CN105703388A - Photovoltaic grid-connected power generation system based on middle and high voltage direct current access - Google Patents
Photovoltaic grid-connected power generation system based on middle and high voltage direct current access Download PDFInfo
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- CN105703388A CN105703388A CN201410427022.6A CN201410427022A CN105703388A CN 105703388 A CN105703388 A CN 105703388A CN 201410427022 A CN201410427022 A CN 201410427022A CN 105703388 A CN105703388 A CN 105703388A
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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
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- 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 provides a photovoltaic grid-connected power generation system based on middle and high voltage direct current access. The system comprises at least one middle and high voltage direct current power generation unit and a centralized middle and high voltage PV grid-connected inverter. The output end of each middle and high voltage direct current power generation unit is connected to one path of middle and high voltage direct current bus and is used for outputting middle and high voltage direct current voltage to the path of middle and high voltage direct current bus. Each path of middle voltage and high voltage direct current bus which is respectively connected to the output end of each of the middle and high voltage direct current power generation unit is connected in parallel to form a path of middle and high voltage direct current bus which then is connected to the direct current side of the centralized middle and high voltage PV grid-connected inverter. The alternating current side of the centralized middle and high voltage PV grid-connected inverter is accessed to a middle and high voltage direct current power grid. A modular multilevel topology structure is employed by the centralized middle and high voltage PV grid-connected inverter. According to the photovoltaic grid-connected power generation system, the line loss can be reduced, the cost can be reduced, and the reliability is high.
Description
Technical field
The present invention is applied to solar photovoltaic technology field, relates to the photovoltaic system current collection circuit based on mesohigh direct current accesses and designs and grid integration technology, is specifically related to a kind of grid-connected photovoltaic system accessed based on mesohigh direct current。
Background technology
Along with the increase day by day of photovoltaic generation scale, photovoltaic production capacity is no longer limited to the energy as a supplement, and the direction being towards fungible energy source strides forward。But, unbalanced due to economic development and Renewable resource layout, distance between energy centre and the load center of China is very big, and the solar electricity generation field as energy centre is concentrated mainly on remote districts, northwest, and the developed area as load center then concentrates on East Coastal；Meanwhile, solar electrical energy generation needs electrical network to provide extra peak, but the peak modulation capacity of remote districts, northwest is not enough, causes that what solar electrical energy generation was faced with large-scale development sends the problem of dissolving outside。Under the impact of this " energy revolution ", the concept of existing photovoltaic generation, the structure of photovoltaic plant, generate electricity by way of merging two or more grid systems device and corresponding running technology are more and more unable to do what one wishes in tackling the dissolving of ultra-large renewable new forms of energy。
As shown in Figure 1, the structure of the photovoltaic plant of current main flow, namely traditional grid-connected photovoltaic system includes: be connected with mesohigh AC network with connected mode in parallel and carry the individual centralized parallel network power generation unit 100 of n of electric energy to it, each centralized parallel network power generation unit 100 all includes m subelement 101 and duplex frequency boostering transformer 102, this m subelement 101 is all connected with the former avris of duplex frequency boostering transformer 102, each subelement 101 all includes N number of photovoltaic array (N number of photovoltaic array that is one group photovoltaic array) 1011, header box 1012, DC power distribution cabinet 1013 and photovoltaic combining inverter 1014, each photovoltaic array 1011 consists of the mode of series connection and/or parallel connection multiple solar panels all in accordance with its required output DC voltage and rated power grade, the input of header box 1012 is accessed after the parallel connection of N number of photovoltaic array 1011, this header box 1012 is for the Cheng Yilu that confluxed by the direct current energy that N number of photovoltaic array 1011 exports respectively, its outfan is connected with the input of DC power distribution cabinet 1013, the outfan of DC power distribution cabinet 1013 is connected with the DC side (also referred to as input) of photovoltaic combining inverter 1014, owing to the DC voltage of photovoltaic combining inverter 1014 is usually no more than 1kV, therefore photovoltaic combining inverter 1014 is alternatively referred to as low pressure photovoltaic combining inverter, in order to improve the whole efficiency of grid-connected photovoltaic system, photovoltaic combining inverter 1014 generally has maximal power tracing (MPPT, MaximumPowerPointTracking) function, namely by its built-in maximal power tracing algorithm, its input power is carried out maximal power tracing, so that connected N number of photovoltaic array Maximum Power Output, the AC (also referred to as outfan) of the photovoltaic combining inverter 1014 of each subelement 101 is all connected to the former avris of duplex frequency boostering transformer 102 with connected mode in parallel, energy is fed to mesohigh AC network with current source form by Synchronization Control, visible, what prior art adopted is the connected mode of low-voltage, high-current parallel connection, the secondary side of the duplex frequency boostering transformer 102 of each centralized parallel network power generation unit 100 is connected to mesohigh AC network, so that the electric energy of photovoltaic combining inverter 1014 output is delivered to mesohigh AC network after boosting to mesohigh step by step by duplex frequency boostering transformer 102, thus realizing the long distance delivery of the energy。Here, m, n, N are the integer more than 1, and its concrete value can be set according to practical situation by those skilled in the art。
But, along with being continuously increased of generation of electricity by new energy capacity, and transmission of electricity, being showing improvement or progress day by day of distribution technique, there is following restriction in existing photovoltaic generation, transmission operation pattern:
(1) in each centralized parallel network power generation unit 100, low-voltage transmission circuit (voltage this circuit is less than 1kV) is all adopted to connect up from the outfan of each group of photovoltaic array 1011 to the former avris of duplex frequency boostering transformer 102, and what adopt is the in parallel connected mode of low-voltage, high-current, causing low-voltage, high-current transmission line is long, line loss is excessive, the problem of the 2%-3% of total system (line loss be generally) occurs, and this problem can worsen further along with generating scale, the increase of capacity。
(2) current, hold quantitative limitation owing to being subject to DC losses and low pressure photovoltaic combining inverter, large-sized photovoltaic power station typically requires the dozens or even hundreds of low pressure photovoltaic combining inverter of configuration and corresponding inversion machine room and distribution, monitoring device。The peak power of the low pressure photovoltaic combining inverter product of industrial quarters is generally 500kW, if a centralized parallel network power generation unit 100 includes the photovoltaic array of 1MW, photovoltaic plant for a 20MW, it is accomplished by 20 inverter machine rooms of configuration, each inverter machine room is both needed to be equipped with header box 1012, DC power distribution cabinet 1013, each two sets of low pressure photovoltaic combining inverter 1014, and a set of duplex frequency boostering transformer 102, thus causing that the initial stage input cost of generation of electricity by new energy is high, the fund operation cycle is long, and overall rate of return on investment is low。
(3) experiments verify that, by low pressure photovoltaic combining inverter, the output of photovoltaic array is carried out maximal power tracing, the permeability of its MPPT is relatively low, and, the vulnerability to jamming for uneven illumination problem (it can be caused by the discordance of the blocking of cloud, peripheral obstacle shade, each photovoltaic array self character) is also relatively weak。
(4) the peak efficiencies nominal 98.7% of the low pressure photovoltaic combining inverter product of current main flow, its actual efficiency in actual moving process is about 97%, if continuing to study, emphasis and the energy analyzed and optimize concentrate on single grid-connected power electronic equipment (i.e. single centralized parallel network power generation unit), no matter from standpoint of efficiency, still from a cost perspective, all there is no the space that can promote too much, the strategy of the angle looked at problem and the problem of solution of only changing, it is possible to make whole system obtain further, profound optimization。
Summary of the invention
The technical problem to be solved is for drawbacks described above existing in prior art, it is provided that one can either reduce line loss, can reduce again cost and the grid-connected photovoltaic system accessed based on mesohigh direct current that reliability is high。
Solve the technology of the present invention problem be the technical scheme is that
The described grid-connected photovoltaic system accessed based on mesohigh direct current includes: mesohigh DC generation unit and centralized mesohigh photovoltaic combining inverter, described mesohigh DC generation unit adopts at least one, the outfan of each mesohigh DC generation unit all accesses a road mesohigh dc bus, for exporting mesohigh DC voltage to this road mesohigh dc bus, the DC side of road mesohigh dc bus access set Chinese style mesohigh photovoltaic combining inverter again is formed with the outfan of each mesohigh DC generation unit after each road mesohigh dc bus parallel connection being connected respectively, the AC of described centralized mesohigh photovoltaic combining inverter accesses mesohigh AC network；Described centralized mesohigh photovoltaic combining inverter adopts modular multilevel topological structure。
Preferably, described centralized mesohigh photovoltaic combining inverter includes three facies units of parallel connection, the sys node of these three facies unit is as the direct current input node of described inverter, each facies unit all includes the upper brachium pontis of series connection and lower brachium pontis, the series connection node of the upper brachium pontis of each facies unit and lower brachium pontis exchanges output node as this facies unit, the upper brachium pontis of each facies unit, lower brachium pontis all include exchanging the inductance that output node is connected with it, and are connected between described inductance and direct current input node and are sequentially connected in series multiple subelement。
Preferably, the plurality of subelement all adopts the subelement of a kinds of structures, the subelement of a described kinds of structures to be any one in semi-bridge type subelement, bridge-type subelement and clamp double type subelement,
Or, the plurality of subelement adopts the subelement of two types structure, and the quantity sum of the subelement of the two type structure is equal to the quantity of the plurality of subelement, the subelement of the two type structure is any two kinds in semi-bridge type subelement, bridge-type subelement and clamp double type subelement。
Preferably, when the plurality of subelement is semi-bridge type subelement, an equal IGCT in parallel between input and the outfan of each semi-bridge type subelement。
Preferably, each described mesohigh DC generation unit all includes photovoltaic array and cascade DC boosting unit, described photovoltaic array adopts many groups, often group photovoltaic array all includes multiple photovoltaic arrays of parallel connection, each outfan organizing photovoltaic array is connected with the input of described cascade DC boosting unit, the outfan of described cascade DC boosting unit accesses a road mesohigh dc bus, for exporting confluxing in series after the dc voltage boost of each group of photovoltaic array output to this road mesohigh dc bus again。
Preferably, described cascade DC boosting unit includes multiple mesohigh header boxs that outfan is sequentially connected in series, the progression of series connection is no less than 2 grades, and the mesohigh header box that these outfans are sequentially connected in series has two terminations, the cathode output end of mesohigh header box being wherein positioned at an end accesses a road mesohigh dc bus with the cathode output end of the mesohigh header box being positioned at another end, the cathode output end of the previous mesohigh header box of the equal series connection with it of cathode output end of all the other each mesohigh header boxs is connected, the cathode output end of the later mesohigh header box of the equal series connection with it of cathode output end of all the other each mesohigh header boxs is connected；
In each mesohigh DC generation unit, the often all corresponding mesohigh header box of group photovoltaic array, and after often organizing the multiple photovoltaic array parallel connections in photovoltaic array, access the input of corresponding mesohigh header box, described mesohigh header box is for confluxing into a road DC voltage by the DC voltage of one group of photovoltaic array output of its correspondence, and Bing Duigai road DC voltage exports after carrying out boosting process。
Preferably, in each mesohigh DC generation unit, each mesohigh header box all includes bus-bar and the high-frequency step-up transformer of the high class of insulation, the DC voltage of the described bus-bar multiple photovoltaic arrays output for being included by one group of photovoltaic array of its correspondence confluxes into a road DC voltage, the high-frequency step-up transformer of the described high class of insulation for carrying out boosting process to this road DC voltage, and realizes the electrical isolation between one group of photovoltaic array of its correspondence and the mesohigh dc bus of place mesohigh DC generation unit access；The isolation voltage grade of the high-frequency step-up transformer of the described high class of insulation is far above the running voltage of one group of photovoltaic array of its correspondence。
Preferably, in each mesohigh DC generation unit, each mesohigh header box also includes isolated form DC/DC changer, for following the tracks of the maximum power point of one group of photovoltaic array of its correspondence, so that the output of the one of its correspondence group of photovoltaic array reaches maximum。
Preferably, described centralized mesohigh photovoltaic combining inverter works in current source mode。
Preferably, described electricity generation system also includes isolation switch, its quantity is identical with the quantity of mesohigh DC generation unit and one_to_one corresponding, the road mesohigh dc bus that each outfan isolating the corresponding mesohigh DC generation unit of the input switched accesses connects, again through the DC side of a road mesohigh dc bus access set Chinese style mesohigh photovoltaic combining inverter after the outfan parallel connection that each isolation switchs。
Preferably, described electricity generation system also includes charging circuit, its input is connected with the AC of centralized mesohigh photovoltaic combining inverter, its outfan is connected to mesohigh AC network, for cushioning the impact to centralized mesohigh photovoltaic combining inverter of the described grid-connected photovoltaic system powered on moment mesohigh AC network。
Preferably, described charging circuit includes charging resistor, switch and chopper, and described charging resistor is in parallel with chopper again after connecting with switch。
Beneficial effect:
1) in grid-connected photovoltaic system of the present invention, each outlet side organizing photovoltaic array of each mesohigh DC generation unit adopts low-voltage direct cable between the input of the mesohigh header box of its correspondence, and the outfan of each mesohigh header box of each mesohigh DC generation unit adopts mesohigh direct current cables between the DC side of centralized mesohigh photovoltaic combining inverter, and low-voltage direct cable has higher energy loss compared to mesohigh direct current cables, visible, with in the grid-connected photovoltaic system of prior art from the outfan of each group of photovoltaic array 1011 to the former avris of duplex frequency boostering transformer 102 all adopt low-voltage transmission circuit compared with, the low-voltage transmission circuit (i.e. low-voltage cable) that the present invention adopts is shorter, decrease line loss accordingly；
In addition, grid-connected photovoltaic system of the present invention can export confluxing in series after the dc voltage boost of each group photovoltaic array output in each mesohigh DC generation unit to a road mesohigh dc bus again, the DC side of road mesohigh dc bus access set Chinese style mesohigh photovoltaic combining inverter again is formed with the outfan of each mesohigh DC generation unit after each road mesohigh dc bus parallel connection being connected respectively, its AC accesses mesohigh AC network, therefore adopt be mesohigh small area analysis series connection connected mode, and as stated in the Background Art, what the grid-connected photovoltaic system of prior art adopted is the connected mode of low-voltage, high-current parallel connection, simultaneously, change due to system topological, eliminate duplex frequency boostering transformer and decrease the quantity of low pressure photovoltaic combining inverter, therefore the line loss of grid-connected photovoltaic system compared with prior art can be down to minimum by the present invention, also improve system effectiveness accordingly, experiments verify that, the present invention compared with prior art can improve the whole efficiency about 2% of grid-connected photovoltaic system。
2) grid-connected photovoltaic system of the present invention is compared with prior art, eliminates the duplex frequency boostering transformer that efficiency is low, loss is big；And, grid-connected photovoltaic system of the present invention has only to adopt a set of powerful inverter (i.e. centralized mesohigh photovoltaic combining inverter, its magnitude is generally tens megawatts) and corresponding inversion machine room and distribution, monitoring device, with the grid-connected photovoltaic system of prior art needs adopt multiple inversion machine room, each inversion machine room need to configure a set of duplex frequency boostering transformer, many set low pressure photovoltaic combining inverters are compared with relevant device, significantly reduce the initial stage input cost of generation of electricity by new energy, shorten the fund operation cycle, improve overall rate of return on investment, this is less for density of registered inhabitants, the central and west regions that loss is higher have expected advantage；
In addition, at needs System Expansion, when volume reduction, grid-connected photovoltaic system of the present invention is Jin Xu mono-tunnel inversion link also, namely (direct current turns AC transform circuit to adopt one-level DC/AC translation circuit, realized by centralized mesohigh photovoltaic combining inverter), achieve that and generate electricity by way of merging two or more grid systems and energy management, compared with the grid-connected photovoltaic system of prior art, eliminate multichannel inversion link (the multiple low pressure photovoltaic combining inverters 1014 included by the centralized parallel network power generation unit of each in existing grid-connected photovoltaic system 100 realize), that is, a centralized mesohigh photovoltaic combining inverter is adopted to instead of the numerous low pressure photovoltaic combining inverters adopted in prior art, not only increase system effectiveness, additionally aid system power control, fault supports and buffering, and system effectiveness optimization。
3) output of one group of photovoltaic array of its correspondence is carried out maximal power tracing by the mesohigh header box of each mesohigh DC generation unit by grid-connected photovoltaic system of the present invention, with the grid-connected photovoltaic system of prior art by compared with the output of its one group of corresponding photovoltaic array carries out maximal power tracing by the photovoltaic combining inverter of each centralized parallel network power generation unit, the permeability of MPPT is higher, and, for uneven illumination problem, (it can blocking by cloud, peripheral obstacle shade, the discordance of each photovoltaic array self character causes) the grid-connected photovoltaic system mismatch problems that causes has better adaptability, namely vulnerability to jamming is stronger。
4) grid-connected photovoltaic system of the present invention from the outfan of photovoltaic array to mesohigh AC network between the equipment that adopts compared with prior art, simplify the electrical structure of system, decrease device category and quantity, reduce system cost, the design of system, construction and later stage power station O&M efficiency is made to be obtained for and be substantially improved, make whole system obtain further, profound optimization, there is important engineer applied and be worth。
5) the centralized mesohigh photovoltaic combining inverter of grid-connected photovoltaic system of the present invention adopts modular multilevel (MMC, ModularMultilevelConverter) topological structure, it is easy to produces, install and safeguards；Simultaneously, the scheme of the subelement mixing series connection of dissimilar structure can be adopted, so that centralized mesohigh photovoltaic combining inverter has dc-side short-circuit fault rejection ability, improve the reliability of system, and compared to traditional photovoltaic combining inverter more cost advantage。
6) the centralized mesohigh photovoltaic combining inverter of grid-connected photovoltaic system of the present invention works in current source mode, namely constant dc current die pressing type it is operated in, by adopting the mode of Direct Current Control to produce required electric current, it is controlled without to the voltage of its DC side。
7) each mesohigh header box of grid-connected photovoltaic system of the present invention is only subjected to the 1/m (m is the quantity of mesohigh header box in this mesohigh DC generation unit) of the mesohigh DC bus-bar voltage that place mesohigh DC generation unit accesses, therefore described mesohigh header box can adopt low pressure device to realize the high-power output of mesohigh, the such as high-frequency step-up transformer of the high class of insulation, thereby through the cost of the method reduction mesohigh header box of high frequency, improve its power density。
8) the mesohigh DC generation unit of grid-connected photovoltaic system of the present invention and centralized mesohigh photovoltaic combining inverter all can adopt the structure of high modularization, this modular construction is easy to System Expansion, be conducive to shortening engineering design and process-cycle, reduce cost；And, for each mesohigh DC generation unit, power switch and the passive device of identical capacity can be adopted so that this modular construction has very strong substitutability, it is simple to system maintenance and Redundancy Design。
9) grid-connected photovoltaic system of the present invention can be regarded as the flexible electricity generation system of a kind of mesohigh DC bus structure based on large-scale photovoltaic power station。The demonstrative project in domestic " new forms of energy+flexible transmission " field is only embodied on wind power generation at present, and the middle-and-high voltage system for photovoltaic generation there is no relevant practical exploration。Grid-connected photovoltaic system of the present invention is by adopting multiterminal element access, high MPPT permeability and concentrating the mesohigh scheme of inversion grid connection, electric energy efficiently, stably it is fed to, it is possible to certain basis will be established in the application and development in extensive " photovoltaic generation+flexible transmission " field for future to mesohigh AC network。
Accompanying drawing explanation
Fig. 1 is the schematic diagram of grid-connected photovoltaic system in prior art；
Fig. 2 is the schematic diagram of the grid-connected photovoltaic system accessed based on mesohigh direct current described in the embodiment of the present invention；
Fig. 3 is the three-phase topological structure schematic diagram of the centralized mesohigh photovoltaic combining inverter in Fig. 2；
Fig. 4 is the topological structure schematic diagram of semi-bridge type subelement described in the embodiment of the present invention；
Fig. 5 is the topological structure schematic diagram of bridge-type subelement described in the embodiment of the present invention；
Fig. 6 is the topological structure schematic diagram of clamp double type subelement described in the embodiment of the present invention。
In figure: the centralized parallel network power generation unit of 100-；101-subelement；1011-photovoltaic array；1012-header box；1013-DC power distribution cabinet；1014-photovoltaic combining inverter；102-duplex frequency boostering transformer；200-mesohigh DC generation unit；201-photovoltaic array；202-cascade DC boosting unit；203-mesohigh header box；300,500-mesohigh dc bus；400-isolates switch；The centralized mesohigh photovoltaic combining inverter of 600-；700-charging circuit；800-booster transformer。
Detailed description of the invention
For making those skilled in the art be more fully understood that technical scheme, below in conjunction with drawings and Examples, the present invention is described in further detail。
It should be noted that, the all electric pressures " mesohigh " (no matter being direct current or exchange) occurred in the present invention all covers between 3kV～800kV, such as, its electric pressure can be but not limited to: 6kV, 10kV, 20kV, 35kV, 66kV, 110kV, 220kV, 330kV, 500kV, 750kV etc.。
Embodiment:
As shown in Figure 2, the present embodiment provides a kind of grid-connected photovoltaic system accessed based on mesohigh direct current, comprising: n mesohigh DC generation unit 200,400,1 centralized mesohigh photovoltaic combining inverter 600 of n isolation switch and 1 charging circuit 700, described mesohigh DC generation unit 200 and isolation switch 400 quantity is identical and one_to_one corresponding, wherein, n is the integer more than 0。
Each mesohigh DC generation unit 200 passes through the isolation switch 400 of its correspondence and is connected in parallel, by increasing the quantity of the isolation switch 400 of mesohigh DC generation unit 200 and correspondence thereof, it is possible to the capacity of lifting and extension system easily；And, each mesohigh DC generation unit 200, each isolation switch 400, centralized mesohigh photovoltaic combining inverter 600 and charging circuit 700 all adopt the structure of high modularization, it is simple to system maintenance and Redundancy Design。
In addition, as shown in Figure 2, described grid-connected photovoltaic system may also include the booster transformer 800 between the outfan being connected to charging circuit 700 and mesohigh AC network, it is used for when the alternating voltage that the AC of centralized mesohigh photovoltaic combining inverter 600 exports is lower than the electric pressure of mesohigh AC network to be accessed, the alternating voltage that the AC of centralized mesohigh photovoltaic combining inverter 600 is exported carries out boosting process, so that it meets the electric pressure of mesohigh AC network to be accessed, certainly, if the alternating voltage of the AC output of centralized mesohigh photovoltaic combining inverter 600 meets the electric pressure of mesohigh AC network to be accessed, booster transformer 800 then need not be set, namely the outfan of charging circuit 700 is directly accessed mesohigh AC network。
Specifically, the outfan of each mesohigh DC generation unit 200 all accesses a road mesohigh dc bus 300, for exporting mesohigh DC voltage to this road mesohigh dc bus 300, it is connected with the input of each corresponding isolation switch 400 respectively with each road mesohigh dc bus 300 that the outfan of each mesohigh DC generation unit 200 connects, again through the DC side (also referred to as input) of a road mesohigh dc bus 500 access set Chinese style mesohigh photovoltaic combining inverter 600 after the outfan parallel connection of each isolation switch 400, to realize the electrical isolation between mesohigh dc bus 300 and mesohigh dc bus 500, the AC (also referred to as outfan) of described centralized mesohigh photovoltaic combining inverter 600 is connected with the input of charging circuit 700, the outfan of charging circuit 700 is connected to mesohigh AC network (now, the alternating voltage of the AC output of centralized mesohigh photovoltaic combining inverter 600 meets the electric pressure of mesohigh AC network to be accessed), for cushioning the impact to centralized mesohigh photovoltaic combining inverter 600 of the described grid-connected photovoltaic system powered on moment mesohigh AC network, thus realizing the long distance delivery of the energy。Can be seen that, being mostly DC generation and transmission line of electricity in grid-connected photovoltaic system described in the present embodiment, only pole is partially arc shaped alternating current circuit (i.e. charging circuit 700 between AC and the mesohigh AC network of centralized mesohigh photovoltaic combining inverter 600)。
In the present embodiment, described isolation switch 400 can adopt the existing on-off circuit with isolation features；Described centralized mesohigh photovoltaic combining inverter 600 can adopt the inverter of existing megawatt of magnitude, and this centralized photovoltaic network inverter is compared to the multichannel inverter adopted in prior art, its single watt of cost reduces, therefore its cooling system can adopt water-cooled to design, compared with being generally adopted air-cooled design with the cooling system of the photovoltaic combining inverter of the grid-connected photovoltaic system of prior art, drastically increase the reliability of system, therefore to be particularly suited for northwest China's dust storm big for grid-connected photovoltaic system of the present invention, the terrible weather environment of extremely hot and severe cold；Described charging circuit 700 includes charging resistor, switch and chopper, and described charging resistor is in parallel with chopper again after connect with switch, certainly, described charging circuit 700 also can adopt existing other there is the circuit module cushioning the impact function that powers on。
Wherein, described centralized mesohigh photovoltaic combining inverter adopts modular multilevel topological structure, it is easy to produces, install and safeguards；And, described centralized mesohigh photovoltaic combining inverter works in current source mode, is namely operated in constant dc current die pressing type, by adopting the mode of Direct Current Control to produce required electric current, is controlled without to the voltage of its DC side。Preferably, as it is shown on figure 3, described centralized mesohigh photovoltaic combining inverter 600 includes three facies units of parallel connection, respectively A facies unit, B facies unit and C facies unit, the sys node O of these three facies unit1With sys node O2Direct current input node as described inverter accesses mesohigh dc bus 500, each facies unit all includes the upper brachium pontis of series connection and lower brachium pontis, the series connection node (i.e. series connection node A in Fig. 3, series connection node B or series connection node C) of the upper brachium pontis of each facies unit and lower brachium pontis is connected to the input of charging circuit 700 as the output node that exchanges of this facies unit, the upper brachium pontis of each facies unit, lower brachium pontis all include exchanging the inductance L that output node is connected with it, and are connected to described inductance L and direct current input node (i.e. sys node O1Or sys node O2) between and be sequentially connected in series multiple subelement, the input of each subelement is the terminal 1 in Fig. 3, and outfan is the terminal 2 in Fig. 3, and multiple subelements of the upper brachium pontis of each facies unit are connected to inductance L and sys node O1Between, multiple subelements of the lower brachium pontis of each facies unit are connected to inductance L and sys node O2Between, thus the DC voltage on mesohigh dc bus 500 being converted into alternating voltage and exporting to charging circuit 700。Consider the advantage of symmetrical structure, the structure of preferred each facies unit, composition and annexation are all identical, and the upper brachium pontis of each facies unit is identical with the composition of lower brachium pontis, symmetrical configuration, namely, the upper brachium pontis of each facies unit is identical with the quantity of multiple subelements that lower brachium pontis includes, and the type structure of employing and annexation are also identical。
In the upper brachium pontis and lower brachium pontis of each facies unit, inductance L can adopt coupling buffer inductance, it is possible to adopts non-coupled buffer inductance；Multiple subelements can all adopt the subelement of a kinds of structures, the subelement of a described kinds of structures is any one in semi-bridge type subelement, bridge-type subelement and clamp double type subelement, certainly, the subelement of a described kinds of structures is alternatively the subelement of other existing structure；Or, multiple subelements can adopt the subelement of two types structure, the quantity sum of the subelement of the two type structure is equal to the quantity of the plurality of subelement, and the subelement of both types structure is according to certain quantitative proportion mixing series connection, the subelement of preferred same kind structure is sequentially connected in series, the subelement of the two type structure is semi-bridge type subelement, in bridge-type subelement and clamp double type subelement any two kinds, semi-bridge type subelement and clamp double type subelement is adopted for multiple subelements that the upper brachium pontis of A facies unit includes, the quantity assuming the plurality of subelement is p, wherein the quantity of semi-bridge type subelement is x, the quantity of clamp double type subelement is y, and p, x, y is positive integer, then x+y=p, x semi-bridge type subelement is sequentially connected in series, y clamp double type subelement is sequentially connected in series, on described in brachium pontis, inductance L, x semi-bridge type subelement, y clamp double type subelement is sequentially connected in series at exchange output node A and direct current input node O1Between, or, inductance L, y clamp double type subelement, x semi-bridge type subelement are sequentially connected in series at exchange output node A and direct current input node O1Between, the structure of this mixing series connection had both taken into account the low cost of semi-bridge type subelement and high efficiency advantage, the suppression dc-side short-circuit fault of clamp double type subelement can be relied on again, guarantee the advantage of high system reliability, certainly, the subelement of the two type structure can also be the subelement of other two kinds of existing structures；Or, multiple subelements can adopt the subelement of three kinds of (or more than) type structures, the quantity sum of the subelement of described three kinds (or more than) type structures is equal to the quantity of the plurality of subelement, and the subelement of these three (or more than) type structure is according to certain quantitative proportion mixing series connection, the subelement of described three types structure is semi-bridge type subelement, bridge-type subelement and clamp double type subelement, certainly, the subelement of the subelement of described three kinds (or more than) type structures (or the more than) existing structure that can also be other three kinds。
As shown in Figure 4, described semi-bridge type subelement includes: transistor T1 and the diode D1 with its reverse parallel connection, transistor T2 and the diode D2 with its reverse parallel connection, with electric capacity C0, the colelctor electrode of transistor T1 is connected with one end (positive terminal) of electric capacity C0, the emitter stage of transistor T1 is connected with the colelctor electrode of transistor T2, the emitter stage of transistor T2 is connected with the other end (negative pole end) of electric capacity C0, wherein, the input that series connection node is described semi-bridge type subelement (i.e. terminal 1 in Fig. 4) of the colelctor electrode of the emitter stage of transistor T1 and transistor T2, the outfan that series connection node is described semi-bridge type subelement (i.e. terminal 2 in Fig. 4) of the other end of the emitter stage of transistor T2 and electric capacity C0。
As shown in Figure 5, described bridge-type subelement includes: transistor T11 and the diode D11 with its reverse parallel connection, transistor T21 and the diode D21 with its reverse parallel connection, transistor T12 and the diode D12 with its reverse parallel connection, transistor T22 and the diode D22 with its reverse parallel connection, with electric capacity C1, the emitter stage of transistor T11 is connected with the colelctor electrode of transistor T21, the colelctor electrode of transistor T11, the colelctor electrode of transistor T12 is all connected with one end (positive terminal) of electric capacity C1, the emitter stage of transistor T21, the emitter stage of transistor T22 is all connected with the other end (negative pole end) of electric capacity C1, the emitter stage of transistor T12 is connected with the colelctor electrode of transistor T22, wherein, the input that series connection node is described bridge-type subelement (i.e. terminal 1 in Fig. 5) of the colelctor electrode of the emitter stage of transistor T11 and transistor T21, the outfan that series connection node is described bridge-type subelement (i.e. terminal 2 in Fig. 5) of the colelctor electrode of the emitter stage of transistor T12 and transistor T22。
As shown in Figure 6, described clamp double type subelement includes: transistor T11 ' and the diode D11 ' with its reverse parallel connection, transistor T21 ' and the diode D21 ' with its reverse parallel connection, transistor T12 ' and the diode D12 ' with its reverse parallel connection, transistor T22 ' and the diode D22 ' with its reverse parallel connection, transistor T0 and the diode D0 with its reverse parallel connection, diode D3, diode D4, electric capacity C2 and electric capacity C3, the emitter stage of transistor T11 ' is connected with the colelctor electrode of transistor T21 ', the colelctor electrode of transistor T11 ', the negative electrode of diode D3 is all connected with one end (positive terminal) of electric capacity C2, the emitter stage of transistor T21 ', the negative electrode of diode D4 is all connected with the other end (negative pole end) of electric capacity C2, the colelctor electrode of transistor T0 is connected with the anode of diode D3, the emitter stage of transistor T0 is connected with the negative electrode of diode D4, the colelctor electrode of transistor T12 ', the anode of diode D3 is all connected with one end (positive terminal) of electric capacity C3, the emitter stage of transistor T22 ', the anode of diode D4 is all connected with the other end (negative pole end) of electric capacity C3, the emitter stage of transistor T12 ' is connected with the colelctor electrode of transistor T22 ', wherein, the input that series connection node is described clamp double type subelement (i.e. terminal 1 in Fig. 6) of the colelctor electrode of the emitter stage of transistor T11 ' and transistor T21 ', the outfan that series connection node is described clamp double type subelement (i.e. terminal 2 in Fig. 6) of the colelctor electrode of the emitter stage of transistor T12 ' and transistor T22 '。
Transistor in above-mentioned semi-bridge type subelement, bridge-type subelement and clamp double type subelement can adopt insulated gate bipolar transistor (IGBT, InsulatedGateBipolarTransistor), IEGT (IEGT, InjectionEnhancedGateTransistor) or other type of transistor。
Preferably; when multiple subelements that upper brachium pontis and the lower brachium pontis of each facies unit include are semi-bridge type subelement; namely semi-bridge type subelement is when individually applying; an equal IGCT in parallel between the input (terminal 1) of each semi-bridge type subelement and outfan (terminal 2); described IGCT flows through the electric current of the diode D2 with transistor T2 reverse parallel connection for bypass under transistor T2 is short-circuited failure condition, and the diode D2 of protection and transistor T2 reverse parallel connection is unlikely to damage。But, the multiple subelements included when upper brachium pontis and the lower brachium pontis of each facies unit adopt the subelement of two kinds or above type structure, and the subelement of these two kinds or above type structure is when including semi-bridge type subelement, namely the subelement of half-bridge subelement and other type structure mixes when connecting, then semi-bridge type subelement does not need parallel thyristors。
In the present embodiment, each mesohigh DC generation unit 200 all includes m group photovoltaic array 201 and cascade DC boosting unit 202；Often group photovoltaic array 201 all includes N number of photovoltaic array 201 of parallel connection, each photovoltaic array 201 consists of the mode of series connection and/or parallel connection multiple solar panels all in accordance with its required output DC voltage and rated power grade, here, the series connection of multiple solar panels and/or parallel connection refer to, the plurality of solar panel is sequentially connected in series, or all in parallel between the plurality of solar panel, or connect with all the other solar panels again after some solar panel parallel connection；Each outfan organizing photovoltaic array 201 is connected with the input of described cascade DC boosting unit 202, the outfan of described cascade DC boosting unit 202 accesses a road mesohigh dc bus 300, for output of confluxing in series again after dc voltage boost that each group of photovoltaic array 201 is exported to this road mesohigh dc bus 300, and output to the output voltage of this road mesohigh dc bus 300 should meet mesohigh AC network required voltage grade, such as, the electric pressure of mesohigh dc bus 300 can be about 2 times of the ac line voltage of place AC power station, concrete numerical value as output voltage can by those skilled in the art's group number according to the quantity of mesohigh header box in each mesohigh DC generation unit and photovoltaic array, and the quantity of photovoltaic array that often group photovoltaic array includes determines；It is connected with the input of each corresponding isolation switch 400 respectively with each road mesohigh dc bus 300 that the outfan of the cascade DC boosting unit 202 of each mesohigh DC generation unit 200 connects。In the present embodiment, m, N are the integer more than 1, and usually, N takes 8-20, can be set according to practical situation by those skilled in the art as the concrete value of n, m, N。
Described cascade DC boosting unit 202 can adopt existing any one to be realized by circuit module of output of confluxing in series again after dc voltage boost that each group of photovoltaic array 201 exports；And, maximum in order to make the output of each group of photovoltaic array 201 reach, described cascade DC boosting unit 202 also can have the function of the maximum power point following the tracks of each group of photovoltaic array respectively, can be realized by integrated DC/DC changer in described cascade DC boosting unit 202, naturally it is also possible to adopt other the circuit module being capable of maximal power tracing function to realize；Additionally, described cascade DC boosting unit 202 also can have the function that the mesohigh dc bus 300 that each group of photovoltaic array 201 and place mesohigh DC generation unit access carries out electrical isolation。
Preferably, described cascade DC boosting unit 202 includes m the mesohigh header box 203 that outfan is sequentially connected in series, the progression of series connection is no less than 2 grades, and the mesohigh header box 203 that these outfans are sequentially connected in series has two terminations, the cathode output end of mesohigh header box 203 being wherein positioned at an end accesses a road mesohigh dc bus 300 with the cathode output end of the mesohigh header box 203 being positioned at another end, the cathode output end of the previous mesohigh header box 203 of the equal series connection with it of cathode output end of all the other each mesohigh header boxs 203 is connected, the cathode output end of the later mesohigh header box 203 of the equal series connection with it of cathode output end of all the other each mesohigh header boxs 203 is connected, here, " front " direction refers to the direction from bottom to up in Fig. 2, " afterwards " direction refers to the direction (vice versa) from top to bottom in Fig. 2, for " mesohigh header box " and with its " the previous mesohigh header box connected ", should " the previous mesohigh header box of series connection " can be the mesohigh header box 1 in Fig. 2, should " mesohigh header box " can be the mesohigh header box 2 in Fig. 2；For " mesohigh header box " and with its " the later mesohigh header box connected ", should " the later mesohigh header box of series connection " can be the mesohigh header box 2 in Fig. 2, should " mesohigh header box " can be the mesohigh header box 1 in Fig. 2；In each mesohigh DC generation unit 200, the often all corresponding mesohigh header box 203 of group photovoltaic array 201, and after often organizing N number of photovoltaic array 201 parallel connection in photovoltaic array 201, access the input of corresponding mesohigh header box 203, therefore the input of described cascade DC boosting unit 202 includes the input of m mesohigh header box 203, each outfan organizing photovoltaic array 201 outfan referring to each group of photovoltaic array 201 that is connected with the input of described cascade DC boosting unit 202 is connected with the input of corresponding mesohigh header box 203 respectively, described mesohigh header box 203 confluxes into a road DC voltage for the DC voltage (i.e. the DC voltage of photovoltaic array 201 output of N number of parallel connection) exported by one group of photovoltaic array 201 of its correspondence, Bing Duigai road DC voltage exports from its outfan after carrying out boosting process。
Further, in each mesohigh DC generation unit 200, each mesohigh header box 203 is respectively provided with the function of the maximum power point of one group of photovoltaic array 201 of its correspondence independently tracked, so that the output of the one of its correspondence group of photovoltaic array 201 reaches maximum；Meanwhile, each mesohigh header box 203 also can have the function that the mesohigh dc bus 300 that the one of its correspondence group of photovoltaic array 201 and place mesohigh DC generation unit access carries out electrical isolation。
In order to make mesohigh header box have above-mentioned functions, preferably, in each mesohigh DC generation unit 200, each mesohigh header box 203 all includes the high-frequency step-up transformer of bus-bar and the high class of insulation, and (its operating frequency exceedes intermediate frequency, namely more than 10kHz), described bus-bar is for confluxing into a road DC voltage by the DC voltage that one group of photovoltaic array 201 of its correspondence exports, this bus-bar can adopt existing confluence copper bar, the high-frequency step-up transformer of the described high class of insulation is for carrying out boosting process to this road DC voltage, and realize the electrical isolation between one group of photovoltaic array 201 of its correspondence and the mesohigh dc bus 300 of place mesohigh DC generation unit access, actual insulation grade and operating frequency range as this high-frequency step-up transformer can be chosen according to the running voltage of one group of photovoltaic array of its correspondence voluntarily by those skilled in the art, and the isolation voltage grade running voltage far above one group of photovoltaic array of its correspondence of this high-frequency step-up transformer need to be met, the multiple of the running voltage of the corresponding one group of photovoltaic array of the isolation voltage grade of this high-frequency step-up transformer can be determined according to the electric pressure (i.e. the electric pressure of place transformer station) of mesohigh AC network, the quantity of mesohigh header box 203 that the scope of this multiple can be or comprise in each mesohigh DC generation unit 200, this multiple can also be or close to the electric pressure of mesohigh AC network divided by 1kV, such as, if the electric pressure of mesohigh AC network is 10kV, then described multiple can be or close to 10kV ÷ 1kV=10 times, if the electric pressure of mesohigh AC network is 35kV, then described multiple can be or close to 35kV ÷ 1kV=35 times。Further, in each mesohigh DC generation unit 200, each mesohigh header box 203 also includes isolated form DC/DC changer, its input is connected with the outfan of the high-frequency step-up transformer of the high class of insulation, its outfan is the outfan of described mesohigh header box 203, for following the tracks of the maximum power point of one group of photovoltaic array 201 of its correspondence, so that the output of the one of its correspondence group of photovoltaic array 201 reaches maximum。
In order to reduce mesohigh header box insulation against ground voltage, preferably, in m the mesohigh header box 203 that described outfan is sequentially connected in series, output voltage equal to or the cathode output end ground connection of the mesohigh header box 203 of the mid-point voltage of mesohigh dc bus 300 accessed closest to its place mesohigh DC generation unit or cathode output end ground connection。That is, in this m mesohigh header box 203, if the output voltage of certain mesohigh header box is exactly equal to the mid-point voltage of mesohigh dc bus 300, the then cathode output end ground connection of this mesohigh header box or cathode output end ground connection, if there is no the mesohigh header box of such output voltage, then compared to the output voltage of all the other (m-1) individual mesohigh header box, closest to the cathode output end ground connection of that mesohigh header box of mid-point voltage or the cathode output end ground connection of mesohigh dc bus 300。
In order to shorten the length of low-voltage direct cable as far as possible, effectively reduce DC losses, improve system effectiveness, preferably, in each mesohigh DC generation unit 200, each mesohigh header box 203 is installed near one group of photovoltaic array 201 of its correspondence, for instance be arranged on the lower section of the solar panel that this group photovoltaic array includes, so that the length of the low-voltage direct cable between the corresponding one group of photovoltaic array 201 of each mesohigh header box 203 is the shortest。
In the present embodiment, owing to mesohigh header box 203 is capable of the electrical isolation between one group of photovoltaic array 201 of its correspondence and the mesohigh dc bus 300 of place mesohigh DC generation unit access, therefore described isolation switch 400 is selectable unit, if grid-connected photovoltaic system described in the present embodiment does not include isolation switch 400, the DC side of a road mesohigh dc bus 500 access set Chinese style mesohigh photovoltaic combining inverter 600 is more directly formed with the outfan of the cascade DC boosting unit 202 of each mesohigh DC generation unit 200 after each road mesohigh dc bus 300 parallel connection being then connected respectively；Described charging circuit 700 is also selectable unit, if grid-connected photovoltaic system described in the present embodiment does not include charging circuit 700, then the AC of centralized mesohigh photovoltaic combining inverter is directly accessed mesohigh AC network。
In sum, grid-connected photovoltaic system described in the present embodiment from the outfan of photovoltaic array to mesohigh AC network between the equipment that adopts compared with prior art, decrease the length of low-voltage direct cable, reduce line loss, eliminate efficiency low, the duplex frequency boostering transformer that loss is big, simplify the electrical structure of system, decrease device category and quantity, reduce system cost, make the design of system, construction and later stage power station O&M efficiency are obtained for and are substantially improved, whole system is made to obtain further, profound optimization, there is important engineer applied be worth。
It is understood that the principle that is intended to be merely illustrative of the present of embodiment of above and the illustrative embodiments that adopts, but the invention is not limited in this。For those skilled in the art, without departing from the spirit and substance in the present invention, it is possible to make various modification and improvement, these modification and improvement are also considered as protection scope of the present invention。
Claims (12)
1. the grid-connected photovoltaic system accessed based on mesohigh direct current, it is characterized in that, including: mesohigh DC generation unit and centralized mesohigh photovoltaic combining inverter, described mesohigh DC generation unit adopts at least one, the outfan of each mesohigh DC generation unit all accesses a road mesohigh dc bus, for exporting mesohigh DC voltage to this road mesohigh dc bus, the DC side of road mesohigh dc bus access set Chinese style mesohigh photovoltaic combining inverter again is formed with the outfan of each mesohigh DC generation unit after each road mesohigh dc bus parallel connection being connected respectively, the AC of described centralized mesohigh photovoltaic combining inverter accesses mesohigh AC network；Described centralized mesohigh photovoltaic combining inverter adopts modular multilevel topological structure。
2. grid-connected photovoltaic system according to claim 1, it is characterized in that, described centralized mesohigh photovoltaic combining inverter includes three facies units of parallel connection, the sys node of these three facies unit is as the direct current input node of described inverter, each facies unit all includes the upper brachium pontis of series connection and lower brachium pontis, the series connection node of the upper brachium pontis of each facies unit and lower brachium pontis exchanges output node as this facies unit, the upper brachium pontis of each facies unit, lower brachium pontis all includes exchanging the inductance that output node is connected with it, and be connected between described inductance and direct current input node and be sequentially connected in series multiple subelement。
3. grid-connected photovoltaic system according to claim 2, it is characterised in that
The plurality of subelement all adopts the subelement of a kinds of structures, the subelement of a described kinds of structures to be any one in semi-bridge type subelement, bridge-type subelement and clamp double type subelement,
Or, the plurality of subelement adopts the subelement of two types structure, and the quantity sum of the subelement of the two type structure is equal to the quantity of the plurality of subelement, the subelement of the two type structure is any two kinds in semi-bridge type subelement, bridge-type subelement and clamp double type subelement。
4. grid-connected photovoltaic system according to claim 3, it is characterised in that when the plurality of subelement is semi-bridge type subelement, an equal IGCT in parallel between input and the outfan of each semi-bridge type subelement。
5. grid-connected photovoltaic system according to claim 1, it is characterized in that, each described mesohigh DC generation unit all includes photovoltaic array and cascade DC boosting unit, described photovoltaic array adopts many groups, often group photovoltaic array all includes multiple photovoltaic arrays of parallel connection, each outfan organizing photovoltaic array is connected with the input of described cascade DC boosting unit, the outfan of described cascade DC boosting unit accesses a road mesohigh dc bus, for exporting confluxing in series again after the dc voltage boost of each group of photovoltaic array output to this road mesohigh dc bus。
6. grid-connected photovoltaic system according to claim 5, it is characterised in that
Described cascade DC boosting unit includes multiple mesohigh header boxs that outfan is sequentially connected in series, the progression of series connection is no less than 2 grades, and the mesohigh header box that these outfans are sequentially connected in series has two terminations, the cathode output end of mesohigh header box being wherein positioned at an end accesses a road mesohigh dc bus with the cathode output end of the mesohigh header box being positioned at another end, the cathode output end of the previous mesohigh header box of the equal series connection with it of cathode output end of all the other each mesohigh header boxs is connected, the cathode output end of the later mesohigh header box of the equal series connection with it of cathode output end of all the other each mesohigh header boxs is connected；
In each mesohigh DC generation unit, the often all corresponding mesohigh header box of group photovoltaic array, and after often organizing the multiple photovoltaic array parallel connections in photovoltaic array, access the input of corresponding mesohigh header box, described mesohigh header box is for confluxing into a road DC voltage by the DC voltage of one group of photovoltaic array output of its correspondence, and Bing Duigai road DC voltage exports after carrying out boosting process。
7. grid-connected photovoltaic system according to claim 6, it is characterized in that, in each mesohigh DC generation unit, each mesohigh header box all includes bus-bar and the high-frequency step-up transformer of the high class of insulation, the DC voltage of the described bus-bar multiple photovoltaic arrays output for being included by one group of photovoltaic array of its correspondence confluxes into a road DC voltage, the high-frequency step-up transformer of the described high class of insulation is for carrying out boosting process to this road DC voltage, and realize the electrical isolation between one group of photovoltaic array of its correspondence and the mesohigh dc bus of place mesohigh DC generation unit access；The isolation voltage grade of the high-frequency step-up transformer of the described high class of insulation is far above the running voltage of one group of photovoltaic array of its correspondence。
8. grid-connected photovoltaic system according to claim 7, it is characterized in that, in each mesohigh DC generation unit, each mesohigh header box also includes isolated form DC/DC changer, for following the tracks of the maximum power point of one group of photovoltaic array of its correspondence, so that the output of the one of its correspondence group of photovoltaic array reaches maximum。
9. the grid-connected photovoltaic system according to any one of claim 1～8, it is characterised in that described centralized mesohigh photovoltaic combining inverter works in current source mode。
10. the grid-connected photovoltaic system according to any one of claim 1～8, it is characterized in that, described electricity generation system also includes isolation switch, its quantity is identical with the quantity of mesohigh DC generation unit and one_to_one corresponding, the road mesohigh dc bus that each outfan isolating the corresponding mesohigh DC generation unit of the input switched accesses connects, again through the DC side of a road mesohigh dc bus access set Chinese style mesohigh photovoltaic combining inverter after the outfan parallel connection that each isolation switchs。
11. the grid-connected photovoltaic system according to any one of claim 1～8, it is characterized in that, described electricity generation system also includes charging circuit, its input is connected with the AC of centralized mesohigh photovoltaic combining inverter, its outfan is connected to mesohigh AC network, for cushioning the impact to centralized mesohigh photovoltaic combining inverter of the described grid-connected photovoltaic system powered on moment mesohigh AC network。
12. grid-connected photovoltaic system according to claim 11, it is characterised in that
Described charging circuit includes charging resistor, switch and chopper, and described charging resistor is in parallel with chopper again after connecting with switch。
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| CN204103504U (en) | 2015-01-14 |
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