CN110707699B - Modular multi-level hybrid distribution transformer - Google Patents

Modular multi-level hybrid distribution transformer Download PDF

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Publication number
CN110707699B
CN110707699B CN201911078170.0A CN201911078170A CN110707699B CN 110707699 B CN110707699 B CN 110707699B CN 201911078170 A CN201911078170 A CN 201911078170A CN 110707699 B CN110707699 B CN 110707699B
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converter
modular multilevel
winding
transformer
series
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CN110707699A (en
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周堃
梁得亮
柳轶彬
蔡生亮
罗雅婷
张立石
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Xian Jiaotong University
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Xian Jiaotong University
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    • 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
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • 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
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • H02J3/1878—Arrangements for adjusting, eliminating or compensating reactive power in networks using tap changing or phase shifting transformers
    • 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
    • Y02E40/20—Active power filtering [APF]
    • 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
    • Y02E40/30—Reactive power compensation
    • 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
    • Y02E40/40—Arrangements for reducing harmonics

Abstract

The invention discloses a modular multilevel hybrid distribution transformer, which comprises a modular multilevel converter and a transformer body, wherein the modular multilevel converter is composed of a plurality of power unit submodules. The converter comprises a modular multilevel parallel converter and a modular multilevel series converter, both of which are composed of a plurality of power unit submodules, the modular multilevel parallel converter is connected with a current compensation winding, and the current of a power grid is regulated and controlled through a magnetic potential balance principle; the modular multilevel series converter is connected with a voltage compensation winding to adjust the load voltage; the transformer body comprises a main transformer, an auxiliary transformer and a filter inductor. Each phase of the main transformer comprises a main side winding, a secondary side winding and a current compensation winding, and each phase of the secondary transformer comprises a series winding and a voltage compensation winding. The modularized multi-level hybrid distribution transformer can reduce the switching frequency of devices, reduce higher harmonics and be applied to occasions with higher power.

Description

Modular multi-level hybrid distribution transformer
Technical Field
The invention relates to a modular multi-level hybrid distribution transformer, and belongs to the technical field of transformers.
Background
The traditional distribution transformer has reliable operation and basic functions of voltage grade conversion, electric energy transmission and the like. The development of smart grids puts high demands on the controllability of distribution transformers. Therefore, scholars such as Sandeep bala and Jyoti safety of ABB scientific research institutions have proposed the design idea of hybrid distribution transformers. The modular multilevel converter is characterized in that the modular multilevel converter is connected into a distribution transformer, and the high controllability of the distribution transformer is realized by converting partial power through the converter, so that the modular multilevel converter is very suitable for being used as an intelligent transformer for a next generation power distribution network.
In most current distribution scenarios, the load capacity is often large, although the converters in the hybrid distribution transformer only contribute a fraction of the total power. However, since the load capacity is large, the converter still needs to have a large capacity. Thus, the application of the existing hybrid distribution transformer in high-capacity occasions is limited.
In the prior art, a hybrid distribution transformer suitable for high-capacity occasions is realized through a multi-winding transformer scheme, but the number of windings is large, and the number of converter units is large. The converter adopts a parallel connection scheme in nature, and circulating current exists. A way to combine modular multilevel technology with hybrid distribution transformers is then proposed.
Disclosure of Invention
To solve the above-mentioned drawbacks of the prior art, an object of the present invention is to provide a modular multi-level hybrid distribution transformer. The modular multilevel converter is connected into the distribution transformer, and the high capacity of the hybrid distribution transformer is realized through the high direct-current bus voltage.
In order to achieve the purpose, the invention adopts the following technical scheme:
a modular multi-level hybrid distribution transformer mainly comprises two parts, namely a transformer body and a modular multi-level converter. The transformer is composed of a main transformer module and a series transformer module; the modular multilevel converter is composed of a modular multilevel parallel converter and a modular multilevel series converter which are formed by cascading a plurality of power unit submodules, and each bridge arm is formed by connecting a plurality of submodules formed by IGBT half bridges and direct current capacitors in series. The modularized multi-level parallel converter of the modularized multi-level converter is connected with the current compensation winding of the transformer body, and the modularized multi-level series converter of the modularized multi-level converter is connected with the voltage compensation winding of the transformer body.
The modularized multi-level converter is mainly divided into two parts, the modularized multi-level parallel converter and the modularized multi-level series converter share one high-voltage direct-current bus capacitor, the high-voltage direct-current bus capacitor is formed by connecting two capacitors in series, and a middle point is led out.
The modular multilevel converter performs signal modulation by means of multilevel modulation technologies such as carrier phase shift and the like so as to reduce the content of higher harmonics in compensation current, and meanwhile, the cascaded structure can meet the requirements of high-capacity and high-voltage equipment.
The main transformer is formed by three-phase windings, each phase winding comprising a main side winding (A)1X1、B1Y1、C1Z1) A secondary winding (a)2x2、b2y2、c2z2) And a current compensation winding (a)3x3、b3y3、c3z3) And the series transformer module is also formed by three-phase windings, each phase winding comprising a series winding (a)4x4、b4y4、c4z4) And a voltage compensation winding (a)5x5、b5y5、c5z5) (ii) a The main side winding and the series winding of the main transformer are firstly connected into a whole, and then the triangle connection method is adopted to access the power grid. The three-phase secondary winding, the three-phase current compensation winding and the three-phase voltage compensation winding are all connected in a star-shaped neutral point leading-out mode.
The modularized multi-level parallel converter of the modularized multi-level converter is used for compensating reactive power of a load by compensating reactive current and harmonic current of the load. The modular multilevel series converter of the modular multilevel converter is responsible for meeting the requirement of a load terminal on voltage under the conditions of harmonic wave, non-rated and asymmetric input voltage of a power grid. The modular multilevel converter unit is composed of six phase units, each phase unit is provided with an upper bridge arm and a lower bridge arm, each bridge arm is composed of a plurality of sub-modules, and each sub-module is composed of an IGBT half-bridge serving as a switch unit and a direct current capacitor. The modular multilevel parallel converter and the modular multilevel series converter have the same number of power unit modules of each bridge arm. The power units are independent of each other, and the direct current capacitors of the modules can provide a plurality of direct current power supplies which are isolated from each other for the outside.
Compared with the prior art, the invention at least has the following technical effects:
on the basis of the hybrid distribution transformer, the invention adopts the current transformer based on the modularized multi-level technology, thereby effectively improving the compensation capacity of the hybrid distribution transformer. Meanwhile, the modular level converter unit is controlled by means of multi-level modulation technologies such as carrier phase shift and the like, the same switching efficiency can be equivalently realized during the period of adopting lower switching frequency, and therefore the load voltage of the hybrid distribution transformer and the high-frequency harmonic in the power grid current are effectively reduced.
Drawings
Fig. 1 is a schematic diagram of the overall structure of a modular multilevel hybrid distribution transformer.
Fig. 2 is a power cell sub-module schematic diagram of a modular multilevel hybrid distribution transformer converter.
Connection terminals of the elements are labeled in FIG. 1 "○”。
Detailed Description
For better clarity of the description of the objects, technical solutions and advantages of the present invention, the following detailed description of the present invention is provided with reference to the accompanying drawings and embodiments. The embodiments described herein are merely illustrative and are not intended to limit the present invention.
The modular multilevel hybrid distribution transformer adopts a modular multilevel technology, and applies a modular multilevel converter integrated with a plurality of power unit submodules to a multi-winding transformer. The modular multilevel converter comprises a modular multilevel parallel converter and a modular multilevel series converter, wherein the modular multilevel parallel converter and the modular multilevel series converter share a direct current bus capacitor, and the converter adopts a modular multilevel technology and is cascaded with a plurality of power unit sub-modules. The transformer body comprises a main transformer concentrically wound on three upper iron core columns and an auxiliary transformer concentrically wound on three lower iron core columns, wherein the main transformer comprises a main side winding, an auxiliary side winding and a current compensation winding, and the auxiliary transformer comprises a series winding and a voltage compensation winding.
The modular multilevel hybrid distribution transformer is mainly divided into a transformer main body module and a modular multilevel converter. As shown in fig. 1, the transformer main body module of the modular multi-level hybrid distribution transformer of the present invention is formed by connecting a main transformer module and a series transformer module end to end. Each phase winding of the main transformer module consists of a main side winding, an auxiliary side winding and a current compensation winding. A. B, C the main side windings of each phase are respectively A1X1、B1Y1、C1Z1(ii) a A. B, C each phase secondary winding is a2x2、b2y2、c2z2(ii) a A. B, C each phase current compensation winding is a3x3、b3y3、c3z3。
As shown in fig. 1, each phase winding of the series transformer module is composed of a series winding and a voltage compensation winding. A. B, C each phase of series windings is a4x4、b4y4、c4z4(ii) a A. B, C each phase voltage compensation winding is a5x5、b5y5、c5z5。
As shown in fig. 1, the primary winding and the series winding of the main transformer are firstly connected into a whole, and then are connected into the power grid by adopting a delta connection method, and the secondary winding supplies power to the load.
As shown in fig. 1, a converter module of the modular multi-level hybrid distribution transformer of the present invention is a modular multi-level converter integrating a plurality of power cell sub-modules, the modular multi-level converter is composed of a modular multi-level parallel converter and a modular multi-level series converter, the modular multi-level parallel converter includes three phase units, each phase unit has two bridge arms: each bridge arm is composed of a plurality of power unit submodules which are SM1 and SM2 … … SMn in sequence. Also, modular multilevel seriesThe converter comprises three phase units, wherein each phase unit is provided with two bridge arms: each bridge arm is composed of a plurality of power unit submodules which are SM1 and SM2 … … SMn in sequence. The modular multilevel parallel converter and the modular multilevel series converter share one direct current bus capacitor, and two capacitors C with the same capacity1、C2Are connected in series and the capacitance midpoint J is connected0And leading out to provide a zero sequence compensation path. Three-phase bridge arm middle point (u in figure 1) of modular multi-level parallel converter of modular multi-level converter1、v1、w1) The three-phase output is the three-phase output of the modular multi-level parallel converter; three-phase leg midpoint (u in fig. 1) on the modular multilevel series converter side2、v2、w2) The three-phase output of the modular multilevel series converter is provided.
As shown in fig. 2, a single power unit sub-module is formed by connecting two IGBTs in series, and each IGBT is provided with an anti-parallel diode. And two ends of the two IGBTs are connected with an energy storage capacitor in parallel. The output of a single power unit module is led out from the middle points of the two IGBTs, and the output ends of the submodules of each power unit are connected end to end.
The output of the modularized multi-level parallel converter of the modularized multi-level converter is connected with a current compensation winding of the transformer body, and the output of the modularized multi-level serial converter is connected with a voltage compensation winding of the transformer body, and the modularized multi-level parallel converter comprises the following specific steps: A. b, C compensation winding a for each phase current3x3、b3y3、c3z3Head terminal a of3、b3、c3Modular multilevel parallel converter side output (i.e. u) to modular multilevel converter1、v1、w1) Connected, terminal x3、y3、z3Capacitor midpoints J connected together and corresponding to direct-current bus capacitors in modular multilevel converter0Connecting; A. b, C compensating winding a for each phase voltage5x5、b5y5、c5z5Head terminal a of5、b5、c5And moduleModular multilevel series converter side output (i.e. u) for multilevel converters2、v2、w2) Connected, terminal x5、y5、z5Direct current bus capacitor C connected together and in modular multilevel converter1And C2Corresponding capacitance midpoint J0Are connected.
The modular multilevel converter integrates a plurality of sub-modules, and power modules are cascaded to form a power bridge arm, so that each power unit only transmits partial capacity in the total capacity, the power requirement of a single converter can be effectively reduced, and the capacity of the whole device is greatly improved under the condition that the energy transmitted by the single power unit is the same; the switching frequency can be reduced under the same waveform to reduce the switching loss; meanwhile, as the number of output levels is large, the output voltage is closer to a sine wave, and the harmonic content is smaller, the output filter can be reduced, the jump of the output voltage is smaller, the electromagnetic interference is reduced, and the electromagnetic compatibility is better.
The whole device not only has the basic functions of a common hybrid transformer, but also can reduce the harmonic content of output voltage and improve the application voltage grade by adopting the modular multilevel technology to realize the hybrid distribution transformer, thereby meeting the requirements of high-power application occasions. In a word, the invention adopts a modularized multi-level technology, provides a novel modularized multi-level hybrid distribution transformer based on a hybrid distribution transformer structure, has larger control capacity and richer control functions, and has important significance for realizing the intellectualization of a power distribution network.

Claims (5)

1. A modular multilevel hybrid distribution transformer, characterized by: the distribution transformer comprises a transformer body and a modular multilevel converter, wherein the transformer body comprises a main transformer module and an auxiliary transformer module, each phase of winding of the main transformer comprises a main side winding, an auxiliary side winding and a current compensation winding, and each phase of winding of the auxiliary transformer comprises a series winding and a voltage compensation winding; the main side winding and the series winding of the main transformer are firstly connected into a whole, then the main side winding and the series winding are connected into a power grid by adopting a delta connection method, the three-phase secondary side winding, the three-phase current compensation winding and the three-phase voltage compensation winding all adopt a star-shaped neutral point leading-out connection method, the modular multilevel converter comprises a modular multilevel parallel converter connected with the current compensation winding in the hybrid distribution transformer and a modular multilevel series converter connected with the voltage compensation winding in the hybrid distribution transformer, and each bridge arm of the modular multilevel parallel converter and each bridge arm of the modular multilevel series converter are formed by connecting a plurality of submodules formed by IGBT half bridges and direct current capacitors in series.
2. The modular multilevel hybrid distribution transformer of claim 1, wherein: each bridge arm of the modular multilevel parallel converter and each bridge arm of the modular multilevel series converter are formed by connecting a plurality of sub-modules formed by IGBT half bridges and direct current capacitors in series, the two converters share one high-voltage direct current bus capacitor, the direct current bus capacitor is formed by connecting the two capacitors in series, the midpoint of the direct current bus capacitor is led out, and the alternating current sides of the modular multilevel parallel converter and the modular multilevel series converter are respectively connected with a filter inductor.
3. The modular multilevel hybrid distribution transformer of claim 1, wherein: the modular multilevel converter performs signal modulation by means of multilevel modulation technologies such as carrier phase shift and the like so as to reduce the content of higher harmonics in compensation current, and meanwhile, the cascaded structure can meet the requirements of high-capacity and high-voltage equipment.
4. The modular multilevel hybrid distribution transformer of claim 1, wherein: the head end of a current compensation winding of the modular multi-level hybrid distribution transformer is connected to the output end of the modular multi-level parallel converter, the head end of a voltage compensation winding of the modular multi-level hybrid distribution transformer is connected to the output end of the modular multi-level serial converter, and the current compensation winding of the modular multi-level hybrid distribution transformer and the tail end of the voltage compensation winding of the modular multi-level hybrid distribution transformer are connected to the middle point of a high-voltage direct-current bus capacitor.
5. The modular multilevel hybrid distribution transformer of claim 2, wherein: the modular multilevel parallel converter and the modular multilevel series converter have the same number of power unit modules of each bridge arm, each power unit is independent, and the direct current capacitor of each module can provide a plurality of direct current power supplies which are isolated from each other.
CN201911078170.0A 2019-11-06 2019-11-06 Modular multi-level hybrid distribution transformer Active CN110707699B (en)

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CN116505534B (en) * 2023-06-25 2023-09-12 东北电力大学 Modeling method of direct type AC/AC type hybrid distribution transformer

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CN205377675U (en) * 2016-03-03 2016-07-06 华北电力大学 Three -phase hybrid transformer based on three -phase bridge
CN107546983B (en) * 2017-01-17 2019-08-02 湖南大学 A kind of high-power high no-load voltage ratio modularization two-way DC converter of isolated form

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