CN106301054B - A kind of modified POD modulation strategy of cascaded H-bridges photovoltaic DC-to-AC converter - Google Patents
A kind of modified POD modulation strategy of cascaded H-bridges photovoltaic DC-to-AC converter Download PDFInfo
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- CN106301054B CN106301054B CN201610795774.7A CN201610795774A CN106301054B CN 106301054 B CN106301054 B CN 106301054B CN 201610795774 A CN201610795774 A CN 201610795774A CN 106301054 B CN106301054 B CN 106301054B
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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 a kind of modified POD modulation strategy of cascaded H-bridges photovoltaic DC-to-AC converter, comprising: obtains 16 switch states that described two H bridge modules include according to the switch state of each H bridge module or so bridge arm；When the DC input voitage of described two H bridge modules is identical, the sum of corresponding described two H bridge module parasitic capacitor voltages of each switch state in 16 switch states are calculated；All switch states that total the sum of the parasitic capacitor voltage of described two H bridge modules remains unchanged are selected, and form two kinds of Switch State Combination in Power Systems；It according to described two Switch State Combination in Power Systems, is compared by modulating wave with carrier wave, generates PWM drive signal, and control the switching tube of described two H bridge modules, which effectively improves the inhibitory effect of photovoltaic combining inverter leakage current.
Description
Technical field
The invention belongs to active inverter technical fields, are related to a kind of drain current suppressing side applied to photovoltaic DC-to-AC converter
The modified POD modulation strategy of method more particularly to a kind of cascaded H-bridges photovoltaic DC-to-AC converter, it is suitable for photovoltaic power generation grid-connecting fields.
Background technique
Photovoltaic DC-to-AC converter (Photovoltaic inverter) is a kind of electric power adjustment dress being made of semiconductor devices
It sets, direct current power is mainly used for be converted into AC power；It is generally made of boosting circuit and inversion bridge type return, circuit of boosting
DC voltage needed for dc voltage boost to inverter output control solar cell；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 be carried out by photovoltaic panel it is independently-powered, convenient for real
The now MPPT control of each module, therefore H bridge topology is especially suitable for photovoltaic DC-to-AC converter.Compared with traditional inverter, H bridge light
Volt inverter has clear superiority, such as switching frequency is low, filter is small in size, is easy to modularization etc..
Voltage needed for H bridge photovoltaic DC-to-AC converter can reach grid-connected by cascade module, therefore such inverter does not need to become
Depressor further reduces the cost, and improves power density.But H bridge photovoltaic DC-to-AC converter lacks the buffer action of transformer, photovoltaic
There are the connection of direct electric appliance between plate and power grid, the parasitic capacitance between photovoltaic panel and the earth is caused to be formed into a loop, generates electric leakage
Stream.So seriously affecting the efficiency and reliability of system, or even threaten to personal safety；Therefore, how to inhibit photovoltaic inverse
The leakage current for becoming device just becomes of crucial importance.
There is following regulation to the leakage current of photovoltaic parallel in system in Chinese photovoltaic standard GB/T30427-2013: if photovoltaic is inverse
The rated output for becoming device is less than 30kVA, then the amplitude of leakage current has to be lower than 300mA, and otherwise photovoltaic DC-to-AC converter should be in 0.3s
It disconnects and exports fault-signal.The low-pressure grid-connection instruction VDE0126-1-1 of Germany also has relevant regulation to leakage current.
Currently, traditional drain current suppressing method can be summarized as following three kinds, it is respectively as follows: and 1) uses modified topology,
Such as H5 topology, H6 topology and Heric topology；2) passive filter, such as common mode inductance and electromagnetic interface filter are used；3) it uses
New modulation strategy.
In terms of above three, scholars have carried out correlative study, such as document " High-efficiency single-
phase transformerless PV H6inverter with hybrid modulation method”BaojianJi,
JianhuaWang,Jianfeng Zhao,《IEEE Transactions on Industrial Elect-ronics》,
2013,60 (5), 2104-2115 (" hybrid modulation method of high-efficiency single-phase non-isolation type H6 inverter ", " IEEE journals-industry
Electronic journal ", the 5th phase page 2104-2115 of volume 60 in 2013) using 6 topology of Cascade H, although inhibiting to a certain extent
Leakage current, but compared with traditional H4 topology, modulation strategy is relative complex, and scalability is poor, and cost is 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), 5265-5277 (" cascade connection multi-level photovoltaic inverter leakage current analyses
With inhibition ", " IEEE journal-power electronics periodical ", the 10th phase page 5265-5277 of volume 29 in 2014) and document
“Eliminating Ground Current in a TransformerlessPhotovoltaic Application”
Freijedo,Alejandro G.Yepes,JanoMalvar,et al.《IEEE Transacion-sonEnergy
Conversion ", 2010,25 (1), 140-147 (" leakage current for eliminating non-isolation type photovoltaic application occasion ", " IEEE journal-
Energy convert periodical ", the 1st phase page 140-147 of volume 25 in 2010) propose by each H bridge add passive filter come
The scheme for inhibiting leakage current, although the program can effectively inhibit leakage current, 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
The method that Transformerless PV Inverter " proposes injection triple-frequency harmonics, reduces the size of common-mode voltage, still, 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
It is related, it is also related with the differential mode voltage of other modules, therefore the modulation strategy is to be applied to multiple H bridge modules, it is also necessary into
One step research.
Document " Hybrid Multicarrier Modulation to Reduce Leakage Current in a
Trans formerless Cascaded Multilevel Inverter for Photovoltaic Systems”
Rajasekar Selvamuthukumaran,AbhishekGarg,and Rajesh Gupta.《IEEE Transactions
On Power Electronics ", 2015,30 (4): 1779-1783 (" is used for non-isolation type cascaded multilevel inverter photovoltaic
The mixing multi-carrier modulation strategy of system ", " IEEE journal-power electronics periodical ", the 4th phase 1779-1783 of volume 30 in 2015
Page) propose a kind of modified POD (Phase Opposite Disposition) modulation strategy, it is cut using common-mode voltage in switch
Amplitude changes the smallest principle to inhibit leakage current when changing, but still has high frequency division by the common-mode voltage that the modulation strategy obtains
Amount, therefore the leakage current of cascaded H-bridges is not effectively inhibited really.
Summary of the invention
In order to solve above-mentioned current leakage, the present invention is mentioned from the angle of the third drain current suppressing method
A kind of new modified POD modulation strategy out can be such that the sum of parasitic capacitor voltage keeps constant or low frequency variation, effectively inhibit
The leakage current of cascaded H-bridges.
The embodiment provides a kind of modified POD modulation strategy of cascaded H-bridges photovoltaic DC-to-AC converter, feature exists
In the suppressing method includes:
16 switch shapes that described two H bridge modules include are obtained according to the switch state of each H bridge module or so bridge arm
State；
When the DC input voitage of described two H bridge modules is identical, each switch in 16 switch states is calculated
The sum of corresponding described two H bridge module parasitic capacitor voltages of state；
Select all switch states that total the sum of the parasitic capacitor voltage of described two H bridge modules remains unchanged, and group
At two kinds of Switch State Combination in Power Systems；
It according to described two Switch State Combination in Power Systems, is compared by modulating wave with carrier wave, generates PWM drive signal, and
The switching tube of described two H bridge modules is controlled.
In one embodiment of the invention, when generating PWM drive signal, the carrier wave uses two carrier signals
Tri1, tri2, and at that time between (0, T/2) when, tri1>tri2,0.5<tri1<1,0<tri2<0.5；Meta position at that time
When between (T/2, T), carrier wave tri1 and carrier wave tri2 are reversed, and tri1 < tri2,0 < tri1 < 0.5,0.5 < tri2 < 1, adjust
Wave v processedrefNegative half-cycle carried out reverse phase, and modulation degree is 0.9.
In one embodiment of the invention, described two H are obtained according to the switch state of each H bridge module or so bridge arm
16 switch states that bridge module includes, comprising:
Shutdown and the opening state of the switching tube on each H bridge module or so bridge arm are represented with number 0,1 respectively, then it is described
The switch function S of two H bridge modulesa1/Sb1/Sa2/Sb2It is as follows that 16 switch states of generation are combined in different conditions: 0101,
0100,0111,0110,0001,1101,0000,1111,0011,1100,0010,1110,1001,1000,1011,1010；Its
In, Sa1The switch function of the left bridge arm upper tube of representation module one, Sb1The switch function of the right bridge arm upper tube of representation module one, Sa2It indicates
The switch function of the left bridge arm upper tube of module two, Sb2The switch function of the right bridge arm upper tube of representation module two；The upper and lower of each bridge arm opens
Close pipe complementary duty.
In one embodiment of the invention, if the DC input voitage of two H bridge modules it is identical and be vpv, then each H
Bridge output-vpv、0、vpvThree kinds of level, two H bridge modules share -2vpv、-vpv、0、vpv、2vpvFive kinds of output levels；Described 16
A switch state ultimately forms the -2v of two H bridge modulespv、-vpv、0、vpv、2vpvFive kinds of output levels.
In one embodiment of the invention, each switch state corresponding described two in 16 switch states is calculated
The sum of a H bridge module parasitic capacitor voltage, comprising:
Wherein, vcpv1And vcpv2The parasitic capacitor voltage value of respectively two H bridge modules, va1n1、vb1n1、va2n2And vb2n2Point
It Wei not four bridge arm output end a of described two H bridge modules1、b1、a2And b2To common point n1And n2Voltage；vgFor network voltage.
In one embodiment of the invention, two kinds of Switch State Combination in Power Systems are formed, comprising:
Select to send as an envoy to the sum of parasitic capacitor voltage as vpvAll switch states, and according to two H bridge module output levels
When switching, the least principle of switching tube action number forms two kinds of Switch State Combination in Power Systems are as follows: 1010-1000-1100-0011-
0001-0101 and 1010-1110-1100-0011-0111-0101.
In one embodiment of the invention, it according to described two Switch State Combination in Power Systems, is carried out by modulating wave and carrier wave
Compare, generate PWM drive signal, and control the switching tube of described two H bridge modules, comprising:
The PWM drive signal of the first Switch State Combination in Power Systems 1010-1000-1100-0011-0001-0101 generates
Mode includes:
As modulating wave vrefWhen positioned at (0, T/2) half period section, Sa1=1, Sb2=0；Sb1By modulating wave and carrier wave tri2
Compare to obtain, if vref> tri2, Sb1=0, otherwise Sb1=1；Sa2It is obtained compared with carrier wave tri1 by modulating wave, if vref> tri1,
Sa2=1, otherwise Sa2=0；
As modulating wave vrefWhen positioned at the half period section (T/2, T), then Sa1=0, Sb2=1；Sb1By modulating wave vrefWith carrier wave
Tri1 is relatively obtained, if vref< tri1, Sb1=0, otherwise Sb1=1；Sa2By modulating wave vrefIt is obtained compared with carrier wave tri2, if
vref< tri2, Sa2=1, otherwise Sa2=0；
The PWM drive signal of second of Switch State Combination in Power Systems 1010-1110-1100-0011-0111-0101 generates
Mode includes:
As modulating wave vrefWhen positioned at (0, T/2) half period section, Sa1=1, Sb2=0；Sb1By modulating wave and carrier wave tri1
Compare to obtain, if vref> tri1, Sb1=0, otherwise Sb1=1；Sa2It is obtained compared with carrier wave tri2 by modulating wave, if vref> tri2,
Sa2=1, otherwise Sa2=0；
As modulating wave vrefWhen positioned at the half period section (T/2, T), then Sa1=0, Sb2=1；Sb1By modulating wave vrefWith carrier wave
Tri2 is relatively obtained, if vref< tri2, Sb1=0, otherwise Sb1=1；Sa2By modulating wave vrefIt is obtained compared with carrier wave tri1, if
vref< tri1, Sa2=1, otherwise Sa2=0.
In one embodiment of the invention, the carrier wave is triangular carrier, and the carrier wave side in its adjacent half period section
To opposite.
Compared with prior art, the invention has the benefit that
Not adding passive filtering inductance and in the case where not changing existing topological structure, pass through new modified
POD modulation strategy keeps constant the sum of parasitic capacitor voltage or low frequency sinusoidal amount, reduces H bridge photovoltaic DC-to-AC converter significantly
Leakage current.
Detailed description of the invention
It, below will be to embodiment or existing skill in order to clearly illustrate the embodiment of the present invention or technical solution in the prior art
Attached drawing needed in art description is briefly described.Drawings in the following description are some embodiments of the invention, right
In those of ordinary skill in the art, without creative efforts, it can also be obtained according to these attached drawings others
Attached drawing.
Fig. 1 is a kind of schematic flow diagram of drain current suppressing method provided in an embodiment of the present invention.
Fig. 2 is the schematic flow diagram of another drain current suppressing method provided in an embodiment of the present invention.
Fig. 3 is the schematic diagram of two module-cascades H bridge photovoltaic DC-to-AC converter provided in an embodiment of the present invention.
Fig. 4 is two module-cascades H bridge photovoltaic DC-to-AC converter equivalent model provided in an embodiment of the present invention.
Fig. 5 is the realization principle figure of the first Switch State Combination in Power Systems provided in an embodiment of the present invention.
Fig. 6 is the realization principle figure of second of Switch State Combination in Power Systems provided in an embodiment of the present invention.
Specific embodiment
Technical solution in order to enable those skilled in the art to better understand the present invention, with reference to the accompanying drawing and specific embodiment party
Case is described in further detail a kind of drain current suppressing method applied to cascaded H-bridges five-electrical level inverter of the present invention.Example
Only represent possible variation.Unless explicitly requested, otherwise individual components and functionality is optional, and the sequence operated can be with
Variation.The part of some embodiments and feature can be included in or replace the forehead point and feature of other embodiments.This
The range of the embodiment of invention includes equivalent obtained by the entire scope of claims and all of claims
Object.
The present invention is described in further details with reference to the accompanying drawing.
Embodiment one
Referring to Figure 1, Fig. 1 is a kind of modified POD tune for cascaded H-bridges photovoltaic DC-to-AC converter that the embodiment of the present invention one provides
System strategy, wherein the suppressing method includes:
16 switch shapes that described two H bridge modules include are obtained according to the switch state of each H bridge module or so bridge arm
State；
When the DC input voitage of described two H bridge modules is identical, each switch in 16 switch states is calculated
The sum of corresponding described two H bridge module parasitic capacitor voltages of state；
Select all switch states that total the sum of the parasitic capacitor voltage of described two H bridge modules remains unchanged, and group
At two kinds of Switch State Combination in Power Systems；
It according to described two Switch State Combination in Power Systems, is compared by modulating wave with carrier wave, generates PWM drive signal, and
The switching tube of described two H bridge modules is controlled.
Wherein, generate PWM drive signal when, the carrier wave use two carrier signals tri1, tri2, and at that time between be located at
When between (0, T/2), tri1>tri2,0.5<tri1<1,0<tri2<0.5；When between at that time between (T/2, T), carrier wave
Tri1 and carrier wave tri2 are reversed, and tri1 < tri2,0 < tri1 < 0.5,0.5 < tri2 < 1, modulating wave vrefNegative half-cycle into
Reverse phase is gone, and modulation degree is 0.9.
16 switch shapes that described two H bridge modules include are obtained according to the switch state of each H bridge module or so bridge arm
State, comprising:
Shutdown and the opening state of the switching tube on each H bridge module or so bridge arm are represented with number 0,1 respectively, then it is described
The switch function S of two H bridge modulesa1/Sb1/Sa2/Sb2It is as follows that 16 switch states of generation are combined in different conditions: 0101,
0100,0111,0110,0001,1101,0000,1111,0011,1100,0010,1110,1001,1000,1011,1010；Its
In, Sa1The switch function of the left bridge arm upper tube of representation module one, Sb1The switch function of the right bridge arm upper tube of representation module one, Sa2It indicates
The switch function of the left bridge arm upper tube of module two, Sb2The switch function of the right bridge arm upper tube of representation module two；The upper and lower of each bridge arm opens
Close pipe complementary duty.
Wherein, if the DC input voitage of two H bridge modules it is identical and be vpv, then each H bridge output-vpv、0、vpvThree kinds
Level, two H bridge modules share -2vpv、-vpv、0、vpv、2vpvFive kinds of output levels；16 switch states ultimately form two
- the 2v of a H bridge modulepv、-vpv、0、vpv、2vpvFive kinds of output levels.
Further, it is parasitic that the corresponding described two H bridge modules of each switch state in 16 switch states are calculated
The sum of capacitance voltage, comprising:
Wherein, vcpv1And vcpv2The parasitic capacitor voltage value of respectively two H bridge modules, va1n1、vb1n1、va2n2And vb2n2Point
It Wei not four bridge arm output end a of described two H bridge modules1、b1、a2And b2To common point n1And n2Voltage；vgFor network voltage.
Further, select to send as an envoy to the sum of parasitic capacitor voltage as vpvAll switch states, and according to two H bridge modules
When output level switches, the least principle of switching tube action number forms two kinds of Switch State Combination in Power Systems are as follows: 1010-1000-1100-
0011-0001-0101 and 1010-1110-1100-0011-0111-0101.
It according to described two Switch State Combination in Power Systems, is compared by modulating wave with carrier wave, generates PWM drive signal, and
The switching tube of described two H bridge modules is controlled, comprising:
The PWM drive signal of the first Switch State Combination in Power Systems 1010-1000-1100-0011-0001-0101 generates
Mode includes:
As modulating wave vrefWhen positioned at (0, T/2) half period section, Sa1=1, Sb2=0；Sb1By modulating wave and carrier wave tri2
Compare to obtain, if vref> tri2, Sb1=0, otherwise Sb1=1；Sa2It is obtained compared with carrier wave tri1 by modulating wave, if vref> tri1,
Sa2=1, otherwise Sa2=0；
As modulating wave vrefWhen positioned at the half period section (T/2, T), then Sa1=0, Sb2=1；Sb1By modulating wave vrefWith carrier wave
Tri1 is relatively obtained, if vref< tri1, Sb1=0, otherwise Sb1=1；Sa2By modulating wave vrefIt is obtained compared with carrier wave tri2, if
vref< tri2, Sa2=1, otherwise Sa2=0；
The PWM drive signal of second of Switch State Combination in Power Systems 1010-1110-1100-0011-0111-0101 generates
Mode includes:
As modulating wave vrefWhen positioned at (0, T/2) half period section, Sa1=1, Sb2=0；Sb1By modulating wave and carrier wave tri1
Compare to obtain, if vref> tri1, Sb1=0, otherwise Sb1=1；Sa2It is obtained compared with carrier wave tri2 by modulating wave, if vref> tri2,
Sa2=1, otherwise Sa2=0；
As modulating wave vrefWhen positioned at the half period section (T/2, T), then Sa1=0, Sb2=1；Sb1By modulating wave vrefWith carrier wave
Tri2 is relatively obtained, if vref< tri2, Sb1=0, otherwise Sb1=1；Sa2By modulating wave vrefIt is obtained compared with carrier wave tri1, if
vref< tri1, Sa2=1, otherwise Sa2=0.
Wherein, the carrier wave is triangular carrier, and the carrier wave in its adjacent half period section is contrary.
The present embodiment guarantees that the sum of parasitic capacitor voltage is constant or low frequency becomes by new modified POD modulation strategy
Amount, restrained effectively the leakage current of cascaded H-bridges, solving cascaded H-bridges photovoltaic combining inverter in the prior art cannot be effective
The problem of inhibiting leakage current has achieved the effect that preferably to inhibit cascaded H-bridges photovoltaic combining inverter leakage current.
Embodiment two
Fig. 2 is referred to, Fig. 2 is a kind of modified POD tune of cascaded H-bridges photovoltaic DC-to-AC converter provided by Embodiment 2 of the present invention
System strategy, wherein the suppressing method includes:
Step a if the DC input voitage of two H bridge modules is equal, and is vpv, it is all to write out that two modules include column
16 switch states；
Step b, the parasitic capacitor voltage of the corresponding each module of calculating 16 switch states and total parasitic capacitance
The sum of voltage；Selecting the sum of described parasitic capacitor voltage is vpvAll switch states；
Step c, when being switched according to two H bridge module output levels, the least principle of switching tube action number forms two kinds
Switch State Combination in Power Systems；
Step d is compared by modulating wave with carrier wave according to described two Switch State Combination in Power Systems, generates PWM driving letter
Number, and the switching tube of described two H bridge modules is controlled, to realize the inhibition of leakage current.
Fig. 3 is the schematic diagram of two module-cascades H bridge photovoltaic DC-to-AC converter provided in an embodiment of the present invention.In figure, Cpv1With
Cpv2Parasitic capacitance between photovoltaic array and the earth, vpv1And vpv2For 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 power grid
Voltage.
If the DC input voitage of two H bridge modules is equal, and is vpv, column write out all 16 that two modules include and open
Off status (Sa1/Sb1/Sa2/Sb2), and calculate the parasitic capacitor voltage and total parasitism of the corresponding each module of each switch state
The sum of capacitance voltage.
Wherein, Sa1The switch function of the left bridge arm upper tube of representation module 1, Sb1The switch letter of the right bridge arm upper tube of representation module 1
Number, Sa2The switch function of the left bridge arm upper tube of representation module 2, Sb2The switch function of the right bridge arm upper tube of representation module 2.In addition, each
Switch function can take 0 or 1,1 representation switch pipe to be connected, the shutdown of 0 representation switch pipe, the complementation work of switching tube up and down of each bridge arm
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 bridge arm output end a1、b1、a2And b2To common point n1And n2Voltage.By taking the positive half period of power network current as an example, it is assumed that net
Side filter inductance L1=L2, due to leakage current very little, therefore L1And L2The voltage of upper generation is approximately equal and is vL, meanwhile, net side filter
The voltage of wave inductance parasitic resistance is vR；
According to Fig. 4, formula can be obtained by Kirchhoff's law:
It can be obtained by above three formula:
Due to network voltage vgPredominantly power frequency component, to the influence of leakage current very little in parasitic capacitance, analysis hereafter
It does not consider further that, therefore parasitic capacitance Cpv1And Cpv2Voltage vcpv1And vcpv2It can be expressed as:
Table 1 is the switch state and 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+vcpv2For posting for two H bridge modules
The sum of raw capacitance voltage.As can be seen that two H bridge modules there are five level to export, be respectively as follows: 2vpv、vpv、0、-vpvWith-
2vpv.Different switch function Sa1/Sb1/Sa2/Sb2When control switch pipe, make the sum of the parasitic capacitor voltage of two H bridge modules
v’cpv1+v’cpv2In 0~2vpvBetween occur high frequency variation, to generate leakage current.
The switch state and parasitic capacitor voltage of 1 two H bridge modules of table
It is calculated according to table 1 as a result, the sum of the parasitic capacitor voltage that selects to send as an envoy to is vpvAll switch states, and according to
When two H bridge module output level switchings, the least principle of switching tube action number forms the following two kinds Switch State Combination in Power Systems, point
Not are as follows: 1010-1000-1100-0011-0001-0101 and 1010-1110-1100-0011-0111-0101.
According to selected two kinds of Switch State Combination in Power Systems, generates PWM drive signal switch tube and controlled, realization side
Formula is that modulating wave is compared to obtain pwm signal with two carrier waves.
Wherein, two carrier signals are tri1, tri2, and at that time between (0, T/2) when, tri1>tri2,0.5<
Tri1 < 1,0 < tri2 < 0.5；When between at that time between (T/2, T), carrier wave tri1 and carrier wave tri2 are reversed, and tri1 <
Tri2,0 < tri1 < 0.5,0.5 < tri2 < 1, modulating wave vrefNegative half-cycle carried out reversely, it is consistent with positive half period waveform,
For steamed bun shape, and modulation degree is 0.9.
The first Switch State Combination in Power Systems of embodiment is realized as shown in Figure 5, and specific manner of comparison is as follows:
(1) as modulating wave vrefWhen positioned at (0, T/2) half period section, Sa1=1, Sb2=0；Sb1By modulating wave and carrier wave
Tri2 is relatively obtained, if vref> tri2, Sb1=0, otherwise Sb1=1；Sa2It is obtained compared with carrier wave tri1 by modulating wave, if vref>
Tri1, Sa2=1, otherwise Sa2=0；
(2) as modulating wave vrefWhen positioned at the half period section (T/2, T), then Sa1=0, Sb2=1；Sb1By modulating wave vrefWith
Carrier wave tri1 is relatively obtained, if vref< tri1, Sb1=0, otherwise Sb1=1；Sa2By modulating wave vrefIt is obtained compared with carrier wave tri2,
If vref< tri2, Sa2=1, otherwise Sa2=0；
Second of Switch State Combination in Power Systems of embodiment is realized as shown in Figure 6, and specific manner of comparison is as follows:
(1) as modulating wave vrefWhen positioned at (0, T/2) half period section, Sa1=1, Sb2=0；Sb1By modulating wave and carrier wave
Tri1 is relatively obtained, if vref> tri1, Sb1=0, otherwise Sb1=1；Sa2It is obtained compared with carrier wave tri2 by modulating wave, if vref>
Tri2, Sa2=1, otherwise Sa2=0；
(2) as modulating wave vrefWhen positioned at the half period section (T/2, T), then Sa1=0, Sb2=1；Sb1By modulating wave vrefWith
Carrier wave tri2 is relatively obtained, if vref< tri2, Sb1=0, otherwise Sb1=1；Sa2By modulating wave vrefIt is obtained compared with carrier wave tri1,
If vref< tri1, Sa2=1, otherwise Sa2=0；
Using this method by new modified POD modulation strategy, guarantee that the sum of parasitic capacitor voltage is constant or low frequency becomes
Amount, restrained effectively the leakage current of cascaded H-bridges.
The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it cannot be said that
Specific implementation of the invention is only limited to these instructions.For those of ordinary skill in the art to which the present invention belongs, exist
Under the premise of not departing from present inventive concept, a number of simple deductions or replacements can also be made, all shall be regarded as belonging to of the invention
Protection scope.
Claims (2)
1. a kind of modified POD modulation strategy of cascaded H-bridges photovoltaic DC-to-AC converter, which is characterized in that the modified POD modulates plan
Slightly include:
Step 1: obtaining 16 switches that described two H bridge modules include according to the switch state of two H bridge modules or so bridge arm
State；
Shutdown and the opening state of the switching tube on each H bridge module or so bridge arm are represented with number 0,1 respectively, then it is described two
The switch function S of H bridge modulea1/Sb1/Sa2/Sb20100 combine that generate 16 switch states as follows in different conditions: 0101,
0111,0110,0001,1101,0000,1111,0011,1100,0010,1110,1001,1000,1011,1010；Wherein, Sa1
The switch function of the left bridge arm upper tube of representation module one, Sb1The switch function of the right bridge arm upper tube of representation module one, Sa2Representation module two
The switch function of left bridge arm upper tube, Sb2The switch function of the right bridge arm upper tube of representation module two；The switching tube up and down of each bridge arm is mutual
Mend work；
Step 2: calculating and each being opened in 16 switch states when the DC input voitage of described two H bridge modules is identical
The sum of corresponding described two H bridge module parasitic capacitor voltages of off status；Include:
Wherein, vcpv1And vcpv2The parasitic capacitor voltage value of respectively two H bridge modules, va1n1、vb1n1、va2n2And vb2n2Respectively
Four bridge arm output end a of described two H bridge modules1、b1、a2And b2To common point n1And n2Voltage；vgFor network voltage；
If the DC input voitage of described two H bridge modules is identical and is vpv, then each H bridge output-vpv、0、vpvThree kinds of level,
16 switch states ultimately form the -2v of described two H bridge modulespv、-vpv、0、vpv、2vpvFive kinds of output levels；
Step 3: all switch states that total the sum of the parasitic capacitor voltage of described two H bridge modules remains unchanged are selected, and
Form two kinds of Switch State Combination in Power Systems；
Select to send as an envoy to the sum of parasitic capacitor voltage as vpvAll switch states, and switched according to two H bridge module output levels
When, the least principle of switching tube action number forms two kinds of Switch State Combination in Power Systems are as follows:
The first is 1010-1000-1100-0011-0001-0101
Second is 1010-1110-1100-0011-0111-0101
Step 4: passing through modulating wave v according to described two Switch State Combination in Power SystemsrefIt is compared with carrier wave, generates PWM driving letter
Number, and the switching tube of described two H bridge modules is controlled；Include:
The PWM drive signal generating mode of the first Switch State Combination in Power Systems 1010-1000-1100-0011-0001-0101
Include:
As modulating wave vrefWhen positioned at (0, T/2) half period section, Sa1=1, Sb2=0；Sb1By modulating wave vrefWith carrier wave tri2 ratio
It relatively obtains, if vref> tri2, Sb1=0, otherwise Sb1=1；Sa2By modulating wave vrefIt is obtained compared with carrier wave tri1, if vref>
Tri1, Sa2=1, otherwise Sa2=0；
As modulating wave vrefWhen positioned at the half period section (T/2, T), then Sa1=0, Sb2=1；Sb1By modulating wave vrefWith carrier wave tri1
Compare to obtain, if vref< tri1, Sb1=0, otherwise Sb1=1；Sa2By modulating wave vrefIt is obtained compared with carrier wave tri2, if vref<
Tri2, Sa2=1, otherwise Sa2=0；
The PWM drive signal generating mode of second of Switch State Combination in Power Systems 1010-1110-1100-0011-0111-0101
Including；
As modulating wave vrefWhen positioned at (0, T/2) half period section, Sa1=1, Sb2=0；Sb1By modulating wave vrefWith carrier wave tri1 ratio
It relatively obtains, if vref> tri1, Sb1=0, otherwise Sb1=1；Sa2By modulating wave vrefIt is obtained compared with carrier wave tri2, if vref>
Tri2, Sa2=1, otherwise Sa2=0；
As modulating wave vrefWhen positioned at the half period section (T/2, T), then Sa1=0, Sb2=1；Sb1By modulating wave vrefWith carrier wave tri2
Compare to obtain, if vref< tri2, Sb1=0, otherwise Sb1=1；Sa2By modulating wave vrefIt is obtained compared with carrier wave tri1, if vref<
Tri1, Sa2=1, otherwise Sa2=0；
Wherein, generate PWM drive signal when, the carrier wave use two carrier signals tri1, tri2, and at that time between be located at (0,
When between T/2), tri1>tri2,0.5<tri1<1,0<tri2<0.5；When between at that time between (T/2, T), carrier wave tri1 and
Carrier wave tri2 is reversed, and tri1 < tri2,0 < tri1 < 0.5,0.5 < tri2 < 1, modulating wave vrefNegative half-cycle carried out instead
Phase, and modulation degree is 0.9.
2. modified POD modulation strategy according to claim 1, which is characterized in that the carrier wave is triangular carrier, and its
The carrier wave in adjacent half period section is contrary.
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| CN105450059A (en) * | 2015-12-22 | 2016-03-30 | 合肥工业大学 | Modulation method for suppressing leakage current of two-H-bridge cascaded inverter |
| CN105871239A (en) * | 2016-04-29 | 2016-08-17 | 阳光电源股份有限公司 | Method for suppressing leakage current of cascade multi-level inverter and inverter |
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| CN105450059A (en) * | 2015-12-22 | 2016-03-30 | 合肥工业大学 | Modulation method for suppressing leakage current of two-H-bridge cascaded inverter |
| CN105871239A (en) * | 2016-04-29 | 2016-08-17 | 阳光电源股份有限公司 | Method for suppressing leakage current of cascade multi-level inverter and inverter |
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