WO2021253352A1 - 变换器的控制方法、变换器及光伏发电系统 - Google Patents

变换器的控制方法、变换器及光伏发电系统 Download PDF

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Publication number
WO2021253352A1
WO2021253352A1 PCT/CN2020/096888 CN2020096888W WO2021253352A1 WO 2021253352 A1 WO2021253352 A1 WO 2021253352A1 CN 2020096888 W CN2020096888 W CN 2020096888W WO 2021253352 A1 WO2021253352 A1 WO 2021253352A1
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Prior art keywords
voltage
output
interval
converter
photovoltaic
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PCT/CN2020/096888
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English (en)
French (fr)
Inventor
顾桂磊
徐志武
王雨
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华为数字能源技术有限公司
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Application filed by 华为数字能源技术有限公司 filed Critical 华为数字能源技术有限公司
Priority to AU2020454270A priority Critical patent/AU2020454270B2/en
Priority to CN202080005595.3A priority patent/CN114080748B/zh
Priority to CN202311557671.3A priority patent/CN117856321A/zh
Priority to EP20937180.6A priority patent/EP3965278A4/en
Priority to PCT/CN2020/096888 priority patent/WO2021253352A1/zh
Priority to JP2022520928A priority patent/JP7308360B2/ja
Publication of WO2021253352A1 publication Critical patent/WO2021253352A1/zh
Priority to US17/696,596 priority patent/US11994893B2/en
Priority to US17/851,374 priority patent/US11862981B2/en

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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
    • G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
    • G05F1/66—Regulating electric power
    • G05F1/67—Regulating electric power to the maximum power available from a generator, e.g. from solar cell
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
    • H02S40/00—Components or accessories in combination with PV modules, not provided for in groups H02S10/00 - H02S30/00
    • H02S40/30—Electrical components
    • H02S40/32—Electrical components comprising DC/AC inverter means associated with the PV module itself, e.g. AC modules
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • H02J2300/26—The renewable source being solar energy of photovoltaic origin involving maximum power point tracking control for photovoltaic sources
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
    • H02M1/007—Plural converter units in cascade
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
    • H02M1/0077—Plural converter units whose outputs are connected in series
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

Definitions

  • This application relates to the field of photovoltaic power generation technology, and in particular to a control method of an inverter, an inverter, and a photovoltaic power generation system.
  • each photovoltaic module is usually connected to a converter (also called an optimizer) with an independent MPPT (Maximum Power Point Tracking) function, and the output of the converter Connect the inverter through a certain series-parallel combination.
  • a converter also called an optimizer
  • MPPT Maximum Power Point Tracking
  • the converter can convert the input voltage/current of the photovoltaic module into different output voltage/current, realize the MPPT function of the photovoltaic module level, and maximize the power generation of the system.
  • the existing converter control method adopts a fixed voltage-limiting method, that is, the converter sets a fixed voltage-limiting point, and the converter controls the output The voltage is less than or equal to the fixed voltage limit point.
  • the inverter's input voltage control strategy In order to match the converter's fixed voltage limiting method, the inverter's input voltage control strategy must be adjusted and changed from the original MPPT mode to a fixed input voltage control mode. However, when multiple photovoltaic modules in the photovoltaic string are severely shaded, the input voltage operating point of the inverter will be greater than the voltage limit point of the photovoltaic string. The input voltage loop of the inverter will cause the inverter The input current is reduced to zero, and then the power of the photovoltaic string drops to zero, which seriously affects the power generation.
  • the embodiment of the application discloses a control method of a converter, a converter and a photovoltaic power generation system, which can adapt the existing MPPT control strategy of the inverter while realizing the voltage limit output, and avoid the situation that the power of the photovoltaic string drops to zero. Occurs, which can ensure the stability of the photovoltaic power generation system and increase the power generation capacity of the system.
  • an embodiment of the present application discloses a control method of a converter, which is used to control the output of the converter.
  • the input end of the converter is connected to at least one photovoltaic module, and the output end of the converter is connected to the inverter.
  • the converter is used to output the energy generated by the at least one photovoltaic module after conversion.
  • the control method includes:
  • the output PV curve of the converter is determined according to the PV curve of the output power and voltage of the photovoltaic module; the output PV curve includes at least a connected analog voltage limit interval and a constant power interval; the analog voltage limit interval refers to The output voltage of the converter corresponding to any point in the interval is proportional to the output voltage of the photovoltaic module and has the same proportional coefficient; the constant power interval means that the output voltages corresponding to any two points in the interval are different, and any two points in the interval have different output voltages.
  • the difference between the output powers corresponding to the points is less than a first preset threshold; the voltage output of the converter is controlled according to the output PV curve.
  • the output PV curve of the converter since the output PV curve of the converter includes the analog voltage limit interval, the output PV curve of the converter is partly similar to the output PV curve of the photovoltaic module, which is achieved by simulating the output characteristics of the photovoltaic module.
  • Limiting voltage so that the photovoltaic module connected with the converter can be equivalent to the photovoltaic module, that is, from the point of view of the downstream inverter, the photovoltaic module equipped with the converter can be regarded as a new photovoltaic module.
  • it can adapt the existing MPPT control strategy of the inverter while realizing the voltage-limiting output, which can ensure the stability of the photovoltaic power generation system and increase the power generation capacity of the system.
  • the power corresponding to the first end point of the analog voltage limiting interval corresponds to the maximum output power of the photovoltaic module, and the first end point corresponds to The voltage of is determined by the voltage corresponding to the maximum power point of the photovoltaic module and the proportional coefficient; the constant power interval is connected to the first end point.
  • the voltage corresponding to the second end of the analog voltage limiting interval is the maximum output voltage of the converter, and the power corresponding to the second end is 0;
  • the maximum output voltage is determined by the open circuit voltage of the photovoltaic module and the proportional coefficient, or the maximum output voltage is determined by the maximum input voltage of the inverter and the number of photovoltaic modules connected in series in each photovoltaic string.
  • the analog voltage limiting interval is similar to the part between the maximum power point in the output PV curve of the photovoltaic module and the open circuit voltage of the photovoltaic module, so that the output of the photovoltaic module connected to the inverter is more similar to the output of the photovoltaic module. Alike.
  • the output The PV curve also includes a fixed voltage limiting interval connected to the analog voltage limiting interval; the fixed voltage limiting interval means that the output voltage corresponding to any point in the interval is fixed; the first end point is far away from the fixed voltage limiting interval Interval.
  • the voltage corresponding to the fixed voltage-limiting interval is the maximum output voltage of the converter, so as to realize the voltage-limiting output and avoid the inverter caused by the excessively high voltage of the photovoltaic string.
  • the overvoltage protection of the device is even invalid.
  • the maximum output voltage is determined by the open circuit voltage of the photovoltaic module and the proportional coefficient, or the maximum output voltage is determined by the maximum input voltage of the inverter and the number of photovoltaic modules connected in series in each photovoltaic string .
  • the second end point of the simulated pressure-limiting interval is the first end point of the fixed pressure-limiting interval; the first end point of the simulated pressure-limiting interval corresponds to The voltage of is determined by the voltage corresponding to the maximum power point of the photovoltaic module and the extension coefficient; the extension coefficient is greater than the proportional coefficient.
  • the voltage corresponding to the first end point of the analog voltage limiting interval is less than the voltage corresponding to the fixed voltage limiting interval, and is equal to the voltage corresponding to the fixed voltage limiting interval.
  • the difference between the corresponding voltages is greater than the preset voltage to avoid the situation that the photovoltaic string power drops to zero due to the short analog voltage limit interval.
  • one end point of the constant power interval corresponds to the maximum power point of the photovoltaic module.
  • the output PV curve of the converter further includes a through section connected to the constant power section; the through section and the maximum output PV curve of the photovoltaic module The curves from the power point to the short-circuit current point overlap, so that the photovoltaic module connected to the inverter can be completely equivalent to the output of the photovoltaic module itself.
  • the output PV curve further includes a current limit interval connected to the constant power interval; the current limit interval refers to the output current corresponding to any two points in the interval The difference between is smaller than the second preset threshold, and the output power of the converter linearly decreases as the output voltage decreases.
  • the scale factor is determined by the maximum allowable input voltage of the inverter and the open circuit voltage of each photovoltaic string; the open circuit voltage of each photovoltaic string is the The product of the number of photovoltaic modules connected in series in the string and the open circuit voltage of each photovoltaic module.
  • an embodiment of the present application discloses a converter, the input end of the converter is connected to at least one photovoltaic module, the output end of the converter is connected to the inverter; the converter is used to connect the at least one photovoltaic module The energy generated by the component is output after transformation.
  • the converter includes a DC/DC circuit, a sampling circuit and a controller.
  • the DC/DC circuit is used to adjust the output voltage and output current of the photovoltaic module.
  • the sampling circuit is used to sample the output voltage and output current of the photovoltaic module.
  • the controller is used to determine the PV curve of the output power and voltage of the photovoltaic module according to the collected voltage and current.
  • the controller is also used to determine the output PV curve of the converter according to the output power voltage PV curve of the photovoltaic module; the output PV curve includes at least a connected analog voltage limiting interval and a constant power interval; the simulation
  • the voltage limit interval means that the output voltage of the converter corresponding to any point in the interval is proportional to the output voltage of the photovoltaic module and has the same proportional coefficient;
  • the constant power interval means that the output voltages corresponding to any two points in the interval are different, And the difference between the output powers corresponding to any two points in the interval is less than the first preset threshold.
  • the controller is also used to control the voltage output of the converter according to the output PV curve.
  • the output PV curve of the converter includes the analog voltage limit interval
  • the output PV curve of the converter is partly similar to the output PV curve of the photovoltaic module, that is, the output characteristics of the photovoltaic module are simulated.
  • the photovoltaic module connected with the converter can be equivalent to the photovoltaic module, that is, from the perspective of the downstream inverter, the photovoltaic module equipped with the converter can be regarded as a new photovoltaic module.
  • the components can be adapted to the existing MPPT control strategy of the inverter while achieving the voltage limit output, which can ensure the stability of the photovoltaic power generation system and increase the power generation capacity of the system.
  • the power corresponding to the first end of the analog voltage limiting interval corresponds to the maximum output power of the photovoltaic module
  • the first end corresponds to The voltage of is determined by the voltage corresponding to the maximum power point of the photovoltaic module and the proportional coefficient; the constant power interval is connected to the first end point.
  • the voltage corresponding to the second end of the analog voltage limiting interval is the maximum output voltage of the converter, and the power corresponding to the second end is 0;
  • the maximum output voltage is determined by the open circuit voltage of the photovoltaic module and the proportional coefficient, or the maximum output voltage is determined by the maximum input voltage of the inverter and the number of photovoltaic modules connected in series in each photovoltaic string.
  • the analog voltage limiting interval is similar to the part between the maximum power point in the output PV curve of the photovoltaic module and the open circuit voltage of the photovoltaic module, so that the output of the photovoltaic module connected to the inverter is more similar to the output of the photovoltaic module. Alike.
  • the output The PV curve also includes a fixed voltage limiting interval connected to the analog voltage limiting interval; the fixed voltage limiting interval means that the output voltage corresponding to any point in the interval is fixed; the first end point is far away from the fixed voltage limiting interval Interval.
  • the voltage corresponding to the fixed voltage-limiting interval is the maximum output voltage of the converter, so as to realize the voltage-limiting output and avoid the inverter caused by the excessively high voltage of the photovoltaic string.
  • the overvoltage protection of the device is even invalid.
  • the maximum output voltage is determined by the open circuit voltage of the photovoltaic module and the proportional coefficient, or the maximum output voltage is determined by the maximum input voltage of the inverter and the number of photovoltaic modules connected in series in each photovoltaic string .
  • the second end point of the simulated pressure-limiting interval is the first end point of the fixed pressure-limiting interval; the first end point of the simulated pressure-limiting interval corresponds to The voltage of is determined by the voltage corresponding to the maximum power point of the photovoltaic module and the extension coefficient; the extension coefficient is greater than the proportional coefficient.
  • the voltage corresponding to the first end point of the analog voltage limiting interval is less than the voltage corresponding to the fixed voltage limiting interval, and is equal to the voltage corresponding to the fixed voltage limiting interval.
  • the difference between the corresponding voltages is greater than the preset voltage to avoid the situation that the photovoltaic string power drops to zero due to the short analog voltage limit interval.
  • one end point of the constant power interval corresponds to the maximum power point of the photovoltaic module.
  • the output PV curve of the converter further includes a through section connected to the constant power section; the through section is the maximum value of the output PV curve of the photovoltaic module.
  • the output PV curve further includes a current limit interval connected to the constant power interval; the current limit interval refers to the output current corresponding to any two points in the interval The difference between is smaller than the second preset threshold, and the output power of the converter linearly decreases as the output voltage decreases.
  • the scale factor is determined by the maximum allowable input voltage of the inverter and the open circuit voltage of each photovoltaic string; the open circuit voltage of each photovoltaic string is the The product of the number of photovoltaic modules connected in series in the string and the open circuit voltage of each photovoltaic module.
  • an embodiment of the present application discloses a photovoltaic power generation system, which includes at least one photovoltaic string and an inverter; the input end of the inverter is connected to the at least one photovoltaic string.
  • Each photovoltaic string includes a plurality of photovoltaic modules combined together in series.
  • Each photovoltaic module includes at least one photovoltaic module and the inverter according to any one of claims 11-20.
  • the input end of the converter is connected to the at least one photovoltaic component, and is used to convert the energy generated by the at least one photovoltaic component and output it.
  • an embodiment of the present application discloses a computer-readable storage medium, the computer-readable storage medium stores a computer program, the computer program includes at least one piece of code, the at least one piece of code can be executed by a computer to control the computer to execute The method described in the first aspect and any possible implementation of the first aspect.
  • Figure 1 is a schematic structural diagram of a photovoltaic power generation system in an embodiment of the application.
  • Fig. 2 is a graph of output PV of a photovoltaic module in an embodiment of the application.
  • Fig. 3 is a flowchart of a control method of the inverter in an embodiment of the application.
  • Fig. 4 is a schematic diagram of the output PV curve of the converter in the first embodiment of the application.
  • Fig. 5 is a schematic diagram of the output PV curve of the photovoltaic string in the first embodiment of the application.
  • Fig. 6 is a schematic diagram of the output PV curve of the converter in the second embodiment of the application.
  • FIG. 7 is a schematic diagram of the output PV curve of the photovoltaic string in the second embodiment of the application.
  • FIG. 8 is a schematic diagram of the output PV curve of the converter in the third embodiment of the application.
  • FIG. 9 is a schematic diagram of the output PV curve of the converter in the fourth embodiment of the application.
  • FIG. 10 is a schematic diagram of the output PV curve of the inverter in the fifth embodiment of the application.
  • FIG. 11 is a schematic diagram of the output PV curve of the converter in the sixth embodiment of the application.
  • Fig. 12 is a functional block diagram of a converter in an embodiment of the application.
  • This application provides a photovoltaic power generation system, a converter applied to the photovoltaic power generation system, and a control method thereof.
  • the control method simulates the output characteristics of the photovoltaic module, so that the output power voltage (PV) curve of the converter is at least partially similar to the output PV curve of the photovoltaic module, so that the voltage limit output can be adjusted while the inverter has been adjusted.
  • PV output power voltage
  • Some MPPT control strategies can avoid the situation that the photovoltaic string power drops to zero, thereby ensuring the stability of the photovoltaic power generation system and increasing the power generation capacity of the system.
  • FIG. 1 is a schematic structural diagram of a photovoltaic power generation system 1000 according to an embodiment of the application.
  • the photovoltaic power generation system 1000 includes at least one photovoltaic string 100, an inverter 300 and a power grid 500.
  • each photovoltaic string 100 includes a plurality of photovoltaic modules 101 combined together in series. In other embodiments, the photovoltaic string 100 may also include only one photovoltaic module 101.
  • Each photovoltaic module 101 includes at least one photovoltaic module 10 and an inverter 20. When each photovoltaic module 101 includes a plurality of photovoltaic groups 10, the plurality of photovoltaic modules 10 are connected in series or/and parallel to the converter 20.
  • the photovoltaic module 10 is also called a solar panel, which is a core part of a photovoltaic power generation system, which converts solar energy into electric energy, provides a direct current output, and transmits it to a storage battery for storage, or to drive a load to work.
  • a and/or B in this application includes A and B, A or B.
  • the converter 20, also called an optimizer, is a power conversion device installed between the photovoltaic module 10 and the inverter 300, which can eliminate the series-parallel mismatch of the photovoltaic module 10, reduce the probability of the photovoltaic module 10 being bypassed, and It has the MPPT (Maximum Power Point Tracking, maximum power point tracking) function of a single photovoltaic module 10.
  • the converter 20 is used to optimize the output power of the photovoltaic module 10 connected to it, so as to ensure that the output power of the photovoltaic power generation system 1000 is maximized.
  • the converter 20 can also be used to scan the IV curve of the photovoltaic module 10 connected to it to detect whether the photovoltaic module 10 connected to it is defective or damaged.
  • I refers to current
  • V refers to voltage.
  • the IV curve can also indicate the current power generation capacity, working conditions and other information of the photovoltaic module 10.
  • the input end of the inverter 300 is connected to at least one photovoltaic string 100 and is used to convert the direct current output by the at least one photovoltaic string 100 into alternating current and output it to the grid 500.
  • the power grid 500 is also called a power grid, and includes substations and transmission and distribution lines of various voltages in the power system, that is, three units of power transformation, power transmission, and power distribution, which are used to transmit and distribute electrical energy and change voltage.
  • the photovoltaic power generation system 1000 may include multiple inverters 300, and the AC side of the inverter 300 may be connected to a step-up transformer (not shown) and then connected to the grid 500.
  • the number of inverters 300 included in the photovoltaic power generation system 1000 and whether the AC side of the inverter 300 is connected to a booster may be determined according to the specific application environment, which is not specifically limited here.
  • the multiple inverters 300 may communicate with each other through a communication bus.
  • the communication bus may be an Industry Standard Architecture (ISA) bus, Peripheral Component (PCI) bus, or Extended Industry Standard Architecture (EISA) bus, etc.
  • ISA Industry Standard Architecture
  • PCI Peripheral Component
  • EISA Extended Industry Standard Architecture
  • the bus can be divided into address bus, data bus, control bus, etc., for example, 485 bus.
  • the photovoltaic power generation system 1000 may further include a host computer (not shown in the figure) for communicating with the converter 20 and the inverter 300.
  • the upper computer can be an independent communication host or a mobile terminal device.
  • the host computer can communicate with the inverter 300 and the converter 20 through wireless communication (such as WiFi, Lora, Zigbee, etc.) or PLC communication.
  • the host computer can also be integrated in other equipment of the photovoltaic power generation system 1000, such as the inverter 300, the combiner box, the grid-connected box, or one of the converters 20.
  • FIG. 2 is a graph of the output PV of the photovoltaic module in an embodiment of the application.
  • the output voltage and output power characteristics of photovoltaic modules under light are called PV curves.
  • the voltage corresponding to point A is the open circuit voltage Voc of the photovoltaic module, which is defined as the corresponding module voltage when the photovoltaic module outputs no load.
  • the voltage corresponding to point B is the maximum power point voltage Vmpp of the photovoltaic module, which is defined as the module voltage corresponding to the maximum output power of the photovoltaic module.
  • the output of the photovoltaic module also changes with the solar radiation intensity and the temperature of the photovoltaic module itself. Since the solar radiation intensity and its own temperature are changing, it is obvious that the optimal operating point is also changing. Relative to these changes, the working point of the photovoltaic module is always at the maximum power point, and the photovoltaic power generation system always obtains the maximum power output from the photovoltaic module. This kind of control is the maximum power tracking control.
  • the biggest feature of the inverter used in the photovoltaic power generation system is that it includes the Maximum Power Point Tracking (MPPT) function.
  • MPPT Maximum Power Point Tracking
  • FIG. 3 is a flowchart of a control method of the converter in an embodiment of the application.
  • the control method of the converter specifically includes the following steps.
  • Step S11 Determine the output PV curve of the converter according to the output power voltage PV curve of the photovoltaic module.
  • the output PV curve of the converter includes at least a connected analog voltage limit interval and a constant power interval.
  • the analog voltage limit interval means that the output voltage of the converter corresponding to any point in the interval is proportional to the output voltage of the photovoltaic module and has the same proportional coefficient.
  • the constant power interval means that the output voltages corresponding to any two points in the interval are different, and the difference between the output powers corresponding to any two points in the interval is smaller than the first preset threshold. That is, in the constant power interval, the output voltage of the converter changes while the output power is approximately unchanged.
  • the output PV curve of the photovoltaic module can be obtained by sampling the output voltage and output current of the photovoltaic module through a converter.
  • Step S12 controlling the voltage output of the converter according to the output PV curve of the converter.
  • the output PV curve of the inverter since the output PV curve of the inverter includes the analog voltage limit interval, the output PV curve of the inverter is partly similar to the output PV curve of the photovoltaic module, that is, the output PV curve of the photovoltaic module is simulated.
  • the new photovoltaic components can adapt to the inverter's existing MPPT control strategy while achieving voltage-limiting output, which can ensure the stability of the photovoltaic power generation system and increase the power generation capacity of the system.
  • the scale factor is determined by the maximum allowable input voltage of the inverter and the open circuit voltage of each photovoltaic string.
  • the open circuit voltage of each photovoltaic string is the product of the number of photovoltaic modules connected in series in the string and the open circuit voltage of each photovoltaic module.
  • the open circuit voltage of each photovoltaic string is the sum of the open circuit voltages of the photovoltaic modules connected in series in the string.
  • a single-phase photovoltaic power generation system is taken as an example for description, and the maximum allowable input voltage of the inverter is 600V.
  • the conversion efficiency of the converter in each embodiment of the present application is calculated based on 100%. It can be understood that in engineering applications, the conversion efficiency of the converter is lower than 100%. The following describes how to determine the proportional coefficient, how to determine the analog voltage limit interval and the constant power interval in conjunction with specific embodiments.
  • FIG. 4 is a schematic diagram of the output PV curve of the variator in the first embodiment of the application.
  • the curve L1 is the output PV curve of the photovoltaic module
  • the curve L21 is the output PV curve of the converter.
  • the output PV curve L21 of the converter includes an analog voltage limit interval CD and a constant power interval DE.
  • the converter in the embodiment of the present application is a buck converter.
  • the converter simulates the output characteristics of the photovoltaic module and works in the step-down mode.
  • the output PV curve of the converter is similar to the PV curve of the photovoltaic module, and at any point in the interval, the converter output voltage and the converter input voltage (That is, the output voltage of the photovoltaic module) is proportional and the proportional coefficient K is the same.
  • the power corresponding to the first end D of the analog voltage limiting interval CD is the maximum power of the photovoltaic module, and the voltage corresponding to the first end D of the analog voltage limiting interval It is determined by the voltage corresponding to the maximum power point of the photovoltaic module and the proportional coefficient K.
  • the voltage corresponding to the second terminal C of the analog voltage limiting interval CD is the maximum output voltage of the converter.
  • the maximum output voltage is determined by the open circuit voltage of the photovoltaic module and the proportional coefficient K, or the maximum output voltage is determined by the maximum input voltage of the inverter and the number of photovoltaic strings.
  • the maximum output voltage of each converter is determined by the open circuit voltage of each photovoltaic component and the proportional coefficient K.
  • the constant power interval DE is close to the first end point D of the analog voltage limiting interval CD, and has the same end point D.
  • the converter has a constant power output and works in a step-down mode.
  • the input voltage of the converter is always at point B, and the output voltage is allowed to vary from point D to point E. That is, the voltage corresponding to the second end point E of the constant power interval DE is less than the voltage corresponding to the first end point D of the constant power interval DE.
  • the DE interval can be regarded as a constant power interval. Therefore, the constant power interval DE means that the output voltages corresponding to any two points in the interval are different, and the difference between the output powers corresponding to any two points in the interval is smaller than the first preset threshold.
  • the first preset threshold can be set according to actual application conditions and the hardware parameters of the converter, as long as the power in the constant power DE interval fluctuates within a preset range.
  • the output curve L21 of the converter also includes a current limiting interval EH connected to the constant power interval DE.
  • the current limiting interval EH means that the difference between the output currents corresponding to any two points in the interval is smaller than the second preset threshold. That is, in the current-limiting interval EH, the converter has a current-limiting output. At any point in the interval, the output current of the converter is approximately unchanged, and the output power of the converter decreases linearly as the output voltage decreases.
  • the second preset threshold can be set according to actual application conditions and the hardware parameters of the converter, as long as the current in the current limiting interval EH fluctuates within the preset range. In this way, damage to the converter itself and the inverter caused by the large current output by the converter can be avoided.
  • the second end point of the constant power interval DE and the first end point of the current-limiting interval EH are the same, and both are points E.
  • the power corresponding to point E corresponds to the maximum power of the photovoltaic module
  • the voltage corresponding to point E is the maximum voltage in the current limiting interval of the converter.
  • the second end point H of the current limit interval corresponds to the short-circuit current point F of the PV curve of the photovoltaic module, but the second end point H of the current limit interval represents the output short-circuit point of the converter, and the input voltage of the converter at point H is A
  • the voltage corresponding to point that is, the photovoltaic module is working at point A at this time. It can be understood that the voltage corresponding to the point E is determined by the hardware characteristics of the converter. Therefore, the voltage at the point E may be preset according to the characteristics of the converter.
  • the curve L21 shown in Figure 4 is the output PV curve of the inverter of a photovoltaic module. Since the photovoltaic string includes 20 photovoltaic modules, the output PV curve of the photovoltaic string is the superposition of the output PV curves of the 20 inverters. . Specifically, as shown in FIG. 5, the curve L3 in FIG. 5 is the output PV curve of a photovoltaic string including 20 photovoltaic modules. It can be seen from Figure 5 that the output PV curve L3 of the photovoltaic string is similar to the output PV curve of the photovoltaic module, except that the voltage and power corresponding to each point are expanded by 20 times.
  • the analog voltage limiting interval CD is an interval that simulates the output characteristics of the photovoltaic module, even if the inverter is configured, the entire photovoltaic string can still be regarded as a new photovoltaic module, and then the inverter The existing MPPT can work normally without any changes.
  • FIG. 6 is a schematic diagram of the output PV curve of the variator in the second embodiment of the application.
  • the output PV curve L22 of the converter further includes a fixed voltage limiting interval G1C1 connected to the analog voltage limiting interval C1D1.
  • the fixed voltage limiting interval G1C1 means that the output voltage corresponding to any point in the interval is fixed.
  • the voltage corresponding to the fixed voltage limiting interval G1C1 is the maximum output voltage of the converter.
  • the fixed voltage limiting interval G1C1 and the analog voltage limiting interval C1D1 have the same end point C1, and the power corresponding to the other end point D1 of the analog voltage limiting interval C1D1 corresponds to the maximum power of the photovoltaic module.
  • the converter since a fixed voltage limiting interval G1C1 is set, and a higher voltage at point D1 is allowed to be set, the converter has a higher conversion efficiency, which improves the conversion efficiency of the converter compared to the first embodiment.
  • the scale factor K should be expanded.
  • the expanded scale factor is called the stretch coefficient. It can be understood that the more the extension coefficient is greater than the proportional coefficient, the greater the amplitude of the simulated pressure-limiting interval C1D1 moves to the right.
  • the extension coefficient is too large, the simulated pressure-limiting interval C1D1 will be very close to the fixed pressure-limiting interval G1C1, which makes the simulated pressure-limiting interval G1C1 very close.
  • the interval C1D1 is too small, which affects the MPPT of the inverter.
  • the voltage corresponding to the end point D1 of the analog voltage limiting interval G1C1 should be less than the voltage corresponding to the fixed voltage limiting interval G1C1, and is equal to The difference between the voltages corresponding to the fixed voltage limiting interval G1C1 is greater than the preset voltage, for example, the preset voltage may be 2V.
  • the converter works in the step-down mode throughout the PV curve L22.
  • the output PV curve L22 shown in Figure 6 is the output PV curve of the inverter of a photovoltaic module. Since the photovoltaic string includes 20 photovoltaic modules, the output PV curve of the photovoltaic string is the output PV curve of 20 inverters. Overlay. Specifically, as shown in Fig. 7, the output PV curve L5 in Fig. 7 is the output PV curve of a photovoltaic string including 20 photovoltaic modules, and the photovoltaic string PV curve L5 is a superposition of the output PV curves of 20 inverters.
  • the simulated voltage limit interval C1D1 is the interval for simulating the characteristics of photovoltaic modules.
  • the photovoltaic module equipped with the converter can be regarded as a new photovoltaic module.
  • the existing MPPT of the inverter can be regarded as a new photovoltaic module. It works normally, no changes are required.
  • FIG. 8 is a schematic diagram of the output PV curve of the inverter in the third embodiment of the application.
  • the converter works in the boost mode in the analog voltage limit interval C2D2.
  • the converter works in step-up mode in the constant power interval D2B.
  • the input voltage of the converter is always at point B, and the output voltage is allowed to vary from point D2 to point B; the converter works in step-down mode in the constant power interval BE2.
  • the input voltage of the converter is always at point B, and the output voltage is allowed to vary from point B to point E2.
  • FIG. 9 is a schematic diagram of the output PV curve of the inverter in the fourth embodiment of the application.
  • the output PV curve further includes a fixed pressure limiting interval G3C3.
  • FIG. 10 is a schematic diagram of the output PV curve of the inverter in the fifth embodiment of the application.
  • the difference from the third embodiment is that the end point E4 of the constant power interval D4E4 is the maximum power point B of the photovoltaic module, and the output PV curve of the converter further includes a through interval connected to the constant power interval E4H.
  • the straight-through interval E4H coincides with the curve from the maximum power point B to the short-circuit current point F of the output PV curve of the photovoltaic module. That is, the output voltage of the converter in the through interval E4H is equal to the input voltage, which is equivalent to a photovoltaic module.
  • the converter is a boost converter. Specifically, the converter works in the boost mode in the analog voltage limiting interval C4D4. The converter works in the boost mode in the constant power interval D4E4, the input voltage of the converter is always at point B, and the output voltage is allowed to vary from point D4 to point E4.
  • FIG. 11 is a schematic diagram of the output PV curve of the converter in the sixth embodiment of the application.
  • the output PV curve further includes a fixed pressure limiting interval G5C5.
  • the converter is a boost converter. Specifically, the converter works in the boost mode in the analog voltage limit interval C5D5, and the converter works in the boost mode in the constant power interval D5E5.
  • the converter input voltage is always at point B, and the output voltage is allowed to be between D5 and E5. Variety.
  • FIG. 12 is a functional block diagram of a converter in an embodiment of the application. That is, the converter 20 in FIG. 1 can be realized by the structure in FIG. 12.
  • the converter 20 includes a DC/DC circuit 21, a sampling circuit 22, a controller 23, and a memory 24.
  • the functions of the DC/DC circuit 21, the sampling circuit 22, the controller 23, and the memory 24 can be implemented by integrated circuits.
  • the DC-to-DC DC/DC circuit 21, the sampling circuit 22, the controller 23, and the memory 24 are integrated on the PCB.
  • PCB printed Circuit Board, printed circuit board.
  • Printed circuit board also known as printed circuit board, is an important electronic component, a support for electronic components, and a carrier for electrical connection of electronic components.
  • the DC/DC circuit 21 is correspondingly connected to at least one photovoltaic component, which serves as the input terminal of the converter 20 and is used to adjust the output voltage of the photovoltaic component 10.
  • the converter 20 may include a plurality of DC/DC circuits 21, and each DC/DC circuit 21 is connected to at least one photovoltaic module 10.
  • the DC/DC circuit 21 can work in a power conversion mode for power conversion of the DC power of the photovoltaic module 10 at the input end, and then output the converted DC power to the output end; or, it can work In the straight-through mode, the input terminal and the output terminal are directly connected.
  • the DC/DC circuit 21 can be configured according to specific application environments, for example, a buck circuit, a boost circuit, or a buck-boost circuit.
  • the sampling circuit 22 is electrically connected to the DC/DC circuit 21 for detecting the output voltage of the photovoltaic module 10 and the current corresponding to the output voltage.
  • the sampling circuit 22 may include a sensor, such as a current sensor.
  • the controller 23 is electrically connected to the DC/DC circuit 21, the sampling circuit 22, and the memory 24, respectively.
  • the controller 23 refers to a component that can coordinate various components according to the functional requirements of the instruction. It is the nerve center and command center of the system. It is usually composed of the instruction register IR (Instruction Register), the program counter PC (Program Counter), and the operation controller OC. (Operation Controller) The three components are extremely important for coordinating the orderly work of the entire system.
  • the controller 23 here may refer to one or more devices, circuits, and/or processing cores for processing data (e.g., computer program instructions).
  • the controller 23 may be a processor, or may be a collective term for multiple processing elements.
  • the processor can be a general-purpose central processing unit (Central Processing Unit, CPU), or it can be an application-specific integrated circuit (ASIC), or one or more programs used to control the execution of the program of this application.
  • Integrated circuit for example: one or more microprocessors (Digital Signal Processor, DSP), or one or more Field Programmable Gate Array (Field Programmable Gate Array, FPGA).
  • the processor may include one or more CPUs.
  • the controller 23 is used to execute the aforementioned control method to control the output of the inverter 100.
  • the memory 24 can be a read-only memory (ROM) or other types of static storage devices that can store static information and instructions, random access memory (RAM), or other types that can store information and instructions
  • the dynamic storage device can also be electrically erasable programmable read-only memory (Electrically Erasable Programmable Read-Only Memory, EEPROM), CD-ROM (Compact Disc Read-Only Memory, CD-ROM), or other optical disk storage, CD-ROM Storage (including compact discs, laser discs, optical discs, digital versatile discs, Blu-ray discs, etc.), magnetic disk storage media or other magnetic storage devices, or can be used to carry or store desired program codes in the form of instructions or data structures and can be used by Any other medium accessed by the computer, but not limited to this.
  • the memory 24 may exist independently.
  • the memory 24 can also be integrated with the controller 23. It can be used to store data such as current, voltage, and power of the photovoltaic module 10.
  • the memory 24 is also used to store application program code for executing the solution of the present application, and the controller 23 controls the execution. That is, the controller 23 is used to execute the application program code stored in the memory 24.
  • the structure illustrated in the embodiment of the present application does not constitute a specific limitation on the converter 20.
  • the converter 20 may include more or fewer components than shown, or combine certain components, or split certain components, or arrange different components.
  • the illustrated components can be implemented in hardware, software, or a combination of software and hardware.
  • the computer program product includes one or more computer instructions.
  • the computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable devices.
  • the computer instructions may be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions may be transmitted from a website, computer, server, or data center.
  • the computer-readable storage medium may be any available medium that can be accessed by a computer or a data storage device such as a server or a data center integrated with one or more available media.
  • the usable medium may be a magnetic medium, (for example, a floppy disk, a hard disk, and a magnetic tape), an optical medium (for example, a DVD), or a semiconductor medium (for example, a solid state disk).

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Abstract

光伏发电系统中的变换器及其控制方法。变换器（20）的输入端连接至少一个光伏组件（10），且输出端连接逆变器（300）。控制方法包括：根据光伏组件（10）的输出功率和电压的PV曲线确定变换器（20）的输出PV曲线；根据输出PV曲线控制变换器（20）的电压输出；其中，输出PV曲线至少包括相连接的模拟限压区间和恒功率区间；模拟限压区间是指区间内任意一点所对应的变换器（20）输出电压与光伏组件（10）的输出电压成比例且比例系数相同；恒功率区间是指区间内任意两点所对应的输出电压不同，且区间内任意两点所对应的输出功率之间的差值小于第一预设阈值。该控制方法能够在实现限压输出的同时适配逆变器（300）已有的MPPT控制策略，避免光伏组串（100）功率掉零的情况发生。

Description

变换器的控制方法、变换器及光伏发电系统 技术领域
本申请涉及光伏发电技术领域，尤其涉及变换器的控制方法、变换器及光伏发电系统。
背景技术
目前，为了解决光伏组件串并联失配问题，通常会在每个光伏组件连接一个具有独立MPPT(Maximum Power Point Tracking，最大功率点跟踪)功能的变换器(也称优化器)，变换器的输出通过一定的串并联组合后接入逆变器。在采用分布式MPPT技术的光伏系统中，变换器可以将光伏组件的输入电压/电流转换为不同的输出电压/电流，实现光伏组件级别的MPPT功能，最大限度提高系统发电量。
光伏发电系统配置有变换器后，由于变换器可以限压输出，在配置光伏组件时灵活性更大，单个光伏组串中光伏组件串联数量的上限可以提高，允许光伏发电系统有更高的超配比。为了实现限压输出，避免光伏组串电压过高导致逆变器过压保护甚至是失效，现有变换器控制方法采用固定限压法，也即变换器设置固定限压点，变换器控制输出电压小于等于固定限压点。
为了配合变换器的固定限压法，逆变器的输入电压控制策略须做调整变更，由原先的MPPT模式修改为固定输入电压控制模式。然而，当光伏组串中的多个光伏组件被严重遮挡时，会导致逆变器的输入电压工作点大于光伏组串的限压点，通过逆变器输入电压环的作用会使逆变器输入电流减小至零，进而出现光伏组串功率掉零的情况，严重影响发电量。
发明内容
本申请实施例公开了一种变换器的控制方法、变换器及光伏发电系统，能够在实现限压输出的同时适配逆变器已有的MPPT控制策略，避免光伏组串功率掉零的情况发生，进而能够保证光伏发电系统的稳定性，提高系统的发电量。
第一方面，本申请实施例公开一种变换器的控制方法，用于对变换器的输出进行控制，所述变换器的输入端连接至少一个光伏组件，所述变换器的输出端连接逆变器；所述变换器用于将所述至少一个光伏组件所产生的能量经过变换后输出。所述控制方法包括：
根据所述光伏组件的输出功率和电压的PV曲线确定所述变换器的输出PV曲线；所述输出PV曲线至少包括相连接的模拟限压区间和恒功率区间；所述模拟限压区间是指区间内任意一点所对应的变换器输出电压与所述光伏组件的输出电压成比例且比例系数相同；所述恒功率区间是指区间内任意两点所对应的输出电压不同，且区间内任意两点所对应的输出功率之间的差值小于第一预设阈值；根据所述输出PV曲线控制所述变换器的电压输出。
第一方面的技术方案，由于变换器的输出PV曲线包括了模拟限压区间，使得变换器的输出PV曲线和光伏组件的输出PV曲线部分相似，也即通过模拟光伏组件输出特性的方式来实现限压，进而使得连接有变换器的光伏组件可以等效为光伏组件，也即从后级的逆变器角度来看，配置有变换器后的光伏组件可以看成是一个新的光伏组件，从而能够在实 现限压输出的同时适配逆变器已有的MPPT控制策略，能够保证光伏发电系统的稳定性，提高系统的发电量。
根据第一方面，在一种可能的实现方式中，所述模拟限压区间的第一端点所对应的功率与所述光伏组件的最大输出功率相对应，且所述第一端点所对应的电压由所述光伏组件的最大功率点所对应的电压及所述比例系数确定；所述恒功率区间连接所述第一端点。如此，当所述逆变器采用MPPT策略时可以很快的找到最大功率点，且可以避免出现光伏组串功率掉零的情况发生。
根据第一方面，在一种可能的实现方式中，所述模拟限压区间第二端点所对应的电压为所述变换器的最大输出电压，所述第二端点所对应的功率为0；所述最大输出电压由所述光伏组件的开路电压及所述比例系数确定，或者，所述最大输出电压由逆变器的最大输入电压及每个光伏组串中所串联的光伏组件的数量确定。如此，所述模拟限压区间与光伏组件的输出PV曲线中的最大功率点至光伏组件的开路电压的之间的部分相似，使得连接有变换器后的光伏组件的输出与光伏组件的输出更加相像。
根据第一方面，在一种可能的实现方式中，为了在适配逆变器的MPPT控制策略前提下，使得变换器的输出PV曲线多样化，以提高变换器的适配性，所述输出PV曲线还包括与所述模拟限压区间连接的固定限压区间；所述固定限压区间是指区间内任意一点所对应输出电压固定不变；所述第一端点远离所述固定限压区间。
根据第一方面，在一种可能的实现方式中，所述固定限压区间所对应的电压为所述变换器的最大输出电压，以实现限压输出，避免光伏组串电压过高导致逆变器过压保护甚至是失效。所述最大输出电压由所述光伏组件的开路电压及所述比例系数确定，或者，所述最大输出电压由逆变器的最大输入电压及每个光伏组串中所串联的光伏组件的数量确定。
根据第一方面，在一种可能的实现方式中，所述模拟限压区间的第二端点为所述固定限压区间的第一端点；所述模拟限压区间的第一端点所对应的电压由所述光伏组件的最大功率点所对应的电压及伸展系数确定；所述伸展系数大于所述比例系数。如此，可以使得模拟限压区间与固定限压区间存在交点，并使得当所述变换器为降压变换器时，在恒功率期间的输出电压增大，进而能够提高转换效率。
根据第一方面，在一种可能的实现方式中，所述模拟限压区间的第一端点所对应的电压小于所述固定限压区间所对应的电压，且与所述固定限压区间所对应的电压之间的差值大于预设电压，以避免因模拟限压区间过短而导致光伏组串功率掉零的情况发生。
根据第一方面，在一种可能的实现方式中，当所述变换器仅为升压变换器时，所述恒功率区间的一个端点对应所述光伏组件的最大功率点。
根据第一方面，在一种可能的实现方式中，所述变换器的输出PV曲线还包括与所述恒功率区间连接的直通区间；所述直通区间与所述光伏组件的输出PV曲线的最大功率点至短路电流点之间的曲线重合，进而使得连接有变换器的光伏组件可以完全等效于光伏组件本身的输出。
根据第一方面，在一种可能的实现方式中，所述输出PV曲线还包括与所述恒功率区间连接的限流区间；所述限流区间是指区间内任意两点所对应的输出电流之间的差值小于第二预设阈值，且变换器的输出功率随输出电压降低而线性下降。通过设置限流区间，可 以避免变换器因输出电压过低时输出大电流而损坏变换器或者逆变器。
根据第一方面，在一种可能的实现方式中，所述比例系数由所述逆变器的最大允许输入电压及每个光伏组串的开路电压确定；每个光伏组串的开路电压为该组串中串联的光伏组件的数量与每个光伏组件的开路电压的乘积。
第二方面，本申请实施例公开一种变换器，所述变换器的输入端连接至少一个光伏组件，所述变换器的输出端连接逆变器；所述变换器用于将所述至少一个光伏组件所产生的能量经过变换后输出。所述变换器包括DC/DC电路、采样电路和控制器。所述DC/DC电路用于对光伏组件输出电压和输出电流进行调节。所述采样电路用于对光伏组件输出电压和输出电流进行采样。所述控制器用于根据采集到的电压和电流确定光伏组件的输出功率和电压的PV曲线。所述控制器还用于根据所述光伏组件的输出功率电压PV曲线确定所述变换器的输出PV曲线；所述输出PV曲线至少包括相连接的模拟限压区间和恒功率区间；所述模拟限压区间是指区间内任意一点所对应的变换器输出电压与所述光伏组件的输出电压成比例且比例系数相同；所述恒功率区间是指区间内任意两点所对应的输出电压不同，且区间内任意两点所对应的输出功率之间的差值小于第一预设阈值。所述控制器还用于根据所述输出PV曲线控制所述变换器的电压输出。
第二方面所描述的技术方案，由于变换器的输出PV曲线包括了模拟限压区间，使得变换器的输出PV曲线和光伏组件的输出PV曲线部分相似，也即通过模拟光伏组件输出特性的方式来实现限压，进而使得连接有变换器的光伏组件可以等效为光伏组件，也即从后级的逆变器角度来看，配置有变换器后的光伏组件可以看成是一个新的光伏组件，从而能够在实现限压输出的同时适配逆变器已有的MPPT控制策略，能够保证光伏发电系统的稳定性，提高系统的发电量。
根据第二方面，在一种可能的实现方式中，所述模拟限压区间的第一端点所对应的功率与所述光伏组件的最大输出功率相对应，且所述第一端点所对应的电压由所述光伏组件的最大功率点所对应的电压及所述比例系数确定；所述恒功率区间连接所述第一端点。如此，当所述逆变器采用MPPT策略时可以很快的找到最大功率点，且可以避免出现光伏组串功率掉零的情况发生。
根据第二方面，在一种可能的实现方式中，所述模拟限压区间第二端点所对应的电压为所述变换器的最大输出电压，所述第二端点所对应的功率为0；所述最大输出电压由所述光伏组件的开路电压及所述比例系数确定，或者，所述最大输出电压由逆变器的最大输入电压及每个光伏组串中所串联的光伏组件的数量确定。如此，所述模拟限压区间与光伏组件的输出PV曲线中的最大功率点至光伏组件的开路电压的之间的部分相似，使得连接有变换器后的光伏组件的输出与光伏组件的输出更加相像。
根据第二方面，在一种可能的实现方式中，为了在适配逆变器的MPPT控制策略前提下，使得变换器的输出PV曲线多样化，以提高变换器的适配性，所述输出PV曲线还包括与所述模拟限压区间连接的固定限压区间；所述固定限压区间是指区间内任意一点所对应输出电压固定不变；所述第一端点远离所述固定限压区间。
根据第二方面，在一种可能的实现方式中，所述固定限压区间所对应的电压为所述变 换器的最大输出电压，以实现限压输出，避免光伏组串电压过高导致逆变器过压保护甚至是失效。所述最大输出电压由所述光伏组件的开路电压及所述比例系数确定，或者，所述最大输出电压由逆变器的最大输入电压及每个光伏组串中所串联的光伏组件的数量确定。
根据第二方面，在一种可能的实现方式中，所述模拟限压区间的第二端点为所述固定限压区间的第一端点；所述模拟限压区间的第一端点所对应的电压由所述光伏组件的最大功率点所对应的电压及伸展系数确定；所述伸展系数大于所述比例系数。如此，可以使得模拟限压区间与固定限压区间存在交点，并使得当变换器为降压变换器时在恒功率期间的输出电压增大，进而能够提高转换效率。
根据第二方面，在一种可能的实现方式中，所述模拟限压区间的第一端点所对应的电压小于所述固定限压区间所对应的电压，且与所述固定限压区间所对应的电压之间的差值大于预设电压，以避免因模拟限压区间过短而导致光伏组串功率掉零的情况发生。
根据第二方面，在一种可能的实现方式中，当所述变换器仅为升压变换器时，所述恒功率区间的一个端点对应所述光伏组件的最大功率点。
根据第二方面，在一种可能的实现方式中，所述变换器的输出PV曲线还包括与所述恒功率区间连接的直通区间；所述直通区间与所述光伏组件的输出PV曲线的最大功率点至短路电流点之间的曲线重合，进而使得连接有变换器的光伏组件可以完全等效于光伏组件本身的输出。
根据第二方面，在一种可能的实现方式中，所述输出PV曲线还包括与所述恒功率区间连接的限流区间；所述限流区间是指区间内任意两点所对应的输出电流之间的差值小于第二预设阈值，且变换器的输出功率随输出电压降低而线性下降。
根据第二方面，在一种可能的实现方式中，所述比例系数由所述逆变器的最大允许输入电压及每个光伏组串的开路电压确定；每个光伏组串的开路电压为该组串中串联的光伏组件的数量与每个光伏组件的开路电压的乘积。
第三方面，本申请实施例公开一种光伏发电系统，包括至少一个光伏组串及逆变器；所述逆变器的输入端与所述至少一个光伏组串连接。每个光伏组串包括多个以串联方式组合在一起的光伏模块。每个光伏模块包括至少一个光伏组件及如权利要求11-20任一项所述变换器。所述变换器的输入端与所述至少一个光伏组件连接，用于将所述至少一个光伏组件所产生的能量经过变换后输出。
第四方面，本申请实施例公开一种计算机可读存储介质，该计算机可读存储介质存储有计算机程序，该计算机程序包含至少一段代码，该至少一段代码可由计算机执行，以控制所述计算机执行第一方面以及第一方面中任一可能的实现方式描述的方法。
附图说明
图1为本申一请实施例中的光伏发电系统的结构示意图。
图2为本申请一实施例中的光伏组件的输出PV曲线图。
图3为本申请一实施例中的变换器的控制方法的流程图。
图4为本申请第一实施例中的变换器的输出PV曲线示意图。
图5为本申请第一实施例中的光伏组串的输出PV曲线示意图。
图6为本申请第二实施例中的变换器的输出PV曲线示意图。
图7为本申请第二实施例中的光伏组串的输出PV曲线示意图。
图8为本申请第三实施例中的变换器的输出PV曲线示意图。
图9为本申请第四实施例中的变换器的输出PV曲线示意图。
图10为本申请第五实施例中的变换器的输出PV曲线示意图。
图11为本申请第六实施例中的变换器的输出PV曲线示意图。
图12为本申请一实施例中的变换器的原理框图。
具体实施方式
本申请提供一种光伏发电系统、应用于光伏发电系统中的变换器及其控制方法。该控制方法模拟光伏组件的输出特性，使得变换器的输出功率电压(Power Voltage，PV)曲线和光伏组件的输出PV曲线至少部分相似，从而能够在实现限压输出的同时适配逆变器已有的MPPT控制策略，避免光伏组串功率掉零的情况发生，进而能够保证光伏发电系统的稳定性，提高系统的发电量。
下面结合附图，对本申请的实施例进行描述。
请参阅图1，图1为本申请一实施例提供的光伏发电系统1000的结构示意图。如图1所示，所述光伏发电系统1000包括至少一个光伏组串100、逆变器300及电网500。
本申请实施例中，每个光伏组串100包括多个以串联方式组合在一起的光伏模块101。其他实施例中，光伏组串100也可以只包括一个光伏模块101。每个光伏模块101包括至少一个光伏组件10及变换器20。当每个光伏模块101包括多个光伏组10时，多个光伏组件10串联或/和并联后接入变换器20。
其中，光伏组件10也称为太阳能电池板，是光伏发电系统中的核心部分，将太阳能转化为电能，提供直流电输出，并传输至蓄电池中存储起来，或推动负载工作。
需要说明的是，单体太阳电池不能直接作为电源使用的，需要将若干单体电池串联或/和并联连接和严密封装成组件，是最小不可分割的光伏电池组合装置。此外，本申请中的“A和/或B”包括了A和B，A或B。
变换器20也称优化器，是一种安装在光伏组件10和逆变器300之间的功率变换装置，可以消除光伏组件10的串并联失配，降低光伏组件10被旁路的概率，并具有单个光伏组件10的MPPT(Maximum Power Point Tracking，最大功率点跟踪)功能。本申请实施例中，变换器20用于对与其相连的光伏组件10的输出功率进行优化，以保证光伏发电系统1000输出功率最大化。
其他实施方式中，变换器20还可以用于对与其相连的光伏组件10进行IV曲线扫描，以检测与其相连的光伏组件10是否存在缺陷或损坏。其中，I是指电流，V是指电压。此外，IV曲线还能指示光伏组件10当前的发电能力、工作状况等信息。
逆变器300的输入端与至少一个光伏组串100相连，用于将至少一个光伏组串100输出的直流电转换成交流电后输出至电网500。
电网500也称为电力网，包括电力系统中各种电压的变电所及输配电线路，即变电、输电、配电三个单元，用于输送与分配电能，改变电压。
可以理解，光伏发电系统1000可以包括多个逆变器300，且逆变器300的交流侧可以接升压变压器(图未示)再接电网500。具体的，光伏发电系统1000所包括的逆变器300的数量以及逆变器300的交流侧是否接升压器，可以依据具体应用环境而定，此处不做具体限定。
需要说明的是，在一种实施例中，当光伏发电系统1000包括多台逆变器300时，多台逆变器300之间可以采用通信总线进行通信。通信总线可以是工业标准体系结构(Industry Standard Architecture，ISA)总线、外部设备互连(Peripheral Component，PCI)总线或扩展工业标准体系结构(Extended Industry Standard Architecture，EISA)总线等。该总线可以分为地址总线、数据总线、控制总线等，例如，485总线。
此外，在一具体的实施方式中，光伏发电系统1000还可包括一个上位机(图未示)，用于与变换器20和逆变器300进行通信。其中，上位机可以是独立的通信主机，也可以是移动终端设备。上位机可以通过无线通信(如WiFi、Lora、Zigbee等)或者PLC通信与逆变器300和变换器20进行通信。此外，上位机还可以集成在光伏发电系统1000的其它设备中，例如集成在逆变器300、汇流箱、并网箱或者其中一个变换器20中。
请参阅图2，图2为本申请一实施例中的光伏组件的输出PV曲线图。其中，光伏组件在光照下的输出电压和输出功率特性称之为PV曲线。从图2中可以看出，由于光伏组件的输出功率具有随着输出电压的增大先增大而后减小的变化趋势，因此存在能获取最大功率的最佳工作点。其中，A点所对应的电压为光伏组件的开路电压Voc，定义为光伏组件输出空载时对应的组件电压。B点所对应的电压为光伏组件的最大功率点电压Vmpp，定义为光伏组件输出功率最大时对应的组件电压。
此外，光伏组件的输出还随太阳辐射强度和光伏组件的自身温度而变化的，由于太阳辐射强度和自身温度是变化着的，显然最佳工作点也是在变化的。相对于这些变化，始终让光伏组件的工作点处于最大功率点，光伏发电系统始终从光伏组件获取最大功率输出，这种控制就是最大功率跟踪控制。光伏发电系统用的变换器的最大特点就是包括了最大功率点跟踪(Maximum Power Point Tracking，MPPT)功能。
目前，光伏组件串联时需要结合当地最低气温和选用的光伏组件参数来确定光伏组串中光伏组件串联数量的上限，避免低温场景下，光伏组串电压过高导致逆变器过压保护甚至是失效。光伏发电系统配置有变换器后，由于变换器可以限压输出，在配置光伏组件时灵活性更大，单个光伏组串中光伏组件串联数量的上限可以提高，允许光伏发电系统有更高的超配比。因此，研究合适的变换器控制方法，实现限压输出，同时又不影响逆变器已有的控制策略，显得尤其重要。
请参阅图3，图3为本申请一实施例中的变换器的控制方法的流程图。该变换器的控制方法具体包括如下步骤。
步骤S11，根据光伏组件的输出功率电压PV曲线确定变换器的输出PV曲线。所述变换器的输出PV曲线至少包括相连接的模拟限压区间和恒功率区间。
其中，所述模拟限压区间是指区间内任意一点所对应的变换器输出电压与所述光伏组 件的输出电压成比例且比例系数相同。所述恒功率区间是指区间内任意两点所对应的输出电压不同，且区间内任意两点所对应的输出功率之间的差值小于第一预设阈值。也即，在所述恒功率区间内，所述变换器输出电压变化而输出功率近似不变。
需要说明的是，该光伏组件的输出PV曲线，可以通过变换器来控制光伏组件的输出电压和输出电流并采样来获得。
步骤S12，根据所述变换器的输出PV曲线控制所述变换器的电压输出。
本申请实施例所公开的变换器控制方法，由于变换器的输出PV曲线包括了模拟限压区间，使得变换器的输出PV曲线和光伏组件的输出PV曲线部分相似，也即通过模拟光伏组件输出特性的方式来实现限压，进而使得连接有变换器的光伏组件可以等效为光伏组件，也即从后级的逆变器角度来看，配置有变换器后的光伏组件可以看成是一个新的光伏组件，从而能够在实现限压输出的同时适配逆变器已有的MPPT控制策略，能够保证光伏发电系统的稳定性，提高系统的发电量。
在一些实施方式中，所述比例系数由所述逆变器的最大允许输入电压及每个光伏组串的开路电压确定。其中，每个光伏组串的开路电压为该组串中串联的光伏组件的数量与每个光伏组件的开路电压的乘积。
可以理解，当每串中的光伏组件的参数不同时，每个光伏组串的开路电压为该组串中串联的所述光伏组件的开路电压之和。
本申请各实施例中，均以单相光伏发电系统为例进行说明，逆变器最大允许输入电压为600V。光伏组件的参数相同，且均为：光伏组件开路电压(A点)，Voc＝38.25V；光伏组件短路电流(F点)，Isc＝9.95A；光伏组件最大功率点(B点)，Vmpp＝30.69V，Impp＝8.48A，Pmpp＝260.12W。可以理解，其他实施实施例中，光伏组件的参数还可以是其他参数，在此不做限定。
此外，本申请各个实施例中的变换器的转换效率均是以100％来计算的。可以理解，在工程应用中，变换器的转换效率是低于100％的。下面结合具体实施例，对如何确定比例系数、如何确定所述模拟限压区间和所述恒功率区间进行说明。
请参阅图4，图4为本申请第一实施例中的变化器的输出PV曲线示意图。其中，曲线L1为光伏组件的输出PV曲线，曲线L21为变换器的输出PV曲线。具体地，变换器的输出PV曲线L21包括模拟限压区间CD及恒功率区间DE。本实施方式中，单个光伏组串中串联的光伏组件的数量为20，因此比例系数K＝逆变器最大允许输入电压/光伏组件开路电压总和＝600V/38.25V*20＝0.7843。本申请实施方式中的变换器为降压变换器。
所述模拟限压区间CD的起点C点电压＝38.25V(A点电压)*0.7843＝30V，也即变换器输出电压上限C点电压＝600V/20＝30V。模拟限压区间CD的终点D点电压＝30.69V(B点电压)*0.7843＝24.07V。在模拟限压区间CD内，变换器模拟光伏组件输出特性，工作于降压模式，变换器输出PV曲线和光伏组件PV曲线形状相似，且区间内任意一点，变换器输出电压和变换器输入电压(即光伏组件输出电压)成比例并且比例系数K相同。
因此，本实施方式中，所述模拟限压区间CD的第一端点D所对应的功率为所述光伏组件的最大功率，且所述模拟限压区间的第一端点D所对应的电压由所述光伏组件的最大功率点所对应的电压及所述比例系数K确定。所述模拟限压区间CD的第二端点C所对应 的电压为所述变换器的最大输出电压。所述最大输出电压由所述光伏组件的开路电压及所述比例系数K确定，或者，所述最大输出电压由逆变器的最大输入电压和光伏组串的数量确定。当光伏组串中的光伏组件的参数不同时，则每个变换器的最大输出电压由每个光伏组件的开路电压及所述比例系数K确定。
恒功率区间DE靠近模拟限压区间CD的第一端点D，且具有相同的端点D。在恒功率区间DE内，变换器为恒功率输出，工作于降压模式，变换器的输入电压始终为B点，输出电压允许在D点～E点之间变化。也即，所述恒功率区间DE的第二端点E所对应的电压小于恒功率区间DE的第一端点D所对应的电压。
可以理解，在工程应用中，由于变换器输出D点电压高于E点电压，变换器D点的转换效率略高于E点的转换效率，因此D点的功率略高于E点的功率，但由于D点功率和E点功率近似相等，所以DE区间可看作是恒功率区间。因此，恒功率区间DE是指区间内任意两点所对应的输出电压不同，且区间内任意两点所对应的输出功率之间的差值小于第一预设阈值。其中，第一预设阈值可以根据实际应用情况及变换器的硬件参数而设定，只要恒功率DE区间的功率在预设范围内波动即可。
作为一种具体的实现，变换器的输出曲线L21还包括与恒功率区间DE连接的限流区间EH。所述限流区间EH是指区间内任意两点所对应的输出电流之间的差值小于第二预设阈值。也即，在限流区间EH内，变换器为限流输出，区间内任意一点，变换器输出电流近似不变，变换器输出功率随输出电压降低而线性下降。可以理解，该第二预设阈值可以根据实际应用情况及变换器的硬件参数而设定，只要限流区间EH的电流在预设范围内波动即可。如此，可以避免因变换器输出大电流对变换器自身和逆变器所带来的损坏。
其中，恒功率区间DE的第二端点和限流区间EH的第一端点相同，均为E点。其中E点所对应的功率对应光伏组件的最大功率，E点所对应的电压为变换器限流区间的最大电压。限流区间的第二端点H与光伏组件的PV曲线的短路电流点F相对应，但限流区间的第二端点H表示变换器的输出短路点，变换器在H点时的输入电压为A点所对应的电压，也即，此时光伏组件工作在A点。可以理解，所述E点所对应的电压由变换器的硬件特性确定，因此，E点电压可以是根据变换器的特性而预设定。
图4中所示的曲线L21为一个光伏组件的变换器的输出PV曲线，而光伏组串由于包括了20个光伏组件，因此光伏组串的输出PV曲线为20个变换器输出PV曲线的叠加。具体地，如图5所示，其中图5中的曲线L3为包括20个光伏组件的光伏组串的输出PV曲线。从图5中可以看出，光伏组串的输出PV曲L3和光伏组件的输出PV曲线相似，仅仅是每个点所对应的电压和功率扩大了20倍。因此，对于逆变器而言，由于模拟限压区间CD为模拟光伏组件输出特性的区间，即使配置有变换器，但整个光伏组串仍可以看成是一个新的光伏组件，进而逆变器已有的MPPT可正常工作，不需要做变更。稳态后，由于逆变器MPPT，逆变器输入电压稳定在D点(481.4V＝24.07V*20)，并在D点附近波动。
当光伏组串中有6个光伏组件被严重遮挡后(功率为零)，光伏组串的输出PV曲线将变为曲线L4，稳态后，由于逆变器MPPT，逆变器输入电压稳定在D’点(336.98V＝24.07V*14)，并在D’点附近波动，进而无光伏组串功率掉零风险。
请参阅图6，图6为本申请第二实施例中的变化器的输出PV曲线示意图。与第一实施 例不同的是，在本申请实施例中，变换器的输出PV曲线L22还包括与模拟限压区间C1D1连接的固定限压区间G1C1。所述固定限压区间G1C1是指区间内任意一点所对应输出电压固定不变。本实施方式中，所述固定限压区间G1C1所对应的电压为变换器的最大输出电压。该变换器最大输出电压G1点＝C1点＝600V/20＝30V。
此外，所述固定限压区间G1C1和所述模拟限压区间C1D1具有相同的端点C1，所述模拟限压区间C1D1的另一个端点D1所对应的功率与所述光伏组件的最大功率对应。本实施方式中，由于设置了固定限压区间G1C1，进而允许设置较高的D1点电压，变换器转换效率较高，相较于第一实施例提高了变换器的转换效率。
为了使得模拟限压区间C1D1向右移动与固定限压区间G1C1有交点C1，比例系数K应该扩大，本申请实施例中，将扩大后的比例系数称为伸展系数。可以理解，伸展系数大于比例系数越多，模拟限压区间C1D1向右移动的幅度越大，当伸展系数过大时，模拟限压区间C1D1将非常靠近固定限压区间G1C1，而使得模拟限压区间C1D1过小，进而影响逆变器的MPPT，因此，一些实施方式中，所述模拟限压区间G1C1的端点D1所对应的电压应小于所述固定限压区间G1C1所对应的电压，且与所述固定限压区间G1C1所对应的电压之间的差值大于预设电压，例如，预设电压可以为2V。
具体地，所述伸展系数可以是0.9，因此变换器输出电压上限G1点＝C1点＝600V/20＝30V，变换器输出D1点＝30.69V*0.9＝27.62V。本申请实施例中，变换器在整个PV曲线L22内均工作于降压模式。
图6中所示的输出PV曲线L22为一个光伏组件的变换器的输出PV曲线，而光伏组串由于包括了20个光伏组件，因此光伏组串的输出PV曲线为20个变换器输出PV曲线的叠加。具体地，如图7所示，其中图7中的输出PV曲线L5为包括20个光伏组件的光伏组串的输出PV曲线，光伏组串PV曲线L5为20个变换器输出PV曲线的叠加，模拟限压区间C1D1为模拟光伏组件特性的区间，从后级的逆变器角度来看，配置有变换器后的光伏组件可以看成是一个新的光伏组件，逆变器已有的MPPT可正常工作，不需要做变更。稳态后，由于逆变器MPPT，逆变器输入电压稳定在D1点(552.4V＝27.62V*20)，并在D1点附近波动。
当光伏组串中6个光伏组件被严重遮挡后(功率为零)，光伏组串PV曲线L5将变为光伏组串PV曲线L6，稳态后，由于逆变器MPPT，逆变器输入电压稳定在D1’点(386.68V＝27.62V*14)，并在D1’点附近波动，无光伏组串功率掉零风险。
请参阅图8，图8为本申请第三实施例中的变换器的输出PV曲线的示意图。本申请实施例中，单个光伏组串中串联的光伏组件的数量为14，因此比例系数K＝逆变器最大允许输入电压/光伏组件开路电压总和＝600V/38.25V*14＝1.1204，变换器输出的最大电压C2点＝600V/14＝42.86V。模拟限压区间C2D2的端点D2点电压＝30.69V*1.1204＝34.39V。
需要说明的是，与第一实施例不同的是，变换器在模拟限压区间C2D2工作于升压模式。变换器在恒功率区间D2B区间工作于升压模式，变换器的输入电压始终为B点，输出电压允许在D2点～B点之间变化；变换器在恒功率区间BE2工作于降压模式，变换器的输入电压始终为B点，输出电压允许在B点～E2点之间变化。
请参阅图9，图9为本申请第四实施例中的变换器的输出PV曲线的示意图。与第三实 施例不同的是，所述输出PV曲线还包括固定限压区间G3C3。本实施方式中，变换器输出电压上限G3点＝C3点＝600V/14＝42.86V；伸展系数取1.3，因此模拟限压区间C3D3的端点D3所对应的电压＝30.69V*1.3＝39.90V。
请参阅图10，图10为本申请第五实施例中的变换器的输出PV曲线的示意图。与第三实施例不同的是，所述恒功率区间D4E4的端点E4为所述光伏组件的最大功率点B，且所述变换器的输出PV曲线还包括与所述恒功率区间连接的直通区间E4H。所述直通区间E4H与所述光伏组件的输出PV曲线的最大功率点B至短路电流点F之间的曲线重合。也即，变换器在直通区间E4H的输出电压等于输入电压，等价为光伏组件。
本实施方式中，变换器为升压变换器。具体地，变换器在模拟限压区间C4D4工作于升压模式。变换器在恒功率区间D4E4工作于升压模式，变换器的输入电压始终为B点，输出电压允许在D4点～E4点之间变化。
请参阅图11，图11为本申请第六实施例中的变换器的输出PV曲线的示意图。与第五实施例不同的是，所述输出PV曲线还包括固定限压区间G5C5。本实施方式中，变换器输出电压上限G5点＝C5点＝600V/14＝42.86V；伸展系数取1.3，因此模拟限压区间C5D5的端点D5所对应的电压＝30.69V*1.3＝39.90V。
本实施方式中，变换器为升压变换器。具体地，变换器在模拟限压区间C5D5工作于升压模式，变换器在恒功率区间D5E5工作于升压模式，变换器输入电压始终为B点，输出电压允许在D5点～E5点之间变化。
请参阅图12，图12为本申请一实施例中的变换器的原理框图。也即，图1中的变换器20可以通过图12中的结构来实现。如图12所示，变换器20包括DC/DC电路21、采样电路22、控制器23和存储器24。其中，DC/DC电路21、采样电路22、控制器23和存储器24的功能可以用集成电路来实现，将直流转直流DC/DC电路21、采样电路22、控制器23和存储器24集成在PCB(Printed Circuit Board，印制电路板)上。印制电路板又称印刷线路板，是重要的电子部件，是电子元器件的支撑体，是电子元器件电气连接的载体。
本申请实施例中，DC/DC电路21对应连接至少一个光伏组件，作为变换器20的输入端，用于调节光伏组件10的输出电压。在其他实施例中，变换器20可以包括多个DC/DC电路21，每个DC/DC电路21与至少一个光伏组件10连接。
在一具体的实施例中，DC/DC电路21可以工作于功率变换模式，用于对输入端的光伏组件10的直流电能进行功率变换，再输出变换后的直流电能到输出端；或者，可以工作于直通模式，将输入端和输出端直接连通。在具体的实际应用中，DC/DC电路21可以根据具体应用环境进行电路设置，例如设置buck电路、boost电路或者buck-boost电路等。
采样电路22与DC/DC电路21电连接，用于检测光伏组件10的输出电压和与该输出电压所对应的电流。在具体的实际应用中，采样电路22可以包括传感器，例如电流传感器。
控制器23分别与DC/DC电路21、采样电路22和存储器24电连接。控制器23是指能够将各个部件按照指令的功能要求协调工作的部件，是系统的神经中枢和指挥中心，通常由指令寄存器IR(Instruction Register)、程序计数器PC(Program Counter)和操作控制器OC(Operation Controller)三个部件组成，对协调整个系统有序工作极为重要。这里的控制器23可以指一个或多个设备、电路、和/或用于处理数据(例如计算机程序指令)的处理 核。
其他实施例中，控制器23可以是一个处理器，也可以是多个处理元件的统称。例如，处理器可以是一个通用中央处理器(Central Processing Unit，CPU)，也可以是特定应用集成电(application-specific Integrated Circuit，ASIC)，或一个或多个用于控制本申请方案程序执行的集成电路，例如：一个或多个微处理器(Digital Signal Processor，DSP)，或，一个或者多个现场可编程门阵列(Field Programmable Gate Array，FPGA)。在具体实现中，作为一种实施例，处理器可以包括一个或多个CPU。
本实施方式中，控制器23用于执行前述的控制方法以控制变换器100的输出。
存储器24可以是只读存储器(read-only memory，ROM)或可存储静态信息和指令的其他类型的静态存储设备，随机存取存储器(random access memory，RAM)或者可存储信息和指令的其他类型的动态存储设备，也可以是电可擦可编程只读存储器(Electrically Erasable Programmable Read-Only Memory，EEPROM)、只读光盘(Compact Disc Read-Only Memory，CD-ROM))或其他光盘存储、光碟存储(包括压缩光碟、激光碟、光碟、数字通用光碟、蓝光光碟等)、磁盘存储介质或者其他磁存储设备、或者能够用于携带或存储具有指令或数据结构形式的期望的程序代码并能够由计算机存取的任何其他介质，但不限于此。存储器24可以是独立存在。存储器24也可以和控制器23集成在一起。可以用于存储光伏组件10的电流、电压及功率等数据。
本申请实施例中，存储器24还用于存储执行本申请方案的应用程序代码，并由控制器23来控制执行。也即，所述控制器23用于执行所述存储器24中存储的应用程序代码。
可以理解的是，本申请实施例示意的结构并不构成对变换器20的具体限定。在本申请另一些实施例中，变换器20可以包括比图示更多或更少的部件，或者组合某些部件，或者拆分某些部件，或者不同的部件布置。图示的部件可以以硬件，软件或软件和硬件的组合实现。
所属领域的技术人员可以清楚地了解到，为描述的方便和简洁，上述描述的装置和各个单元的具体工作过程，可以参考前述方法实施例中的对应过程，在此不再赘述。
本说明书中各个实施例采用递进的方式描述，每个实施例重点说明的都是与其他实施例的不同之处，各个实施例之间相同相似部分互相参见即可。对于实施例公开的方法而言，由于其与实施例公开的装置相对应，所以描述的比较简单，相关之处参见装置部分说明即可。
需要说明的是，对于前述的各个方法实施例，为了简单描述，故将其都表述为一系列的动作组合，但是本领域技术人员应该知悉，本申请并不受所描述的动作顺序的限制，因为依据本申请，某一些步骤可以采用其他顺序或者同时进行。
本申请实施例方法中的步骤可以根据实际需要进行顺序调整、合并和删减。
本申请的各实施方式可以任意进行组合，以实现不同的技术效果。
在上述实施例中，可以全部或部分地通过软件、硬件、固件或者其任意组合来实现。当使用软件实现时，可以全部或部分地以计算机程序产品的形式实现。所述计算机程序产品包括一个或多个计算机指令。在计算机上加载和执行所述计算机程序指令时，全部或部分地产生按照本申请所述的流程或功能。所述计算机可以是通用计算机、专用计算机、计 算机网络、或者其他可编程装置。所述计算机指令可以存储在计算机可读存储介质中，或者从一个计算机可读存储介质向另一个计算机可读存储介质传输，例如，所述计算机指令可以从一个网站站点、计算机、服务器或数据中心通过有线(例如同轴电缆、光纤、数字用户线)或无线(例如红外、无线、微波等)方式向另一个网站站点、计算机、服务器或数据中心进行传输。所述计算机可读存储介质可以是计算机能够存取的任何可用介质或者是包含一个或多个可用介质集成的服务器、数据中心等数据存储设备。所述可用介质可以是磁性介质，(例如，软盘、硬盘、磁带)、光介质(例如，DVD)、或者半导体介质(例如固态硬盘Solid State Disk)等。
总之，以上所述仅为本发明技术方案的实施例而已，并非用于限定本发明的保护范围。凡根据本发明的揭露，所作的任何修改、等同替换、改进等，均应包含在本发明的保护范围之内。

Claims (21)

  1. 一种变换器的控制方法，用于对变换器的输出进行控制，所述变换器的输入端连接至少一个光伏组件，所述变换器的输出端连接逆变器；所述变换器用于将所述至少一个光伏组件所产生的能量经过变换后输出；其特征在于，所述控制方法包括：
    根据所述光伏组件的输出功率和电压的PV曲线确定所述变换器的输出PV曲线，所述输出PV曲线至少包括相连接的模拟限压区间和恒功率区间，所述模拟限压区间是指区间内任意一点所对应的变换器输出电压与所述光伏组件的输出电压成比例且比例系数相同，所述恒功率区间是指区间内任意两点所对应的输出电压不同，且区间内任意两点所对应的输出功率之间的差值小于第一预设阈值；
    根据所述输出PV曲线控制所述变换器的电压输出。
  2. 如权利要求1所述的控制方法，其特征在于，所述模拟限压区间的第一端点所对应的功率与所述光伏组件的最大输出功率相对应，且所述第一端点所对应的电压由所述光伏组件的最大功率点所对应的电压及所述比例系数确定；所述恒功率区间连接所述第一端点。
  3. 如权利要求2所述的控制方法，其特征在于，所述模拟限压区间第二端点所对应的电压为所述变换器的最大输出电压，所述第二端点所对应的功率为0；所述最大输出电压由所述光伏组件的开路电压及所述比例系数确定，或者，所述最大输出电压由逆变器的最大输入电压及每个光伏组串中所串联的光伏组件的数量确定。
  4. 如权利要求2所述的控制方法，其特征在于，所述输出PV曲线还包括与所述模拟限压区间连接的固定限压区间；所述固定限压区间是指区间内任意一点所对应输出电压固定不变；所述第一端点远离所述固定限压区间。
  5. 如权利要求4所述的控制方法，其特征在于，所述模拟限压区间的第二端点为所述固定限压区间的第一端点；所述模拟限压区间的第一端点所对应的电压由所述光伏组件的最大功率点所对应的电压及伸展系数确定；所述伸展系数大于所述比例系数。
  6. 如权利要求5所述的控制方法，其特征在于，所述模拟限压区间的第一端点所对应的电压小于所述固定限压区间所对应的电压，且与所述固定限压区间所对应的电压之间的差值大于预设电压。
  7. 如权利要求1-6任一项所述的控制方法，其特征在于，当所述变换器仅为升压变换器时，所述恒功率区间的一个端点对应所述光伏组件的最大功率点。
  8. 如权利要求7所述的控制方法，其特征在于，所述变换器的输出PV曲线还包括与所述恒功率区间连接的直通区间；所述直通区间与所述光伏组件的输出PV曲线的最大功 率点至短路电流点之间的曲线重合。
  9. 如权利要求1-6任一项所述的控制方法，其特征在于，所述输出PV曲线还包括与所述恒功率区间连接的限流区间；所述限流区间是指区间内任意两点所对应的输出电流之间的差值小于第二预设阈值，且变换器的输出功率随输出电压降低而线性下降。
  10. 如权利要求1-9任一项所述的控制方法，其特征在于，所述比例系数由所述逆变器的最大允许输入电压及每个光伏组串的开路电压确定；每个光伏组串的开路电压为该组串中串联的光伏组件的数量与每个光伏组件的开路电压的乘积。
  11. 一种变换器，所述变换器的输入端连接至少一个光伏组件，所述变换器的输出端连接逆变器；所述变换器用于将所述至少一个光伏组件所产生的能量经过变换后输出；其特征在于，所述变换器包括：
    DC/DC电路，用于对光伏组件输出电压和输出电流进行调节；
    采样电路，用于对光伏组件输出电压和输出电流进行采样；以及
    控制器，用于根据采集到的电压和电流确定光伏组件的输出功率和电压的PV曲线；
    所述控制器还用于根据所述光伏组件的PV曲线确定所述变换器的输出PV曲线；所述输出PV曲线至少包括相连接的模拟限压区间和恒功率区间，所述模拟限压区间是指区间内任意一点所对应的变换器输出电压与所述光伏组件的输出电压成比例且比例系数相同，所述恒功率区间是指区间内任意两点所对应的输出电压不同，且区间内任意两点所对应的输出功率之间的差值小于第一预设阈值；
    所述控制器还用于根据所述输出PV曲线控制所述变换器的电压输出。
  12. 如权利要求11所述的变换器，其特征在于，所述模拟限压区间的第一端点所对应的功率与所述光伏组件的最大输出功率相对应，且所述第一端点所对应的电压由所述光伏组件的最大功率点所对应的电压及所述比例系数确定；所述恒功率区间连接所述第一端点。
  13. 如权利要求12所述的变换器，其特征在于，所述模拟限压区间第二端点所对应的电压为所述变换器的最大输出电压，所述第二端点所对应的功率为0；所述最大输出电压由所述光伏组件的开路电压及所述比例系数确定，或者，所述最大输出电压由逆变器的最大输入电压及每个光伏组串中所串联的光伏组件的数量确定。
  14. 如权利要求12所述的变换器，其特征在于，所述输出PV曲线还包括与所述模拟限压区间连接的固定限压区间；所述固定限压区间是指区间内任意一点所对应输出电压固定不变；所述第一端点远离所述固定限压区间。
  15. 如权利要求14所述的变换器，其特征在于，所述模拟限压区间的第二端点为所述固定限压区间的第一端点；所述模拟限压区间的第一端点所对应的电压由所述光伏组件的 最大功率点所对应的电压及伸展系数确定；所述伸展系数大于所述比例系数。
  16. 如权利要求15所述的变换器，其特征在于，所述模拟限压区间的第一端点所对应的电压小于所述固定限压区间所对应的电压，且与所述固定限压区间所对应的电压之间的差值大于预设电压。
  17. 如权利要求11-16任一项所述的变换器，其特征在于，当所述变换器仅为升压变换器时，所述恒功率区间的一个端点对应所述光伏组件的最大功率点。
  18. 如权利要求17所述的变换器，其特征在于，所述变换器的输出PV曲线还包括与所述恒功率区间连接的直通区间；所述直通区间与所述光伏组件的输出PV曲线的最大功率点至短路电流点之间的曲线重合。
  19. 如权利要求11-16任一项所述的变换器，其特征在于，所述输出PV曲线还包括与所述恒功率区间连接的限流区间；所述限流区间是指区间内任意两点所对应的输出电流之间的差值小于第二预设阈值，且变换器的输出功率随输出电压降低而线性下降。
  20. 如权利要求11-19任一项所述的变换器，其特征在于，所述比例系数由所述逆变器的最大允许输入电压及每个光伏组串的开路电压确定；每个光伏组串的开路电压为该组串中串联的光伏组件的数量与每个光伏组件的开路电压的乘积。
  21. 一种光伏发电系统，包括至少一个光伏组串及逆变器；所述逆变器的输入端与所述至少一个光伏组串连接；其特征在于，每个光伏组串包括多个以串联方式组合在一起的光伏模块；每个光伏模块包括至少一个光伏组件及如权利要求11-20任一项所述变换器；所述变换器的输入端与所述至少一个光伏组件连接，用于将所述至少一个光伏组件所产生的能量经过变换后输出至所述逆变器。
PCT/CN2020/096888 2020-06-18 2020-06-18 变换器的控制方法、变换器及光伏发电系统 WO2021253352A1 (zh)

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