DC / DC branch parallel detection method and device and photovoltaic inverter thereof

Abstract

The invention relates to the field of circuit parallel detection, in particular to a DC / DC branch parallel detection method and device and a photovoltaic inverter thereof, and the method comprises the steps: detecting the input voltage of a plurality of DC / DC branches before the photovoltaic inverter is started; a first DC / DC branch is selected from the multiple DC / DC branches, a second DC / DC branch is determined from the remaining DC / DC branches, and the second DC / DC branch meets the condition that the absolute value of the difference value between the input voltage of the second DC / DC branch and the input voltage of the first DC / DC branch is smaller than a first preset value; the first DC / DC branch is started to enable the input voltage of the first DC / DC branch to drop, a third DC / DC branch is determined from the second DC / DC branches, and the third DC / DC branch meets the condition that the absolute value of the difference value between the input voltage of the third DC / DC branch and the input voltage of the first DC / DC branch is smaller than a second preset value; and determining that the first DC / DC branch and the third DC / DC branch are connected in parallel to the same photovoltaic string. According to the invention, the input wiring mode of the plurality of DC / DC branches at the input side of the photovoltaic inverter can be automatically detected, the labor cost is reduced, and the reliability of the detection result is improved.

Description

Technical Field

[0001] This application relates to the field of parallel detection of circuits, and particularly to a method and device for parallel detection of DC / DC branches and a photovoltaic inverter thereof. Background Art

[0002] An inverter is a power adjustment device composed of semiconductor devices, mainly used to convert DC electrical energy into AC electrical energy. For a photovoltaic inverter, on its photovoltaic input side, there are usually multiple photovoltaic DC / DC branches, and each photovoltaic DC / DC branch can be connected to a separate photovoltaic string.

[0003] With the development of photovoltaic panel technology, the current provided by a single photovoltaic string is getting larger and larger. It is necessary to connect two or more DC / DC branches in parallel to the same photovoltaic string to reduce the current magnitude on the photovoltaic input side. When two DC / DC branches are separately connected to two different photovoltaic strings, the two DC / DC branches need to be separately controlled. When two DC / DC branches are connected in parallel to the same photovoltaic string, the control of one of the DC / DC branches needs to follow that of the other DC / DC branch. In actual use, there may be a situation where the above two connection methods are mixed. Therefore, it is necessary to determine the connection method of multiple DC / DC branches on the photovoltaic input side of the photovoltaic inverter to determine the control mode. In the related art, for the method of judging whether multiple DC / DC branches on the photovoltaic input side are in parallel, when installing engineers install photovoltaic panels and photovoltaic inverters on site, they manually set the connection method to parallel or series and record the connection relationship between the photovoltaic panels and the photovoltaic inverter. However, this method increases the labor cost and is prone to errors. Summary of the Invention

[0004] This application aims to solve at least one of the technical problems existing in the prior art. To this end, embodiments of this application provide a method and device for parallel detection of DC / DC branches and a photovoltaic inverter thereof, which can automatically detect the input wiring method of multiple DC / DC branches on the input side of the photovoltaic inverter, reduce the labor cost and improve the reliability of the detection result at the same time.

[0005] In a first aspect, embodiments of this application provide a method for parallel detection of DC / DC branches, which is applied to a photovoltaic inverter. The photovoltaic inverter includes a processor and multiple DC / DC branches connected thereto. The input end of the DC / DC branch is connected to a photovoltaic string. The method executed by the processor includes:

[0006] Before the photovoltaic inverter starts, detect the input voltages of multiple DC / DC branches;

[0007] Select a first DC / DC branch from multiple DC / DC branches, and determine a second DC / DC branch from the remaining DC / DC branches. The second DC / DC branch satisfies that the absolute value of the difference between its input voltage and the input voltage of the first DC / DC branch is less than a first preset value;

[0008] Turn on the first DC / DC branch to decrease the input voltage of the first DC / DC branch, and determine a third DC / DC branch from the second DC / DC branches. The third DC / DC branch satisfies that the absolute value of the difference between its input voltage and the input voltage of the first DC / DC branch is less than a second preset value;

[0009] Determine that the first DC / DC branch and the third DC / DC branch are connected in parallel to the same photovoltaic string;

[0010] Control the third DC / DC branch to follow the first DC / DC branch for voltage output.

[0011] The technical solution of the first aspect of the present application has at least one of the following advantages or beneficial effects: Before the photovoltaic inverter starts, the input voltages of multiple DC / DC branches are detected first to ensure that the input voltages of each DC / DC branch meet their own start-up voltages; Any one of the multiple DC / DC branches is selected as the first DC / DC branch, and among the remaining DC / DC branches, the DC / DC branch whose absolute value of the difference between the input voltage and the input voltage of the first DC / DC branch is less than the first preset difference is determined as the second DC / DC branch. It is preliminarily determined that the first DC / DC branch and the second DC / DC branch may be connected in parallel to the same photovoltaic string, or the first DC / DC branch and the second DC / DC branch are respectively connected to two photovoltaic strings with similar open-circuit voltages. Further detect the connection relationship between the first DC / DC branch and the second DC / DC branch, turn on the first DC / DC branch to lower the input voltage of the first DC / DC branch, and identify from the second DC / DC branch the DC / DC branch whose input voltage follows the decrease and the absolute value of the difference between its input voltage and the input voltage of the first DC / DC branch is less than the second preset value as the third DC / DC branch, determine that the connection relationship between the first DC / DC branch and the third DC / DC branch is parallel to the same photovoltaic string, and control the third DC / DC branch to follow the first DC / DC branch for voltage output. In the present application, multiple DC / DC branches are automatically detected and screened according to the input voltage, and then the input voltage of the first DC / DC branch is reduced to determine that the DC / DC branch whose input voltage follows the change and the absolute value of the difference between its input voltage and the input voltage of the first DC / DC branch is less than the first preset value is the third DC / DC branch, so as to determine that the first DC / DC branch and the third DC / DC branch are connected in parallel to the same photovoltaic string. There is no need for installation engineers to artificially divide and record the connection relationship between the photovoltaic panels and the photovoltaic inverter when installing the photovoltaic panels and the photovoltaic inverter, which saves labor costs and improves the reliability of the parallel detection results. In addition, controlling the third DC / DC branch to follow the first DC / DC branch for voltage output makes the output voltages of the parallel DC / DC branches consistent, so as to improve the stability and reliability of the photovoltaic inverter.

[0012] According to some embodiments of the present application, a fourth DC / DC branch is determined from the second DC / DC branches, and the fourth DC / DC branch is the other DC / DC branches in the second DC / DC branches except the third DC / DC branch;

[0013] Select a fifth DC / DC branch from the fourth DC / DC branches, turn on the fifth DC / DC branch to reduce the input voltage of the fifth DC / DC branch, and determine a sixth DC / DC branch from the remaining DC / DC branches of the fourth DC / DC branches, where the absolute value of the difference between the input voltage of the sixth DC / DC branch and the input voltage of the fifth DC / DC branch is less than the second preset value;

[0014] Determine that the fifth DC / DC branch and the sixth DC / DC branch are connected in parallel to the same photovoltaic string;

[0015] Control the sixth DC / DC branch to follow the fifth DC / DC branch for voltage output.

[0016] According to some embodiments of the present application, the turning on the first DC / DC branch to reduce the input voltage of the first DC / DC branch and determining the third DC / DC branch from the second DC / DC branches includes:

[0017] Turn on the first DC / DC branch and detect the input voltage of the first DC / DC branch;

[0018] When the input voltage of the first DC / DC branch drops to the first preset voltage, detect the input voltage of the second DC / DC branch;

[0019] Traverse all the second DC / DC branches. If the absolute value of the difference between the input voltage of any second DC / DC branch and the first preset voltage is less than the second preset value, determine the current second DC / DC branch as the third DC / DC branch.

[0020] According to some embodiments of the present application, the absolute value of the difference between the first preset voltage and the open-circuit voltage of the photovoltaic string corresponding to the first DC / DC branch is greater than the third preset value.

[0021] According to some embodiments of the present application, the determining the second DC / DC branch from the remaining DC / DC branches includes:

[0022] Detect the input voltage of the first DC / DC branch;

[0023] Detect the input voltages of the other DC / DC branches except the first DC / DC branch. If the absolute value of the difference between the input voltage of any DC / DC branch and the input voltage of the first DC / DC branch is less than the first preset value, determine the current DC / DC branch as the second DC / DC branch.

[0024] According to some embodiments of the present application, after detecting the input voltages of multiple DC / DC branches, the method further includes:

[0025] Determining whether the input voltage of the DC / DC branch is less than a fourth preset value, where the fourth preset value represents the turn-on voltage of the DC / DC branch;

[0026] If the input voltage of the DC / DC branch is less than the fourth preset value, a fault reminder is issued.

[0027] According to some embodiments of the present application, the value range of the second preset value is 5V to 20V.

[0028] In a second aspect, an embodiment of the present application provides a parallel detection device, including: a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor runs the computer program, it executes the method described in the technical solution of the first aspect above.

[0029] In a third aspect, an embodiment of the present application provides a photovoltaic inverter, including a DC / DC branch and the parallel detection device described in the technical solution of the second aspect above. The DC / DC branch is used to connect to a photovoltaic string, and the parallel detection device is used to detect the input voltage of the DC / DC branch.

[0030] In a fourth aspect, an embodiment of the present application provides a computer-readable storage medium storing computer-executable instructions for executing the method described in the technical solution of the first aspect above.

[0031] Other features and advantages of the present application will be described in the subsequent description, and some of them will become obvious from the description, or can be understood by implementing the present application. The objectives and other advantages of the present application can be achieved and obtained through the structures specifically pointed out in the description, claims, and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a flowchart of a method for parallel detection of a DC / DC branch provided by an embodiment of the present application;

[0033] Figure 2 is a schematic structural diagram of a DC / DC branch connected in parallel to a photovoltaic string provided by an embodiment of the present application;

[0034] Figure 3 is a schematic structural diagram of a connection between multiple DC / DCs and photovoltaic strings provided by an embodiment of the present application;

[0035] Figure 4It is a flowchart of another parallel detection method for the DC / DC branch provided by an embodiment of the present application;

[0036] Figure 5 It is a flowchart of a method for determining a third DC / DC branch from a second DC / DC branch provided by an embodiment of the present application;

[0037] Figure 6 It is a flowchart of a method for determining a second DC / DC branch from the remaining DC / DC branches provided by an embodiment of the present application;

[0038] Figure 7 It is a flowchart of a method for determining that there is a fault in the input voltage of the DC / DC branch provided by an embodiment of the present application;

[0039] Figure 8 It is a schematic structural diagram of a parallel detection device provided by an embodiment of the present application. Detailed implementation manners

[0040] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application. In addition, the features, operations or characteristics described in the specification can be combined in any appropriate manner to form various embodiments. At the same time, the steps or actions in the method description can also be adjusted in the order that can be obvious to those skilled in the art. Therefore, the various sequences in the specification and drawings are only for clearly describing a certain embodiment and do not mean that they are the necessary sequences unless it is stated that a certain sequence must be followed.

[0041] In the description of the present application, the meaning of "several" is one or more, the meaning of "multiple" is more than two, and understandings such as "greater than", "less than", "exceeding", etc. do not include the present number, and understandings such as "above", "below", "within", etc. include the present number. If there is a description of "first", "second", etc., it is only for the purpose of distinguishing technical features and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or implicitly indicating the sequence of the indicated technical features.

[0042] The serial numbers assigned to the components herein, such as "first", "second", etc., are only used to distinguish the described objects and do not have any sequential or technical meanings. And the "connection" and "coupling" mentioned in the present application, unless otherwise specified, both include direct and indirect connection (coupling).

[0043] A photovoltaic inverter is a power adjustment device composed of semiconductor devices, mainly used to convert DC electrical energy into AC electrical energy. In addition, the photovoltaic inverter also has the functions of maximizing the performance of solar cells and system fault protection. On the input side of the photovoltaic inverter, multiple photovoltaic DC / DC branches can be connected, and each photovoltaic DC / DC branch has a corresponding DC / DC branch to control it, and each DC / DC branch is independent of each other. With the development of photovoltaic panel technology, the current provided by a single photovoltaic string is getting larger and larger. At this time, two DC / DC branches or multiple DC / DC branches need to be connected in parallel to the same photovoltaic string. When two DC / DC branches are separately connected to different photovoltaic strings, the two DC / DC branches need to be controlled separately. When two DC / DC branches are connected in parallel to the same photovoltaic string, the control of one of the DC / DC branches needs to follow the other DC / DC branch. In actual use, there may be a situation where the above two connection methods are mixed. Therefore, it is necessary to judge the connection method of multiple DC / DC branches on the photovoltaic input side of the photovoltaic inverter to determine the control mode. In the related art, the method for judging whether multiple DC / DC branches on the photovoltaic input side are connected in parallel is that when installing engineers install photovoltaic panels and photovoltaic inverters on site, they manually set multiple DC / DC branches to be connected in parallel to the same photovoltaic string or multiple DC / DC branches to be separately connected to different photovoltaic strings, record the connection relationship between the photovoltaic panels and the photovoltaic inverter, and control the switches of multiple DC / DC branches according to the connection method of multiple DC / DC branches recorded by the installation engineers. This method requires installation engineers to artificially divide the connection relationship between DC / DC branches, increasing the labor cost, prone to errors, and prone to causing control chaos or even failure of DC / DC branches.

[0044] Based on this, the embodiments of the present application provide a method and device for detecting the parallel connection of DC / DC branches and its photovoltaic inverter, which can automatically detect the input wiring method of multiple DC / DC branches on the input side of the photovoltaic inverter, reduce the labor cost and improve the reliability of the detection result at the same time.

[0045] Refer to Figure 1 , Figure 1 is a flowchart of a method for detecting the parallel connection of DC / DC branches provided by the embodiments of the present application, including steps S100 to S500. Specifically,

[0046] Step S100: Before the photovoltaic inverter starts, detect the input voltages of multiple DC / DC branches;

[0047] Step S200: Select a first DC / DC branch from multiple DC / DC branches, and determine a second DC / DC branch from the remaining DC / DC branches. The second DC / DC branch satisfies that the absolute value of the difference between its input voltage and the input voltage of the first DC / DC branch is less than a first preset value.

[0048] Step S300: Turn on the first DC / DC branch to cause the input voltage of the first DC / DC branch to drop, and determine a third DC / DC branch from the second DC / DC branches. The third DC / DC branch satisfies that the absolute value of the difference between its input voltage and the input voltage of the first DC / DC branch is less than a second preset value.

[0049] Step S400: Determine that the first DC / DC branch and the third DC / DC branch are connected in parallel to the same photovoltaic string.

[0050] Step S500: Control the third DC / DC branch to follow the first DC / DC branch for voltage output.

[0051] In some embodiments of the present application, the parallel connection detection method of the DC / DC branches includes, before the photovoltaic inverter is started, first detecting the input voltages of multiple DC / DC branches to ensure that the input voltage of each DC / DC branch meets its own startup voltage. Select any one of the multiple DC / DC branches as the first DC / DC branch, and identify, from the remaining DC / DC branches, the DC / DC branch whose absolute value of the difference between its input voltage and the input voltage of the first DC / DC branch is less than a first preset difference as the second DC / DC branch, and preliminarily determine that the first DC / DC branch and the second DC / DC branch with the absolute value of the difference between the input voltages less than the first preset difference may be connected in parallel to the same photovoltaic string or the first DC / DC branch and the second DC / DC branch are respectively connected to two photovoltaic strings with similar open-circuit voltages.

[0052] To determine the control mode of each DC / DC branch, it is necessary to further detect the connection relationship between the first DC / DC branch and the second DC / DC branch. Turn on the first DC / DC branch to cause the input voltage of the first DC / DC branch to drop, identify, from the second DC / DC branches, the DC / DC branch whose input voltage follows the drop and the absolute value of the difference between its input voltage and the input voltage of the first DC / DC branch is less than a second preset value, and determine it as the third DC / DC branch. Since the absolute value of the difference between the input voltages of the first DC / DC branch and the third DC / DC branch is less than the first preset difference, it is determined that the connection relationship between the first DC / DC branch and the third DC / DC branch is to be connected in parallel to the same photovoltaic string, and the third DC / DC branch is controlled to follow the first DC / DC branch for voltage output.

[0053] In this application, multiple DC / DC branches are automatically detected and screened according to the input voltage, and then the input voltage of the first DC / DC branch is reduced to determine that the DC / DC branch whose input voltage follows the change of the first DC / DC branch and the absolute value of the difference between the input voltage of the first DC / DC branch is less than the first preset value is the third DC / DC branch, so as to determine that the first DC / DC branch and the third DC / DC branch are connected in parallel to the same photovoltaic string. There is no need for installation engineers to artificially divide and record the connection relationship between photovoltaic panels and photovoltaic inverters during the installation of photovoltaic panels and photovoltaic inverters, saving labor costs and improving the reliability of parallel detection results at the same time.

[0054] It should be noted that in the energy management system, the follow-up control of two parallel DC / DC branches is usually achieved through the master-slave control method. Among them, one DC / DC branch serves as the master controller, and the other DC / DC branch serves as the slave controller. The master controller is responsible for controlling the output voltage, and the slave controller adjusts according to the output voltage of the master controller to keep the output voltage consistent with the output voltage of the master controller. Specifically, the master controller obtains the information of the output voltage through the feedback circuit and conducts control, and the slave controller adjusts its own output voltage by comparing the output voltage of the master controller with its own output voltage to keep it consistent with the output voltage of the master controller. Through the above follow-up control method, the output voltages of the parallel DC / DC branches can be made consistent to improve the stability and reliability of the photovoltaic inverter. In practical applications, the follow-up control usually needs to consider multiple factors, such as the selection of the master controller and the slave controller, the design of the control algorithm, the design of the feedback circuit, etc., to ensure the stability and accuracy of the follow-up control.

[0055] It can be understood that the first DC / DC branch serves as the master controller, and the third DC / DC branch serves as the slave controller to adjust its own output voltage to keep it consistent with the output voltage of the first DC / DC branch following the output voltage of the first DC / DC branch. The processor outputs a PWM waveform to control the output voltage of the first DC / DC branch, and then the output voltage of the third DC / DC branch follows the first DC / DC branch to adjust its own output voltage so that the output voltage of the third DC / DC branch is consistent with the output voltage of the first DC / DC branch, thereby realizing the voltage output of the third DC / DC branch following the first DC / DC branch.

[0056] It should be noted that in some embodiments of this application, it is determined through the above parallel detection method of the DC / DC branch that the other DC / DC branches in the second DC / DC branch except the third DC / DC branch are not connected in parallel to the same photovoltaic string as the first DC / DC branch. Therefore, the processor controls the other DC / DC branches in the second DC / DC branch except the third DC / DC branch separately.

[0057] It should be noted that in some embodiments of the present application, in order to ensure that the sampling error of the input voltage of the DC / DC branch is as small as possible, the value range of the first preset value is set to 5V to 20V. Among multiple DC / DC branches, a DC / DC branch whose absolute value of the difference from the input voltage of the first DC / DC branch is between 5V and 20V is selected and determined as the second DC / DC branch. Since the difference in the input voltage between the first DC / DC branch and the second DC / DC branch is 5V to 20V and is relatively small, it is preliminarily determined that the first DC / DC branch and the second DC / DC branch are connected in parallel to the same photovoltaic string or are respectively connected to two photovoltaic strings with similar open-circuit voltages. Those skilled in the art can set the size of the first preset value according to the actual situation, and the embodiments of the present application do not limit the value range of the first preset value.

[0058] It should be noted that in some embodiments of the present application, in order to ensure that the sampling error of the input voltage of the DC / DC branch is as small as possible, the value range of the second preset value is 5V to 20V. By setting the value range of the second preset value to 5V to 20V, after gradually decreasing the voltage of the first DC / DC branch, a DC / DC branch whose absolute value of the difference from the input voltage of the first DC / DC branch is between 5V and 20V is selected from the second DC / DC branch and determined as the third DC / DC branch. Since the second preset value is 5V to 20V, that is, the absolute value of the difference in the input voltage between the first DC / DC branch and the third DC / DC branch is relatively small, it is determined that the first DC / DC branch and the third DC / DC branch are connected in parallel to the same photovoltaic string.

[0059] Refer to Figure 2 , Figure 2It is a schematic diagram of a structure in which DC / DC branches are connected in parallel to a photovoltaic string provided by an embodiment of the present application. In some embodiments of the present application, if there are two DC / DC branches on the input side of a photovoltaic inverter, then the parallel detection method for the DC / DC branches includes, before the photovoltaic inverter is powered on, first detecting the input voltages of the two DC / DC branches, and then determining whether the absolute value of the difference between the input voltages of the two DC / DC branches is within the value range of 5V to 20V. If the absolute value of the difference between the input voltages of the two DC / DC branches is greater than 20V, it is preliminarily determined that the two DC / DC branches are not connected in parallel to the same photovoltaic string, the photovoltaic inverter is started, and the two DC / DC branches are controlled separately. If the absolute value of the difference between the input voltages of the two DC / DC branches is between 5V and 20V, the connection relationship between the two DC / DC branches is further distinguished. Any one of the DC / DC branches is turned on and its input voltage is gradually reduced. At this time, it is determined again whether the absolute value of the difference between the input voltages of the two DC / DC branches is less than 5V to 20V. If the difference between the input voltages of the two DC / DC branches is greater than 20V, it is determined that the two DC / DC branches are not connected in parallel to the same photovoltaic string, and the photovoltaic inverter is started to control the two DC / DC branches separately; if the absolute value of the difference between the input voltages of the two DC / DC branches satisfies the condition of being between 5V and 20V, the photovoltaic inverter is started and enters the parallel control mode, where the two DC / DC branches include the first DC / DC branch and the second DC / DC branch, and the parallel control mode satisfies that the control of the second DC / DC branch follows the control of the first DC / DC branch.

[0060] The first DC / DC branch serves as the main controller, and the second DC / DC branch serves as the slave controller to adjust its own output voltage following the output voltage of the first DC / DC branch to keep it consistent with the output voltage of the first DC / DC branch. The first DC / DC branch is responsible for controlling the output voltage. The processor outputs a PWM waveform to control the output voltage of the first DC / DC branch, and then the output voltage of the second DC / DC branch follows the first DC / DC branch to adjust its own output voltage so that the output voltage of the second DC / DC branch is consistent with the output voltage of the first DC / DC branch, thereby realizing that the second DC / DC branch follows the first DC / DC branch for voltage output.

[0061] Refer to Figure 3 , Figure 3FIG. 0 is a schematic structural diagram of a connection of multiple DC / DCs and photovoltaic strings. In some embodiments of the present application, if there are multiple DC / DC branches on the input side of the photovoltaic inverter. For example, there are 10 DC / DC branches on the input side of the photovoltaic inverter, numbered from the first DC / DC branch to the tenth DC / DC branch respectively. The parallel detection method of the DC / DC branches includes, before the photovoltaic inverter is powered on, detecting the input voltages of the first DC / DC branch to the tenth DC / DC branch, and determining whether the absolute value of the difference in the input voltages of any two DC / DC branches or the absolute value of the difference in the input voltages of any multiple DC / DC branches among the 10 DC / DC branches is less than a first preset value. If the absolute values of the differences between the input voltage of the first DC / DC branch and the input voltages of the second DC / DC branch to the fifth DC / DC branch are all less than the first preset value, and the absolute values of the differences between the input voltage of the first DC / DC branch and the input voltages of the sixth DC / DC branch to the tenth DC / DC branch are greater than the first preset value. Since the value range of the first preset value is set to 5V to 20V, ensuring that the sampling error of the input voltage of the DC / DC branch is as small as possible, it can be determined that the first DC / DC branch and the second DC / DC branch to the fifth DC / DC branch may be connected in parallel to the same photovoltaic string or are respectively connected to two photovoltaic strings with similar open-circuit voltages; the sixth DC / DC branch to the tenth DC / DC branch is not connected in parallel to the first DC / DC branch to the same photovoltaic string. Therefore, the sixth DC / DC branch to the tenth DC / DC branch are controlled separately.

[0062] Turn on the first DC / DC branch to cause its voltage to drop, and detect the input voltages of the second DC / DC branch to the fifth DC / DC branch. If the absolute values of the differences between the input voltage of the first DC / DC branch and the input voltages of the second DC / DC branch and the third DC / DC branch are less than a second preset value, and the absolute values of the differences between the input voltage of the first DC / DC branch and the input voltages of the fourth DC / DC branch and the fifth DC / DC branch are greater than the second preset value, it is determined that the first DC / DC branch and the fourth DC / DC branch and the fifth DC / DC branch are respectively connected to different photovoltaic strings. Therefore, using the first DC / DC branch as the main controller and the second DC / DC branch and the third DC / DC branch as the slave controllers, control the second DC / DC branch and the third DC / DC branch to follow the first DC / DC branch for voltage output, and control the fourth DC / DC branch and the fifth DC / DC branch for voltage output respectively.

[0063] In some embodiments of the present application, after determining that the first DC / DC branch and the third DC / DC branch are connected in parallel to the same photovoltaic string, the photovoltaic inverter is started to convert the direct current generated by the photovoltaic string into alternating current for household or industrial use. After the present application confirms any two or more DC / DC branches connected in parallel to the same photovoltaic string, it starts any two or more DC / DC branches connected in parallel to the same photovoltaic string for power conversion, which can timely convert the direct current generated by the photovoltaic string into alternating current for household or industrial use, improving the power conversion efficiency; at the same time, it can perform measures such as overload protection and short-circuit protection on the electric energy to ensure the safe operation of the photovoltaic power generation system.

[0064] In addition, in the embodiments of the present application, it is not necessary to determine the connection relationship between all DC / DC branches on the input side of the photovoltaic inverter before starting the DC / DC branch, effectively avoiding the sudden start of multiple DC / DC branches on the input side of the photovoltaic inverter resulting in a large current mutation and excessive load, which is prone to short circuit and will also fail to convert the electric energy stored in the photovoltaic string in time.

[0065] So that the inverter can also refer to Figure 4 , Figure 4 FIG. is a flowchart of another method for detecting the parallel connection of DC / DC branches provided by the embodiments of the present application, including steps S600 to S900. Specifically,

[0066] Step S600: Determine a fourth DC / DC branch from the second DC / DC branches. The fourth DC / DC branch is other DC / DC branches in the second DC / DC branches except the third DC / DC branch;

[0067] Step S700: Select a fifth DC / DC branch from the fourth DC / DC branches, turn on the fifth DC / DC branch to make the input voltage of the fifth DC / DC branch drop, and determine a sixth DC / DC branch from the remaining DC / DC branches in the fourth DC / DC branches. The sixth DC / DC branch satisfies that the absolute value of the difference between its input voltage and the input voltage of the fifth DC / DC branch is less than a second preset value;

[0068] Step S800: Determine that the fifth DC / DC branch and the sixth DC / DC branch are connected in parallel to the same photovoltaic string;

[0069] Step S900: Control the sixth DC / DC branch to follow the fifth DC / DC branch for voltage output.

[0070] In some embodiments of the present application, the parallel connection detection method for the DC / DC branch further includes selecting, from the second DC / DC branch, other DC / DC branches except the second DC / DC branch as the fourth DC / DC branch, arbitrarily selecting one DC / DC branch from the fourth DC / DC branch as the fifth DC / DC branch, and detecting the DC / DC branches in the fourth DC / DC branch that are connected in parallel to the same photovoltaic string as the fifth DC / DC branch. Specifically, the fifth DC / DC branch is turned on to gradually decrease the input voltage of the fifth DC / DC branch, and in the fourth DC / DC branch, a DC / DC branch whose input voltage follows the change of the fifth DC / DC branch and the absolute value of the difference between its input voltage and the input voltage of the fifth DC / DC branch is less than a second preset value is selected as the sixth DC / DC branch. Since the absolute value of the difference between the input voltages of the fifth DC / DC branch and the sixth DC / DC branch is a relatively small second preset value, it is determined that the fifth DC / DC branch and the sixth DC / DC branch are connected in parallel to the same photovoltaic string, and the sixth DC / DC branch is controlled to follow the fifth DC / DC branch for voltage output.

[0071] In some embodiments of the present application, the fifth DC / DC branch is used as the main controller, and the sixth DC / DC branch is used as the slave controller to adjust its own output voltage to be consistent with the output voltage of the fifth DC / DC branch following the output voltage of the fifth DC / DC branch. The fifth DC / DC branch is responsible for controlling the output voltage. The processor outputs a PWM waveform to control the output voltage of the fifth DC / DC branch, and then the output voltage of the sixth DC / DC branch follows the fifth DC / DC branch to adjust its own output voltage so that the output voltage of the sixth DC / DC branch is consistent with the output voltage of the fifth DC / DC branch, thereby realizing the sixth DC / DC branch following the fifth DC / DC branch for voltage output.

[0072] After determining the fourth DC / DC branch, multiple DC / DC branches are automatically detected and screened according to the input voltage, and then the input voltage of the fifth DC / DC branch is reduced to determine that the DC / DC branch whose input voltage follows the change and the absolute value of the difference from the input voltage of the fifth DC / DC branch is less than a first preset value is the sixth DC / DC branch, so as to determine that the fifth DC / DC branch and the sixth DC / DC branch are connected in parallel to the same photovoltaic string. There is no need for the installation engineer to manually divide and record the connection relationship between the photovoltaic panels and the photovoltaic inverter when installing the photovoltaic panels and the photovoltaic inverter, which saves labor costs and improves the reliability of the parallel connection detection results at the same time.

[0073] In some embodiments of the present application,

[0074] Referring to Figure 5 , Figure 5It is a flowchart of a method for determining a third DC / DC branch from a second DC / DC branch provided by an embodiment of the present application, including steps S310 to S330. Specifically,

[0075] Step S310: Turn on the first DC / DC branch and detect the input voltage of the first DC / DC branch;

[0076] Step S320: When the input voltage of the first DC / DC branch drops to a first preset voltage, detect the input voltage of the second DC / DC branch;

[0077] Step S330: Traverse all the second DC / DC branches. If the absolute value of the difference between the input voltage of any second DC / DC branch and the first preset voltage is less than a second preset value, determine the current second DC / DC branch as the third DC / DC branch.

[0078] In some embodiments of the present application, the method for determining the third DC / DC branch from the second DC / DC branch includes turning on the first DC / DC branch to gradually decrease the input voltage of the first DC / DC branch. When the input voltage of the first DC / DC branch drops to the first preset voltage, detect the input voltage of the second DC / DC branch. Sequentially traverse the input voltages of all the second DC / DC branches. If the absolute value of the difference between the input voltage of any second DC / DC branch and the first preset voltage is less than the second preset value, it is determined that the current second DC / DC branch is the third DC / DC branch, and it is determined that the first DC / DC branch and the third DC / DC branch are connected in parallel to the same photovoltaic string.

[0079] It should be noted that in some embodiments of the present application, the absolute value of the difference between the first preset voltage and the open-circuit voltage of the photovoltaic string corresponding to the first DC / DC branch is greater than a third preset value, and the value range of the third preset value should be significantly larger than the value range of the first preset value. In the embodiments of the present application, since the value range of the first preset value is 5V to 20V, therefore, the value range of the third preset value can be set to 30V to 55V. Lowering the voltage of the first DC / DC branch to a value such that the absolute value of the difference from the open-circuit voltage of the photovoltaic string corresponding to the first DC / DC branch is greater than 30V to 55V is beneficial for clearly distinguishing that the first DC / DC branch is performing a buck operation, so as to more accurately automatically detect the DC / DC branch that follows the voltage change of the first DC / DC branch, and determine that the DC / DC branch whose absolute value of the difference between its input voltage and the input voltage of the first DC / DC branch is between 5V and 20V is the third DC / DC branch, thereby determining that the first DC / DC branch and the third DC / DC branch are connected in parallel to the same photovoltaic string.

[0080] By automatically detecting and traversing all the second DC / DC branches in sequence, and determining the DC / DC branch whose absolute value of the difference between the current input voltage and the first preset voltage is less than the second preset value as the third DC / DC branch, it is not necessary for the installation engineer to manually divide and record the connection relationship between the photovoltaic panels and the photovoltaic inverters when installing the photovoltaic panels and the photovoltaic inverters, saving labor costs and improving the reliability of the parallel detection results at the same time.

[0081] Refer to Figure 6 , Figure 6 is a flowchart of a method for determining the second DC / DC branch from the remaining DC / DC branches provided by an embodiment of the present application, including steps S210 to S220. Specifically,

[0082] Step S210: Detect the input voltage of the first DC / DC branch;

[0083] Step S220: Detect the input voltages of other DC / DC branches except the first DC / DC branch. If the absolute value of the difference between the input voltage of any DC / DC branch and the input voltage of the first DC / DC branch is less than the first preset value, determine the current DC / DC branch as the second DC / DC branch.

[0084] In some embodiments of the present application, the method for determining the second DC / DC branch from the remaining DC / DC branches includes detecting the input voltage of the first DC / DC branch, and detecting the input voltages of multiple other DC / DC branches except the first DC / DC branch, and judging the voltage difference between the input voltage of the first DC / DC branch and the input voltages of multiple other DC / DC branches except the first DC / DC branch. If the absolute value of the difference between the input voltage of any DC / DC branch and the input voltage of the first DC / DC branch is less than the first preset value, then determine the current DC / DC branch as the second DC / DC branch. Since in the embodiments of the present application, the value range of the first preset value is 5V to 20V, it ensures that the sampling error of the input voltage of the second DC / DC branch is as small as possible, improving the reliability of the parallel detection results. Therefore, it can be preliminarily determined that the first DC / DC branch and the second DC / DC branch may be connected in parallel to the same photovoltaic string, or the first DC / DC branch and the second DC / DC branch are respectively connected to two photovoltaic strings with similar open-circuit voltages.

[0085] Refer to Figure 7 , Figure 7 is a flowchart of a method for judging that there is a fault in the input voltage of the DC / DC branch provided by an embodiment of the present application, including steps S100 to S120. Specifically,

[0086] Step S100: Detect the input voltages of multiple DC / DC branches;

[0087] Step S110: Determine whether the input voltage of the DC / DC branch is less than a fourth preset value, where the fourth preset value represents the startup voltage of the DC / DC branch;

[0088] Step S120: If the input voltage of the DC / DC branch is less than the fourth preset value, issue a fault reminder.

[0089] In some embodiments of the present application, the method for determining whether there is a fault in the input voltage of the DC / DC branch includes, before starting the photovoltaic inverter, first detecting the input voltages of multiple DC / DC branches, and determining whether the input voltage of the DC / DC branch is less than a fourth preset value, where the fourth preset value represents the startup voltage of the DC / DC branch. When the input voltage of the DC / DC branch is less than the fourth preset value, a fault reminder is issued to warn that the current DC / DC branch does not meet the startup condition. By first judging the voltages of multiple DC / DC branches before starting the photovoltaic inverter, it is ensured that the input voltages of each DC / DC branch meet their own startup voltages, effectively avoiding damage to the photovoltaic inverter, thereby implementing measures such as overload protection and short-circuit protection for electric energy, and ensuring the safe operation of the photovoltaic power generation system.

[0090] Refer to Figure 8 , Figure 8FIG. 0 is a schematic structural diagram of a parallel detection device 1000 provided by an embodiment of the present application. The device includes a processor 1001, which can be implemented by using a general-purpose CPU (Central Processing Unit), a microprocessor, an application-specific integrated circuit (ASIC), or one or more integrated circuits, etc., and is used to execute relevant programs to implement a parallel detection method for a DC / DC branch provided by an embodiment of the present application; a memory 1002, which can be implemented in the form of a read-only memory 1002 (ROM), a static storage device, a dynamic storage device, or a random access memory 1002 (RAM), etc. The memory 1002 can store an operating system and other application programs. When implementing the technical solutions provided by the embodiments of this specification through software or firmware, the relevant program codes are stored in the memory 1002 and are called by the processor 1001 to execute the embodiments of the present application; an input / output interface 1003, which is used to implement information input and output; a communication interface 1004, which is used to implement communication interaction between this device and other devices, and can implement communication through a wired method (such as USB, network cable, etc.) or through a wireless method (such as mobile network, WIFI, Bluetooth, etc.); a bus, which transmits information between various components of the device (such as the processor 1001, the memory 1002, the input / output interface 1003, and the communication interface 1004); where the processor 1001, the memory 1002, the input / output interface 1003, and the communication interface 1004 are communicatively connected to each other inside the device through the bus.

[0091] An embodiment of the present application also provides a photovoltaic inverter. The photovoltaic inverter includes a DC / DC branch and the parallel detection device described in the above embodiment. Among them, the DC / DC branch is used to connect a photovoltaic string, and the parallel detection device is used to detect the input voltage of the DC / DC branch. A photovoltaic inverter is a power adjustment device composed of semiconductor devices, mainly used to convert direct current electrical energy into alternating current. In addition, the photovoltaic inverter also has the functions of maximizing the performance of solar cells and system fault protection. The photovoltaic inverter can isolate and protect the electrical energy stored in the photovoltaic string to avoid harm to the human body and equipment caused by the electrical energy. At the same time, the photovoltaic inverter can also take measures such as overload protection and short-circuit protection for the electrical energy to ensure the safe operation of the photovoltaic power generation system.

[0092] The PV inverter provided by the embodiment of the present application includes a parallel connection detection device, and the parallel connection detection device is used to detect the connection relationship of the DC / DC branches on the input side of the PV inverter. The DC / DC branch parallel connection detection method provided by the embodiment of the present application includes automatically detecting and screening a plurality of DC / DC branches according to the input voltage, selecting a first DC / DC branch, and selecting, from the remaining DC / DC branches, the DC / DC branches whose absolute value of the difference between the input voltage and the voltage of the first DC / DC branch is less than a first preset value as the second DC / DC branches. Then, the input voltage of the first DC / DC branch is reduced to determine, from the second DC / DC branches, the DC / DC branches whose input voltage follows the change of the first DC / DC branch and whose absolute value of the difference between the input voltage and the input voltage of the first DC / DC branch is less than a second preset value as the third DC / DC branches, so as to determine that the first DC / DC branch and the third DC / DC branch are connected in parallel to the same PV string, turn on the first DC / DC branch, and enable the third DC / DC branch to control the voltage output following the third DC / DC branch.

[0093] After determining the parallel connection of the first DC / DC branch and the third DC / DC branch, continue to determine the connection relationship of the other DC / DC branches in the second DC / DC branches except the third DC / DC branch. Specifically, arbitrarily select a DC / DC branch except the third DC / DC branch from the second DC / DC branches as the fourth DC / DC branch, and arbitrarily select a DC / DC branch from the fourth DC / DC branch as the fifth DC / DC branch. Turn on the fifth DC / DC branch, and gradually decrease the input voltage of the fifth DC / DC branch until it reaches a second preset voltage, where the absolute value of the difference between the second preset voltage and the open-circuit voltage of the corresponding PV string is greater than a third preset value. Determine, from the remaining DC / DC branches of the fourth DC / DC branch, the DC / DC branches whose voltage follows the change of the fifth DC / DC branch and whose absolute value of the difference between the input voltage and the input voltage of the fifth DC / DC branch is less than the second preset value as the sixth DC / DC branches, and determine that the fifth DC / DC branch and the sixth DC / DC branch are connected in parallel to the same PV string. Turn on the fifth DC / DC branch, and control the sixth DC / DC branch to follow the fifth DC / DC branch for voltage output. The parallel connection detection method provided by the embodiment of the present application does not require the installation engineer to manually divide and record the connection relationship between the PV panels and the PV inverter when installing the PV panels and the PV inverter, saving labor costs and improving the reliability of the parallel connection detection results at the same time.

[0094] The DC / DC branches on the input side of the photovoltaic inverter accurately determine the connection relationship between different DC / DC branches through the above-mentioned DC / DC branch parallel detection method of the present application, so as to accurately control the startup of each DC / DC branch, enabling the photovoltaic inverter to convert DC electrical energy into AC electrical energy for household or industrial use.

[0095] Those of ordinary skill in the art can understand that all or some of the steps and systems in the methods disclosed above can be implemented as software, firmware, hardware, and their appropriate combinations. Some physical components or all physical components can be implemented as software executed by a processor, such as a central processing unit, a digital signal processor, or a microprocessor, or implemented as hardware, or implemented as an integrated circuit, such as an application-specific integrated circuit. Such software can be distributed on a computer-readable medium, which can include a computer-readable storage medium (or non-transitory medium) and a communication medium (or transitory medium). As is well known to those of ordinary skill in the art, the term computer-readable storage medium includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information, such as computer-readable instructions, data structures, program modules, or other data. Computer-readable storage media include, but are not limited to, RAM, ROM, EEPROM, flash memory, or other memory technologies, CD-ROM, digital versatile disk (DVD), or other optical disk storage, magnetic cassette, tape, magnetic disk storage, or other magnetic storage devices, or any other medium that can be used to store the desired information and can be accessed by a computer. In addition, as is well known to those of ordinary skill in the art, a communication medium typically contains computer-readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transmission mechanism, and can include any information delivery medium.

[0096] The above is a specific description of the preferred embodiment of the present application, but the present application is not limited to the above-mentioned implementation manner. Those skilled in the art can make various equivalent deformations or substitutions without departing from the spirit of the present application, and these equivalent deformations or substitutions are all included within the scope defined by the claims of the present application.

Claims

1. A parallel detection method for a DC / DC branch, characterized in that, applied to a photovoltaic inverter, the photovoltaic inverter includes a processor and a plurality of DC / DC branches connected thereto, the input end of the DC / DC branch is connected to a photovoltaic string, and the method executed by the processor includes: Before the photovoltaic inverter starts, detect the input voltages of a plurality of DC / DC branches; Select a first DC / DC branch from a plurality of DC / DC branches, and determine a second DC / DC branch from the remaining DC / DC branches, where the second DC / DC branch satisfies that the absolute value of the difference between its input voltage and the input voltage of the first DC / DC branch is less than a first preset value; Turn on the first DC / DC branch to make the input voltage of the first DC / DC branch drop, and determine a third DC / DC branch from the second DC / DC branches, where the third DC / DC branch satisfies that the absolute value of the difference between its input voltage and the input voltage of the first DC / DC branch is less than a second preset value; Determine that the first DC / DC branch and the third DC / DC branch are connected in parallel to the same photovoltaic string; Control the third DC / DC branch to follow the first DC / DC branch for voltage output.

2. The parallel detection method for a DC / DC branch according to claim 1, characterized in that, further comprising: Determine a fourth DC / DC branch from the second DC / DC branches, where the fourth DC / DC branch is the other DC / DC branches in the second DC / DC branches except the third DC / DC branch; Select a fifth DC / DC branch from the fourth DC / DC branches, turn on the fifth DC / DC branch to make the input voltage of the fifth DC / DC branch drop, and determine a sixth DC / DC branch from the remaining DC / DC branches of the fourth DC / DC branches, where the sixth DC / DC branch satisfies that the absolute value of the difference between its input voltage and the input voltage of the fifth DC / DC branch is less than the second preset value; Determine that the fifth DC / DC branch and the sixth DC / DC branch are connected in parallel to the same photovoltaic string; Control the sixth DC / DC branch to follow the fifth DC / DC branch for voltage output.

3. The parallel detection method for a DC / DC branch according to claim 1, characterized in that, The step of turning on the first DC / DC branch to make the input voltage of the first DC / DC branch drop, and determining a third DC / DC branch from the second DC / DC branches includes: Turn on the first DC / DC branch and detect the input voltage of the first DC / DC branch; When the input voltage of the first DC / DC branch drops to a first preset voltage, detect the input voltage of the second DC / DC branch; Traverse all the second DC / DC branches. If the absolute value of the difference between the input voltage of any second DC / DC branch and the first preset voltage is less than the second preset value, determine the current second DC / DC branch as the third DC / DC branch.

4. The parallel connection detection method for the DC / DC branch according to claim 3, characterized in that, the absolute value of the difference between the first preset voltage and the open-circuit voltage of the photovoltaic string corresponding to the first DC / DC branch is greater than a third preset value.

5. The parallel connection detection method for the DC / DC branch according to claim 1, characterized in that, determining the second DC / DC branch from the remaining DC / DC branches includes: detecting the input voltage of the first DC / DC branch; detecting the input voltages of the other DC / DC branches except the first DC / DC branch, and if the absolute value of the difference between the input voltage of any DC / DC branch and the input voltage of the first DC / DC branch is less than a first preset value, determining the current DC / DC branch as the second DC / DC branch.

6. The parallel connection detection method for the DC / DC branch according to claim 1, characterized in that, after detecting the input voltages of the multiple DC / DC branches, it further includes: judging whether the input voltage of the DC / DC branch is less than a fourth preset value, and the fourth preset value represents the startup voltage of the DC / DC branch; if the input voltage of the DC / DC branch is less than the fourth preset value, a fault reminder is issued.

7. The parallel connection detection method for the DC / DC branch according to claim 1, characterized in that, the value range of the second preset value is 5V to 20V.

8. A parallel connection detection device, characterized in that, it includes: a memory, a processor, and a computer program stored on the memory and executable on the processor, and when the processor runs the computer program, it executes the method according to any one of claims 1 to 7.

9. A photovoltaic inverter, characterized in that, it includes a DC / DC branch and the parallel connection detection device according to claim 8, the DC / DC branch is used to connect a photovoltaic string, and the parallel connection detection device is used to detect the input voltage of the DC / DC branch.

10. A computer-readable storage medium, characterized in that: it stores computer-executable instructions, and the computer-executable instructions are used to execute the method according to any one of claims 1 to 7.

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