CN204103503U - A kind of grid-connected photovoltaic system based on the access of mesohigh direct current - Google Patents
A kind of grid-connected photovoltaic system based on the access of mesohigh direct current Download PDFInfo
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Abstract
The utility model provides a kind of grid-connected photovoltaic system based on the access of mesohigh direct current, comprise at least one mesohigh DC generation unit and the centralized photovoltaic combining inverter of mesohigh, each DC generation unit comprises many group photovoltaic arrays and cascade DC boosting unit, often organize photovoltaic array and include multiple photovoltaic arrays in parallel, the output of each group of photovoltaic array is connected with the input of cascade DC boosting unit, the output of cascade DC boosting unit accesses a road mesohigh DC bus, for exporting this road mesohigh DC bus to by confluxing in the mode of series connection again after the dc voltage boost of each group of photovoltaic array output, the each road mesohigh DC bus parallel connection be connected with the output of each cascade DC boosting unit respectively forms the DC side that a road mesohigh DC bus accesses the centralized photovoltaic combining inverter of mesohigh more afterwards, its AC access mesohigh AC network.Described grid-connected photovoltaic system can either reduce line loss, can reduce costs again.
Description
Technical field
The utility model is applied to solar photovoltaic technology field, relates to the photovoltaic system current collection line design based on the access of mesohigh direct current and grid integration technology, is specifically related to a kind of grid-connected photovoltaic system based on the access of mesohigh direct current.
Background technology
Along with the increase day by day of photovoltaic generation scale, photovoltaic production capacity is no longer confined to the energy as a supplement, but strides forward towards the direction of fungible energy source.But, unbalanced due to economic development and renewable resource layout, distance between the energy centre of China and load center is very large, solar electricity generation field as energy centre mainly concentrates on remote districts, northwest, and the developed area as load center then concentrates on East Coastal; Meanwhile, the peak that solar power generation needs electrical network to provide extra, but the peak modulation capacity of remote districts, northwest is not enough, what cause solar power generation to be 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 the dissolving of the ultra-large renewable new forms of energy of reply.
As shown in Figure 1, the structure of the photovoltaic plant of current main flow, namely also traditional grid-connected photovoltaic system comprises: to be connected with mesohigh AC network with the connected mode of parallel connection and to the individual centralized parallel network power generation unit 100 of n of its transmission of electric energy, each centralized parallel network power generation unit 100 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 includes N number of photovoltaic array (N number of photovoltaic array i.e. one group of photovoltaic array) 1011, header box 1012, DC power distribution cabinet 1013 and photovoltaic combining inverter 1014, the output dc voltage of each photovoltaic array 1011 all needed for it and rated power grade are made up of the mode of multiple solar panel by series connection and/or parallel connection, the input of access header box 1012 after N number of photovoltaic array 1011 is in parallel, this header box 1012 to conflux Cheng Yilu for the direct current energy exported respectively by N number of photovoltaic array 1011, its output is connected with the input of DC power distribution cabinet 1013, the output of DC power distribution cabinet 1013 is connected with the DC side (also referred to as input) of photovoltaic combining inverter 1014, because the DC voltage of photovoltaic combining inverter 1014 is generally no more than 1kV, therefore photovoltaic combining inverter 1014 also can be described 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, Maximum Power Point Tracking) function, namely by its built-in maximal power tracing algorithm, maximal power tracing is carried out to its input power, to make connected N number of photovoltaic array Maximum Power Output, the AC (also referred to as output) of the photovoltaic combining inverter 1014 of each subelement 101 is all connected to the former avris of duplex frequency boostering transformer 102 with the connected mode of parallel connection, 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 all connected to mesohigh AC network, mesohigh AC network is delivered to after boosting to mesohigh with the electric energy making photovoltaic combining inverter 1014 export (this electric energy with the form of current source and with mesohigh AC network same frequency) step by step by duplex frequency boostering transformer 102, thus realize the long distance delivery of the energy.Here, m, n, N are the integer being greater than 1, and its concrete value can be set according to actual conditions by those skilled in the art.
But, along with the continuous increase 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 former avris from the output of each group of photovoltaic array 1011 to duplex frequency boostering transformer 102, and what adopt is the connected mode of low-voltage, high-current parallel connection, cause the problem that low-voltage, high-current transmission line is long, line loss is excessive (line loss is generally the 2%-3% of total system) to occur, and this problem can worsen further along with the increase of generating scale, capacity.
(2) current, owing to being subject to DC losses and low pressure photovoltaic combining inverter holds quantitative limitation, large-sized photovoltaic power station needs to configure dozens or even hundreds of low pressure photovoltaic combining inverter and corresponding inversion machine room and distribution, watch-dog usually.The maximum power of the low pressure photovoltaic combining inverter product of industrial quarters is generally 500kW, if a centralized parallel network power generation unit 100 comprises the photovoltaic array of 1MW, for the photovoltaic plant of a 20MW, just need configuration 20 inverter machine rooms, each inverter machine room all needs to be equipped with header box 1012, DC power distribution cabinet 1013, each two covers of low pressure photovoltaic combining inverter 1014, and a set of duplex frequency boostering transformer 102, thus cause the initial stage input cost of generation of electricity by new energy high, the fund operation cycle is long, and overall rate of return on investment is low.
(3) through experimental verification, by low pressure photovoltaic combining inverter, maximal power tracing is carried out to the power output of photovoltaic array, the permeability of its MPPT is lower, and the vulnerability to jamming for uneven illumination problem (it can be caused by the inconsistency 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 continue to study, the emphasis analyzed and optimize and energy concentrate on single grid-connected power electronic equipment (i.e. single centralized parallel network power generation unit), no matter from standpoint of efficiency, or from cost angle, all there is no the space that can promote too much, the angle of looking at problem that only changes and the strategy of dealing with problems, whole system is just likely made to obtain further, profound optimization.
Utility model content
Technical problem to be solved in the utility model is for above-mentioned defect existing in prior art, provides one to reduce line loss, the grid-connected photovoltaic system based on the access of mesohigh direct current that can reduce costs again.
The technical scheme that solution the utility model technical problem adopts is:
The described grid-connected photovoltaic system based on the access of mesohigh direct current comprises: mesohigh DC generation unit and the centralized photovoltaic combining inverter of mesohigh, described mesohigh DC generation unit adopts at least one, each mesohigh DC generation unit includes photovoltaic array and cascade DC boosting unit, described photovoltaic array adopts many groups, often organize photovoltaic array and include multiple photovoltaic arrays in parallel, the output of each group of photovoltaic array is connected with the input of described cascade DC boosting unit, the output of described cascade DC boosting unit accesses a road mesohigh DC bus, for exporting this road mesohigh DC bus to by confluxing in the mode of series connection again after the dc voltage boost of each group of photovoltaic array output, the each road mesohigh DC bus parallel connection be connected with the output of the cascade DC boosting unit of each mesohigh DC generation unit respectively forms the DC side that a road mesohigh DC bus accesses the centralized photovoltaic combining inverter of mesohigh more afterwards, the AC access mesohigh AC network of the centralized photovoltaic combining inverter of described mesohigh.It should be noted that, " many " that occur in the utility model all refer to " at least two ".
Preferably, described cascade DC boosting unit comprises multiple mesohigh header boxs that output is connected successively, the progression of series connection is no less than 2 grades, and the mesohigh header box that these outputs are connected successively has two terminations, the cathode output end being wherein positioned at the mesohigh header box of 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 a rear 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, often organize all corresponding mesohigh header box of photovoltaic array, and often the multiple photovoltaic array parallel connections organized in photovoltaic array access the input of corresponding mesohigh header box afterwards, the direct voltage that described mesohigh header box is used for one of its correspondence group of photovoltaic array exports confluxes into a road direct voltage, and Bing Duigai road direct voltage exports after carrying out boosting process.
Preferably, in each mesohigh DC generation unit, each mesohigh header box all has the function of the maximum power point of one group of photovoltaic array of its correspondence independently tracked, reaches maximum to make the power output of one of its correspondence group of photovoltaic array.
Preferably, in each mesohigh DC generation unit, each mesohigh header box includes the high-frequency step-up transformer of bus-bar and the high class of insulation, the direct voltage that multiple photovoltaic arrays that described bus-bar is used for one of its correspondence group of photovoltaic array to comprise export confluxes into a road direct voltage, the high-frequency step-up transformer of the described high class of insulation is used for carrying out boosting process to this road direct 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 operating voltage of one group of photovoltaic array of its correspondence.
Preferably, in each mesohigh DC generation unit, each mesohigh header box also comprises isolated form DC/DC converter, for following the tracks of the maximum power point of one group of photovoltaic array of its correspondence, reaches maximum to make the power output of one of its correspondence group of photovoltaic array.
Preferably, in multiple mesohigh header boxs that described output is connected successively, output voltage equals or closest to the cathode output end ground connection of the mesohigh header box of the mid-point voltage of the mesohigh DC bus of its place mesohigh DC generation unit access or cathode output end ground connection.
Preferably, in each mesohigh DC generation unit, each mesohigh header box is installed near one group of photovoltaic array of its correspondence, the shortest with the length of the low-voltage direct cable between the one group of photovoltaic array making each mesohigh header box corresponding with it.
Preferably, described electricity generation system also comprises isolating switch, its quantity and one_to_one corresponding identical with the quantity of mesohigh DC generation unit, one road mesohigh DC bus of the output access of the cascade DC boosting unit of the mesohigh DC generation unit that the input of each isolating switch is corresponding with it connects, again by the DC side of the centralized photovoltaic combining inverter of a road mesohigh DC bus access mesohigh after the output parallel connection of each isolating switch.
Preferably, the centralized photovoltaic combining inverter of described mesohigh adopts the inverter of megawatt magnitude.
Preferably, the cooling system that the centralized photovoltaic combining inverter of described mesohigh adopts is cooling by water system.
Beneficial effect:
1) in grid-connected photovoltaic system described in the utility model, the outlet side of each group of photovoltaic array of each mesohigh DC generation unit to the mesohigh header box of its correspondence input between adopt low-voltage direct cable, and the output of each mesohigh header box of each mesohigh DC generation unit to the centralized photovoltaic combining inverter of mesohigh DC side between adopt mesohigh direct current cables, 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 output of each group of photovoltaic array 1011 to all adopting the former avris of duplex frequency boostering transformer 102 compared with low-voltage transmission circuit, the low-voltage transmission circuit (i.e. low-voltage cable) that the utility model adopts is shorter, correspondingly decrease line loss,
In addition, conflux in the mode of series connection again after the dc voltage boost that each group of photovoltaic array in each mesohigh DC generation unit can export by grid-connected photovoltaic system described in the utility model and export a road mesohigh DC bus to, the each road mesohigh DC bus parallel connection be connected with the output of each mesohigh DC generation unit respectively forms the DC side that a road mesohigh DC bus accesses the centralized photovoltaic combining inverter of mesohigh more afterwards, its AC access mesohigh AC network, therefore employing is the connected mode that mesohigh small area analysis is connected, and as stated in the Background Art, the connected mode of low-voltage, high-current parallel connection that what the grid-connected photovoltaic system of prior art adopted is, simultaneously, due to the change of system topological, eliminate duplex frequency boostering transformer and the quantity decreasing 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 utility model, also correspondingly improve system effectiveness, through experimental verification, the utility model compared with prior art can improve the whole efficiency about 2% of grid-connected photovoltaic system.
2) grid-connected photovoltaic system described in the utility model compared with prior art, eliminates the duplex frequency boostering transformer that efficiency is low, loss is large, and, grid-connected photovoltaic system described in the utility model only needs to adopt a set of powerful inverter (i.e. centralized photovoltaic combining inverter of mesohigh, its magnitude is generally tens megawatts) and corresponding inversion machine room and distribution, watch-dog, with need in the grid-connected photovoltaic system of prior art to adopt multiple inversion machine room, each inversion machine room need configure a set of duplex frequency boostering transformer, many covers low pressure photovoltaic combining inverter is 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 subtracting appearance, grid-connected photovoltaic system described in the utility model 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 the centralized photovoltaic combining inverter of mesohigh), just can realize generating 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 comprised by the centralized parallel network power generation of each in existing grid-connected photovoltaic system unit 100 realize), that is, a centralized photovoltaic combining inverter of mesohigh is adopted to instead of the low pressure photovoltaic combining inverter of the One's name is legion adopted in prior art, not only increase system effectiveness, also contribute to system power to control, fault supports and buffering, and system effectiveness optimization.
3) grid-connected photovoltaic system described in the utility model carries out maximal power tracing by the power output of mesohigh header box to one of its correspondence group of photovoltaic array of each mesohigh DC generation unit, undertaken compared with maximal power tracing with the grid-connected photovoltaic system of prior art by the power output of low pressure photovoltaic combining inverter to its one group of corresponding photovoltaic array 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 inconsistency 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 described in the utility model from the output 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 are obtained for significantly promote, make whole system obtain further, profound optimization, there is important engineer applied and be worth.
5) each mesohigh header box of grid-connected photovoltaic system described in the utility model only need bear the 1/m (m is the quantity of mesohigh header box in this mesohigh DC generation unit) of the mesohigh DC bus-bar voltage of place mesohigh DC generation unit access, therefore described mesohigh header box can adopt low withstand voltage device to realize the high-power output of mesohigh, thus the cost of mesohigh header box is reduced by the method for high frequency, improve its power density.
6) the mesohigh DC generation unit of grid-connected photovoltaic system described in the utility model and the centralized photovoltaic combining inverter of mesohigh all can adopt the structure of high modularization, this modular construction is convenient to System Expansion, be conducive to shortening engineering design and process-cycle, reduce costs; And, for each mesohigh DC generation unit, power switch and the passive device of identical capacity can be adopted, make this modular construction have very strong substitutability, be convenient to system maintenance and Redundancy Design.
7) the centralized photovoltaic combining inverter of the mesohigh of grid-connected photovoltaic system described in the utility model reduces due to single watt of cost, therefore its cooling system can adopt water-cooled to design, compared with generally adopting air-cooled design with the cooling system of the low pressure photovoltaic combining inverter of the grid-connected photovoltaic system of prior art, drastically increase the reliability of system, therefore grid-connected photovoltaic system described in the utility model is particularly useful for the terrible weather environment of large, the extremely hot and severe cold of northwest China's dust storm.
8) grid-connected photovoltaic system described in the utility model can be regarded as a kind of flexible electricity generation system of the 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 there is no relevant practical exploration for the middle-and-high voltage system of photovoltaic generation.Grid-connected photovoltaic system described in the utility model is by adopting the mesohigh scheme of multiterminal element access, high MPPT permeability and concentrated inversion grid connection, efficiently, be stably fed to electric energy to mesohigh AC network, certain basis can be established for the application and development in following extensive " photovoltaic generation+flexible transmission " field.
Accompanying drawing explanation
Fig. 1 is the schematic diagram of grid-connected photovoltaic system in prior art;
Fig. 2 for described in the utility model embodiment based on the schematic diagram of grid-connected photovoltaic system of mesohigh direct current access.
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-isolating switch; The centralized photovoltaic combining inverter of 600-mesohigh; 700-step-up transformer.
Embodiment
For making those skilled in the art understand the technical solution of the utility model better, below in conjunction with drawings and Examples, the utility model is described in further detail.
It should be noted that, " mesohigh " (no matter being direct current or interchange) occurred in the utility model all covers all electric pressures between 3kV ~ 800kV, such as, its electric pressure can be but be 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 based on the access of mesohigh direct current, it comprises: n mesohigh DC generation unit 200, a n isolating switch 400 and 1 centralized photovoltaic combining inverter 600 of mesohigh, wherein, n be greater than 0 integer, mesohigh DC generation unit 200 and one_to_one corresponding identical with the quantity of isolating switch 400.Each mesohigh DC generation unit 200 is connected in parallel by the isolating switch 400 of its correspondence, by increasing the quantity of the isolating switch 400 of mesohigh DC generation unit 200 and correspondence thereof, can promote the capacity with expanding system easily; And each mesohigh DC generation unit 200, each isolating switch 400 and the centralized photovoltaic combining inverter 600 of mesohigh all adopt the structure of high modularization, are convenient to system maintenance and Redundancy Design.In addition, as shown in Figure 2, described grid-connected photovoltaic system also can comprise the step-up transformer 700 between AC and mesohigh AC network being connected to the centralized photovoltaic combining inverter 600 of mesohigh, when it is for electric pressure lower than mesohigh AC network to be accessed of the alternating voltage that exports at the AC of the centralized photovoltaic combining inverter of mesohigh 600, boosting process is carried out to the alternating voltage that the AC of the centralized photovoltaic combining inverter 600 of mesohigh exports, with the electric pressure making it meet mesohigh AC network to be accessed, certainly, if the alternating voltage that the AC of the centralized photovoltaic combining inverter of mesohigh 600 exports meets the electric pressure of mesohigh AC network to be accessed, then do not need to arrange step-up transformer 700, namely the AC of the centralized photovoltaic combining inverter 600 of mesohigh directly accesses mesohigh AC network.
In the present embodiment, described isolating switch 400 can adopt the existing switching circuit with isolation features; The centralized photovoltaic combining inverter of described mesohigh 600 can adopt the inverter of existing megawatt magnitude, and its cooling system can adopt cooling by water system.
Particularly, each mesohigh DC generation unit 200 includes m group photovoltaic array 201 and cascade DC boosting unit 202, often organize photovoltaic array 201 and include N number of photovoltaic array 201 in parallel, the output dc voltage of each photovoltaic array 201 all needed for it and rated power grade are made up of the mode of multiple solar panel by series connection and/or parallel connection, here, multiple solar panel series connection and/or parallel connection refer to, the plurality of solar panel is connected successively, 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, the output of each group of photovoltaic array 201 is connected with the input of described cascade DC boosting unit 202, the output of described cascade DC boosting unit 202 accesses a road mesohigh DC bus 300, this road mesohigh DC bus 300 is exported to for confluxing in the mode of series connection again after the dc voltage boost that exported by each group of photovoltaic array 201, and the output voltage exporting this road mesohigh DC bus 300 to 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 according to the quantity of mesohigh header box and the group number of photovoltaic array in each mesohigh DC generation unit, and the quantity often organizing the photovoltaic array that photovoltaic array comprises is determined, the each road mesohigh DC bus 300 connected with the output of the cascade DC boosting unit 202 of each mesohigh DC generation unit 200 is connected with the input of each corresponding isolating switch 400 respectively, accessed the DC side (also referred to as input) of the centralized photovoltaic combining inverter 600 of mesohigh again by a road mesohigh DC bus 500 after the output parallel connection of each isolating switch 400, to realize the electrical isolation between mesohigh DC bus 300 and mesohigh DC bus 500, the AC (also referred to as output) of the centralized photovoltaic combining inverter 600 of described mesohigh accesses mesohigh AC network (now, the alternating voltage of the AC output of the centralized photovoltaic combining inverter of mesohigh 600 meets the electric pressure of mesohigh AC network to be accessed), thus realize the long distance delivery of the energy.In the present embodiment, m, N are the integer being greater than 1, and usually, N gets 8-20, can be set as the concrete value of n, m, N by those skilled in the art according to actual conditions.Can find out, grid-connected photovoltaic system described in the present embodiment only relates to DC generation and transmission line, does not have alternating current circuit.
Described cascade DC boosting unit 202 after can adopting the existing dc voltage boost that each group of photovoltaic array 201 can export by any one again with series connection mode conflux export circuit module realize; And, reach maximum to make the power output of each group of photovoltaic array 201, 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, realize by integrated DC/DC converter in described cascade DC boosting unit 202, other the circuit module that can realize maximal power tracing function can certainly be adopted to realize; In addition, described cascade DC boosting unit 202 also can have the function of the mesohigh DC bus 300 that each group of photovoltaic array 201 and place mesohigh DC generation unit access being carried out electrical isolation.
Preferably, described cascade DC boosting unit 202 comprises m the mesohigh header box 203 that output is connected successively, the progression of series connection is no less than 2 grades, and the mesohigh header box 203 that these outputs are connected successively has two terminations, the cathode output end being wherein positioned at the mesohigh header box 203 of 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 a rear 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 of connecting ", this " previous mesohigh header box of series connection " can be the mesohigh header box 1 in Fig. 2, this " mesohigh header box " can be the mesohigh header box 2 in Fig. 2, for " mesohigh header box " and with its " a rear mesohigh header box of connecting ", this " rear mesohigh header box of series connection " can be the mesohigh header box 2 in Fig. 2, and this " mesohigh header box " can be the mesohigh header box 1 in Fig. 2, in each mesohigh DC generation unit 200, often organize all corresponding mesohigh header box 203 of photovoltaic array 201, and often organize the input of the corresponding mesohigh header box 203 of N number of photovoltaic array 201 rear access in parallel in photovoltaic array 201, therefore the input of described cascade DC boosting unit 202 comprises the input of m mesohigh header box 203, the output of each group of photovoltaic array 201 output 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 is for confluxing into a road direct voltage by one of its correspondence group of direct voltage that photovoltaic array 201 exports (i.e. the direct voltage of photovoltaic array 201 output of N number of parallel connection), Bing Duigai road direct voltage exports from its output after carrying out boosting process.
Further, in each mesohigh DC generation unit 200, each mesohigh header box 203 all has the function of the maximum power point of one group of photovoltaic array 201 of its correspondence independently tracked, reaches maximum to make the power output of one of its correspondence group of photovoltaic array 201; Meanwhile, each mesohigh header box 203 also can have the function of the mesohigh DC bus 300 that one of its correspondence group of photovoltaic array 201 and place mesohigh DC generation unit access being carried out electrical isolation.
In order to make mesohigh header box, there is above-mentioned functions, preferably, in each mesohigh DC generation unit 200, each mesohigh header box 203 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), the direct voltage that multiple photovoltaic arrays that described bus-bar is used for one of its correspondence group of photovoltaic array 201 to comprise export confluxes into a road direct voltage, this bus-bar can adopt existing confluence copper bar, the high-frequency step-up transformer of the described high class of insulation is used for carrying out boosting process to this road direct voltage, and the electrical isolation realized between one group of photovoltaic array 201 of its correspondence and the mesohigh DC bus 300 of place mesohigh DC generation unit access, can be chosen voluntarily according to the operating voltage of one of its correspondence group of photovoltaic array by those skilled in the art as the actual insulation grade of this high-frequency step-up transformer and operating frequency range, and the operating voltage of isolation voltage grade far above one group of photovoltaic array of its correspondence of this high-frequency step-up transformer need be met, the multiple of the operating voltage of one group of photovoltaic array that the isolation voltage grade of this high-frequency step-up transformer is corresponding with it can be determined according to the electric pressure of mesohigh AC network (i.e. the electric pressure of place transformer station), the scope of this multiple can be or close to the quantity of the mesohigh header box 203 comprised 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 doubly, if the electric pressure of mesohigh AC network is 35kV, then described multiple can be or close to 35kV ÷ 1kV=35 doubly.Further, in each mesohigh DC generation unit 200, each mesohigh header box 203 also comprises isolated form DC/DC converter, its input is connected with the output of the high-frequency step-up transformer of the high class of insulation, its output is the output 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, reach maximum to make the power output of one of its correspondence group of photovoltaic array 201.
In order to reduce mesohigh header box insulation against ground voltage, preferably, in m the mesohigh header box 203 that described output is connected successively, output voltage equals or closest to the cathode output end ground connection of the mesohigh header box 203 of the mid-point voltage of the mesohigh DC bus 300 of its place mesohigh DC generation unit access or cathode output end ground connection.That is, in this m mesohigh header box 203, if the output voltage of certain mesohigh header box equals the mid-point voltage of mesohigh DC bus 300 just, 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 cathode output end ground connection or the cathode output end ground connection of that mesohigh header box of the mid-point voltage of mesohigh DC bus 300.
In order to shorten the length of low-voltage direct cable as far as possible, effective reduction 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, such as, be arranged on the below of the solar panel that this group photovoltaic array comprises, the shortest with the length of the low-voltage direct cable between the one group of photovoltaic array 201 making each mesohigh header box 203 corresponding with it.
In the present embodiment, because mesohigh header box 203 can 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, therefore described isolating switch 400 is selectable unit, if grid-connected photovoltaic system described in the present embodiment does not comprise isolating switch 400, directly the DC side that a road mesohigh DC bus 500 accesses the centralized photovoltaic combining inverter 600 of mesohigh is again formed after each road mesohigh DC bus 300 be then connected with the output of the cascade DC boosting unit 202 of each mesohigh DC generation unit 200 is respectively in parallel.
Below, for a mesohigh DC bus-bar voltage be ± the 20MW grid-connected photovoltaic system of 30kV is described:
Described grid-connected photovoltaic system comprises 4 mesohigh DC generation unit, 4 isolating switches and 1 centralized photovoltaic combining inverter of mesohigh, the rated power grade of each mesohigh DC generation unit is about 5MW, it comprises 60 mesohigh header boxs of 60 groups of photovoltaic arrays and correspondence thereof, the power grade often organizing photovoltaic array is about 80-100kW, often organizing an integrated rated power in mesohigh header box corresponding to photovoltaic array is the isolation type DC-DC converter of 100kW, to realize the maximal power tracing of this group photovoltaic array, and this isolation type DC-DC converter realizes electrical isolation by the high-frequency step-up transformer of the high class of insulation integrated in the mesohigh header box of place, thus effectively reduce volume and the cost of isolation type DC-DC converter, the output of the isolation type DC-DC converter in each mesohigh header box builds 60kV DC bus-bar voltage by the cascade system of series connection, consider the insulation of device and withstand voltage, ± 30kV mesohigh DC bus structure is constructed by the mode of neutral earthing (i.e. output voltage equal or closest to the cathode output end ground connection of the mesohigh header box of the mid-point voltage of the mesohigh DC bus of its place mesohigh DC generation unit access or cathode output end ground connection), thus make 4 mesohigh DC generation unit be connected to ± 30kV mesohigh DC bus respectively, then the input of corresponding isolating switch is accessed respectively, accessed the DC side of the centralized photovoltaic combining inverter of mesohigh of 20MW again by a road mesohigh DC bus (this road mesohigh DC bus-bar voltage is also 60kV) after the output parallel connection of each isolating switch, 35kV AC transmission line is fed energy to by the centralized photovoltaic combining inverter of the mesohigh of this 20MW.
In sum, grid-connected photovoltaic system described in the present embodiment from the output 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 large, 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 significantly promote, whole system is made to obtain further, profound optimization, there is important engineer applied be worth.
Be understandable that, the illustrative embodiments that above execution mode is only used to principle of the present utility model is described and adopts, but the utility model is not limited thereto.For those skilled in the art, when not departing from spirit of the present utility model and essence, can make various modification and improvement, these modification and improvement are also considered as protection range of the present utility model.
Claims (10)
1. the grid-connected photovoltaic system based on the access of mesohigh direct current, it is characterized in that, comprise: mesohigh DC generation unit and the centralized photovoltaic combining inverter of mesohigh, described mesohigh DC generation unit adopts at least one, each mesohigh DC generation unit includes photovoltaic array and cascade DC boosting unit, described photovoltaic array adopts many groups, often organize photovoltaic array and include multiple photovoltaic arrays in parallel, the output of each group of photovoltaic array is connected with the input of described cascade DC boosting unit, the output of described cascade DC boosting unit accesses a road mesohigh DC bus, for exporting this road mesohigh DC bus to by confluxing in the mode of series connection again after the dc voltage boost of each group of photovoltaic array output, the each road mesohigh DC bus parallel connection be connected with the output of the cascade DC boosting unit of each mesohigh DC generation unit respectively forms the DC side that a road mesohigh DC bus accesses the centralized photovoltaic combining inverter of mesohigh more afterwards, the AC access mesohigh AC network of the centralized photovoltaic combining inverter of described mesohigh.
2. grid-connected photovoltaic system according to claim 1, is characterized in that,
Described cascade DC boosting unit comprises multiple mesohigh header boxs that output is connected successively, the progression of series connection is no less than 2 grades, and the mesohigh header box that these outputs are connected successively has two terminations, the cathode output end being wherein positioned at the mesohigh header box of 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 a rear 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, often organize all corresponding mesohigh header box of photovoltaic array, and often the multiple photovoltaic array parallel connections organized in photovoltaic array access the input of corresponding mesohigh header box afterwards, the direct voltage that described mesohigh header box is used for one of its correspondence group of photovoltaic array exports confluxes into a road direct voltage, and Bing Duigai road direct voltage exports after carrying out boosting process.
3. grid-connected photovoltaic system according to claim 2, it is characterized in that, in each mesohigh DC generation unit, each mesohigh header box all has the function of the maximum power point of one group of photovoltaic array of its correspondence independently tracked, reaches maximum to make the power output of one of its correspondence group of photovoltaic array.
4. grid-connected photovoltaic system according to claim 2, it is characterized in that, in each mesohigh DC generation unit, each mesohigh header box includes the high-frequency step-up transformer of bus-bar and the high class of insulation, the direct voltage that multiple photovoltaic arrays that described bus-bar is used for one of its correspondence group of photovoltaic array to comprise export confluxes into a road direct voltage, the high-frequency step-up transformer of the described high class of insulation is used for carrying out boosting process to this road direct voltage, and the electrical isolation realized 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 operating voltage of one group of photovoltaic array of its correspondence.
5. grid-connected photovoltaic system according to claim 4, it is characterized in that, in each mesohigh DC generation unit, each mesohigh header box also comprises isolated form DC/DC converter, for following the tracks of the maximum power point of one group of photovoltaic array of its correspondence, reach maximum to make the power output of one of its correspondence group of photovoltaic array.
6. grid-connected photovoltaic system according to claim 2, it is characterized in that, in multiple mesohigh header boxs that described output is connected successively, output voltage equals or closest to the cathode output end ground connection of the mesohigh header box of the mid-point voltage of the mesohigh DC bus of its place mesohigh DC generation unit access or cathode output end ground connection.
7. grid-connected photovoltaic system according to claim 2, it is characterized in that, in each mesohigh DC generation unit, each mesohigh header box is installed near one group of photovoltaic array of its correspondence, the shortest with the length of the low-voltage direct cable between the one group of photovoltaic array making each mesohigh header box corresponding with it.
8. grid-connected photovoltaic system according to claim 1, it is characterized in that, described electricity generation system also comprises isolating switch, its quantity and one_to_one corresponding identical with the quantity of mesohigh DC generation unit, one road mesohigh DC bus of the output access of the cascade DC boosting unit of the mesohigh DC generation unit that the input of each isolating switch is corresponding with it connects, again by the DC side of the centralized photovoltaic combining inverter of a road mesohigh DC bus access mesohigh after the output parallel connection of each isolating switch.
9. the grid-connected photovoltaic system according to any one of claim 1-8, is characterized in that, the centralized photovoltaic combining inverter of described mesohigh adopts the inverter of megawatt magnitude.
10. the grid-connected photovoltaic system according to any one of claim 1-8, is characterized in that, the cooling system that the centralized photovoltaic combining inverter of described mesohigh adopts is cooling by water system.
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| CN105680476A (en) * | 2016-03-09 | 2016-06-15 | 湖南馨雅林工程技术有限公司 | Direct-current boost concentrated inversion photovoltaic power generation system |
| CN105703389A (en) * | 2014-08-25 | 2016-06-22 | 特变电工新疆新能源股份有限公司 | Photovoltaic grid-connected power generation system based on middle and high voltage direct current access |
| WO2021232691A1 (en) * | 2020-05-20 | 2021-11-25 | 中国华能集团有限公司 | High-voltage photovoltaic power generation system |
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| CN107910888A (en) * | 2017-09-06 | 2018-04-13 | 中南大学 | A kind of MPPT grid-connected control methods for photovoltaic series connection micro-capacitance sensor |
| CN109167390B (en) * | 2018-09-21 | 2021-11-26 | 华为数字能源技术有限公司 | Photovoltaic power generation inverter system |
| CN113872245B (en) * | 2021-11-05 | 2024-04-12 | 阳光电源股份有限公司 | Distributed inversion system and starting method thereof |
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| US20110241433A1 (en) * | 2010-03-30 | 2011-10-06 | General Electric Company | Dc transmission system for remote solar farms |
| WO2014121826A1 (en) * | 2013-02-06 | 2014-08-14 | Abb Technology Ltd | Solar power plant, method of controlling a solar power plant and a dc/dc conversion system |
| CN103368200A (en) * | 2013-06-25 | 2013-10-23 | 南车株洲电力机车研究所有限公司 | Single-ended VSC-HVDC photovoltaic power generation system |
| CN103441525A (en) * | 2013-08-12 | 2013-12-11 | 深圳市合兴加能科技有限公司 | Intrinsically-safe photovoltaic grounding system |
| CN204103503U (en) * | 2014-08-25 | 2015-01-14 | 特变电工新疆新能源股份有限公司 | A kind of grid-connected photovoltaic system based on the access of mesohigh direct current |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN105703389A (en) * | 2014-08-25 | 2016-06-22 | 特变电工新疆新能源股份有限公司 | Photovoltaic grid-connected power generation system based on middle and high voltage direct current access |
| CN105703389B (en) * | 2014-08-25 | 2019-06-25 | 特变电工新疆新能源股份有限公司 | A kind of grid-connected photovoltaic system based on the access of mesohigh direct current |
| CN105680476A (en) * | 2016-03-09 | 2016-06-15 | 湖南馨雅林工程技术有限公司 | Direct-current boost concentrated inversion photovoltaic power generation system |
| WO2021232691A1 (en) * | 2020-05-20 | 2021-11-25 | 中国华能集团有限公司 | High-voltage photovoltaic power generation system |
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