CN113078829A - MMC topology with interconnected upper bridge arm sub-modules and high-frequency chain and control method - Google Patents

MMC topology with interconnected upper bridge arm sub-modules and high-frequency chain and control method Download PDF

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Publication number
CN113078829A
CN113078829A CN202110461394.0A CN202110461394A CN113078829A CN 113078829 A CN113078829 A CN 113078829A CN 202110461394 A CN202110461394 A CN 202110461394A CN 113078829 A CN113078829 A CN 113078829A
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bridge arm
switch tube
power switch
phase
current
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孙孝峰
刘学敏
滕甲训
李昕
王宝诚
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Yanshan University
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Yanshan 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
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • 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
    • H02M1/14—Arrangements for reducing ripples from dc input or output
    • 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

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

Abstract

The invention discloses an MMC topology and a control method for high-frequency chain interconnection of upper and lower bridge arm sub-modules, which comprise a modular multilevel converter structure, a half-bridge and capacitor structure, a two-winding high-frequency transformer and a three-phase bridge arm, wherein the half-bridge, the capacitor structure and the half-bridge structure are connected in parallel to form an isolation sub-module, the two half-bridges, the capacitor structure and the isolation transformer form a high-frequency link, each phase of bridge arm in the three-phase bridge arm is uniformly divided into an upper bridge arm and a lower bridge arm, and each phase of upper bridge arm comprises n sub-modules and an upper1、L3、L5Each phase of lower bridge arm comprises n submodules and a lower bridge arm inductor L2、L4、L6The isolation type high-frequency transformer interconnects the isolation submodules corresponding to the upper bridge arm and the lower bridge arm of the same phase together, and the submodules corresponding to the upper bridge arm and the lower bridge armThe blocks are connected through a high-frequency chain to form a combined module unit, and an integrated module design is formed. The invention inhibits SM capacitor voltage ripple, reduces the capacitance value requirement and realizes the voltage balance of the upper and lower bridge arm sub-modules.

Description

MMC topology with interconnected upper bridge arm sub-modules and high-frequency chain and control method
Technical Field
The invention relates to the field of power electronic converters, in particular to an MMC topology and a control method for high-frequency chain interconnection of upper and lower bridge arm sub-modules.
Background
Along with the increase of the power generation proportion of renewable energy sources and the development of a flexible direct current technology, the voltage level and the power level of a power system are gradually improved, and the function of a power electronic converter suitable for medium-high voltage high-power occasions is increasingly remarkable. The application of high-voltage and high-capacity power transmission fields such as draught fans and locomotive traction and the like puts higher requirements on the performance of the power electronic converter. In order to improve the voltage-withstanding grade and the output waveform quality of the power electronic converter, a solution adopting technologies such as multiplexing and multilevel is provided at present, and because the control required by the multiplexing technology is very complicated, the multilevel technology is adopted in the high-voltage high-power converter.
With the development of multi-level converters, modular multi-level converters (MMC) stand out and are receiving wide attention in applications in medium-high voltage and high-power occasions. The MMC has the advantages of high modularization degree, easiness in realizing redundancy, convenience in expansion and maintenance, capability of outputting high level, good harmonic performance and the like, and meanwhile, the MMC has the advantages that a public direct-current bus can be applied to higher power levels, and the performance requirements of high-voltage and high-power occasions on the power electronic converter are met. However, in the MMC, the direct-current voltage is supported by each sub-module capacitor, and there is no large capacitor concentrated on the direct-current side, and the voltage fluctuation of the sub-modules is caused by the structural characteristics, so that the voltage fluctuation sense of the sub-modules is inhibited by the capacitors with large capacitance values. The application of the capacitor with large capacitance value can bring about the improvement of volume and cost, and greatly reduce the power density of the converter. Therefore, the capacitance value requirement of the MMC sub-module is reduced, the capacitance volume is reduced, and the method has important significance for the practical engineering application of the MMC.
At present, many scholars research on a voltage fluctuation suppression strategy of an MMC sub-module, and the scholars propose schemes of injecting common-mode voltage in an alternating current side and injecting circulating current in a phase unit, but the stress of a sine wave injection switch tube limits the amplitude of output voltage, and the injection of other types of waveforms such as square waves and multi-frequency mixed high-frequency circulating current has the problem that the circulating current is difficult to track and control. Some researchers have proposed a scheme of increasing a series switch device to reduce the dc link voltage, but the series switch needs to bear the entire dc link voltage, and has a high requirement on the withstand voltage of the switch, and the economy is poor. The scholars propose a scheme of connecting the upper bridge arm and the lower bridge arm through the flying capacitor, which can realize the power balance between the upper bridge arm and the lower bridge arm and effectively inhibit the capacitor voltage fluctuation of the sub-module. Still other scholars propose to set up the power channel between the adjacent submodule piece of same bridge arm, carry out energy transfer and realize the power balance between the submodule piece electric capacity, reduce the ripple of submodule piece electric capacity voltage. The above schemes need to perform complex closed-loop control based on the voltage state of the sub-module, the control process is complex, the response speed is slow, and when the scheme is applied to motor driving, voltage fluctuation suppression in a full speed range is difficult to realize.
Disclosure of Invention
The invention provides an MMC topology and a control method for high-frequency chain interconnection of upper and lower bridge arm sub-modules, which can realize sub-module capacitor voltage ripple suppression without complex control, reduce capacitor volume, realize voltage balance of the upper and lower bridge arm sub-modules, and simultaneously carry out combined module unit design to improve consistency of power density and topology parameters.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
the MMC topology comprises a modular multilevel converter structure, a half-bridge and capacitor structure, a half-bridge structure, a two-winding high-frequency transformer and a three-phase bridge arm, wherein the half-bridge, the capacitor structure and the half-bridge structure are connected in parallel to form an isolation sub-module, the two half-bridge structures and the two-winding high-frequency transformer form a high-frequency link, each phase of bridge arm in the three-phase bridge arm is equally divided into an upper bridge arm and a lower bridge arm, and each phase of upper bridge arm comprises n sub-modules and an upper bridge arm inductor L1、L3、L5Each phase of lower bridge arm comprises n submodules and a lower bridge arm inductor L2、L4、L6The two-winding high-frequency transformer correspondingly isolates the upper bridge arm and the lower bridge arm of the same phaseThe submodules are interconnected together to form a combined module unit.
Further, the isolation sub-module comprises a first power switch tube Q1A second power switch tube Q2A first capacitor C1A second capacitor C2And a third power switch tube Q3And a fourth power switch tube Q4(ii) a The two-winding high-frequency transformer TiComprising a first winding N1A second winding N2(ii) a The first power switch tube Q1Collector and third power switch tube Q3Is connected with the collector of the second power switch tube Q2Emitter of and fourth power switch tube Q4The emitting electrodes are connected; the first power switch tube Q1Emitter and second power switch tube Q2Is connected with the collector of the third power switch tube Q3Emitter of and fourth power switch tube Q4The collector electrodes are connected; the first capacitor C1And one end of the third power switch tube Q3Is connected to the collector of the first capacitor C1And the other end of the first capacitor C2Connecting; the second capacitor C2The other end of the first power switch tube is connected with an emitting electrode of a fourth power switch tube; the two-winding high-frequency transformer T1First winding N1Is connected to the first capacitor C1And a second capacitor C2The middle point of the bridge arm, the first winding N1Is connected to the third power switch tube Q3And a fourth power switch tube Q4The middle point of the bridge arm; the second winding N2Is connected to the first capacitor C of the isolation submodule in the other bridge arm corresponding to the isolation submodule1And a second capacitor C2Bridge arm midpoint of the composition, the second winding N2The different name end of the first power switch tube Q and the corresponding isolation submodule3And a fourth power switch tube Q4The middle points of the formed bridge arms are connected.
Further, the first power switch tube Q of the first isolation submodule of each phase upper bridge arm1And a second power switch tube Q2Formed middle point and medium voltage DC busThe positive electrodes of the two electrodes are connected; the second power switch tube Q2Emitter of (2) and first power switch tube Q of next combined module unit1The emitting electrodes are connected; the upper bridge arm inductor L1、L3、L5And the second power switch tube Q of the last isolation submodule of each phase upper bridge arm2Is connected with the three-phase upper bridge arm inductance L1、L3、L5The other end of the first connecting rod is respectively connected with a phase a, a phase b and a phase c of the medium-voltage alternating current bus; three-phase lower bridge arm inductance L2、L4、L6One end of the three-phase lower bridge arm inductor is respectively connected with the a phase, the b phase and the c phase of the medium-voltage alternating-current bus2、L4、L6And the other end of the first power switch tube Q of the first isolation submodule of each phase lower half-bridge arm1The emitter of (3) is connected; second power switch tube Q of each phase lower half-bridge arm isolation submodule2Emitter of (2) and first power switching tube Q of next isolation submodule1The emitting electrodes are connected; second power switch tube Q of last isolation submodule of lower half-bridge arm2Is connected with the negative pole of the medium voltage direct current bus.
Furthermore, the input current of the submodule of the modular multilevel converter structure comprises a direct current component and an alternating current component, the alternating current part mainly comprises a fundamental frequency component and a frequency multiplication component 2, and in the modular unit of the Modular Multilevel Converter (MMC) topology, the fundamental frequency component i in the fluctuating currentf1-ua、if1-ub、if1-ucAnd if1-da、if1-db、if1-dcOpposite phase, 2 multiplied frequency component if2-ua、if2-ub、if2-ucAnd if2-da、if2-db、if2-dcThe phases are the same.
Furthermore, the combined module unit formed by connecting the two-winding high-frequency transformer with the isolation submodules corresponding to the upper bridge arm and the lower bridge arm is respectively provided with an upper bridge arm current and a lower bridge arm current, an equivalent model is established for the bridge arm currents in the flow path of the combined module unit, the impedance of a high-frequency link is small, the free flow of the fluctuating current is not influenced, and therefore the equivalent model can be ignored; the current flowing into the ports of the sub-modules of the upper bridge arm and the lower bridge arm is equivalent to a controlled current source, and the capacitors of the two sub-modules which are interconnected through a high-frequency link are equivalent to be directly connected in parallel; the two sub-module capacitor voltages are clamped with each other, and the generated ripple currents with opposite phases are mutually counteracted.
A control method of MMC topology with interconnected high-frequency chains of upper and lower bridge arm sub-modules comprises half-bridge and capacitor structure control and high-frequency link control, wherein the half-bridge and capacitor structure control adopts double closed-loop control of independent voltage and current under abc coordinates, the double closed-loop control comprises direct-current side voltage outer loop control and alternating-current side current inner loop control, and the modulation mode adopts a carrier phase-shifting pulse width modulation technology; and the high-frequency link control adopts open-loop PWM with fixed duty ratio.
Further, the specific steps of the control of the half-bridge and the capacitor structure are as follows:
1) dividing three-phase input AC voltage and current by abc/dq conversion to obtain d-and q-axis components of voltage and current, and outputting voltage with given value U* DCSubtracting the actual value U of the output voltageDCThe d-axis component i of the input current is subtracted from the output value of the PI regulatordThe d-axis component u of the output value and the input voltage obtained after PI regulationdAdding and subtracting the q-axis component i of the input currentqMultiplication with ω L to obtain d-axis modulation component ed *；
2) Given value i of input current q-axis componentq *By subtracting the actual value i of the q-axis component of the input currentqAdding the output value after PI regulation to the q-axis component of the input voltage, and subtracting the d-axis component i of the input currentdMultiplying by ω L to obtain q-axis modulation component eq *；
3) Carrying out dq/abc conversion on the values obtained in the step 1) and the step 2) to obtain a three-phase modulation component ea *、eb *、ec *The three-phase modulation wave component is subjected to a carrier phase shift modulation strategy to obtain a driving signal S of a half-bridge and capacitor structuresm。
Furthermore, the driving signals at two sides of the transformer in all the combined module units are the same, and the driving signals are the same with the duty ratio of 50 percentStep signal, third power switch tube Q3And a fourth power switch tube Q4The driving signal complements the driving control signal frequency of the switch tube in the combined module unit to be f, and the duty ratio is D.
Due to the adoption of the technical scheme, the invention has the technical progress that:
1. the MMC system has higher power density, the content of odd-number-order components with opposite phases in the fluctuation current of the combined module unit is higher, the autonomous flowing natural elimination of the part of the fluctuation current can be realized, the low-frequency fluctuation power which needs to be inhibited by the capacitor is reduced, the requirement of the corresponding system on the capacitor is reduced, the size of the capacitor with smaller capacity value is correspondingly smaller, and the power density of the system is favorably improved;
2. the MMC system is simple to control, only double closed-loop control of AC/DC conversion needs to be completed, the high-frequency link adopts independent open-loop PWM with fixed duty ratio, and a complex voltage fluctuation suppression strategy does not need to be designed to simplify the control process of the system;
3. the MMC system has high response speed and wide application range, can realize the autonomous flow of real-time ground fluctuation power in an omega full-range state, does not need to depend on the voltage state of a monitoring submodule for control, and has faster dynamic response because the energy storage in the operation of the system is reduced by the reduction of the capacitance;
4. the MMC system is beneficial to modular design and has higher system parameter consistency. The submodules corresponding to the upper bridge arm and the lower bridge arm are connected through a high-frequency chain to form a combined module unit, and the combined module unit has the advantages of high integration level, simple system building procedure, high parasitic parameter consistency and the like in practical application;
5. the MMC system is convenient to maintain and high in reliability. Because only the submodules corresponding to the upper bridge arm and the lower bridge arm are interconnected, the sweep range is smaller when faults such as submodule short circuit occur. Meanwhile, the combined module unit is convenient for system maintenance and device replacement.
Drawings
FIG. 1 is an electrical schematic diagram of an MMC topology structure of high-frequency chain interconnection of upper and lower bridge arm sub-modules according to the present invention;
FIG. 2 is an electrical schematic diagram of an isolation sub-module of an MMC topology structure of high-frequency chain interconnection of upper and lower bridge arm sub-modules according to the present invention;
FIG. 3 is an electrical schematic diagram of a combined modular unit of an MMC topology structure with interconnected high-frequency chains of upper and lower bridge arm sub-modules according to the present invention;
FIG. 4 is a schematic diagram of fundamental frequency current ripple components of sub-modules of a conventional three-phase MMC topology structure according to the present invention;
FIG. 5 is a high-frequency chain working principle diagram of an MMC topology structure of high-frequency chain interconnection of upper and lower bridge arm sub-modules according to the present invention;
FIG. 6 is an equivalent model of a high-frequency chain working process of an MMC topological structure of high-frequency chain interconnection of upper and lower bridge arm sub-modules according to the present invention;
FIG. 7 is a schematic diagram of a MMC topology structure control method for high-frequency chain interconnection of upper and lower bridge arm sub-modules according to the present invention;
wherein, MVAC is medium voltage AC bus, MVDC is medium voltage DC bus, UdcIs the medium voltage dc bus voltage; I-SM is an isolation submodule; HFL is a high frequency chain part in the modular unit; q1、Q2、Q3、Q4The first power switch tube, the second power switch tube, the third power switch tube and the fourth power switch tube are respectively arranged in the isolation submodule; c1Is a first capacitor; c2A second capacitor; t is1Is a two-winding high-frequency transformer, N1First winding of a two-winding high-frequency transformer, N2A second winding of the two-winding high-frequency transformer; l is1、L3、L5Is an upper bridge arm inductance, L2、L4、L6Is a lower bridge arm inductance; i.e. if1-ua、if1-ub、if1-ucThe fundamental frequency components i of the upper bridge arms of the phases a, b and c are respectivelyf1-da、if1-db、if1-dcThe fundamental frequency components of the lower bridge arm of the a phase, the b phase and the c phase are if2-ua、if2-ub、if2-ucThe frequency multiplication components and i of the upper bridge arm 2 of the phases a, b and c respectivelyf2-da、if2-db、if2-dcThe frequency multiplication components of the lower bridge arm 2 of the phases a, b and c are respectively; i.e. iLIs the current flowing through the transformer; u. ofci、ucjAre respectively asThe capacitance voltage of the ith and jth sub-modules; ci1、Ci2The first capacitor and the second capacitor of the ith sub-module are respectively; cj1、Cj2The first capacitor and the second capacitor are respectively of the jth sub-module; ci、CjEquivalent capacitors of the ith and jth sub-modules respectively; i.e. ici、icjEquivalent capacitance currents of the ith and jth sub-modules are respectively; u. ofcIs the equivalent voltage of the interconnection sub-module capacitor; u shape* DCIs a reference value of the dc output voltage; u. ofa、ub、ucEach phase voltage is a three-phase AC input voltage; i.e. ia、ib、icEach phase current is a three-phase AC input current; ω t is the phase of the phase-locked loop output; u. ofd、uqD-axis component and q-axis component after performing abc/dq conversion on the three-phase alternating-current input voltage respectively; i.e. id、iqD-axis component and q-axis component after dq conversion is carried out on the three-phase alternating current input current respectively; i.e. id *Reference value, i, for input current on d-axisq *A reference value of the input current on the q axis; e.g. of the typed *、eq *D-axis and q-axis decoupling values after current feedforward decoupling are respectively obtained; e.g. of the typea *、eb *、ec *Three-phase modulation signals output after dq/abc conversion are respectively carried out; ssmIs a driving signal of the MMC sub-module; f is the switching frequency; d is the duty cycle; sHFLIs the drive signal for the HFL.
Detailed Description
The present invention will be described in further detail with reference to the following examples:
as shown in fig. 1, fig. 2, fig. 3, fig. 4, fig. 5, fig. 6, and fig. 7, an MMC topology structure and a control method for high-frequency chain interconnection of upper and lower bridge arm sub-modules are provided. As shown in fig. 1, in an MMC topology with interconnected upper and lower bridge arm high-frequency chains, a first power switch tube Q of a first isolation submodule of each phase of the upper bridge arm1And a second power switch tube Q2The middle point of the composition is connected with the positive electrode of a medium voltage direct current bus (MVDC); the second power switch tube Q2Of the emitterFirst power switch tube Q of next isolation submodule1The emitting electrodes are connected; the upper bridge arm inductor L1、L3、L5And the second power switch tube Q of the last isolation submodule of each phase upper bridge arm2Is connected with the three-phase upper bridge arm inductance L1、L3、L5The other end of the first phase is respectively connected with a phase a, a phase b and a phase c of a medium voltage alternating current bus (MVAC); three-phase lower bridge arm inductance L2、L4、L6One end of the three-phase lower bridge arm inductor is respectively connected with the a phase, the b phase and the c phase of the medium-voltage alternating-current bus2、L4、L6And the other end of the first power switch tube Q of the first isolation submodule of each phase lower half-bridge arm1The emitter of (3) is connected; second power switch tube Q of each phase lower half-bridge arm isolation submodule2Emitter of (2) and first power switching tube Q of next isolation submodule1The emitting electrodes are connected; second power switch tube Q of last isolation submodule of lower half-bridge arm2Is connected with the negative pole of the medium voltage direct current bus.
As shown in fig. 2, the isolation sub-module includes a first power switch Q1A second power switch tube Q2A first capacitor C1A second capacitor C2And a third power switch tube Q3And a fourth power switch tube Q4(ii) a The first power switch tube Q1Collector and third power switch tube Q3Is connected with the collector of the second power switch tube Q2Emitter of and fourth power switch tube Q4The emitting electrodes are connected; the first power switch tube Q1Emitter and second power switch tube Q2Is connected with the collector of the third power switch tube Q3Emitter of and fourth power switch tube Q4The collector electrodes are connected; the first capacitor C1And one end of the third power switch tube Q3Is connected to the collector of the first capacitor C1And the other end of the first capacitor C2Connecting; the second capacitor C2The other end of the first power switch tube is connected with an emitting electrode of a fourth power switch tube;
as shown in fig. 3Said two-winding high-frequency transformer T1Comprising a first winding N1A second winding N2(ii) a The two-winding high-frequency transformer T1First winding N1Is connected to the first capacitor C1And a second capacitor C2The middle point of the bridge arm, the first winding N1Is connected to the third power switch tube Q3And a fourth power switch tube Q4The middle point of the bridge arm; the second winding N2The same name end of the first capacitor C and the corresponding isolation submodule1And a second capacitor C2The middle points of the formed bridge arms are connected, and the second winding N2The different name end of the first power switch tube Q and the corresponding isolation submodule3And a fourth power switch tube Q4The middle points of the formed bridge arms are connected.
As shown in fig. 4, the sub-module input current of the modular multilevel converter includes a dc component and an ac component, the ac component mainly includes a fundamental frequency and a frequency-doubled 2 component, and the ripple current mainly includes a fundamental frequency and a frequency-doubled 2 component. In the modular unit of the MMC topology upper and lower bridge arm combination type, the fundamental frequency component i in the fluctuating currentf1-ua、if1-ub、if1-ucAnd if1-da、if1-db、if1-dcOpposite phase, 2 multiplied frequency component if2-ua、if2-ub、if2-ucAnd if2-da、if2-db、if2-dcThe phases are the same. Therefore, the invention designs a power channel capable of realizing free flow of energy, and provides a scheme for realizing mutual offset of free flow by utilizing opposite phases of fluctuating power.
As shown in fig. 5, the third power switch tube Q3And a fourth power switch tube Q4Drive signal SHFLComplementary, fifth power switch tube Q5And a sixth power switch tube Q6Driving signal complementation, third power switch tube Q3And a fifth power switch tube Q5The driving signals are the same, and the fourth power switch tube Q3And a sixth power switch tube Q6The driving signals are the same, and the driving signals on the primary side and the secondary side are synchronous signals with the duty ratio D fixed to be 50%. Interconnected submodulesThe medium fluctuation power has phase difference and is counteracted by a high-frequency link; when the capacitance voltage in the ith isolation submodule is higher than the capacitance voltage of the jth isolation submodule interconnected with the ith isolation submodule, the fluctuating current flows from the capacitance of the ith isolation submodule to the capacitance of the jth isolation submodule through the transformer, and the balance of the two capacitance voltages is realized.
As shown in fig. 6, an equivalent model is established for the bridge arm current in the flow path of the combined module unit, the impedance of the high-frequency link is small, and the free flow of the fluctuating current is not affected, so that the impedance can be ignored in the equivalent model. The current flowing into the ports of the sub-modules of the upper bridge arm and the lower bridge arm is equivalent to a controlled current source, and the capacitors of the two sub-modules which are interconnected through the high-frequency link are equivalent to be directly connected in parallel. The two sub-module capacitor voltages are clamped with each other, and the generated ripple currents with opposite phases are mutually counteracted.
As shown in fig. 7, the method for controlling the high-frequency chain mutual topology based on the upper and lower bridge arm submodules of the MMC includes AC/DC converter control and high-frequency chain open-loop modulation, where the AC/DC converter control is double closed-loop control of voltage and current, including output direct-current voltage outer-loop control and alternating-current side current inner-loop control, the voltage outer-loop control ensures stable voltage at the medium-voltage direct-current side, the current inner-loop control realizes unit power factor operation, and the modulation mode is carrier phase-shift pulse width modulation (CPS-SPWM) modulation. The specific control loop of the AC/DC conversion control comprises the following steps: dividing three-phase input AC voltage and current by abc/dq conversion to obtain d-and q-axis components of voltage and current, and outputting voltage with given value UDC *Subtracting the actual value U of the output voltageDCThe d-axis component i of the input current is subtracted from the output value of the PI regulatordThe d-axis component u of the output value and the input voltage obtained after PI regulationdAdding and subtracting the q-axis component i of the input currentqMultiplying the d-axis decoupling value by the omega L to obtain a d-axis decoupling value ed *(ii) a Given value i of q-axis component of input currentq *By subtracting the actual value i of the q-axis component of the input currentqAdding the output value after PI regulation to the q-axis component of the input voltage, and subtracting the d-axis component i of the input currentdMultiplying the obtained product by omega L to obtain a q-axis decoupling value eq *(ii) a The above two steps are combinedThe decoupling value is converted into a three-phase modulation wave e through dq/abca *、eb *、ec *The three-phase modulation wave is subjected to a carrier phase-shifting pulse width modulation strategy to obtain a driving signal S of a power switch tube in the submodule (namely, a first power switch tube and a second power switch tube in the isolation submodule)sm. The high frequency link adopts open loop PWM modulation with fixed duty cycle, and the control method thereof is explained in the above description with reference to fig. 3, and is not described herein again.
According to the MMC topological structure based on the interconnection of the high-frequency chains of the sub-modules of the upper bridge arm and the lower bridge arm, on the basis of a conventional MMC, the corresponding sub-modules of the upper bridge arm and the lower bridge arm are cascaded together through the high-frequency links to form a combined type module unit. The structure and control of all high-frequency links are completely the same, and a channel is provided for free transfer of fluctuation power of the sub-modules. The driving signals of the switching tubes of the high-frequency link are controlled to be synchronous control signals with the duty ratio of 50%, the control signals of the two switching tubes of the half-bridge structure in the high-frequency link are complementary, the impedance in the high-frequency link is small, the capacitors in the combined module unit can be equivalently directly interconnected, and the characteristics of opposite phases of fluctuating power are utilized to realize the mutual offset of the autonomous flowing of the fluctuating power.

Claims (8)

1. The utility model provides a MMC topology of upper and lower bridge arm submodule piece high frequency chain interconnection which characterized in that: the bridge arm of each phase in the three-phase bridge arm is divided into an upper bridge arm and a lower bridge arm, each upper bridge arm comprises n submodules and an upper bridge arm inductor L, and each upper bridge arm comprises n submodules and an upper bridge arm inductor L1、L3、L5Each phase of lower bridge arm comprises n submodules and a lower bridge arm inductor L2、L4、L6The two-winding high-frequency transformer interconnects the corresponding isolation sub-modules of the upper bridge arm and the lower bridge arm of the same phase to form a combined module unit.
2. The method of claim 1The MMC topology for interconnecting the high-frequency chains of the upper bridge arm submodule and the lower bridge arm submodule is characterized in that: the isolation submodule comprises a first power switch tube Q1A second power switch tube Q2A first capacitor C1A second capacitor C2And a third power switch tube Q3And a fourth power switch tube Q4(ii) a The two-winding high-frequency transformer TiComprising a first winding N1A second winding N2(ii) a The first power switch tube Q1Collector and third power switch tube Q3Is connected with the collector of the second power switch tube Q2Emitter of and fourth power switch tube Q4The emitting electrodes are connected; the first power switch tube Q1Emitter and second power switch tube Q2Is connected with the collector of the third power switch tube Q3Emitter of and fourth power switch tube Q4The collector electrodes are connected; the first capacitor C1And one end of the third power switch tube Q3Is connected to the collector of the first capacitor C1And the other end of the first capacitor C2Connecting; the second capacitor C2The other end of the first power switch tube is connected with an emitting electrode of a fourth power switch tube; the two-winding high-frequency transformer T1First winding N1Is connected to the first capacitor C1And a second capacitor C2The middle point of the bridge arm, the first winding N1Is connected to the third power switch tube Q3And a fourth power switch tube Q4The middle point of the bridge arm; the second winding N2Is connected to the first capacitor C of the isolation submodule in the other bridge arm corresponding to the isolation submodule1And a second capacitor C2Bridge arm midpoint of the composition, the second winding N2The different name end of the first power switch tube Q and the corresponding isolation submodule3And a fourth power switch tube Q4The middle points of the formed bridge arms are connected.
3. The MMC topology of upper and lower bridge arm submodule high frequency chain interconnection of claim 2, characterized in that: the first isolation submodule of each phase upper bridge armFirst power switch tube Q of block1And a second power switch tube Q2The middle point of the composition is connected with the anode of a medium-voltage direct-current bus; the second power switch tube Q2Emitter of (2) and first power switch tube Q of next combined module unit1The emitting electrodes are connected; the upper bridge arm inductor L1、L3、L5And the second power switch tube Q of the last isolation submodule of each phase upper bridge arm2Is connected with the three-phase upper bridge arm inductance L1、L3、L5The other end of the first connecting rod is respectively connected with a phase a, a phase b and a phase c of the medium-voltage alternating current bus; three-phase lower bridge arm inductance L2、L4、L6One end of the three-phase lower bridge arm inductor is respectively connected with the a phase, the b phase and the c phase of the medium-voltage alternating-current bus2、L4、L6And the other end of the first power switch tube Q of the first isolation submodule of each phase lower half-bridge arm1The emitter of (3) is connected; second power switch tube Q of each phase lower half-bridge arm isolation submodule2Emitter of (2) and first power switching tube Q of next isolation submodule1The emitting electrodes are connected; second power switch tube Q of last isolation submodule of lower half-bridge arm2Is connected with the negative pole of the medium voltage direct current bus.
4. The MMC topology of upper and lower bridge arm submodule high frequency chain interconnection of claim 2, characterized in that: the input current of the submodule of the modular multilevel converter structure comprises a direct current component and an alternating current component, the alternating current component mainly comprises a fundamental frequency component and a frequency multiplication component 2, and a fundamental frequency component i in a fluctuating current in an upper bridge arm and a lower bridge arm combined module unit of an MMC topologyf1-ua、if1-ub、if1-ucAnd if1-da、if1-db、if1-dcOpposite phase, 2 multiplied frequency component if2-ua、if2-ub、if2-ucAnd if2-da、if2-db、if2-dcThe phases are the same.
5. The MMC topology of upper and lower bridge arm submodule high frequency chain interconnection of claim 4, characterized in that: the combined module unit formed by connecting the two-winding high-frequency transformer with the upper bridge arm and the lower bridge arm and corresponding to the isolation sub-modules is respectively provided with an upper bridge arm current and a lower bridge arm current, an equivalent model is established for the bridge arm currents in the flow path of the combined module unit, the impedance of a high-frequency link is small, the free flow of fluctuating currents is not influenced, and therefore the equivalent model can be ignored; the current flowing into the ports of the sub-modules of the upper bridge arm and the lower bridge arm is equivalent to a controlled current source, and the capacitors of the two sub-modules which are interconnected through a high-frequency link are equivalent to be directly connected in parallel; the two sub-module capacitor voltages are clamped with each other, and the generated ripple currents with opposite phases are mutually counteracted.
6. A control method of an MMC topology with interconnected upper and lower bridge arm sub-modules in a high-frequency chain is characterized by comprising the following steps: the method comprises half-bridge and capacitor structure control and high-frequency link control, wherein the half-bridge and capacitor structure control adopts double closed-loop control of independent voltage and current under abc coordinates, the double closed-loop control comprises direct-current side voltage outer loop control and alternating-current side current inner loop control, and the modulation mode adopts a carrier phase-shift pulse width modulation technology; and the high-frequency link control adopts open-loop PWM with fixed duty ratio.
7. The method for controlling the MMC topology of the high-frequency chain interconnection of the upper bridge arm submodule and the lower bridge arm submodule according to claim 6, is characterized in that: the specific steps of the half-bridge and capacitor structure control are as follows:
1) dividing three-phase input AC voltage and current by abc/dq conversion to obtain d-and q-axis components of voltage and current, and outputting voltage with given value U* DCSubtracting the actual value U of the output voltageDCThe d-axis component i of the input current is subtracted from the output value of the PI regulatordThe d-axis component u of the output value and the input voltage obtained after PI regulationdAdding and subtracting the q-axis component i of the input currentqMultiplication with ω L to obtain d-axis modulation component ed *；
2) Given value i of input current q-axis componentq *By subtracting the actual value i of the q-axis component of the input currentqTransfusion after PI regulationAdding the output value to the q-axis component of the input voltage, and subtracting the d-axis component i of the input currentdMultiplying by ω L to obtain q-axis modulation component eq *；
3) Carrying out dq/abc conversion on the values obtained in the step 1) and the step 2) to obtain a three-phase modulation component ea *、eb *、ec *The three-phase modulation wave component is subjected to a carrier phase shift modulation strategy to obtain a driving signal S of a half-bridge and capacitor structuresm。
8. The method for controlling the MMC topology of the high-frequency chain interconnection of the upper bridge arm submodule and the lower bridge arm submodule according to claim 6, is characterized in that: the driving signals at two sides of the transformer in all the combined module units are the same and are synchronous signals with the duty ratio of 50%, and the third power switch tube Q3And a fourth power switch tube Q4The driving signal complements the driving control signal frequency of the switch tube in the combined module unit to be f, and the duty ratio is D.
CN202110461394.0A 2021-04-27 2021-04-27 MMC topology with interconnected upper bridge arm sub-modules and high-frequency chain and control method Pending CN113078829A (en)

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