CN108173442B - Isolated modular multilevel converter based on high-frequency chain technology - Google Patents

Isolated modular multilevel converter based on high-frequency chain technology Download PDF

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CN108173442B
CN108173442B CN201810047646.3A CN201810047646A CN108173442B CN 108173442 B CN108173442 B CN 108173442B CN 201810047646 A CN201810047646 A CN 201810047646A CN 108173442 B CN108173442 B CN 108173442B
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switch tube
active switch
active
diode
voltage
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CN108173442A (en
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刘闯
蔡国伟
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Northeast Electric Power University
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Northeast Dianli University
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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
    • 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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
    • H02M3/33592—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
    • H02M1/007—Plural converter units in cascade

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Inverter Devices (AREA)

Abstract

The invention discloses an isolated modular multilevel converter based on a high-frequency chain technology, wherein the converter is of a three-phase system structure and comprises a single-stage high-frequency isolated submodule; also includes threeA plurality of high voltage DC ports P connected in parallelH、NHEach phase unit consists of an upper bridge arm and a lower bridge arm, and the electrical connection points N of the upper bridge arm and the lower bridge arm of the three phase units1、N2、N3The outgoing lines are connected with filter inductors in series and then are high-voltage alternating-current ports a, b and c, and each bridge arm consists of n novel single-stage high-frequency isolated submodules and a bridge arm reactor LmComposition is carried out; the single-stage high-frequency isolation type submodule comprises a front-stage part, a high-frequency transformer part and a rear-stage part, wherein the alternating current side of the front-stage part is connected with the primary side of the high-frequency transformer. The invention combines the high-frequency chain technology with the modular multilevel technology, thereby ensuring that the high-voltage side of each module does not need to be supported by a capacitor and controlled by voltage sharing, and simultaneously overcoming the problems of secondary side current conversion, voltage spike and the like of the traditional single-stage converter.

Description

Isolated modular multilevel converter based on high-frequency chain technology
Technical Field
The invention relates to the technical field of isolated modular multilevel power conversion, in particular to an isolated modular multilevel converter based on a high-frequency chain technology.
Background
The isolation type medium-high voltage alternating current and direct current hybrid conversion technology plays an important role in the fields of future new energy alternating current and direct current hybrid smart power grids, high-power motor driving, ship electric driving and the like. At present, cascaded H-bridge type and Modular Multilevel Converter (MMC) type topological structures which belong to two-stage power conversion systems are widely adopted, and the problems that a large number of voltage stabilizing capacitors are needed on independent direct current sides of modules to buffer secondary power fluctuation of a single-phase system exist, so that the device is large in size, low in power density and high in cost; meanwhile, voltage imbalance exists among the modules, complex voltage balance control is needed, and system reliability is reduced.
Disclosure of Invention
In order to solve the problems, the invention provides an isolated modular multilevel converter based on a high-frequency chain technology, which combines the high-frequency chain technology with the modular multilevel technology, so that the high-voltage side of each module does not need to be supported by a capacitor and controlled by voltage sharing, and meanwhile, the problems of secondary side conversion, voltage spike and the like of the traditional single-stage converter are solved, and the isolated modular multilevel converter has three basic ports of high-voltage alternating current, high-voltage direct current and low-voltage direct current.
In order to achieve the purpose, the invention adopts the technical scheme that:
the isolated modular multilevel converter is based on a high-frequency chain technology, is of a three-phase system structure and comprises a single-stage high-frequency isolated submodule;
also comprises three high-voltage direct current ports P connected in parallelH、NHEach phase unit consists of an upper bridge arm and a lower bridge armElectrical connection point N of upper and lower bridge arms of three phase units1、N2、N3The outgoing lines are connected with filter inductors in series and then are high-voltage alternating-current ports a, b and c, and each bridge arm consists of n novel single-stage high-frequency isolated submodules and a bridge arm reactor LmComposition is carried out;
the single-stage high-frequency isolation type submodule comprises a preceding stage part, a high-frequency transformer part and a subsequent stage part, wherein the alternating current side of the preceding stage part is connected with the primary side of the high-frequency transformer, the alternating current side of the subsequent stage part is connected with the secondary side of the high-frequency transformer, and the positive and negative electrode ports of the preceding stage part of each single-stage high-frequency isolation type submodule are respectively connected in parallel to be used as a public low-voltage direct current port PL、NLThe ports of the rear stage part are connected in series to form a high-voltage direct-current side port PH、NH；
Positive pole end P of upper bridge arm of three phase unitsHa、PHb、PHcConnected as positive pole P of high voltage DC port of the converterHNegative pole end N of lower bridge arm of three phase units 2Ha、NHb、NHcNegative pole N connected as high voltage DC port of the converterHThe two poles jointly form a high-voltage direct-current port P of the topological structureH、NH。
Further, the front stage part of the single-stage high-frequency isolation type submodule comprises a low-voltage side direct current capacitor CdcLAnd an active H-bridge consisting of four active switches (such as IGBTs, etc.) with anti-parallel diodes; the latter part comprises a voltage clamp circuit 7 and an active H-bridge consisting of four active switches with anti-parallel diodes, such as IGBTs etc.
Further, the active H-bridge of the front stage part 4 comprises a first active switching transistor Q1A second active switch tube Q2A third active switch tube Q3And a fourth active switch tube Q4The collector of each active switch tube is respectively connected with the cathode of the corresponding freewheeling diode, and the emitter of each active switch tube is respectively connected with the anode of the corresponding freewheeling diode;
first active switch tube Q1And a third active switch tube Q3After being connected in series with the low-voltage side direct current capacitor CdcLParallel connection, a first active switch tube Q1Emitter and third active switching tube Q3Is connected with the collector and serves as a primary side E of the high-frequency transformer, and a second active switch tube Q2Emitter and fourth active switching tube Q4The collector of the first active switch tube Q is connected with the other end F which is the primary side of the high-frequency transformer1Collector electrode and CdcLIs connected with the positive pole of the third active switch tube Q3Emitter and CdcLThe negative electrodes are connected; second active switch tube Q2And a fourth active switch tube Q4After being connected in series with the low-voltage side direct current capacitor CdcLParallel second active switch tube Q2Collector electrode and CdcLIs connected with the positive pole of the fourth active switch tube Q4Emitter and CdcLThe negative electrodes are connected; first active switch tube Q1And a second active switch tube Q2Collector electrode of (1) and (C)dcLIs connected with the positive pole of the sub-module and is used as the positive pole A of the front stage part of the sub-module, and a third active switch tube Q3And a fourth active switch tube Q4Emitter and C ofdcLIs connected with and serves as the cathode B of the preceding part of the submodule.
Further, the active H-bridge of the rear stage part comprises a fifth active switch tube Q5A sixth active switch tube Q6A seventh active switch tube Q7An eighth active switch tube Q8The collector of each active switch tube is respectively connected with the cathode of the corresponding freewheeling diode, and the emitter of each active switch tube is respectively connected with the anode of the corresponding freewheeling diode; fifth active switch tube Q5Emitter and seventh active switching tube Q7Is connected with the collector and serves as a secondary side end G of the high-frequency transformer, and a sixth active switching tube Q6Emitter and eighth active switching tube Q8The collector of the transformer is connected with the other end H which is used as the secondary side of the high-frequency transformer; fifth active switch tube Q5And a sixth active switch tube Q6And the collector of the first active switch tube is connected with the positive electrode C as the rear stage part of the submodule, and the seventh active switch tube Q7And an eighth active switch tube Q8Of the emitterAnd the negative electrode D is connected with the negative electrode D and serves as a post-stage part of the submodule.
Further, the voltage clamping circuit includes a first diode D1A second diode D2A third diode D3A fourth diode D4A first capacitor C1A first resistor R1First diode D1And a second diode D2Are respectively connected with the first capacitor C after being connected in series1A first resistor R1Parallel, a second diode D2And a fourth diode D4Are respectively connected with the first capacitor C after being connected in series1A first resistor R1Parallel, first diode D1A second diode D2Cathode and first capacitor C1A first resistor R1Is connected to the anode of a second diode D2A fourth diode D4Anode and first capacitor C1A first resistor R1Is connected to the negative electrode of a first diode D1Anode of and a third diode D3Is connected with the secondary side end G of the high-frequency transformer, and a second diode D2Anode of and a fourth diode D4The cathode of the transformer is connected with the other end H of the secondary side of the high-frequency transformer.
Furthermore, the modulation ratio of the upper bridge arm and the lower bridge arm is an alternating current-direct current mixed modulation ratio duAnd d1Wherein d isuModulation ratio of upper arm, d1Modulation ratio of lower arm, and duAnd d1By a DC common modulation ratio D and a per-phase AC modulation ratio Da、db、dcIn which d isaA ac modulation ratio of A, dbModulation ratio of B-phase AC, dcIs the C-phase ac modulation ratio.
Further, the high-frequency transformer portion is composed of a high-frequency transformer T which can realize the functions of power transmission, electrical isolation, voltage class conversion and the like on the high-voltage side and the low-voltage side, and the bridge arm reactor LmBesides reducing harmonic distortion rate of bridge arm current, the converter can also inhibit interphase circulation and short-circuit circulation generated by short-circuit fault on a direct current side, and protect a power electronic switch of the converter. TheThe topological structure can realize flexible energy transmission among three ports of high-voltage alternating current, high-voltage direct current and low-voltage direct current, and can meet the requirements of various operation modes of an alternating current-direct current hybrid system.
The invention has the following beneficial effects:
(1) and the high-voltage side of each high-frequency isolation type sub-module is not provided with a direct-current capacitor. The structure adopts a high-frequency chain technology, the high-voltage side pulse width modulation is realized through the switch combination of the front-stage and rear-stage driving H-bridge power tubes of the sub-modules, and the pulse width modulation voltage wave is directly supported by a low-voltage side direct current capacitor of a front-stage part through a high-frequency transformer, so that the high-voltage side of the rear-stage part does not need to be supported by the capacitor any more; meanwhile, all frequency doubling power fluctuation of three phases is transferred to a common low-voltage direct-current bus and counteracted mutually, so that the common low-voltage direct-current bus does not need a large amount of capacitors for supporting, compared with a traditional two-stage isolation type alternating-current and direct-current hybrid conversion system, a large amount of voltage stabilizing capacitors can be reduced, the size of the device is reduced, the cost is reduced, and the device has the characteristics of high power density and the like.
(2) The converter does not require a separate voltage balancing control. The terminal voltage of each submodule is directly clamped by the bus voltage at the low-voltage direct-current side through a high-frequency transformer, the steady-state and dynamic characteristics of the output voltages of the upper bridge arm terminal and the lower bridge arm terminal are consistent, compared with an MMC type complex sampling circuit and complex voltage-sharing control, the converter does not need voltage-sharing control, the complexity of control is reduced, and meanwhile the reliability and the economical efficiency of a system are improved.
(3) The converter does not require a bidirectional switching tube. Because the voltage of the high-voltage side port of each submodule is always positive, the converter does not need a bidirectional switch tube, and the problems of secondary side current conversion and voltage peak caused by leakage inductance of the traditional single-stage converter are avoided.
Drawings
Fig. 1 is a three-phase topology structure diagram of an isolated modular multilevel converter based on a high-frequency link technology according to the present invention;
FIG. 2 is a diagram of a single phase unit topology of the present invention;
FIG. 3 is a high frequency isolation type sub-module topology structure diagram of the present invention;
in the figure: pH-a high voltage dc positive port;
NH-a high voltage dc negative port;
PL-a low voltage dc positive port;
NL-a low voltage dc negative port;
a-a high voltage alternating current phase A port;
b-a high voltage alternating current phase B port;
c-a high voltage alternating current (C) phase port;
SMn-submodules, n being their number;
Lm-bridge arm reactors;
Lf-an ac side filter inductance;
N1-a phase upper and lower bridge arm connection points;
N2-b phase upper and lower leg connection points;
N3-c phase upper and lower leg connection points;
CdcL-a low voltage dc capacitor;
a T-high frequency transformer;
A. b-positive and negative electrode ports of the front part of the submodule;
C. d-positive and negative electrode ports of the rear part of the submodule;
E. f, a primary side port of the high-frequency transformer;
G. an auxiliary side port of the H-high frequency transformer;
Q1～Q4-a front-end part active switching transistor, such as an Insulated Gate Bipolar Transistor (IGBT);
Q5～Q8-a post-stage partially active switching transistor, such as an Insulated Gate Bipolar Transistor (IGBT);
D1～D4-a post-stage partial voltage clamping circuit diode;
C1-a post-stage partial voltage clamping circuit capacitance;
R1-a voltage clamp circuit resistance in the post-stage section;
PHa、PHb、PHcpositive terminal of upper armA mouth;
NHa、NHb、NHc-the negative terminal of the lower leg;
Pc、Ncpositive and negative terminals of the clamping circuit of the rectifier bridge of the rear part of the submodule.
Detailed Description
In order that the objects and advantages of the invention will be more clearly understood, the invention is further described in detail below with reference to examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
As shown in fig. 1, an isolated modular multilevel converter based on a high-frequency link technology is provided in an embodiment of the present invention, where the converter 1 includes three identical phase units 2, each phase unit is divided into an upper bridge arm and a lower bridge arm as shown in fig. 2, and each bridge arm includes n sub-modules and a bridge arm reactor LmAnd (4) forming.
Each single-stage high-frequency isolation type submodule 3 comprises a preceding stage part 4, a high-frequency transformer part 5 and a subsequent stage part 6, the topological structure of the submodule is shown in figure 3, the high-frequency alternating current side of the preceding stage part is connected with the primary side of a high-frequency transformer T, the high-frequency alternating current side of the subsequent stage part is connected with the secondary side of the high-frequency transformer T, and the preceding stage side ports of all the submodules are connected in parallel to form a common low-voltage direct current side port (P)L、NL) The rear stage side ports are connected in series to form a high-voltage direct-current side port (P)H、NH) Positive terminal (P) of arm on three phase unitHa、PHb、PHc) Connected as positive pole P of high voltage DC port of the converterHSimilarly, the negative terminal (N) of the lower arm of the three-phase unitHa、NHb、NHc) Negative pole N connected as high voltage DC port of the converterH. The front stage part comprises 4 active switching tubes (such as IGBT) Q with anti-parallel diodes1～Q4Composed H bridge and low-voltage side DC capacitor CdcLThe latter part comprises 4 active switching tubes (such as IGBT) Q with anti-parallel diodes5～Q8Formed H-bridge and voltage clamp circuit, said circuit having an inverseActive tube Q of parallel diode1～Q8The collectors of which are respectively connected with the cathodes of the respective freewheeling diodes and the emitters of which are respectively connected with the anodes of the respective freewheeling diodes.
Q in preceding stage part1And Q3After being connected in series with the low-voltage side direct current capacitor CdcLIn parallel, said Q1Emitter and Q3Are connected and used as primary terminals E, Q of the high-frequency transformer2Emitter and Q4Is connected with the collector and serves as the other end F, Q of the primary side of the high-frequency transformer1Collector electrode and CdcLAre connected to the positive pole of Q3Emitter and CdcLThe negative electrodes are connected; said Q2And Q4After being connected in series with the low-voltage side direct current capacitor CdcLParallel connection, Q2Collector electrode and CdcLAre connected to the positive pole of Q4Emitter and CdcLThe negative electrodes are connected; said Q1、Q2Collector electrode of (1) and (C)dcLThe positive electrode of the single-stage high-frequency isolation type submodule is connected with and serves as positive electrode ports A and Q of a preceding stage part of the single-stage high-frequency isolation type submodule3、Q4Emitter and C ofdcLIs connected with the negative pole and is used as the negative pole port B of the front stage part of the submodule.
In the latter part Q5Emitter and Q7Are connected and used as secondary terminals G, Q of the high-frequency transformer6Emitter and Q8The collector of the transformer is connected with the other end H which is used as the secondary side of the high-frequency transformer; said Q5、Q6And as positive electrode port C, Q of the sub-module rear stage part7、Q8And is connected to and serves as the negative terminal D of the subsequent part of the submodule. The voltage clamping circuit (7) in the latter stage part comprises a capacitor C1Resistance R14 diodes D1～D4Said D is1And D3After being connected in series, are respectively connected with C1、R1In parallel, said D2And D4After being connected in series, are respectively connected with C1、R1Parallel connection, D1、D2And C1、R1Are connected to the positive electrode of D2、D4Of (2) an anodeAnd C1、R1Is connected to the negative electrode of D1And D3The cathode and the secondary side end G of the high-frequency transformer are connected, D2And D4The cathode of the transformer is connected with the other end H of the secondary side of the high-frequency transformer.
When the converter works, the modulation ratio of the upper bridge arm submodule and the lower bridge arm submodule is an alternating current-direct current mixed modulation ratio duAnd d1(duModulation ratio of upper arm, d1Lower arm modulation ratio) while duAnd d1The common DC modulation ratio D and the AC modulation ratio (D) of each phasea、db、dc) And (4) forming.
Taking phase a as an example, when the DC modulation ratio is 0.5, damIt is required to be equal to or greater than zero and equal to or less than 0.5 to satisfy formula (1).
Figure GSB0000183759430000051
Meanwhile, as shown in fig. 2, the output port voltage of the post-stage part of each sub-module is always positive, and the high-voltage dc port voltage, the high-voltage ac port voltage, and the low-voltage dc port voltage satisfy the formula (2).
Figure GSB0000183759430000061
The foregoing is only a preferred embodiment of the present invention, and it should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be construed as the protection scope of the present invention.

Claims (3)

1. Many level converter of isolated form modularization based on high frequency chain technique, its characterized in that: the converter (1) is of a three-phase system structure and comprises a novel single-stage high-frequency isolation type submodule (3);
also comprises three high-voltage direct current ports (P) connected in parallelH、NH) Each phase unit (2) consists of an upper bridge arm and a lower bridge arm, and threeElectrical connection points of upper and lower arms of phase units (N)1、N2、N3) The outgoing lines are connected with filter inductors in series and then are high-voltage alternating-current ports (a, b and c), and each bridge arm consists of n novel single-stage high-frequency isolated submodules (3) and a bridge arm reactor LmComposition is carried out;
the novel single-stage high-frequency isolation type submodule (3) comprises a preceding stage part (4), a high-frequency transformer part (5) and a rear stage part (6), the alternating current side of the preceding stage part is connected with the primary side of the high-frequency transformer, the alternating current side of the rear stage part is connected with the secondary side of the high-frequency transformer, and the positive and negative electrode ports of the preceding stage part of each novel single-stage high-frequency isolation type submodule (3) are respectively connected in parallel to serve as a public low-voltage direct current port (P)L、NL) The ports of the rear stage part are connected in series to form a high-voltage direct current side port (P)H、NH)；
Positive pole ends (P) of upper bridge arms of three phase units (2)Ha、PHb、PHc) Connected as positive pole P of high voltage DC port of the converterHNegative pole end (N) of lower bridge arm of three phase units (2)Ha、NHb、NHc) Negative pole N connected as high voltage DC port of the converterH；
The preceding stage part (4) of the novel single-stage high-frequency isolation type submodule comprises a low-voltage side direct-current capacitor CdcLAnd an active H-bridge consisting of four active switches with anti-parallel diodes; the rear-stage part (6) comprises a voltage clamping circuit (7) and an active H bridge consisting of four active switches with anti-parallel diodes;
the active H-bridge of the preceding stage part (4) comprises a first active switching tube Q1A second active switch tube Q2A third active switch tube Q3And a fourth active switch tube Q4The collector of each active switch tube is respectively connected with the cathode of the corresponding freewheeling diode, and the emitter of each active switch tube is respectively connected with the anode of the corresponding freewheeling diode;
first active switch tube Q1And a third active switch tube Q3After being connected in series with the low-voltage side direct current capacitor CdcLParallel connection, a first active switch tube Q1Emitter and third active switching tube Q3Is connected with the collector and serves as a primary side E of the high-frequency transformer, and a second active switch tube Q2Emitter and fourth active switching tube Q4The collector of the first active switch tube Q is connected with the other end F which is the primary side of the high-frequency transformer1Collector electrode and CdcLIs connected with the positive pole of the third active switch tube Q3Emitter and CdcLThe negative electrodes are connected; second active switch tube Q2And a fourth active switch tube Q4After being connected in series with the low-voltage side direct current capacitor CdcLParallel second active switch tube Q2Collector electrode and CdcLIs connected with the positive pole of the fourth active switch tube Q4Emitter and CdcLThe negative electrodes are connected; first active switch tube Q1And a second active switch tube Q2Collector electrode of (1) and (C)dcLIs connected with the positive pole of the sub-module and is used as the positive pole A of the front stage part of the sub-module, and a third active switch tube Q3And a fourth active switch tube Q4Emitter and C ofdcLThe negative electrode of the sub-module is connected with and used as a negative electrode B of the front-stage part of the sub-module;
the active H-bridge of the rear-stage part (6) comprises a fifth active switching tube Q5A sixth active switch tube Q6A seventh active switch tube Q7An eighth active switch tube Q8The collector of each active switch tube is respectively connected with the cathode of the corresponding freewheeling diode, and the emitter of each active switch tube is respectively connected with the anode of the corresponding freewheeling diode; fifth active switch tube Q5Emitter and seventh active switching tube Q7Is connected with the collector and serves as a secondary side end G of the high-frequency transformer, and a sixth active switching tube Q6Emitter and eighth active switching tube Q8The collector of the transformer is connected with the other end H which is used as the secondary side of the high-frequency transformer; fifth active switch tube Q5And a sixth active switch tube Q6And the collector of the first active switch tube is connected with the positive electrode C as the rear stage part of the submodule, and the seventh active switch tube Q7And an eighth active switch tube Q8And connected to each other and functioning as a cathode D of the subsequent part of the submodule.
2. The isolated modular multilevel converter based on high frequency link technology of claim 1, wherein: the voltage clamping circuit (7) comprises a first diode D1A second diode D2A third diode D3A fourth diode D4A first capacitor C1A first resistor R1First diode D1And a third diode D3Are respectively connected with the first capacitor C after being connected in series1A first resistor R1Parallel, a second diode D2And a fourth diode D4Are respectively connected with the first capacitor C after being connected in series1A first resistor R1Parallel, first diode D1A second diode D2Cathode and first capacitor C1A first resistor R1Is connected to the anode of a third diode D3A fourth diode D4Anode and first capacitor C1A first resistor R1Is connected to the negative electrode of a first diode D1Anode of and a third diode D3Is connected with the secondary side end G of the high-frequency transformer, and a second diode D2Anode of and a fourth diode D4The cathode of the transformer is connected with the other end H of the secondary side of the high-frequency transformer.
3. The isolated modular multilevel converter based on high frequency link technology of claim 1, wherein: the modulation ratio of the upper bridge arm and the lower bridge arm is an AC-DC mixed modulation ratio duAnd d1Wherein d isuModulation ratio of upper arm, d1Modulation ratio of lower arm, and duAnd d1By a DC common modulation ratio D and a per-phase AC modulation ratio Da、db、dcIn which d isaA ac modulation ratio of A, dbModulation ratio of B-phase AC, dcIs the C-phase ac modulation ratio.
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