CN112398360A - Single-phase three-level micro photovoltaic inverter and open-loop control method and system thereof - Google Patents

Single-phase three-level micro photovoltaic inverter and open-loop control method and system thereof Download PDF

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CN112398360A
CN112398360A CN202011247021.5A CN202011247021A CN112398360A CN 112398360 A CN112398360 A CN 112398360A CN 202011247021 A CN202011247021 A CN 202011247021A CN 112398360 A CN112398360 A CN 112398360A
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switching device
current
switching
grid
reference value
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CN112398360B (en
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罗潇
於锋
丁雷青
李晓莉
彭勇
王建军
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State Grid Shanghai Electric Power Co Ltd
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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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • 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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • 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 invention discloses a single-phase three-level micro photovoltaic inverter and an open-loop control method and a system thereof. Furthermore, the open-loop control method is simple and effective, so that the inverter realizes the inversion control of the direct current of the photovoltaic panel, and outputs the sine alternating current which can meet the grid-connected requirement.

Description

Single-phase three-level micro photovoltaic inverter and open-loop control method and system thereof
Technical Field
The invention relates to the field of power electronic inverter driving and control, in particular to a single-phase three-level micro photovoltaic inverter and an open-loop control method and system thereof.
Background
With the rapid development of economic levels and industrial technologies worldwide, the energy demand is also increasing. Moreover, with the development of scientific technology, the non-regenerability of the traditional energy and the irreversible damage to the environment caused by the unlimited exploitation of the traditional energy, people tend to replace the traditional energy with a new clean and renewable energy. There are many types of renewable energy sources, including wind, water, geothermal, solar, etc., with solar being the most readily discovered and utilized renewable energy source. In recent years, as people pay more and more attention to power generation by using solar energy, photovoltaic power generation technology is rapidly developed.
The main core of the solar photovoltaic power generation system is a photovoltaic inverter which is used for inverting direct current generated by a solar photovoltaic panel into alternating current which can be accepted by a power grid and sending the alternating current into the power grid. In the conventional photovoltaic inverter system, a plurality of photovoltaic panels are connected in series to share one inverter, so that the size and power of the inverter are large, and the inverter is accompanied by large power loss and serious heating phenomenon. In addition, due to the serial connection of the photovoltaic panels, when one photovoltaic panel fails or is shielded by a shadow and cannot normally work, the one photovoltaic panel cannot normally work, and the efficiency of photovoltaic power generation is reduced. Therefore, micro photovoltaic inverters have received much attention from researchers.
The micro photovoltaic inverter is a novel device which is modularized, can be used in a plug-and-play mode and can convert direct current of a single solar cell module into alternating current, and is born in American silicon valley. The research and application of the micro inverter are the leading edge and the hot spot of the current global power conversion technology research, and the micro inverter has the characteristics of high energy efficiency, long service life, small volume, high reliability, safe operation, convenient installation and the like, marks a new breakthrough of the photovoltaic technology, and has wide prospects in the aspect of various distributed photovoltaic power generation applications. But for the application of the micro photovoltaic inverter, a reasonable control algorithm is required to be designed to realize the conversion from direct current to alternating current.
Disclosure of Invention
The invention aims to provide a single-phase three-level micro photovoltaic inverter and an open-loop control method and a system thereof. Furthermore, the open-loop control method is simple and effective, so that the inverter realizes the inversion control of the direct current of the photovoltaic panel, and outputs the sine alternating current which can meet the grid-connected requirement.
In order to achieve the purpose, the invention is realized by the following technical scheme:
a single-phase three-level micro photovoltaic inverter, comprising:
filtering and follow current inductance L1The input end of the filter is connected with the DC side photovoltaic panel, and the filtering and follow current inductor L1The photovoltaic power generation device is used for keeping the output current of the photovoltaic panel on the direct current side stable and reducing current ripples;
first clamping diode DAIts input terminal and the filtering and follow current inductance L1Is connected to the output terminal of the first clamping diode DAThe output end is connected with a third clamping diode DCAn input terminal of (1);
second clamping diode DBThe filtering and follow current inductance L1Is connected in turn to a fifth switching device SAAnd a sixth switching device SBA second clamping diode DBSaid second clamping diode DBThe output end is connected with the direct current side photovoltaic panel;
a capacitor C having one end connected to the first clamping diode DAIs connected to the other end of the capacitor C is connected to the fifth switching device SAAnd a sixth switching device SBTo (c) to (d);
first switching device S1One end of which is connected with the third clamping diode DCIs connected with the output end of the first switch and is connected with a third switch S at the other end3Device, the third switching device S3The photovoltaic panel is connected with the direct current side photovoltaic panel;
second switching device S2One end of which is connected with the third clamping diode DCIs connected to the output terminal of the first switching device, and the other end of the first switching device is connected to a fourth switching device S4Said fourth switching device S4The photovoltaic panel is connected with the direct current side photovoltaic panel;
one end of the grid-connected AC side is connected to the first switching device S1And the third switching device S3The other end of the grid-connected AC side is connected to the second switching device S2And said fourth switching device S4Said first switching device S1A second switching device S2A third switching device S3And a fourth switching device S4The inverter is used for inverting the direct-current voltage of the photovoltaic panel on the direct-current side into the alternating-current voltage which can be received on the grid-connected alternating-current side.
Optionally, an open-loop control method for a single-phase three-level micro photovoltaic inverter includes:
s1, acquiring a capacitor voltage reference value v according to the frequency requirement of the grid-connected alternating current sidec refAnd a reference value of the capacitance current ic ref；
S2, obtaining a grid-connected AC side current reference value i according to the power generated by the DC side photovoltaic panel and the reference voltage amplitude of the grid-connected AC sideac ref；
S3, according to the capacitance current reference value ic refAnd a grid-connected AC side current reference value iac refObtaining a fifth switching device SAOn duty cycle d ofAAnd a sixth switching device SBOn duty cycle d ofB；
S4, according to the grid-connected AC side voltage reference value vac refPositive and negative judgment third switching device S3Third switching signal GS3And a fourth switchPart S4Of the fourth switching signal GS4In combination with a fifth switching device SAOn duty cycle d ofAAnd a sixth switching device SBOn duty cycle d ofBObtaining a first switching signal GS1Second switching signal GS2The fifth switching signal GSAAnd a sixth switching signal GSBTo control the first switching devices S respectively1A second switching device S2A fifth switching device SAAnd a sixth switching device SB；
And S5, sending all the switching signals to corresponding switching devices of the inverter to drive the inverter.
Optionally, in the step S1,
grid-connected AC side voltage reference value vac refAnd a grid-connected AC side current reference value iac refAccording to formula (1):
Figure BDA0002770358320000031
instantaneous power P at grid-connected AC sideacAs shown in the formula (2),
Figure BDA0002770358320000032
pulsating power P at double line frequencyrThe reference value v of the capacitor voltage can be obtained by completely buffering by the capacitor Cc refAnd a reference value of the capacitance current ic ref：
Figure BDA0002770358320000033
Figure BDA0002770358320000034
Figure BDA0002770358320000035
Wherein, VacRepresenting the amplitude, I, of the reference voltage on the grid-connection AC sideacRepresenting the amplitude of the reference current of the grid-connected alternating current side; vcRepresenting the mean value of the capacitor voltage, is a design variable, and needs to satisfy Vc>Pdc/ωCbSin (2 ω t); ω ═ 2 pi f represents the electrical angular velocity on the grid-connected ac side, and f represents the voltage frequency on the grid-connected ac side; cbRepresenting capacitance value of the capacitor; pdcRepresenting the generated power of the photovoltaic panel.
Optionally, in the step S2,
generated power P according to photovoltaic paneldcAnd obtaining a grid-connected alternating current side current reference value i by combining the formula (1) and the formula (3)ac ref：
Figure BDA0002770358320000041
Optionally, in the step S3,
the conduction duty ratios of four working states of the single-phase three-level micro photovoltaic inverter are respectively d1、d2、d3And d4Wherein d is1+d2+d3+d 41, in state 1, the fifth switching device SAAnd a sixth switching device SBOn, fifth switching device S in State 2AAnd a sixth switching device SBOff, fifth switching device S in state 3AOpen and sixth switching device SBOff, fifth switching device S in state 4AOff and sixth switching device SBOn, fifth switching device SAOn duty cycle d ofAAnd a sixth switching device SBOn duty cycle d ofBExpressed as formula (7):
Figure BDA0002770358320000042
an opening according to the formula (8)Off period TsInternal grid-connected AC side current reference value iac refDC input current IdcAnd a capacitive reference current ic refTo obtain the fifth switching device S shown in formula (9)AOn duty cycle d ofAAnd a sixth switching device SBOn duty cycle d ofB：
Figure BDA0002770358320000043
Figure BDA0002770358320000044
Wherein, VdcThe voltage generated by the photovoltaic panel on the direct current side can be measured by a voltage sensor.
Optionally, in the step S4,
a fifth switching device S obtained by equation (9)AOn duty cycle d ofAAnd a sixth switching device SBOn duty cycle d ofBAnd period of TsAmplitude of 1 triangular carrier wave WaveComparing to obtain a fifth switching signal GS according to the formula (10)AAnd a sixth switching signal GSB：
Figure BDA0002770358320000051
Obtaining a grid-connected AC side voltage reference value v according to a formula (1)ac refAnd the third switching device S is obtained by the formula (11)3Third switching signal GS3And a fourth switching device S4Of the fourth switching signal GS4：
Figure BDA0002770358320000052
The fifth switching signal GS obtained according to the formula (10) and the formula (11)AThe sixth switching signal GSBAnd a third switching signal GS3And the fourth switching signal GS4Obtaining a first switching signal GS1And a second switching signal GS2：
Figure BDA0002770358320000053
Where 0 denotes turning off the switching device and 1 denotes activating the switching device.
Optionally, a system of the open-loop control method for the single-phase three-level micro photovoltaic inverter includes:
a capacitor voltage reference value acquisition module for acquiring a capacitor voltage reference value vc ref；
A capacitance current reference value obtaining module for obtaining a capacitance current reference value ic ref；
The grid-connected AC side reference current acquisition module receives the information of the capacitance voltage reference value acquisition module, and is used for acquiring a grid-connected AC side current reference value iac ref；
A switch on ratio obtaining module for receiving the information of the capacitance voltage reference value obtaining module, the capacitance current reference value obtaining module and the grid-connected AC side reference current obtaining module and obtaining a fifth switch device SAOn duty cycle d ofAAnd a sixth switching device SBOn duty cycle d ofB；
An inverter bridge switching signal module for obtaining a third switching device S3Third switching signal GS3And a fourth switching device S4Of the fourth switching signal GS4；
A switching signal acquisition module for acquiring the first switching device S1First switching signal GS of1A second switching device S2Second switching signal GS2A fifth switching device SAOf the fifth switching signal GSAAnd a sixth switching device SBSixth switching signal GS ofB；
And the output module is used for sending each switching signal to the corresponding switching device of the inverter so as to drive the inverter.
Compared with the prior art, the invention has the following advantages:
in the single-phase three-level micro photovoltaic inverter and the open-loop control method and system thereof, the inverter consists of a filtering and follow-up current inductor, a capacitor, a plurality of clamping diodes and a switching device, and can well invert the direct current voltage of a photovoltaic panel at the direct current side into the alternating current voltage which can be received at the grid-connected alternating current side.
Further, in the open-loop control method of the inverter, a capacitor voltage reference value v is obtained firstc refAnd a reference value of the capacitance current ic ref(ii) a Secondly, the power P generated according to the photovoltaic paneldcAnd an AC reference voltage amplitude VacObtaining a grid-connected AC side current reference value iac ref(ii) a Then, the capacitance current is referenced to the value ic refAnd a grid-connected AC side current reference value iac refThe sending switch conducting ratio obtaining module obtains a fifth switching device SAOn duty cycle d ofAAnd a sixth switching device SBOn duty cycle d ofB. Then according to the grid-connected AC side voltage reference value vac refTo obtain a third switching device S3Third switching signal GS3And a fourth switching device S4Of the fourth switching signal GS4In combination with a fifth switching device SAOn duty cycle d ofAAnd a sixth switching device SBOn duty cycle d ofBObtaining a first switching signal GS1Second switching signal GS2The fifth switching signal GSAAnd a sixth switching signal GSB. Finally, all the switching signals are sent to the corresponding switching devices to drive the inverter. The open-loop control method simply and effectively enables the inverter to realize the inversion control of the direct current of the photovoltaic panel, and outputs the alternating voltage and current with higher sine degree and lower harmonic content which can meet the grid-connected requirement.
Drawings
FIG. 1 is a schematic diagram of the open-loop control principle of a single-phase three-level micro photovoltaic inverter according to the present invention;
fig. 2(a) is a partial schematic diagram of a single-phase three-level micro photovoltaic inverter of the present invention in state 1;
FIG. 2(b) is a partial schematic view of a single-phase three-level micro photovoltaic inverter of the present invention in state 2;
FIG. 2(c) is a partial schematic diagram of a single-phase three-level micro photovoltaic inverter of the present invention in state 3;
FIG. 2(d) is a partial schematic diagram of a single-phase three-level micro photovoltaic inverter of the present invention in state 4;
FIG. 3 is a schematic flow chart of an open-loop control method for a single-phase three-level micro photovoltaic inverter according to the present invention;
FIG. 4 is a simulation result of the output current of the single-phase three-level micro photovoltaic inverter of the present invention;
fig. 5 is a simulation result of the output voltage of the single-phase three-level micro photovoltaic inverter of the present invention.
Detailed Description
The present invention will now be further described by way of the following detailed description of a preferred embodiment thereof, taken in conjunction with the accompanying drawings.
As shown in fig. 1, it is a schematic diagram of the open-loop control principle of a single-phase three-level micro photovoltaic inverter 7 according to the present invention, wherein the single-phase three-level micro photovoltaic inverter 7 (may be simply referred to as inverter) comprises: filtering and follow current inductance L1A first clamping diode DAA second clamping diode DBA third clamping diode DCCapacitor C, first switching device S1A second switching device S2A third switching device S3And a fourth switching device S4A fifth switching device SAAnd a sixth switching device SB。
Wherein, UdcAnd the direct-current voltage is used for outputting power to a grid-connected alternating-current side. The filtering and follow current inductance L1Input end and direct current side lightA voltage board connection, the filtering and follow current inductance L1The method is used for keeping the output current of the photovoltaic panel on the direct current side stable and reducing current ripples. The first clamping diode DAInput terminal and the filtering and follow current inductance L1Is connected to the output terminal of the first clamping diode DAThe output end is connected with a third clamping diode DCTo the input terminal of (1). The filtering and follow current inductance L1Is connected in turn to a fifth switching device SAAnd a sixth switching device SBA second clamping diode DBSaid second clamping diode DBThe output end is connected with the DC side photovoltaic panel. One end of the capacitor C and the first clamping diode DAIs connected to the other end of the capacitor C is connected to the fifth switching device SAAnd a sixth switching device SBIn the meantime. The first clamping diode DAA second clamping diode DBA third clamping diode DCThe capacitor C is used for preventing current from flowing back to a direct current side from the capacitor C and a grid-connected alternating current side.
The first switching device S1One end of the third clamping diode DCIs connected with the output end of the first switch and is connected with a third switch S at the other end3Device, the third switching device S3And the photovoltaic panel is connected with the direct current side photovoltaic panel. The second switching device S2One end of the third clamping diode DCIs connected to the output terminal of the first switching device, and the other end of the first switching device is connected to a fourth switching device S4Said fourth switching device S4And the photovoltaic panel is connected with the direct current side photovoltaic panel. One end of the grid-connected AC side is connected to the first switching device S1And the third switching device S3The other end of the grid-connected AC side is connected to the second switching device S2And said fourth switching device S4Said first switching device S1A second switching device S2A third switching device S3And a fourth switching device S4The inverter is used for inverting the direct-current voltage of the photovoltaic panel on the direct-current side into the alternating-current voltage which can be received on the grid-connected alternating-current side.
Wherein the fifth switching device SAAnd a firstSix-switch device SBFor realizing 4 operating states of the inverter 7. As shown in fig. 2(a), when the inverter 7 is in the state 1, the fifth switching device SAAnd a sixth switching device SBAnd (4) opening. As shown in fig. 2(b), when the inverter 7 is in the state 2, the fifth switching device SAAnd a sixth switching device SBAnd (6) turning off. As shown in fig. 2(c), when the inverter 7 is in the state 3, the fifth switching device SAOpen and sixth switching device SBAnd (6) turning off. As shown in fig. 2(d), when the inverter 7 is in the state 4, the fifth switching device SAOff and sixth switching device SBAnd (4) opening.
In this embodiment, the capacitor C is a dual-frequency power compensation capacitor, and can divide the voltage output to the grid-connected ac side into three levels, which are respectively the 0 level in the state 1 and the state 4, and the U in the state 2dcLevel, and U of state 3dc+vcLevel (v)cThe voltage across the capacitor C).
Further, as shown in fig. 3, the present invention also discloses an open-loop control method of the single-phase three-level micro-pv inverter 7 (i.e. an open-loop control algorithm of the inverter 7), wherein the amplitude V of the reference voltage on the grid-connected ac sideacFrequency f, generated power P of the photovoltaic paneldcPeriod TsAverage value of capacitor voltage VcKnown from existing information.
Specifically, the open-loop control method includes:
s1, acquiring a capacitor voltage reference value v according to the frequency requirement of the grid-connected alternating current sidec refAnd obtaining a reference value i of the capacitor current according to the relation between the voltage and the current at the two ends of the capacitor Cc ref。
In step S1, the grid-connected ac side voltage reference value vac refAnd a grid-connected AC side current reference value iac refAccording to formula (1):
Figure BDA0002770358320000081
instantaneous power P at grid-connected AC sideacAs shown in the formula (2),
Figure BDA0002770358320000082
pulsating power P at double line frequencyrThe reference value v of the capacitor voltage can be obtained by completely buffering by the capacitor Cc refAnd a reference value of the capacitance current ic ref：
Figure BDA0002770358320000091
Figure BDA0002770358320000092
Figure BDA0002770358320000093
Wherein, VacRepresenting the amplitude, I, of the reference voltage on the grid-connection AC sideacRepresenting the amplitude of the reference current of the grid-connected alternating current side; vcRepresenting the mean value of the capacitor voltage, is a design variable, and needs to satisfy Vc>Pdc/ωCbSin (2 ω t); ω ═ 2 pi f represents the electrical angular velocity on the grid-connected ac side, and f represents the voltage frequency on the grid-connected ac side; cbRepresenting capacitance value of the capacitor; pdcThe generated power of the photovoltaic panel is represented as a given value in the open-loop control method of the present invention.
S2, obtaining a grid-connected AC side current reference value i according to the power generated by the DC side photovoltaic panel and the reference voltage amplitude of the grid-connected AC sideac ref。
Wherein, in the step S2, the generated power P according to the photovoltaic paneldcAnd obtaining a grid-connected alternating current side current reference value i by combining the formula (1) and the formula (3)ac ref：
Figure BDA0002770358320000094
S3, according to the capacitance current reference value ic refAnd a grid-connected AC side current reference value iac refObtaining a fifth switching device SAOn duty cycle d ofAAnd a sixth switching device SBOn duty cycle d ofB。
In the step S3, the conduction duty ratios of the four working states of the single-phase three-level micro photovoltaic inverter 7 are d1、d2、d3And d4(corresponding to State 1, State 2, State 3, and State 4, respectively), where d1+d2+d3+d 41, in state 1, the fifth switching device SAAnd a sixth switching device SBOn, fifth switching device S in State 2AAnd a sixth switching device SBOff, fifth switching device S in state 3AOpen and sixth switching device SBOff, fifth switching device S in state 4AOff and sixth switching device SBOn, fifth switching device SAOn duty cycle d ofAAnd a sixth switching device SBOn duty cycle d ofBCan be expressed as formula (7):
Figure BDA0002770358320000095
one switching period T according to equation (8)sInternal grid-connected AC side current reference value iac refDC input current IdcAnd a capacitive reference current ic refTo obtain the fifth switching device S shown in formula (9)AOn duty cycle d ofAAnd a sixth switching device SBOn duty cycle d ofB：
Figure BDA0002770358320000101
Figure BDA0002770358320000102
Wherein, VdcThe voltage generated by the photovoltaic panel on the direct current side can be measured by a voltage sensor.
S4, according to the grid-connected AC side voltage reference value vac refPositive and negative judgment third switching device S3Third switching signal GS3And a fourth switching device S4Of the fourth switching signal GS4In combination with a fifth switching device SAOn duty cycle d ofAAnd a sixth switching device SBOn duty cycle d ofBObtaining a first switching signal GS1Second switching signal GS2The fifth switching signal GSAAnd a sixth switching signal GSBTo control the first switching devices S respectively1A second switching device S2A fifth switching device SAAnd a sixth switching device SB。
Specifically, in step S4, the fifth switching device S obtained by equation (9)AOn duty cycle d ofAAnd a sixth switching device SBOn duty cycle d ofBAnd period of TsAmplitude of 1 triangular carrier wave WaveComparing to obtain a fifth switching signal GS according to the formula (10)AAnd a sixth switching signal GSB：
Figure BDA0002770358320000103
Obtaining a grid-connected AC side voltage reference value v according to a formula (1)ac refAnd the third switching device S is obtained by the formula (11)3Third switching signal GS3And a fourth switching device S4Of the fourth switching signal GS4：
Figure BDA0002770358320000104
The fifth switching signal GS obtained according to the formula (10) and the formula (11)AThe sixth switching signal GSBAnd a third switching signal GS3And the fourth switching signal GS4Obtaining a first switching signal GS1And a second switching signal GS2：
Figure BDA0002770358320000111
Where 0 denotes turning off the switching device and 1 denotes activating the switching device.
And S5, sending all the switching signals to the corresponding switching devices of the inverter 7 to drive the inverter 7.
Based on the same inventive concept, as shown in fig. 1, the invention also discloses a system of the open-loop control method for the single-phase three-level micro photovoltaic inverter 7, which comprises: the device comprises a capacitance voltage reference value acquisition module 1, a capacitance current reference value acquisition module 2, a grid-connected alternating current side reference current acquisition module 3, a switch conduction ratio acquisition module 5, an inverter bridge switch signal module 4, a switch signal acquisition module 6 and an output module.
The capacitance voltage reference value obtaining module 1 is used for obtaining a capacitance voltage reference value vc refThe capacitance current reference value obtaining module 2 is used for obtaining a capacitance current reference value ic refThe grid-connected alternating current side reference current acquisition module 3 receives the information of the capacitance voltage reference value acquisition module 1, and the grid-connected alternating current side reference current acquisition module 3 is used for acquiring a grid-connected alternating current side current reference value iac ref. The switch on ratio obtaining module 5 receives the information of the capacitance voltage reference value obtaining module 1, the capacitance current reference value obtaining module 2 and the grid-connected alternating current side reference current obtaining module 3, and obtains a fifth switching device SAOn duty cycle d ofAAnd a sixth switching device SBOn duty cycle d ofB. The inverter bridge switching signal module 4 is used for obtaining a third switching device S3Third switching signal GS3And a fourth switching device S4Of the fourth switching signalGS4. The switching signal obtaining module 6 is used for obtaining a first switching device S1First switching signal GS of1A second switching device S2Second switching signal GS2A fifth switching device SAOf the fifth switching signal GSAAnd a sixth switching device SBSixth switching signal GS ofB. The output module (not shown in the figure) is used for sending each switching signal to the corresponding switching device of the inverter 7 to drive the inverter 7.
In one embodiment, the signal generated by the open-loop control method and system for the single-phase three-level micro photovoltaic inverter 7 of the invention is used for controlling the inverter 7 to output a current simulation result. As shown in fig. 4, it can be seen that, based on the above control method and system, the photovoltaic inverter 7 can obtain an output current with low harmonic content and high sine degree. As shown in FIG. 5, it can be seen that the grid-connected AC side output voltage v is the simulation result of the output voltage of the inverter 7acCan also maintain higher sine degree and accurately track the voltage reference value v at the grid-connected AC sideac refA change in (c).
In summary, in the single-phase three-level micro photovoltaic inverter 7, the open-loop control method and the system of the present invention, the inverter 7 is composed of a filtering and a current-continuing inductor L1The capacitor C, the clamping diodes and the switching device can invert the direct-current voltage of the photovoltaic panel at the direct-current side into alternating-current voltage meeting grid-connected requirements, and grid-connected control of electric energy is achieved. In the open-loop control method of the inverter 7, a capacitor voltage reference value v is firstly obtainedc refAnd a reference value of the capacitance current ic ref(ii) a Secondly, the power P generated according to the photovoltaic paneldcAnd an AC reference voltage amplitude VacObtaining a grid-connected AC side current reference value iac ref(ii) a Then, the capacitance current is referenced to the value ic refAnd a grid-connected AC side current reference value iac refThe sending-in switch conduction ratio obtaining module 5 obtains a fifth switching device SAOn duty cycle d ofAAnd a sixth switching device SBOn duty cycle d ofB. Then according to andvoltage reference value v of network AC sideac refTo obtain a third switching device S3Third switching signal GS3And a fourth switching device S4Of the fourth switching signal GS4In combination with a fifth switching device SAOn duty cycle d ofAAnd a sixth switching device SBOn duty cycle d ofBObtaining a first switching signal GS1Second switching signal GS2The fifth switching signal GSAAnd a sixth switching signal GSB. Finally, all the switching signals are sent to the corresponding switching devices to drive the inverter 7. The open-loop control method simply and effectively enables the inverter 7 to realize the inversion control of the direct current of the photovoltaic panel, outputs the sine alternating current which can meet the grid-connected requirement, has simple steps, is easy to realize, and is suitable for large-scale popularization and application.
While the present invention has been described in detail with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be determined from the following claims.

Claims (7)

1. A single-phase three-level micro photovoltaic inverter, comprising:
filtering and follow current inductance L1The input end of the filter is connected with the DC side photovoltaic panel, and the filtering and follow current inductor L1The photovoltaic power generation device is used for keeping the output current of the photovoltaic panel on the direct current side stable and reducing current ripples;
first clamping diode DAIts input terminal and the filtering and follow current inductance L1Is connected to the output terminal of the first clamping diode DAThe output end is connected with a third clamping diode DCAn input terminal of (1);
second clamping diode DBThe filtering and follow current inductance L1Is connected in turn to a fifth switching device SAAnd a sixth switching device SBA second clamping diode DBSaid second clamping diode DBThe output end is connected with the direct current side photovoltaic panel;
a capacitor C having one end connected to the first clamping diode DAIs connected to the other end of the capacitor C is connected to the fifth switching device SAAnd a sixth switching device SBTo (c) to (d);
first switching device S1One end of which is connected with the third clamping diode DCIs connected with the output end of the first switch and is connected with a third switch S at the other end3Device, the third switching device S3The photovoltaic panel is connected with the direct current side photovoltaic panel;
second switching device S2One end of which is connected with the third clamping diode DCIs connected to the output terminal of the first switching device, and the other end of the first switching device is connected to a fourth switching device S4Said fourth switching device S4The photovoltaic panel is connected with the direct current side photovoltaic panel;
one end of the grid-connected AC side is connected to the first switching device S1And the third switching device S3The other end of the grid-connected AC side is connected to the second switching device S2And said fourth switching device S4Said first switching device S1A second switching device S2A third switching device S3And a fourth switching device S4The inverter is used for inverting the direct-current voltage of the photovoltaic panel on the direct-current side into the alternating-current voltage which can be received on the grid-connected alternating-current side.
2. A method for open-loop control of a single-phase three-level micro pv inverter as claimed in claim 1, comprising:
s1, acquiring a capacitor voltage reference value v according to the frequency requirement of the grid-connected alternating current sidec refAnd a reference value of the capacitance current ic ref；
S2, obtaining a grid-connected AC side current reference value i according to the power generated by the DC side photovoltaic panel and the reference voltage amplitude of the grid-connected AC sideac ref；
S3, according to the capacitance current reference value ic refAndgrid AC side current reference value iac refObtaining a fifth switching device SAOn duty cycle d ofAAnd a sixth switching device SBOn duty cycle d ofB；
S4, according to the grid-connected AC side voltage reference value vac refPositive and negative judgment third switching device S3Third switching signal GS3And a fourth switching device S4Of the fourth switching signal GS4In combination with a fifth switching device SAOn duty cycle d ofAAnd a sixth switching device SBOn duty cycle d ofBObtaining a first switching signal GS1Second switching signal GS2The fifth switching signal GSAAnd a sixth switching signal GSBTo control the first switching devices S respectively1A second switching device S2A fifth switching device SAAnd a sixth switching device SB；
And S5, sending all the switching signals to corresponding switching devices of the inverter to drive the inverter.
3. The open-loop control method of a single-phase three-level micro photovoltaic inverter as claimed in claim 2, wherein in the step S1,
grid-connected AC side voltage reference value vac refAnd a grid-connected AC side current reference value iac refAccording to formula (1):
Figure FDA0002770358310000021
instantaneous power P at grid-connected AC sideacAs shown in the formula (2),
Figure FDA0002770358310000022
pulsating power P at double line frequencyrThe reference value v of the capacitor voltage can be obtained by completely buffering by the capacitor Cc refAnd capacitorStream reference value ic ref：
Figure FDA0002770358310000023
Figure FDA0002770358310000024
Figure FDA0002770358310000025
Wherein, VacRepresenting the amplitude, I, of the reference voltage on the grid-connection AC sideacRepresenting the amplitude of the reference current of the grid-connected alternating current side; vcRepresenting the mean value of the capacitor voltage, is a design variable, and needs to satisfy Vc>Pdc/ωCbSin (2 ω t); ω ═ 2 pi f represents the electrical angular velocity on the grid-connected ac side, and f represents the voltage frequency on the grid-connected ac side; cbRepresenting capacitance value of the capacitor; pdcRepresenting the generated power of the photovoltaic panel.
4. The open-loop control method of a single-phase three-level micro photovoltaic inverter as claimed in claim 3, wherein in the step S2,
generated power P according to photovoltaic paneldcAnd obtaining a grid-connected alternating current side current reference value i by combining the formula (1) and the formula (3)ac ref：
Figure FDA0002770358310000031
5. The open-loop control method of a single-phase three-level micro photovoltaic inverter as claimed in claim 4, wherein in the step S3,
the conduction duty ratios of four working states of the single-phase three-level micro photovoltaic inverter are respectively d1、d2、d3And d4Wherein d is1+d2+d3+d41, in state 1, the fifth switching device SAAnd a sixth switching device SBOn, fifth switching device S in State 2AAnd a sixth switching device SBOff, fifth switching device S in state 3AOpen and sixth switching device SBOff, fifth switching device S in state 4AOff and sixth switching device SBOn, fifth switching device SAOn duty cycle d ofAAnd a sixth switching device SBOn duty cycle d ofBExpressed as formula (7):
Figure FDA0002770358310000032
one switching period T according to equation (8)sInternal grid-connected AC side current reference value iac refDC input current IdcAnd a capacitive reference current ic refTo obtain the fifth switching device S shown in formula (9)AOn duty cycle d ofAAnd a sixth switching device SBOn duty cycle d ofB：
Figure FDA0002770358310000033
Figure FDA0002770358310000034
Wherein, VdcThe voltage generated by the photovoltaic panel on the direct current side can be measured by a voltage sensor.
6. The open-loop control method of a single-phase three-level micro photovoltaic inverter as claimed in claim 5, wherein in the step S4,
a fifth switching device S obtained by equation (9)AOn duty cycle d ofAAnd a sixth switching device SBOn duty cycle d ofBAnd period of TsAmplitude of 1 triangular carrier wave WaveComparing to obtain a fifth switching signal GS according to the formula (10)AAnd a sixth switching signal GSB：
Figure FDA0002770358310000041
Obtaining a grid-connected AC side voltage reference value v according to a formula (1)ac refAnd the third switching device S is obtained by the formula (11)3Third switching signal GS3And a fourth switching device S4Of the fourth switching signal GS4：
Figure FDA0002770358310000042
The fifth switching signal GS obtained according to the formula (10) and the formula (11)AThe sixth switching signal GSBAnd a third switching signal GS3And the fourth switching signal GS4Obtaining a first switching signal GS1And a second switching signal GS2：
Figure FDA0002770358310000043
Where 0 denotes turning off the switching device and 1 denotes activating the switching device.
7. A system for the open-loop control method of a single-phase three-level micro photovoltaic inverter according to any one of claims 2 to 6, comprising:
a capacitor voltage reference value acquisition module for acquiring a capacitor voltage reference value vc ref；
A capacitance current reference value acquisition module forIn obtaining a reference value i of the capacitance currentc ref；
The grid-connected AC side reference current acquisition module receives the information of the capacitance voltage reference value acquisition module, and is used for acquiring a grid-connected AC side current reference value iac ref；
A switch on ratio obtaining module for receiving the information of the capacitance voltage reference value obtaining module, the capacitance current reference value obtaining module and the grid-connected AC side reference current obtaining module and obtaining a fifth switch device SAOn duty cycle d ofAAnd a sixth switching device SBOn duty cycle d ofB；
An inverter bridge switching signal module for obtaining a third switching device S3Third switching signal GS3And a fourth switching device S4Of the fourth switching signal GS4；
A switching signal acquisition module for acquiring the first switching device S1First switching signal GS of1A second switching device S2Second switching signal GS2A fifth switching device SAOf the fifth switching signal GSAAnd a sixth switching device SBSixth switching signal GS ofB；
And the output module is used for sending each switching signal to the corresponding switching device of the inverter so as to drive the inverter.
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