CN203747431U - DC/AC converter for photovoltaic power-generation grid-connected system based on phase-shifting transformer - Google Patents

DC/AC converter for photovoltaic power-generation grid-connected system based on phase-shifting transformer Download PDF

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CN203747431U
CN203747431U CN201320636596.5U CN201320636596U CN203747431U CN 203747431 U CN203747431 U CN 203747431U CN 201320636596 U CN201320636596 U CN 201320636596U CN 203747431 U CN203747431 U CN 203747431U
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phase
current
unsteady flow
flow bridge
phase unsteady
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高毅夫
陈琳琳
刘昆
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Beijing Kaimen Control Engineering Co Ltd
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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
    • 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
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/10—Flexible AC transmission systems [FACTS]

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Abstract

The utility model discloses a DC/AC converter for a photovoltaic power-generation grid-connected system based on a phase-shifting transformer. The converter is characterized in that the converter employs the phase-shifting transformer for the connection with a power grid; the output side of the phase-shifting transformer is a Y-shaped winding [7] which is connected with the power grid; the input side of the phase-shifting transformer is provided with Y-shaped and triangular windings [5, 6] which are respectively connected with two three-phase current-transformation bridges [3, 4], thereby forming a 12 pulse-wave DC/AC converter; the converter employs a control strategy of asymmetrical current, and controls and generates asymmetrical Y-shaped and triangular winding currents with different phases according to a specific rule of conversion, thereby enabling the current of a grid side of the phase-shifting transformer to be a sine-wave current. The converter provided by the utility model is high in overall efficiency of a system, and is high in conversion efficiency of energy at a direct-current side. A power factor can be continuously adjusted in a lead-lag manner, so the converter is suitable for a photovoltaic power-generation system with demands for various types of capacities.

Description

Photovoltaic power generation grid-connecting system DC/AC converter based on phase shifting transformer
Technical field
The utility model belongs to photovoltaic power generation grid-connecting technology.
Background technology
At present, the low profile photovoltaic converter kind that is less than 6kW is more numerous and diverse, is single phase system substantially, transless structure, the leakage current and the larger problem of harmonic wave that exist direct current injection, common-mode voltage to produce in various degree, thereby the difficulty that networks.The medium-sized photovoltaic converter constituted mode of 6～100kW is also numerous and diverse various, and existing single phase system also has three-phase system, or by the three-phase system of single-phase combination; Existing transless structure, also has the system through transformer output; Also there is the same problem of low profile photovoltaic converter in the system of transless structure, also has the difficult problem that networks; Although there is not the problem of the isolation that networks through the system of transformer output, have the problem of efficiency and harmonic wave.Be greater than large-sized photovoltaic converter using voltage-source type or the current source inverter of 100kW, general all through transformer output, although there is not the problem of the isolation that networks, also there is the problem of efficiency and harmonic wave.In addition the current system problems such as also ubiquity system forms complexity, cost is high, overall efficiency is low, the DC input voitage scope of permission is little.
The standard of the states such as for the topological structure of photovoltaic power generation grid-connecting system, the standard of every country is not quite similar, American-European is stricter to the requirement networking, and it is critical limitation condition that output transformer is set.The country that output transformer be there is no to strict restriction, to the restriction of networking physical condition also substantially with coming to the same thing of networking through transformer, this means that transformerless structure needs more complicated solution, needs to pay the cost of other side.
In sum, there is problem in various degree in existing photovoltaic power generation grid-connecting converter, the extensive use with photovoltaic generation that develops rapidly along with photovoltaic power generation technology, the technical scheme of improving photovoltaic power generation grid-connecting converter also continues to bring out, but yet there are no up to now the achievement in research appearance of novelty.
Summary of the invention
The utility model research to as if for the thyristor 12 pulse wave DC/AC converters of photovoltaic power generation grid-connecting system, this is the typical structure of DC/AC converter, the input side Y of its phase shifting transformer is connected with △ group three-phase bridge with Y group three-phase bridge respectively with △ winding, the electric current of Y and △ winding is synthetic through phase shifting transformer, at the ac output current of the outlet side synthesis system of phase shifting transformer.Its phase shifting transformer winding construction of the DC/AC converter of this spline structure is simple, and outlet is easy, and winding utilization is high, is applicable to the application of the various power of photovoltaic power generation grid-connecting system.
The purpose of this utility model is conversion mechanism, topological structure and the control technology of further investigation DC/AC converter, on the basis of comprehensive prior art, researches and develops a kind of high-quality, DC/AC converter of being applicable to being incorporated into the power networks.
Main points of the present utility model be harmonic wave inhibition at DC/AC converter, controlledization of thyristor, DC input voitage on a large scale controlled, be applicable to having obtained aspect being incorporated into the power networks breakthrough progress.
The feature of the photovoltaic power generation grid-connecting system DC/AC converter of the utility model based on phase shifting transformer is to adopt phase shifting transformer to be connected with electrical network, phase shifting transformer outlet side is Y shape winding [7], be connected with electrical network, input side is respectively Y shape and two windings of △ shape [5] and [6], connect respectively two three-phase unsteady flow bridges [3] and [4], form 12 pulse wave DC/AC converters, the control strategy of asymmetrical current is carried out in employing to two three-phase unsteady flow bridges, by the particular transform rule of (1) formula and (2) formula, control generation respectively asymmetric mutually, and phase place is not identical Y winding [5] electric current and △ winding [6] electric current also, make two windings exchange resultant current and do not comprise 6 (2k) ± 1 (k=1, 2, ) subharmonic, the electric current that makes phase shifting transformer outlet side Y shape winding [7] is sine-wave current, by the particular transform rule of (1) formula and (2) formula, controlling the input current waveform of two three-phase unsteady flow bridges realizes by many level DCs Current Control and allocation units [2], for many level synthetic etc. incremental steps shape triangular current waveform, [22] be Y winding three-phase unsteady flow bridge input current waveform, [23] be △ winding three-phase unsteady flow bridge input current waveform, but differ 30 ° with Y three-phase unsteady flow bridge in phase place, [24] be to control by (1) formula rule of conversion the phase shifting transformer input side Y winding A phase current waveform obtaining, [25] be to control by (2) formula rule of conversion the phase shifting transformer input side △ winding A phase current waveform obtaining, [26] be the resultant current waveform that phase shifting transformer outlet side obtains, for approaching sinusoidal wave waveform, there is low harmonic wave, DC voltage and current is adjustable continuously, system synthesis efficiency is high, the feature that is applicable to grid-connected application.
I BY ( ωt ) = I dc { 1 2 + Σ k = 1 ∞ 7 + 4 3 36 ( 2 k - 1 ) 2 - 1 cos [ 6 ( 2 k - 1 ) ωt ] + Σ k = 1 ∞ 1 144 k 2 - 1 cos ( 12 kωt ) } - - - ( 1 )
I BΔ ( ωt ) = I dc { 1 2 - Σ k = 1 ∞ 7 + 4 3 36 ( 2 k - 1 ) 2 - 1 cos [ 6 ( 2 k - 1 ) ωt ] + Σ k = 1 ∞ 1 144 k 2 - 1 cos ( 12 kωt ) } - - - ( 2 )
In formula:
I bY: Y bridge direct current
I b Δ: Δ bridge direct current
I dc: solar energy pole plate electric current
k＝1，2，……?。
Accompanying drawing explanation
Accompanying drawing 1 is the photovoltaic power generation grid-connecting system DC/AC converter topology structure chart based on phase shifting transformer, and in Fig. 1,1 is solar energy pole plate DC power supply; The 2nd, many level DCs Current Control and allocation units; The 3rd, Y winding three-phase unsteady flow bridge; The 4th, △ winding three-phase unsteady flow bridge; The 5th, phase shifting transformer input side Y shape winding; The 6th, phase shifting transformer input side △ shape winding; The 7th, phase shifting transformer output side winding, Y connection; The 8th, AC network.
Accompanying drawing 2 is photovoltaic power generation grid-connecting system DC/AC converter based on phase shifting transformer oscillograms when the incremental steps shape triangular waves such as employing, and in Fig. 2,21 is solar energy pole plate direct current I dcwaveform; The 22nd, Y winding three-phase unsteady flow bridge input current I bYwaveform; The 23rd, △ winding three-phase unsteady flow bridge input current I b△ waveform; The 24th, phase shifting transformer input side Y shape winding A phase I aYcurrent waveform, B phase I bYcurrent waveform and C phase I cYcurrent waveform and A phase I aYcurrent waveform is similar, and difference is only to differ 120 ° and 240 ° with A respectively; The 25th, phase shifting transformer input side △ shape winding A phase I a Δcurrent waveform, B phase I b Δcurrent waveform and C phase I c Δcurrent waveform and A phase I a Δcurrent waveform is similar, and difference is only to differ 120 ° and 240 ° with A respectively; The 26th, phase shifting transformer output, i.e. net side A phase I acurrent waveform, B phase I bcurrent waveform and C phase I ccurrent waveform and A phase I acurrent waveform is similar, and difference is only to differ 120 ° and 240 ° with A respectively.
Embodiment
Tradition 12 pulse wave DC/AC converters are DC quantity to be averagely allocated to two three-phase unsteady flow bridges convert, and the total percent harmonic distortion THD that exchanges output is greater than 8%, and such conversion quality can not meet harmonic wave networking standard.How to distribute DC quantity to two three-phase unsteady flow bridges, just realize the alternating current that direct current is transformed to high quality sine waveform?
Mean allocation DC quantity give the result of two three-phase unsteady flow bridges be their interchange output waveform contain 6k ± 1 (k=1,2 ...) subharmonic, two three-phase unsteady flow bridge 6 (2k-1) ± 1 (k=1 wherein, 2 ...) subharmonic equal and opposite in direction, single spin-echo; 6 (2k) ± 1 (k=1,2 ...) subharmonic equal and opposite in direction, phase place is identical.Therefore, after the interchange of two three-phase unsteady flow bridges output is synthetic, 6 (2k-1) ± 1 (k=1,2 ...) subharmonic cancels each other, and 6 (2k) ± 1 (k=1,2 ...) subharmonic with for converter, exchange output harmonic component.If unequal, distribute direct current to two three-phase unsteady flow bridges, but by particular transform rule, direct current is distributed to two three-phase unsteady flow bridges, make two three-phase unsteady flow bridges exchange output and do not comprise 6 (2k) ± 1 (k=1,2,) subharmonic, just can make converter exchange and be output as sine wave.
Particular transform rule by (1) formula and (2) formula is distributed to two three-phase unsteady flow bridges by direct current, and I bY(ω t) and I b Δ(ω t) synchronizes with the ac output current of Y three-phase unsteady flow bridge, Δ three-phase unsteady flow bridge, the ac output current of Y three-phase unsteady flow bridge and Δ three-phase unsteady flow bridge is asymmetrical waveform, and waveform and phase place are all not identical yet, but the synthetic alternating current of two three-phase unsteady flow bridges, the electric current of net side is sine-wave current.
Actually realizing above-mentioned electric current, is the incremental steps shape triangular wave such as to use to be similar in the electric current that imposes on two three-phase unsteady flow bridges, etc. incremental steps shape triangular current waveform, adopts many level DCs Current Control and allocation units [2] for following principle to realize:
(1) direct current is all divided into m branch road, each branch road is connected to two gate-controlled switches, and two gate-controlled switch complimentary action form complementary switch pair, are connected respectively to Y three-phase unsteady flow bridge and Δ three-phase unsteady flow bridge;
(2) every 30 °/m, switch a complementary switch pair, make the electric current that flows into Y three-phase unsteady flow bridge increase a branch road amount, also make the electric current that flows into Δ three-phase unsteady flow bridge reduce by a branch road amount simultaneously, interval through m 30 °/m, when all branch currents all flow into after Y three-phase unsteady flow bridge, make again the electric current that flows into Y three-phase unsteady flow bridge reduce by a branch road amount every 30 °/m, also make the electric current that flows into Δ three-phase unsteady flow bridge increase a branch road amount simultaneously, until flow into the electric current of Y three-phase unsteady flow bridge, reduce to zero, repeat above process, just can by direct current by etc. the rule of incremental steps shape triangular wave distribute to Y three-phase unsteady flow bridge and Δ three-phase unsteady flow bridge.
Adopt the photovoltaic power generation grid-connecting system DC/AC converter based on phase shifting transformer of above-mentioned principle and direct current distribution method to there is following characteristic:
low harmonic wave hypermutation obversion amount, this converter ac output current harmonic content is propped up way m with the direct current of many level DCs Current Control and allocation units and is increased and reduce, and the relation of converter output AC electric current THD and m is shown in table 1;
The relation table of table 1.THD and m
m 2 3 4 5 6 7 8 9
THD 7.77％ 5.25％ 3.99％ 3.28％ 2.77％ 2.45％ 2.20％ 2.02％
According to table 1, when m >=6, the harmonic value of converter is limited in the scope of < 3%, and converter outlet side needn't arrange filter, can meet networking requirement;
thyristor is control entirely, by etc. incremental steps shape triangular current impose on Y three-phase unsteady flow bridge and Δ three-phase unsteady flow bridge, the electric current that has caused switching device in Y three-phase unsteady flow bridge and Δ three-phase unsteady flow bridge by set etc. incremental steps shape triangular current rule change, when the switching device of formation Y three-phase unsteady flow bridge and Δ three-phase unsteady flow bridge is thyristor, when the incremental steps shape triangular current such as applying and starting to gate circuit transistor gate triggering signal, thyristor is open-minded, during waiting incremental steps shape triangular current to be zero, thyristor current flows is that zero being forced to turn-offed, be that thyristor is opened and controlled by gate pole, electric current for zero turn-off control by etc. incremental steps shape triangular current provide, both combinations make thyristor can be used as full control switch use, the full control of thyristor makes Trigger Angle phase shift range become-180 °～180 °, power factor can be leading, lag behind and regulate continuously, can realize the control that power factor is " 1 ",
use soft switch theory, in the electric current that flows into Y three-phase unsteady flow bridge is zero interval, make the thyristor commutation of Y three-phase unsteady flow bridge, at the electric current that flows into Δ three-phase unsteady flow bridge, be zero interval, make the thyristor commutation of Δ three-phase unsteady flow bridge, the thyristor of Y three-phase unsteady flow bridge and Δ three-phase unsteady flow bridge is commutation under zero condition at electric current, and thyristor turn-offs when electric current is zero, open-minded when voltage is zero, without switching loss, thyristor operating frequency 50Hz, switching frequency is low, thereby gross efficiency is high;
the adjustable range of direct current is large, and the control of direct current is realized by many level DCs Current Control and allocation units [2], by regulating the amplitude of three-phase unsteady flow bridge [32] and [33] electric current, can carry out to direct current the adjusting on a large scale of 0～rated value;
isolated grid-connected by phase shifting transformer, system reliability is high.
Compared with prior art, photovoltaic power generation grid-connecting system DC/AC converter based on phase shifting transformer has that overall system efficiency is high, DC side energy transformation excellent in efficiency, the green feature without harmonic pollution in electric power net, adopt this novel DC/AC converter, the DC/DC link of boosting can be set, current transformer output filtering link can be set, and grid side also can configure reactive power compensation and filter.In addition, this novel DC/AC converter also has the feature that power factor can lead-lag regulates, was applicable to the photovoltaic power generation grid-connecting application of various capacity requirements continuously, particularly realized the full control of thyristor, can bring into play that the withstand voltage height of thyristor, current capacity scope are large, device performance stable, system realizes the advantage such as simple, cheap and builds the high performance-price ratio DC/AC converter without grid-connected obstacle, has boundless application prospect.

Claims (3)

1. the photovoltaic power generation grid-connecting system DC/AC converter based on phase shifting transformer, it is characterized in that adopting phase shifting transformer to be connected with electrical network, phase shifting transformer outlet side is Y shape winding [7], be connected with electrical network, input side is respectively Y shape and two windings [5 of △ shape, 6], connect respectively two three-phase unsteady flow bridges [3, 4], form 12 pulse wave DC/AC converters, the control strategy of asymmetrical current is carried out in employing to two three-phase unsteady flow bridges, by the particular transform rule of (1) formula and (2) formula, control generation respectively asymmetric mutually, and phase place is not identical Y winding [5] electric current and △ winding [6] electric current also, make two windings exchange resultant current and do not comprise 6*2*k ± 1 subharmonic, wherein, k=1, 2, the electric current that makes phase shifting transformer outlet side Y shape winding [7] is sine-wave current, by the particular transform rule of (1) formula and (2) formula, controlling the input current waveform of two three-phase unsteady flow bridges realizes by many level DCs Current Control and allocation units [2], for many level synthetic etc. incremental steps shape triangular current waveform, △ winding three-phase unsteady flow bridge input current waveform and Y winding three-phase unsteady flow bridge input current waveform differ 30 °, (1) formula and (2) formula are as follows:
In formula:
I bY: Y bridge direct current
I b Δ: Δ bridge direct current
I dc: solar energy pole plate electric current
k＝1，2，……?。
2. the photovoltaic power generation grid-connecting system DC/AC converter based on phase shifting transformer according to claim 1, described many level DCs Current Control and allocation units [2] adopt following principle to realize:
(1) direct current is all divided into m branch road, each branch road is connected to two gate-controlled switches, two gate-controlled switch complimentary action, form complementary switch pair, be connected respectively to Y three-phase unsteady flow bridge and Δ three phase transformation gate-controlled switch complimentary action, form complementary switch pair, be connected respectively to Y three-phase unsteady flow bridge and Δ three-phase unsteady flow bridge;
(2) every 30 °/m, switch a complementary switch pair, make the electric current that flows into Y three-phase unsteady flow bridge increase a branch road amount, also make the electric current that flows into Δ three-phase unsteady flow bridge reduce by a branch road amount simultaneously, interval through m 30 °/m, when all branch currents all flow into after Y three-phase unsteady flow bridge, make again the electric current that flows into Y three-phase unsteady flow bridge reduce by a branch road amount every 30 °/m, also make the electric current that flows into Δ three-phase unsteady flow bridge increase a branch road amount simultaneously, until flow into the electric current of Y three-phase unsteady flow bridge, reduce to zero, repeat above process, just by direct current by etc. the rule of incremental steps shape triangular wave distribute to Y three-phase unsteady flow bridge and Δ three-phase unsteady flow bridge.
3. the photovoltaic power generation grid-connecting system DC/AC converter based on phase shifting transformer according to claim 2, also has following characteristic:
this converter ac output current harmonic content is propped up way m with the direct current of many level DCs Current Control and synthesis unit and is increased and reduce, and the relation of converter output AC electric current THD and m is shown in table 1;
The relation table of table 1.THD and m
m 2 3 4 5 6 7 8 9 THD 7.77％ 5.25％ 3.99％ 3.28％ 2.77％ 2.45％ 2.20％ 2.02％
According to table 1, when m >=6, the harmonic value of converter is limited in the scope of < 3%;
thyristor is control entirely, by etc. incremental steps shape triangular current impose on Y three-phase unsteady flow bridge and Δ three-phase unsteady flow bridge, the electric current that has caused switching device in Y three-phase unsteady flow bridge and Δ three-phase unsteady flow bridge by set etc. incremental steps shape triangular current rule change, when the switching device of formation Y three-phase unsteady flow bridge and Δ three-phase unsteady flow bridge is thyristor, when the incremental steps shape triangular current such as applying and starting to gate circuit transistor gate triggering signal, thyristor is open-minded, during waiting incremental steps shape triangular current to be zero, thyristor current flows is that zero being forced to turn-offed, be that thyristor is opened and controlled by gate pole, electric current for zero turn-off control by etc. incremental steps shape triangular current provide, both combinations make thyristor can be used as full control switch use, the full control of thyristor makes Trigger Angle phase shift range become-180 °～180 °, power factor can be leading, lag behind and regulate continuously, can realize the control that power factor is " 1 ",
use soft switch theory, in the electric current that flows into Y three-phase unsteady flow bridge is zero interval, make the thyristor commutation of Y three-phase unsteady flow bridge, at the electric current that flows into Δ three-phase unsteady flow bridge, be zero interval, make the thyristor commutation of Δ three-phase unsteady flow bridge, the thyristor of Y three-phase unsteady flow bridge and Δ three-phase unsteady flow bridge is commutation under zero condition at electric current, thyristor turn-offs when electric current is zero, open-minded when voltage is zero, without switching loss, thyristor operating frequency 50Hz.
CN201320636596.5U 2013-10-15 2013-10-15 DC/AC converter for photovoltaic power-generation grid-connected system based on phase-shifting transformer Expired - Fee Related CN203747431U (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105790305A (en) * 2016-04-20 2016-07-20 清华大学 Offshore wind power grid connection system based on full-bridge MMC DC-side serial connection and control method thereof
CN107465191A (en) * 2017-09-30 2017-12-12 国网青海省电力公司 Photovoltaic plant DC/DC DC/AC Harmonic Control Methods

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105790305A (en) * 2016-04-20 2016-07-20 清华大学 Offshore wind power grid connection system based on full-bridge MMC DC-side serial connection and control method thereof
CN105790305B (en) * 2016-04-20 2018-12-11 清华大学 Based on the concatenated offshore wind farm grid-connected system of full-bridge MMC DC side and its control method
CN107465191A (en) * 2017-09-30 2017-12-12 国网青海省电力公司 Photovoltaic plant DC/DC DC/AC Harmonic Control Methods
CN107465191B (en) * 2017-09-30 2020-10-13 国网青海省电力公司 Photovoltaic power station DC/DC-DC/AC harmonic control method

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