Photovoltaic control system and iv curve scanning method thereof

Abstract

The application provides a photovoltaic control system and an IV curve scanning method thereof. Part of photovoltaic optimizers is selected from any photovoltaic optimizer group string of multiple photovoltaic optimizer group strings to form a first scanning group, and part of photovoltaic optimizers is selected from another photovoltaic optimizer group string to form a second scanning group. IV curve scanning is simultaneously performed on photovoltaic modules connected with the photovoltaic optimizers in the first scanning group and the second scanning group. The photovoltaic optimizers in the first scanning group and the second scanning group are rotated within the same photovoltaic optimizer group string. IV curve scanning is simultaneously performed on the first scanning group and the second scanning group again, until the photovoltaic optimizer group string where the first scanning group and the second scanning group are located completes IV curve scanning on all photovoltaic modules. IV curve scanning is performed in parallel between each photovoltaic optimizer group string, and IV curve scanning is performed in series within each photovoltaic optimizer group string, so that the number of photovoltaic optimizers simultaneously performing IV curve scanning is reduced, and the output power is less affected.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic power generation technology, and in particular to a photovoltaic control system and its IV curve scanning method. Background Technology

[0002] A photovoltaic (PV) power generation system typically consists of multiple PV modules and inverters, with each module connected in series to form a string. The number of PV modules in each string varies depending on the open-circuit voltage (Voc) of each individual module and the input voltage of the inverter. If the maximum power points of the different strings are inconsistent, or if there are substandard PV modules, the inverter's output power will decrease, thus affecting the power generation. In severe cases, this can even cause normal PV modules to transfer current to substandard modules, resulting in hot spots.

[0003] Existing technologies can obtain the current-voltage (IV) curve of the entire string by adjusting the inverter's bus voltage. Through intelligent diagnostic algorithms, the aging degree and operating status of the string can be detected, such as short circuits in bypass diodes or string shading. Using IV curve scanning can increase the power generation of photovoltaic power generation systems and reduce operation and maintenance costs.

[0004] A photovoltaic optimizer is a type of maximum power point tracking (MPPT) device that has emerged in recent years and is installed between photovoltaic modules and inverters. It can eliminate series-parallel mismatch of photovoltaic modules and has the function of scanning the IV curve of a single photovoltaic module.

[0005] In existing technologies, for photovoltaic power generation systems with photovoltaic optimizers, the IV curve scanning of all photovoltaic modules is generally achieved simultaneously by controlling each photovoltaic optimizer. This can lead to large fluctuations in the output power of the photovoltaic power generation system, affecting the stability of grid-connected power. Summary of the Invention

[0006] This application provides a photovoltaic control system and its IV curve scanning method to solve the problem of large fluctuations in the output power of a photovoltaic power generation system during IV curve scanning.

[0007] Firstly, this application provides a photovoltaic control system, specifically including multiple photovoltaic optimizer strings and an inverter. An inverter may include multiple front-end boost units, a back-end inverter unit (specifically a back-end DC / AC inverter unit), and a controller. The controller may be connected to each of the multiple front-end boost units and the back-end inverter unit. The multiple front-end boost units may each be connected to a back-end inverter unit. Specifically, the output of each front-end boost unit may be connected to the input of the back-end DC / AC inverter unit, and the output of the back-end DC / AC inverter unit may be connected to the input of the power grid. Each of the multiple front-end boost units may be connected to one of the multiple photovoltaic optimizer strings. Specifically, each of the multiple photovoltaic optimizer strings is connected one-to-one to the input of one of the multiple front-end boost units. Each of the multiple photovoltaic optimizer strings may include multiple photovoltaic optimizers connected in series, and each photovoltaic optimizer is used to connect to at least one photovoltaic module. The front-end boost unit in the photovoltaic optimizer and inverter is mainly used to achieve maximum power point tracking (MPPT) for the photovoltaic modules. The back-end DC / AC inverter unit in the inverter is mainly used to convert DC power into AC power with the same frequency as the grid, thereby achieving grid-connected power generation. The number of photovoltaic optimizers in each photovoltaic optimizer string can be the same, or the number of photovoltaic optimizers in each photovoltaic optimizer string can be different; there is no limitation here.

[0008] Specifically, the controller in the inverter can simultaneously perform IV curve scanning on the photovoltaic modules connected to the photovoltaic optimizers in the first and second scan groups. The first scan group can be formed by selecting a subset of photovoltaic optimizers from any one of the multiple photovoltaic optimizer strings, and the second scan group can be formed by selecting a subset of photovoltaic optimizers from another photovoltaic optimizer string. The controller can also rotate the photovoltaic optimizers within the first and second scan groups within the same photovoltaic optimizer string, and then simultaneously perform IV curve scanning on both groups until the photovoltaic optimizer strings containing the first and second scan groups have completed IV curve scanning for all photovoltaic modules.

[0009] In this application, the first scan group can be composed of a portion of photovoltaic optimizers randomly selected from any photovoltaic optimizer string, and the second scan group can be composed of a portion of photovoltaic optimizers randomly selected from any other photovoltaic optimizer string. That is, the photovoltaic optimizers in both the first and second scan groups are randomly selected. Furthermore, the number of photovoltaic optimizers included in the first and second scan groups, which perform IV curve scanning simultaneously, can be the same or different. For example, to minimize the fluctuation of the output power of the photovoltaic power generation system when the scan groups perform IV curve scanning at different times, a photovoltaic optimizer can be randomly selected from any photovoltaic optimizer string to form the first scan group, and a photovoltaic optimizer can be randomly selected from any other photovoltaic optimizer string to form the second scan group. That is, both the first and second scan groups contain a randomly selected photovoltaic optimizer. Furthermore, the number of photovoltaic optimizers rotating to form the first (or second) scan group within the same photovoltaic optimizer string can be the same or different. For example, the first scan group within the same photovoltaic optimizer string can be formed by a randomly selected photovoltaic optimizer, and the next scan group can be formed by two or more randomly selected photovoltaic optimizers.

[0010] It should also be noted that a photovoltaic control system can contain two or more photovoltaic optimizer strings. The photovoltaic optimizer strings to which the first scan group and the second scan group belong are different. The terms "first" and "second" in "first scan group" and "second scan group" are only used to specify different scan groups, not to specify the number of scan groups or the photovoltaic optimizer string numbers to which the scan groups belong. Furthermore, the number of first and second scan groups performing IV curve scans simultaneously can be multiple. For example, if the photovoltaic control system includes three, four, or more photovoltaic optimizer strings, then correspondingly, the number of scan groups performing IV curve scans simultaneously can include three, four, or more scan groups. Moreover, the number of scan groups performing IV curve scans simultaneously can also be less than the number of photovoltaic optimizer strings. For example, if the photovoltaic control system includes three or more photovoltaic optimizer strings, the number of scan groups performing IV curve scans simultaneously can be only two, namely the first scan group and the second scan group. In addition, in order to make the fluctuation of the output power of the photovoltaic power generation system more consistent when the scanning groups perform IV curve scanning at different times, the number of scanning groups performing IV curve scanning at the same time each time can be the same or different. For example, the number of scanning groups performing IV curve scanning at the same time can be two, namely the first scanning group and the second scanning group, and the number of scanning groups performing IV curve scanning at the same time in the next time can be three, namely the first scanning group, the second scanning group and the third scanning group.

[0011] The photovoltaic control system provided in this application randomly selects a portion of photovoltaic optimizers from each photovoltaic optimizer string to form a first scanning group and a second scanning group. The photovoltaic control system performs I / V curve scanning sequentially in units of scanning groups, allowing the first and second scanning groups between different photovoltaic optimizer strings to perform I / V curve scanning in parallel, while the first and second scanning groups within each photovoltaic optimizer string can perform I / V curve scanning serially. Because at any given moment only the photovoltaic optimizers included in the first and second scanning groups perform I / V curve scanning on their connected photovoltaic modules, and all photovoltaic optimizers other than those included in the first and second scanning groups are in normal working condition, the number of photovoltaic optimizers performing I / V curve scanning simultaneously in the photovoltaic power generation system is reduced, resulting in a smaller impact on the output power of the photovoltaic power generation system and avoiding the problem of large fluctuations in the output power of the photovoltaic power generation system.

[0012] Specifically, the process of the photovoltaic optimizer in the photovoltaic control system provided in this application embodiment to realize IV curve scanning can be as follows: the photovoltaic optimizer can control its own switching transistor to ensure that the photovoltaic optimizer is directly turned off, so that the photovoltaic module remains open. Then, the photovoltaic optimizer adjusts the output voltage of the photovoltaic module to reduce it to 0, and records the IV curve of the photovoltaic module to generate IV curve scanning data, thereby completing the scanning.

[0013] Specifically, the photovoltaic optimizer in the photovoltaic control system provided in this application is generally a buck converter circuit, such as a buck circuit or a buck-boost circuit. Using the aforementioned IV curve scanning process may result in the inability to scan the low-voltage region of the photovoltaic module. Therefore, before performing the IV curve scan, the controller can also switch each of the multiple front-stage boost units to buck mode, reducing the output voltage of each photovoltaic optimizer string to a preset value Vtarget, thereby ensuring that the photovoltaic optimizer performs IV curve scanning on the low-voltage region of the photovoltaic module.

[0014] In one embodiment of this application, the controller can further unicast query the IV curve scan data of all photovoltaic optimizers after determining that all photovoltaic optimizer strings have completed the IV curve scan of all photovoltaic modules. Specifically, after determining that all photovoltaic optimizers have completed the IV curve scan, the controller can simultaneously unicast an IV curve scan data query instruction to all photovoltaic optimizers; each photovoltaic optimizer will receive the IV curve scan data query instruction at approximately the same time, and after receiving the IV curve scan data query instruction, each photovoltaic optimizer will upload its recorded IV curve scan data to the controller, that is, the controller will receive the IV curve scan data sent by each photovoltaic optimizer at approximately the same time.

[0015] In another embodiment of this application, the controller can unicast a query for the IV curve scanning data of the photovoltaic optimizers included in the first and second scan groups after each time it is determined that all photovoltaic optimizers included in the first and second scan groups have completed IV curve scanning. Specifically, the controller can query the scanning results after each photovoltaic optimizer included in the first and second scan groups has completed IV curve scanning, that is, unicast an IV curve scanning data query command to the photovoltaic optimizers included in the first and second scan groups; after receiving the IV curve scanning data query command, the photovoltaic optimizers included in the first and second scan groups will upload their respective recorded IV curve scanning data to the controller, that is, the controller will receive the IV curve scanning data sent by the photovoltaic optimizers included in the first and second scan groups at approximately the same time, and the controller will also receive the IV curve scanning data sent by photovoltaic optimizers included in different first and second scan groups at different times.

[0016] Secondly, this application also provides an IV curve scanning method for a photovoltaic control system. The photovoltaic control system may specifically include multiple photovoltaic optimizer strings and an inverter. An inverter may include multiple front-end boost units, a rear-end inverter unit (specifically, a rear-end DC / AC inverter unit), and a controller. The controller may be connected to each of the multiple front-end boost units and the rear-end inverter unit. The multiple front-end boost units may each be connected to a rear-end inverter unit. Specifically, the output of each front-end boost unit may be connected to the input of the rear-end DC / AC inverter unit, and the output of the rear-end DC / AC inverter unit may be connected to the input of the power grid. Each of the multiple front-end boost units may be connected to one of the multiple photovoltaic optimizer strings. Specifically, each of the multiple photovoltaic optimizer strings is connected one-to-one to the input of one of the multiple front-end boost units. Each of the multiple photovoltaic (PV) optimizer strings can include multiple PV optimizers connected in series, with each PV optimizer used to connect to at least one PV module. The front-end boost converter in the PV optimizer and inverter is primarily used to achieve maximum power point tracking (MPPT) for the PV modules, while the back-end DC / AC inverter in the inverter is primarily used to convert DC power into AC power at the same frequency as the grid, thereby achieving grid-connected power generation. The number of PV optimizers in each PV optimizer string can be the same, or the number of PV optimizers in each PV optimizer string can be different; this is not limited here.

[0017] The IV curve scanning method may specifically include: selecting a portion of photovoltaic optimizers from any one of the photovoltaic optimizer strings to form a first scanning group; selecting a portion of photovoltaic optimizers from another photovoltaic optimizer string to form a second scanning group; simultaneously performing IV curve scanning on the photovoltaic modules connected to the photovoltaic optimizers in the first and second scanning groups; rotating the photovoltaic optimizers in the first and second scanning groups within the same photovoltaic optimizer string; and then simultaneously performing IV curve scanning on the first and second scanning groups again until the photovoltaic optimizer strings containing the first and second scanning groups have completed IV curve scanning of all photovoltaic modules.

[0018] In this application, the first scan group can be composed of a portion of photovoltaic optimizers randomly selected from any photovoltaic optimizer string, and the second scan group can be composed of a portion of photovoltaic optimizers randomly selected from any other photovoltaic optimizer string. That is, the photovoltaic optimizers in both the first and second scan groups are randomly selected. Furthermore, the number of photovoltaic optimizers included in the first and second scan groups, which perform IV curve scanning simultaneously, can be the same or different. For example, to minimize the fluctuation of the output power of the photovoltaic power generation system when the scan groups perform IV curve scanning at different times, a photovoltaic optimizer can be randomly selected from any photovoltaic optimizer string to form the first scan group, and a photovoltaic optimizer can be randomly selected from any other photovoltaic optimizer string to form the second scan group. That is, both the first and second scan groups contain a randomly selected photovoltaic optimizer. Furthermore, the number of photovoltaic optimizers rotating to form the first (or second) scan group within the same photovoltaic optimizer string can be the same or different. For example, the first scan group within the same photovoltaic optimizer string can be formed by a randomly selected photovoltaic optimizer, and the next scan group can be formed by two or more randomly selected photovoltaic optimizers.

[0019] It should also be noted that a photovoltaic control system can contain two or more photovoltaic optimizer strings. The photovoltaic optimizer strings to which the first scan group and the second scan group belong are different. The terms "first" and "second" in "first scan group" and "second scan group" are only used to specify different scan groups, not to specify the number of scan groups or the photovoltaic optimizer string numbers to which the scan groups belong. Furthermore, the number of first and second scan groups performing IV curve scans simultaneously can be multiple. For example, if the photovoltaic control system includes three, four, or more photovoltaic optimizer strings, then correspondingly, the number of scan groups performing IV curve scans simultaneously can include three, four, or more scan groups. Moreover, the number of scan groups performing IV curve scans simultaneously can also be less than the number of photovoltaic optimizer strings. For example, if the photovoltaic control system includes three or more photovoltaic optimizer strings, the number of scan groups performing IV curve scans simultaneously can be only two, namely the first scan group and the second scan group. In addition, in order to make the fluctuation of the output power of the photovoltaic power generation system more consistent when the scanning groups perform IV curve scanning at different times, the number of scanning groups performing IV curve scanning at the same time each time can be the same or different. For example, the number of scanning groups performing IV curve scanning at the same time can be two, namely the first scanning group and the second scanning group, and the number of scanning groups performing IV curve scanning at the same time in the next time can be three, namely the first scanning group, the second scanning group and the third scanning group.

[0020] The I / V curve scanning method for a photovoltaic control system provided in this application involves randomly selecting a portion of photovoltaic optimizers from each photovoltaic optimizer string to form a first scanning group and a second scanning group. The photovoltaic control system performs I / V curve scanning sequentially in units of scanning groups. This allows the first and second scanning groups between different photovoltaic optimizer strings to perform I / V curve scanning in parallel, while the first and second scanning groups within each photovoltaic optimizer string can perform I / V curve scanning serially. Because at any given moment, only the photovoltaic optimizers included in the first and second scanning groups perform I / V curve scanning on their connected photovoltaic modules, and all other photovoltaic optimizers besides those included in the first and second scanning groups are in normal working condition, the number of photovoltaic optimizers simultaneously performing I / V curve scanning in the photovoltaic power generation system is reduced. This minimizes the impact on the output power of the photovoltaic power generation system and avoids the problem of large fluctuations in the output power of the photovoltaic power generation system.

[0021] Specifically, the photovoltaic optimizer in the IV curve scanning method of the photovoltaic control system provided in this application is generally a buck converter circuit, such as a buck circuit or a buck-boost circuit. Using the above-mentioned IV curve scanning process will result in the inability to scan the low-voltage region of the photovoltaic module. Therefore, the IV curve scanning method may further include: before performing the IV curve scan, controlling each of the multiple front-stage boost units to switch to buck mode, reducing the output voltage of each photovoltaic optimizer string in the multiple photovoltaic optimizer strings to a preset value Vtarget, so as to ensure that the photovoltaic optimizer performs IV curve scanning on the low-voltage region of the photovoltaic module.

[0022] In one embodiment of this application, the IV curve scanning method may further include: after determining that all photovoltaic optimizer strings have completed the IV curve scanning of all photovoltaic modules, unicasting a query for the IV curve scanning data of all photovoltaic optimizers. Specifically, after determining that all photovoltaic optimizers have completed the IV curve scanning, the controller may simultaneously unicast an IV curve scanning data query instruction to all photovoltaic optimizers; each photovoltaic optimizer will receive the IV curve scanning data query instruction at approximately the same time, and after receiving the IV curve scanning data query instruction, each photovoltaic optimizer will upload its recorded IV curve scanning data to the controller, that is, the controller will receive the IV curve scanning data sent by each photovoltaic optimizer at approximately the same time.

[0023] In another embodiment of this application, the IV curve scanning method may further include: after determining that all photovoltaic optimizers included in the first and second scanning groups have completed IV curve scanning, unicasting a query for the IV curve scanning data of the photovoltaic optimizers included in the first and second scanning groups. Specifically, the controller may query the scanning results after all photovoltaic optimizers included in the first and second scanning groups have completed IV curve scanning, that is, unicasting an IV curve scanning data query instruction to the photovoltaic optimizers included in the first and second scanning groups; after receiving the IV curve scanning data query instruction, the photovoltaic optimizers included in the first and second scanning groups will upload their respective recorded IV curve scanning data to the controller, that is, the controller will receive the IV curve scanning data sent by the photovoltaic optimizers included in the first and second scanning groups at approximately the same time, and the controller will also receive the IV curve scanning data sent by photovoltaic optimizers included in different first and second scanning groups at different times. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a photovoltaic power generation system;

[0025] Figure 2 This is a schematic diagram of the IV curve of a photovoltaic module;

[0026] Figure 3 The flowchart of the existing IV curve scanning method is shown.

[0027] Figure 4 This is a schematic diagram of the structure of the photovoltaic control system provided in the embodiments of this application;

[0028] Figure 5 This is a flowchart illustrating the IV curve scanning method provided in an embodiment of this application. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this application clearer, a further detailed description of this application will be provided below in conjunction with the accompanying drawings. However, the exemplary embodiments can be implemented in various forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided to make this application more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and therefore repeated descriptions of them will be omitted. Terms describing position and direction as described in this application are illustrative based on the accompanying drawings, but changes may be made as needed, and all such changes are included within the scope of protection of this application. The accompanying drawings of this application are for illustrating relative positional relationships only and do not represent actual scale.

[0030] It should be noted that specific details are set forth in the following description to provide a full understanding of this application. However, this application can be implemented in many ways other than those described herein, and those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below. The following descriptions are preferred embodiments for carrying out this application; however, these descriptions are for the purpose of illustrating the general principles of this application and are not intended to limit the scope of this application. The scope of protection of this application shall be determined by the appended claims.

[0031] To facilitate understanding of the embodiments of this application, the relevant technologies involved in the embodiments of this application will be introduced first below.

[0032] Reference Figure 1Existing photovoltaic (PV) power generation systems may include: multiple PV modules, multiple PV optimizers, and one inverter. Each PV module includes at least one PV panel, which can be connected in series or in parallel; this is not limited here. The output of one or more PV modules is connected to a PV optimizer. Multiple PV optimizers connected in series form a PV optimizer string, which is connected to the input of a front-end boost unit in the inverter. The output of each front-end boost unit in the inverter is connected to the input of a subsequent DC / AC inverter unit. The output of the subsequent DC / AC inverter unit is connected to the input of the power grid. The PV optimizers and the front-end boost units in the inverter are mainly used to achieve maximum power point tracking (MPPT) for the PV modules. The subsequent DC / AC inverter units in the inverter are mainly used to convert DC power into AC power at the same frequency as the power grid, thereby achieving grid-connected power generation. Figure 1 The example uses a photovoltaic module connected to a photovoltaic optimizer as an illustration, and illustrates two strings: string 1 is connected to front-end boost unit 1, and string 2 is connected to front-end boost unit 2. String 1 contains N photovoltaic optimizers, and string 2 contains M photovoltaic optimizers. M can be equal to N, or M can be different from N.

[0033] Reference Figure 2 The IV curve scanning of photovoltaic modules involves collecting the voltage and current values ​​of the photovoltaic module from the open-circuit voltage to the short-circuit current (Isc) point, then plotting the current-voltage curve, and finally diagnosing whether there are any abnormalities in the photovoltaic module by analyzing the IV curve.

[0034] Reference Figure 3 ,against Figure 1 The photovoltaic power generation system with a photovoltaic optimizer shown below uses the following existing module-level IV curve scanning strategy:

[0035] S1. On the inverter side: The inverter acts as the host and broadcasts the IV curve scan start command to all photovoltaic optimizers.

[0036] S2. On the photovoltaic optimizer side: After receiving the IV curve scan start command broadcast by the inverter, each photovoltaic optimizer starts the IV curve scan.

[0037] S3. On the photovoltaic optimizer side: After each photovoltaic optimizer completes the IV curve scan, it records its own IV curve scan data.

[0038] S4. On the inverter side: The inverter unicasts IV curve scan data to each photovoltaic optimizer.

[0039] S5. On the photovoltaic optimizer side: After receiving the query command, each photovoltaic optimizer uploads its own IV curve scan data.

[0040] The aforementioned IV curve scanning strategy for photovoltaic modules in photovoltaic power generation systems with photovoltaic optimizers involves scanning the IV curve of all photovoltaic optimizers simultaneously. This can lead to large fluctuations in the output power of the photovoltaic power generation system at any given moment, affecting the stability of grid-connected power.

[0041] To address this, this application provides a novel photovoltaic control system and its IV curve scanning method, which adjusts the IV curve scanning strategy of each photovoltaic optimizer, reduces large fluctuations in the output power of the photovoltaic power generation system at the same instant, and ensures grid-connected power stability.

[0042] The terminology used in the following embodiments is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. As used in the specification and appended claims of this application, the singular expressions “a,” “an,” and “the” are intended to also include expressions such as “one or more,” unless the context clearly indicates otherwise. It should also be understood that in the following embodiments of this application, “at least one” means one, two, or more.

[0043] References to "one embodiment" and similar terms used in this specification mean that one or more embodiments of this application include a particular feature, structure, or characteristic described in connection with that embodiment. Therefore, phrases such as "in one embodiment," "in some embodiments," and "in other embodiments" appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "having," and variations thereof mean "including, but not limited to," unless otherwise specifically emphasized.

[0044] Reference Figure 4The photovoltaic control system provided in this application embodiment may specifically include multiple photovoltaic optimizer strings and an inverter. An inverter may include multiple front-end boost units, a back-end inverter unit (specifically a back-end DC / AC inverter unit), and a controller. The controller may be connected to each of the multiple front-end boost units and the back-end inverter unit. The multiple front-end boost units may each be connected to a back-end inverter unit. Specifically, the output of each front-end boost unit may be connected to the input of the back-end DC / AC inverter unit, and the output of the back-end DC / AC inverter unit may be connected to the input of the power grid. Each of the multiple front-end boost units may be connected to one of the multiple photovoltaic optimizer strings. Specifically, each of the multiple photovoltaic optimizer strings is connected one-to-one to the input of one of the multiple front-end boost units. Each of the multiple photovoltaic optimizer strings may include multiple photovoltaic optimizers connected in series, and each photovoltaic optimizer is used to connect to at least one photovoltaic module. The front-end boost unit in photovoltaic optimizers and inverters is mainly used to achieve maximum power point tracking of photovoltaic modules, while the back-end DC / AC inverter unit in inverters is mainly used to convert DC power into AC power with the same frequency as the grid, thereby achieving grid-connected power generation. Figure 4 The example shown uses a photovoltaic module connected to a photovoltaic optimizer as an illustration, and illustrates two photovoltaic optimizer strings. Photovoltaic optimizer string 1 is connected to front-end boost unit 1, and photovoltaic optimizer string 2 is connected to front-end boost unit 2. Photovoltaic optimizer string 1 contains N photovoltaic optimizers, and photovoltaic optimizer string 2 contains M photovoltaic optimizers. The number of photovoltaic optimizers in each photovoltaic optimizer string can be the same, that is, M can be equal to N, or the number of photovoltaic optimizers in each photovoltaic optimizer string can be different, that is, M can be not equal to N. There is no limitation here.

[0045] Specifically, the controller in the inverter can simultaneously perform IV curve scanning on the photovoltaic modules connected to the photovoltaic optimizers in the first and second scan groups. The first scan group can be formed by selecting a subset of photovoltaic optimizers from any one of the multiple photovoltaic optimizer strings, and the second scan group can be formed by selecting a subset of photovoltaic optimizers from another photovoltaic optimizer string. The controller can also rotate the photovoltaic optimizers within the first and second scan groups within the same photovoltaic optimizer string, and then simultaneously perform IV curve scanning on both groups until the photovoltaic optimizer strings containing the first and second scan groups have completed IV curve scanning for all photovoltaic modules.

[0046] In this application, the first scan group can be composed of a portion of photovoltaic optimizers randomly selected from any photovoltaic optimizer string, and the second scan group can be composed of a portion of photovoltaic optimizers randomly selected from any other photovoltaic optimizer string. That is, the photovoltaic optimizers in both the first and second scan groups are randomly selected. Furthermore, the number of photovoltaic optimizers included in the first and second scan groups, which perform IV curve scanning simultaneously, can be the same or different. For example, to minimize the fluctuation of the output power of the photovoltaic power generation system when the scan groups perform IV curve scanning at different times, a photovoltaic optimizer can be randomly selected from any photovoltaic optimizer string to form the first scan group, and a photovoltaic optimizer can be randomly selected from any other photovoltaic optimizer string to form the second scan group. That is, both the first and second scan groups contain a randomly selected photovoltaic optimizer. Furthermore, the number of photovoltaic optimizers rotating to form the first (or second) scan group within the same photovoltaic optimizer string can be the same or different. For example, the first scan group within the same photovoltaic optimizer string can be formed by a randomly selected photovoltaic optimizer, and the next scan group can be formed by two or more randomly selected photovoltaic optimizers.

[0047] It should also be noted that a photovoltaic control system can contain two or more photovoltaic optimizer strings. The photovoltaic optimizer strings to which the first scan group and the second scan group belong are different. The terms "first" and "second" in "first scan group" and "second scan group" are only used to specify different scan groups, not to specify the number of scan groups or the photovoltaic optimizer string numbers to which the scan groups belong. Furthermore, the number of first and second scan groups performing IV curve scans simultaneously can be multiple. For example, if the photovoltaic control system includes three, four, or more photovoltaic optimizer strings, then correspondingly, the number of scan groups performing IV curve scans simultaneously can include three, four, or more scan groups. Moreover, the number of scan groups performing IV curve scans simultaneously can also be less than the number of photovoltaic optimizer strings. For example, if the photovoltaic control system includes three or more photovoltaic optimizer strings, the number of scan groups performing IV curve scans simultaneously can be only two, namely the first scan group and the second scan group. In addition, in order to make the fluctuation of the output power of the photovoltaic power generation system more consistent when the scanning groups perform IV curve scanning at different times, the number of scanning groups performing IV curve scanning at the same time each time can be the same or different. For example, the number of scanning groups performing IV curve scanning at the same time can be two, namely the first scanning group and the second scanning group, and the number of scanning groups performing IV curve scanning at the same time in the next time can be three, namely the first scanning group, the second scanning group and the third scanning group.

[0048] The photovoltaic control system provided in this application randomly selects a portion of photovoltaic optimizers from each photovoltaic optimizer string to form a first scanning group and a second scanning group. The photovoltaic control system performs I / V curve scanning sequentially in units of scanning groups, allowing the first and second scanning groups between different photovoltaic optimizer strings to perform I / V curve scanning in parallel, while the first and second scanning groups within each photovoltaic optimizer string can perform I / V curve scanning serially. Because at any given moment only the photovoltaic optimizers included in the first and second scanning groups perform I / V curve scanning on their connected photovoltaic modules, and all photovoltaic optimizers other than those included in the first and second scanning groups are in normal working condition, the number of photovoltaic optimizers performing I / V curve scanning simultaneously in the photovoltaic power generation system is reduced, resulting in a smaller impact on the output power of the photovoltaic power generation system and avoiding the problem of large fluctuations in the output power of the photovoltaic power generation system.

[0049] Specifically, the process of the photovoltaic optimizer in the photovoltaic control system provided in this application embodiment to realize IV curve scanning can be as follows: the photovoltaic optimizer can control its own switching transistor to ensure that the photovoltaic optimizer is directly turned off, so that the photovoltaic module remains open. Then, the photovoltaic optimizer adjusts the output voltage of the photovoltaic module to reduce it to 0, and records the IV curve of the photovoltaic module to generate IV curve scanning data, thereby completing the scanning.

[0050] Specifically, the photovoltaic optimizer in the photovoltaic control system provided in this application is generally a buck converter circuit, such as a buck circuit or a buck-boost circuit. Using the aforementioned IV curve scanning process may result in the inability to scan the low-voltage region of the photovoltaic module. Therefore, before performing the IV curve scan, the controller can also switch each of the multiple front-stage boost units to buck mode, reducing the output voltage of each photovoltaic optimizer string to a preset value Vtarget, thereby ensuring that the photovoltaic optimizer performs IV curve scanning on the low-voltage region of the photovoltaic module.

[0051] In one embodiment of this application, the controller can further unicast query the IV curve scan data of all photovoltaic optimizers after determining that all photovoltaic optimizer strings have completed the IV curve scan of all photovoltaic modules. Specifically, after determining that all photovoltaic optimizers have completed the IV curve scan, the controller can simultaneously unicast an IV curve scan data query instruction to all photovoltaic optimizers; each photovoltaic optimizer will receive the IV curve scan data query instruction at approximately the same time, and after receiving the IV curve scan data query instruction, each photovoltaic optimizer will upload its recorded IV curve scan data to the controller, that is, the controller will receive the IV curve scan data sent by each photovoltaic optimizer at approximately the same time.

[0052] Alternatively, in another embodiment of this application, the controller can unicast a query for the IV curve scanning data of the photovoltaic optimizers included in the first and second scan groups after each time it is determined that all photovoltaic optimizers included in the first and second scan groups have completed IV curve scanning. Specifically, the controller can query the scanning results after each photovoltaic optimizer included in the first and second scan groups has completed IV curve scanning, that is, unicast an IV curve scanning data query instruction to the photovoltaic optimizers included in the first and second scan groups; after receiving the IV curve scanning data query instruction, the photovoltaic optimizers included in the first and second scan groups will upload their respective recorded IV curve scanning data to the controller, that is, the controller will receive the IV curve scanning data sent by the photovoltaic optimizers included in the first and second scan groups at approximately the same time, and the controller will also receive the IV curve scanning data sent by photovoltaic optimizers included in different first and second scan groups at different times.

[0053] Based on the same inventive concept, referring to Figure 5 This application also provides an IV curve scanning method for the photovoltaic control system described above. The specific structure of the photovoltaic control system is described above and will not be detailed here. The IV curve scanning method may specifically include the following steps:

[0054] S1. Select a portion of photovoltaic optimizers from any one of the multiple photovoltaic optimizer strings to form a first scan group, and select a portion of photovoltaic optimizers from another of the multiple photovoltaic optimizer strings to form a second scan group.

[0055] S2. Simultaneously perform IV curve scanning on the photovoltaic modules connected to the photovoltaic optimizer in the first and second scanning groups.

[0056] S3. Rotate the photovoltaic optimizers in the first and second scan groups within the same photovoltaic optimizer string;

[0057] S4. Then simultaneously perform IV curve scanning on the first scan group and the second scan group until the photovoltaic optimizer string containing the first scan group and the second scan group completes the IV curve scanning of all photovoltaic modules.

[0058] In step S1 of this application, the first scan group can be composed of a portion of photovoltaic optimizers randomly selected from any photovoltaic optimizer string, and the second scan group can be composed of a portion of photovoltaic optimizers randomly selected from any other photovoltaic optimizer string. That is, the photovoltaic optimizers in both the first and second scan groups are randomly selected. Furthermore, the number of photovoltaic optimizers included in the first and second scan groups, which perform IV curve scanning simultaneously, can be the same or different. For example, in order to minimize the fluctuation of the output power of the photovoltaic power generation system when the scan groups perform IV curve scanning at different times, a photovoltaic optimizer can be randomly selected from any photovoltaic optimizer string to form the first scan group, and a photovoltaic optimizer can be randomly selected from any other photovoltaic optimizer string to form the second scan group. That is, both the first and second scan groups contain a randomly selected photovoltaic optimizer. Furthermore, the number of photovoltaic optimizers rotating to form the first (or second) scan group within the same photovoltaic optimizer string can be the same or different. For example, the first scan group within the same photovoltaic optimizer string can be formed by a randomly selected photovoltaic optimizer, and the next scan group can be formed by two or more randomly selected photovoltaic optimizers.

[0059] It should also be noted that a photovoltaic control system can contain two or more photovoltaic optimizer strings. The photovoltaic optimizer strings to which the first scan group and the second scan group belong are different. The terms "first" and "second" in "first scan group" and "second scan group" are only used to specify different scan groups, not to specify the number of scan groups or the photovoltaic optimizer string numbers to which the scan groups belong. Furthermore, the number of first and second scan groups performing IV curve scans simultaneously can be multiple. For example, if the photovoltaic control system includes three, four, or more photovoltaic optimizer strings, then correspondingly, the number of scan groups performing IV curve scans simultaneously can include three, four, or more scan groups. Moreover, the number of scan groups performing IV curve scans simultaneously can also be less than the number of photovoltaic optimizer strings. For example, if the photovoltaic control system includes three or more photovoltaic optimizer strings, the number of scan groups performing IV curve scans simultaneously can be only two, namely the first scan group and the second scan group. In addition, in order to make the fluctuation of the output power of the photovoltaic power generation system more consistent when the scanning groups perform IV curve scanning at different times, the number of scanning groups performing IV curve scanning at the same time each time can be the same or different. For example, the number of scanning groups performing IV curve scanning at the same time can be two, namely the first scanning group and the second scanning group, and the number of scanning groups performing IV curve scanning at the same time in the next time can be three, namely the first scanning group, the second scanning group and the third scanning group.

[0060] The I / V curve scanning method for a photovoltaic control system provided in this application involves randomly selecting a portion of photovoltaic optimizers from each photovoltaic optimizer string to form a first scanning group and a second scanning group. The photovoltaic control system performs I / V curve scanning sequentially in units of scanning groups. This allows the first and second scanning groups between different photovoltaic optimizer strings to perform I / V curve scanning in parallel, while the first and second scanning groups within each photovoltaic optimizer string can perform I / V curve scanning serially. Because at any given moment, only the photovoltaic optimizers included in the first and second scanning groups perform I / V curve scanning on their connected photovoltaic modules, and all other photovoltaic optimizers besides those included in the first and second scanning groups are in normal working condition, the number of photovoltaic optimizers simultaneously performing I / V curve scanning in the photovoltaic power generation system is reduced. This minimizes the impact on the output power of the photovoltaic power generation system and avoids the problem of large fluctuations in the output power of the photovoltaic power generation system.

[0061] Specifically, the photovoltaic optimizer in the IV curve scanning method of the photovoltaic control system provided in this application is generally a buck converter circuit, such as a buck circuit or a buck-boost circuit. Using the above-mentioned IV curve scanning process will result in the inability to scan the low-voltage region of the photovoltaic module. Therefore, the IV curve scanning method may further include: before performing the IV curve scan, controlling each of the multiple front-stage boost units to switch to buck mode, reducing the output voltage of each photovoltaic optimizer string in the multiple photovoltaic optimizer strings to a preset value Vtarget, so as to ensure that the photovoltaic optimizer performs IV curve scanning on the low-voltage region of the photovoltaic module.

[0062] In one embodiment of this application, the IV curve scanning method may further include: after determining that all photovoltaic optimizer strings have completed the IV curve scanning of all photovoltaic modules, unicasting a query for the IV curve scanning data of all photovoltaic optimizers. Specifically, after determining that all photovoltaic optimizers have completed the IV curve scanning, the controller may simultaneously unicast an IV curve scanning data query instruction to all photovoltaic optimizers; each photovoltaic optimizer will receive the IV curve scanning data query instruction at approximately the same time, and after receiving the IV curve scanning data query instruction, each photovoltaic optimizer will upload its recorded IV curve scanning data to the controller, that is, the controller will receive the IV curve scanning data sent by each photovoltaic optimizer at approximately the same time.

[0063] Alternatively, in another embodiment of this application, the IV curve scanning method may further include: after determining that all photovoltaic optimizers included in the first and second scan groups have completed IV curve scanning, unicasting a query for the IV curve scanning data of the photovoltaic optimizers included in the first and second scan groups. Specifically, the controller may query the scanning results after all photovoltaic optimizers included in the first and second scan groups have completed IV curve scanning, that is, unicasting an IV curve scanning data query instruction to the photovoltaic optimizers included in the first and second scan groups; after receiving the IV curve scanning data query instruction, the photovoltaic optimizers included in the first and second scan groups will upload their respective recorded IV curve scanning data to the controller, that is, the controller will receive the IV curve scanning data sent by the photovoltaic optimizers included in the first and second scan groups at approximately the same time, and the controller will also receive the IV curve scanning data sent by photovoltaic optimizers included in different first and second scan groups at different times.

[0064] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A photovoltaic control system, characterized in that, The photovoltaic control system includes an inverter and multiple photovoltaic optimizer strings. The inverter includes multiple front-end boost units, a back-end inverter unit, and a controller. The controller is connected to both the multiple front-end boost units and the back-end inverter unit. The multiple front-end boost units are connected to the back-end inverter unit. Each of the multiple front-end boost units is connected to one of the multiple photovoltaic optimizer strings. Each of the multiple photovoltaic optimizer strings includes multiple photovoltaic optimizers connected in series. Each photovoltaic optimizer is used to connect to at least one photovoltaic module. The controller is configured to: simultaneously perform IV curve scanning on the photovoltaic modules connected to the photovoltaic optimizers in the first and second scanning groups; select a portion of photovoltaic optimizers from any one of the multiple photovoltaic optimizer strings to form the first scanning group; select a portion of photovoltaic optimizers from another photovoltaic optimizer string to form the second scanning group; rotate the photovoltaic optimizers in the first and second scanning groups within the same photovoltaic optimizer string; and then simultaneously perform IV curve scanning on the first and second scanning groups until the photovoltaic optimizer strings containing the first and second scanning groups have completed IV curve scanning of all photovoltaic modules; the photovoltaic optimizers in the first and second scanning groups are randomly selected.

2. The photovoltaic control system as described in claim 1, characterized in that, Each of the plurality of photovoltaic optimizers is a buck circuit or a buck-boost circuit; The controller is also configured to: before performing IV curve scanning, control each of the plurality of front-stage boost units to switch to buck mode, thereby reducing the output voltage of each of the plurality of photovoltaic optimizer strings to a preset value.

3. The photovoltaic control system as described in claim 1 or 2, characterized in that, The controller is also configured to: after determining that all photovoltaic optimizer strings have completed the IV curve scan of all photovoltaic modules, unicast query the IV curve scan data of all photovoltaic optimizers.

4. The photovoltaic control system as described in claim 1 or 2, characterized in that, The controller is further configured to: unicast query the IV curve scan data of the photovoltaic modules in the first scan group and the second scan group when it is determined that the photovoltaic optimizers included in the first scan group and the second scan group have completed the IV curve scan of the photovoltaic modules.

5. The photovoltaic control system as described in claim 1 or 2, characterized in that, The controller is specifically configured to include a randomly selected photovoltaic optimizer in both the first scan group and the second scan group.

6. A method for scanning the IV curve of a photovoltaic control system, applied to a photovoltaic control system, characterized in that, The photovoltaic control system includes an inverter and multiple photovoltaic optimizer strings. The inverter includes multiple front-end boost units, a back-end inverter unit, and a controller. The controller is connected to both the multiple front-end boost units and the back-end inverter unit. The multiple front-end boost units are connected to the back-end inverter unit. Each of the multiple front-end boost units is connected to one of the multiple photovoltaic optimizer strings. Each of the multiple photovoltaic optimizer strings includes multiple photovoltaic optimizers connected in series. Each photovoltaic optimizer is used to connect to at least one photovoltaic module. The IV curve scanning method includes: A first scan group is formed by selecting a portion of photovoltaic optimizers from any one of the multiple photovoltaic optimizer strings, and a second scan group is formed by selecting a portion of photovoltaic optimizers from another photovoltaic optimizer string; the photovoltaic optimizers in the first scan group and the second scan group are randomly selected. Simultaneously perform IV curve scanning on the photovoltaic modules connected to the photovoltaic optimizers in the first and second scanning groups; The photovoltaic optimizers in the first scan group and the second scan group are rotated within the same photovoltaic optimizer string; Then, IV curve scanning is performed on the first scan group and the second scan group simultaneously until the photovoltaic optimizer string containing the first scan group and the second scan group completes the IV curve scanning of all photovoltaic modules.

7. The IV curve scanning method as described in claim 6, characterized in that, Each of the plurality of photovoltaic optimizers is a buck circuit or a buck-boost circuit; The IV curve scanning method further includes: Before performing IV curve scanning, each of the multiple front-stage boost units is switched to buck mode to reduce the output voltage of each of the multiple photovoltaic optimizer strings to a preset value.

8. The IV curve scanning method as described in claim 6 or 7, characterized in that, Also includes: After confirming that all photovoltaic optimizer strings have completed the IV curve scan of all photovoltaic modules, unicast query is performed on the IV curve scan data of all photovoltaic optimizers.

9. The IV curve scanning method as described in claim 6 or 7, characterized in that, Also includes: When it is determined that the photovoltaic optimizers included in the first scan group and the second scan group have completed the IV curve scan of the photovoltaic module, the IV curve scan data of the photovoltaic module in the first scan group and the second scan group are unicasted.

10. The IV curve scanning method as described in claim 6 or 7, characterized in that, Both the first scan group and the second scan group contain a randomly selected photovoltaic optimizer.

Images