CN115189576A - LLC resonant direct-current converter based on MMC and control strategy thereof - Google Patents

LLC resonant direct-current converter based on MMC and control strategy thereof Download PDF

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Publication number
CN115189576A
CN115189576A CN202210569288.9A CN202210569288A CN115189576A CN 115189576 A CN115189576 A CN 115189576A CN 202210569288 A CN202210569288 A CN 202210569288A CN 115189576 A CN115189576 A CN 115189576A
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bridge
full
voltage
mmc
resonant
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公铮
亓俊鹏
郑长明
戴鹏
伍小杰
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China University of Mining and Technology CUMT
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China University of Mining and Technology CUMT
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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
    • 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
    • H02M3/3353—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 at least two simultaneously operating switches on the input side, e.g. "double forward" or "double (switched) flyback" converter
    • 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
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • 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
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • 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
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
    • 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
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention discloses an LLC resonance direct current converter based on MMC, which comprises: the full-bridge MMC structure composed of full-bridge sub-modules, an LLC resonant cavity, an isolation transformer, an uncontrolled rectifying circuit and an output filter capacitor belong to the field of direct current converters; the full-bridge MMC structure adopts a quasi-square wave modulation strategy capable of boosting, the LLC resonant cavity adopts pulse frequency modulation, the converter can achieve high voltage gain under the condition of not depending on the transformation ratio of a transformer, meanwhile, small-range smooth adjustment is conducted on output voltage, the rectifier diode can achieve zero current shutoff, and the converter is suitable for application occasions such as renewable energy grid connection.

Description

LLC resonant direct-current converter based on MMC and control strategy thereof
Technical Field
The invention relates to an LLC resonant direct-current converter based on MMC and a control strategy thereof, in particular to a direct-current converter which can carry out wide-range conversion on input voltage and smoothly regulate output voltage without a transformer, and belongs to the field of direct-current converters.
Background
With the rapid development of human civilization in the world, the demand of human beings for energy is higher and higher, so that fossil energy is gradually exhausted. Renewable energy sources such as wind energy, solar energy and tidal energy have the advantages of cleanness, recyclability, no pollution and the like, are low in cost and are beneficial to sustainable development of the society, and therefore the development of renewable energy sources is an essential measure for adjusting energy structure. In order to realize the collection of large-scale renewable energy sources and simultaneously keep a power system to stably operate, a direct-current power grid is generated. The high-voltage large-capacity direct-current converter has the functions of collecting renewable energy sources and connecting direct-current power grids with different voltage levels, is one of the most core devices of the direct-current power grids, and is urgent to research the high-voltage large-capacity direct-current converter required by the construction of the direct-current power grids in order to realize the rapid development of the direct-current power grids in China. The traditional direct current converter mainly comprises a double-active-bridge converter, a resonance converter, an IPOS structure and the like, but the traditional direct current converter has the following problems: the problem of voltage sharing and current sharing usually exists between the switching devices of the double-active-bridge converter, so that the reliability of a system is reduced; the output voltage regulation range of the resonant converter is small, and the boosting is mainly completed by a transformer; the IPOS structure needs a large number of medium-frequency transformers with high insulation levels, the device is large in size, and the overhauling and maintenance difficulty is increased. Therefore, there is a need for a dc converter that can achieve a wide-range smooth regulation of output voltage without relying on a transformer.
Disclosure of Invention
The invention provides an LLC resonant direct-current converter based on MMC, which can realize wide-range smooth regulation of output voltage without depending on the transformer transformation ratio, aims to apply the field of renewable energy collection and grid connection, and has the characteristics of flexible output voltage control and large capacity.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
the LLC resonant direct-current converter based on the MMC comprises a full-bridge MMC structure consisting of full-bridge sub-modules, an LLC resonant cavity, an isolation transformer, an uncontrolled rectifying circuit and an output filter capacitor, wherein the full-bridge MMC structure comprises four bridge arms, and each bridge arm consists of x full-bridge sub-modules and a bridge arm inductor L arm The LLC resonant cavity is formed by a resonant inductor L r Resonant capacitor C r And excitation inductance L m Is formed of a resonant inductor L r Inductance L of bridge arm arm The isolation transformer is an intermediate frequency transformer with the transformation ratio of 1 and plays a role in fault isolation, the uncontrolled rectifier circuit is composed of a rectifier diode, and the output filter capacitor plays a role in maintaining output voltage.
Furthermore, the full-bridge MMC structure adopts a boost quasi square wave modulation strategy to boost the input voltage and realize large-range coarse adjustment by using a formula n = ((U =) oref /U dc ) Calculating + 1)/2, rounding the calculation result to obtain the value of n, and then the working mode of the full-bridge MMC structure is n/- (n-1), wherein U oref For outputting reference voltages, U dc For direct current input voltage, n represents n full-bridge sub-modules which are positively input, and- (n-1) represents n-1 full-bridge sub-modules which are negatively input, wherein the voltage gain is 2n-1, and the capacitor voltage U of the full-bridge sub-modules c I.e. the dc input voltage U dc And a phase a upper bridge arm and a phase b lower bridge arm are specified as a first pair of crossed bridge arms, the rest are a second pair of crossed bridge arms, and the full-bridge MMC structure has the working mode that: the first pair of cross bridge arms in the first half period positively inputs n full bridge submodules, the second pair of cross bridge arms negatively inputs n-1 full bridge submodules, the working states of the two pairs of cross bridge arms in the second half period are exchanged, and the output amplitude of the alternating current side is (2 n-1) U dc When the working states of the two pairs of crossed bridge arms are exchanged, the states of the full-bridge submodules are switched according to a certain sequence, steps can be introduced into the upper edge and the lower edge of the square wave voltage, the voltage change rate is reduced, the positive input state of the full-bridge submodules is defined to be 1, the negative input state of the full-bridge submodules is defined to be-1, and the cut-off state of the full-bridge submodules is defined to be 0, when the working states of the two pairs of crossed bridge arms are exchanged, in order to ensure that the bridge arm voltage and the direct current voltage are balanced, the sum of the states of all the full-bridge submodules in each phase of bridge arm at every moment is 1, and a delay time t passes through each time under the premise d Switching the full-bridge submodule once, when the working mode of the full-bridge MMC structure is n/- (n-1), the first half period of a flag bit is 1, the second half period of the flag bit is 0, when the flag bit is changed from 1 to 0, the working state of a first pair of crossed bridge arms is changed from n to- (n-1), and the working state of a second pair of crossed bridge arms is changed from- (c) - (n-1)n-1) is changed into n, and the switching sequence of the full-bridge sub-modules is as follows: first delay time t d And the number of positive input sub-modules of the first pair of crossed bridge arms is n-2, the number of negative input sub-modules is 1, the number of removal sub-modules is 1, the number of positive input sub-modules of the second pair of crossed bridge arms is 2, the number of negative input sub-modules is n-2, and the process is repeated until the working states of all bridge arms are exchanged, and the same process is carried out when the zone bit is changed from 0 to 1. The switching principle of the full-bridge submodule is as follows: and sampling and sequencing the capacitor voltage of the full-bridge sub-modules, positively charging the full-bridge sub-modules with the lowest capacitor voltage, and negatively charging the sub-modules with the highest capacitor voltage to discharge so as to keep the balance of the capacitor voltage of the full-bridge sub-modules.
Furthermore, the LLC resonant cavity has two resonant frequencies, respectively resonant inductance L r And a resonance capacitor C r First resonant frequency of common resonance, resonant inductance L r Resonant capacitor C r And excitation inductance L m Common resonance's second resonant frequency, full-bridge MMC structure's operating frequency is restricted between two resonant frequency, utilizes the control closed loop, controls the operating frequency of full-bridge MMC structure, and then the accurate square wave voltage frequency of control output, changes LLC resonant cavity gain from this, realizes output voltage minizone smooth regulation, makes it follow output reference voltage.
Further, full-bridge MMC structure cooperates with LLC resonant cavity structure jointly, through the voltage gain of changing the mode and the operating frequency control converter of full-bridge MMC structure, the voltage gain of this converter is the product of the voltage gain and the LLC resonant cavity gain of full-bridge MMC structure promptly, carries out the wide range regulation to output voltage from this.
Compared with the prior art, the invention has the beneficial effects that:
compared with the existing high-voltage large-capacity direct-current converter, the LLC resonant direct-current converter based on the MMC can perform wide-range smooth regulation on output voltage, high-gain boosting and voltage regulation can be realized without depending on a transformer, the control on the output voltage is more flexible, and meanwhile, a secondary side rectifier diode can be turned off at zero current.
Drawings
FIG. 1 shows an LLC resonant DC-DC converter topology based on MMC
FIG. 2 shows the main operating waveforms of the converter
FIG. 3 shows three operating phases of the converter
FIG. 4 is a diagram of the actual output voltage waveform when the output reference voltage suddenly changes
FIG. 5 is a diagram of the voltage waveform of the capacitor of the full-bridge submodule
Detailed Description
The invention is further described with reference to the following figures and specific examples.
As shown in fig. 1, the LLC resonant dc-to-ac converter main circuit based on MMC comprises a full-bridge MMC structure composed of full-bridge submodules, an LLC resonant cavity, an isolation transformer, an uncontrolled rectifier circuit, and an output filter capacitor, wherein the full-bridge MMC structure is composed of a two-phase bridge arms a and b, which are divided into an upper bridge arm and a lower bridge arm, each bridge arm is composed of x full-bridge submodules and a bridge arm inductor L arm The full-bridge MMC structure adopts a boost quasi square wave modulation strategy. LLC resonant cavity is composed of resonant inductor L r Resonant capacitor C r And excitation inductance L m Is formed of a resonant inductor L r Inductance L of bridge arm arm And the LLC resonant cavity is modulated by pulse frequency. The uncontrolled rectifier circuit is composed of four rectifier diodes, and zero current turn-off can be realized. The isolation transformer is a medium-frequency transformer with the transformation ratio of 1 and plays a role in fault isolation. The full-bridge MMC structure boosts the input voltage and realizes large-range coarse adjustment, the LLC resonant cavity carries out small-range smooth adjustment on the input voltage by changing the working frequency of the full-bridge MMC structure, the converter adopts frequency closed-loop control, and the coarse adjustment and the fine adjustment of the full-bridge MMC structure are combined to realize wide-range smooth adjustment of the output voltage.
The converter can calculate the working mode of the full-bridge MMC structure according to the output reference voltage by using the formula n = ((U) oref /U dc ) + 1)/2 calculation, in which the reference voltage U is output oref 12.6kV in the first 5 seconds and 8.8kV in the last 5 seconds, and a DC input voltage U dc 1.5kV, rounding off the calculation to a value of n of 4 in the first 5 seconds,the last 5 seconds are 3, the first 5 seconds of the working mode of the full-bridge MMC structure are 4/-3, the gain is 7, and the input voltage U is realized dc And large-range coarse adjustment is carried out, and the LLC resonant cavity carries out small-range fine adjustment on the input voltage by controlling the closed loop. The positive input state, the negative input state and the cut-off state of a single full-bridge submodule are respectively recorded as 1, -1 and 0, 4 represents that 4 full-bridge submodules are positively input, 3 represents that 3 full-bridge submodules are negatively input, and the capacitor rated voltage U of the full-bridge submodule is at the moment c For a DC input voltage U dc 3/-2 are the same and will not be described further. And the phase a upper bridge arm and the phase b lower bridge arm are specified as a first pair of crossed bridge arms, the rest are a second pair of crossed bridge arms, and the working modes of the full-bridge MMC structure are as follows: the flag bit of the first half cycle is 1, the first pair of crossed bridge arms positively inputs 4 full-bridge submodules, the second pair of crossed bridge arms negatively inputs 3 full-bridge submodules, the flag bit of the second half cycle is 0, the working states of the two pairs of crossed bridge arms are exchanged, and the output amplitude of the alternating current side is 7U dc The voltage gain of the square wave voltage of (2), i.e. the full bridge MMC structure, is 7. In order to reduce the voltage change rate and reduce the insulation design difficulty of the isolation transformer, steps are introduced to the upper edge and the lower edge of the square wave voltage output at the alternating current side.
The specific method for generating the voltage step comprises the following steps: when the working states of two pairs of crossed bridge arms are exchanged, the states of the full-bridge submodules are switched according to a certain sequence, and meanwhile, the balance between the bridge arm voltage and the direct current voltage needs to be ensured, namely the sum of the states of all the full-bridge submodules in each phase of bridge arm at each moment is 1, and in the premise, a delay time t passes each time d And carrying out one-time switching on the full-bridge submodule. When the zone bit is changed from 1 to 0, the working state of the first pair of crossed bridge arms is changed from n to-3, the working state of the second pair of crossed bridge arms is changed from-3 to 4, and the switching sequence of the full-bridge sub-modules is as follows: first delay time t d In the method, the number of positive input submodules of a first pair of crossed bridge arms is 3, the number of excision submodules is 1, the number of positive input submodules of a second pair of crossed bridge arms is 1, the number of negative input submodules is 3, and a second delay time t d In the method, the number of positive input sub-modules of the first pair of crossed bridge arms is 2, the number of negative input sub-modules is 1, the number of excision sub-modules is 1, and the number of positive input sub-modules of the second pair of crossed bridge arms is 2The number is 2, the number of the negative input sub-modules is 2, and so on until the working states of all bridge arms are exchanged, the same process is carried out when the zone bit is changed from 0 to 1.
The switching principle of the full-bridge submodule is as follows: and (3) sampling and sequencing the capacitor voltage of the full-bridge sub-modules, positively charging the full-bridge sub-modules with the lowest capacitor voltage, and negatively charging the sub-modules with the highest capacitor voltage to discharge so as to keep the balance of the capacitor voltage of the full-bridge sub-modules, wherein the capacitor voltage of the full-bridge sub-modules is shown in fig. 5.
The operating waveforms of an LLC resonant DC-DC converter based on MMC are shown in FIG. 2, where u ac Outputting AC side quasi square wave voltage U for full-bridge MMC structure ac ，i r Is a current flowing through the resonant inductor L r Resonant current of i m For passing through the excitation inductance L m Excitation current of i D1 Is flowed through D 1 Current of the rectifier diode, i D2 Is flowed through D 2 Rectifying the diode current, the converter operates between a first resonant frequency and a second resonant frequency in three operating phases as shown in fig. 3. Assuming that all elements in the circuit are ideal elements, the output capacitor C o Is large enough to be approximately equivalent to a constant voltage source, neglecting the output voltage U o Ripple, ignoring all losses in the circuit.
Stage one (t) 0 ～t 1 ): at this time, the exciting current is equal to the resonant current, and the full-bridge MMC structure outputs active power to the alternating current side due to the exciting inductance L m The inductance value is larger, the resonance current can be regarded as approximately constant, and the excitation inductance L is at the moment m The voltage at both ends is no longer clamped by the output voltage, and the resonant inductor L r Resonant capacitor C r And an excitation inductance L m Common resonance, zero current turn-off by secondary side diode, C o And the output voltage is kept unchanged when the load is powered.
Stage two (t) 1 ～t 2 ): at the moment, the full-bridge MMC structure outputs alternating current quasi square wave voltage U ab For a DC input voltage U dc Resonant current i r With excitation current i m Starting to rise, resonant inductance L r And a resonance capacitor C r Common resonance, transformer rectificationCurrent side output power, secondary side diode D 1 And D 4 Conduction, L m The voltage at both ends is clamped to U by the output voltage o 。
Stage three (t) 2 ～t 3 ): at this time, the exciting current i m Equal to the resonant current i r Full-bridge MMC structure outputs active power to alternating current side due to L m The inductance value is larger, the resonance current can be regarded as approximately constant, and the excitation inductance L is at the moment m The voltage at both ends is no longer clamped by the output voltage, L r 、C r And L m Common resonance, the secondary side diode realizes zero current turn-off, C o And the output voltage is kept unchanged when the load is powered.
t 3 At the moment, the switching states of all bridge arms are exchanged, and the alternating-current side quasi square wave voltage U is ac And when the value becomes a negative value, the system enters the next half working period, the principle of the system is completely the same as that of the first half working period, and the modes are symmetrical, so that the details are not repeated. As can be seen from fig. 4, the converter can follow the output reference voltage more accurately.
The invention provides an LLC resonant direct-current converter based on MMC, which can realize high-gain boosting and wide-range smooth regulation of output voltage without depending on a transformer, has a wider voltage regulation range compared with the traditional direct-current converter, can realize zero-current turn-off of a secondary rectifier diode, and is suitable for application occasions such as renewable energy grid connection and the like.

Claims (5)

1. The LLC resonant direct-current converter based on MMC and the control strategy thereof are characterized in that: the converter comprises a full-bridge MMC structure consisting of full-bridge submodules, an LLC resonant cavity, an isolation transformer, an uncontrolled rectifying circuit and an output filter capacitor, wherein the full-bridge MMC structure comprises four bridge arms, and each bridge arm consists of x full-bridge submodules and a bridge arm inductor L arm The LLC resonant cavity consists of a resonant inductor L r Resonant capacitor C r And excitation inductance L m Is formed of a resonant inductor L r Inductance L of bridge arm arm The isolation transformer is an intermediate frequency transformer with the transformation ratio of 1, and has the function of fault isolation and uncontrolledThe rectifying circuit is composed of a rectifying diode, and the output filter capacitor plays a role in maintaining output voltage.
2. An LLC resonant dc-dc converter based on MMC and a control strategy therefor as claimed in claim 1, wherein: the full-bridge MMC structure adopts the quasi-square wave modulation strategy that can step up, and the LLC resonant cavity adopts pulse frequency modulation, and the full-bridge MMC structure steps up and realizes coarse adjustment on a large scale input voltage, and the LLC resonant cavity carries out the fine setting of minivered range through adjusting frequency to input voltage, adopts frequency closed loop control, and both coarse and fine settings combine to make output voltage follow output reference voltage.
3. An LLC resonant dc-dc converter based on MMC and a control strategy therefor as claimed in claim 2, wherein: the operation mode of the full-bridge MMC structure can be calculated according to the output reference voltage by using the formula n = ((U) oref /U dc ) Calculating + 1)/2, rounding the calculation result to obtain the value of n, and obtaining the working mode n/(n-1) of the full-bridge MMC structure, wherein U oref For outputting reference voltages, U dc For direct current input voltage, n represents n full-bridge sub-modules which are positively input, and- (n-1) represents n-1 full-bridge sub-modules which are negatively input, wherein the voltage gain is 2n-1, and the capacitor voltage U of the full-bridge sub-modules c I.e. the dc input voltage U dc And a phase a upper bridge arm and a phase b lower bridge arm are defined as a first pair of crossed bridge arms, the rest are a second pair of crossed bridge arms, and the working mode of the full-bridge submodule is as follows: the first pair of crossed bridge arms in the first half period are positively charged with n full-bridge submodules, the second pair of crossed bridge arms are negatively charged with n-1 full-bridge submodules, the working states of the two pairs of crossed bridge arms in the second half period are exchanged, and the output amplitude of the alternating current side is (2 n-1) U dc When the working states of the two pairs of crossed bridge arms are exchanged, the state of the full-bridge submodule is switched according to a certain sequence, steps can be introduced into the upper edge and the lower edge of the square wave voltage output from the alternating current side, the voltage change rate is reduced, the square wave voltage is called as scalable quasi-square wave modulation, the LLC resonant cavity has two resonant frequencies which are respectively a resonant inductor L r And a resonance capacitor C r First resonant frequency of common resonance, resonant inductance L r Resonant capacitor C r And excitation inductance L m Common resonance's second resonant frequency, the operating frequency restriction of full-bridge MMC structure utilizes the control closed loop between two resonant frequency, controls the operating frequency of full-bridge MMC structure, and then control output accurate square wave voltage frequency, changes LLC resonant cavity gain from this, realizes output voltage minizone smooth regulation, makes it follow output reference voltage.
4. The LLC resonant DC converter and control strategy thereof as claimed in claim 3, wherein: the positive input state, the negative input state and the cut-off state of the full-bridge submodule are specified to be 1, the negative input state and the cut-off state are specified to be 0, when the working states of two pairs of crossed bridge arms are exchanged, in order to ensure that the bridge arm voltage and the direct current voltage are balanced, the sum of the states of all the full-bridge submodules in each phase of bridge arm at each moment is 1, and in the premise, a delay time t passes each time d When the operating mode of the full-bridge MMC structure is n/- (n-1), the first half period of a flag bit is 1, the second half period of the flag bit is 0, when the flag bit is changed from 1 to 0, the operating state of a first pair of cross bridge arms is changed from n to- (n-1), the operating state of a second pair of cross bridge arms is changed from- (n-1) to n, and the switching sequence of the full-bridge submodule is as follows: first delay time t d The number of positive input submodules of the first pair of cross bridge arms is n-1, the number of cut-off submodules is 1, the number of positive input submodules of the second pair of cross bridge arms is 1, the number of negative input submodules is n-1, and the second delay time t d And in the method, the number of positive input sub-modules of the first pair of crossed bridge arms is n-2, the number of negative input sub-modules is 1, the number of removal sub-modules is 1, the number of positive input sub-modules of the second pair of crossed bridge arms is 2, the number of negative input sub-modules is n-2, and the like is repeated until the working states of all bridge arms are completely exchanged.
5. An LLC resonant DC converter and control strategy thereof according to claim 3 or 4, characterized in that: when the full-bridge MMC structure normally works, full-bridge submodule capacitor voltage is sampled, sequenced and switched at the frequency of 10kHz, the full-bridge submodule with the lowest capacitor voltage is positively switched into charge, and the full-bridge submodule with the highest capacitor voltage is negatively switched into discharge, so that the balance of the full-bridge submodule capacitor voltage is kept.
CN202210569288.9A 2022-05-24 2022-05-24 LLC resonant direct-current converter based on MMC and control strategy thereof Pending CN115189576A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115483841A (en) * 2022-10-19 2022-12-16 浙江大学杭州国际科创中心 Voltage ratio adjusting method and related assembly

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115483841A (en) * 2022-10-19 2022-12-16 浙江大学杭州国际科创中心 Voltage ratio adjusting method and related assembly
CN115483841B (en) * 2022-10-19 2024-05-28 浙江大学杭州国际科创中心 Voltage transformation ratio adjusting method and related assembly

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