CN113852351B

CN113852351B - Photovoltaic module fault point positioning system and method

Info

Publication number: CN113852351B
Application number: CN202111169470.7A
Authority: CN
Inventors: 张永
Original assignee: FONRICH NEW ENERGY TECHNOLOGY Ltd SHANGHAI
Current assignee: FONRICH NEW ENERGY TECHNOLOGY Ltd SHANGHAI
Priority date: 2021-10-08
Filing date: 2021-10-08
Publication date: 2024-01-12
Anticipated expiration: 2041-10-08
Also published as: CN113852351A

Abstract

The invention mainly relates to a system and a method for positioning a fault point of a photovoltaic module. A plurality of photovoltaic modules connected in parallel by a plurality of battery strings and each including a plurality of photovoltaic modules connected in series by cables, a string current flowing through any one of the battery strings being measured in the any one of the battery strings; and measuring the branch current provided by each monitored photovoltaic module to the cable in any battery string; and comparing the string current with the branch current, judging whether an expected difference exists between the string current and the branch current, if so, considering that the monitored photovoltaic module has faults, and if not, considering that the monitored photovoltaic module operates normally.

Description

Photovoltaic module fault point positioning system and method

Technical Field

The invention mainly relates to the field of photovoltaic power generation, in particular to a photovoltaic module fault point positioning system and a photovoltaic module fault point positioning method in a photovoltaic power generation system containing a photovoltaic module, which not only ensure that the photovoltaic module operates in a safe and reliable environment, but also realize the fault investigation of the photovoltaic module.

Background

Parallel faults or ground faults are a troublesome problem in photovoltaic systems. Parallel faults or ground faults may or may not cause arcing in the photovoltaic system, but merely electrical leakage. The location where such a fault occurs may also be between the photovoltaic module and earth, between cables and earth, etc. There is temporarily no corresponding detection means to cope with parallel faults or ground faults in the conventional scheme. How to detect parallel faults, ground faults, if these faults are manifested as possible parallel arcs, or insulation leaks, then the problem is how to accurately detect the exact location of the fault, including not only the photovoltaic module, but also the external of the module, and the discharge between the cable or between the cable and the earth.

The photovoltaic module is used as an important core component of the photovoltaic power generation system, the overall effect of the power generation system is directly affected by the excellent performance of the photovoltaic module, but in practice, the photovoltaic module is subjected to more constraint factors, and the characteristic difference of each photovoltaic module can cause the loss of the coupling combination efficiency. The photovoltaic module array is generally in series-parallel connection, and if a certain battery module is shaded or dust or shielded or aged to reduce power, other modules in series-parallel connection may be affected by the reduction of voltage and current intensity. In order to ensure the safety and reliability of the operation of the photovoltaic array, it is important to fully exert the maximum power generation efficiency of each photovoltaic module and ensure that the photovoltaic modules are in a normal operation state.

Based on the monitoring pressure of the photovoltaic power station on the component, it is necessary to establish a reasonable set of monitoring and management mechanism, through which the parameter data of the component board can be extracted from the component board, and the data can be fed back to the owner or user. Real-time parameters such as output voltage and current of the photovoltaic modules, power and environmental temperature of the photovoltaic modules need to be monitored in time, especially abnormal conditions such as damage or aging of the modules need to be monitored in time, so that the monitoring data information can provide basis for improvement and optimization of each photovoltaic module, and the failed or aged modules can be rapidly positioned and repaired in time. Whether an attempt is made to achieve active control of the battery assembly by an external device or to send parameter information of the battery assembly locally to the external device involves communication problems with the photovoltaic assembly monitoring system. The intelligent management of the photovoltaic module comprises the safety management, the shutdown management, the output power management and the like of the photovoltaic module besides the conventional working parameter monitoring.

The main reason of the poor detection capability of the traditional fault arc detection means is that: one or more sets of fault arc parameter characteristics are required to be firstly made, then the actually detected current parameter information is compared with the fault arc parameter characteristics, if the actually detected current parameter information accords with the fault arc parameter characteristics, the actual arc event is considered to occur, otherwise, if the actually detected current parameter information does not accord with the fault arc parameter characteristics, the actual arc event is considered not to occur. The biggest drawbacks are that the power system of each scene to be tested has a difference and the inverter model of each scene to be tested is different, so that the traditional fault arc detection means always has detection errors or even errors, and the inherent drawbacks are almost irresistible.

The application mainly solves the problems that the parallel fault or the ground fault can cause electric arcs or can not cause electric arcs but only leak electricity, and is one of the troublesome difficulties. Another troublesome problem is that the location of the fault may be between the component and ground, between the cable and the cable, between the cable and the ground, etc. Such faults generated in the photovoltaic system in the prior art are not detected by corresponding detection means, and countermeasures are lacking.

Disclosure of Invention

The application discloses a photovoltaic module fault point positioning method provides a single battery string or provides a plurality of battery strings connected in parallel, and each battery string comprises a plurality of photovoltaic modules connected in series by cables, wherein:

measuring a string current flowing through any battery string in the any battery string; and

also measuring a branch current at each monitored point in the any battery string;

and comparing the group string current with the branch current, judging whether an expected difference exists between the group string current and the branch current, if so, considering that the monitored point is faulty, and if not, considering that the monitored point is normal.

The method is characterized in that:

the expected differences include:

the current difference between the string current and the branch current is not within a predetermined current fluctuation range.

The method is characterized in that:

the expected differences include:

the branch current has a plurality of high frequency components located within a specified high frequency current band as compared to the series current.

The method is characterized in that:

the expected differences include:

the peak-to-valley difference between the peak and valley of the branch current (branch current peak-to-valley difference) exceeds the peak-to-valley difference between the peak and valley of the set of string currents (set string current peak-to-valley difference).

The method is characterized in that:

the monitored points at least comprise all photovoltaic modules and local cables.

The method is characterized in that:

the fault includes at least a direct current arc fault or a leakage current fault.

The method is characterized in that:

each photovoltaic module is provided with a first device for collecting said branch current at a monitored point;

a second device configured on the cable for collecting at least the set of string currents;

communication is established between the first and second devices, the second devices transmitting a group string current to each of the first devices, each of the first devices determining whether a fault has occurred at a monitored point in the vicinity of itself.

The method is characterized in that:

the first device is selected from:

the method comprises the steps of connecting the photovoltaic module into a photovoltaic junction box of a battery string, removing the photovoltaic module from the battery string or recovering the photovoltaic module in a removed state from the battery string to be connected into a shutdown device of the battery string, setting the photovoltaic module at a power optimizer of a maximum power point of the photovoltaic module, and performing voltage conversion on an initial voltage of the photovoltaic module.

The method is characterized in that:

A plurality of first devices corresponding to the plurality of photovoltaic modules of any one of the strings are arranged in series connection, the output current of each first device being indicative of the branch current it provides to the cable.

The method is characterized in that:

the second device is selected from any one of a current sensor, a combiner box or an inverter.

The method is characterized in that:

the first device comprises a switch arranged between the photovoltaic module and the cable, and the first device immediately operates the switch to be turned off when judging that the monitored point nearby the first device fails so as to disconnect the photovoltaic module matched with the first device from the cable.

The application also discloses a positioning system of photovoltaic module fault point provides single group battery cluster or provides a plurality of group battery clusters of parallel connection, and every group battery cluster includes a plurality of photovoltaic modules that are connected together by the cable series connection, includes:

each photovoltaic module is provided with a first device for receiving output power, and a plurality of first devices corresponding to a plurality of photovoltaic modules under any battery pack string are connected in series through cables;

each first device is also adapted to collect the branch current it supplies to the cable;

A second device that collects a set of string currents flowing through the any one of the battery strings;

establishing communication between the first and second devices, each first device transmitting the branch current it provides to the cable to the second device, the second device determining whether a fault has occurred at the monitored point of each first device; or alternatively

Establishing communication between the first and second devices, the second device sending the information of the group string current to each first device, and the first device judging whether a fault occurs at the monitored point of the first device;

The positioning system of the photovoltaic module fault point is characterized in that:

the first device is selected from:

the method comprises the steps of connecting a photovoltaic module into a photovoltaic junction box of a battery string, removing the photovoltaic module from the battery string or recovering the photovoltaic module in a removed state from a shutdown device connected to the battery string, setting the photovoltaic module at a power optimizer of a maximum power point of the shutdown device, and performing voltage conversion on an initial voltage of the photovoltaic module;

The second device is selected from any one of a current sensor or a combiner box or an inverter.

the expected differences include:

the current difference between the string current and the branch current is not within a predetermined current fluctuation range; or (b)

The branch current has more high-frequency components in a specified high-frequency current frequency band than the series current; or (b)

The peak-to-valley difference between the peak and valley of the branch current exceeds the peak-to-valley difference between the peak and valley of the set of string currents.

The application also discloses a method for positioning the fault point of the photovoltaic module, which comprises the steps of providing a single battery string or providing a plurality of battery strings connected in parallel, wherein each battery string comprises a plurality of photovoltaic modules P1-PN connected in series by cables:

each photovoltaic module is provided with a first device for receiving output power of the photovoltaic module, a plurality of first devices J1-JN corresponding to a plurality of photovoltaic modules P1-PN under any battery pack string are connected in series through cables, and a positive integer N is larger than 1;

establishing communication among different first devices J1-JN, wherein the first device JK receives branch current information of other first devices J1-JN except the first device JK, and K is more than or equal to 1 and less than or equal to N;

The first device JK compares its branch current with the set of branch currents of said other ones:

if there is an expected difference between the branch current of the first device JK and at least a portion of the branch currents in the set, then a fault is considered to occur at the monitored point of the first device JK, otherwise the monitored point of the first device JK is considered to be normal.

The method is characterized in that:

the monitored point at least comprises a photovoltaic module PK matched with the first equipment JK, the first equipment JK and a local cable connected with the first equipment JK.

if there is no expected difference between the branch current of the first device JK and the branch currents of the first devices J (k+1) to JN;

however, there is an expected difference between the branch current of the first device JK and the branch currents of the first devices J1 to J (K-1); then the cable between the first device JK and the first device J (K-1) is considered to have failed.

Drawings

So that the manner in which the above recited objects, features and advantages of the present application can be understood in detail, a more particular description of the invention, briefly summarized below, may be had by reference to the appended drawings.

Fig. 1 shows a photovoltaic module for supplying power to a bus in series and an energy collecting device is arranged on the bus.

Fig. 2 is a schematic diagram of a photovoltaic module configured with a voltage converter to raise or lower the voltage of the photovoltaic module.

Fig. 3 shows that the energy collecting device provided on the bus may be an inverter, a junction box, or the like.

Fig. 4 is a connection of a photovoltaic module to a bus by a photovoltaic junction box equipped with a data acquisition module.

Fig. 5 is a connection of a photovoltaic module to a bus by means of a shut-down device equipped with a data acquisition module.

Fig. 6 is a connection of a photovoltaic module to a bus through a voltage converter equipped with a data acquisition module.

Fig. 7 is a diagram of the transmission of information such as voltage and current of a photovoltaic module from a first device to a second device configured.

Detailed Description

The solution according to the invention will now be described more clearly and completely in connection with the following examples, which are given by way of illustration only and not by way of all examples, on the basis of which those skilled in the art will attain solutions without inventive effort.

Referring to fig. 1, in the photovoltaic power generation field, a photovoltaic module, that is, a photovoltaic cell is a core component for power generation, and a solar panel is divided into a single crystal silicon cell, a polycrystalline silicon solar cell, an amorphous silicon solar cell, and the like in a main flow technical direction. The large-scale centralized photovoltaic power station adopts a huge number of photovoltaic modules, and the small-scale distributed household small-sized power station adopts a relatively small number of photovoltaic modules. Silicon-based photovoltaic modules have a life span of up to twenty years, which is a requirement in the art, so real-time and permanent monitoring of the photovoltaic modules is essential. Many internal factors and external factors can cause low power generation efficiency of the photovoltaic module, such as manufacturing differences or installation differences between the photovoltaic modules themselves, shadow shielding or maximum power tracking adaptation, and the like can cause the reduction of module conversion efficiency. Taking common shadow shielding as an example, if part of the photovoltaic modules are shielded by clouds, buildings, tree shadows, pollutants and the like, the part of the photovoltaic modules are changed into loads by power supplies and no electric energy is generated, the local temperature of the photovoltaic modules at the position with serious hot spot effect is usually higher, even exceeds 150 ℃, so that the local area of the modules is burnt or is permanently damaged by dark spots, welding spots are melted, packaging bodies are aged, glass burst, corrosion and the like, and the long-term safety and reliability of the photovoltaic modules are greatly hidden, so that the prevention of mismatch among the photovoltaic modules is particularly important, and the timely discovery of faults and positioning faults is more important.

Referring to fig. 1, in terms of a safety management method of a photovoltaic module: the plurality of photovoltaic modules P1-PN supply power to the bus bar in series and assuming that the bus bar includes a positive bus bar B1 and a negative bus bar B2, the positive electrode of one battery string of the plurality of photovoltaic modules P1-PN in series is coupled to the so-called positive bus bar B1, and in correspondence with this, the negative electrode of the aforementioned battery string of the plurality of photovoltaic modules P1-PN in series is coupled to the so-called negative bus bar B2. For example, each photovoltaic module is equipped with a photovoltaic junction box, and the main function of the photovoltaic junction box in the photovoltaic system is to connect the power energy source generated by the photovoltaic module with an external circuit, and allow the photovoltaic junction box to be provided with bypass diodes in certain fields, so that when the photovoltaic module is abnormal, for example, a hot spot effect occurs, the abnormal photovoltaic module can be bypassed through the bypass diodes of the photovoltaic junction box.

Referring to fig. 1, a photovoltaic module P1 is provided with a first device J1. In the present embodiment, assuming that the first device is a photovoltaic junction box, the positive electrode of the photovoltaic module P1 is connected to the positive bus bar B1 by the first device J1, and the negative electrode of the photovoltaic module P1 is connected to the positive electrode of P2 by the first device J1 according to the connection function of the photovoltaic junction box. The first device is a photovoltaic junction box, the positive electrode of the photovoltaic module P2 is connected to the negative electrode of the P1 by the first device J2, and the negative electrode of the photovoltaic module P2 is connected to the positive electrode of the P3 by the first device J2 according to the connection function of the photovoltaic junction box. And similarly, if the first device is a photovoltaic junction box, the positive electrode of the photovoltaic module P3 is connected to the negative electrode of the P2 by the first device J3, and according to the connection function of the photovoltaic junction box, the negative electrode of the photovoltaic module P3 is connected to the positive electrode of the P4 by the first device J3. And so on, a plurality of photovoltaic modules are connected in series to form a battery string which can provide a higher voltage level. The connectors between the photovoltaic modules and the bus bars are also called photovoltaic junction boxes (PV junction boxes).

Referring to fig. 1, the photovoltaic module PN is equipped with a first device JN. In this embodiment, assuming that the first device is a photovoltaic junction box, the positive electrode of the photovoltaic module PN is connected to the negative electrode of the PN-1 by the first device JN, and the negative electrode of the photovoltaic module PN is connected to the negative bus B2 by the first device JN according to the connection function of the photovoltaic junction box. It follows that the different photovoltaic modules are in a series relationship and the different first devices are also in a series relationship, where N is a positive integer greater than 1.

Referring to fig. 1, in an alternative embodiment, a plurality of battery strings may be connected in parallel, and each battery string includes a plurality of photovoltaic modules P1 to PN connected in series, where each photovoltaic module is configured with a first device for receiving its output power, for example, the photovoltaic module P1 is configured with a first device J1 for receiving the output power of P1, and for example, other photovoltaic modules PN are configured with a first device JN for receiving the output power of PN. The plurality of photovoltaic modules under any one string of the battery packs, for example, the plurality of first devices J1 to JN corresponding to P1 to PN, are connected in series with each other by a cable, which is generally an electrically conductive cable or so-called power line or power supply line, or the like. In the present embodiment, the positive output terminal of the first device J1 is set to be connected to the positive bus B1 and the negative output terminal of the first device JN is set to be connected to the negative bus B2. After the output power of each photovoltaic module is subjected to power conversion or not by the corresponding first equipment, the output power of the photovoltaic modules is gathered together and then sent to an energy collecting device mentioned below by the first equipment connected in series.

Referring to fig. 1, the first stage photovoltaic module P1 has a division voltage V1. The partial voltage output by a similar second stage photovoltaic module P2 is denoted V2. And the divided voltage output by the PN of the N-th stage photovoltaic module is VN. The total bus voltage which can be provided by any group of photovoltaic modules is calculated to be about V _BUS Equal to v1+v2+v3+ … VN. The respective output powers of the multi-stage photovoltaic modules are mutually superimposed on the bus, and the power collected by the bus is much higher than that of a single photovoltaic module.

Referring to fig. 1, the first device J1 uses a photovoltaic junction box in the present embodiment. The branch voltage V1 output by the photovoltaic module P1 to the cable can be characterized by the output voltage of the first device J1, and the branch current output by the photovoltaic module P1 to the cable is characterized by the current I1 output by the first device J1. The partial voltage VN of the first device JN, for example, which is output to the cable by the photovoltaic module PN, can also be characterized by the output voltage of the first device JN, and the branch current of the photovoltaic module PN output to the cable is characterized by the current IN output by the first device JN, which is characteristic of the junction box. The cable is sometimes referred to as a busbar.

Referring to fig. 1, IN an alternative embodiment, a plurality of first devices, such as J1 to JN, corresponding to a plurality of photovoltaic modules, such as P1 to PN, of a battery string are set IN series, the output current of the first device J1 configured by the monitored photovoltaic module P1 characterizes the branch current I1 of the photovoltaic module P1 supplying cable, the output current of the first device J2 configured by the photovoltaic module P2 characterizes the branch current I2 of the photovoltaic module P2 supplying cable, the output current of the first device JN configured by the photovoltaic module PN characterizes the branch current IN of the photovoltaic module PN supplying cable, and so on.

Referring to fig. 2, the first device is provided that each of the voltage converters, for example, the multi-stage photovoltaic modules P1-PN, is configured with one voltage converter, and at the same time, the output powers of the voltage converters corresponding to the multi-stage photovoltaic modules P1-PN are required to be superimposed on each other on the dc bus and thereby used as the bus power. In this case, the plurality of voltage converters are connected in series. The first device J1, such as a voltage converter, converts the electric energy extracted from the corresponding photovoltaic module P1 into its own output power, and the first device J1, such as a voltage converter, also performs a process of boosting or reducing or boosting or reducing the initial voltage of the corresponding photovoltaic module P1, and then outputs the voltage. The voltage converter, i.e., the DC/DC converter, may be a step-up voltage converter or a step-up switching power supply, a step-down voltage converter or a step-down switching power supply, a step-up voltage converter or a step-down switching power supply. The first device has a step-up or step-down voltage regulating function. According to the same theory, it can be known that the remaining first devices JN, such as the voltage converter, convert the electrical energy extracted from the corresponding photovoltaic module PN into its own output power, and the first devices JN, such as the voltage converter, further perform the processes of boosting, reducing, or boosting, and outputting the initial voltage of the corresponding photovoltaic module PN. The second device 100 may inverter the dc power on the bus to the desired ac power using the inverter INVT, noting that there are a variety of other alternative examples of the second device.

Referring to fig. 2, the first device is a voltage converter that performs voltage conversion on an initial voltage of a component. The split voltage provided by the first stage photovoltaic assembly P1 to the cable in a series relationship is characterized by the output voltage V1 of the first device J1 and the branch current provided by the first stage photovoltaic assembly to the cable is characterized by the current I1 output by the first device J1. The output voltage V1 is a voltage output by the converter, i.e., the first device J1 after performing conversion such as voltage boosting or voltage dropping. The first device J1 is a voltage converter for performing voltage conversion on an initial voltage of the photovoltaic module P1 in this example. In this example, the output voltage V1 may be higher than the initial voltage output by the corresponding photovoltaic module P1 or lower than the initial voltage output by the photovoltaic module P1. A group of output terminals of the voltage converter, that is, a capacitor is often connected between the positive output terminal and the negative output terminal of the first device J1, so as to ensure that the output voltage of the voltage converter is relatively gentle and reduce ripple waves. The positive output and the negative output of the first device herein or hereinafter of the first device, respectively, may be replaced by the terms first output and second output.

Referring to fig. 2, the first device is a voltage converter that performs up-down conversion on an initial voltage of a component. The partial voltage of the last-stage photovoltaic module PN supplied to the cable IN the series relationship is characterized by the output voltage VN of the first device JN and the branch current supplied to the cable by the last-stage photovoltaic module is characterized by the first device JN output current IN. The output voltage VN is a voltage output by the converter, i.e., the first device JN after performing conversion such as voltage boosting or voltage dropping. The first device JN is in this example a voltage converter for performing voltage conversion on an initial voltage of the photovoltaic module PN. In this example, the output voltage VN may be higher than the initial voltage corresponding to the output of the photovoltaic module PN or lower than the initial voltage of the output of the photovoltaic module PN.

Referring to fig. 2, it is assumed that the output voltage of the first device J1 is V1. Similarly, assume that the output voltage of the first device J2 is denoted as V2. And so on, the voltage output by the nth stage first device JN is VN. The total bus voltage which can be provided by any group of photovoltaic modules is calculated to be about V _BUS Equal to v1+v2+v3+ … VN. The respective output powers of the multi-stage photovoltaic modules are mutually superimposed on the bus, and the power collected by the bus is much higher than that of a single photovoltaic module.

Referring to fig. 3, the energy collecting device used by the second apparatus 100 allows other energy collecting devices, such as a junction box CB, which is typically used to collect energy of a photovoltaic module, in addition to the inverter INVT, and also allows various chargers or boost converters, which charge a storage battery. The second device can raise the voltage level of the bus by using the boost converter, and then perform inversion conversion on the bus voltage with the higher voltage level.

Referring to fig. 3, a plurality of battery strings are connected in parallel and each battery string includes a plurality of photovoltaic modules connected in series by cables, for example, a first battery string illustrated in an upper half of the figure includes a plurality of photovoltaic modules P1 to PN connected in series by cables, and a second battery string illustrated in a lower half of the figure includes a plurality of photovoltaic modules P1 to PN connected in series by cables. In fact more parallel battery strings are not shown in the figures.

Referring to fig. 4, the data acquisition module is configured to acquire one or more target data of the photovoltaic module. The target data collected by the data collection module comprises initial voltage and initial current of the photovoltaic module, and output voltage or output current which is output to the bus by the first equipment. The data acquisition module may detect the initial voltage of the photovoltaic module using a voltage detection module such as a voltage detector VT or a voltage sensor, and the like, and detect the output voltage of the first device using a voltage detection module such as a voltage detector VT or a voltage sensor, and the like. The initial current of the photovoltaic module may be detected using a current detector CT or a current sensor or the like, and the output current of the first device may be detected using a current detector CT or a current sensor or the like. The initial voltage and initial current of the photovoltaic module are supplied to the first device and the output voltage and output current of the first device are supplied to the cable. The data acquisition module may also include a temperature sensor for monitoring the ambient temperature in which the photovoltaic module is located, or an illumination radiometer for monitoring the effective illuminance of the sun illumination of the ambient environment in which the photovoltaic module is located. The target data may also be referred to as operating parameters, the data types of which include, but are not limited to, voltage, current, temperature, output power, effective illumination radiation, etc. of the photovoltaic module. The branch current provided to the cable by each monitored photovoltaic module is in fact: the output current of the first device configured by the monitored photovoltaic assembly characterizes the branch current provided by the monitored photovoltaic assembly to the cable.

Referring to fig. 4, the first devices J1 to JN include the above-mentioned current detector CT or current sensor or the like current detection module to detect the output current of the photovoltaic module or the first device. For example, the branch current I1 provided by each monitored photovoltaic module, e.g., P1, to the cable is measured in any string of cells, and the branch current provided by the photovoltaic module P1 to the cable is represented by the output current I1 of the first device J1, since the photovoltaic module P1 is not directly connected to the cable but indirectly connected to the cable via the first device J1. The initial current and initial voltage of the photovoltaic module P1 are supplied to the first device J1 and the output power of P1 is received by the latter. If the branch current IN provided to the cable by each monitored photovoltaic module, e.g., PN, is measured IN this string, the branch current provided to the cable by the photovoltaic module PN is represented by the output current IN of the first device JN, since the photovoltaic module PN is not directly connected to the cable but indirectly connected to the cable by the first device JN. The initial current and initial voltage of the photovoltaic module PN are supplied to the first device JN and the PN output power is received by the latter

Referring to fig. 4, the first device JN includes a controller IC1. Many types of controller ICs 1 currently have data acquisition modules that collect the aforementioned target data. For example, the controller IC1 is also called a microprocessor and allows it to function as a self-contained temperature sensor or a voltage current detection module. The controller IC1 may be configured with additional data acquisition modules to collect target data provided it does not have such modules. After knowing the parameter information such as the target data, the controller IC1 can generally control the matched communication module CM1 to send the target data. The communication mechanism of the communication module CM1 includes two types of wired communication and wireless communication: for example, all existing wireless communication schemes such as WIFI, ZIGBEE, 433MHZ communication, infrared or bluetooth can be used, and for example, a scheme of deliberately using power line carrier communication is also used. In an alternative embodiment of the present application, the communication module CM1 includes a power line carrier modulator, which is configured to transmit the target data to the data receiver in a power line carrier manner. The coupling element 10 is shown coupling a power line carrier from a power line carrier modulator to a bus, the coupling element 10 being for example a transformer with primary and secondary windings or for example a signal coupler with a coupling coil. The coupling transformer may be used, for example, to transfer a power line carrier to a primary winding and a secondary winding connected to a busbar or busbar leg as part of the busbar, the carrier being transferred to the busbar by the coupling of the primary and secondary sides. Typical methods of use of signal couplers with magnetic rings and coupling coils are, for example, to pass a busbar or busbar branch directly through the magnetic ring of the signal coupler around which the coupling coil is wound, and to which a power line carrier is fed to be sensed from a power supply busbar so that contactless signal transfer can be carried out. In summary, the coupling element may employ all signal coupling schemes disclosed in the prior art, and injection inductive coupler technology, cable snap-in inductive coupler technology, and switchable full impedance matched cable snap-in inductive coupler are all alternatives to the present application. The general principle is that the controller delivers the target data to the communication module and the communication module transmits the target data to the data receiver through wired or wireless means.

Referring to fig. 4, regarding wired communication and wireless communication, considering that the geographical environment where the photovoltaic module is located is a relatively bad place such as a building rooftop or a desert zone or a suburban mountain, wireless communication generally brings about higher additional expense cost and is also inferior in terms of durability and reliability, after all, the photovoltaic module has a general service life of up to twenty years, so that the communication between the master node and the slave node and between the slave node adopts a power line carrier as a preferred option. But also allows the frequencies of the power line carrier signals emitted by the different first devices to be different.

Referring to fig. 4, the second device 100 includes a controller IC2 and a communication module CM2, and also allows for a carrier signal coupling element 20 with a complementary function for sensing the power line carrier signal from the busbar, note that the first device is transmitting and loading the power line carrier signal onto the busbar or cable at the photovoltaic module, and the second device is sensing and capturing the power line carrier signal from the cable back to the second device. The communication module and the coupling element are sometimes integrated together, e.g. they comprise any of the type of rogowski air coil sensor or high frequency sensor, codec or shunt etc. It is worth elucidating that the first device is also identical to the second device described above: has a data receiving function of wired or wireless communication. The same is true of the second device as the first device described above: has a data transmission function of wired or wireless communication. For example, when the second device actively polls different first devices and requires each first device to receive a polling signal, the second device needs to return the target data collected and stored by itself to the second device, the second device corresponds to a master node and each first device corresponds to a slave node. The first device is illustrated and described in this example using a photovoltaic junction box as an alternative example, although the wired communication functions and the wireless communication functions provided by the first device and the second device described above are equally applicable to this example.

Referring to fig. 4, the second apparatus 100 has the above-mentioned conventional current detector CT or current sensor and the like current detection module to detect the string current IS of the battery string. The string current is a current flowing through the battery string, and also a current flowing through each of the photovoltaic modules P1 to PN or a current flowing through each of the first devices J1 to JN.

Referring to fig. 4, after the second device 100 and each of the first devices J1 to JN establish a communication mechanism, the branch current provided by each photovoltaic module to the cable is sent to the second device 100 by the first device configured by the branch current, and one of the core tasks of the second device 100 determines whether a fault occurs at each photovoltaic module.

Referring to fig. 4, a branch current provided to a cable by the photovoltaic module P1, such as I1, is transmitted to the second device 100 by the first device J1 configured therewith. The second device 100 compares the string current IS and the branch current I1 to determine whether there IS an expected difference between the currents IS and I1, e.g., the current difference between the string current IS and the branch current I1 (i.e., the difference of IS minus I1) IS not within a predetermined current fluctuation range (e.g., I _MIN To I _MAX ) Within this, the failure of the photovoltaic module P1 is considered to be possible to be the failure of the photovoltaic module itselfIt is also possible that the first device J1 has failed. Ideally, the string current and the branch current are equal and the current difference value is zero, so that the photovoltaic module is normal, but the string current and the branch current always have unavoidable fluctuation and have measurement errors in normal conditions, so that the fluctuation range of the current can exclude the abnormality. As long as the current difference (IS minus I1 difference) between the string current and the branch current IS within a predetermined current fluctuation range, it can be considered that the monitored photovoltaic module IS functioning properly, i.e. there IS no expected difference. The opposite IS very evident, as long as the current difference between the string current and the branch current (IS minus I1) IS not within the predetermined current fluctuation range, it can be considered that a fault occurs at the monitored photovoltaic module, i.e. that such expected difference exists. Expected differences include: the current difference between the string current and the branch current is not within a predetermined current fluctuation range.

Referring to fig. 4, a branch current, such as IN1, supplied to the cable by the photovoltaic module PN is transmitted to the second device 100 by the first device JN configured. The second device 100 compares the string current IS and the branch current IN to determine whether there IS an expected difference between the currents IS and IN, e.g., the difference between the string current IS and the branch current IN (the difference of IS minus IN) IS not within a predetermined current fluctuation range (e.g., I _MIN To I _MAX ) And if the photovoltaic module PN fails, the fault of the photovoltaic module PN can be considered to be that the first equipment JN fails.

Referring to fig. 4, a branch current provided to a cable by the photovoltaic module P1, such as I1, is transmitted to the second device 100 by the first device J1 configured therewith. The second device 100 compares the string current IS with the branch current I1 to determine whether there IS an expected difference between the currents IS and I1, for example, the branch current I1 has a higher number of high frequency components than the string current IS within a specified high frequency current band, which can be represented by F1 to F2 (e.g., 1KHZ to 100 KHZ). It is considered that the photovoltaic module P1 is faulty, that the photovoltaic module P1 itself may be faulty, that the first device J1 is faulty, and that the fault is mostly a current surge caused by dc arcing or leakage, for example, a short circuit or aging of insulation between the photovoltaic module and the line at the first device, a bad contact to the earth leakage or the line, and the like. Ideally, the string current and the branch current are equal, and the current difference value of the string current and the branch current is zero, so that the photovoltaic module can be proved to be normal, but the current surge at the position where arc or electric leakage occurs under the conditions of arc discharge or electric leakage is far worse than at the string current. As long as both the branch current and the string current are relatively gentle and no high frequency component suddenly appears, the monitored photovoltaic module may be considered to be functioning properly, i.e. without any expected differences. The opposite is very evident, as long as the branch current has more high-frequency components than the string current within the specified high-frequency current frequency band (F1 to F2), it can be considered that there is a fault at the monitored photovoltaic module, i.e. that there is such an expected difference. The expected differences at this time include: the branch current has a higher frequency component than the string current within the specified high frequency current band. How to capture the high frequency components of the current is known in the art.

Referring to fig. 4, a branch current, such as IN, supplied to a cable by the photovoltaic module PN is transmitted to the second device 100 by the first device JN configured therewith. The second device 100 compares the string current IS with the branch current IN to determine whether there IS an expected difference between the currents IS and IN, for example, the branch current IN has a higher frequency component than the string current IS IN within a specified high frequency current band, which can be represented by F1 to F2 (for example, 0.1KHZ to 3 KHZ). It is considered that the photovoltaic module PN is faulty, that is, the photovoltaic module PN itself is faulty, that is, the first device JN is faulty, and that the fault is mostly a current surge caused by dc arcing or leakage. Even if the string current has high frequency components, the branch current has more high frequency components than the string current, and the branch current has more high frequency components within the specified high frequency current band than the string current. The distribution points of the high-frequency components in the branch current in the high-frequency current frequency band are wider than those of the high-frequency components in the group string current in the high-frequency current frequency band, and the branch current is also more than the group string current in the specific high-frequency current frequency band.

Referring to fig. 4, a branch current provided to a cable by the photovoltaic module P1, such as I1, is transmitted to the second device 100 by the first device J1 configured therewith. The second device 100 compares the string current IS with the branch current I1, determines whether there IS an expected difference between the currents IS and I1, and if the peak-to-valley difference Δi1 between the peak value and the valley value of the branch current I1 exceeds the peak-to-valley difference Δis between the peak value and the valley value of the string current IS, considers that the photovoltaic module P1 IS faulty, which may be that the photovoltaic module P1 itself IS faulty or that the first device J1 IS faulty. The distance between the peak value of the branch current I1 and the valley value of the branch current I1 IS mostly the current surge caused by direct current arc discharge or electric leakage, and the current surge at the position where arc discharge or electric leakage occurs under the conditions of arc discharge or electric leakage IS far more serious than that at the group string current, so the peak-valley difference Δi1 between the peak value of the branch current I1 and the valley value of the branch current I1 IS far more than the peak-valley difference Δis between the peak value of the group string current IS and the valley value of the IS. Ideally, the string current and the branch current are equal, and the current difference value of the string current and the branch current is zero, so that the photovoltaic module can be proved to be normal, but the current oscillation at the position where the arc or the electric leakage occurs under the conditions of arc discharge or electric leakage is far worse than that at the string current. As long as both the branch current and the string current are relatively gentle and no current oscillation occurs suddenly, it can be considered that the monitored photovoltaic module is functioning properly, i.e. there is no expected difference. The opposite is quite evident, as long as the oscillation range between the peak and the valley of the branch current exceeds the oscillation range between the peak and the valley of the group string current, it can be considered that a fault, i.e. such an expected difference, is present at the monitored photovoltaic module. The expected differences at this time include: the peak-to-valley difference between the peak and valley of the branch current exceeds the peak-to-valley difference between the peak and valley of the string current.

Referring to fig. 4, a branch current, such as IN, supplied to a cable by the photovoltaic module PN is transmitted to the second device 100 by the first device JN configured therewith. The second device 100 compares the string current IS with the branch current IN, determines whether an expected difference exists between the current IS and the current IN, and considers that the photovoltaic module PN has a fault if the peak-to-valley difference Δin between the peak value and the valley value of the branch current IN exceeds the peak-to-valley difference Δis between the peak value and the valley value of the string current IS. It may be that the photovoltaic module PN itself has failed or that the first device JN has failed. The distance between the peak value of the branch current IN and the valley value of the branch current IN IS mostly the current surge caused by direct current arc discharge or electric leakage, and the current surge at the position where arc discharge or electric leakage occurs under the conditions of arc discharge or electric leakage IS far more serious than that at the group string current, so the peak-valley difference delta IN between the peak value of the branch current IN and the valley value of the branch current IN IS far more than that between the peak value of the group string current IS and the valley value of the IS.

Referring to fig. 4, this example is a photovoltaic junction box. The photovoltaic junction box can be replaced by a shutdown device for disconnecting the photovoltaic module from the cable or recovering the photovoltaic module in the disconnected state from the cable, the photovoltaic junction box can be replaced by a power optimizer for setting the photovoltaic module at a maximum power point, and the photovoltaic junction box can be replaced by a voltage converter capable of performing voltage conversion on the initial voltage of the photovoltaic module. The solution of fig. 4 also applies to the embodiments of fig. 5 to 6.

Referring to fig. 5, in the shutdown device supporting the rapid shutdown management of the photovoltaic module, a first device JN capable of controlling whether the photovoltaic module is shutdown as shown in the drawing is taken as an example of the shutdown device. The shutdown management objective that the circuit of the first device JN, such as the shutdown device, expects to realize is to determine whether the photovoltaic module needs to be shutdown in time: photovoltaic systems installed or built into buildings must include a quick turn-off function to reduce the risk of electrical shock to emergency handling personnel. Although the component shut-off device is described by taking the component shut-off device realizing the shut-off function as an example, the component shut-off device functionally integrates at least the data acquisition function and the component shut-off function. Explanation about the component shutdown function: the first device JN, such as a shutdown device, can disconnect the corresponding photovoltaic module PN from the cable and does not supply power to the bus, and the first device JN, such as the shutdown device, or resumes the disconnected photovoltaic module PN to the cable and supplies power to the bus again. For example, the positive output of the first device J1 is connected to the positive bus B1 and the negative output of the first device JN is connected to the negative bus B2. And the positive output end of the next first device in the plurality of first devices connected in series is connected to the negative output end of the adjacent previous first device, or the positive output end of the next first device in the plurality of first devices is connected to the negative output end of the adjacent previous first device, so that the plurality of first devices are connected in series to form a battery string. Each photovoltaic module in the battery string is configured with a first device for receiving its output power, for example, any photovoltaic module PN in the battery string is configured with a first device JN for receiving its PN output power, and a plurality of first devices corresponding to a plurality of photovoltaic modules P1 to PN in any battery string are connected in series with each other, for example, J1 to JN in series, through cables. The connection relation of the first device is applicable here to the examples of fig. 1-7.

Referring to fig. 5, a bypass diode or a complementary switch may be disposed between the positive output terminal (first output terminal) and the negative output terminal (second output terminal) of the first device JN. The complementary switch is a switch complementary to switch S1: if switch S1 is on then its complementary switch is off and switch S1 is off then its complementary switch is on. The meaning of arranging the bypass diode or the complementary switch is to prevent the battery string from forming a disconnection at the first device JN. The bypass diode or complementary switch of the first device JN is turned on if the photovoltaic module PN is turned off. If the photovoltaic module PN is restored to the cable or the battery string, the bypass diode or the complementary switch is turned off.

Referring to fig. 5, the first device JN sets a switch S1 between the negative electrode of the photovoltaic module PN and the conductive cable or alternatively sets a switch S1 between the positive electrode of the photovoltaic module PN and the conductive cable. The first device JN collects one or more target data of the photovoltaic module through the data collection module, if the target data is abnormal, the controller IC1 can control the photovoltaic module PN to be turned off, for example, the controller IC1 operates to turn off the switch S1, and whether the initial voltage or the initial current of the photovoltaic module is abnormal or the output voltage or the output current of the first device supplied to the cable is abnormal, the controller IC1 can drive or control the switch S1 to be turned off. Based on the communication mechanism established between the first device and the second device, if the command sent by the second device 100 to the first device JN includes a turn-off command, the first device will also actively drive or control the switch S1 to turn off when receiving such a command. At the same time, in other alternative embodiments, the shutdown management is also supported, for example, the first device J1 supporting the rapid shutdown of the photovoltaic module P1 is used to operate the shutdown switch S1 configured by the photovoltaic module to turn off or on, so as to control whether the photovoltaic module P1 is shutdown. And so on, other optional examples also support shutdown management, such as the first device J2 supporting rapid shutdown of the photovoltaic module P2 is used to operate the shutdown switch S1 configured by the photovoltaic module to turn off or on, so as to control whether the photovoltaic module P2 is shutdown. The first device is illustrated in this example with the shut-down device as an alternative example, although the wired communication function and the wireless communication function of the first device and the second device provided in the foregoing are equally applicable to this example, and the first device and the second device each have bidirectional communication capability. The shutdown device removes the photovoltaic module from the battery string or resumes the photovoltaic module in the removed state to the battery string.

Referring to fig. 5, the second device 100 reads the respective target data of the photovoltaic modules P1 to PN, such as the voltage supplied to the cable and the branch current supplied to the cable, in such a manner that: the second device 100 polls the series of first devices J1-JN corresponding to the photovoltaic modules P1-PN in turn, and when the second device 100 polls any one of the first devices such as JN, the first device such as JN that is being queried needs to return the target data of the photovoltaic module PN corresponding to the first device to the second device 100. This way of reading data is now illustrated by way of example: when the controller IC2 of the second device 100 inquires about the first device such as J1, the controller IC1 of the inquired first device such as J1 needs to return the target data of the photovoltaic module P1 to the controller IC2. Continuing with the example of this data reading approach: when the controller IC2 of the second device 100 inquires about the first device such as J2, the controller IC1 of the inquired first device such as J2 needs to return the target data of the photovoltaic module P2 to the controller IC2. In summary, such data reading can be considered as: the controller configured by the second device, namely the master node, polls the controllers configured by the first devices, namely the slave nodes, in turn, when the second device polls any one of the first devices, the controller of the first device to be inquired returns target data of one photovoltaic module corresponding to the controller, such as voltage input to the cable and branch current input to the cable, to the controller configured by the second device. In order to avoid confusion, the controller of the first device may be referred to as a first controller and its communication module may be referred to as a first communication module, while the controller of the second device may be referred to as a second controller and its communication module may be referred to as a second communication module. Other alternatives to the controller are: a field programmable gate array or a complex programmable logic device or a field programmable analog gate array or a semi-custom ASIC or processor or microprocessor or digital signal processor or integrated circuit or software firmware program stored in memory, etc. The above-described data reading method of polling is applicable to a shutdown device, a power optimizer, a voltage converter, or the like, in addition to the illustrated photovoltaic junction box.

Referring to fig. 6, each of the photovoltaic modules P1-PN is configured with a voltage converter, which is also called a switching regulator and is most commonly implemented in a switching power supply circuit topology such as a buck converter circuit, a boost converter circuit, a buck-boost converter circuit, and the like. The controller IC1 of the first device JN is often designed as a driving chip, and the controller drives a voltage converter or a converting circuit to convert an input voltage absorbed from the photovoltaic module P1 into an output voltage, where the voltage converter is also referred to as a power stage circuit, and the controller IC1 is also referred to as a power controller, and the controller IC1 is most commonly referred to in the industry as various power management controllers or power management chips for managing a switching power supply. This example allows the first device to simply implement basic buck conversion or boost conversion on the initial voltage of the photovoltaic module, for example, the output voltage of the first device is regarded as the divided voltage output by the photovoltaic module to the bus, and the initial voltage of the photovoltaic module is transmitted to the first device, where the output voltage of the first device is the voltage obtained after the initial voltage of the photovoltaic module is reduced or boosted. The first device does not need power optimization at this time.

With reference to fig. 6, the problems of interest in distributed or centralized photovoltaic power plants are: shadow masking causes mismatch between numerous photovoltaic modules. The problem is that the output characteristics of the battery of the photovoltaic module are reflected in that the output voltage and the output current are closely related to external factors such as light intensity, ambient temperature and the like, and the uncertainty of the external factors causes the corresponding voltages of the maximum output power and the maximum power point to change along with the change of the external factors. For example, the power output by the photovoltaic module has randomness and severe fluctuation, and the random uncontrollable characteristic has high probability of causing great impact on the power grid and also can have negative influence on some important load operation. Based on these doubts, achieving photovoltaic module maximum power point tracking in consideration of external factors is a core goal for achieving energy and revenue maximization in the industry.

Referring to fig. 6, the principle and features of the conventional MPPT method for power optimization: as early output power control for photovoltaic modules mainly utilized voltage feedback method Constant Voltage Tracking, this tracking method neglected the effect of temperature on the open circuit voltage of the solar cell, so open circuit voltage method and short circuit current method were proposed, their commonalities being basically very similar to the processing maximum power point. For more accurate capturing of the maximum power point, a disturbance observation method, a duty cycle disturbance method, even a conductance increment method, and the like are proposed. The disturbance observation method is based on the principle that the current array power is measured, then a small voltage component disturbance is added to the original output voltage, the output power can be changed, the power change direction can be known by measuring the changed power and comparing the power before and after the change, if the power is increased, the original disturbance is continuously used, and if the power is reduced, the original disturbance direction is changed. The duty ratio disturbance working principle is as follows: the interface between the photovoltaic array and the load generally adopts a voltage converter controlled by a pulse width modulation signal, so that the input and output relation of the converter can be adjusted by adjusting the duty ratio of the pulse width modulation signal, thereby realizing the function of impedance matching, and the magnitude of the duty ratio substantially determines the magnitude of the output power of the photovoltaic cell. The maximum difference between the conductivity increment method and the disturbance observation method is that the logic judgment formula and the measurement parameter are the same, and the increment conductivity method is used for changing the output voltage of the photovoltaic cell to reach the maximum power point, but the logic judgment formula is modified to reduce the oscillation phenomenon near the maximum power point so as to adapt to the climate with the instantaneous change of sunlight intensity and temperature. The actual measurement method, the fuzzy logic method, the power mathematical model, the intermittent scanning tracking method, the optimal gradient method or the three-point gravity center comparison method and the like belong to the less common maximum power point tracking method. It can be known that the so-called MPPT algorithm used in the photovoltaic energy industry is diverse, and the description thereof will not be repeated.

Referring to fig. 6, each of the photovoltaic modules P1-PN is configured with a voltage converter, but the voltage converter is not simply a voltage converter, but is also called an optimizer for power optimization. Each power optimizer is configured to set an initial current and an initial voltage of a corresponding photovoltaic module at a maximum power point. For example, the first device J1 shown in the figure, such as the power optimizer, sets the photovoltaic module P1 corresponding thereto at the maximum power point, for example, the first device J2 shown in the figure, such as the power optimizer, sets the photovoltaic module P2 corresponding thereto at the maximum power point, and for example, the first device JN shown in the figure, such as the power optimizer, sets the photovoltaic module PN corresponding thereto at the maximum power point. The power optimizer performs power optimization on the photovoltaic module, and in this example, the controller IC1 of the first device JN may be configured to operate the power optimizer to perform voltage conversion actions such as voltage boosting or voltage dropping or voltage boosting and dropping, so as to set the initial current and the initial voltage of the photovoltaic module, that is, the input voltage and the input current of the first device, to the maximum power point of the photovoltaic module PN. The first device may also be provided with a power management function to maximize the power generation efficiency of the photovoltaic module.

Referring to fig. 6, the power optimizer is a dc-to-dc converted voltage converter, and is also a single component level battery maximum power tracking device. After the power optimizer optimizes the maximum power of the single component, the total power collected is transmitted to the inverter to convert direct current into alternating current, and then the direct current is supplied to local use or direct grid connection. The inverter may typically be a pure inverter device without maximum power tracking or an inverter device equipped with a two-stage maximum power tracking. The main topology of the mainstream power optimizer adopts a conventional BUCK or BOOST or BUCK-BOOST or CUK circuit architecture.

Referring to fig. 7, the photovoltaic modules P1-PN supply power to the bus bars in series, and the partial voltage output to the cables is collected at each of the photovoltaic modules P1-PN. For example, the photovoltaic module P1 collects the partial voltage V1 output to the cable by the first device J1, the photovoltaic module P2 collects the partial voltage V2 output to the cable by the first device J2, and so on, it can be known that the photovoltaic module PN collects the partial voltage VN output to the cable by the first device JN. The partial voltage output from any one photovoltaic module to the cable may be the initial voltage of the photovoltaic module itself, but may also be the output voltage output to the cable by the first device. The first device J1 needs to transmit the divided voltage V1 to the second device 100, and the second device J2 also needs to transmit its divided voltage V2 to the second device 100, and the first device J3 needs to transmit the divided voltage V3 to the second device, and the first device JN needs to transmit the divided voltage VN to the second device 100.

Referring to fig. 7, the photovoltaic modules P1-PN supply power to the bus bars in series, and the branch current they supply to the cables is collected at each of the photovoltaic modules P1-PN. For example, the photovoltaic module P1 collects the branch current I1 that is input to the cable by the first device J1, the photovoltaic module P2 may collect the branch current I2 that is input to the cable by the first device J2, and so on, it can be known that the photovoltaic module PN collects the branch current IN that is output to the cable by the first device JN. The branch current output to the cable by any one photovoltaic module may be the initial current of the photovoltaic module itself, but may also be the branch current output to the cable by the first device. The first device J1 sends the branch current I1 to the second device 100 and the second device J2 also needs to send the branch current I2 to the second device 100, the first device J3 needs to send the branch current I3 to the second device and the first device JN needs to send the branch current IN to the second device 100. After the second device 100 knows the branch current provided by each photovoltaic module to the cable, the second device 100 can compare or compare the branch current output by each photovoltaic module to the cable with the total string current IS on the cable to determine whether the photovoltaic module has a fault.

Referring to fig. 7, the second apparatus 100 includes a disconnection switch S2 disposed on a cable, and the disconnection switch S2 may be disposed on a positive bus or a negative bus. The second device 100 compares the branch current output by each photovoltaic module to the string current on the cable, and the second device 100 can control the disconnection switch S2 to be turned off so as to disconnect the cable immediately. The second device 100 includes a controller IC2, where the controller IC2 analyzes and determines a relationship between the branch current and the string current IS of each photovoltaic module, and if the controller IC2 has determined that any photovoltaic module fails, the controller IC2 may drive the switch S2 to turn off. Or the controller IC2 simply gives an early warning message to warn that the photovoltaic module is malfunctioning but does not drive the switch S2 to be turned off. The second device 100 IS selected from a current sensor, which may be used to monitor the string current IS and compare the relationship of I1 to IN with the string current IS, and may be selected from a combiner box or an inverter.

Referring to fig. 7, the disconnection of the bus bar due to the abnormal event of the photovoltaic modules may cause a disadvantage, and the disconnection of the cable is equivalent to cutting off the power line carrier communication path between the second device and the first device, so that the second device cannot further inquire about the specific real-time working state and real-time target data of each photovoltaic module, but is necessary to disconnect the bus bar in time on the premise of ensuring safety. The biggest concern that the second device cannot interrogate the real-time target data of the photovoltaic modules is that it cannot accurately determine which photovoltaic module is malfunctioning: because whichever photovoltaic module fails, the most urgent thing is to turn off the bus bar in time, even though the failure at this time may not be a true failure but a tolerable failure. In an alternative embodiment, when the first device configured by each photovoltaic module sends the divided voltage and the branch current to the second device, a time stamp is further marked on the data of each divided voltage and the branch current, so that the time point of each target data is marked.

Referring to fig. 7, a first device J1, such as a photovoltaic module P1, is configured to time stamp the data format of each of the partial voltage V1 and its current I1 when transmitting the partial voltage V1 of P1 and its current I1 to a second device 100. Although the bus is in the disconnected state, the second device 100 is aware of the partial voltage V1 and its current I1 before the bus is disconnected, since the partial voltage and the partial current are time stamped. The same thing applies to the first device JN when transmitting the partial voltage VN of PN and its current IN to the second device 100, with a time stamp IN the respective data formats of the partial voltage VN and its current IN. Although the bus is IN the open state, the second device 100 knows the partial voltage VN and its current IN before the bus is open, since the partial voltage and the partial current are time stamped. Whereby the controller IC2 of the second device 100 can analyze the voltage and current distribution of all the photovoltaic modules before the bus bar is disconnected, the second device 100 can locate the fault location (calculate which photovoltaic module is faulty) and determine whether the fault occurring at that location is a real fault (unacceptable fault). Thus, after the bus is disconnected, the time-stamped partial voltage and partial current can be used for analyzing whether each photovoltaic module fails.

Referring to fig. 7, not only the partial voltage of the bus bar output thereof is collected at each photovoltaic module, but also the partial current of the bus bar output thereof is collected at each photovoltaic module. If the branch voltage V1 output to the bus by the collection photovoltaic module P1 and the branch current I1 output to the bus by the collection photovoltaic module P1 are obtained. If the branch voltage V2 output to the bus by the collection photovoltaic module P2 and the branch current I2 output to the bus by the collection photovoltaic module P2 are obtained. If the collection photovoltaic module P3 outputs the branch voltage V3 to the bus and the collection photovoltaic module outputs the branch current I3 to the bus. If the branch voltage V4 output to the bus by the collection photovoltaic module P4 and the branch current I4 output to the bus by the collection photovoltaic module P4 are obtained. If the branch voltage VN output by the collection photovoltaic module PN to the bus and the branch current IN output by the collection photovoltaic module to the bus are obtained. The second device 100 compares the string current and the branch current, determines whether an expected difference exists between them, if so, considers that a fault occurs at the monitored photovoltaic module, and if not, considers that the monitored photovoltaic module operates normally. The fault point positioning method can position the fault point from P1 to PN.

Referring to fig. 7, the accidents of arcing and firing caused by poor contact, aging, short circuit, etc. are more and more frequent, and it is seen that the detection of dc arc faults is increasingly important in photovoltaic systems. Once the direct current arc fault occurs, the photovoltaic system has no zero crossing point protection and the photovoltaic component generates continuous energy under the irradiation of sunlight, so that the fault arc of the system has a stable combustion environment. If measures are taken effectively in time, high temperature phenomena of thousands of DEG C can be generated and fire disaster is caused, and certain substances are melted and even evaporated to generate a large amount of toxic gases, so that the life safety of human bodies is endangered and the social economy is greatly lost.

Referring to fig. 7, the divided arcs can be roughly divided into direct current arcs and alternating current arcs according to current properties. The known alternating current application time is early, and the alternating current fault arc has a mature detection method and commercial products, however, the starting time of a photovoltaic system is late, and the intrinsic characteristics of the direct current arc are different from those of alternating current, for example, the direct current has no zero crossing characteristic like the alternating current, so that the detection means of the alternating current arc cannot be applied to the photovoltaic occasion. The variables affecting the electrical properties of the direct current arc are more numerous and various, and the arc is more complicated due to the different use environments of the photovoltaic. It is generally recognized in the industry that it is difficult to build mathematical models of dc arcs, and although some arc models are mentioned, these simplified models are usually based on studies of certain single characteristics or very limited characteristics of the arc, and in fact, noise necessarily present in a photovoltaic environment and sporadic disturbances of the power system are extremely prone to misleading arc detection, causing erroneous detection results, dynamically changing light intensity and ambient temperature, and a large amount of switching noise are all sources of misjudgement. One of the targets of the application is to detect the true direct current arc faults existing in the photovoltaic system so as to avoid serious accidents such as fire disasters caused by fault arcs.

Referring to fig. 7, the foregoing informs "communication is established between the first devices J1-JN and the second device 100, and the branch current such as IN provided by each photovoltaic module to the cable is sent to the second device by the first device such as JN configured by the branch current, and the second device determines whether a fault occurs at the photovoltaic module. However, the specific serial architecture in which each string of cells includes a plurality of photovoltaic modules connected in series by cables causes great trouble, and a failure of a photovoltaic module is detected by neighbors around its periphery. For example, if the first device such as J4 and the photovoltaic module thereof have a dc arc, and the first devices such as J3 and J5 are connected in series and adjacent to the first device such as J4, the series architecture of the battery strings may cause the output currents of the first devices such as J3 and J5, for example, I3 and I5, to have a larger number of high-frequency components than the string currents in the specified high-frequency current frequency band, the current difference between the string currents and the current I3 or I5 may not be within the predetermined current fluctuation range, and the peak-valley difference between the peak and valley of the branch current I3 or I5 exceeds the peak-valley difference between the peak and valley of the string currents. The main reason is that the high frequency arcing signals, etc., will naturally propagate along the cable, and the mixing of the high frequency arcing signals into the branch currents I3 and I5 will erroneously assume that the first device, e.g., J3 and J5, is malfunctioning and the second device has little ability to discriminate between the true ground conditions of the first device, e.g., J3 and J5. In general, the closer to the real faulty first device, such as the adjacent first devices J3 and J5 of J4, the higher the false alarm rate, the lower the false alarm rate of the other adjacent first devices further from the real faulty first device, the higher the high-frequency arc discharge signal is attenuated gradually.

Referring to fig. 7, in an alternative embodiment, when the second device 100 determines that there is a fault at the photovoltaic module, that is, there is an expected difference between the string current and the branch current, the second device 100 controls the break switch S2 to perform the on and off operations at a set duty ratio, and the value of the duty ratio is presented as a stepwise increment. That is, the value of the duty cycle is not fixed but is stepwise increased stepwise in a given step size. It must be noted that the value of the duty cycle is presented as a stepwise increment, while the second device 100 is required to continuously compare the branch current provided by the photovoltaic module initially considered to be faulty to the cable with the string current, and determine whether there is an expected difference between them, if so, the monitored photovoltaic module is considered to be faulty, and if not, the monitored photovoltaic module is considered to be operating normally. Once the expected difference exists between the branch current provided by the primary faulty photovoltaic module and the group string current again, the value of the duty cycle is immediately locked and does not increase, and the value of the duty cycle at the moment is defined as the critical duty cycle. The present embodiment also requires that the second device 100 controls the break switch S2 to perform the on and off operations at a critical duty cycle, under which the first device and the photovoltaic module are brought to an energy condition for fault reproduction, in which the fault occurring at the monitored photovoltaic module is a real fault, not a false fault caused by the proximity effect. It is an important benefit that not only the photovoltaic module or first device, which is freed from false faults, but also the photovoltaic module or first device, in this condition, does not continue to burn and deteriorate steadily even in the face of faults such as arcing, because the fault event is interrupted by a critical duty cycle. For example, when the arcing phenomenon of the arc at the first device such as J4 and the corresponding photovoltaic module still described above is taken as an example, false alarms adjacent to the first device such as J4 with real faults are suppressed, the arc fault at the first device such as J4 and the corresponding photovoltaic module is in the critical state of the arc, which can be understood that the high frequency component or the arc caused by the arcing phenomenon at the position is almost in the critical state between generation and annihilation, it is difficult to propagate to the first devices J3 and J5, or even if the high frequency component and the arc signal propagate to the adjacent first devices, the high frequency component or the arc signal quickly decays to a negligible extent.

Referring to fig. 7, whereby in this example, it is still necessary to "measure the string current flowing through any one of the battery strings" in that battery string; and also measuring in the any string of battery packs, the branch current provided by each monitored photovoltaic module to the cable; and comparing the string current with the branch current, judging whether an expected difference exists between the string current and the branch current, if so, preliminarily considering that the monitored photovoltaic module has faults, and if not, considering that the monitored photovoltaic module operates normally. The second device includes a disconnection switch S2 arranged on the cable, and at this time, the second device controls the disconnection switch S2 to perform an on and off operation with a set one duty ratio, the value of which is set to be stepwise increased; comparing the branch current which is initially considered to be faulty and is provided for the cable with the current string current, and once the phenomenon that the expected difference exists between the branch current which is initially considered to be faulty and the current string current is again generated, the value of the duty ratio at the moment is not increased any more, and the value of the duty ratio at the moment is defined as the critical duty ratio; and the second equipment controls the breaking switch S2 to perform on and off operations at a critical duty ratio, under the critical duty ratio condition, if the phenomenon that the expected difference exists continuously between the branch current provided by the failed photovoltaic module to the cable and the current string current is primarily considered, the failure at the failed photovoltaic module is primarily considered to be a real failure, otherwise, the failure at the failed photovoltaic module is primarily considered to be a false failure. The branch current provided to the cable at this time and the current string current may be negative currents for the photovoltaic module previously primarily considered to be faulty in this example. Other adjacent photovoltaic modules of the truly failed photovoltaic module may be prevented from being mistaken for failed in this example. The high frequency component induced at the failed photovoltaic module under critical duty cycle conditions is in a critical switching state between generation and annihilation. The photovoltaic module that failed, such as a dc arc failure, does not burn continuously. The expected differences in this example are preferably: the branch current has a higher frequency component than the string current within the specified high frequency current band. After the fault point is located, the second device can immediately operate the disconnection switch S2 to cut off so as to disconnect the cable for ensuring the safety. Note that the phenomenon that the expected difference appears again in this example is better and is not suitable to be directly used as a basis for judging faults, because the photovoltaic module is greatly affected by factors such as illumination intensity and ambient temperature, and the amplitude of the output current and the voltage naturally has instability. For example, shadow shielding or inattention of light may produce instantaneous changes in current and voltage, which may cause a disadvantage in that it is difficult to distinguish whether the current and voltage changes are due to environmental causes or arc faults. The high frequency components induced at the truly failing photovoltaic modules in this example decay to a negligible extent before propagating to the adjacent photovoltaic modules.

Referring to fig. 7, the main reason of the poor detection capability of the conventional arc detection means is: one or more sets of fault arc parameter characteristics are required to be firstly made, then the actually detected current parameter information is compared with the fault arc parameter characteristics, if the actually detected current parameter information accords with the fault arc parameter characteristics, the actual arc event is considered to occur, otherwise, if the actually detected current parameter information does not accord with the fault arc parameter characteristics, the actual arc event is considered not to occur. The biggest drawbacks are that the power system of each scene to be tested has a difference and the inverter model of each scene to be tested is different, so that the traditional fault arc detection means always has detection errors or even errors, and the inherent drawbacks are almost irresistible.

Referring to fig. 7, it should be noted that the arc event is not necessarily a high hazard dc arc fault. Actions such as plug switches or motor rotations can cause arcing in the power system, but such arcing is not sustained but is transient and does not negatively affect the proper operation of the system and equipment, and is referred to as a good arc, i.e., a normal arc. And the arc which is caused by the reasons of line short circuit, insulation aging, poor line contact and the like and can continuously burn and easily ignite surrounding inflammables is called a bad arc, namely a direct current fault arc. There is no good solution in the conventional technology to discriminate whether an arc event is a normal arc or a dc fault arc, and it is a problem to be solved urgently to discriminate whether a good arc or a bad arc.

Referring to fig. 7, for example, a positive output terminal of a first device J1 is connected to a positive bus B1 and a negative output terminal of a first device JN is connected to a negative bus B2, and a positive output terminal of a subsequent first device of a plurality of first devices connected in series is connected to a negative output terminal of an adjacent previous first device, or a positive output terminal of a subsequent first device of a plurality of first devices connected in series is connected to a negative output terminal of an adjacent previous first device, thereby connecting the plurality of first devices in series to form a battery string. Each photovoltaic module in the battery string is configured with a first device for receiving its output power, for example, any photovoltaic module PN in the battery string is configured with a first device JN for receiving its PN output power, and a plurality of first devices corresponding to a plurality of photovoltaic modules P1 to PN in any battery string are connected in series with each other, for example, J1 to JN in series, through cables.

Referring to fig. 7, for each photovoltaic module PN, a first device JN for collecting its branch current IS provided, and on the busbar or cable, a second device 100 for collecting at least the string current IS on the cable IS provided. Communication is established between the first and second devices, and the branch current IN of each photovoltaic module JN is sent to the second device by the first device configured by the branch current IN and the second device 100 determines whether a fault has occurred at the photovoltaic module PN.

Referring to fig. 7, the first device JN includes a first controller IC1 and a first communication module CM1 and the second device 100 includes a second controller IC2 and a second communication module CM2; and the first controller IC1 of the first device JN transmits the branch current IN of the corresponding photovoltaic module PN to the second device 100 using the matched first communication module CM 1. The second controller IC2 of the second device receives the branch current of each photovoltaic module by the second communication module CM2 and determines by the second controller whether a fault has occurred at each photovoltaic module. The mode of communication between the first device JN and the second device 100 includes at least power line carrier communication or wireless communication.

Referring to fig. 7, the present application can locate, in particular, which photovoltaic module failed, relative to a conventional failure detection scheme. While conventional fault detection schemes are mostly only aware of the failure of the string, it is difficult to know which photovoltaic module in the string failed. For example, if arc detection is an arc abnormality that monitors the string current, it is only possible to confirm that a fault arc has occurred inside the string, but it is difficult to learn which photovoltaic module in the string has failed. Because the high frequency current associated with the arcing event surges inside the entire string, the detected arcing event only proves that arcing is occurring inside the string, but cannot determine which photovoltaic module in the string is experiencing the arcing event. The fault positioning system and the fault positioning method applied to the photovoltaic module have obvious advantages, and can be used for efficiently positioning faults and achieving safety targets.

Referring to fig. 1, IN an alternative example of a method for locating a fault point of a photovoltaic module, a single string of cells or a plurality of strings of cells connected IN parallel are provided, each string of cells including a plurality of photovoltaic modules such as P1-PN connected IN series by cables, a string current IS flowing through any string of cells IS measured IN any string of cells and a branch current at each monitored point IS also measured IN any string of cells, for example, a corresponding branch current I1 at the photovoltaic module P1, for example, a corresponding branch current I2 at the photovoltaic module P2, for example, a corresponding branch current IK at the photovoltaic module PK IS measured, and a positive integer K mentioned satisfies the condition 1.ltoreq.k.ltoreq.n, for example, a corresponding branch current IN at the photovoltaic module PN IS measured. The branch current I1 equivalent to the local cable connected with the photovoltaic module P1 is measured, the branch current I2 equivalent to the local cable connected with the photovoltaic module P2 is measured, the branch current IK equivalent to the local cable connected with the photovoltaic module PK is measured, and the branch current IN equivalent to the local cable connected with the photovoltaic module PN is measured. So the monitored points at least comprise the positions of the photovoltaic modules P1-PN; and the location of the local cables, it is understood that the location of the local cables connected to the respective photovoltaic modules P1-PN. Comparing the string current with the branch current and judging whether an expected difference exists between the string current and the branch current (such as comparing IK with IS), if so, considering that a fault occurs at a monitored point (such as a photovoltaic module PK or a cable connected with the photovoltaic module PK), and if not, considering that the monitored point operates normally. If a fault occurs between the photovoltaic module PK and the ground, or between a cable connected to the photovoltaic module PK and other cables, or between the positive and negative poles of the photovoltaic module PK, or between the cable connected to the photovoltaic module PK and the ground, a parallel fault or a ground fault may cause an arc, or may cause no arc but only electric leakage.

Referring to fig. 1, in an alternative embodiment, each photovoltaic module is configured with a first device for collecting branch current at a monitored point. For example, a photovoltaic module PK IS provided with a first device JK for collecting the branch current at a monitored point, for example, the branch current IK at the monitored point of the first device JK, and a second device 100 for collecting at least the string current IS provided on the cable. Communication may be established between the first devices JK and the second device 100, the second device 100 sending the group string current IS to the respective first devices, e.g. JK, each first device, e.g. the first device JK, determining if a fault has occurred at this monitored point in its vicinity. The output current of the first device JK characterizes the branch current IK it supplies to the cable. The controller IC1 of the first device JK may compare the string current with the branch current to determine if there IS an expected difference between IK and IS, if so, consider that a fault has occurred at the monitored point, e.g., the monitored point of the first device JK, and if not, consider that the monitored point IS operating normally. The fault may be that the photovoltaic module PK paired by the first device JK fails, or of course, that a cable connected to the first device JK fails, or naturally that the first device JK itself fails. The fault type is, for example, a parallel fault that may cause a parallel arc or a ground fault that causes insulation leakage, or the like.

Referring to fig. 1, in an alternative example, the first device includes a switch disposed between the photovoltaic module and the cable, and the first device immediately operates the switch to turn off to disconnect the photovoltaic module paired therewith from the cable when it determines that a fault has occurred at the monitored point in the vicinity of itself. For example, the first device JN of the shutdown device includes a switch S1 disposed between the paired photovoltaic module PN and the cable, and when the first device JN determines that a monitored point near itself (e.g., the monitored point of JN) fails, the first device immediately operates the switch S1 to shut down, and disconnects the paired photovoltaic module PN from the cable. The controller or microprocessor of the first device configuration may drive or operate the switch S1 to turn off.

Referring to fig. 1, a first device JN of a voltage converter, for example, includes switches disposed between a photovoltaic module PN paired with the first device JN and a cable, and when the first device JN determines that a monitored point (e.g., JN) near the first device JN is faulty, the first device immediately operates the switches to turn off the switches so as to disconnect the photovoltaic module PN paired with the first device JN from the cable. The switches in the voltage converter are usually power level switches, and the buck DC/DC converter, the boost DC/DC converter, or the buck DC/DC converter include power level switches, which are not described in detail in view of common knowledge of the industry of power level switches in the voltage converter. The voltage converter may be additionally provided with a switch S1 as shown in fig. 5, and if the additionally provided switch is turned off, the first device JN of the voltage converter is disconnected from the photovoltaic module PN.

Referring to fig. 1, in an alternative example, each photovoltaic module is configured with a first device receiving its output power, and the first devices J1-JN corresponding to the photovoltaic modules P1-PN under the string are connected in series with each other by cables. Each first device is also adapted to collect the branch current it supplies to the cable; the second device collects the group string current. Communication is established between the first and second devices, for example between the first devices J1-JN and 100, each of which sends the branch current it supplies to the cable to the second device 100, and the second device 100 determines whether a fault has occurred at the monitored point of each first device. Or the second device 100 sends the information of the group string current IS to each of the first devices J1-JN, and the first device determines whether the monitored point of itself IS faulty, for example, the first device J1 determines whether the monitored point of itself IS faulty, the first device J2 determines whether the monitored point of itself IS faulty, and the first device JN determines whether the monitored point of itself IS faulty. The first equipment or the second equipment compares the group string current and the branch current, judges whether the expected difference exists between the group string current and the branch current (such as between I1 and IS, between I2 and IS and the like), if so, the monitored point IS considered to be faulty, and if not, the monitored point IS considered to be normal.

Referring to fig. 1, in an alternative example, a single battery string or a plurality of battery strings connected in parallel may be provided, each battery string including photovoltaic modules P1-PN connected in series by cables, each photovoltaic module being configured with a first device for receiving its output power, and a plurality of first devices J1-JN corresponding to the photovoltaic modules P1-PN under any battery string being connected in series to each other by cables, the positive integer N being greater than 1. The first device is used to collect the branch current it supplies to the cable. In an embodiment in which no second device is used, communication is established between different first devices J1-JN, the first device JK receiving branch current information of the other of the plurality of first devices J1-JN than the first device JK. K is more than or equal to 1 and N is more than or equal to N. For example, IN the assumed example, the first device J1 needs to collect the branch current information of the other devices except the first device J1 IN the plurality of first devices J1-JN, such as the branch currents I2-IN of the other devices, i.e. the first devices J2-JN. For example, in the assumed example, the first device J3 needs to collect the branch current information of the other devices except the first device J3, such as collecting the branch current information of the other devices, i.e., the first devices J1-J2, J4-JN. For example, in the assumed example, the first device JN needs to collect the branch current information of the other devices J1-JN except the first device JN, such as collecting the branch current information of the other devices, i.e., the first devices J1 to J (N-1). The communication may be power line carrier communication, wireless communication, or the like. The first device JK compares its branch current IK with the set of branch currents I1 to I (K-1), I (k+1) to IN of said other, which of course can be represented by the remaining first devices J1 to J (K-1), J (k+1) to JN, e.g. a controller or microprocessor or the like with which the first device JK can perform this task: if there is an expected difference between the branch current of the first device JK and at least a portion of the branch currents in the set, then a fault is considered to occur at the monitored point of the first device JK, otherwise the monitored point of the first device JK is considered to be normal. In alternative embodiments, however, there is no expected difference between the "at least a portion of the branch current" referred to herein above, but there is an expected difference between the branch current IK of the first device JK and this portion of the branch current. For example, if there is an expected difference between the branch current IK of the first device JK and at least a portion of the branch currents in the set (e.g., I1 to I (K-1), etc.), a fault is considered to occur at the monitored point of the first device JK, otherwise the monitored point of the first device JK is considered to be normal, and there is no expected difference between the portions of the branch currents from I1 to I (K-1), etc. Of course, if there is an expected difference between the branch current IK of the first device JK and all other branch currents in the set, it is considered that a fault occurs at the monitored point of the first device JK, otherwise, the monitored point of the first device JK is considered to be normal, that is, there is an expected difference between IK and each of the sets, but there is no expected difference between the insides of the respective branch currents in the sets.

Referring to fig. 1, in an alternative example, a single battery string or a plurality of battery strings connected in parallel may be provided, each battery string including photovoltaic modules P1-PN connected in series by cables, each photovoltaic module being configured with a first device for receiving its output power, and a plurality of first devices J1-JN corresponding to the photovoltaic modules P1-PN under any battery string being connected in series to each other by cables, the positive integer N being greater than 1. The first device is used to collect the branch current it supplies to the cable. In an embodiment in which no second device is used, communication is established between different first devices J1-JN, the first device JK receiving branch current information of the other of the plurality of first devices J1-JN than the first device JK. K is more than or equal to 1 and N is more than or equal to N. In an alternative example, the first device JK compares the branch current IK with the set of branch currents of the other devices J1 to J (K-1), J (k+1) to JN: if there is no expected difference between the branch current of the first device JK and the branch currents of the first devices J (k+1) to JN; however, there is an expected difference between the branch current of the first device JK and the branch currents of the first devices J1 to J (K-1); the cable between the first device JK and the first device J (K-1) is considered to be faulty. For example, assuming that twenty photovoltaic modules in total constitute one battery string, corresponding to n=20, the output current of the first photovoltaic module P1 to the tenth photovoltaic module P10 is 9 amperes, or the output current of the first device J1 to the tenth first device J10 is 9 amperes; meanwhile, in the same one string of the battery packs, the output currents of the eleventh to twentieth photovoltaic modules P11 to P20 are 8 amps, or the output currents of the eleventh to twentieth first devices J11 to J20 are 8 amps, then it is considered that a parallel fault or a ground fault has occurred between the photovoltaic modules P10 and P11 and it is also considered that a parallel fault or a ground fault has occurred between the first devices J10 and J11.

Referring to fig. 1, in an alternative example, communication is established between different first devices J1-JN, the first device JK receives branch current information of other devices of the plurality of first devices J1-JN except the first device JK, and the first device JK compares a set of its branch current and the branch current of the other devices: if there is an expected difference between the branch current of the first device JK and at least a portion of the branch currents in the set, and the at least a portion of the branch currents do not differ from each other, then it is considered that a fault has occurred at the monitored point of the first device JK, and on the contrary, it is considered that the monitored point of the first device JK is normal.

Referring to fig. 3, in an alternative example, the fault described above may occur at the photovoltaic module, at the cable and between the cable connectors that are mated, or between the photovoltaic module and ground, between the cable and ground; the monitored point may include both the photovoltaic module and the cable or first device. The location of the fault occurrence may refer not only to the location of the photovoltaic module, but also to the location of the cable fault point. In fig. 3, a parallel fault, i.e. a parallel fault between cables, may occur between the first battery string positive bus bar and the second battery string positive bus bar, and a ground fault may also occur between a cable at, for example, the positive or negative electrode of a certain photovoltaic module and the ground, which form a parallel discharge and a ground discharge, respectively. A parallel fault or ground fault may cause a parallel arc, or may simply be a leakage fault.

The foregoing description and drawings set forth exemplary embodiments of the specific structure of the embodiments, and the above disclosure presents presently preferred embodiments, but is not intended to be limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above description. Therefore, the appended claims should be construed to cover all such variations and modifications as fall within the true spirit and scope of the invention. Any and all equivalent ranges and contents within the scope of the claims should be considered to be within the intent and scope of the present invention.

Claims

1. A method for locating a fault point of a photovoltaic module provides a single battery string or provides a plurality of battery strings connected in parallel, each battery string comprises a plurality of photovoltaic modules P1-PN connected in series by cables, and the method is characterized in that:

however, there is an expected difference between the branch current of the first device JK and the branch currents of the first devices J1 to J (K-1);

then it is considered that a fault has occurred at the cable between the first device JK and the first device J (K-1), said fault including at least a direct current arc fault or a leakage current fault;

the expected differences include: the current difference between the branch currents is not within a predetermined current fluctuation range.

2. The method according to claim 1, characterized in that:

a second device is configured on the cable for collecting at least a string current flowing through the battery string.

3. The method according to claim 1, characterized in that:

the first device is selected from:

4. The method according to claim 2, characterized in that:

5. The method according to claim 1, characterized in that:

the first device JK includes a switch disposed between the photovoltaic module PK and the cable, and when the first device JK determines that a fault occurs, the switch is turned off immediately, and the photovoltaic module PK paired with the switch is disconnected from the cable.

6. A method for locating a fault point of a photovoltaic module provides a single battery string or provides a plurality of battery strings connected in parallel, each battery string comprises a plurality of photovoltaic modules P1-PN connected in series by cables, and the method is characterized in that:

the expected differences include: a part of the branch current has a higher frequency component in a specified high frequency current band than another part of the branch current.

7. The method according to claim 6, wherein:

the first device is selected from:

8. The method according to claim 6, wherein:

9. A method for locating a fault point of a photovoltaic module provides a single battery string or provides a plurality of battery strings connected in parallel, each battery string comprises a plurality of photovoltaic modules P1-PN connected in series by cables, and the method is characterized in that:

the expected differences include: the peak-to-valley difference between the peak and valley of one part of the branch current exceeds the peak-to-valley difference between the peak and valley of another part of the branch current.

10. The method according to claim 9, wherein: