Photovoltaic system and method for determining maximum input power

Abstract

A photovoltaic system and a method for determining maximum input power. In the photovoltaic system, the input end of each DC-DC conversion circuit (200a, 200b) is connected to a corresponding photovoltaic string (100a, 100b); the output ends of multiple DC-DC conversion circuits (200a, 200b) are connected in parallel to the input end of a DC-AC conversion circuit (200c); a controller (400) performs a local current-voltage IV curve scan on each DC-DC conversion circuit (200a, 200b); during the local IV curve scan, the total input power of the multiple DC-DC conversion circuits (200a, 200b) is controlled to remain unchanged as before the local IV curve scan, the maximum input power of each DC-DC conversion circuit (200a, 200b) is obtained, and the sum of the maximum input powers of all DC-DC conversion circuits (200a, 200b) is obtained based on the maximum input power of each DC-DC conversion circuit (200a, 200b); and the scan voltage of the local IV curve scan is less than the open-circuit voltage. In order to improve the scanning efficiency, only a part of the IV curve is scanned to obtain the maximum input power under the power-limited state, which is convenient for subsequent power scheduling and control.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic power generation technology, and in particular to a photovoltaic system and a method for determining maximum input power. Background Art

[0002] Currently, many PV power plants include multiple PV sub-arrays, each of which includes multiple PV arrays. PV power plants sometimes require that the PV sub-arrays operate not at their maximum power point but rather with power-limited output. This means that the inverters in the PV sub-arrays control the output power of the PV array according to the power limit specified in the power limit instruction, rather than allowing the PV array to output its maximum power uncontrolled. During power-limited control, the output power of the PV array is less than the maximum output power of the PV array.

[0003] However, in actual work, it is necessary to predict the maximum input power of the photovoltaic sub-array under power limitation, that is, it is necessary to predict the maximum input power of each inverter in the photovoltaic sub-array. Summary of the Invention

[0004] The present application provides a photovoltaic system and a method for determining a maximum input power, which can obtain the maximum input power of an inverter under power-limited operation.

[0005] The photovoltaic system provided in an embodiment of the present application includes: a controller, a direct current (DC)-alternating current (DC)-AC conversion circuit, and multiple direct current (DC)-DC conversion circuits; the input end of each DC-DC conversion circuit is used to connect to a corresponding photovoltaic string; the output ends of the multiple DC-DC conversion circuits are connected in parallel to the input end of the DC-AC conversion circuit; because multiple DC-DC conversion circuits are included, in order to obtain maximum input power, it is necessary to obtain the sum of the input powers of all DC-DC conversion circuits. The controller performs a local current-voltage IV curve scan on each DC-DC conversion circuit. During the local IV curve scan, the total input power is kept consistent with that before the local IV curve scan to obtain the maximum input power of each DC-DC conversion circuit. The sum of the maximum input powers of all DC-DC conversion circuits is obtained based on the maximum input power of each DC-DC conversion circuit; the scanning voltage of the local IV curve scan is less than the open-circuit voltage, that is, the scan is performed locally rather than from the short-circuit voltage to the open-circuit voltage, thereby saving scanning time and improving scanning efficiency.

[0006] To ensure that the inverter achieves maximum input power while operating in a power-limited state, the controller maintains the total input power of the inverter while performing a local IV curve scan. When the input power of the DC-DC converter circuit undergoing a local IV curve scan changes, the input power of the DC-DC converter circuits not undergoing the local IV curve scan is controlled to follow suit, ensuring that the sum of the input powers of all DC-DC converter circuits remains constant. Therefore, the IV curve scan performed to achieve maximum input power in a power-limited state is a local scan, not a global scan. This is not a traditional IV curve scan, which scans from maximum voltage to minimum voltage. To improve scanning efficiency, the embodiments of the present application only perform a local IV curve scan. As long as the maximum power point is covered during the scan, the maximum input power of the photovoltaic power station operating in a power-limited state can be determined through local IV curve scanning, facilitating subsequent power scheduling and control. The technical solution provided by the embodiments of the present application performs an IV curve scan on each DC-DC converter circuit in the photovoltaic system, avoiding power estimation errors caused by shading or failure of individual photovoltaic strings, and more accurately determining the system's maximum input power.

[0007] This application does not specifically limit the number of scanning paths. For example, the scanning can be performed one by one, or the paths can be divided into groups first. Each group can include multiple DC-DC conversion circuits, and the scanning is performed group by group. They are introduced below.

[0008] In one possible implementation, a case of performing local IV curve scanning on at least two circuits is described as follows: a first DC-DC converter circuit and a second DC-DC converter circuit; an input end of the first DC-DC converter circuit is connected to a corresponding photovoltaic string; an input end of the second DC-DC converter circuit is connected to the corresponding photovoltaic string; an output end of the first DC-DC converter circuit and an output end of the second DC-DC converter circuit are connected in parallel to an input end of a DC-AC converter circuit; a controller is configured to control a change in an input voltage of the first DC-DC converter circuit to perform a local IV curve scan and obtain a first maximum input power of the first DC-DC converter circuit; during the local IV curve scan of the first DC-DC converter circuit, the input power of the second DC-DC converter circuit is adjusted so that the sum of the input power of the first DC-DC converter circuit and the input power of the second DC-DC converter circuit is consistent with that before the local IV curve scan; and so on and so forth, to obtain a second maximum input power of the second DC-DC converter circuit; and the sum of the maximum input powers of all DC-DC converter circuits is obtained based on the first maximum input power and the second maximum input power.

[0009] In one possible implementation, the controller obtains a first maximum input power of the first DC-DC conversion circuit according to the scanning voltage and the scanning current. During the scanning process, the power of multiple sampling points is obtained, and the maximum input power is selected from them.

[0010] In one possible implementation, in order to obtain the maximum input power, it is necessary to record the scan voltage and scan current at each sampling point during the scanning process, and obtain the corresponding power based on the product of the scan voltage and scan current. The controller controls the input voltage of the first DC-DC conversion circuit to gradually decrease to perform a local IV curve scan, and records the scan voltage and scan current of the first DC-DC conversion circuit during the local IV curve scan. The scan is stopped when the input power of the first DC-DC conversion circuit decreases and the scan voltage is less than the voltage before the local IV curve scan. The above are the conditions for stopping the local I curve scan, thereby ensuring that the scanning process covers the maximum input power to avoid incomplete scanning and missing the maximum input power point.

[0011] In one possible implementation, another specific scanning method is provided below, in which the criterion for stopping the scanning is different from that described above. The controller controls the input voltage of the first DC-DC conversion circuit to gradually decrease to perform a local IV curve scan, and records the scanning voltage and scanning current of the first DC-DC conversion circuit during the local IV curve scan. The scanning is stopped when the input power of the first DC-DC conversion circuit is equal to the input power before the local IV curve scan and the scanning voltage is less than the voltage before the local IV curve scan.

[0012] In one possible implementation, the starting point of the local IV curve scan is described below. The controller controls the input voltage of the first DC-DC conversion circuit to gradually decrease from a first voltage to perform a local IV curve scan. The first voltage is the input voltage of the first DC-DC conversion circuit corresponding to the maximum input power of the second DC-DC conversion circuit when the total input power of the multiple DC-DC conversion circuits is consistent with that before the local IV curve scan. The solution provided in the embodiment of the present application is to first control the output voltage of the photovoltaic string to increase from the current operating point E until the input power of the other DC-DC conversion circuits can no longer increase, that is, the input power of the other DC-DC conversion circuits limits the input voltage of the scanned DC-DC conversion circuit from continuing to increase. The maximum voltage is then used as the starting voltage for the local IV curve scan, and the local IV curve scan is performed from the starting voltage to the left, that is, gradually decreasing.

[0013] In one possible implementation, the following describes a method for maintaining a constant common input power. During an IV curve scan, the controller adjusts the input power of the second DC-DC converter circuit based on the input power of the first DC-DC converter circuit, such that the sum of the input power of the first DC-DC converter circuit and the input power of the second DC-DC converter circuit equals the power limit command value of the photovoltaic system. Generally, when a photovoltaic system operates at power limit, it controls the operation of the DC-DC converter circuit according to the power limit command value. This power limit command value can be issued by the dispatch center corresponding to the photovoltaic power station or set by the photovoltaic system itself, and is not specifically limited in this embodiment of the present application.

[0014] In one possible implementation, a process of performing local IV curve scanning on each of the multiple groups is described below. The multiple DC-DC conversion circuits include a total of N circuits, and the N DC-DC conversion circuits are divided into at least two groups: a first group includes K circuits and a second group includes NK circuits; K is an integer greater than or equal to 2; and a controller is configured to perform local IV curve scanning on each of the K DC-DC conversion circuits in the first group. During the local IV curve scanning, the total input power of the N DC-DC conversion circuits is controlled to be consistent with that before the local IV curve scanning, and the maximum input power of each DC-DC conversion circuit in the K circuits is obtained. Similarly, the maximum input power of each DC-DC conversion circuit in the NK circuits is obtained, and the sum of the maximum input powers of the N DC-DC conversion circuits is obtained based on the maximum input power of each DC-DC conversion circuit.

[0015] In one possible implementation, the controller gradually reduces the input voltage of each DC-DC converter circuit in the K circuits to perform a local IV curve scan. The controller then records the scanned voltage and current of each DC-DC converter circuit in the K circuits until the input power of each DC-DC converter circuit in the K circuits decreases and the scanned voltage is less than the voltage before the local IV curve scan. The scan is then stopped. This is the condition for stopping the local I curve scan, ensuring that the scan covers the maximum input power, thus avoiding incomplete scanning and missing the maximum input power point.

[0016] In one possible implementation, another specific scanning method is provided below. The criterion for stopping the scanning is different from that described above. The controller controls the input voltage of each DC-DC conversion circuit in the K circuit to gradually decrease to perform a local IV curve scan, and records the scan voltage and scan current of each DC-DC conversion circuit in the K circuit. The scanning is stopped when the input power of each DC-DC conversion circuit in the K circuit is equal to the input power before the local IV curve scan and the scan voltage is less than the voltage before the local IV curve scan.

[0017] In one possible implementation, the controller obtains the maximum input power of each of the K DC-DC converter circuits based on the scan voltage and scan current of each of the K DC-DC converter circuits. During the scan process, the scan current and scan voltage corresponding to multiple sampling points are obtained, and the input power is obtained by multiplying the scan current and scan voltage. The maximum input power is selected from the obtained values.

[0018] In one possible implementation, the starting point of the local IV curve scan is described below. The controller controls the input voltage of each DC-DC conversion circuit in the K channels to gradually decrease from a second voltage to perform the local IV curve scan. The second voltage is the input voltage of each DC-DC conversion circuit in the K channels corresponding to the maximum total input power of the NK channels DC-DC conversion circuits when the total input power of the multiple DC-DC conversion circuits is consistent with that before the local IV curve scan.

[0019] The embodiments of the present application do not limit the implementation form of the inverter. It can be a centralized inverter or a string inverter, etc. In one possible implementation, the DC-AC conversion circuit, the multi-channel DC-DC conversion circuit and the controller are integrated inside the string inverter.

[0020] In a possible implementation, the photovoltaic system may include a combiner box, multiple DC-DC conversion circuits are integrated inside the combiner box, and the DC-AC conversion circuit is integrated inside a centralized inverter.

[0021] Based on the photovoltaic system provided in the above embodiment, the embodiment of the present application further provides a method for determining the maximum input power of the photovoltaic system. The various advantages of the above photovoltaic system are applicable to the following method and will not be repeated here.

[0022] An embodiment of the present application also provides a method for determining the maximum input power of a photovoltaic system, wherein the photovoltaic system includes a direct current (DC)-alternating current (DC)-AC conversion circuit and multiple direct current (DC)-DC conversion circuits; the input end of each DC-DC conversion circuit is used to connect to a corresponding photovoltaic string; the output ends of the multiple DC-DC conversion circuits are connected in parallel to the input end of the DC-AC conversion circuit; the method includes: performing a local current-voltage IV curve scan on each DC-DC conversion circuit; during the local IV curve scan, controlling the total input power of the multiple DC-DC conversion circuits to be consistent with that before the local IV curve scan, to obtain the maximum input power of each DC-DC conversion circuit; obtaining the sum of the maximum input powers of all DC-DC conversion circuits based on the maximum input power of each DC-DC conversion circuit; and the scanning voltage of the local IV curve scan is less than the open-circuit voltage.

[0023] In one possible implementation, a multi-channel DC-DC conversion circuit includes at least: a first DC-DC conversion circuit and a second DC-DC conversion circuit; a local current-voltage IV curve scan is performed on each DC-DC conversion circuit; during the local IV curve scan, a total input power of the multi-channel DC-DC conversion circuit is controlled to be consistent with that before the local IV curve scan to obtain a maximum input power of each DC-DC conversion circuit, specifically including: controlling the input voltage of the first DC-DC conversion circuit to perform the local IV curve scan to obtain a first maximum input power of the first DC-DC conversion circuit; during the IV curve scan of the first DC-DC conversion circuit, adjusting the input power of the second DC-DC conversion circuit to ensure that the sum of the input power of the first DC-DC conversion circuit and the input power of the second DC-DC conversion circuit is consistent with that before the local IV curve scan; and so on and so forth to obtain a second maximum input power of the second DC-DC conversion circuit; and obtaining the sum of the maximum input powers of all DC-DC conversion circuits based on the maximum input power of each DC-DC conversion circuit, specifically including: obtaining the sum of the maximum input powers of all DC-DC conversion circuits based on the first maximum input power and the second maximum input power.

[0024] In one possible implementation, controlling the input voltage change of the first DC-DC conversion circuit to perform a local IV curve scan specifically includes: controlling the input voltage of the first DC-DC conversion circuit to gradually decrease to perform the local IV curve scan, and recording the scan voltage and scan current of the first DC-DC conversion circuit during the IV curve scan, until the input power of the first DC-DC conversion circuit decreases and the scan voltage is less than the voltage before the local IV curve scan, and then stopping the scan.

[0025] In one possible implementation, controlling the input voltage change of the first DC-DC conversion circuit to perform a local IV curve scan specifically includes: controlling the input voltage of the first DC-DC conversion circuit to gradually decrease to perform the local IV curve scan, and recording the scan voltage and scan current of the first DC-DC conversion circuit during the IV curve scan, until the input power of the first DC-DC conversion circuit is equal to the input power before the local IV curve scan and the scan voltage is less than the voltage before the local IV curve scan, and then stopping the scan.

[0026] In one possible implementation, controlling the input voltage of the first DC-DC conversion circuit to gradually decrease to perform a local IV curve scan specifically includes: controlling the input voltage of the first DC-DC conversion circuit to gradually decrease from a first voltage to perform a local IV curve scan, where the first voltage is the input voltage of the first DC-DC conversion circuit corresponding to a maximum input power of the second DC-DC conversion circuit when the total input power of the multiple DC-DC conversion circuits is consistent with that before the local IV curve scan.

[0027] In one possible implementation, the multiple DC-DC conversion circuits include a total of N circuits, and the N DC-DC conversion circuits are divided into at least two groups: a first group includes K circuits and a second group includes NK circuits; K is an integer greater than or equal to 2; a current and voltage IV curve scan is performed on each DC-DC conversion circuit; during the IV curve scan, a total input power of the multiple DC-DC conversion circuits is controlled to be consistent with that before the local IV curve scan, so as to obtain a maximum input power of each DC-DC conversion circuit. Specifically, the method includes: performing a local IV curve scan on each of the K DC-DC conversion circuits in the first group; during the local IV curve scan, controlling the total input power of the N DC-DC conversion circuits to be consistent with that before the local IV curve scan, and obtaining the maximum input power of each DC-DC conversion circuit in the K circuits; and so on, to obtain the maximum input power of each DC-DC conversion circuit in the NK circuits.

[0028] In one possible implementation, local IV curve scanning is performed on each of the K DC-DC conversion circuits in the first group, specifically including: gradually decreasing the input voltage of each of the K DC-DC conversion circuits to perform local IV curve scanning, and recording the scan voltage and scan current of each of the K DC-DC conversion circuits until the input power of each of the K DC-DC conversion circuits decreases and the scan voltage is less than the voltage before the local IV curve scan, and then stopping the scanning; or gradually decreasing the input voltage of each of the K DC-DC conversion circuits to perform local IV curve scanning, and recording the scan voltage and scan current of each of the K DC-DC conversion circuits until the input power of each of the K DC-DC conversion circuits is equal to the input power before the local IV curve scan and the scan voltage is less than the voltage before the local IV curve scan, and then stopping the scanning.

[0029] In one possible implementation, controlling the input voltage of each DC-DC conversion circuit in the K paths to gradually decrease to perform a local IV curve scan specifically includes: controlling the input voltage of each DC-DC conversion circuit in the K paths to gradually decrease starting from a second voltage to perform an IV curve scan; the second voltage is the input voltage of each DC-DC conversion circuit in the K paths corresponding to the maximum input power of the NK paths DC-DC conversion circuits when the total input power of the multiple DC-DC conversion circuits is consistent with that before the local IV curve scan.

[0030] In one possible implementation, N DC-DC converter circuits are divided into m groups, and local IV curve scanning is performed group by group. Specifically, each group includes Kj DC-DC converter circuits, and the Kj DC-DC converter circuits simultaneously perform local IV curve scanning, where j = 1, 2, ..., m. A controller is configured to perform local IV curve scanning on each of the m groups of DC-DC converter circuits. During the local IV curve scanning process, the total input power of the m groups of DC-DC converter circuits is controlled to remain constant, and the maximum input power of the Kj DC-DC converter circuits in the jth group is obtained. The sum of the maximum input powers of the N DC-DC converter circuits is then calculated based on the maximum input power of each DC-DC converter circuit. Specifically, the m groups are scanned group by group. The Kj circuits in the same group can be scanned simultaneously, but each Kj circuit also scans its own local IV curve to obtain its corresponding maximum input power. This is then used to obtain the sum of the maximum input powers of the group. Finally, after the scanning of the m groups is completed, the sum of the maximum input powers of the m groups is obtained.

[0031] It can be seen from the above technical solutions that the embodiments of the present application have the following advantages:

[0032] To obtain the total maximum input power, the embodiments of the present application require the maximum input power of each inverter. A photovoltaic power station may include multiple inverters, and the maximum input power of the photovoltaic power station is the sum of the maximum input powers of all inverters. Similarly, for a single inverter, the maximum input power of the inverter is the sum of the input powers of all DC-DC converter circuits. The technical solution provided by this embodiment is that the controller obtains the maximum input power of each DC-DC converter circuit separately, and then adds the maximum input powers of all DC-DC converter circuits to obtain the maximum input power of the inverter. To ensure that the inverter does not operate in a power-limited state when obtaining the maximum input power, the controller controls the total input power of the inverter to remain unchanged during the local IV curve scan. For example, when the input power of a DC-DC converter circuit undergoing a local IV curve scan changes, the input power of the DC-DC converter circuits not undergoing the local IV curve scan is controlled to follow suit, so that the sum of the input powers of all DC-DC converter circuits remains unchanged. The IV curve scan performed to obtain the maximum input power when the photovoltaic system is operating in a power-limited state is a local scan, not a global scan. This is different from the traditional IV curve scan, which scans from the open-circuit voltage to the short-circuit voltage of the photovoltaic string, that is, from the maximum voltage to the minimum voltage. In contrast, in the embodiments of the present application, only a local IV curve scan is performed to improve scanning efficiency. As long as the maximum power point is covered during the scan, the maximum input power of the photovoltaic power station operating in the power-limited state can be obtained through the local IV curve scan, facilitating subsequent power scheduling and control. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of a photovoltaic system provided in an embodiment of the present application;

[0034] Figure 2 A schematic diagram of an IV curve provided in an embodiment of the present application;

[0035] Figure 3 A schematic diagram of another photovoltaic system provided in an embodiment of the present application;

[0036] Figure 4A A schematic diagram of a local IV curve scan provided in an embodiment of the present application;

[0037] Figure 4B for Figure 4A The corresponding PV curve of the DC-DC converter circuit without local IV curve scanning;

[0038] Figure 4C A schematic diagram of another local IV curve scan provided in an embodiment of the present application;

[0039] Figure 5A schematic diagram of another photovoltaic system provided in an embodiment of the present application;

[0040] Figure 6 A schematic diagram of another photovoltaic system provided in an embodiment of the present application;

[0041] Figure 7 A schematic diagram of a household photovoltaic system provided in an embodiment of the present application;

[0042] Figure 8 A flowchart of a method for determining maximum input power provided in an embodiment of the present application;

[0043] Figure 9 A flowchart of another method for determining maximum input power provided in an embodiment of the present application;

[0044] Figure 10 A flowchart of another method for determining maximum input power provided in an embodiment of the present application. DETAILED DESCRIPTION

[0045] The terms "first," "second," and so forth in the following description are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified with "first," "second," and so forth may explicitly or implicitly include one or more of such features. Throughout the description of this application, unless otherwise specified, "plurality" means two or more.

[0046] In addition, in this application, directional terms such as "upper" and "lower" may be defined including but not limited to the orientation relative to the schematic placement of the components in the drawings. It should be understood that these directional terms may be relative concepts. They are used for relative descriptions and clarifications, and they may change accordingly according to changes in the orientation of the components in the drawings.

[0047] In this application, unless otherwise specified or limited, the term "connection" should be understood broadly. For example, "connection" can mean fixed connection, detachable connection, or integration; it can mean direct connection or indirect connection through an intermediate medium. In addition, the term "coupling" can refer to the method of electrical connection for signal transmission. "Coupling" can mean direct electrical connection or indirect electrical connection through an intermediate medium.

[0048] System Example

[0049] In order to enable those skilled in the art to better understand the technical solutions provided by the embodiments of the present application, the photovoltaic system provided by the embodiments of the present application is introduced below.

[0050] The embodiments of the present application do not specifically limit the specific architecture of the photovoltaic system. As long as there are multiple parallel direct current-direct current (DC-DC) conversion circuits in the photovoltaic system, the input end of the DC-DC conversion circuit is connected to the corresponding photovoltaic string. The technical solutions provided by the embodiments of the present application are applicable to large-scale photovoltaic power station application scenarios, small and medium-sized distributed power station application scenarios, and household photovoltaic power generation systems. The technical solutions provided by the embodiments of the present application can be applied to string inverters as well as centralized inverters.

[0051] The following first introduces the technical solution provided in the embodiment of the present application as an example of applying it to a photovoltaic system corresponding to a string inverter.

[0052] See also Figure 1 , which is a schematic diagram of a photovoltaic system provided in an embodiment of the present application.

[0053] The photovoltaic system provided in this embodiment includes: a photovoltaic array 100 , a string inverter 200 , and further includes a transformer 300 .

[0054] String inverter 200 differs from centralized inverters in that it comprises two stages: a DC-DC converter circuit in the first stage and a DC-AC converter circuit 200c in the second stage. The first stage DC-DC converter circuit may include multiple DC-DC converter circuits, with the outputs of these multiple DC-DC converter circuits connected in parallel to the input of DC-AC converter circuit 200c. For ease of description and understanding, the following uses two DC-DC converter circuits as an example.

[0055] like Figure 1 As shown, the input end of the first DC-DC conversion circuit 200a is connected to the corresponding photovoltaic string 100a and photovoltaic string 100b, and the photovoltaic string 100a and photovoltaic string 100b can be connected in parallel to the input end of the first DC-DC conversion circuit 200a. Figure 1 In the description, two photovoltaic strings are used as an example. The input end of the first DC-DC conversion circuit 200a can be connected to more photovoltaic strings. The input end of the second DC-DC conversion circuit 200b is also connected to the corresponding two photovoltaic strings.

[0056] The output of the first DC-DC converter circuit 200a and the output of the second DC-DC converter circuit 200b are connected in parallel to the input of the DC-AC converter circuit 200c. It should be understood that the input of the DC-AC converter circuit 200c can also be connected to more DC-DC converter circuits.

[0057] During actual operation of a photovoltaic system, the PV strings are not operating at their maximum power point (MPP), meaning they are not outputting maximum power. Instead, they are operating in a power-limited state in response to controller commands. Therefore, without scanning the PV string's current-voltage IV curve, the maximum output power of the PV string and, consequently, the maximum input power of the string inverter cannot be determined. However, PV power plants need to predict the maximum input power of the string inverter to facilitate subsequent power scheduling.

[0058] IV curve scanning means that the output voltage of the photovoltaic string is scanned from the open circuit voltage to the short circuit voltage to obtain the curve relationship between the output current and output voltage of the photovoltaic string, such as Figure 2 The figure shows a schematic diagram of an IV curve.

[0059] from Figure 2 It can be seen that the horizontal axis corresponds to the output voltage of the photovoltaic string, and the vertical axis corresponds to the output current of the photovoltaic string.

[0060] The relationship between the output voltage and output current of a photovoltaic string is: when the output voltage increases, the output current gradually decreases.

[0061] To obtain the total maximum input power, the embodiments of the present application require the maximum input power of each inverter. A photovoltaic power station may include multiple inverters, and the maximum input power of the photovoltaic power station is the sum of the maximum input powers of all inverters. Similarly, for a single inverter, the maximum input power of that inverter is the sum of the input powers of all DC-DC converter circuits. The following describes a method for obtaining the maximum input power of a single inverter, with reference to the accompanying figures. The technical solution provided by this embodiment is that the controller obtains the maximum input power of each DC-DC converter circuit separately, then sums the maximum input powers of all DC-DC converter circuits to obtain the maximum input power of the inverter. To ensure that the inverter does not operate in a power-limited state when obtaining the maximum input power, the controller controls the total input power of the inverter to remain constant during the local IV curve scan. For example, when the input power of a DC-DC converter circuit undergoing a local IV curve scan changes, the input power of the DC-DC converter circuits not undergoing the local IV curve scan is controlled to follow suit, so that the sum of the input powers of all DC-DC converter circuits remains constant. It should be noted that the IV curve scan performed in this embodiment to obtain the maximum input power when the photovoltaic system is operating in a power-limited state is a local scan, not a global scan. This is different from the traditional IV curve scan, which scans from the open-circuit voltage to the short-circuit voltage of the photovoltaic string, that is, from the maximum voltage to the minimum voltage. In contrast, in this embodiment, to improve scanning efficiency, only a local IV curve scan is performed, as long as the maximum power point is covered during the scanning process.

[0062] See also Figure 3 , which is a schematic diagram of another photovoltaic system provided in an embodiment of the present application.

[0063] The photovoltaic system provided in the embodiment of the present application includes: a controller 400, a DC-AC conversion circuit 200c, multiple DC-DC conversion circuits, and multiple photovoltaic strings; the input end of each DC-DC conversion circuit is connected to the corresponding photovoltaic string; the output ends of the multiple DC-DC conversion circuits are connected in parallel to the input end of the DC-AC conversion circuit;

[0064] The controller 400 is configured to perform a local current-voltage IV curve scan on each DC-DC converter circuit. During the local IV curve scan, the controller controls the total input power of the multiple DC-DC converter circuits to be consistent with that before the local IV curve scan, obtains the maximum input power of each DC-DC converter circuit, and obtains the sum of the maximum input powers of all DC-DC converter circuits based on the maximum input power of each DC-DC converter circuit. The scan voltage of the local IV curve scan is less than the open-circuit voltage.

[0065] The output end of the string inverter 200 may be connected to a transformer 300 .

[0066] It should be noted that when performing a local IV curve scan, the total input power of the multiple parallel DC-DC conversion circuits should remain unchanged as much as possible, that is, the power limit requirements of the photovoltaic system should be met. Controlling the total input power of the multiple DC-DC conversion circuits to be consistent with that before the local IV curve scan means that the total power is within a preset range. As long as the total input power fluctuates within the preset range, it is considered that the total input power remains consistent.

[0067] In the embodiments of the present application, to improve the efficiency of IV curve scanning and quickly obtain the maximum input power of the inverter, the controller 400 can perform a partial IV curve scan on each DC-DC converter circuit, rather than performing a full IV curve scan on each DC-DC converter circuit. Specifically, the scan does not need to be performed from the open-circuit voltage to the short-circuit voltage; the scan only needs to cover the maximum power point. Generally, the scan voltage range for a partial IV curve scan is smaller than the scan voltage for a conventional full IV curve scan, that is, the scan voltage range for a partial IV curve scan is smaller than the open-circuit voltage and larger than the short-circuit voltage.

[0068] Figure 3 and Figure 1 The difference is that the controller 400 is added, and the rest of the connection relationship is the same as Figure 1 Continuing with the example of the input end of the first DC-DC conversion circuit 200a being connected to two photovoltaic strings, namely photovoltaic string 100a and photovoltaic string 100b, similarly, the input end of the second DC-DC conversion circuit 200b being connected to two photovoltaic strings.

[0069] See also Figure 4A , this figure is a schematic diagram of the principle of local IV curve scanning provided in an embodiment of the present application.

[0070] Figure 4A What is shown is the power-voltage curve of the photovoltaic string, that is, the PV curve diagram, the horizontal axis is the output voltage of the photovoltaic string, and the vertical axis is the output power of the photovoltaic string.

[0071] from Figure 4A It can be seen that the output power first increases with the increase of the output voltage, reaches the maximum power point C, and then gradually decreases with the increase of the output voltage.

[0072] Generally, in order to make the working state more stable, during actual power-limited operation, the steady-state working point is located to the right of the maximum power point, such as point B.

[0073] When the controller 400 performs a local IV curve scan on the DC-DC conversion circuit, for example, scanning from the current working steady-state point C to the left, that is, controlling the input voltage of the DC-DC conversion circuit to decrease, and at the same time forcing the input power to increase, in order to obtain the power at the maximum power point, it is necessary to cross the maximum power point and continue to scan to the left. For example, when scanning to point A, the input power is obtained by the scanning voltage and scanning current of the scanned sampling point. It is found that during the scanning from point B to point C, the power of point B is the largest, and during the scanning from point A to point B, the power of point B is also the largest, then point B is the maximum power point.

[0074] It should be understood that after a DC-DC conversion circuit completes a partial IV curve scan, it will continue to operate at point C before the IV curve scan.

[0075] from Figure 4A It can be seen that when obtaining the maximum input power of a DC-DC converter circuit, only a partial IV curve scan is required, as long as the scanned portion covers the maximum power point.

[0076] For example, taking a two-way DC-DC conversion circuit as an example, Figure 4A The following describes the power variation process of one DC-DC converter circuit while another DC-DC converter circuit is performing a partial IV curve scan.

[0077] See also Figure 4B , the figure is Figure 4A The corresponding PV curve of the DC-DC converter circuit without local IV curve scanning.

[0078] from Figure 4B It can be seen that Figure 4AWhen the input power of one DC-DC converter circuit changes, the input power of the other parallel DC-DC converter circuit changes accordingly, that is, changes between point B and point C, thereby ensuring that the total input power of the two parallel DC-DC converter circuits remains consistent with that before the local IV curve scan.

[0079] It should be understood that if the DC-DC conversion circuit that does not perform local IV curve scanning includes multiple channels, then all of them correspond to Figure 4B The power change process shown will not be described in detail here.

[0080] The following will continue to explain using two DC-DC conversion circuits as an example. Figure 3 , that is, the multi-channel DC-DC conversion circuit at least includes: a first DC-DC conversion circuit 200a and a second DC-DC conversion circuit 200b; the input end of the first DC-DC conversion circuit 200a is connected to the corresponding photovoltaic string; the input end of the second DC-DC conversion circuit 200b is connected to the corresponding photovoltaic string; the output end of the first DC-DC conversion circuit 200a and the output end of the second DC-DC conversion circuit 200b are connected in parallel to the input end of the DC-AC conversion circuit.

[0081] The controller is configured to control the input voltage change of the first DC-DC conversion circuit 200a to perform a local IV curve scan and obtain a first maximum input power of the first DC-DC conversion circuit 200a; during the local IV curve scan of the first DC-DC conversion circuit 200a, adjust the input power of the second DC-DC conversion circuit 200b so that the sum of the input power of the first DC-DC conversion circuit 200a and the input power of the second DC-DC conversion circuit 200b is consistent with that before the local IV curve scan; and so on, after obtaining the maximum input power of the first DC-DC conversion circuit 200a, adjust the input power of the second DC-DC conversion circuit 200b. b performs a local IV curve scan, i.e., controls the input voltage change of the second DC-DC conversion circuit 200b to perform a local IV curve scan, and obtains the maximum input power of the second DC-DC conversion circuit 200b. During the local IV curve scan of the second DC-DC conversion circuit 200b, adjusts the input power of the first DC-DC conversion circuit 200a so that the sum of the input power of the first DC-DC conversion circuit 200a and the input power of the second DC-DC conversion circuit 200b is consistent with that before the local IV curve scan. Finally, the sum of the maximum input powers of all DC-DC conversion circuits is obtained based on the first maximum input power and the second maximum input power.

[0082] The above is only an example of two DC-DC conversion circuits connected in parallel. When N DC-DC conversion circuits are connected in parallel, it is necessary to obtain the maximum input power of the N DC-DC conversion circuits separately in time sharing, and then add the maximum input power of the N DC-DC conversion circuits to obtain the maximum input power of the inverter.

[0083] The following uses two DC-DC conversion circuits as an example to introduce two specific implementation methods for local IV curve scanning.

[0084] The first method: Scan until the input power changes from gradually increasing to gradually decreasing.

[0085] The controller is specifically configured to control the input voltage of the first DC-DC conversion circuit to gradually decrease to perform a local IV curve scan, and record the scan voltage and scan current of the first DC-DC conversion circuit during the local IV curve scan, until the scan is stopped when the input power of the first DC-DC conversion circuit decreases and the scan voltage is less than the voltage before the local IV curve scan.

[0086] from Figure 4A The PV curve shows that before the local IV curve scan, the first DC-DC converter circuit operates at steady-state point C, located to the right of maximum power point B. When the input voltage of the first DC-DC converter circuit is gradually reduced to perform the local IV curve scan, due to the characteristics of the PV curve, as the voltage decreases, the power increases. That is, during the initial local IV curve scan, the power changes from small to large, i.e., gradually increases. After crossing maximum power point B, as the voltage gradually decreases, the power no longer increases, but instead decreases from large to small, i.e., gradually decreases. At this point, the local IV curve scan is considered to have covered the maximum power point, and the scan can be stopped. The controller is specifically configured to obtain a first maximum input power for the first DC-DC converter circuit based on the scan voltage and scan current. Specifically, the controller can obtain the input power based on the product of the scan voltage and scan current at the sampling point during the local IV curve scan. By comparing the input power corresponding to the next sampling point with the input power corresponding to the previous sampling point, the changing trend of the input power can be determined.

[0087] In order to ensure that the first local IV curve scanning method is not affected by power fluctuations, several more sampling points can be collected after the input power changes from large to small, so as to avoid the input power changing from large to small due to power fluctuations without covering the maximum power point.

[0088] The second method: Scan until the input power is equal to the input power before scanning.

[0089] from Figure 4AThe PV curve shows that, except for the maximum power point, each power corresponds to two different voltages: one voltage to the right of the maximum power point, and the other to the left. For example, before the local IV curve scan, the input power of the first DC-DC converter circuit is P1. The local IV curve scan is performed until the input power increases from a low level to a high level, and then decreases from a high level to P1, and then stops.

[0090] The controller is specifically configured to gradually reduce the input voltage of the first DC-DC converter circuit to perform a local IV curve scan, and record the scan voltage and scan current of the first DC-DC converter circuit during the local IV curve scan. The scan is then stopped when the input power of the first DC-DC converter circuit matches the input power before the local IV curve scan and the scan voltage is less than the voltage before the local IV curve scan. Specifically, the power at the steady-state point corresponding to the scan before the scan is obtained, and the input power corresponding to the sampling point is gradually obtained during the scan. The scan is stopped when the input power increases from a small value to a large value, and then increases from a large value to the power before the scan.

[0091] The second local IV curve scanning method can ensure that the maximum input power is obtained more accurately, because by scanning until the power corresponding to the steady-state point is equal, it can be guaranteed that the maximum power point has been crossed.

[0092] Generally, the PV curve has only one maximum power point, such as Figure 4A As shown, the PV curve has only one peak. However, some PV strings may have multiple peaks. The following example uses a PV curve with two peaks as an example.

[0093] See also Figure 4C , which is a schematic diagram of another PV curve provided in an embodiment of the present application.

[0094] For PV curves with multiple peaks, Figure 4C There are two peaks, C1 and C2, where the power corresponding to C2 is greater than that corresponding to C1. E is the operating point when the power is limited.

[0095] If the local IV curve is scanned directly from the current operating point, that is, the current operating voltage, to the left, that is, the output voltage of the PV string is controlled to decrease, the true maximum power point may be missed, that is, the local IV curve scan does not cover the maximum power point. Therefore, in order to avoid the above situation, when scanning the local IV curve, the output voltage of the PV string can be controlled to increase first, and then the output voltage of the PV string can be controlled to decrease.

[0096] The following combination Figure 4C Another scanning method provided in an embodiment of the present application is introduced.

[0097] That is, the voltage starting point for the local IV curve scan described in the above embodiments is not the operating voltage before the scan, but the first voltage. The first voltage is the input voltage of the first DC-DC converter circuit corresponding to the maximum input power of the second DC-DC converter circuit when the total input power of the multiple DC-DC converter circuits is the same as before the local IV curve scan. That is, when performing the local IV curve scan, the controller controls the input voltage of the first DC-DC converter circuit to gradually decrease from the first voltage to perform the local IV curve scan. The operating point before the scan is E. If the scan is performed leftward from E, the maximum power point C2 will be missed. Therefore, the solution provided in the embodiments of the present application is to control the output voltage of the photovoltaic string to increase from the current operating point E until the input power of the other DC-DC converter circuits cannot increase further. In other words, the input power of the other DC-DC converter circuits limits the input voltage of the scanned DC-DC converter circuit from increasing further. This maximum voltage is then used as the starting voltage for the local IV curve scan, and the local IV curve scan is performed from this starting voltage to the left, i.e., gradually decreasing.

[0098] For example, Figure 4C In the example, a local IV curve scan is performed from point B to the left, and the input voltage of the first DC-DC converter circuit is controlled to decrease from the voltage corresponding to point B. At this time, the scan passes through points C2, E, C1, and A.

[0099] In addition, in order to scan more comprehensively, in the case of multiple peaks, in addition to scanning to a power equal to that before scanning, the scanning voltage must also be less than the voltage of the local IV curve before scanning.

[0100] It should be understood that, in order to ensure that the local IV curve scanning process does not affect the limited power output, the controller adjusts the input power of the second DC-DC converter circuit based on the input power of the first DC-DC converter circuit during the local IV curve scanning process of the first converter circuit, so that the sum of the input power of the first DC-DC converter circuit and the input power of the second DC-DC converter circuit is the photovoltaic system's power limit command value. Similarly, during the local IV curve scanning process of the second converter circuit, the controller adjusts the input power of the first DC-DC converter circuit based on the input power of the second DC-DC converter circuit, so that the sum of the input power of the first DC-DC converter circuit and the input power of the second DC-DC converter circuit is the photovoltaic system's power limit command value. Alternatively, the power limit command value may fluctuate within a preset range and be considered consistent. The power limit command value is issued by the photovoltaic power station or the controller of the string inverter. For string inverters, multiple DC-DC converter circuits can correspond to the same controller.

[0101] The above embodiments are described using at least two DC-DC converter circuits as an example, and local IV curve scanning is performed on each DC-DC converter circuit individually, i.e., only one DC-DC converter circuit is scanned simultaneously, and local IV curve scanning is performed one by one. When a photovoltaic system includes too many DC-DC converter circuits, performing local IV curve scanning on each DC-DC converter circuit individually will take too long, affecting efficiency. Therefore, local IV curve scanning can be performed simultaneously on multiple DC-DC converter circuits. However, when performing local IV curve scanning on multiple DC-DC converter circuits simultaneously, each DC-DC converter circuit independently scans its own corresponding IV curve to obtain its corresponding maximum input power.

[0102] Another photovoltaic system provided in an embodiment of the present application can perform local IV curve scanning on the DC-DC conversion circuits in groups, with each group including at least two DC-DC conversion circuits. The embodiment of the present application does not limit the number of DC-DC conversion circuits included in each group, as long as it is greater than or equal to two. Furthermore, the embodiment of the present application does not limit the specific number of groups, and can be allocated according to actual needs. The groups can be evenly distributed or unevenly distributed. It should be understood that in order to keep the total input power consistent with that before the local IV curve scan, the smaller the fluctuation, the better, and the local IV curve scan should be performed in evenly distributed groups as much as possible.

[0103] For example, in one possible implementation, N DC-DC converter circuits are divided into m groups, where m is an integer greater than or equal to 2. Local IV curve scanning is performed on each group. For example, each group includes Kj DC-DC converter circuits, where j = 1, 2, 3, ..., m, and Kj is an integer greater than or equal to 2. The Kj values ​​in each group can be equal or unequal, and this embodiment is not specifically limited thereto. When performing local IV curve scanning on the grouped circuits, the Kj DC-DC converter circuits perform local IV curve scanning simultaneously.

[0104] For example, a photovoltaic system has a multi-channel DC-DC conversion circuit comprising N circuits in total, and the N DC-DC conversion circuits are divided into m groups, each group comprising Kj DC-DC conversion circuits; the Kj of each group may be equal or unequal. When the N circuits are divided into m groups, they may be divided evenly or unevenly. For the sake of convenience, the following takes even division as an example. For example, if 12 circuits are included and divided into 3 groups, each group comprises 4 circuits. For example, if 13 circuits are included and evenly divided, the remainder may be divided into one of the groups, and the circuits may be divided into 3 groups. Then, each of the 2 groups comprises 4 circuits, and the last group may comprise 5 circuits. For example, if 11 circuits are included and evenly divided into 3 groups, then each of the 2 groups comprises 4 circuits, and the last group may comprise 3 circuits. And so on, and they are not listed one by one here. When the division is uneven, it can be divided arbitrarily, and is not specifically limited in the embodiments of the present application.

[0105] The controller is configured to perform local IV curve scanning on m groups of DC-DC conversion circuits one by one. During the local IV curve scanning process, the controller controls the total input power of the m groups of DC-DC conversion circuits to be consistent with that before the local IV curve scanning, obtains the maximum input power of Kj DC-DC conversion circuits in the jth group, and obtains the sum of the maximum input powers of the N DC-DC conversion circuits based on the maximum input power of each DC-DC conversion circuit, where j = 1, 2, ..., m.

[0106] That is, the m groups are scanned one by one, and the IV curves of the Kj paths in the same group can be scanned simultaneously. However, the Kj paths also scan their own local IV curves separately to obtain their corresponding maximum input powers, and then obtain the sum of the maximum input powers in a group. Finally, after the scanning of the m groups is completed, the sum of the maximum input powers of the m groups is obtained.

[0107] For ease of understanding, the following description takes the example of N-channel DC-DC conversion circuits being divided into at least two groups.

[0108] The multi-channel DC-DC conversion circuit includes a total of N channels, and the N-channel DC-DC conversion circuits are divided into at least the following two groups: the first group includes K channels and the second group includes NK channels; K is an integer greater than or equal to 2; the embodiment of the present application does not specifically limit whether K is equal to NK, and they can be equal or unequal.

[0109] like Figure 6 As shown, continuing to take two combiner boxes as an example, a first MPPT combiner box 200A and a second MPPT combiner box 200B, the N-way DC-DC conversion circuits are divided into two groups, corresponding to the two combiner boxes respectively.

[0110] The first MPPT combiner box 200A includes K DC-DC converter circuits, namely, the first DC-DC converter circuit 200m through the Kth DC-DC converter circuit 200n. Similarly, the second MPPT combiner box 200B includes NK DC-DC converter circuits, namely, the K+1th DC-DC converter circuit 200p through the Nth DC-DC converter circuit 200e.

[0111] The controller is configured to perform local IV curve scanning on each of the K DC-DC conversion circuits in the first group. During the local IV curve scanning process, the controller controls the total input power of the N DC-DC conversion circuits to be consistent with that before the local IV curve scanning, thereby obtaining the maximum input power of each DC-DC conversion circuit in the K circuits, and similarly obtaining the maximum input power of each DC-DC conversion circuit in the NK circuits. The controller then obtains the sum of the maximum input powers of the N DC-DC conversion circuits based on the maximum input power of each DC-DC conversion circuit.

[0112] When performing local IV curve scanning on the NK-path DC-DC conversion circuits, the input power of the K-path DC-DC conversion circuit is adjusted so that the total input power of the N-path DC-DC conversion circuits is consistent with that before the local IV curve scanning, and the maximum input power of each DC-DC conversion circuit in the NK paths is obtained respectively.

[0113] It should be noted that when the local IV curves of paths K are scanned simultaneously, paths K can simultaneously reach their maximum power points. Therefore, the maximum input power of each DC-DC converter circuit in paths K can be simultaneously obtained. Similarly, when the local IV curves of paths NK are scanned simultaneously, paths NK can also be controlled to simultaneously reach their maximum power points. In other words, the maximum input power of each DC-DC converter circuit in paths NK can be simultaneously obtained.

[0114] Specifically, when each DC-DC conversion circuit performs a local IV curve scan, it can be similar to the above-mentioned case of performing local IV curve scanning one by one. The first method is to stop the local IV curve scanning when the scanning power changes from large to small; the second method is to stop the local IV curve scanning when the scanning power is equal to the power before the scan.

[0115] The first one:

[0116] The controller is specifically configured to gradually reduce the input voltage of each DC-DC converter circuit in the K paths to perform an IV curve scan, and record the scanned voltage and scanned current of each DC-DC converter circuit in the K paths until the input power of each DC-DC converter circuit in the K paths decreases and the scanned voltage is less than the voltage before the local IV curve scan, at which point the scan is stopped. The controller then obtains the maximum input power of each DC-DC converter circuit in the K paths based on the scanned voltage and scanned current of each DC-DC converter circuit in the K paths.

[0117] The second type:

[0118] The controller is specifically configured to gradually reduce the input voltage of each DC-DC converter circuit in the K paths to perform an IV curve scan, and to record the scanned voltage and scanned current of each DC-DC converter circuit in the K paths until the input power of each DC-DC converter circuit in the K paths equals the input power before the IV curve scan and the scanned voltage is less than the voltage before the local IV curve scan. The controller then stops scanning. The controller obtains the maximum input power of each DC-DC converter circuit in the K paths based on the scanned voltage and scanned current of each DC-DC converter circuit in the K paths.

[0119] The above only describes the conditions for stopping a local IV curve scan. To improve scanning efficiency and ensure coverage of the maximum input power point, the voltage corresponding to the start of the scan can be as large as possible. The following describes a method for determining the scanning voltage corresponding to the scan start point. For example, a controller controls the input voltage of each DC-DC converter circuit in a K-channel to gradually decrease from a second voltage to perform a local IV curve scan; the second voltage is the input voltage of each DC-DC converter circuit in a K-channel that corresponds to the maximum total input power of the NK-channel DC-DC converter circuit when the total input power of the multiple DC-DC converter circuits is consistent with that before the local IV curve scan.

[0120] For ease of understanding, the following description uses a string inverter as an example, where N DC-DC converter circuits are divided into two groups, where M is 2, with the first group consisting of K circuits and the second group consisting of NK circuits. Here, K = NK, but K may not equal NK. The present application embodiments are applicable to both of these situations.

[0121] The N DC-DC conversion circuits included in the string inverter are recorded as the 1st, 2nd, 3rd, ..., Nth DC-DC conversion circuits. The string inverter is in power-limited state, and the total input power is recorded as P lmt .

[0122] Step 1:

[0123] The controller controls the input power of the 1st, 2nd, 3rd, ..., Kth DC-DC conversion circuits to decrease, and at the same time increases the input power of the K+1th, K+2th, ..., Nth DC-DC conversion circuits to control the total input power to be maintained at P lmt , until the input power of the K+1th, K+2th, ..., Nth DC-DC conversion circuit reaches the maximum input power; record the input power of the 1st, 2nd, 3rd, ..., Kth DC-DC conversion circuit as P l , where l = 1, 2, 3, ..., K. Record the input voltage of the 1st, 2nd, 3rd, ..., Kth DC-DC conversion circuit as U l , where l = 1, 2, 3,…, K.

[0124] Step 1 is to obtain the starting scan voltage for the 1-K DC-DC converter circuits during the IV curve scan. This involves gradually decreasing the voltage from the starting scan voltage to perform the IV curve scan. Step 1 is a preliminary step for the IV curve scan. When the input power of the K+1 to N DC-DC converter circuits is at its maximum, this corresponds to the maximum input voltage for the 1-K DC-DC converter circuits. Because the total input power remains constant, when the input power of the K+1 to N DC-DC converter circuits cannot be increased any further, the corresponding input voltage for the 1-K DC-DC converter circuits cannot be increased any further.

[0125] For a string inverter, the controller may be a controller of the string inverter. The DC-DC conversion circuit may be a boost circuit, such as a Boost circuit. Alternatively, the DC-DC conversion circuit may be another type of conversion circuit, such as a Buck circuit or a BuckBoost circuit.

[0126] Step 2:

[0127] The controller controls the 1st, 2nd, 3rd, ..., Kth DC-DC conversion circuits to be in the local IV curve scanning mode, that is, the U obtained from step 1 is l Start to gradually reduce the input voltage of the 1st, 2nd, 3rd, ..., Kth DC-DC conversion circuit, l = 1, 2, 3, ..., K; at the same time, control the input power of the K+1th, K+2th, ..., Nth DC-DC conversion circuit to maintain the total input power at P lmt .

[0128] Step 3:

[0129] Record the curve of the input power versus input voltage of the 1st, 2nd, 3rd, ..., Kth DC-DC conversion circuits, and determine the maximum power point voltage of the 1st, 2nd, 3rd, ..., Kth DC-DC conversion circuits as U mppt_l , the maximum input power is P mppt_l .

[0130] Step 4:

[0131] Repeat the above process for the remaining NK DC-DC converter circuits until the maximum power point voltage U of all DC-DC converter circuits is obtained. mppt_j and the maximum input power P mppt_j , where j = 1, 2, 3,…, K.

[0132] Step 5:

[0133] Calculate the maximum power input of all DC-DC conversion circuits, denoted as P max , which is the estimated maximum input power of the string inverter.

[0134] When the PV system includes a centralized inverter instead of a string inverter, and the input of the centralized inverter is connected to a combiner box, the maximum input power estimated above is the maximum input power of the combiner box.

[0135] Figure 3 The corresponding embodiments are introduced using a string inverter as an example. It should be understood that all technical solutions provided in the embodiments of the present application are not only applicable to photovoltaic systems corresponding to string inverters, but also to photovoltaic systems corresponding to centralized inverters, as long as the photovoltaic system includes a DC-DC conversion circuit with multiple output ends connected in parallel, that is, a DC-DC converter.

[0136] like Figure 3 As shown, when the photovoltaic system includes a string inverter 200 , the DC-AC conversion circuit 200 c , the multiple DC-DC conversion circuits 200 a and 200 b , and the controller 400 may be integrated inside the string inverter 200 . Figure 3 This is for illustrative purposes only. Controller 400 can also be located outside string inverter 200. In other words, string inverter 200 would only include DC-AC converter circuit 200c and multiple DC-DC converter circuits 200a and 200b. Controller 400 controls the input voltage of each DC-DC converter circuit, thereby completing the IV curve scan.

[0137] The technical solutions provided in the above embodiments can also be applied to photovoltaic systems including centralized inverters, see Figure 5 , which is a schematic diagram of another photovoltaic system provided in an embodiment of the present application.

[0138] Generally, the centralized inverter 600 is electrically far away from the photovoltaic strings and therefore cannot directly control the output voltage of the photovoltaic strings. Therefore, a combiner box can be used to control the output voltage of the photovoltaic strings. Alternatively, a photovoltaic optimizer can be directly added between the DC-DC conversion circuit and the photovoltaic strings to control the output voltage of the photovoltaic strings and implement IV curve scanning of the photovoltaic strings. Figure 5 The example of implementing IV curve scanning using a combiner box is used to introduce the method. Each combiner box may include a controller, and the controller of each combiner box may implement changes in the input voltage of the DC-DC converter circuit, thereby completing a local IV curve scan.

[0139] The description herein uses a Maximum Power Point Tracking (MPPT) combiner box as an example. Specifically, multiple MPPT combiner boxes may be included. The output terminals of the multiple combiner boxes may be connected in parallel to the input terminal of the centralized inverter 600. In this embodiment, the description herein uses at least two MPPT combiner boxes as an example, namely, a first MPPT combiner box 200A and a second MPPT combiner box 200B.

[0140] Each MPPT combiner box may include multiple DC-DC conversion circuits. In this embodiment, at least two DC-DC conversion circuits are used as an example. For example, a first MPPT combiner box 200A includes a first DC-DC conversion circuit 200a and a second DC-DC conversion circuit 200b. The input of each DC-DC conversion circuit is connected to a corresponding photovoltaic string. For example, the input of first DC-DC conversion circuit 200a is connected to photovoltaic strings 100a and 100b. The outputs of the multiple DC-DC conversion circuits in each combiner box are connected in parallel. For example, the output of first DC-DC conversion circuit 200a is connected in parallel to the output of second DC-DC conversion circuit 200b.

[0141] Similarly, the second MPPT combiner box 200B includes a third DC-DC converter circuit 200s and a fourth DC-DC converter circuit 200d. The input of each DC-DC converter circuit is connected to a corresponding photovoltaic string. For example, the input of the third DC-DC converter circuit 200s is connected to photovoltaic strings 100c and 100d. The outputs of the multiple DC-DC converter circuits in each combiner box are connected in parallel. For example, the output of the third DC-DC converter circuit 200s is connected in parallel to the output of the fourth DC-DC converter circuit 200d.

[0142] The centralized inverter 600 includes a DC-AC conversion circuit 400a. The output end of the centralized inverter 600 can be connected to the transformer 300, and the output end of the transformer 300 can be connected to the AC power grid.

[0143] The first controller of the first MPPT combiner box 200A obtains the first maximum input power of the first MPPT combiner box 200A, and the second controller of the second MPPT combiner box 200B obtains the second maximum input power of the second MPPT combiner box 200B. The first controller sends the first maximum input power to the host computer, and the second controller sends the second maximum input power to the host computer. The host computer obtains the total maximum input power of the photovoltaic system based on the first maximum input power and the second maximum input power.

[0144] The embodiments of this application do not limit the number of AC phases supported by the photovoltaic system. For example, it can support three-phase AC or single-phase AC. For example, for a household photovoltaic system, the household photovoltaic system supports single-phase AC power, which can directly supply household electrical appliances such as refrigerators, air conditioners, and washing machines.

[0145] See also Figure 7 , which is a schematic diagram of a household photovoltaic system provided in an embodiment of the present application.

[0146] Generally, a home photovoltaic system may use a string inverter 500 , which outputs single-phase alternating current. In contrast, a three-phase inverter outputs three-phase alternating current.

[0147] The input of the string inverter 500 in a home photovoltaic system is connected to the photovoltaic string 100a via a DC switch S1, and to the photovoltaic string 100b via a DC switch S2. The string inverter 500 may include a DC-DC conversion circuit and a DC-AC conversion circuit. The output of the string inverter 500 is connected to the single-phase AC input via an AC switch KM. In the event of a fault or during startup or shutdown, the AC switch KM can be controlled to open and close.

[0148] The photovoltaic system provided in the embodiment of the present application can obtain the maximum input power of the system when the photovoltaic system is operating at a power limit, which is convenient for subsequent control and power scheduling. Since the solution provided in the embodiment of the present application performs a local IV curve scan, the scanning speed can be increased and the maximum input power can be obtained as quickly as possible. In addition, the technical solution provided in the embodiment of the present application is to perform an IV curve scan on each DC-DC conversion circuit in the photovoltaic system. Therefore, the power estimation deviation caused by shading or failure of individual photovoltaic strings can be avoided. The technical solution provided in the embodiment of the present application can more accurately obtain the maximum input power of the system.

[0149] Method Example

[0150] Based on the photovoltaic system provided in the above embodiment, the embodiment of the present application further provides a method for determining the maximum input power, which is described in detail below with reference to the accompanying drawings.

[0151] See also Figure 8 , which is a flow chart of a method for determining the maximum input power of a photovoltaic system provided in an embodiment of the present application.

[0152] The method for determining the maximum input power of a photovoltaic system provided in an embodiment of the present application is applied to the photovoltaic system described in the above embodiment, wherein the photovoltaic system includes: a direct current (DC)-alternating current (DC)-AC conversion circuit, multiple direct current (DC)-DC conversion circuits, and multiple photovoltaic strings; the input end of each DC-DC conversion circuit is connected to a corresponding photovoltaic string; the output ends of the multiple DC-DC conversion circuits are connected in parallel to the input end of the DC-AC conversion circuit;

[0153] The method includes:

[0154] S701: Perform a local current and voltage IV curve scan on each DC-DC conversion circuit respectively; during the local IV curve scan, control the total input power of the multiple DC-DC conversion circuits to be consistent with that before the local IV curve scan, and obtain the maximum input power of each DC-DC conversion circuit.

[0155] Since the photovoltaic system operates in a power-limited state, each DC-DC converter circuit does not operate at its maximum power point. To obtain the maximum input power of the system, it is necessary to obtain the maximum input power of each DC-DC converter circuit and then add the maximum input power of each DC-DC converter circuit to obtain the total maximum input power.

[0156] In order to improve the scanning efficiency and obtain the total maximum input power as quickly as possible, a local IV curve scan is performed on each DC-DC conversion circuit. The scanning voltage of the local IV curve scan is less than the open circuit voltage, and the scanning voltage of the local IV curve scan is also greater than the short circuit voltage.

[0157] S702: Obtain the sum of the maximum input powers of all DC-DC conversion circuits according to the maximum input power of each DC-DC conversion circuit.

[0158] When scanning the local IV curve, in order to ensure that the system operates in a power-limited state, the total input power needs to remain consistent with that before the scan.

[0159] In specific implementation, the local IV curve scanning can be performed one by one by one DC-DC conversion circuit in a time-sharing manner, or the local IV curve scanning can be performed simultaneously by several DC-DC conversion circuits.

[0160] The maximum input power determination method provided in the embodiment of the present application can obtain the maximum input power when the photovoltaic system is operating in a power-limited state. When power loss is ignored, the input power of all DC-DC conversion circuits is the maximum input power of the entire photovoltaic system. Since the photovoltaic system is operating in a power-limited state, each photovoltaic string does not output its maximum power. Therefore, it is necessary to perform a local IV curve scan separately to obtain the power corresponding to the maximum power point. In order not to affect the normal power-limited state, the total input power of all DC-DC conversion circuits is maintained unchanged. When controlling some DC-DC conversion circuits to perform local IV curve scanning, the input power of the remaining DC-DC conversion circuits that are not subjected to local IV curve scanning is also controlled to change accordingly. By analogy, the maximum input power of all DC-DC conversion circuits is obtained, and the sum of the maximum input power of all DC-DC conversion circuits is the predicted maximum input power of the photovoltaic system, which is convenient for subsequent control of the photovoltaic power station and the overall scheduling of the power station power.

[0161] The following is an example of how to perform local IV curve scanning on a DC-DC converter circuit in a time-sharing manner. For ease of description, the process of obtaining maximum input power is described using a two-way DC-DC converter circuit as an example. A multi-way DC-DC converter circuit includes at least: a first DC-DC converter circuit and a second DC-DC converter circuit;

[0162] See also Figure 9 , this figure is a flowchart of another method for determining maximum input power provided in an embodiment of the present application.

[0163] Performing a local IV curve scan on each DC-DC conversion circuit; during the local IV curve scan, controlling the total input power of the multiple DC-DC conversion circuits to remain unchanged, and obtaining the maximum input power of each DC-DC conversion circuit, specifically including:

[0164] S801: Controlling the input voltage change of the first DC-DC conversion circuit to perform a local IV curve scan to obtain a first maximum input power of the first DC-DC conversion circuit; while the first DC-DC conversion circuit is performing the local IV curve scan, adjusting the input power of the second DC-DC conversion circuit so that the sum of the input power of the first DC-DC conversion circuit and the input power of the second DC-DC conversion circuit is consistent with that before the local IV curve scan.

[0165] S802: Similarly, a second maximum input power of the second DC-DC converter circuit is obtained. Similarly, when the second DC-DC converter circuit performs a partial IV curve scan, the input power of the first DC-DC converter circuit needs to be adjusted so that the total input power is consistent with that before the partial IV curve scan.

[0166] The sum of the maximum input powers of all DC-DC conversion circuits is obtained according to the maximum input power of each DC-DC conversion circuit, specifically including:

[0167] S803: Obtain the sum of the maximum input powers of all DC-DC conversion circuits according to the first maximum input power and the second maximum input power.

[0168] The specific local IV curve scanning process is introduced below.

[0169] The first method is to control the input voltage change of the first DC-DC converter circuit to perform a local IV curve scan, specifically including:

[0170] The input voltage of the first DC-DC conversion circuit is controlled to gradually decrease to perform an IV curve scan, and the scan voltage and scan current of the first DC-DC conversion circuit are recorded during the IV curve scan. The scan is stopped when the input power of the first DC-DC conversion circuit decreases and the scan voltage is less than the voltage before the local IV curve scan.

[0171] The second method is to control the input voltage change of the first DC-DC converter circuit to perform a local IV curve scan, specifically including:

[0172] The input voltage of the first DC-DC conversion circuit is controlled to gradually decrease to perform an IV curve scan, and the scan voltage and scan current of the first DC-DC conversion circuit are recorded during the IV curve scan. The scan is stopped when the input power of the first DC-DC conversion circuit is equal to the input power before the IV curve scan and the scan voltage is less than the voltage before the local IV curve scan.

[0173] Controlling the input voltage of the first DC-DC conversion circuit to gradually decrease and perform IV curve scanning, specifically including:

[0174] The input voltage of the first DC-DC conversion circuit is controlled to gradually decrease from a first voltage to perform an IV curve scan, where the first voltage is the input voltage of the first DC-DC conversion circuit corresponding to the maximum input power of the second DC-DC conversion circuit when the total input power of the multiple DC-DC conversion circuits remains unchanged.

[0175] The multi-channel DC-DC conversion circuit includes N channels in total, and the N channels of DC-DC conversion circuit include M groups, where M is an integer greater than or equal to 2; each group includes K channels of DC-DC conversion circuits; and K is an integer greater than or equal to 1;

[0176] Performing a current and voltage IV curve scan on each DC-DC converter circuit separately; during the IV curve scan, controlling the total input power of the multiple DC-DC converter circuits to remain unchanged, and obtaining the maximum input power of each DC-DC converter circuit, specifically including:

[0177] IV curve scanning is performed on each of the K DC-DC conversion circuits in the first group. During the IV curve scanning process, the total input power of the M groups of DC-DC conversion circuits is controlled to remain unchanged, and the maximum input power of each DC-DC conversion circuit in the K paths is obtained.

[0178] For the convenience of description, the following is an example of dividing the system into at least two groups to perform local IV curve scanning.

[0179] The multi-channel DC-DC conversion circuit includes N channels in total, and the N channels are divided into at least two groups: a first group includes K channels and a second group includes NK channels; K is an integer greater than or equal to 2;

[0180] See also Figure 10 , which is a flow chart of another method for determining maximum input power provided in an embodiment of the present application.

[0181] Perform current and voltage IV curve scanning on each DC-DC conversion circuit separately; during the IV curve scanning process, control the total input power of the multiple DC-DC conversion circuits to be consistent with that before the local IV curve scanning, and obtain the maximum input power of each DC-DC conversion circuit, specifically including S901 and S902.

[0182] S901: Performing a local IV curve scan on each of the K DC-DC converter circuits in the first group. During the local IV curve scan, controlling the total input power of the N DC-DC converter circuits to be consistent with that before the local IV curve scan, and obtaining the maximum input power of each of the K DC-DC converter circuits.

[0183] S902: Similarly, the maximum input power of each DC-DC conversion circuit in the NK circuits of the second group is obtained.

[0184] S903: Obtain the maximum input power of the photovoltaic system according to the maximum input power of the DC-DC conversion circuit in the K path and the maximum input power of each DC-DC conversion circuit in the NK paths.

[0185] Perform local IV curve scanning on the first group of K DC-DC converter circuits, specifically including:

[0186] Controlling the input voltage of each DC-DC conversion circuit in the K circuits to gradually decrease to perform a local IV curve scan, and recording the scan voltage and scan current of each DC-DC conversion circuit in the K circuits until the input power of each DC-DC conversion circuit in the K circuits decreases and the scan voltage is less than the voltage before the local IV curve scan, then stopping the scan;

[0187] or,

[0188] The input voltage of each DC-DC conversion circuit in the K circuit is controlled to gradually decrease to perform a local IV curve scan, and the scan voltage and scan current of each DC-DC conversion circuit in the K circuit are recorded until the input power of each DC-DC conversion circuit in the K circuit is equal to the input power before the local IV curve scan and the scan voltage is less than the voltage before the local IV curve scan, then the scan is stopped.

[0189] The input voltage of each DC-DC conversion circuit in the K circuit is controlled to gradually decrease to perform a local IV curve scan, specifically including:

[0190] The input voltage of each DC-DC conversion circuit in the K paths is controlled to gradually decrease from the second voltage to perform an IV curve scan; the second voltage is the input voltage of each DC-DC conversion circuit in the K paths corresponding to the maximum input power of the NK paths DC-DC conversion circuit when the total input power of the multiple DC-DC conversion circuits is consistent with that before the local IV curve scan.

[0191] The maximum input power determination method provided in the embodiment of the present application can obtain the maximum input power of the system when the photovoltaic system is operating at a power limit, which is convenient for subsequent control and power scheduling. Since the solution provided in the embodiment of the present application performs a local IV curve scan, the scanning speed can be increased and the maximum input power can be obtained as quickly as possible. In addition, the technical solution provided in the embodiment of the present application is to perform an IV curve scan on each DC-DC conversion circuit in the photovoltaic system. Therefore, the power estimation deviation caused by shading or failure of individual photovoltaic strings can be avoided. The technical solution provided in the embodiment of the present application can more accurately obtain the maximum input power of the system.

[0192] It should be understood that in this application, "at least one (item)" means one or more, and "plurality" means two or more. "And / or" is used to describe the association relationship of associated objects, indicating that three relationships may exist. For example, "A and / or B" can mean: only A exists, only B exists, and A and B exist at the same time, where A and B can be singular or plural. The character " / " generally indicates that the previous and next associated objects are in an "or" relationship. "At least one of the following items" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, at least one of a, b or c can mean: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, c can be single or multiple.

[0193] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A photovoltaic system, characterized in that: include: Controller, DC-AC conversion circuit and multi-channel DC-DC conversion circuit; The input end of each DC-DC conversion circuit is used to connect to the corresponding photovoltaic string; the output ends of the multiple DC-DC conversion circuits are connected in parallel to the input end of the DC-AC conversion circuit; The controller is configured to perform a local current-voltage IV curve scan on each of the DC-DC conversion circuits, and during the local current-voltage IV curve scan, control the total input power of the multiple DC-DC conversion circuits to be consistent with that before the local current-voltage IV curve scan, obtain the maximum input power of each of the DC-DC conversion circuits, and obtain the sum of the maximum input powers of all the DC-DC conversion circuits based on the maximum input power of each of the DC-DC conversion circuits; The scanning voltage of the local current-voltage IV curve scanning is less than the open circuit voltage; The multi-channel DC-DC conversion circuit includes at least: a first channel DC-DC conversion circuit and a second channel DC-DC conversion circuit; The controller is specifically configured to control the input voltage of the first DC-DC conversion circuit to gradually decrease from a first voltage to perform the local IV curve scan, where the first voltage is the input voltage of the first DC-DC conversion circuit corresponding to when the input power of the second DC-DC conversion circuit is maximum.

2. The system according to claim 1, wherein: The input end of the first DC-DC conversion circuit is connected to the corresponding photovoltaic string; the input end of the second DC-DC conversion circuit is connected to the corresponding photovoltaic string; the output end of the first DC-DC conversion circuit and the output end of the second DC-DC conversion circuit are connected in parallel to the input end of the DC-AC conversion circuit; The controller is configured to control the input voltage change of the first DC-DC conversion circuit to perform the local IV curve scan and obtain a first maximum input power of the first DC-DC conversion circuit; during the local IV curve scan of the first DC-DC conversion circuit, adjust the input power of the second DC-DC conversion circuit so that the sum of the input power of the first DC-DC conversion circuit and the input power of the second DC-DC conversion circuit is consistent with that before the local IV curve scan; and so on to obtain a second maximum input power of the second DC-DC conversion circuit; and obtain the sum of the maximum input powers of all DC-DC conversion circuits based on the first maximum input power and the second maximum input power.

3. The system according to claim 2, characterized in that The controller is specifically configured to control the input voltage of the first DC-DC conversion circuit to gradually decrease to perform the local IV curve scanning, and record the scanning voltage and scanning current of the first DC-DC conversion circuit during the local IV curve scanning process, until the scanning is stopped when the input power of the first DC-DC conversion circuit decreases and the scanning voltage is less than the voltage before the local IV curve scanning.

4. The system according to claim 2, wherein: The controller is specifically configured to control the input voltage of the first DC-DC conversion circuit to gradually decrease to perform the local IV curve scanning, and record the scanning voltage and scanning current of the first DC-DC conversion circuit during the local IV curve scanning process until the input power of the first DC-DC conversion circuit is equal to the input power before the local IV curve scanning and the scanning voltage is less than the voltage before the local IV curve scanning, and then stop scanning.

5. The system according to claim 3, wherein: The controller is specifically configured to obtain a first maximum input power of the first DC-DC conversion circuit according to the scanning voltage and the scanning current.

6. The system according to claim 4, characterized in that The controller is specifically configured to obtain a first maximum input power of the first DC-DC conversion circuit according to the scanning voltage and the scanning current.

7. The system according to any one of claims 1 to 6, characterized in that The controller is specifically configured to adjust the input power of the second DC-DC conversion circuit according to the input power of the first DC-DC conversion circuit during the IV curve scanning process, so that the sum of the input power of the first DC-DC conversion circuit and the input power of the second DC-DC conversion circuit is equal to the power limit command value of the photovoltaic system.

8. The system according to claim 1, wherein: The multi-channel DC-DC conversion circuit comprises N channels in total, and the N channels of the DC-DC conversion circuit are divided into at least two groups: a first group comprises K channels and a second group comprises NK channels; K is an integer greater than or equal to 2; The controller is configured to perform the local IV curve scan on each of the K DC-DC conversion circuits of the first group. During the local IV curve scan, the controller controls the total input power of the N DC-DC conversion circuits to be consistent with that before the local IV curve scan, obtains the maximum input power of each of the K DC-DC conversion circuits, and similarly obtains the maximum input power of each of the NK DC-DC conversion circuits. The sum of the maximum input powers of the N DC-DC conversion circuits is obtained based on the maximum input power of each DC-DC conversion circuit.

9. The system according to claim 8, characterized in that The controller is specifically configured to control the input voltage of each of the K DC-DC conversion circuits to gradually decrease to perform the local IV curve scan, and record the scan voltage and scan current of each of the K DC-DC conversion circuits until the input power of each of the K DC-DC conversion circuits decreases and the scan voltage is less than the voltage before the local IV curve scan, and then stop scanning.

10. The system according to claim 8, wherein: The controller is specifically configured to control the input voltage of each DC-DC conversion circuit in the K paths to gradually decrease to perform the local IV curve scan, and record the scan voltage and scan current of each DC-DC conversion circuit in the K paths until the input power of each DC-DC conversion circuit in the K paths is equal to the input power before the local IV curve scan and the scan voltage is less than the voltage before the local IV curve scan, and then stop scanning.

11. The system according to claim 8 or 9, characterized in that The controller is specifically configured to obtain the maximum input power of each DC-DC conversion circuit in the K paths according to the scan voltage and the scan current of each DC-DC conversion circuit in the K paths.

12. The system according to claim 8 or 9, characterized in that The controller is specifically configured to control the input voltage of each of the K DC-DC conversion circuits to gradually decrease from a second voltage to perform the local IV curve scan; the second voltage is the input voltage of each of the K DC-DC conversion circuits corresponding to the maximum total input power of the NK DC-DC conversion circuits when the total input power of the multiple DC-DC conversion circuits is consistent with that before the local IV curve scan.

13. The system according to any one of claims 1-6, 8-10, characterized in that The DC-AC conversion circuit, the multi-channel DC-DC conversion circuit and the controller are integrated inside the string inverter.

14. The system according to any one of claims 1-6, 8-10, characterized in that The multi-channel DC-DC conversion circuit is integrated inside the combiner box, and the DC-AC conversion circuit is integrated inside the centralized inverter.

15. A method for determining the maximum input power of a photovoltaic system, characterized in that: The photovoltaic system includes a DC-AC conversion circuit and multiple DC-DC conversion circuits; the input end of each DC-DC conversion circuit is used to connect to a corresponding photovoltaic string; the output ends of the multiple DC-DC conversion circuits are connected in parallel to the input end of the DC-AC conversion circuit; The method includes: Performing a local current and voltage IV curve scan on each of the DC-DC conversion circuits; during the local current and voltage IV curve scan, controlling the total input power of the multiple DC-DC conversion circuits to be consistent with that before the local current and voltage IV curve scan, and obtaining the maximum input power of each of the DC-DC conversion circuits; The sum of the maximum input powers of all the DC-DC conversion circuits is obtained according to the maximum input power of each DC-DC conversion circuit; the scanning voltage of the local current-voltage IV curve scanning is less than the open circuit voltage; The multi-channel DC-DC conversion circuit includes at least: a first channel DC-DC conversion circuit and a second channel DC-DC conversion circuit; The performing local current and voltage IV curve scanning on each of the DC-DC conversion circuits respectively includes: controlling the input voltage of the first DC-DC conversion circuit to gradually decrease to perform the local IV curve scanning; Controlling the input voltage of the first DC-DC conversion circuit to gradually decrease to perform the local IV curve scanning specifically includes: controlling the input voltage of the first DC-DC conversion circuit to gradually decrease from a first voltage to perform the local IV curve scanning, where the first voltage is the input voltage of the first DC-DC conversion circuit corresponding to when the input power of the second DC-DC conversion circuit is maximum.

16. The method according to claim 15, characterized in that Performing a local current and voltage IV curve scan on each of the DC-DC conversion circuits; during the local IV curve scan, controlling the total input power of the multiple DC-DC conversion circuits to be consistent with that before the local IV curve scan, and obtaining the maximum input power of each of the DC-DC conversion circuits, specifically comprising: controlling the input voltage change of the first DC-DC conversion circuit to perform a local IV curve scan, thereby obtaining a first maximum input power of the first DC-DC conversion circuit; while the first DC-DC conversion circuit is performing the IV curve scan, adjusting the input power of the second DC-DC conversion circuit so that the sum of the input power of the first DC-DC conversion circuit and the input power of the second DC-DC conversion circuit is consistent with that before the local IV curve scan; and so on and so forth, thereby obtaining a second maximum input power of the second DC-DC conversion circuit; Obtaining the sum of the maximum input powers of all the DC-DC conversion circuits according to the maximum input power of each DC-DC conversion circuit specifically includes: The sum of the maximum input powers of all DC-DC conversion circuits is obtained according to the first maximum input power and the second maximum input power.

17. The method according to claim 16, characterized in that The controlling the input voltage change of the first DC-DC conversion circuit to perform the local IV curve scanning specifically includes: The input voltage of the first DC-DC conversion circuit is controlled to gradually decrease to perform the local IV curve scanning, and the scanning voltage and scanning current of the first DC-DC conversion circuit are recorded during the IV curve scanning process. The scanning is stopped when the input power of the first DC-DC conversion circuit decreases and the scanning voltage is less than the voltage before the local IV curve scanning.

18. The method according to claim 16, characterized in that The controlling the input voltage change of the first DC-DC conversion circuit to perform the local IV curve scanning specifically includes: The input voltage of the first DC-DC conversion circuit is controlled to gradually decrease to perform the local IV curve scanning, and the scanning voltage and scanning current of the first DC-DC conversion circuit are recorded during the IV curve scanning process until the input power of the first DC-DC conversion circuit is equal to the input power before the local IV curve scanning and the scanning voltage is less than the voltage before the local IV curve scanning, and then the scanning is stopped.

19. The method according to claim 15, characterized in that The multi-channel DC-DC conversion circuit comprises N channels in total, and the N channels of the DC-DC conversion circuit are divided into at least two groups: a first group comprises K channels and a second group comprises NK channels; K is an integer greater than or equal to 2; Performing a current and voltage IV curve scan on each of the DC-DC conversion circuits; during the IV curve scanning process, controlling the total input power of the multiple DC-DC conversion circuits to be consistent with that before the local IV curve scanning, and obtaining the maximum input power of each of the DC-DC conversion circuits, specifically comprising: The local IV curve scan is performed on each of the K DC-DC conversion circuits of the first group. During the local IV curve scan, the total input power of the N DC-DC conversion circuits is controlled to be consistent with that before the local IV curve scan, and the maximum input power of each of the K DC-DC conversion circuits is obtained. Similarly, the maximum input power of each of the NK DC-DC conversion circuits is obtained.

20. The method according to claim 19, characterized in that Performing the local IV curve scan on each of the K-way DC-DC conversion circuits of the first group specifically includes: controlling the input voltage of each of the K DC-DC conversion circuits to gradually decrease to perform the local IV curve scan, and recording the scan voltage and scan current of each of the K DC-DC conversion circuits until the input power of each of the K DC-DC conversion circuits decreases and the scan voltage is less than the voltage before the local IV curve scan, then stopping the scan; or, The input voltage of each DC-DC conversion circuit in the K paths is controlled to gradually decrease to perform the local IV curve scanning, and the scanning voltage and scanning current of each DC-DC conversion circuit in the K paths are recorded until the input power of each DC-DC conversion circuit in the K paths is equal to the input power before the local IV curve scanning and the scanning voltage is less than the voltage before the local IV curve scanning, then the scanning is stopped.

21. The method according to claim 20, characterized in that The step of controlling the input voltage of each DC-DC conversion circuit in the K circuits to gradually decrease to perform the local IV curve scanning specifically includes: The input voltage of each of the K DC-DC conversion circuits is controlled to gradually decrease from a second voltage to perform the IV curve scanning; the second voltage is the input voltage of each of the K DC-DC conversion circuits corresponding to the maximum input power of the NK DC-DC conversion circuits when the total input power of the multiple DC-DC conversion circuits is consistent with that before the local IV curve scanning.

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