CN106301054A - A kind of modified model POD modulation strategy of cascaded H-bridges photovoltaic DC-to-AC converter - Google Patents
A kind of modified model POD modulation strategy of cascaded H-bridges photovoltaic DC-to-AC converter Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—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
- H02M7/53—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 using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/539—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency
- H02M7/5395—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency by pulse-width modulation
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/12—Arrangements for reducing harmonics from ac input or output
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/12—Arrangements for reducing harmonics from ac input or output
- H02M1/123—Suppression of common mode voltage or current
-
- 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
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
Abstract
The present invention discloses the modified model POD modulation strategy of a kind of cascaded H-bridges photovoltaic DC-to-AC converter, including: obtain, according to the on off state of each H bridge module left and right brachium pontis, 16 on off states that said two H bridge module comprises；When the DC input voitage of said two H bridge module is identical, calculate the said two H bridge module parasitic capacitor voltage sum that each on off state in described 16 on off states is corresponding；Select all on off states that the total parasitic capacitor voltage sum of said two H bridge module keeps constant, and form two kinds of Switch State Combination in Power Systems；According to the two Switch State Combination in Power Systems, being compared with carrier wave by modulating wave, generate PWM drive signal, and be controlled the switching tube of said two H bridge module, this modulation strategy is effectively improved the inhibition of photovoltaic combining inverter leakage current.
Description
Technical field
The invention belongs to active inverter technical field, relate to a kind of drain current suppressing side being applied to photovoltaic DC-to-AC converter
Method, particularly relates to the modified model POD modulation strategy of a kind of cascaded H-bridges photovoltaic DC-to-AC converter, and it is applicable to photovoltaic power generation grid-connecting field.
Background technology
Photovoltaic DC-to-AC converter (Photovoltaic inverter) is that a kind of electric power being made up of semiconductor device adjusts dress
Put, be mainly used in direct current power to be converted into alternating electromotive force；Typically it is made up of boosting loop and inversion bridge type return, loop of boosting
DC voltage needed for the output of the dc voltage boost of solar cell to inverter is controlled；Inversion bridge type return is then after boosting
DC voltage be equivalently converted into the alternating voltage of conventional frequency.
For H bridge photovoltaic DC-to-AC converter, the low-voltage direct side of each of which module can carry out independently-powered by photovoltaic panel, it is simple to real
The MPPT of existing each module controls, and therefore H bridge topology is particularly well-suited to photovoltaic DC-to-AC converter.Compared with traditional inverter, H bridge light
Volt inverter possesses clear superiority, and such as switching frequency is low, wave filter volume is little, be prone to modularity etc..
H bridge photovoltaic DC-to-AC converter can reach grid-connected required voltage by cascade module, and therefore such inverter need not become
Depressor, reduces cost further, improves power density.But, H bridge photovoltaic DC-to-AC converter lacks the buffer action of transformator, photovoltaic
There is direct electrical equipment between plate and electrical network to connect, cause the parasitic capacitance between photovoltaic panel and the earth to form loop, produce electric leakage
Stream.So having a strong impact on efficiency and the reliability of system, even personal safety is threatened；Therefore, how to suppress photovoltaic inverse
The leakage current becoming device just becomes of crucial importance.
In China's photovoltaic standard GB/T30427-2013, the leakage current to photovoltaic parallel in system has specified below: if photovoltaic is inverse
The specified output becoming device is less than 30kVA, then the amplitude of leakage current have to be lower than 300mA, and otherwise photovoltaic DC-to-AC converter should be in 0.3s
Disconnect and export fault-signal.The low-pressure grid-connection instruction VDE0126-1-1 of Germany also has relevant regulation to leakage current.
At present, traditional drain current suppressing method can be summarized as following three kinds, is respectively as follows: 1) use modified model topology,
Such as H5 topology, H6 topological sum Heric topology etc.；2) passive filter is used, such as common mode inductance and electromagnetic interface filter etc.；3) use
New modulation strategy.
In terms of above three, scholars have all carried out correlational study, such as document " High-efficiency single-
phase transformerless PV H6inverter with hybrid modulation method”BaojianJi,
Jianhua Wang,Jianfeng Zhao,《IEEE Transactions on Industrial Elect-ronics》,
2013,60 (5), 2,104 2115 (" hybrid modulation method of high-efficiency single-phase non-isolation type H6 inverter ", " IEEE journal-industry
Electronic journal ", volume 60 the 5th phase page 2,104 2115 in 2013) use Cascade H 6 topology, although inhibit to a certain extent
Leakage current, but compared with traditional H4 topology, its modulation strategy is relative complex, and autgmentability is poor, and cost is along with cascade module number
Amount increases and increases.
Document " Analysis and suppression of leakage current in
cascadedmultilevell-inverter based PV systems”Y.Zhou and H.Li,《IEEE
TransPowerElectro-nics ", 2014,29 (10), 5,265 5277 (" cascade connection multi-level photovoltaic inverter leakage current analyses
With suppression ", " IEEE journal-power electronics periodical ", volume 29 the 10th phase page 5,265 5277 in 2014) and document
“Eliminating Ground Current in a TransformerlessPhotovoltaicApplication”
Freijedo,Alejandro G.Yepes,JanoMalvar,et al.《IEEE Transacion-sonEnergy
Conversion ", 2010,25 (1), 140-147 (" eliminating the leakage current of non-isolation type photovoltaic application occasion ", " IEEE journal-
Energy conversion periodical ", volume 25 the 1st phase page 140 147 in 2010) propose by adding passive filter in each H bridge
The scheme of suppression leakage current, although the program can suppress leakage current effectively, but along with the increase of H bridge cascade quantity, inversion
The volume of device is consequently increased with cost.
Document " A New Modulation Technique to Eliminate Leakage Current in
Transformerless PV Inverter " propose inject triple-frequency harmonics method, reduce common-mode voltage size, but, should
Modulation strategy is only applicable to single H bridge module, for multiple H bridge modules, leakage current not only with the common-mode voltage of this module
Relevant, also relevant with the differential mode voltage of other module, therefore this modulation strategy is to be applied to multiple H bridge module, in addition it is also necessary to enter
One step research.
Document " Hybrid Multicarrier Modulation to Reduce Leakage Current in a
Transformerless Cascaded Multilevel Inverter for Photovoltaic Systems”
Rajasekar Selvamuthukumaran,AbhishekGarg,and Rajesh Gupta.《IEEE Transactions
On Power Electronics ", 2015,30 (4): 1779-1783 (" for non-isolation type cascaded multilevel inverter photovoltaic
The mixing multi-carrier modulation strategy of system ", " IEEE journal-power electronics periodical ", the 4th phase 1,779 1783 of volume 30 in 2015
Page) POD (the Phase Opposite Disposition) modulation strategy of a kind of correction is proposed, use common-mode voltage to cut at switch
The principle that when changing, amplitude change is minimum is to suppress leakage current, but the common-mode voltage obtained by this modulation strategy yet suffers from high frequency division
Amount, does not suppresses the leakage current of cascaded H-bridges the most effectively.
Summary of the invention
In order to solve above-mentioned leakage problem, the present invention, by the angle from the third drain current suppressing method, carries
Go out a kind of new modified model POD modulation strategy, parasitic capacitor voltage sum can be made to keep constant or low frequency variation, effectively suppress
The leakage current of cascaded H-bridges.
The embodiment provides the modified model POD modulation strategy of a kind of cascaded H-bridges photovoltaic DC-to-AC converter, its feature exists
In, described suppressing method includes:
On off state according to each H bridge module left and right brachium pontis obtains 16 switch shapes that said two H bridge module comprises
State；
When the DC input voitage of said two H bridge module is identical, calculate each switch in described 16 on off states
The said two H bridge module parasitic capacitor voltage sum that state is corresponding；
Select all on off states that the total parasitic capacitor voltage sum of said two H bridge module keeps constant, and group
Become two kinds of Switch State Combination in Power Systems；
According to the two Switch State Combination in Power Systems, compared with carrier wave by modulating wave, generate PWM drive signal, and
The switching tube of said two H bridge module is controlled.
In one embodiment of the invention, when generating PWM drive signal, described carrier wave uses two carrier signals
Tri1, tri2, and at that time between when being positioned between (0, T/2), tri1>tri2,0.5<tri1<1,0<tri2<0.5；Meta at that time
Time between (T/2, T), carrier wave tri1 and carrier wave tri2 is all reverse, and tri1 < tri2, and 0 < tri1 < 0.5,0.5 < tri2 < 1, adjust
Ripple v processedrefNegative half-cycle carried out reversely, and modulation degree is 0.9.
In one embodiment of the invention, said two H is obtained according to the on off state of each H bridge module left and right brachium pontis
16 on off states that bridge module comprises, including:
Represent shutoff and the opening state of switching tube on the brachium pontis of each H bridge module left and right respectively by numeral 0,1, then described
The switch function S of two H bridge modulesa1/Sb1/Sa2/Sb216 on off states are produced as follows: 0101 in different conditions combination,
0100,0111,0110,0001,1101,0000,1111,0011,1100,0010,1110,1001,1000,1011,1010；Its
In, Sa1The switch function of pipe, S on the left brachium pontis of representation module oneb1The switch function of pipe, S on the right brachium pontis of representation module onea2Represent
The switch function of pipe, S on the left brachium pontis of module twob2The switch function of pipe on the right brachium pontis of representation module two；Opening up and down of each brachium pontis
Close pipe complementary duty.
In one embodiment of the invention, if the DC input voitage of two H bridge modules is identical and be vpv, the most each H
Bridge output-vpv、0、vpvThree kinds of level, two total-2v of H bridge modulepv、-vpv、0、vpv、2vpvFive kinds of output levels；Described 16
Individual on off state ultimately forms the-2v of two H bridge modulespv、-vpv、0、vpv、2vpvFive kinds of output levels.
In one embodiment of the invention, calculate that in described 16 on off states, each on off state is corresponding described two
Individual H bridge module parasitic capacitor voltage sum, including:
Wherein, vcpv1And vcpv2It is respectively the parasitic capacitor voltage value of two H bridge modules, va1n1、vb1n1、va2n2And vb2n2Point
Wei four brachium pontis outfan a of said two H bridge module1、b1、a2And b2To common point n1And n2Voltage；vgFor line voltage.
In one embodiment of the invention, form two kinds of Switch State Combination in Power Systems, including:
Selection parasitic capacitor voltage sum of sening as an envoy to is vpvAll on off states, and according to two H bridge module output levels
During switching, switching tube action frequency minimum principle composition two kinds of Switch State Combination in Power Systems be:
1010-1000-1100-0011-0001-0101 and 1010-1110-1100-0011-0111-0101.
In one embodiment of the invention, according to the two Switch State Combination in Power Systems, carried out with carrier wave by modulating wave
Relatively, generate PWM drive signal, and the switching tube of said two H bridge module is controlled, including:
The PWM drive signal of the first described Switch State Combination in Power Systems 1010-1000-1100-0011-0001-0101 generates
Mode includes:
As modulating wave vrefWhen being positioned at (0, T/2) half period interval, Sa1=1, Sb2=0；Sb1By modulating wave and carrier wave tri2
Relatively obtain, if vref> tri2, Sb1=0, otherwise Sb1=1；Sa2Compared with carrier wave tri1 by modulating wave and obtain, if vref> tri1,
Sa2=1, otherwise Sa2=0；
As modulating wave vrefWhen being positioned at (T/2, T) half period interval, then Sa1=0, Sb2=1；Sb1By modulating wave vrefWith carrier wave
Tri1 compares and obtains, if vref< tri1, Sb1=0, otherwise Sb1=1；Sa2By modulating wave vrefCompare with carrier wave tri2 and obtain, if
vref< tri2, Sa2=1, otherwise Sa2=0；
The PWM drive signal of Switch State Combination in Power Systems 1010-1110-1100-0011-0111-0101 described in the second generates
Mode includes:
As modulating wave vrefWhen being positioned at (0, T/2) half period interval, Sa1=1, Sb2=0；Sb1By modulating wave and carrier wave tri1
Relatively obtain, if vref> tri1, Sb1=0, otherwise Sb1=1；Sa2Compared with carrier wave tri2 by modulating wave and obtain, if vref> tri2,
Sa2=1, otherwise Sa2=0；
As modulating wave vrefWhen being positioned at (T/2, T) half period interval, then Sa1=0, Sb2=1；Sb1By modulating wave vrefWith carrier wave
Tri2 compares and obtains, if vref< tri2, Sb1=0, otherwise Sb1=1；Sa2By modulating wave vrefCompare with carrier wave tri1 and obtain, if
vref< tri1, Sa2=1, otherwise Sa2=0.
In one embodiment of the invention, described carrier wave is triangular carrier, and the carrier wave side that its adjacent half period is interval
To on the contrary.
Compared with prior art, the invention have the benefit that
Without passive filtering inductance and in the case of not changing existing topological structure, by new modified model
POD modulation strategy, makes parasitic capacitor voltage sum keep constant or low frequency sinusoidal amount, significantly decreases H bridge photovoltaic DC-to-AC converter
Leakage current.
Accompanying drawing explanation
In order to understand the explanation embodiment of the present invention or technical scheme of the prior art, below will be to embodiment or existing skill
In art description, the required accompanying drawing used is briefly described.Accompanying drawing in describing below is some embodiments of the present invention, right
In those of ordinary skill in the art, on the premise of not paying creative work, it is also possible to obtain other according to these accompanying drawings
Accompanying drawing.
The schematic flow diagram of a kind of drain current suppressing method that Fig. 1 provides for the embodiment of the present invention.
The schematic flow diagram of the another kind of drain current suppressing method that Fig. 2 provides for the embodiment of the present invention.
The schematic diagram of two module-cascade H bridge photovoltaic DC-to-AC converters that Fig. 3 provides for the embodiment of the present invention.
Two module-cascade H bridge photovoltaic DC-to-AC converter equivalent models that Fig. 4 provides for the embodiment of the present invention.
The first Switch State Combination in Power Systems that Fig. 5 provides for the embodiment of the present invention realize schematic diagram.
The second Switch State Combination in Power Systems that Fig. 6 provides for the embodiment of the present invention realize schematic diagram.
Detailed description of the invention
For making those skilled in the art be more fully understood that technical scheme, below in conjunction with the accompanying drawings and specific embodiment party
The case drain current suppressing method that be applied to cascaded H-bridges five-electrical level inverter a kind of to the present invention is described in further detail.Example
Only represent possible change.Unless explicitly requested, otherwise individually components and functionality is optional, and the order operated is permissible
Change.The part of some embodiments and feature can be included in or replace the forehead of other embodiments and divide and feature.This
The scope of the embodiment of invention includes the gamut of claims, and all obtainable equivalent of claims
Thing.
Below in conjunction with the accompanying drawings the present invention is described in further details.
Embodiment one
Refer to the modified model POD that Fig. 1, Fig. 1 are a kind of cascaded H-bridges photovoltaic DC-to-AC converters that the embodiment of the present invention one provides adjust
System strategy, wherein, described suppressing method includes:
On off state according to each H bridge module left and right brachium pontis obtains 16 switch shapes that said two H bridge module comprises
State；
When the DC input voitage of said two H bridge module is identical, calculate each switch in described 16 on off states
The said two H bridge module parasitic capacitor voltage sum that state is corresponding；
Select all on off states that the total parasitic capacitor voltage sum of said two H bridge module keeps constant, and group
Become two kinds of Switch State Combination in Power Systems；
According to the two Switch State Combination in Power Systems, compared with carrier wave by modulating wave, generate PWM drive signal, and
The switching tube of said two H bridge module is controlled.
Wherein, generate PWM drive signal time, described carrier wave use two carrier signals tri1, tri2, and at that time between be positioned at
Time between (0, T/2), tri1>tri2,0.5<tri1<1,0<tri2<0.5；When being positioned between at that time between (T/2, T), carrier wave
Tri1 and carrier wave tri2 is all reverse, and tri1 < tri2,0 < tri1 < 0.5,0.5 < tri2 < 1, modulating wave vrefNegative half-cycle enter
Go reversely, and modulation degree has been 0.9.
On off state according to each H bridge module left and right brachium pontis obtains 16 switch shapes that said two H bridge module comprises
State, including:
Represent shutoff and the opening state of switching tube on the brachium pontis of each H bridge module left and right respectively by numeral 0,1, then described
The switch function S of two H bridge modulesa1/Sb1/Sa2/Sb216 on off states are produced as follows: 0101 in different conditions combination,
0100,0111,0110,0001,1101,0000,1111,0011,1100,0010,1110,1001,1000,1011,1010；Its
In, Sa1The switch function of pipe, S on the left brachium pontis of representation module oneb1The switch function of pipe, S on the right brachium pontis of representation module onea2Represent
The switch function of pipe, S on the left brachium pontis of module twob2The switch function of pipe on the right brachium pontis of representation module two；Opening up and down of each brachium pontis
Close pipe complementary duty.
Wherein, if the DC input voitage of two H bridge modules is identical and be vpv, the most each H bridge output-vpv、0、vpvThree kinds
Level, two total-2v of H bridge modulepv、-vpv、0、vpv、2vpvFive kinds of output levels；Described 16 on off states ultimately form two
-the 2v of individual H bridge modulepv、-vpv、0、vpv、2vpvFive kinds of output levels.
Further, the said two H bridge module that in described 16 on off states, each on off state is corresponding is calculated parasitic
Capacitance voltage sum, including:
Wherein, vcpv1And vcpv2It is respectively the parasitic capacitor voltage value of two H bridge modules, va1n1、vb1n1、va2n2And vb2n2Point
Wei four brachium pontis outfan a of said two H bridge module1、b1、a2And b2To common point n1And n2Voltage；vgFor line voltage.
Further, selecting parasitic capacitor voltage sum of sening as an envoy to is vpvAll on off states, and according to two H bridge modules
Output level switching time, switching tube action frequency minimum principle composition two kinds of Switch State Combination in Power Systems be:
1010-1000-1100-0011-0001-0101 and 1010-1110-1100-0011-0111-0101.
According to the two Switch State Combination in Power Systems, compared with carrier wave by modulating wave, generate PWM drive signal, and
The switching tube of said two H bridge module is controlled, including:
The PWM drive signal of the first described Switch State Combination in Power Systems 1010-1000-1100-0011-0001-0101 generates
Mode includes:
As modulating wave vrefWhen being positioned at (0, T/2) half period interval, Sa1=1, Sb2=0；Sb1By modulating wave and carrier wave tri2
Relatively obtain, if vref> tri2, Sb1=0, otherwise Sb1=1；Sa2Compared with carrier wave tri1 by modulating wave and obtain, if vref> tri1,
Sa2=1, otherwise Sa2=0；
As modulating wave vrefWhen being positioned at (T/2, T) half period interval, then Sa1=0, Sb2=1；Sb1By modulating wave vrefWith carrier wave
Tri1 compares and obtains, if vref< tri1, Sb1=0, otherwise Sb1=1；Sa2By modulating wave vrefCompare with carrier wave tri2 and obtain, if
vref< tri2, Sa2=1, otherwise Sa2=0；
The PWM drive signal of Switch State Combination in Power Systems 1010-1110-1100-0011-0111-0101 described in the second generates
Mode includes:
As modulating wave vrefWhen being positioned at (0, T/2) half period interval, Sa1=1, Sb2=0；Sb1By modulating wave and carrier wave tri1
Relatively obtain, if vref> tri1, Sb1=0, otherwise Sb1=1；Sa2Compared with carrier wave tri2 by modulating wave and obtain, if vref> tri2,
Sa2=1, otherwise Sa2=0；
As modulating wave vrefWhen being positioned at (T/2, T) half period interval, then Sa1=0, Sb2=1；Sb1By modulating wave vrefWith carrier wave
Tri2 compares and obtains, if vref< tri2, Sb1=0, otherwise Sb1=1；Sa2By modulating wave vrefCompare with carrier wave tri1 and obtain, if
vref< tri1, Sa2=1, otherwise Sa2=0.
Wherein, described carrier wave is triangular carrier, and the carrier wave in its interval of adjacent half period is in opposite direction.
The present embodiment, by new modified model POD modulation strategy, it is ensured that parasitic capacitor voltage sum is constant or low frequency becomes
Amount, restrained effectively the leakage current of cascaded H-bridges, and solving prior art cascade H bridge photovoltaic combining inverter can not be effective
The problem of suppression leakage current, has reached preferably to suppress the effect of cascaded H-bridges photovoltaic combining inverter leakage current.
Embodiment two
Refer to the modified model POD that Fig. 2, Fig. 2 are a kind of cascaded H-bridges photovoltaic DC-to-AC converters that the embodiment of the present invention two provides adjust
System strategy, wherein, described suppressing method includes:
Step a, if the DC input voitage of two H bridge modules is equal, and is vpv, it is all that row write out that two modules comprise
16 on off states；
Step b, calculates the parasitic capacitor voltage of each module corresponding to described 16 on off states and total parasitic capacitance
Voltage sum；Selecting described parasitic capacitor voltage sum is vpvAll on off states；
Step c, during according to two H bridge module output level switchings, the principle composition two kinds that switching tube action frequency is minimum
Switch State Combination in Power Systems；
Step d, according to the two Switch State Combination in Power Systems, is compared with carrier wave by modulating wave, generates PWM and drives letter
Number, and the switching tube of said two H bridge module is controlled, thus realize the suppression of leakage current.
The schematic diagram of two module-cascade H bridge photovoltaic DC-to-AC converters that Fig. 3 provides for the embodiment of the present invention.In figure, Cpv1With
Cpv2For the parasitic capacitance between photovoltaic array and the earth, vpv1And vpv2It is the DC input voitage of two modules, Cin1And Cin2For
DC side input capacitance, L1And L2For grid side filter inductance, R1And R2For the dead resistance of grid side filter inductance, vgFor electrical network
Voltage.
If the DC input voitage of two H bridge modules is equal, and it is vpv, row write out all 16 that two modules comprise and open
Off status (Sa1/Sb1/Sa2/Sb2), and calculate the parasitic capacitor voltage of each module corresponding to each on off state and total parasitism
Capacitance voltage sum.
Wherein, Sa1The switch function of pipe, S on the left brachium pontis of representation module 1b1The switch letter of pipe on the right brachium pontis of representation module 1
Number, Sa2The switch function of pipe, S on the left brachium pontis of representation module 2b2The switch function of pipe on the right brachium pontis of representation module 2.It addition, it is each
Switch function can take 0 or 1,1 representation switch pipe conducting, and 0 representation switch pipe turns off, the complementation work of switching tube up and down of each brachium pontis
Make.
Fig. 4 is the cascaded H-bridges photovoltaic DC-to-AC converter equivalent model of two modules.Wherein, va1n1、vb1n1、va2n2And vb2n2Respectively
For each brachium pontis outfan a1、b1、a2And b2To common point n1And n2Voltage.As a example by the positive half period of power network current, it is assumed that net
Side filter inductance L1=L2, owing to leakage current is the least, therefore L1And L2The voltage approximately equal of upper generation and be vL, meanwhile, the filter of net side
The voltage of ripple inductance parasitic resistance is vR；
According to Fig. 4, Kirchhoff's law can obtain formula:
Can be obtained by above three formulas:
Due to line voltage vgPredominantly power frequency component, the least to the influence of leakage current in parasitic capacitance, analysis hereafter
Do not consider further that, therefore parasitic capacitance Cpv1And Cpv2Voltage vcpv1And vcpv2Can be expressed as:
Table 1 is on off state and the parasitic capacitor voltage of two H bridge modules, wherein vabFor total output voltage, vcpv1For H
The parasitic capacitor voltage of bridge module 1, vcpv2For the parasitic capacitor voltage of H bridge module 2, vcpv1+vcpv2It is posting of two H bridge modules
Raw capacitance voltage sum.It can be seen that two H bridge modules has five level outputs, it is respectively as follows: 2vpv、vpv、0、-vpvWith-
2vpv.Different switch function Sa1/Sb1/Sa2/Sb2When controlling switching tube, make the parasitic capacitor voltage sum of two H bridge modules
v’cpv1+v’cpv20～2vpvBetween there is high frequency change, thus produce leakage current.
The on off state of 1 two H bridge modules of table and parasitic capacitor voltage
The result calculated according to table 1, selecting parasitic capacitor voltage sum of sening as an envoy to is vpvAll on off states, and according to
During two H bridge module output level switchings, the principle composition the following two kinds Switch State Combination in Power Systems that switching tube action frequency is minimum, point
It is not:
1010-1000-1100-0011-0001-0101 and 1010-1110-1100-0011-0111-0101.
According to two kinds of selected Switch State Combination in Power Systems, generate PWM drive signal switch tube and be controlled, its realization side
Formula is modulating wave and two carrier waves compare and obtain pwm signal.
Wherein, two carrier signals are tri1, tri2, and at that time between when being positioned between (0, T/2), tri1>tri2,0.5<
Tri1 < 1,0 < tri2 < 0.5；When being positioned between at that time between (T/2, T), carrier wave tri1 and carrier wave tri2 is all reverse, and tri1 <
Tri2,0 < tri1 < 0.5,0.5 < tri2 < 1, modulating wave vrefNegative half-cycle carried out reversely, consistent with positive half period waveform,
For steamed bread shape, and modulation degree is 0.9.
Realizing the first Switch State Combination in Power Systems of embodiment as shown in Figure 5, concrete manner of comparison is as follows:
(1) as modulating wave vrefWhen being positioned at (0, T/2) half period interval, Sa1=1, Sb2=0；Sb1By modulating wave and carrier wave
Tri2 compares and obtains, if vref> tri2, Sb1=0, otherwise Sb1=1；Sa2Compared with carrier wave tri1 by modulating wave and obtain, if vref>
Tri1, Sa2=1, otherwise Sa2=0；
(2) as modulating wave vrefWhen being positioned at (T/2, T) half period interval, then Sa1=0, Sb2=1；Sb1By modulating wave vrefWith
Carrier wave tri1 compares and obtains, if vref< tri1, Sb1=0, otherwise Sb1=1；Sa2By modulating wave vrefCompare with carrier wave tri2 and obtain,
If vref< tri2, Sa2=1, otherwise Sa2=0；
Realizing the second Switch State Combination in Power Systems of embodiment as shown in Figure 6, concrete manner of comparison is as follows:
(1) as modulating wave vrefWhen being positioned at (0, T/2) half period interval, Sa1=1, Sb2=0；Sb1By modulating wave and carrier wave
Tri1 compares and obtains, if vref> tri1, Sb1=0, otherwise Sb1=1；Sa2Compared with carrier wave tri2 by modulating wave and obtain, if vref>
Tri2, Sa2=1, otherwise Sa2=0；
(2) as modulating wave vrefWhen being positioned at (T/2, T) half period interval, then Sa1=0, Sb2=1；Sb1By modulating wave vrefWith
Carrier wave tri2 compares and obtains, if vref< tri2, Sb1=0, otherwise Sb1=1；Sa2By modulating wave vrefCompare with carrier wave tri1 and obtain,
If vref< tri1, Sa2=1, otherwise Sa2=0；
Use the method by new modified model POD modulation strategy, it is ensured that parasitic capacitor voltage sum is constant or low frequency becomes
Amount, restrained effectively the leakage current of cascaded H-bridges.
Above content is to combine concrete preferred implementation further description made for the present invention, it is impossible to assert
Being embodied as of the present invention is confined to these explanations.For general technical staff of the technical field of the invention,
On the premise of present inventive concept, it is also possible to make some simple deduction or replace, all should be considered as belonging to the present invention's
Protection domain.
Claims (8)
1. the modified model POD modulation strategy of a cascaded H-bridges photovoltaic DC-to-AC converter, it is characterised in that described suppressing method includes:
On off state according to each H bridge module left and right brachium pontis obtains 16 on off states that said two H bridge module comprises；
When the DC input voitage of said two H bridge module is identical, calculate each on off state in described 16 on off states
Corresponding said two H bridge module parasitic capacitor voltage sum；
Select all on off states that the total parasitic capacitor voltage sum of said two H bridge module keeps constant, and form two
Plant Switch State Combination in Power Systems；
According to the two Switch State Combination in Power Systems, compared with carrier wave by modulating wave, generate PWM drive signal, and to institute
The switching tube stating two H bridge modules is controlled.
Suppressing method the most according to claim 1, it is characterised in that when generating PWM drive signal, described carrier wave uses two
Individual carrier signal tri1, tri2, and at that time between when being positioned between (0, T/2), tri1>tri2,0.5<tri1<1,0<tri2<
0.5；When being positioned between at that time between (T/2, T), carrier wave tri1 and carrier wave tri2 is all reverse, and tri1 < tri2, and 0 < tri1 < 0.5,
0.5 < tri2 < 1, modulating wave vrefNegative half-cycle carried out reversely, and modulation degree is 0.9.
Suppressing method the most according to claim 2, it is characterised in that according to the switch shape of each H bridge module left and right brachium pontis
State obtains 16 on off states that said two H bridge module comprises, including:
Shutoff and opening state, the then said two of switching tube on the brachium pontis of each H bridge module left and right is represented respectively by numeral 0,1
The switch function S of H bridge modulea1/Sb1/Sa2/Sb216 on off states are produced as follows: 0101,0100 in different conditions combination,
0111,0110,0001,1101,0000,1111,0011,1100,0010,1110,1001,1000,1011,1010；Wherein, Sa1
The switch function of pipe, S on the left brachium pontis of representation module oneb1The switch function of pipe, S on the right brachium pontis of representation module onea2Representation module two
The switch function of pipe, S on left brachium pontisb2The switch function of pipe on the right brachium pontis of representation module two；The switching tube up and down of each brachium pontis is mutual
Mend work.
Suppressing method the most according to claim 3, it is characterised in that if the DC input voitage of two H bridge modules is identical
And be vpv, the most each H bridge output-vpv、0、vpvThree kinds of level, two total-2v of H bridge modulepv、-vpv、0、vpv、2vpvFive kinds defeated
Go out level；Described 16 on off states ultimately form the-2v of two H bridge modulespv、-vpv、0、vpv、2vpvFive kinds of output levels.
Suppressing method the most according to claim 4, it is characterised in that calculate each switch shape in described 16 on off states
The said two H bridge module parasitic capacitor voltage sum that state is corresponding, including:
Wherein, vcpv1And vcpv2It is respectively the parasitic capacitor voltage value of two H bridge modules, va1n1、vb1n1、va2n2And vb2n2It is respectively
Four brachium pontis outfan a of said two H bridge module1、b1、a2And b2To common point n1And n2Voltage；vgFor line voltage.
Suppressing method the most according to claim 5, it is characterised in that form two kinds of Switch State Combination in Power Systems, including:
Selection parasitic capacitor voltage sum of sening as an envoy to is vpvAll on off states, and according to the switching of two H bridge module output levels
Time, switching tube action frequency minimum principle composition two kinds of Switch State Combination in Power Systems be: 1010-1000-1100-0011-0001-
0101 and 1010-1110-1100-0011-0111-0101.
Suppressing method the most according to claim 6, it is characterised in that according to the two Switch State Combination in Power Systems, by adjusting
Ripple processed compares with carrier wave, generates PWM drive signal, and is controlled the switching tube of said two H bridge module, including:
The PWM drive signal generating mode of the first described Switch State Combination in Power Systems 1010-1000-1100-0011-0001-0101
Including:
As modulating wave vrefWhen being positioned at (0, T/2) half period interval, Sa1=1, Sb2=0；Sb1Compared with carrier wave tri2 by modulating wave
Obtain, if vref> tri2, Sb1=0, otherwise Sb1=1；Sa2Compared with carrier wave tri1 by modulating wave and obtain, if vref> tri1, Sa2=
1, otherwise Sa2=0；
As modulating wave vrefWhen being positioned at (T/2, T) half period interval, then Sa1=0, Sb2=1；Sb1By modulating wave vrefWith carrier wave tri1
Relatively obtain, if vref< tri1, Sb1=0, otherwise Sb1=1；Sa2By modulating wave vrefCompare with carrier wave tri2 and obtain, if vref<
Tri2, Sa2=1, otherwise Sa2=0；
The PWM drive signal generating mode of Switch State Combination in Power Systems 1010-1110-1100-0011-0111-0101 described in the second
Including:
As modulating wave vrefWhen being positioned at (0, T/2) half period interval, Sa1=1, Sb2=0；Sb1Compared with carrier wave tri1 by modulating wave
Obtain, if vref> tri1, Sb1=0, otherwise Sb1=1；Sa2Compared with carrier wave tri2 by modulating wave and obtain, if vref> tri2, Sa2=
1, otherwise Sa2=0；
As modulating wave vrefWhen being positioned at (T/2, T) half period interval, then Sa1=0, Sb2=1；Sb1By modulating wave vrefWith carrier wave tri2
Relatively obtain, if vref< tri2, Sb1=0, otherwise Sb1=1；Sa2By modulating wave vrefCompare with carrier wave tri1 and obtain, if vref<
Tri1, Sa2=1, otherwise Sa2=0.
Suppressing method the most according to claim 1, it is characterised in that described carrier wave is triangular carrier, and its adjacent half cycle
The phase carrier wave in interval is in opposite direction.
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