CN105790619A - Power-adaption capacitance-voltage balance control method for MMC sub-modules - Google Patents

Power-adaption capacitance-voltage balance control method for MMC sub-modules Download PDF

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Publication number
CN105790619A
CN105790619A CN201610008110.1A CN201610008110A CN105790619A CN 105790619 A CN105790619 A CN 105790619A CN 201610008110 A CN201610008110 A CN 201610008110A CN 105790619 A CN105790619 A CN 105790619A
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China
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submodule
brachium pontis
voltage
individual
excision
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CN201610008110.1A
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CN105790619B (en
Inventor
王业
高磊
李鹏
李群
袁宇波
管益斌
徐宁
肖学权
汪萍
周卫
易新
曹海欧
杜云龙
黄浩声
卜强生
孔祥平
林金娇
宋亮亮
杨毅
宋爽
黄哲晨
弓新月
庞福滨
张星宇
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State Grid Corp of China SGCC
State Grid Jiangsu Electric Power Co Ltd
Electric Power Research Institute of State Grid Jiangsu Electric Power Co Ltd
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State Grid Corp of China SGCC
State Grid Jiangsu Electric Power Co Ltd
Electric Power Research Institute of State Grid Jiangsu Electric Power Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • 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
    • 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
    • H02M7/4835—Converters with outputs that each can have more than two voltages levels comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage
    • 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
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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

Abstract

The invention discloses a power-adaption capacitance-voltage balance control method for MMC sub-modules. A framework is located on a modular multilevel converter employing the nearest level approach modulation strategy; and the strategy can be applied to valve base control of the modular multilevel converter included in engineering of flexible DC transmission, a unified power flow controller and the like. Compared with a traditional switching strategy, the control method has the advantages that the switching frequency of sub-module IGBTs can be greatly reduced under the condition of basically not increasing the voltage fluctuation of the sub-modules, and the service lifetime of the IGBTs is prolonged. The algorithm can adaptively change the switching strategy for the sub-modules according to the change of the transmission power, so that the capacitance-voltage fluctuation magnitudes of the sub-modules are always kept within a fixed range; the switching frequency of the sub-module IGBTs can be reduced at the proper time; and the service lifetime of the sub-module IGBTs is prolonged.

Description

The MMC submodule capacitor voltage balance control method of power adaptive
Technical field
The present invention relates to the MMC submodule capacitor voltage balance control method of a kind of power adaptive, belong to technical field of power systems.
Background technology
In view of the deficiency that existing traditional multi-level changer exists in higher applied voltage grade, active power transfer occasion etc., modular multilevel technology (MMC) is just becoming the study hotspot in high pressure many level field with the structure of its uniqueness and technical advantage.Compared with traditional multi-level changer, it inherits tradition Cascade Topology Structure advantage in number of devices, modular construction, the active power conversion occasion constant suitable in ac output frequency, voltage and power grade requirement is high, MMC has many structures suitable in high-power application scenario and output characteristic.
In Practical Project, tradition submodule grading ring joint generally select will submodule capacitor voltage sort after put into or excise the strategy of corresponding submodule according to bridge arm current set direction, it controls target and is: each submodule voltage deviation can both be kept at any time minimum.But it has two shortcomings: 1, when carrying active power change, adopt traditional algorithm that submodule capacitor voltage fluctuation can be caused to change along with the change of transmission power, when conveying is gained merit bigger, submodule capacitor voltage fluctuation also can be relatively big, be unfavorable for system stable operation and loop current suppression；2, this method does not account for the on off operating mode that submodule is original, simply by each submodule of frequent switching, reduces the voltage deviation of each submodule to greatest extent, so it can cause significantly high IGBT switching loss.
Summary of the invention
Purpose: in order to overcome the deficiencies in the prior art, the present invention provides the MMC submodule capacitor voltage balance control method of a kind of power adaptive.
Technical scheme: for solving above-mentioned technical problem, the technical solution used in the present invention is:
The MMC submodule capacitor voltage balance control method of a kind of power adaptive, it is characterised in that be framed in adopting nearest level to approach on the modularization multi-level converter of modulation strategy；(being introduced for A phase, the biphase step of B, C is identical with A phase), comprises the following steps:
Step 1) detect upper brachium pontis all submodule capacitor voltage maximum fluctuation value δ U and additive regulating submodule Ns numerical value in 3 power frequency periods respectively:
(1) if δ is U < ZminUNAnd Ns > 0 and Ns numerical value did not change within 1s, then perform Ns=Ns-1；
(2) if δ is U > ZmaxUNAnd Ns < N and Ns numerical value did not change within 1s, then perform Ns=Ns+1；
(3) if (1) (2) are all unsatisfactory for, then Ns numerical value is constant；
Step 2) detect when previous step is long brachium pontis, submodule number that lower brachium pontis has been put into and the submodule number that do not put into, if upper brachium pontis, the submodule number that lower brachium pontis has been put into and the submodule number not put into are not all 0, then perform step 3) to step 6), if upper brachium pontis, the submodule number that lower brachium pontis has been put into and the submodule number not put into have one to be 0, then perform special handling；
Step 3) obtain upper brachium pontis respectively, submodule that lower brachium pontis has been put into and each submodule instantaneous voltage of not putting into, upper brachium pontis, submodule voltage that lower brachium pontis has been put into and the submodule voltage not put into are ranked up respectively, form four sub-sequence of modules；
Step 4) these four sub-sequence of modules are processed, retrieve the submodule sequence being ready for putting into or excising eight groups new；
Step 5) according to this step-length time modulating wave voltameter calculate the submodule number that this step-length upper and lower bridge arm should put into respectively, calculate this step-length step-length relative last time with the submodule number not put into further according to the previous step submodule number that time long, upper brachium pontis, lower brachium pontis have been put into needs put into or the submodule quantity of many excisions more；
Step 6) from submodule sequence eight groups new, determine that the concrete submodule needing to put into or excise is numbered according to bridge arm current direction and self adaptation Switching Strategy, carry out putting into or excising；
Step 7) submodule number that upper brachium pontis, lower brachium pontis previous step length have been put into be zero or the submodule number that do not put into carry out special handling when being zero.
Step 1) in, capacitance voltage maximum fluctuation value δ U refers to the difference of all submodule voltage max of the upper and lower brachium pontis of A phase and voltage minimum in 3 cycles, and Ns refers to the quantity that this step-length additive regulating submodule sets.
Step 2) in, upper brachium pontis when detecting a step-length respectively, the submodule number that lower brachium pontis has been put into and the submodule number not put into refer to the submodule number n detecting that brachium pontis has been put intopyThe submodule number n not put intopw, submodule number n that lower brachium pontis has been put intonyThe submodule number n not put intonw。
Step 3) in, form four collated submodule sequences and respectively go up the submodule sequence X that brachium pontis has put intopyThe submodule sequence X not put intopw, submodule sequence X that lower brachium pontis has put intonyThe submodule sequence X not put intonw。
Step 4) in, retrieve eight groups of submodule sequences being ready for putting into or excising and refer to:
(1) by XpyThe submodule that middle voltage is the highest takes out, and puts X intopwIn, rearrangement, ultimately form sequence Xpgin；
(2) by XpyThe submodule that middle voltage is minimum takes out, and puts X intopwIn, rearrangement, ultimately form sequence Xpdin；
(3) by XnyThe submodule that middle voltage is the highest takes out, and puts X intonwIn, rearrangement, ultimately form sequence Xngin；
(4) by XnyThe submodule that middle voltage is minimum takes out, and puts X intonwIn, rearrangement, ultimately form sequence Xndin；
(5) by XpwThe submodule that middle voltage is the highest takes out, and puts X intopyIn, rearrangement, ultimately form sequence Xpgout；
(6) by XpwThe submodule that middle voltage is minimum takes out, and puts X intopyIn, rearrangement, ultimately form sequence Xpdout；
(7) by XnwThe submodule that middle voltage is the highest takes out, and puts X intonyIn, rearrangement, ultimately form sequence Xngout；
(8) by XnwThe submodule that middle voltage is minimum takes out, and puts X intonyIn, rearrangement, ultimately form sequence Xndout。
Step 5) in,
The submodule number that this step-length of upper brachium pontis should put into utilizes formulaCalculate, n in formulaupRepresenting in this step-length the submodule number that should put into that brachium pontis calculates according to modulating wave voltameter, N represents the submodule number of the total input of upper and lower bridge arm, UrefRepresent modulating wave instantaneous voltage, UcRepresent submodule capacitor voltage；
The submodule number that lower this step-length of brachium pontis should put into utilizes formulaCalculate, n in formuladownRepresent the submodule number that should put into that in this step-length, lower brachium pontis calculates according to modulating wave voltameter；
Then this upper and lower bridge arm should put into or excise several submodule nupAnd ndownThe submodule quantity having been put into upper and lower bridge arm in last time step-length and the submodule quantity not put into carry out contrast and can draw: (1) if nup-npy=m (m > 0), it was shown that upper brachium pontis needs to put into m submodule；(2) if nup-npy=m (m < 0), shows that upper brachium pontis needs m submodule of excision；(3) if nup-npy=0, it was shown that upper brachium pontis need not put into or excise submodule, then the triggering pulse that valve is sent by this step-length is same with previous step appearance；Lower brachium pontis is with upper brachium pontis in like manner；Subsequent step 5 is performed again in (1) (2) two kinds of situations), in (3) situation, then wait that next step-length returns step 1 when arriving).
Step 6) in, Switching Strategy refers to:
(1) when upper brachium pontis needs to put into submodule m, N is carried outSNumerical value judges, if NS>npy, then N is madeS=npy, otherwise NSNumerical value is constant, carries out logical judgment again, when upper bridge arm current is be more than or equal to 0, then from XpyMiddle excision NsThe submodule that individual voltage is the highest, simultaneously from XpginIn choose the m+N that voltage is minimumsIndividual submodule puts into (due to from XpyBefore middle excision submodule, XpginJust formed, so if be detected that XpginThe middle submodule needing to put into comprises XpyMiddle that N preparing excisionsIndividual submodule, then for this NsIndividual submodule does not carry out excising and putting into operation)；
(2) when upper brachium pontis needs to put into submodule m, N is carried outSNumerical value judges, if NS>npy, then N is madeS=npy, otherwise NSNumerical value is constant, carries out logical judgment again, when upper bridge arm current is less than 0, then from XpyMiddle excision NsThe submodule that individual voltage is minimum, simultaneously from XpdinIn choose the m+N that voltage is the highestsIndividual submodule puts into (due to from XpyBefore middle excision submodule, XpdinJust formed, so if be detected that XpdinThe middle submodule needing to put into comprises XpyMiddle that N preparing excisionsIndividual submodule, then for this NsIndividual submodule does not carry out excising and putting into operation)；
(3) brachium pontis needs to put into submodule m instantly, carries out NSNumerical value judges, if NS>nny, then N is madeS=nny, otherwise NSNumerical value is constant, carries out logical judgment again, when bridge arm current is be more than or equal to 0 instantly, then from XnyMiddle excision NsThe submodule that individual voltage is the highest, simultaneously from XnginIn choose the m+N that voltage is minimumsIndividual submodule puts into (due to from XnyBefore middle excision submodule, XnginJust formed, so if be detected that XnginThe middle submodule needing to put into comprises XnyMiddle that N preparing excisionsIndividual submodule, then for this NsIndividual submodule does not carry out excising and putting into operation)；
(4) brachium pontis needs to put into submodule m instantly, carries out NSNumerical value judges, if NS>nny, then N is madeS=nny, otherwise NSNumerical value is constant, carries out logical judgment again, when bridge arm current is less than 0 instantly, then from XnyMiddle excision NsThe submodule that individual voltage is minimum, simultaneously from XndinIn choose the m+N that voltage is the highestsIndividual submodule puts into (due to from XnyBefore middle excision submodule, XndinJust formed, so if be detected that XndinThe middle submodule needing to put into comprises XnyMiddle that N preparing excisionsIndividual submodule, then for this NsIndividual submodule does not carry out excising and putting into operation)；
(5) when upper brachium pontis needs excision submodule m, N is carried outSNumerical value judges, if NS>npw, then N is madeS=npw, otherwise NSNumerical value is constant, carries out logical judgment again, when upper bridge arm current is be more than or equal to 0, then from XpwIn find out NsThe submodule that individual voltage is minimum, is fed into XpyIn, simultaneously from XpdoutIn choose the m+N that voltage is the highestsThe excision of individual submodule is (due to XpyBefore middle input submodule, XpdoutJust formed, so if be detected that XpdoutThe middle submodule needing excision comprises XpwMiddle preparation is selected and is fed into XpyThat NsIndividual submodule, then for this NsIndividual submodule does not carry out putting into and excising operation)；
(6) when upper brachium pontis needs excision submodule m, N is carried outSNumerical value judges, if NS>npw, then N is madeS=npw, otherwise NSNumerical value is constant, carries out logical judgment again, when upper bridge arm current is less than 0, then from XpwIn find out NsThe submodule that individual voltage is the highest, is fed into XpyIn, simultaneously from XpgoutIn choose the m+N that voltage is minimumsThe excision of individual submodule is (due to XpyBefore middle input submodule, XpgoutJust formed, so if be detected that XpgoutThe middle submodule needing excision comprises XpwMiddle preparation is selected and is fed into XpyThat NsIndividual submodule, then for this NsIndividual submodule does not carry out putting into and excising operation)；
(7) brachium pontis needs excision submodule m instantly, carries out NSNumerical value judges, if NS>nnw, then N is madeS=nnw, otherwise NSNumerical value is constant, carries out logical judgment again, when bridge arm current is be more than or equal to 0 instantly, then from XnwIn find out NsThe submodule that individual voltage is minimum, is fed into XnyIn, simultaneously from XndoutIn choose the m+N that voltage is the highestsThe excision of individual submodule is (due to XnyBefore middle input submodule, XndoutJust formed, so if be detected that XndoutThe middle submodule needing excision comprises XnwMiddle preparation is selected and is fed into XnyThat NsIndividual submodule, then for this NsIndividual submodule does not carry out putting into and excising operation)；
(8) brachium pontis needs excision submodule m instantly, carries out NSNumerical value judges, if NS>nnw, then N is madeS=nnw, otherwise NSNumerical value is constant, carries out logical judgment again, when bridge arm current is less than 0 instantly, then from XnwIn find out NsThe submodule that individual voltage is the highest, is fed into XnyIn, simultaneously from XngoutIn choose the m+N that voltage is minimumsThe excision of individual submodule is (due to XnyBefore middle input submodule, XngoutJust formed, so if be detected that XngoutThe middle submodule needing excision comprises XnwMiddle preparation is selected and is fed into XnyThat NsIndividual submodule, then for this NsIndividual submodule does not carry out putting into and excising operation).
It addition, special handling refers to:
(1) when the submodule number put into when upper brachium pontis or lower brachium pontis previous step length is zero: when bridge arm current is be more than or equal to 0, then the submodule directly not put into from upper brachium pontis or lower brachium pontis chooses m the submodule input that voltage is minimum；When bridge arm current is less than 0, then the submodule directly not put into from upper brachium pontis or lower brachium pontis chooses m the submodule input that voltage is the highest；Now it is left out excision；
(2) when the submodule number not put into when upper brachium pontis or lower brachium pontis previous step length is zero (namely go up brachium pontis or lower brachium pontis has put into N number of submodule): when bridge arm current is be more than or equal to 0, then from the submodule of upper brachium pontis or lower brachium pontis input, m the submodule excision that voltage is the highest is directly chosen；When bridge arm current is less than 0, then from the submodule of upper brachium pontis or lower brachium pontis input, directly choose m the submodule excision that voltage is minimum；Now it is left out putting into.
Beneficial effect: the MMC submodule capacitor voltage balance control method of power adaptive provided by the invention, it is framed in adopting nearest level to approach on the modularization multi-level converter of modulation strategy, this algorithm can according to the change of transmission power, adaptive change submodule Switching Strategy, submodule capacitor voltage fluctuating margin is made to remain within the specific limits, and the switching frequency of submodule IGBT can be reduced in due course, improve the submodule IGBT life-span.
Accompanying drawing explanation
Fig. 1 is the topological diagram of modularization multi-level converter MMC provided by the invention；
In figure, P, N represent inverter direct current both positive and negative polarity bus, idRepresent DC current, UdRepresent DC voltage.Upa1To Upa(N/2)Represent the capacitance voltage (being not drawn into redundant module) of N/2 submodule of brachium pontis in a phase；Upb1To Upb(N/2)Represent the capacitance voltage (being not drawn into redundant module) of N/2 submodule of brachium pontis in b phase；Upc1To Upc(N/2)Represent the capacitance voltage (being not drawn into redundant module) of N/2 submodule of brachium pontis in c phase.Una1To Una(N/2)Represent the capacitance voltage (being not drawn into redundant module) of lower N/2 the submodule of brachium pontis of a phase；Unb1To Unb(N/2)Represent the capacitance voltage (being not drawn into redundant module) of lower N/2 the submodule of brachium pontis of b phase；Unc1To Unc(N/2)Represent the capacitance voltage (being not drawn into redundant module) of lower N/2 the submodule of brachium pontis of c phase.ipa、ipbAnd ipcRepresent that a, b and c go up bridge arm current mutually；ina、inbAnd incRepresent that a, b and c descend bridge arm current mutually；isa、isbAnd iscRepresent exchange a, b and c phase current；Rs and Ls represents AC resistance and reactance, U respectivelysa、UsbAnd UscRepresent system voltage respectively；The frame table in Fig. 1 upper right corner shows the structure chart of submodule, UjkSome submodule voltage, T in expression or in lower brachium pontis1And T2Represent two IGBT pipes, D respectively1And D2Representing two diodes in parallel with IGBT respectively, C represents submodule electric capacity；
Fig. 2 is that upper brachium pontis puts into excision strategic process figure；
Fig. 3 is that lower brachium pontis puts into excision strategic process figure；
Fig. 4 is active power reference value from 2.4*104W changes to 3.36*104In W process, this control strategy achieves the self adaptation of antithetical phrase module capacitance voltage pulsation and reduces control；
Fig. 5 is active power reference value from 2.4*104W changes to 1.6*104In W process, this control strategy achieves the self adaptation of antithetical phrase module capacitance voltage pulsation increases control.
Detailed description of the invention
Fig. 1 is the topological diagram of modularization multi-level converter provided by the invention.In conjunction with Fig. 2 and Fig. 3 for A phase, upper and lower bridge arm is put into or the strategy of excision illustrates:
Step 1: upper brachium pontis all submodule capacitor voltage maximum fluctuation value δ U and additive regulating submodule Ns numerical value in 3 power frequency periods of detection respectively:
(1) if δ is U < ZminUNAnd Ns > 0 and Ns numerical value did not change within 1s, then perform Ns=Ns-1；
(2) if δ is U > ZmaxUNAnd Ns < N and Ns numerical value did not change within 1s, then perform Ns=Ns+1；
(3) if (1) (2) are all unsatisfactory for, then Ns numerical value is constant；
Step 2: detect the submodule number n that when previous step is long, upper and lower brachium pontis has been put intopyAnd nny, the submodule number n that do not put intopwAnd nnwIf submodule number and the submodule number not put into that upper and lower brachium pontis has been put into are not all 0, then perform step 3 to step 6, if the submodule number that has been put into of upper and lower brachium pontis and the submodule number not put into have one to be 0, then perform special handling.
Step 3: obtain the submodule that upper and lower brachium pontis has been put into and each submodule instantaneous voltage not put into respectively, the submodule voltage that upper and lower brachium pontis is had been put into and the submodule voltage not put into are ranked up respectively, form four sub-sequence of modules, respectively Xpy、Xpw、XnyAnd Xnw。
Step 4: these four sub-sequence of modules are processed, retrieves the submodule sequence being ready for putting into or excising eight groups new, is respectively as follows:
(1) by XpyMiddle NSThe submodule that individual voltage is the highest takes out, and puts X intopwIn, rearrangement, ultimately form sequence Xpgin；
(2) by XpyMiddle NSThe submodule that individual voltage is minimum takes out, and puts X intopwIn, rearrangement, ultimately form sequence Xpdin；
(3) by XnyMiddle NSThe submodule that individual voltage is the highest takes out, and puts X intonwIn, rearrangement, ultimately form sequence Xngin；
(4) by XnyMiddle NSThe submodule that individual voltage is minimum takes out, and puts X intonwIn, rearrangement, ultimately form sequence Xndin；
(5) by XpwMiddle NSThe submodule that individual voltage is the highest takes out, and puts X intopyIn, rearrangement, ultimately form sequence Xpgout；
(6) by XpwMiddle NSThe submodule that individual voltage is minimum takes out, and puts X intopyIn, rearrangement, ultimately form sequence Xpdout；
(7) by XnwMiddle NSThe submodule that individual voltage is the highest takes out, and puts X intonyIn, rearrangement, ultimately form sequence Xngout；
(8) by XnwMiddle NSThe submodule that individual voltage is minimum takes out, and puts X intonyIn, rearrangement, ultimately form sequence Xndout。
Step 5: modulating wave voltameter during according to this step-length calculates the submodule number that this step-length upper and lower bridge arm should put into respectively, calculate this step-length step-length relative last time further according to the previous step submodule number that time long, upper and lower brachium pontis has been put into the submodule number not put into needs put into or the submodule quantity excised more more.
The submodule number that this step-length of upper brachium pontis should put into utilizes formulaCalculate, n in formulaupRepresenting in this step-length the submodule number that should put into that brachium pontis calculates according to modulating wave voltameter, N represents the submodule number of the total input of upper and lower bridge arm, UrefRepresent modulating wave instantaneous voltage, UcRepresent submodule capacitor voltage.
The submodule number that lower this step-length of brachium pontis should put into utilizes formulaCalculate, n in formuladownRepresent the submodule number that should put into that in this step-length, lower brachium pontis calculates according to modulating wave voltameter.
Then this upper and lower bridge arm should put into or excise several submodule and only need to use nupAnd ndownThe submodule quantity having been put into upper and lower bridge arm in last time step-length and the submodule quantity not put into carry out contrast and can draw: (1) if nup-npy=m (m > 0), it was shown that upper brachium pontis needs to put into m submodule；(2) if nup-npy=m (m < 0), shows that upper brachium pontis needs m submodule of excision；(3) if nup-npy=0, it was shown that upper brachium pontis need not put into or excise submodule, then the triggering pulse that valve is sent by this step-length is same with previous step appearance.Lower brachium pontis is with upper brachium pontis in like manner.In (1) (2) two kinds of situations, perform subsequent step 6 again, in (3) situation, then wait that next step-length returns step 1 when arriving.
Step 6: determine the concrete submodule numbering needing to put into or excise according to bridge arm current direction and self adaptation Switching Strategy from submodule sequence eight groups new, carry out putting into or excising.Concrete self adaptation Switching Strategy is:
(1) when upper brachium pontis needs to put into submodule m, N is carried outSNumerical value judges, if NS>npy, then N is madeS=npy, otherwise NSNumerical value is constant, carries out logical judgment again, when upper bridge arm current is be more than or equal to 0, then from XpyMiddle excision NsThe submodule that individual voltage is the highest, simultaneously from XpginIn choose the m+N that voltage is minimumsIndividual submodule puts into (due to from XpyBefore middle excision submodule, XpginJust formed, so if be detected that XpginThe middle submodule needing to put into comprises XpyMiddle that N preparing excisionsIndividual submodule, then for this NsIndividual submodule does not carry out excising and putting into operation)；
(2) when upper brachium pontis needs to put into submodule m, N is carried outSNumerical value judges, if NS>npy, then N is madeS=npy, otherwise NSNumerical value is constant, carries out logical judgment again, when upper bridge arm current is less than 0, then from XpyMiddle excision NsThe submodule that individual voltage is minimum, simultaneously from XpdinIn choose the m+N that voltage is the highestsIndividual submodule puts into (due to from XpyBefore middle excision submodule, XpdinJust formed, so if be detected that XpdinThe middle submodule needing to put into comprises XpyMiddle that N preparing excisionsIndividual submodule, then for this NsIndividual submodule does not carry out excising and putting into operation)；
(3) brachium pontis needs to put into submodule m instantly, carries out NSNumerical value judges, if NS>nny, then N is madeS=nny, otherwise NSNumerical value is constant, carries out logical judgment again, when bridge arm current is be more than or equal to 0 instantly, then from XnyMiddle excision NsThe submodule that individual voltage is the highest, simultaneously from XnginIn choose the m+N that voltage is minimumsIndividual submodule puts into (due to from XnyBefore middle excision submodule, XnginJust formed, so if be detected that XnginThe middle submodule needing to put into comprises XnyMiddle that N preparing excisionsIndividual submodule, then for this NsIndividual submodule does not carry out excising and putting into operation)；
(4) brachium pontis needs to put into submodule m instantly, carries out NSNumerical value judges, if NS>nny, then N is madeS=nny, otherwise NSNumerical value is constant, carries out logical judgment again, when bridge arm current is less than 0 instantly, then from XnyMiddle excision NsThe submodule that individual voltage is minimum, simultaneously from XndinIn choose the m+N that voltage is the highestsIndividual submodule puts into (due to from XnyBefore middle excision submodule, XndinJust formed, so if be detected that XndinThe middle submodule needing to put into comprises XnyMiddle that N preparing excisionsIndividual submodule, then for this NsIndividual submodule does not carry out excising and putting into operation)；
(5) when upper brachium pontis needs excision submodule m, N is carried outSNumerical value judges, if NS>npw, then N is madeS=npw, otherwise NSNumerical value is constant, carries out logical judgment again, when upper bridge arm current is be more than or equal to 0, then from XpwIn find out NsThe submodule that individual voltage is minimum, is fed into XpyIn, simultaneously from XpdoutIn choose the m+N that voltage is the highestsThe excision of individual submodule is (due to XpyBefore middle input submodule, XpdoutJust formed, so if be detected that XpdoutThe middle submodule needing excision comprises XpwMiddle preparation is selected and is fed into XpyThat NsIndividual submodule, then for this NsIndividual submodule does not carry out putting into and excising operation)；
(6) when upper brachium pontis needs excision submodule m, N is carried outSNumerical value judges, if NS>npw, then N is madeS=npw, otherwise NSNumerical value is constant, carries out logical judgment again, when upper bridge arm current is less than 0, then from XpwIn find out NsThe submodule that individual voltage is the highest, is fed into XpyIn, simultaneously from XpgoutIn choose the m+N that voltage is minimumsThe excision of individual submodule is (due to XpyBefore middle input submodule, XpgoutJust formed, so if be detected that XpgoutThe middle submodule needing excision comprises XpwMiddle preparation is selected and is fed into XpyThat NsIndividual submodule, then for this NsIndividual submodule does not carry out putting into and excising operation)；
(7) brachium pontis needs excision submodule m instantly, carries out NSNumerical value judges, if NS>nnw, then N is madeS=nnw, otherwise NSNumerical value is constant, carries out logical judgment again, when bridge arm current is be more than or equal to 0 instantly, then from XnwIn find out NsThe submodule that individual voltage is minimum, is fed into XnyIn, simultaneously from XndoutIn choose the m+N that voltage is the highestsThe excision of individual submodule is (due to XnyBefore middle input submodule, XndoutJust formed, so if be detected that XndoutThe middle submodule needing excision comprises XnwMiddle preparation is selected and is fed into XnyThat NsIndividual submodule, then for this NsIndividual submodule does not carry out putting into and excising operation)；
(8) brachium pontis needs excision submodule m instantly, carries out NSNumerical value judges, if NS>nnw, then N is madeS=nnw, otherwise NSNumerical value is constant, carries out logical judgment again, when bridge arm current is less than 0 instantly, then from XnwIn find out NsThe submodule that individual voltage is the highest, is fed into XnyIn, simultaneously from XngoutIn choose the m+N that voltage is minimumsThe excision of individual submodule is (due to XnyBefore middle input submodule, XngoutJust formed, so if be detected that XngoutThe middle submodule needing excision comprises XnwMiddle preparation is selected and is fed into XnyThat NsIndividual submodule, then for this NsIndividual submodule does not carry out putting into and excising operation).
Step 7: the submodule number that upper and lower brachium pontis previous step length has been put into be zero or the submodule number that do not put into need to carry out special handling when being zero:
(1) when the submodule number put into when upper brachium pontis or lower brachium pontis previous step length is zero: when bridge arm current is be more than or equal to 0, then the submodule directly not put into from upper brachium pontis or lower brachium pontis chooses m the submodule input that voltage is minimum；When bridge arm current is less than 0, then the submodule directly not put into from upper brachium pontis or lower brachium pontis chooses m the submodule input that voltage is the highest；Now it is left out excision；
(2) when the submodule number not put into when upper brachium pontis or lower brachium pontis previous step length is zero (namely go up brachium pontis or lower brachium pontis has put into N number of submodule): when bridge arm current is be more than or equal to 0, then from the submodule of upper brachium pontis or lower brachium pontis input, m the submodule excision that voltage is the highest is directly chosen；When bridge arm current is less than 0, then from the submodule of upper brachium pontis or lower brachium pontis input, directly choose m the submodule excision that voltage is minimum；Now it is left out putting into.
For verifying that this algorithm is implemented on the superior function in the field such as flexible DC power transmission, THE UPFC, at laboratory constructing modular multilevel converter dynamic model, and traditional nearest level is approached modulation strategy, another kind of comparatively popular modulation strategy and this strategy be applied to this model, observe switching frequency total for brachium pontis IGBT and submodule capacitor voltage in three kinds of algorithm a phases and fluctuate situation.
This model is 9 level MMC inverter models, and wherein upper and lower bridge arm is respectively arranged with 10 submodules, puts into 8 time normal, and 2 is redundant module, submodule rated voltage 200V, DC rated voltage ± 800V, and modulation ratio is 0.75, sets Zmin=5%, Zmax=10%.
When power adjustment instruction changes, actual power can be changed with value and power reference, then generally, when value and power reference rises, submodule capacitor voltage fluctuation can become big, and when value and power reference declines, submodule capacitor voltage fluctuation will diminish.
Fig. 4 is value and power reference when rising, and model adopts after this control strategy the waveform of each submodule capacitor voltage of brachium pontis in A phase.
As seen from Figure 4, before 0.8s, value and power reference gives 2.4*104W, additive regulating submodule quantity is 1, and submodule capacitor voltage relatively fluctuates as stable, substantially fluctuates at about 194-210V, more than Zmin*UN, and less than Zmax*UN, therefore additional submodule quantity will not change.As 0.8s, value and power reference is by 2.4*104W rises to 3.36*104W, submodule capacitor voltage fluctuation begins to ramp up, and substantially fluctuates at about 193-214V, and now submodule capacitor voltage fluctuation has been above Zmax*UN, according to this algorithm flow, fluctuate continuously more than Z in the submodule capacitor voltage judging 3 cyclesmax*UNAfterwards (0.88s), algorithm adaptive increase additive regulating submodule quantity is 2, and the fluctuation of final submodule capacitor voltage is stable between 196.6-215.5, less than Zmax*UN。
The cost reducing submodule capacitor voltage fluctuation is that submodule IGBT switching frequency increases, but relative IGBT switching frequency, control submodule capacitor voltage fluctuation out-of-limit more important.When 1s-1.1s listed by table 1, do not use brachium pontis all submodules IGBT switching frequency and all submodule IGBT switching frequencies of brachium pontis in use this algorithm A phase in this algorithm A phase.
Table 1
As can be seen from Table 1, using this algorithm relatively not use this algorithm, submodule IGBT switching frequency adds 32 times within this 0.1s.
Fig. 5 is value and power reference when declining, and model adopts after this control strategy the waveform of each submodule capacitor voltage of brachium pontis in A phase.
As seen from Figure 5, before 0.8s, value and power reference gives 2.4*104W, additive regulating submodule quantity is 2, and submodule capacitor voltage relatively fluctuates as stable, substantially fluctuates at about 197-210V, more than Zmin*UN, and less than Zmax*UN, therefore additional submodule quantity will not change.As 0.8s, value and power reference is by 2.4*104W rises to 1.6*104W, submodule capacitor voltage fluctuation begins to decline, and substantially fluctuates at about 198-207V, and now submodule capacitor voltage fluctuates already less than Zmin*UN, according to this algorithm flow, fluctuate continuously less than Z in the submodule capacitor voltage judging 3 cyclesmin*UNAfterwards (0.955s), algorithm adaptive reduction additive regulating submodule quantity is 1, and the fluctuation of final submodule capacitor voltage is stable between 196-207, more than Zmax*UN。
When submodule capacitor voltage fluctuation is only small, it is possible under the premise that submodule capacitor voltage fluctuation is not out-of-limit, to sacrifice submodule capacitor voltage fluctuation for cost, reduces submodule IGBT switching frequency, extend the IGBT life-span.When 1s-1.1s listed by table 2, do not use brachium pontis all submodules IGBT switching frequency and all submodule IGBT switching frequencies of brachium pontis in use this algorithm A phase in this algorithm A phase.
Table 2
As can be seen from Table 2, using this algorithm relatively not use this algorithm, submodule IGBT switching frequency decreases 32 times within this 0.1s.
The above is only the preferred embodiment of the present invention; it is noted that, for those skilled in the art; under the premise without departing from the principles of the invention, it is also possible to make some improvements and modifications, these improvements and modifications also should be regarded as protection scope of the present invention.

Claims (8)

1. the MMC submodule capacitor voltage balance control method of a power adaptive, it is characterised in that be framed in adopting nearest level to approach on the modularization multi-level converter of modulation strategy；Comprise the following steps:
Step 1) detect upper brachium pontis all submodule capacitor voltage maximum fluctuation value δ U and additive regulating submodule Ns numerical value in 3 power frequency periods respectively:
(1) if δ is U < ZminUNAnd Ns > 0 and Ns numerical value did not change within 1s, then perform Ns=Ns-1；
(2) if δ is U > ZmaxUNAnd Ns < N and Ns numerical value did not change within 1s, then perform Ns=Ns+1；
(3) if (1) (2) are all unsatisfactory for, then Ns numerical value is constant；
Step 2) detect when previous step is long brachium pontis, submodule number that lower brachium pontis has been put into and the submodule number that do not put into, if upper brachium pontis, the submodule number that lower brachium pontis has been put into and the submodule number not put into are not all 0, then perform step 3) to step 6), if upper brachium pontis, the submodule number that lower brachium pontis has been put into and the submodule number not put into have one to be 0, then perform special handling；
Step 3) obtain upper brachium pontis respectively, submodule that lower brachium pontis has been put into and each submodule instantaneous voltage of not putting into, upper brachium pontis, submodule voltage that lower brachium pontis has been put into and the submodule voltage not put into are ranked up respectively, form four sub-sequence of modules；
Step 4) these four sub-sequence of modules are processed, retrieve the submodule sequence being ready for putting into or excising eight groups new；
Step 5) according to this step-length time modulating wave voltameter calculate the submodule number that this step-length upper and lower bridge arm should put into respectively, calculate this step-length step-length relative last time with the submodule number not put into further according to the previous step submodule number that time long, upper brachium pontis, lower brachium pontis have been put into needs put into or the submodule quantity of many excisions more；
Step 6) from submodule sequence eight groups new, determine that the concrete submodule needing to put into or excise is numbered according to bridge arm current direction and self adaptation Switching Strategy, carry out putting into or excising；
Step 7) submodule number that upper brachium pontis, lower brachium pontis previous step length have been put into be zero or the submodule number that do not put into carry out special handling when being zero.
2. the MMC submodule capacitor voltage balance control method of power adaptive according to claim 1, it is characterized in that: step 1) in, capacitance voltage maximum fluctuation value δ U refers to the difference of all submodule voltage max of the upper and lower brachium pontis of A phase and voltage minimum in 3 cycles, and Ns refers to the quantity that this step-length additive regulating submodule sets.
3. the MMC submodule capacitor voltage balance control method of power adaptive according to claim 1, it is characterized in that: step 2) in, upper brachium pontis when detecting a step-length respectively, the submodule number that lower brachium pontis has been put into and the submodule number not put into refer to the submodule number n detecting that brachium pontis has been put intopyThe submodule number n not put intopw, submodule number n that lower brachium pontis has been put intonyThe submodule number n not put intonw。
4. the MMC submodule capacitor voltage balance control method of power adaptive according to claim 1, it is characterised in that: step 3) in, form four collated submodule sequences and respectively go up the submodule sequence X that brachium pontis has put intopyThe submodule sequence X not put intopw, submodule sequence X that lower brachium pontis has put intonyThe submodule sequence X not put intonw。
5. the MMC submodule capacitor voltage balance control method of power adaptive according to claim 4, it is characterised in that: step 4) in, retrieve eight groups of submodule sequences being ready for putting into or excising and refer to:
(1) by XpyThe submodule that middle voltage is the highest takes out, and puts X intopwIn, rearrangement, ultimately form sequence Xpgin；
(2) by XpyThe submodule that middle voltage is minimum takes out, and puts X intopwIn, rearrangement, ultimately form sequence Xpdin；
(3) by XnyThe submodule that middle voltage is the highest takes out, and puts X intonwIn, rearrangement, ultimately form sequence Xngin；
(4) by XnyThe submodule that middle voltage is minimum takes out, and puts X intonwIn, rearrangement, ultimately form sequence Xndin；
(5) by XpwThe submodule that middle voltage is the highest takes out, and puts X intopyIn, rearrangement, ultimately form sequence Xpgout；
(6) by XpwThe submodule that middle voltage is minimum takes out, and puts X intopyIn, rearrangement, ultimately form sequence Xpdout；
(7) by XnwThe submodule that middle voltage is the highest takes out, and puts X intonyIn, rearrangement, ultimately form sequence Xngout；
(8) by XnwThe submodule that middle voltage is minimum takes out, and puts X intonyIn, rearrangement, ultimately form sequence Xndout。
6. the MMC submodule capacitor voltage balance control method of power adaptive according to claim 1, it is characterised in that: step 5) in,
The submodule number that this step-length of upper brachium pontis should put into utilizes formulaCalculate, n in formulaupRepresenting in this step-length the submodule number that should put into that brachium pontis calculates according to modulating wave voltameter, N represents the submodule number of the total input of upper and lower bridge arm, UrefRepresent modulating wave instantaneous voltage, UcRepresent submodule capacitor voltage；
The submodule number that lower this step-length of brachium pontis should put into utilizes formulaCalculate, n in formuladownRepresent the submodule number that should put into that in this step-length, lower brachium pontis calculates according to modulating wave voltameter；
Then this upper and lower bridge arm should put into or excise several submodule nupAnd ndownThe submodule quantity having been put into upper and lower bridge arm in last time step-length and the submodule quantity not put into carry out contrast and can draw: (1) if nup-npy=m (m > 0), it was shown that upper brachium pontis needs to put into m submodule；(2) if nup-npy=m (m < 0), shows that upper brachium pontis needs m submodule of excision；(3) if nup-npy=0, it was shown that upper brachium pontis need not put into or excise submodule, then the triggering pulse that valve is sent by this step-length is same with previous step appearance；Lower brachium pontis is with upper brachium pontis in like manner；Subsequent step 5 is performed again in (1) (2) two kinds of situations), in (3) situation, then wait that next step-length returns step 1 when arriving).
7. the MMC submodule capacitor voltage balance control method of power adaptive according to claim 4, it is characterised in that: step 6) in, Switching Strategy refers to:
(1) when upper brachium pontis needs to put into submodule m, N is carried outSNumerical value judges, if NS>npy, then N is madeS=npy, otherwise NSNumerical value is constant, carries out logical judgment again, when upper bridge arm current is be more than or equal to 0, then from XpyMiddle excision NsThe submodule that individual voltage is the highest, simultaneously from XpginIn choose the m+N that voltage is minimumsIndividual submodule puts into (due to from XpyBefore middle excision submodule, XpginJust formed, so if be detected that XpginThe middle submodule needing to put into comprises XpyMiddle that N preparing excisionsIndividual submodule, then for this NsIndividual submodule does not carry out excising and putting into operation)；
(2) when upper brachium pontis needs to put into submodule m, N is carried outSNumerical value judges, if NS>npy, then N is madeS=npy, otherwise NSNumerical value is constant, carries out logical judgment again, when upper bridge arm current is less than 0, then from XpyMiddle excision NsThe submodule that individual voltage is minimum, simultaneously from XpdinIn choose the m+N that voltage is the highestsIndividual submodule puts into (due to from XpyBefore middle excision submodule, XpdinJust formed, so if be detected that XpdinThe middle submodule needing to put into comprises XpyMiddle that N preparing excisionsIndividual submodule, then for this NsIndividual submodule does not carry out excising and putting into operation)；
(3) brachium pontis needs to put into submodule m instantly, carries out NSNumerical value judges, if NS>nny, then N is madeS=nny, otherwise NSNumerical value is constant, carries out logical judgment again, when bridge arm current is be more than or equal to 0 instantly, then from XnyMiddle excision NsThe submodule that individual voltage is the highest, simultaneously from XnginIn choose the m+N that voltage is minimumsIndividual submodule puts into (due to from XnyBefore middle excision submodule, XnginJust formed, so if be detected that XnginThe middle submodule needing to put into comprises XnyMiddle that N preparing excisionsIndividual submodule, then for this NsIndividual submodule does not carry out excising and putting into operation)；
(4) brachium pontis needs to put into submodule m instantly, carries out NSNumerical value judges, if NS>nny, then N is madeS=nny, otherwise NSNumerical value is constant, carries out logical judgment again, when bridge arm current is less than 0 instantly, then from XnyMiddle excision NsThe submodule that individual voltage is minimum, simultaneously from XndinIn choose the m+N that voltage is the highestsIndividual submodule puts into (due to from XnyBefore middle excision submodule, XndinJust formed, so if be detected that XndinThe middle submodule needing to put into comprises XnyMiddle that N preparing excisionsIndividual submodule, then for this NsIndividual submodule does not carry out excising and putting into operation)；
(5) when upper brachium pontis needs excision submodule m, N is carried outSNumerical value judges, if NS>npw, then N is madeS=npw, otherwise NSNumerical value is constant, carries out logical judgment again, when upper bridge arm current is be more than or equal to 0, then from XpwIn find out NsThe submodule that individual voltage is minimum, is fed into XpyIn, simultaneously from XpdoutIn choose the m+N that voltage is the highestsThe excision of individual submodule is (due to XpyBefore middle input submodule, XpdoutJust formed, so if be detected that XpdoutThe middle submodule needing excision comprises XpwMiddle preparation is selected and is fed into XpyThat NsIndividual submodule, then for this NsIndividual submodule does not carry out putting into and excising operation)；
(6) when upper brachium pontis needs excision submodule m, N is carried outSNumerical value judges, if NS>npw, then N is madeS=npw, otherwise NSNumerical value is constant, carries out logical judgment again, when upper bridge arm current is less than 0, then from XpwIn find out NsThe submodule that individual voltage is the highest, is fed into XpyIn, simultaneously from XpgoutIn choose the m+N that voltage is minimumsThe excision of individual submodule is (due to XpyBefore middle input submodule, XpgoutJust formed, so if be detected that XpgoutThe middle submodule needing excision comprises XpwMiddle preparation is selected and is fed into XpyThat NsIndividual submodule, then for this NsIndividual submodule does not carry out putting into and excising operation)；
(7) brachium pontis needs excision submodule m instantly, carries out NSNumerical value judges, if NS>nnw, then N is madeS=nnw, otherwise NSNumerical value is constant, carries out logical judgment again, when bridge arm current is be more than or equal to 0 instantly, then from XnwIn find out NsThe submodule that individual voltage is minimum, is fed into XnyIn, simultaneously from XndoutIn choose the m+N that voltage is the highestsThe excision of individual submodule is (due to XnyBefore middle input submodule, XndoutJust formed, so if be detected that XndoutThe middle submodule needing excision comprises XnwMiddle preparation is selected and is fed into XnyThat NsIndividual submodule, then for this NsIndividual submodule does not carry out putting into and excising operation)；
(8) brachium pontis needs excision submodule m instantly, carries out NSNumerical value judges, if NS>nnw, then N is madeS=nnw, otherwise NSNumerical value is constant, carries out logical judgment again, when bridge arm current is less than 0 instantly, then from XnwIn find out NsThe submodule that individual voltage is the highest, is fed into XnyIn, simultaneously from XngoutIn choose the m+N that voltage is minimumsThe excision of individual submodule is (due to XnyBefore middle input submodule, XngoutJust formed, so if be detected that XngoutThe middle submodule needing excision comprises XnwMiddle preparation is selected and is fed into XnyThat NsIndividual submodule, then for this NsIndividual submodule does not carry out putting into and excising operation).
8. the MMC submodule capacitor voltage balance control method of power adaptive according to claim 1, it is characterised in that: special handling refers to:
(1) when the submodule number put into when upper brachium pontis or lower brachium pontis previous step length is zero: when bridge arm current is be more than or equal to 0, then the submodule directly not put into from upper brachium pontis or lower brachium pontis chooses m the submodule input that voltage is minimum；When bridge arm current is less than 0, then the submodule directly not put into from upper brachium pontis or lower brachium pontis chooses m the submodule input that voltage is the highest；Now it is left out excision；
(2) when the submodule number not put into when upper brachium pontis or lower brachium pontis previous step length is zero: when bridge arm current is be more than or equal to 0, then from the submodule of upper brachium pontis or lower brachium pontis input, m the submodule excision that voltage is the highest is directly chosen；When bridge arm current is less than 0, then from the submodule of upper brachium pontis or lower brachium pontis input, directly choose m the submodule excision that voltage is minimum；Now it is left out putting into.
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CN110867885B (en) * 2019-11-26 2021-03-09 全球能源互联网研究院有限公司 Submodule alternation control method of direct current energy consumption device
US20230041013A1 (en) * 2020-03-30 2023-02-09 Mitsubishi Electric Corporation Power conversion device
CN114839470A (en) * 2022-07-06 2022-08-02 西安交通大学 Capacitor monitoring method, device, equipment and medium for submodule of MMC system
CN114839470B (en) * 2022-07-06 2022-10-11 西安交通大学 Capacitor monitoring method, device, equipment and medium for submodule of MMC system

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