Photovoltaic string monitoring device

Abstract

The utility model discloses a photovoltaic string monitoring device, which is used for being connected between inversion direct current access equipment and a photovoltaic string, and comprises a positive electrode diode, a negative electrode diode and four equivalent bridging resistors, the positive electrode diode enables the positive electrode of the photovoltaic string to send current to the positive electrode access end of the inversion direct current access equipment, and the negative electrode diode enables the negative electrode of the photovoltaic string to send current to the negative electrode access end of the inversion direct current access equipment; the negative electrode diode enables the negative electrode access end of the inversion direct current access equipment to send current to the negative electrode end of the photovoltaic group string, the first equivalent bridging resistor and the second equivalent bridging resistor in the four equivalent bridging resistors are connected in series, and the third equivalent bridging resistor and the fourth equivalent bridging resistor in the four equivalent bridging resistors are connected in series. The first equivalent bridging resistor and the second equivalent bridging resistor are connected in parallel with the third equivalent bridging resistor and the fourth equivalent bridging resistor, and a voltage monitoring port is arranged between the first equivalent bridging resistor and the second equivalent bridging resistor so as to output string monitoring voltage for monitoring whether the photovoltaic string is abnormal or not. The device disclosed by the utility model can improve the operation stability of the photovoltaic power station.

Description

Technical Field

[0001] The utility model relates to the technical field of power system monitoring, in particular to a photovoltaic string monitoring device. Background Art

[0002] With the continuous development of new energy technologies, new energy power generation technology projects have become the mainstream of new energy power projects, and the proportion of solar power generation in the total power generation of the society has increased significantly year by year. Centralized and distributed photovoltaic power generation projects have also increased exponentially every year.

[0003] In recent years, high-power inverter DC access equipment in photovoltaic power generation projects has been widely used in existing and newly built large-scale centralized and distributed photovoltaic power stations due to its advantages such as high conversion efficiency and flexible application methods. Among them, the inverter DC access equipment may include string inverters and DC combiner boxes for connecting at least one photovoltaic string. Furthermore, a large number of photovoltaic strings are often connected to high-power inverter DC access equipment, and the most common faults of photovoltaic strings are "string insulation is too low" and "string current backflow"; among them, the string insulation is too low fault is that the positive part of the photovoltaic string or the negative part of the photovoltaic string has insulation damage. When the positive insulation is damaged, the negative voltage to the ground increases sharply, and when the negative insulation is damaged, the positive voltage to the ground increases sharply. When a string insulation failure occurs, the faulty photovoltaic string needs to be decoupled as soon as possible to prevent the inverter of the photovoltaic power station from shutting down due to protection. Therefore, it is necessary to quickly detect the string insulation failure when the photovoltaic string insulation failure occurs. If the photovoltaic string insulation failure cannot be detected as soon as possible, it may cause an operation accident in the photovoltaic power station. Furthermore, the string current backflow failure is the uneven voltage between different photovoltaic strings under the same inverter DC access device, which causes the current of the high-voltage photovoltaic string to flow back into the low-voltage photovoltaic string. When the string current backflow failure occurs, the inverter of the photovoltaic power station will reduce the power operation, resulting in a serious reduction in power generation efficiency.

[0004] However, after the photovoltaic strings of the current photovoltaic power station collect current in the DC combiner box, they are input into the indoor high-power inverter through the DC bus. Therefore, it is impossible to effectively monitor whether each photovoltaic string has a low string insulation fault, nor to prevent the current of the high-voltage photovoltaic string from flowing back into the low-voltage photovoltaic string, resulting in poor power generation efficiency of the photovoltaic power station. Utility Model Content

[0005] In view of this, the utility model provides a photovoltaic string monitoring device, the main purpose of which is to solve the technical problem that the photovoltaic power station cannot quickly identify the photovoltaic string insulation low fault and cannot prevent the string current backflow fault, resulting in low operating power generation efficiency of the photovoltaic power station.

[0006] To achieve the above purpose, the utility model provides a photovoltaic string monitoring device, which is used to be connected between the inverter DC access device and the photovoltaic string of the photovoltaic power station, and the photovoltaic string monitoring device includes:

[0007] A positive diode, wherein the positive terminal of the positive diode is connected to the positive terminal of the photovoltaic string, and the negative terminal of the positive diode is connected to the positive access terminal of the inverter DC access device;

[0008] A negative electrode diode, wherein the negative terminal of the negative electrode diode is connected to the negative terminal of the photovoltaic string, and the positive terminal of the negative electrode diode is connected to the negative electrode access terminal of the inverter DC access device;

[0009] a first equal-value bridge resistor, wherein a first end of the first equal-value bridge resistor is connected between a positive terminal of the positive diode and a positive terminal of the photovoltaic string;

[0010] a second equal-value bridge resistor, wherein a first end of the second equal-value bridge resistor is connected between the negative terminal of the negative diode and the negative terminal of the photovoltaic string, and a second end of the second equal-value bridge resistor is connected to a second end of the first equal-value bridge resistor;

[0011] a third equal-value bridge resistor, wherein a first end of the third equal-value bridge resistor is connected to a first end of the first equal-value bridge resistor, and a second end of the third equal-value bridge resistor is grounded;

[0012] a fourth equal-value bridge resistor, wherein a first end of the fourth equal-value bridge resistor is connected to a first end of the second equal-value bridge resistor, and a second end of the fourth equal-value bridge resistor is connected to a second end of the third equal-value bridge resistor;

[0013] A voltage monitoring port is provided between the second end of the first equal-value bridge resistor and the second end of the second equal-value bridge resistor, and is used to output a string monitoring voltage for monitoring whether there is an abnormality in the photovoltaic string.

[0014] Optionally, the photovoltaic string monitoring device also includes: a first overcurrent protector, wherein the first access end of the first overcurrent protector is connected between the positive terminal of the positive diode and the positive terminal of the photovoltaic string, and the second access end of the first overcurrent protector is connected to the first end of the first equivalent bridge resistor; a second overcurrent protector, wherein the first access end of the second overcurrent protector is connected between the negative terminal of the negative diode and the negative terminal of the photovoltaic string, and the second access end of the second overcurrent protector is connected to the first end of the second equivalent bridge resistor.

[0015] Optionally, the photovoltaic string monitoring device further includes: a Hall sensor, which is used to surround a grounding wire between the second end of the third equivalent bridge resistor and ground in an input through-hole of the Hall sensor to determine a ground leakage current of the grounding wire.

[0016] Optionally, the photovoltaic string monitoring device also includes: a first voltage comparator, wherein the positive power supply access terminal of the first voltage comparator is connected to the first external power supply for obtaining a positive voltage from the first external power supply, the negative power supply access terminal of the first voltage comparator is grounded, the negative input terminal of the first voltage comparator is connected to the voltage monitoring port, the positive input terminal of the first voltage comparator is connected to the second external power supply for obtaining a first reference positive voltage, and the output terminal of the first voltage comparator is used to output a first string monitoring voltage for judging whether an abnormality occurs on the positive side of the photovoltaic string; a second voltage comparator, wherein the positive power supply access terminal of the second voltage comparator is connected to the third external power supply for obtaining a positive voltage from the third external power supply, the negative power supply access terminal of the second voltage comparator is grounded, the negative input terminal of the second voltage comparator is connected to the fourth external power supply for obtaining a first reference negative voltage, the positive input terminal of the second voltage comparator is connected to the voltage monitoring port, and the output terminal of the second voltage comparator is used to output a second string monitoring voltage for judging whether an abnormality occurs on the negative side of the photovoltaic string.

[0017] Optionally, the Hall sensor is also used to convert the ground leakage current into a voltage signal; the Hall sensor is provided with a voltage sampling port for outputting the voltage signal at the voltage sampling port; the photovoltaic string monitoring device also includes: a third voltage comparator, the positive power supply access terminal of the third voltage comparator is connected to the fifth external power supply, and is used to obtain the positive voltage from the fifth external power supply, the negative power supply access terminal of the third voltage comparator is grounded, the negative input terminal of the third voltage comparator is connected to the voltage sampling port, and the positive input terminal of the third voltage comparator is connected to the sixth external power supply, and is used to obtain the second reference positive voltage, the third The output end of the voltage comparator is used to output a third string monitoring voltage for judging whether the photovoltaic string has abnormal current leakage; the fourth voltage comparator, the positive power supply access end of the fourth voltage comparator is connected to the seventh external power supply, and is used to obtain the positive voltage from the seventh external power supply, the negative power supply access end of the fourth voltage comparator is grounded, the negative input end of the fourth voltage comparator is connected to the eighth external power supply, and is used to obtain the second reference negative voltage, the positive input end of the fourth voltage comparator is connected to the voltage sampling port, and the output end of the fourth voltage comparator is used to output a fourth string monitoring voltage for judging whether the photovoltaic string has abnormal current leakage.

[0018] Optionally, the photovoltaic string monitoring device also includes: a high-impedance DC isolated power supply, the first power access terminal of the high-impedance DC isolated power supply is connected to the second access terminal of the first overcurrent protector, the second power access terminal of the high-impedance DC isolated power supply is connected to the second access terminal of the second overcurrent protector to obtain a working power supply, and the first positive output terminal of the high-impedance DC isolated power supply is respectively connected to the positive power access terminal of the first voltage comparator, the positive power access terminal of the second voltage comparator, the positive power access terminal of the third voltage comparator, and the positive power access terminal of the fourth voltage comparator, for providing the positive voltage.

[0019] Optionally, the photovoltaic string monitoring device also includes: a first potentiometer, the output end of the first potentiometer is connected to the positive input end of the first voltage comparator, the first lead end of the first potentiometer is connected to the first positive output end of the high-impedance DC isolation power supply, and the second lead end of the first potentiometer is grounded; a second potentiometer, the output end of the second potentiometer is connected to the negative input end of the second voltage comparator, the first lead end of the second potentiometer is connected to the first negative output end of the high-impedance DC isolation power supply, and the second lead end of the second potentiometer is grounded; a third potentiometer, the output end of the third potentiometer is connected to the positive input end of the third voltage comparator, the first lead end of the third potentiometer is connected to the first positive output end of the high-impedance DC isolation power supply, and the second lead end of the third potentiometer is grounded; a fourth potentiometer, the output end of the fourth potentiometer is connected to the negative input end of the fourth voltage comparator, the first lead end of the fourth potentiometer is connected to the first negative output end of the high-impedance DC isolation power supply, and the second lead end of the fourth potentiometer is grounded.

[0020] Optionally, the photovoltaic string monitoring device also includes: a first OR gate, a first input end of the first OR gate is connected to the output end of the first voltage comparator, and a second input end of the first OR gate is connected to the output end of the second voltage comparator; a NOT gate, an input end of the NOT gate is connected to the output end of the first OR gate; a first reminder light, an input end of the first reminder light is connected to the output end of the first voltage comparator; a second reminder light, an input end of the second reminder light is connected to the output end of the NOT gate; and a third reminder light, an input end of the third reminder light is connected to the output end of the second voltage comparator.

[0021] Optionally, the photovoltaic string monitoring device also includes: a second OR gate, a first input end of the second OR gate is connected to the output end of the third voltage comparator, and a second input end of the second OR gate is connected to the output end of the fourth voltage comparator; an AND gate, a first input end of the AND gate is connected to the output end of the first OR gate, and a second input end of the AND gate is connected to the output end of the second OR gate; and a fourth reminder light, an input end of the fourth reminder light is connected to the output end of the AND gate.

[0022] Optionally, the photovoltaic string monitoring device also includes: a first resistor, wherein the first end of the first resistor is connected to the second access end of the first overcurrent protector; a first variable resistor, wherein the first end of the first variable resistor is connected to the second end of the first resistor, and the second end of the first variable resistor is connected to the first end of the first equivalent bridge resistor; a second resistor, wherein the first end of the second resistor is connected to the second access end of the second overcurrent protector; a second variable resistor, wherein the first end of the second variable resistor is connected to the second end of the second resistor, and the second end of the second variable resistor is connected to the first end of the second equivalent bridge resistor.

[0023] The utility model provides a photovoltaic string monitoring device, which can effectively prevent the photovoltaic string connected to the inverter DC access device from having a string current backflow fault by arranging a positive diode between the positive terminal of the photovoltaic string and the positive access terminal of the inverter DC access device, so that the current can only flow from the positive terminal of the photovoltaic string to the inverter DC access device, and arranging a negative diode between the negative terminal of the photovoltaic string and the negative access terminal of the inverter DC access device, so that the current can only flow from the inverter DC access device to the negative terminal of the photovoltaic string. The first equivalent bridge resistor, the second equivalent bridge resistor, the third equivalent bridge resistor and the fourth equivalent bridge resistor between the terminals constitute a voltage monitoring sampling loop. When the insulation of the positive pole part or the negative pole part of the photovoltaic string is damaged, the string monitoring voltage at the voltage monitoring port will change sharply. It is only necessary to monitor whether the string monitoring voltage exceeds the normal value of the voltage to ground between the positive and negative strings when the photovoltaic string is operating normally, so as to quickly determine whether the photovoltaic string has a low insulation fault, which can significantly improve the monitoring speed of the low insulation fault of the string, thereby significantly improving the operating stability of the photovoltaic power station.

[0024] The above description is only an overview of the technical solution of the utility model. In order to more clearly understand the technical means of the utility model, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the utility model more obvious and easy to understand, the specific implementation methods of the utility model are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings:

[0026] Figure 1 One of the structural schematic diagrams of a photovoltaic string monitoring device provided by an embodiment of the utility model is shown;

[0027] Figure 2 A second structural schematic diagram of a photovoltaic string monitoring device provided by an embodiment of the utility model is shown;

[0028] Figure 3 A third structural schematic diagram of a photovoltaic string monitoring device provided by an embodiment of the utility model is shown;

[0029] Figure 4 A fourth structural schematic diagram of a photovoltaic string monitoring device provided by an embodiment of the utility model is shown;

[0030] Figure 5 A schematic structural diagram of a reminder light provided by an embodiment of the utility model is shown. DETAILED DESCRIPTION

[0031] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0032] In order to further explain the technical means and effects adopted by the utility model to achieve the predetermined utility model purpose, the specific implementation methods, structures, features and effects of the utility model application are described in detail below in conjunction with the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures, or characteristics in one or more embodiments may be combined in any suitable form.

[0033] Combine the following Figures 1 to 5 A photovoltaic string monitoring device according to some embodiments of the present invention is described.

[0034] like Figure 1 As shown, a photovoltaic string monitoring device 200 proposed in one embodiment of the utility model is used to be connected between an inverter DC access device 100 and a photovoltaic string 300 of a photovoltaic power station. The inverter DC access device 100 may be a string inverter or a DC combiner box, both of which may be connected to at least one photovoltaic string 300.

[0035] In the above embodiment, the photovoltaic string monitoring device 200 includes a positive diode 210, a negative diode 220, a first equal-value bridge resistor RA, a second equal-value bridge resistor RB, a third equal-value bridge resistor RC and a fourth equal-value bridge resistor RD.

[0036] Specifically, the positive terminal of the positive diode 210 is connected to the positive terminal of the photovoltaic string 300, and the negative terminal of the positive diode 210 is connected to the positive access terminal of the inverter DC access device 100; by using the unidirectional conduction principle of the diode, the current can only flow from the positive terminal of the photovoltaic string 300 to the inverter DC access device 100, and the current of the inverter DC access device 100 cannot flow into the positive part of the photovoltaic string 300. Further, the negative terminal of the negative diode 220 is connected to the negative terminal of the photovoltaic string 300, and the positive terminal of the negative diode 220 is connected to the negative access terminal of the inverter DC access device 100; the current can only flow from the inverter DC access device 100 to the negative terminal of the photovoltaic string 300. Here, the positive access terminal of the inverter DC access device 100 is used to access the positive pole of the photovoltaic string 300, and the negative access terminal of the inverter DC access device 100 is used to access the negative pole of the photovoltaic string 300, so as to transmit the DC power generated by the photovoltaic string 300 to the inverter DC access device 100, and the inverter DC access device 100 converts the received DC power into AC power.

[0037] By setting a diode between the photovoltaic string and the inverter DC access device in the above manner, it is possible to effectively prevent the current of the high-voltage photovoltaic string from flowing back into the low-voltage photovoltaic string due to uneven voltage between different photovoltaic strings under the same string inverter or DC combiner box, thereby completely eliminating the occurrence of string current backflow failure.

[0038] Further, the first end of the first equivalent bridge resistor RA is connected between the positive end of the positive diode 210 and the positive end of the photovoltaic string 300, the first end of the second equivalent bridge resistor RB is connected between the negative end of the negative diode 220 and the negative end of the photovoltaic string 300, and the second end of the second equivalent bridge resistor RB is connected to the second end of the first equivalent bridge resistor RA; the first end of the third equivalent bridge resistor RC is connected to the first end of the first equivalent bridge resistor RA, and the second end of the third equivalent bridge resistor RC is grounded; the first end of the fourth equivalent bridge resistor RD is connected to the first end of the second equivalent bridge resistor RB, and the second end of the fourth equivalent bridge resistor RD is connected to the second end of the third equivalent bridge resistor RC; further, a voltage monitoring port V1 is provided between the second end of the first equivalent bridge resistor RA and the second end of the second equivalent bridge resistor RB, for outputting a string monitoring voltage for monitoring whether there is an abnormality in the photovoltaic string 300.

[0039] Here, the first equivalent bridge resistor RA, the second equivalent bridge resistor RB, the third equivalent bridge resistor RC and the fourth equivalent bridge resistor RD constitute a voltage monitoring sampling loop, and the third equivalent bridge resistor RC and the fourth equivalent bridge resistor RD are connected to the ground to limit their potential to zero. When the photovoltaic string is well insulated from the ground and no string insulation failure occurs, the potential of the voltage monitoring port V1 does not exceed the preset potential interval of the reference source. The preset potential interval of the reference source is the potential interval that the first equivalent bridge resistor RA and the second equivalent bridge resistor RB should be in when the photovoltaic string does not have a string insulation failure, which is determined in advance through experiments or tests.

[0040] Furthermore, when poor insulation occurs on the positive side of the photovoltaic string, the potential of the string monitoring voltage at the voltage monitoring port V1 increases positively and exceeds the maximum value of the preset potential interval of the reference source. At this time, the string monitoring voltage can be collected. If it is found that the string monitoring voltage at the voltage monitoring port V1 is greater than the maximum value of the preset potential interval of the reference source, it can be determined that the photovoltaic string has a low string insulation fault and poor insulation occurs on the positive side of the photovoltaic string. Conversely, when the insulation on the negative side of the photovoltaic string decreases, the potential of the voltage monitoring port V1 decreases and is lower than the minimum value of the preset potential interval of the reference source. At this time, if it is found that the string monitoring voltage at the voltage monitoring port V1 is less than the minimum value of the preset potential interval of the reference source, it can be determined that the photovoltaic string has a low string insulation fault and poor insulation occurs on the negative side of the photovoltaic string. Here, the string monitoring voltage can be introduced into an external high-sensitivity data processing calculator, and the high-sensitivity data processing calculator performs the above judgment work.

[0041] The photovoltaic string monitoring device proposed in the embodiment of the utility model sets a positive diode between the positive terminal of the photovoltaic string and the positive access terminal of the inverter DC access device, so that the current can only flow from the positive terminal of the photovoltaic string to the inverter DC access device, and sets a negative diode between the negative terminal of the photovoltaic string and the negative access terminal of the inverter DC access device, so that the current can only flow from the inverter DC access device to the negative terminal of the photovoltaic string, which can effectively prevent the photovoltaic string connected to the inverter DC access device from having a string current backflow fault; further, a voltage monitoring sampling loop is formed by setting a first equivalent bridge resistor, a second equivalent bridge resistor, a third equivalent bridge resistor and a fourth equivalent bridge resistor between the positive terminal of the photovoltaic string and the negative terminal of the photovoltaic string When the insulation of the positive or negative strings of the PV strings is damaged, the string monitoring voltage at the voltage monitoring port will change sharply. It is only necessary to monitor whether the string monitoring voltage exceeds the normal value of the voltage to ground between the positive and negative strings when the PV strings are operating normally, so as to quickly determine whether the PV strings have a low insulation fault and determine the fault point where the low insulation fault occurs. This can significantly improve the monitoring speed of the low insulation fault, thereby significantly improving the operating stability of the PV power station, and can detect the bad state of the PV strings in advance, so as to facilitate the advance discovery of the weak insulation points of the DC PV strings so as to eliminate the defects at an early stage, reduce the occurrence of inverter accidents, and thus improve the power generation efficiency and service life of the PV power station.

[0042] In one embodiment of the present invention, optionally, Figure 2 As shown, the photovoltaic string monitoring device 200 also includes a first overcurrent protector RD1 and a second overcurrent protector RD2. The first overcurrent protector RD1 and the second overcurrent protector RD2 can be high-voltage fuses. Specifically, the first access end of the first overcurrent protector RD1 is connected between the positive terminal of the positive diode 210 and the positive terminal of the photovoltaic string 300, and the second access end of the first overcurrent protector RD1 is connected to the first end of the first equivalent bridge resistor RA; further, the first access end of the second overcurrent protector RD2 is connected between the negative terminal of the negative diode 220 and the negative terminal of the photovoltaic string 300, and the second access end of the second overcurrent protector RD2 is connected to the first end of the second equivalent bridge resistor RB. In the above embodiment, the first equal-value bridge resistor, the second equal-value bridge resistor, the third equal-value bridge resistor, the fourth equal-value bridge resistor and the voltage monitoring port are protected by the first overcurrent protector and the second overcurrent protector, and the voltage monitoring sampling loop where the first equal-value bridge resistor, the second equal-value bridge resistor, the third equal-value bridge resistor and the fourth equal-value bridge resistor are located can be short-circuited, thereby improving the operating reliability of the device.

[0043] In one embodiment of the present invention, optionally, Figure 2 As shown, the photovoltaic string monitoring device 200 also includes a Hall sensor 230, and the Hall sensor 230 is used to surround the grounding wire between the second end of the third equal-value bridge resistor RC and the ground in the input through hole of the Hall sensor 230 to determine the ground leakage current of the grounding wire. The Hall sensor 230 may include a current output terminal, and when the grounding wire has a ground leakage current, the Hall sensor 230 will also output the monitoring current to the outside through the current output terminal.

[0044] Here, when the insulation of the photovoltaic string is good, no current flows in the grounding wire. When the insulation on the positive or negative side of the photovoltaic string is reduced, the grounding wire corresponding to the Hall sensor 230 has a leakage current to the ground, and the Hall sensor 230 generates a monitoring current based on the leakage current to the ground in the grounding wire based on the Hall effect; further, it can be judged whether the monitoring current exceeds the monitoring current range, wherein the monitoring current range can be the range in which the monitoring current should be when the insulation of the photovoltaic string is good, which is predetermined according to experiments or tests. At this time, the current monitoring current can be compared with the monitoring current range to determine whether the monitoring current exceeds the monitoring current range. If the monitoring current exceeds the monitoring current range, it means that the photovoltaic string has a low insulation fault. Here, the monitoring current can be introduced into an external high-sensitivity data processing calculator, and the high-sensitivity data processing calculator performs the above judgment work. In the above embodiment, by judging whether there is a leakage current to the ground in the grounding wire through the monitoring current output by the Hall sensor, the leakage current generated by the low insulation fault of the string can be quickly monitored, and the monitoring speed of the low insulation fault of the string can be significantly improved, thereby significantly improving the operation stability of the photovoltaic power station.

[0045] In one embodiment of the present invention, optionally, Figure 3As shown, the photovoltaic string monitoring device 200 also includes a first voltage comparator COMP1 and a second voltage comparator COMP2. Each voltage comparator can determine the voltage value of its positive access terminal and negative access terminal. When the voltage of the positive access terminal is less than the voltage of the negative access terminal, its output terminal outputs a high level; the positive power supply access terminal of the first voltage comparator COMP1 is connected to the first external power supply E1, and is used to obtain the positive voltage from the first external power supply E1, the negative power supply access terminal of the first voltage comparator COMP1 is grounded, the negative input terminal of the first voltage comparator COMP1 is connected to the voltage monitoring port V1, and the positive input terminal of the first voltage comparator COMP1 is connected to the second external power supply E2, and is used to obtain the first reference positive voltage. Here, the first reference positive voltage is determined in advance through testing or experiments. When the photovoltaic string does not have a low string insulation fault, the maximum value of the voltage on its positive side can be connected to the second external power supply E2 that outputs the first reference positive voltage and the positive input terminal of the first voltage comparator COMP1 to provide the first reference positive voltage. Here, the output terminal V3 of the first voltage comparator COMP1 is used to output the first string monitoring voltage for judging whether the positive side of the photovoltaic string 300 is abnormal; specifically, when the positive side of the photovoltaic string has a low string insulation fault, the voltage at the voltage monitoring port V1 increases positively. When it exceeds the first reference positive voltage, the first voltage comparator COMP1 outputs a high level. At this time, it is only necessary to monitor whether the first string monitoring voltage is high to confirm whether the positive side of the photovoltaic string has a low string insulation fault.

[0046] Further, the positive power supply access terminal of the second voltage comparator COMP2 is connected to the third external power supply E3, and is used to obtain the positive voltage from the third external power supply E3. The negative power supply access terminal of the second voltage comparator COMP2 is grounded, and the negative input terminal of the second voltage comparator COMP2 is connected to the fourth external power supply E4, and is used to obtain the first reference negative voltage. The positive input terminal of the second voltage comparator COMP2 is connected to the voltage monitoring port V1. Here, the first reference negative voltage is determined in advance through testing or experiments. When the photovoltaic string 300 does not have a string insulation low fault, the minimum value of the voltage on its negative side can be connected to the fourth external power supply E4 that outputs the first reference negative voltage and the negative input terminal of the second voltage comparator COMP2 to provide the first reference negative voltage. Here, the output terminal V4 of the second voltage comparator COMP2 is used to output the second string monitoring voltage for judging whether there is an abnormality on the negative side of the photovoltaic string 300. Specifically, when a low string insulation fault occurs on the negative side of the photovoltaic string, the voltage at the voltage monitoring port V1 increases negatively. When it exceeds the first reference negative voltage, the second voltage comparator COMP2 outputs a high level. At this time, it is only necessary to monitor whether the second string monitoring voltage is at a high level to confirm whether a low string insulation fault occurs on the negative side of the photovoltaic string. In the above embodiment, it is possible to determine whether a low string insulation fault occurs on the photovoltaic string by determining whether the first string monitoring voltage and the second string monitoring voltage output by the voltage comparator are at a high level, and to determine the insulation condition of the photovoltaic string. The partition position of the fault point can be located during fault inspection, so as to facilitate early judgment of the poor insulation condition of the photovoltaic string, and to facilitate rapid discovery and handling of equipment defects.

[0047] In one embodiment of the present invention, optionally, Figure 3 As shown, the Hall sensor 230 is also used to convert the ground leakage current into a voltage signal; the Hall sensor 230 is provided with a voltage sampling port V2, which is used to output the voltage signal at the voltage sampling port V2; specifically, the Hall sensor 230 can detect the magnitude of the ground leakage current flowing through the grounding wire based on the principle that the Hall sensor 230 can generate a voltage signal based on the current value sensed by it.

[0048] Furthermore, the photovoltaic string monitoring device 200 also includes a third voltage comparator COMP3 and a fourth voltage comparator COMP4. The positive power supply access terminal of the third voltage comparator COMP3 is connected to the fifth external power supply E5, and is used to obtain the positive voltage from the fifth external power supply E5, the negative power supply access terminal of the third voltage comparator COMP3 is grounded, the negative input terminal of the third voltage comparator is connected to the voltage sampling port V2, and the positive input terminal of the third voltage comparator COMP3 is connected to the sixth external power supply E6, and is used to obtain the second reference positive voltage.

[0049] Here, the second reference positive voltage is determined in advance by testing or experiment, and when the photovoltaic string 200 does not have a low string insulation fault, the current on the ground side between the positive side and the negative side is converted into the maximum value of the voltage signal by the Hall sensor. The sixth external power supply E6 that outputs the second reference positive voltage can be connected to the positive input terminal of the third voltage comparator COMP3 to provide a second reference positive voltage. Here, the output terminal V5 of the third voltage comparator COMP3 is used to output the third string monitoring voltage for judging whether the photovoltaic string has a current leakage abnormality; specifically, when the photovoltaic string 200 has a low string insulation fault on the positive side, the voltage signal at the voltage sampling port V2 increases positively, and when it exceeds the second reference positive voltage, the third voltage comparator COMP3 outputs a high level. At this time, it is only necessary to monitor whether the third string monitoring voltage is high to confirm whether the photovoltaic string has a low string insulation fault on the positive side.

[0050] Further, the positive power supply access terminal of the fourth voltage comparator COMP4 is connected to the seventh external power supply E7, and is used to obtain the positive voltage from the seventh external power supply E7, the negative power supply access terminal of the fourth voltage comparator COMP4 is grounded, the negative input terminal of the fourth voltage comparator COMP4 is connected to the eighth external power supply E8, and is used to obtain the second reference negative voltage, and the positive input terminal of the fourth voltage comparator COMP4 is connected to the voltage sampling port V2. Here, the second reference negative voltage is determined in advance by testing or experiment, and when the photovoltaic string 200 does not have a string insulation low fault, the current on the ground side between the positive side and the negative side is converted into the minimum value of the voltage signal by the Hall sensor. The eighth external power supply E8 that outputs the second reference negative voltage can be connected to the negative input terminal of the fourth voltage comparator COMP4 to provide a second reference negative voltage. Here, the output terminal V6 of the fourth voltage comparator COMP4 is used to output the fourth string monitoring voltage for judging whether the photovoltaic string 200 has a current leakage abnormality. Specifically, when a low string insulation fault occurs on the negative side of the photovoltaic string 200, the voltage signal at the voltage sampling port V2 increases in a negative direction. When it exceeds the second reference negative voltage, the fourth voltage comparator COMP4 outputs a high level. At this time, it is only necessary to monitor whether the fourth string monitoring voltage is at a high level to confirm whether a low string insulation fault occurs on the negative side of the photovoltaic string. In the above embodiment, whether a low string insulation fault occurs on the photovoltaic string can be determined by whether the third string monitoring voltage and the fourth string monitoring voltage output by the voltage comparator are at a high level, thereby improving the speed of detecting whether a low string insulation fault occurs on the photovoltaic string.

[0051] In one embodiment of the present invention, optionally, Figure 4As shown, the photovoltaic string monitoring device also includes a high-impedance DC isolation power supply E, the first power supply access terminal of the high-impedance DC isolation power supply E is connected to the second access terminal of the first overcurrent protector RD1, and the second power supply access terminal of the high-impedance DC isolation power supply E is connected to the second access terminal of the second overcurrent protector RD2, forming the main circuit of the device to obtain working power from the photovoltaic string 300, and the first positive output terminal of the high-impedance DC isolation power supply E is respectively connected to the positive power supply access terminal of the first voltage comparator COMP1, the positive power supply access terminal of the second voltage comparator COMP2, the positive power supply access terminal of the third voltage comparator COMP3, and the positive power supply access terminal of the fourth voltage comparator COMP4, for providing the positive voltage. In the above embodiment, the first overcurrent protector and the second overcurrent protector can provide effective isolation and protection for the high-impedance DC isolation power supply, and the high-impedance DC isolation power supply obtains the working power supply from the photovoltaic string, and performs voltage conversion on the working power supply to generate the power supply DC required by the voltage comparator. Further, the voltage comparator is uniformly powered by the high-impedance DC isolation power supply.

[0052] In one embodiment of the present invention, optionally, Figure 4 As shown, the photovoltaic string monitoring device 200 also includes a first potentiometer R01, a second potentiometer R02, a third potentiometer R03 and a fourth potentiometer R04. Among them, the first potentiometer R01, the second potentiometer R02, the third potentiometer R03 and the fourth potentiometer R04 can be potentiometers used as alarm value adjustment resistors. Here, the potentiometer is a resistor element whose resistance value can be adjusted according to a certain change rule. The potentiometer is usually composed of a resistor body and a movable brush. When the brush moves along the resistor body, a resistance value or voltage that is in a certain relationship with the displacement amount is obtained at the output end.

[0053] Specifically, the output end of the first potentiometer R01 is connected to the positive input end of the first voltage comparator COMP1, the first lead end of the first potentiometer R01 is connected to the first positive output end of the high-impedance DC isolation power supply E to obtain the positive voltage output by the high-impedance DC isolation power supply E, and the second lead end of the first potentiometer R01 is grounded. Furthermore, a first protective resistor R10 may be connected in series between the output end of the first potentiometer R01 and the first positive output end of the high-impedance DC isolation power supply E. Here, the voltage received by the positive input end of the first voltage comparator COMP1 may be the first reference positive voltage by adjusting the resistance value of the first potentiometer R01.

[0054] Further, the output end of the second potentiometer R02 is connected to the negative input end of the second voltage comparator COMP2, the first lead end of the second potentiometer R02 is connected to the first negative output end of the high-impedance DC isolation power supply E to obtain the negative voltage output by the high-impedance DC isolation power supply E, and the second lead end of the second potentiometer R02 is grounded; further, a second protective resistor R20 may be connected in series between the output end of the second potentiometer R02 and the first negative output end of the high-impedance DC isolation power supply E. Here, the voltage received by the negative input end of the second voltage comparator COMP2 may be the first reference negative voltage by adjusting the resistance value of the second potentiometer R02.

[0055] Further, the output end of the third potentiometer R03 is connected to the positive input end of the third voltage comparator COMP3, the first lead end of the third potentiometer R03 is connected to the first positive output end of the high-impedance DC isolation power supply E to obtain the positive voltage output by the high-impedance DC isolation power supply E, and the second lead end of the third potentiometer R03 is grounded; further, a third protection resistor R30 may be connected in series between the output end of the third potentiometer R03 and the first positive output end of the high-impedance DC isolation power supply E. Here, the voltage received by the positive input end of COMP3 may be the second reference positive voltage by adjusting the resistance value of the third potentiometer R03.

[0056] Further, the output end of the fourth potentiometer R04 is connected to the negative input end of the fourth voltage comparator COMP4, the first lead end of the fourth potentiometer R04 is connected to the first negative output end of the high impedance DC isolation power supply E to obtain the negative voltage output by the high impedance DC isolation power supply E, and the second lead end of the fourth potentiometer R04 is grounded. Further, a fourth protection resistor R40 can be connected in series between the output end of the fourth potentiometer R04 and the first negative output end of the high impedance DC isolation power supply E. Here, the voltage received by the negative input end of the fourth voltage comparator COMP4 can be the second reference negative voltage by adjusting the resistance value of the fourth potentiometer R04. In the above embodiment, a high impedance DC isolation power supply can provide a reference positive voltage and a reference negative voltage for the voltage comparator, and the voltage value of the reference positive voltage or the reference negative voltage input to the voltage comparator is adjusted by the potentiometer corresponding to each voltage comparator, and the voltage value of the reference positive voltage or the reference negative voltage input to each voltage comparator can be flexibly determined, thereby improving the operability and adaptability of the photovoltaic string monitoring device.

[0057] In one embodiment of the present invention, optionally, Figure 4As shown, the photovoltaic string monitoring device 200 further includes a first OR gate OR1, a NOT gate NOT, a first reminder light L1, a second reminder light L2, and a third reminder light L3. The first reminder light L1 may be a red light, the second reminder light L2 may be a green light, and the third reminder light L3 may be a blue light. The specific method for determining the light color may be determined according to actual conditions.

[0058] Specifically, the first input end of the first OR gate OR1 is connected to the output end V3 of the first voltage comparator COMP1, and the second input end of the first OR gate OR1 is connected to the output end V4 of the second voltage comparator COMP2. The input end of the NOT gate NOT is connected to the output end of the first OR gate OR1. Further, the input end of the first reminder light L1 is connected to the output end V3 of the first voltage comparator COMP1; the input end of the second reminder light L2 is connected to the output end of the NOT gate NOT; and the input end of the third reminder light L3 is connected to the output end V4 of the second voltage comparator COMP2. Here, if the photovoltaic string is well insulated from the ground, at this time, the first voltage comparator COMP1 and the second voltage comparator COMP2 both output low level, the first OR gate OR1 outputs low level, and the NOT gate NOT outputs high level, so that the second reminder light L2 turns on green, indicating that the photovoltaic string has no string insulation low fault. Furthermore, if the insulation on the positive side of the photovoltaic string is poor, the string monitoring voltage of the voltage monitoring port V1 increases and exceeds the first reference positive voltage set by the first potentiometer R01. At this time, the first voltage comparator COMP1 outputs a high level, causing the first OR gate OR1 to output a high level and the NOT gate NOT to output a low level, causing the second reminder light L2 to go out, indicating that a fault has occurred in the photovoltaic string 300, and the first reminder light L1 lights up red, indicating to the outside world that a low string insulation fault has occurred on the positive side of the photovoltaic string 300.

[0059] Furthermore, when insulation reduction occurs on the negative pole side of the photovoltaic string, the potential of the voltage monitoring port V1 decreases. When the potential of the voltage monitoring port V1 is lower than the first reference negative pole voltage set by the second potentiometer R02, the voltage comparator COMP2 outputs a high level, the first OR gate OR1 outputs a high level, causing the NOT gate NOT to output a low level, causing the second reminder light L2 to go out, indicating that a fault has occurred in the photovoltaic string 300, and the third reminder light L3 lights up in blue, indicating to the outside world that a low string insulation fault has occurred on the negative pole side of the photovoltaic string 300.

[0060] Furthermore, the first reminder light L1, the second reminder light L2 and the third reminder light L3 can be set at the line monitor of the inverter DC access device of the power station, so that the staff can issue corresponding light reminders when the photovoltaic string 300 has a low string insulation fault. In the above embodiment, by observing the changes in the indicator lights of the online monitor, the insulation status of the photovoltaic string is judged, and the partition position of the fault point is located during the fault inspection, which is convenient for judging the poor insulation status of the photovoltaic string in advance and facilitating the rapid discovery and handling of equipment defects.

[0061] In one embodiment of the present invention, optionally, Figure 4 As shown, the photovoltaic string monitoring device 200 also includes a second OR gate OR2, an AND gate AND, and a fourth reminder light L4, and a leakage current monitoring loop can be formed by the third voltage comparator COMP3, the fourth voltage comparator COMP4, the second OR gate OR2, the AND gate AND, and the fourth reminder light L4. Specifically, the first input end of the second OR gate OR2 is connected to the output end V5 of the third voltage comparator COMP3, and the second input end of the second OR gate OR2 is connected to the output end V6 of the fourth voltage comparator COMP4; further, the first input end of the AND gate AND is connected to the output end of the first OR gate OR1, and the second input end of the AND gate AND is connected to the output end of the second OR gate OR2; further, the input end of the fourth reminder light L4 is connected to the output end of the AND gate AND.

[0062] Here, when the insulation of the photovoltaic string 300 is good, no current flows through the grounding wire side, the voltage sampling port V2 on the secondary side of the Hall sensor 230 outputs a zero potential, the potential value does not exceed the reference point preset potential interval, the third voltage comparator COMP3 and the fourth voltage comparator COMP4 both have no high level output, and the second OR gate OR2 outputs a low level, wherein the reference point preset potential interval is determined in advance through experiments or tests, and is the potential that the voltage sampling port V2 should output when the insulation of the photovoltaic string 300 is good. Conversely, when the insulation of the positive side of the photovoltaic string 300 decreases, the output potential of the voltage sampling port V2 on the secondary side of the Hall sensor 230 increases positively, exceeds the second reference positive voltage preset by R03, the third voltage comparator COMP3 outputs a high level, and outputs a high level through the second OR gate OR2 circuit, and to the AND gate AND, so that the AND gate AND outputs a high level, so that the fourth reminder light L4 lights up, indicating that the photovoltaic string has a string insulation low fault. Furthermore, when the insulation of the negative side of the photovoltaic string 300 is reduced, the potential of the voltage sampling port V2 on the secondary side of the Hall sensor 230 is reduced and is lower than the second reference negative voltage set by R04, and the fourth voltage comparator COMP4 outputs a high level, and outputs a high level to the AND gate AND through the second OR gate OR2, so that the AND gate AND outputs a high level, and the fourth reminder light L4 is turned on, indicating that the photovoltaic string has a low string insulation fault. In the above embodiment, it can be determined whether the photovoltaic string has a low string insulation fault by the grounding side current. When the photovoltaic string has a low string insulation fault, the staff can be informed of the fault in time based on the reminder light at the line monitor of the inverter DC access device of the power station, thereby improving the monitoring capability of the photovoltaic string.

[0063] Furthermore, the first reminder light, the second reminder light, the third reminder light and the fourth reminder light have the same reminder light structure. Figure 5As shown, the structure of the reminder light includes a first reminder light resistor R51, a second reminder light resistor R52, a transistor 500 and a light emitting diode L. Among them, the first end of the first reminder light resistor R51 is used to connect the output end of the first voltage comparator or the output end of the NOT gate or the output end of the second voltage comparator or the output end of the AND gate; the second end of the first reminder light resistor R51 is connected to the base of the transistor 500, the emitter of the transistor 500 is grounded, the collector of the transistor 500 is connected to the first end of the second reminder light resistor R52, the second end of the second reminder light resistor R52 is connected to the cathode of the light emitting diode L, and the anode of the light emitting diode L is connected to the positive power supply V+. As an example, if the reminder light is the first reminder light, the first end of the first reminder light resistor R51 is used to connect the output end of the first voltage comparator. When the output end of the first voltage comparator outputs a high level, the level output by the first voltage comparator can be amplified based on the transistor 500 to drive the first reminder light to emit light. The working principle of other reminder lights can refer to the above description of the first reminder light, which will not be repeated here.

[0064] In one embodiment of the present invention, optionally, Figure 4 As shown, the photovoltaic string monitoring device 200 also includes a first resistor R1, a first variable resistor R3, a second resistor R2 and a second variable resistor R4. Specifically, the first end of the first resistor R1 is connected to the second access end of the first overcurrent protector RD1, the first end of the first variable resistor R3 is connected to the second end of the first resistor R1, and the second end of the first variable resistor R3 is connected to the first end of the first equivalent bridge resistor RA; the first end of the second resistor R2 is connected to the second access end of the second overcurrent protector RD2; the first end of the second variable resistor R4 is connected to the second end of the second resistor R2, and the second end of the second variable resistor R4 is connected to the first end of the second equivalent bridge resistor RB. Here, the voltage monitoring sampling loop can be formed by the first resistor R1, the first variable resistor R3, the second resistor R2 and the second variable resistor R4, the first equivalent bridge resistor RA, the second equivalent bridge resistor RB, the third equivalent bridge resistor RC and the fourth equivalent bridge resistor RD. Four equivalent resistors, namely the first equivalent bridge resistor RA, the second equivalent bridge resistor RB, the third equivalent bridge resistor RC and the fourth equivalent bridge resistor RD, are connected in a bridge shape. The first resistor R1 and the second resistor R2 are connected in series on both sides and then connected to the first overcurrent protector RD1 and the second overcurrent protector RD2. The first variable resistor R3 and the second variable resistor R4 are respectively positive and negative pole ratio calibration resistors. The third equivalent bridge resistor RC and the fourth equivalent bridge resistor RD are connected to the ground to limit them to zero potential.

[0065] Furthermore, the current monitoring sampling loop is composed of a Hall sensor 230, and the grounding wire passes through the Hall sensor 230 to detect the leakage current to the ground, and converts the change in the DC current flowing through into the change in the potential of the voltage sampling port V2. Here, in order to prevent the string monitoring voltage output to the first voltage comparator COMP1 and the second voltage comparator COMP2 from exceeding the maximum tolerance voltage of the comparator, and to ensure that the comparison circuit can work normally and reliably, the upper limit of the ground potential of the voltage monitoring port V1 can be limited by adjusting the resistance ratio of the first resistor R1 and the first equal-value bridge resistor RA. Similarly, the lower limit of the ground potential of the voltage monitoring port V1 can be limited by adjusting the resistance ratio of the second resistor R2 and the second equal-value bridge resistor RB.

[0066] As an example, if the maximum withstand voltage value of the first voltage comparator COMP1 and the second voltage comparator COMP2 is -20.3V--0--+20.3V, now taking the DC voltage limit of 1500V of the photovoltaic string 300 as an example, the resistance values ​​of the first resistor R1 and the second resistor R2 as current limiting resistors are set to 29800Ω respectively, and the resistance values ​​of the first equivalent bridge resistor RA, the second equivalent bridge resistor RB, the third equivalent bridge resistor RC and the fourth equivalent bridge resistor RD as bridge resistors are set to 200Ω respectively, and the resistance ratio of the current limiting resistor to the bridge resistor is 149:1. When the photovoltaic string system is well insulated, the potential of the voltage monitoring port V1 is zero potential. When the positive insulation of the photovoltaic string 300 system is damaged, the ground fault at the positive lead-in line side is analyzed in the limit state. At this time, the voltage between the positive pole of the string and the ground is zero, and the voltage between the negative pole and the ground increases to 1500V. It can be calculated that the resistance value flowing through the voltage monitoring sampling loop is 29950Ω, and the current flowing through the grounding wire is U / R=50.8mA. At this time, the potential of the voltage monitoring port V1 is equal to +20.3V. Here, the first variable resistor R3 and the second variable resistor R4 are also current limiting resistors. When the first resistor R1 and the second resistor R2 are connected to the circuit, if the resistance value of the first resistor R1 is smaller than its preset resistance value, the resistance value of the first variable resistor R3 can be appropriately increased so that the resistance ratio of the current limiting resistor to the bridge resistor meets the requirements. If the resistance value of the second resistor R2 is smaller than its preset resistance value, the resistance value of the second variable resistor R4 can be appropriately increased so that the resistance ratio of the current limiting resistor to the bridge resistor meets the requirements. When the first resistor R1 and the second resistor R2 are connected to the circuit, if the resistance value of the first resistor R1 and the resistance value of the second resistor R2 meet the requirements, the resistance values ​​of the first variable resistor R3 and the second variable resistor R4 can be set to zero to improve the operability of the device.

[0067] Further, when the negative pole of the photovoltaic string 300 is extremely grounded, the voltage of the positive pole to the ground is -1500V, and the potential of the voltage monitoring port V1 can be calculated as -20.3V according to the above method, and the current flowing through the grounding wire is -50.8mA, so it is concluded that the potential change range of the voltage monitoring port V1 is -20.3V to 20.3V. The DC current flowing through the primary side of the Hall sensor 230 varies from -50.8mA to 50.8mA. In addition, the string monitoring voltage output to the first voltage comparator COMP1 and the second voltage comparator COMP2 can be kept within the high tolerance voltage value of the first voltage comparator COMP1 and the second voltage comparator COMP2. In the above embodiment, the resistance values ​​of the first resistor, the second resistor, the first equivalent bridge resistor, the second equivalent bridge resistor, the third equivalent bridge resistor and the fourth equivalent bridge resistor can be set according to the tolerance voltage value of the first voltage comparator and the second voltage comparator, so that the string monitoring voltage is kept within the tolerance voltage value of the first voltage comparator and the second voltage comparator. At the same time, when the Hall sensor has specific requirements on the variation range of the DC current passing through its primary side, the above-mentioned resistance value change can also be used to make the Hall sensor keep the DC current passing through its primary side within its current variation range, thereby ensuring that the Hall sensor and the voltage comparator can operate stably.

[0068] It is understandable that the circuit composition of the photovoltaic string monitoring device, the selection of the components of the photovoltaic string monitoring device, and the type of signals interacting within the photovoltaic string monitoring device can be selected and set according to the actual scenario of the production design, and this embodiment does not make specific restrictions. In addition, the method for determining the fault state of the photovoltaic string based on the string monitoring voltage, the ground leakage current, the first string monitoring voltage, the second string monitoring voltage, the third string monitoring voltage, the fourth string monitoring voltage and the monitoring current can also be implemented by the program module in the prior art, and this embodiment does not make specific restrictions. It should be noted that the circuit function of the photovoltaic string monitoring device provided in this embodiment is mainly realized through the circuit connection relationship between the modules, and does not rely on the program module in a certain module.

[0069] The above-mentioned embodiments only express several implementation methods of the utility model, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the utility model patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the utility model, which all belong to the protection scope of the utility model. Therefore, the protection scope of the utility model patent shall be based on the attached claims.

Claims

1. A photovoltaic string monitoring device, used to be connected between the inverter DC access device and the photovoltaic string of a photovoltaic power station, characterized in that: The photovoltaic string monitoring device comprises: A positive diode, wherein the positive terminal of the positive diode is connected to the positive terminal of the photovoltaic string, and the negative terminal of the positive diode is connected to the positive access terminal of the inverter DC access device; A negative electrode diode, wherein the negative terminal of the negative electrode diode is connected to the negative terminal of the photovoltaic string, and the positive terminal of the negative electrode diode is connected to the negative electrode access terminal of the inverter DC access device; a first equal-value bridge resistor, wherein a first end of the first equal-value bridge resistor is connected between a positive terminal of the positive diode and a positive terminal of the photovoltaic string; a second equal-value bridge resistor, wherein a first end of the second equal-value bridge resistor is connected between the negative terminal of the negative diode and the negative terminal of the photovoltaic string, and a second end of the second equal-value bridge resistor is connected to a second end of the first equal-value bridge resistor; a third equal-value bridge resistor, wherein a first end of the third equal-value bridge resistor is connected to a first end of the first equal-value bridge resistor, and a second end of the third equal-value bridge resistor is grounded; a fourth equal-value bridge resistor, wherein a first end of the fourth equal-value bridge resistor is connected to a first end of the second equal-value bridge resistor, and a second end of the fourth equal-value bridge resistor is connected to a second end of the third equal-value bridge resistor; A voltage monitoring port is provided between the second end of the first equal-value bridge resistor and the second end of the second equal-value bridge resistor, and is used to output a string monitoring voltage for monitoring whether there is an abnormality in the photovoltaic string.

2. The photovoltaic string monitoring device according to claim 1, characterized in that: The photovoltaic string monitoring device further comprises: A first overcurrent protector, wherein a first access terminal of the first overcurrent protector is connected between the positive terminal of the positive diode and the positive terminal of the photovoltaic string, and a second access terminal of the first overcurrent protector is connected to a first end of the first equal-value bridge resistor; A second overcurrent protector, wherein a first access terminal of the second overcurrent protector is connected between the negative terminal of the negative diode and the negative terminal of the photovoltaic string, and a second access terminal of the second overcurrent protector is connected to a first terminal of the second equal-value bridge resistor.

3. The photovoltaic string monitoring device according to claim 2, characterized in that: The photovoltaic string monitoring device further comprises: A Hall sensor is used to surround a grounding conductor between the second end of the third equal-value bridge resistor and the ground in an input through hole of the Hall sensor to determine a leakage current of the grounding conductor to the ground.

4. The photovoltaic string monitoring device according to claim 3, characterized in that: The photovoltaic string monitoring device further comprises: A first voltage comparator, wherein a positive power supply access terminal of the first voltage comparator is connected to a first external power supply and is used to obtain a positive voltage from the first external power supply, a negative power supply access terminal of the first voltage comparator is grounded, a negative input terminal of the first voltage comparator is connected to the voltage monitoring port, a positive input terminal of the first voltage comparator is connected to a second external power supply and is used to obtain a first reference positive voltage, and an output terminal of the first voltage comparator is used to output a first string monitoring voltage for determining whether an abnormality occurs on the positive side of the photovoltaic string; A second voltage comparator, wherein the positive power supply access terminal of the second voltage comparator is connected to the third external power supply and is used to obtain a positive voltage from the third external power supply, the negative power supply access terminal of the second voltage comparator is grounded, the negative input terminal of the second voltage comparator is connected to the fourth external power supply and is used to obtain a first reference negative voltage, the positive input terminal of the second voltage comparator is connected to the voltage monitoring port, and the output terminal of the second voltage comparator is used to output a second string monitoring voltage for determining whether an abnormality occurs on the negative side of the photovoltaic string.

5. The photovoltaic string monitoring device according to claim 4, characterized in that: The Hall sensor is used to convert the ground leakage current into a voltage signal; the Hall sensor is provided with a voltage sampling port, which is used to output the voltage signal at the voltage sampling port; The photovoltaic string monitoring device further comprises: A third voltage comparator, wherein the positive power supply access terminal of the third voltage comparator is connected to the fifth external power supply and is used to obtain a positive voltage from the fifth external power supply, the negative power supply access terminal of the third voltage comparator is grounded, the negative input terminal of the third voltage comparator is connected to the voltage sampling port, the positive input terminal of the third voltage comparator is connected to the sixth external power supply and is used to obtain a second reference positive voltage, and the output terminal of the third voltage comparator is used to output a third string monitoring voltage for judging whether a current leakage abnormality occurs in the photovoltaic string; A fourth voltage comparator, wherein the positive power supply access terminal of the fourth voltage comparator is connected to the seventh external power supply and is used to obtain a positive voltage from the seventh external power supply, the negative power supply access terminal of the fourth voltage comparator is grounded, the negative input terminal of the fourth voltage comparator is connected to the eighth external power supply and is used to obtain a second reference negative voltage, the positive input terminal of the fourth voltage comparator is connected to the voltage sampling port, and the output terminal of the fourth voltage comparator is used to output a fourth string monitoring voltage for determining whether an abnormal current leakage occurs in the photovoltaic string.

6. The photovoltaic string monitoring device according to claim 5, characterized in that: The photovoltaic string monitoring device further comprises: A high-impedance DC isolated power supply, wherein the first power access terminal of the high-impedance DC isolated power supply is connected to the second access terminal of the first overcurrent protector, and the second power access terminal of the high-impedance DC isolated power supply is connected to the second access terminal of the second overcurrent protector to obtain a working power supply, and the first positive output terminal of the high-impedance DC isolated power supply is respectively connected to the positive power access terminal of the first voltage comparator, the positive power access terminal of the second voltage comparator, the positive power access terminal of the third voltage comparator, and the positive power access terminal of the fourth voltage comparator, for providing the positive voltage.

7. The photovoltaic string monitoring device according to claim 6, characterized in that: The photovoltaic string monitoring device further comprises: A first potentiometer, wherein an output end of the first potentiometer is connected to a positive input end of the first voltage comparator, a first lead end of the first potentiometer is connected to a first positive output end of the high-impedance DC isolation power supply, and a second lead end of the first potentiometer is grounded; A second potentiometer, wherein the output end of the second potentiometer is connected to the negative input end of the second voltage comparator, the first lead end of the second potentiometer is connected to the first negative output end of the high-impedance DC isolation power supply, and the second lead end of the second potentiometer is grounded; A third potentiometer, wherein the output end of the third potentiometer is connected to the positive input end of the third voltage comparator, the first lead end of the third potentiometer is connected to the first positive output end of the high-impedance DC isolation power supply, and the second lead end of the third potentiometer is grounded; A fourth potentiometer, wherein the output end of the fourth potentiometer is connected to the negative input end of the fourth voltage comparator, the first lead end of the fourth potentiometer is connected to the first negative output end of the high-impedance DC isolation power supply, and the second lead end of the fourth potentiometer is grounded.

8. The photovoltaic string monitoring device according to claim 6, characterized in that: The photovoltaic string monitoring device further comprises: a first OR gate, wherein a first input terminal of the first OR gate is connected to the output terminal of the first voltage comparator, and a second input terminal of the first OR gate is connected to the output terminal of the second voltage comparator; A NOT gate, wherein an input terminal of the NOT gate is connected to an output terminal of the first OR gate; a first reminder light, wherein an input end of the first reminder light is connected to an output end of the first voltage comparator; a second reminder light, wherein an input end of the second reminder light is connected to an output end of the NOT gate; A third reminder light, wherein an input end of the third reminder light is connected to an output end of the second voltage comparator.

9. The photovoltaic string monitoring device according to claim 8, characterized in that: The photovoltaic string monitoring device further comprises: a second OR gate, wherein a first input terminal of the second OR gate is connected to the output terminal of the third voltage comparator, and a second input terminal of the second OR gate is connected to the output terminal of the fourth voltage comparator; An AND gate, wherein a first input terminal of the AND gate is connected to an output terminal of the first OR gate, and a second input terminal of the AND gate is connected to an output terminal of the second OR gate; A fourth reminder light, wherein an input end of the fourth reminder light is connected to an output end of the AND gate.

10. The photovoltaic string monitoring device according to claim 6, characterized in that: The photovoltaic string monitoring device further comprises: A first resistor, wherein a first end of the first resistor is connected to a second access end of the first overcurrent protector; a first variable resistor, wherein a first end of the first variable resistor is connected to a second end of the first resistor, and a second end of the first variable resistor is connected to a first end of the first equal-value bridge resistor; a second resistor, wherein a first end of the second resistor is connected to a second access end of the second overcurrent protector; A second variable resistor, wherein a first end of the second variable resistor is connected to a second end of the second resistor, and a second end of the second variable resistor is connected to a first end of the second equal-value bridge resistor.

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