CN108631633B - MMC-based hybrid capacitor voltage type dual-sub-module series connection topological structure - Google Patents

MMC-based hybrid capacitor voltage type dual-sub-module series connection topological structure Download PDF

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CN108631633B
CN108631633B CN201810539892.0A CN201810539892A CN108631633B CN 108631633 B CN108631633 B CN 108631633B CN 201810539892 A CN201810539892 A CN 201810539892A CN 108631633 B CN108631633 B CN 108631633B
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capacitor
diode
switching unit
submodule
sub
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CN108631633A (en
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赵怡波
郭燚
张震
赵燃
邱冠超
李晗
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Shanghai Maritime University
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Shanghai Maritime 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
    • H02M7/53—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 using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse 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
    • 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0048—Circuits or arrangements for reducing losses
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

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

Abstract

The invention discloses a mixed capacitance voltage type dual-submodule series topological structure based on MMC, comprising: the first half-bridge submodule is provided with a first switch unit, a second switch unit and a first capacitor; the first switch unit is connected with the second switch unit in series in the forward direction and then connected with the first capacitor in parallel; the second half-bridge submodule is provided with a third switching unit, a fourth switching unit and a second capacitor; the third switching unit and the fourth switching unit are connected in series in the forward direction and then connected in parallel with the second capacitor; the first capacitor and the second capacitor have different parameters; the first half-bridge submodule is connected with the fifth switching unit in series in the reverse direction and then connected with the second half-bridge submodule in series in the forward direction; one end of the sixth diode is connected with the first half-bridge sub-module, and the other end of the sixth diode is connected with the second half-bridge sub-module. The invention can output more level numbers, can reduce the quantity of IGBTs, capacitors and diodes under the requirement of the same level number, reduces the operation cost and the device loss, and greatly saves the cost.

Description

MMC-based hybrid capacitor voltage type dual-sub-module series connection topological structure
Technical Field
The invention relates to the field of MMC (modular multilevel converter), in particular to a mixed capacitance voltage type bi-submodule series connection topological structure based on MMC.
Background
The problems of peak regulation and scheduling of the traditional alternating current or conventional direct current large-scale centralized access power grid cannot be well solved. Because the voltage source converter with two levels and three levels has less levels and poorer output voltage waveform, a high-frequency PWM technology is required to be adopted to improve the output waveform, and the mode not only needs to install high-requirement switching devices and a large number of filters, but also has larger loss in the power transmission process.
And the flexible direct current transmission system who adopts MMC (Modular Multilevel Converter) has introduced the Modular design theory, to the MMC of high voltage large capacity, the concatenation submodule piece figure of adoption is very many to can control the level number through increasing and decreasing submodule piece figure, the voltage step wave of output is very close the sine wave, and the wave form high quality need not to install the wave filter. The MMC adopts a step wave approximation technology, so that the loss caused by the switching frequency is greatly reduced. Due to the submodule redundancy characteristic of the MMC, the stability of the converter is improved.
The basic topological structure of the MMC sub-module has three types: the invention provides a mixed capacitor voltage type dual-sub-module series topology, which is further improved on the dual-sub-module series topology, so that the required quantity of the IGBTs, the quantity of the capacitors, the quantity of the diodes and the loss of the devices are greatly reduced, the loss of the devices is reduced, and the cost can be greatly saved in the economic aspect.
Disclosure of Invention
The invention aims to provide a mixed capacitance voltage type dual-sub-module series topology structure based on MMC, which is further improved on a dual-sub-module series topology, the first capacitance and the second capacitance of two half-bridge sub-modules are set with different parameters, so that the output level number of the sub-modules is increased, and under the condition of outputting the same level number, the quantity of IGBTs, the quantity of capacitors and the quantity of diodes required by the mixed capacitance voltage type dual-sub-module series topology are greatly reduced, the loss of devices is reduced, and the cost can be greatly saved in the aspect of economy. The structure can effectively reduce the manufacturing cost of the device and reduce the loss of the device.
In order to achieve the above object, the present invention provides a mixed capacitance voltage type dual sub-module series topology structure based on MMC, comprising:
the first half-bridge module is provided with a first switch unit, a second switch unit and a first capacitor; the first switch unit is connected with the second switch unit in series in the forward direction and then connected with the first capacitor in parallel;
a second half-bridge sub-module provided with a third switching unit, a fourth switching unit and a second capacitor; the third switching unit is connected with the second capacitor in parallel after being connected with the fourth switching unit in series in the forward direction; the first capacitance and the second capacitance have different parameters;
the first half-bridge submodule is connected with the second half-bridge submodule in a forward series mode after being connected with the first switch unit in a reverse series mode;
and one end of the sixth diode is connected with the first half-bridge sub-module, and the other end of the sixth diode is connected with the second half-bridge sub-module.
Preferably, the first switching unit comprises a first IGBT tube and a first diode; the first IGBT tube is connected with the first diode in an anti-parallel mode, the negative electrode of the first diode is connected with the collector electrode of the first IGBT tube, and the positive electrode of the first diode is connected with the emitter electrode of the first IGBT tube;
the second switching unit comprises a second IGBT tube and a second diode; the second IGBT tube is connected with the second diode in an anti-parallel mode, the negative electrode of the second diode is connected with the collector electrode of the second IGBT tube, and the positive electrode of the second diode is connected with the emitter electrode of the second IGBT tube;
and the emitter of the first IGBT tube is connected with the collector of the second IGBT tube, the anode of the first capacitor is connected with the cathode of the first diode, and the cathode of the first capacitor is connected with the anode of the second diode.
Preferably, the third switching unit includes a third IGBT tube and a third diode; the third IGBT tube is connected with the third diode in an anti-parallel mode, the negative electrode of the third diode is connected with the collector electrode of the third IGBT tube, and the positive electrode of the third diode is connected with the emitter electrode of the third IGBT tube;
the fourth switching unit comprises a fourth IGBT tube and a fourth diode, the fourth IGBT tube is connected with the fourth diode in an anti-parallel mode, the negative electrode of the fourth diode is connected with the collector electrode of the fourth IGBT tube, and the positive electrode of the fourth diode is connected with the emitter electrode of the fourth IGBT tube;
and the emitter of the third IGBT tube is connected with the collector of the fourth IGBT tube, the anode of the second capacitor is connected with the cathode of the third diode, and the cathode of the second capacitor is connected with the anode of the fourth diode.
Preferably, the fifth switching unit includes a fifth IGBT and a fifth diode, the fifth IGBT and the fifth diode are connected in anti-parallel, a cathode of the fifth diode is connected to a collector of the fifth IGBT, and an anode of the fifth diode is connected to an emitter of the fifth IGBT;
and the emitter of the second IGBT tube is connected with the emitter of the fifth IGBT tube, and the collector of the fifth IGBT tube is connected with the collector of the third IGBT tube.
Preferably, the anode of the sixth diode is connected to the emitter of the fourth IGBT tube, and the cathode of the sixth diode is connected to the collector of the first IGBT tube.
Preferably, the midpoint of the first half-bridge sub-module and the second half-bridge sub-module is an output point of the MMC sub-module;
the capacitance reference value of the first capacitor is set as C, and the capacitance voltage reference value of the first capacitor is 0.5UC(ii) a The capacitance reference value of the second capacitor is 0.5C, and the capacitance voltage reference value of the second capacitor is UC。
Preferably, the mixed capacitance voltage type dual-sub-module series topology based on the MMC comprises four working states, namely a first working state, a second working state, a third working state and a fourth working state;
when the first working state is started, the first switching unit and the fourth switching unit are turned off, and the second switching unit and the third switching unit are turned on; in the first working state, the first capacitor and the second capacitor are bypassed, and the external voltage of the submodule is zero;
when the second working state is realized, the second switch unit and the fourth switch unit are turned off, and the first switch unit and the third switch unit are turned on; in the second working state, the first capacitor is connected in series to the circuit, the second capacitor is bypassed, and the external voltage of the submodule is 0.5UC；
In the third working state, the first switch is onThe second switching unit and the fourth switching unit are turned on; in the third working state, the second capacitor is connected in series to the circuit, the first capacitor is bypassed, and the external voltage of the submodule is UC；
In a fourth working state, the second switching unit and the third switching unit are turned off, and the first switching unit and the fourth switching unit are turned on; in the fourth working state, the first capacitor and the second capacitor are connected in series in the circuit, and the external voltage of the sub-module is 1.5UC。
Preferably, the first operating state comprises a first operating mode and a fifth operating mode; wherein the first operating mode comprises: when current enters the submodule from the middle point of the first half-bridge submodule, the current flows through the second switching unit, the fifth switching unit and the third switching unit and flows out from the middle point of the second half-bridge submodule; the fifth operating mode includes: the current enters the submodule from the middle point of the second half-bridge submodule, flows through the third switching unit, the fifth switching unit and the second switching unit and flows out from the middle point of the first half-bridge submodule;
the second working state comprises a second working mode and a sixth working mode; wherein, include in the second mode: the current enters from the middle point of the first half-bridge submodule, flows through the first switching unit, the first capacitor, the fifth switching unit and the third switching unit, flows out from the middle point of the second half-bridge submodule and charges the first capacitor; the sixth operating mode includes: the current enters from the middle point of the second half-bridge submodule, flows through the third switching unit, the fifth switching unit, the first capacitor and the first switching unit, flows out from the middle point of the first half-bridge submodule, and the first capacitor discharges;
the third working state comprises a third working mode and a seventh working mode; wherein the third operating mode comprises: the current enters from the middle point of the first half-bridge submodule, flows through the second switch unit, the fifth switch unit, the second capacitor and the fourth switch unit, flows out from the middle point of the second half-bridge submodule and charges the second capacitor; the seventh operating mode includes: the current enters from the middle point of the second half-bridge submodule, flows through the fourth switching unit, the second capacitor, the fifth switching unit and the second switching unit, flows out from the middle point of the first half-bridge submodule, and the second capacitor discharges;
the fourth working state comprises a fourth working mode and an eighth working mode; wherein the fourth operating mode comprises: the current enters from the middle point of the first half-bridge submodule, flows through the first switch unit, the first capacitor, the fifth switch unit, the second capacitor and the fourth switch unit, flows out from the middle point of the second half-bridge submodule and charges the first capacitor and the second capacitor; the sixth operating mode includes: the current enters from the middle point of the second half-bridge submodule, flows through the fourth switching unit, the second capacitor, the fifth switching unit, the first capacitor and the first switching unit, and flows out from the middle point of the first half-bridge submodule, and the first capacitor and the second capacitor are discharged.
Preferably, the MMC-based hybrid capacitor voltage type dual-sub-module series topology structure is a single-phase seven-level MMC topology structure; the single-phase seven-level MMC topological structure is provided with an upper bridge arm and a lower bridge arm, the upper bridge arm comprises a first sub-module, a second sub-module and an upper bridge arm inductor, and the lower bridge arm comprises a third sub-module, a fourth sub-module and a lower bridge arm inductor;
the first submodule, the second submodule, the upper bridge arm inductor, the third submodule, the fourth submodule and the lower bridge arm inductor are sequentially connected in series and connected with a direct-current voltage source to form a loop.
Preferably, the upper bridge arm voltage is the sum of the first sub-module voltage and the second sub-module voltage, and the lower bridge arm voltage is the sum of the third sub-module voltage and the fourth sub-module voltage.
Compared with the prior art, the invention has the beneficial effects that: according to the invention, the improvement is carried out on the basis of the serial topological structure of the double sub-modules, the mixed type capacitor is arranged, and different capacitor parameters are set, so that each serial topological structure of the double sub-modules can output more level numbers, for example, the first capacitor and the second capacitor of two half-bridge sub-modules are set with different parameters, so that the output level numbers of the sub-modules are increased, therefore, in the working condition operation process of the MMC, under the condition of the same level number requirement, the mixed capacitor voltage type serial topological structure of the double sub-modules based on the MMC can reduce the number of IGBTs, the number of capacitors and the number of diodes, reduce the operation cost and the device loss, and can greatly save the cost in the economic aspect.
Drawings
FIG. 1 is a schematic diagram of a mixed capacitance voltage type dual sub-module series topology based on MMC in an embodiment of the present invention;
FIG. 2 is a schematic diagram of a single-phase MMC main circuit topology based on a mixed-capacitor voltage-type dual-sub-module series topology structure in the embodiment of the present invention;
FIG. 3 is a schematic diagram of four working states based on a mixed-capacitor voltage-type dual-sub-module series topology according to an embodiment of the present invention;
FIG. 4 is a schematic voltage diagram of an alternating current side of a single-phase seven-level mixed-capacitor-voltage-type-based MMC with a tandem topological structure of double sub-modules in the embodiment of the present invention;
FIG. 5 is a comparison graph of the number of IGBT tubes used under the condition that different types of MMC output at the same level in the embodiment of the invention;
FIG. 6 is a comparison graph of the number of diode tubes used in the case of the same level output by different types of MMC in the embodiment of the present invention;
FIG. 7 is a comparison graph of the capacitance usage amounts of different types of MMCs in the same level output case according to the embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The following describes a voltage-type dual-submodule series topology structure based on a hybrid capacitor according to an embodiment of the present invention, with reference to the drawings of the specification.
FIG. 1 is a diagram of an M-based system according to an embodiment of the present inventionThe mixed capacitance voltage type dual-submodule series topology structure of the MC comprises two half-bridge submodules (a first half-bridge submodule and a second half-bridge submodule) and a fifth switch unit T5And a sixth diode D. The first half bridge module and the fifth switch unit T5And after the reverse series connection, the second half-bridge sub-module is connected with the second half-bridge sub-module in a forward series connection.
The first half-bridge module comprises a first switching unit T1A second switch unit T2And a first capacitor C1First switch unit T1And a second switching unit T2Is connected in series in the forward direction and then is connected with a first capacitor C1And (4) connecting in parallel.
The second half-bridge submodule comprises a third switching unit T3A fourth switching unit T4And a second capacitor C2A third switching unit T3And a fourth switching unit T4Is connected with a second capacitor C after being connected in series in the forward direction2And (4) connecting in parallel.
The parameter settings of the first and second capacitors are different.
Wherein the first switch unit T1The IGBT comprises a first IGBT (Insulated Gate Bipolar Transistor) and a first diode, wherein the first IGBT is connected with the first diode in an anti-parallel mode, the negative electrode of the first diode is connected with the collector electrode of the first IGBT, and the positive electrode of the first diode is connected with the emitter electrode of the first IGBT. Second switch unit T2The IGBT device comprises a second IGBT tube and a second diode, wherein the second IGBT tube is connected with the second diode in an anti-parallel mode, the negative electrode of the second diode is connected with the collector electrode of the second IGBT tube, and the positive electrode of the second diode is connected with the emitter electrode of the second IGBT tube. The emitter of the first IGBT tube is connected with the collector of the second IGBT tube, and a first capacitor C1Is connected to the cathode of a first diode, a first capacitor C1Is connected to the anode of the second diode.
Third switch unit T3The IGBT device comprises a third IGBT tube and a third diode, wherein the third IGBT tube is connected with the third diode in an anti-parallel mode, the negative electrode of the third diode is connected with the collector electrode of the third IGBT tube, and the positive electrode of the third diode is connected with the emitter electrode of the third IGBT tube. Fourth switching unit T4Comprises thatThe fourth IGBT tube is connected with the fourth diode in an anti-parallel mode, the negative electrode of the fourth diode is connected with the collector electrode of the fourth IGBT tube, and the positive electrode of the fourth diode is connected with the emitting electrode of the fourth IGBT tube. The emitter of the third IGBT tube is connected with the collector of the fourth IGBT tube, and a second capacitor C2Is connected with the cathode of the third diode, and a second capacitor C2Is connected to the anode of the fourth diode.
Fifth switching unit T5The IGBT device comprises a fifth IGBT tube and a fifth diode, wherein the fifth IGBT tube is connected with the fifth diode in an anti-parallel mode, the negative electrode of the fifth diode is connected with the collector electrode of the fifth IGBT tube, and the positive electrode of the fifth diode is connected with the emitter electrode of the fifth IGBT tube. And an emitter of the second IGBT tube is connected with an emitter of the fifth IGBT tube, and a collector of the fifth IGBT tube is connected with a collector of the third IGBT tube.
And the anode of the sixth diode D is connected with the emitter of the fourth IGBT tube, and the cathode of the sixth diode D is connected with the collector of the first IGBT tube.
As shown in fig. 1, the voltage U between point a (which is the midpoint of the first half-bridge sub-module) and point B (which is the midpoint of the second half-bridge sub-module)smThe output voltage of the MMC sub-module is obtained; current i between point A and point BsmThe current is introduced for the output voltage. A first capacitor C1Has a capacitance reference value of C, a first capacitance of C1Voltage reference value of 0.5UC(ii) a Second capacitor C2Has a capacitance reference value of 0.5C, a second capacitance C2Has a voltage reference value of UC。
Fig. 2 is a schematic diagram of a single-phase seven-level MMC topology based on a mixed-capacitor voltage-type tandem topology according to an embodiment of the present invention.
As shown in FIG. 2, the DC side voltage is UdcThe output voltage at the AC side is Ua. The upper bridge arm comprises a first sub-module SM1Second submodule SM2And the lower bridge arm comprises a third submodule SM3Fourth submodule SM4And a lower bridge arm inductance. Wherein a first sub-module SM1Second submodule SM2Go up bridgeArm inductor, third submodule SM3Fourth submodule SM4And the lower bridge arm inductor are sequentially connected in series and are connected with a direct current voltage source to form a loop. Upper bridge arm voltage UpaFor the first sub-module voltage USM1And a second sub-module voltage USM2Sum, lower arm voltage UnaFor the third sub-module voltage USM3And a fourth sub-module voltage USM4And (4) summing.
Fig. 3 is a schematic diagram of four working states of a hybrid capacitance voltage type dual-sub-module series topology according to an embodiment of the present invention. As shown in fig. 3, each operating state can be divided into two operating modes, eight operating modes in total, according to the switching state and the current direction of the IGBT; in normal operation, the fifth switch unit T5Is always in the conducting state, and if not specifically stated, the conducting is defaulted.
As shown in fig. 3, when the first switching unit T is turned on1And a fourth switching unit T4Off, second switching unit T2And a third switching unit T3When conducting, the first operating state is called a first operating state, which may also be called a "bypass state" or a "cut-off state", and there are two operating modes (a first operating mode and a fifth operating mode, respectively) in the first operating state: when current enters the submodule from A, the current flows through the second switch unit T2A fifth switching unit T5A third switch unit T3And flows out of B, which is called a first working mode; the current enters the submodule from B and flows through the third switching unit T3A fifth switching unit T5A second switch unit T2And flows out of A, called the fifth working mode; in a first operating state, the first capacitor C1And a second capacitor C2Are bypassed, and the external voltage (i.e. the output voltage between the points AB and AB) of the whole dual sub-module is zero.
As shown in fig. 3, when the second switching unit T is turned on2And a fourth switching unit T4Off, first switching unit T1And a third switching unit T3When the switch is switched on, the switch is called a second working state, and the second working state also has two working modes (a second working mode and a sixth working mode respectively)). In the second operating mode, current enters from A and flows through the first switching unit T1A first capacitor C1A fifth switching unit T5And a third switching unit T3From B, to the first capacitor C in this mode1Charging is carried out; corresponding to the sixth operation mode, current enters from B and flows through the third switching unit T3A fifth switching unit T5A first capacitor C1And a first switching unit T1Flowing from A, in this mode to the first capacitor C1And (4) discharging. In a second operating state, the first capacitor C1A second capacitor C connected in series to the circuit2By-pass, the external voltage of the whole dual sub-module is 0.5UC。
As shown in fig. 3, when the first switching unit T is turned on1And a third switching unit T3Off, second switching unit T2And a fourth switching unit T4When conducting, it is called the third working state. The third operating state still has two operating modes (a third operating mode and a seventh operating mode, respectively). In the third operating mode, current enters from A and flows through the second switching unit T2A fifth switching unit T5A second capacitor C2And a fourth switching unit T4From B, to a second capacitor C in this mode2Charging is carried out; in the seventh working mode, the current enters from B and flows through the fourth switching unit T4A second capacitor C2A fifth switching unit T5And a second switching unit T2Flowing from A, in this mode, a second capacitance C2Discharging; in a third operating state, the second capacitor C2Connected in series to the circuit, a first capacitor C1By-pass, integral dual sub-module has an external voltage of UC。
As shown in fig. 3, when the second switching unit T is turned on2And a third switching unit T3Off, first switching unit T1And a fourth switching unit T4When turned on, the switch is called a fourth operating state, and two operating modes (a fourth operating mode and an eighth operating mode, respectively) exist in the fourth operating state. In the fourth operating mode, current enters from A and flows through the fourthA switch unit T1A first capacitor C1A fifth switching unit T5A second capacitor C2And a fourth switching unit T4From B, to the first capacitor C in this mode1And a second capacitor C2Charging is carried out; in the sixth working mode, the current enters from B and flows through the fourth switching unit T4A second capacitor C2A fifth switching unit T5A first capacitor C1And a first switching unit T1Flowing from A, in this mode, the first capacitance C1And a second capacitor C2Discharging; in a fourth operating state, the first capacitor C1And a second capacitor C2Are all connected in series in the circuit, and the external voltage of the integral dual sub-module is 1.5UC。
In table 1, for five switches, the number 1 is on state, and 0 corresponds to off state; according to the switch combination in table 1, the "on" and "off" of the first capacitor and the second capacitor in the sub-module can be controlled respectively; after the capacitor voltage-sharing control is used, the voltage of each sub-module capacitor is basically kept unchanged, so that each mixed capacitor voltage type dual sub-module can be regarded as a dual sub-module which can generate 0U and 0.5UC、UCAnd 1.5UCThe controllable voltage sources with four voltages can control all mixed capacitor voltage type dual sub-modules according to table 1 to generate required output voltages.
Table 1 eight operation mode tables based on mixed capacitance voltage type dual sub-module series topology structure in the embodiment of the present invention
Figure BDA0001678551990000091
Fig. 4 is a schematic voltage diagram of an ac side of a single-phase seven-level hybrid capacitor voltage type dual sub-module series topology-based MMC in an embodiment of the present invention.
The single-phase 7-level mixed capacitor voltage type dual-submodule series topology circuit comprises four submodules, wherein the voltage of each submodule is set to be Usm1、Usm2、Usm3And Usm4The upper bridge arm and the lower bridge arm have voltages ofUpaAnd UnaThe point O is a zero voltage point, and the voltage of the point a on the AC side is UaWhen the bridge is in steady-state operation, the bridge arm inductance voltage can be ignored, and the direct-current side voltage is UdcThe voltage equation in the following equation needs to be satisfied:
Figure BDA0001678551990000092
in order to ensure the voltage stability of a direct current side, the voltage sum of the input sub-modules of the bridge arm of the MMC remains unchanged at any moment, each sub-module can generate four voltages, and the MMC can generate 7 voltages at a point a by combining an expression:
ua＝0,±0.5uC,±uC,±1.5uC
based on the above principle, the MMC can realize rectification and inversion by selecting a proper modulation method and a proper control strategy, and in order to perform more intuitively, the MMC can generate a voltage waveform as shown in fig. 4 by using a modulation method of recent level approximation and taking a sine wave as a modulation wave.
As can be seen from table 2, further analyzing fig. 4, seven time periods A, B, C, D, E, F, G correspond to seven different levels, the input conditions of the upper and lower bridge arm sub-modules are shown in table 2, and the total input amount of the first capacitor and the second capacitor in the upper and lower bridge arm sub-modules is 2 at any time, so that the voltage on the dc side is ensured to be UdcKeeping the same; under the constraint condition, the number of the first capacitor and the second capacitor in the bridge arm is switched to achieve the AC side voltage UaFor the purpose of a sine wave.
Table 2 single-phase seven-level mixed-capacitor-voltage-based tandem topology structure of dual sub-modules according to embodiments of the present invention
MMC sub-module input mode analysis table
Figure BDA0001678551990000101
Figure BDA0001678551990000111
Table 3 is a comparison table of the number of different types of MMC single bridge arm devices in the embodiment of the present invention. Further analysis shows that if the number of the upper bridge arm sub-modules is N, the level number of the MMC (HCVDS-MMC) based on the mixed capacitance voltage type dual sub-module series topology structure is 3N +1, and under the condition of the same sub-module number, the level number of the MMC (DS-MMC) based on the clamping dual sub-module is only 2 xN + 1; the level number, the capacitance number, the IGBT number and the like of four types of MMC based on a half-bridge submodule topology (H-MMC), a full-bridge submodule topology (F-MMC), a clamping submodule (DS-MMC) and a mixed capacitance voltage type submodule series topology (HCVDS-MMC) are summarized in table 3.
Under the condition that the number of half-bridge sub-modules is N, because each sub-module of the MMC (DS-MMC) based on the clamping bi-sub-module and the MMC (HCVDS-MMC) based on the mixed capacitance voltage type bi-sub-module series topology structure comprises two capacitors, the capacitor number, the IGBT number and the diode number of the MMC (DS-MMC) and the MMC (F-MMC) based on the half-bridge sub-module topology and the full-bridge sub-module topology are all larger than that of the MMC (H-MMC) based on the half-bridge sub-module topology and that of the MMC; on the contrary, the number of levels based on mixed capacitance voltage type dual sub-module series topology MMC (HCVDS-MMC) and clamping dual sub-module MMC (DS-MMC) is more than that based on full-bridge sub-module topology MMC (F-MMC) and half-bridge sub-module topology MMC (H-MMC).
TABLE 3 comparison table of the number of different types of MMC single bridge arm devices in the embodiment of the invention
MMC type Number of capacitors Number of submodules Number of IGBTs Number of diodes Number of levels
H-MMC N N 2N 2N N+1
F-MMC N N 4N 4N N+1
DS-MMC 2N N 5N 6N 2N+1
HCVDS-MMC 2N N 5N 6N 3N+1
Fig. 5 is a comparison graph of the number of IGBT used for different types of MMC under the same level output in the embodiment of the present invention. In order to perform detailed and intuitive analysis, the relation curve between the number of the IGBT tubes and the number of the levels of different types of MMC is obtained by taking the number of the levels as a reference standard. FIG. 6 is a comparison graph of the number of diode tubes used in the same level output of different types of MMC in the embodiment of the present invention. For detailed and intuitive analysis, the relation curve between the number of diodes of different types of MMC and the number of levels is obtained by taking the number of levels as a reference standard. Fig. 7 is a comparison graph of the capacitance usage amounts of different types of MMCs outputting at the same level in the embodiment of the present invention. In order to perform detailed and intuitive analysis, the level number is taken as a reference standard, and a relation curve between the capacitance number and the level number of different types of MMC is obtained. Wherein, the abscissa is the number of levels, and the ordinate is the number of IGBTs.
As shown by combining fig. 5, fig. 6 and fig. 7, the embodiment of the present invention shows that, under the same number of levels, the number of devices required by the MMC (F-MMC) based on the full-bridge sub-module topology is the largest, the number of devices required by the MMC (H-MMC) based on the half-bridge sub-module topology is smaller than the first two based on the clamping dual-sub-module MMC (DS-MMC), and the number of devices required by the MMC (HCVDS-MMC) based on the mixed-capacitor voltage-type dual-sub-module series topology is the smallest. With the increase of the number of levels, the hybrid capacitance voltage type dual-submodule series topology MMC (HCVDS-MMC) based on the hybrid capacitance voltage type dual-submodule series topology MMC can greatly save devices and save cost.
While the present invention has been described in detail with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be determined from the following claims.

Claims (2)

1. The utility model provides a mixed electric capacity voltage type bimodulus series connection topological structure based on MMC which characterized in that contains:
a first half-bridge module provided with a first switching unit (T)1) A second switch unit (T)2) And a first capacitance (C)1) (ii) a The first switch unit (T)1) And the second switch unit (T)2) Is connected in series in the forward direction and then is connected with the first capacitor (C)1) Parallel connection;
a second half-bridge submodule provided with a third switching unit (T)3) And a fourth switching unit (T)4) And a second capacitance (C)2) (ii) a The third switching unit (T)3) And the fourth switching unit (T)4) Is connected in series in the forward direction and then is connected with the second capacitor (C)2) Parallel connection; the first capacitor (C)1) And said second capacitance (C)2) The parameters of (2) are different;
fifth switch unit (T)5) Said first half-bridge module and said fifth switching unit (T)5) After the reverse series connection, the second half-bridge sub-module is connected with the second half-bridge sub-module in a forward series connection;
a sixth diode (D) having one end connected to the first half-bridge sub-module and the other end connected to the second half-bridge sub-module;
the first capacitor (C)1) Is set to C, the first capacitance (C)1) The reference value of the capacitor voltage is 0.5UC(ii) a The second capacitance (C)2) Is 0.5C, the second capacitance (C)2) Has a reference value of UC；
The topological structure comprises four working states, namely a first working state, a second working state, a third working state and a fourth working state;
wherein, in the first working state, the first switch unit (T)1) And a fourth switching unit (T)4) Off, second switching unit (T)2) And a third switching unit (T)3) Conducting; in a first operating state, the first capacitor (C)1) And a second capacitance (C)2) The sub-modules are all bypassed, and the external voltage of the sub-modules is zero;
in a second operating state, the second switch unit (T)2) And a fourth switching unit (T)4) Off, the first switching unit (T)1) And a third switching unit (T)3) Conducting; in the second operating state, the first capacitor (C)1) In series with the circuit, a second capacitor (C)2) By-pass, the sub-module has an external voltage of 0.5UC；
In the third working state, the first switchUnit (T)1) And a third switching unit (T)3) Off, second switching unit (T)2) And a fourth switching unit (T)4) Conducting; in a third operating state, the second capacitor (C)2) Connected in series to the circuit, a first capacitor (C)1) By-pass, the sub-module has an external voltage of UC；
In a fourth operating state, the second switch unit (T)2) And a third switching unit (T)3) Off, the first switching unit (T)1) And a fourth switching unit (T)4) Conducting; in a fourth operating state, the first capacitor (C)1) And a second capacitance (C)2) Are all connected in series in the circuit, and the external voltage of the sub-modules is 1.5UC；
The first working state comprises a first working mode and a fifth working mode;
wherein the first operating mode comprises: when current enters the submodule from the midpoint of the first half-bridge submodule, it flows through the second switching unit (T)2) A fifth switch unit (T)5) And a third switching unit (T)3) And out of the midpoint of the second half-bridge submodule;
the fifth operating mode includes: the current enters the submodule from the middle point of the second half-bridge submodule and flows through the third switching unit (T)3) A fifth switch unit (T)5) A second switch unit (T)2) And out of the midpoint of the first half-bridge submodule;
the second working state comprises a second working mode and a sixth working mode;
wherein, include in the second mode: the current enters from the middle point of the first half-bridge submodule and flows through the first switch unit (T)1) A first capacitor (C)1) A fifth switch unit (T)5) And a third switching unit (T)3) From the midpoint of the second half-bridge submodule, to the first capacitor (C)1) Charging is carried out;
the sixth operating mode includes: the current enters from the middle point of the second half-bridge submodule and flows through the third switching unit (T)3) A fifth switch unit (T)5) A first capacitor (C)1) And a first switch sheetYuan (T)1) From the midpoint of the first half-bridge submodule, a first capacitance (C)1) Discharging;
the third working state comprises a third working mode and a seventh working mode;
wherein the third operating mode comprises: the current enters from the middle point of the first half-bridge submodule and flows through the second switch unit (T)2) A fifth switch unit (T)5) A second capacitor (C)2) And a fourth switching unit (T)4) From the midpoint of the second half-bridge submodule, to a second capacitor (C)2) Charging is carried out;
the seventh operating mode includes: the current enters from the middle point of the second half-bridge submodule and flows through the fourth switch unit (T)4) A second capacitor (C)2) A fifth switch unit (T)5) And a second switching unit (T)2) From the midpoint of the first half-bridge submodule, a second capacitor (C)2) Discharging;
the fourth working state comprises a fourth working mode and an eighth working mode;
wherein the fourth operating mode comprises: the current enters from the middle point of the first half-bridge submodule and flows through the first switch unit (T)1) A first capacitor (C)1) A fifth switch unit (T)5) A second capacitor (C)2) And a fourth switching unit (T)4) From the midpoint of the second half-bridge submodule, to the first capacitor (C)1) And a second capacitance (C)2) Charging is carried out;
the sixth operating mode includes: the current enters from the middle point of the second half-bridge submodule and flows through the fourth switch unit (T)4) A second capacitor (C)2) A fifth switch unit (T)5) A first capacitor (C)1) And a first switching unit (T)1) From the midpoint of the first half-bridge submodule, a first capacitance (C)1) And a second capacitance (C)2) Discharging;
the first switch unit (T)1) The IGBT device comprises a first IGBT tube and a first diode; the first IGBT tube is connected with the first diode in anti-parallel, and the cathode of the first diode is connected with the first IGBT tubeThe collector electrode is connected, and the anode of the first diode is connected with the emitter electrode of the first IGBT tube;
the second switch unit (T)2) The IGBT device comprises a second IGBT tube and a second diode; the second IGBT tube is connected with the second diode in an anti-parallel mode, the negative electrode of the second diode is connected with the collector electrode of the second IGBT tube, and the positive electrode of the second diode is connected with the emitter electrode of the second IGBT tube;
the emitter of the first IGBT tube is connected with the collector of the second IGBT tube, and a first capacitor (C)1) Is connected to the cathode of said first diode, a first capacitor (C)1) The cathode of the second diode is connected with the anode of the second diode;
the third switching unit (T)3) The IGBT device comprises a third IGBT tube and a third diode; the third IGBT tube is connected with the third diode in an anti-parallel mode, the negative electrode of the third diode is connected with the collector electrode of the third IGBT tube, and the positive electrode of the third diode is connected with the emitter electrode of the third IGBT tube;
the fourth switch unit (T)4) The IGBT device comprises a fourth IGBT tube and a fourth diode, wherein the fourth IGBT tube is connected with the fourth diode in an anti-parallel mode, the negative electrode of the fourth diode is connected with the collector electrode of the fourth IGBT tube, and the positive electrode of the fourth diode is connected with the emitter electrode of the fourth IGBT tube;
the emitter of the third IGBT tube is connected with the collector of the fourth IGBT tube, and the second capacitor (C)2) Is connected to the cathode of the third diode, and the second capacitor (C)2) The cathode of the second diode is connected with the anode of the fourth diode;
the fifth switch unit (T)5) The diode comprises a fifth IGBT tube and a fifth diode, wherein the fifth IGBT tube is connected with the fifth diode in an anti-parallel mode, the negative electrode of the fifth diode is connected with the collector electrode of the fifth IGBT tube, and the positive electrode of the fifth diode is connected with the emitter electrode of the fifth IGBT tube;
an emitter of the second IGBT tube is connected with an emitter of the fifth IGBT tube, and a collector of the fifth IGBT tube is connected with a collector of the third IGBT tube;
the anode of the sixth diode (D) is connected with the emitter of the fourth IGBT tube, and the cathode of the sixth diode (D) is connected with the collector of the first IGBT tube;
the topological structure is a single-phase seven-level MMC topological structure;
the single-phase seven-level MMC topological structure is provided with an upper bridge arm and a lower bridge arm, wherein the upper bridge arm comprises a first Submodule (SM)1) A second Submodule (SM)2) And an upper leg inductance, the lower leg comprising a third Submodule (SM)3) Fourth Submodule (SM)4) And a lower bridge arm inductance;
wherein the first sub-module (SM)1) A second Submodule (SM)2) Upper bridge arm inductance, third Submodule (SM)3) Fourth Submodule (SM)4) The lower bridge arm inductor is sequentially connected in series and is connected with a direct current voltage source to form a loop;
the voltage of each submodule is set to be Usm1、Usm2、Usm3And Usm4The upper bridge arm and the lower bridge arm are respectively UpaAnd UnaThe point O is a zero voltage point, and the voltage of the point a on the AC side is UaWhen in steady state operation, the voltage at the DC side is UdcThe constraint condition set is a voltage equation in the following formula:
Figure FDA0002504010100000041
at any moment, the MMC bridge arm inputs the voltage sum of the submodules to be kept unchanged, each submodule generates four voltages, and the MMC generates 7 voltages at a point a:
ua＝0,±0.5uC,±uC,±1.5uC。
2. the MMC-based mixed-capacitance voltage-mode dual-sub-module series topology of claim 1,
upper bridge arm voltage (U)pa) Is the first sub-module voltage (U)SM1) And a second sub-module voltage (U)SM2) Sum, lower arm voltage (U)na) Is the third sub-module voltage (U)SM3) And a fourth sub-module voltage (U)SM4) And (4) summing.
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