A DC power supply system and a DC arc detection method and device thereof

Abstract

The present invention provides a DC power supply system and a DC arc detection method and device thereof, which simultaneously collect the AC signal and various DC signals of an inverter; when there is external noise introduced into the AC side of the inverter, the noise can be crosstalked to its DC side through the inverter; and the operation of the inverter itself may also cause noise, and the noise may appear on both sides of it at the same time; therefore, according to the AC signal and the various DC signals, it can be judged whether the DC power supply system has noise interference; if there is noise interference, the arc detection data is denoised, so that the arc detection data can be adjusted according to the actual noise situation of the system; and then according to the data results after denoising, it is judged whether the inverter has arcing; compared with the prior art, it can reduce the false alarm rate and improve the detection rate, and can be applicable to the situation where high-power inverters or inverters with nonlinear loads are prone to harmonic deterioration.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a direct current power supply system and a direct current arc detection method and device thereof. Background Art

[0002] In the field of photovoltaic power generation, photovoltaic modules need to rely on a large number of wiring terminals to connect to each other. Loose, aging, poor contact and other reasons of the wiring terminals may cause DC arcs. Considering the characteristics of photovoltaic power generation systems, as long as there is light, there will be a steady stream of energy injected into the DC end of the photovoltaic power generation system. Therefore, the expansion of the application scale of photovoltaic power generation will increase the number of fire accidents that may be caused by arcs on the DC end. This has led to an increasing number of DC arc detection systems being used in the photovoltaic industry, especially the distributed photovoltaic industry.

[0003] At present, the mainstream arc detection method on the DC side of photovoltaic power generation is to sample the AC current signal on the DC side cable, and then obtain and process the relevant frequency domain values ​​by performing FFT (fast Fourier transform) or wavelet transform on it; then determine whether a DC arc occurs by checking whether the rate of change of the frequency domain value exceeds a certain amount.

[0004] For the arc detection solution, more precise sensors and more advanced algorithms are currently introduced to better collect and process data, thereby achieving detection optimization. However, the optimized detection solution is still prone to false alarms and missed alarms in situations where high-power inverters or inverters with nonlinear loads are prone to harmonic deterioration. Summary of the invention

[0005] In view of this, the present invention provides a DC power supply system and a DC arc detection method and device thereof to reduce the false alarm rate and improve the detection rate.

[0006] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0007] A first aspect of the present invention provides a DC arc detection method for a DC power supply system, comprising:

[0008] Acquire an AC signal and various DC signals of an inverter in the DC power supply system;

[0009] Determining whether the inverter has noise interference according to the AC signal and each of the DC signals;

[0010] If the inverter has the noise interference, denoising the arc detection data of the inverter;

[0011] According to the data result after denoising, it is determined whether arcing occurs in the inverter.

[0012] Optionally, the AC signal and each of the DC signals are corresponding detection signals when the power of the inverter is greater than a preset value;

[0013] The arc detection data of the inverter is subjected to denoising, comprising:

[0014] The data weight of the frequency band signal interfered by the noise in the arc detection data within the entire frequency band range is reduced.

[0015] Optionally, the noise interference includes: AC side load noise interference, and / or equipment operation noise interference.

[0016] Optionally, judging whether the inverter has noise interference according to the AC signal and each of the DC signals includes:

[0017] Determine the DC harmonics of the inverter according to the DC signals; determine the AC harmonics of the inverter according to the AC signals;

[0018] Determine whether the interference of the AC harmonic is greater than a first threshold, and whether associated harmonic values ​​of the same frequency band appear in each of the DC harmonics and the AC harmonics;

[0019] If the interference of the AC harmonic is greater than the first threshold, and / or at least one of the DC harmonics and the AC harmonic has a related harmonic value in the same frequency band, it is determined that the inverter has the AC side load noise interference;

[0020] If associated harmonic values ​​of the same frequency band appear in at least two of the DC harmonics, it is determined that the inverter has the equipment operation noise interference.

[0021] Optionally, if the DC power supply system includes a plurality of inverters connected in parallel on the AC side, after the step of determining the DC harmonics of each inverter according to each DC signal is performed for each inverter, the method further includes:

[0022] Determining whether associated harmonic values ​​of the same frequency band appear in the DC harmonics between different inverters;

[0023] If there are at least two DC harmonics between different inverters and associated harmonic values ​​in the same frequency band, it is determined that each inverter has the AC side load noise interference.

[0024] Optionally, reducing the data weight of the frequency band signal of the noise interference in the arc detection data within the entire frequency band range includes:

[0025] When the inverter is subject to the AC side load noise interference, the amplitude and frequency of each frequency band signal of the noise interference in the arc detection data are processed and analyzed respectively to reduce the data weight within the entire frequency band;

[0026] and / or,

[0027] When the inverter is subject to the noise interference of the device operation, the amplitude and frequency of each pair of frequency band signals of the associated harmonic values ​​are processed and analyzed to reduce the data weight within the entire frequency band.

[0028] Optionally, the AC signal and each of the DC signals are corresponding detection signals when the power of the inverter is less than or equal to a preset value;

[0029] The arc detection data of the inverter is subjected to denoising, comprising:

[0030] The initial noise value of the arc detection data of the corresponding road is revised.

[0031] Optionally, judging whether the inverter has noise interference according to the AC signal and each of the DC signals includes:

[0032] Determine the DC harmonics of the inverter according to the DC signals; determine the AC harmonics of the inverter according to the AC signals;

[0033] Determine whether the interference of the AC harmonics is greater than a second threshold, and whether the interference of the DC harmonics of each channel is greater than a third threshold;

[0034] If the interference of the AC harmonic is greater than the second threshold, it is determined that there is pre-operation noise interference on the AC side of the inverter;

[0035] If there is at least one path of the DC harmonics whose interference is greater than the third threshold, it is determined that there is pre-operation noise interference in the corresponding path of the DC side of the inverter.

[0036] Optionally, revising the initial noise value of the arc detection data of the corresponding path includes:

[0037] If the interference of the AC harmonic is greater than the second threshold, the AC noise interference value is determined according to the AC harmonic; and / or, if there is at least one DC harmonic whose interference is greater than the third threshold, the DC noise interference value of the corresponding path is determined according to the corresponding DC harmonic;

[0038] The DC noise interference value and / or the AC noise interference value are summed with a preset noise value to serve as the initial noise value of the corresponding path.

[0039] Optionally, the AC noise interference value is proportional to: the total sum of the differences between the actual frequency domain value of each frequency value in the AC harmonic and the preset frequency domain value;

[0040] The DC noise interference value is proportional to: the total sum of the differences between the actual frequency domain values ​​of each frequency value in the DC harmonics of the corresponding path and the preset frequency domain values.

[0041] Optionally, obtaining an AC signal and various DC signals of an inverter in the DC power supply system includes:

[0042] When the power of the inverter is less than or equal to a preset value, acquiring the AC signal of the inverter and each of the DC signals; and,

[0043] When the power of the inverter is greater than the preset value, the AC signal of the inverter and the DC signals of each channel are obtained.

[0044] Optionally, judging whether arcing occurs in the inverter according to the data result after denoising, includes:

[0045] The data results are transformed into time domain and frequency domain, and when the change rate of the relevant frequency domain value exceeds a threshold value, it is determined that an arc occurs in the corresponding path on the DC side of the inverter.

[0046] A second aspect of the present invention further provides a DC arc detection device for a DC power supply system, comprising: a control unit, at least one DC side detection device and at least one AC side detection device;

[0047] The DC side detection device is used to collect the corresponding DC signal of the inverter in the DC power supply system;

[0048] The AC side detection device is used to collect the AC signal of the inverter;

[0049] The control unit is used to execute the DC arc detection method for a DC power supply system according to any one of claims 1 to 12.

[0050] Optionally, the AC side detection device is: an arc transformer or a Hall sensor.

[0051] Optionally, each phase cable on the AC side of the inverter is respectively provided with a corresponding AC side detection device; or, if the inverter is a three-phase inverter and the load it carries is a single-phase load, the AC side detection device is only provided on one phase cable carrying the single-phase load.

[0052] The third aspect of the present invention further provides a DC power supply system, comprising: at least one inverter, at least one DC power supply, and at least one DC arc detection device of the DC power supply system as described in any paragraph of the second aspect above; wherein:

[0053] The AC side of the inverter is used to connect to a power grid and / or a load;

[0054] Each of the DC sides of the inverter is connected to a corresponding DC power supply;

[0055] The control unit in the DC arc detection device is communicatively connected with the control unit in the inverter.

[0056] Optionally, when the number of the inverters is greater than 1, the AC sides of the inverters are connected in parallel, and the DC power sources connected to the inverters are: photovoltaic strings and / or energy storage batteries.

[0057] Optionally, the main circuit of the inverter includes: an inverter circuit and n DCDC conversion circuits; n is a positive integer;

[0058] The input end of each DCDC conversion circuit is connected to at least one corresponding DC power supply respectively;

[0059] The output end of each DCDC conversion circuit is connected in parallel to the DC side of the inverter circuit through a DC bus; a bus capacitor is provided between the positive and negative poles of the DC bus;

[0060] The inverter circuit and each of the DCDC conversion circuits are controlled by a control unit in the inverter.

[0061] Optionally, the DC arc detection device is arranged inside the corresponding inverter.

[0062] The DC arc detection method of a DC power supply system provided in the present application, when collecting the DC signals of each channel of the inverter in the DC power supply system, also collects the AC signal of the inverter; when there is external noise introduced on the AC side of the inverter, the noise can be crosstalked to its DC side through the inverter; and the operation of the inverter itself may also cause noise, and the noise may appear on its DC side and AC side at the same time; therefore, according to the AC signal and each DC signal, it can be judged whether there is noise interference in the DC power supply system; if there is noise interference, the arc detection data of the DC power supply system is denoised, so that the arc detection data can be adjusted according to the actual noise situation of the system; and then according to the data results after denoising, it is judged whether the inverter has arcing; compared with the prior art, it can reduce the false alarm rate and improve the detection rate, and can be applicable to large-power inverters or inverters with nonlinear loads, which are prone to cause harmonic deterioration. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0064] Figure 1 A schematic diagram of the structure of a DC power supply system provided by an embodiment of the present invention;

[0065] Figure 2 , Figure 3a , Figure 3b and Figure 4 Four flow charts of a DC arc detection method for a DC power supply system provided by an embodiment of the present invention;

[0066] Figure 5 A frequency domain diagram of DC cable noise in the absence of interference after operation provided by an embodiment of the present invention;

[0067] Figure 6 A frequency domain diagram of DC cable noise in the case of interference after operation provided by an embodiment of the present invention;

[0068] Figure 7 A frequency domain diagram of AC cable noise without interference after operation provided by an embodiment of the present invention;

[0069] Figure 8 A frequency domain diagram of AC cable noise in the presence of interference after operation provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0070] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0071] In this application, the terms "comprises", "comprising" or any other variation thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element.

[0072] The present invention provides a DC arc detection method for a DC power supply system, so as to reduce the false alarm rate and improve the detection rate.

[0073] The DC power supply system is Figure 1 As shown, the DC side of the inverter (such as Figure 1 The positive input cables of PV1, ..., PVn) shown in the figure are respectively provided with DC side detection devices CT1, ..., CTn, and the AC side detection devices CTa, CTb, CTc are respectively provided on the AC side cables of the inverter; Figure 1 Take a three-phase grid-connected inverter as an example for demonstration. If it is a single-phase grid-connected inverter, then only one arc sensor is needed on the AC side to collect the signal on the single-phase AC cable; each sensor outputs the detected signal Sig 1, ..., Sig n, Sig a, Sig b, Sig c to the control unit, such as the arc fault detector AFD, which analyzes and processes each detected signal, and determines whether a DC arc appears in each circuit on the DC side through an arc detection algorithm; if a DC arc appears, the control unit in the inverter is notified through communication to perform a wave sealing operation on the main circuit. In actual applications, the AFD and each sensor can be arranged inside the inverter, or independently arranged outside the inverter, depending on the specific application environment, and are all within the protection scope of this application.

[0074] See also Figure 2 , the DC arc detection method comprises:

[0075] S10, acquiring an AC signal of an inverter and various DC signals in a DC power supply system.

[0076] Considering that more and more distributed and household inverters are directly connected to the mains without transformers, and the operating noise of other loads on the mains will be directly transmitted to the DC side of the inverter, resulting in poor signal quality of the DC side signal, this method acquires the AC signal of the inverter while acquiring the various DC signals of the inverter for subsequent application. Moreover, the acquisition process can be directly collected by the detection device or acquired by communication; in addition, the acquired AC signal and DC signal can be current, voltage, power, etc., which are not specifically limited here and can be determined according to the application environment, and are all within the protection scope of this application.

[0077] S20: Determine whether there is noise interference in the inverter according to the AC signal and the DC signals.

[0078] Ideally, the frequency of the AC signal on the AC side of the inverter should be the fundamental frequency of the power grid, and there should be no AC signal on the DC side. When an arc occurs on any DC side, an AC signal will exist on the corresponding DC side, and the arc can be detected by collecting the data on the DC side and processing and analyzing the data on the AFD. However, in actual applications, when there is external noise on the AC side of the inverter, the noise can not only be collected by the AC side detection device, but also be crosstalked to the DC side through the inverter. The operation of the inverter itself may also cause noise, which may appear on all DC sides and the AC side at the same time. Therefore, after obtaining the AC signal and the DC signals on each side, they can be compared and judged to determine whether there is noise interference.

[0079] If there is noise interference, step S30 should be executed.

[0080] S30: De-noising the arc detection data of the inverter.

[0081] After determining that there is noise interference, this embodiment performs denoising on each channel of DC signals currently acquired during arc detection, that is, denoising is performed on the original arc detection data to reduce the influence of these noise interferences on arc detection, so as to make the detection application of arc detection data closer to the actual situation of system operation, thereby reducing the false alarm rate and improving the detection rate. Then step S40 can be executed.

[0082] S40: Determine whether arcing occurs in the inverter according to the data result after denoising.

[0083] In practical applications, after obtaining the denoised data results, the time domain and frequency domain transformations can be performed, and when the change rate of the relevant frequency domain value exceeds the threshold, it is determined that the corresponding path on the DC side of the inverter has arced. Specifically, the current DC signals obtained in real time or periodically can be denoised, and then FFT or wavelet transformation can be performed to obtain and process the relevant frequency domain values; then, by checking whether the change rate of the frequency domain value exceeds a certain amount, it is determined whether a DC arc has occurred, thereby completing the arc detection of each path on the DC side of the inverter.

[0084] Of course, if there is no noise interference in the DC power supply system, the DC signals currently collected can be transformed in the time domain and frequency domain, and then directly based on the original data, when the change rate of the relevant frequency domain value exceeds the threshold, it can be determined that a DC arc has occurred in the corresponding path on the DC side of the inverter.

[0085] It is worth noting that the prior art introduces more sophisticated sensors and more advanced algorithms, and the false alarm rate and missed alarm rate are both high in the case of high-power inverters or inverters with nonlinear loads, which are prone to cause harmonic deterioration. However, in this embodiment, a detection device is added to the AC side of the inverter, and the corresponding current signal spectrum data on the AC and DC cables are synchronously collected during AFD operation. Then, the two aspects of data are combined to make arc judgments, which can reduce the false alarm rate and missed alarm rate even in the case of high-power inverters or inverters with nonlinear loads, which are prone to cause harmonic deterioration.

[0086] In addition, there is another solution in the prior art that uses other characteristics of the arc, such as radiation characteristics, light emission, and heat generation characteristics, and introduces corresponding equipment, such as infrared cameras, for detection; however, this solution is too expensive and difficult to install and arrange in distributed and household scenarios. The DC arc detection method provided in this embodiment only adds an AC side sensor, which has low hardware cost and is easy to install and arrange, which is conducive to promotion.

[0087] Furthermore, the DC arc detection method provided in this embodiment does not deteriorate the background noise of the inverter, but can weaken the influence of noise on arc detection, and has high reliability.

[0088] On the basis of the previous embodiment, in actual applications, the AC signal and each DC signal obtained in step S10 can be the corresponding detection signal when the power of the inverter is greater than the preset value, that is, the corresponding detection signal after the inverter is running. Since the DC side arc detection of the inverter may be affected in both the grid-connected operation and the off-grid operation state, step S10 is performed after the inverter is off-grid or grid-connected. At this time, the noise interference in step S20 includes: AC side load noise interference, and / or equipment operation noise interference. Among them, the AC side load noise interference refers to the noise interference introduced from the outside by the load set on the AC side, and its frequency is different from the grid frequency; the equipment operation noise interference refers to the noise interference caused by the operation of the inverter itself, such as the switching action of each switch tube in the main circuit of the inverter may bring noise interference of the corresponding frequency.

[0089] See also Figure 3a , step S20 specifically includes:

[0090] S201. Determine the DC harmonics of the inverter according to the DC signals; and determine the AC harmonics of the inverter according to the AC signals.

[0091] S202: Determine whether the interference of the AC harmonics is greater than a first threshold, and whether associated harmonic values ​​of the same frequency band appear in the DC harmonics and AC harmonics.

[0092] If the interference of the AC harmonics is greater than the first threshold, and / or at least one DC harmonic and the AC harmonic have associated harmonic values ​​in the same frequency band, step S203 is executed; if at least two DC harmonics have associated harmonic values ​​in the same frequency band, step S204 is executed.

[0093] S203: Determine whether there is AC side load noise interference in the inverter.

[0094] S204: Determine whether the inverter has equipment operation noise interference.

[0095] It should be noted that the DC power supply system may include one inverter or multiple inverters connected in parallel on the AC side; in particular, when the DC power supply system includes multiple inverters, if there is external noise introduced on the AC side of the inverter, that is, AC side load noise interference, the noise may be crosstalked to the DC side through each inverter, causing the DC side of each inverter to resonate at the same frequency; in this case, after step S201, the following may be added:

[0096] S205: Determine whether there are associated harmonic values ​​in the same frequency band in the DC harmonics between different inverters.

[0097] If there are at least two DC harmonics between different inverters that have associated harmonic values ​​in the same frequency band, step S206 is executed.

[0098] S206: Determine whether each inverter has AC side load noise interference.

[0099] In practical applications, the various judgment contents in steps S202 and S204 can be executed simultaneously or sequentially, for example, first judging whether the interference of the AC harmonics is greater than the first threshold, then judging whether the associated harmonic values ​​of the same frequency band appear in each DC harmonic; and finally judging whether there is at least one DC harmonic in each DC harmonic that has an associated harmonic value of the same frequency band as the AC harmonic. It can be determined according to the specific application environment, all of which are within the protection scope of this application.

[0100] Moreover, if the interference of the AC harmonics is less than or equal to the first threshold, there are no associated harmonic values ​​of the same frequency band in the DC harmonics and the AC harmonics, and there are no associated harmonic values ​​of the same frequency band in the DC harmonics between different inverters, then it is determined that there is no AC side load noise interference and equipment operation noise interference in the inverter, and step S30 (not shown in the figure) is not executed.

[0101] In addition, when step S10 is executed after the inverter is running, at this time, step S30 is specifically: reduce the data weight of the frequency band signal of the noise interference in the arc detection data within the entire frequency band. In practical applications, the result of reducing the data weight can be to reduce it to a preset fixed value, or to reduce it to a value that corresponds to the harmonic amplitude of the corresponding frequency band signal. The larger the harmonic amplitude, the smaller the relevant data weight. Alternatively, it can be directly reduced to zero, that is, the data weight of the frequency band signal of the noise interference is eliminated. It depends on the specific application environment, and it is within the protection scope of this application.

[0102] See also Figure 3a , the step S30 may specifically include: S301 and / or S302.

[0103] S301. When there is AC side load noise interference in the inverter, the amplitude and frequency of each frequency band signal of the noise interference in the arc detection data are processed and analyzed respectively to reduce the data weight within the entire frequency band.

[0104] Among the AC harmonics after operation, except for the fundamental frequency of the power grid, all other frequencies are caused by noise; for example, signals other than the grid-connected frequency of 50Hz or 60Hz are abnormal signals or interference signals caused by noise. As long as the arc detection algorithm involves it, the data weight of the corresponding frequency band signal needs to be weakened or even eliminated.

[0105] S302: When the inverter is subject to equipment operation noise interference, the amplitude and frequency of each pair of frequency band signals of associated harmonic values ​​are processed and analyzed to reduce the data weight within the entire frequency band.

[0106] In addition, in practical applications, the AC signal and the various DC signals obtained in step S10 may also be corresponding detection signals when the power of the inverter is less than or equal to a preset value. For example, step S10 is performed before the inverter is off-grid or on-grid. At this time, see Figure 3b , step S20 specifically includes:

[0107] S211. Determine the DC harmonics of the inverter according to the DC signals; and determine the AC harmonics of the inverter according to the AC signals.

[0108] S212: Determine whether the interference of the AC harmonics is greater than the second threshold, and whether the interference of the DC harmonics of each channel is greater than the third threshold.

[0109] Taking the mth line on the DC side as an example, the AC current on the collected cable may contain DC harmonics of multiple frequencies. When i represents a frequency value of the DC harmonic, and X≤i≤Y, in Hz, it can be expressed as Ndc(f) i It represents the frequency domain value of the AC current on the mth cable on the DC side at frequency f=i. If Ndc(f0) i represents the preset frequency domain value at frequency f=i, then Ndc(f) i -Ndc(f0) i It can represent the difference between the actual frequency domain value of the frequency f=i in the DC harmonic and the preset frequency domain value. By summing the above differences of each frequency in the DC harmonic, the interference of the DC harmonic can be obtained; when When it is established, it indicates that the interference of DC harmonics is less than or equal to the third threshold R.

[0110] For each line on the DC side, the AC harmonics are the same, and the AC current on the collected AC cable may also have AC harmonics of multiple frequencies. When i represents a frequency value in the AC harmonic, and X≤i≤Y, the unit is Hz, it can be expressed as Nac(f) i It means the frequency domain value of the AC current on the cable at frequency f=i is collected; if Nac(f0) i represents the preset frequency domain value at frequency f=i, then Nac(f) i -Nac(f0) i It can represent the difference between the actual frequency domain value of the frequency f=i in the AC harmonic and the preset frequency domain value. By summing the above differences of each frequency in the AC harmonic, the interference of the AC harmonic can be obtained. When it is established, it indicates that the interference of the AC harmonic is less than or equal to the second threshold R.

[0111] In practical applications, the values ​​of the second threshold and the third threshold can be equal, for example, both can be the R mentioned above, or they can be different, without specific limitation; in addition, it can be determined first whether the interference of the AC harmonics is greater than the second threshold, and then whether the interference of the DC harmonics is greater than the third threshold, but the practical application is not limited to this, and it depends on the specific application environment.

[0112] If the interference of the AC harmonics is greater than the second threshold, step S213 is performed. If there is at least one DC harmonic whose interference is greater than the third threshold, step S214 is performed.

[0113] S213: Determine whether there is pre-operation noise interference on the AC side of the inverter.

[0114] S214: Determine whether there is pre-operation noise interference in the corresponding circuit on the DC side of the inverter.

[0115] If the interference of the AC harmonics is less than or equal to the second threshold, and the interference of each DC harmonic is less than or equal to the third threshold, it is determined that there is no pre-operation noise interference on the AC side and each DC side of the inverter, and step S30 is not executed (not shown in the figure).

[0116] In addition, when step S10 is performed before the inverter is operated, step S30 includes: revising the initial value of the noise of the corresponding path in the arc detection data. Figure 3b , which specifically include:

[0117] S311. If the interference of the AC harmonic is greater than the second threshold, determine the AC noise interference value according to the AC harmonic; and / or, if there is at least one DC harmonic whose interference is greater than the third threshold, determine the DC noise interference value of the corresponding path according to the corresponding DC harmonic.

[0118] Among them: the AC noise interference value is proportional to: the total sum of the differences between the actual frequency domain value of each frequency value in the AC harmonic and the preset frequency domain value. The DC noise interference value is proportional to: the total sum of the differences between the actual frequency domain value of each frequency value in the corresponding DC harmonic and the preset frequency domain value.

[0119] Specifically, the DC noise interference value of the corresponding path is determined according to the corresponding DC harmonics, and the formula used can be:

[0120]

[0121] Where, N(dc) m is the DC noise interference value of the mth line on the DC side, Ndc(f) iNdc(f0) is the frequency domain value of the AC current on the mth cable on the DC side at frequency f=i; i is a preset frequency domain value at frequency f=i; i is a frequency value in the DC harmonic, and X≤i≤Y, unit Hz; j is the first coefficient.

[0122] According to the AC harmonics, the AC noise interference value can be determined by the formula:

[0123]

[0124] Where, N(ac) is the AC noise interference value, Nac(f) i is the frequency domain value of the AC current on the AC cable at frequency f = i; Nac(f0) i is the preset frequency domain value when the frequency f=i; i is a frequency value in the AC harmonic, and X≤i≤Y, unit Hz; k is the second coefficient.

[0125] S312: summing the DC noise interference value and / or the AC noise interference value with the preset noise value to serve as the initial noise value of the corresponding path.

[0126] The noise default value is N 0 , for the initial noise value N of the corresponding road m There are several cases for the calculation of:

[0127] (1) When and When both are true, the initial noise value N of the corresponding path m The calculation formula is: N m =N 0 .

[0128] (2) When and When both are not true, the initial noise value N of the corresponding path m The calculation formula is: N m =N(dc) m +N(ac)+N 0 .

[0129] (3) When Not true. When it is established, the initial noise value N of the corresponding path m The calculation formula is: N m =N(dc) m +N 0 .

[0130] (4) When Established, If it does not hold, the initial noise value N of the corresponding path mThe calculation formula is: N m =N(ac)+N 0 .

[0131] That is, the noise preset value N 0 The function is to preset a value N when there is no special interference signal in the power grid. 0 As the standard for judging the arc, N m =N 0 ; If there is an interference signal, the initial noise value N is m = preset value + interference part, the interference part depends on the specific situation, which is N(dc) m and at least one of N(ac).

[0132] It should be noted that the interference part N(dc) m The calculation of and N(ac) is to solve the total sum of the differences between the actual frequency domain values ​​of each frequency within a frequency range and the preset values. The specific frequency selection range [X, Y] can be determined according to the actual application environment, wherein X is less than a smaller preset threshold value and can be equal to 0, and Y is greater than a larger preset threshold value and can also be a value approaching infinity, all of which are within the protection scope of the present application.

[0133] On the basis of the above embodiments, in actual applications, the acquisition of the AC and DC signals of the inverter includes a part executed before operation and a part executed after operation. Figure 4 , the step S10 can be divided into two specific steps S101 and S102; wherein:

[0134] S11. When the power of the inverter is less than or equal to a preset value, an AC signal and various DC signals of the inverter are obtained.

[0135] S12: When the power of the inverter is greater than a preset value, the AC signal of the inverter and each DC signal are obtained.

[0136] Regardless of whether there are single or multiple inverters in the DC power supply system, the corresponding AC and DC signals of each inverter will be collected and acquired before and after operation. Moreover, the harmonic signals on both sides in the above two cases can be used to execute subsequent steps. The step S10 executed before operation corresponds to the following step S30: S31, revising the initial noise value of the corresponding arc detection data; and the step S10 executed after operation corresponds to the following step S30: S32, reducing the data weight of the frequency band signal of the noise interference in the arc detection data within the entire frequency band.

[0137] That is to say, after determining the existence of noise interference, this embodiment, on the basis of the original arc detection data, revises the noise initial value of the corresponding path, and reduces the data weight of the frequency band signal of the noise interference, by at least one of these two methods, so that the detection application of arc detection data is closer to the actual situation of system operation. Compared with the situation in the prior art where the noise initial value and the data weight are fixed, the present application can reduce the false alarm rate and improve the detection rate.

[0138] The following is a complete description of the execution process of the DC arc detection method in chronological order:

[0139] Before the inverter is running, the arc detection process that needs to be performed is as follows:

[0140] Step 1: Obtain the harmonic signals on both sides of the AC and DC collected before operation, that is, the AC signal and each DC signal.

[0141] Step 2: Determine whether the AC side harmonic exceeds the set value, that is, determine whether the AC harmonic interference before operation is greater than the second threshold. If it exceeds, go to step 4; if not, go to step 3.

[0142] Step 3: Determine whether the DC side harmonic value exceeds the set value, that is, whether the interference of the DC harmonic before operation is greater than the third threshold. If so, proceed to step 5, otherwise proceed to step 6.

[0143] Step 4: The abnormal AC harmonic value data is sent to the arc detection algorithm as the initial noise value of the algorithm.

[0144] Step 5: The abnormal DC harmonic value data is fed into the arc detection algorithm as the initial noise value of the algorithm.

[0145] Step 6: The initial noise value of the arc detection algorithm is equal to the preset noise value.

[0146] From the above content, it can be concluded that this method can pre-evaluate the harmonic content of the inverter AC side before operation, and regard the frequency domain signals outside 50Hz / 60Hz as interference signals, so as to judge the potential impact of nonlinear load or other AC side interference on arc detection; it can also judge whether there are special interference signals on the DC side. For example, normal photovoltaic modules are considered to have no interference. If other DC sources are used to replace photovoltaic modules in actual applications, it is possible to introduce the harmonic interference of the current source itself; in addition, aging photovoltaic modules and their connectors may also cause nonlinear parasitic parameters in the circuit, which in turn leads to harmonic interference, that is, it is also possible to introduce the harmonic interference of the current source itself; these situations are considered to be interference for the DC side. Moreover, through the above process, it is judged whether there are interference signals input to AC and DC before operation, and the appropriate value of the initial noise value is determined according to whether there is an interference signal and the size of the interference signal, that is, the initial model value of the arc detection algorithm is determined by collecting information before grid connection.

[0147] After the inverter is running, the arc detection process that needs to be performed is as follows:

[0148] Step 1: When the machine is running, continuously obtain the collected AC and DC harmonics, that is, the AC signal and various DC signals after operation.

[0149] Step 2: Determine whether the harmonics on the AC side exceed the set value, that is, whether the interference of the AC harmonics after operation is greater than the first threshold. If so, proceed to step 5; if not, proceed to step 3.

[0150] Step 3: Determine whether there are two or more cables on the DC side with associated harmonic values ​​in the same frequency band, that is, whether associated harmonic values ​​in the same frequency band appear in the DC harmonics after each line is in operation. Specifically, it can be determined by A_Ndc(f). c =S*B_Ndc(f) c Is it true? Among them, A_Ndc(f) c Indicates the frequency domain value of the DC cable of channel A at f = c, B_Ndc(f) c A_Ndc(f) represents the frequency domain value of the DC cable of channel B at f=c. c =S*B_Ndc(f) c Indicates that the DC cables of channel A and channel B have associated harmonic frequency domain values ​​at f=c. Assuming a machine has 6 photovoltaic inputs PV, if PV1 to PV5 all have 5KHz oscillations, it is believed that this noise is not the noise introduced by arcing, but the interference caused by the operation of the machine itself. Figure 5 and Figure 6As shown in the figure, the frequency domain values ​​of 16KHz and its multiples are highly synchronized. They appear on multiple DC cables. This is the switching frequency noise of the inverter body, which is a normal working status signal. c =S*B_Ndc(f) c If yes, go to step 6; otherwise, go to step 4.

[0151] Step 4: Determine whether the AC and DC cables have associated harmonic values ​​in the same frequency band, that is, among the DC harmonics after operation, whether there is at least one DC harmonic after operation and the AC harmonic after operation with associated harmonic values ​​in the same frequency band, specifically, it can be determined A_Ndc(f) c =S*B_Nac(f) c Is it true? Among them, A_Ndc(f) c Indicates the frequency domain value of the DC cable of channel A at f = c, B_Nac(f) c A_Ndc(f) represents the frequency domain value of the DC cable of channel B at f=c. c =S*B_Nac(f) c Indicates that the A channel DC cable and the B channel AC cable have related harmonic frequency domain values ​​at f = c. If A_Ndc(f) c =S*B_Nac(f) c If yes, go to step 6; otherwise, go to step 7.

[0152] Step 5: Determine whether there is external noise introduced on the AC side, that is, whether there is noise interference after operation, and send abnormal harmonic data, such as harmonic data other than 50Hz / 60Hz, to the arc detection algorithm.

[0153] Step 6: Determine whether there is external noise introduced on the AC side or noise introduced by the operation of the machine itself. The arc detection algorithm will reduce the weight of the signal in this frequency band. In practical applications, it can be at least one of the reducer signal frequency proportion, frequency domain amplitude proportion, and nonlinearity proportion. There is no limitation here, and it depends on the specific application environment, which is within the protection scope of this application.

[0154] Step 7: The arc detection algorithm is run with default weights.

[0155] After operation, this method can be used to identify DC oscillations, or to identify interference from the AC side that crosstalks to the DC side, making it difficult for arc detection to distinguish whether continuous arcing occurs.

[0156] Figure 5 The figure shows the frequency domain diagram of DC cable noise without interference after operation. Figure 6 Shown is a frequency domain plot of the DC cable noise after operation with interference. Figure 5 and Figure 6It can be seen that the 8KHz, 16KHz and the multiples of 16KHz, 32KHz, 48KHz, 64KHz, and 80KHz in the two figures are the switching frequency signals generated during the operation of the machine. The frequency domain value of each DC side cable in the above frequency bands is relatively large, so the arc detection weight of the above frequency bands is directly eliminated or weakened when the arc detection algorithm is running. Figure 5 and Figure 6 , it can be seen Figure 6 Switching frequencies of 24KHz and 40KHz appear in the signal processing. These two are introduced as interference signals. Therefore, when the arc detection algorithm is running, the arc detection weights of these two frequency bands are eliminated or weakened.

[0157] Figure 7 The figure shows the frequency domain diagram of AC cable noise without interference after operation. Figure 8 The figure shows the frequency domain of AC cable noise after operation with interference. Figure 7 and Figure 8 It can be seen that both figures have 50Hz and 16KHz, of which 50Hz is the grid frequency and 16KHz is the inverter switching frequency. Figure 8 There are AC side interference frequencies of 10KHz and its double frequency 20KHz in the system. Therefore, when the arc detection algorithm is running, it is necessary to eliminate or weaken the arc detection weight of this frequency band.

[0158] The DC arc detection method provided in this embodiment relies on the signal collection and signal time-sharing processing methods of multiple points of AC and DC to optimize the distinction and processing of interference signals on the AC side, normal noise of the machine itself and noise when an arc occurs on the DC side; when DC oscillation causes interference in the machine, the influence of interference signals on arc detection can be effectively reduced, the arc false alarm rate can be reduced, and the detection rate can be improved; and when there is interference caused by nonlinear loads on the AC side, the influence of interference signals on arc detection can be effectively reduced, the arc false alarm rate can be reduced, and the detection rate can be improved; the quality of the power grid can also be judged according to the harmonic characteristics of the AC side, and potential faults on the AC side can be monitored; the cost is low, and the technology is simple and reliable.

[0159] Another embodiment of the present invention provides a DC arc detection device for a DC power supply system, such as Figure 1 As shown, it includes: a control unit, at least one DC side detection device CT1, ..., CTn and at least one AC side detection device CTa, CTb, CTc.

[0160] The control unit may be an arc fault detector AFD, the DC side detection device is generally an arc transformer, and the AC side detection device may be an arc transformer or a Hall sensor. As long as the frequency of the arc can be identified, they are within the protection scope of the present application.

[0161] Furthermore, the DC side detection device is used to collect the corresponding DC signal of the inverter in the DC power supply system; the AC side detection device is used to collect the AC signal of the inverter; and the AFD can obtain the operating status of the load, and classify and process the data of the AC and DC side detection devices, so as to execute the DC arc detection method of the DC power supply system as described in any of the above embodiments; the specific execution process of the method can be referred to the above embodiments, which will not be repeated here.

[0162] In practical applications, a corresponding AC side detection device may be provided on each phase cable of the AC side of the inverter; for example Figure 1 The three-phase inverter described in the invention has a corresponding AC side detection device, such as CTa, CTb or CTc, on each phase cable; after collecting the AC current of the three channels, a differential signal can be obtained as the AC signal after comparison. If it is a single-phase grid-connected inverter, the AC side only needs one arc sensor to collect the signal on the single-phase AC cable to obtain the AC signal.

[0163] Alternatively, in practical applications, when the inverter is a three-phase inverter and the load it carries is a single-phase load, a corresponding AC side detection device can be set only on the one-phase cable carrying the single-phase load to directly collect the AC signal.

[0164] In practical applications, the appropriate AC side detection device setting method can be selected according to specific circumstances, and the above DC arc detection method can be implemented.

[0165] Another embodiment of the present invention further provides a DC power supply system, such as Figure 1 As shown, it includes: at least one inverter, at least one DC power supply and at least one DC arc detection device of the DC power supply system as described in the above embodiment; wherein:

[0166] The AC side of the inverter is used to connect to the grid and / or load.

[0167] Each DC side of the inverter is connected to a corresponding DC power source, such as a photovoltaic string (such as Figure 1 PV1, ..., PVn) or energy storage batteries shown in the figure; moreover, each DC side of the inverter can be connected to one or more PV strings connected in parallel.

[0168] When the number of inverters in the system is greater than 1, the AC sides of the inverters are connected in parallel, and the DC power sources connected to the inverters are: photovoltaic strings and / or energy storage batteries. In practical applications, the DC power sources connected to different inverters can be the same or different, depending on the specific application environment, and are all within the scope of protection of this application.

[0169] The AFD in the DC arc detection device is communicatively connected with the control unit in the inverter, thereby enabling two-way communication between the two.

[0170] The main circuit of the inverter includes: an inverter circuit and n DCDC conversion circuits; n is a positive integer; wherein the input end of each DCDC conversion circuit is respectively connected to at least one corresponding DC power supply; the output end of each DCDC conversion circuit is connected in parallel to the DC side of the inverter circuit through a DC bus; a bus capacitor is provided between the positive and negative poles of the DC bus; the inverter circuit and each DCDC conversion circuit are controlled by a control unit inside the corresponding inverter. In practical applications, the DC power supplies connected to the input ends of each DCDC conversion circuit can be the same or different, depending on the specific application environment, and are all within the protection scope of this application.

[0171] In addition, in practical applications, each DCDC conversion circuit can be Figure 1 The BOOST circuits 1, ..., BOOST circuits n shown in the figure are not limited thereto and may be determined according to the specific application environment and are all within the protection scope of the present application.

[0172] like Figure 1 As shown, n BOOST circuits are connected in parallel and output to the bus capacitor, which is then sent to the three-phase grid after passing through the inverter circuit. The DC side detection devices CT1-CTn are installed on the DC side PV1+ to PVn+ cables to collect the noise signals corresponding to Sig1-Sign on the DC cables and send them to the AFD; the AC side detection devices CTa-CTc are installed on the AC side three-phase outgoing cables to collect the Siga-Sigc signals and send them to the AFD. The AFD communicates bidirectionally with the control unit of the inverter. When the DC arc detection device is in operation, the signals collected by the detection devices on both the AC and DC sides are analyzed to comprehensively determine whether a DC arc occurs on the cable.

[0173] It is worth noting that the DC arc detection device can be set inside the inverter or independently of the inverter; when there are multiple inverters in the system, each inverter can be provided with its own DC arc detection device, or they can share the same external DC arc detection device to realize arc detection for each inverter respectively; it depends on the specific application environment and is within the protection scope of this application.

[0174] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can refer to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can refer to the partial description of the method embodiment. The system and system embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without creative work.

[0175] Professionals may further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in the above description according to function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0176] With respect to the above description of the disclosed embodiments, the features described in the various embodiments in this specification may be replaced or combined with each other to enable professionals in the field to implement or use the present invention. Various modifications to these embodiments will be apparent to professionals in the field, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A DC arc detection method for a DC power supply system, characterized in that: include: Acquiring an AC signal and various DC signals of the inverter in the DC power supply system through a detection device arranged on the DC side of the inverter and a detection device arranged on the AC side of the inverter; Determining whether the inverter has noise interference according to the AC signal and each of the DC signals; If the inverter has the noise interference, denoising the arc detection data of the inverter; According to the data result after denoising, judging whether arcing occurs in the inverter; Wherein, judging whether the inverter has noise interference according to the AC signal and each of the DC signals includes: Determine the DC harmonics of the inverter according to the DC signals; determine the AC harmonics of the inverter according to the AC signals; Determine whether the interference of the AC harmonic is greater than a first threshold, and whether associated harmonic values ​​of the same frequency band appear in each of the DC harmonics and the AC harmonics; If the interference of the AC harmonic is greater than the first threshold, and / or at least one of the DC harmonics and the AC harmonic has a related harmonic value in the same frequency band, it is determined that the inverter has the AC side load noise interference; If associated harmonic values ​​of the same frequency band appear in at least two of the DC harmonics, it is determined that the inverter has equipment operation noise interference; Wherein, the AC signal and each of the DC signals are corresponding detection signals when the power of the inverter is greater than a preset value; The arc detection data of the inverter is subjected to denoising, comprising: Reduce the data weight of the frequency band signal of the noise interference in the arc detection data within the entire frequency band; The step of reducing the data weight of the frequency band signal of the noise interference in the arc detection data within the entire frequency band range includes: When the inverter is subject to the AC side load noise interference, the amplitude and frequency of each frequency band signal of the noise interference in the arc detection data are processed and analyzed respectively to reduce the data weight within the entire frequency band; and / or, When the inverter is subject to the noise interference of the device operation, the amplitude and frequency of each pair of frequency band signals of the associated harmonic values ​​are processed and analyzed to reduce the data weight within the entire frequency band.

2. The DC arc detection method of a DC power supply system according to claim 1, characterized in that: The noise interference includes: AC side load noise interference, and / or equipment operation noise interference.

3. The DC arc detection method of a DC power supply system according to claim 1, characterized in that: If the DC power supply system includes a plurality of inverters connected in parallel on the AC side, after the step of determining the DC harmonics of each inverter according to each DC signal is performed for each inverter, the method further includes: Determining whether associated harmonic values ​​of the same frequency band appear in the DC harmonics between different inverters; If there are at least two DC harmonics between different inverters and associated harmonic values ​​in the same frequency band, it is determined that each inverter has the AC side load noise interference.

4. The DC arc detection method of a DC power supply system according to claim 1, characterized in that: The AC signal and each of the DC signals are corresponding detection signals when the power of the inverter is less than or equal to a preset value; The arc detection data of the inverter is subjected to denoising, comprising: The initial noise value of the arc detection data of the corresponding road is revised.

5. The DC arc detection method for a DC power supply system according to claim 4, characterized in that: Judging whether the inverter has noise interference according to the AC signal and each of the DC signals includes: Determine the DC harmonics of the inverter according to the DC signals; determine the AC harmonics of the inverter according to the AC signals; Determine whether the interference of the AC harmonics is greater than a second threshold, and whether the interference of the DC harmonics of each channel is greater than a third threshold; If the interference of the AC harmonic is greater than the second threshold, it is determined that there is pre-operation noise interference on the AC side of the inverter; If there is at least one path of the DC harmonics whose interference is greater than the third threshold, it is determined that there is pre-operation noise interference in the corresponding path of the DC side of the inverter.

6. The DC arc detection method for a DC power supply system according to claim 5, characterized in that: The initial noise value of the arc detection data of the corresponding road is revised, including: If the interference of the AC harmonic is greater than the second threshold, the AC noise interference value is determined according to the AC harmonic; and / or, if there is at least one DC harmonic whose interference is greater than the third threshold, the DC noise interference value of the corresponding path is determined according to the corresponding DC harmonic; The DC noise interference value and / or the AC noise interference value are summed with a preset noise value to serve as the initial noise value of the corresponding path.

7. The DC arc detection method of a DC power supply system according to claim 6, characterized in that: The AC noise interference value is proportional to: the total sum of the differences between the actual frequency domain value and the preset frequency domain value of each frequency value in the AC harmonic; The DC noise interference value is proportional to: the total sum of the differences between the actual frequency domain values ​​of each frequency value in the DC harmonics of the corresponding path and the preset frequency domain values.

8. The DC arc detection method for a DC power supply system according to any one of claims 1 to 7, characterized in that: Acquiring an AC signal and various DC signals of an inverter in the DC power supply system, including: When the power of the inverter is less than or equal to a preset value, acquiring the AC signal of the inverter and each of the DC signals; and, When the power of the inverter is greater than the preset value, the AC signal of the inverter and the DC signals of each channel are obtained.

9. The DC arc detection method for a DC power supply system according to any one of claims 1 to 7, characterized in that: Judging whether arcing occurs in the inverter according to the data result after denoising, including: The data results are transformed into time domain and frequency domain, and when the change rate of the relevant frequency domain value exceeds a threshold value, it is determined that an arc occurs in the corresponding path on the DC side of the inverter.

10. A DC arc detection device for a DC power supply system, characterized in that: include: A control unit, at least one DC side detection device and at least one AC side detection device; The DC side detection device is used to collect the corresponding DC signal of the inverter in the DC power supply system; The AC side detection device is used to collect the AC signal of the inverter; The control unit is used to execute the DC arc detection method for a DC power supply system according to any one of claims 1 to 9.

11. The DC arc detection device for a DC power supply system according to claim 10, characterized in that: The AC side detection device is: an arc transformer or a Hall sensor.

12. The DC arc detection device of the DC power supply system according to claim 10 or 11, characterized in that: A corresponding AC side detection device is respectively provided on each phase cable of the AC side of the inverter; or, if the inverter is a three-phase inverter and the load it carries is a single-phase load, the AC side detection device is only provided on one phase cable carrying the single-phase load.

13. A DC power supply system, characterized in that: include: At least one inverter, at least one DC power supply and at least one DC arc detection device of a DC power supply system according to any one of claims 10 to 12; wherein: The AC side of the inverter is used to connect to a power grid and / or a load; Each of the DC sides of the inverter is connected to a corresponding DC power supply; The control unit in the DC arc detection device is communicatively connected with the control unit in the inverter.

14. The DC power supply system according to claim 13, characterized in that: When the number of the inverters is greater than 1, the AC sides of the inverters are connected in parallel, and the DC power sources connected to the inverters are: photovoltaic strings and / or energy storage batteries.

15. The DC power supply system according to claim 13 or 14, characterized in that: The main circuit of the inverter includes: an inverter circuit and n DCDC conversion circuits; n is a positive integer; The input end of each DCDC conversion circuit is connected to at least one corresponding DC power supply respectively; The output end of each DCDC conversion circuit is connected in parallel to the DC side of the inverter circuit through a DC bus; a bus capacitor is provided between the positive and negative poles of the DC bus; The inverter circuit and each of the DCDC conversion circuits are controlled by a control unit in the inverter.

16. The DC power supply system according to claim 13 or 14, characterized in that: The DC arc detection device is arranged inside the corresponding inverter.

Images