Combiner box DC series fault arc detection device and method

Abstract

The present application discloses a detection device and method for a DC series fault arc in a combiner box, which relates to the technical field of DC series fault arc detection, and includes a current detection module, a voltage detection module, a temperature detection module, a signal processing communication main control module, and an ultraviolet detection module of multiple photovoltaic strings; the multiple current detection modules are respectively installed at the corresponding guide hole outlets of the current detection column of the combiner box, and are connected to the signal processing communication main control module; the voltage detection module is used to be connected in parallel with the input end of the circuit breaker connected to the combiner box, and collect the voltage value of the circuit breaker input end; the temperature detection module is used to be fixed on the shell of the combiner box, and collect the working temperature of the combiner box; the ultraviolet detection module is used to be installed at the circuit breaker input end of the combiner box, and collect the ultraviolet information of the circuit breaker input end. The present application has the effect of detecting fault arcs based on the time-frequency domain characteristics of the arc, and adopts time domain and wavelet analysis technology.

Description

Technical Field

[0001] The present application relates to the technical field of DC series fault arc detection, and in particular to a device and method for detecting a DC series fault arc in a combiner box. Background Art

[0002] Photovoltaic power generation is considered inherently safe, but in reality, this is a blind spot in public awareness. As photovoltaic systems expand in scale and number, and their operational timelines lengthen, weathering and damage to cables, aging and damage to electronic components, and poor contact in connectors are causing arc faults, once a rare occurrence, to become increasingly frequent.

[0003] Arcing is a gas discharge phenomenon caused by current passing through an insulating medium. In light of the hazardous nature of DC arc faults in photovoltaic systems, the United States implemented NEC 690.12 in 2014, and UL1699B was introduced the same year. In 2015, China implemented the "Electrical Fire Monitoring Systems (Part 4: Arc Fault Detection Devices)." Improving the flame retardancy of photovoltaic modules is a fundamental solution to photovoltaic fires, but a decisive breakthrough in the flame retardancy of EVA films used in photovoltaic modules has yet to be achieved.

[0004] Research on arc faults encompasses arc time-frequency, spectral, and chaotic characteristics. Analysis encompasses the voltage and current in the circuit during arc discharge, as well as the accompanying acoustic, optical, and electromagnetic radiation. Analysis techniques include time-frequency analysis, wavelet analysis, neural networks, and Mahalanobis distance analysis. Currently, the mainstream research approach focuses on analyzing current, identifying time-frequency characteristics, and using time-frequency and / or wavelet analysis techniques. This article follows this mainstream industry research approach, based on the fact that over 80% of DC arc fault light is ultraviolet. The research focuses on time-frequency characteristics, analyzing current and ultraviolet light, and employing a combination of time-domain and wavelet analysis techniques. The difficulty in detecting arc faults lies in the threshold: false positives at low thresholds and missed positives at high thresholds. Using BP neural networks or support vector machines to determine the threshold, theoretically robust but realistically unreliable. The thresholds recommended by arc detector manufacturers are often overly conservative, focusing on arc fires while ignoring power losses, leading to biased analysis.

[0005] Effective arc fault detection requires not only real-time arc detection but also the detection of arc fault precursors to prevent potential problems before they occur. If the circuit is disconnected when the arc stabilizes, it is already too late. Therefore, it is necessary to detect fault signs during the arc's unstable phase to avoid serious consequences. In other words, attention must be paid to the photovoltaic system's non-self-sustaining discharge, the transition from non-self-sustaining to self-sustaining discharge, and self-sustaining discharge. The operation and maintenance concept has evolved from post-maintenance repairs, regular inspections, and condition-based maintenance. Drawing on the operation and maintenance concept of condition-based maintenance, three low, medium, and high thresholds for faults are designed: low-threshold arc faults are detected and counted to guide the time allocation for operation and maintenance inspections; medium-threshold arc faults are detected and counted to allocate operation and maintenance inspection task lists and issue warnings; high-threshold arc faults are detected and counted to automatically disconnect the circuit to extinguish the arc and issue an alarm. Condition-based operation and maintenance of arc faults addresses both arc fires and photovoltaic output.

[0006] Chinese patent publication number CN102684152B discloses a photovoltaic bus-specific arc fault detection and arc extinguishing device. The device includes a first fly-eye lens with a large attenuation characteristic for the arc spectrum and a second fly-eye lens with a broad-spectrum light transmittance characteristic. The first fly-eye lens and the second fly-eye lens respectively cover a first photosensitive tube group and a second photosensitive tube group. The first photosensitive tube group only outputs a photoelectric signal of scattered sunlight, while the second photosensitive tube group outputs a photoelectric signal of scattered sunlight and arc light. The output ends of the first photosensitive tube group and the second photosensitive tube group are connected to a signal topology processing module, which outputs an amplified photoelectric signal of the arc light. This photoelectric signal is the arc fault detection signal.

[0007] Chinese patent publication number CN102854426B discloses a method for determining a DC arc fault based on real-time measurement of the proportion of frequency components in multiple frequency bands.

[0008] Chinese patent publication number CN103245897B discloses a method for detecting DC arc faults in photovoltaic systems using multiple criteria.

[0009] However, the photovoltaic bus-specific fault arc detection and arc extinguishing device extracts arc light signals through two compound eye lenses, which has the problems of complex structure and poor applicability; the method for judging DC arc faults based on real-time measurement of the proportion of multi-band frequency components and the detection method of DC fault arcs in photovoltaic systems using multiple criteria use the proportion of multi-band frequency components to judge arc faults, multiple criteria to detect fault arcs, and focus on the detection of stable arc self-sustaining discharge, which leads to the neglect of non-self-sustaining discharge, the transition from non-self-sustaining to self-sustaining discharge, and the characteristics of arc ultraviolet light. It has great limitations and needs to be improved. Summary of the Invention

[0010] In view of this, the first object of this application is to provide a device for detecting a DC series fault arc in a combiner box, so as to detect the precursor of a fault arc. The specific scheme is as follows:

[0011] A detection device for a DC series fault arc in a combiner box, comprising a current detection module, a voltage detection module, a temperature detection module, a signal processing and communication main control module, and an ultraviolet detection module for multiple photovoltaic strings;

[0012] The multiple current detection modules are respectively installed at the corresponding guide hole outlet ends of the current detection column of the combiner box and connected to the signal processing and communication main control module;

[0013] The voltage detection module is configured to be connected in parallel to the input terminal of the circuit breaker connected to the combiner box and collect the voltage value of the input terminal of the circuit breaker;

[0014] The temperature detection module is used to be fixed on the housing of the combiner box and collect the operating temperature of the combiner box;

[0015] The ultraviolet detection module is used to be installed at the circuit breaker input end of the combiner box to collect ultraviolet information at the circuit breaker input end.

[0016] Preferably, the circuit breaker is used to receive the photovoltaic energy collected by the combiner box and output through the positive / negative busbar, and transmit the photovoltaic energy to the inverter, the AC low-voltage switchgear and the step-up transformer.

[0017] Preferably, the circuit breaker is further connected in parallel with a surge protection device.

[0018] Preferably, the signal processing and communication main control module is provided with a magnetic isolation communicator.

[0019] Preferably: the multiple current detection modules of the photovoltaic strings include a current detection module of the first photovoltaic string, a current detection module of the second photovoltaic string, a current detection module of the third photovoltaic string and a current detection module of the fourth photovoltaic string, and the current detection module of the first photovoltaic string, the current detection module of the second photovoltaic string, the current detection module of the third photovoltaic string and the current detection module of the fourth photovoltaic string are all provided with a Hall current sensor circuit, and the Hall current sensor circuit includes a Hall current sensor unit for the cable of the corresponding photovoltaic string to pass through and an operational amplifier unit, and the operational amplifier unit is a Butterworth filter and is used to condition the photovoltaic string current signal collected by the Hall current sensor unit.

[0020] Preferably, the signal processing and communication main control module includes a signal processing main control unit and an RS485 communication unit. The MCU of the signal processing main control unit is ATmega128. The RS485 communication unit is provided with a magnetic isolation communicator, which is ADM2483.

[0021] A second object of the present application is to provide a method for detecting a DC series fault arc in a combiner box, including a preparation process for the method and an operation process for the method;

[0022] The preparation process includes the following steps:

[0023] Step 1. Set arc detection parameters: including analysis period T, number of ultraviolet data points N_ultraviolet, current sampling frequency f s , the number of time windows is w+1, the current frequency domain is 10-100kHz, and the wavelet transform decomposition is j+1 frequency band;

[0024] Step 2, analysis period T: sample N current data, read N_ultraviolet ultraviolet data and current effective value s;

[0025] Step 3: Set the threshold:

[0026] include s_ultraviolet_threshold_high / s 2 ;

[0027] σ / μ_threshold_low, σ / μ_threshold_middle, σ / μ_threshold_high;

[0028] μs_ MAXMIN / μ_threshold_low, μs_ MAXMIN / μ_threshold_middle;

[0029] μs_ MAXMIN / μ_threshold_high;

[0030] μe / s 2 _threshold_middle and μe / s 2 _threshold_high;

[0031] The operation process includes the following steps:

[0032] Step 1: Use the following formula:

[0033] s MAX _ultraviolet=MAX[s_ultraviolet(1),...,s_ultraviolet(N_ultraviolet)];

[0034] s MAX _ultraviolet / s2 =s MAX _ultraviolet÷s 2 ;

[0035] Among them, s MAX _ultraviolet is the maximum value of ultraviolet; s_ultraviolet(i) is the ultraviolet value, and 1≤i≤N_ultraviolet; s MAX _ultraviolet / s 2 is the maximum value of ultraviolet light; s is the relative current sampling value;

[0036] Get the maximum value of UV relative to the effective current s MAX _ultraviolet / s 2 ;

[0037] Step 2: Use the following formula:

[0038]

[0039]

[0040]

[0041] Where μ is the mean; σ is the variance; s(k) is the current sampling value, and 1≤k≤N; the current variance σ / μ relative to the mean is obtained;

[0042] Step 3: Use the following formula:

[0043] s MAXMIN (i)=MAX[s(i,1)…s(i,l)]-MIN[s(i,1)…s(i,l)],i∈[0,w];

[0044] S MAXMIN =[s MAXMIN (0), s MAXMIN (1), s MAXMIN (2),…,s MAXMIN (w)];

[0045]

[0046] Where s(i, j) is the current sampling value, and 0≤i≤w, 1≤j≤l, (1+w)*l=N; s MAXMIN (i) is the peak-to-peak current, and 0≤i≤w; S MAXMIN is the current peak-to-peak value array; μs_ MAXMIN / μ is the mean value of the peak-to-peak current;

[0047] Get the relative average current peak-to-peak value μs_MAXMIN / μ.

[0048] Step 4: Use the following formula:

[0049]

[0050]

[0051]

[0052] E=[e o ,e1,e2,....,e j ];

[0053]

[0054] Among them, h0 and h1 are the high-pass and low-pass filter coefficients respectively; c m is the coefficient of wavelet transform frequency band m; e m is the energy of wavelet transform frequency band m; μe / s 2 is the frequency band energy mean relative to the effective value of the current;

[0055] Get the frequency band energy mean μe / s of the relative current RMS value 2 ;

[0056] Step 5: Judge and control in sequence:

[0057] 1) When s MAX _ultraviolet / s 2 ≥s_ultraviolet_threshold_high / s 2 or μs _MAXMIN / μ≥μs _MAXMIN / μ_threshold_high or σ / μ≥σ / μ_threshold_high or μe / s 2 ≥μe / s 2 _threshold_high, an alarm is issued, the operating parameters are recorded and stored, the circuit is cut off and the arc is extinguished, and the process continues with step 6; otherwise, the process continues with step 2);

[0058] 2) When μs _MAXMIN / μ≥μs _MAXMIN / μ_threshold_middle or σ / μ≥σ / μ_threshold_middle or μe / s 2 ≥μe / s 2 _threshold_middle, an early warning is issued, and the storage operating parameters and the operation and maintenance checklist are recorded and stored, and the process continues with step 6; otherwise, the process continues with step 3);

[0059] 3) When μs _MAXMIN / μ≥μs _MAX_MIN / μ_threshold_low or σ / μ ≥ σ / μ_threshold_low, store the operating condition parameters and guide the operation and maintenance inspection time allocation, and continue with step 6; otherwise, continue with step 4);

[0060] 4) Record and store the operating parameters and proceed to step 6;

[0061] Among them, s_ultraviolet_threshold_high / s 2 UV is the relative current effective value; μs _MAXMIN / μ_threshold_high is the peak-to-peak mean high threshold of the current relative to the mean; σ / μ_threshold_high is the variance high threshold relative to the mean; μe / s 2 _threshold_high is the high threshold of the frequency band energy average relative to the current effective value; μs _MAXMIN / μ_threshold_middle is the current peak-to-peak mean threshold relative to the mean; σ / μ_threshold_middle is the variance threshold relative to the mean; μe / s 2 _threshold_middle is the middle threshold of the frequency band energy mean relative to the effective current value; μs _MAX_MIN / μ_threshold_low is the current peak-to-peak mean low threshold relative to the mean; σ / μ_threshold_low is the variance low threshold relative to the mean;

[0062] Step 6: Wait for the next analysis cycle T, and continue with step 1 after entering the next analysis cycle T.

[0063] Preferably: in the preparation process, the number of ultraviolet sampling data points in the analysis period T = N_ultraviolet; the signal analysis period T, the current sampling frequency f s , the number of current sampling data points N = T × f s ; T is divided into w+1 time windows, and each time window is set with current sampling data l, and N = (w+1)×l; the current frequency domain analysis takes the 10-100kHz frequency band; the wavelet transform is decomposed into j+1 frequency bands.

[0064] As can be seen from the above solutions, the present application provides a device and method for detecting a DC series fault arc in a combiner box. The device and method for detecting a DC series fault arc in a combiner box have the following beneficial effects:

[0065] 1. Detect arc faults by collecting PV string current and combiner box ultraviolet light, and using time domain and wavelet analysis techniques based on the time-frequency characteristics of the arc.

[0066] 2. The UV sensor assists in the detection of current characteristics, improving the safety of the device;

[0067] 3. Drawing on the operational achievements of condition-based maintenance, we designed three fault thresholds: low, medium, and high. This takes into account the respective demands of arc fires and photovoltaic output, minimizing the cost-effectiveness of photovoltaic operation and maintenance.

[0068] 4. The reliability of the device is increased by installing a magnetic isolation communicator in the signal processing and communication main control module. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without any creative work.

[0070] Figure 1 This is a principle block diagram of the detection device for DC series fault arc in a combiner box disclosed in this application;

[0071] Figure 2 This is a schematic diagram of the connection structure of the photovoltaic power station disclosed in this application;

[0072] Figure 3 This is a schematic diagram of the connection structure of the detection device for DC series fault arc in a combiner box disclosed in this application;

[0073] Figure 4 This is a circuit diagram of the Hall current sensor of the first photovoltaic string disclosed in this application;

[0074] Figure 5 This is a circuit diagram of the ultraviolet detection module of the combiner box disclosed in this application;

[0075] Figure 6 This is a circuit diagram of the signal processing and communication main control module of the combiner box disclosed in this application;

[0076] Figure 7 This is a flow chart of the DC series fault arc detection method for a combiner box disclosed in this application;

[0077] Figure 8 A flow chart for preparing the combiner box DC series fault arc detection method disclosed in this application;

[0078] Figure 9This is an operational flow chart of the combiner box DC series fault arc detection method disclosed in this application.

[0079] Explanation of the accompanying reference numerals: 100, current detection module of the first photovoltaic string; 120, Hall current sensor circuit; 121, Hall current sensor unit; 122, operational amplifier unit; 200, current detection module of the second photovoltaic string; 220, Hall current sensor circuit; 221, Hall current sensor unit; 222, operational amplifier unit; 300, current detection module of the third photovoltaic string; 320, Hall current sensor circuit; 321, Hall current sensor unit; 322, operational amplifier unit; 400, current detection module of the fourth photovoltaic string; 420, Hall current sensor circuit; 421, Hall current sensor unit; 422, operational amplifier unit; 500, voltage detection module; 600, temperature detection module; 700, signal processing and communication main control module; 710, signal processing main control unit; 720, RS485 communication unit; 800, ultraviolet detection module. DETAILED DESCRIPTION

[0080] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0081] like Figure 1 As shown, a device for detecting a DC series fault arc in a combiner box includes current detection modules for multiple photovoltaic strings, a voltage detection module 500, a temperature detection module 600, a signal processing and communication main control module 700, and an ultraviolet detection module 800. The multiple current detection modules are respectively installed at the corresponding guide hole outlet ends of the current detection column of the combiner box and connected to the signal processing and communication main control module 700; the voltage detection module 500 is used to be connected in parallel with the input end of the circuit breaker connected to the combiner box, thereby collecting the voltage value at the circuit breaker input end; the temperature detection module 600 is used to be fixed on the housing of the combiner box, thereby collecting the operating temperature of the combiner box; the ultraviolet detection module 800 is used to be installed at the circuit breaker input end of the combiner box, thereby collecting ultraviolet information at the circuit breaker input end. At this time, the ultraviolet sensor assists in the detection of current characteristics, which will play a role in improving the safety of the device;

[0082] like Figure 1 、 Figure 2 、 Figure 3As shown, the photovoltaic power station consists of a photovoltaic array, a combiner box, an inverter, an AC low-voltage switchgear, and a step-up transformer. The photovoltaic array is composed of multiple photovoltaic modules connected in series and parallel, and is used to output photovoltaic energy at a rated voltage and current. The positive and negative ends of the photovoltaic array are connected to string + and string - cables, respectively, which are connected to the combiner box's string positive and string negative terminals. The cables from the positive string terminals are routed through the guide holes on the combiner box's current sensing posts, passing through the corresponding current sensing modules, anti-reverse diodes, and fuses before being connected to the positive busbar. The cables from the negative string terminals of the combiner box do not have current sensing modules, and the rest of the configuration is similar to that of the combiner box's string positive terminals. The circuit breaker receives the photovoltaic energy collected by the combiner box via the positive / negative busbars and transmits it to the inverter, AC low-voltage switchgear, and step-up transformer. A surge protection device is also connected in parallel to the circuit breaker.

[0083] It should be mentioned that the signal processing and communication main control module 700 is provided with a magnetic isolation communicator. The magnetic isolation communicator provided in the signal processing and communication main control module 700 will significantly increase the reliability of the device. The current detection modules of the multiple photovoltaic strings include a current detection module 100 for the first photovoltaic string, a current detection module 200 for the second photovoltaic string, a current detection module 300 for the third photovoltaic string, and a current detection module 400 for the fourth photovoltaic string. The current detection module 100 for the first photovoltaic string, the current detection module 200 for the second photovoltaic string, the current detection module 300 for the third photovoltaic string, and the current detection module 400 for the fourth photovoltaic string are all provided with Hall current sensor circuits 420, 320, 220, and 120. The Hall current sensor circuit 420, 320, 220, 120 includes a Hall current sensor unit 421, 321, 221, 121 through which the corresponding photovoltaic string cable passes, and an operational amplifier unit 422, 322, 222, 122 of model OP-27. The operational amplifier unit 422, 322, 222, 122 is a Butterworth filter and is used to condition the photovoltaic string current signal collected by the Hall current sensor unit 421, 321, 221, 121. The signal processing and communication main control module 700 includes a signal processing main control unit 710 and an RS485 communication unit 720. The MCU of the signal processing main control unit 710 is ATmega128, and the RS485 communication unit 720 is provided with a magnetic isolation communicator, which is ADM2483. Pins 3 and 2 of the ATmega128 are connected to pins 3 and 6 of the ADM2483 respectively (see Figure 6 ), pins 13 and 12 of ADM2483 are exported as B485 and A485 respectively, and connected to the Modbus network.

[0084] like Figure 4 、 Figure 5 、 Figure 6As shown, R121, R122, and C122 are connected, the other end of R121 is connected to pin 9 of HBC06LTS3.3, the other end of R122 is connected to C121 and pin 3 of OPT-27; the other end of C121 is grounded, and the other end of C122 is connected to pin 6 of OPT-27; R123 and R124 are connected and connected to pin 2 of OPT-27, the other end of R123 is grounded, and the other end of R124 is connected to pin 6 of OPT-27; pin 6 of OPT-27 is connected to pin 61 of ATmega128 of signal processing and communication main control module 700; at the same time, the Hall effect of current detection module 200 of the second photovoltaic string, current detection module 300 of the third photovoltaic string, and current detection module 400 of the fourth photovoltaic string The outputs of the current sensor circuits 420, 320, 220, and 120 are respectively connected to the ATmega128 pins 60, 59, and 58 of the signal processing and communication main control module 700; the output of the voltage detection module 500 is connected to the ATmega128 pin 57 of the signal processing and communication main control module 700, and the output of the temperature detection module 600 is connected to the ATmega128 pin 56 of the signal processing and communication main control module 700; the ultraviolet detection module 800 is based on the digital ultraviolet sensor GUVB-C31SM, pin 1 of the GUVB-C31SM is grounded, pin 4 is connected to VCC, and pins 2 and 3 of the GUVB-C31SM are respectively connected to the ATmega128 pins 26 and 25 of the signal processing and communication main control module 700.

[0085] It should be noted that the voltage detection module 500 is similar to the current detection module, and the model of the Hall voltage sensor is HBVOSA3.3; the temperature detection module 600 is based on the DS18B20 chip and communicates with the signal processing and communication main control module 700 through a single bus; the ultraviolet sensor GUVB-C31SM plays the role of monitoring the ultraviolet rays in the arc light in the junction box.

[0086] The present application also provides a method for detecting a DC series fault arc in a combiner box, such as Figure 7 、 Figure 8 、 Figure 9 As shown, it includes the preparation process of the combiner box DC series fault arc detection method and the operation process of the combiner box DC series fault arc detection method;

[0087] The preparation process includes the following steps:

[0088] Step 1. Set arc detection parameters: including analysis period T, number of ultraviolet data points N_ultraviolet, current sampling frequency f s , the number of time windows is w+1, the current frequency domain is 10-100kHz, and the wavelet transform decomposition is j+1 frequency band;

[0089] Step 2, analysis period T: sample N current data, read N_ultraviolet ultraviolet data and current effective value s; and the number of current sampling data points N = T × f s ; Each time window is set with current sampling data l, and N = (w + 1) × l;

[0090] Step 3: Set the threshold:

[0091] include s_ultraviolet_threshold_high / s 2 ;

[0092] σ / μ_threshold_low, σ / μ_threshold_middle, σ / μ_threshold_high;

[0093] μs_ MAXMIN / μ_threshold_low, μs_ MAXMIN / μ_threshold_middle;

[0094] μs_ MAXMIN / μ_threshold_high;

[0095] μe / s 2 _threshold_middle and μe / s 2 _threshold_high;

[0096] The operation process includes the following steps:

[0097] Step 1: Use the following formula:

[0098] s MAX _ultraviolet=MAX[s_ultraviolet(1),...,s_ultraviolet(N_ultraviolet)];

[0099] s MAX _ultraviolet / s 2 =s MAX _ultraviolet÷s 2 ;

[0100] Among them, s MAX _ultraviolet is the maximum value of ultraviolet; s_ultraviolet(i) is the ultraviolet value, and 1≤i≤N_ultraviolet; s MAX _ultraviolet / s 2 is the maximum value of ultraviolet light; s is the relative current sampling value;

[0101] Get the maximum value of UV relative to the effective current s MAX _ultraviolet / s 2 ;

[0102] Step 2: Use the following formula:

[0103]

[0104]

[0105]

[0106] Where μ is the mean; σ is the variance; s(k) is the current sampling value, and 1≤k≤N; the current variance σ / μ relative to the mean is obtained;

[0107] Step 3: Use the following formula:

[0108] s MAXMIN (i)=MAX[s(i,1)…s(i,l)]-MIN[s(i,1)…s(i,l)],i∈[0,w];

[0109] S MAXMIN =[s MAXMIN (0), s MAXMIN (1), s MAXMIN (2),…,s MAXMIN (w)];

[0110]

[0111] Where s(i, j) is the current sampling value, and 0≤i≤w, 1≤j≤l, (1+w)*l=N; s MAXMIN (i) is the peak-to-peak current, and 0≤i≤w; S MAXMIN is the current peak-to-peak value array; μs_ MAXMIN / μ is the mean value of the peak-to-peak current;

[0112] Get the relative average current peak-to-peak value μs_ MAXMIN / μ.

[0113] Step 4: Use the following formula:

[0114]

[0115]

[0116]

[0117] E=[e o,e1,e2,....,e j ];

[0118]

[0119] Among them, h0 and h1 are the high-pass and low-pass filter coefficients respectively; c m is the coefficient of wavelet transform frequency band m; e m is the energy of wavelet transform frequency band m; μe / s 2 is the frequency band energy mean relative to the effective value of the current;

[0120] Get the frequency band energy mean μe / s of the relative current RMS value 2 ;

[0121] Step 5: Judge and control in sequence:

[0122] 1) When s MAX _ultraviolet / s 2 ≥s_ultraviolet_threshold_high / s 2 or μs _MAXMIN / μ≥μs _MAXMIN / μ_threshold_high or σ / μ≥σ / μ_threshold_high or μe / s 2 ≥μe / s 2 _threshold_high, an alarm is issued, the operating parameters are recorded and stored, the circuit is cut off and the arc is extinguished, and the process continues with step 6; otherwise, the process continues with step 2);

[0123] 2) When μs _MAXMIN / μ≥μs _MAXMIN / μ_threshold_middle or σ / μ≥σ / μ_threshold_middle or μe / s 2 ≥μe / s 2 _threshold_middle, an early warning is issued, and the storage operating parameters and the operation and maintenance checklist are recorded and stored, and the process continues with step 6; otherwise, the process continues with step 3);

[0124] 3) When μs _MAXMIN / μ≥μs _MAX_MIN / μ_threshold_low or σ / μ ≥ σ / μ_threshold_low, store the operating condition parameters and guide the operation and maintenance inspection time allocation, and continue with step 6; otherwise, continue with step 4);

[0125] 4) Record and store the operating parameters and proceed to step 6;

[0126] Among them, s_ultraviolet_threshold_high / s 2 UV is the relative current effective value; μs _MAXMIN / μ_threshold_high is the peak-to-peak mean high threshold of the current relative to the mean; σ / μ_threshold_high is the variance high threshold relative to the mean; μe / s 2 _threshold_high is the high threshold of the frequency band energy average relative to the current effective value; μs _MAXMIN / μ_threshold_middle is the current peak-to-peak mean threshold relative to the mean; σ / μ_threshold_middle is the variance threshold relative to the mean; μe / s 2 _threshold_middle is the middle threshold of the frequency band energy mean relative to the effective current value; μs _MAX_MIN / μ_threshold_low is the current peak-to-peak mean low threshold relative to the mean; σ / μ_threshold_low is the variance low threshold relative to the mean;

[0127] Step 6: Wait for the next analysis cycle T, and continue with step 1 after entering the next analysis cycle T.

[0128] References to "first," "second," "third," "fourth," and the like (if any) herein are intended to distinguish similar objects and are not necessarily intended to describe a particular order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate so that the embodiments described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "including" and "having," as well as any variations thereof, are intended to cover non-exclusive inclusions, e.g., a process, method, or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such processes, methods, or apparatus.

[0129] It should be noted that the descriptions of "first", "second", etc. in this application are for descriptive purposes only and should not be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of such features. In addition, the technical solutions between the various embodiments can be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in this field. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0130] This document uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A detection device for a DC series fault arc in a combiner box, characterized in that: It includes current detection modules, voltage detection modules, temperature detection modules, signal processing and communication main control modules and ultraviolet detection modules of multiple photovoltaic strings; A plurality of the current detection modules are respectively installed at the outlet ends of the corresponding guide holes of the current detection column of the combiner box and connected to the signal processing and communication main control module; The voltage detection module is used to be connected in parallel with the input terminal of the circuit breaker connected to the combiner box to collect the voltage value of the input terminal of the circuit breaker; The temperature detection module is used to be fixed on the shell of the combiner box to collect the working temperature of the combiner box; The ultraviolet detection module is used to be installed at the circuit breaker input end of the combiner box to collect ultraviolet information at the circuit breaker input end; Among them, the detection method based on the detection device includes a preparation process of the combiner box DC series fault arc detection method and an operation process of the combiner box DC series fault arc detection method; The preparation process includes the following steps: Step 1: Set arc detection parameters: including analysis period T, number of ultraviolet data points N_ultraviolet, current sampling frequency f s , the number of time windows is w+1, the current frequency domain is 10-100kHz, and the wavelet transform is used to decompose the j+1 frequency band; Step 2, analysis period T: sampling N current data, reading N_ultraviolet ultraviolet data and current effective value s; Step 3: Set the threshold: Includes s_ultraviolet_threshold_high / s 2 ; σ / µ_threshold_low, σ / µ_threshold_middle, σ / µ_threshold_high; µs_ MAXMIN / µ_threshold_low、µs_ MAXMIN / µ_threshold_ middle; µs_ MAXMIN / µ_threshold_high; µe / s 2 _threshold_middle and µe / s 2 _threshold_high; The operation process includes the following steps: Step 1: Use the following formula: ； ； Among them, s MAX _ultraviolet is the maximum value of ultraviolet; s_ultraviolet(i) is the ultraviolet value, and 1≤i≤N_ultraviolet; s MAX _ultraviolet / s 2 is the maximum value of ultraviolet light of the relative current effective value; s is the relative current sampling value; Get the maximum value of UV relative to the effective current value s MAX _ultraviolet / s 2 ; Step 2: Use the following formula: ； ； ； Wherein, μ is the mean; σ is the variance; s(k) is the current sampling value, and 1≤k≤N; the current variance σ / μ relative to the mean is obtained; where k is a variable located at the current sampling data point number 1 to N; Step 3, by the following formula: ； ； ； Where, s(i,j) is the current sampling value, and 0≤i≤w, 1≤j≤l, (1+w)*l = N; s MAXMIN (i) is the peak current value, and 0≤i≤w; S MAXMIN is the current peak-to-peak value array; µs_ MAXMIN / µ is the average value of the peak-to-peak current; where w is the number of time windows, and l is the current sampling data set for each time window; Get the relative mean current peak-to-peak value µs_ MAXMIN / µ; Step 4: Use the following formula: ； ； ； ； Among them, h0 and h1 are the high-pass and low-pass filter coefficients respectively; c m is the coefficient of wavelet transform frequency band m; e m is the energy of wavelet transform frequency band m; µe / s 2 It is the frequency band energy mean value relative to the effective value of current; Get the frequency band energy mean value µe / s of the relative current RMS value 2 ; Step 5: Judge and control in sequence: 1) When s MAX _ultraviolet / s 2 ≥s_ultraviolet_threshold_high / s 2 or µs _MAXMIN / µ≥µs _MAXMIN / µ_threshold_high or σ / µ≥σ / µ_threshold_high or µe / s 2 ≥µe / s 2 _threshold_high, an alarm is issued, the operating parameters are recorded and stored, and the circuit is cut off to extinguish the arc, and then continue with step 6; otherwise, continue with step 2); 2) When µs _MAXMIN / µ≥µs _MAXMIN / µ_threshold_middle or σ / µ≥σ / µ_threshold_middle or µe / s 2 ≥µe / s 2 _threshold_middle, an early warning is issued, and the storage condition parameters and the distribution operation and maintenance checklist are recorded, and the process continues to step 6; otherwise, the process continues to step 3); 3) When µs _MAXMIN / µ≥µs _MAX_MIN / µ_threshold_low or σ / µ≥σ / µ_threshold_low, store the operating condition parameters and guide the allocation of operation and maintenance inspection time, and continue with step 6, otherwise continue with 4); 4) Record and store the operating parameters and proceed to step 6; Among them, s_ultraviolet_threshold_high / s 2 is the relative current effective value of ultraviolet light; µs _MAXMIN / µ_threshold_high is the current peak-to-peak mean high threshold relative to the mean; σ / µ_threshold_high is the variance high threshold relative to the mean; µe / s 2 _threshold_high is the high threshold of the frequency band energy average relative to the current effective value; µs _MAXMIN / µ_threshold_middle is the current peak-to-peak mean middle threshold relative to the mean; σ / µ_threshold_middle is the variance middle threshold relative to the mean; µe / s 2 _threshold_middle is the middle threshold of the frequency band energy mean relative to the effective value of the current; µs _MAX_MIN / µ_threshold_low is the current peak-to-peak mean low threshold relative to the mean; σ / µ_threshold_low is the variance low threshold relative to the mean; Step 6: Wait for the next analysis cycle T, and continue with step 1 after entering the next analysis cycle T.

2. The detection device for a DC series fault arc in a combiner box according to claim 1, characterized in that: The circuit breaker is used to receive the photovoltaic energy collected by the combiner box and output through the positive / negative combiner plate, and transmit the photovoltaic energy to the inverter, the AC low-voltage switch cabinet and the step-up transformer.

3. The detection device for a DC series fault arc in a combiner box according to claim 2, characterized in that: The circuit breaker is also connected in parallel with a surge protection device.

4. The device for detecting a DC series fault arc in a combiner box according to claim 1, characterized in that: The signal processing communication main control module is provided with a magnetic isolation communicator.

5. The detection device for a DC series fault arc in a combiner box according to claim 1, characterized in that: The multiple current detection modules of the photovoltaic strings include a current detection module of a first photovoltaic string, a current detection module of a second photovoltaic string, a current detection module of a third photovoltaic string and a current detection module of a fourth photovoltaic string. The current detection module of the first photovoltaic string, the current detection module of the second photovoltaic string, the current detection module of the third photovoltaic string and the current detection module of the fourth photovoltaic string are all provided with a Hall current sensor circuit. The Hall current sensor circuit includes a Hall current sensor unit through which the cable of the corresponding photovoltaic string passes and an operational amplifier unit. The operational amplifier unit is a Butterworth filter and is used to condition the photovoltaic string current signal collected by the Hall current sensor unit.

6. The device for detecting a DC series fault arc in a combiner box according to claim 1, characterized in that: The signal processing communication main control module comprises a signal processing main control unit and an RS485 communication unit. The MCU of the signal processing main control unit is ATmega128. The RS485 communication unit is provided with a magnetic isolation communicator, which is ADM2483.

7. The detection device for a DC series fault arc in a combiner box according to claim 1, characterized in that: In the preparation process, the number of ultraviolet sampling data points in the analysis period T = N_ultraviolet; signal analysis period T, current sampling frequency f s , the number of current sampling data points N = T × f s ; T is divided into w+1 time windows, and each time window is set with current sampling data l, and N = (w+1)×l; the current frequency domain analysis takes the 10-100kHz frequency band; the wavelet transform is decomposed into j+1 frequency bands.

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