A photovoltaic power generation system, a photovoltaic inverter, and a method for IV curve scanning

Abstract

The present application provides a photovoltaic power generation system, a photovoltaic inverter and a method for IV curve scanning, relating to the technical field of photovoltaic power generation. Among them, the photovoltaic power generation system includes: a controller and M groups of DC-DC circuits, each group including N DC-DC circuits, M being a positive integer and N being an integer greater than 1. The input end of each DC-DC circuit is connected to at least one path of photovoltaic units, and each path of photovoltaic units includes at least one photovoltaic module. The controller controls the N DC-DC circuits in each group to start online IV curve scanning in sequence, and the time interval between the start of online IV curve scanning of two adjacent DC-DC circuits is less than the time taken for one DC-DC circuit to perform online IV curve scanning. The photovoltaic power generation system can reduce the power fluctuation output during online IV curve scanning, reduce the time taken for the photovoltaic power generation system to perform online IV curve scanning, and further reduce the impact of online IV curve scanning on the grid-connected power quality.

Description

Technical Field

[0001] The present application relates to the technical field of photovoltaic power generation, and in particular to a photovoltaic power generation system, a photovoltaic inverter, a busbar box, a photovoltaic optimizer, and a method for IV curve scanning. Background Art

[0002] Photovoltaic power generation is a technology that converts light energy into electrical energy by using the photovoltaic effect at the semiconductor interface, and has been developing rapidly. As the core component in a photovoltaic power generation system, a photovoltaic module is used to convert light energy into electrical energy. Therefore, the health status of the photovoltaic module directly affects the power generation of the photovoltaic power generation system. When environmental factors such as temperature and light intensity are constant, the output current of the photovoltaic module changes with its output voltage, and a current-voltage curve (hereinafter referred to as "IV curve") can be plotted.

[0003] Refer to Figure 1 , which is a schematic diagram of the IV curve of a healthy photovoltaic module.

[0004] For a healthy photovoltaic module, its IV curve is parabolic; if the photovoltaic module is damaged or blocked, its IV curve will be distorted, and the health status of the photovoltaic module can be diagnosed through IV curve scanning technology.

[0005] The currently applied IV curve scanning technology can be divided into two types: offline IV curve scanning and online IV curve scanning. Among them, the offline IV curve scanning technology requires maintenance personnel to manually carry an IV detector to the side of the photovoltaic module, disconnect the photovoltaic module from the photovoltaic power generation system and connect it to the IV curve instrument for detection. This method has a very long detection time, a large workload, and a large power loss of the photovoltaic power generation system during the detection period. The online IV curve scanning performs online IV curve scanning on the photovoltaic strings connected to the power conversion circuit of the photovoltaic system, which can avoid manual operation and reduce the scanning time and the power loss of the photovoltaic power generation system during the scanning period.

[0006] However, during the current online IV curve scanning process, the input voltage of the photovoltaic string in the scanning state fluctuates, and its input power also fluctuates accordingly, which in turn causes the output power of the inverter, maximum power point tracking (MPPT) device, etc. connected to the photovoltaic string to fluctuate, affecting the grid-connected power quality of the photovoltaic power generation system. For example, problems such as harmonics and voltage flicker may occur. Summary of the Invention

[0007] To solve the above problems, the present application provides a photovoltaic power generation system, a photovoltaic inverter, a busbar box, a photovoltaic optimizer, and a method for IV curve scanning, which can reduce the time taken for online IV curve scanning, and can also reduce the power fluctuation of the photovoltaic power generation system during online IV curve scanning, thereby reducing the impact of online IV curve scanning on the grid-connected power quality.

[0008] In a first aspect, the present application provides a photovoltaic power generation system, which includes a controller and M groups of direct current (DC)-DC circuits, each group including N DC-DC circuits, where M is a positive integer and N is an integer greater than 1. Among them, the input end of each DC-DC circuit is connected to at least one path of photovoltaic units, and each path of photovoltaic units includes at least one photovoltaic module. The controller is configured to control the N DC-DC circuits in each group to start online IV curve scanning in sequence, and the controller controls the time interval between the start of online IV curve scanning of two adjacent DC-DC circuits to be less than the time taken for one DC-DC circuit to perform online IV curve scanning.

[0009] For each group of DC-DC circuits of the photovoltaic power generation system, after the first DC-DC circuit starts online IV curve scanning, the remaining DC-DC circuits in each path do not wait for the previous path to complete scanning before starting scanning, but perform online IV curve scanning in sequence, and the time interval is less than the time taken for a single DC-DC circuit to perform online IV curve scanning, that is, staggered scanning is controlled. At this time, the N DC-DC circuits in each group perform peak-shifting output. On the one hand, online IV curve scanning can be performed on the photovoltaic units connected to multiple DC-DC circuits at the same time, saving scanning time. On the other hand, the total output power of the photovoltaic power generation system can be made relatively stable, avoiding a large fluctuation in the total output power during online IV curve scanning, thereby reducing the negative impact of online IV curve scanning on the grid-connected power quality.

[0010] In combination with the first aspect, in a first possible implementation manner, when the controller controls each DC-DC circuit to perform online IV curve scanning, it first increases the input voltage of the DC-DC circuit until the input current of the DC-DC circuit is zero. At this time, the input voltage of the DC-DC circuit is the sum of the open-circuit voltages of all the photovoltaic units 10 connected thereto, and then controls the input voltage of the DC-DC circuit to gradually decrease to zero. During this process, the corresponding relationship between the input voltage and input current of the DC-DC circuit is obtained at a preset sampling interval, and then the scanning result of the IV curve is obtained.

[0011] In combination with the first aspect, in the second possible implementation manner, the controller is specifically configured to, after controlling the first DC-DC circuit in each group to start the online IV curve scanning, control the k-th DC-DC circuit to start the online IV curve scanning when the input voltage of the (k-1)-th DC-DC circuit decreases to be less than a preset voltage threshold, so that the time interval is less than the time taken for one DC-DC circuit to perform the online IV curve scanning, where k = 2, 3,..., N.

[0012] For the other DC-DC circuits in each group except the first DC-DC circuit, the time to start the online IV curve scanning is when the input voltage of the previous DC-DC circuit decreases to be less than the preset voltage value, that is, the previous DC-DC circuit has not completed the online IV curve scanning yet, so peak-shifted output is achieved.

[0013] In combination with the first aspect, in the third possible implementation manner, the time for each DC-DC circuit to perform the online IV curve scanning is the same, and the preset voltage threshold is the product of the sum of the open-circuit voltages of the photovoltaic units connected to the (k-1)-th DC-DC circuit and a first preset ratio. Among them, the sum of the open-circuit voltages of the photovoltaic units connected to the (k-1)-th DC-DC circuit is the real-time measurement data when the (k-1)-th DC-DC circuit performs the online IV curve scanning.

[0014] In combination with the first aspect, in the fourth possible implementation manner, the preset voltage threshold is the product of the sum of the preset open-circuit voltages of the photovoltaic units connected to the (k-1)-th DC-DC circuit and a first preset ratio. The rated open-circuit voltage range of each photovoltaic unit is a known device parameter, and the preset open-circuit voltage of each photovoltaic unit can be determined according to the rated open-circuit voltage range. For example, the maximum value, minimum value or intermediate value in the rated open-circuit voltage range can be selected.

[0015] In combination with the first aspect, in the fifth possible implementation manner, the controller is specifically configured to, after controlling the first DC-DC circuit in each group to start the online IV curve scanning, the remaining DC-DC circuits start the online IV curve scanning in sequence at a preset time interval, and the preset time interval is less than the time taken for one DC-DC circuit to perform the online IV curve scanning. Furthermore, after the first DC-DC circuit starts the scanning first, there are multiple DC-DC circuits performing the scanning simultaneously for a period of time afterwards, and peak-shifted output is performed.

[0016] In combination with the first aspect, in the sixth possible implementation manner, the preset time interval is negatively correlated with the size of N. The more DC-DC circuits are connected to the photovoltaic system, the higher the power of the photovoltaic power generation system. At this time, the preset time interval can be reduced, so as to shorten the time taken for the online IV curve scanning on the premise of maintaining the relatively stable total output power of the photovoltaic power generation system.

[0017] In combination with the first aspect, in the seventh possible implementation manner, the preset time interval is the product of the time taken for an online IV curve scan of a DC-DC circuit and a second preset ratio.

[0018] In combination with the first aspect, in the eighth possible implementation manner, the controller controls M groups of DC-DC circuits to perform online IV curve scans synchronously. That is, it simultaneously controls the first DC-DC circuits of multiple groups of DC-DC circuits to start scanning.

[0019] In combination with the first aspect, in the ninth possible implementation manner, the photovoltaic power generation system further includes a direct current - alternating current (AC) circuit. The DC-AC circuit and M groups of DC-DC circuits form an inverter. The positive output ports of the M groups of DC-DC circuits are connected in parallel to the positive input port of the DC-AC circuit, and the negative output ports of the M groups of DC-DC circuits are connected in parallel to the negative input port of the DC-AC circuit. This inverter is a string inverter.

[0020] In combination with the first aspect, in the tenth possible implementation manner, the controller is further used to control the working state of the DC-AC circuit. That is, the controller is integrated with the controller of the DC-AC circuit to form the controller of the inverter.

[0021] In combination with the first aspect, in the eleventh possible implementation manner, M groups of DC-DC circuits form a DC busbar box; the positive output ports of the M groups of DC-DC circuits are connected in parallel to form the positive output port of the DC busbar box; the negative output ports of the M groups of DC-DC circuits are connected in parallel to form the negative output port of the DC busbar box.

[0022] In combination with the first aspect, in the twelfth possible implementation manner, the DC-DC circuit is a PV optimizer, and N PV optimizers in each group form a PV optimizer sub-string. The positive output port of the i-th PV optimizer is connected to the negative output port of the (i - 1)-th PV optimizer, the negative output port of the i-th PV optimizer is connected to the positive output port of the (i + 1)-th PV optimizer, the positive output port of the first PV optimizer is the positive output port of the PV optimizer sub-string, and the negative output port of the N-th PV optimizer is the negative output port of the PV optimizer sub-string, where i = 2, 3, …, N - 1. The output end of the PV optimizer sub-string can be connected to the input end of a subsequent MPPT boost busbar box, or a string inverter, or a central inverter through a DC cable. Multiple PV optimizer sub-strings can also be connected in series again.

[0023] Second aspect, the present application also provides a photovoltaic inverter, which is a string-type inverter. The input end is connected to a photovoltaic unit, and the photovoltaic unit includes at least one photovoltaic module. The photovoltaic inverter includes a controller, a DC-AC circuit, and M groups of DC-DC circuits, each group including N DC-DC circuits, where M is a positive integer and N is an integer greater than 1. Among them, the positive output ports of the M groups of DC-DC circuits are connected in parallel to the positive input port of the DC-AC circuit, and the negative output ports of the M groups of DC-DC circuits are connected in parallel to the negative input port of the DC-AC circuit. The input end of each DC-DC circuit is connected to at least one path of the photovoltaic unit; the DC-DC circuit is used to perform DC conversion on the direct current obtained from the photovoltaic unit and then transmit it to the DC-AC circuit. The DC-AC circuit is used to convert the obtained direct current into alternating current. The controller is used to control the N DC-DC circuits in each group to start online IV curve scanning in sequence, and control the time interval between the start of online IV curve scanning of two adjacent DC-DC circuits to be less than the time taken for one DC-DC circuit to perform online IV curve scanning.

[0024] For each group of DC-DC circuits of the photovoltaic inverter, after the first DC-DC circuit starts online IV curve scanning, the remaining DC-DC circuits do not wait for the previous one to complete the scanning before starting to scan, but perform online IV curve scanning in sequence, and the time interval is less than the time taken for the first DC-DC circuit to perform online IV curve scanning, that is, interleaved scanning is achieved. At this time, the N DC-DC circuits in each group perform peak-shifted output. On the one hand, it is possible to simultaneously perform online IV curve scanning on the photovoltaic units connected to multiple DC-DC circuits, saving scanning time. On the other hand, it can make the total output power of the photovoltaic inverter relatively stable, avoiding a large fluctuation in the total output power during online IV curve scanning, and thus reducing the negative impact of online IV curve scanning of the photovoltaic inverter on the grid power quality.

[0025] Combined with the second aspect, in a first possible implementation manner, when the controller controls each DC-DC circuit to perform online IV curve scanning in sequence, it first increases the input voltage of the DC-DC circuit until the input current of the DC-DC circuit is zero, and then controls the input voltage of the DC-DC circuit to gradually decrease to zero.

[0026] Combined with the second aspect, in a second possible implementation manner, the controller is specifically used to control the first DC-DC circuit in each group to start online IV curve scanning, and then control the k-th DC-DC circuit to start online IV curve scanning when the input voltage of the (k - 1)-th DC-DC circuit decreases to less than a preset voltage threshold, so that the time interval is less than the time taken for one DC-DC circuit to perform online IV curve scanning, where k = 2, 3,..., N.

[0027] In combination with the second aspect, in the third possible implementation manner, the online IV curve scanning time of each DC-DC circuit is the same, and the preset voltage threshold is the product of the sum of the open-circuit voltages of the photovoltaic units connected to the (k-1)th DC-DC circuit and the first preset ratio.

[0028] In combination with the second aspect, in the fourth possible implementation manner, the preset voltage threshold is the product of the sum of the preset open-circuit voltages of the photovoltaic units connected to the (k-1)th DC-DC circuit and the first preset ratio.

[0029] In combination with the second aspect, in the fifth possible implementation manner, the controller is specifically configured to, after controlling the first DC-DC circuit in each group to start online IV curve scanning, control the remaining DC-DC circuits to start online IV curve scanning in sequence at preset time intervals, and the preset time interval is less than the time taken for one DC-DC circuit to perform online IV curve scanning.

[0030] In a third aspect, the present application further provides a DC busbar box. The input end of the DC busbar box is connected to a photovoltaic unit, and the photovoltaic unit includes at least one photovoltaic module. The DC busbar box includes a controller and M groups of DC-DC circuits, and each group includes N DC-DC circuits, where M is a positive integer and N is an integer greater than 1. The input end of each DC-DC circuit is connected to at least one path of photovoltaic unit; the positive output ports of the M groups of DC-DC circuits are connected in parallel to form the positive output port of the DC busbar box; the negative output ports of the M groups of DC-DC circuits are connected in parallel to form the negative output port of the DC busbar box. The controller is used to control the N DC-DC circuits in each group to start online IV curve scanning in sequence, and the time interval between the start of online IV curve scanning of two adjacent DC-DC circuits is less than the time taken for one DC-DC circuit to perform online IV curve scanning.

[0031] In combination with the third aspect, in the first possible implementation manner, when the controller controls each DC-DC circuit to perform online IV curve scanning in sequence, it first increases the input voltage of the DC-DC circuit until the input current of the DC-DC circuit is zero, and then controls the input voltage of the DC-DC circuit to gradually decrease to zero.

[0032] In combination with the third aspect, in the second possible implementation manner, the controller is specifically configured to, after controlling the first DC-DC circuit in each group to start online IV curve scanning, control the kth DC-DC circuit to start online IV curve scanning when the input voltage of the (k-1)th DC-DC circuit decreases to be less than the preset voltage threshold, so that the time interval is less than the time taken for one DC-DC circuit to perform online IV curve scanning, where k = 2, 3,..., N.

[0033] Combined with the third aspect, in the third possible implementation manner, the online IV curve scanning time of each DC-DC circuit is the same, and the preset voltage threshold is the product of the sum of the open-circuit voltages of the photovoltaic units connected to the (k-1)th DC-DC circuit and the first preset ratio.

[0034] Combined with the third aspect, in the fourth possible implementation manner, the preset voltage threshold is the product of the sum of the preset open-circuit voltages of the photovoltaic units connected to the (k-1)th DC-DC circuit and the first preset ratio.

[0035] Combined with the third aspect, in the fifth possible implementation manner, the controller is specifically configured to control the first DC-DC circuit in each group to start online IV curve scanning, and then the remaining DC-DC circuits start online IV curve scanning in sequence at preset time intervals, and the preset time interval is less than the time taken for one DC-DC circuit to perform online IV curve scanning.

[0036] Fourth aspect, the present application further provides a photovoltaic optimizer for connecting photovoltaic units, and the photovoltaic units include at least one photovoltaic module. The photovoltaic optimizer is connected in series with at least one photovoltaic optimizer to form a photovoltaic optimizer sub-string, and the output end of the photovoltaic optimizer sub-string can be connected to the input end of a subsequent MPPT boost busbar box, or a string inverter, or a centralized inverter through a DC cable. The photovoltaic optimizer includes a controller and a DC-DC circuit. The input end of the DC-DC circuit is connected to at least one path of photovoltaic units; the positive output end of the DC-DC circuit is the positive output end of the photovoltaic optimizer, and the negative output end of the DC-DC circuit is the negative output end of the photovoltaic optimizer. The controller is configured to control the DC-DC circuit to start online IV curve scanning, and the time interval for controlling the start of online IV curve scanning of the previous series-connected photovoltaic optimizer is less than the time taken for one DC-DC circuit to perform online IV curve scanning.

[0037] Fifth aspect, the present application further provides an online IV curve scanning method applied to the photovoltaic power generation system provided in the above implementation manners. The method includes the following steps:

[0038] Control the N DC-DC circuits in each group to start online IV curve scanning in sequence, and control the time interval between the start of online IV curve scanning of two adjacent DC-DC circuits to be less than the time taken for one DC-DC circuit to perform online IV curve scanning.

[0039] Using this method, after the first DC-DC circuit starts the online IV curve scanning, the remaining each DC-DC circuit does not wait for the previous one to complete the scanning before starting its own scanning. Instead, they perform the online IV curve scanning in sequence, and the time interval is less than the time taken for a single DC-DC circuit to perform the online IV curve scanning, that is, interleaved scanning is achieved. At this time, the N DC-DC circuits in each group output with staggered peaks. On the one hand, it can simultaneously perform the online IV curve scanning on the photovoltaic units connected to multiple DC-DC circuits, saving the scanning time. On the other hand, it can make the total output power of the photovoltaic power generation system relatively stable, avoiding a sharp fluctuation in the total output power during the online IV curve scanning, and thus reducing the negative impact of the online IV curve scanning on the grid-connected power quality.

[0040] Combined with the fifth aspect, in the first possible implementation manner, controlling the time interval between the start of the online IV curve scanning of two adjacent DC-DC circuits to be less than the time taken for a single DC-DC circuit to perform the online IV curve scanning specifically includes:

[0041] After controlling the first DC-DC circuit to start the online IV curve scanning, control the k-th DC-DC circuit to start the online IV curve scanning when the input voltage of the (k - 1)-th DC-DC circuit decreases to less than the preset voltage threshold, where k = 2, 3,..., N.

[0042] Combined with the fifth aspect, in the second possible implementation manner, the time for each DC-DC circuit to perform the online IV curve scanning is the same, and the preset voltage threshold is the product of the sum of the open-circuit voltages of the photovoltaic units connected to the (k - 1)-th DC-DC circuit and the first preset ratio.

[0043] Combined with the fifth aspect, in the third possible implementation manner, the preset voltage threshold is the product of the sum of the preset open-circuit voltages of the photovoltaic units connected to the (k - 1)-th DC-DC circuit and the first preset ratio.

[0044] Combined with the fifth aspect, in the fourth possible implementation manner, controlling the time interval between the start of the online IV curve scanning of two adjacent DC-DC circuits to be less than the time taken for a single DC-DC circuit to perform the online IV curve scanning specifically includes:

[0045] After controlling the first DC-DC circuit in each group to start the online IV curve scanning, the remaining DC-DC circuits start the online IV curve scanning in sequence at a preset time interval, and the preset time interval is less than the time taken for a single DC-DC circuit to perform the online IV curve scanning.

[0046] Combined with the fifth aspect, in the fifth possible implementation manner, the preset time interval is the product of the time taken for a single DC-DC circuit to perform the online IV curve scanning and the second preset ratio.

[0047] In combination with the fifth aspect, in a sixth possible implementation manner, the method further includes the following steps:

[0048] Control M groups of DC-DC circuits to perform online IV curve scanning synchronously. Description of the Drawings

[0049] Figure 1 Schematic diagram of the IV curve of a healthy photovoltaic module;

[0050] Figure 2 Schematic diagram of a photovoltaic power generation system based on a string inverter;

[0051] Figure 3 Schematic diagram of a string inverter;

[0052] Figure 4 Schematic diagram of a photovoltaic power generation system based on a centralized inverter and an MPPT boost combiner box;

[0053] Figure 5 Schematic diagram of an MPPT boost combiner box;

[0054] Figure 6 Schematic diagram of a photovoltaic power generation system based on a photovoltaic optimizer and a string inverter;

[0055] Figure 7 Schematic diagram of a photovoltaic power generation system provided by an embodiment of the present application;

[0056] Figure 8 Schematic diagram of another photovoltaic power generation system provided by an embodiment of the present application;

[0057] Figure 9 Schematic diagram of the timing when the DC-DC circuit provided by an embodiment of the present application starts scanning Figure 1 ;

[0058] Figure 10 Schematic diagram of the timing when the DC-DC circuit provided by an embodiment of the present application starts scanning Figure 2 ;

[0059] Figure 11 Schematic diagram of the output power when the photovoltaic power generation system provided by an embodiment of the present application performs online IV curve scanning;

[0060] Figure 12 Schematic diagram of yet another photovoltaic power generation system provided by an embodiment of the present application;

[0061] Figure 13 Schematic diagram of still another photovoltaic power generation system provided by an embodiment of the present application;

[0062] Figure 14Schematic diagram of another photovoltaic power generation system provided by an embodiment of the present application;

[0063] Figure 15 Flowchart of an online IV curve scanning method provided by an embodiment of the present application;

[0064] Figure 16 Schematic diagram of a photovoltaic inverter provided by an embodiment of the present application;

[0065] Figure 17 Schematic diagram of a DC busbar box provided by an embodiment of the present application;

[0066] Figure 18 Schematic diagram of a PV optimizer provided by an embodiment of the present application. Detailed implementation manners

[0067] To enable those skilled in the art to better understand the technical solutions provided by the embodiments of the present application, the application scenarios of the technical solutions provided by the present application will be introduced first below.

[0068] The photovoltaic power generation system provided by the embodiments of the present application applies the online IV curve scanning technology, which will be described separately below in combination with different types of photovoltaic power generation systems.

[0069] First, the photovoltaic power generation system based on a string inverter will be described below.

[0070] Refer to Figure 2 , which is a schematic diagram of a photovoltaic power generation system based on a string inverter.

[0071] This photovoltaic power generation system includes a photovoltaic unit 10, a string inverter 11, an AC busbar box / switch box 12, and a transformer 13.

[0072] Among them, each photovoltaic unit 10 includes one or more photovoltaic modules. Among them, a photovoltaic module is a DC power source formed by series and parallel packaging of solar cells.

[0073] When the photovoltaic unit 10 includes multiple photovoltaic modules, the multiple photovoltaic modules can form a photovoltaic string through the head-to-tail series connection of the positive and negative poles to form the photovoltaic unit 10; the multiple photovoltaic modules can also be first connected in series to form multiple photovoltaic strings, and then the multiple photovoltaic strings are connected in parallel to form the photovoltaic unit 10.

[0074] The DC side of the string inverter 11 is connected to one or more photovoltaic units 10. In practical applications, the DC side of the string inverter 11 is generally connected to multiple photovoltaic units 10.

[0075] The string inverter will be specifically introduced below.

[0076] Refer to Figure 3, This figure is a schematic diagram of a string inverter.

[0077] The string inverter 11 includes a two-stage power conversion circuit. The first stage is a DC-DC circuit 111, that is, a DC-DC boost circuit, and the second stage is a DC-AC circuit 112, that is, an inverter circuit. Among them, the string inverter 11 generally includes multiple DC-DC circuits 111. The positive output ports of the multiple DC-DC circuits 111 are connected in parallel to the positive input port of the DC side of the DC-AC circuit 112, and the negative output ports of the multiple DC-DC circuits 111 are connected in parallel to the negative input port of the DC side of the DC-AC circuit 112.

[0078] The AC outgoing terminal of the DC-AC circuit 112 is the output terminal of the string inverter 11.

[0079] Each DC-DC circuit 111 is connected to at least one photovoltaic unit 10. The positive input port of each DC-DC circuit 111 is connected to the positive electrode of the photovoltaic unit 10, and the negative input port of each DC-DC circuit 111 is connected to the negative electrode of the photovoltaic unit 10.

[0080] The alternating current output by multiple string inverters 11 is collected after passing through the AC busbar box / switch box 12, and then connected to the AC power grid 14 through the transformer 13, or can also be directly connected to a single-phase or three-phase AC power grid.

[0081] The online IV curve scanning technology applied to the above photovoltaic power generation system controls the input voltage of the DC-DC circuit 111 in the string inverter 11, and thus achieves the effect of scanning the output voltage of the photovoltaic unit, that is, realizes the IV curve scanning of the photovoltaic unit.

[0082] Next, a photovoltaic power generation system based on a centralized inverter and an MPPT boost busbar box will be described.

[0083] See Figure 4 , This figure is a schematic diagram of a photovoltaic power generation system based on a centralized inverter and an MPPT boost busbar box.

[0084] The illustrated photovoltaic power generation system includes a photovoltaic unit 10, an MPPT boost busbar box 20, a centralized inverter 21, and a transformer 13.

[0085] Among them, the MPPT boost busbar box is a kind of DC-DC boost converter, which will be specifically described below with reference to the accompanying drawings.

[0086] See Figure 5 , This figure is a schematic diagram of the MPPT boost busbar box.

[0087] The MPPT boost combiner box 20 generally includes at least two DC-DC circuits 111. Each of the DC-DC circuits 111 is respectively connected to at least one photovoltaic unit 10. The positive input port of each DC-DC circuit 111 is connected to the positive electrode of the photovoltaic unit 10, and the negative input port of the DC-DC circuit 111 is connected to the negative electrode of the photovoltaic unit 10.

[0088] The positive output ports of each DC-DC circuit 111 are connected in parallel to the positive electrode of the output DC bus, and the negative output ports of each DC-DC circuit 111 are connected in parallel to the negative electrode of the output DC bus.

[0089] The positive and negative electrodes of the DC bus are respectively used as the positive and negative output ports of the MPPT boost combiner box 20, and are connected to the positive and negative input ports of the subsequent DC load or the centralized inverter 21 through DC cables.

[0090] The centralized inverter 21 is used to convert the single or multiple parallel DC inputs connected to the DC side into AC output, and generally adopts DC-AC single-stage power conversion. The AC power output by the centralized inverter 21 is fed into the AC grid 14 after passing through the transformer 13.

[0091] Since the centralized inverter 21 is generally at a relatively long electrical distance from the photovoltaic unit 10, at this time, it is necessary to use the DC-DC circuit 111 in the MPPT boost combiner box 20 to control the output voltage of the photovoltaic unit to achieve the IV curve scanning of the photovoltaic unit.

[0092] Next, a photovoltaic power generation system based on a photovoltaic optimizer and a string inverter will be described.

[0093] See Figure 6 , which is a schematic diagram of a photovoltaic power generation system based on a photovoltaic optimizer and a string inverter.

[0094] The illustrated photovoltaic power generation system includes a photovoltaic unit 10, a photovoltaic optimizer 30, a string inverter 11, an AC switch 31, and an ammeter 32.

[0095] Among them, the photovoltaic optimizer 30 is a DC-DC converter, its input side is connected to the photovoltaic unit 10, and its output side is connected to the string inverter or the centralized inverter in series, and is used to increase or decrease the output voltage of the photovoltaic unit. Figure 6 In

[0096] The photovoltaic optimizer 30 includes a DC-DC circuit, and the DC-DC circuit is a buck circuit, a boost circuit or a buck-boost circuit. The positive input port of the DC-DC circuit is connected to the positive electrode of the photovoltaic unit 10, and the negative input port of the DC-DC circuit is connected to the negative electrode of the photovoltaic unit 10.

[0097] The positive pole of the DC-DC circuit is connected to the positive pole of the output DC bus, serving as the positive output port of the PV optimizer 30; the negative pole of the DC-DC circuit is connected to the negative pole of the output DC bus, serving as the negative output port of the PV optimizer 30.

[0098] In a PV power generation system applying the PV optimizer 30, generally multiple PV optimizers 30 are connected in series to form a sub-string.

[0099] For example, N PV optimizers are connected in series end to end, that is, the positive output port of the i-th PV optimizer is connected to the negative output port of the (i - 1)-th PV optimizer, and the negative output port of the i-th PV optimizer is connected to the positive output port of the (i + 1)-th PV optimizer, where i = 2, 3, …, N - 1. The positive output port of the first PV optimizer serves as the positive output port of the PV optimizer sub-string, and the negative output port of the N-th PV optimizer serves as the negative output port of the PV optimizer sub-string. The output end of the PV optimizer sub-string is connected to the input end of a post-stage MPPT boost combiner box, or a string inverter, or a central inverter via a DC cable. In the figure, connecting the string inverter 11 is taken as an example.

[0100] The alternating current output by the string inverter 11 is fed into the AC grid after passing through the transformer 13.

[0101] When performing an on-line IV curve scan, for the DC-DC circuits of the string inverter 11 connected to Figure 2 and the DC-DC circuits of the MPPT boost combiner box 20 connected to Figure 4 and the PV units of the DC-DC circuits of the string inverter 11 connected to Figure 6 perform an IV curve scan.

[0102] In one implementation, a serial scan method is adopted, and multiple DC-DC circuits sequentially perform an IV curve scan one by one, that is, first perform an IV curve scan on the PV units connected to the first DC-DC circuit, and after completion, then perform an IV curve scan on the PV units connected to the second DC-DC circuit, and so on, until the scanning of all PV units is completed.

[0103] The time consumption of the serial scan method is relatively long. During the scan, the illumination condition may fluctuate due to environmental condition changes, affecting the obtained scan curve and diagnostic result. And during the scan, the output power of the PV converter will continuously fluctuate, reducing the grid-connected power quality of the PV power generation system.

[0104] In another possible implementation, a parallel scanning method is adopted, that is, the IV curve scanning is performed on the photovoltaic units connected to multiple DC-DC circuits simultaneously. Although this method reduces the scanning time, the output power of the photovoltaic converter fluctuates violently during the scanning, seriously reducing the grid-connected power quality of the photovoltaic power generation system.

[0105] To solve the above problems, the embodiments of the present application provide a photovoltaic power generation system, a photovoltaic inverter, a busbar box, a photovoltaic optimizer and an IV curve scanning method, which can perform IV curve scanning on the photovoltaic units connected to multiple DC-DC circuits simultaneously, saving the scanning time, and can also avoid the total output power of the photovoltaic power generation system from fluctuating violently during the online IV curve scanning, thereby reducing the negative impact of the online IV curve scanning on the grid-connected power quality.

[0106] The technical solutions of the present application will be described in detail below with reference to the accompanying drawings.

[0107] The terms "first", "second", etc. used in the following description of the present application are only for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features.

[0108] In the present application, unless otherwise clearly specified and limited, the term "connection" should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or integrated; it can be a direct connection or an indirect connection through an intermediate medium.

[0109] See Figure 7 , which is a schematic diagram of a photovoltaic power generation system provided by an embodiment of the present application.

[0110] The photovoltaic power generation system includes a photovoltaic unit 10, a controller 40, and M groups of DC-DC circuits.

[0111] Wherein, M is a positive integer.

[0112] Each group of DC-DC circuits includes N DC-DC circuits 111a1 - 111aN.

[0113] Wherein, N is a positive integer greater than 1.

[0114] The photovoltaic unit 10 includes at least one photovoltaic module. When the photovoltaic unit 10 includes multiple photovoltaic modules, the multiple photovoltaic modules can form a photovoltaic string by connecting the positive and negative poles in series end to end to form the photovoltaic unit 10; the multiple photovoltaic modules can also be first connected in series to form multiple photovoltaic strings, and then the multiple photovoltaic strings are connected in parallel to form the photovoltaic unit 10. The embodiments of the present application do not specifically limit the number of photovoltaic modules included in the photovoltaic unit.

[0115] For each DC-DC circuit, its input terminal is connected to at least one photovoltaic unit 10. The positive input port of the DC-DC circuit is connected to the positive electrode of the photovoltaic unit 10, and the negative input port of the DC-DC circuit is connected to the negative electrode of the photovoltaic unit 10.

[0116] The DC-DC circuit is used to perform DC conversion on the direct current input by the photovoltaic unit 10 and then output it.

[0117] The controller 40 is used to control the DC-DC circuits in each group to start the online IV curve scanning in sequence, and the time interval between the start of the online IV curve scanning of two adjacent DC-DC circuits is less than the time taken for one DC-DC circuit to perform the online IV curve scanning. The following is a specific description.

[0118] When the controller 40 controls the N DC-DC circuits 111a1 - 111aN in each group to perform scanning in sequence, the DC-DC circuit 111a1 starts the online IV curve scanning first, the DC-DC circuit 111a2 starts the online IV curve scanning after T1, the DC-DC circuit 111a3 starts the online IV curve scanning after T2, …, the DC-DC circuit 111aN starts the online IV curve scanning after T N-1 After that, then T1, T2, … T N-1 Represents the time interval. Let T0 represent the time taken for one DC-DC circuit to perform the online IV curve scanning, then T1, T2, … T N-1 Are all less than T0.

[0119] The embodiments of the present application do not make specific limitations on the size of the time interval. In addition, the above time intervals T1, T2, … T N-1 Can be the same or different, and the embodiments of the present application do not make specific limitations. In a preferred implementation manner, the above time intervals are the same to further reduce the fluctuation of the total output power of the N DC-DC circuits during the online IV curve scanning and facilitate control.

[0120] It should be noted that the adjacent in this solution does not refer to the physical adjacency, but the adjacency in the order of starting the IV curve scanning.

[0121] The controller 40 may be an Application Specific Integrated Circuit (ASIC), a Programmable Logic Device (PLD), a Digital Signal Processor (DSP), or a combination thereof. The above PLD may be a Complex Programmable Logic Device (CPLD), a Field-programmable Gate Array (FPGA), a Generic Array Logic (GAL), or any combination thereof. The embodiments of the present application do not make specific limitations thereon.

[0122] Each group of DC-DC circuits 111a1-111aN includes a controllable switch tube. The embodiments of the present application do not specifically limit the type of the controllable switch tube. For example, it may be an Insulated Gate Bipolar Transistor (IGBT), a Metal Oxide Semiconductor Field Effect Transistor (MOSFET, hereinafter referred to as MOS tube), a Silicon Carbide Metal Oxide Semiconductor (SiC MOSFET), etc. The controller 40 may send a control signal to the controllable switch tube to control the working state of the controllable switch tube. The control signal may be a Pulse Width Modulation (PWM) signal, a Pulse Frequency Modulation (PFM) signal, etc. The embodiments of the present application do not make specific limitations thereon.

[0123] In summary, the photovoltaic power generation system controls the N DC-DC circuits in each group to start online IV curve scanning in sequence. After the first group of DC-DC circuits starts online IV curve scanning, the remaining DC-DC circuits do not wait for the previous one to complete the scanning before starting, but perform staggered scanning, that is, the time interval for starting the scanning is less than the time used for online IV curve scanning of one DC-DC circuit. At this time, the N DC-DC circuits perform peak-shifting output. On the one hand, it can simultaneously perform online IV curve scanning on the photovoltaic units connected to multiple DC-DC circuits, saving scanning time. On the other hand, it can make the total output power of the photovoltaic power generation system relatively stable, avoiding drastic fluctuations in the total output power during online IV curve scanning, and thus reducing the negative impact of online IV curve scanning on the grid-connected power quality.

[0124] The application scenarios of the technical solution provided in this application include: large-scale photovoltaic power station scenarios, medium and small-scale distributed photovoltaic power station scenarios, household photovoltaic power generation systems, etc.

[0125] The following is an illustration in combination with specific implementation manners. In the following descriptions of the embodiments of this application, M = 1 is taken as an example. When M is an integer greater than 1, the principle is similar, and this application will not elaborate one by one. In addition, the number of photovoltaic units 10 connected to each DC-DC circuit is the same in the following descriptions.

[0126] See Figure 8 , which is a schematic diagram of another photovoltaic power generation system provided by the embodiment of this application.

[0127] The controller 40 specifically includes a control unit 401 and an output storage unit 402. Among them, the control unit 401 is used to control the N DC-DC circuits to perform online IV curve scanning, that is, the control unit 401 can control the working states of the N DC-DC circuits.

[0128] The data storage unit 402 includes a memory, and the memory can include a volatile memory (Volatile Memory, VM), such as a random access memory (Random-access Memory, RAM). The memory can also include a non-volatile memory (Non-volatile Memory, NVM), such as a read-only memory (Read-only Memory, ROM), a flash memory, a hard disk drive (hard disk drive, HDD) or a solid-state drive (Solid-state Drive, SSD); the memory can also include a combination of the above types of memories. The memory can refer to one memory or include multiple memories. Data transmission of the scanning data can be performed between the control unit 401 and the data storage unit 402.

[0129] The host computer 50 is a computer that can directly issue control commands, and is used to send a scanning instruction for online IV curve scanning to the controller.

[0130] After the controller 40 obtains the scanning instruction issued by the host computer 50, it starts to perform online IV curve scanning. When the control unit 401 of the controller controls the N DC-DC circuits to perform scanning in sequence, it can be controlled according to voltage or time, which will be specifically described below.

[0131] The first type: control according to voltage.

[0132] When the control unit 401 controls each DC-DC circuit to perform online IV curve scanning, it first increases the input voltage of this DC-DC circuit until the input current of this DC-DC circuit is zero. At this time, the input voltage of this DC-DC circuit is the sum of the open-circuit voltages of all the photovoltaic units 10 connected. The control unit 401 obtains this open-circuit voltage at this time and transmits the result to the host computer 50 and / or stores it in the data storage unit 402.

[0133] The control unit 401 then controls the input voltage of this DC-DC circuit to gradually decrease to zero. And during this process, the corresponding relationship between the input voltage and the input current of this DC-DC circuit is obtained at a preset sampling interval, so as to obtain the scanning result of the IV curve. Among them, the input current corresponding to the zero input voltage is the sum of the short-circuit currents of all the photovoltaic units 10 connected to this DC-DC circuit.

[0134] The scanning result can be transmitted to the host computer 50 and / or stored in the data storage unit 402.

[0135] The embodiment of the present application does not limit the specific implementation manner of controlling the input voltage of this DC-DC circuit to gradually decrease to zero, but this manner needs to show a rule of overall decrease. For example, in some embodiments, when the control unit 401 controls the input voltage to decrease, it can control the input voltage to first decrease, then remain unchanged, and then decrease, and so on in a cycle until it decreases to zero.

[0136] For the N DC-DC circuits, the control unit 401 first controls the first DC-DC circuit to start online IV curve scanning. For the remaining N-1 DC-DC circuits, it controls the k-th DC-DC circuit to start online IV curve scanning when the input voltage of the (k-1)-th DC-DC circuit decreases to less than a preset voltage threshold, so that the time interval is less than the time taken for one DC-DC circuit to perform online IV curve scanning. Wherein, k = 2, 3,..., N.

[0137] For the convenience of understanding, the following takes N = 4 as an example for illustration. The principle is similar when N takes other values.

[0138] See Figure 9 , which is a timing diagram of the start of scanning of the DC-DC circuit provided by the embodiment of the present application Figure 1 .

[0139] Among them, V oc represents the sum of the open-circuit voltages of all photovoltaic units 10 connected to each DC-DC circuit, and V A represents a preset voltage threshold value.

[0140] At time 0 (i.e., the initial time), the first DC-DC circuit starts online IV curve scanning. The control unit 401 first controls the input voltage of the first DC-DC circuit to rise until the input current of this DC-DC circuit is zero, and then controls the input voltage of this DC-DC circuit to gradually decrease. When it decreases to less than the preset voltage threshold V A at time T1, at this time, the control unit 401 controls the second DC-DC circuit to start online IV curve scanning. And so on, when the input voltage of the second DC-DC circuit decreases to less than the preset voltage threshold V A at time T2, the control unit 401 controls the third DC-DC circuit to start online IV curve scanning. When the input voltage of the third DC-DC circuit decreases to less than the preset voltage threshold V A at time T3, the control unit 401 controls the fourth DC-DC circuit to start online IV curve scanning.

[0141] It can be seen from Figure 9 that within the time period from T1 to T2 + T0, multiple DC-DC circuits are scanning simultaneously. And the multiple DC-DC circuits perform peak-shifted output, which can make the total output power of the photovoltaic power generation system relatively stable during the scanning period and reduce the fluctuation. In addition, when N = 4, if the existing serial IV curve online scanning technology is used, the time required is 4T0, while the scanning time shown in the figure is T3 + T0, that is, the solution provided by the embodiment of the present application can also shorten the time required for online IV curve scanning.

[0142] In some embodiments, the preset voltage threshold is positively correlated with the value of N. The more DC-DC circuits are connected to the photovoltaic system, the higher the power of the photovoltaic power generation system. At this time, the preset voltage threshold can be increased, so as to shorten the time required for online IV curve scanning on the premise of maintaining the relative stability of the total output power of the photovoltaic power generation system.

[0143] For example, in a possible implementation manner, when starting 5 DC-DC circuits, the preset voltage threshold is V A1 ; when starting 10 DC-DC circuits, the preset time interval is V A2 , then at this time V A1 < V A2 .

[0144] The corresponding relationship between the preset voltage threshold and the number N of DC-DC circuits can be determined in advance and stored in the data storage unit 402.

[0145] In some embodiments, according to the V obtained during the IV curve scan of the previous DC-DC circuit oc , the moment to start the online IV curve scan is determined, that is, the preset voltage threshold is the product of the sum of the open circuit voltages of the photovoltaic units connected to the (k-1)-th DC-DC circuit and the first preset ratio.

[0146] Among them, the first preset ratio can be determined according to the actual situation, and the embodiments of the present application do not make specific limitations here.

[0147] In other embodiments, the preset voltage threshold is the product of the sum of the preset open circuit voltages of the photovoltaic units connected to the (k-1)-th DC-DC circuit and the first preset ratio. The rated open circuit voltage range of each photovoltaic unit is a known device parameter, and the preset open circuit voltage of each photovoltaic unit can be determined according to the rated open circuit voltage range. For example, the maximum value, minimum value or intermediate value in the rated open circuit voltage range can be selected.

[0148] The second method: control according to time.

[0149] The control unit 401 first controls the first DC-DC circuit to start the online IV curve scan, and then controls the remaining DC-DC circuits to start the online IV curve scan in sequence at preset time intervals.

[0150] Among them, the preset time interval is less than the time required for a DC-DC circuit to perform an online IV curve scan.

[0151] When the control unit 401 controls a DC-DC circuit to perform an online IV curve scan, it first raises the input voltage of this DC-DC circuit until the input current of the DC-DC circuit is zero. At this time, the input voltage of this DC-DC circuit is the sum of the open circuit voltages V of all the photovoltaic units 10 connected oc , and the control unit 401 obtains this open circuit voltage V at this time oc , and transmits the detection result to the host computer 50 and / or stores it in the data storage unit 402.

[0152] The control unit 401 further controls the input voltage of this DC-DC circuit to gradually decrease to zero, and during this process, obtains the corresponding relationship between the input voltage and input current of this DC-DC circuit at a preset sampling interval, thereby obtaining the scanning result of the IV curve. Among them, the input current corresponding to the zero input voltage is the sum of the short-circuit currents of all the photovoltaic units 10 connected to this DC-DC circuit. The scanning result can be transmitted to the host computer 50 and / or saved in the data storage unit 402.

[0153] The embodiments of the present application do not limit the specific implementation manner of controlling the input voltage of this DC-DC circuit to gradually decrease to zero, but overall shows a decreasing pattern.

[0154] For the convenience of understanding, hereinafter, N is taken as 4 as an example for illustration, and the principle is similar when N takes other values.

[0155] See Figure 10 This figure is a timing diagram showing the start of scanning of the DC-DC circuit provided by the embodiments of the present application. Figure 2 .

[0156] At the moment 0 (i.e., the initial moment), the first DC-DC circuit starts the online IV curve scanning. The second DC-DC circuit starts the online IV curve scanning after T1. The third DC-DC circuit starts the online IV curve scanning after T2. The fourth DC-DC circuit starts the online IV curve scanning after T3. T1, T2, and T3 represent preset time intervals, and the preset time intervals can be the same or different. Let T0 represent the time taken for a DC-DC circuit to perform the online IV curve scanning, then each preset time interval is less than T0.

[0157] It can be seen from Figure 10 that during the online IV curve scanning process, multiple DC-DC circuits may be scanning simultaneously. And since the control unit 401 controls each DC-DC circuit to perform the online IV curve scanning, first raises the input voltage of the DC-DC circuit until the input current of the DC-DC circuit is zero, and then controls the input voltage of the DC-DC circuit to gradually decrease to zero, there is a peak-shifting output for multiple DC-DC circuits, which can make the total output power of the photovoltaic power generation system relatively stable during the scanning period.

[0158] In some embodiments, the preset time interval is negatively correlated with the value of N. The more DC-DC circuits are connected to the photovoltaic system, the higher the power of the photovoltaic power generation system. At this time, the preset time interval can be reduced, thereby shortening the time taken for the online IV curve scanning on the premise of maintaining the relative stability of the total output power of the photovoltaic power generation system.

[0159] For example, in a possible implementation, the control unit 40 controls the multi-channel DC-DC circuits to perform scans in sequence at the same preset time interval. When starting 5 DC-DC circuits, the preset time intervals T1, T2, T3, and T4 are the same and are all ΔT1; when starting 10 DC-DC circuits, the preset time intervals T1, T2, … T9 are the same and are all ΔT2, and at this time, ΔT2 < ΔT1.

[0160] For another example, in another possible implementation, the control unit 40 controls the multi-channel DC-DC circuits to perform scans in sequence at different preset time intervals. When starting 4 DC-DC circuits, the preset time intervals are T1, T2, and T3 respectively; when starting 10 DC-DC circuits, the preset time intervals are t1, t2, t3, … t9 respectively, and at this time, t1 < T1, t2 < T2, t3 < T3.

[0161] The corresponding relationship between the preset time interval and the number N of DC-DC circuits can be determined in advance and stored in the data storage unit 402.

[0162] In some embodiments, the preset time interval is the product of the time taken for an online IV curve scan of one DC-DC circuit and a second preset ratio. The second preset ratio can be determined according to the actual situation, and the embodiments of the present application do not make specific limitations here.

[0163] In the above description, a photovoltaic power generation system including a group of DC-DC circuits is taken as an example for illustration. When the photovoltaic power generation system includes multiple groups of DC-DC circuits, the controller 40 can control the multiple groups of DC-DC circuits to perform online IV curve scans synchronously. That is, simultaneously control the first DC-DC circuit of each group of DC-DC circuits to start scanning.

[0164] The technical effects of the photovoltaic power generation system will be described below in combination with the simulation waveforms.

[0165] See Figure 11 , this figure is a schematic diagram of the output power when the photovoltaic power generation system provided by the embodiment of the present application performs an online IV curve scan.

[0166] To more clearly demonstrate the technical effects of the solution of this application, this figure is a schematic diagram when a 3-way DC-DC performs an online IV curve scan in a cycle. It can be seen from this attached figure that the first DC-DC circuit starts the scan first. After a period of time, multiple DC-DC circuits perform the scan simultaneously. However, since the start times of the DC-DC circuits performing the scan simultaneously are different, that is, there is a staggered output. Specifically, for the DC-DC circuits performing the scan simultaneously, the output powers of several of them are relatively low, and the output powers of several others are relatively high. After being superimposed on each other, the total output power of the photovoltaic power generation system is maintained relatively stable, avoiding drastic fluctuations.

[0167] In summary, by using the photovoltaic power generation system provided in the embodiments of this application, it is possible to simultaneously perform an online IV curve scan on the photovoltaic units connected to multiple DC-DC circuits, saving the scan time. It can also make the total output power of the photovoltaic power generation system relatively stable, avoiding drastic fluctuations in the total output power during the online IV curve scan, and thus reducing the negative impact of the online IV curve scan on the grid-connected power quality.

[0168] Next, another implementation manner of this photovoltaic power generation system will be described.

[0169] Refer to Figure 12 , this figure is a schematic diagram of another photovoltaic power generation system provided in the embodiments of this application.

[0170] This photovoltaic power generation system is a photovoltaic power generation system based on a string inverter, and the corresponding relevant descriptions can be referred to Figure 2 for corresponding relevant descriptions.

[0171] This photovoltaic power generation system further includes a DC-AC circuit (which can also be called an inverter circuit) 112. M groups of DC-DC circuits 111 and the DC-AC circuit 112 form a string inverter 11. Among them, the positive output port of each DC-DC circuit is connected in parallel to the positive input port of the DC-AC circuit 112, and the negative output port of each DC-DC circuit is connected in parallel to the negative input port of the DC-AC circuit 112.

[0172] The DC-AC circuit 112 is used to convert the direct current input by the DC-DC circuit into alternating current and then output it.

[0173] The control unit 401 can also be integrated with the controller of the DC-AC circuit 112, that is, the controller can also control the control state of the DC-AC circuit 112.

[0174] In some embodiments, this controller is the controller of the string inverter 11.

[0175] For the working principle of the controller, reference can be made to the description in the above embodiments, which will not be elaborated here.

[0176] For each group of DC-DC circuits of the string inverter 11, after the first DC-DC circuit starts the online IV curve scanning, the remaining DC-DC circuits in each group do not wait for the previous one to complete the scanning before starting their own scans. Instead, they perform the online IV curve scanning in sequence, and the time interval is less than the time taken for one DC-DC circuit to perform the online IV curve scanning, achieving interleaved scanning. At this time, the N DC-DC circuits in each group output with staggered peaks, enabling the online IV curve scanning of the photovoltaic units connected to multiple DC-DC circuits simultaneously, saving the scanning time, and also making the total output power of the string inverter 11 relatively stable, reducing the negative impact of the string inverter 11 on the grid power quality during the online IV curve scanning.

[0177] Next, another implementation manner of the photovoltaic power generation system will be described.

[0178] Refer to Figure 13 , which is a schematic diagram of another photovoltaic power generation system provided by an embodiment of the present application.

[0179] The photovoltaic power generation system includes a DC busbar box 20. For relevant descriptions, reference can be made to Figure 4 the corresponding relevant explanations.

[0180] At this time, the positive output ports of the M groups of DC-DC circuits are connected in parallel to form the positive output port of the DC busbar box 20, and the negative output ports of the M groups of DC-DC circuits are connected in parallel to form the negative output port of the DC busbar box 20.

[0181] For the working principle of the controller, reference can be made to the description in the above embodiments, which will not be elaborated here.

[0182] In some embodiments, the DC busbar box 20 is specifically an MPPT boost busbar box, which is used to perform DC conversion on the direct current input by the photovoltaic unit and track the maximum power point of the photovoltaic unit.

[0183] The output end of the DC busbar box 20 can be connected to a DC load or an inverter.

[0184] At this time, the controller can be integrated with the controller of the DC busbar box 20. For the working principle of the controller, reference can be made to the description in the above embodiments, which will not be elaborated here.

[0185] For each group of DC-DC circuits in the DC busbar box 20, after the first DC-DC circuit starts the online IV curve scanning, the remaining DC-DC circuits do not wait for the previous one to complete the scanning before starting their own scans. Instead, they perform the online IV curve scanning sequentially, with a time interval less than the time taken for one DC-DC circuit to perform the online IV curve scanning, achieving interleaved scanning. At this time, the N DC-DC circuits in each group output with staggered peaks, enabling the online IV curve scanning of the photovoltaic units connected to multiple DC-DC circuits simultaneously, saving scanning time, and making the total output power of the DC busbar box 20 relatively stable, reducing the negative impact of the DC busbar box 20 on the grid-connected power quality during the online IV curve scanning.

[0186] The following describes another implementation of the photovoltaic power generation system.

[0187] See Figure 14 , which is a schematic diagram of another photovoltaic power generation system provided by an embodiment of the present application.

[0188] The photovoltaic power generation system includes a photovoltaic optimizer 30, which can refer to Figure 6 the corresponding relevant description.

[0189] The photovoltaic optimizer 30 is a DC-DC circuit, which is used to step up or step down the direct current input by the photovoltaic module and then output it. At this time, the photovoltaic power generation system includes M groups of photovoltaic optimizers, and each group includes N photovoltaic optimizers.

[0190] In the photovoltaic power generation system applying the photovoltaic optimizer 30, generally, multiple photovoltaic optimizers 30 are connected in series to form a photovoltaic optimizer sub-string 60.

[0191] For example, the N photovoltaic optimizers in each group are connected in series at the head and tail, that is, the positive output port of the i-th photovoltaic optimizer is connected to the negative output port of the i - 1-th photovoltaic optimizer, and the negative output port of the i-th photovoltaic optimizer is connected to the positive output port of the i + 1-th photovoltaic optimizer, where i = 2, 3,..., N - 1. The positive output port of the first photovoltaic optimizer serves as the positive output port of the photovoltaic optimizer sub-string 60, and the negative output port of the N-th photovoltaic optimizer serves as the negative output port of the photovoltaic optimizer sub-string 60. The output end of the photovoltaic optimizer sub-string 60 is connected to the input end of the subsequent MPPT boost busbar box, or the string inverter, or the centralized inverter through a DC cable.

[0192] In a possible implementation, the controller can be integrated with the controller of the photovoltaic optimizer. At this time, the number of controllers is the same as the number of photovoltaic optimizers, and the host computer 50 issues scanning instructions to each controller simultaneously.

[0193] In another possible implementation, the controller of the photovoltaic optimizer is independently set, and all the photovoltaic optimizers can be controlled by one controller or a plurality of controllers to perform online IV curve scanning.

[0194] For the working principle of the controller, reference can be made to the description in the above embodiments, which will not be elaborated here.

[0195] For the photovoltaic power generation system applying the photovoltaic optimizer sub-string 60, after the first path of photovoltaic optimizer starts online IV curve scanning, the remaining paths of photovoltaic optimizers do not wait for the previous path to complete scanning before starting scanning, but perform online IV curve scanning in sequence, and the time interval is less than the time taken for one path of photovoltaic optimizer to perform online IV curve scanning, realizing staggered scanning. That is, at this time, the photovoltaic optimizers perform peak-shifting output, and online IV curve scanning can be simultaneously performed on the photovoltaic units connected to multiple paths of photovoltaic optimizers, saving scanning time, and also making the total output power of the photovoltaic optimizer sub-string 60 relatively stable, reducing the negative impact of the photovoltaic optimizer sub-string 60 on the grid power quality during online IV curve scanning.

[0196] Based on the photovoltaic power generation system provided in the above embodiments, an embodiment of the present application further provides an online IV curve scanning method, which is applied to a photovoltaic power generation system. The photovoltaic power generation system includes photovoltaic units and M groups of DC-DC circuits, each group includes N paths of DC-DC circuits, M is a positive integer, and N is an integer greater than 1. The input end of each path of DC-DC circuit is connected to at least one path of photovoltaic unit, and each path of photovoltaic unit includes at least one photovoltaic module. The method includes:

[0197] Controlling the N paths of DC-DC circuits in each group to start online IV curve scanning in sequence, and controlling the time interval between the start of online IV curve scanning of adjacent two paths of DC-DC circuits to be less than the time taken for one path of DC-DC circuit to perform online IV curve scanning.

[0198] The following will be specifically described with reference to the drawings. The following method takes controlling the N paths of DC-DC circuits in one group to perform online IV curve scanning as an example, and the same method can be used for synchronous control of the remaining groups.

[0199] See Figure 15 , which is a flowchart of an online IV curve scanning method provided by an embodiment of the present application.

[0200] The method includes the following steps:

[0201] S1601: Issue a scanning instruction.

[0202] The scanning instruction is used to instruct the N paths of DC-DC circuits in each group to perform online IV curve scanning.

[0203] S1602: Control the first DC-DC circuit to start online IV curve scanning.

[0204] S1603: Increase the input voltage of the first DC-DC circuit until its input current is 0.

[0205] At this time, the input voltage of this DC-DC circuit is the sum of the open-circuit voltages Voc of the connected photovoltaic units.

[0206] S1604: Obtain the sum of the open-circuit voltages Voc of the photovoltaic units connected to the first DC-DC circuit.

[0207] S1605: Control the input voltage of the first DC-DC circuit to gradually decrease from Voc to zero.

[0208] S1606: Control the remaining N - 1 DC-DC circuits to start online IV curve scanning in sequence, and the time interval between the start of online IV curve scanning of adjacent two DC-DC circuits is less than the interval for one DC-DC circuit to perform online IV curve scanning.

[0209] This step can be controlled according to voltage or time, and the specific description is as follows:

[0210] The first type: Control according to voltage

[0211] For N DC-DC circuits, after controlling the first DC-DC circuit to start online IV curve scanning, for the remaining N - 1 DC-DC circuits, control the k-th DC-DC circuit to start online IV curve scanning when the input voltage of the (k - 1)-th DC-DC circuit decreases to less than the preset voltage threshold, so that the time interval is less than the time used for one DC-DC circuit to perform online IV curve scanning. Where k = 2, 3,..., N.

[0212] The preset voltage threshold is positively correlated with the value of N. The more DC-DC circuits are connected to the photovoltaic system, the higher the power of the photovoltaic power generation system. At this time, the preset voltage threshold can be increased, so as to shorten the time used for online IV curve scanning on the premise of maintaining the relatively stable total output power of the photovoltaic power generation system.

[0213] In some embodiments, according to the Voc obtained when performing IV curve scanning on the previous DC-DC circuit, determine the moment to start online IV curve scanning, that is, this preset voltage threshold is the product of the sum of the open-circuit voltages of the photovoltaic units connected to the (k - 1)-th DC-DC circuit and the first preset ratio.

[0214] In some other embodiments, the preset voltage threshold is the product of the sum of the preset open-circuit voltages of the photovoltaic units connected to the (k - 1)-th DC-DC circuit and a first preset ratio. The rated open-circuit voltage range of each photovoltaic unit is a known device parameter, and the preset open-circuit voltage can be determined according to the rated open-circuit voltage range. For example, the maximum value, minimum value, or intermediate value within the rated open-circuit voltage range can be selected.

[0215] The second method: control according to time.

[0216] First, control the first DC-DC circuit to start the online IV curve scanning, and then control the remaining DC-DC circuits to start the online IV curve scanning in sequence at a preset time interval.

[0217] In some embodiments, the preset time interval is negatively correlated with the value of N. The more DC-DC circuits are connected to the photovoltaic system, the higher the power of the photovoltaic power generation system. At this time, the preset time interval can be reduced, so as to shorten the time used for the online IV curve scanning on the premise of maintaining the relative stability of the total output power of the photovoltaic power generation system.

[0218] S1607: Obtain the input voltage and input current of each DC-DC circuit.

[0219] S1608: Plot the IV curve of the photovoltaic unit connected to each DC-DC circuit.

[0220] The above step division is only for illustrative purposes and does not constitute a limitation on the method of the present application. For those skilled in the art of this technology, without departing from the principle of this method, other possible implementation manners can also be adopted. For example, the IV curve can be plotted after all DC-DC circuits have completed the online IV curve scanning.

[0221] In summary, by using the method provided in the embodiments of the present application, after the first DC-DC circuit starts the online IV curve scanning, the remaining DC-DC circuits do not wait for the previous one to complete the scanning before starting the scanning, but perform the online IV curve scanning in sequence, and the time interval is less than the time used for the online IV curve scanning of a single DC-DC circuit, that is, staggered scanning is achieved. At this time, the N DC-DC circuits in each group perform peak-shifting output. On the one hand, the online IV curve scanning of the photovoltaic units connected to multiple DC-DC circuits can be performed simultaneously, saving the scanning time. On the other hand, the total output power of the photovoltaic power generation system can be made relatively stable, avoiding a large fluctuation in the total output power during the online IV curve scanning, and thus reducing the negative impact of the online IV curve scanning on the grid-connected power quality.

[0222] The embodiments of the present application also provide a photovoltaic inverter, which will be specifically described below with reference to the drawings.

[0223] SeeFigure 16 , which is a schematic diagram of a photovoltaic inverter provided by an embodiment of the present application.

[0224] The photovoltaic inverter 11 includes M groups of DC-DC circuits 111, a DC-AC circuit 112, and a controller, where M is a positive integer. Among them, the controller specifically includes a control unit 401 and a data storage unit 402.

[0225] Each group includes N DC-DC circuits, where N is an integer greater than 1.

[0226] The input end of each DC-DC circuit 111 is connected to at least one path of photovoltaic units, and each path of photovoltaic units includes at least one photovoltaic module.

[0227] The positive input port of the DC-DC circuit 111 is connected to the positive output end of the photovoltaic unit, and the negative input port of the DC-DC circuit 111 is connected to the negative output end of the photovoltaic unit. The positive output ports of each DC-DC circuit are connected in parallel to the positive input port of the DC-AC circuit 112, and the negative output ports of each DC-DC circuit are connected in parallel to the negative input port of the DC-AC circuit 112.

[0228] The DC-DC circuit 111 is used to perform DC conversion on the direct current obtained from the photovoltaic unit and then transmit it to the DC-AC circuit 112.

[0229] The DC-AC circuit 112 is used to convert the obtained direct current into alternating current.

[0230] When the controller controls each DC-DC circuit to perform an online IV curve scan, it first raises the input voltage of this DC-DC circuit until the input current of this DC-DC circuit is zero. At this time, the input voltage of this DC-DC circuit is the sum of the open-circuit voltages of all the connected photovoltaic units. At this time, this open-circuit voltage is obtained, and the result is transmitted to the upper computer and / or saved in the data storage unit 402.

[0231] Then the controller controls the input voltage of this DC-DC circuit to gradually decrease to zero, and during this process, the corresponding relationship between the input voltage and input current of this DC-DC circuit is obtained according to a preset sampling interval, and then the scan result of the IV curve is obtained. Among them, the input current corresponding to the input voltage of zero is the sum of the short-circuit currents of all the photovoltaic units 10 connected to this DC-DC circuit.

[0232] For the N DC-DC circuits, the controller controls the N DC-DC circuits in each group to start the online IV curve scan in sequence, and the time interval between the start of the online IV curve scan of two adjacent DC-DC circuits is less than the time taken for one DC-DC circuit to perform the online IV curve scan.

[0233] In a possible implementation, the controller first controls the first DC-DC circuit to start the online IV curve scanning. For the remaining N - 1 DC-DC circuits, it controls the k-th DC-DC circuit to start the online IV curve scanning when the input voltage of the (k - 1)-th DC-DC circuit decreases to be less than a preset voltage threshold, so that the time interval is less than the time taken for one DC-DC circuit to perform the online IV curve scanning. Here, k = 2, 3, …, N.

[0234] In some embodiments, the preset voltage threshold is positively correlated with the magnitude of N. The more DC-DC circuits are connected to the photovoltaic system, the higher the power of the photovoltaic power generation system. At this time, the preset voltage threshold can be increased, so as to shorten the time taken for the online IV curve scanning on the premise of maintaining the relatively stable total output power of the photovoltaic power generation system.

[0235] In some embodiments, the moment to start the online IV curve scanning is determined according to the Voc obtained when performing the IV curve scanning on the previous DC-DC circuit, that is, the preset voltage threshold is the product of the sum of the open-circuit voltages of the photovoltaic units connected to the (k - 1)-th DC-DC circuit and a first preset ratio.

[0236] In some other embodiments, the preset voltage threshold is the product of the sum of the preset open-circuit voltages of the photovoltaic units connected to the (k - 1)-th DC-DC circuit and a first preset ratio. The rated open-circuit voltage range of each photovoltaic unit is a known device parameter, and each preset open-circuit voltage can be determined according to the rated open-circuit voltage range, for example, selecting the maximum value, the minimum value or the intermediate value in the rated open-circuit voltage range.

[0237] In another possible implementation, the controller first controls the first DC-DC circuit to start the online IV curve scanning, and then controls the remaining DC-DC circuits to start the online IV curve scanning in sequence at a preset time interval.

[0238] In some embodiments, the preset time interval is negatively correlated with the magnitude of N. The more DC-DC circuits are connected to the photovoltaic system, the higher the power of the photovoltaic power generation system. At this time, the preset time interval can be decreased, so as to shorten the time taken for the online IV curve scanning on the premise of maintaining the relatively stable total output power of the photovoltaic power generation system.

[0239] The preset time interval is the product of the time taken for one DC-DC circuit to perform the online IV curve scanning and a second preset ratio.

[0240] In summary, for each group of DC-DC circuits of the PV inverter, after the first DC-DC circuit starts the online IV curve scanning, the remaining DC-DC circuits in each path do not wait for the previous path to complete the scanning before starting the scanning. Instead, they perform the online IV curve scanning in sequence, and the time interval is less than the time taken for the first DC-DC circuit to perform the online IV curve scanning, that is, interleaved scanning is achieved. At this time, the N DC-DC circuits in each group perform peak-shifted output. On the one hand, it is possible to simultaneously perform the online IV curve scanning on the PV units connected to multiple DC-DC circuits, saving the scanning time. On the other hand, it can make the total output power of the PV inverter relatively stable, avoiding a large fluctuation in the total output power during the online IV curve scanning, and thus reducing the negative impact of the online IV curve scanning of the PV inverter on the grid power quality.

[0241] The embodiment of the present application also provides a DC busbar box, which will be specifically described below with reference to the drawings.

[0242] See Figure 17 , which is a schematic diagram of a DC busbar box provided by an embodiment of the present application.

[0243] The DC busbar box 20 includes a controller and M groups of DC-DC circuits 111, where M is a positive integer. Among them, the controller includes a control unit 401 and a data storage unit 402.

[0244] The input end of each DC-DC circuit 111 is connected to at least one path of PV units, and each path of PV units includes at least one PV module.

[0245] The positive input end of the DC-DC circuit 111 is connected to the positive output end of the PV unit, and the negative input end of the DC-DC circuit 111 is connected to the negative output end of the PV unit.

[0246] The positive output ports of the M groups of DC-DC circuits 111 are connected in parallel to form the positive output port of the DC busbar box 20.

[0247] The negative output ports of the M groups of DC-DC circuits 111 are connected in parallel to form the negative output port of the DC busbar box 20.

[0248] The controller controls the N DC-DC circuits in each group to start the online IV curve scanning in sequence, and the time interval between the start of the online IV curve scanning of two adjacent DC-DC circuits is less than the time taken for one DC-DC circuit to perform the online IV curve scanning.

[0249] For the specific control method of the controller, reference can be made to the description of the above embodiments, and the embodiments of the present application will not be elaborated herein.

[0250] In summary, by using the DC busbar box, it is possible to simultaneously perform online IV curve scanning on photovoltaic units connected by multiple DC-DC circuits, saving scanning time. It can also make the total output power of the photovoltaic inverter relatively stable, avoiding drastic fluctuations in the total output power during online IV curve scanning, thereby reducing the negative impact of the online IV curve scanning photovoltaic inverter on the grid power quality.

[0251] The embodiment of the present application also provides a photovoltaic optimizer, which will be specifically described below with reference to the drawings.

[0252] See Figure 18 , which is a schematic diagram of a photovoltaic inverter sub-string provided by the embodiment of the present application.

[0253] The photovoltaic optimizer 30 includes a DC-DC circuit for boosting or bucking the DC power input by the photovoltaic module and then outputting it. At this time, the photovoltaic power generation system includes M groups of photovoltaic optimizers, and each group includes N photovoltaic optimizers.

[0254] The input end of the DC-DC circuit is connected to at least one path of photovoltaic units, and each path of photovoltaic units includes at least one photovoltaic module.

[0255] The positive input end of the DC-DC circuit (i.e., the positive input end of the photovoltaic optimizer 30) is connected to the positive output end of the photovoltaic unit, and the negative input end of the DC-DC circuit (i.e., the negative input end of the photovoltaic optimizer 30) is connected to the negative output end of the photovoltaic unit.

[0256] The positive output end of the DC-DC circuit is the positive output end of the photovoltaic optimizer 30, and the negative output end of the DC-DC circuit is the negative output end of the photovoltaic optimizer 30.

[0257] In the photovoltaic power generation system applying the photovoltaic optimizer 30, generally, multiple photovoltaic optimizers 30 are connected in series to form a photovoltaic optimizer sub-string 60.

[0258] For example, the N photovoltaic optimizers in each group are connected in series end to end, that is, the positive output port of the i-th photovoltaic optimizer is connected to the negative output port of the (i - 1)-th photovoltaic optimizer, and the negative output port of the i-th photovoltaic optimizer is connected to the positive output port of the (i + 1)-th photovoltaic optimizer, where i = 2, 3,..., N - 1. The positive output port of the first photovoltaic optimizer is used as the positive output port of the photovoltaic optimizer sub-string 60, and the negative output port of the N-th photovoltaic optimizer is used as the negative output port of the photovoltaic optimizer sub-string 60.

[0259] The formed M photovoltaic optimizer sub-strings 60 can be further connected in series.

[0260] The output end of the photovoltaic optimizer sub-string 60 is connected to the input end of the subsequent MPPT boost busbar box, or string inverter, or central inverter through a DC cable.

[0261] In a possible implementation, the controller can be integrated with the controller of the photovoltaic optimizer. At this time, the number of controllers is the same as the number of photovoltaic optimizers, and the host computer issues a scanning instruction to each controller simultaneously.

[0262] In another possible implementation, the controller and the controller of the photovoltaic optimizer are independently arranged. All photovoltaic optimizers can be controlled by one controller or a certain number of controllers to perform an online IV curve scan. For example, one controller controls one photovoltaic optimizer sub-string 60.

[0263] For the specific control method of the controller, reference can be made to the description of the above embodiments, and the embodiments of the present application will not be elaborated herein.

[0264] In summary, for the photovoltaic power generation system applying this photovoltaic optimizer sub-string, an online IV curve scan can be simultaneously performed on the photovoltaic units connected by multiple DC-DC circuits, saving the scanning time. It can also make the total output power of the photovoltaic inverter relatively stable, avoiding a sharp fluctuation in the total output power during the online IV curve scan, and thus reducing the negative impact of the online IV curve scan of the photovoltaic inverter on the grid-connected power quality.

[0265] It should be understood that in the present 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 simultaneously. 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 item (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.

[0266] Each embodiment in this specification is described in a progressive manner. The same or similar parts between each embodiment can be referred to each other, and the key points of each embodiment are the differences from other embodiments. In addition, some or all of the units and modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art can understand and implement it without creative work.

[0267] The above are only specific embodiments of the present application. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present application, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present application.

Claims

1. A photovoltaic power generation system, characterized in that, The photovoltaic power generation system includes a controller and M groups of DC-DC circuits, each group including N DC-DC circuits, where M is a positive integer and N is an integer greater than 1; The input end of each DC-DC circuit is used to connect at least one path of photovoltaic units, and each path of photovoltaic units includes at least one photovoltaic module; The controller is used to control the N DC-DC circuits in each group to start online IV curve scanning in sequence, and the time interval between the start of online IV curve scanning of adjacent two DC-DC circuits is less than the time taken for one DC-DC circuit to perform online IV curve scanning.

2. The photovoltaic power generation system according to claim 1, characterized in that, When the controller controls each DC-DC circuit to perform online IV curve scanning, it first increases the input voltage of the DC-DC circuit until the input current of the DC-DC circuit is zero, and then controls the input voltage of the DC-DC circuit to gradually decrease to zero.

3. The photovoltaic power generation system according to claim 2, wherein Specifically, the controller is used to, after controlling the first DC-DC circuit in each group to start online IV curve scanning, control the k-th DC-DC circuit to start online IV curve scanning when the input voltage of the (k - 1)-th DC-DC circuit decreases to less than a preset voltage threshold, where k = 2, 3,..., N.

4. The photovoltaic power generation system according to claim 3, wherein, The time for each DC-DC circuit to perform online IV curve scanning is the same, and the preset voltage threshold is the product of the sum of the open-circuit voltages of the photovoltaic units connected to the (k - 1)-th DC-DC circuit and a first preset ratio.

5. The photovoltaic power generation system according to claim 3, wherein The preset voltage threshold is the product of the sum of the preset open-circuit voltages of the photovoltaic units connected to the (k - 1)-th DC-DC circuit and a first preset ratio.

6. The photovoltaic power generation system according to claim 2, characterized in that, Specifically, the controller is used to, after controlling the first DC-DC circuit in each group to start online IV curve scanning, the remaining DC-DC circuits start online IV curve scanning in sequence at a preset time interval, and the preset time interval is less than the time taken for one DC-DC circuit to perform online IV curve scanning.

7. The photovoltaic power generation system according to claim 6, wherein The preset time interval is negatively correlated with the magnitude of N.

8. The photovoltaic power generation system according to claim 6 or 7, characterized in that The preset time interval is the product of the time taken for one DC-DC circuit to perform online IV curve scanning and a second preset ratio.

9. The photovoltaic power generation system according to any one of claims 1-8, characterized in that The controller controls the M groups of DC-DC circuits to perform online IV curve scanning synchronously.

10. The photovoltaic power generation system according to any one of claims 1-9, characterized in that, The photovoltaic power generation system further includes a DC-AC circuit, and the DC-AC circuit and the M groups of DC-DC circuits form an inverter; The positive output ports of the M groups of DC-DC circuits are connected in parallel to the positive input port of the DC-AC circuit, and the negative output ports of the M groups of DC-DC circuits are connected in parallel to the negative input port of the DC-AC circuit.

11. The photovoltaic power generation system according to claim 10, characterized in that, The controller is further used to control the working state of the DC-AC circuit.

12. The photovoltaic power generation system according to any one of claims 1-9, characterized in that, The M groups of DC-DC circuits form a DC busbar box; The positive output ports of the M groups of DC-DC circuits are connected in parallel to form the positive output port of the DC busbar box; The negative output ports of the M groups of DC-DC circuits are connected in parallel to form the negative output port of the DC busbar box.

13. The photovoltaic power generation system according to any one of claims 1-9, characterized in that, The DC-DC circuit is a photovoltaic optimizer, and the N photovoltaic optimizers in each group form a photovoltaic optimizer sub-string; The positive output port of the i-th photovoltaic optimizer is connected to the negative output port of the (i - 1)-th photovoltaic optimizer, the negative output port of the i-th photovoltaic optimizer is connected to the positive output port of the (i + 1)-th photovoltaic optimizer, the positive output port of the 1st photovoltaic optimizer is the positive output port of the photovoltaic optimizer sub-string, the negative output port of the N-th photovoltaic optimizer is the negative output port of the photovoltaic optimizer sub-string, and i = 2, 3, …, N - 1.

14. An online IV curve scanning method, characterized in that, Applied to a photovoltaic power generation system, the photovoltaic power generation system includes M groups of DC-DC circuits, each group including N DC-DC circuits, M is a positive integer, and N is an integer greater than 1; the input end of each DC-DC circuit is used to connect at least one path of photovoltaic units, and each path of photovoltaic units includes at least one photovoltaic module. The method includes: Controlling the N DC-DC circuits in each group to start online IV curve scanning in sequence, and controlling the time interval between the start of online IV curve scanning of adjacent two DC-DC circuits to be less than the time taken for one DC-DC circuit to perform online IV curve scanning.

15. The method according to claim 14, wherein The controlling the time interval between the start of online IV curve scanning of adjacent two DC-DC circuits to be less than the time taken for one DC-DC circuit to perform online IV curve scanning specifically includes: After controlling the first DC-DC circuit to start online IV curve scanning, controlling the k-th DC-DC circuit to start online IV curve scanning when the input voltage of the (k - 1)-th DC-DC circuit decreases to be less than a preset voltage threshold, where k = 2, 3, …, N.

16. The method according to claim 15, wherein The time taken for each DC-DC circuit to perform online IV curve scanning is the same, and the preset voltage threshold is the product of the sum of the open circuit voltages of the photovoltaic units connected to the (k - 1)-th DC-DC circuit and a first preset ratio.

17. The method according to claim 15, wherein The preset voltage threshold is the product of the sum of the preset open circuit voltages of the photovoltaic units connected to the (k - 1)-th DC-DC circuit and a first preset ratio.

18. The method according to claim 14, characterized in that, The controlling the time interval between the start of online IV curve scanning of adjacent two DC-DC circuits to be less than the time taken for one DC-DC circuit to perform online IV curve scanning specifically includes: After controlling the first DC-DC circuit in each group to start online IV curve scanning, the remaining DC-DC circuits start online IV curve scanning in sequence at a preset time interval, and the preset time interval is less than the time taken for one DC-DC circuit to perform online IV curve scanning.

19. The method according to claim 18, wherein The preset time interval is the product of the time taken for one DC-DC circuit to perform online IV curve scanning and a second preset ratio.

20. The method according to any one of claims 14-19, characterized in that, The method further includes: Controlling the M groups of DC-DC circuits to perform online IV curve scanning synchronously.

21. A photovoltaic inverter, characterized in that, For connecting photovoltaic units, the photovoltaic units include at least one photovoltaic module, and the photovoltaic inverter includes a controller, a DC-AC circuit, and M groups of DC-DC circuits, where each group includes N DC-DC circuits, M is a positive integer, and N is an integer greater than 1; The positive output ports of the M groups of the DC-DC circuits are connected in parallel to the positive input port of the DC-AC circuit, and the negative output ports of the M groups of the DC-DC circuits are connected in parallel to the negative input port of the DC-AC circuit. The input end of each DC-DC circuit is connected to at least one path of the photovoltaic units; The DC-DC circuit is configured to perform DC conversion on the direct current obtained from the photovoltaic unit and then transmit it to the DC-AC circuit; The DC-AC circuit is configured to convert the obtained direct current into alternating current; The controller is configured to control the N paths of the DC-DC circuits in each group to start online IV curve scanning in sequence, and the time interval between the start of online IV curve scanning of two adjacent DC-DC circuits is less than the time taken for one DC-DC circuit to perform online IV curve scanning.

22. The photovoltaic inverter according to claim 21, wherein When the controller controls each DC-DC circuit to perform online IV curve scanning in sequence, it first increases the input voltage of the DC-DC circuit until the input current of the DC-DC circuit is zero, and then controls the input voltage of the DC-DC circuit to gradually decrease to zero.

23. The photovoltaic inverter according to claim 22, wherein Specifically, after the controller controls the first path of the DC-DC circuit in each group to start online IV curve scanning, it controls the k-th path of the DC-DC circuit to start online IV curve scanning when the input voltage of the (k - 1)-th path of the DC-DC circuit decreases to less than a preset voltage threshold, where k = 2, 3,..., N.

24. The photovoltaic inverter according to claim 23, wherein, The time for each DC-DC circuit to perform online IV curve scanning is the same, and the preset voltage threshold is the product of the sum of the open-circuit voltages of the photovoltaic units connected to the (k - 1)-th path of the DC-DC circuit and a first preset ratio.

25. The photovoltaic inverter according to claim 23, wherein, The preset voltage threshold is the product of the sum of the preset open-circuit voltages of the photovoltaic units connected to the (k - 1)-th path of the DC-DC circuit and a first preset ratio.

26. The photovoltaic inverter according to claim 22, characterized in that, Specifically, after the controller controls the first path of the DC-DC circuit in each group to start online IV curve scanning, the remaining DC-DC circuits start online IV curve scanning in sequence at a preset time interval, and the preset time interval is less than the time taken for one DC-DC circuit to perform online IV curve scanning.

27. The photovoltaic inverter according to claim 26, wherein, The preset time interval is the product of the time taken for one DC-DC circuit to perform online IV curve scanning and a second preset ratio.

28. A DC busbar box, characterized in that, It is used to connect photovoltaic units. The photovoltaic unit includes at least one photovoltaic module. The DC busbar box includes a controller and M groups of DC-DC circuits, each group includes N DC-DC circuits, M is a positive integer, and N is an integer greater than 1; The input end of each DC-DC circuit is connected to at least one path of the photovoltaic units; The positive output ports of the M groups of the DC-DC circuits are connected in parallel to form the positive output port of the DC busbar box; The negative output ports of the M groups of the DC-DC circuits are connected in parallel to form the negative output port of the DC busbar box; The controller is configured to control the N DC-DC circuits in each group to start online IV curve scanning in sequence, and the time interval between the start of online IV curve scanning of adjacent two DC-DC circuits is less than the time taken for one DC-DC circuit to perform online IV curve scanning.

29. A photovoltaic optimizer, characterized in that, It is used to connect to a photovoltaic unit, which includes at least one photovoltaic module, and is used to form a photovoltaic optimizer sub-string after being connected in series with at least one photovoltaic optimizer. The photovoltaic optimizer includes a controller and a DC-DC circuit; The input end of the DC-DC circuit is connected to at least one path of the photovoltaic unit; The positive output end of the DC-DC circuit is the positive output end of the photovoltaic optimizer, and the negative output end of the DC-DC circuit is the negative output end of the photovoltaic optimizer; The controller is configured to control the DC-DC circuit to start online IV curve scanning, and the time interval for controlling the start of online IV curve scanning of the previous series-connected photovoltaic optimizer is less than the time taken for one DC-DC circuit to perform online IV curve scanning.

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