CN105207507A - MMC sub-module for reducing capacitance volume - Google Patents

MMC sub-module for reducing capacitance volume Download PDF

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Publication number
CN105207507A
CN105207507A CN201510581134.1A CN201510581134A CN105207507A CN 105207507 A CN105207507 A CN 105207507A CN 201510581134 A CN201510581134 A CN 201510581134A CN 105207507 A CN105207507 A CN 105207507A
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electric capacity
switching tube
main capacitance
mode
mmc submodule
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CN201510581134.1A
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CN105207507B (en
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黄迪
曾正
邵伟华
冉立
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Chongqing University
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Chongqing University
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Abstract

The invention provides an MMC sub-module for reducing the capacitance volume. The MMC sub-module at least comprises a capacitor unit and a switch unit connected with the capacitor unit. The capacitor unit comprises a main capacitor and an auxiliary capacitor. The switch unit comprises a switch which is connected with the main capacitor and the auxiliary capacitor in series and used for controlling and changing the series and parallel structure of the main capacitor and the auxiliary capacitor, the switch is controlled to enable the main capacitor to generate voltage fluctuation, and voltage fluctuation of the main capacitor is compensated by means of the auxiliary capacitor. The characteristic that large ripple currents can flow through a metal thin film capacitor is utilized, the large voltage fluctuation can be generated on the capacitors by means of a control algorithm, under the circumstance of ensuring voltage ripples of the MMC sub-module, the energy utilization efficiency of the capacitors is improved, the energy density is higher than that of a traditional MMC sub-module, the volume and the mass of the capacitors in the MMC sub-module are reduced, and the volume of the MMC sub-module and the volume of a current converter are reduced.

Description

Reduce the MMC submodule of electric capacity volume
Technical field
The present invention relates to power domain, particularly relate to a kind of MMC submodule reducing electric capacity volume.
Background technology
Modular multilevel converter (ModularMultilevelConverter, be called for short MMC) be that a new generation does not need transformer and realizes the one in the multiphase converter of high, medium voltage electricity conversion, since R.Marquart and A.Lesnicar of university of Munich, Germany Federal Defence Forces in 2002 proposes MMC jointly, the features such as MMC is high with its degree of modularity, step voltage is low, output waveform quality is high, troubleshooting capability is strong, devices switch frequency is low become the voltage source converter structure of current flexible direct-current transmission field main flow the most.In recent years put into operation in a large number based on the flexible DC power transmission engineering of MMC, but due to the capacitance of MMC submodule comparatively large, submodule volume is comparatively large, has had a strong impact on floor space and the cost of MMC DC transmission engineering.
According to existing engineering practice, MMC submodule electric capacity shared volume in submodule exceedes 50% of submodule volume, and weight reaches submodule weight more than 90% especially.If effective scheme can be taked to reduce the volume of submodule electric capacity, significant economic benefit will be brought.There be limited evidence currently of has the research reducing MMC submodule electric capacity volume aspect, K.Ilves etc. are Capacitorvoltagerippleshapinginmodularmultilevelconverte rsallowingforoperatingregionextension (Proc.37thAnnu.Conf.IEEEInd.Electron.Soc. at title, Nov.2011, pp.4403-4408) shape of capacitance voltage waveform is adjusted in article by inserting circulation, the moment that voltage fluctuation of capacitor peak value is occurred needs the moment exporting ceiling voltage close with brachium pontis as far as possible, thus reduce capacitance voltage level, relax the restriction of voltage fluctuation of capacitor rate.But this scheme can increase bridge arm current value, increase the rated value of the power device adopted and increase power loss.
Summary of the invention
In view of this, the invention provides a kind of MMC submodule reducing electric capacity volume, to solve the problem.
The MMC submodule of reduction electric capacity volume provided by the invention, the switch element at least comprising capacitor cell and be connected with described capacitor cell, described capacitor cell comprises main capacitance and from electric capacity, described switch element comprises and to be connected and for the switch of control break main capacitance and the series parallel structure from electric capacity with main capacitance with from capacitances in series respectively, main capacitance is made to produce voltage fluctuation by control switch, and by compensating from the voltage fluctuation of electric capacity to main capacitance.
Further, described switch is the switching tube being provided with anti-paralleled diode.
Further, described switching tube comprises S l, S 11, S 12, S 13, S 21, S 22, described main capacitance is C 11, describedly comprise C from electric capacity 21, C 22, described switching tube S lthe input of current collection very MMC submodule, launch the output of very MMC submodule; Described switching tube S 11emitter be connected with input, collector electrode with from electric capacity C 21positive pole connect; Described switching tube S 12with switching tube S 21differential concatenation, wherein switching tube S 12emitter be connected with input, switching tube S 21emitter with from electric capacity C 22positive pole connect; Described switching tube S 13with switching tube S 22differential concatenation, wherein switching tube S 13emitter be connected with input, switching tube S 22emitter with from electric capacity C 22negative pole connect; Described main capacitance C 11positive pole respectively with from electric capacity C 21negative pole and from electric capacity C 22negative pole connects, main capacitance C 11negative pole be connected with output.
Further, described capacitor cell comprises three kinds of mode of operations, and mode of operation one is main capacitance C 11with from electric capacity C 21series connection access electrical network, mode of operation two is main capacitance C 11with from electric capacity C 22series connection access electrical network, mode of operation three is main capacitance C 11independent access electrical network.
Further, when the operate power of transmission system is under full power state, described capacitor cell all can use three kinds of mode of operations.
Further, when transmission system operate power higher than system nominal power 50% and lower than rated power 75% time, control capacitance unit is under mode of operation two or mode of operation three.
Further, when transmission system operate power lower than system nominal power 50% time, control capacitance unit is only under mode of operation three.
Further, also comprise system control module, described system control module comprises Outer Loop Power Controller and inner ring current controller, described Outer Loop Power Controller obtains the current reference value of inner ring current controller according to meritorious and idle reference value, described inner ring current controller, by regulating inverter output voltage, makes electric current follow the tracks of its reference value fast.
Beneficial effect of the present invention: the present invention utilizes metal thin film capacitor can flow through the characteristic of larger ripple current, make on electric capacity, produce larger voltage fluctuation by control algolithm, when ensureing MMC submodule voltage ripple, improve the energy utilization efficiency of electric capacity, achieve the energy density higher than traditional MMC submodule, reduce volume and the quality of electric capacity in MMC submodule, thus reduce the volume of MMC submodule and even converter.
Accompanying drawing explanation
Below in conjunction with drawings and Examples, the invention will be further described:
Fig. 1 is structural representation of the present invention.
Fig. 2 is three kinds of mode of operation schematic diagrames of capacitor cell of the present invention.
Fig. 3 is the operation principle schematic diagram of capacitor cell of the present invention.
Fig. 4 is that three-phase exports phase voltage waveform and total harmonic distortion value schematic diagram thereof.
Fig. 5 is three-phase output current phase waveform and total harmonic distortion value schematic diagram thereof.
Fig. 6 is C in brachium pontis submodule in a phase 11, C 21and C 22on magnitude of voltage.
Fig. 7 is the voltage equivalence value that submodule exports.
Embodiment
Below in conjunction with drawings and Examples, the invention will be further described: Fig. 1 is principle schematic of the present invention, Fig. 2 is three kinds of mode of operation schematic diagrames of capacitor cell of the present invention, Fig. 3 is the operation principle schematic diagram of capacitor cell of the present invention, and Fig. 4 is that three-phase exports phase voltage waveform and total harmonic distortion value schematic diagram thereof.Fig. 5 is three-phase output current phase waveform and total harmonic distortion value schematic diagram thereof, and Fig. 6 is C in brachium pontis submodule in a phase 11, C 21and C 22on magnitude of voltage, Fig. 7 be submodule export voltage equivalence value.
The MMC submodule of the reduction electric capacity volume in the present embodiment, the switch element at least comprising capacitor cell and be connected with described capacitor cell, described capacitor cell comprises main capacitance and from electric capacity, described switch element comprises and to be connected and for the switch of control break main capacitance and the series parallel structure from electric capacity with main capacitance with from capacitances in series respectively, main capacitance is made to produce voltage fluctuation by control switch, and by compensating from the voltage fluctuation of electric capacity to main capacitance, in the present embodiment, changed main by control switch, connection in series-parallel relation is changed from electric capacity, main capacitance is made to produce larger voltage fluctuation, then compensated by the voltage fluctuation of voltage fluctuation to main capacitance from electric capacity, adopt and make the ripple of port voltage reach system requirements in this way.
As shown in Figure 1, in the present embodiment, switch adopts the switching tube being provided with anti-paralleled diode, and adopt 6 IGBT with anti-paralleled diode as switching tube in the present embodiment, wherein switching tube comprises S l, S 11, S 12, S 13, S 21, S 22, described main capacitance is C 11, describedly comprise C from electric capacity 21, C 22, described switching tube S lthe input of current collection very MMC submodule, launch the output of very MMC submodule; Described switching tube S 11emitter be connected with input, collector electrode with from electric capacity C 21positive pole connect; Described switching tube S 12with switching tube S 21differential concatenation, wherein switching tube S 12emitter be connected with input, switching tube S 21emitter with from electric capacity C 22positive pole connect; Described switching tube S 13with switching tube S 22differential concatenation, wherein switching tube S 13emitter be connected with input, switching tube S 22emitter with from electric capacity C 22negative pole connect; Described main capacitance C 11positive pole respectively with from electric capacity C 21negative pole and from electric capacity C 22negative pole connects, main capacitance C 11negative pole be connected with output.The port voltage of MMC submodule is U sM, the input current of MMC submodule is i sM; The output voltage ripple allowed is V ripple, wherein electric capacity C 11voltage be v c11, electric capacity C 21voltage be v c21, electric capacity C 22voltage be v c22.Its operation principle as shown in Figure 4, utilizes metal thin film capacitor by the characteristic of larger ripple current, by changing the connection in series-parallel relation of three electric capacity to the control of the switch be in series with three electric capacity, makes at electric capacity C 11the voltage fluctuation that upper generation is larger, then utilizes electric capacity C 21with electric capacity C 22on voltage fluctuation to electric capacity C 11on voltage fluctuation compensate, make the ripple of port voltage reach system requirements.
In the present embodiment, capacitor cell comprises three kinds of mode of operations, and mode of operation one is main capacitance C 11with from electric capacity C 21series connection access electrical network, mode of operation two is main capacitance C 11with from electric capacity C 22series connection access electrical network, mode of operation three is main capacitance C 11independent access electrical network.As shown in Figure 2, the current direction figure under the first mode of operation that Fig. 2 (a) is submodule, under this kind of mode of operation, switch S 11closed, electric capacity C 11with electric capacity C 21series connection access electrical network.Current direction figure under the second mode of operation that Fig. 2 (b) is submodule, under this kind of mode of operation, switch S 12and switch S 21closed, electric capacity C 11and C 22capacitances in series access electrical network.Current direction figure under the third mode of operation that Fig. 2 (c) is submodule, under this kind of mode of operation, switch S 13and switch S 22closed, electric capacity C 11independent access electrical network.
In the present embodiment, when the operate power of transmission system is under full power state, described capacitor cell all can use three kinds of mode of operations; When transmission system operate power higher than system nominal power 50% and lower than rated power 75% time, in order to reduce the switching loss of system, by control make capacitor cell be under mode of operation two or mode of operation three; When transmission system operate power lower than system nominal power 50% time, control capacitance unit is only under mode of operation three.Now the power of system transfers is lower, only needs access electric capacity C 11the ripple requirement of system can be reached.According to the control whether MMC system accesses submodule, submodule has 6 kinds of on off states, as shown in table 1
Table 1
In the present embodiment, also comprise system control module, described system control module comprises Outer Loop Power Controller and inner ring current controller, described Outer Loop Power Controller obtains the current reference value of inner ring current controller according to meritorious and idle reference value, described inner ring current controller, by regulating inverter output voltage, makes electric current follow the tracks of its reference value fast.Outer ring controller in the present embodiment obtains the dq shaft current reference value of inner ring current controller according to meritorious and idle reference value.Inner ring current controller, by regulating inverter output voltage, makes dq shaft current follow the tracks of its reference value fast.There are 5 order harmonic components of negative phase-sequence in the present embodiment, therefore need to eliminate 5 subharmonic in the inner ring current controller of system in the output current of system, and concrete elimination controls with 2 change of current inhibitor similar.In system circulation, find the harmonic current of 4 positive sequences simultaneously, in loop current suppression device, therefore need the controller adding suppression 4 positive sequence harmonics.Calculated the output AC voltage ripple of voltage source converter by inner ring current controller and loop current suppression controller, then shift to modulation by carrier wave and capacitance voltage Balance route obtains the switching signal of concrete submodule.
In the present embodiment, by having built 11 level three-phase MMC emulation platforms on Matlab/Simulink, the major parameter of emulation is: direct voltage is 20kV, rated power 9.6MW, submodule capacitor's capacity and voltage 2mF/2kV, brachium pontis inductance 13mH, voltage ripple is 0.2 (peak-to-peak value).In emulation, the modulator approach of MMC adopts phase-shifting carrier wave pulse-width modulation.As shown in Figure 4,5, 6, by controlling accordingly to make electric capacity C 11, C 21and C 22on voltage similar to the schematic diagram shown in Fig. 3, at electric capacity C 11on have a larger voltage fluctuation, then use electric capacity C 21and C 22voltage fluctuation is above to C 11on fluctuation compensate.As shown in Figure 7, electric capacity C is made 21and C 22voltage fluctuation is above to C 11on fluctuation compensate the requirement that submodule output equivalent voltage can be made to reach voltage ripple.
Enumerate a specific embodiment to be below described in detail:
In the present embodiment, the capacity ratio that the electric capacity selected by MMC submodule and traditional MMC submodule use is more as shown in table 2, and according to the requirement of system parameters, to choose rated voltage be the electric capacity of 2500V is C 11, to choose rated voltage be the electric capacity of 600V is C 21with electric capacity C 22, the capacitance of selected three electric capacity is 1mF.The former MMC submodule C that substitutes 0capacitance is 2mF, and rated voltage is 2500V, and capacitor production firm is ElectronicConcepts.
Electric capacity Brand Capacitance (mF) Rated voltage (V) Volume (cm 3)
C o Electronic Concepts 2*1 2500 19990
C 11 Electronic Concepts 1 2500 9995
C 21 Electronic Concepts 1 600 500
C 22 Electronic Concepts 1 600 500
Table 2
As can be seen from Table 2, choose electric capacity C11, C21 and C22 by the solution of the present invention and be about 60% of atom module volume with traditional MMC submodule electric capacity phase specific volume, decrease 40%, thus the floor space of converter volume and even current conversion station can be reduced.
What finally illustrate is, above embodiment is only in order to illustrate technical scheme of the present invention and unrestricted, although with reference to preferred embodiment to invention has been detailed description, those of ordinary skill in the art is to be understood that, can modify to technical scheme of the present invention or equivalent replacement, and not departing from aim and the scope of technical solution of the present invention, it all should be encompassed in the middle of right of the present invention.

Claims (8)

1. one kind is reduced the MMC submodule of electric capacity volume, it is characterized in that: the switch element at least comprising capacitor cell and be connected with described capacitor cell, described capacitor cell comprises main capacitance and from electric capacity, described switch element comprises and to be connected and for the switch of control break main capacitance and the series parallel structure from electric capacity with main capacitance with from capacitances in series respectively, main capacitance is made to produce voltage fluctuation by control switch, and by compensating from the voltage fluctuation of electric capacity to main capacitance.
2. the MMC submodule of reduction electric capacity volume according to claim 1, is characterized in that: described switch is the switching tube being provided with anti-paralleled diode.
3. the MMC submodule of reduction electric capacity volume according to claim 2, is characterized in that: described switching tube comprises S l, S 11, S 12, S 13, S 21, S 22, described main capacitance is C 11, describedly comprise C from electric capacity 21, C 22, described switching tube S lthe input of current collection very MMC submodule, launch the output of very MMC submodule; Described switching tube S 11emitter be connected with input, collector electrode with from electric capacity C 21positive pole connect; Described switching tube S 12with switching tube S 21differential concatenation, wherein switching tube S 12emitter be connected with input, switching tube S 21emitter with from electric capacity C 22positive pole connect; Described switching tube S 13with switching tube S 22differential concatenation, wherein switching tube S 13emitter be connected with input, switching tube S 22emitter with from electric capacity C 22negative pole connect; Described main capacitance C 11positive pole respectively with from electric capacity C 21negative pole and from electric capacity C 22negative pole connects, main capacitance C 11negative pole be connected with output.
4. the MMC submodule of reduction electric capacity volume according to claim 3, it is characterized in that: described capacitor cell comprises three kinds of mode of operations, mode of operation one is main capacitance C 11with from electric capacity C 21series connection access electrical network, mode of operation two is main capacitance C 11with from electric capacity C 22series connection access electrical network, mode of operation three is main capacitance C 11independent access electrical network.
5. the MMC submodule of reduction electric capacity volume according to claim 4, it is characterized in that: when the operate power of transmission system is under full power state, described capacitor cell all can use three kinds of mode of operations.
6. the MMC submodule of reduction electric capacity volume according to claim 4, it is characterized in that: when transmission system operate power higher than system nominal power 50% and lower than rated power 75% time, control capacitance unit is under mode of operation two or mode of operation three.
7. the MMC submodule of reduction electric capacity volume according to claim 4, is characterized in that: when transmission system operate power lower than system nominal power 50% time, control capacitance unit is only under mode of operation three.
8. the MMC submodule of the reduction electric capacity volume according to the arbitrary claim of claim 1-7, it is characterized in that: also comprise system control module, described system control module comprises Outer Loop Power Controller and inner ring current controller, described Outer Loop Power Controller obtains the current reference value of inner ring current controller according to meritorious and idle reference value, described inner ring current controller, by regulating inverter output voltage, makes electric current follow the tracks of its reference value fast.
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Cited By (4)

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Publication number Priority date Publication date Assignee Title
CN106787824A (en) * 2017-02-09 2017-05-31 南方电网科学研究院有限责任公司 Submodule circuit, control method and modular multilevel converter
CN108414856A (en) * 2018-02-26 2018-08-17 南方电网科学研究院有限责任公司 Service life evaluation method and device for submodule capacitor of modular multilevel converter
CN109995258A (en) * 2019-05-15 2019-07-09 重庆大学 A kind of inverse-impedance type diode clamp bit submodule and its fault current blocking-up method
CN113176428A (en) * 2021-03-16 2021-07-27 上海交通大学 Current distortion eliminating system and method for working condition simulation of cascaded converter

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CN102904417A (en) * 2011-12-24 2013-01-30 许继集团有限公司 Adaptive modulation method for submodule capacitor voltage of modular multi-level commutation device
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Cited By (6)

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Publication number Priority date Publication date Assignee Title
CN106787824A (en) * 2017-02-09 2017-05-31 南方电网科学研究院有限责任公司 Submodule circuit, control method and modular multilevel converter
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CN109995258A (en) * 2019-05-15 2019-07-09 重庆大学 A kind of inverse-impedance type diode clamp bit submodule and its fault current blocking-up method
CN113176428A (en) * 2021-03-16 2021-07-27 上海交通大学 Current distortion eliminating system and method for working condition simulation of cascaded converter

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