CN107565839A - A kind of design and control method for reducing bridge-type MMC submodule electric capacity - Google Patents
A kind of design and control method for reducing bridge-type MMC submodule electric capacity Download PDFInfo
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Abstract
The invention discloses a kind of design and control method for reducing bridge-type MMC submodule electric capacity, by the negative level fan-out capability for utilizing bridge-type submodule in the steady state, in the case where keeping transverter transmission capacity and DC voltage constant, increase AC phase voltage peak value, make index of modulation m2＞ 1, alternating voltage lifting operation is realized, reduces the fluctuation of submodule capacitor voltage to a certain extent.On the basis of pressure-raising operation, with reference to two frequency multiplication circulation optimal controls, submodule capacitor voltage stability bandwidth in full operation area can be made further to reduce, so as to effectively reduce submodule capacitor requirements, reduce the cost of submodule.
Description
Technical field
The invention belongs to multilevel power electronic converter technical field, and bridge-type MMC is reduced more particularly, to one kind
The design and control method of submodule electric capacity.
Background technology
Modularization multi-level converter (Modular Multilevel Converter, MMC) by its switching device without
Sound state voltage-sharing, easily extension, system effectiveness be high and the advantages such as output waveform quality is good, it has also become is changed in flexible DC power transmission
Flow the first choice topology of device.
In the existing flexible DC power transmission engineering based on MMC, the transverter based on semi-bridge type submodule topology is used.
Semi-bridge type MMC does not possess direct-current short circuit failure defense ability, it is necessary to be realized by AC breaker or DC side breaker
The removing of DC side failure.But DC Line Fault can only be realized in phase current zero crossing according to AC breaker, breaker
Removing, delay after a failure and between breaker effective action be present, dc-side short-circuit fault can be caused to develop into AC
Short trouble, and AC circuit breaker reclosing time sequence is complex；According to DC side breaker, because DC current did not had
Zero point, the technical difficulty of dc circuit breaker is big, according to CIGRE literature surveys, can be applied to ± 500kV and ± 800kV high straightening
It is respectively 10 years and 15 years or so to flow the breaker development time.
Bridge-type MMC can be carried out based on the bridge-type submodule for possessing negative level fan-out capability to direct-current short circuit failure
Initiative Defense.But due to number increase of the bridge-type submodule compared to semi-bridge type submodule switching device, therefore can produce
The problem of loss of high construction cost and operation, these problems also limit bridge-type MMC actual soft to a certain extent
Application in property DC transmission engineering.Existing submodule capacitor requirements reduce scheme mainly by injecting two frequencys multiplication in bridge arm
Circulation, realize the reduction of submodule capacitor voltage fluctuation.But there is the through-flow deficiency of increase switching device in such scheme.
As can be seen here, construction cost existing for existing bridge-type MMC application technologies is high, running wastage is big, and is difficult to not
In the case that increase switching device is through-flow, the technical problem that voltage fluctuation of capacitor reduces is realized.
The content of the invention
For the disadvantages described above or Improvement requirement of prior art, the invention provides one kind to reduce bridge-type MMC submodules
The design and control method of electric capacity, thus solve construction cost height, running wastage existing for existing bridge-type MMC application technologies
Greatly, and be difficult to do not increase switching device it is through-flow in the case of, realize voltage fluctuation of capacitor reduce technical problem.
To achieve the above object, the invention provides a kind of design and controlling party for reducing bridge-type MMC submodule electric capacity
Method, including：
(1) transverter transmission capacity S, DC voltage U are keptdcIt is constant, export energy using bridge-type submodule negative level
Power, lift AC voltage peak so that index of modulation m2＞ 1；
(2) after lifting AC voltage peak, the increase of bridge arm maximum output voltage is constant in submodule electric capacity rated voltage
In the case of, to meet bridge arm maximum output voltage demand, the submodule number of each bridge arm isN is each bridge
The original submodule number of arm, m1For raw modulation coefficient, 0 ＜ m1≤1；
(3) as index of modulation m2＞ 1, the bridge arm submodule number of each bridge arm areWhen, obtain harmonic circulating current
Under suppression, submodule capacitor voltage stability bandwidth ε, then using two frequency multiplication circulation control algolithms, work as power-factor angle[- π,
π] region in when, calculate difference two double frequency voltage UhUnder being combined with phase angle [alpha], the submodule capacitor voltage of each power-factor angle
The minimum value ε of stability bandwidthmin；
(4) with εminIn maximum as the control targe under full operation area, obtain under the control targe each power because
The double frequency voltage of target two and target phase angles corresponding to number angle, bridge arm is superimposed to by the double frequency voltage of target two and target phase angles
Voltage instruction value, under conditions of submodule switching device through-current capability is not increased, make submodule capacitor voltage stability bandwidth notable
Reduce.
Further, it is after the lifting of AC voltage peak：Wherein, UamFor AC
Voltage peak.
Further, when harmonic circulating current is effectively suppressed, submodule capacitor voltage stability bandwidth ε is：
Wherein, C represents submodule capacitance, VcSubmodule capacitor voltage is represented, ω represents fundamental frequency angular speed.
Further, two 0≤U of double frequency voltage in step (3)h≤0.5Udc, the π of 0≤α of phase angle≤2.
In general, by the contemplated above technical scheme of the present invention compared with prior art, it can obtain down and show
Beneficial effect：
The present invention keeping transverter transmission by using the negative level fan-out capability of bridge-type submodule, holding in the steady state
In the case that amount and DC voltage are constant, increase AC phase voltage peak value, as index of modulation m2During ＞ 1, exchange is realized
Side pressure-raising operation, can be such that submodule capacitor voltage stability bandwidth reduces to a certain extent.Further, appropriate control bridge is passed through
The frequency multiplication circulation of arm two, can further reduce submodule capacitor voltage on the premise of the through-current capability of switching device is not increased
It stability bandwidth, can so reduce submodule capacitance, advantageously reduce the volume of submodule, weight and cost.
Brief description of the drawings
Fig. 1 is a kind of design and control method for reducing bridge-type MMC submodule electric capacity provided in an embodiment of the present invention
Flow chart；
Fig. 2 is m in full operation area in the case of the loop current suppression that the embodiment of the present invention 1 provides1=1 and m2When=1.414
Submodule capacitor voltage stability bandwidth curve；
Fig. 3 (a) is row for the national games under natural circulation, loop current suppression and the circulation optimal control that the embodiment of the present invention 2 provides
Voltage fluctuation of capacitor rate curve in region；
Fig. 3 (b) is row for the national games under natural circulation, loop current suppression and the circulation optimal control that the embodiment of the present invention 2 provides
Bridge arm current virtual value curve in region.
Embodiment
In order to make the purpose , technical scheme and advantage of the present invention be clearer, it is right below in conjunction with drawings and Examples
The present invention is further elaborated.It should be appreciated that the specific embodiments described herein are merely illustrative of the present invention, and
It is not used in the restriction present invention.As long as in addition, technical characteristic involved in each embodiment of invention described below
Conflict can is not formed each other to be mutually combined.
As shown in figure 1, a kind of design and control method for reducing bridge-type MMC submodule electric capacity, including：
(1) transverter transmission capacity S, DC voltage U are keptddcIt is constant, export energy using bridge-type submodule negative level
Power, lift AC voltage peak so that index of modulation m2＞ 1；It is after the AC voltage peak lifting：Wherein, UamFor AC voltage peak.
(2) after lifting AC voltage peak, the increase of bridge arm maximum output voltage is constant in submodule electric capacity rated voltage
In the case of, to meet bridge arm maximum output voltage demand, the submodule number of each bridge arm isN is each bridge
The original submodule number of arm, m1For raw modulation coefficient, 0 ＜ m1≤1；
(3) as index of modulation m2＞ 1, the bridge arm submodule number of each bridge arm areWhen, derive harmonic circulating current
Under suppression, submodule capacitor voltage stability bandwidth ε.On this basis, using two frequency multiplication circulation control algolithms, in power-factor angle
When in the region of [- π, π], two double frequency voltage U of difference are calculatedhUnder being combined with phase angle [alpha], the submodule electricity of each power-factor angle
Hold the minimum value ε of voltage fluctuation ratemin；Two 0≤U of double frequency voltageh≤0.5Udc, the π of 0≤α of phase angle≤2, harmonic circulating current had
When effect suppresses, submodule capacitor voltage stability bandwidth ε is：
Wherein, C represents submodule capacitance, VcSubmodule capacitor voltage is represented, ω represents fundamental frequency angular speed.
(4) with εminIn maximum as control targe, obtain the double frequency voltage of target two and the mesh under each power-factor angle
Phase angle is marked, the double frequency voltage of target two and target phase angles are superimposed to bridge arm voltage command value, is not increasing submodule switch
Under conditions of device through-current capability, significantly reduce submodule capacitor voltage stability bandwidth.
Embodiment 1
The embodiment of the present invention 1 to illustrate keep transverter transmission capacity and DC voltage it is constant in the case of,
AC phase voltage is lifted, it is m to make the index of modulation2=1.414, reduce submodule capacitor voltage stability bandwidth, reduce submodule
Superiority in terms of capacitor requirements.
For clearer explanation, analyzed as follows：
Assuming that on the premise of transverter is operated in rectification state, and harmonic circulating current is effectively suppressed, using bridge arm in a phases as
Example, can obtain bridge arm voltage, electric current is：
Wherein, vpa, ipaFor bridge arm voltage and electric current in a phases, UdcFor DC side rated voltage, idc, iaRespectively DC side
Electric current and AC phase current instantaneous value, m are the index of modulation, and ω is fundamental frequency angular speed,For power-factor angle, t is system operation
Time.
Keeping transverter transmission capacity S and DC voltage UdcIn the case of constant, DC side electric current and transverter
Transmission capacity relation is represented by：
Therefore, upper bridge arm instantaneous power ppaFor：
Wherein, ppaFor upper bridge arm instantaneous power.
By taking bridge arm in a phases as an example, its energy stored can be obtained by being integrated to instantaneous power, be shown below：
Wherein, EmEnergy is stored for upper bridge arm.
To calculate Em, it is necessary first to calculate ppaZero crossing.Submodule capacitor voltage stability bandwidth ε and bridge arm storage ENERGY Em
Relation be：
Wherein, ε is submodule capacitor voltage stability bandwidth, and N is bridge arm submodule number, and C is submodule capacitance, VcFor son
Module capacitance voltage.
Therefore, in different modulating Coefficient m and power factorIn the range of, the expression formula of submodule capacitor voltage stability bandwidth
For：
Above-mentioned expression formula can also be expressed as：
Preferably, to meet bridge arm maximum output voltage demand, as index of modulation m2When=1.414, bridge arm maximum output
Voltage is m11.207 times when=1.Therefore in the case where submodule electric capacity rated voltage is constant, each bridge arm submodule
Number needs to increase as original 1.207 times.
In transverter transmission capacity S and DC voltage UdcNecessarily, under conditions of bridge arm circulation is effectively suppressed, m1=
1 and m2When=1.414 (m=1 and m=1.414), the voltage fluctuation of capacitor rate ε under full operation area is as shown in Fig. 2 in accompanying drawing.
Wherein, solid line and dotted line point ratio are m1=1 and m2When=1.414, the voltage fluctuation of capacitor rate curve under full operation area.Observation
Fig. 2 curves are understood：
1) compared to m1=1, using bridge-type submodule negative level fan-out capability, realize that AC pressure-raising is run, make tune
Coefficient m processed2=1.414, the stability bandwidth of submodule capacitor voltage can be made reduce to a certain extent in full operation area.
2) still, in Practical Project, the selection principle of submodule capacitance parameter should meet entirely for voltage fluctuation of capacitor rate
Maximum fluctuation rate under operation area.And and m1=1 compares, and by lifting AC voltage peak, makes the index of modulation be
1.414, the maximum fluctuation rate under full operation area is reduced to 0.65p.u. (as shown in A1 in Fig. 2 and B1) from 0.98p.u., drops
Low amplitude is smaller.
Therefore consider further to reduce submodule capacitor voltage stability bandwidth by two frequency multiplication circular current control methods.
Embodiment 2
This example to illustrate keep transverter transmission capacity and DC voltage it is constant in the case of, utilize pressure-raising
Operation makes m2=1.414 schemes combined with two frequency multiplication circulation optimal controls, reducing submodule capacitor voltage stability bandwidth, reducing
Superiority in terms of submodule capacitor requirements.
For clearer explanation, analyzed as follows：
The first step：Calculate under each power-factor angle, minimum voltage fluctuation of capacitor rate in different circulation injecting schemes, and select
The maximum of wherein stability bandwidth is selected as final control targe εtarget；Two 0≤U of double frequency voltage in different circulation injecting schemesh
≤0.5Udc, the π of 0≤α of phase angle≤2.
Second step：Control targe ε in the first steptarget, calculate it is all make stability bandwidth meet 0.98 εtarget≤ε
≤1.02εtargetTwo double frequency voltage UhAnd phase angle [alpha]；
3rd step：Calculate each group of (U of gained in second steph, α) corresponding to bridge arm current, wherein meeting bridge arm currentMinimum UhWith α as final control targe (IrmsmaxRepresent under nature circulation state, bridge arm
The maximum of electric current).If all of UhThe limitation requirement of bridge arm current is all unsatisfactory for α, then changes the control in the first step
Target εtarget, i.e. εtarget_NEW=1.02 εtarget。
By above-mentioned control method, can further subtract under conditions of submodule switching device through-current capability is not increased
The stability bandwidth of small capacitances voltage.
Validity to illustrate the invention, the parameter of MMC systems as shown in table 1 is taken to be calculated.Voltage fluctuation of capacitor with
The a reference value of bridge arm current is respectively m1When=1, the maximum of fluctuation and electric current under full operation area.Controlled according to above-mentioned circulation
Scheme, voltage fluctuation of capacitor and bridge arm current curve under full operation area are drawn, as shown in Figure 3.Wherein, three songs of Fig. 3 (a)
Line represents m respectively2When=1.414, under natural circulation, loop current suppression and circulation optimal control, the electric capacity in full operation area
Voltage fluctuation rate curve；Three curves of Fig. 3 (b) represent m respectively2When=1.414, natural circulation, loop current suppression and circulation are excellent
Change under control, the bridge arm current virtual value curve in full operation area；
The pressure-raising of table 1 is run, and makes index of modulation m2When=1.414, system parameter table
| Systematic parameter | Numerical value |
| Transverter transmission capacity | 400MVA |
| Specified alternating voltage | 346.35kV |
| Rated direct voltage | ±200kV |
| Bridge arm submodule number | 242 |
| Bridge arm inductance | 0.248H (13%) |
| Submodule electric capacity | 7424μF |
As can be seen from Figure 3：
1) control program that the AC pressure-raising operation proposed using this patent is combined with two frequency multiplication circulation optimal controls,
Submodule capacitor voltage stability bandwidth can be further reduced, is reduced to submodule capacitor voltage stability bandwidth in full operation area
0.34p.u., so as to reduce submodule capacitor requirements, reduce transverter cost.
2) the circulation optimization control scheme and by this programme proposed, the same of submodule capacitor voltage can also reduced
When, bridge arm current virtual value is not increased.Indicate effectiveness of the invention.
Analyzed according to embodiment 1 and embodiment 2, it is known that in Practical Project, the selection principle of submodule capacitance parameter is
Voltage fluctuation of capacitor rate should meet the maximum fluctuation rate under full operation area.And and m1=1 compares, by lifting AC voltage
Peak value, it is 1.414 to make the index of modulation, and the maximum fluctuation rate under full operation area is reduced to 0.65p.u. from 0.98p.u..Therefore
Consider that other controls further reduce submodule capacitor voltage stability bandwidth.Keep transverter transmission capacity and DC voltage not
Become, lift AC voltage, ac-side current can be reduced, so as to reduce the bridge arm current of transverter.Therefore, selection is suitable
Two frequency multiplication circulation control scheme, can further reduce submodule on the premise of the through-current capability of switching device is not increased
Block voltage fluctuation of capacitor rate.When the index of modulation is 1.414, using two frequency multiplication circulation system optimizing controls, do not increasing switch
It in the case of the through-current capability of device, can be further reduced to the voltage fluctuation of capacitor rate in full operation area
0.34p.u., so as to reduce submodule capacitor requirements, reduce submodule block cost.
As it will be easily appreciated by one skilled in the art that the foregoing is merely illustrative of the preferred embodiments of the present invention, not to
The limitation present invention, all any modification, equivalent and improvement made within the spirit and principles of the invention etc., all should be included
Within protection scope of the present invention.
Claims (4)
- A kind of 1. design and control method for reducing bridge-type MMC submodule electric capacity, it is characterised in that including：(1) transverter transmission capacity S, DC voltage U are keptdcIt is constant, using bridge-type submodule negative level fan-out capability, carry Rise AC voltage peak so that index of modulation m2＞ 1；(2) after lifting AC voltage peak, bridge arm maximum output voltage increase, in the feelings that submodule electric capacity rated voltage is constant Under condition, to meet bridge arm maximum output voltage demand, the submodule number of each bridge arm isN is each bridge arm Original submodule number, m1For raw modulation coefficient, 0 ＜ m1≤1；(3) as index of modulation m2＞ 1, the bridge arm submodule number of each bridge arm areWhen, obtain harmonic circulating current suppression Under, submodule capacitor voltage stability bandwidth ε, then using two frequency multiplication circulation control algolithms, work as power-factor angleAt [- π, π] When in region, two double frequency voltage U of difference are calculatedhUnder being combined with phase angle [alpha], the submodule capacitor voltage fluctuation of each power-factor angle The minimum value ε of ratemin；(4) with εminIn maximum as the control targe under full operation area, obtain each power-factor angle under the control targe The corresponding double frequency voltage of target two and target phase angles, the double frequency voltage of target two and target phase angles are superimposed to bridge arm voltage Command value, under conditions of submodule switching device through-current capability is not increased, significantly reduce submodule capacitor voltage stability bandwidth.
- 2. a kind of design and control method for reducing bridge-type MMC submodule electric capacity as claimed in claim 1, its feature exist In being after AC voltage peak lifting：Wherein, UamFor AC voltage peak.
- 3. a kind of design and control method for reducing bridge-type MMC submodule electric capacity as claimed in claim 1 or 2, its feature It is, under the harmonic circulating current suppresses, submodule capacitor voltage stability bandwidth ε is：Wherein, C represents submodule capacitance, VcSubmodule capacitor voltage is represented, ω represents fundamental frequency angular speed.
- 4. a kind of design and control method for reducing bridge-type MMC submodule electric capacity as claimed in claim 1 or 2, its feature It is, two 0≤U of double frequency voltage in the step (3)h≤0.5Udc, the π of 0≤α of phase angle≤2.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109039126A (en) * | 2018-08-24 | 2018-12-18 | 华中科技大学 | A kind of control method reducing the loss of bridge-type MMC submodule |
| CN112701894A (en) * | 2021-01-26 | 2021-04-23 | 北京四方继保自动化股份有限公司 | Loop current injection MMC module voltage fluctuation suppression method considering bridge arm current |
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| CN104485830A (en) * | 2014-12-09 | 2015-04-01 | 清华大学 | Method for reducing capacitance value of modular multilevel converter |
| CN105391329A (en) * | 2015-12-11 | 2016-03-09 | 华中科技大学 | Full-bridge type MMC (modular multilevel converter) alternating voltage-boosting operation method |
| JP2016063610A (en) * | 2014-09-17 | 2016-04-25 | 株式会社東芝 | Power conversion device |
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2016063610A (en) * | 2014-09-17 | 2016-04-25 | 株式会社東芝 | Power conversion device |
| CN104485830A (en) * | 2014-12-09 | 2015-04-01 | 清华大学 | Method for reducing capacitance value of modular multilevel converter |
| CN105391329A (en) * | 2015-12-11 | 2016-03-09 | 华中科技大学 | Full-bridge type MMC (modular multilevel converter) alternating voltage-boosting operation method |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109039126A (en) * | 2018-08-24 | 2018-12-18 | 华中科技大学 | A kind of control method reducing the loss of bridge-type MMC submodule |
| CN112701894A (en) * | 2021-01-26 | 2021-04-23 | 北京四方继保自动化股份有限公司 | Loop current injection MMC module voltage fluctuation suppression method considering bridge arm current |
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