String type inverter

Abstract

The invention provides a string type inverter, and relates to the technical field of photovoltaic power generation, the string type inverter comprises a controller and M groups of DC-DC circuits, each group comprises 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 with at least one photovoltaic unit, and each photovoltaic unit comprises at least one photovoltaic module. The controller controls the N DC-DC circuits of each group to start online IV curve scanning in sequence, and the time interval of starting online IV curve scanning of every two adjacent DC-DC circuits is smaller than the time used by one DC-DC circuit to perform online IV curve scanning. The photovoltaic power generation system can reduce the power fluctuation output during the online IV curve scanning, reduces the time for the photovoltaic power generation system to carry out the online IV curve scanning, and further reduces the influence of the online IV curve scanning on the grid-connected electric energy quality.

Description

Technical Field

[0001] This application relates to the field of photovoltaic power generation technology, and in particular to a string inverter. Background Technology

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

[0003] See Figure 1 The figure shows 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 shaded, its IV curve will be distorted. The health status of the photovoltaic module can be diagnosed by IV curve scanning technology.

[0005] Currently applied IV curve scanning technologies can be divided into two types: offline IV curve scanning and online IV curve scanning. Offline IV curve scanning requires maintenance personnel to manually carry an IV tester to the photovoltaic modules, disconnect the modules from the photovoltaic power generation system, and connect the IV curve analyzer for testing. This method is very time-consuming, labor-intensive, and results in significant power loss in the photovoltaic power generation system during the testing period. Online IV curve scanning, on the other hand, performs online IV curve scanning on the photovoltaic strings connected to the power conversion circuit of the photovoltaic system, avoiding manual operation and reducing scanning time and power loss in the photovoltaic power generation system during the scanning process.

[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. This leads to fluctuations in the output power of the inverters and maximum power point tracking (MPPT) devices connected to the photovoltaic string, which affects the grid-connected power quality of the photovoltaic power generation system, and may cause problems such as harmonics and voltage flicker. Summary of the Invention

[0007] To address the aforementioned issues, this application provides a photovoltaic power generation system, a photovoltaic inverter, a combiner box, a photovoltaic optimizer, and a method for IV curve scanning. This method reduces the time required for online IV curve scanning and decreases power fluctuations in the photovoltaic power generation system during online IV curve scanning, thereby reducing the impact of online IV curve scanning on grid-connected power quality.

[0008] In a first aspect, this application provides a photovoltaic power generation system or a string inverter. The string inverter 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. The input terminal of each DC-DC circuit is connected to at least one photovoltaic unit, and each photovoltaic unit includes at least one photovoltaic module. The controller controls the N DC-DC circuits in each group to sequentially begin online IV curve scanning, and the time interval between the controller controlling two adjacent DC-DC circuits to begin online IV curve scanning is less than the time required for one DC-DC circuit to perform online IV curve scanning.

[0009] For each DC-DC circuit in this photovoltaic power generation system, 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 its scan before starting their own scan. Instead, they perform online IV curve scanning sequentially, with the time interval being less than the time required for a single DC-DC circuit to perform online IV curve scanning. This means that staggered scanning is achieved. At this time, the N DC-DC circuits in each group output at off-peak times. On the one hand, online IV curve scanning can be performed on photovoltaic units connected by multiple DC-DC circuits simultaneously, saving scanning time. On the other hand, the total output power of the photovoltaic power generation system is relatively stable, avoiding drastic fluctuations in total output power during online IV curve scanning, thereby reducing the negative impact of online IV curve scanning on grid-connected power quality.

[0010] In conjunction with the first aspect, in the first possible implementation, 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 connected photovoltaic units 10. Then, it controls the input voltage of the DC-DC circuit to gradually decrease to zero. During this process, the correspondence between the input voltage and the input current of the DC-DC circuit is obtained according to the preset sampling interval, thereby obtaining the scanning result of the IV curve.

[0011] In conjunction with the first aspect, in the second possible implementation, the controller is specifically used to control the k-th DC-DC circuit to start online IV curve scanning after controlling the first DC-DC circuit of each group 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, k = 2, 3, ..., N.

[0012] For the DC-DC circuits in each group other than the first DC-DC circuit, the online IV curve scanning begins when the input voltage of the previous DC-DC circuit decreases to less than the preset voltage value, that is, the previous DC-DC circuit has not yet completed the online IV curve scanning, thus achieving staggered output.

[0013] In conjunction with the first aspect, in the third possible implementation, the online IV curve scanning time for 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. 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 of the online IV curve scanning performed by the (k-1)th DC-DC circuit.

[0014] In conjunction with the first aspect, in the fourth possible implementation, 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 based on the rated open-circuit voltage range, for example, by selecting the maximum, minimum, or intermediate value within the rated open-circuit voltage range.

[0015] In conjunction with the first aspect, in the fifth possible implementation, the controller is specifically used to control the first DC-DC circuit of each group to start online IV curve scanning, and then the remaining DC-DC circuits start online IV curve scanning sequentially according to a preset time interval. The preset time interval is less than the time taken for one DC-DC circuit to perform online IV curve scanning. Thus, after the first DC-DC circuit starts scanning first, multiple DC-DC circuits will scan simultaneously for a period of time and perform staggered output.

[0016] In conjunction with the first aspect, in the sixth possible implementation, the preset time interval is negatively correlated with the magnitude of N. The more DC-DC circuits connected to the photovoltaic system, the higher the power of the photovoltaic power generation system. In this case, the preset time interval can be reduced, thereby shortening the time for online IV curve scanning while maintaining a relatively stable total output power of the photovoltaic power generation system.

[0017] In conjunction with the first aspect, in the seventh possible implementation, the preset time interval is the product of the time taken for one DC-DC circuit to perform online IV curve scanning and the second preset ratio.

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

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

[0020] In conjunction with the first aspect, in the tenth possible implementation, the controller is also used to control the operating 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 conjunction with the first aspect, in the eleventh possible implementation, M groups of DC-DC circuits form a DC combiner 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 combiner box; 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 combiner box.

[0022] In conjunction with the first aspect, in the twelfth possible implementation, the DC-DC circuit is a photovoltaic optimizer, and each group of N photovoltaic optimizers forms a photovoltaic optimizer substring. 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. The positive output port of the 1st photovoltaic optimizer is the positive output port of the photovoltaic optimizer substring, and the negative output port of the Nth photovoltaic optimizer is the negative output port of the photovoltaic optimizer substring, i = 2, 3, ..., N-1. The output of the photovoltaic optimizer substring can be connected to the input of the subsequent MPPT boost combiner box, string inverter, or centralized inverter via DC cables. Multiple photovoltaic optimizer substrings can also be connected in series again.

[0023] Secondly, this application also provides a photovoltaic inverter, which is a string inverter with its input terminal connected to a photovoltaic unit, the photovoltaic unit including 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. The positive output ports of the M groups of DC-DC circuits are connected in parallel to the positive input ports 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 ports of the DC-AC circuit. The input terminal of each DC-DC circuit is connected to at least one photovoltaic unit. The DC-DC circuit is used to convert the DC power obtained from the photovoltaic unit into DC power and then transmit it to the DC-AC circuit. The DC-AC circuit is used to convert the obtained DC power into AC power. The controller is used to control the N DC-DC circuits in each group to sequentially start online IV curve scanning, 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.

[0024] For each DC-DC circuit of this 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 its scan before starting their own scan. Instead, they perform online IV curve scanning sequentially, with the time interval being less than the time taken for the first DC-DC circuit to perform online IV curve scanning. This achieves staggered scanning, allowing each group of N DC-DC circuits to output at off-peak times. On the one hand, this allows for simultaneous online IV curve scanning of photovoltaic units connected to multiple DC-DC circuits, saving scanning time. On the other hand, it ensures a more stable total output power of the photovoltaic inverter, avoiding drastic fluctuations in total output power during online IV curve scanning. This reduces the negative impact of online IV curve scanning on grid-connected power quality.

[0025] In conjunction with the second aspect, in the first possible implementation, 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] In conjunction with the second aspect, in the second possible implementation, the controller is specifically used to control the first DC-DC circuit of 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, k = 2, 3, ..., N.

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

[0028] In conjunction with the second aspect, in the fourth possible implementation, 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 conjunction with the second aspect, in the fifth possible implementation, the controller is specifically used to control the first DC-DC circuit of each group to start online IV curve scanning, and then the remaining DC-DC circuits to start online IV curve scanning sequentially according to a preset time interval, wherein the preset time interval is less than the time taken for one DC-DC circuit to perform online IV curve scanning.

[0030] Thirdly, this application also provides a DC combiner box. The input terminal of the DC combiner box is connected to a photovoltaic unit, which includes at least one photovoltaic module. The DC combiner box 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 terminal of each DC-DC circuit is connected to at least one 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 combiner 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 combiner box. The controller is used to control the N DC-DC circuits of each group to start online IV curve scanning sequentially, 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 conjunction with the third aspect, in the first possible implementation, 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 conjunction with the third aspect, in the second possible implementation, the controller is specifically used to control the first DC-DC circuit of 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, k = 2, 3, ..., N.

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

[0034] In conjunction with the third aspect, in the fourth possible implementation, 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] In conjunction with the third aspect, in the fifth possible implementation, the controller is specifically used to control the first DC-DC circuit of each group to start online IV curve scanning, and then the remaining DC-DC circuits to start online IV curve scanning sequentially according to a preset time interval, wherein the preset time interval is less than the time taken for one DC-DC circuit to perform online IV curve scanning.

[0036] Fourthly, this application also provides a photovoltaic optimizer for connecting photovoltaic units, each photovoltaic unit including at least one photovoltaic module. The photovoltaic optimizer is connected in series with at least one other photovoltaic optimizer to form a photovoltaic optimizer substring. The output of the photovoltaic optimizer substring can be connected via a DC cable to the input of a downstream MPPT boost combiner box, a string inverter, or a centralized inverter. The photovoltaic optimizer includes a controller and a DC-DC circuit. The input of the DC-DC circuit is connected to at least one photovoltaic unit; the positive output of the DC-DC circuit is the positive output of the photovoltaic optimizer, and the negative output of the DC-DC circuit is the negative output of the photovoltaic optimizer. The controller is used to control the DC-DC circuit to start online IV curve scanning, and the time interval between the start of online IV curve scanning of the previously connected photovoltaic optimizer is less than the time required for online IV curve scanning of a single DC-DC circuit.

[0037] Fifthly, this application also provides an online IV curve scanning method, applied to the photovoltaic power generation system provided by the above implementation. The method includes the following steps:

[0038] The system controls the N DC-DC circuits in each group to start online IV curve scanning sequentially, and 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.

[0039] Using this method, 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 its scan before starting their own scan. Instead, they perform online IV curve scanning sequentially, with the time interval being less than the time required for a single DC-DC circuit to perform online IV curve scanning. This achieves staggered scanning, allowing each group of N DC-DC circuits to output at off-peak times. On the one hand, this allows for simultaneous online IV curve scanning of photovoltaic units connected to multiple DC-DC circuits, saving scanning time. On the other hand, it ensures a more stable total output power of the photovoltaic power generation system, avoiding drastic fluctuations in total output power during online IV curve scanning, thereby reducing the negative impact of online IV curve scanning on grid-connected power quality.

[0040] In conjunction with the fifth aspect, in the first possible implementation, the time interval between controlling two adjacent DC-DC circuits to begin online IV curve scanning is less than the time required for one DC-DC circuit to perform online IV curve scanning, specifically including:

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

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

[0043] In conjunction with the fifth aspect, in the third possible implementation, 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] In conjunction with the fifth aspect, in the fourth possible implementation, the time interval between controlling two adjacent DC-DC circuits to begin online IV curve scanning is less than the time required for one DC-DC circuit to perform online IV curve scanning. Specifically, this includes:

[0045] After the first DC-DC circuit in each group starts online IV curve scanning, the remaining DC-DC circuits start online IV curve scanning sequentially according to a preset time interval, which is less than the time taken for one DC-DC circuit to perform online IV curve scanning.

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

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

[0048] The control group M DC-DC circuits synchronously perform online IV curve scanning. Attached Figure Description

[0049] Figure 1 A schematic diagram of the IV curve for a healthy photovoltaic module;

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

[0051] Figure 3 This is a schematic diagram of a string inverter;

[0052] Figure 4 This is a schematic diagram of a photovoltaic power generation system based on a centralized inverter and an MPPT boost combiner box.

[0053] Figure 5 A schematic diagram of an MPPT booster junction box;

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

[0055] Figure 7 A schematic diagram of a photovoltaic power generation system provided in an embodiment of this application;

[0056] Figure 8 This is a schematic diagram of another photovoltaic power generation system provided in the embodiments of this application;

[0057] Figure 9 A timing diagram illustrating the start of scanning of the DC-DC circuit provided in the embodiments of this application. Figure 1 ;

[0058] Figure 10 A timing diagram illustrating the start of scanning of the DC-DC circuit provided in the embodiments of this application. Figure 2 ;

[0059] Figure 11 A schematic diagram of the output power of the photovoltaic power generation system provided in this application embodiment during online IV curve scanning;

[0060] Figure 12 A schematic diagram of yet another photovoltaic power generation system provided in this application embodiment;

[0061] Figure 13 A schematic diagram of another photovoltaic power generation system provided in the embodiments of this application;

[0062] Figure 14This is a schematic diagram of another photovoltaic power generation system provided in the embodiments of this application;

[0063] Figure 15 A flowchart illustrating an online IV curve scanning method provided in this application embodiment;

[0064] Figure 16 This is a schematic diagram of a photovoltaic inverter provided in an embodiment of this application;

[0065] Figure 17 A schematic diagram of a DC combiner box provided for an embodiment of this application;

[0066] Figure 18 This is a schematic diagram of a photovoltaic optimizer provided in an embodiment of this application. Detailed Implementation

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

[0068] The photovoltaic power generation system provided in this application uses online IV curve scanning technology, which will be described below in conjunction with different types of photovoltaic power generation systems.

[0069] The following section will first describe a photovoltaic power generation system based on a string inverter.

[0070] See Figure 2 The figure shows a schematic diagram of a photovoltaic power generation system based on a string inverter.

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

[0072] Each photovoltaic unit 10 includes one or more photovoltaic modules. The photovoltaic module is a DC power source composed of solar cells connected in series and parallel.

[0073] When the photovoltaic unit 10 includes multiple photovoltaic modules, the multiple photovoltaic modules can be connected in series with the positive and negative terminals to form a photovoltaic string, thereby forming the photovoltaic unit 10; the multiple photovoltaic modules can also be connected in series to form multiple photovoltaic strings, and the multiple photovoltaic strings can be connected in parallel to form the photovoltaic unit 10.

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

[0075] The string inverter will be described in detail below.

[0076] See Figure 3The diagram shows a schematic of a string inverter.

[0077] The string inverter 11 includes two stages of power conversion circuits. The first stage is a DC-DC circuit 111, i.e., a DC-DC boost circuit, and the second stage is a DC-AC circuit 112, i.e., an inverter circuit. The string inverter 11 typically 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 output 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 terminal of the photovoltaic unit 10, and the negative input port of each DC-DC circuit 111 is connected to the negative terminal of the photovoltaic unit 10.

[0080] The AC power output from the multi-channel string inverter 11 is collected after passing through the AC combiner box / switch box 12, and then connected to the AC power grid 14 through the transformer 13. It 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, thereby achieving the effect of scanning the output voltage of the photovoltaic unit, that is, realizing the IV curve scanning of the photovoltaic unit.

[0082] The following describes a photovoltaic power generation system based on a centralized inverter and an MPPT boost combiner box.

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

[0084] The photovoltaic power generation system shown in the figure includes a photovoltaic unit 10, an MPPT booster combiner box 20, a centralized inverter 21, and a transformer 13.

[0085] The MPPT boost combiner box is a type of DC-DC boost converter, which will be described in detail below with reference to the attached diagram.

[0086] See Figure 5 The figure shows a schematic diagram of the MPPT booster junction box.

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

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

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

[0090] The centralized inverter 21 is used to convert single or multiple parallel DC inputs connected to the DC side into AC outputs, typically employing a single-stage DC-AC power conversion. The AC output from the centralized inverter 21 is fed into the AC power grid 14 via transformer 13.

[0091] Since the centralized inverter 21 is generally far from the photovoltaic unit 10, the DC-DC circuit 111 in the MPPT boost combiner box 20 is needed to control the output voltage of the photovoltaic unit in order to achieve the IV curve scanning of the photovoltaic unit.

[0092] The following describes a photovoltaic power generation system based on a photovoltaic optimizer and a string inverter.

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

[0094] The photovoltaic power generation system shown in the figure includes a photovoltaic unit 10, a photovoltaic optimizer 30, a string inverter 11, an AC switch 31, and an electricity meter 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 a string inverter or a centralized inverter in series to increase or decrease the output voltage of the photovoltaic unit. Figure 6 Take the Sino-Israeli access string inverter 11 as an example.

[0096] The photovoltaic optimizer 30 includes a DC-DC circuit, which can be 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 terminal of the photovoltaic unit 10, and the negative input port of the DC-DC circuit is connected to the negative terminal of the photovoltaic unit 10.

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

[0098] In a photovoltaic power generation system that uses a photovoltaic optimizer 30, multiple photovoltaic optimizers 30 are typically connected in series to form substrings.

[0099] For example, N photovoltaic (PV) optimizers are connected in series, meaning 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 substring, and the negative output port of the N-th PV optimizer serves as the negative output port of the PV optimizer substring. The output terminals of the PV optimizer substring are connected via DC cables to the input terminals of the subsequent MPPT boost combiner box, string inverter, or centralized inverter. The diagram uses a string inverter 11 as an example.

[0100] The AC power output from the string inverter 11 is fed into the AC power grid via the transformer 13.

[0101] When performing online IV curve scanning, the access... Figure 2 The DC-DC circuit of the string inverter 11, and its connection Figure 4 The DC-DC circuit of the MPPT boost combiner box 20, and the connection Figure 6 The photovoltaic unit of the DC-DC circuit of the medium-sized string inverter 11 is scanned for IV curves.

[0102] In one implementation, a serial scanning method is used, in which multiple DC-DC circuits sequentially perform IV curve scanning one by one. That is, the IV curve is first scanned on the photovoltaic unit connected to the first DC-DC circuit, and after that, the IV curve is scanned on the photovoltaic unit connected to the second DC-DC circuit, and so on, until all photovoltaic units are scanned.

[0103] The serial scanning method is relatively time-consuming, and during the scanning process, changes in environmental conditions may cause fluctuations in lighting conditions, affecting the acquired scan curves and diagnostic results. Furthermore, the scanning process can lead to continuous fluctuations in the output power of the photovoltaic converter, reducing the grid-connected power quality of the photovoltaic power generation system.

[0104] Another possible implementation uses a parallel scanning method, which involves simultaneously scanning the IV curves of photovoltaic units connected to multiple DC-DC circuits. While this method reduces scanning time, the output power of the photovoltaic converter fluctuates drastically during the scanning period, severely degrading the grid-connected power quality of the photovoltaic power generation system.

[0105] To address the above issues, this application provides a photovoltaic power generation system, a photovoltaic inverter, a combiner box, a photovoltaic optimizer, and an IV curve scanning method. This method can simultaneously perform IV curve scanning on photovoltaic units connected to multiple DC-DC circuits, saving scanning time and avoiding drastic fluctuations in the total output power of the photovoltaic power generation system during online IV curve scanning. This reduces the negative impact of online IV curve scanning on grid-connected power quality.

[0106] The technical solution of this 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 this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated.

[0108] In this application, unless otherwise expressly specified and limited, the term "connection" shall be interpreted broadly. For example, "connection" may be a fixed connection, a detachable connection, or an integral part; it may be a direct connection or an indirect connection through an intermediate medium.

[0109] See Figure 7 The figure is a schematic diagram of a photovoltaic power generation system provided in an embodiment of this application.

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

[0111] Where M is a positive integer.

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

[0113] Where 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 be connected in series with their positive and negative terminals to form a photovoltaic string, thereby forming the photovoltaic unit 10. Alternatively, the multiple photovoltaic modules can be connected in series to form multiple photovoltaic strings, and then the multiple photovoltaic strings can be connected in parallel to form the photovoltaic unit 10. The embodiments of this 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 terminal of the photovoltaic unit 10, and the negative input port of the DC-DC circuit is connected to the negative terminal of the photovoltaic unit 10.

[0116] The DC-DC circuit is used to convert the DC power input to the photovoltaic unit 10 into DC power and output it.

[0117] The controller 40 is used to control each group of DC-DC circuits 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 start online IV curve scanning, as explained in detail below.

[0118] When controller 40 controls the N-channel DC-DC circuits 111a1-111aN of each group to scan sequentially, DC-DC circuit 111a1 starts online IV curve scanning first, DC-DC circuit 111a2 starts online IV curve scanning after T1, DC-DC circuit 111a3 starts online IV curve scanning after T2, ..., DC-DC circuit 111aN starts online IV curve scanning after T1. N-1 Then online IV curve scanning begins, with T1, T2, ... T N-1 Indicates the time interval. Let T0 represent the time taken for one DC-DC circuit to perform an online IV curve scan, then T1, T2, ..., T... N-1 All are less than T0.

[0119] This application does not specifically limit the size of the time interval in its embodiments. Furthermore, the time intervals T1, T2, ... T mentioned above are... N-1 The time intervals can be the same or different, and this application does not impose specific limitations on the embodiments. In a preferred implementation, the above time intervals are the same to further reduce the fluctuation of the total output power of the N-channel DC-DC circuit during online IV curve scanning and to facilitate control.

[0120] It should be noted that the "adjacent" in this scheme does not refer to physical proximity, but rather to proximity in the order in which the IV curve scan begins.

[0121] The controller 40 can be an application-specific integrated circuit (ASIC), a programmable logic device (PLD), a digital signal processor (DSP), or a combination thereof. The PLD can be a complex programmable logic device (CPLD), a field-programmable gate array (FPGA), a generic array logic (GAL), or any combination thereof; this embodiment does not specifically limit its application in this application.

[0122] Each DC-DC circuit 111a1-111aN includes a controllable switching transistor. This application embodiment does not specifically limit the type of controllable switching transistor; for example, it can be an Insulated Gate Bipolar Transistor (IGBT), a Metal Oxide Semiconductor Field-Effect Transistor (MOSFET), or a Silicon Carbide Metal Oxide Semiconductor (SiC MOSFET). The controller 40 can send control signals to the controllable switching transistor to control its operating state. This control signal can be a Pulse Width Modulation (PWM) signal or a Pulse Frequency Modulation (PFM) signal, etc., and this application embodiment does not specifically limit its use.

[0123] In summary, this photovoltaic power generation system controls each group of N DC-DC circuits to sequentially begin online IV curve scanning. 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 its scan before starting their own scan. Instead, they perform staggered scanning, meaning the time interval between the start of each scan is less than the time required for one DC-DC circuit to perform online IV curve scanning. This allows the N DC-DC circuits to output at off-peak times. On the one hand, this allows for simultaneous online IV curve scanning of photovoltaic units connected to multiple DC-DC circuits, saving scanning time. On the other hand, it ensures a more stable total output power of the photovoltaic power generation system, avoiding drastic fluctuations in total output power during online IV curve scanning, thereby reducing the negative impact of online IV curve scanning on grid-connected power quality.

[0124] The application scenarios of the technical solutions provided in this application include: large-scale photovoltaic power plant scenarios, small and medium-sized distributed photovoltaic power plant scenarios, and residential photovoltaic power generation systems.

[0125] The specific implementation method will be explained below. The following descriptions in this application embodiment all use M=1 as an example. The principle is similar when M is an integer greater than 1, and will not be described in detail here. Furthermore, the number of photovoltaic units 10 connected to each DC-DC circuit is the same in the following descriptions.

[0126] See Figure 8 This figure is a schematic diagram of another photovoltaic power generation system provided in an embodiment of this application.

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

[0128] The data storage unit 402 includes a memory, which may include volatile memory (VM), such as random-access memory (RAM). The memory may also include non-volatile memory (NVM), such as read-only memory (ROM), flash memory, hard disk drive (HDD), or solid-state drive (SSD); a combination of these types of memory may also be included. The memory may refer to a single memory or may include multiple memories. Scan data can be transferred 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, used to send scanning instructions to the controller to perform online IV curve scanning.

[0130] After the controller 40 receives the scanning command from the host computer 50, it begins online IV curve scanning. When the controller's control unit 401 controls the N DC-DC circuits to scan sequentially, it can be controlled based on voltage or time, as explained below.

[0131] The first method: control based on 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 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 connected photovoltaic units 10. The control unit 401 then obtains the open-circuit voltage 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 the DC-DC circuit to gradually decrease to zero. During this process, it acquires the correspondence between the input voltage and input current of the DC-DC circuit according to a preset sampling interval, thereby obtaining the scanning result of the IV curve. The input current corresponding to the zero input voltage is the sum of the short-circuit currents of all photovoltaic units 10 connected to the DC-DC circuit.

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

[0135] This application does not limit the specific implementation method of controlling the input voltage of the DC-DC circuit to gradually decrease to zero, but the method needs to present an overall decreasing pattern. 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, then decrease again, and so on until it decreases to zero.

[0136] For 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, the control unit 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 below 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. Here, k = 2, 3, ..., N.

[0137] To make it easier to understand, we will use a value of 4 for N as an example. The principle is similar when N takes other values.

[0138] See Figure 9 This figure is a timing diagram of the DC-DC circuit starting to scan according to an embodiment of this application. Figure 1 .

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

[0140] At time 0 (the initial time), the first DC-DC circuit begins 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 the DC-DC circuit is zero. Then, it controls the input voltage of the DC-DC circuit to gradually decrease, decreasing to less than the preset voltage threshold V at time T1. A At this time, control unit 401 controls the second DC-DC circuit to start online IV curve scanning. Similarly, at time T2, the input voltage of the second DC-DC circuit decreases to below the preset voltage threshold V. A Control unit 401 controls the third DC-DC circuit to start online IV curve scanning. At time T3, the input voltage of the third DC-DC circuit decreases to less than the preset voltage threshold V. A The control unit 401 controls the fourth DC-DC circuit to start online IV curve scanning.

[0141] Depend on Figure 9 It can be seen that multiple DC-DC circuits are simultaneously scanning between time T1 and T2+T0. Furthermore, the staggered output of these multiple DC-DC circuits ensures a relatively stable total output power of the photovoltaic power generation system during the scanning period, reducing fluctuations. In addition, when N is 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. Therefore, the solution provided in this embodiment can further shorten the time required for online IV curve scanning.

[0142] In some embodiments, the preset voltage threshold is positively correlated with the magnitude of N. The more DC-DC circuits connected to the photovoltaic system, the higher the power of the photovoltaic power generation system. In this case, the preset voltage threshold can be increased, thereby shortening the time required for online IV curve scanning while maintaining a relatively stable total output power of the photovoltaic power generation system.

[0143] For example, in one possible implementation, when the 5-channel DC-DC circuit is activated, the preset voltage threshold is V. A1 When the 10-channel DC-DC circuit is activated, the preset time interval is V. A2 Then V A1 <V A2 .

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

[0145] In some embodiments, the V obtained during IV curve scanning of the preceding DC-DC circuit is used. oc The timing for starting the online IV curve scan is determined, i.e., the preset voltage threshold is the product of the sum of the open-circuit voltages of each photovoltaic unit connected to the (k-1)th DC-DC circuit and the first preset ratio.

[0146] The first preset ratio can be determined according to the actual situation, and this application embodiment does 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 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 based on the rated open-circuit voltage range, for example, by selecting the maximum, minimum, or intermediate value within the rated open-circuit voltage range.

[0148] The second method: control based on time.

[0149] The control unit 401 first controls the first DC-DC circuit to start online IV curve scanning, and then controls the remaining DC-DC circuits to start online IV curve scanning sequentially according to a preset time interval.

[0150] The preset time interval is less than the time required for one DC-DC circuit to perform online IV curve scanning.

[0151] When the control unit 401 controls one DC-DC circuit to perform online IV curve scanning, it first increases the input voltage of that DC-DC circuit until the input current of the DC-DC circuit is zero. At this time, the input voltage of that DC-DC circuit is the sum of the open-circuit voltages V of all connected photovoltaic units 10. oc The control unit 401 then acquires the open-circuit voltage V. oc The detection results are transmitted to the host computer 50 and / or stored in the data storage unit 402.

[0152] The control unit 401 then controls the input voltage of the DC-DC circuit to gradually decrease to zero. During this process, it acquires the correspondence between the input voltage and input current of the DC-DC circuit according to a preset sampling interval, thereby obtaining the scanning result of the IV curve. The input current corresponding to zero input voltage is the sum of the short-circuit currents of all photovoltaic units 10 connected to the DC-DC circuit. The scanning result can be transmitted to the host computer 50 and / or stored in the data storage unit 402.

[0153] The embodiments of this application do not limit the specific implementation method of controlling the input voltage of the DC-DC circuit to gradually decrease to zero, but the overall trend is one of decreasing.

[0154] To make it easier to understand, we will continue to use the value of N as an example below. The principle is similar when N takes other values.

[0155] See Figure 10 This figure is a timing diagram of the DC-DC circuit starting to scan according to an embodiment of this application. Figure 2 .

[0156] At time 0 (the initial time), the first DC-DC circuit begins online IV curve scanning. The second DC-DC circuit begins online IV curve scanning after T1, the third DC-DC circuit after T2, and the fourth DC-DC circuit after T3. T1, T2, and T3 represent preset time intervals, which can be the same or different. Let T0 represent the time taken for one DC-DC circuit to perform online IV curve scanning; then all preset time intervals are less than T0.

[0157] Depend on Figure 10 It can be seen that during the online IV curve scanning process, multiple DC-DC circuits may be scanning simultaneously. Because the control unit 401 controls each DC-DC circuit to perform online IV curve scanning by first increasing the input voltage until the input current is zero, and then gradually decreasing the input voltage to zero, multiple DC-DC circuits can stagger their output, ensuring a relatively stable total output power of the photovoltaic power generation system during the scanning period.

[0158] In some embodiments, the preset time interval is negatively correlated with the magnitude of N. The more DC-DC circuits connected to the photovoltaic system, the higher the power of the photovoltaic power generation system. In this case, the preset time interval can be reduced, thereby shortening the time for online IV curve scanning while maintaining a relatively stable total output power of the photovoltaic power generation system.

[0159] For example, in one possible implementation, the control unit 40 controls multiple DC-DC circuits to scan sequentially at the same preset time interval. When 5 DC-DC circuits are activated, the preset time intervals T1, T2, T3, and T4 are the same and are all ΔT1; when 10 DC-DC circuits are activated, the preset time intervals T1, T2, ... T9 are the same and are all ΔT2, then ΔT2 < ΔT1.

[0160] For example, in another possible implementation, the control unit 40 controls multiple DC-DC circuits to scan sequentially at different preset time intervals. When four DC-DC circuits are activated, the preset time intervals are T1, T2, and T3, respectively; when ten DC-DC circuits are activated, the preset time intervals are t1, t2, t3, ..., t9, respectively. In this case, t1 < T1, t2 < T2, and t3 < T3.

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

[0162] In some embodiments, 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. The second preset ratio can be determined according to actual conditions, and is not specifically limited in this embodiment.

[0163] The above explanation uses a photovoltaic power generation system comprising one set of DC-DC circuits as an example. When the photovoltaic power generation system comprises multiple sets of DC-DC circuits, the controller 40 can control multiple sets of DC-DC circuits to simultaneously perform online IV curve scanning. That is, it simultaneously controls the first DC-DC circuit of each of the multiple sets of DC-DC circuits to start scanning.

[0164] The technical effects of this photovoltaic power generation system are illustrated below using simulation waveforms.

[0165] See Figure 11 The figure is a schematic diagram of the output power of the photovoltaic power generation system provided in this application embodiment when performing online IV curve scanning.

[0166] To more clearly illustrate the technical effects of this application, the figure is a schematic diagram of three DC-DC circuits performing online IV curve scanning in a cyclic manner. As can be seen from the figure, the first DC-DC circuit begins scanning first, followed by a period where multiple DC-DC circuits scan simultaneously. However, because the simultaneous scanning DC-DC circuits begin scanning at different times, staggered output is achieved. Specifically, for the simultaneously scanning DC-DC circuits, some have lower output power while others have higher output power. This cumulative effect keeps the total output power of the photovoltaic power generation system relatively stable, avoiding drastic fluctuations.

[0167] In summary, the photovoltaic power generation system provided in this application embodiment can simultaneously perform online IV curve scanning on photovoltaic units connected by multiple DC-DC circuits, saving scanning time and making the total output power of the photovoltaic power generation system more stable, avoiding drastic fluctuations in the total output power during online IV curve scanning, thereby reducing the negative impact of online IV curve scanning on grid-connected power quality.

[0168] The following describes another way to implement this photovoltaic power generation system.

[0169] See 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 based on a string inverter and can be referenced. Figure 2 The corresponding explanations.

[0171] The photovoltaic power generation system also includes a DC-AC circuit (also known as an inverter circuit) 112, and M sets of DC-DC circuits 111 and DC-AC circuits 112 form a string inverter 11. 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] DC-AC circuit 112 is used to convert the direct current input to the DC-DC circuit into alternating current for output.

[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, the controller is the controller of the string inverter 11.

[0175] The working principle of the controller can be found in the description of the above embodiments, and will not be repeated here.

[0176] For each DC-DC circuit in the string inverter 11, 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 its scan before starting their own scan. Instead, they perform online IV curve scanning sequentially, with the time interval being less than the time taken for one DC-DC circuit to perform online IV curve scanning. This achieves staggered scanning, allowing each group of N DC-DC circuits to output at off-peak times. This enables simultaneous online IV curve scanning of photovoltaic units connected to multiple DC-DC circuits, saving scanning time and ensuring a more stable total output power for the string inverter 11. It also reduces the negative impact of the string inverter 11 on grid-connected power quality during online IV curve scanning.

[0177] The following describes another way to implement this photovoltaic power generation system.

[0178] See Figure 13 This figure is a schematic diagram of another photovoltaic power generation system provided in the embodiments of this application.

[0179] The photovoltaic power generation system includes a DC combiner box 20, which can be referenced. Figure 4 The corresponding 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 combiner 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 combiner box.

[0181] The working principle of the controller can be found in the description of the above embodiments, and will not be repeated here.

[0182] In some embodiments, the DC combiner box 20 is specifically an MPPT boost combiner box, used to convert the DC power input to the photovoltaic unit into DC power and to track the maximum power point of the photovoltaic unit.

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

[0184] The controller at this time can be integrated with the controller of the DC combiner box 20. For the working principle of the controller, please refer to the description in the above embodiments, which will not be repeated here.

[0185] For each group of DC-DC circuits in the DC combiner box 20, 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 its scan before starting their own scan. Instead, they perform online IV curve scanning sequentially, with the time interval being less than the time taken for one DC-DC circuit to perform online IV curve scanning. This achieves staggered scanning, allowing each group of N DC-DC circuits to output at off-peak times. This enables simultaneous online IV curve scanning of photovoltaic units connected to multiple DC-DC circuits, saving scanning time and ensuring a more stable total output power for the DC combiner box 20. It also reduces the negative impact of the DC combiner box 20 on grid-connected power quality during online IV curve scanning.

[0186] The following describes another way to implement this photovoltaic power generation system.

[0187] See Figure 14 This figure is a schematic diagram of another photovoltaic power generation system provided in an embodiment of this application.

[0188] This photovoltaic power generation system includes a photovoltaic optimizer 30, which can be referenced. Figure 6 The corresponding explanations.

[0189] Photovoltaic optimizer 30, also known as a DC-DC circuit, is used to boost or reduce the DC power input to the photovoltaic modules before outputting it. In this case, the photovoltaic power generation system includes M groups of photovoltaic optimizers, with each group containing N photovoltaic optimizers.

[0190] In a photovoltaic power generation system that uses a photovoltaic optimizer 30, multiple photovoltaic optimizers 30 are generally connected in series to form a photovoltaic optimizer substring 60.

[0191] For example, the N photovoltaic optimizers in each group are connected in series, meaning 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 photovoltaic optimizer substring 60, and the negative output port of the N-th photovoltaic optimizer serves as the negative output port of photovoltaic optimizer substring 60. The output terminals of photovoltaic optimizer substring 60 are connected via DC cables to the input terminals of the subsequent MPPT boost combiner box, string inverter, or centralized inverter.

[0192] In one possible implementation, the controller can be integrated with the controller of the photovoltaic optimizer, in which case the number of controllers is the same as the number of photovoltaic optimizers, and the host computer 50 simultaneously issues scanning commands to each controller.

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

[0194] The working principle of the controller can be found in the description of the above embodiments, and will not be repeated here.

[0195] For photovoltaic power generation systems using this photovoltaic optimizer substring 60, after the first photovoltaic optimizer starts online IV curve scanning, each of the remaining photovoltaic optimizers does not wait for the previous one to complete its scan before starting its own scan. Instead, they perform online IV curve scanning sequentially, with the time interval being less than the time taken for one photovoltaic optimizer to perform an online IV curve scan. This achieves staggered scanning, meaning that the photovoltaic optimizers output at off-peak times. This allows for simultaneous online IV curve scanning of photovoltaic units connected to multiple photovoltaic optimizers, saving scanning time and ensuring a more stable total output power for the photovoltaic optimizer substring 60. It also reduces the negative impact of the photovoltaic optimizer substring 60 on grid-connected power quality during online IV curve scanning.

[0196] Based on the photovoltaic power generation system provided in the above embodiments, this application also provides an online IV curve scanning method applied to a photovoltaic power generation system. The photovoltaic power generation system includes photovoltaic units 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 terminal of each DC-DC circuit is connected to at least one photovoltaic unit, and each photovoltaic unit includes at least one photovoltaic module. The method includes:

[0197] The system controls the N DC-DC circuits in each group to start online IV curve scanning sequentially, and 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.

[0198] The following description, in conjunction with the accompanying drawings, provides a detailed explanation. The method described below uses the control of N DC-DC circuits in one group for online IV curve scanning as an example; the same method can be used for synchronous control of the remaining groups.

[0199] See Figure 15 The figure is a flowchart of an online IV curve scanning method provided in an embodiment of this application.

[0200] The method includes the following steps:

[0201] S1601: Issue scan command.

[0202] The scan command is used to instruct the N DC-DC circuits in each group to perform an online IV curve scan.

[0203] S1602: Controls 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 point, the input voltage of the DC-DC circuit is the sum of the open-circuit voltages of the connected photovoltaic units, Voc.

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

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

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

[0209] This step can be controlled based on voltage or time, as explained below:

[0210] The first method: control based on voltage.

[0211] For an N-channel DC-DC circuit, after controlling the first DC-DC circuit to begin online IV curve scanning, for the remaining N-1 DC-DC circuits, the k-th DC-DC circuit is controlled to begin online IV curve scanning when the input voltage of the (k-1)-th DC-DC circuit decreases to below 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. Here, k = 2, 3, ..., N.

[0212] The preset voltage threshold is positively correlated with the value of N. The more DC-DC circuits connected to the photovoltaic system, the higher the power of the photovoltaic power generation system. In this case, the preset voltage threshold can be increased, thereby shortening the time for online IV curve scanning while maintaining a relatively stable total output power of the photovoltaic power generation system.

[0213] In some embodiments, the time to start online IV curve scanning is determined based on the Voc obtained when performing 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 each photovoltaic unit connected to the (k-1)th DC-DC circuit and a first preset ratio.

[0214] 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 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 based on the rated open-circuit voltage range, for example, by selecting the maximum, minimum, or intermediate value within the rated open-circuit voltage range.

[0215] The second method: control based on time.

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

[0217] In some embodiments, the preset time interval is negatively correlated with the magnitude of N. The more DC-DC circuits connected to the photovoltaic system, the higher the power of the photovoltaic power generation system. In this case, the preset time interval can be reduced, thereby shortening the time for online IV curve scanning while maintaining a relatively stable 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 division of steps is for illustrative purposes only and does not constitute a limitation on the method of this application. For those skilled in the art, other possible implementation methods can be adopted without departing from the principle of the method, such as drawing the IV curve after all DC-DC circuits have completed online IV curve scanning.

[0221] In summary, using the method provided in this application embodiment, after the first DC-DC circuit starts online IV curve scanning, each of the remaining DC-DC circuits does not wait for the previous circuit to complete its scan before starting its scan. Instead, they perform online IV curve scanning sequentially, with the time interval being less than the time required for a single DC-DC circuit to perform online IV curve scanning. This achieves staggered scanning, allowing each group of N DC-DC circuits to output at off-peak times. On the one hand, this allows for simultaneous online IV curve scanning of photovoltaic units connected to multiple DC-DC circuits, saving scanning time. On the other hand, it ensures a more stable total output power of the photovoltaic power generation system, avoiding drastic fluctuations in total output power during online IV curve scanning, thereby reducing the negative impact of online IV curve scanning on grid-connected power quality.

[0222] This application also provides a photovoltaic inverter, which will be described in detail below with reference to the accompanying drawings.

[0223] See Figure 16 The figure is a schematic diagram of a photovoltaic inverter provided in an embodiment of this application.

[0224] The photovoltaic inverter 11 includes M sets of DC-DC circuits 111, DC-AC circuits 112, and a controller, where M is a positive integer. Specifically, the controller 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] Each DC-DC circuit 111 has its input connected to at least one photovoltaic unit, and each photovoltaic unit includes at least one photovoltaic module.

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

[0228] DC-DC circuit 111 is used to convert the DC power obtained from the photovoltaic unit into DC power and then transmit it to DC-AC circuit 112.

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

[0230] 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 connected photovoltaic units. The open-circuit voltage is then acquired and the result is transmitted to the host computer and / or stored in the data storage unit 402.

[0231] The controller then gradually reduces the input voltage of the DC-DC circuit to zero. During this process, it acquires the correspondence between the input voltage and input current of the DC-DC circuit according to a preset sampling interval, thereby obtaining the scanning result of the IV curve. The input current corresponding to the zero input voltage is the sum of the short-circuit currents of all photovoltaic units 10 connected to the DC-DC circuit.

[0232] For an N-channel DC-DC circuit, the controller controls each group of N-channel DC-DC circuits to start online IV curve scanning sequentially, 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.

[0233] In one possible implementation, the controller first controls the first DC-DC circuit to begin online IV curve scanning. For the remaining N-1 DC-DC circuits, the controller controls the k-th DC-DC circuit to begin online IV curve scanning when the input voltage of the (k-1)-th DC-DC circuit decreases to below 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. 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 connected to the photovoltaic system, the higher the power of the photovoltaic power generation system. In this case, the preset voltage threshold can be increased, thereby shortening the time required for online IV curve scanning while maintaining a relatively stable total output power of the photovoltaic power generation system.

[0235] In some embodiments, the time to start online IV curve scanning is determined based on the Voc obtained when performing 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 each photovoltaic unit connected to the (k-1)th DC-DC circuit and a first preset ratio.

[0236] 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 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 based on the rated open-circuit voltage range, for example, by selecting the maximum, minimum, or intermediate value within the rated open-circuit voltage range.

[0237] In another possible implementation, the controller first controls the first DC-DC circuit to start online IV curve scanning, and then controls the remaining DC-DC circuits to start online IV curve scanning sequentially according to 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 connected to the photovoltaic system, the higher the power of the photovoltaic power generation system. In this case, the preset time interval can be reduced, thereby shortening the time for online IV curve scanning while maintaining a 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 online IV curve scanning and the second preset ratio.

[0240] In summary, for each DC-DC circuit of this 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 its scan before starting their own scan. Instead, they perform online IV curve scanning sequentially, with the time interval being less than the time taken for the first DC-DC circuit to perform online IV curve scanning. This achieves staggered scanning, allowing each group of N DC-DC circuits to output at off-peak times. On the one hand, this allows for simultaneous online IV curve scanning of photovoltaic units connected to multiple DC-DC circuits, saving scanning time. On the other hand, it ensures a more stable total output power of the photovoltaic inverter, avoiding drastic fluctuations in total output power during online IV curve scanning. This reduces the negative impact of online IV curve scanning on grid-connected power quality.

[0241] This application also provides a DC combiner box, which will be described in detail below with reference to the accompanying drawings.

[0242] See Figure 17 The figure is a schematic diagram of a DC combiner box provided in an embodiment of this application.

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

[0244] Each DC-DC circuit 111 has its input connected to at least one photovoltaic unit, and each photovoltaic unit includes at least one photovoltaic module.

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

[0246] The positive output ports of the M-group DC-DC circuit 111 are connected in parallel to form the positive output port of the DC combiner box 20.

[0247] The negative output ports of the M-group DC-DC circuit 111 are connected in parallel to form the negative output port of the DC combiner box 20.

[0248] The controller controls the N DC-DC circuits in each group to start online IV curve scanning sequentially, 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.

[0249] For details on the specific control methods of the controller, please refer to the description of the above embodiments. The embodiments of this application will not be repeated here.

[0250] In summary, this DC combiner box allows for simultaneous online IV curve scanning of multiple DC-DC connected photovoltaic units, saving scanning time and ensuring a more stable total output power of the photovoltaic inverter. This avoids drastic fluctuations in total output power during online IV curve scanning, thereby reducing the negative impact of online IV curve scanning on grid-connected power quality.

[0251] This application also provides a photovoltaic optimizer, which will be described in detail below with reference to the accompanying drawings.

[0252] See Figure 18 The figure is a schematic diagram of a photovoltaic inverter substring provided in an embodiment of this application.

[0253] The photovoltaic optimizer 30 includes a DC-DC circuit for boosting or reducing the DC power input to the photovoltaic modules before outputting it. In this case, the photovoltaic power generation system includes M groups of photovoltaic optimizers, each group comprising N photovoltaic optimizers.

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

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

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

[0257] In a photovoltaic power generation system that uses a photovoltaic optimizer 30, multiple photovoltaic optimizers 30 are generally connected in series to form a photovoltaic optimizer substring 60.

[0258] For example, the N photovoltaic optimizers in each group are connected in series, meaning 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 1st photovoltaic optimizer serves as the positive output port of the photovoltaic optimizer substring 60, and the negative output port of the Nth photovoltaic optimizer serves as the negative output port of the photovoltaic optimizer substring 60.

[0259] The resulting M photovoltaic optimizer substrings, numbering 60, can be further connected in series.

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

[0261] In one possible implementation, the controller can be integrated with the controller of the photovoltaic optimizer, in which case the number of controllers is the same as the number of photovoltaic optimizers, and the host computer simultaneously issues scanning commands to each controller.

[0262] In another possible implementation, the controller is set up independently from the controller of the photovoltaic optimizer. One or more controllers can control all photovoltaic optimizers for online IV curve scanning. For example, one controller controls one photovoltaic optimizer substring 60.

[0263] For details on the specific control methods of the controller, please refer to the description of the above embodiments. The embodiments of this application will not be repeated here.

[0264] In summary, for photovoltaic power generation systems using this photovoltaic optimizer substring, online IV curve scanning can be performed simultaneously on photovoltaic units connected by multiple DC-DC circuits, saving scanning time and making the total output power of the photovoltaic inverter more stable. This avoids drastic fluctuations in the total output power during online IV curve scanning, thereby reducing the negative impact of online IV curve scanning of photovoltaic inverters on grid-connected power quality.

[0265] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) 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, and c can be single or multiple.

[0266] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on its differences from other embodiments. Furthermore, some or all of the units and modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0267] The above description is only a specific embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A string inverter, characterized in that, The photovoltaic power generation system includes a controller and a two-stage power conversion circuit. The two-stage power converter includes multiple DC-DC circuits. The first stage is a DC-DC circuit, i.e., a DC-DC boost circuit, and the second stage is a DC-AC circuit, i.e., an inverter circuit. The first stage DC-DC circuit includes multiple DC-DC circuits. The positive output ports of the multiple DC-DC circuits are connected in parallel to the positive input port of the DC side of the DC-AC circuit, and the negative output ports of the multiple DC-DC circuits are connected in parallel to the negative input port of the DC side of the DC-AC circuit. Each DC-DC circuit is used to connect at least one photovoltaic unit. The positive input port of each DC-DC circuit is connected to the positive terminal of the photovoltaic unit, and the negative input port of each DC-DC circuit is connected to the negative terminal of the photovoltaic unit. The photovoltaic unit includes multiple photovoltaic modules connected in series with their positive and negative terminals to form a photovoltaic string. The controller is used to control the N DC-DC circuits in each group to start online IV curve scanning sequentially, 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.

2. The string inverter 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 string inverter according to claim 2, characterized in that, The controller is specifically used to control the first DC-DC circuit of 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, where k = 2, 3, ..., N.

4. The string inverter according to claim 3, characterized in that, The online IV curve scanning time is the same for each of the DC-DC circuits, and the preset voltage threshold is the product of the sum of the open-circuit voltages of each photovoltaic unit connected to the (k-1)th DC-DC circuit and the first preset ratio.

5. The string inverter according to claim 3, characterized in that, 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.

6. The string inverter according to claim 2, characterized in that, The controller is specifically used to control the first DC-DC circuit in each group to start online IV curve scanning, and then the remaining DC-DC circuits to start online IV curve scanning sequentially according to a preset time interval, wherein the preset time interval is less than the time taken for one DC-DC circuit to perform online IV curve scanning.

7. The string inverter according to claim 6, characterized in that, The preset time interval is negatively correlated with the magnitude of N.

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

9. The string inverter according to any one of claims 1-8, characterized in that, When the controller controls the DC-DC circuits to scan sequentially, the first DC-DC circuit starts scanning the IV curve from the initial time, the second DC-DC circuit starts scanning the IV curve at T1, the third DC-DC circuit starts scanning the IV curve after T2, and so on, with the Nth DC-DC circuit starting scanning the IV curve after TN-1. T1, T2, ... TN-1 represent time intervals, and T0 represents the time taken for one DC-DC circuit to perform an online IV curve scan. T1, T2, ... TN-1 are all less than T0.

10. The string inverter according to claim 9, characterized in that, The T1, T2, ... TN-1 are either different or the same, in order to further reduce the fluctuation of the total output power of the N-channel DC-DC circuit during online IV curve scanning.

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