CN111610410A - SSTDR technology-based photovoltaic cable sub-health detection and positioning method - Google Patents
SSTDR technology-based photovoltaic cable sub-health detection and positioning method Download PDFInfo
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- CN111610410A CN111610410A CN202010464547.2A CN202010464547A CN111610410A CN 111610410 A CN111610410 A CN 111610410A CN 202010464547 A CN202010464547 A CN 202010464547A CN 111610410 A CN111610410 A CN 111610410A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/11—Locating faults in cables, transmission lines, or networks using pulse reflection methods
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S13/06—Systems determining position data of a target
Abstract
The invention relates to the technical field of photovoltaic cable detection, in particular to a photovoltaic cable sub-health detection and positioning method based on SSTDR technology, wherein a spread spectrum signal with excellent correlation characteristics and a wider frequency spectrum is adopted as a detected incident signal, a photovoltaic system direct current bus is accessed, when a cable is damaged, the impedance of the damaged position of the cable is not matched with the characteristic impedance of the cable, the incident signal is reflected at the moment, and the reflection coefficient is in direct proportion to the damage degree of the cable; according to the invention, parameters such as voltage, current, irradiance and temperature in the photovoltaic system are measured without an additional sensor, and the sub-health state detection of the photovoltaic cable can be realized by carrying out numerical analysis processing on the cross-correlation value of the incident signal and the reflected signal according to the change of the impedance value when the DC bus cable is in sub-health. Compared with the conventional positioning method, the method has a good effect on positioning the damaged position of the cable in a weak damaged state.
Description
Technical Field
The invention relates to the technical field of photovoltaic cable detection, in particular to a photovoltaic cable sub-health detection and positioning method based on an SSTDR technology.
Background
In order to ensure safe and efficient operation of the photovoltaic system, the monitoring technology of the operation state of the photovoltaic system draws extensive attention in the industry. In a large photovoltaic power station, a photovoltaic direct-current bus (connecting a direct-current power distribution cabinet and an inverter) is generally laid in a place below about 0.8 m underground, and is easily corroded by soil, corroded by rainwater, stressed and the like to cause the problems of aging and damage of an insulating layer and the like, and the state of a cable with the problems is defined as a sub-health state. Compared with a healthy cable, the cable in a sub-health state generally has no obvious difference in operation state, but has potential safety hazard, and the cable works in the sub-health state for a long time, and most faults such as cable electric arc, grounding, short circuit, circuit breaking and the like can be caused. Thus, if sub-health problems with the dc bus can be detected and located, more serious failures can be avoided.
At present, cable fault detection methods mainly include an impedance method, a traveling wave method, an acoustic detection method and the like. The typical method of the impedance method is a bridge method, the measurement method is simple, but for high-resistance faults, the current flowing through a bridge is small, so the requirement on the measurement accuracy of a current meter is high, and meanwhile, the bridge method is used for acquiring detailed parameters of a cable in advance, which is difficult for engineering practice. The acoustic measurement method is an accurate positioning method, mainly carries out positioning by detecting the sound generated by a cable fault point, but when a cable protective layer is relatively intact, the discharge sound is relatively weak, and a high-precision sound receiving device is needed at the moment.
The traveling wave method is to inject high-frequency pulse signals into the cable, signal emission occurs when the pulse signals meet impedance mismatching points, and fault location of the cable can be achieved by calculating time difference between the injected signals and the reflected signals. A spread spectrum time domain frequency domain reflection method (SSTDR) is a traveling wave method, the current method for positioning the impedance mismatch point of a cable through the SSTDR is mainly obtained by multiplying a signal time delay tau by the propagation speed v of a traveling wave in the cable and dividing the multiplied value by 2, however, because the position of the mismatch point is directly read from the waveform according to the waveform ordinate, if the cable mismatch is small, the obtained waveform is not easy to directly find the impedance mismatch point, namely the signal time delay value tau is not easy to accurately read, and therefore, the impedance mismatch point is directly foundAccording to the formula dis ═ v0The tau/2 calculation can generate inaccurate positioning results, and in serious cases, the positioning fails directly.
Disclosure of Invention
The invention aims to provide a photovoltaic cable sub-health detection and positioning method based on an SSTDR technology, so as to solve the problems in the background technology.
In order to achieve the purpose, the invention provides the following technical scheme: a photovoltaic cable sub-health detection and positioning method based on an SSTDR technology comprises the following steps:
s1: acquiring the total length L of the photovoltaic cable and setting a distance error reference value M;
s2: SSTDR signals are injected from the initial end of the line to obtain four possible damaged positions;
wherein: s21: respectively collecting information of a complete line m0 and a line m1 to be detected;
s22: drawing respective waveform diagrams a0 and a1 by taking the cross-correlation value R (t) as an ordinate and the length dis as an abscissa;
s23: subtracting the ordinate of the waveform of the cable to be measured and the ordinate of the intact waveform to obtain a waveform b 1;
s24: dividing b1 data into n groups of data by taking k data as a group in a length L1 range;
s25: respectively solving the data points with the maximum ordinate in the n groups of data, putting the data points into a set omega, and putting four groups of data (X1, X2, X3 and X4) with the maximum ordinate in the set omega into a set omega 1;
s3: injecting SSTDDR signals from a line terminal, obtaining four possible breakage positions according to the method in S2) and obtaining a set omega 2, and setting four numbers as Y1, Y2, Y3 and Y4;
s4: and respectively adding the positions in the omega 1 and the omega 2 and judging whether the positions are the sub-health wave crest positions of the cable or not by the total length of the line. Adding the obtained abscissa of the data in the Ω 1 and Ω 2, and based on dis ═ v0 × τ)/2, if the absolute value of the subtraction between the total length L of the line and the length of the sum of the X abscissa of a certain number X in Ω 1 and the Yabs value of a certain number Y of Ω 2 is smaller than the distance error reference value M, that is, | Xabs + Yabs-L | < M, storing the data X in the set Ω 3, where Ω 3 is the finally obtained positioning data of the damaged wave peak of the cable.
Preferably, M in S1) ranges from 4 to 6M.
Preferably, the SSTDR detection devices used in S2) and S3) are respectively connected to the dc bus of the photovoltaic system and the ground.
Preferably, the specific size of the k pieces of data in S24) is related to the chip duration Tc and the chip period N of the PN sequence used in the detection process, where Tc is 8e-8S and the chip period N is 127, and the calculated line length L1 takes L1 — m (L-4) and k in S24) takes 6 according to the obtained waveform and data.
Compared with the prior art, the invention has the beneficial effects that: according to the invention, parameters such as voltage, current, irradiance and temperature in the photovoltaic system are measured without an additional sensor, and the sub-health state detection of the photovoltaic cable can be realized by carrying out numerical analysis processing on the cross-correlation value of the incident signal and the reflected signal according to the change of the impedance value when the DC bus cable is in sub-health. Compared with the conventional positioning method, the method has a good effect on positioning the damaged position of the cable in a weak damaged state.
Drawings
FIG. 1 is a schematic flow diagram of the overall process of the present invention;
FIG. 2 is a schematic flow chart of a method S2 according to the present invention;
FIG. 3 is a diagram of the result of the initial waveform during the detection process of the present invention;
FIG. 4 is a diagram of the result of the initial waveform during the detection process of the present invention;
FIG. 5 is a flowchart of the decision in the process of S4 of the present invention;
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the description of the present invention, it should be noted that the terms "vertical", "upper", "lower", "horizontal", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of describing the present invention and simplifying the description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention.
In the description of the present invention, it should also be noted that, unless otherwise explicitly specified or limited, the terms "disposed," "mounted," "connected," and "connected" are to be construed broadly and may, for example, be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
Referring to fig. 1-5, the present invention provides a technical solution: a photovoltaic cable sub-health detection and positioning method based on an SSTDR technology comprises the following steps:
s1: acquiring the total length L of the photovoltaic cable as 90M, and setting a corresponding distance error reference value M as 4M;
s2: injecting SSTDDR signals from the initial end of the line to obtain four possible damaged positions, wherein the SSTDDR detection device is respectively connected with a direct current bus of the photovoltaic system and the ground;
wherein: s21: respectively collecting information of a complete line m0 and a line m1 to be detected;
s22: drawing respective waveform diagrams a0 and a1 by taking the cross-correlation value R (t) as an ordinate and the length dis as an abscissa; wherein dis is defined by dis ═ v0τ/2 is obtained, in which v0The transmission speed of the traveling wave in the transmission line is represented, tau is the time delay value of the reflected signal, and the cross-correlation value R (t) is represented as:
wherein s (t) is an incident signal; r (t-tau) is the time delay value of the reflected signal r (t);
r(t)＝∑aks(t-Tk) + n (t) is the reflected signal, akN (T) is a noise signal, TkIs the delay time of the reflected signal;
s23: subtracting the ordinate of the waveform of the cable to be detected from the ordinate of the intact waveform to obtain a waveform b1, wherein when the damage position of the cable in a sub-health state is set to be 20m, the obtained b1 waveform is shown in fig. 3;
s24: dividing b1 data into n groups of data by grouping 6 data in a range of length L1 ═ 90-4 m;
s25: respectively solving the data points with the maximum ordinate in the n groups of data, putting the data points into a set omega, and putting four groups of data (X1, X2, X3 and X4) with the maximum ordinate in the set omega into a set omega 1;
s3: injecting an SSTDDR signal from a line terminal, wherein the SSTDDR detection device is respectively connected with a direct current bus of the photovoltaic system and the ground; also following the method in S2), four possible breakage positions are obtained, as a result of which the set Ω 2 is obtained, and these four numbers are also set to Y1, Y2, Y3, Y4;
s4: and respectively adding the positions in the omega 1 and the omega 2 and subtracting the total length of the line, and judging whether the position is the sub-health wave crest position of the cable according to the comparison between the absolute value and the error reference value. Adding the abscissa of the obtained data in Ω 1 and Ω 2, and based on dis ═ v0 × τ)/2, if the absolute value of the subtraction between the total line length L and the length of the sum of the X abscissa of a certain number X in Ω 1 and the Yabs value of a certain number Y in Ω 2 is less than 4m, i.e., | Xabs + Yabs-L | < 4, then the data X is stored in the set Ω 3, and Ω 3 is the finally obtained positioning data of the cable damage peak.
And respectively taking one data Y in the data X and the data Q2 in the data Q1, recording the abscissa of the data Y as Xabs and Yabs, and if | Xabs + Yabs-L | is less than 4, determining that a cable damage sub-health point is positioned, and outputting X as a damage point.
The following table is the result of photovoltaic cable sub-health detection and positioning according to the above strategy:
although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (4)
1. A photovoltaic cable sub-health detection and positioning method based on SSTDR technology is characterized in that: the method comprises the following steps:
s1: acquiring the total length L of the photovoltaic cable and setting a distance error reference value M;
s2: SSTDR signals are injected from the initial end of the line to obtain four possible damaged positions;
wherein: s21: respectively collecting information of a complete line m0 and a line m1 to be detected;
s22: drawing respective waveform diagrams a0 and a1 by taking the cross-correlation value R (t) as an ordinate and the length dis as an abscissa;
s23: subtracting the ordinate of the waveform of the cable to be measured and the ordinate of the intact waveform to obtain a waveform b 1;
s24: dividing b1 data into n groups of data by taking k data as a group in a length L1 range;
s25: respectively solving the data points with the maximum ordinate in the n groups of data, putting the data points into a set omega, and putting four groups of data (X1, X2, X3 and X4) with the maximum ordinate in the set omega into a set omega 1;
s3: injecting SSTDDR signals from a line terminal, and obtaining four possible breakage positions according to the method in S2) to obtain a set omega 2, and setting the four numbers as Y1, Y2, Y3 and Y4;
s4: respectively taking the position in omega 1 and omega 2 to add and circuitJudging whether the full length is the cable sub-health peak position, adding the abscissa of the obtained data in omega 1 and omega 2, and calculating according to dis ═ v0Tau)/2, if the absolute value of the subtraction of the length of the sum of the X abscissa of a certain number X in omega 1 and the Yabs value of a certain number Y in omega 2 and the total line length L is smaller than the distance error reference value M, that is, | Xabs + Yabs-L | < M, the data X is stored in the set omega 3, and omega 3 is the finally obtained positioning data of the damaged wave crest of the cable.
2. The SSTDR technology-based photovoltaic cable sub-health detection and positioning method as claimed in claim 1, wherein: m in the S1) ranges from 4M to 6M.
3. The SSTDR technology-based photovoltaic cable sub-health detection and positioning method as claimed in claim 1, wherein: the SSTDR detection devices used in S2) and S3) are respectively connected with a direct current bus of a photovoltaic system and the ground.
4. The SSTDR technology-based photovoltaic cable sub-health detection and positioning method as claimed in claim 1, wherein: the specific size of the k pieces of data in S24) is related to the chip duration Tc and the chip period N of the PN sequence used in the detection process, where Tc is 8e-8S and the chip period N is 127 in this experiment, and the calculated line length L1 takes the value of k in L1 (L-4) m and S24) takes 6 from the obtained waveforms and data.
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