Fault detection method of photovoltaic string, control device, photovoltaic system and medium

Abstract

The invention discloses a photovoltaic string fault detection method, a control device, a photovoltaic system and a medium, and the method comprises the steps: detecting a photovoltaic string to obtain a detection parameter, and determining a filling factor of the photovoltaic string according to the detection parameter; when the filling factor is larger than or equal to a first threshold value, it is determined that no aging fault or shielding fault occurs in the photovoltaic string, and the first threshold value is determined according to the initial filling factor of the photovoltaic string in the fault-free state; when the filling factor is smaller than a first threshold value, a first resistance value and a second resistance value are determined according to the detection parameters, the fault type of the photovoltaic string is determined according to the first resistance value and the second resistance value, the first resistance value is used for representing the equivalent series resistance value when the current of the photovoltaic string approaches zero, and the second resistance value is used for representing the equivalent series resistance value when the current of the photovoltaic string approaches zero. The second resistance value is used for representing an equivalent parallel resistance value when the voltage of the photovoltaic string approaches zero. According to the embodiment of the invention, the diagnosis period of the photovoltaic string can be shortened, and the diagnosis process of the photovoltaic string is simplified on the whole.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic power generation, and in particular to a fault detection method, a control device, a photovoltaic system and a storage medium for a photovoltaic string. Background Art

[0002] With the rapid development of photovoltaic technology, photovoltaic power generation has been widely promoted. As an important part of a photovoltaic power generation system, a photovoltaic module array needs to perform photovoltaic power generation in an outdoor environment. Since the photovoltaic panels are placed outdoors, they are exposed to long-term sunlight, rain, and dust accumulation, which will accelerate the aging of the photovoltaic panels. In addition, the photovoltaic panels may also be interfered by external factors such as bird droppings, shadow occlusion, and external damage. The above-mentioned interferences will all cause the power generation capacity of the photovoltaic panels to decline, thereby affecting the power generation efficiency of the photovoltaic power generation system. In severe cases, the photovoltaic panels may be damaged and completely lose their power generation capacity.

[0003] In the related art, a scheme of a photovoltaic string current-voltage curve diagnosis system is adopted, which can realize the rapid current-voltage scanning and fault diagnosis of a photovoltaic string, greatly reducing the operation and maintenance labor cost and being favored by the market. However, in the process of fault diagnosis of a photovoltaic string through the current-voltage curve, multiple characteristic values need to be recorded, and comprehensive analysis is performed based on multiple characteristic values to achieve the fault detection of the photovoltaic string, which brings problems such as a long fault diagnosis cycle and a complex fault diagnosis process, further reducing the diagnosis efficiency of the photovoltaic system. Summary of the Invention

[0004] The embodiments of the present application provide a fault detection method, a control device, a photovoltaic system and a storage medium, which shorten the diagnosis cycle of a photovoltaic string and simplify the diagnosis process of the photovoltaic string.

[0005] In a first aspect, the embodiments of the present application provide a fault detection method for a photovoltaic string, including:

[0006] Detecting the photovoltaic string to obtain detection parameters, and determining the fill factor of the photovoltaic string according to the detection parameters;

[0007] When the fill factor is greater than or equal to a first threshold, it is determined that the photovoltaic string does not have an aging fault or an occlusion fault, where the first threshold is determined according to the initial fill factor of the photovoltaic string in a fault-free state;

[0008] When the fill factor is less than the first threshold, a first resistance value and a second resistance value are determined according to the detection parameters, and the fault type of the photovoltaic string is determined according to the first resistance value and the second resistance value, where the first resistance value is used to represent the equivalent series resistance value when the current of the photovoltaic string approaches zero, and the second resistance value is used to represent the equivalent parallel resistance value when the voltage of the photovoltaic string approaches zero.

[0009] The fault detection method according to the embodiment of the first aspect of the present application has at least the following beneficial effects: detecting a photovoltaic string to obtain detection parameters, and determining the fill factor of the photovoltaic string according to the detection parameters. First, use the fill factor for fault diagnosis, reduce the amount of fault diagnosis calculation, improve the fault detection efficiency, and can quickly determine whether there is an aging fault or an occlusion fault. When the fill factor is greater than or equal to the first threshold, it is determined that the photovoltaic string does not have an aging fault or an occlusion fault, and the subsequent detection process for aging faults or occlusion faults does not need to be carried out, and the detection process for aging faults or occlusion faults is directly ended, further shortening the fault diagnosis cycle of the photovoltaic string; when the fill factor is less than the first threshold, it is determined that there is an aging fault or an occlusion fault, and the equivalent series resistance value when the current of the photovoltaic string approaches zero, that is, the first resistance value, is determined, and the equivalent parallel resistance value when the voltage of the photovoltaic string approaches zero, that is, the second resistance value, is determined. The specific fault type of the photovoltaic string is determined according to the first resistance value and the second resistance value, and it is judged whether the photovoltaic string is an aging fault or an occlusion fault, so as to accurately determine the fault type. The embodiment of the present application helps to quickly determine the fault type through the above judgment process, simplifies the diagnosis process of the photovoltaic string as a whole, thereby reducing the maintenance cost and time, and improving the diagnosis efficiency of the photovoltaic system.

[0010] In some embodiments of the present application, the detection parameters include an open-circuit voltage value, a short-circuit current value, a maximum power voltage, and a maximum power current; the fill factor is determined according to the open-circuit voltage value, the short-circuit current value, the maximum power voltage, and the maximum power current.

[0011] In some embodiments of the present application, the method further includes:

[0012] When the open-circuit voltage value is less than the second threshold, it is determined that the fault type of the photovoltaic string is a short-circuit fault, where the second threshold is determined according to the initial open-circuit voltage value of the photovoltaic string in a fault-free state;

[0013] When the short-circuit current value is less than the third threshold, it is determined that the fault type of the photovoltaic string is an open-circuit fault, where the third threshold is determined according to the initial short-circuit current value of the photovoltaic string in a fault-free state.

[0014] In some embodiments of the present application, determining the fault type of the photovoltaic string according to the first resistance value and the second resistance value includes:

[0015] When the first resistance value is greater than the fourth threshold and / or the second resistance value is less than the fifth threshold, it is determined that the fault type of the photovoltaic string is an aging fault;

[0016] When the first resistance value is less than or equal to the fourth threshold and / or the second resistance value is greater than or equal to the fifth threshold, it is determined that the fault type of the photovoltaic string is an occlusion fault.

[0017] In some embodiments of the present application, the fourth threshold and the fifth threshold are obtained by the following steps:

[0018] According to the equivalent series resistance value when the current of the photovoltaic string approaches zero in the fault-free state, a third resistance value is obtained, and according to the equivalent parallel resistance value when the voltage of the photovoltaic string approaches zero in the fault-free state, a fourth resistance value is obtained;

[0019] According to the third resistance value and the number of photovoltaic panels of the photovoltaic string, the fourth threshold is determined, and according to the fourth resistance value, the fifth threshold is determined.

[0020] In some embodiments of the present application, the detecting the photovoltaic string to obtain detection parameters includes:

[0021] Detecting the photovoltaic string to obtain the current-voltage curve of the photovoltaic string;

[0022] According to the current-voltage curve, the detection parameters of the photovoltaic string are determined.

[0023] In some embodiments of the present application, the determining the first resistance value and the second resistance value according to the detection parameters includes:

[0024] Deriving the current-voltage curve and determining the first resistance value according to the derivation result where the current approaches zero, and determining the second resistance value according to the derivation result where the voltage approaches zero.

[0025] In some embodiments of the present application, the method further includes:

[0026] After the photovoltaic string is powered on for the first time, detecting the photovoltaic string to obtain the initial current-voltage curve of the photovoltaic string;

[0027] According to the initial current-voltage curve, the initial fill factor, the initial open-circuit voltage value, and the initial short-circuit current value are determined.

[0028] In a second aspect, an embodiment of the present application further provides a control device, including: a memory, a processor, and a computer program stored on the memory and executable on the processor, and when the processor executes the computer program, the fault detection method described in the first aspect is implemented.

[0029] In a third aspect, an embodiment of the present application further provides a photovoltaic system, including a photovoltaic string and the control device described in the second aspect.

[0030] Fourthly, an embodiment of the present application further provides a computer-readable storage medium storing computer-executable instructions for causing a computer to execute the fault detection method as described in the first aspect.

[0031] Other features and advantages of the present application will be described in the following specification, and in part will be obvious from the specification, or will be understood by implementing the present application. The objectives and other advantages of the present application can be realized and obtained by the structures particularly pointed out in the specification and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The drawings are used to provide a further understanding of the technical solutions of the present application, and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solutions of the present application, and do not constitute a limitation to the technical solutions of the present application.

[0033] Figure 1 is a flowchart of a fault detection method provided by an embodiment of the present application;

[0034] Figure 2 is a flowchart of a fault detection method provided by another embodiment of the present application;

[0035] Figure 3 is Figure 1 a flowchart of the specific method for step S103 in

[0036] Figure 4 is a flowchart of determining the fourth threshold and the fifth threshold in an embodiment of the present application;

[0037] Figure 5 is Figure 1 a flowchart of the specific method for step S101 in

[0038] Figure 6 is Figure 1 another flowchart of the specific method for step S103 in

[0039] Figure 7 is a flowchart of a fault detection method provided by another embodiment of the present application;

[0040] Figure 8 is a schematic diagram of a current-voltage curve provided by an example of the present application;

[0041] Figure 9 is a schematic diagram of a control device provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] In order to make the objectives, technical solutions and advantages of the present application more clearly understood, 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 reordered or adjusted in an obvious manner by 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 necessary sequences, unless it is stated that a certain sequence must be followed.

[0043] In the description of the present application, the meaning of "a number of" is one or more, the meaning of "a plurality of" is more than two, and understandings such as "greater than", "less than", "exceeding", etc. do not include the recited number, and understandings such as "above", "below", "within", etc. include the recited number. If the first and the second are described, 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 relationship of the indicated technical features.

[0044] The serial numbers assigned to the components herein, such as "the first", "the second", etc., are only used to distinguish the described objects and do not have any sequential or technical meaning. The "connection" and "coupling" mentioned in the present application, unless otherwise specified, both include direct and indirect connection (coupling).

[0045] In the description of the present application, unless otherwise clearly defined, words such as "installation", "connection", etc. should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above words in the present application in combination with the specific content of the technical solution.

[0046] With the rapid development of photovoltaic technology, photovoltaic power generation has been widely promoted. As an important part of a photovoltaic power generation system, photovoltaic power generation needs to be carried out in an outdoor environment. The photovoltaic panels are placed outdoors, exposed to long-term sunlight, rain, and dust accumulation, which will accelerate the aging of the photovoltaic panels. Moreover, the photovoltaic panels may also be interfered by external factors such as bird droppings, shadow occlusion, and external damage. The above-mentioned interferences will all cause the power generation capacity of the photovoltaic panels to decline, thereby affecting the power generation efficiency of the photovoltaic power generation system. In severe cases, it will even cause the photovoltaic panels to be damaged and completely lose their power generation capacity.

[0047] In the related art, the solution of the photovoltaic string current-voltage curve diagnosis system can realize the rapid current-voltage scanning and fault diagnosis of the photovoltaic string, greatly reducing the operation and maintenance labor cost and being favored by the market. However, in the process of fault diagnosis of the photovoltaic string through the current-voltage curve, it is necessary to record multiple characteristic values and perform comprehensive analysis based on multiple characteristic values to realize the fault detection of the photovoltaic string, which brings the problems of long fault diagnosis cycle and complex fault diagnosis process, and further reduces the diagnosis efficiency of the photovoltaic system.

[0048] Based on the above situation, the embodiments of the present application provide a fault detection method, a control device, a photovoltaic system and a storage medium: detecting a photovoltaic string to obtain detection parameters, and determining the fill factor of the photovoltaic string according to the detection parameters. First, use the fill factor for fault diagnosis to reduce the amount of fault diagnosis calculation and improve the fault detection efficiency. It can quickly determine whether there is an aging fault or an occlusion fault. When the fill factor is greater than or equal to the first threshold, it is determined that the photovoltaic string does not have an aging fault or an occlusion fault, and there is no need to perform the detection process of the aging fault or the occlusion fault subsequently, and the detection process of the aging fault or the occlusion fault is directly ended, further shortening the fault diagnosis cycle of the photovoltaic string; when the fill factor is less than the first threshold, it is determined that there is an aging fault or an occlusion fault, and the equivalent series resistance value when the current of the photovoltaic string approaches zero, that is, the first resistance value, is determined, and the equivalent parallel resistance value when the voltage of the photovoltaic string approaches zero, that is, the second resistance value, is determined. According to the first resistance value and the second resistance value, the specific fault type of the photovoltaic string is determined, and it is judged whether the photovoltaic string is an aging fault or an occlusion fault, realizing the accurate determination of the fault category. In the embodiments of the present application, the above judgment process helps to quickly determine the fault type, simplifies the diagnosis process of the photovoltaic string as a whole, thereby reducing the maintenance cost and time, and improving the diagnosis efficiency of the photovoltaic system.

[0049] The following further elaborates on the embodiments of the present application in conjunction with the drawings.

[0050] In some embodiments, a photovoltaic string refers to connecting multiple photovoltaic panels together in a certain way to form a string of panels. This can increase the voltage and current output of the entire photovoltaic system, thereby more effectively converting solar energy into electrical energy.

[0051] Among them, a photovoltaic string usually consists of multiple photovoltaic panels, connecting wires and connectors. The photovoltaic panels are connected together through connecting wires and connectors to form a series or parallel circuit. Through reasonable string design, the efficiency and performance of the photovoltaic system can be maximized, making photovoltaic power generation a reliable and clean energy option.

[0052] As Figure 1 shown, Figure 1It is a flowchart of a fault detection method for a photovoltaic string provided by an embodiment of the present application. The fault detection method of the embodiment of the present application includes, but is not limited to, steps S101 to S103.

[0053] Step S101: Detect the photovoltaic string to obtain detection parameters, and determine the fill factor of the photovoltaic string according to the detection parameters;

[0054] In some embodiments, detecting the photovoltaic string to obtain detection parameters can obtain the detailed working characteristics of the photovoltaic string, and determine the fill factor of the photovoltaic string according to the detection parameters, so as to facilitate subsequent fault diagnosis of the photovoltaic string through the fill factor and improve the fault diagnosis efficiency of the photovoltaic string.

[0055] It should be noted that the fill factor is one of the important indicators of the photovoltaic string. It can be used to evaluate the working condition of the photovoltaic string and reflects the power conversion efficiency of the photovoltaic string under the actual working state. Among them, the larger the fill factor, the higher the circuit efficiency of the photovoltaic string, and more power can be output. The decrease of the fill factor will lead to an increase in the circuit loss of the photovoltaic string, thereby reducing the energy conversion efficiency of the photovoltaic system. Among them, the material, ambient temperature, and light intensity of the photovoltaic string have a greater impact on the fill factor. For example, as the temperature rises, the internal resistance of the photovoltaic device increases, thereby reducing the output of current and voltage. Therefore, as the temperature rises, the fill factor will decrease. Therefore, by monitoring the change of the fill factor, faults in the photovoltaic string can be detected in time, the problems existing in the photovoltaic string can be determined more quickly, and the overall process of fault diagnosis can be further simplified.

[0056] It can be understood that using the fill factor for fault detection can improve the maintenance efficiency of the photovoltaic system. Compared with the traditional inspection method, through fill factor monitoring, the problems existing in the photovoltaic string can be determined more quickly and accurately, which helps to quickly locate and solve the faults, thereby reducing the maintenance cost and time.

[0057] In some embodiments, the detection parameters include the open-circuit voltage value, short-circuit current value, maximum power voltage, and maximum power current; the fill factor is determined according to the open-circuit voltage value, short-circuit current value, maximum power voltage, and maximum power current. Among them, the open-circuit voltage value is the voltage value when the photovoltaic string is open-circuited, the short-circuit current value is the current value when the photovoltaic string is short-circuited, the maximum power voltage is the voltage value when the photovoltaic string operates at the maximum power point, and the maximum power current is the current value when the photovoltaic string operates at the maximum power point.

[0058] It should be noted that the fill factor in this embodiment is obtained by comparing the product of the maximum power voltage and the maximum power current with the product of the open-circuit voltage value and the short-circuit current value, as shown below:

[0059] FF = Vmp * Imp / (Voc * Isc);

[0060] Among them, FF is the fill factor, Vmp is the maximum power voltage, Imp is the maximum power current, Voc is the open - circuit voltage value, and Isc is the short - circuit current value.

[0061] Step S102: When the fill factor is greater than or equal to the first threshold, it is determined that the photovoltaic string does not have an aging fault or an occlusion fault;

[0062] It should be noted that the first threshold is determined according to the initial fill factor of the photovoltaic string in the fault - free state. Among them, the determination process of the initial fill factor is similar to the determination process of the fill factor, and both use the initial open - circuit voltage value, initial short - circuit current value, initial maximum power voltage, and initial maximum power current of the photovoltaic string in the fault - free state for determination. This embodiment will not elaborate here.

[0063] In some embodiments, when the fill factor is greater than or equal to the first threshold, it can be directly determined that the photovoltaic string has an aging fault or an occlusion fault, and there is no need to perform fault diagnosis operations of the same type (aging fault and occlusion fault). For example, in this embodiment, the aging fault of the photovoltaic string is detected through the fill factor. When the fill factor is greater than or equal to the first threshold, it is determined that the photovoltaic string does not have an aging fault, and subsequent aging fault judgment of the photovoltaic string through other parameters is not required; or, in this embodiment, whether the photovoltaic string is occluded is detected through the fill factor. When the fill factor is greater than or equal to the first threshold, it is determined that the photovoltaic string does not have an occlusion fault, and subsequent occlusion judgment of the photovoltaic string through other parameters is not required, which can shorten the fault diagnosis cycle of the photovoltaic string as a whole and further simplify the diagnosis process of the photovoltaic string.

[0064] It can be understood that the first threshold in this embodiment can be within the range of 0.05 - 0.2. For example, the first threshold is 0.08, 0.1, 1.5, etc. This embodiment does not make specific limitations.

[0065] Step S103: When the fill factor is less than the first threshold, determine the first resistance value and the second resistance value according to the detection parameters, and determine the fault type of the photovoltaic string according to the first resistance value and the second resistance value.

[0066] It should be noted that the first resistance value is used to characterize the equivalent series resistance value when the current of the photovoltaic string approaches zero, and the second resistance value is used to characterize the equivalent parallel resistance value when the voltage of the photovoltaic string approaches zero.

[0067] In some embodiments, when the fill factor is less than the first threshold, it indicates that there is an aging fault or an occlusion fault in the photovoltaic string, but the specific fault type is not determined. Then, it is necessary to determine the first resistance value and the second resistance value according to the detection parameters, and then make a further judgment based on the first resistance value and the second resistance value, so as to improve the accuracy of the fault diagnosis of the photovoltaic string, and determine the fault type of the photovoltaic string according to the first resistance and the second resistance value, which helps to quickly determine the fault type, thereby reducing the maintenance cost and time, improving the diagnosis efficiency of the photovoltaic system, and at the same time facilitating the formulation of a more accurate maintenance plan in the future, improving the pertinence and effectiveness of maintenance.

[0068] It can be understood that in this embodiment, the photovoltaic string is initially diagnosed for faults according to the fill factor. After it is determined that there is an aging fault or an occlusion fault according to the fill factor, the specific fault type is determined according to the first resistance value and the second resistance value, that is, the first resistance value and the second resistance value are judged on the basis of the fill factor, without waiting for other parameters to be comprehensively analyzed during the fault diagnosis process. Instead, after the initial diagnosis according to the fill factor, other parameters are used for analysis, so as to shorten the diagnosis cycle of the photovoltaic string, simplify the diagnosis process of the photovoltaic string as a whole, and this embodiment can directly judge whether there is a fault according to the self-characteristics of the photovoltaic string, without the need to additionally increase equipment, saving the input cost, and the analysis process is simple and reliable.

[0069] It should be noted that the fault types of the photovoltaic string include but are not limited to shadow occlusion faults, aging faults, short-circuit faults, open-circuit faults, and so on.

[0070] Refer to Figure 2 , Figure 2 is a flowchart of a fault detection method provided by another embodiment of the present application. It includes but is not limited to the following steps S201 to step S202.

[0071] Step S201: When the open-circuit voltage value is less than the second threshold, determine that the fault type of the photovoltaic string is a short-circuit fault;

[0072] It should be noted that the second threshold is determined according to the initial open-circuit voltage value of the photovoltaic string in the fault-free state.

[0073] In some embodiments, in this embodiment, the open-circuit voltage value is used to judge whether there is a short-circuit fault in the photovoltaic string. When the open-circuit voltage value is less than the second threshold, it is determined that the fault type of the photovoltaic string is a short-circuit fault, realizing the judgment of the short-circuit fault of the photovoltaic string, and avoiding problems such as equipment overload, wire heating, and battery component damage.

[0074] It should be noted that when partial short - circuit occurs in the photovoltaic string, its voltage will decrease significantly. Therefore, in this embodiment, the open - circuit voltage value is used to determine whether there is a short - circuit fault in the photovoltaic string. When the open - circuit voltage value is greater than or equal to the second threshold, there is no such short - circuit fault.

[0075] It can be understood that the second threshold can be set by the user according to their needs. For example, if the initial open - circuit voltage value is 20V, the second threshold can be set to 30% of the initial open - circuit voltage value, that is, 6V; or the second threshold can be set to 70% of the initial open - circuit voltage value, that is, 14V, etc. This embodiment does not make specific limitations.

[0076] Step S202: When the short - circuit current value is less than the third threshold, determine that the fault type of the photovoltaic string is an open - circuit fault.

[0077] It should be noted that the third threshold is determined according to the initial short - circuit current value of the photovoltaic string in the fault - free state.

[0078] In some embodiments, in this embodiment, the short - circuit current value is used to determine whether there is an open - circuit fault in the photovoltaic string. When the short - circuit current value is less than the third threshold, it is determined that the fault type of the photovoltaic string is an open - circuit fault, realizing the judgment of the open - circuit fault of the photovoltaic string and improving the safety of the photovoltaic string.

[0079] It should be noted that when partial open - circuit occurs in the photovoltaic string, its current will decrease significantly. Therefore, in this embodiment, the short - circuit current value is used to determine whether there is an open - circuit fault in the photovoltaic string. When the short - circuit current value is greater than or equal to the third threshold, there is no such open - circuit fault.

[0080] It can be understood that the third threshold can be set by the user according to their needs. For example, if the initial short - circuit current value is 20A, the third threshold can be set to 30% of the initial open - circuit voltage value, that is, 6A; or the third threshold can be set to 70% of the initial open - circuit voltage value, that is, 14A, etc. This embodiment does not make specific limitations.

[0081] It is worth noting that the initial open - circuit voltage value and the initial short - circuit current value are also related to the environmental information where the photovoltaic string is located. Among them, the environmental information includes but is not limited to temperature information, longitude information, latitude information, light intensity, etc. of the environment where the photovoltaic string is located. This embodiment does not make specific limitations.

[0082] In some embodiments, the fault detection method for the photovoltaic string of this embodiment further includes repairing the fault. During the process of repairing the fault, first, determine the specific type of the fault. When the fault type is a short - circuit fault or an open - circuit fault, adjust the environmental information of the photovoltaic string. For example, increase or decrease the environmental temperature of the photovoltaic string, increase the light intensity, decrease the light intensity, etc. By adjusting the environmental information, further adjust the open - circuit voltage value and the short - circuit current value, so as to adjust the voltage value and the current value of the photovoltaic string, realize the correction of the short - circuit fault and the open - circuit fault, improve the safety of the photovoltaic string, protect the safety of the photovoltaic system, and further improve the performance of the photovoltaic string; when the fault type is an occlusion fault, a surface cleaning component can be set on the photovoltaic string, and control the surface cleaning component to clean the surface of the photovoltaic string, so as to eliminate the occluder on the surface of the photovoltaic string; when the fault type is an aging fault, a prompting device can be set to notify the maintenance personnel to perform maintenance or replacement, so as to realize the comprehensive maintenance of the photovoltaic system and extend the service life of the photovoltaic system.

[0083] It should be noted that after repairing the fault, continue to detect the detection parameters of the photovoltaic string in real - time to realize the real - time monitoring of the photovoltaic string.

[0084] Refer to Figure 3 , Figure 3 is Figure 1 The flowchart of the specific method for step S103 in

[0085] Step S301: When the first resistance value is greater than the fourth threshold and / or the second resistance value is less than the fifth threshold, determine that the fault type of the photovoltaic string is an aging fault;

[0086] In some embodiments, during the process of determining the fault type of the photovoltaic string according to the first resistance value and the second resistance value, when the first resistance value is greater than the fourth threshold, it indicates that the equivalent series resistance value when the current of the current photovoltaic string approaches zero is greater than the equivalent series resistance value when the current of the photovoltaic string is in a fault - free state approaches zero, that is, the slope of the current photovoltaic string when the current approaches zero is greater than the slope in the fault - free state. When the second resistance value is less than the fifth threshold, it indicates that the equivalent parallel resistance value when the voltage of the current photovoltaic string approaches zero is less than the equivalent parallel resistance value when the voltage of the photovoltaic string is in a fault - free state approaches zero, that is, the slope of the current photovoltaic string when the voltage approaches zero is less than the slope in the fault - free state. Then, at this time, determine that the fault type of the photovoltaic string is an aging fault, so as to realize the accurate judgment of the aging fault.

[0087] It should be noted that in this embodiment, if either the first resistance value is greater than the fourth threshold or the second resistance value is less than the fifth threshold, it can be considered that the photovoltaic string has an aging fault.

[0088] Step S302: When the first resistance value is less than or equal to the fourth threshold and / or the second resistance value is greater than or equal to the fifth threshold, determine that the fault type of the photovoltaic string is an occlusion fault.

[0089] In some embodiments, when the first resistance value is less than or equal to the fourth threshold, it indicates that the equivalent series resistance value when the current of the current photovoltaic string approaches zero is less than or equal to the equivalent series resistance value when the current of the photovoltaic string is in a fault-free state, that is, the slope of the current photovoltaic string when the current approaches zero is less than or equal to the slope in the fault-free state. When the second resistance value is greater than or equal to the fifth threshold, it indicates that the equivalent parallel resistance value when the voltage of the current photovoltaic string approaches zero is less than or equal to the equivalent parallel resistance value when the voltage of the photovoltaic string is in a fault-free state, that is, the slope of the current photovoltaic string when the voltage approaches zero is greater than or equal to the slope in the fault-free state. At this time, determine that the fault type of the photovoltaic string is an occlusion fault, thereby realizing an accurate judgment of the occlusion fault.

[0090] It should be noted that when the photovoltaic string is shaded, there will be a point where the current-voltage curve suddenly drops. As the shaded area increases, the drop becomes more obvious; when the photovoltaic string has an aging fault, its maximum power will decrease, that is, near the vertical axis (current value), the slope of the curve of the aging fault is greater than the slope of the curve of the shaded occlusion, and at the same time, near the horizontal axis (voltage value), the slope of the curve of the aging fault is less than the slope of the curve of the shaded occlusion.

[0091] Refer to Figure 4 , Figure 4 is a flowchart for determining the fourth threshold and the fifth threshold provided by another embodiment of the present application. It includes but is not limited to steps S401 to S402.

[0092] Step S401: Obtain a third resistance value according to the equivalent series resistance value when the current of the photovoltaic string approaches zero in a fault-free state, and determine the equivalent parallel resistance value when the voltage of the photovoltaic string approaches zero in a fault-free state to obtain a fourth resistance value;

[0093] In some embodiments, a third resistance value is obtained based on the equivalent series resistance value when the current of the photovoltaic string approaches zero in a fault-free state, that is, the equivalent series resistance value in the initial current-voltage curve of the photovoltaic module, and an equivalent parallel resistance value is determined when the voltage of the photovoltaic string approaches zero in a fault-free state to obtain a fourth resistance value, that is, the equivalent parallel resistance value in the initial current-voltage curve of the photovoltaic module, which facilitates judging the resistance change of the photovoltaic string, and further judging whether the photovoltaic string has a shading fault or an aging fault.

[0094] It should be noted that the calculation process of the third resistance value is the same as that of the first resistance value, and the calculation process of the fourth resistance value is the same as that of the second resistance value, which will not be elaborated in this embodiment.

[0095] Step S402: Determine a fourth threshold according to the third resistance value and the number of photovoltaic panels in the photovoltaic string, and determine a fifth threshold according to the fourth resistance value.

[0096] In some embodiments, a fourth threshold is determined according to the third resistance value and the number of photovoltaic panels in the photovoltaic string. Among them, the fourth threshold can be set between 0.5k and 5k, where k is the number of photovoltaic panels in the photovoltaic string, and the fifth threshold can be between 50 and 500, which is convenient for judging whether the first resistance value or the second resistance value has a significant increase or decrease.

[0097] It can be understood that taking the number of photovoltaic panels in the photovoltaic string as 3 as an example, the fourth threshold can be set between 1.5 and 15 at this time. For example, 3, 5, 9, etc.; the fifth threshold can be 60, 70, 80, etc., and this embodiment does not make specific limitations.

[0098] Refer to Figure 5 , Figure 5 is Figure 1 the flowchart of the specific method for step S101 in

[0099] Step S501: Detect the photovoltaic string to obtain the current-voltage curve of the photovoltaic string;

[0100] Step S502: Determine the detection parameters of the photovoltaic string according to the current-voltage curve.

[0101] In steps S501 to S502 of some embodiments, during the process of detecting a photovoltaic string to obtain detection parameters, the change in the voltage output by the photovoltaic string is detected, and the photovoltaic voltage and photovoltaic current during the voltage change process are recorded to obtain the current-voltage curve of the photovoltaic string. Then, the detection parameters of the photovoltaic string are determined according to the current-voltage curve, so that various parameters of the photovoltaic string in the current-voltage curve can be obtained. Through the current-voltage curve, the detailed working characteristics of the photovoltaic string can be obtained, and whether there is a fault in the photovoltaic string can be intuitively identified.

[0102] It should be noted that in this embodiment, the output voltage of the photovoltaic string can be controlled to change gradually through a photovoltaic inverter, and each photovoltaic string is scanned through the inverter to obtain the current-voltage curve of each photovoltaic string. Among them, the abscissa of the current-voltage curve is voltage, with the unit of V, and the ordinate is current, with the unit of A.

[0103] It is worth noting that when the photovoltaic string is shaded, there will be a point where the curve on the current-voltage curve suddenly drops. As the shaded area increases, the drop becomes more obvious; when the photovoltaic string has an aging fault, its maximum power will decrease. Therefore, the area enclosed by the curve of the photovoltaic string with an aging fault is smaller than the area enclosed by the curve in the normal state, and the slope of the curve with an aging fault close to the ordinate is greater than the slope of the curve in the normal state close to the ordinate, and the slope close to the abscissa is smaller than the slope of the curve in the normal state close to the abscissa. Similarly, the slope of the curve with an aging fault close to the ordinate is greater than the slope of the curve with shading close to the ordinate, and the slope close to the abscissa is smaller than the slope of the curve with shading close to the abscissa; when the photovoltaic string has an open-circuit fault, its current will decrease significantly; when the photovoltaic string has a short-circuit fault, its voltage will decrease significantly.

[0104] Refer to Figure 6 , Figure 6 is Figure 1 Another flowchart of the specific method for step S103 in

[0105] Step S601: Take the derivative of the current-voltage curve and determine the first resistance value according to the derivative result at the point where the current approaches zero, and determine the second resistance value according to the derivative result at the point where the voltage approaches zero.

[0106] In some embodiments, during the process of determining the first resistance value and the second resistance value according to the detection parameters, take the derivative of the current-voltage curve and determine the first resistance value according to the derivative result at the point where the current approaches zero, so as to obtain the equivalent series resistance value when the current of the photovoltaic string approaches zero, and determine the second resistance value according to the derivative result at the point where the voltage approaches zero, so as to obtain the equivalent parallel resistance value when the voltage of the photovoltaic string approaches zero.

[0107] It should be noted that the first resistance value is obtained through the following formula:

[0108]

[0109] That is, the first resistance value is obtained by calculating the slope of the current-voltage curve near V->Voc and I->0, where Voc is the open-circuit voltage value.

[0110] The second resistance value is obtained through the following formula:

[0111]

[0112] That is, the second resistance value is obtained by calculating the slope of the current-voltage curve near V->0 and I->Isc, where Isc is the short-circuit current value.

[0113] It can be understood that the first resistance value can be represented by the slope where the current approaches zero in the current-voltage curve, and the second resistance value can be represented by the slope where the voltage approaches zero in the current-voltage curve.

[0114] Refer to Figure 7 , Figure 7 is a flowchart of a fault detection method provided by another embodiment of the present application. It includes but is not limited to the following steps S701 to step S702.

[0115] Step S701: After the photovoltaic string is powered on for the first time, detect the photovoltaic string to obtain the initial current-voltage curve of the photovoltaic string;

[0116] Step S702: Determine the initial fill factor, the initial open-circuit voltage value, and the initial short-circuit current value according to the initial current-voltage curve.

[0117] In steps S701 to S702 of some embodiments, during initial installation, it is necessary to obtain the initial current-voltage curve of the photovoltaic string, that is, after the photovoltaic string is powered on for the first time, detect the photovoltaic string to obtain the initial current-voltage curve of the photovoltaic string, which is convenient for subsequent diagnosis of whether the photovoltaic string has a fault. Among them, the initial current-voltage curve is the current-voltage curve corresponding to the photovoltaic module in a fault-free state. Then, determine the initial fill factor, the initial open-circuit voltage value, and the initial short-circuit current value according to the initial current-voltage curve, which is convenient for providing a basis for the subsequent diagnosis of the photovoltaic string and can accurately determine whether the photovoltaic string has a fault.

[0118] To more clearly and understandably explain the above-mentioned fault detection method for the photovoltaic string, the following will be described with specific examples.

[0119] Example 1:

[0120] Refer to Figure 8, Figure 8 It is a schematic diagram of the current-voltage curve provided by an example of this application.

[0121] Among them, Curve 1 is the I-V curve of the photovoltaic string under normal conditions, Curve 2 is the I-V curve of the photovoltaic string with an occlusion fault, Curve 3 is the I-V curve of the photovoltaic string with an aging fault, Curve 4 is the I-V curve of the photovoltaic string with a short-circuit fault, and Curve 5 is the I-V curve of the photovoltaic string with an open-circuit fault.

[0122] First, at the initial installation, the initial I-V curve of the photovoltaic string needs to be obtained, which can be obtained from the photovoltaic panel manufacturer or measured on-site. Specifically, through the control of the photovoltaic inverter, the photovoltaic output voltage is gradually changed, and the photovoltaic voltage and current during the process are recorded to obtain the I-V curve of the photovoltaic string.

[0123] The following parameters are extracted from the above curves: Voc open-circuit voltage, that is, the voltage when the photovoltaic string is open-circuited; Isc short-circuit current, that is, the current when the photovoltaic string is short-circuited; Vmp maximum power voltage, that is, the voltage when the photovoltaic string operates at the maximum power point; Imp maximum power current, that is, the current when the photovoltaic string operates at the maximum power point; FF fill factor, FF = Vmp * Imp / (Voc * Isc); Rs series resistance; Rsh parallel resistance.

[0124] The above series resistance Rs can be approximately calculated as follows:

[0125]

[0126] That is, the slope of the I-V curve near V->Voc and I->0.

[0127] The above parallel resistance Rsh can be approximately calculated as follows:

[0128]

[0129] That is, the slope of the I-V curve near V->0 and I->Isc.

[0130] Then, during the operation, the I-V curve of the photovoltaic string is obtained regularly. Specifically, through the control of the photovoltaic inverter, the photovoltaic output voltage is gradually changed, and the photovoltaic voltage and current during the process are recorded to obtain the I-V curve of the photovoltaic string.

[0131] Similarly, the following parameters are extracted from the above curves: Voc, Isc, Vmp, Imp, FF, Rs, Rsh, and based on this, fault diagnosis of the photovoltaic string is performed.

[0132] Since the four parameters Voc, Isc, Vmp, and Imp among the above seven parameters are greatly affected by external factors such as light intensity and ambient temperature, the three parameters FF, Rs, and Rsh are preferably used for fault diagnosis.

[0133] First, judge the fill factor FF of the parameter. If the current FF is significantly smaller than the initial FF, it is judged that there is partial shading or component aging fault in the photovoltaic string. If there is no significant decrease, the next step is directly skipped. The significant decrease means that the difference is greater than the threshold, and the threshold can be taken as 0.05 - 0.2.

[0134] On this basis, judge the series resistance Rs and shunt resistance Rsh of the parameter. If the current Rs is significantly larger than the initial Rs, or the current Rsh is significantly smaller than the initial Rsh, it is judged that there is component aging fault in the photovoltaic string, otherwise it is judged that there is partial shading problem. The significant increase of Rs means that the difference is greater than the threshold, and the threshold can be taken as 0.5*k - 5*k, where k refers to the number of series-connected photovoltaic panels in the string. The significant decrease of Rsh means that the difference is greater than the threshold, and the threshold can be taken as 50 - 500.

[0135] Furthermore, the open-circuit voltage Voc of the parameter can be used to judge whether there is partial short-circuit fault. If the current Voc is significantly smaller than the initial Voc, it is judged that there is partial short-circuit fault, otherwise there is no such fault. The short-circuit current Isc of the parameter can be used to judge whether there is partial open-circuit fault. If the current Isc is significantly smaller than the initial Isc, it is judged that there is partial open-circuit fault, otherwise there is no such fault. Since Voc and Isc are greatly affected by external factors such as light intensity and ambient temperature, the above judgments can be corrected by integrating information such as the current weather conditions, temperature, and installation latitude to improve the accuracy.

[0136] It should be noted that judging whether there is partial short-circuit fault according to the open-circuit voltage Voc of the parameter and judging whether there is open-circuit fault according to the short-circuit current can occur after judging the fill factor, series resistance, and shunt resistance, or can occur after judging the fill factor, series resistance, and shunt resistance, or can occur between judging the fill factor, series resistance, and shunt resistance. This embodiment does not make specific limitations.

[0137] In summary, this solution can determine common problems such as shadow occlusion, aging, short circuit, and open circuit of photovoltaic panels through the photovoltaic inverter itself, without the need to add additional equipment, saving cost investment. First, the fill factor is used for fault diagnosis, reducing the amount of fault diagnosis calculation and improving the fault detection efficiency. It can quickly determine whether there is an aging fault or occlusion fault. When the fill factor does not decrease significantly, it is determined that the photovoltaic string does not have an aging fault or occlusion fault, and there is no need to perform the same type of fault detection process subsequently, directly ending the detection process for aging faults or occlusion faults, shortening the fault diagnosis cycle of the photovoltaic string and simplifying the diagnosis process of the photovoltaic string. When the fill factor decreases significantly, the subsequent fault detection process is carried out according to the series resistance Rs and the parallel resistance Rsh, improving the accuracy of subsequent detection. Finally, the fault type of the photovoltaic string is determined according to the series resistance Rs and the parallel resistance Rsh, which helps to quickly determine the fault type, thereby reducing the maintenance cost and time and improving the diagnosis efficiency of the photovoltaic system.

[0138] As Figure 9 shown, Figure 9 is a schematic diagram of a control device provided by an embodiment of the present application.

[0139] The control device 1000 of the embodiment of the present application includes one or more processors 1001 and a memory 1002. Figure 9 Here, one processor 1001 and one memory 1002 are taken as examples.

[0140] The processor 1001 and the memory 1002 can be connected through a bus or other means. Figure 9 Here, connection through a bus is taken as an example.

[0141] The memory 1002, as a non-transitory computer-readable storage medium, can be used to store non-transitory software programs and non-transitory computer-executable programs. In addition, the memory 1002 can include high-speed random access memory, and can also include non-transitory memory, such as at least one magnetic disk storage device, a flash memory device, or other non-transitory solid-state storage devices. In some embodiments, the memory 1002 may optionally include a memory 1002 remotely set relative to the processor 1001, and these remote memories can be connected to the control device 1000 through a network. Examples of the above network include but are not limited to the Internet, an enterprise intranet, a local area network, a mobile communication network, and combinations thereof.

[0142] Those skilled in the art can understand that Figure 9 the device structure shown in

[0143] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, that is, they may be located in one place or distributed to multiple network nodes. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution in this embodiment.

[0144] As a non-transitory computer-readable storage medium, the memory can be used to store non-transitory software programs and non-transitory computer-executable programs. In addition, the memory may include high-speed random access memory, and may also include non-transitory memory, such as at least one magnetic disk storage device, a flash memory device, or other non-transitory solid-state storage devices. In some embodiments, the memory may optionally include a memory remotely disposed relative to the processor, and these remote memories can be connected to the processor through a network. Examples of the above networks include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0145] The non-transitory software programs and instructions required to implement the fault detection method of the above embodiments are stored in the memory. When executed by the processor, they execute the above embodiments.

[0146] It should be noted that this embodiment also provides a photovoltaic system, which includes a photovoltaic string and a control device as Figure 8 shown. Since the photovoltaic system of this application embodiment has the control device of the above embodiment, and the control device of the above embodiment can execute the fault detection method of the above embodiment, therefore, the specific implementation manners and technical effects of the photovoltaic system of this application embodiment can refer to the specific implementation manners and technical effects of the fault detection method of any of the above embodiments.

[0147] The device embodiments or system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution in this embodiment.

[0148] In addition, an embodiment of the present application also provides a computer-readable storage medium, which stores computer-executable instructions, and the computer-executable instructions are executed by a processor or a controller.

[0149] Those of ordinary skill in the art will understand that all or some of the steps and systems disclosed in the above methods 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 can be implemented as hardware, or can be 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. The computer-readable storage medium includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technologies, CD-ROM, digital versatile disk (DVD) or other optical disk storage, magnetic cassettes, tapes, 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, the 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.

[0150] The above is a specific description of the preferred embodiment of the present application. However, the present application is not limited to the above embodiments. 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 in the scope defined by the present application.

Claims

1. A photovoltaic string fault detection method, characterized in that: include: Detecting the photovoltaic string to obtain detection parameters, and determining a fill factor of the photovoltaic string according to the detection parameters; When the filling factor is greater than or equal to a first threshold, it is determined that the photovoltaic string has no aging fault or shielding fault, wherein the first threshold is determined according to the initial filling factor of the photovoltaic string in a fault-free state; When the filling factor is less than the first threshold, a first resistance value and a second resistance value are determined according to the detection parameters, and the fault type of the photovoltaic string is determined according to the first resistance value and the second resistance value, wherein the first resistance value is used to characterize the equivalent series resistance value when the current of the photovoltaic string approaches zero, and the second resistance value is used to characterize the equivalent parallel resistance value when the voltage of the photovoltaic string approaches zero.

2. The fault detection method according to claim 1, characterized in that: The detection parameters include an open circuit voltage value, a short circuit current value, a maximum power voltage, and a maximum power current; and the fill factor is determined according to the open circuit voltage value, the short circuit current value, the maximum power voltage, and the maximum power current.

3. The fault detection method according to claim 2, characterized in that: The method further comprises: When the open circuit voltage value is less than a second threshold, determining that the fault type of the photovoltaic string is a short circuit fault, wherein the second threshold is determined according to an initial open circuit voltage value of the photovoltaic string in a fault-free state; When the short-circuit current value is less than a third threshold, it is determined that the fault type of the photovoltaic string is an open circuit fault, wherein the third threshold is determined according to an initial short-circuit current value of the photovoltaic string in a fault-free state.

4. The fault detection method according to claim 1, characterized in that: The determining the fault type of the photovoltaic string according to the first resistance value and the second resistance value includes: When the first resistance value is greater than a fourth threshold value and / or the second resistance value is less than a fifth threshold value, determining that the fault type of the photovoltaic string is an aging fault; When the first resistance value is less than or equal to the fourth threshold value and / or the second resistance value is greater than or equal to the fifth threshold value, it is determined that the fault type of the photovoltaic string is a shielding fault.

5. The fault detection method according to claim 4, characterized in that: The fourth threshold and the fifth threshold are obtained by the following steps: According to the equivalent series resistance value of the photovoltaic string when the current approaches zero in a fault-free state, a third resistance value is obtained, and the equivalent parallel resistance value of the photovoltaic string when the voltage approaches zero in a fault-free state is determined to obtain a fourth resistance value; The fourth threshold is determined according to the third resistance value and the number of photovoltaic panels in the photovoltaic string, and the fifth threshold is determined according to the fourth resistance value.

6. The fault detection method according to claim 1, characterized in that: The detecting the photovoltaic string to obtain the detection parameters includes: Detecting the photovoltaic string to obtain a current-voltage curve of the photovoltaic string; A detection parameter of the photovoltaic string is determined according to the current-voltage curve.

7. The fault detection method according to claim 6, characterized in that: The determining the first resistance value and the second resistance value according to the detection parameter comprises: The current-voltage curve is derived and a first resistance value is determined according to a derivative result at a point where the current approaches zero, and a second resistance value is determined according to a derivative result at a point where the voltage approaches zero.

8. The fault detection method according to claim 3, characterized in that: The method further comprises: After the photovoltaic string is powered on for the first time, detecting the photovoltaic string to obtain an initial current-voltage curve of the photovoltaic string; The initial fill factor, the initial open circuit voltage value, and the initial short circuit current value are determined according to the initial current-voltage curve.

9. A control device comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the fault detection method according to any one of claims 1 to 8 when executing the computer program.

10. A photovoltaic system, characterized in that: The invention comprises a photovoltaic string and a control device according to claim 9.

11. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer-executable instructions, and the computer-executable instructions are used to enable a computer to execute the fault detection method according to any one of claims 1 to 8.

Images