CN106208782B - Cascaded H-bridges photovoltaic inverter leakage current suppressing method based on Model Predictive Control - Google Patents
Cascaded H-bridges photovoltaic inverter leakage current suppressing method based on Model Predictive Control Download PDFInfo
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Classifications
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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
- H02M7/5387—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 in a bridge configuration
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- H02J3/383—
-
- 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
- H02M1/0003—Details of control, feedback or regulation circuits
- H02M1/0038—Circuits or arrangements for suppressing, e.g. by masking incorrect turn-on or turn-off signals, e.g. due to current spikes in current mode control
-
- 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
- H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
- H02M1/007—Plural converter units in cascade
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- 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 cascaded H-bridges photovoltaic inverter leakage current suppressing method based on Model Predictive Control, the method includes：It writes out all 256 kinds of on off states of four H bridge cascaded inverters and calculates the sum of corresponding photovoltaic cell parasitic capacitor voltage VcValue；Selecting switch state and composition Switch State Combination in Power Systems；Calculate the output voltage V of inverter ac sidek；The voltage V of on-line checking k moment power gridsg(k) and power network current i (k), and value i (k+1) of the power network current at the k+1 moment is calculated；The network voltage V obtained to on-line checkingg(k) phase is locked, phase theta is obtained, the given value of current value i at k+1 moment is calculated by θ*(k+1), and with the Current calculation value i (k+1) at k+1 moment valuation functions h is substituted into together；The minimum corresponding Switch State Combination in Power Systems of valuation functions h is selected, and passes through driving circuit driving switch pipe as output quantity.This method can not only effectively inhibit system leakage current, and extend single-phase non-isolated cascaded H-bridges photovoltaic combining inverter that is convenient, and being suitable for even number H bridges.
Description
Technical field
The present invention relates to a kind of cascaded H-bridges photovoltaic inverter leakage current suppressing methods based on Model Predictive Control；It is suitable
For the grid-connected field of non-isolation type.
Background technology
Compared with conventional inverter, cascaded H-bridges multi-electrical level inverter is with grid current harmonic is small, switching frequency is low, filter
Wave device is small and the advantages that being easy to modularization, therefore has obtained the concern of more and more scholars.
In addition, the DC side of each module of cascaded H-bridges multi-electrical level inverter can be independently-powered by one piece of photovoltaic panel, make it solely
Vertical MPPT controls are possibly realized, therefore the more level topological structures of cascaded H-bridges are particularly suitable for photovoltaic combining inverter.
Due to cascaded H-bridges inverter module structure, grid-connected required voltage can be reached by cascading certain quantity,
Therefore raising voltage and the transformer of buffer action can be saved, further reduces the cost and improve power density.
There is directly electrical connection but due to lacking transformer isolation, between photovoltaic panel and power grid, it can be in photovoltaic panel
Leakage current is generated in parasitic capacitance between the earth, leakage current can influence the efficiency of system, reduce system reliability, threaten people
Safety and generation electromagnetic interference of body etc., therefore be highly desirable to inhibit leakage current.
At present, traditional drain current suppressing method can be mainly divided into following three kinds：1) improved topological structure is used, such as
The topologys such as H5, H6；2) using passive filter, such as common mode inductance, electromagnetic interface filter；3) seek suitable modulation strategy.
However, unlike single module inverter topology, the ingredient of cascaded H-bridges topology leakage current not only with this module
Output is related, also associated with the output of other cascade modules.Therefore, the suppressing method of single H bridges leakage current can not be straight
The inhibition for applying to cascaded H-bridges topology leakage current is connect, causes method and grade that existing single module inverter inhibits leakage current
There is a little mismatch between connection H bridge inverter drain current suppressing methods.
For this purpose, scholars have done many effort with attempting in terms of the drain current suppressing of Cascade H bridge inverter, such as 2016
IEEE documents " Single Phase Cascaded H5Inverter with Leakage Current Elimination
(" 5 photovoltaic DC-to-AC converter common mode current of non-isolation type Cascade H is special by for Transformerless Photovoltaic System "
Property analysis " --- IEEE energy sciences in 2016 can plenary session collection of thesis) propose and a kind of inhibit electric leakage about 5 topology of Cascade H
The modulation strategy of stream although inhibiting leakage current to a certain extent, can be answered very much as number of modules increases modulation strategy
It is miscellaneous, it is unfavorable for system extension and modularized design.In addition, 5 topology of Cascade H proposed, compared to H4 topologys, cost and loss are all
It can be increased.
IEEE documents " Analysis and Suppression of Leakage Current in 2014
Cascaded-Multilevel–Inverter-Based PV Systems,”Y.Zhou and H.Li,《IEEE
Trans.Power Electron.》, 2014,29 (10), 5265-5277 (" cascade connection multi-level photovoltaic inverter leakage current analyses
With inhibiting ",《IEEE journals-power electronics periodical》, the 10th phase page 5265-5277 of volume 29 in 2014) and it proposes in DC side
It adds common-mode filter respectively with exchange side and inhibits leakage current, but its switching frequency is set as 10kHz, this is with using cascaded topology
The original intention for reducing switching frequency is not met.IEEE documents " A Modulation Strategy for Single- in 2013
phase HB-CMI to Reduce Leakage Ground Current in Transformer-less PV
(" cascade connection multi-level photovoltaic inverter leakage current is analyzed and inhibited " --- IEEE energy sciences can be complete within 2013 by Applications "
Body proceeding) modulation strategy that proposes causes parasitic capacitor voltage to change by power frequency staircase waveform, but the modulation strategy is opposite
It is more complicated and be not easy to system extension.In addition, 105450059 A of Chinese invention patent application prospectus CN were in 2015
Disclosed in December 22《Inhibit the modulator approach of two H bridge cascaded inverter leakage currents》, modulation is laminated to traditional carrier wave and is carried out
It improves, it is proposed that a kind of new modulation strategy can inhibit containing there are two the single-phase non-isolated cascaded H-bridges photovoltaic DC-to-AC converters of H bridges
Leakage current, but this method is only used for the situation of two H bridges, it is impossible to spread over multiple H bridges, there is certain limitation,
It is not easy to practical implementation.
In conclusion for single-phase non-isolated cascaded H-bridges photovoltaic DC-to-AC converter, existing drain current suppressing method is mainly deposited
In following problem：
(1) prior art is concentrated mainly on containing there are two the leakage currents of the single-phase non-isolated cascaded H-bridges photovoltaic DC-to-AC converter of H bridges
Inhibit, this largely limits the expanded application of single-phase non-isolated cascaded H-bridges photovoltaic DC-to-AC converter more multimode, fails fully
Play the advantage of cascaded H-bridges photovoltaic DC-to-AC converter；
(2) the drain current suppressing method of the existing single-phase non-isolated cascaded H-bridges photovoltaic DC-to-AC converter containing multiple H bridges mainly changes
Become existing topology or use new topological realization.Such as common-mode filter is added respectively, using grade in DC side and exchange side
Join H5 or H6 topologys, this can undoubtedly increase cost and the loss of system, reduce the power density of inverter.
Invention content
It is inverse for non-isolation type photovoltaic the technical problem to be solved in the present invention is to overcome the limitation of above-mentioned various schemes
Become device and lead to the problem of leakage current in parasitic capacitance between photovoltaic panel and the earth due to lacking transformer isolation, it is proposed that
For one kind based on Model Predictive Control drain current suppressing method, this method has extension convenient, calculates the advantages such as simple and at low cost.
The technical issues of to solve the present invention, used technical solution key step is as follows：
1st, a kind of cascaded H-bridges photovoltaic combining inverter drain current suppressing method based on Model Predictive Control, including selection
Switch State Combination in Power Systems and the voltage and electric current for detecting power grid, key step are as follows：
Step 1, if four module DC voltages of four H bridge cascaded inverters are identical, and are denoted as Vdc, and calculated with following formula
The sum of corresponding photovoltaic cell parasitic capacitor voltage VcValue,
Wherein, VgFor the voltage of power grid, S1aFor the switch function of the left bridge arm upper tube of first H bridge, S1bIt is right for first H bridge
The switch function of bridge arm upper tube, S2aFor the switch function of the left bridge arm upper tube of second H bridge, S2bFor the right bridge arm upper tube of second H bridge
Switch function, S3aFor the switch function of the left bridge arm upper tube of third H bridges, S3bSwitch letter for the right bridge arm upper tube of third H bridges
Number, S4aFor the switch function of the 4th left bridge arm upper tube of H bridges, S4bFor the switch function of the 4th right bridge arm upper tube of H bridges, and it is full
Foot：
Switch function progress permutation and combination is obtained into Switch State Combination in Power Systems S1a/S1b/S2a/S2b/S3a/S3b/S4a/S4bValue,
Obtain four H bridge cascaded inverters S1a/S1b/S2a/S2b/S3a/S3b/S4a/S4bAll 256 kinds of on off states；
Step 2, all 256 kinds of on off states of the four H bridge cascaded inverters write out according to step 1, according to maintenance light
Lie prostrate the sum of battery parasitic capacitance voltage VcFor power frequency sinusoidal quantity andRequirement,
The on off state met the requirements is selected, forms following Switch State Combination in Power Systems：
10101010-10100010-10110010-10011110-11110110-01100001-01001101-
01011101-01010101, for this Switch State Combination in Power Systems altogether comprising 9 kinds of on off states, each on off state corresponds to an output
Level, specially：
On off state 1：S1a=1, S1b=0, S2a=1, S2b=0, S3a=1, S3b=0, S4a=1, S4b=0
On off state 2：S1a=1, S1b=0, S2a=1, S2b=0, S3a=0, S3b=0, S4a=1, S4b=0
On off state 3：S1a=1, S1b=0, S2a=1, S2b=1, S3a=0, S3b=0, S4a=1, S4b=0
On off state 4：S1a=1, S1b=0, S2a=0, S2b=1, S3a=1, S3b=1, S4a=1, S4b=0
On off state 5：S1a=1, S1b=1, S2a=1, S2b=1, S3a=0, S3b=1, S4a=1, S4b=0
On off state 6：S1a=0, S1b=1, S2a=1, S2b=0, S3a=0, S3b=0, S4a=0, S4b=1
On off state 7：S1a=0, S1b=1, S2a=0, S2b=0, S3a=1, S3b=1, S4a=0, S4b=1
On off state 8：S1a=0, S1b=1, S2a=0, S2b=1, S3a=1, S3b=1, S4a=0, S4b=1
On off state 9：S1a=0, S1b=1, S2a=0, S2b=1, S3a=0, S3b=1, S4a=0, S4b=1
Step 3, the 9 kinds of on off states selected according to step 2 calculate the output level V of inverter ac sidekValue,
Wherein,Its value is [- 4, -3, -2, -1,0,1,2,3,4] Vdc, share 9 kinds of level；
Step 4, the single-phase non-isolated Cascade H bridge inverter of on-line checking is in the voltage V of k moment power gridsg(k) and power network current
I (k), and the output voltage V for the inverter ac side that step 3 is calculatedkThe discrete model letter of grid-connected current is substituted into together
Number, predicts value i (k+1) of the power network current at the k+1 moment, wherein, discrete model function meets following formula：
In formula, TsIt it is the sampling period of network voltage, L and R are respectively the single-phase non-isolated cascaded H-bridges photovoltaic DC-to-AC converter
Inductance value and corresponding resistance value, VkIt is k moment inverter acs side output voltage；
Step 5, network voltage V step 4 on-line checking obtainedg(k) into horizontal lock, phase theta is obtained, is calculated by θ
One with network voltage with frequently with given value of current value i* (k+1) of the sinusoidal quantity of phase as+1 moment of kth, and obtained with step 4
Calculated value i (k+1) of the power network current at the k+1 moment substitute into valuation functions h together, selection send as an envoy to valuation functions h it is minimum one
A output level；Wherein, valuation functions h=| i*(k+1)-i(k+1)|；
Step 6, it selects to correspond to according to the output level of step 5 selection, in the Switch State Combination in Power Systems selected from step 2
On off state, and pass through driving circuit driving switch pipe as output quantity.
The present invention is relative to the advantage of the prior art：
1st, strong applicability can not only effectively inhibit system leakage current, and extend conveniently, suitable for four H bridge modules
Cascade photovoltaic DC-to-AC converter.
2nd, it does not need to realize by changing existing topology or using new topology, be controlled by switch proposed by the present invention
System strategy can realize the drain current suppressing of the single-phase non-isolated cascaded H-bridges photovoltaic DC-to-AC converter to four H bridges, can not only drop
The cost and switching loss of low system, and the power density of inverter can be improved.
Description of the drawings
Fig. 1 is containing there are four the single-phase cascaded H-bridges photovoltaic DC-to-AC converter topological structures of H bridges.
Fig. 2 is containing there are four the equivalent circuits of the single-phase cascaded H-bridges photovoltaic DC-to-AC converter of H bridges.
Fig. 3 is the control block diagram for inhibiting leakage current method based on Model Predictive Control.
Specific embodiment
In order to make the purpose , technical scheme and advantage of the present invention be clearer, with reference to the accompanying drawings and embodiments, it is right
The present invention makees further clearly and completely to describe.
Cascaded H-bridges photovoltaic inverter leakage current suppressing method disclosed by the invention based on Model Predictive Control is applicable to
Inhibit the leakage current of the tandem photovoltaic inverter of four H bridges.
Fig. 1 is the single-phase non-isolated cascaded H-bridges photovoltaic combining inverter topological structure described in this patent, comprising four H bridges,
Each H bridge DC sides are independently-powered by one piece or polylith photovoltaic battery panel, and each H bridges exchange side is serially connected, and passes through difference
Mould inductance L1And L2It is connect with power grid, the characteristics of this cascaded H-bridges topology is maximum is each H bridges exchange side can be exported to be superimposed
To form more level.Wherein, parameter Cpvk1And Cpvk2(k=1,2,3,4) be the parasitic capacitance of photovoltaic panel over the ground, the capacitance size
It is related with the external factor such as the area of photovoltaic panel and weather, L1And L2For net side filter inductance；R1And R2For net side filter inductance
Dead resistance；VgFor exchange side point of common coupling voltage.
Fig. 2 is single-phase four module-cascades H bridge equivalent circuits, wherein C shown in Fig. 1pvk=Cpvk1//Cpvk2.With power network current
It is analyzed for positive half period, and remembers net side filter inductance L1=L2, R1=R2。
Fig. 3 is the control block diagram based on Model Predictive Control that patent of the present invention proposes, rate-determining steps include：On-line checking
Single-phase non-isolated Cascade H bridge inverter is in the voltage V of k moment power gridsg(k) and power network current i (k), and grid-connected current is substituted into
Discrete model function predicts value i (k+1) of the power network current at the k+1 moment；Phase is locked to the network voltage that on-line checking obtains,
Obtain phase theta, by θ calculate one with network voltage with frequency with mutually and electric current of the sinusoidal quantity as+1 moment of kth that amplitude is A
Set-point i*(k+1)；By the given value of current value i at+1 moment of kth*(k+1) with power network current the k+1 moment calculated value i (k+1)
Substitute into valuation functions together, selection is sent as an envoy to an output level of valuation functions minimum；According to the output level selected, into one
Step selects corresponding on off state, and pass through the switching tube of driving circuit cascaded H bridge photovoltaic DC-to-AC converters as output quantity.
It is disclosed by the invention to be based on model prediction control for the single-phase cascaded H-bridges photovoltaic DC-to-AC converter of four H bridges shown in Fig. 1
The basic step of the cascaded H-bridges photovoltaic inverter leakage current suppressing method of system is as follows：
Referring to Fig. 1, Fig. 2, Fig. 3.
Step 1, if four module DC voltages of four H bridge cascaded inverters are identical, and are denoted as Vdc, calculate four H bridges
All 256 kinds of on off state (S of cascaded inverter1a/S1b/S2a/S2b/S3a/S3b/S4a/S4b) and corresponding photovoltaic cell parasitism
The sum of capacitance voltage VcValue,
Wherein, VgFor the voltage of power grid, S1aFor the switch function of the left bridge arm upper tube of first H bridge, S1bIt is right for first H bridge
The switch function of bridge arm upper tube, S2aFor the switch function of the left bridge arm upper tube of second H bridge, S2bFor the right bridge arm upper tube of second H bridge
Switch function, S3aFor the switch function of the left bridge arm upper tube of third H bridges, S3bSwitch letter for the right bridge arm upper tube of third H bridges
Number, S4aFor the switch function of the 4th left bridge arm upper tube of H bridges, S4bFor the switch function of the 4th right bridge arm upper tube of H bridges, and it is full
Foot：
Each switch function S1a、S1b、S2a、S2b、S3a、S3b、S4a、S4bValue for 0 or 1, the value of switch function is arranged
Row group is incorporated as on off state S1a/S1b/S2a/S2b/S3a/S3b/S4a/S4bValue, totally 28Kind, this 28The value of kind on off state is just
It is 256 kinds of all on off state (S of four H bridge cascaded inverters1a/S1b/S2a/S2b/S3a/S3b/S4a/S4b)；
According to fig. 2, it can be obtained by Kirchhoff's second law, parasitic capacitor voltage VckMeet following formula：
After arrangement, parasitic capacitor voltage V is calculatedckMeet following formula：
Wherein, VCMkAnd VDMkThe common-mode voltage and differential mode voltage of kth (k=1,2,3,4) a module are represented respectively；
According to defined switch function S1a、S1b、S2a、S2b、S3a、S3b、S4a、S4b, four each bridge arms of module of calculating
Output terminals A1、B1、A2、B2、A3、B3、A4And B4Voltage V1a、V1b、V2a、V2b、V3a、V3b、V4aAnd V4bValue,
V1a=S1aVdc,
V1b=S1bVdc,
V2a=S2aVdc,
V2b=S2bVdc,
V3a=S3aVdc,
V3b=S3bVdc,
V4a=S4aVdc,
V4b=S4bVdc；
Finally, according to system parasitic capacitance voltage V obtained aboveck, system leakage current ileakAnd four each bridges of module
The output terminals A of arm1、B1、A2、B2、A3、B3、A4And B4Voltage V1a、V1b、V2a、V2b、V3a、V3b、V4aAnd V4bValue, calculate four
The sum of the voltage of a module H bridges cascaded inverter parasitic capacitance VcValue,
Wherein, m meets following formula：
By the 256 kinds of on off state (S write out1a/S1b/S2a/S2b/S3a/S3b/S4a/S4b) 256 kinds of photovoltaic electrics are calculated
The sum of pond parasitic capacitor voltage Vc；
Step 2, all 256 kinds of on off states of the four H bridge cascaded inverters write out according to step 1, according to maintenance light
Lie prostrate the sum of battery parasitic capacitance voltage VcFor power frequency sinusoidal quantity andRequirement, choose
The on off state met the requirements is selected, according to above-mentioned requirements, final choice goes out the 9 kinds of on off states met the requirements, and composition is following to be opened
Off status combines：
10101010-10100010-10110010-10011110-11110110-01100001-01001101-
01011101-0100101, each on off state correspond to an output level；
The sum of 9 kinds of on off states of the four H bridge cascaded inverters selected and the voltage of corresponding parasitic capacitance VcAnd m
Value is as shown in table 1：
The on off state of 1 four modules of table and m values
| Output voltage | S1a/S1b/S2a/S2b/S3a/S3b/S4a/S4b | m |
| -4Vdc | 01010101 | 2 |
| -3Vdc | 01011101 | 2 |
| -2Vdc | 01001101 | 2 |
| -Vdc | 01100001 | 2 |
| 0 | 11110110 | 2 |
| Vdc | 10011110 | 2 |
| 2Vdc | 10110010 | 2 |
| 3Vdc | 10100010 | 2 |
| 4Vdc | 10101010 | 2 |
As shown in Table 1, this corresponding m value of 9 kinds of on off states selected is 2, this cause parasitic capacitance voltage it
And VcPower frequency sinusoidal quantity can be kept constant, and metTherefore, selection this 9
Kind on off state can form Switch State Combination in Power Systems；
Step 3, the 9 kinds of on off states selected according to step 2 calculate the output voltage V of inverter ac sidek, wherein,Its value is [- 4, -3, -2, -1,0,1,2,3,4] Vdc, share 9 kinds of level；
Step 4, the single-phase non-isolated Cascade H bridge inverter of on-line checking is in the voltage V of k moment power gridsg(k) and power network current
I (k), and the output voltage V for the inverter ac side that step 3 is calculatedkThe discrete model letter of grid-connected current is substituted into together
Number, predicts value i (k+1) of the power network current at the k+1 moment, wherein, discrete model function meets following formula：
In formula, TsIt it is the sampling period of network voltage, L and R are respectively the single-phase non-isolated cascaded H-bridges photovoltaic DC-to-AC converter
Inductance value and corresponding resistance value, and R=R1+R2, L=L1+L2, the value of sampling instant k with the operation of controller and
It is continuously increased, k=1,2,3 ...；
Step 5, phase is locked to the network voltage that on-line checking obtains, obtains phase theta, one and network voltage are calculated by θ
With frequency with mutually and given value of current value i* (k+1) of the sinusoidal quantity as+1 moment of kth that amplitude is A, and the power grid obtained with step 4
Calculated value i (k+1) of the electric current at the k+1 moment substitutes into valuation functions h together, selects one group of switch shape of valuation functions h minimums
State combines.Wherein, valuation functions h=| i*(k+1)-i(k+1)|.Because only that making valuation functions minimum, power grid electricity just can guarantee
The tracking effect of stream is best, meets the elementary object of cutting-in control；
Step 6, it selects to correspond to according to the output level of step 5 selection, in the Switch State Combination in Power Systems selected from step 2
On off state, and pass through driving circuit driving switch pipe as output quantity.
Unlike existing modulation technique, the cascaded H-bridges photovoltaic inversion proposed by the present invention based on Model Predictive Control
Device drain current suppressing method does not need to carrier wave and participates in modulation, but is substituted by the method that Model Predictive Control selects on off state
Carrier modulation.According to above-mentioned steps, the sum of photovoltaic cell parasitic capacitor voltage can be maintained as power frequency sinusoidal quantity, so as to fulfill cascade
H bridges photovoltaic inverter leakage current inhibits.
The method of cascaded H-bridges photovoltaic inverter leakage current disclosed by the invention based on Model Predictive Control is applied to four
The tandem photovoltaic grid-connected system of H bridges.Based on the embodiment of the present invention, those skilled in the art is not making creative work
Under the premise of the other embodiments that obtain, the protection domain of this patent should all be belonged to.
Claims (1)
1. a kind of cascaded H-bridges photovoltaic inverter leakage current suppressing method based on Model Predictive Control, including selecting switch state
Combination and the voltage and electric current of detection power grid, which is characterized in that key step is as follows：
Step 1, if four module DC voltages of four H bridge cascaded inverters are identical, and are denoted as Vdc, and calculated and corresponded to following formula
The sum of photovoltaic cell parasitic capacitor voltage VcValue,
Wherein, VgFor the voltage of power grid, S1aFor the switch function of the left bridge arm upper tube of first H bridge, S1bFor first right bridge arm of H bridges
The switch function of upper tube, S2aFor the switch function of the left bridge arm upper tube of second H bridge, S2bFor opening for second right bridge arm upper tube of H bridges
Close function, S3aFor the switch function of the left bridge arm upper tube of third H bridges, S3bFor the switch function of the right bridge arm upper tube of third H bridges,
S4aFor the switch function of the 4th left bridge arm upper tube of H bridges, S4bFor the switch function of the 4th right bridge arm upper tube of H bridges, and meet：
Switch function progress permutation and combination is obtained into Switch State Combination in Power Systems S1a/S1b/S2a/S2b/S3a/S3b/S4a/S4bValue, obtain
Four H bridge cascaded inverters S1a/S1b/S2a/S2b/S3a/S3b/S4a/S4bAll 256 kinds of on off states；
Step 2, all 256 kinds of on off states of the four H bridge cascaded inverters write out according to step 1, according to maintenance photovoltaic electric
The sum of pond parasitic capacitor voltage VcFor power frequency sinusoidal quantity andRequirement, select
The on off state met the requirements forms following Switch State Combination in Power Systems：
10101010-10100010-10110010-10011110-11110110-01100001-01001101-01011101-
01010101, this Switch State Combination in Power Systems is altogether comprising 9 kinds of on off states, each on off state corresponds to an output level, specifically
For：
On off state 1：S1a=1, S1b=0, S2a=1, S2b=0, S3a=1, S3b=0, S4a=1, S4b=0
On off state 2：S1a=1, S1b=0, S2a=1, S2b=0, S3a=0, S3b=0, S4a=1, S4b=0
On off state 3：S1a=1, S1b=0, S2a=1, S2b=1, S3a=0, S3b=0, S4a=1, S4b=0
On off state 4：S1a=1, S1b=0, S2a=0, S2b=1, S3a=1, S3b=1, S4a=1, S4b=0
On off state 5：S1a=1, S1b=1, S2a=1, S2b=1, S3a=0, S3b=1, S4a=1, S4b=0
On off state 6：S1a=0, S1b=1, S2a=1, S2b=0, S3a=0, S3b=0, S4a=0, S4b=1
On off state 7：S1a=0, S1b=1, S2a=0, S2b=0, S3a=1, S3b=1, S4a=0, S4b=1
On off state 8：S1a=0, S1b=1, S2a=0, S2b=1, S3a=1, S3b=1, S4a=0, S4b=1
On off state 9：S1a=0, S1b=1, S2a=0, S2b=1, S3a=0, S3b=1, S4a=0, S4b=1
Step 3, the 9 kinds of on off states selected according to step 2 calculate the output level V of inverter ac sidekValue, wherein,Its value is [- 4, -3, -2, -1,0,1,2,3,4] Vdc, share 9 kinds of level；
Step 4, the single-phase non-isolated Cascade H bridge inverter of on-line checking is in the voltage V of k moment power gridsg(k) and power network current i (k),
And the output voltage V for the inverter ac side that step 3 is calculatedkThe discrete model function of grid-connected current is substituted into together, in advance
Value i (k+1) of the power network current at the k+1 moment is measured, wherein, discrete model function meets following formula：
In formula, TsIt it is the sampling period of network voltage, L and R are respectively the electricity of the single-phase non-isolated cascaded H-bridges photovoltaic DC-to-AC converter
Inductance value and corresponding resistance value, VkIt is k moment inverter acs side output voltage；
Step 5, network voltage V step 4 on-line checking obtainedg(k) into horizontal lock, obtain phase theta, by θ calculate one with
Network voltage is the same as frequently the same as given value of current value i of the sinusoidal quantity of phase as+1 moment of kth*(k+1), the power grid and with step 4 obtained
Calculated value i (k+1) of the electric current at the k+1 moment substitutes into valuation functions h together, selects a minimum valuation functions h output of sening as an envoy to
Level；Wherein, valuation functions h=| i*(k+1)-i(k+1)|；
Step 6, according to the output level of step 5 selection, corresponding open is selected in the Switch State Combination in Power Systems selected from step 2
Off status, and pass through driving circuit driving switch pipe as output quantity.
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