CN107957528B - Photovoltaic system ground fault detection method - Google Patents
Photovoltaic system ground fault detection method Download PDFInfo
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- CN107957528B CN107957528B CN201810056839.5A CN201810056839A CN107957528B CN 107957528 B CN107957528 B CN 107957528B CN 201810056839 A CN201810056839 A CN 201810056839A CN 107957528 B CN107957528 B CN 107957528B
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- 238000001514 detection method Methods 0.000 title claims abstract description 21
- 238000000034 method Methods 0.000 claims abstract description 12
- 238000005259 measurement Methods 0.000 claims description 16
- 238000012360 testing method Methods 0.000 claims description 2
- 238000012545 processing Methods 0.000 abstract description 3
- 238000010586 diagram Methods 0.000 description 4
- 238000001228 spectrum Methods 0.000 description 3
- 230000032683 aging Effects 0.000 description 2
- 239000004020 conductor Substances 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 206010002515 Animal bite Diseases 0.000 description 1
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- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
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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
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
- H02S50/00—Monitoring or testing of PV systems, e.g. load balancing or fault identification
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
Abstract
The invention provides a method for detecting a ground fault of a photovoltaic system, which comprises the following steps: after the SSTDR detection device is connected with the photovoltaic system, a reference value C without ground fault is establishedb(ii) a Obtaining a photovoltaic system error reference value N under the condition of no ground faultrefContinuously scanning the photovoltaic system and calculating the deviation value S of the photovoltaic system; and judging whether a ground fault occurs according to the deviation value S of the photovoltaic system and the preset threshold value, and giving an alarm if the ground fault occurs. The invention does not need additional sensors to measure parameters such as voltage, current, irradiance, temperature and the like in the photovoltaic system. According to the change of the impedance value of the photovoltaic system in the ground fault, the detection of the ground fault of the photovoltaic system is realized by carrying out numerical analysis processing on the cross-correlation value of the incident signal and the reflected signal.
Description
The technical field is as follows:
the invention belongs to the field of photovoltaic system fault detection, and particularly relates to a photovoltaic system ground fault detection method.
Background art:
photovoltaic power generation has been rapidly developed due to its cleanliness and no pollution, and some serious problems are highlighted, among which the electrical system safety problem caused by photovoltaic system aging is particularly prominent. Ground faults are considered to be one of the most common faults in photovoltaic systems. The photovoltaic system has a complex structure and a large number of connecting devices, and due to aging, thermal stress, mechanical stress, animal bite and the like, insulation damage of photovoltaic components, junction boxes, cables, device interconnecting wires and the like is caused, so that a ground fault is formed when a current-carrying conductor and the ground form a path through which current can pass. Ground faults can create electrical arcs and, in severe cases, can cause fires that burn out the photovoltaic array. In addition, when a ground fault occurs, the exposed conductive part of the photovoltaic system has fault voltage to the ground, so that great potential safety hazard exists to a human body. For such safety issues, the american national electrical code document No. 690.5 specifies that any photovoltaic system with system voltages above 50V requires ground fault protection.
According to whether the photovoltaic direct current bus is connected with the ground or not, the photovoltaic system can be divided into a grounded photovoltaic system and an ungrounded photovoltaic system. As shown in fig. 2, a grounded photovoltaic system, a dotted line indicates that an uncharged metal conductor (such as a photovoltaic module metal frame, a grounding frame, an equipment housing, etc.) in the photovoltaic system is reliably connected to the ground, an inverter-side dc bus is connected to the ground through a fuse, and points a and B in the drawing are possible ground fault points; the ungrounded type photovoltaic system is different from the grounded type photovoltaic system in that the dc bus is not connected to the ground.
At present, scholars at home and abroad have proposed some protection strategies for the ground fault of the photovoltaic system. In a grounded photovoltaic system, a ground-fault detection and interruption (GFDI) circuit breaker is used to monitor the current to ground of the photovoltaic system, and when the current exceeds a preset threshold, the circuit is opened to protect the system. Such GFDI devices are essentially fault-sensitive based on the magnitude of the fault current, such as a fuse. But when the ground fault current in the photovoltaic system is less than the threshold of the GFDI device, the path will not be opened and a ground fault missed condition will occur. In addition, the negative dc bus at point a in fig. 1 is not detected when a ground fault occurs, which is a detection blind area of the GFDI. In recent years, researchers have proposed methods based on parametric measurements combined with intelligent algorithms for photovoltaic ground fault detection, but generally these methods require additional sensors to collect data and perform extensive calculations.
Disclosure of Invention
The invention provides a method for detecting a ground fault of a photovoltaic system, and aims to solve the problem of accurately detecting the ground fault when the ground fault occurs in the photovoltaic system.
The technical scheme adopted by the invention is characterized in that: the method comprises the following steps:
step A: establishing a reference value of the SSTDDR detection device of the photovoltaic system;
and B: acquiring a reference value of a ground fault error of a photovoltaic system;
and C: scanning the photovoltaic system and calculating a ground fault deviation value of the photovoltaic system;
step D: and judging whether the ground fault occurs according to the ground fault deviation value of the photovoltaic system and a preset threshold value.
Preferably, the SSTDR detection device in the above step is respectively connected with the direct current bus of the photovoltaic system and the ground.
Preferably, the reference value of the photovoltaic system SSTDDR detection device in the step A is the average value of the cross-correlation operation results of the incident signal and the reflected signal,expressed as:
in the formula, CiIs the ith measurement, N-10 is the number of measurements, CbAre averages.
Preferably, the photovoltaic system error reference value in step B is represented as:
where T is the period of the incident signal and CRAs a result of the cross-correlation of the incident signal and the reflected signal,
Cjis the j-th measurement, M is 10, N is the number of measurementsrefIs CbAnd CRThe absolute value of the difference is related to the area enclosed by the horizontal axis of time.
Preferably, the reference value and the reference value in the steps a and B are obtained through testing when the photovoltaic system has no ground fault.
Preferably, the deviation value in the above step C is expressed as,
where T is the period of the incident signal and CfIs the average value of the results of the cross-correlation operation in the current state,
Ckis the k-th measurement, X is 10, and the deviation S is CbAnd CfThe absolute value of the difference is related to the area enclosed by the horizontal axis of time.
Preferably, the deviation value in the step D is compared with a threshold value preset by the photovoltaic system, and if the deviation value exceeds the threshold value, the ground fault occurs and an alarm is given, wherein the threshold value is 2 times Nref。
The invention has the beneficial effects that:
the invention does not need additional sensors to measure parameters such as voltage, current, irradiance, temperature and the like in the photovoltaic system. According to the change of the impedance value of the photovoltaic system in the ground fault, the detection of the ground fault of the photovoltaic system is realized by carrying out numerical analysis processing on the cross-correlation value of the incident signal and the reflected signal.
Drawings
FIG. 1 is a flow chart of a method of the present invention;
FIG. 2 is a grounded photovoltaic system;
FIG. 3 is a block diagram of a method implementation of the present invention;
fig. 4 is a diagram of a decision result of the present invention.
Detailed Description
For a more detailed description of the present invention, reference will now be made in detail to the preferred embodiments, examples of which are illustrated in the accompanying drawings:
the photovoltaic system ground fault detection method is based on a spread spectrum Time Domain Reflectometry (SSTDDR). A spread spectrum signal having excellent correlation characteristics and a wide frequency spectrum is used as an incident signal for detection, and is connected to a photovoltaic system through a coaxial cable. The incident signal is reflected when the termination impedance of the cable does not match the characteristic impedance of the cable, and the amplitude and phase of the reflected signal changes as the termination impedance changes. According to the invention, the impedance of the photovoltaic system to ground is regarded as the impedance of the cable terminal, the nature of the reflected signal can be changed according to the impedance change when the photovoltaic system has ground fault, the incident signal and the reflected signal are subjected to correlation operation, and the fault is detected by carrying out numerical processing analysis on the correlation operation result value.
As shown in fig. 1, an embodiment of the present invention provides a method for detecting a ground fault of a photovoltaic system, including the following steps:
step A: and creating a photovoltaic system SSTDR detection device reference value.
Fig. 3 shows a block diagram of a method for detecting a ground fault of a photovoltaic system, in which an SSTDR detection device is connected to a dc bus of the photovoltaic system and the ground, respectively.
Establishing a reference value C of an SSTDR detection device for a photovoltaic system without ground faultbI.e. the average of the results of the cross-correlation of the incident and reflected signals, expressed as：
In the formula, CiIs the ith measurement, N is 10, in order to reduce the error, CbAre averages.
And B: and acquiring a reference value of the ground fault error of the photovoltaic system.
For comparing data difference when the ground fault occurs, acquiring a photovoltaic system error reference value N without the ground faultrefExpressed as:
where T is the period of the incident signal and CRAs a result of the cross-correlation of the incident signal and the reflected signal,
Cjthe measurement number is j, and M is 10. N is a radical ofrefIs CbAnd CRThe absolute value of the difference is related to the area enclosed by the horizontal axis of time.
And C: and scanning the photovoltaic system and calculating a ground fault deviation value of the photovoltaic system.
After establishing the reference value and the error reference value, the photovoltaic system is continuously scanned, i.e. the incident signal is continuously injected and the deviation value S is calculated, expressed as:
where T is the period of the incident signal and CfIs the average value of the results of the cross-correlation operation in the current state,
Ckis the k-th measurement, X is 10, and the deviation S is CbAnd CfThe absolute value of the difference being enclosed by the horizontal axis of timeThe area of (a).
Step D: and judging whether the ground fault occurs according to the deviation value of the photovoltaic system and a preset threshold value.
Presetting a fault judgment threshold value for the photovoltaic system, and taking 2 times NrefFig. 4 is a diagram showing a result of determination when a ground fault occurs at each position in fig. 3, and a broken line indicates a threshold value. And when the deviation value is larger than the preset value, judging that the ground fault occurs and giving an alarm.
Although the above-described process has been described in detail for the specific embodiments of the present invention, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive faculty based on the technical solution of the present invention.
Claims (1)
1. A method for detecting a ground fault of a photovoltaic system is characterized by comprising the following steps: the method comprises the following steps:
step A: establishing a reference value of the SSTDDR detection device of the photovoltaic system;
and B: acquiring a reference value of a ground fault error of a photovoltaic system;
and C: scanning the photovoltaic system and calculating a ground fault deviation value of the photovoltaic system;
step D: judging whether a ground fault occurs according to the ground fault deviation value of the photovoltaic system and a preset threshold value;
the SSTDDR detection device in the step A is respectively connected with a direct current bus of the photovoltaic system and the ground;
the reference value of the photovoltaic system SSTDDR detection device in the step A is the average value of the cross-correlation operation results of the incident signal and the reflected signal, and is represented as follows:
in the formula, CiThe ith measurement value is the ith measurement value when the first time has no ground fault, N is 10 times of measurement, and C isbIs an average value;
the photovoltaic system ground fault error reference value in the step B is represented as:
where T is the period of the incident signal and CRAs a result of the cross-correlation of the incident signal and the reflected signal,
Cjthe j-th measurement value is obtained when the second time has no ground fault, M is 10 and is the measurement times, N isrefIs CbAnd CRThe absolute value of the difference value and the area enclosed by the horizontal axis of time;
the reference value and the reference value in the step A and the step B are obtained through testing when the photovoltaic system has no ground fault;
the deviation value in said step C is represented by,
where T is the period of the incident signal and CfIs the average value of the results of the cross-correlation operation in the current state,
Ckwhen the current state is the k-th measurement value, X is 10 as the measurement times, and the deviation value S is CbAnd CfThe absolute value of the difference value and the area enclosed by the horizontal axis of time;
comparing the deviation value in the step D with a preset threshold value of the photovoltaic system, and if the deviation value exceeds the threshold value, generating a ground fault and giving an alarm, wherein the threshold value is 2 times Nref。
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| CN101387682A (en) * | 2008-10-27 | 2009-03-18 | 清华大学 | Single-phase earth fault detecting method based on residual current harmonic component |
| US20100188240A1 (en) * | 2009-01-29 | 2010-07-29 | Wells Charles H | Continuous condition monitoring of transformers |
| CN103499769A (en) * | 2013-09-23 | 2014-01-08 | 武汉大学 | Self-adaptive line selection method for single-phase earth fault of resonant earthed system |
| CN103913663A (en) * | 2014-04-21 | 2014-07-09 | 南京航空航天大学 | Online detection method and protection device for direct current system arc faults |
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Patent Citations (6)
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|---|---|---|---|---|
| CN101387682A (en) * | 2008-10-27 | 2009-03-18 | 清华大学 | Single-phase earth fault detecting method based on residual current harmonic component |
| US20100188240A1 (en) * | 2009-01-29 | 2010-07-29 | Wells Charles H | Continuous condition monitoring of transformers |
| CN103499769A (en) * | 2013-09-23 | 2014-01-08 | 武汉大学 | Self-adaptive line selection method for single-phase earth fault of resonant earthed system |
| CN103913663A (en) * | 2014-04-21 | 2014-07-09 | 南京航空航天大学 | Online detection method and protection device for direct current system arc faults |
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