iAc positive port e2i. Reactor jXnnOne port of the voltage source converter is connected with a voltage source converter V2(n-1)(i-n-1) AC negative port f2(n-1)The other port is connected with a voltage source converter V2nAc positive port e2nVoltage source converter V2nAc negative port f of2nThe connection diagram is shown in fig. 10 for the ac port y.
The inductance values of the reactors in the reactor group are equal (the following equation is satisfied when the reactor group is provided only on one side), and the reactor jXn is recordedjAnd jXmiRespectively has an inductance of lni、lmiIt should satisfy:
Figure BDA0002368090490000071
in the formula, LxThe sum of the series connection of the inductance values of the reactors in each reactor group satisfies the following conditions:
Figure BDA0002368090490000072
wherein, KTIs constant, usually over a range KT∈[0.04,0.4]。
Furthermore, the switching devices of the adjacent modules participating in the circulation are extracted to form a circulation equivalent circuit diagram shown in fig. 6, and the circulation equivalent circuit diagram comprises a single-phase voltage source converter V1iRight bridge arm and single-phase voltage source converter V2iRight bridge arm and single-phase voltage source converter V1(i+1)Left bridge arm and single-phase voltage source converter V2(i+1)Left bridge arm and direct current capacitor UdciDC capacitor Udc(i+1)And an equivalent reactor Lnn (the inductance value of the equivalent reactor Lnn is L)x) (ii) a Wherein, the single-phase voltage source converter V1iAnd V1(i+1)The left bridge arm is respectively composed of two Insulated Gate Bipolar Transistors (IGBT) S1And S2Series-connected single-phase voltage source converters V2iAnd V2(i+1)The left bridge arm is respectively composed of two Insulated Gate Bipolar Transistors (IGBT) S4And S3Are connected in series; DC capacitor UdciThe anode and the cathode of the single-phase voltage source converter are respectively connected with a single-phase voltage source converter V1iAnd V2iPositive electrode parallel common terminal, single-phase voltage source converter V1iAnd V2iNegative pole of (1) is connected with a common terminal in parallel, and a direct current capacitor Udc(i+1)The anode and the cathode of the single-phase voltage source converter are respectively connected with a single-phase voltage source converter V1(i+1)And V2(i+1)Positive electrode parallel common terminal, single-phase voltage source converter V1iAnd V2iThe negative electrode of the first diode is connected with the common terminal in parallel; single-phase voltage source converter V1iMidpoint 1 of two insulated gate bipolar transistors in left bridge arm and single-phase voltage source converter V1(i+1)The middle points 2 of two insulated gate bipolar transistors in the left bridge arm are connected, and a single-phase voltage source converter V2iMiddle points a and d of two insulated gate bipolar transistors in right bridge arm single-phase voltage source converter V2(i+1)The middle points b of the two insulated gate bipolar transistors in the right bridge arm are connected through equivalent inductors Lx after being folded. Single-phase voltage source converter V with O point1(i+1)And V2(i+1)The DC capacitor cathode, O' point is a single-phase voltage source converter V1iAnd V2iThe negative pole of the direct current capacitor is provided with a single-phase voltage source converter V1iAnd V2iThe modulation wave signal is Uref1Single-phase voltage source converter V1(i+1)And V2(i+1)The modulation wave signal is Uref2The following relationship is satisfied:
Figure BDA0002368090490000081
Figure BDA0002368090490000082
wherein t is the operation time of the cascaded multilevel converter 10 in the embodiment; v1For single-phase voltage source converters V1iAnd V1(i+1)Output peak voltage of, V2For single-phase voltage source converters V2iAnd V2(i+1)Output peak voltage of f1For single-phase voltage source converters V1iAnd V1(i+1)Output voltage frequency ofRate, f2For single-phase voltage source converters V2iAnd V2(i+1)The frequency of the output voltage of (a),
Figure BDA0002368090490000083
for single-phase voltage source converters V1iAnd V1(i+1)The phase of the output of (a) is,
Figure BDA0002368090490000084
for single-phase voltage source converters V2iAnd V2(i+1)The voltage across the equivalent reactor Lnn is:
UL＝UaO-UbO＝UaO'+UO'O-UbO(8)
wherein, UaOFor using a single-phase voltage source converter V1(i+1)Single-phase voltage source converter V with DC capacitor negative electrode as reference2iTwo insulated gate bipolar transistors S in right bridge arm4And S3Voltage at the midpoint output, UbOFor using a single-phase voltage source converter V1(i+1)Single-phase voltage source converter V with DC capacitor negative electrode as reference2(i+1)Two insulated gate bipolar transistors S in right bridge arm4And S3Voltage at the midpoint output, UaO’For using a single-phase voltage source converter V1iSingle-phase voltage source converter V with DC capacitor negative electrode as reference2iTwo insulated gate bipolar transistors S in right bridge arm1And S2Voltage at the midpoint output, UOO’For using a single-phase voltage source converter V1(i+1)Single-phase voltage source converter V with DC capacitor negative electrode as reference1iThe voltage output by the cathode of the direct current capacitor.
Neglecting the switching characteristic secondary current in the reactor, only calculating the fundamental wave component, and analyzing the output voltage of the H bridge as follows under the SPWM modulation according to the prior published documents:
Figure BDA0002368090490000085
Figure BDA0002368090490000086
UO'O＝U1O-U1O'(11)
the voltage across the reactor can be calculated by the formula (9), the formula (10) and the formula (11) as follows:
Figure BDA0002368090490000087
the phase difference between the output voltages of the rectifying side and the inverting side is set as
Figure BDA0002368090490000088
The output frequency is the same, then
Figure BDA0002368090490000089
Considering that the direct-current voltage of each converter in actual work is small in voltage difference controlled by a voltage-sharing algorithm, considering that U isdc＝Udc1＝Udc2The equation (12) is simplified to obtain:
Figure BDA0002368090490000091
thereby obtaining the voltage difference amplitude U between two ends of the reactorL_RMPComprises the following steps:
Figure BDA0002368090490000092
the magnitude of the circulating current can be calculated by equation (14) as:
Figure BDA0002368090490000093
it can be seen from the analysis of formula (15) that the magnitude of the circulating current is related to the magnitude and phase of the voltage on the rectifying side and the voltage on the inverting side, and therefore the magnitude of the circulating current can be directly controlled by controlling the magnitude and phase angle of the output voltage on the rectifying side and the output voltage on the inverting side.
Further, when fm＝fnFor restraining the chain-link converterThe voltage of the direct current capacitors of the groups 2 and 4 fluctuates, and a direct current filter group 3 is installed at each direct current port where the chain type converter group 2 and the chain type converter group 4 are connected with each other. The dc filter bank 3 comprises n dc filters F1，F2，…，Fi，…，Fn. DC filter F1One side port g1Simultaneous and single-phase voltage source converter V11And V21D of the direct current positive port11And d21Phase-connected, DC filter F1The other side port h1Simultaneous and voltage source converter V11And V21D.c. negative port c11And c21Connecting; further, a DC filter FiOne side port giSimultaneous and single-phase voltage source converter V1iAnd V2iD of the direct current positive port1iAnd d2iPhase-connected, DC filter FiThe other side port hiSimultaneous and voltage source converter V1iAnd V2iD.c. negative port c1iAnd c2iAre connected.
All the direct current filters have the same structure and adopt an RLC single-tuned filtering structure, and the ith direct current filter F is usediThe description is given for the sake of example. As shown in fig. 7, the dc filter FiBy a filter inductance LsiFilter capacitor CsiFilter resistor RsiFormed in series, wherein the filter inductance LsiAnd a filter capacitor CsiForming a series resonant circuit resonant frequency of fwAnd satisfies the following conditions:
Figure BDA0002368090490000094
filter resistor RsiAnd the damping is increased to inhibit low-frequency oscillation. Increasing the filter resistance RsiThe damping of the system can be improved, the system is more stable, however, the loss is increased by increasing the resistance, so the selection of the damping resistance is in compromise with the damping and the loss of the system.
As shown in fig. 8, the cascaded multi-level converter 20 according to embodiment 2 of the present invention may be formed by connecting the outlet of the cascaded multi-level converter 10 according to embodiment 1 of the present invention to the single-phase bifilar transformer 5, and the cascaded multi-level converter 20 may also be used to connect different single-phase power grid sources M, N. Compared with the cascaded multi-level converter 10, the cascaded multi-level converter 20 of the present embodiment has more flexible voltage level of the grid connected to both ends.
Primary side ports k and p of the single-phase double-winding transformer 5 are used as alternating current ports of the cascade multilevel converter 20 and are connected to a single-phase power grid power supply N; secondary side port k' of single-phase double-winding transformer 5 and positive port e of chain type converter group 421Connected reactor jXn1The secondary port p' of the single-phase double-winding transformer 5 is connected with the negative port f of the chain type converter group 42nAre connected. The rated apparent power capacity of the single-phase double-winding transformer 5 is S, and the rated voltage transformation ratio of the primary side ports k and p and the secondary side ports k 'and p' of the single-phase double-winding transformer 5 is Rn: 1, should satisfy:
Rn＝Vn/Va(17)
wherein R isnIs a positive real number, and usually has a value range of [0.1, 10 ]]In the meantime.
Referring to fig. 9, in embodiment 1 of the present invention, an ac port x of a multilevel converter 10 and a reactor jXn are cascaded1AC port y of cascade multi-level converter 10 and single-phase voltage source converter V between output ends2nAc negative port f of2nThe ac filter 6 is connected in parallel to form the cascaded multi-level converter 30 according to embodiment 3 of the present invention, one end of the cascaded multi-level converter 30 is connected to the single-phase power grid power supply M, and the other end supplies power to the single-phase passive power grid N'. As shown in fig. 9, the port v of the ac filter 6 is connected to the ac port x of the cascaded multilevel converter 30, and the port r of the ac filter 6 is connected to the ac port y of the cascaded multilevel converter 30. Compared with the cascaded multi-level converter 10 of the embodiment 1 of the invention, the cascaded multi-level converter 30 can be used as a voltage source to supply power to a load.
The AC filter 6 is composed of a filter capacitor CfAnd a filter resistor RfFormed in series with an equivalent reactor Lx(i.e. the inductance of each reactor in each reactor groupThe series sum equivalent reactor) or the single-phase double-winding transformer 5 forms a low-pass filter, and the turning frequency of the low-pass filter is recorded as f0。f0Usually greater than 2fnAnd C isfSatisfies the following conditions:
Figure BDA0002368090490000101
increasing damping filter resistance RfThe damping of the system can be improved, the system is more stable, however, the loss is increased by increasing the resistance, so the selection of the damping resistance is in compromise with the damping and the loss of the system.
Referring to fig. 10, a single-phase double-winding transformer 5 is arranged between the ac filter 6 and the ac side of the chain-type converter group 4 in the cascade multi-level converter 30 according to embodiment 3 of the present invention, so as to form the cascade multi-level converter 40 according to embodiment 4 of the present invention, wherein one end of the cascade multi-level converter 40 is connected to the single-phase power grid power supply M, and the other end of the cascade multi-level converter supplies power to the single-phase passive power grid N'. The primary side ports k and p of the single-phase double-winding transformer 5 are respectively connected with the ports V and r of the alternating current filter 6, and the secondary side ports k 'and p' of the single-phase double-winding transformer 5 are respectively connected with the single-phase voltage source converter V21jXn1 on AC side and single-phase voltage source converter V2nAc negative port f of2nAre connected. Filter capacitor C in AC filter 6fSatisfies the following conditions:
Figure BDA0002368090490000102
wherein L isyThe nominal value of the short-circuit reactance is converted from the rated apparent power capacity S of the single-phase double-winding transformer 5 to the side of the primary side port k and the side of the primary side port p.
Compared with the cascaded multi-level converter 20 of the embodiment 2 of the invention, the cascaded multi-level converter 40 of the embodiment has more flexible voltage level of the access load.
The embodiment of the invention is designed by taking the cascaded multi-level converter 10 with the single-phase direct-current ports interconnected as an example. As shown in fig. 1, the single-phase double-winding transformer 1 is a cascade multi-level voltage with 16 link numbers nThe rated apparent power capacity S of the source type converter groups 2 and 4 is 20MW, and the transformation ratio of the single-phase double-winding transformer 1 is 1: 1, the primary side is connected with a 27.5kV voltage class power grid, and the frequency f of the power gridm50Hz single-phase voltage source converter V11、V12、…、V1i、…、V1nAnd V21、V22、…、V2i、…、V2nThe topological structure of the single-phase voltage source converter is a two-level H-bridge type single-phase voltage source converter, as shown in figure 5, the voltage grade of the direct-current side voltage of one single-phase voltage source converter is Ud3kV, effective value U of output voltage at AC sidea1.72kV, DC side capacitance Ci16000uf, filtering capacitor C of filtering branch at DC sidesi1600uf, filter inductance Lsi1.58mH, make the resonance frequency f of the filter branchw100Hz, and the damping resistance Rsi is 0.01 omega, so as to restrain low-frequency oscillation.
Inductance value jXn1～jXmmSelecting, taking KTTotal inductance value is 0.2:
Figure BDA0002368090490000111
then the optional outlet reactance jXn1～jXmmAll inductance values are Lx/n＝5.9×10-6H. Reactor jXn1、jXm1The terminals x, y of (2) are connected with another voltage class of 27.5kV and frequency fn50Hz grid.
The present invention and its embodiments have been described above schematically, without limitation, and what is shown in the drawings is only one of the embodiments of the present invention and is not actually limited thereto. Therefore, if the person skilled in the art receives the teaching, it is within the scope of the present invention to design the similar manner and embodiments without departing from the spirit of the invention.

Claims (8)

1. A cascade multilevel converter with single-phase direct-current ports interconnected is characterized by comprising a first single-phase double-winding transformer (1), two cascade multilevel voltage source type converter groups (2 and 4) and a reactor group positioned at the alternating current side of any cascade multilevel voltage source type converter group (2 or 4) or two cascade multilevel voltage source type converter groups (2 and 4);
the first cascade multilevel voltage source type converter group (2) comprises n first single-phase voltage source converters V which have the same structure and are sequentially connected in series1i1, 2, …, n, a first single-phase voltage source converter V11Ac positive terminal and first single-phase voltage source converter V1nThe alternating current negative port of the converter group (2) is respectively used as an alternating current positive port and an alternating current negative port of the first cascade multi-level voltage source type converter group; the second cascade multilevel voltage source type converter group (4) comprises n second single-phase voltage source converters V which have the same structure and are connected in series in sequence2iSecond single-phase voltage source converter V21Ac positive port and second single-phase voltage source converter V2nThe alternating current negative port of the converter group (4) is respectively used as an alternating current positive port and an alternating current negative port of the second cascade multi-level voltage source type converter group; corresponding first single-phase voltage source converter V1iAnd a second single-phase voltage source converter V2iThe homopolar direct current ports are connected; an alternating current port of the first cascade multilevel voltage source type converter group (2) is connected to a single-phase power grid power supply M through the first single-phase double-winding transformer (1), and an alternating current port of the second cascade multilevel voltage source type converter group (4) is connected to a single-phase power grid power supply N;
the reactor group comprises n reactors with the same structure; in a reactor group positioned at the alternating current side of the first cascade multilevel voltage source type converter group (2), a first reactor is connected with a first single-phase voltage source converter V11The alternating current positive port of the transformer is connected with the secondary side port z' of the first single-phase double-winding transformer (1), and the rest reactors are sequentially connected between two adjacent first single-phase voltage source converters; in the reactor group positioned at the alternating current side of the second cascade multilevel voltage source type converter group (4), the first reactor is connected with the second single-phase voltage source converter V21The other reactors are sequentially connected between two adjacent second single-phase voltage source converters;
the inductance values of all reactors in the reactor group are equal, and the sum of the series connection of the inductance values of all reactors is recorded as LxThe following formula is satisfied:
Figure FDA0002368090480000011
in the formula (I), the compound is shown in the specification,
KTis a constant, value range KT∈[0.04,0.4]；
VaIs rated voltage V between AC positive and negative ports of a cascade multi-level voltage source type converter group connected with a reactor groupa＝n×Ua，UaThe rated voltage effective value of each single-phase voltage source converter alternating current port in the cascade multilevel voltage source type converter group is obtained;
s is the rated apparent power capacity of the cascade multi-level voltage source type converter group connected with the reactor group, and S is nxVa×Ia，IaThe rated current effective value of each single-phase voltage source converter alternating current port in the cascade multilevel voltage source type converter group is obtained;
fnthe rated power of a single-phase power supply N is accessed to an alternating current port of a second cascade multi-level voltage source type converter group (4).
2. Cascaded multilevel converter according to claim 1, characterized in that between the dc sides of two cascaded multilevel voltage source type converter banks there is a dc filter bank (3), which dc filter bank (3) comprises n structurally identical dc filters Fi,D.C. filter Fi,One side port of the converter is connected in parallel with a first single-phase voltage source converter V1iAnd a second single-phase voltage source converter V2iD.c. positive port, d.c. filter Fi,The other side port of the first single-phase voltage source converter V is connected in parallel1iAnd a second single-phase voltage source converter V2iA direct current negative port; each direct current filter is respectively formed by connecting a first filter inductor, a first filter capacitor and a first filter resistor in series.
3. The cascaded multi-level converter as claimed in claim 1, wherein in the two cascaded multi-level voltage source-converter groups, each single-phase voltage source-converter adopts any one of a two-level H-bridge structure, a three-level midpoint clamping H-bridge structure, a three-level flying capacitor H-bridge structure and a cross-connected three-level H-bridge structure.
4. A cascaded multilevel converter according to claim 1 or 2, characterized in that a second single phase double winding transformer (5) is arranged between the ac port of the second cascaded multilevel voltage source converter group (4) and the single phase grid supply N, the second single phase double winding transformer (5) having a nominal apparent power capacity S.
5. Cascaded multilevel converter according to claim 1 or 2, characterized in that the single-phase grid power source N is replaced by a single-phase passive grid N ', an ac filter (6) is connected in parallel between the ac port of the second cascaded multilevel voltage source-type converter bank (4) and the single-phase passive grid N', and the ac filter (6) is formed by a second filter capacitor and a second filter resistor connected in series.
6. Cascaded multilevel converter according to claim 4, wherein the single-phase grid power source N is replaced by a single-phase passive grid N ', an AC filter (6) is connected in parallel between the AC port of the second cascaded multilevel voltage source-type converter set (4) and the single-phase passive grid N', and the AC filter (6) is formed by connecting a second filter capacitor and a second filter resistor in series.
7. Cascaded multilevel converter according to claim 5, characterized in that a second single phase double winding transformer (5) is arranged between the AC port of the second cascaded multilevel voltage source-type converter group (4) and the AC filter (6), the second single phase double winding transformer (5) having a nominal apparent power capacity S.
8. Cascaded multilevel converter according to claim 6, characterized in that a second single phase double winding transformer (5) is arranged between the AC port of the second cascaded multilevel voltage source-type converter group (4) and the AC filter (6), the second single phase double winding transformer (5) having a nominal apparent power capacity S.
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