A photovoltaic power generation system, a power control method and a busbar box

Abstract

The present application discloses a photovoltaic power generation system, a power control method and a busbar box. The system includes: an inverter and at least one busbar box; the busbar box includes a plurality of DC-DC circuits and a controller; the output ends of the plurality of DC-DC circuits in the busbar box are connected in parallel to the input end of the inverter; the input end of each DC-DC circuit is connected to a corresponding photovoltaic string; the controller is used to control the busbar box to output the maximum power when the output voltage of the busbar box is greater than or equal to a first preset voltage and less than or equal to a second preset voltage; when the output voltage of the busbar box is greater than the second preset voltage, control the output power of the busbar box to decrease as the output voltage increases; the second preset voltage is greater than the first preset voltage; the maximum power is the sum of the maximum powers of all the photovoltaic strings connected to the busbar box. The busbar box has a virtual PV curve and independently completes the adjustment of the output power without relying on the high-speed communication between the inverter and the busbar box.

Description

Technical Field

[0001] The present application relates to the technical field of photovoltaic power generation, and particularly to a photovoltaic power generation system, a power control method, and a busbar box. Background Art

[0002] At present, photovoltaic power generation systems mainly include a single-stage power conversion mode and a two-stage power conversion mode. Among them, the single-stage power conversion mode means that the direct current of a photovoltaic array is converted into alternating current through a direct current - alternating current (DC - AC) circuit, and the two-stage power conversion mode means that the direct current of a photovoltaic array undergoes a first-stage direct current conversion through a direct current - direct current (DC - DC) circuit and then is converted into alternating current through a second-stage DC - AC circuit.

[0003] Since the two-stage power conversion mode is more efficient than the single-stage power conversion mode, the two-stage power conversion mode is increasingly widely used in photovoltaic power generation systems.

[0004] However, since 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 between the two is slow, the power control will be affected. Summary of the Invention

[0005] The present application provides a photovoltaic power generation system and a power control method, which can enable rapid power control between a DC - DC circuit and a DC - AC circuit without relying on high-speed communication between the two.

[0006] An embodiment of the present application provides a photovoltaic power generation system, including: an inverter and at least one busbar box; the busbar box includes a plurality of direct current - direct current (DC - DC) circuits and a controller; the output ends of the plurality of DC - DC circuits in the busbar box are connected in parallel to the input end of the inverter; the input end of each DC - DC circuit is connected to a corresponding photovoltaic string, and generally the input end of the busbar box is connected to a plurality of photovoltaic strings; the controller of the busbar box is configured to control the busbar box to output the maximum power when the output voltage of the busbar box is greater than or equal to a first preset voltage and less than or equal to a second preset voltage; when the output voltage of the busbar box is greater than the second preset voltage, control the output power of the busbar box to decrease as the output voltage increases; the second preset voltage is greater than the first preset voltage; the maximum power is the sum of the maximum powers of all the photovoltaic strings connected to the busbar box.

[0007] Generally, the first preset voltage is greater than or equal to the maximum value of the voltages corresponding to the maximum power points of all the photovoltaic strings connected to the combiner box; the second preset voltage is greater than or equal to the lowest DC voltage when the inverter is in the linear modulation region. That is, it is greater than the DC bus voltage required by the inverter, which 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, therefore, the second preset voltage can be set according to the DC bus voltage sent by the inverter.

[0008] To solve the technical problem that power control highly depends on high-speed communication, the embodiments of the present application provide a power control solution that can control the output power of the DC-DC circuit without relying on high-speed communication. This solution no longer depends on the power limit instruction sent by the controller of the inverter, but the combiner box independently realizes the control of its own output power. For the inverter, the combiner box can be 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, therefore, the output voltage and output power of the combiner box also have characteristics similar to the PV curve of the photovoltaic string. The combiner box can control the output power according to the interval where 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 low, it does not affect the fast control of the output power by the combiner box.

[0009] When the output voltage of the combiner box is greater than the second preset voltage, for the specific control method of the output power of the combiner box, as long as the output power of the combiner box decreases as the output voltage of the combiner box increases, it can decrease proportionally or non-proportionally. No specific limitation is made in the embodiments of the present application.

[0010] In a possible implementation manner, 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 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 is greater than the maximum value of the open-circuit voltages of all the photovoltaic strings connected to the combiner box.

[0011] In a possible implementation manner, 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:

[0012]

[0013] where P outmax is the maximum power; u out is the output voltage of the combiner box, U mppt2 is the second preset voltage, and U oc is the open-circuit voltage of the combiner box.

[0014] In a possible implementation, the busbar box includes at least two of the following: a first busbar box and a second busbar box;

[0015] The second preset voltage of the first busbar box is greater than the first preset voltage of the second busbar box, and the second preset voltage of the second busbar box is greater than the first preset voltage of the first busbar box.

[0016] In a possible implementation, the controller of the busbar box is configured to adjust the output power of the busbar box by adjusting the output voltage of the corresponding photovoltaic string.

[0017] In a possible implementation, it further includes: an inverter controller;

[0018] The inverter controller is configured to control the output power of the inverter according to the power limit command value.

[0019] The embodiment of the present application further provides a power control method for a photovoltaic power generation system. The system includes: an inverter and at least one busbar box; the busbar box includes multiple DC-DC circuits and a controller; the output ends of the multiple DC-DC circuits in the busbar box 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; the method includes: when the output voltage of the busbar box is greater than or equal to the first preset voltage and less than or equal to the second preset voltage, controlling the busbar box to output the maximum power; when the output voltage of the busbar box is greater than the second preset voltage, controlling the output power of the busbar box to decrease as the output voltage increases; the second preset voltage is greater than the first preset voltage; the maximum power is the sum of the maximum powers of all the photovoltaic strings connected to the busbar box.

[0020] In a possible implementation, the first preset voltage is greater than or equal to the maximum value of the voltages corresponding to the maximum power points of all the photovoltaic strings connected to the busbar box; the second preset voltage is greater than or equal to the lowest DC voltage when the inverter is in the linear modulation region.

[0021] In a possible implementation, controlling the output power of the busbar box to decrease as the output voltage increases specifically includes: controlling the output power of the busbar box to decrease as the output voltage increases according to the output voltage of the busbar box, the open-circuit voltage of the busbar box, and the second preset voltage; the open-circuit voltage of the busbar box is greater than the maximum value of the open-circuit voltages of all the photovoltaic strings connected to the busbar box.

[0022] In a possible implementation, specifically, the output power of the busbar box is controlled to decrease as the output voltage increases according to the following formula:

[0023]

[0024] where P outmax is the maximum power; u outis the output voltage of the busbar box, U mppt2 is the second preset voltage, U oc is the open-circuit voltage of the busbar box.

[0025] In a possible implementation, it further includes: adjusting the output voltage of the corresponding photovoltaic string to adjust the output power of the busbar box.

[0026] The embodiment of the present application further provides a busbar box, including: a multi-channel DC-DC circuit and a controller of the busbar box; the input end of each DC-DC circuit is connected to the corresponding photovoltaic string; the output ends of the multi-channel DC-DC circuits are connected in parallel for connecting the input end of the inverter; the controller of the busbar box is used to control the busbar box to output the maximum power when the output voltage of the busbar box is greater than or equal to the first preset voltage and less than or equal to the second preset voltage; the maximum power is the sum of the maximum powers of all the photovoltaic strings connected to the busbar box; the second preset voltage is greater than the first preset voltage; when the output voltage of the busbar box is greater than the second preset voltage, control the output power of the busbar box to decrease as the output voltage increases.

[0027] In a possible implementation, the first preset voltage is greater than or equal to the maximum value of the voltages corresponding to the maximum power points of all the photovoltaic strings connected to the busbar box; the second preset voltage is greater than or equal to the lowest DC voltage when the inverter is in the linear modulation region; the controller of the busbar box is specifically used to control the output power of the busbar box to decrease as the output voltage increases according to the output voltage of the busbar box, the open-circuit voltage of the busbar box, and the second preset voltage; the open-circuit voltage of the busbar box is greater than the maximum value of the open-circuit voltages of all the photovoltaic strings connected to the busbar box.

[0028] From the above technical solutions, it can be seen that the embodiments of the present application have the following advantages:

[0029] In the embodiments of the present application, the control of the output power of the busbar box no longer depends on the power limit instruction sent by the controller of the inverter. Instead, the busbar box independently realizes the control of the output power. For the inverter, the busbar box can be regarded as a photovoltaic string, that is, the busbar 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 busbar box also have characteristics similar to the PV curve of the photovoltaic string. When the output voltage of the busbar box is greater than or equal to the first preset voltage and less than or equal to the second preset voltage, the busbar box is controlled to output the maximum power. The maximum power is the sum of the maximum powers of all the photovoltaic strings connected to the busbar box. When the output voltage of the busbar box is greater than the second preset voltage, the output power of the busbar box is controlled to decrease as the output voltage increases, that is, it shows a drooping characteristic. The busbar box can control the output power according to the interval where 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 busbar box and the inverter. Even if the communication speed between the inverter and the busbar box is low, it does not affect the fast control of the output power by the busbar box. Description of the Drawings

[0030] Figure 1 It is a schematic diagram of a photovoltaic power generation system provided by an embodiment of the present application;

[0031] Figure 2 It is a schematic diagram of the PV curve of a photovoltaic string provided by an embodiment of the present application;

[0032] Figure 3 It is a schematic diagram of another photovoltaic power generation system provided by an embodiment of the present application;

[0033] Figure 4 It is a schematic diagram of the PV curve of a busbar box provided by an embodiment of the present application;

[0034] Figure 5 It is a schematic diagram of yet another photovoltaic power generation system provided by an embodiment of the present application;

[0035] Figure 6 It is a schematic diagram of the PV curves of multiple busbar boxes provided by an embodiment of the present application;

[0036] Figure 7 It is a flowchart of the power control method for a photovoltaic power generation system provided by an embodiment of the present application;

[0037] Figure 8 It is a schematic diagram of a busbar box provided by an embodiment of the present application. Detailed Embodiments

[0038] In the following description, terms such as "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present application, unless otherwise specified, the meaning of "a plurality" is two or more.

[0039] In addition, in the present application, orientation terms such as "upper" and "lower" may include, but are not limited to, being defined relative to the schematic placement of components in the drawings. It should be understood that these directional terms may be relative concepts, which are used for relative description and clarification and may change accordingly with the change in the orientation of the components placed in the drawings.

[0040] In the present application, unless otherwise clearly specified and defined, the term "connection" should be understood in a broad sense. For example, "connection" may be a fixed connection, a detachable connection, or integrated; it may be directly connected or indirectly connected through an intermediate medium. In addition, the term "coupling" may be a way of realizing electrical connection for signal transmission. "Coupling" may be a direct electrical connection or an indirect electrical connection through an intermediate medium.

[0041] System embodiments

[0042] To enable those skilled in the art to better understand the technical solutions provided by the embodiments of the present application, the two-stage photovoltaic power generation system provided by the embodiments of the present application will be introduced below.

[0043] See Figure 1 , which is a schematic diagram of a photovoltaic power generation system provided by an embodiment of the present application.

[0044] In the embodiments of the present application, a three-phase alternating current output by the photovoltaic power generation system is taken as an example for introduction.

[0045] The photovoltaic power generation system includes: a photovoltaic array PV, a DC-DC circuit 100, and a DC-AC circuit 200.

[0046] Among them, 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.

[0047] In the embodiments of the present application, the specific implementation form of the DC-DC circuit 100 is not specifically limited. For example, it may include a boost circuit, a buck circuit, or a buck-boost circuit.

[0048] One implementation is that the input end of the DC-AC circuit 200 is connected to multiple DC-DC circuits 100. The output ends of the multiple DC-DC circuits 100 are connected in parallel. The multiple DC-DC circuits 100 are integrated in a cabinet, for example, they can be integrated in a busbar box. The DC-AC circuit 200 is integrated in an inverter.

[0049] In actual operation, the DC-DC circuit 100 generally does not operate at the maximum power point. Instead, it controls its output power according to the power limit instruction sent by the controller of the inverter. That is, in most cases, the output power is smaller than the maximum power, and it operates in a power limit state. Among them, the controller of the inverter is located on one side of the DC-AC circuit 200. Generally, the distance between the inverter and the busbar box is relatively far. The operation of the DC-DC circuit 100 needs to be controlled by the instruction of the controller. For example, the DC-DC circuit adjusts its output power according to the power limit instruction of the controller. The signal sent by the controller to the DC-DC circuit 100 depends on high-speed communication. When the communication speed between the DC-DC circuit 100 and the controller is slow, it will seriously affect the response speed of the DC-DC circuit 100. Therefore, the power corresponding to the power limit instruction cannot be output in time.

[0050] Figure 1 Just for illustration. In actual operation, the input end of the DC-AC circuit 200 can be connected to the output ends of multiple DC-DC circuits, that is, the output ends of the multiple DC-DC circuits are connected in parallel. The input end of each DC-DC circuit is connected to its corresponding photovoltaic string. To increase the power, the input end of each DC-DC circuit can be connected to multiple photovoltaic strings connected in parallel.

[0051] To solve the technical problem that power control highly depends on high-speed communication, the embodiment of the present application provides a power control solution, which can control the output power of the DC-DC circuit 100 without relying on high-speed communication.

[0052] For the control of the output power of the busbar box in the embodiment of the present application, it no longer depends on the power limit instruction sent by the controller of the inverter. Instead, the busbar box independently realizes the control of the output power. For the inverter, the busbar box can be regarded as a photovoltaic string, that is, the busbar box is virtualized as a photovoltaic source. Since the photovoltaic string has an output power-output voltage curve, that is, a PV curve, as Figure 2 shown. This figure is a schematic diagram of the PV curve of a photovoltaic string provided by the embodiment of the present application.

[0053] Figure 2 where the abscissa is the output voltage of the photovoltaic string and the ordinate is the output power of the photovoltaic string.

[0054] From Figure 2As can be seen, 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 controls the output power according to the virtual PV curve, so it does not depend on the power limit instruction sent from the inverter side, and thus does not depend on the high-speed communication between the combiner box and the inverter, getting rid of the influence brought by high-speed communication.

[0055] The following will introduce in detail the photovoltaic power generation system provided by the embodiments of the present application with reference to the accompanying drawings.

[0056] See Figure 3 , which is a schematic diagram of another photovoltaic power generation system provided by the embodiments of the present application.

[0057] For the convenience of understanding and description, in the embodiments of the present application, the combiner box including at least two DC-DC circuits is taken as an example for introduction. In specific implementation, the number of DC-DC circuits can be set according to actual needs.

[0058] It should be noted that the DC bus voltage refers to the output voltage of the combiner box, that is, the input voltage of the inverter.

[0059] In the embodiments of the present application, the combiner box having the maximum power point tracking (MPPT, Maximum Power Point Tracking) function is taken as an example for introduction. It should be understood that the combiner box may not have the MPPT function, and no specific limitation is made in the embodiments of the present application.

[0060] The photovoltaic power generation system provided by the embodiments of the present application includes: an inverter 400 and at least one MPPT combiner box 200; the combiner box 200 includes multiple DC-DC circuits and a controller (not shown in the figure); the output ends of the multiple DC-DC circuits in the combiner box 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.

[0061] Figure 3 In

[0062] The controller of the busbar box controls the output power according to the output voltage. Specifically, when the output voltage of the busbar box is greater than or equal to the first preset voltage and less than or equal to the second preset voltage, it controls the busbar box to output the maximum power; where the maximum power is the sum of the maximum powers of all the photovoltaic strings connected to the busbar box. When the output voltage of the busbar box is greater than the second preset voltage, it controls the output power of the busbar box to decrease as the output voltage increases; where the second preset voltage is greater than the first preset voltage.

[0063] To enable those skilled in the art to better understand the technical solutions introduced in the embodiments of the present application, the first preset voltage and the second preset voltage will be introduced below in conjunction with a curve graph.

[0064] See Figure 4 , which is a schematic PV curve diagram of a busbar box provided by an embodiment of the present application.

[0065] For ease of understanding, Figure 4 in, an example is given where a busbar box includes a DC-DC circuit, and the input end of the DC-DC circuit is connected to a photovoltaic string.

[0066] Figure 4 In, curve M is the input PV curve of the busbar box, and curve N is the output PV curve of the busbar box. Since the input end of the busbar box is connected to the photovoltaic string, that is, curve M is the PV curve of the photovoltaic string.

[0067] To enable both the photovoltaic string and the busbar box to operate in a stable state, that is, the output voltage range of the busbar box is greater than or equal to the first preset voltage, that is, Figure 4 in is greater than Umppt1.

[0068] Among them, the first preset voltage is greater than or equal to the maximum value of the voltages corresponding to the maximum power points of all the photovoltaic strings connected to the busbar box. That is, the first preset voltage is not less than the maximum value of the voltages corresponding to the maximum power points of all the photovoltaic strings connected to the busbar box. For example, if the busbar box is connected to 4 photovoltaic strings, then the first preset voltage is greater than or equal to the maximum value of the voltages corresponding to the maximum power points of the 4 photovoltaic strings, that is, greater than or equal to the maximum value of the 4 voltages.

[0069] 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 value of the line voltage at the AC output end of the inverter. Since the inverter has requirements for the DC bus voltage during operation, therefore, the second preset voltage can be set according to the DC bus voltage sent by the inverter.

[0070] Figure 4The Uoc in it is the open-circuit voltage corresponding to the virtual PV curve of the combiner box. The open-circuit voltage Uoc of the combiner box needs to be greater than the maximum value of the open-circuit voltages of all the PV strings connected to the combiner box. For example, continuing with the example where the input end of the combiner box is connected to 4 PV strings, the Uoc of the combiner box should be greater than the maximum value of the open-circuit voltages of the 4 PV strings.

[0071] From Figure 4 It can be seen that there is a straight-line stage in the PV curve of the combiner box, that is, when the output voltage is between Umppt1 and Umppt2, the output power of the combiner box is a constant value, that is, the maximum power. The maximum power is the sum of the maximum powers of all the 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.

[0072] When the output voltage of the combiner box is greater than Umppt2, the output power of the combiner box shows a monotonically decreasing trend with the increase of the output voltage.

[0073] The embodiments of this application do not limit that the output power shows a monotonically decreasing trend with the increase of the output voltage. For example, it can be the same as the monotonically decreasing trend of the PV strings at the input end, or it can be a linearly monotonically decreasing proportional decrease, or it can be a parabola-like decrease, as long as it ensures a monotonic decrease.

[0074] The following provides a possible implementation of the monotonic decrease. For example, 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;

[0075] 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 following formula based on the output voltage of the combiner box, the open-circuit voltage of the combiner box, and the second preset voltage:

[0076]

[0077] Where 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.

[0078] It can be seen from the above formula that the greater the output voltage of the combiner box, the smaller the output power of the combiner box.

[0079] The above formula is only an example, and it can also be other simple variants of the above formula, as long as it ensures that the output power of the combiner box shows a decreasing trend with the increase of the output voltage.

[0080] As can be seen from the above analysis, for the technical solution provided by the embodiments of the present application, the power control of the busbar box for its own output power does not depend on the power limit instruction sent by the inverter side, but always controls its own output power according to its own output voltage.

[0081] In specific implementation, the controller of the busbar box can adjust the output power of the busbar box by adjusting the output voltage of the photovoltaic string connected to its input end. Since the output power of the photovoltaic string will be affected when its output voltage changes, that is, it satisfies the characteristics of the PV curve, and in the case of ignoring power loss, the output power of the photovoltaic string is the input power of the busbar box, and the input power of the busbar box is equal to the output power of the busbar box.

[0082] For the control of the output power of the inverter, it 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, and there is no need to send a power limit instruction to the busbar box to adjust its own output power. Therefore, the influence of the communication speed between the inverter and the busbar box can be eliminated. In the embodiments of the present application, the control of the output power of the busbar box for itself can also be realized under low-speed communication. The output power of the inverter essentially comes from the output power of the busbar box. Therefore, the output power of the inverter is Figure 4 a straight line parallel to the horizontal axis in, and this straight line has an intersection with the PV curve of the busbar box, and the intersection is the power limit point of the inverter.

[0083] In the above embodiments, only one busbar box is taken as an example for introduction. The following introduces the case where at least two busbar boxes are connected to the input end of the inverter.

[0084] See Figure 5 , which is a schematic diagram of another photovoltaic power generation system provided by the embodiments of the present application.

[0085] Figure 5 Two busbar boxes in can be taken as an example for introduction. Continuing with the MPPT busbar box as an example, it should be understood that more busbar boxes can be connected to the input end of the inverter 400. Figure 5 The two busbar boxes in are the first MPPT busbar box 200A and the second MPPT busbar box 200B respectively.

[0086] The first MPPT busbar box of 200A includes at least two DC-DC conversion circuits, namely the first DC-DC conversion circuit 200a and the second DC-DC conversion circuit 200b. The input end of the first DC-DC conversion circuit 200a is connected to the corresponding photovoltaic strings 100a and 100b. Generally, the photovoltaic strings 100a and 100b are connected in parallel at the input end of the first DC-DC conversion circuit 200a. Similarly, the second DC-DC conversion circuit 200b is connected to its corresponding photovoltaic string.

[0087] The second MPPT busbar box of 200B includes at least two DC-DC conversion circuits, namely the third DC-DC conversion circuit 200c and the fourth DC-DC conversion circuit 200d. The input end of the third DC-DC conversion circuit 200c is connected to the corresponding photovoltaic strings 100c and 100d. Generally, the photovoltaic strings 100c and 100d are connected in parallel at the input end of the third DC-DC conversion circuit 200c. Similarly, the fourth DC-DC conversion circuit 200d is connected to its corresponding photovoltaic string.

[0088] When the input end of the inverter is connected to multiple busbar boxes, there is a common interval for the maximum power of the multiple busbar boxes, thereby realizing the maximum power point tracking of the multiple busbar boxes. Therefore, in order to make there be a common interval for the maximum power of the multiple busbar boxes, taking two busbar boxes as an example, it is necessary that the second preset voltage of the first busbar box is greater than the first preset voltage of the second busbar box, and the second preset voltage of the second busbar box is greater than the first preset voltage of the first busbar box, that is, the second preset voltage of each busbar box needs to be greater than the first preset voltage of all busbar boxes to ensure that there is a common interval for the maximum power of all busbar boxes.

[0089] For those skilled in the art to better understand that there is a common interval for the maximum power of the PV curves of multiple busbar boxes, reference can be made to Figure 6 This figure is a schematic diagram of the PV curves of multiple busbar boxes provided by the embodiment of the present application.

[0090] From Figure 6 it can be seen that the curves N1, N2, and N3 respectively represent the PV curves of three different busbar boxes.

[0091] There is a common MPPT interval in the maximum power intervals of N1, N2, and N3. Figure 6 The three unlabeled curves in

[0092] For example, the first preset voltage and the second preset voltage corresponding to the maximum power range of N1 are 1000V and 1150V respectively, and the first preset voltage and the second preset voltage corresponding to the maximum power range of N2 are 1050V and 1200V respectively. Then the voltage range corresponding to the overlapping maximum power of N1 and N2 is from 1050V to 1150V.

[0093] The photovoltaic power generation system provided by the embodiments of the present application virtualizes the output power droop characteristics of the busbar box to be similar to those of a photovoltaic panel. From the perspective of the inverter connected to the rear stage of the busbar box, the busbar box can be regarded as a new photovoltaic string, and thus the output power of the busbar box can be quickly scheduled without relying on high-speed communication. The embodiments of the present application can regard each busbar box as a photovoltaic source. When there are multiple busbar boxes, setting the maximum power ranges of multiple busbar boxes can achieve the power control of multiple busbar boxes. For the inverter, the inverter can adopt the power control method of a single-stage power conversion system to quickly achieve power scheduling. That is, when the busbar box is regarded as a PV source, the two-stage photovoltaic power generation system can be equivalent to a single-stage photovoltaic power generation system, and the control is achieved according to the power scheduling method of the single-stage photovoltaic power generation system.

[0094] Method embodiments

[0095] Based on the photovoltaic power generation system provided in the above embodiments, the embodiments of the present application further provide a power control method for a photovoltaic power generation system, which will be introduced in detail below with reference to the drawings.

[0096] See Figure 7 , which is a flowchart of a power control method for a photovoltaic power generation system provided by the embodiments of the present application.

[0097] The power control method for the photovoltaic power generation system provided in this embodiment is applied to the photovoltaic power generation system provided in the above embodiments. The system includes: an inverter and at least one busbar box; the busbar box includes multiple DC-DC circuits and a controller; the output ends of the multiple DC-DC circuits in the busbar box 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.

[0098] The method includes:

[0099] S701: Obtain the output voltage of the busbar box.

[0100] The method provided by the embodiments of the present application is applicable to each busbar box. The controller of a single busbar box can achieve the control of the corresponding busbar box. The photovoltaic power generation system can include a voltage detection circuit, which can collect the output voltage of the busbar box in real time.

[0101] S702: When the output voltage of the busbar box is greater than or equal to the first preset voltage and less than or equal to the second preset voltage, control the busbar box to output the 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 the photovoltaic strings connected to the busbar box. That is, when the output voltage of the busbar box is within the voltage range formed by the first preset voltage and the second preset voltage, the busbar box always outputs the maximum power.

[0102] S703: When the output voltage of the busbar box is greater than the second preset voltage, control the output power of the busbar box to decrease as the output voltage increases. That is, when the output voltage of the busbar box is greater than the second preset voltage, the output voltage of the busbar box shows a monotonically drooping characteristic.

[0103] In a possible implementation, the first preset voltage is greater than or equal to the maximum value of the voltages corresponding to the maximum power points of all the photovoltaic strings connected to the busbar box; the second preset voltage is greater than or equal to the DC bus voltage of the inverter.

[0104] Among them, the first preset voltage is greater than or equal to the maximum value of the voltages corresponding to the maximum power points of all the photovoltaic strings connected to the busbar box. That is, the first preset voltage is not less than the maximum value of the voltages corresponding to the maximum power points of all the photovoltaic strings connected to the busbar box. For example, if the busbar box is connected to 4 photovoltaic strings, then the first preset voltage is greater than or equal to the maximum value of the voltages corresponding to the maximum power points of the 4 photovoltaic strings, that is, greater than or equal to the maximum value among the 4 voltages.

[0105] The second preset voltage is greater than or equal to the lowest DC voltage when the inverter is in the linear modulation region, that is, greater than the required DC bus voltage of the inverter, that is, the peak value of the line voltage at the AC output end of the inverter. Since the inverter has requirements for the DC bus voltage during operation, therefore, the second preset voltage can be set according to the DC bus voltage sent by the inverter.

[0106] In the photovoltaic power generation system provided by the embodiments of the present application, the busbar box is virtualized as a photovoltaic source, so that it has a PV curve similar to that of the photovoltaic string, and then controls the output power according to this PV curve, without relying on the power limit instruction of the inverter to control. Therefore, it is not affected by the communication speed between the inverter and the busbar box, can get rid of the limitation of the communication speed, and the busbar box independently completes the control of its own output power.

[0107] In the embodiments of the present application, the specific control method of the output power of the busbar box when the output voltage of the busbar box is greater than the second preset voltage is not specifically limited. As long as the output power of the busbar box decreases as the output voltage of the busbar box increases, it can decrease proportionally or non - proportionally. Neither is specifically limited in the embodiments of the present application.

[0108] One possible implementation is that the controller of the busbar box controls the output power of the busbar box to decrease as the output voltage increases, specifically including:

[0109] Control the output power of the busbar box to decrease as the output voltage increases according to the output voltage of the busbar box, the open-circuit voltage of the busbar box, and the second preset voltage; the open-circuit voltage of the busbar box is greater than the maximum value of the open-circuit voltages of all the photovoltaic strings connected to the busbar box.

[0110] When the output voltage of the busbar box is greater than the second preset voltage, the controller can specifically control the output power P of the busbar box according to the output voltage of the busbar box, the open-circuit voltage of the busbar box, and the second preset voltage according to the following formula out to decrease as the output voltage increases:

[0111]

[0112] where P outmax is the maximum power; u out is the output voltage of the busbar box, U mppt2 is the second preset voltage, and U oc is the open-circuit voltage of the busbar box.

[0113] The power control method provided by the embodiments of the present application may further include: adjusting the output voltage of the corresponding photovoltaic string to adjust the output power of the busbar box. That is, the controller of the busbar box can adjust the output power of the busbar box by adjusting the output voltage of the photovoltaic string connected to the input end of the busbar box. Since there is a characteristic relationship of the current-voltage curve between the output voltage and output current of the photovoltaic string, the controller of the busbar box can also change the output power by adjusting the input current of the busbar box.

[0114] All the content introduced in the above embodiments of the photovoltaic power generation system is applicable to the power control method introduced in this embodiment, and the repeated parts will not be described herein again.

[0115] Embodiment of the busbar box

[0116] Based on the photovoltaic power generation system and the power control method provided in the above embodiments, the embodiments of the present application further provide a busbar box. The following is a detailed introduction with reference to the drawings.

[0117] See Figure 8 , which is a schematic diagram of a busbar box provided by an embodiment of the present application.

[0118] The busbar box provided by the embodiments of the present application can be the busbar box in any of the above embodiments, including: a plurality of DC-DC circuits and a controller 500 of the busbar box.

[0119] The input end of each DC-DC circuit is connected to the corresponding photovoltaic string.

[0120] The output terminals of the multi-channel DC-DC circuits are connected in parallel to be used for connecting the input terminal of the inverter.

[0121] The controller 500 of the busbar box is configured to control the busbar box to output the maximum power when the output voltage of the busbar box is greater than or equal to the first preset voltage and less than or equal to the second preset voltage; the maximum power is the sum of the maximum powers of all the photovoltaic strings connected to the busbar box; the second preset voltage is greater than the first preset voltage; when the output voltage of the busbar box is greater than the second preset voltage, the output power of the busbar box is controlled to decrease as the output voltage increases.

[0122] It should be noted that the busbar box provided by the embodiment of the present application is applicable to any busbar box. If the input terminal of the inverter is connected to multiple busbar boxes, each busbar box can adopt the above control method to control its own output power. When the input terminal of the inverter is connected to multiple busbar boxes and maximum power point tracking is realized, as long as there is a common interval in the virtual PV curves of the multiple busbar boxes.

[0123] The embodiment of the present application does not limit the number of photovoltaic strings connected to the input terminal of the busbar box, which can be set according to the power requirement, and multiple photovoltaic strings are connected in parallel to the input terminal of the busbar box.

[0124] The output power of the busbar box provided by the embodiment of the present application presents the PV curve characteristics of the photovoltaic string type, that is, when the output voltage of the busbar box is greater than the second preset voltage, the output power of the busbar box decreases as the output voltage of the busbar box increases. The controller of the busbar box can independently adjust the output power of the busbar box according to the PV curve characteristics, without relying on the power limit instruction sent from the inverter side. Therefore, it does not depend on the high-speed communication between the inverter and the busbar box. Even if the communication speed between the inverter and the busbar box is low, it does not affect the control of the output power of the busbar box by itself. For the inverter, the inverter can adopt the power control method of a single-stage power conversion system to quickly realize power scheduling. That is, when the busbar box is regarded as a 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.

[0125] The first preset voltage is greater than or equal to the maximum value of the voltages corresponding to the maximum power points of all the photovoltaic strings connected to the combiner box. For example, if there are N photovoltaic strings corresponding to N voltages at the maximum power points, the maximum value among the N voltages is taken. 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 when the inverter is in the linear modulation region, that is, greater than the required DC bus voltage of the inverter, which is the peak value of the line voltage at the AC output end of the inverter. When the inverter operates, there are generally requirements for the DC bus voltage. For example, if the output end of the inverter is connected to the AC grid, the DC bus voltage of the inverter is set according to the effective value of the voltage of the AC grid and should be greater than the effective value of the line voltage of the AC grid.

[0126] The controller 500 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 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 is greater than the maximum value of the open-circuit voltages of all the photovoltaic strings connected to the combiner box.

[0127] All the content introduced in the above embodiments of the photovoltaic power generation system is applicable to the combiner box introduced in this embodiment, and the repeated parts will not be elaborated here.

[0128] 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 the characteristics of a PV curve similar to that of a photovoltaic string, that is, a droop characteristic. When the output voltage is within a certain range, the output power is the maximum power, that is, the fixed output maximum power. When the output voltage is greater than this range, the output power decreases as the output voltage increases, that is, it presents a droop characteristic. The combiner box independently completes the control of its own output power without relying on the control command of the inverter. Therefore, it does not need to rely on the high-speed communication between the inverter and the combiner box. Even if the communication speed between the inverter and the combiner box is low, it does not affect the control of the output power of the combiner box by itself. And the control of the output power of the inverter can be directly carried out according to the single-stage power conversion system, that is, the inverter directly regards the combiner box as a photovoltaic input source. The inverter can control its own output current to control its own output power.

[0129] It should be understood that in this application, "at least one (item)" means one or more, and "a plurality" means two or more. "And / or" is used to describe the association relationship of associated objects, indicating that there can be three relationships. For example, "A and / or B" can represent: only A exists, only B exists, and both A and B exist at the same time. Among them, A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after. "At least one (one) of the following" or its similar expression refers to any combination of these items, including any combination of single items (one) or plural items (ones). For example, at least one (one) of a, b, or c can represent: 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.

[0130] As described above, the above embodiments are only used to illustrate the technical solutions of this application, rather than limiting them; although this application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A photovoltaic power generation system, characterized in that, Including: An inverter and at least one combiner box; the combiner box includes multiple DC-DC circuits and a controller; The output ends of the multiple DC-DC circuits in the combiner box are connected in parallel to the input end of the inverter; The input end of each DC-DC circuit is connected to a corresponding photovoltaic string; The controller of the combiner box is configured to control the combiner box to output the maximum power when the output voltage of the combiner box is greater than or equal to a first preset voltage and less than or equal to a second preset voltage; when the output voltage of the combiner box is greater than the second preset voltage, control the output power of the combiner box to decrease as the output voltage increases; the second preset voltage is greater than the first preset voltage; the maximum power is the sum of the maximum powers of all the photovoltaic strings connected to the combiner box; the first preset voltage is greater than or equal to the maximum value of the voltages corresponding to the maximum power points of all the photovoltaic strings connected to the combiner box; the second preset voltage is greater than or equal to the lowest DC voltage when the inverter is in the linear modulation region.

2. The system according to claim 1, wherein 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 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 is greater than the maximum value of the open-circuit voltages of all the photovoltaic strings connected to the combiner box.

3. The system according to claim 2, wherein 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: Among them, P outmax is the maximum power; u out is the output voltage of the busbar box, U mppt2 is the second preset voltage, U oc is the open-circuit voltage of the busbar box.

4. The system according to claim 1, wherein 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.

5. The system according to any one of claims 1-4, characterized in that, The controller of the combiner box is configured to adjust the output power of the combiner box by adjusting the output voltage of the corresponding photovoltaic string.

6. The system according to any one of claims 1-4, characterized in that, Further including: An inverter controller; The inverter controller is configured to control the output power of the inverter according to a power limit command value.

7. A power control method for a photovoltaic power generation system, characterized in that, The system includes: an inverter and at least one combiner box; the combiner box includes multiple DC-DC circuits and a controller; the output ends of the multiple DC-DC circuits in the combiner box are connected in parallel to the input end of the inverter; the input end of each DC-DC circuit is connected to a corresponding photovoltaic string; The method includes: When the output voltage of the combiner box is greater than or equal to a first preset voltage and less than or equal to a second preset voltage, control the combiner box to output the maximum power; When the output voltage of the combiner box is greater than the second preset voltage, control the output power of the combiner box to decrease as the output voltage increases; The second preset voltage is greater than the first preset voltage; the maximum power is the sum of the maximum powers of all the photovoltaic strings connected to the busbar box; the first preset voltage is greater than or equal to the maximum value of the voltages corresponding to the maximum power points of all the photovoltaic strings connected to the busbar box; the second preset voltage is greater than or equal to the lowest DC voltage when the inverter is in the linear modulation region.

8. The method according to claim 7, wherein Controlling the output power of the busbar box to decrease as the output voltage increases specifically includes: Controlling the output power of the busbar box to decrease as the output voltage increases according to the output voltage of the busbar box, the open-circuit voltage of the busbar box, and the second preset voltage; the open-circuit voltage of the busbar box is greater than the maximum value of the open-circuit voltages of all the photovoltaic strings connected to the busbar box.

9. The method according to claim 8, characterized in that, Specifically, control the output power of the busbar box to decrease as the output voltage increases according to the following formula: where P outmax is the maximum power; u out is the output voltage of the busbar box, U mppt2 is the second preset voltage, U oc is the open-circuit voltage of the busbar box.

10. The method according to any one of claims 7-9, characterized in that, It further includes: Adjusting the output voltage of the corresponding photovoltaic string to adjust the output power of the busbar box.

11. A busbar box, characterized in that, It includes: Multiple DC-DC circuits and a controller of the busbar box; The input end of each DC-DC circuit is connected to the corresponding photovoltaic string; The output ends of the multiple DC-DC circuits are connected in parallel for connecting to the input end of the inverter; The controller of the busbar box is used to control the busbar box to output the maximum power when the output voltage of the busbar box is greater than or equal to the first preset voltage and less than or equal to the second preset voltage; The maximum power is the sum of the maximum powers of all the photovoltaic strings connected to the busbar box; The second preset voltage is greater than the first preset voltage; when the output voltage of the busbar box is greater than the second preset voltage, control the output power of the busbar box to decrease as the output voltage increases; the first preset voltage is greater than or equal to the maximum value of the voltages corresponding to the maximum power points of all the photovoltaic strings connected to the busbar box; the second preset voltage is greater than or equal to the lowest DC voltage when the inverter is in the linear modulation region.

12. The busbar box according to claim 11, characterized in that, The controller of the busbar box is specifically used to control the output power of the busbar box to decrease as the output voltage increases according to the output voltage of the busbar box, the open-circuit voltage of the busbar box, and the second preset voltage; the open-circuit voltage of the busbar box is greater than the maximum value of the open-circuit voltages of all the photovoltaic strings connected to the busbar box.

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