CN113938038A - MMC-based high-frequency alternating current bus electric energy routing structure and control strategy - Google Patents
MMC-based high-frequency alternating current bus electric energy routing structure and control strategy Download PDFInfo
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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
- H02M7/219—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 in a bridge configuration
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
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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
- H02M1/00—Details of apparatus for conversion
- H02M1/32—Means for protecting converters other than automatic disconnection
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
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- 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
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/30—Reactive power compensation
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Abstract
The invention relates to a high-frequency alternating current bus electric energy routing structure and a control strategy based on MMC, belonging to the technical field of electric energy conversion, wherein the routing structure comprises a medium-voltage conversion stage, a high-frequency isolation stage and a low-voltage stage; the control strategy comprises medium-voltage conversion stage AC/DC conversion control, high-frequency isolation stage control and control of a low-voltage output end of a high-frequency alternating current bus. The modular multilevel converter, the isolation transformer and the full-bridge structure are combined to form a high-frequency alternating-current bus electric energy routing structure and realize electric isolation, so that the electric energy conversion links can be reduced, the capacitance volume of the modular multilevel converter is reduced, the voltage fluctuation inhibition and automatic equalization of sub-modules are realized, the power density is improved, and the system control is simplified.
Description
Technical Field
The invention relates to a high-frequency alternating current bus electric energy routing structure and a control strategy based on an MMC, and belongs to the technical field of electric energy conversion.
Background
With the improvement of the power generation permeability of the distributed energy and the increase of the proportion of direct current loads such as electric vehicles, LED power supplies and the like, the power grid structure is diversified day by day, and the traditional power transmission and distribution network and the traditional operation mode are difficult to meet the requirement of the coordinated and stable operation of the system. The method is connected with various forms of energy and loads, and realizes the source-network-load-storage coordinated operation, so that the method becomes a new requirement for the development of future intelligent power grids and green power grids. In order to fully utilize distributed energy and meet the operation requirements of various loads, an energy internet with energy coordination management capability becomes a typical development trend, wherein an electric energy route with multiple voltage levels and multiple ports is a key device in the energy internet.
The MMC-based electric energy route plays an important role in an intelligent power grid and an alternating current-direct current hybrid power distribution network, can realize mutual allocation between alternating current and direct current power grids with different voltage grades and different energy forms, and improves the flexible regulation and control capability and reliability of the alternating current-direct current power grid. The MMC-based common direct current bus electric energy routing structure has been researched by some students, in order to realize multi-port output and multi-energy form conversion, the students provide a three-stage electric energy routing structure, the MMC is used as an input stage, a MVDC port is connected with a DAB structure with serial input and serial output connected in parallel to realize isolation and form a common direct current bus, and then each port is formed through an alternating current-direct current conversion link. The scholars propose that every sub-module is cascaded with DAB, and all DAB output ends are connected in parallel to form an electric energy routing structure of a common direct current bus. The scheme that the sub-modules are cascaded with DAB to form the common direct current bus has the advantages that the number of switches and transformers is large, the cost is high, the common direct current bus is used as an electric energy conversion hub to realize the conversion links required by alternating current-direct current conversion, and the energy conversion efficiency of the system is seriously influenced.
The MMC-based electric energy routing limits the improvement of system power density because the number of modules of the MMC structure is large and a large-size capacitor is needed for inhibiting the fluctuation of the capacitor voltage of the sub-modules, and meanwhile, various control loops are needed to be designed for the stable operation of the multilevel structure, so that the system control complexity is high. At present, for a strategy for solving the fluctuation of capacitance and voltage of a submodule of an MMC structure, a proposal of injecting common-mode voltage at an alternating current side and injecting circulating current at a phase unit to inhibit the fluctuation of voltage is provided by a learner, but the problems of increased bridge arm current, poor quality of direct current output waveform and the like exist. And this manner of suppressing voltage fluctuations typically requires closed loop control, increasing the complexity of the control system.
Disclosure of Invention
The invention aims to provide a high-frequency alternating current bus electric energy routing structure and a control strategy based on an MMC, which can reduce electric energy conversion links, provide multiple types of ports, reduce capacitance requirements, realize voltage balance of all sub-modules and simplify system control.
In order to achieve the purpose, the invention adopts the technical scheme that:
a high-frequency alternating-current bus electric energy routing structure based on MMC comprises a medium-voltage conversion stage, a high-frequency isolation stage and a low-voltage stage; the medium-voltage conversion stage is a modular multilevel converter with a three-phase six-bridge arm structure and is provided with medium-voltage alternating current and direct current ports; the high-frequency isolation level comprises a full-bridge structure and a four-winding high-frequency isolation transformer, the full-bridge structure is cascaded behind the sub-module, three windings on the primary side of the four-winding high-frequency isolation transformer are respectively connected with three inter-phase transverse full bridges to form an isolation combined unit, and the secondary sides of the four-winding high-frequency isolation transformer are connected in parallel to form a high-frequency alternating current bus; the low-voltage stage comprises a two-winding high-frequency isolation transformer, a synchronization unit and a phase-shifting unit, the synchronization unit is of a full-bridge structure, the phase-shifting unit is of an inductor and a full-bridge structure, the synchronization unit and the phase-shifting unit are both connected into a high-frequency alternating current bus through the two-winding high-frequency isolation transformer, and the output end of the low-voltage stage is a voltage clamping type low-voltage direct current port and a power controllable low-voltage direct current port respectively.
The technical scheme of the invention is further improved as follows: the medium-voltage conversion-stage modular multilevel converter is of a three-phase six-bridge-arm structure, each phase of bridge arm is equally divided into an upper bridge arm and a lower bridge arm, and the three-phase upper bridge arm respectively comprises n sub-modules and an upper bridge arm inductor Lg1、Lg3、Lg5The three-phase lower bridge arm comprises n submodules and a lower bridge arm inductor Lg2、Lg4、Lg6(ii) a The submodule comprises a first power switch tube S1A second power switch tube S2A first capacitor C, a first power switch tube S of a first submodule of each phase upper bridge arm1And a second power switch tube S2The middle point of the composition is connected with the anode of a medium-voltage direct-current bus; the second power switch tube S2Emitter of and the first power switch tube S of the next submodule1The emitting electrodes are connected; the upper bridge arm inductor Lg1、Lg3、Lg5One end of the first power switch tube S is respectively connected with the second power switch tube S of the last submodule of each phase upper bridge arm2Is connected with the three-phase upper bridge arm inductance Lg1、Lg3、Lg5The 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 Lg2、Lg4、Lg6One 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 busg2、Lg4、Lg6The other end of the first power switch tube S is respectively connected with the first power switch tube S of the first submodule of each phase of the lower half bridge arm1The emitter of (3) is connected; second power switch tube S of each phase lower half-bridge arm submodule2Emitter of (2) and first power switch tube S of next group of sub-modules1The emitting electrodes are connected; second power switch tube S of last submodule of lower half-bridge arm2Is connected with the negative pole of the medium voltage direct current bus.
The technical scheme of the invention is further improved as follows: the isolation combination unit of the high-frequency isolation stage comprises three full-bridge structures and a four-winding high-frequency isolation transformer, wherein the full-bridge structure comprises a first power switch tube Q1A second power switch tube Q2And a third power switch tube Q3And a fourth power switch tube Q4The four-winding high-frequency transformer T comprises a first winding N1A second winding N2A third winding N3A fourth winding N4The first power switch tube S of the sub-module1Emitter and second workRate switching tube S2The collector electrodes are connected; one end of the first capacitor C of the submodule and the first power switch tube S1The other end of the first capacitor C of the submodule is connected with a second power switch tube S2The emitter of (3) is connected; the first power switch tube S of the sub-module1Collector and full-bridge first power switch tube Q1Collector and third power switch tube Q3The collector electrodes are connected; the second power switch tube S of the sub-module2Emitter and full-bridge second power switch tube Q2Emitter and fourth power switch tube Q4The emitting electrodes are connected; the full-bridge first power switch tube Q1Emitter and second power switch tube Q2The collector electrodes are connected; the full-bridge third power switch tube Q3Emitter of and fourth power switch tube Q4The collector electrodes are connected; the first winding N1The same name end of the first power switch tube Q is connected to a first power switch tube Q of an A-phase full-bridge structure in three full-bridge structures at the same transverse positiona1And a second power switch tube Qa2The middle point of the bridge arm formed by the first winding N1The different name end of the third power switch tube Q is connected with the full-bridge structurea3And a fourth power switch tube Qa4The middle point of the bridge arm; the second winding N2The same-name end of the first power switch tube Q is connected to a B-phase full-bridge structure in three full-bridge structures at the same transverse positionb1And a second power switch tube Qb2The middle point of the bridge arm formed by the second winding N2The different name end of the third power switch tube Q is connected with the full-bridge structureb3And a fourth power switch tube Qb4The middle point of the bridge arm; the third winding N3The same-name end of the first power switch tube Q is connected to a C-phase full-bridge structure in three full-bridge structures at the same transverse positionc1And a second power switch tube Qc2The middle point of the bridge arm formed by the third winding N3The different name end of the third power switch tube Q is connected with the full-bridge structurec3And a fourth power switch tube Qc4The middle point of the bridge arm; the first, the second and the third windings are positioned in the original of the isolated four-winding high-frequency transformerAnd the fourth winding is positioned on the secondary side, and the transformation ratio of the three windings on the primary side is 1:1:1, determining the transformation ratio of the fourth winding to the primary side three windings according to the application condition; and the fourth windings of all the four-winding high-frequency isolation transformers are connected in parallel to form a high-frequency alternating current bus.
The technical scheme of the invention is further improved as follows: the low-voltage-level synchronization unit and the phase-shifting unit are connected to a high-frequency alternating-current bus through a two-winding high-frequency isolation transformer to form a low-voltage direct-current port; the synchronous unit comprises a first power switch tube Qs1A second power switch tube Qs2And a third power switch tube Qs3And a fourth power switch tube Qs4A first capacitor CsThe first power switch tube Qs1Emitter and second power switch tube Qs2The collector electrodes are connected; the third power switch tube Qs3Emitter of and fourth power switch tube Qs4The collector electrodes are connected; the first power switch tube Qs1Collector and third power switch tube Qs3The collector electrodes are connected; the second power switch tube Qs2Emitter of and fourth power switch tube Qs4The emitting electrodes are connected; the first capacitor CsIs connected to the third power switch tube Qs3The other end of the collector is connected to a fourth power switch tube Qs4An emitter of (1); two ends of a primary side winding of the two-winding high-frequency isolation transformer are connected with a high-frequency alternating current bus, and one end of a secondary side winding is connected to a first power switch tube Q and a second power switch tube Q of the synchronous units1、Qs2The middle point of the bridge arm and the other end of the bridge arm are connected to a third power switch tube Q and a fourth power switch tube Qs3、Qs4The midpoint of the bridge arm; the phase shift unit comprises a first power switch tube Qsc1A second power switch tube Qsc2And a third power switch tube Qsc3And a fourth power switch tube Qsc4A first inductor L and a first capacitor Csc(ii) a The first power switch tube Qsc1Emitter and second power switch tube Qsc2The collector electrodes are connected; the third power switch tube Qsc3Emitter of and fourth power switch tube Qsc4The collector electrodes are connected; the first power switch tubeQsc1Collector and third power switch tube Qsc3The collector electrodes are connected; the second power switch tube Qsc2Emitter of and fourth power switch tube Qsc4The emitting electrodes are connected; the first capacitor CscIs connected to the third power switch tube Qsc3The other end of the collector is connected to a fourth power switch tube Qsc4An emitter of (1); one end of the first inductor L is connected to the first power switch tube Qsc1And a second power switch tube Qsc2The other end of the middle point of the bridge arm is connected to one end of a secondary side winding of the two-winding high-frequency isolation transformer; two ends of a primary side winding of the two-winding high-frequency isolation transformer are connected with a high-frequency alternating current bus, one end of a secondary side winding is connected to a first inductor L of the phase shifting unit, and the other end of the secondary side winding is connected to a third power switching tube Q and a fourth power switching tube Q of the phase shifting unitsc3、Qsc4The midpoint of the bridge arm.
The technical scheme of the invention is further improved as follows: 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 the fundamental frequency component i in the fluctuating current of the submodule corresponding to the upper bridge arm and the lower bridge arm in the MMCf-ua、if-ub、if-ucAnd if-da、if1-db、if-dcOpposite phase, 2 multiplied frequency component i2f-ua、i2f-ub、i2f-ucAnd i2f-da、i2f-db、i2f-dcThe phases are the same, fundamental frequency components and 2 frequency multiplication components among the submodules corresponding to the three phases are in positive sequences and negative sequences, and the three-phase symmetrical characteristic is realized; an equivalent model is established for a high-frequency alternating current bus structure, the input side of the high-frequency alternating current bus is equivalent to a three-phase controlled current source parallel capacitor, and the leakage inductances of primary side windings of a transformer are respectively Lla、Llb、Llc(ii) a The reactance on the secondary side and the low-voltage side of the HFAC is equivalent to Zreq(ii) a The high-frequency alternating-current bus provides a flowing channel for the fluctuation power of the MMC three-phase sub-module through the isolation combination unit and is equivalent to a neutral point, the fluctuation power has three-phase symmetry, so that the fluctuation power can be mutually offset at the high-frequency alternating-current bus, and meanwhile, 2-frequency multiplication circulating current in a bridge arm is naturally eliminated.
A control strategy of a high-frequency alternating current bus electric energy routing structure based on MMC comprises medium-voltage conversion level AC/DC conversion control, high-frequency isolation level control and control of a low-voltage output end of a high-frequency alternating current bus; the medium-voltage conversion stage AC/DC conversion control is to realize AC/DC conversion of MMC by adopting closed-loop control, the closed-loop control comprises direct-current side control and alternating-current side control, the direct-current side control adopts direct-current voltage control or power loop control, and the alternating-current side control comprises alternating-current side current control, alternating-current side voltage control or torque and rotation speed control; the MMC modulation mode adopts a carrier modulation mode or a step wave modulation mode, the high-frequency isolation level control is that the full-bridge structure of the submodule cascade is controlled by a synchronous open-loop signal with a given duty ratio and frequency, and the control of the low-voltage output end of the high-frequency alternating current bus comprises the synchronous control of a voltage clamping port and the phase-shifting control of a power controllable port.
The technical scheme of the invention is further improved as follows: the specific method for controlling the high-frequency isolation stage is to isolate a first power switch tube Q in a full-bridge structure of the combined unit1And a second power switch tube Q2The driving signals are complementary, the first power switch tube Q1And a third power switch tube Q3The driving signals are the same, and the second power switch tube Q2And a fourth power switch tube Q4The driving signals are the same, all full-bridge structures in all the isolation combination units are driven synchronously, the full-bridge structures are driving signals with the frequency f and the duty ratio D of 50%, and open-loop PWM modulation is adopted.
The technical scheme of the invention is further improved as follows: the control scheme of the low-voltage output end of the high-frequency alternating-current bus comprises the following steps:
1) the synchronous unit of the voltage clamp type port adopts synchronous control, and the full bridge of the synchronous unit adopts an open-loop PWM modulation mode which is the same as that of the full bridge in the isolation combination unit;
2) the phase-shifting unit of the power controllable port adopts phase-shifting control, and a phase-shifting angle exists between the driving signal of the full bridge of the phase-shifting unit and the driving signal of the full bridge in the isolation combination unitjSetting the low-voltage DC output voltage to a given value ULdcrSubtracting the actual value U of the low-voltage DC output voltageLdcThe phase shift angle is obtained by a PI regulatorjAnd obtaining a control signal through amplitude limiting control, and obtaining a driving signal of the full-bridge structure of the phase-shifting unit through PWM modulation.
Due to the adoption of the technical scheme, the invention has the following technical effects:
the electric energy routing system has higher power density, can reduce electric energy conversion links, realizes elimination of fluctuation power of capacitance voltage of the MMC sub-module, greatly reduces the capacitance volume required by the sub-module, and improves the power density of the system.
The electric energy routing system has the advantages of simple structure, flexible and reliable port configuration, simple structure, high uniformity and convenience for modular combination and design, and realizes multi-port electric energy conversion by taking the high-frequency alternating current bus formed by the full-bridge structure as a frame; electric energy can be transmitted between any two ports, electric isolation is realized between the ports, and the device is stable and reliable in operation and flexible in application.
The electric energy routing system is simple to control, the MMC level only needs to complete voltage and current double closed-loop control of basic AC/DC conversion, a bridge arm 2 frequency doubling circulating current restraining and submodule voltage equalizing strategy does not need to be designed, the primary side and the synchronizing unit of the high-frequency isolation level both adopt the simplest open-loop control mode, the phase-shifting unit of the high-frequency AC bus side and the primary side of the high-frequency isolation transformer adopt phase-shifting control, the control method is simple, a large number of detection circuits and control calculation links are omitted, and the response speed of the system is improved.
Drawings
FIG. 1 is an electrical schematic diagram of an MMC-based high frequency AC bus power routing architecture of the present invention;
FIG. 2 is an electrical schematic diagram of an MMC sub-module in an MMC-based high-frequency AC bus electric energy routing structure of the present invention;
FIG. 3 is an electrical schematic diagram of a full bridge structure in the high frequency AC bus power routing structure based on MMC in the present invention;
FIG. 4 is an electrical schematic diagram of an isolation combination unit in the MMC-based high-frequency AC bus electric energy routing structure of the present invention;
FIG. 5 is an electrical schematic diagram of a high frequency AC bus structure in the high frequency AC bus electrical energy routing structure based on MMC of the present invention;
FIG. 6a is a schematic diagram of sub-module fundamental frequency ripple current components of a conventional three-phase MMC of the present invention;
FIG. 6b is a schematic diagram of a frequency-doubled fluctuating current component of a conventional three-phase MMC topology submodule 2 according to the present invention;
FIG. 7 is an equivalent circuit diagram of a high frequency AC bus structure in the MMC-based high frequency AC bus electric energy routing structure of the present invention;
FIG. 8 is a block diagram of a control scheme of an MMC-based high-frequency AC bus power routing architecture of the present invention;
FIG. 9 is a schematic diagram of a specific control strategy of the high-frequency AC bus electric energy routing structure based on MMC in the present invention.
Wherein, MVAC is a medium voltage alternating current bus, MVDC is a medium voltage direct current bus, LVDC is a low voltage output port, UMVDCThe voltage of the medium-voltage direct current bus and the HFAC are low-voltage high-frequency alternating current buses; SM is a submodule; FB is in a full-bridge structure; FBL is a phase-shifting unit structure; s1、S2The first power switch tube and the second power switch tube are respectively a submodule; c is a first capacitor of the sub-module; qa1、Qa2、Qa3、Qa4、Qb1、Qb2、Qb3、Qb4、Qc1、Qc2、Qc3、Qc4The first power switch tube, the second power switch tube, the third power switch tube and the fourth power switch tube are respectively connected with an A, B, C phase submodule cascade full bridge; t isiIs a four-winding high-frequency isolation transformer, N1、N2、N3、N4The first winding, the second winding, the third winding and the fourth winding of the high-frequency four-winding transformer are respectively arranged; t issiIs a two-winding high-frequency isolation transformer; csA first capacitor which is a synchronization unit; cscA first capacitor of the phase shift unit; l is a phase-shifting inductor (a first inductor of the phase-shifting unit); l isg1、Lg3、Lg5Is an upper bridge arm inductance, Lg2、Lg4、Lg6Is a lower bridge arm inductance; i.e. if-ua、if-ub、if-ucThe fundamental frequency component i of the fluctuating current of the bridge arm sub-modules on the a phase, the b phase and the c phase respectivelyf-da、if-db、i1-dcThe fundamental frequency component and i of the ripple current of the sub-modules of the lower bridge arm of the phases a, b and c are respectively2f-ua、i2f-ub、i2f-ucThe ripple current of the bridge arm sub-modules on the a phase, the b phase and the c phase is respectively 2 frequency multiplication components and i2f-da、i2f-db、i2f-dcRespectively a, b and c phase lower bridge arm submodule fluctuating current 2 frequency multiplication components; l isla、Llb、LlcLeakage inductances of a first winding, a second winding and a third winding on the primary side of the transformer are respectively; zreqThe equivalent reactance of the fourth winding at the secondary side of the transformer and the loads at the HFAC side and the LVDC side; i.e. ica、icb、iccThe currents flowing into the three-phase full bridge are respectively the primary side of the transformer; u. ofN' is the amplitude of the HFAC voltage; u. ofca、ucb、uccRespectively the capacitor voltage of the phase sub-modules a, b and c; j is a function of1Is a phase shift angle; u shapeMdcrA reference value for the medium voltage dc output voltage; u shapeLdcrOutputting a voltage reference value for the low-voltage direct-current bus; u. ofa,b,cEach phase voltage is a three-phase AC input voltage; i.e. ia,b,cEach 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 input voltage respectively; i.e. id、iqD-axis component and q-axis component after dq conversion is carried out on the three-phase input current respectively; i.e. idrReference value, i, for input current on d-axisqrA reference value of the input current on the q axis; u. ofrefRespectively carrying out dq/abc conversion and then outputting three-phase modulation signals; ssmIs a driving signal of the MMC sub-module; f is the switching frequency; d is the open loop duty cycle; sFBThe driving signal is a driving signal of a full-bridge structure at the primary side of the transformer; sSFBDriving signals for a full-bridge structure of synchronous units; sSFBLThe phase-shifting unit is a full-bridge driving signal.
Detailed Description
The invention is described in further detail below with reference to the following figures and specific embodiments:
an MMC-based high-frequency AC bus electric energy routing structure is shown in figure 1 and comprises a medium-voltage conversion stage, a high-frequency isolation stage and a low-voltage stage. The medium-voltage conversion stage is a modular multilevel converter with a three-phase six-bridge arm structure and is provided with medium-voltage alternating current and direct current ports; the high-frequency isolation level comprises a full-bridge structure and a four-winding high-frequency isolation transformer, the full-bridge structure is cascaded behind the sub-module, three windings on the primary side of the four-winding high-frequency isolation transformer are respectively connected with three inter-phase transverse full bridges to form an isolation combined unit, and the secondary sides of the four-winding high-frequency isolation transformer are connected in parallel to form a high-frequency alternating current bus; the low-voltage stage comprises a two-winding high-frequency isolation transformer, a synchronization unit and a phase-shifting unit, a high-frequency alternating current bus is connected through the two-winding high-frequency isolation transformer, and the output ends of the two-winding high-frequency isolation transformer are respectively a voltage clamping type low-voltage direct current port and a power controllable low-voltage direct current port.
The medium-voltage conversion-stage modular multilevel converter is of a three-phase six-bridge-arm structure, each phase of bridge arm is equally divided into an upper bridge arm and a lower bridge arm, and the three-phase upper bridge arm respectively comprises n sub-modules and an upper bridge arm inductor Lg1、Lg3、Lg5The three-phase lower bridge arm comprises n submodules and a lower bridge arm inductor Lg2、Lg4、Lg6(ii) a The submodule comprises a first power switch tube S1A second power switch tube S2A first capacitor C; the first power switch tube S of the sub-module1Emitter and second power switch tube S2The collector electrodes are connected; one end of the first capacitor C of the submodule and the first power switch tube S1The other end of the first capacitor C of the submodule is connected with a second power switch tube S2As shown in fig. 2. The medium-voltage conversion-stage modular multilevel converter is of a three-phase six-bridge-arm structure, each phase of bridge arm is equally divided into an upper bridge arm and a lower bridge arm, and the three-phase upper bridge arm respectively comprises n half-bridges and sub-modules of a capacitor structure and an upper bridge arm inductor Lg1、Lg3、Lg5The three-phase lower bridge arm comprises n submodules and a lower bridge arm inductor Lg2、Lg4、Lg6(ii) a The submodule comprises a first power switch tube S1A second power switch tube S2A first capacitor C, a first power switch tube S of a first submodule of each phase upper bridge arm1And a second power switch tube S2OfThe middle point is connected with the anode of the medium-voltage direct-current bus; the second power switch tube S2Emitter of and the first power switch tube S of the next submodule1The emitting electrodes are connected; the upper bridge arm inductor Lg1、Lg3、Lg5One end of the first power switch tube S is respectively connected with the second power switch tube S of the last submodule of each phase upper bridge arm2Is connected with the three-phase upper bridge arm inductance Lg1、Lg3、Lg5The 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 Lg2、Lg4、Lg6One 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 busg2、Lg4、Lg6The other end of the first power switch tube S is respectively connected with the first power switch tube S of the first submodule of each phase of the lower half bridge arm1The emitter of (3) is connected; second power switch tube S of each phase lower half-bridge arm submodule2Emitter of (2) and first power switch tube S of next group of sub-modules1The emitting electrodes are connected; second power switch tube S of last submodule of lower half-bridge arm2Is connected with the negative pole of the medium voltage direct current bus.
As shown in fig. 3, the full-bridge structure includes a first power switch Q1A second power switch tube Q2And a third power switch tube Q3And a fourth power switch tube Q4(ii) a The full-bridge first power switch tube Q1Emitter and second power switch tube Q2The collector electrodes are connected; the full-bridge third power switch tube Q3Emitter of and fourth power switch tube Q4The collector electrodes are connected; the full-bridge first power switch tube Q1Collector and third power switch tube Q3The collector electrodes are connected; the full-bridge second power switch tube Q2Emitter of and fourth power switch tube Q4Are connected. The submodule first power switch tube S in fig. 21Collector of (2) and the full-bridge first power switch Q in fig. 31Collector and third power switch tube Q3The collector electrodes are connected; the second power switch tube S of the sub-module2Emitter and emitter ofBridge second power switch tube Q2Emitter and fourth power switch tube Q4Are connected.
As shown in fig. 4, the isolation combination unit of the high-frequency isolation stage includes three horizontal full-bridge structures and a four-winding high-frequency isolation transformer; the four-winding high-frequency transformer T comprises a first winding N1A second winding N2A third winding N3A fourth winding N4. The first winding N1The same name end of the first power switch tube Q is connected to a first power switch tube Q of an A-phase full-bridge structure in three full-bridge structures at the same transverse positiona1And a second power switch tube Qa2The middle point of the bridge arm formed by the first winding N1The different name end of the third power switch tube Q is connected with the full-bridge structurea3And a fourth power switch tube Qa4The middle point of the bridge arm; the second winding N2The same-name end of the first power switch tube Q is connected to a B-phase full-bridge structure in three full-bridge structures at the same transverse positionb1And a second power switch tube Qb2The middle point of the bridge arm formed by the second winding N2The different name end of the third power switch tube Q is connected with the full-bridge structureb3And a fourth power switch tube Qb4The middle point of the bridge arm; the third winding N3The same-name end of the first power switch tube Q is connected to a C-phase full-bridge structure in three full-bridge structures at the same transverse positionc1And a second power switch tube Qc2The middle point of the bridge arm formed by the third winding N3The different name end of the third power switch tube Q is connected with the full-bridge structurec3And a fourth power switch tube Qc4The middle point of the bridge arm; the first winding, the second winding and the third winding are positioned on the primary side of the isolated four-winding high-frequency transformer, the fourth winding is positioned on the secondary side, the transformation ratio of the three windings on the primary side is 1:1:1, and the transformation ratio of the fourth winding to the three windings on the primary side is determined according to the application condition.
As shown in fig. 5, the fourth windings of all the isolation and combination units are connected in parallel to form a high frequency alternating current bus (HFAC); the synchronous unit and the phase-shifting unit are connected to the HFAC through a two-winding high-frequency isolation transformer. The synchronous unit comprises a first power switch tubeQs1A second power switch tube Qs2And a third power switch tube Qs3And a fourth power switch tube Qs4A first capacitor Cs. The first power switch tube Qs1Emitter and second power switch tube Qs2The collector electrodes are connected; the third power switch tube Qs3Emitter of and fourth power switch tube Qs4The collector electrodes are connected; the first power switch tube Qs1Collector and third power switch tube Qs3The collector electrodes are connected; the second power switch tube Qs2Emitter of and fourth power switch tube Qs4The emitting electrodes are connected; the first capacitor CsIs connected to the third power switch tube Qs3The other end of the collector is connected to a fourth power switch tube Qs4An emitter of (1). Two ends of a primary side winding of the two-winding high-frequency isolation transformer are connected with a high-frequency alternating current bus, and one end of a secondary side winding is connected to a first power switch tube Q and a second power switch tube Q of the synchronous units1、Qs2The middle point of the bridge arm and the other end of the bridge arm are connected to a third power switch tube Q and a fourth power switch tube Qs3、Qs4The midpoint of the bridge arm. The phase shift unit comprises a first power switch tube Qsc1A second power switch tube Qsc2And a third power switch tube Qsc3And a fourth power switch tube Qsc4A first inductor L and a first capacitor Csc. The first power switch tube Qsc1Emitter and second power switch tube Qsc2The collector electrodes are connected; the third power switch tube Qsc3Emitter of and fourth power switch tube Qsc4The collector electrodes are connected; the first power switch tube Qsc1Collector and third power switch tube Qsc3The collector electrodes are connected; the second power switch tube Qsc2Emitter of and fourth power switch tube Qsc4The emitting electrodes are connected; the first capacitor CscIs connected to the third power switch tube Qsc3The other end of the collector is connected to a fourth power switch tube Qsc4An emitter of (1); one end of the first inductor L is connected to the first power switch tube Qsc1And a second power switch tube Qsc2Midpoint of bridge armAnd the other end of the secondary side winding of the two-winding high-frequency isolation transformer is connected to one end of the secondary side winding of the two-winding high-frequency isolation transformer. Two ends of a primary side winding of the two-winding high-frequency isolation transformer are connected with a high-frequency alternating current bus, one end of a secondary side winding is connected to a first inductor L of the phase shifting unit, and the other end of the secondary side winding is connected to a third power switching tube Q and a fourth power switching tube Q of the phase shifting unitsc3、Qsc4The midpoint of the bridge arm. The electric energy routing structure realizes that three links of AC/DC-DC/AC-AC/DC are needed for electric energy conversion from MVAC to LVDC, one link of AC/DC is needed for electric energy conversion from MVAC to MVDC, three links of DC/DC-DC/AC-AC/DC are needed for electric energy conversion from MVDC to LVDC, and fewer links of electric energy conversion are needed.
As shown in FIG. 6a, the input current of the submodule of MMC structure includes DC component and AC component, the AC component mainly includes fundamental frequency and 2 frequency multiplication component, and fundamental frequency fluctuating current i is between the submodules corresponding to the upper and lower bridge armsf-ua、if-ub、if-ucAnd if-da、if-db、if-dcThe phases are opposite, and the fundamental frequency fluctuating current has positive sequence among three transverse submodules and three-phase symmetry.
As shown in FIG. 6b, 2 frequency multiplication ripple current i between the sub-modules corresponding to the upper and lower bridge arms2f-ua、i2f-ub、i2f-ucAnd i2f-da、i2f-db、i2f-dcThe phase is the same, 2 frequency multiplication fluctuation current phases are in a negative sequence among three transverse sub-modules and have three-phase symmetry characteristics.
As shown in FIG. 7, an equivalent model is established for the high-frequency AC bus structure, and the voltages of the primary side sub-modules of the isolated high-frequency transformer are respectively equal to the voltage uca、ucb、uccThe leakage inductance of the transformer winding is Lla、Llb、Llc(ii) a The amplitude of the HFAC voltage is equivalent to uN'. Because the fluctuating power has three-phase symmetrical characteristic, the fluctuating power can be mutually offset at a neutral point formed by the HFAC, and meanwhile, the generated 2-frequency multiplication circulating current in the bridge arm can be naturally eliminated.
The electric energy routing structure realizes three links of AC/DC conversion which is formed by MMC, DC/AC conversion of an isolation combination unit and AC/DC conversion which is formed by a transformer and a synchronization and phase-shifting unit when the electric energy is converted from medium-voltage alternating current to low-voltage direct current, one link of AC/DC conversion which is formed by MMC is required when the electric energy is converted from the medium-voltage alternating current to the medium-voltage direct current, and three links of DC/DC conversion which is formed by MMC, DC/AC conversion of the isolation combination unit, and AC/DC conversion which is formed by the transformer and the synchronization and phase-shifting unit when the medium-voltage direct current is converted to the low-voltage direct current.
A control strategy of a high-frequency AC bus electric energy routing structure based on MMC, as shown in fig. 8, includes AC/DC conversion control of a medium-voltage conversion stage, isolation combination stage control and control of a low-voltage output end of a high-frequency AC bus, where the medium-voltage conversion stage AC/DC control adopts closed-loop control, the closed-loop control includes DC side control and AC side control, the DC side control adopts DC voltage control or power loop control, and the AC side control includes AC side current control, AC side voltage control or torque and rotation speed control; the MMC modulation mode can adopt a carrier modulation mode or a step wave modulation mode, the isolation combination level control is synchronous open-loop signal control of a full-bridge structure cascaded with the sub-modules by adopting a given duty ratio and frequency, and the control of the low-voltage output end of the high-frequency alternating-current bus comprises synchronous control of a voltage clamping type port and phase-shifting control of a power controllable type port.
One specific control loop is shown in fig. 9: the output voltage of the DC side is given value UMdcrSubtracting the actual voltage output value UMdcThe difference is modulated by a PI regulator, and the output value of the modulation and the component i of the input current on the d axisdPerforming PI regulation to obtain the component u of the output value and the input voltage on the d axisdAdding and subtracting a component i of the input current in the q axisqThe output value multiplied by omega L realizes the pair idThe feed forward decoupling of (1); given value i of q-axis component of output currentqrSubtracting the component i of the actual input current in the q-axisqAdding the output value after PI regulation to the component of the input voltage in the q axis, and subtracting the component i of the input current in the d axisdOutput value multiplied by ω LTo i is realizedqThe feed forward decoupling of (1); the decoupling value of the step is converted by dq/abc to obtain a three-phase modulation wave urefThe three-phase modulation wave obtains a driving signal S of a half-bridge and capacitor structure through a carrier phase-shifting modulation strategysm(ii) a The full-bridge structure of the isolation combination unit is controlled by open-loop PWM (pulse-width modulation), and a full-bridge first power switch tube Q1And a second power switch tube Q2The driving signals are complementary, the first power switch tube Q1And a third power switch tube Q3The driving signals are the same, and the second power switch tube Q2And a fourth power switch tube Q4The driving signals are the same, all full-bridge structures in all the isolation combination units are driven synchronously and are driving signals with the frequency f and the duty ratio D fixed to 50%; the output end of the high-frequency alternating current bus synchronization unit adopts synchronous control, the full bridge of the synchronization unit adopts an open-loop PWM modulation mode which is the same as that of the full bridge in the isolation combination unit, and the corresponding switch tube driving signals are the same. The output end of the high-frequency alternating-current bus phase-shifting unit adopts phase-shifting control, and a phase-shifting angle F exists between a driving signal of a full bridge of the phase-shifting unit and a driving signal of the full bridge in the isolation combined unit1Setting the low-voltage DC output voltage to a given value ULdcrSubtracting the actual value U of the low-voltage DC output voltageLdcObtaining phase shift angle through PI regulator, obtaining control signal through amplitude limiting control, obtaining drive signal S of full-bridge structure of phase shift unit through PWM modulationSFBL(ii) a According to the invention, due to the structural characteristics of HFAC, the natural elimination of the MMC bridge arm 2 frequency multiplication circulating current can be realized, so that a bridge arm 2 frequency multiplication circulating current suppression strategy does not need to be designed.
According to the invention, an MMC-based high-frequency alternating-current bus electric energy routing topological structure is connected with an isolation combination unit formed by a full-bridge transformer and a four-winding transformer in a cascading manner behind an MMC sub-module, and secondary side windings of the four-winding high-frequency isolation transformer in the isolation combination unit are connected in parallel to form HFAC. HFAC provides a path and a neutral point for MMC-level symmetrical fluctuating power and unbalanced power among the submodules, the fluctuating power is mutually offset by utilizing the three symmetries, and each submodule realizes voltage clamping through the HFAC, so that the capacity value requirement is reduced, and the power density is improved. The HFAC access synchronization and phase shift unit forms two direct current ports, the conversion links required for electric energy conversion among the ports are less, and the system control is simple.
Claims (8)
1. The utility model provides a high frequency exchanges bus electric energy route structure based on MMC which characterized in that: the high-frequency isolation transformer comprises a medium-voltage transformation stage, a high-frequency isolation stage and a low-voltage stage; the medium-voltage conversion stage is a modular multilevel converter with a three-phase six-bridge arm structure and is provided with medium-voltage alternating current and direct current ports; the high-frequency isolation level comprises a full-bridge structure and a four-winding high-frequency isolation transformer, the full-bridge structure is cascaded behind the sub-module, three windings on the primary side of the four-winding high-frequency isolation transformer are respectively connected with three inter-phase transverse full bridges to form an isolation combined unit, and the secondary sides of the four-winding high-frequency isolation transformer are connected in parallel to form a high-frequency alternating current bus; the low-voltage stage comprises a two-winding high-frequency isolation transformer, a synchronization unit and a phase-shifting unit, the synchronization unit is of a full-bridge structure, the phase-shifting unit is of an inductor and a full-bridge structure, the synchronization unit and the phase-shifting unit are both connected into a high-frequency alternating current bus through the two-winding high-frequency isolation transformer, and the output end of the low-voltage stage is a voltage clamping type low-voltage direct current port and a power controllable low-voltage direct current port respectively.
2. The MMC-based high-frequency AC bus electric energy routing structure of claim 1, wherein: the medium-voltage conversion-stage modular multilevel converter is of a three-phase six-bridge-arm structure, each phase of bridge arm is equally divided into an upper bridge arm and a lower bridge arm, and the three-phase upper bridge arm respectively comprises n sub-modules and an upper bridge arm inductor Lg1、Lg3、Lg5The three-phase lower bridge arm comprises n submodules and a lower bridge arm inductor Lg2、Lg4、Lg6(ii) a The submodule comprises a first power switch tube S1A second power switch tube S2A first capacitor C, a first power switch tube S of a first submodule of each phase upper bridge arm1And a second power switch tube S2The middle point of the composition is connected with the anode of a medium-voltage direct-current bus; the second power switch tube S2Emitter of and the first power switch tube S of the next submodule1The emitting electrodes are connected; the upper bridge arm inductor Lg1、Lg3、Lg5Respectively at one end ofThe second power switch tube S of the last submodule of each phase upper bridge arm2Is connected with the three-phase upper bridge arm inductance Lg1、Lg3、Lg5The 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 Lg2、Lg4、Lg6One 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 busg2、Lg4、Lg6The other end of the first power switch tube S is respectively connected with the first power switch tube S of the first submodule of each phase of the lower half bridge arm1The emitter of (3) is connected; second power switch tube S of each phase lower half-bridge arm submodule2Emitter of (2) and first power switch tube S of next group of sub-modules1The emitting electrodes are connected; second power switch tube S of last submodule of lower half-bridge arm2Is connected with the negative pole of the medium voltage direct current bus.
3. The MMC-based high-frequency AC bus electric energy routing structure of claim 1, wherein: the isolation combination unit of the high-frequency isolation stage comprises three full-bridge structures and a four-winding high-frequency isolation transformer, wherein the full-bridge structure comprises a first power switch tube Q1A second power switch tube Q2And a third power switch tube Q3And a fourth power switch tube Q4The four-winding high-frequency transformer T comprises a first winding N1A second winding N2A third winding N3A fourth winding N4The first power switch tube S of the sub-module1Emitter and second power switch tube S2The collector electrodes are connected; one end of the first capacitor C of the submodule and the first power switch tube S1The other end of the first capacitor C of the submodule is connected with a second power switch tube S2The emitter of (3) is connected; the first power switch tube S of the sub-module1Collector and full-bridge first power switch tube Q1Collector and third power switch tube Q3The collector electrodes are connected; the second power switch tube S of the sub-module2Emitter and full-bridge second power switch tube Q2Is transmitted byPole and fourth power switch tube Q4The emitting electrodes are connected; the full-bridge first power switch tube Q1Emitter and second power switch tube Q2The collector electrodes are connected; the full-bridge third power switch tube Q3Emitter of and fourth power switch tube Q4The collector electrodes are connected; the first winding N1The same name end of the first power switch tube Q is connected to a first power switch tube Q of an A-phase full-bridge structure in three full-bridge structures at the same transverse positiona1And a second power switch tube Qa2The middle point of the bridge arm formed by the first winding N1The different name end of the third power switch tube Q is connected with the full-bridge structurea3And a fourth power switch tube Qa4The middle point of the bridge arm; the second winding N2The same-name end of the first power switch tube Q is connected to a B-phase full-bridge structure in three full-bridge structures at the same transverse positionb1And a second power switch tube Qb2The middle point of the bridge arm formed by the second winding N2The different name end of the third power switch tube Q is connected with the full-bridge structureb3And a fourth power switch tube Qb4The middle point of the bridge arm; the third winding N3The same-name end of the first power switch tube Q is connected to a C-phase full-bridge structure in three full-bridge structures at the same transverse positionc1And a second power switch tube Qc2The middle point of the bridge arm formed by the third winding N3The different name end of the third power switch tube Q is connected with the full-bridge structurec3And a fourth power switch tube Qc4The middle point of the bridge arm; the first, second and third windings are positioned on the primary side of the isolated four-winding high-frequency transformer, the fourth winding is positioned on the secondary side, and the transformation ratio of the three windings on the primary side is 1:1:1, determining the transformation ratio of the fourth winding to the primary side three windings according to the application condition; and the fourth windings of all the four-winding high-frequency isolation transformers are connected in parallel to form a high-frequency alternating current bus.
4. The MMC-based high-frequency AC bus electric energy routing structure of claim 1, wherein: the low-voltage-level synchronous unit and the phase-shifting unit are connected with a high-frequency alternating current bus through a two-winding high-frequency isolation transformerLines form a low voltage dc port; the synchronous unit comprises a first power switch tube Qs1A second power switch tube Qs2And a third power switch tube Qs3And a fourth power switch tube Qs4A first capacitor CsThe first power switch tube Qs1Emitter and second power switch tube Qs2The collector electrodes are connected; the third power switch tube Qs3Emitter of and fourth power switch tube Qs4The collector electrodes are connected; the first power switch tube Qs1Collector and third power switch tube Qs3The collector electrodes are connected; the second power switch tube Qs2Emitter of and fourth power switch tube Qs4The emitting electrodes are connected; the first capacitor CsIs connected to the third power switch tube Qs3The other end of the collector is connected to a fourth power switch tube Qs4An emitter of (1);
two ends of a primary side winding of the two-winding high-frequency isolation transformer are connected with a high-frequency alternating current bus, and one end of a secondary side winding is connected to a first power switch tube Q and a second power switch tube Q of the synchronous units1、Qs2The middle point of the bridge arm and the other end of the bridge arm are connected to a third power switch tube Q and a fourth power switch tube Qs3、Qs4The midpoint of the bridge arm; the phase shift unit comprises a first power switch tube Qsc1A second power switch tube Qsc2And a third power switch tube Qsc3And a fourth power switch tube Qsc4A first inductor L and a first capacitor Csc(ii) a The first power switch tube Qsc1Emitter and second power switch tube Qsc2The collector electrodes are connected; the third power switch tube Qsc3Emitter of and fourth power switch tube Qsc4The collector electrodes are connected; the first power switch tube Qsc1Collector and third power switch tube Qsc3The collector electrodes are connected; the second power switch tube Qsc2Emitter of and fourth power switch tube Qsc4The emitting electrodes are connected; the first capacitor CscIs connected to the third power switch tube Qsc3The other end of the collector is connected to a fourth power switch tube Qsc4An emitter of (1); the first electricityOne end of the inductor L is connected to the first power switch tube Qsc1And a second power switch tube Qsc2The other end of the middle point of the bridge arm is connected to one end of a secondary side winding of the two-winding high-frequency isolation transformer; two ends of a primary side winding of the two-winding high-frequency isolation transformer are connected with a high-frequency alternating current bus, one end of a secondary side winding is connected to a first inductor L of the phase shifting unit, and the other end of the secondary side winding is connected to a third power switching tube Q and a fourth power switching tube Q of the phase shifting unitsc3、Qsc4The midpoint of the bridge arm.
5. The MMC-based high-frequency AC bus electric energy routing structure of claim 1, wherein: 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 the fundamental frequency component i in the fluctuating current of the submodule corresponding to the upper bridge arm and the lower bridge arm in the MMCf-ua、if-ub、if-ucAnd if-da、if1-db、if-dcOpposite phase, 2 multiplied frequency component i2f-ua、i2f-ub、i2f-ucAnd i2f-da、i2f-db、i2f-dcThe phases are the same, fundamental frequency components and 2 frequency multiplication components among the submodules corresponding to the three phases are in positive sequences and negative sequences, and the three-phase symmetrical characteristic is realized; an equivalent model is established for a high-frequency alternating current bus structure, the input side of the high-frequency alternating current bus is equivalent to a three-phase controlled current source parallel capacitor, and the leakage inductances of primary side windings of a transformer are respectively Lla、Llb、Llc(ii) a The reactance on the secondary side and the low-voltage side of the HFAC is equivalent to Zreq(ii) a The high-frequency alternating-current bus provides a flowing channel for the fluctuation power of the MMC three-phase sub-module through the isolation combination unit and is equivalent to a neutral point, the fluctuation power has three-phase symmetry, so that the fluctuation power can be mutually offset at the high-frequency alternating-current bus, and meanwhile, 2-frequency multiplication circulating current in a bridge arm is naturally eliminated.
6. A control strategy of a high-frequency alternating current bus power routing structure based on MMC as claimed in any of claims 1-5, characterized in that: the method comprises the steps of medium-voltage conversion level AC/DC conversion control, high-frequency isolation level control and control of a low-voltage output end of a high-frequency alternating-current bus; the medium-voltage conversion stage AC/DC conversion control is to realize AC/DC conversion of MMC by adopting closed-loop control, the closed-loop control comprises direct-current side control and alternating-current side control, the direct-current side control adopts direct-current voltage control or power loop control, and the alternating-current side control comprises alternating-current side current control, alternating-current side voltage control or torque and rotation speed control; the MMC modulation mode adopts a carrier modulation mode or a step wave modulation mode, the high-frequency isolation level control is that the full-bridge structure of the submodule cascade is controlled by a synchronous open-loop signal with a given duty ratio and frequency, and the control of the low-voltage output end of the high-frequency alternating current bus comprises the synchronous control of a voltage clamping port and the phase-shifting control of a power controllable port.
7. The MMC-based control strategy for a high-frequency AC bus power routing structure of claim 6, wherein: the specific method for controlling the high-frequency isolation stage is to isolate a first power switch tube Q in a full-bridge structure of the combined unit1And a second power switch tube Q2The driving signals are complementary, the first power switch tube Q1And a third power switch tube Q3The driving signals are the same, and the second power switch tube Q2And a fourth power switch tube Q4The driving signals are the same, all full-bridge structures in all the isolation combination units are driven synchronously, the full-bridge structures are driving signals with the frequency f and the duty ratio D of 50%, and open-loop PWM modulation is adopted.
8. The MMC-based control strategy for a high-frequency AC bus power routing structure of claim 6, wherein: the control scheme of the low-voltage output end of the high-frequency alternating-current bus comprises the following steps:
1) the synchronous unit of the voltage clamp type port adopts synchronous control, and the full bridge of the synchronous unit adopts an open-loop PWM modulation mode which is the same as that of the full bridge in the isolation combination unit;
2) the phase-shifting unit of the power controllable port adopts phase-shifting control, and a phase-shifting angle exists between the driving signal of the full bridge of the phase-shifting unit and the driving signal of the full bridge in the isolation combination unitjOutput low voltage DCGiven voltage value ULdcrSubtracting the actual value U of the low-voltage DC output voltageLdcThe phase shift angle is obtained by a PI regulatorjAnd obtaining a control signal through amplitude limiting control, and obtaining a driving signal of the full-bridge structure of the phase-shifting unit through PWM modulation.
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| CN115276434A (en) * | 2022-01-28 | 2022-11-01 | 昆明理工大学 | Electric energy router containing full-bridge submodule and control method thereof |
| CN117748953A (en) * | 2024-01-17 | 2024-03-22 | 山东艾诺智能仪器有限公司 | High-power high-frequency four-quadrant power supply and control method thereof |
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| CN115276434B (en) * | 2022-01-28 | 2024-04-26 | 昆明理工大学 | Electric energy router with full-bridge submodule and control method thereof |
| CN117748953A (en) * | 2024-01-17 | 2024-03-22 | 山东艾诺智能仪器有限公司 | High-power high-frequency four-quadrant power supply and control method thereof |
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| CN113938038B (en) | 2024-04-12 |
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