Multi-string photovoltaic inverter insulation impedance detection method, system and device

Abstract

The present application relates to a method, system and device for detecting the insulation impedance of a multi-string photovoltaic inverter, wherein the method for detecting the insulation impedance of a multi-string photovoltaic inverter comprises: collecting the input voltage value of each photovoltaic string in the multi-string photovoltaic inverter system; comparing the input voltage value of each photovoltaic string to obtain the minimum input voltage value between the input voltage values; calculating the target resistance value on the detection circuit where the minimum input voltage value is located according to the minimum input voltage value; judging whether the target resistance value is less than the resistance threshold value, and if so, determining that the multi-string photovoltaic inverter system has an insulation fault. Through the present application, the problem of inaccurate insulation impedance detection of the multi-string photovoltaic inverter is solved, and the accuracy of insulation impedance detection of the multi-string photovoltaic inverter is improved.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic technology, and in particular to a method, system and device for detecting insulation impedance of a multi-string photovoltaic inverter. Background Art

[0002] In photovoltaic grid-connected power generation technology, the output voltage of photovoltaic cells is relatively high, and because the photovoltaic panels of photovoltaic cells are placed in the open air, weather factors such as dust, rain, snow, and fog will affect the changes in the insulation between the positive and negative electrodes of the photovoltaic cells and the ground. As a high-voltage system, a key indicator of the safety of photovoltaic grid-connected inverters is the degree of insulation. The insulation resistance measurement technology can determine whether the insulation state of the current system is good and the changes in the insulation state. In the photovoltaic system, the insulation impedance of the DC side to the ground can characterize the insulation performance of the DC system. If the impedance is too low, the leakage current generated will pose a threat to people. The current safety standards all require that when the DC insulation impedance to the ground is less than a certain value, the system is not allowed to be connected to the grid. Based on this, the photovoltaic inverter needs to detect the insulation impedance value of the photovoltaic system.

[0003] A string photovoltaic system is a battery group formed by connecting multiple photovoltaic modules in a certain circuit to increase the voltage and power of photovoltaic power generation. It is widely used because it can achieve multi-channel maximum power tracking, effectively take into account the differences between modules of each string photovoltaic, and prevent shadowing and hot spot effects. When the insulation impedance of the string photovoltaic to the ground is lower than the standard value, it will cause leakage of the string photovoltaic to the ground, causing the metal shell of the string photovoltaic to be charged and threatening people's personal safety; and the leakage of the string photovoltaic may cause local heating or electric sparks, and there are safety hazards such as fire. Therefore, insulation detection of string photovoltaics is of great significance to the safety of photovoltaic systems.

[0004] At present, the insulation impedance of the DC end of the photovoltaic inverter to the ground is mainly detected by adding a hardware sampling circuit between the photovoltaic inverter bus and the ground. The sampling circuit detects and calculates the resistance of the photovoltaic inverter bus to the ground, and directly uses the resistance of the photovoltaic inverter bus to the ground as the insulation impedance value of the positive and negative poles of the multi-string input inverter to the ground. However, the premise of the detection of this scheme is that the voltage of the multi-string input inverter is equal to the inverter bus voltage. However, in reality, for the multi-string input inverter, there is often a difference in the input voltage of different strings, resulting in inaccurate insulation impedance values ​​of the multi-string photovoltaic inverters, which can easily cause the photovoltaic inverter to be misprotected or not protected, reducing the safety of the photovoltaic power generation system.

[0005] With regard to the problem of inaccurate insulation impedance detection of multiple groups of photovoltaic inverters in related technologies, no effective solution has been proposed so far. Summary of the invention

[0006] In this embodiment, a method, system and device for detecting insulation impedance of multiple groups of photovoltaic inverters are provided to solve the problem of inaccurate insulation impedance detection of multiple groups of photovoltaic inverters in the related art.

[0007] In a first aspect, a method for detecting insulation impedance of a multi-string photovoltaic inverter is provided in this embodiment, comprising:

[0008] Collect the input voltage value of each photovoltaic string in the multi-string photovoltaic inverter system;

[0009] Compare the input voltage values ​​of each photovoltaic string to obtain the minimum input voltage value among the input voltage values;

[0010] Calculate the target resistance value on the detection circuit where the minimum input voltage value is located according to the minimum input voltage value;

[0011] It is determined whether the target resistance value is less than the resistance threshold value. If so, it is determined that an insulation fault exists in the multi-string photovoltaic inverter system.

[0012] In some embodiments, calculating the target resistance value on the detection circuit where the minimum input voltage value is located according to the minimum input voltage value includes:

[0013] The target resistance value is calculated based on the minimum input voltage value, the bus positive input voltage value, the bus positive resistance value to ground, and the bus negative resistance value to ground.

[0014] In some of the embodiments, if the target resistance value is greater than or equal to the resistance threshold value, it is determined whether the resistance value of the negative pole to ground of the photovoltaic string where the minimum input voltage value is located is less than the resistance threshold value. If so, it is determined that an insulation fault exists in the multi-string photovoltaic inverter system.

[0015] In a second aspect, a multi-string photovoltaic inverter insulation impedance detection system is provided in this embodiment, and the multi-string photovoltaic inverter insulation impedance detection method described in the first aspect is applied. The system includes:

[0016] Inductor, diode, detection circuit, busbar and multiple photovoltaic strings; the busbar includes a busbar positive pole and a busbar negative pole; wherein the busbar positive pole includes a busbar positive pole-to-ground resistance, and the busbar negative pole includes a busbar negative pole-to-ground resistance;

[0017] The input end of each photovoltaic string is connected to the positive pole of the busbar through an inductor and a diode, and the output end of each photovoltaic string is grounded through a corresponding detection circuit.

[0018] In some embodiments, the detection circuit includes a first resistor and a second resistor, and the first resistor and the second resistor are connected in series.

[0019] In some of the embodiments, the negative electrode of the detection circuit of each photovoltaic string is connected to the negative electrode of the busbar.

[0020] In some of the embodiments, the resistance values ​​of the second resistors in the respective detection circuits are equal and are equal to the resistance value of the negative electrode of the busbar to the ground.

[0021] In a third aspect, in this embodiment, a multi-string photovoltaic inverter insulation impedance detection device is provided, which is used in a second multi-string photovoltaic inverter system, including: a voltage acquisition module, a voltage comparison module, a resistance calculation module, a first judgment module and a second judgment module, wherein:

[0022] Voltage collection module, used to collect the input voltage value of each photovoltaic string;

[0023] The voltage comparison module is used to compare the input voltage values ​​of each photovoltaic string to obtain the minimum input voltage value among the input voltage values;

[0024] A resistance calculation module, used for calculating a target resistance value on a detection circuit where the minimum input voltage value is located according to the minimum input voltage value;

[0025] The first judgment module is used to determine whether the target resistance value is less than the resistance threshold value. If so, it is determined that the multi-string photovoltaic inverter system has an insulation fault;

[0026] The second judgment module is used to judge whether the negative pole-to-ground resistance value of the photovoltaic string where the minimum input voltage value is located is less than the resistance threshold value if the target resistance value is greater than or equal to the resistance threshold value. If so, it is determined that the multi-string photovoltaic inverter system has an insulation fault.

[0027] In a fourth aspect, an electronic device is provided in this embodiment, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the insulation impedance detection method for multiple strings of photovoltaic inverters described in the first aspect is implemented.

[0028] In a fifth aspect, in this embodiment, a storage medium is provided, on which a computer program is stored, and when the program is executed by a processor, the insulation impedance detection method of multiple strings of photovoltaic inverters described in the first aspect is implemented.

[0029] Compared with the related art, the insulation impedance detection method of a multi-string photovoltaic inverter provided in the present embodiment collects the input voltage value of each photovoltaic string in the multi-string photovoltaic inverter system; compares the input voltage value of each photovoltaic string to obtain the minimum input voltage value between the input voltage values; calculates the target resistance value on the detection circuit where the minimum input voltage value is located according to the minimum input voltage value; determines whether the target resistance value is less than the resistance threshold value, and if so, determines that the multi-string photovoltaic inverter system has an insulation fault, thereby solving the problem of inaccurate insulation impedance detection of the multi-string photovoltaic inverter and improving the accuracy of insulation impedance detection of the multi-string photovoltaic inverter.

[0030] Details of one or more embodiments of the present application are set forth in the following drawings and description to make other features, objects, and advantages of the present application more readily apparent. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0032] Figure 1 This is a hardware structure block diagram of a terminal of the multi-string photovoltaic inverter insulation impedance detection method of this embodiment.

[0033] Figure 2 The present invention is a topological diagram of a photovoltaic inverter bus-to-ground impedance detection circuit in the prior art.

[0034] Figure 3 4 is a flow chart of the insulation impedance detection method of multiple strings of photovoltaic inverters in this embodiment.

[0035] Figure 4 Schematic diagram of a topological circuit of a multi-string photovoltaic inverter of this embodiment.

[0036] Figure 5 4 is a structural block diagram of the insulation impedance detection device for multiple strings of photovoltaic inverters of this embodiment. DETAILED DESCRIPTION

[0037] In order to more clearly understand the purpose, technical solutions and advantages of the present application, the present application is described and illustrated below in conjunction with the accompanying drawings and embodiments.

[0038] Unless otherwise defined, the technical terms or scientific terms involved in this application shall have the general meaning understood by people with general skills in the technical field to which this application belongs. The words "one", "a", "the", "these" and the like in this application do not indicate a quantitative limitation, and they may be singular or plural. The terms "include", "comprise", "have" and any variants thereof involved in this application are intended to cover non-exclusive inclusions; for example, a process, method and system, product or device comprising a series of steps or modules (units) is not limited to the listed steps or modules (units), but may include unlisted steps or modules (units), or may include other steps or modules (units) inherent to these processes, methods, products or devices. The words "connect", "connected", "coupled" and the like involved in this application are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The "multiple" involved in this application refers to two or more. "And / or" describes the association relationship of associated objects, indicating that there may be three relationships, for example, "A and / or B" may mean: A exists alone, A and B exist at the same time, and B exists alone. Generally, the character " / " indicates that the objects associated with each other are in an "or" relationship. The terms "first", "second", "third", etc. in this application are only used to distinguish similar objects and do not represent a specific ordering of the objects.

[0039] The method embodiment provided in this embodiment can be executed in a terminal, a computer or a similar computing device. For example, running on a terminal, Figure 1 is a hardware structure block diagram of a terminal of the method for detecting insulation impedance of multiple strings of photovoltaic inverters of this embodiment. Figure 1 As shown, the terminal may include one or more ( Figure 1 Only one is shown in the figure) a processor 102 and a memory 104 for storing data, wherein the processor 102 may include but is not limited to a processing device such as a microprocessor MCU or a programmable logic device FPGA. The above terminal may also include a transmission device 106 and an input and output device 108 for communication functions. It can be understood by those skilled in the art that Figure 1 The structure shown is only for illustration and does not limit the structure of the above terminal. Figure 1 More or fewer components as shown, or with Figure 1 Different configurations shown.

[0040] The memory 104 can be used to store computer programs, for example, software programs and modules of application software, such as the computer program corresponding to the insulation impedance detection method of the multi-string photovoltaic inverter in the present embodiment. The processor 102 executes various functional applications and data processing by running the computer program stored in the memory 104, that is, to implement the above method. The memory 104 may include a high-speed random access memory, and may also include a non-volatile memory, such as one or more magnetic storage devices, flash memory, or other non-volatile solid-state memory. In some instances, the memory 104 may further include a memory remotely arranged relative to the processor 102, and these remote memories may be connected to the terminal via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0041] The transmission device 106 is used to receive or send data via a network. The above network includes a wireless network provided by a communication provider of the terminal. In one example, the transmission device 106 includes a network adapter (Network Interface Controller, referred to as NIC), which can be connected to other network devices through a base station so as to communicate with the Internet. In one example, the transmission device 106 can be a radio frequency (Radio Frequency, referred to as RF) module, which is used to communicate with the Internet wirelessly.

[0042] Figure 2 It is a topological diagram of the bus-to-ground impedance detection circuit of the photovoltaic inverter in the prior art, such as Figure 2 As shown, in the existing related technologies, the impedance value of the photovoltaic inverter bus to the ground is mainly detected by adding a hardware sampling circuit between the photovoltaic inverter bus and the ground wire PE to detect the insulation impedance value of PV+ and PV- to the ground, and the detected impedance value of the photovoltaic inverter bus to the ground is equal to the impedance value of each photovoltaic string to the ground. Figure 2 As shown, the detection circuit is arranged between the positive and negative busbars. Specifically, the positive electrode of the detection circuit is connected to the input end of the positive electrode BUS+ of the busbar, the negative electrode of the detection circuit is connected to the negative electrode BUS- of the busbar, and the detection circuit is grounded PE, wherein R1, R2, R3, and R4 are resistors artificially connected between the positive and negative busbars and have known values. R1, R2, R3, and R4 are connected in series, a switch S1 is connected in parallel to R2, and a switch S2 is connected in parallel to R4. R5 is the resistance to ground of the positive electrode BUS+ of the busbar, which can be equivalent to the resistance to ground of the positive electrode of the photovoltaic inverter. R6 is the resistance to ground of the negative electrode BUS- of the busbar, which can be equivalent to the resistance to ground of the negative electrode of the photovoltaic inverter. C1 is the capacitance to ground of the positive electrode of the busbar, and C2 is the capacitance to ground of the negative electrode of the busbar. The resistance to ground of the photovoltaic inverter is detected by adjusting the closing and opening of switches S1 and S2. Specifically,

[0043] When switch S1 is closed and S2 is open, the grounding wire PE is connected to the negative pole of the busbar BUS. - The voltage is:

[0044] (1)

[0045] When switch S2 is closed and S1 is open, the grounding wire PE is connected to the negative pole of the busbar BUS. - The voltage is:

[0046] (2)

[0047] Formulas 1 and 2 can be used to solve R5 and R6.

[0048] However, for a PV inverter with multiple strings input, V bus The maximum PV voltage input will cause the insulation impedance detection value of the low voltage input photovoltaic string to be too large, resulting in inaccurate insulation impedance values ​​of the detected multi-string photovoltaic inverters, which may easily cause the photovoltaic inverter to be misprotected or not protected, reducing the safety of the photovoltaic power generation system. Therefore, in order to ensure the safety of the photovoltaic power generation system, it is necessary to improve the accuracy of the insulation impedance detection of the multi-string photovoltaic inverters.

[0049] In this embodiment, a method for detecting insulation impedance of a multi-string photovoltaic inverter is provided. Figure 3 FIG. 1 is a flow chart of the insulation impedance detection method of a multi-string photovoltaic inverter of this embodiment. Figure 3 As shown, the process includes the following steps:

[0050] Step S301, collecting the input voltage value of each photovoltaic string in the multi-string photovoltaic inverter system.

[0051] String photovoltaic inverters are composed of multiple photovoltaic cells connected in series to form a photovoltaic string. Each (or several) photovoltaic string is connected to a string inverter. Photovoltaic power stations using string structures generally require multiple string inverters to be connected to the grid to meet certain power generation requirements. To ensure the safe operation of multiple string inverters after being connected to the grid, it is necessary to first ensure that the insulation impedance of each photovoltaic string is within the predetermined threshold. Generally, when the insulation impedance value is lower than the limit threshold R=V pv max / 30mA, the photovoltaic string is considered to be faulty and the inverter where the photovoltaic string is located is prohibited from being connected to the grid. pv max The maximum PV voltage allowed to be input to the PV inverter.

[0052] In this embodiment, based on Figure 2As shown, on the basis of obtaining the bus-to-ground impedance value by adding a hardware sampling circuit, the input voltage value of each photovoltaic string and the output voltage value of the bus terminal are detected and recorded, wherein the input voltage value of each photovoltaic string and the output voltage value of the bus terminal can be obtained by detecting a signal processor (digital signal processor for short DSP), which is not specifically limited in this embodiment.

[0053] Step S302, comparing the input voltage values ​​of each photovoltaic string to obtain the minimum input voltage value among the input voltage values.

[0054] The input voltage values ​​of all photovoltaic strings detected are compared, and the minimum input voltage value is obtained and recorded.

[0055] Step S303, calculating a target resistance value on a detection circuit where the minimum input voltage value is located according to the minimum input voltage value;

[0056] According to actual detection, the input voltages of various photovoltaic strings are not the same. In order to ensure the safety of the photovoltaic inverter grid connection, it is necessary to ensure that the resistance value of each photovoltaic string is greater than the specified resistance threshold. In this embodiment, it is deduced through calculation that as long as the resistance value of the detection circuit where the minimum input voltage value is located is calculated, the compliance of the resistance values ​​of all photovoltaic strings can be determined. The target resistance value of the inspection circuit where the minimum input voltage value is located is calculated by the set calculation formula.

[0057] Step S304, determining whether the target resistance value is less than the voltage threshold value, and if so, determining that the multi-string photovoltaic inverter system has an insulation fault.

[0058] The target resistance value obtained by calculation, that is, the resistance value of the photovoltaic string with the minimum input voltage, is compared with the resistance threshold value, that is, the limit threshold R=V pv max / 30mA, if the target resistance value is less than the specified threshold, it is determined that the photovoltaic string with the smallest input voltage does not meet the grid-connected regulations, and further determines that the multi-string photovoltaic inverter system has an insulation fault.

[0059] Through the above steps S301 to S304, the input voltage value of each photovoltaic string in the multi-string photovoltaic inverter system is collected; the input voltage value of each photovoltaic string is compared to obtain the minimum input voltage value between each input voltage value; the target resistance value on the detection circuit where the minimum input voltage value is located is calculated according to the minimum input voltage value; it is determined whether the target resistance value is less than the resistance threshold value, and if so, it is determined that the multi-string photovoltaic inverter system has an insulation fault. Compared with the related art in which a hardware sampling circuit is added between the photovoltaic inverter bus and the grounding wire PE to directly equate the impedance value of the photovoltaic inverter bus to the ground obtained by the detection to the impedance value of each photovoltaic string, the present application obtains a set calculation formula by deriving and converting the multi-string photovoltaic circuit, and obtains the minimum resistance value in each photovoltaic string by the set calculation formula as long as the input voltage of each photovoltaic string is detected, and the minimum resistance value is compared with the resistance threshold value to detect whether the multi-string photovoltaic inverter has an insulation fault, thereby improving the accuracy of the insulation impedance detection of the multi-string photovoltaic inverter.

[0060] In some embodiments, a target resistance value on a detection circuit where the minimum input voltage value is located is calculated based on the minimum input voltage value, including: calculating the target resistance value based on the minimum input voltage value, the bus positive input voltage value, the bus positive resistance value to ground, and the bus negative resistance value to ground.

[0061] Specifically, Figure 4 is a schematic diagram of a topology circuit of a multi-string photovoltaic inverter of this embodiment, such as Figure 4As shown, multiple photovoltaic strings include photovoltaics PV1-PV3, inductors L1-L3, diodes D1-D3, and resistors R3-R8. This embodiment takes a multi-string photovoltaic inverter composed of three photovoltaic strings as an example. The specific number of photovoltaic strings can be determined according to actual conditions, and this embodiment does not make specific limitations. The photovoltaic string PV1 includes a positive pole PV1+ and a negative pole PV-, the photovoltaic string PV2 includes a positive pole PV2+ and a negative pole PV-, and the photovoltaic string PV3 includes a positive pole PV3+ and a negative pole PV-, and each photovoltaic string is connected in parallel. The positive pole PV1+ of the photovoltaic string PV1 is connected to the diode D1 through the inductor L1, and is connected to the positive pole BUS+ of the bus through the diode D1. C1 is the capacitance to ground of the positive pole of the bus, C2 is the capacitance to ground of the negative pole of the bus, R1 is the resistance to ground of the positive pole BUS+ of the bus, and R2 is the resistance to ground of the negative pole BUS- of the bus. The photovoltaic string circuit and the bus are both grounded to PE through resistors. The resistor R3 and the resistor R4 on the string photovoltaic PV1 are connected in series, R3 is the ground resistance of the positive pole PV1+ of the string photovoltaic PV1, R4 is the ground resistance of the negative pole PV- of the string photovoltaic PV1, and the other end of the resistor R4 is connected to the negative pole PV- of the string photovoltaic PV1. The circuit connection mode of other string photovoltaic PV2 and string photovoltaic PV3 is the same as that of string photovoltaic PV1. R5 and R6 are the resistors on the string photovoltaic PV2, R5 is the ground resistance of the positive pole PV2+ of the string photovoltaic PV2, and R6 is the ground resistance of the negative pole PV- of the string photovoltaic PV2; R7 and R8 are the resistors on the string photovoltaic PV3, R7 is the ground resistance of the positive pole PV3+ of the string photovoltaic PV3, and R8 is the ground resistance of the negative pole PV- of the string photovoltaic PV3. Since the negative pole PV- of each group of photovoltaic strings is directly connected to the negative pole BUS- of the busbar in the topological structure, the resistance of the negative pole BUS- of the busbar to ground is the resistance of PV1-, PV2-, and PV3- to ground, that is, R8=R6=R4=R2.

[0062] Take string PV1 as an example, assuming that the voltage on the input side of PV1 is V in , the BUS input voltage is V out , PV1- to ground voltage is V1, BUS- to ground voltage is V3, then:

[0063] (3)

[0064] (4)

[0065] Combining formula (3) and formula (4), and with R4=R2, V1=V3, we get:

[0066] (5)

[0067] From formula (5), we can see that when V in =V outWhen R3=R1;

[0068] When V in <V out hour, ;

[0069] That is V in With V out The greater the difference between R1 and R2, the greater the difference between R3 and R1. Therefore, in the same multi-string photovoltaic inverter, R1, R2 and V out is a constant value and remains unchanged, so V in The smaller the value, the smaller R3 is. Therefore, as long as the resistance value of the minimum input voltage in the multi-string photovoltaic inverter is greater than the resistance threshold value, it can be judged that the resistance values ​​of all other photovoltaic strings are also greater than the resistance threshold value, that is, the multi-string photovoltaic inverter does not have a fault. The ground resistance is the target resistance value that needs to be finally calculated in this embodiment, which is calculated by inputting the minimum input voltage, bus positive input voltage, bus positive ground resistance and bus negative ground resistance obtained by comparison into formula (5). Based on the topological structure circuit of the multi-string photovoltaic inverter, by determining the relationship between the ground resistance and input voltage in the photovoltaic string, the operation of detecting the ground resistance on each photovoltaic string is simplified to the comparison of the input voltage of each photovoltaic string, and the lowest input voltage is found to calculate the ground resistance. Finally, the calculated ground resistance value is compared with the resistance limit value to judge whether the multi-string photovoltaic inverter is faulty, which simplifies the calculation steps and improves the accuracy of insulation impedance detection of the photovoltaic inverter.

[0070] In another embodiment, if the target resistance value is greater than or equal to the resistance threshold value, it is determined whether the negative pole-to-ground resistance value of the photovoltaic string where the minimum input voltage value is located is less than the voltage threshold value. If so, it is determined that an insulation fault exists in the multi-string photovoltaic inverter system.

[0071] When the target resistance value calculated by the above formula (5) for the minimum input voltage in the multi-string photovoltaic system is greater than or equal to the resistance threshold value, it means that the resistance value of the positive pole of the photovoltaic system to the ground meets the requirements of grid connection. At this time, the resistance value of the negative pole of the photovoltaic system to the ground is compared to see whether it is less than the resistance threshold value. If it is less than the resistance threshold value, it is determined that the multi-string photovoltaic inverter system has an insulation fault. Otherwise, it is determined that the multi-string photovoltaic inverter system is normal and can be connected to the grid.

[0072] In this embodiment, a multi-string photovoltaic inverter insulation impedance detection system is also provided. Figure 4As shown, the system includes: inductors L1-L3, diodes D1-D3, detection circuits, busbars BUS, and multiple photovoltaic strings PV1-PV3; the detection circuit includes three circuits where photovoltaic strings PV1, PV2, and PV3 are located, wherein the photovoltaic strings include positive poles PV1+, PV2+, PV3+ and respective negative poles PV-, and the busbar BUS includes the positive pole BUS+ and the negative pole BUS-; wherein R1 is the ground resistance on the positive pole of the busbar, and R2 is the ground resistance on the pseudo negative pole of the busbar. The positive pole PV1+ of the photovoltaic string PV1 is connected to the positive pole BUS+ of the busbar through the inductor L1 and the diode D1, the resistors R3 and R4 are connected in series on the photovoltaic string PV1, and the negative pole PV- of the photovoltaic string is grounded PE through the resistor R4, thereby forming the detection circuit where the photovoltaic string PV1 is located. The connection method of the detection circuits where other photovoltaic strings are located is the same as that of the detection circuit where the photovoltaic string PV1 is located, and the negative pole of the busbar is grounded PE through the resistor R2. The resistance values ​​of the second resistors on each detection circuit are equal and equal to the resistance value R2 of the negative electrode of the busbar BUS- to the ground, that is, R4=R6=R8=R2.

[0073] The insulation impedance detection system for multiple-string photovoltaic inverters detects whether the ground resistance of each photovoltaic string meets the resistance threshold value to determine whether the multiple-string photovoltaic inverter has a fault. By formula derivation, as long as the minimum input voltage value of each photovoltaic string is detected and the target resistance value is calculated by a preset formula, the target resistance value is compared with the resistance threshold value. If the target resistance value is less than the resistance threshold value, it can be confirmed that the multiple-string photovoltaic inverter has a fault. Using this system to detect the insulation impedance value of multiple-string photovoltaic inverters reduces the calculation process and improves the detection accuracy.

[0074] In this embodiment, a multi-string photovoltaic inverter insulation impedance detection device is also provided, which is used to implement the above-mentioned embodiments and preferred implementation modes, and will not be repeated hereafter. The terms "module", "unit", "subunit", etc. used below can implement a combination of software and / or hardware for a predetermined function. Although the devices described in the following embodiments are preferably implemented in software, the implementation of hardware, or a combination of software and hardware, is also possible and conceivable.

[0075] Figure 5 is a structural block diagram of the insulation impedance detection device for multiple strings of photovoltaic inverters of this embodiment, and the insulation impedance detection device for multiple strings of photovoltaic inverters is used in the above-mentioned insulation impedance detection system for multiple strings of photovoltaic inverters. Figure 5 As shown, the device 50 includes: a voltage acquisition module 51, a voltage comparison module 52, a resistance calculation module 53, a first judgment module 54 and a second judgment module 55, wherein:

[0076] The voltage collection module 51 is used to collect the input voltage value of each photovoltaic string;

[0077] The voltage comparison module 52 is used to compare the input voltage values ​​of each photovoltaic string to obtain the minimum input voltage value among the input voltage values;

[0078] The resistance calculation module 53 is used to calculate the target resistance value of the detection circuit where the minimum input voltage value is located according to the minimum input voltage value;

[0079] A first judgment module 54 is used to judge whether the target resistance value is less than the resistance threshold value, and if so, it is determined that the multi-string photovoltaic inverter system has an insulation fault;

[0080] The second judgment module 55 is used to judge whether the negative pole-to-ground resistance value of the photovoltaic string where the minimum input voltage value is located is less than the resistance threshold value if the target resistance value is greater than or equal to the resistance threshold value. If so, it is determined that the multi-string photovoltaic inverter system has an insulation fault.

[0081] It should be noted that the above modules can be functional modules or program modules, and can be implemented by software or hardware. For modules implemented by hardware, the above modules can be located in the same processor; or the above modules can be located in different processors in any combination.

[0082] In this embodiment, an electronic device is further provided, including a memory and a processor, wherein a computer program is stored in the memory, and the processor is configured to run the computer program to execute the steps in any one of the above method embodiments.

[0083] Optionally, the electronic device may further include a transmission device and an input / output device, wherein the transmission device is connected to the processor, and the input / output device is connected to the processor.

[0084] Optionally, in this embodiment, the processor may be configured to perform the following steps through a computer program:

[0085] S1, collecting the input voltage value of each photovoltaic string in the multi-string photovoltaic inverter system.

[0086] S2, comparing the input voltage values ​​of each photovoltaic string to obtain the minimum input voltage value among the input voltage values.

[0087] S3, calculating a target resistance value on a detection circuit where the minimum input voltage value is located according to the minimum input voltage value.

[0088] S4, determining whether the target resistance value is less than the resistance threshold value, and if so, determining that the multi-string photovoltaic inverter system has an insulation fault.

[0089] It should be noted that the specific examples in this embodiment can refer to the examples described in the above embodiments and optional implementation modes, and will not be repeated in this embodiment.

[0090] In addition, in combination with the insulation impedance detection method for multiple strings of photovoltaic inverters provided in the above embodiments, a storage medium may also be provided in this embodiment to implement the method. The storage medium stores a computer program; when the computer program is executed by a processor, any one of the insulation impedance detection methods for multiple strings of photovoltaic inverters in the above embodiments is implemented.

[0091] It should be understood that the specific embodiments described herein are only used to explain the application, rather than to limit it. Based on the embodiments provided in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of this application.

[0092] Obviously, the drawings are only some examples or embodiments of the present application. For ordinary technicians in the field, the present application can also be applied to other similar situations based on these drawings without creative work. In addition, it is understandable that although the work done in this development process may be complicated and lengthy, for ordinary technicians in the field, certain changes in design, manufacturing or production based on the technical content disclosed in this application are only conventional technical means and should not be regarded as insufficient content disclosed in this application.

[0093] The term "embodiment" in this application refers to a specific feature, structure or characteristic described in conjunction with the embodiment that can be included in at least one embodiment of the present application. The appearance of this phrase in various locations in the specification does not necessarily mean the same embodiment, nor does it mean that it is mutually exclusive with other embodiments and is independent or optional. It is clearly or implicitly understood by those of ordinary skill in the art that the embodiments described in this application can be combined with other embodiments without conflict.

[0094] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. Non-relational databases may include distributed databases based on blockchains, etc., but are not limited to this. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but are not limited to this.

[0095] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of patent protection. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the scope of protection of the present application. Therefore, the scope of protection of the present application shall be subject to the attached claims.

Claims

1. A method for detecting insulation impedance of a multi-string photovoltaic inverter, characterized in that: For multi-string photovoltaic inverter systems, including: Collecting the input voltage value of each photovoltaic string in the multi-string photovoltaic inverter system; Comparing the input voltage values ​​of the photovoltaic strings to obtain a minimum input voltage value among the input voltage values; The target resistance value is calculated according to the minimum input voltage value, the bus positive pole input voltage value, the bus positive pole to ground resistance value and the bus negative pole to ground resistance value; wherein the target resistance value is the positive pole to ground resistance value of the photovoltaic string where the minimum input voltage value is located; Determining whether the target resistance value is less than a resistance threshold value, and if so, determining that an insulation fault exists in the multi-string photovoltaic inverter system; Otherwise, it is determined whether the resistance value of the negative pole to ground of the photovoltaic string where the minimum input voltage value is located is less than the resistance threshold value. If so, it is determined that an insulation fault exists in the multi-string photovoltaic inverter system.

2. A multi-string photovoltaic inverter insulation impedance detection system, characterized in that: The method for detecting insulation impedance of multiple photovoltaic inverters according to claim 1 is applied, and the system comprises: Inductor, diode, detection circuit, busbar and multiple photovoltaic strings; the busbar includes a busbar positive pole and a busbar negative pole; wherein the busbar positive pole includes a busbar positive pole-to-ground resistance, and the busbar negative pole includes a busbar negative pole-to-ground resistance; The input end of each photovoltaic string is connected to the positive electrode of the busbar through the inductor and the diode, and the output end of each photovoltaic string is grounded through the corresponding detection circuit.

3. The multi-string photovoltaic inverter insulation impedance detection system according to claim 2, characterized in that: The detection circuit includes a first resistor and a second resistor, and the first resistor and the second resistor are connected in series.

4. The multi-string photovoltaic inverter insulation impedance detection system according to claim 2, characterized in that: The negative electrode of the detection circuit of each photovoltaic string is connected to the negative electrode of the busbar.

5. The multi-string photovoltaic inverter insulation impedance detection system according to claim 2, characterized in that: The resistance values ​​of the second resistors on the respective detection circuits are equal and equal to the resistance value of the negative electrode of the busbar to the ground.

6. A multi-string photovoltaic inverter insulation impedance detection device, characterized in that: For a multi-string photovoltaic inverter system, comprising: a voltage acquisition module, a voltage comparison module, a resistance calculation module, a first judgment module and a second judgment module, wherein: The voltage acquisition module is used to collect the input voltage value of each photovoltaic string; The voltage comparison module is used to compare the input voltage values ​​of each photovoltaic string to obtain the minimum input voltage value among the input voltage values; The resistance calculation module is used to calculate the target resistance value according to the minimum input voltage value, the bus positive pole input voltage value, the bus positive pole to ground resistance value and the bus negative pole to ground resistance value; wherein the target resistance value is the positive pole to ground resistance value of the photovoltaic string where the minimum input voltage value is located; The first judgment module is used to determine whether the target resistance value is less than a resistance threshold value, and if so, determine that an insulation fault exists in the multi-string photovoltaic inverter system; The second judgment module is used to judge whether the negative pole-to-ground resistance value of the photovoltaic string where the minimum input voltage value is located is less than the resistance threshold value if the target resistance value is greater than or equal to the resistance threshold value; if so, it is determined that an insulation fault exists in the multi-string photovoltaic inverter system.

7. An electronic device comprising a memory and a processor, characterized in that: A computer program is stored in the memory, and the processor is configured to run the computer program to execute the insulation impedance detection method for multiple strings of photovoltaic inverters according to claim 1.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for detecting insulation impedance of a multi-string photovoltaic inverter according to claim 1 are implemented.

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