CN112072698A - Multi-path photovoltaic access line-to-line non-full-power type conversion method and system - Google Patents

Multi-path photovoltaic access line-to-line non-full-power type conversion method and system Download PDF

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Publication number
CN112072698A
CN112072698A CN202010908618.3A CN202010908618A CN112072698A CN 112072698 A CN112072698 A CN 112072698A CN 202010908618 A CN202010908618 A CN 202010908618A CN 112072698 A CN112072698 A CN 112072698A
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photovoltaic
line
direct current
type conversion
series
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葛雪峰
史明明
袁宇波
张宸宇
杨景刚
缪惠宇
袁晓冬
陈烨
陈舒
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State Grid Corp of China SGCC
Electric Power Research Institute of State Grid Jiangsu Electric Power Co Ltd
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State Grid Corp of China SGCC
Electric Power Research Institute of State Grid Jiangsu Electric Power Co Ltd
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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
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • 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
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/3353—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having at least two simultaneously operating switches on the input side, e.g. "double forward" or "double (switched) flyback" converter
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • 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
    • H02J2300/26—The renewable source being solar energy of photovoltaic origin involving maximum power point tracking control for photovoltaic sources
    • 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 multi-path photovoltaic accessed line-to-line non-full power type conversion method and a multi-path photovoltaic accessed line-to-line non-full power type conversion system, which adjust each series compensation voltage according to illumination intensity and temperature to realize maximum power point output of a photovoltaic cell. Due to the adoption of the control method provided by the invention, only one parallel direct current compensator is used in the system, so that the volume of the photovoltaic converter is reduced, and the conversion efficiency is improved.

Description

Multi-path photovoltaic access line-to-line non-full-power type conversion method and system
Technical Field
The invention relates to a multi-path photovoltaic access line-to-line non-full-power type conversion method and a multi-path photovoltaic access line-to-line non-full-power type conversion system, and belongs to the field of power electronic automatic control.
Background
In recent years, with the widespread access of distributed power sources, countries around the world have begun to test and put into operation dc distribution networks; the direct-current power distribution network can effectively save a distributed power supply, energy storage and a DC/AC or AC/DC power conversion link of power electronic load, and effectively improve the energy efficiency of the system. When distributed energy such as photovoltaic energy is connected to a direct-current power distribution network, the flexible control of maximum power output or charge-discharge power is realized through a DC/DC full-power interface converter. The size, cost and operating efficiency of the photovoltaic interface converter influence the application and popularization of the photovoltaic interface converter in a power distribution network. In order to improve the operating efficiency of the photovoltaic converter and reduce the equipment volume, researchers reduce the equipment volume and improve the equipment efficiency by improving the modulation strategy, improving the switching frequency and reducing the proportion of passive devices; however, the topology proposed by researchers can reduce the volume of the equipment or improve the efficiency of the equipment to a certain extent, and the volume and the efficiency of the equipment are difficult to be effectively improved.
Disclosure of Invention
The purpose of the invention is as follows: the invention provides a multi-path photovoltaic access line-to-line non-full-power type conversion method and system, which can reduce the volume of a photovoltaic converter.
The technical scheme is as follows: the technical scheme adopted by the invention is a multi-path photovoltaic accessed line-to-line non-full power type conversion system, which comprises a plurality of series direct current compensators and a plurality of parallel direct current compensators, wherein each photovoltaic cell and one of the series direct current compensators are paired pairwise to form a photovoltaic grid-connected system, and each series direct current compensator is connected to the parallel direct current compensator and is accessed into a power grid by the parallel direct current compensator; the line-to-line non-full power type conversion system adjusts each series compensation voltage to realize the maximum power point output of the photovoltaic cell.
The line-to-line non-full power type conversion system comprises a parallel direct current compensator.
The series direct current compensators and the parallel direct current compensators share one direct current chain capacitor.
A control method of a non-full power type conversion system between lines suitable for multi-path photovoltaic access comprises the following steps:
establishing a voltage model between a direct current bus and a photovoltaic direct current collection point;
finding out the relation between the transformation ratio of the isolation transformer in the parallel direct current compensator and the switching duty ratio of the series direct current compensator;
and calculating the operation efficiency of the line-to-line non-full power type conversion system.
The voltage model is
Figure BDA0002662433110000021
In the above formula VPCCFor photovoltaic DC sink voltage, VbusIs a DC bus voltage, RTIs the equivalent resistance between the photovoltaic concentration point and the DC bus, IoutiThe output current of the ith photovoltaic grid-connected system is N, and the N is the number of the photovoltaic grid-connected systems.
Neglecting the internal loss of the converter, and obtaining the result under the condition of defaulting that the output characteristics of all the photovoltaic cells are consistent
Figure BDA0002662433110000022
Figure BDA0002662433110000023
In the above formula VDFiSeries compensation voltage for the ith series DC compensator, DiIs the switching duty cycle of the ith series DC compensator, NSFor the transformation ratio, P, of high-frequency isolating transformers in parallel DC compensatorsTPFor photovoltaic output of total power, PPViThe output power of the ith photovoltaic cell;
the above two formulae are associated with the following formula:
IPVi＝f(VPVi,S)
to obtain
Figure BDA0002662433110000024
Wherein VPViAnd IPViRespectively representing the output voltage and current of the ith photovoltaic cell, wherein S is the illumination intensity, and f represents a functional relation.
Operating efficiency eta of the line-to-line non-full power type conversion systemPPVGComprises the following steps:
Figure BDA0002662433110000025
in the above formula, η is the operating efficiency of the series and parallel DC compensators.
Has the advantages that: the invention provides a multi-path photovoltaic accessed line-to-line non-full power type conversion method and a multi-path photovoltaic accessed line-to-line non-full power type conversion system, which adjust each series compensation voltage according to illumination intensity and temperature to realize maximum power point output of a photovoltaic cell. Due to the adoption of the control method provided by the invention, only one parallel direct current compensator is used in the system, so that the volume of the photovoltaic converter is reduced, and the conversion efficiency is improved.
Drawings
FIG. 1 is a schematic diagram of a line-to-line non-full power type conversion system according to the present invention.
Detailed Description
FIG. 1 is a schematic diagram of a non-full power line-to-line conversion system suitable for multiple photovoltaic access, in which N photovoltaic cells are phase-shiftedThe respective first to nth series dc compensators SDCC1, SDCC2.. SDCC and shunt dc compensators PDCC tap into the dc bus. The system formed by the ith photovoltaic cell and the ith series-connected dc compensator is defined as the ith grid-connected photovoltaic system (i ═ 1,2.. N), and the first to nth series-connected dc compensators SDCC1, SDCC2.. SDCC and the shunt dc compensator PDCC share a dc link capacitor Cin。
VPVi+VDFi＝VPCC (1)
Wherein VPViFor the ith photovoltaic cell PVi output voltage, VDFiIs the series voltage, V, of the ith series DC compensator SDCCiPCCIs the photovoltaic dc collection point voltage, and can be expressed as:
Figure BDA0002662433110000031
wherein R isTIs the equivalent resistance between the photovoltaic concentration point and the DC bus, VbusIs a DC bus voltage, IoutiThe output current of the ith photovoltaic grid-connected system. Further, the series compensation voltage V of the ith series dc compensator SDCCiDFiCan be expressed as:
Figure BDA0002662433110000032
wherein D isiThe duty ratio of the switch of the ith series direct current compensator SDCCi is shown, and Ns is the transformation ratio of a high-frequency isolation transformer in the parallel direct current compensator PDCC.
If the inter-line non-full power converter internal losses are ignored:
Figure BDA0002662433110000033
in the above formula PTPFor photovoltaic output of total power, PPViThe output power of the ith photovoltaic cell PVi, and can be expressed as:
PPVi＝VPViIPVi (5)
in the above formula, VPVi、IPViRespectively, the output voltage and current of the ith photovoltaic cell, and the photovoltaic cell is a controllable current source with an output current IPViCan be expressed as:
IPVi＝f(VPVi,S) (6)
wherein S is the illumination intensity, and f represents the functional relationship. The output current of the photovoltaic cell is related to the output voltage, and the output power of the photovoltaic cell can be regulated and controlled by controlling the output voltage of the photovoltaic cell. The output characteristics of all photovoltaic cells are generally uniform, i.e.
Figure BDA0002662433110000041
Wherein VPVAnd IPVAre the values of the output voltage and the output current of the photovoltaic cell, respectively.
Further in conjunction with the above equations (3) - (7), one can derive:
Figure BDA0002662433110000042
wherein D is the switching duty cycle of the series DC compensator. If the equivalent resistance R between the photovoltaic concentration point and the direct current bus is further ignoredTI.e. RTEqual to zero, equation (8) can be simplified to:
Figure BDA0002662433110000043
and M is the input-output voltage transformation ratio of the photovoltaic direct-current grid-connected system. The output voltage V of the photovoltaic cell can be controlled by regulating and controlling the switching duty ratio D of the series direct current compensatorPVAnd realizing photovoltaic maximum power tracking control.
Operating power P of line-to-line non-full power type conversion systemNFComprises the following steps:
PNF＝2(M-1)PTP
all series direct current compensators SDCC and parallel direct current compensators PDCC use an existing D C-DC converter. Let the operating efficiency of the DC-DC converter be eta, the operating efficiency eta of the line-to-line non-full power type conversion systemPPVGComprises the following steps:
Figure BDA0002662433110000051
in summary, taking M as 1.2 as an example, PNFIs only 0.4PTPAnd the operation efficiency of the line-to-line non-full power type conversion system is as follows:
ηPPVG＝0.6+0.4η
if η is 97%, then ηPPVG98.8 percent; if η is 99%, then ηPPVG99.6%. Therefore, the space-to-space non-full power type conversion system provided by the invention can effectively reduce the volume of the direct current interface converter and obviously improve the efficiency of equipment.

Claims (7)

1. A multi-path photovoltaic accessed line-to-line non-full power type conversion system is characterized by comprising a plurality of series direct current compensators and a plurality of parallel direct current compensators, wherein each photovoltaic cell and one of the series direct current compensators are paired pairwise to form a photovoltaic grid-connected system, and each series direct current compensator is connected to the parallel direct current compensator and accessed to a power grid by the parallel direct current compensator; the line-to-line non-full power type conversion system adjusts each series compensation voltage to realize the maximum power point output of the photovoltaic cell.
2. The multi-channel photovoltaic accessed line-to-line non-full power type conversion system according to claim 1, wherein the line-to-line non-full power type conversion system comprises a parallel direct current compensator.
3. The multi-channel photovoltaic accessed line-to-line non-full power type conversion system according to claim 1, wherein the plurality of series direct current compensators and the parallel direct current compensators share one direct current link capacitor.
4. A multi-path photovoltaic access line-to-line non-full power type conversion method is characterized by comprising the following steps:
according to a voltage model between a direct current bus and a photovoltaic direct current collection point, finding out the relation between the transformation ratio of an isolation transformer in the parallel direct current compensator and the switching duty ratio of the series direct current compensator;
and calculating the operation efficiency of the line-to-line non-full power type conversion system.
5. The method of claim 4, wherein the voltage model is selected from the group consisting of
Figure FDA0002662433100000011
In the above formula VPCCFor photovoltaic DC sink voltage, VbusIs a DC bus voltage, RTIs the equivalent resistance between the photovoltaic concentration point and the DC bus, IoutiThe output current of the ith photovoltaic grid-connected system is N, and the N is the number of the photovoltaic grid-connected systems.
6. The method for the multi-channel photovoltaic access interline non-full power type conversion according to claim 5, characterized in that the series compensation voltage V of the ith series DC compensator SDCCiDFiCan be expressed as:
Figure FDA0002662433100000012
total photovoltaic output power PTPComprises the following steps:
Figure FDA0002662433100000021
in the above formula, DiIs the switching duty cycle of the ith series DC compensator, NSFor the transformation ratio, P, of high-frequency isolating transformers in parallel DC compensatorsPViThe output power of the ith photovoltaic cell;
default D1＝D2...＝DND, the above two formulae are associated with the following formula:
IPVi＝f(VPVi,S)
to obtain
Figure FDA0002662433100000022
Wherein VPViAnd IPViThe output voltage and the current of the ith photovoltaic cell are respectively, S is the illumination intensity, f represents the functional relation, and D is the duty ratio of the series compensator.
7. The method for multi-channel photovoltaic access inter-line non-full power type conversion according to claim 5, wherein the operation efficiency η of the inter-line non-full power type conversion systemPPVGComprises the following steps:
Figure FDA0002662433100000023
in the above formula, η is the operating efficiency of the series and parallel DC compensators.
CN202010908618.3A 2020-09-02 2020-09-02 Multi-path photovoltaic access line-to-line non-full-power type conversion method and system Pending CN112072698A (en)

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US20180233919A1 (en) * 2017-02-10 2018-08-16 Sungrow Power Supply Co., Ltd. Photovoltaic inverter system and operation method thereof
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Application publication date: 20201211