WO2022133695A1 - 一种光伏发电系统、功率控制方法及汇流箱 - Google Patents

一种光伏发电系统、功率控制方法及汇流箱 Download PDF

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Publication number
WO2022133695A1
WO2022133695A1 PCT/CN2020/138170 CN2020138170W WO2022133695A1 WO 2022133695 A1 WO2022133695 A1 WO 2022133695A1 CN 2020138170 W CN2020138170 W CN 2020138170W WO 2022133695 A1 WO2022133695 A1 WO 2022133695A1
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WIPO (PCT)
Prior art keywords
combiner box
voltage
output
power
combiner
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PCT/CN2020/138170
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English (en)
French (fr)
Inventor
于心宇
辛凯
董鹏
高拥兵
张彦忠
Original Assignee
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 PCT/CN2020/138170 priority Critical patent/WO2022133695A1/zh
Priority to EP20966276.6A priority patent/EP4250557A4/en
Priority to CN202080031614.XA priority patent/CN115485968A/zh
Publication of WO2022133695A1 publication Critical patent/WO2022133695A1/zh
Priority to US18/338,770 priority patent/US20230336119A1/en

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    • 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
    • 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
    • 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
    • H02J1/00—Circuit arrangements for dc mains or dc distribution networks
    • H02J1/10—Parallel operation of dc sources
    • H02J1/102—Parallel operation of dc sources being switching converters
    • 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
    • H02S40/34—Electrical components comprising specially adapted electrical connection means to be structurally associated with the PV module, e.g. junction boxes
    • 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

Definitions

  • the present application relates to the technical field of photovoltaic power generation, and in particular, to a photovoltaic power generation system, a power control method and a combiner box.
  • photovoltaic power generation systems mainly include a single-stage power conversion mode and a two-stage power conversion mode.
  • the single-stage power conversion mode means that the DC power of the photovoltaic array is converted into alternating current through a DC-AC (DC-AC) circuit
  • the two-stage power conversion mode means that the DC power of the photovoltaic array passes through a DC-DC (DC-DC) circuit.
  • the first-level DC conversion is converted into alternating current through the second-level DC-AC circuit.
  • the two-stage power conversion mode is more efficient than the single-stage power conversion mode, the two-stage power conversion mode is more and more widely used in photovoltaic power generation systems.
  • the two-stage power conversion mode includes a DC-DC circuit and a DC-AC circuit
  • the power control between the DC-DC circuit and the DC-AC circuit needs to rely on high-speed communication between the two. When the communication speed is slow, the power control will be affected.
  • the present application provides a photovoltaic power generation system and a power control method, which enables fast power control between a DC-DC circuit and a DC-AC circuit without relying on high-speed communication between the two.
  • the embodiments of the present application provide a photovoltaic power generation system, including: an inverter and at least one combiner box; the combiner box includes a multi-channel DC-DC DC-DC circuit and a controller; the multi-channel DC-DC circuit in the combiner box The output ends are connected in parallel to the input end of the inverter; the input end of each DC-DC circuit is connected to the corresponding photovoltaic string, and the input end of the general combiner box is connected to multiple photovoltaic strings; the controller of the combiner box is used for The output voltage of the combiner box is greater than or equal to the first preset voltage and less than or equal to the second preset voltage, and the combiner box is controlled to output the maximum power; the output voltage of the combiner box is greater than the second preset voltage, and the output power of the combiner box is controlled to increase with the output voltage. increase and decrease; the second preset voltage is greater than the first preset voltage; the maximum power is the sum of the maximum powers of all photovoltaic strings connected to the combiner
  • the first preset voltage is greater than or equal to the maximum voltage corresponding to the maximum power point of all photovoltaic strings connected to the combiner box;
  • the second preset voltage is greater than or equal to the lowest DC voltage of the inverter in the linear modulation region. That is, it is greater than the DC bus voltage required by the inverter, that is, the peak line voltage of the AC output terminal of the inverter. Since the inverter has requirements for the DC bus voltage during operation, the second preset voltage can be set according to the DC bus voltage sent by the inverter.
  • an embodiment of the present application provides a power control solution that can control the output power of a DC-DC circuit without relying on high-speed communication.
  • the combiner box can be regarded as a photovoltaic string, that is, the combiner box is virtualized as a photovoltaic source.
  • the string has an output power-output voltage curve, that is, a PV curve. Therefore, the output voltage and output power of the combiner box also have characteristics similar to the PV curve of a photovoltaic string.
  • the combiner box can control the output power according to the interval in which the output voltage is located, so as to get rid of the control of the inverter and not rely on the high-speed communication between the combiner box and the inverter, even if the communication speed between the inverter and the combiner box is relatively high. Low also does not affect the fast control of the output power by the combiner box.
  • the specific control method of the output power of the combiner box as long as the output power of the combiner box decreases with the increase of the output voltage of the combiner box, it can be proportionally reduced , can also be reduced disproportionately.
  • the controller of the combiner box is specifically configured to control the output power of the combiner box to increase with the increase of the output voltage according to the output voltage of the combiner box, the open circuit voltage of the combiner box and the second preset voltage. Decrease; the open-circuit voltage of the combiner box is greater than the maximum open-circuit voltage of all PV strings connected to the combiner box.
  • the controller of the combiner box is specifically configured to control the output power of the combiner box to decrease as the output voltage increases according to the following formula:
  • P outmax is the maximum power
  • u out is the output voltage of the combiner box
  • U mppt2 is the second preset voltage
  • U oc is the open-circuit voltage of the combiner box.
  • the combiner box includes at least two of the following: a first combiner box and a second combiner box;
  • the second preset voltage of the first combiner box is greater than the first preset voltage of the second combiner box, and the second preset voltage of the second combiner box is greater than the first preset voltage of the first combiner box.
  • the controller of the combiner box is used to adjust the output voltage of the corresponding photovoltaic string to adjust the output power of the combiner box.
  • it further includes: an inverter controller;
  • the inverter controller is used to control the output power of the inverter according to the power limit command value.
  • Embodiments of the present application also provide a power control method for a photovoltaic power generation system.
  • the system includes: an inverter and at least one combiner box; the combiner box includes a multi-channel DC-DC DC-DC circuit and a controller; The output terminals of the DC-DC circuits are connected in parallel to the input terminals of the inverter; the input terminals of each DC-DC circuit are connected to the corresponding photovoltaic string; the method includes: the output voltage of the combiner box is greater than or equal to a first preset When the voltage is less than or equal to the second preset voltage, the combiner box is controlled to output the maximum power; the output voltage of the combiner box is greater than the second preset voltage, and the output power of the combiner box is controlled to decrease as the output voltage increases; the second preset voltage greater than the first preset voltage; the maximum power is the sum of the maximum powers of all PV strings connected to the combiner box.
  • the first preset voltage is greater than or equal to the maximum value of the voltage corresponding to the maximum power point of all photovoltaic strings connected to the combiner box; the second preset voltage is greater than or equal to the inverter in the linear modulation region. Minimum DC voltage.
  • controlling the output power of the combiner box to decrease with the increase of the output voltage specifically includes: controlling the combiner box according to the output voltage of the combiner box, the open circuit voltage of the combiner box and the second preset voltage The output power decreases as the output voltage increases; the open-circuit voltage of the combiner box is greater than the maximum open-circuit voltage of all PV strings connected to the combiner box.
  • the output power of the combiner box is controlled to decrease as the output voltage increases according to the following formula:
  • P outmax is the maximum power
  • u out is the output voltage of the combiner box
  • U mppt2 is the second preset voltage
  • U oc is the open-circuit voltage of the combiner box.
  • the method further includes: adjusting the output voltage of the corresponding photovoltaic string to adjust the output power of the combiner box.
  • the embodiment of the present application also provides a combiner box, including: a multi-channel DC-DC circuit and a controller of the combiner box; the input end of each DC-DC circuit is connected to a corresponding photovoltaic string; the output of the multi-channel DC-DC circuit
  • the terminals are connected in parallel to the input terminal of the inverter; the controller of the combiner box is used for the output voltage of the combiner box to be greater than or equal to the first preset voltage and less than or equal to the second preset voltage to control the combiner box to output the maximum power;
  • the power is the sum of the maximum powers of all photovoltaic strings connected to the combiner box; the second preset voltage is greater than the first preset voltage; the output voltage of the combiner box is greater than the second preset voltage, and the output power of the combiner box is controlled to follow the output voltage increase and decrease.
  • the first preset voltage is greater than or equal to the maximum value of the voltage corresponding to the maximum power point of all photovoltaic strings connected to the combiner box;
  • the second preset voltage is greater than or equal to the inverter in the linear modulation region.
  • the open-circuit voltage is greater than the maximum open-circuit voltage of all PV strings connected to the combiner box.
  • the embodiments of the present application have the following advantages:
  • the control of the output power of the combiner box in the embodiment of the present application no longer depends on the power limit command sent by the controller of the inverter, but the combiner box independently realizes the control of the output power.
  • the combiner box can It is regarded as a photovoltaic string, that is, the combiner box is virtualized as a photovoltaic source. Since the photovoltaic string has an output power-output voltage curve, that is, a PV curve, the output voltage and output power of the combiner box also have a similar value to the PV curve of the photovoltaic string. characteristic.
  • the combiner box When the output voltage of the combiner box is greater than or equal to the first preset voltage and less than or equal to the second preset voltage, the combiner box is controlled to output maximum power.
  • the maximum power is the sum of the maximum powers of all PV strings connected to the combiner box.
  • the output power of the combiner box When the output voltage of the combiner box is greater than the second preset voltage, the output power of the combiner box is controlled to decrease as the output voltage increases, that is, it exhibits a drooping characteristic.
  • the combiner box can control the output power according to the interval in which the output voltage is located, so as to get rid of the control of the inverter and not rely on the high-speed communication between the combiner box and the inverter, even if the communication speed between the inverter and the combiner box is relatively high. Low also does not affect the fast control of the output power by the combiner box.
  • FIG. 1 is a schematic diagram of a photovoltaic power generation system provided by an embodiment of the present application
  • FIG. 2 is a schematic diagram of a PV curve of a photovoltaic string provided by an embodiment of the present application
  • FIG. 3 is a schematic diagram of another photovoltaic power generation system provided by an embodiment of the present application.
  • FIG. 4 is a schematic diagram of a PV curve of a combiner box provided by an embodiment of the present application.
  • FIG. 5 is a schematic diagram of yet another photovoltaic power generation system provided by an embodiment of the present application.
  • FIG. 6 is a schematic diagram of PV curves of a plurality of combiner boxes according to an embodiment of the present application.
  • FIG. 7 is a flowchart of a power control method of a photovoltaic power generation system provided by an embodiment of the present application.
  • FIG. 8 is a schematic diagram of a combiner box according to an embodiment of the present application.
  • directional terms such as “upper” and “lower” may include, but are not limited to, definitions relative to the schematic placement of components in the drawings. It should be understood that these directional terms may be relative concepts, They are used for relative description and clarification, which may vary accordingly depending on the orientation in which the components are placed in the drawings.
  • connection should be understood in a broad sense.
  • connection may be a fixed connection, a detachable connection, or an integrated body; it may be directly connected, or Can be indirectly connected through an intermediary.
  • coupled may be a manner of electrical connection that enables signal transmission.
  • Coupling can be a direct electrical connection or an indirect electrical connection through an intermediate medium.
  • FIG. 1 this figure is a schematic diagram of a photovoltaic power generation system provided by an embodiment of the present application.
  • the three-phase alternating current power output by the photovoltaic power generation system is used as an example for introduction.
  • the photovoltaic power generation system includes a photovoltaic array PV, a DC-DC circuit 100 and a DC-AC circuit 200 .
  • the input end of the DC-DC circuit 100 is connected to the photovoltaic array PV, and the input end of the DC-AC circuit 200 is connected to the output end of the DC-DC circuit 100 .
  • the specific implementation form of the DC-DC circuit 100 is not specifically limited in the embodiments of the present application, for example, it may include a boost circuit, a buck circuit, or a buck-boost circuit.
  • An implementation method is that the input end of the DC-AC circuit 200 is connected to the multi-channel DC-DC circuit 100, the output ends of the multi-channel DC-DC circuit 100 are connected in parallel, and the multi-channel DC-DC circuit 100 is integrated in a cabinet, For example, it can be integrated in a combiner box.
  • the DC-AC circuit 200 is integrated in the inverter.
  • the DC-DC circuit 100 In actual work, the DC-DC circuit 100 generally does not work at the maximum power point, but controls its output power according to the power limit command sent by the controller of the inverter, that is, in most cases, the output power is smaller than the maximum power, and works at Power-limited state.
  • the controller of the inverter is located on one side of the DC-AC circuit 200. Generally, the distance between the inverter and the combiner box is relatively long, and the operation of the DC-DC circuit 100 needs to be controlled by the instructions of the controller. For example, the DC-DC circuit adjusts the output power according to the power limit command of the controller.
  • the signal sent by the controller to the DC-DC circuit 100 relies on high-speed communication. When the communication speed between the DC-DC circuit 100 and the controller is slow, the response speed of the DC-DC circuit 100 will be seriously affected, so it cannot be timely Output the power corresponding to the power limit command.
  • FIG. 1 is only a schematic diagram.
  • the input terminal of the DC-AC circuit 200 can be connected to the output terminals of the multi-channel DC-DC circuit, that is, the output terminals of the multi-channel DC-DC circuit are connected in parallel.
  • the input terminal of the DC-DC circuit is connected to its corresponding photovoltaic string.
  • the input terminal of each DC-DC circuit can be connected to multiple parallel photovoltaic strings.
  • the embodiments of the present application provide a power control solution, which can control the output power of the DC-DC circuit 100 without relying on high-speed communication.
  • the control of the output power of the combiner box in the embodiment of the present application no longer depends on the power limit command sent by the controller of the inverter, but the combiner box independently realizes the control of the output power.
  • the combiner box can As a photovoltaic string, the combiner box is virtualized as a photovoltaic source. Since the photovoltaic string has an output power-output voltage curve, that is, a PV curve, as shown in FIG. 2 , which is a photovoltaic string provided by this embodiment of the application Schematic diagram of the PV curve.
  • the abscissa in Figure 2 is the output voltage of the photovoltaic string, and the ordinate is the output power of the photovoltaic string.
  • the PV curve has a drooping characteristic, that is, beyond the maximum power point S, as the output voltage increases, the output power will decrease.
  • the combiner box realizes the output power control according to the virtual PV curve, so it does not depend on the power limit command sent by the inverter side, so it does not depend on the high-speed communication between the combiner box and the inverter, and gets rid of the high-speed communication. influences.
  • FIG. 3 is a schematic diagram of another photovoltaic power generation system provided by the embodiment of the present application.
  • the combiner box includes at least two DC-DC circuits as an example for description.
  • the number of DC-DC circuits can be set according to actual needs.
  • DC bus voltage refers to the output voltage of the combiner box, that is, the input voltage of the inverter.
  • the combiner box has the Maximum Power Point Tracking (MPPT, Maximum Power Point Tracking) function as an example for introduction. It should be understood that the combiner box may also not have the MPPT function, which is not specifically limited in the embodiments of the present application.
  • MPPT Maximum Power Point Tracking
  • the photovoltaic power generation system includes: an inverter 400 and at least one MPPT combiner box 200; the combiner box 200 includes multiple DC-DC DC-DC circuits and a controller (not shown in the figure); the combiner box The output ends of the multiple DC-DC circuits inside are connected in parallel to the input ends of the inverter; the input ends of each DC-DC circuit are connected to the corresponding photovoltaic string.
  • the combiner box includes at least the following two DC-DC circuits as an example for description, ie, a first DC-DC circuit 200a and a second DC-DC circuit 200b.
  • the input end of the first DC-DC circuit 200a is connected to the corresponding photovoltaic string 100a and the photovoltaic string 100b.
  • the input end of the second DC-DC circuit 200b is connected to the corresponding photovoltaic string.
  • the number of photovoltaic strings connected to the input end of the DC-DC circuit is not limited, and all photovoltaic strings can be connected in parallel to the input end of the DC-DC circuit.
  • the controller of the combiner box controls the output power according to the output voltage, and is specifically used to control the combiner box to output the maximum power when the output voltage of the combiner box is greater than or equal to the first preset voltage and less than or equal to the second preset voltage; wherein the maximum power is the combiner box.
  • the first preset voltage and the second preset voltage are described below with reference to graphs.
  • FIG. 4 is a schematic diagram of a PV curve of a combiner box provided by an embodiment of the present application.
  • a combiner box includes a DC-DC circuit, and the input end of the DC-DC circuit is connected to a photovoltaic string as an example for introduction.
  • the curve M in Fig. 4 is the input PV curve of the combiner box, and the curve N is the output PV curve of the combiner box. Since the input end of the combiner box is connected to the PV strings, the curve M is the PV curve of the PV strings.
  • the output voltage range of the combiner box is greater than or equal to the first preset voltage, that is, greater than Umppt1 in FIG. 4 .
  • the first preset voltage is greater than or equal to the maximum value of the voltage corresponding to the maximum power point of all photovoltaic strings connected to the combiner box. That is, the first preset voltage is not less than the maximum value of the voltage corresponding to the maximum power point of all photovoltaic strings connected to the combiner box. For example, if the combiner box is connected to 4 photovoltaic strings, the first preset voltage is greater than or equal to the maximum value of the voltage corresponding to the maximum power point of the 4 photovoltaic strings, that is, greater than or equal to the maximum value of the 4 voltages.
  • the second preset voltage Umppt2 is greater than or equal to the lowest DC voltage of the inverter in the linear modulation region, that is, greater than the DC bus voltage required by the inverter, that is, the peak line voltage of the AC output end of the inverter. Since the inverter has requirements for the DC bus voltage during operation, the second preset voltage can be set according to the DC bus voltage sent by the inverter.
  • Uoc in Fig. 4 is the corresponding open circuit voltage of the virtual PV curve of the combiner box.
  • the open-circuit voltage Uoc of the combiner box needs to be greater than the maximum open-circuit voltage of all PV strings connected to the combiner box. For example, continue to take the input end of the combiner box connected to four photovoltaic strings as an example, the Uoc of the combiner box should be greater than the maximum open-circuit voltage of the four photovoltaic strings.
  • the PV curve of the combiner box has a straight line stage, that is, when the output voltage is between Umppt1 and Umppt2, the output power of the combiner box is a fixed value, that is, the maximum power.
  • the maximum power is the sum of the maximum powers of all PV strings connected to the combiner box. For example, if the combiner box is connected to 4 PV strings, the maximum power is the sum of the powers corresponding to the maximum power points of the 4 PV strings.
  • the output power of the combiner box presents a monotonically decreasing trend with the output voltage.
  • the embodiment of the present application does not limit that the output power exhibits a monotonically decreasing trend with the output voltage.
  • it may be the same as the monotonically decreasing trend of the photovoltaic string at the input end, or it may decrease in a linear monotonically decreasing ratio, or it may be For a parabolic-like decline, as long as it is guaranteed to be a monotonic decline.
  • monotonic drop such as the controller of the combiner box, which is specifically used to control the output power of the combiner box according to the output voltage of the combiner box, the open-circuit voltage of the combiner box and the second preset voltage to increase with the output voltage. increase and decrease;
  • the controller of the combiner box is specifically used to control the output power of the combiner box to decrease with the increase of the output voltage according to the output voltage of the combiner box, the open circuit voltage of the combiner box and the second preset voltage according to the following formula:
  • P out is the output power of the combiner box
  • P outmax is the maximum power
  • u out is the output voltage of the combiner box
  • U mppt2 is the second preset voltage
  • U oc is the open circuit voltage of the combiner box.
  • the control of the output power of the combiner box does not depend on the power limit command sent by the inverter side, but controls its own output at all times according to its own output voltage. power.
  • the controller of the combiner box can adjust the output power of the combiner box by adjusting the output voltage of the photovoltaic string connected to the input end of the combiner box. Since the output voltage of the PV string will affect its own output power, that is, to meet the characteristics of the PV curve, and in the case of ignoring the power loss, the output power of the PV string is the input power of the combiner box, and the input power of the combiner box The power is equal to the output power of the combiner box.
  • the control of the output power of the inverter is realized by the inverter itself, that is, the inverter controller is used to control its own output power according to the power required by the photovoltaic power generation system. That is, the inverter directly controls its own output power without sending a power limit command to the combiner box, and the combiner box adjusts its own output power, so it can get rid of the influence of the communication speed between the inverter and the combiner box.
  • the control of the output power of the combiner box on its own can also be implemented under low-speed communication.
  • the output power of the inverter is essentially derived from the output power of the combiner box. Therefore, the output power of the inverter is a straight line parallel to the horizontal axis in Figure 4.
  • the straight line and the PV curve of the combiner box have an intersection point, and the intersection point is The power limiting point of the inverter.
  • this figure is a schematic diagram of yet another photovoltaic power generation system provided by an embodiment of the present application.
  • two combiner boxes may be used as an example for introduction.
  • the MPPT combiner box as an example, it should be understood that the input end of the inverter 400 may be connected to a larger number of combiner boxes.
  • the two combiner boxes in FIG. 5 are a first MPPT combiner box 200A and a second MPPT combiner box 200B, respectively.
  • the first MPPT combiner box 200A includes at least two DC-DC conversion circuits, namely a first DC-DC conversion circuit 200a and a second DC-DC conversion circuit 200b.
  • the input end of the first DC-DC conversion circuit 200a is connected to the corresponding photovoltaic string 100a and the photovoltaic string 100b.
  • the photovoltaic string 100a and the photovoltaic string 100b are connected in parallel to the input end of the first DC-DC conversion circuit 200a.
  • the second DC-DC conversion circuit 200b is connected to its corresponding photovoltaic string.
  • the second MPPT combiner box 200B includes at least two DC-DC conversion circuits, namely a third DC-DC conversion circuit 200c and a fourth DC-DC conversion circuit 200d.
  • the input end of the third DC-DC conversion circuit 200c is connected to the corresponding photovoltaic string 100c and the photovoltaic string 100d.
  • the photovoltaic string 100c and the photovoltaic string 100d are connected in parallel to the input end of the third DC-DC conversion circuit 200c.
  • the fourth DC-DC conversion circuit 200d is connected to its corresponding photovoltaic string.
  • the maximum power of the multiple combiner boxes exists in a common interval, thereby realizing the maximum power point tracking of the multiple combiner boxes. Therefore, in order to make the maximum power of the multiple combiner boxes exist in a common interval, continuing to take two combiner boxes as an example, the second preset voltage of the first combiner box needs to be greater than the first preset voltage of the second combiner box, and the second The second preset voltage of the box is greater than the first preset voltage of the first combiner box, that is, the second preset voltage of each combiner box needs to be greater than the first preset voltage of all combiner boxes to ensure the maximum power of all combiner boxes. There is a common interval.
  • FIG. 6 is a schematic diagram of PV curves of multiple combiner boxes according to an embodiment of the present application.
  • curves N1, N2 and N3 represent the PV curves of three different combiner boxes, respectively.
  • the maximum power interval of N1, N2 and N3 has a common MPPT interval.
  • the three unlabeled curves in Figure 6 are the PV curves of the PV strings connected to the input ends of the three combiner boxes. Since the maximum power intervals of N1, N2 and N3 are all straight lines, the maximum power tracking of the three combiner boxes can be realized as long as the three straight lines have a common overlapping part. When three combiner boxes are connected to the input end of the inverter, the maximum power is the sum of the maximum powers of the three combiner boxes.
  • the first preset voltage and the second preset voltage corresponding to the maximum power interval of N1 are 1000V and 1150V respectively, and the maximum power interval of N2 corresponding to the first preset voltage and the second preset voltage are 1050V and 1200V respectively, then N1
  • the voltage range corresponding to the maximum power coincident with N2 is 1050V to 1150V.
  • the combiner box is virtualized as the output power droop characteristic similar to that of a photovoltaic panel. From the perspective of the inverter connected to the rear stage of the combiner box, the combiner box can be regarded as a new photovoltaic string. , so that the output power of the combiner box can be quickly dispatched without relying on high-speed communication.
  • each combiner box can be regarded as a photovoltaic source, and when there are multiple combiner boxes, power control of the multiple combiner boxes can be realized by setting the multiple combiner boxes to have a maximum power interval.
  • the inverter can quickly realize power scheduling by adopting the power control method of the single-stage power conversion system. That is, when the combiner box looks at the PV source, the two-stage photovoltaic power generation system can be equivalent to a single-stage photovoltaic power generation system, and the control is realized according to the power scheduling method of the single-stage photovoltaic power generation system.
  • the embodiments of the present application further provide a power control method of the photovoltaic power generation system, which will be described in detail below with reference to the accompanying drawings.
  • FIG. 7 is a flowchart of a power control method of a photovoltaic power generation system provided by an embodiment of the present application.
  • the power control method of the photovoltaic power generation system provided in this embodiment is applied to the photovoltaic power generation system provided by the above embodiment.
  • the system includes: an inverter and at least one combiner box; the combiner box includes a multi-channel DC-DC DC-DC circuit and A controller; the output terminals of the multi-channel DC-DC circuits in the combiner box are connected in parallel to the input terminals of the inverter; the input terminals of each DC-DC circuit are connected to the corresponding photovoltaic strings;
  • the method includes:
  • the methods provided in the embodiments of the present application are applicable to each combiner box, the controller of a single combiner box only needs to control the corresponding combiner box, and the photovoltaic power generation system may include a voltage detection circuit, which can collect the output voltage of the combiner box in real time.
  • the output voltage of the combiner box is greater than or equal to the first preset voltage and less than or equal to the second preset voltage, and the combiner box is controlled to output maximum power.
  • the second preset voltage is greater than the first preset voltage.
  • the maximum power is the sum of the maximum powers of all PV strings connected to the combiner box. That is, when the output voltage of the combiner box is in the voltage interval formed by the first preset voltage and the second preset voltage, the output power of the combiner box always outputs the maximum power.
  • the output voltage of the combiner box is greater than the second preset voltage, and the output power of the combiner box is controlled to decrease as the output voltage increases. That is, when the output voltage of the combiner box is greater than the second preset voltage, the output voltage of the combiner box presents a characteristic of monotonous droop.
  • the first preset voltage is greater than or equal to the maximum voltage corresponding to the maximum power point of all photovoltaic strings connected to the combiner box; the second preset voltage is greater than or equal to the DC bus voltage of the inverter.
  • the first preset voltage is greater than or equal to the maximum value of the voltage corresponding to the maximum power point of all photovoltaic strings connected to the combiner box. That is, the first preset voltage is not less than the maximum value of the voltage corresponding to the maximum power point of all photovoltaic strings connected to the combiner box. For example, if the combiner box is connected to 4 photovoltaic strings, the first preset voltage is greater than or equal to the maximum value of the voltage corresponding to the maximum power point of the 4 photovoltaic strings, that is, greater than or equal to the maximum value of the 4 voltages.
  • the second preset voltage is greater than or equal to the lowest DC voltage of the inverter in the linear modulation region, that is, greater than the DC bus voltage required by the inverter, that is, the peak line voltage at the AC output end of the inverter. Since the inverter has requirements for the DC bus voltage during operation, the second preset voltage can be set according to the DC bus voltage sent by the inverter.
  • the combiner box is virtualized as a photovoltaic source, so that it has a PV curve similar to that of a photovoltaic string, and then the output power is controlled according to the PV curve, without depending on the limit of the inverter. Therefore, it is not affected by the communication speed between the inverter and the combiner box, and can get rid of the limitation of the communication speed.
  • the combiner box can control its own output power by itself.
  • the embodiment of the present application does not specifically limit, when the output voltage of the combiner box is greater than the second preset voltage, the specific control method of the output power of the combiner box, as long as the output power of the combiner box decreases with the increase of the output voltage of the combiner box Small enough, it can be reduced proportionally or disproportionately.
  • the embodiments of the present application There is no specific limitation in the embodiments of the present application.
  • controller of the combiner box controls the output power of the combiner box to decrease as the output voltage increases, specifically including:
  • the output power of the combiner box is controlled to decrease with the increase of the output voltage; the open-circuit voltage of the combiner box is greater than that of all PV strings connected to the combiner box.
  • the maximum value of the open circuit voltage is the maximum value of the open circuit voltage.
  • the controller can specifically control the output power P out of the combiner box according to the output voltage of the combiner box, the open-circuit voltage of the combiner box and the second preset voltage according to the following formula. As the voltage increases, it decreases:
  • P outmax is the maximum power
  • u out is the output voltage of the combiner box
  • U mppt2 is the second preset voltage
  • U oc is the open-circuit voltage of the combiner box.
  • the power control method provided by the embodiment of the present application may further include: adjusting the output voltage of the corresponding photovoltaic string to adjust the output power of the combiner box. That is, the controller of the combiner box can adjust the output power of the combiner box by adjusting the output voltage of the photovoltaic string connected to the input end of the combiner box. Since the output voltage and output current of the photovoltaic string have a characteristic relationship of current-voltage curve, the controller of the combiner box can also change the output power by adjusting the input current of the combiner box.
  • an embodiment of the present application further provides a combiner box.
  • FIG. 8 this figure is a schematic diagram of a combiner box provided by an embodiment of the present application.
  • the combiner box provided in the embodiment of the present application may be the combiner box in any one of the above embodiments, including: a multi-channel DC-DC circuit and a controller 500 of the combiner box.
  • each DC-DC circuit is connected to the corresponding photovoltaic string.
  • the output terminals of the multiple DC-DC circuits are connected in parallel for connecting the input terminals of the inverter.
  • the controller 500 of the combiner box is used for the output voltage of the combiner box to be greater than or equal to the first preset voltage and less than or equal to the second preset voltage to control the combiner box to output maximum power; the maximum power is the maximum power of all photovoltaic strings connected to the combiner box
  • the second preset voltage is greater than the first preset voltage; the output voltage of the combiner box is greater than the second preset voltage, and the output power of the combiner box is controlled to decrease as the output voltage increases.
  • the combiner box provided in the embodiment of the present application is suitable for any combiner box. If the input end of the inverter is connected to multiple combiner boxes, each combiner box can use the above control method to realize its own output power. control. When the input end of the inverter is connected to multiple combiner boxes, to achieve the maximum power point tracking, as long as the virtual PV curves of the multiple combiner boxes have a common interval.
  • the embodiments of the present application do not limit the number of photovoltaic strings connected to the input end of the combiner box, which can be set according to power requirements, and multiple photovoltaic string strings are connected in parallel to the input end of the combiner box.
  • the output power of the combiner box provided by the embodiments of the present application exhibits a PV curve characteristic of the type of photovoltaic string, that is, when the output voltage of the combiner box is greater than the second preset voltage, the output power of the combiner box increases with the output voltage of the combiner box.
  • the increase shows a decreasing trend.
  • the controller of the combiner box can independently adjust the output power of the combiner box according to the PV curve characteristics, without relying on the power limit command sent by the inverter side, so it does not depend on the high speed between the inverter and the combiner box. Communication, even if the communication speed between the inverter and the combiner box is low, it does not affect the combiner box's control of its own output power.
  • the inverter can quickly realize power scheduling by adopting the power control method of the single-stage power conversion system. That is, when the combiner box looks at the PV source, the two-stage photovoltaic power generation system can be equivalent to a single-stage photovoltaic power generation system, and the control is realized according to the power scheduling method of the single-stage photovoltaic power generation system.
  • the first preset voltage is greater than or equal to the maximum value of the voltages corresponding to the maximum power points of all PV strings connected to the combiner box; for example, if N PV strings correspond to the voltages of the N maximum power points, the maximum value of the N voltages is taken. value. N is generally an integer greater than or equal to 2.
  • the second preset voltage is greater than or equal to the lowest DC voltage of the inverter in the linear modulation region, that is, greater than the DC bus voltage required by the inverter, that is, the peak line voltage at the AC output end of the inverter.
  • the DC bus voltage of the inverter is set according to the effective value of the voltage of the AC grid, which is greater than the line of the AC grid. RMS value of the voltage.
  • the controller 500 of the combiner box is specifically configured to control the output power of the combiner box to decrease with the increase of the output voltage according to the output voltage of the combiner box, the open circuit voltage of the combiner box and the second preset voltage; the open circuit voltage of the combiner box Greater than the maximum open-circuit voltage of all PV strings connected to the combiner box.
  • the combiner box provided in the embodiment of the present application can be virtualized as a photovoltaic PV source, so that its output voltage and output power have characteristics similar to the PV curve of a photovoltaic string, that is, droop characteristics.
  • the output power is the maximum power, that is, the fixed output maximum power.
  • the output power decreases with the increase of the output voltage, that is, the droop characteristic is presented.
  • the combiner box completes the control of its own output power independently, and does not need to rely on the control commands of the inverter. Therefore, it does not need to rely on the high-speed communication between the inverter and the combiner box.
  • the inverter's control of its own output power can be directly controlled according to the single-stage power conversion system, that is, the inverter can directly treat the combiner box as a photovoltaic input source.
  • the inverter can control its own output current to control its own output power.
  • At least one (item) refers to one or more, and "a plurality” refers to two or more.
  • “And/or” is used to describe the relationship between related objects, indicating that there can be three kinds of relationships, for example, “A and/or B” can mean: only A, only B, and both A and B exist , where A and B can be singular or plural.
  • the character “/” generally indicates that the associated objects are an “or” relationship.
  • At least one item(s) below” or similar expressions thereof refer to any combination of these items, including any combination of single item(s) or plural items(s).
  • At least one (a) of a, b or c can mean: a, b, c, "a and b", “a and c", “b and c", or "a and b and c" ", where a, b, c can be single or multiple.

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Abstract

本申请公开了一种光伏发电系统、功率控制方法及汇流箱，系统包括：逆变器和至少一个汇流箱；汇流箱包括多路直流-直流DC-DC电路和一个控制器；汇流箱内的多路DC-DC电路的输出端并联在一起连接逆变器的输入端；每路DC-DC电路的输入端连接对应的光伏组串；控制器用于汇流箱的输出电压大于等于第一预设电压小于等于第二预设电压，控制汇流箱输出最大功率；汇流箱的输出电压大于所述第二预设电压，控制汇流箱的输出功率随着输出电压的增大而减小；第二预设电压大于所述第一预设电压；最大功率为汇流箱连接的所有光伏组串的最大功率之和。汇流箱虚拟PV曲线，独立完成输出功率的调节，不依赖逆变器和汇流箱之间的高速通信。

Description

一种光伏发电系统、功率控制方法及汇流箱 技术领域
本申请涉及光伏发电技术领域，尤其涉及一种光伏发电系统、功率控制方法及汇流箱。
背景技术
目前，光伏发电系统主要包括单级功率变换模式和两级功率变换模式。其中单级功率变换模式是指光伏阵列的直流电经过直流-交流(DC-AC)电路变换为交流电，而两级功率变换模式是指光伏阵列的直流电经过直流-直流(DC-DC)电路进行第一级直流变换，再经过第二级DC-AC电路变换为交流电。
由于两级功率变换模式对于单级功率变换模式效率更高，因此，两级功率变换模式在光伏发电系统中的应用越来越广泛。
但是，由于两级功率变换模式中包括DC-DC电路和DC-AC电路，DC-DC电路和DC-AC电路之间的功率控制需要依赖两者之间的高速通信，当两者之间的通信速度较慢时，将影响功率控制。
发明内容
本申请提供了一种光伏发电系统及功率控制方法，能够使DC-DC电路和DC-AC电路之间进行快速的功率控制，而不必依赖于两者之间的高速通信。
本申请实施例提供一种光伏发电系统，包括：逆变器和至少一个汇流箱；汇流箱包括多路直流-直流DC-DC电路和一个控制器；汇流箱内的多路DC-DC电路的输出端并联在一起连接逆变器的输入端；每路DC-DC电路的输入端连接对应的光伏组串，一般汇流箱的输入端连接多路光伏组串；汇流箱的控制器，用于汇流箱的输出电压大于等于第一预设电压小于等于第二预设电压，控制汇流箱输出最大功率；汇流箱的输出电压大于第二预设电压，控制汇流箱的输出功率随着输出电压的增大而减小；第二预设电压大于第一预设电压；最大功率为汇流箱连接的所有光伏组串的最大功率之和。
一般情况下，第一预设电压大于等于汇流箱连接的所有光伏组串的最大功率点对应的电压的最大值；第二预设电压大于等于逆变器处于线性调制区的最低直流电压。即大于逆变器所需的直流母线电压，即逆变器交流输出端的线电压峰值。由于逆变器在工作时，对于直流母线电压是有要求的，因此，第二预设电压可以根据逆变器发送的直流母线电压来设置。
为了解决功率控制高度依赖于高速通信的技术问题，本申请实施例提供一种功率控制的方案，可以不依赖于高速通信，实现DC-DC电路的输出功率的控制，该方案不再依赖于逆变器的控制器发送的限功率指令，而是汇流箱独立实现自身输出功率的控制，对于逆变器来说，汇流箱可以看作光伏组串，即将汇流箱虚拟为光伏源，由于光伏组串具有输出功率-输出电压曲线，即PV曲线，因此，汇流箱的输出电压和输出功率也具有类似光伏组串的PV曲线的特性。汇流箱可以根据输出电压位于的区间来控制输出功率，从而摆脱逆变器的控制，不依赖于汇流箱与逆变器之间的高速通信，即使逆变器与汇流箱之间的通信速度较低也不影响汇流箱对输出功率的快速控制。
当汇流箱的输出电压大于第二预设电压时，汇流箱的输出功率的具体控制方式，只要 汇流箱的输出功率随着汇流箱的输出电压的增加而减小即可，可以成比例减小，也可以不成比例减小。本申请实施例中均不做具体限定。
在一种可能的实现方式中，汇流箱的控制器，具体用于根据汇流箱的输出电压、汇流箱的开路电压和第二预设电压控制汇流箱的输出功率随着输出电压的增大而减小；汇流箱的开路电压大于汇流箱连接的所有光伏组串的开路电压的最大值。
在一种可能的实现方式中，汇流箱的控制器，具体用于按照如下公式控制汇流箱的输出功率随着输出电压的增大而减小：
Figure PCTCN2020138170-appb-000001
其中，P outmax为最大功率；u out为汇流箱的输出电压，U mppt2为第二预设电压，U oc为汇流箱的开路电压。
在一种可能的实现方式中，汇流箱包括以下至少两个：第一汇流箱和第二汇流箱；
第一汇流箱的第二预设电压大于第二汇流箱的第一预设电压，第二汇流箱的第二预设电压大于第一汇流箱的第一预设电压。
在一种可能的实现方式中，汇流箱的控制器，用于调节对应光伏组串的输出电压来调节汇流箱的输出功率。
在一种可能的实现方式中，还包括：逆变器控制器；
逆变器控制器，用于根据限功率指令值控制逆变器的输出功率。
本申请实施例还提供一种光伏发电系统的功率控制方法，系统包括：逆变器和至少一个汇流箱；汇流箱包括多路直流-直流DC-DC电路和一个控制器；汇流箱内的多路DC-DC电路的输出端并联在一起连接逆变器的输入端；每路DC-DC电路的输入端连接对应的光伏组串；该方法包括：汇流箱的输出电压大于等于第一预设电压小于等于第二预设电压，控制汇流箱输出最大功率；汇流箱的输出电压大于第二预设电压，控制汇流箱的输出功率随着输出电压的增大而减小；第二预设电压大于第一预设电压；最大功率为汇流箱连接的所有光伏组串的最大功率之和。
在一种可能的实现方式中，第一预设电压大于等于汇流箱连接的所有光伏组串的最大功率点对应的电压的最大值；第二预设电压大于等于逆变器处于线性调制区的最低直流电压。
在一种可能的实现方式中，控制汇流箱的输出功率随着输出电压的增大而减小，具体包括：根据汇流箱的输出电压、汇流箱的开路电压和第二预设电压控制汇流箱的输出功率随着输出电压的增大而减小；汇流箱的开路电压大于汇流箱连接的所有光伏组串的开路电压的最大值。
在一种可能的实现方式中，具体按照如下公式控制汇流箱的输出功率随着输出电压的增大而减小：
Figure PCTCN2020138170-appb-000002
其中，P outmax为最大功率；u out为汇流箱的输出电压，U mppt2为第二预设电压，U oc为汇流箱的开路电压。
在一种可能的实现方式中，还包括：调节对应的光伏组串的输出电压来调节汇流箱的输出功率。
本申请实施例还提供一种汇流箱，包括：多路DC-DC电路和汇流箱的控制器；每路DC-DC电路的输入端连接对应的光伏组串；多路DC-DC电路的输出端并联在一起用于连接逆变器的输入端；汇流箱的控制器，用于汇流箱的输出电压大于等于第一预设电压小于等于第二预设电压，控制汇流箱输出最大功率；最大功率为汇流箱连接的所有光伏组串的最大功率之和；第二预设电压大于第一预设电压；汇流箱的输出电压大于第二预设电压，控制汇流箱的输出功率随着输出电压的增大而减小。
在一种可能的实现方式中，第一预设电压大于等于汇流箱连接的所有光伏组串的最大功率点对应的电压的最大值；第二预设电压大于等于逆变器处于线性调制区的最低直流电压；汇流箱的控制器，具体用于根据汇流箱的输出电压、汇流箱的开路电压和第二预设电压控制汇流箱的输出功率随着输出电压的增大而减小；汇流箱的开路电压大于汇流箱连接的所有光伏组串的开路电压的最大值。
从以上技术方案可以看出，本申请实施例具有以下优点：
本申请实施例对于汇流箱的输出功率的控制，不再依赖于逆变器的控制器发送的限功率指令，而是汇流箱独立实现输出功率的控制，对于逆变器来说，汇流箱可以看作光伏组串，即将汇流箱虚拟为光伏源，由于光伏组串具有输出功率-输出电压曲线，即PV曲线，因此，汇流箱的输出电压和输出功率也具有类似光伏组串的PV曲线的特性。当汇流箱的输出电压大于等于第一预设电压小于等于第二预设电压，控制所述汇流箱输出最大功率。最大功率为汇流箱连接的所有光伏组串的最大功率之和。当汇流箱的输出电压大于所述第二预设电压，控制汇流箱的输出功率随着输出电压的增大而减小，即呈现下垂的特性。汇流箱可以根据输出电压位于的区间来控制输出功率，从而摆脱逆变器的控制，不依赖于汇流箱与逆变器之间的高速通信，即使逆变器与汇流箱之间的通信速度较低也不影响汇流箱对输出功率的快速控制。
附图说明
图1为本申请实施例提供的一种光伏发电系统的示意图；
图2为本申请实施例提供的一种光伏组串的PV曲线示意图；
图3为本申请实施例提供的另一种光伏发电系统的示意图；
图4为本申请实施例提供的一种汇流箱的PV曲线示意图；
图5为本申请实施例提供的又一种光伏发电系统的示意图；
图6为本申请实施例提供的一种多个汇流箱的PV曲线示意图；
图7为本申请实施例提供的一种光伏发电系统的功率控制方法流程图；
图8为本申请实施例提供的一种汇流箱的示意图。
具体实施方式
以下说明中的“第一”、“第二”等用词仅用于描述目的，而不能理解为指示或暗示相对重要性或者隐含指明所指示的技术特征的数量。由此，限定有“第一”、“第二”等的特征可以明示或者隐含地包括一个或者更多该特征。在本申请的描述中，除非另有说明， “多个”的含义是两个或两个以上。
此外，本申请中，“上”、“下”等方位术语可以包括但不限于相对附图中的部件示意置放的方位来定义的，应当理解到，这些方向性术语可以是相对的概念，它们用于相对于的描述和澄清，其可以根据附图中部件附图所放置的方位的变化而相应地发生变化。
在本申请中，除非另有明确的规定和限定，术语“连接”应做广义理解，例如，“连接”可以是固定连接，也可以是可拆卸连接，或成一体；可以是直接相连，也可以通过中间媒介间接相连。此外，术语“耦接”可以是实现信号传输的电性连接的方式。“耦接”可以是直接的电性连接，也可以通过中间媒介间接电性连接。
系统实施例
为了使本领域技术人员更好地理解本申请实施例提供的技术方案，下面介绍本申请实施例提供的两级式光伏发电系统。
参见图1，该图为本申请实施例提供的一种光伏发电系统的示意图。
本申请实施例中以光伏发电系统输出的三相交流电为例进行介绍。
该光伏发电系统包括：光伏阵列PV、DC-DC电路100和DC-AC电路200。
其中，DC-DC电路100的输入端连接光伏阵列PV，DC-AC电路200的输入端连接DC-DC电路100的输出端。
本申请实施例中不具体限定DC-DC电路100的具体实现形式，例如可以包括升压电路、降压电路或者升降压电路。
一种实现方式是，DC-AC电路200的输入端连接多路DC-DC路100，多路DC-DC路100的输出端并联在一起，多路DC-DC路100集成在一个机柜中，例如可以集成在汇流箱中。DC-AC电路200集成在逆变器中。
实际工作中，DC-DC电路100一般不工作在最大功率点，而是根据逆变器的控制器发送的限功率指令来控制其输出功率，即大部分情况输出功率比最大功率小，工作在限功率状态。其中，逆变器的控制器位于DC-AC电路200的一侧，一般情况下，逆变器和汇流箱之间的距离比较远，DC-DC电路100的工作需要受控于控制器的指令，例如，DC-DC电路根据控制器的限功率指令来调节输出功率。控制器发送给DC-DC电路100的信号依赖于高速通信，当DC-DC电路100和控制器之间的通信速度较慢时，将严重影响DC-DC电路100的响应速度，因此，无法及时输出限功率指令对应的功率。
图1仅是示意，实际工作时，DC-AC电路200的输入端可以连接多路DC-DC电路的输出端，即多路DC-DC电路的输出端并联在一起，每路DC-DC电路的输入端连接自身对应的光伏组串，为了提高功率，每路DC-DC电路的输入端可以连接多个并联在一起的光伏组串。
为了解决功率控制高度依赖于高速通信的技术问题，本申请实施例提供一种功率控制的方案，可以不依赖于高速通信，实现DC-DC电路100输出功率的控制。
本申请实施例对于汇流箱的输出功率的控制，不再依赖于逆变器的控制器发送的限功率指令，而是汇流箱独立实现输出功率的控制，对于逆变器来说，汇流箱可以看作光伏组串，即将汇流箱虚拟为光伏源，由于光伏组串具有输出功率-输出电压曲线，即PV曲线， 如图2所示，该图为本申请实施例提供的一种光伏组串的PV曲线示意图。
图2中的横坐标为光伏组串的输出电压，纵坐标为光伏组串的输出功率。
从图2上可以看出，PV曲线具有下垂特性，即过了最大功率点S以外，随着输出电压的增大，输出功率会下降。汇流箱按照虚拟的PV曲线来实现输出功率的控制，从而不依赖于逆变器侧发送的限功率指令，从而不依赖于汇流箱和逆变器之间的高速通信，摆脱高速通信带来的影响。
下面结合附图详细介绍本申请实施例提供的光伏发电系统。
参见图3，该图为本申请实施例提供的另一种光伏发电系统的示意图。
为了方便理解和描述，本申请实施例中以汇流箱包括至少两路DC-DC电路为例进行介绍。具体实现时，可以根据实际需要来设置DC-DC电路的数量。
需要说明的是，直流母线电压是指汇流箱的输出电压，即逆变器的输入电压。
本申请实施例中以汇流箱具有最大功率点跟踪(MPPT，Maximum Power Point Tracking)功能为例进行介绍。应该理解，该汇流箱也可以不具有MPPT功能，本申请实施例中均不做具体限定。
本申请实施例提供的光伏发电系统包括：逆变器400和至少一个MPPT汇流箱200；汇流箱200包括多路直流-直流DC-DC电路和一个控制器(图中未示出)；汇流箱内的多路DC-DC电路的输出端并联在一起连接所述逆变器的输入端；每路所述DC-DC电路的输入端连接对应的光伏组串。
图3中以汇流箱至少包括以下两路DC-DC电路为例进行介绍，即第一DC-DC电路200a和第二DC-DC电路200b。第一DC-DC电路200a的输入端连接对应的光伏组串100a和光伏组串100b。第二DC-DC电路200b的输入端连接对应的光伏组串。本申请实施例中不限定DC-DC电路的输入端连接的光伏组串的数量，所有光伏组串可以并联后连接在DC-DC电路的输入端。
汇流箱的控制器根据输出电压来控制输出功率，具体用于在汇流箱的输出电压大于等于第一预设电压小于等于第二预设电压时，控制汇流箱输出最大功率；其中最大功率为汇流箱连接的所有光伏组串的最大功率之和。在汇流箱的输出电压大于第二预设电压时，控制汇流箱的输出功率随着输出电压的增大而减小；其中第二预设电压大于第一预设电压；
为了使本领域技术人员更好地理解本申请实施例介绍的技术方案，下面结合曲线图介绍第一预设电压和第二预设电压。
参见图4，该图为本申请实施例提供的一种汇流箱的PV曲线示意图。
为了方便理解，图4中，以一个汇流箱包括一路DC-DC电路，一路DC-DC电路的输入端连接一个光伏组串为例进行介绍。
图4中曲线M为汇流箱的输入PV曲线，曲线N为汇流箱的输出PV曲线。由于汇流箱的输入端连接光伏组串，即曲线M即为光伏组串的PV曲线。
为了使光伏组串和汇流箱均工作在稳定状态，即汇流箱的输出电压区间为大于等于第一预设电压，即图4中大于Umppt1。
其中，第一预设电压大于等于汇流箱连接的所有光伏组串的最大功率点对应的电压的 最大值。即第一预设电压不小于汇流箱连接的所有光伏组串的最大功率点对应的电压的最大值。例如汇流箱连接4个光伏组串，则第一预设电压大于等于4个光伏组串的最大功率点对应的电压的最大值，即大于等于4个电压中的最大值。
第二预设电压Umppt2大于等于逆变器处于线性调制区的最低直流电压，即大于逆变器所需的直流母线电压，即逆变器交流输出端的线电压峰值。由于逆变器在工作时，对于直流母线电压是有要求的，因此，第二预设电压可以根据逆变器发送的直流母线电压来设置。
图4中的Uoc为汇流箱虚拟的PV曲线的对应的开路电压。汇流箱的开路电压Uoc需要大于汇流箱连接的所有光伏组串的开路电压的最大值。例如，继续以汇流箱的输入端连接4个光伏组串为例，汇流箱的Uoc要大于4个光伏组串的开路电压的最大值。
从图4可以看出，汇流箱的PV曲线存在一段直线的阶段，即输出电压位于Umppt1和Umppt2之间时，汇流箱的输出功率为一个定值，即最大功率。最大功率为汇流箱连接的所有光伏组串的最大功率之和。例如，汇流箱连接4个光伏组串，则最大功率为4个光伏组串的最大功率点对应的功率之和。
当汇流箱的输出电压大于Umppt2时，汇流箱的输出功率随着输出电压呈现单调减小的趋势。
本申请实施例并不限定输出功率随着输出电压呈现单调减小的趋势，例如可以与输入端的光伏组串的单调减小趋势相同，也可以为一个线性的单调减小的比例下降，也可以为类似抛物线的下降，只要保证单调下降即可。
下面提供一种可能的单调下降的实现方式，例如汇流箱的控制器，具体用于根据汇流箱的输出电压、汇流箱的开路电压和第二预设电压控制汇流箱的输出功率随着输出电压的增大而减小；
汇流箱的控制器具体用于按照如下公式根据汇流箱的输出电压、汇流箱的开路电压和第二预设电压控制汇流箱的输出功率随着输出电压的增大而减小：
Figure PCTCN2020138170-appb-000003
其中P out为汇流箱的输出功率，P outmax为最大功率；u out为汇流箱的输出电压，U mppt2为第二预设电压，U oc为汇流箱的开路电压。
从以上公式可以看出，汇流箱的输出电压越大，则汇流箱的输出功率越小。
以上公式仅是一种示例，也可以是以上公式的其他简单变型，只要保证汇流箱的输出功率随着输出电压的增大而呈现减小的趋势即可。
由以上分析可知，本申请实施例提供的技术方案，汇流箱对于自身输出功率的控制，并不依赖于逆变器侧发送的限功率指令，而是时刻根据自身的输出电压来控制自身的输出功率。
具体实现时，汇流箱的控制器可以通过调节自身输入端连接的光伏组串的输出电压来调节汇流箱的输出功率。由于光伏组串的输出电压变化时将影响自身的输出功率，即满足PV曲线的特性，而在忽略功率损耗的情况下，光伏组串的输出功率便为汇流箱的输入功率，汇流箱的输入功率等于汇流箱的输出功率。
而对于逆变器的输出功率的控制，由逆变器自身来实现，即逆变器控制器用于根据光伏发电系统需求的功率控制自身的输出功率。即逆变器直接控制自身的输出功率，而不必再向汇流箱发送限功率指令，由汇流箱来调节自身的输出功率，因此可以摆脱逆变器和汇流箱之间的通信速度的影响。本申请实施例中，汇流箱对自身输出功率的控制也可以在低速通信下实现。逆变器的输出功率本质来源于汇流箱的输出功率，因此，逆变器的输出功率在图4中是与横轴平行的一条直线，该直线与汇流箱的PV曲线存在交点，交点便为逆变器的限功率点。
以上实施例中，仅是以一个汇流箱为例进行的介绍，下面介绍逆变器的输入端连接至少两个汇流箱的情况。
参见图5，该图为本申请实施例提供的又一种光伏发电系统的示意图。
图5中可以两个汇流箱为例进行介绍，继续以MPPT汇流箱为例，应该理解，逆变器400的输入端可以连接更多数量的汇流箱。图5中的两个汇流箱分别为第一MPPT汇流箱200A和第二MPPT汇流箱200B。
第一MPPT汇流箱200A至少包括两个DC-DC变换电路，即第一DC-DC变换电路200a和第二DC-DC变换电路200b。第一DC-DC变换电路200a的输入端连接对应的光伏组串100a和光伏组串100b，一般情况下，光伏组串100a和光伏组串100b并联在第一DC-DC变换电路200a的输入端。同理，第二DC-DC变换电路200b连接自身对应的光伏组串。
第二MPPT汇流箱200B至少包括两个DC-DC变换电路，即第三DC-DC变换电路200c和第四DC-DC变换电路200d。第三DC-DC变换电路200c的输入端连接对应的光伏组串100c和光伏组串100d，一般情况下，光伏组串100c和光伏组串100d并联在第三DC-DC变换电路200c的输入端。同理，第四DC-DC变换电路200d连接自身对应的光伏组串。
当逆变器的输入端连接多个汇流箱时，多个汇流箱的最大功率存在公共区间，从而实现多个汇流箱的最大功率点跟踪。因此，为了使多个汇流箱的最大功率存在公共区间，继续以两个汇流箱为例，需要第一汇流箱的第二预设电压大于第二汇流箱的第一预设电压，第二汇流箱的第二预设电压大于第一汇流箱的第一预设电压，即每个汇流箱的第二预设电压需要大于所有汇流箱的第一预设电压，才能保证所有汇流箱的最大功率存在公共区间。
为了本领域技术人员更好地理解多个汇流箱的PV曲线的最大功率存在公共区间，可以参见图6，该图为本申请实施例提供的一种多个汇流箱的PV曲线示意图。
从图6可以看出，曲线N1、N2和N3分别代表三个不同汇流箱的PV曲线。
N1、N2和N3的最大功率区间存在公共MPPT区间，图6中未标号的三条曲线分别是三个汇流箱输入端连接的光伏组串的PV曲线。由于N1、N2和N3的最大功率区间均为一段直线，因此，只要三段直线存在公共交叠部分即可实现三个汇流箱的最大功率跟踪。当逆变器的输入端连接三个汇流箱时，最大功率为三个汇流箱的最大功率之和。
例如N1的最大功率区间对应的第一预设电压和第二预设电压分别为1000V和1150V，N2的最大功率区间对应第一预设电压和第二预设电压分别为1050V和1200V，则N1和N2重合最大功率对应的电压区间为1050V至1150V。
本申请实施例提供的光伏发电系统，将汇流箱虚拟为类似光伏电池板的输出功率下垂 特性，从汇流箱后级连接的逆变器角度来看，汇流箱可以被视为新的光伏组串，进而能够在不依赖高速通信的情况下实现汇流箱的输出功率的快速调度。本申请实施例可以将每个汇流箱视为一个光伏源，多个汇流箱时，设置多个汇流箱存在最大功率区间即可实现多个汇流箱的功率控制。而对于逆变器来说，逆变器可以采用单级功率变换式系统的功率控制方式来快速实现功率调度。即当汇流箱看着PV源时，两级式光伏发电系统可以等效为单级光伏发电系统，按照单级光伏发电系统的功率调度方式来实现控制。
方法实施例
基于以上实施例提供的一种光伏发电系统，本申请实施例还提供一种光伏发电系统的功率控制方法，下面结合附图进行详细介绍。
参见图7，该图为本申请实施例提供的一种光伏发电系统的功率控制方法流程图。
本实施例提供的光伏发电系统的功率控制方法，应用于以上实施例提供的光伏发电系统，该系统包括：逆变器和至少一个汇流箱；汇流箱包括多路直流-直流DC-DC电路和一个控制器；汇流箱内的多路DC-DC电路的输出端并联在一起连接逆变器的输入端；每路DC-DC电路的输入端连接对应的光伏组串；
该方法包括：
S701：获得汇流箱的输出电压。
本申请实施例提供的方法适用于每个汇流箱，单个汇流箱的控制器实现对应汇流箱的控制即可，光伏发电系统可以包括电压检测电路，可以实时采集汇流箱的输出电压。
S702：汇流箱的输出电压大于等于第一预设电压小于等于第二预设电压，控制汇流箱输出最大功率。第二预设电压大于第一预设电压。最大功率为汇流箱连接的所有光伏组串的最大功率之和。即汇流箱的输出电压位于第一预设电压和第二预设电压形成的电压区间时，汇流箱的输出功率一直输出最大功率。
S703：汇流箱的输出电压大于第二预设电压，控制汇流箱的输出功率随着输出电压的增大而减小。即当汇流箱的输出电压大于第二预设电压时，汇流箱的输出电压呈现单调下垂的特征。
一种可能的实现方式，第一预设电压大于等于汇流箱连接的所有光伏组串的最大功率点对应的电压的最大值；第二预设电压大于等于逆变器的直流母线电压。
其中，第一预设电压大于等于汇流箱连接的所有光伏组串的最大功率点对应的电压的最大值。即第一预设电压不小于汇流箱连接的所有光伏组串的最大功率点对应的电压的最大值。例如汇流箱连接4个光伏组串，则第一预设电压大于等于4个光伏组串的最大功率点对应的电压的最大值，即大于等于4个电压中的最大值。
第二预设电压大于等于逆变器处于线性调制区的最低直流电压，即大于逆变器所需的直流母线电压，即逆变器交流输出端的线电压峰值。由于逆变器在工作时，对于直流母线电压是有要求的，因此，第二预设电压可以根据逆变器发送的直流母线电压来设置。
本申请实施例提供的光伏发电系统，将汇流箱虚拟为光伏源，使其具有与光伏组串类似的PV曲线，进而按照该PV曲线进行输出功率的控制，而不必依赖于逆变器的限功率指令来控制，因此，不受逆变器和汇流箱之间的通信速度的影响，可以摆脱通信速度的限制， 汇流箱独自完成自身输出功率的控制。
本申请实施例中不具体限定，当汇流箱的输出电压大于第二预设电压时，汇流箱的输出功率的具体控制方式，只要汇流箱的输出功率随着汇流箱的输出电压的增加而减小即可，可以成比例减小，也可以不成比例减小。本申请实施例中均不做具体限定。
一种可能的实现方式为，汇流箱的控制器控制汇流箱的输出功率随着输出电压的增大而减小，具体包括：
根据汇流箱的输出电压、汇流箱的开路电压和第二预设电压控制汇流箱的输出功率随着输出电压的增大而减小；汇流箱的开路电压大于汇流箱连接的所有光伏组串的开路电压的最大值。
当汇流箱的输出电压大于第二预设电压时，控制器具体可以按照如下公式根据汇流箱的输出电压、汇流箱的开路电压和第二预设电压控制汇流箱的输出功率P out随着输出电压的增大而减小：
Figure PCTCN2020138170-appb-000004
其中，P outmax为最大功率；u out为汇流箱的输出电压，U mppt2为第二预设电压，U oc为汇流箱的开路电压。
本申请实施例提供的功率控制方法，还可以包括：调节对应的光伏组串的输出电压来调节汇流箱的输出功率。即汇流箱的控制器可以通过调节汇流箱的输入端连接的光伏组串的输出电压来调节汇流箱的输出功率。由于光伏组串的输出电压和输出电流存在电流-电压曲线的特性关系，因此，汇流箱的控制器也可以通过调节汇流箱的输入电流来改变输出功率。
以上光伏发电系统实施例中介绍的所有内容适用于本实施例介绍的功率控制方法，重复的部分在此不再赘述。
汇流箱实施例
基于以上实施例提供的光伏发电系统和功率控制方法，本申请实施例还提供一种汇流箱。下面结合附图进行详细介绍。
参见图8，该图为本申请实施例提供的一种汇流箱的示意图。
本申请实施例提供的汇流箱可以为以上任意一个实施例中的汇流箱，包括：多路DC-DC电路和汇流箱的控制器500。
每路DC-DC电路的输入端连接对应的光伏组串。
多路DC-DC电路的输出端并联在一起用于连接逆变器的输入端。
汇流箱的控制器500，用于汇流箱的输出电压大于等于第一预设电压小于等于第二预设电压，控制汇流箱输出最大功率；最大功率为汇流箱连接的所有光伏组串的最大功率之和；第二预设电压大于第一预设电压；汇流箱的输出电压大于第二预设电压，控制汇流箱的输出功率随着输出电压的增大而减小。
需要说明的是，本申请实施例提供的汇流箱适用于任意一个汇流箱，如果逆变器的输入端连接多个汇流箱，则每个汇流箱均可以采用以上的控制方式来实现自身输出功率的控制。当逆变器的输入端连接多个汇流箱时，实现最大功率点追踪时，只要多个汇流箱虚拟 的PV曲线存在公共区间即可。
本申请实施例不限定汇流箱的输入端连接的光伏组串的数量，可以根据功率需求来设置，多个光伏组串并联在汇流箱的输入端。
本申请实施例提供的汇流箱的输出功率呈现与光伏组串类型的PV曲线特性，即当汇流箱的输出电压大于第二预设电压时，汇流箱的输出功率随着汇流箱的输出电压的增加呈现递减的趋势。汇流箱的控制器独立可以根据该PV曲线特性完成对汇流箱的输出功率的调节，而不必依赖逆变器侧发送的限功率指令，因此，不依赖于逆变器和汇流箱之间的高速通信，即使逆变器和汇流箱之间的通信速度较低，也不影响汇流箱对自身输出功率的控制。而对于逆变器来说，逆变器可以采用单级功率变换式系统的功率控制方式来快速实现功率调度。即当汇流箱看着PV源时，两级式光伏发电系统可以等效为单级光伏发电系统，按照单级光伏发电系统的功率调度方式来实现控制。
第一预设电压大于等于汇流箱连接的所有光伏组串的最大功率点对应的电压的最大值；例如，N个光伏组串对应N个最大功率点的电压，则取N个电压中的最大值。N一般为大于等于2的整数。第二预设电压大于等于逆变器处于线性调制区的最低直流电压，即大于逆变器所需的直流母线电压，即逆变器交流输出端的线电压峰值。逆变器工作时，一般对直流母线电压有要求，例如逆变器的输出端连接交流电网，则逆变器的直流母线电压根据交流电网的电压的有效值来设置，要大于交流电网的线电压的有效值。
汇流箱的控制器500，具体用于根据汇流箱的输出电压、汇流箱的开路电压和第二预设电压控制汇流箱的输出功率随着输出电压的增大而减小；汇流箱的开路电压大于汇流箱连接的所有光伏组串的开路电压的最大值。
以上光伏发电系统实施例中介绍的所有内容适用于本实施例介绍的汇流箱，重复的部分在此不再赘述。
本申请实施例提供的汇流箱可以虚拟为光伏PV源，使其输出电压和输出功率具有类似光伏组串的PV曲线的特性，即下垂特性。输出电压在一定区间内时，输出功率为最大功率，即固定输出最大功率。当输出电压大于该区间时，则输出功率随着输出电压的增大而减小，即呈现下垂特性。汇流箱独自完成对自身输出功率的控制，而不需要依赖于逆变器的控制指令，因此，不需要依赖于逆变器与汇流箱之间的高速通信。即使逆变器和汇流箱之间的通信速度较低，也不影响汇流箱对自身输出功率的控制。而逆变器对自身输出功率的控制，可以直接按照单级功率变换系统进行控制即可，即逆变器将汇流箱直接视为光伏输入源进行即可。逆变器可以控制自身的输出电流来控制自身的输出功率。
应当理解，在本申请中，“至少一个(项)”是指一个或者多个，“多个”是指两个或两个以上。“和/或”，用于描述关联对象的关联关系，表示可以存在三种关系，例如，“A和/或B”可以表示：只存在A，只存在B以及同时存在A和B三种情况，其中A，B可以是单数或者复数。字符“/”一般表示前后关联对象是一种“或”的关系。“以下至少一项(个)”或其类似表达，是指这些项中的任意组合，包括单项(个)或复数项(个)的任意组合。例如，a，b或c中的至少一项(个)，可以表示：a，b，c，“a和b”，“a和c”，“b和c”，或“a和b和c”，其中a，b，c可以是单个，也可以是多个。
以上所述，以上实施例仅用以说明本申请的技术方案，而非对其限制；尽管参照前述实施例对本申请进行了详细的说明，本领域的普通技术人员应当理解：其依然可以对前述各实施例所记载的技术方案进行修改，或者对其中部分技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本申请各实施例技术方案的精神和范围。

Claims (14)

  1. 一种光伏发电系统，其特征在于，包括：逆变器和至少一个汇流箱；所述汇流箱包括多路直流-直流DC-DC电路和一个控制器；
    所述汇流箱内的多路DC-DC电路的输出端并联在一起连接所述逆变器的输入端；
    每路所述DC-DC电路的输入端连接对应的光伏组串；
    所述汇流箱的控制器，用于所述汇流箱的输出电压大于等于第一预设电压小于等于第二预设电压，控制所述汇流箱输出最大功率；所述汇流箱的输出电压大于所述第二预设电压，控制所述汇流箱的输出功率随着所述输出电压的增大而减小；所述第二预设电压大于所述第一预设电压；所述最大功率为所述汇流箱连接的所有所述光伏组串的最大功率之和。
  2. 根据权利要求1所述的系统，其特征在于，所述第一预设电压大于等于所述汇流箱连接的所有所述光伏组串的最大功率点对应的电压的最大值；所述第二预设电压大于等于所述逆变器处于线性调制区的最低直流电压。
  3. 根据权利要求1或2所述的系统，其特征在于，所述汇流箱的控制器，具体用于根据所述汇流箱的输出电压、所述汇流箱的开路电压和所述第二预设电压控制所述汇流箱的输出功率随着所述输出电压的增大而减小；所述汇流箱的开路电压大于所述汇流箱连接的所有光伏组串的开路电压的最大值。
  4. 根据权利要求3所述的系统，其特征在于，所述汇流箱的控制器，具体用于按照如下公式控制所述汇流箱的输出功率随着所述输出电压的增大而减小：
    Figure PCTCN2020138170-appb-100001
    其中，P outmax为所述最大功率；u out为所述汇流箱的输出电压，U mppt2为所述第二预设电压，U oc为所述汇流箱的开路电压。
  5. 根据权利要求1所述的系统，其特征在于，所述汇流箱包括以下至少两个：第一汇流箱和第二汇流箱；
    所述第一汇流箱的所述第二预设电压大于所述第二汇流箱的所述第一预设电压，所述第二汇流箱的所述第二预设电压大于所述第一汇流箱的所述第一预设电压。
  6. 根据权利要求1-5任一项所述的系统，其特征在于，所述汇流箱的控制器，用于调节对应所述光伏组串的输出电压来调节所述汇流箱的输出功率。
  7. 根据权利要求1-6任一项所述的系统，其特征在于，还包括：逆变器控制器；
    所述逆变器控制器，用于根据限功率指令值控制所述逆变器的输出功率。
  8. 一种光伏发电系统的功率控制方法，其特征在于，所述系统包括：逆变器和至少一个汇流箱；所述汇流箱包括多路直流-直流DC-DC电路和一个控制器；所述汇流箱内的多路DC-DC电路的输出端并联在一起连接所述逆变器的输入端；每路所述DC-DC电路的输入端连接对应的光伏组串；
    该方法包括：
    所述汇流箱的输出电压大于等于第一预设电压小于等于第二预设电压，控制所述汇流箱输出最大功率；
    所述汇流箱的输出电压大于所述第二预设电压，控制所述汇流箱的输出功率随着所述 输出电压的增大而减小；
    所述第二预设电压大于所述第一预设电压；所述最大功率为所述汇流箱连接的所有所述光伏组串的最大功率之和。
  9. 根据权利要求8所述的方法，其特征在于，所述第一预设电压大于等于所述汇流箱连接的所有所述光伏组串的最大功率点对应的电压的最大值；所述第二预设电压大于等于所述逆变器处于线性调制区的最低直流电压。
  10. 根据权利要求8或9所述的方法，其特征在于，所述控制所述汇流箱的输出功率随着所述输出电压的增大而减小，具体包括：
    根据所述汇流箱的输出电压、所述汇流箱的开路电压和所述第二预设电压控制所述汇流箱的输出功率随着所述输出电压的增大而减小；所述汇流箱的开路电压大于所述汇流箱连接的所有光伏组串的开路电压的最大值。
  11. 根据权利要求10所述的方法，其特征在于，具体按照如下公式控制所述汇流箱的输出功率随着所述输出电压的增大而减小：
    Figure PCTCN2020138170-appb-100002
    其中，P outmax为所述最大功率；u out为所述汇流箱的输出电压，U mppt2为所述第二预设电压，U oc为所述汇流箱的开路电压。
  12. 根据权利要求8-11任一项所述的方法，其特征在于，还包括：调节对应的光伏组串的输出电压来调节所述汇流箱的输出功率。
  13. 一种汇流箱，其特征在于，包括：多路DC-DC电路和汇流箱的控制器；
    每路所述DC-DC电路的输入端连接对应的光伏组串；
    所述多路DC-DC电路的输出端并联在一起用于连接逆变器的输入端；
    所述汇流箱的控制器，用于所述汇流箱的输出电压大于等于第一预设电压小于等于第二预设电压，控制所述汇流箱输出最大功率；所述最大功率为所述汇流箱连接的所有所述光伏组串的最大功率之和；所述第二预设电压大于所述第一预设电压；所述汇流箱的输出电压大于所述第二预设电压，控制所述汇流箱的输出功率随着所述输出电压的增大而减小。
  14. 根据权利要求13所述的汇流箱，其特征在于，所述第一预设电压大于等于所述汇流箱连接的所有所述光伏组串的最大功率点对应的电压的最大值；所述第二预设电压大于等于所述逆变器处于线性调制区的最低直流电压；
    所述汇流箱的控制器，具体用于根据所述汇流箱的输出电压、所述汇流箱的开路电压和所述第二预设电压控制所述汇流箱的输出功率随着所述输出电压的增大而减小；所述汇流箱的开路电压大于所述汇流箱连接的所有光伏组串的开路电压的最大值。
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