CN113437723A

CN113437723A - Method for detecting fault arc

Info

Publication number: CN113437723A
Application number: CN202110759771.9A
Authority: CN
Inventors: 张永
Original assignee: FONRICH NEW ENERGY TECHNOLOGY Ltd SHANGHAI
Current assignee: FONRICH NEW ENERGY TECHNOLOGY Ltd SHANGHAI
Priority date: 2021-07-06
Filing date: 2021-07-06
Publication date: 2021-09-24
Anticipated expiration: 2041-07-06
Also published as: CN113437723B

Abstract

The invention provides a method for detecting a fault arc, and relates to the field of arc detection. And the detection of the fault arc is used for detecting whether the fault arc exists in the line to be detected. On the premise of preliminarily detecting that the direct current arc exists in the line to be detected, timing is started by taking the moment when the direct current arc appears as initial time, timing is firstly carried out to a first moment, and then timing is carried out to another second moment; continuously monitoring the relation between the time point of the reproduction of the direct current arc and the first and second moments: and if the direct current arc occurs again within the period from the first moment to the second moment, judging the direct current arc is a real fault arc event. If the direct current arc does not appear in the period from the first time to the second time, the direct current arc is determined to be a negligible accidental arc event or a non-fault arc event which is an accident.

Description

Method for detecting fault arc

Technical Field

The invention mainly relates to the field of arc detection, in particular to a fault arc detection method applied to a photovoltaic power generation system and used for detecting a direct current arc phenomenon.

Background

In view of the shortage of traditional chemical energy and the development of electric power technology, solar energy is widely concerned, and the application of solar energy in electric power needs to meet the requirement of safe power utilization. The arc, which is common in solar energy, is a gas discharge phenomenon, and a spark, which is generated by a current flowing through an insulating medium such as air, is an intuitive expression of the gas discharge. The early discovery of electric arcs and arc extinction are key factors for maintaining the safety and the reliability of the solar energy system. Although the photovoltaic field tries to find the commonality and regularity of the arcing phenomena in order to find an effective means of accurately detecting the arcing, the difficult reality to avoid is: at present, it is difficult to provide a reasonable and strict detection mechanism for the electric arc and to design a corresponding precise detection instrument in the industry. The quantity production type products capable of truly and effectively detecting the electric arc are quite a few in the market, and the direct current electric arc detection products face a nearly blank market. The objective of the present application is to detect dc arc faults present in a photovoltaic system to avoid fire accidents caused by arcing phenomena.

Dividing the arc by current properties can be roughly divided into direct current arcs and alternating current arcs. The application time of alternating current is earlier, alternating current arcs are relatively easy to identify, mature detection methods and commercial products exist, however, the starting time of a photovoltaic system is later, and the external characteristics of direct current arcs are quite different from those of alternating current, for example, direct current does not have the characteristics of alternating current zero crossing points like alternating current, and therefore the detection means of alternating current arcs cannot be applied to photovoltaic systems. The variables affecting the properties of the direct current arc are complex and diversified originally, and the arc is more complicated due to different photovoltaic use environments: it is difficult to establish a mathematical model of the dc arc. Although partial arc models are mentioned, these simplified models are typically based on some isolated or several very limited characteristics of the arc, and in fact the various types of noise and incidental disturbances of the power system that are necessarily present in a photovoltaic environment are extremely misleading to dc arc detection, leading to misleading results. The radiation intensity and the environmental temperature which are dynamically changed, the switching noise which is greatly existed in the circuit and the like are all interference sources for misjudgment and missed judgment.

The main reasons for the poor detection capability of the currently mainstream fault arc detection means are: one or more sets of fault arc parameter models need to be defined in advance, the actually detected current information is compared with the fault arc parameter models, if the actually detected current related information accords with the fault arc parameter models, a real arc event is considered to occur, otherwise, if the actually detected current related information does not accord with the fault arc parameter models, the real arc event is considered not to occur. The biggest disadvantage is that the power system of each scene to be detected is different, and the inverter model of each scene to be detected is also different, so that the traditional fault arc detection means always has detection errors or even errors, and the inherent disadvantages are almost irresistible.

The accidents of arcing and firing caused by poor contact and aging short circuit in photovoltaic power are more and more frequent, and visible direct current arc fault detection is increasingly important in a photovoltaic system. Once a photovoltaic system has a direct-current arc fault, the fault arc of the system has a stable combustion environment due to no zero-crossing point protection and continuous energy generated by a photovoltaic module under the irradiation of sunlight. If the arc is not extinguished timely and effectively, high temperature of hundreds of degrees centigrade or even more than thousands of degrees centigrade is generated and a fire is caused, and melting of some substances at the fire accident point usually evaporates to generate a large amount of toxic and harmful gases, which endangers the life safety of people and causes great loss of social economy.

In summary, because the spectral characteristics of the arc are variable, it is difficult to determine whether there is a real dc arc simply from the spectral characteristics: since the standard of the fault arc parameter model as the comparison target is not unified at present, the meaning of establishing the standard arc parameter model is not great. Furthermore, the information about the actually detected current is bound to have more or less natural errors, which are factors of the failure to detect the arc or the false alarm of the arc.

Disclosure of Invention

The application relates to a method for detecting a fault arc, which is used for detecting whether the fault arc exists in a line to be detected:

on the premise of preliminarily detecting that the direct current arc exists in the line to be detected, timing is started by taking the moment when the direct current arc appears as initial time, timing is firstly carried out to a first moment, and then timing is carried out to a second moment;

continuously monitoring the relation between the time point when the direct current arc reappears and the first and second moments:

if the direct current arc occurs again within the period from the first moment to the second moment, the direct current arc is judged to be a real fault arc event;

and if the direct current arc does not appear in the period from the first moment to the second moment, judging that the direct current arc is a negligible accidental arc event or a non-fault arc event.

The method described above, wherein: the line to be tested comprises a direct current line which is used for supplying power to the inverter through the photovoltaic assembly.

The method described above, wherein: the cause of the non-fault arc event includes at least harmonic interference introduced by the inverter onto the dc link.

The method described above, wherein: the direct current line is cut off when a real fault arc event occurs, and the direct current line is not cut off when a negligible accidental arc event occurs or when a non-fault arc event occurs.

The method described above, wherein: detecting a high-frequency current component representing a direct current arc condition on the line to be detected, and when the value of the high-frequency current component is not lower than a set threshold value, indicating that the direct current arc is preliminarily detected at the line to be detected.

The method described above, wherein: and detecting a high-frequency current component on the line to be detected, which is used for representing the condition of the direct current arc, by using the arc sensor, wherein the value of the high-frequency current component is not lower than a set threshold value, and the direct current arc is preliminarily detected at the line to be detected.

The application relates to a method for detecting a fault arc, which is characterized in that:

on the premise of preliminarily detecting that the direct current arc exists in the line to be detected, continuously monitoring whether the time interval of the direct current arc is within a preset time range:

and determining that the direct current arc is a real fault arc event only if the time interval does not exceed the preset time, otherwise determining that the direct current arc is a negligible accidental arc event or a non-fault arc event.

on the premise of preliminarily detecting that a direct current arc exists in a line to be detected, synchronously monitoring whether the time required by the reappearance of the direct current arc exceeds a preset time or not, wherein the line to be detected comprises a direct current line which is powered by a photovoltaic module to an inverter:

if the time required by the reproduction of the direct current arc exceeds the preset time or the direct current arc is not reproduced any more, judging that the direct current arc is a negligible accidental arc event or a non-fault arc event, and not cutting off the direct current line;

if the time required for the direct current arc to reappear does not exceed the preset time, the direct current arc is judged to be a real fault arc event and the direct current line is directly cut off.

The method described above, wherein: negligible incidental arcing events include the situation where a direct current arc causes a flash of combustion that self-extinguishes; causes of non-fault arc events include harmonic interference introduced into the dc link by the inverter during dc to ac operation.

on the premise of preliminarily detecting that the direct current arc exists in the line to be detected, timing is started by taking the moment when the direct current arc appears as initial time until a preset time is reached;

continuing to monitor the relationship between the point in time when the direct current arc reappears and the preset time:

if the direct current arc appears again in the preset time, judging that the direct current arc is a real fault arc event;

if the direct current arc does not appear within the preset time, the direct current arc is determined to be a negligible accidental arc event or a non-fault arc event.

determining a dc arc condition in a line under test using a processor, the processor storing an arc detection program for determining whether a dc arc is a real fault arc event, the steps performed by the arc detection program when executed by the processor comprising:

under the premise of preliminarily detecting that the direct current arc exists in the line to be detected, triggering the processor to synchronously calculate whether the time required by the direct current arc reappearing again exceeds a preset time:

if the time required for the direct current arc to reappear exceeds the preset time or the direct current arc is not reappeared any more, the processor judges that the direct current arc is a negligible accidental arc event or a non-fault arc event, and the processor gives a first indication or a first instruction for not cutting off the direct current line;

and if the time required by the direct current arc to reappear does not exceed the preset time, the processor judges that the direct current arc is a real fault arc event and gives a second instruction or a second instruction for cutting off the direct current line.

detecting a dc arc condition in a line under test with an arc sensor configured with a processor, the processor storing an arc detection program for determining whether a dc arc is an actual fault arc event, the steps performed by the arc detection program when executed by the processor comprising:

under the premise that the arc sensor preliminarily detects that the direct current arc exists in the line to be detected, triggering the processor to synchronously calculate whether the time required by the direct current arc reappearing again exceeds a preset time:

if the time required for the direct current arc to reappear exceeds the preset time or the direct current arc is not reappeared any more, the processor judges that the direct current arc is a negligible accidental arc event or a non-fault arc event, and the processor gives a first indication that the direct current line is not cut off;

if the time required for the direct current arc to reappear does not exceed the preset time, the processor judges that the direct current arc is a real fault arc event and gives a second indication that the direct current line needs to be cut off.

Drawings

To make the above objects, features and advantages more comprehensible, embodiments accompanied with figures are described in detail below, and features and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the following figures.

Fig. 1 is a photovoltaic power generation system in which photovoltaic modules are connected in series and then in parallel and supply power to an inverter that performs inversion.

Fig. 2 is a partial circuit block diagram of the fault arc detection system and the processing of the high frequency components.

Fig. 3 shows the presence of a fault arc event or a sporadic arc event or a non-fault arc event on the line under test.

Fig. 4 is a dashed line to indicate inverter-induced disturbances or to indicate an arc that is negligible without sustained combustion.

Fig. 5 is a solid line showing that the dc arc primarily detected by the line under test is an actual fault arc event.

Fig. 6 is a diagram of the need to cut the dc link to eliminate arcing combustion if a real fault arc event occurs.

Fig. 7 is that the sustained combustion event of arcing would be very intense if a real fault arc event occurred.

Fig. 8 shows that dc arcs caused by accidental arcing events or non-fault arcs are no longer recurring.

Fig. 9 shows that the time required for the dc arc to be reproduced exceeds a predetermined time defined in some cases.

Detailed Description

The invention will be described in more detail with reference to the following examples. The described examples are intended to be illustrative only and are not intended to be exhaustive of the embodiments disclosed, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of this invention.

Referring to fig. 1, a photovoltaic module array is the basis for the conversion of light energy to electrical energy in a photovoltaic power generation system. The illustrated photovoltaic module array has strings of cells mounted therein. Regarding the battery string: each battery string is formed by connecting a plurality of photovoltaic modules which are mutually connected in series, and the photovoltaic modules can be replaced by direct current power supplies such as fuel cells or chemical batteries. A plurality of different battery strings are connected in parallel: although each battery string is composed of a plurality of photovoltaic modules and the plurality of photovoltaic modules are connected in series, the plurality of different battery strings are connected in parallel with each other and collectively supply electric energy to an energy collecting device such as a photovoltaic inverter INVT. In a certain battery pack string, the application takes the series-connected multi-stage photovoltaic modules PV1-PVN as an example, the output voltages of the series-connected multi-stage photovoltaic modules PV1-PVN are mutually superposed to provide the total cascade voltage with higher potential to the inverter INVT, and the inverter INVT collects the output power of the series-connected multi-stage photovoltaic modules and then carries out direct current to alternating current inversion. The battery strings such as ST1-STK are connected in parallel and the total current of the series current of each battery string is taken as the input current of the inverter. K and N are positive integers greater than 1.

Referring to fig. 1, the first of the two current methods for detecting an arc fault on the dc side of a photovoltaic power generation system is a detection method based on a voltage-current waveform change. The current across the arc changes instantaneously and the voltage across the arc also changes instantaneously when an arc fault occurs. Such a method has advantages in that the principle of the detection method is easily understood, and voltage and current are objects that can be easily detected and measured, and thus are generally adopted schemes. However, the photovoltaic power generation system is greatly influenced by factors such as illumination intensity and ambient temperature, the amplitude of the output current and voltage is naturally unstable, for example, instantaneous changes of current and voltage are generated due to shadow shielding or sudden and sudden illumination, and the inherent current pulsation of the input side caused by the alternating current output by the inverter also changes the output characteristics of the photovoltaic module. One of the drawbacks of such methods is therefore that it is difficult to distinguish whether the changes in current and voltage are due to environmental causes or changes due to arc faults.

Referring to fig. 1, the second of the two current methods for dc side arc fault detection in photovoltaic power generation systems is a frequency characteristic-based detection method. The arc is accompanied by high-frequency clutter signals and embodies arc characteristics, and the high-frequency clutter signals cannot appear under normal working conditions. The presence of these signals therefore indicates a dc arc fault. Some vendors have produced specialized dc arc fault detectors based on the second category of methods. The detection is carried out at the photovoltaic module and the junction box or the inverter end, and is detection of the arc fault at the direct current side of the whole photovoltaic system instead of detection at the module level. The conflagration hidden danger can appear when the electric arc fault appears, and current scheme can't fix a position the fault point fast, needs the fortune dimension personnel to investigate all photovoltaic module and cables once more, and work load is huge and inefficiency, and the potential safety hazard is great. The time for eliminating the fault arc leads to the shutdown of the whole photovoltaic system, so that the early warning processing and the event response are difficult to achieve accurately and quickly in time, and the loss of the power generation yield of the power station is further caused. The biggest defect of the traditional arc fault detection scheme is that the judgment is missed and the judgment is mistaken, and the photovoltaic system has a large amount of switching noise and environmental factors which can cause interference on the real arc detection. It is therefore important and most tricky to implement string-level arc detection, i.e. to detect the specific string in which an arc is occurring.

Referring to fig. 1, current photovoltaic arc fault techniques all employ passive detection techniques. Specifically, the high-frequency characteristics of the current or voltage of the photovoltaic string are detected and analyzed to distinguish whether an arc fault exists in the system. There are three major factors in photovoltaic systems that make this approach very difficult to implement: the first is that there are many sources of interference in the photovoltaic system, especially interference from the inverter, which is in different operating conditions, and which interferes with the current and voltage on the string side of the dc string differently, and this interference is also related to the ac side of the inverter. Such uncertain disturbances present great difficulties for arc detection. The second is that in many cases the dc arc is very stable and does not change very significantly in current or voltage, thus increasing the difficulty of identifying the arc by current or voltage characteristics, and one of the objectives of the present application is to overcome this doubt. Thirdly, different photovoltaic power stations have different field wiring and operating environments, and a set of unified arc identification method is difficult to find out for different power stations.

Referring to fig. 1, a photovoltaic module is a direct current power supply with strong nonlinearity, a real-time current voltage output by the photovoltaic module changes in real time along with changes in illumination intensity, ambient temperature and the like, any one characteristic curve has a unique maximum power point, and the maximum power point corresponds to a unique photovoltaic module output voltage. The real-time power point of the photovoltaic module always changes along with the changes of factors such as illumination, temperature and shielding degree, and the current flowing through the bus also changes along with the changes of the factors.

Referring to fig. 1, a dc arc is a gas discharge phenomenon, which generates a high intensity instantaneous current in an insulating case. Unlike the ac arc, the dc arc has no zero crossing, meaning that if a dc arc fault occurs, the trigger portion will remain stable burning for a significant period of time without extinguishing. In photovoltaic power stations, direct current arcing can occur due to loose cable joints, poor contact, reliability problems with connectors or certain switches, long-term aging of the insulation, and damage to the insulation due to external forces. As the plant runtime increases, the probability of dc arcs occurring also increases. Regardless of the other contacts and insulation, there are over 80000 optical contacts in a 10MW substation and the possibility of dc arcing at all times. Even though only 1/1000 contact points may have dc arcing during 25 years of plant operation, the plant will have 80 dc arcing events with a very high probability of fire.

Referring to fig. 1, the first photovoltaic module PV1 has an output voltage V_O1The output voltage of the second photovoltaic module PV2 is denoted as V_O2And so on, the output voltage of the Nth photovoltaic module PVN is V_ON: so that the total string level voltage on the first string, i.e., the left string set ST1, is approximately V by calculation_O1+V_O2+…V_ON＝V₁. Different groups of battery packs are connected in series and in parallel and supply power for the inverter. The multi-stage photovoltaic modules PV1 to PVN are connected in series, the respective output voltages of the multi-stage photovoltaic modules being superimposed on a transmission line. Voltage comparison of transmission lineMuch higher than the individual photovoltaic modules, the inverter is shown inverting the transmission line voltage of the direct current from the transmission line to alternating current, which is a conventional solution. The photovoltaic modules are connected in series to form a string and the inverter tries to make the string work at the maximum working point.

Referring to fig. 1, the foregoing is illustrated with the first string ST1 as an alternative example. Such as with an optional set of strings STK: the output voltage of the first photovoltaic module PV1 is V_O1The output voltage of the second photovoltaic module PV2 is denoted as V_O2And so on, the output voltage of the Nth photovoltaic module PVN is V_ON. So that the total string level voltage on the kth string, i.e., the right group string STK, is approximately V by calculation_O1+V_O2+…V_ON＝V_K. The total cascade voltage is the bus voltage of the dc bus, and the bus current will be described further below.

With reference to fig. 1, a concern in distributed or centralized photovoltaic power plants is: shadow occlusion causes mismatches among numerous photovoltaic modules. Problems are also found in: the battery output characteristics of the photovoltaic module are shown in the fact that the output voltage and the output current are closely related to external factors such as light intensity and ambient temperature, and due to uncertainty of the external factors, the corresponding voltage of the maximum output power and the maximum power point changes along with the change of the external factors. For example, the power output by the photovoltaic module has randomness and severe fluctuation, and the random uncontrollable characteristic has high probability of causing great impact on the power grid and may also cause negative influence on the operation of some important loads. Based on these doubts, achieving maximum power point tracking of photovoltaic modules in consideration of external factors is a core goal of the industry to maximize energy and revenue.

Referring to fig. 1, as environmental and conventional energy problems become more severe, the photovoltaic power generation technology has been emphasized by more and more countries and regions and is regarded as a priority development object, and the photovoltaic power generation is one of the most mature and most developed scale power generation modes in the new energy power generation technology. Solar photovoltaic modules are divided into monocrystalline silicon solar cells, polycrystalline silicon solar cells, amorphous silicon solar cells and the like in the current mainstream technology direction, and the service life required by the silicon cells is generally as long as more than twenty years, so that the solar photovoltaic modules are essential for long-term and durable control of the solar photovoltaic modules. It is a well-known problem that many factors cause a reduction in the power generation efficiency of the photovoltaic module, for example, manufacturing differences, installation differences or shading or maximum power tracking adaptation among the photovoltaic modules themselves cause inefficiency. Taking shadow blocking as an example, if some photovoltaic modules are blocked by clouds, buildings, tree shadows, dirt, and the like, some photovoltaic modules become loads from the power supply and no longer generate electric energy and consume the output power of other photovoltaic modules. For example, when the same string of battery plates cannot normally generate electricity due to poor product consistency or shading, the efficiency loss of the whole string of battery packs is serious and the number of battery plate arrays accessed by inverters, especially centralized inverters, is large, the battery plates of each string of battery packs cannot operate at the maximum power point of the battery plates, which are the inducement of the loss of electric energy and generated energy. Because the local temperature of the photovoltaic module at a place with a serious hot spot effect may be higher, some of the photovoltaic modules even exceed 150 ℃, the photovoltaic module is burnt or forms dark spots, welding spots are melted, packaging materials are aged, glass is burst, welding strips are corroded and other permanent damages are caused, and the potential hazards to the safety and the reliability of the photovoltaic module are caused. The photovoltaic system has to solve the problems of real-time management and control of photovoltaic modules and management of the photovoltaic modules, and the specific requirements are that the working state and working parameters of each mounted photovoltaic cell panel can be managed and controlled in real time, the voltage abnormity, current abnormity, temperature abnormity and other abnormal conditions of the photovoltaic modules can be reliably pre-warned, and some countermeasures are taken, so that the adoption of module-level active safety shutdown or other emergency power-off measures for the abnormal battery modules is very significant and necessary.

Referring to fig. 1, the inverter INVT may integrate a maximum power point tracking MPPT function. Photovoltaic power generation is greatly influenced by temperature and irradiance, and in order to obtain more electric energy under the same condition and improve the operation efficiency of a system, the tracking of the maximum power point of a photovoltaic cell becomes a long-standing problem in the development of the photovoltaic industry. Early researches on the maximum power point tracking technology of a photovoltaic array mainly comprise a constant voltage tracking method, a photovoltaic array combination method and an actual measurement method. The constant voltage tracking method is actually equivalent to voltage stabilization control, and does not achieve the purpose of maximum power point tracking. The photovoltaic array combination method is used for adjusting the number of series-parallel connection of photovoltaic arrays according to different loads, and has no real-time property. The actual measurement method is to use an additional photovoltaic array module to establish a reference model of the photovoltaic array at a certain sunshine amount and temperature, and the method does not consider the real-time shading condition and the difference of each solar panel. At present, the maximum power tracking method of the photovoltaic array is mainly divided into a method based on a mathematical model, a self-optimizing method based on disturbance and a method based on an intelligent technology. The method based on the mathematical model is based on establishing an optimized mathematical model as a starting point to construct a solving method and a photovoltaic array characteristic curve so as to obtain the maximum power output of the photovoltaic array, so that the equivalent circuit model of the photovoltaic cell and the correctness of various parameters need to be considered emphatically.

Referring to fig. 1, the principle and features of a conventional MPPT method for power optimization: for example, in the early output power control for photovoltaic modules, a Voltage feedback method Constant Voltage Tracking is mainly used, and the Tracking method ignores the influence of temperature on the open-circuit Voltage of the solar cell, so that an open-circuit Voltage method and a short-circuit current method are proposed, and the common property of the open-circuit Voltage method and the short-circuit current method is basically very similar to the maximum power point. In order to more accurately capture the maximum power point, a disturbance observation method, a duty ratio disturbance method, a conductance increment method and the like are proposed. The disturbance observation method is characterized in that the current array power is measured, then a small voltage component disturbance is added to the original output voltage, the output power is changed, the changed power is measured, the power before and after the change is compared, the power change direction can be known, if the power is increased, the original disturbance is continuously used, and if the power is reduced, the original disturbance direction is changed. The duty ratio disturbance working principle is as follows: the interface between the photovoltaic array and the load usually adopts a voltage converter controlled by a pulse width modulation signal, so that the input and output relationship of the converter can be adjusted by adjusting the duty ratio of the pulse width modulation signal, and the function of impedance matching is realized, and therefore, the magnitude of the duty ratio substantially determines the magnitude of the output power of the photovoltaic cell. The incremental conductance method is a special way to the disturbance observation method, the biggest difference is only in the logical judgment formula and the measurement parameters, although the incremental conductance method still changes the output voltage of the photovoltaic cell to reach the maximum power point, the logical judgment formula is modified to reduce the oscillation phenomenon near the maximum power point, so that the incremental conductance method is suitable for the climate with instantaneous change of the sunlight intensity and the temperature. The actual measurement method, the fuzzy logic method, the power mathematical model, the intermittent scanning tracking method, the optimal gradient method, the three-point gravity center comparison method and the like belong to the most common maximum power point tracking method. Therefore, the MPPT algorithm used in the photovoltaic energy industry is diversified, and repeated description is omitted in the application.

Referring to fig. 1, a photovoltaic module array is the basis for the conversion of light energy to electrical energy in a photovoltaic power generation system. The photovoltaic module array is provided with battery strings, and each battery string is formed by serially connecting photovoltaic modules PV1-PVN in series. The total electrical energy provided by the array of photovoltaic modules is transmitted by a dc transmission line to an energy harvesting device or energy harvesting device comprising an inverter INVT as shown for inverting dc power to ac power or a charger for charging a battery. Usually, a bypass diode connected in parallel with the photovoltaic module is connected between the positive electrode and the negative electrode of each photovoltaic module, so that when the output power of the photovoltaic module is reduced, the photovoltaic module can be bypassed by the bypass diode matched with the photovoltaic module, rather than the photovoltaic module with reduced output power entering a negative pressure region, which would otherwise cause extremely high power dissipation at the two ends of the photovoltaic module, and even cause combustion.

Referring to fig. 1, in the power-voltage curve of each group string, each group string has a unique maximum output power point under the same environmental conditions, and the output power of the photovoltaic module on the left side of the maximum power point shows a rising trend as the output voltage of the photovoltaic module rises. After the maximum power point is reached, the output power of the photovoltaic group string is rapidly reduced, and the reduction speed is far greater than the increase speed, namely the output power of the photovoltaic component on the right side of the maximum power point shows a reduction trend along with the increase of the output voltage of the photovoltaic component. The output voltage corresponding to the maximum power point of the string is about equal to 78-80% of the open circuit voltage.

Referring to fig. 1, the total current 100 obtained by summing the respective cascade currents of the respective string sets ST1-STK is regarded as the input current of the power conversion device, i.e., the inverter INVT, and the dc power generated by the parallel string sets ST1-STK is supplied to the inverter to perform the inversion conversion of the dc power to the ac power. The arc preliminary survey is monitored and the results of the preliminary survey are obtained, for example, at the total current 100 of the current confluence, but may of course be directly surveyed at the sets of strings ST 1-STK.

Referring to fig. 2, the current characteristic of the total current after summing the string currents of the string ST1-STK is detected by the arc sensor DETC. The arc sensor DETC: the processor is typically configured with a processor and additional peripheral hardware for sensing current, such as current data collected by peripheral hardware such as current sensors, which may be used to analyze the current characteristics of the total current flow, provided that the current data is communicated to the processor. Equivalent devices with the same function as the processor: logic devices, software drivers or a plurality of microprocessors or gate arrays, state machines, controllers, singlechips, chips and the like. The arc sensor can be integrated directly into the inverter, since the summed total current itself is to be supplied to the inverter. Of course the arc sensor may also be a stand-alone module and allow it to establish a wired or wireless communication relationship with the inverter. If the arc sensor is not configured with any processor alone, its current data may be communicated to other processors to complete the analysis of the current characteristics.

Referring to fig. 2, the arc sensor DETC may sense a current on a line to be measured from a bus or a straight line using a hall current sensor or the like, and the current processing module 301 is configured with a differentiating circuit and a band pass filter. The current signal sensed by the current sensor is subjected to differential processing by a differential circuit, and then the processing result is output to a band-pass filter, the band-pass filter filters the differential processing result, and a target component falling in a predefined preset frequency band range in the current is gated out, wherein the target component can be called as a high-frequency current component which is used for detecting the direct-current arc condition on a line to be detected. The target component or high-frequency current component falling within the preset frequency band range is a frequency signal sensitive to the arc, and it is necessary to filter other signals except the preset frequency band range. A microprocessor 302 samples and digitally processes the high frequency current component, which is not below a predetermined threshold value indicating that a dc arc is initially detected on the line under test.

Referring to fig. 1, in an alternative embodiment, the fault arc detection method is used to detect whether fault arcs exist in certain lines under test, including dc lines in which photovoltaic modules supply power to inverters INVT. The dc lines may be dc bus lines in the figure or branch lines connecting any group of strings in series. Any one of the strings, for example, STK, is connected between a pair of dc buses, and the total current 100 shown in the figure is actually the bus current of the dc bus. The opposite branch is used to connect a string in series independently, for example, the photovoltaic modules PV1-PVN in string ST1 are connected in series by one branch, and the photovoltaic modules PV1-PVN in string ST2 are connected in series by another branch, so that the photovoltaic modules PV1-PVN in each string are considered to be connected in series by one branch line. In short, the line to be tested can be a direct current bus, a branch line which is connected in series with any string of photovoltaic modules, or a direct current line on other occasions.

Referring to fig. 2, preventing misjudgment is one of the important issues of the arc fault protection technology. Such as misjudgment conditions including normal operating arc, inrush current, non-sinusoidal waveform, various loads, cross-talk, etc. If misjudgment occurs in the stage of judging the fault arc, the normal operation of other electrical equipment can be influenced, and obviously, the protection significance is lost. The low malfunction rate fault arc determination scheme described below just meets the requirements.

Referring to fig. 2, the mismatch of the photovoltaic modules is hidden, and many solar power generation systems may ignore or not be aware of the mismatch problem of the photovoltaic modules, resulting in energy waste. The reasons for the mismatch are manifold, the main mechanism is caused by the mismatch of the combination of voltage and current, the cloud is shielded and fluttered by local foreign objects, the shielding or surface contamination of nearby objects, different installation inclination angles and installation orientations, aging and temperature variation, and other factors, and the mismatch of the photovoltaic module directly induces the unbalanced power loss of the photovoltaic module. The photovoltaic inverter INVT has a maximum power point tracking function.

Referring to fig. 2, an arc generated in a photovoltaic energy system can be classified into a normal arc and an abnormal arc. An arc caused by an operation such as normal shutdown of the circuit breaker is a normal arc, and an arc caused by a fault such as wire aging or poor contact is an abnormal arc, which means that the arc detection is to correctly distinguish a good arc from a bad arc. Because such complex factors often cause great challenges to the detection of the fault arc, and simultaneously, higher requirements are put on a detection algorithm. The fault arc detection method is characterized in that at the initial stage of arc generation, various parameter changes of the arc on the total current or the cascade current at the branch circuit are detected through various sensors, whether the arc is generated is judged through analysis, and not only can the good arc and the bad arc be accurately identified, but also the good arc and the bad arc in series connection and the good arc and the bad arc in parallel connection can be identified.

Referring to fig. 2, the fault arc detection system further includes: the arc sensor DETC is mainly used to detect target components of the current in the line to be measured, such as high-frequency and medium-frequency components. The arc sensor DETC comprises, for example, a high-frequency current sensor or a rogowski coil sensor or the like, for example, which measures a high-frequency component in the current, to which the arc belongs. The line under test tends to capture high frequency components in a manner that approaches or passes through a high frequency current sensor or rogowski coil sensor.

Referring to fig. 2, the fault arc detection system further includes: the current processing module 301 is used for obtaining the target component by filtering and amplifying. The current processing module 301 comprises at least a band-pass filter and an amplifying circuit: the band-pass filter filters the target component in the current, and the amplifying circuit amplifies the target component. Since the detection and analysis is targeted at the high frequency component, but the high frequency component is inevitably mixed with other noise, the band-pass filter can be used to filter out other noise except the high frequency component in the current, and only the high frequency component is retained. The signal strength of the high-frequency component may not be sufficient for direct accurate analysis, so that the target component may be amplified using an amplification circuit. The amplified target component may be sampled as a target of sampling, and the sampling of the target component may or may not be a function of the current processing module. For example, if the current processing module is required to have a sampling function, it may be equipped with a high-speed sampling chip and most of the existing sampling chips are compatible with analog-to-digital conversion functions. Also for example, assuming that the current handling module is not required to have a sampling function, the sampling step may be performed by other modules subsequently. In summary, the current processing module may be equipped with either a sampling module for sampling the high-frequency component or no sampling module.

Referring to fig. 3, the method for detecting fault arc of the line under test includes: it is necessary to monitor a target component such as a high frequency component or a medium-high frequency component of the total current 100 flowing through the line under test. Note that the exemplary waveform of the target component shown in the figure is not a true waveform, but merely serves as a representation or marker, since the most primitive true current waveform of the target component is very disordered and not as regular as in the figure. It is also found that the real waveform of the target component may continue to change unpredictably dynamically over time on the time axis, i.e., on the horizontal axis. It is possible to monitor only the target component falling within a predetermined frequency band range defined in advance. Detecting a high-frequency target component representing the dc arc condition on the line under test, such as the high-frequency current components represented by

curves

101 and 102, wherein the high-frequency current component representing the dc arc condition is, for example, a high-frequency current component falling within a preset frequency band range, and when the value of the high-frequency current component is not lower than a set threshold, such as the high-frequency current component is not lower than threshold ITH1, it indicates that the dc arc is primarily detected at the line under test.

Referring to fig. 3, the microprocessor 302 can also analyze spectral data of the high frequency current component. Generally, spectral analysis refers to analysis of a current signal, such as the high frequency current component, by fourier transformation, and is conventionally composed of both amplitude and phase spectra, most commonly amplitude spectra. Based on the analysis of the amplitude spectrum, the spectrum data of each time interval is set to comprise each frequency component distributed on the frequency domain and the amplitude corresponding to each frequency component. Specifically, the method comprises the following steps: each frequency component (frequency component) distributed in the frequency domain is a frequency distribution point or a spectrum distribution point of the so-called sampled data in the frequency domain after the fast fourier transform is performed, and the frequency component is distributed at which specific frequency value is closely related to the aforementioned high frequency component of the current. After Fourier transformation, more accurate important information such as specific frequency value, amplitude, phase and the like of any frequency component can be obtained. Note that the spectrum data of each time interval includes not only the respective frequency components distributed in the frequency domain but also the amplitudes corresponding to the respective frequency components, because the respective frequency components are known by fourier transform and their respective frequency values are naturally known. Thus, in other words, the spectral data of each time interval includes respective frequency components distributed over the frequency domain and includes frequencies and amplitudes corresponding to the respective frequency components.

Referring to fig. 3, it is noted that an arc event is not necessarily a highly dangerous dc arc fault. Actions such as plugging and unplugging a switch or rotating a motor can cause an electric arc to occur in a power system, but the electric arc does not exist continuously but is transient and does not affect the normal operation of the system and equipment, so the electric arc is called a good arc, namely a normal arc. In addition to normal arcs, arcs which are caused by short circuit of lines, aging of insulation, poor contact of lines and the like, can be continuously combusted, and are easy to ignite surrounding inflammable substances are called bad arcs, namely direct-current fault arcs. It is necessary to discriminate whether the arc is a normal arc or a dc fault arc.

Referring to fig. 3, a non-fault arc represented by a curve 101 includes, for example, a normal operating arc, an inrush current, a non-sinusoidal waveform or a variety of loads, a cross interference, a starting action of an inverter or a switching of an operating state, and the like. Non-fault arc event induced disturbances, such as inverter disturbances, are stable in the time dimension (e.g., on the order of minutes) of the calculation window, since non-fault arc induced disturbances are typically on the order of minutes or seconds. In other words, the occasional jumps in the spectral data caused by non-fault arcing events do not last for a significant portion of the time, and the non-fault arcing events typically disappear quickly after one or more occurrences. Few harmonic disturbances of the inverter occur continuously for short periods of time, for example, at intervals of minutes or more.

Referring to fig. 3, the incidental arcing event represented by curve 101 is negligible. The accidental arc event can not be sustained when the arc discharge phenomenon occurs on the photovoltaic field, for example, and the accidental arc event can be automatically extinguished after burning. In this case, arc protection is not necessary at all and arc protection action is considered as a malfunction.

Referring to fig. 3, the dc arc represented by curve 102 is a real fault arc event. The actual fault arc event continues to burn and the detected arc intensity is a close occurrence on the order of seconds. Therefore, on the premise of preliminarily detecting that the direct current arc exists in the line to be detected: the preliminarily detected arcs can be classified into two categories, a first category such as single arcs caused by harmonic interference of the inverter or negligible incidental arc events, and a second category which is harmful arcs such as real fault arcs. Arc fault protection will only operate if a harmful arc is detected, and will not operate if a single arc occurs. Arcs of the first type are negligible incidental arc events or non-fault arc events, arcs of the second type are fault arcs. The early warning method has the beneficial effects that once the fault electric arc occurs, the early warning is carried out, and the drawn arc is ignited to be extinguished in a bud state.

Referring to fig. 3, in an alternative embodiment, the current sensor allows for the capture of high frequency components in the 1KHZ to 100KHZ band when detecting or sensing a fault arc, as an alternative but not required. Of course, the numerical ranges herein are merely exemplary frequency ranges of the high frequency components, and the frequency ranges of the high frequency signals in the circuit field are substantially applicable to the frequency ranges of the high frequency components in the present application. In the direct current field in particular, the frequency range of the conventional so-called arc signal is suitable for the frequency range of the term "high-frequency component" used herein, for example, 20KHZ to 200 KHZ. The aforementioned frequency band ranges are optional but not necessary options for the preset frequency band ranges of the high frequency current components as referred to in this context.

Referring to fig. 4, the detection method of the fault arc: on the premise of preliminarily detecting that the direct current arc exists in the line to be tested, the arc sensor DETC starts timing by taking the time when the direct current arc appears, such as T1, as the starting time, and can count to a first time T2 and then count to a second time T3. The relationship between the point in time at which the dc arc reappears and the so-called first time T2 and second time T3 is continuously monitored: if no dc arc is present during the period from the first time T2 to the second time T3, it is determined that the primarily detected dc arc is a negligible incidental arc event or a non-fault arc event. For example, when an arc discharge phenomenon occurs in a photovoltaic field, the arc discharge phenomenon cannot be continued, the arc discharge phenomenon is automatically extinguished once the arc discharge occurs, and the arc discharge event belongs to an accidental or isolated arc event or is called a single arc, and at the moment, the arc fault protection action is not necessary. Causes of non-fault arc events include at least harmonic interference introduced by the inverter INVT onto the dc lines.

Referring to fig. 4, the detection method of the fault arc: the processor 302 is configured to compare the high frequency current component detected on the line under test to represent a dc arc condition with a threshold ITH 1. In an alternative embodiment, the frequency of the high frequency current component falls within a predetermined frequency band. A value of the high frequency current component not lower than the set threshold ITH1 indicates that an arc is detected as the portion of curve 101 above ITH 1. The initially detected arc cannot guarantee to be a real arc, and further operation needs to be performed on the initially detected direct current arc to make a conclusion on the initially detected direct current arc: if the direct current arc occurs again within the period from the first moment to the second moment, the direct current arc is judged to be a real fault arc event; and if the direct current arc does not appear in the period from the first moment to the second moment, judging that the direct current arc is an accidental arc or a non-fault arc.

Referring to fig. 5, the detection method of the fault arc: on the premise of preliminarily detecting that the direct current arc exists in the line to be tested, the arc sensor DETC starts timing by taking the time when the direct current arc appears, such as T1, as the starting time, and can count to a first time T2 and then count to a second time T3. The relationship between the point in time at which the dc arc reappears and the so-called first time T2 and second time T3 is continuously monitored: if a so-called dc arc occurs again during the period from the first time T2 to the second time T3, it is determined that the primarily detected dc arc is a real fault arc event rather than an incidental arc event and not a non-fault arc event. A real fault arc may produce sustained combustion.

Referring to fig. 5, the detection method of the fault arc: the processor 302 is configured to compare the high frequency current component detected on the line under test to represent a dc arc condition with a threshold ITH 1. In an alternative embodiment, the frequency of the high frequency current component falls within a predetermined frequency band. A value of the high frequency current component not below the set threshold ITH1 indicates detection of an arc as in the portion of curve 102 above ITH 1. The initially detected arc cannot guarantee to be a real arc, and further operation needs to be performed on the initially detected direct current arc to make a conclusion on the initially detected direct current arc: if the direct current arc occurs again within the period from the first moment to the second moment, the direct current arc is judged to be a real fault arc event; and if the direct current arc does not appear in the period from the first moment to the second moment, judging that the direct current arc is an accidental arc or a non-fault arc.

Referring to fig. 6, the dc link is cut off when a real fault arc event occurs, and is not cut off when a negligible sporadic arc event occurs or when a non-fault arc event occurs. For example, a switch S0 is arranged on the dc line, which switch can disconnect the dc line if it is switched off, and which switch keeps the dc line conductive if it is switched on. Disconnecting the dc link means that there is no voltage current on the bus and the dc side of the inverter is de-energized, whereas conversely, turning on the switch means that normal voltage current continues to be maintained on the bus and the dc side of the inverter is energized normally. If the processor 302 determines that the dc arc occurs again within the period from the first time to the second time, the processor 302 drives the switch S0 to be turned off. In the other case, if the processor 302 determines that the dc arc does not occur again from the first time to the second time, the processor drives the switch S0 to keep on, and does not need to cut off the dc line.

Referring to fig. 6, in an alternative embodiment, the inverter INVT has a maximum power point tracking function, which is explained in detail in the foregoing. In the process of performing maximum power point tracking, the input current of the inverter and the input voltage must be periodically adjusted to find the maximum power point.

Referring to fig. 4, in an alternative embodiment, an alternative example of a method of fault arc detection: on the premise of preliminarily detecting that the direct current arc exists in the line to be detected, whether the time interval of the direct current arc is within a preset time range is continuously monitored. For example, a dc arc occurs again at the fourth time T4, and the time between the fourth time T4 and the first time T1 is the time interval during which the dc arc occurs. The preset time is, for example, the time between the third time T3 and the first time T1 and the preset time can be changed, for example, shifting the third time T3 to the left compresses the preset time and conversely, if shifting the third time T3 to the right extends the preset time. Or, on the premise of preliminarily detecting that the direct-current arc exists in the line to be detected, the next time when the direct-current arc appears is continuously monitored, and the time between the preliminary time when the direct-current arc appears and the next time when the direct-current arc appears is defined as the time interval when the direct-current arc appears. For example, the first time T1 is the initial occurrence of the dc arc and the fourth time T4 is the next occurrence of the arc. If the time interval exceeds the preset time, the direct current arc is determined to be a negligible accidental arc or a non-fault arc.

Referring to fig. 7, in an alternative embodiment, an alternative example of a method of fault arc detection: on the premise of preliminarily detecting that the direct current arc exists in the line to be detected, whether the time interval of the direct current arc is within a preset time range is continuously monitored. For example, a dc arc occurs again at the fifth time T5, and the time between the fifth time T5 and the first time T1 is the time interval during which the dc arc occurs. The preset time is, for example, the time between the sixth time T6 and the first time T1 and the preset time can be changed, for example, shifting the sixth time T6 to the left compresses the preset time and conversely if shifting the sixth time T6 to the right extends the preset time. Or, on the premise of preliminarily detecting that the direct-current arc exists in the line to be detected, the next time when the direct-current arc appears is continuously monitored, and the time between the preliminary time when the direct-current arc appears and the next time when the direct-current arc appears is defined as the time interval when the direct-current arc appears. For example, the first time T1 is the initial occurrence of the dc arc and the fifth time T5 is the next occurrence of the arc. And if the time interval does not exceed the preset time, judging that the direct current arc is a real fault arc event.

Referring to fig. 8, in an alternative embodiment, an alternative example of a method of fault arc detection: on the premise of preliminarily detecting that the direct current arc exists in the line to be detected, synchronously monitoring whether the time required by the direct current arc reappearance exceeds a preset time or not, wherein the preset time is adjustable. The preset time is, for example, the time between the seventh time T7 and the first time T1 and can be changed, for example, shifting the seventh time T7 to the left compresses the preset time and conversely, if shifting the seventh time T7 to the right extends the preset time. The dc arc is no longer recurring, and the dc arc is determined to be a negligible incidental arc event or a non-fault arc event.

Referring to fig. 9, in an alternative embodiment, an alternative example of a method of fault arc detection: on the premise of preliminarily detecting that the direct current arc exists in the line to be detected, synchronously monitoring whether the time required by the direct current arc reappearance exceeds a preset time or not, wherein the preset time is adjustable. The preset time is, for example, the time between the seventh time T7 and the first time T1 and can be changed, for example, shifting the seventh time T7 to the left compresses the preset time and conversely, if shifting the seventh time T7 to the right extends the preset time. And if the time required for the direct current arc to reappear exceeds the preset time, judging that the direct current arc is a negligible accidental arc event or a non-fault arc event.

Referring to fig. 7, in an alternative embodiment, an alternative example of a method of fault arc detection: on the premise of preliminarily detecting that the direct current arc exists in the line to be detected, synchronously monitoring whether the time required by the direct current arc reappearance exceeds a preset time or not, wherein the preset time is adjustable. The preset time is, for example, the time between the sixth time T6 and the first time T1 and the preset time can be changed, for example, shifting the sixth time T6 to the left compresses the preset time and conversely if shifting the sixth time T6 to the right extends the preset time. For example, the first time T1 is the time of the initial occurrence of the dc arc and the fifth time T5 is the time of the next occurrence of the arc. And if the time required for the direct current arc to reappear does not exceed the preset time, judging that the direct current arc is a real fault arc event. The time from the fifth time T5 to the first time T1 is the time required for the dc arc to reappear, and the time required for reappearance does not exceed the preset time, so the fault arc is generated.

Referring to fig. 8, in an alternative embodiment, an alternative example of a method of fault arc detection: on the premise of preliminarily detecting that the direct current arc exists in the line to be detected, timing is started by taking the moment when the direct current arc appears as the starting time and until a preset time is counted, for example, the first moment T1 when the direct current arc appears is taken as the starting time and until the preset time is counted, for example, the seventh moment T7, and the relation between the time point when the direct current arc appears again and the preset time is continuously monitored: and if the direct current arc does not appear within the preset time, judging that the direct current arc is a negligible accidental arc event or a non-fault arc event.

Referring to fig. 7, in an alternative embodiment, an alternative example of a method of fault arc detection: on the premise of preliminarily detecting that the direct current arc exists in the line to be detected, timing is started by taking the moment when the direct current arc appears as the starting time and until a preset time is counted, for example, the first moment T1 when the direct current arc appears is taken as the starting time and until the preset time is counted, for example, the sixth moment T6, and the relation between the time point when the direct current arc appears again and the preset time is continuously monitored: and if the direct current arc occurs again within the preset time, determining that the direct current arc is a real fault arc event. The time between the sixth time T6 and the first time T1 is a preset time counted, and if the dc arc occurs again in the preset time, such as in the sixth time T6, it is determined that the dc arc is a real fault arc event, such as a fault arc due to the dc arc occurring again in the fifth time T5.

Referring to fig. 8, arc detection may be performed by a processor for determining a dc arc condition in a line under test, the processor storing an arc detection program for determining whether the dc arc is a real fault arc event, the steps performed by the arc detection program when executed by the processor including (e.g., using processor 302): for example, on the premise of preliminarily detecting that a dc arc exists in the line to be tested, the processor is triggered to synchronously calculate whether the time required for the dc arc to reappear again exceeds one of the preset times: if the time required for the dc arc to recur exceeds the preset time (example of fig. 9) or the dc arc does not recur anymore (example of fig. 8), the processor determines that the dc arc is a negligible sporadic arc event or a non-fault arc event and the processor gives a first indication not to trip the dc line, for example indicating not to trip the switch S0. In this case, the arc protection is not activated, and only alarm information is given.

Referring to fig. 7, arc detection may be performed by a processor for determining a dc arc condition in a line under test, the processor storing an arc detection program for determining whether the dc arc is a real fault arc event, the steps performed by the arc detection program when executed by the processor including (e.g., using processor 302): for example, on the premise of preliminarily detecting that a dc arc exists in the line to be tested, the processor is triggered to synchronously calculate whether the time required for the dc arc to reappear again exceeds one of the preset times: if the time required for the dc arc to recur does not exceed the preset time (example of fig. 7), the processor determines that the dc arc is a real fault arc event and gives a second indication that the dc line needs to be severed, such as indicating that switch S0 needs to be severed. This condition should enable arc protection, shutting down the bus and shutting down the inverter.

Referring to fig. 7, in an alternative embodiment, the high-frequency current component detected by the arc sensor DETC from the line under test and used for representing the dc arc condition is compared with a set threshold ITH1, i.e. a first threshold, and when the high-frequency current component is not lower than the threshold ITH1, i.e. the first threshold, it indicates that the dc arc is primarily detected at the line under test.

Referring to fig. 7, in an alternative embodiment, if it is determined that the dc arc is a true fault arc event: for example, when the dc arc reappears during the period from the first time point to the second time point, for example, when the time interval described above does not exceed the preset time, for example, when the time required for the dc arc to reappear does not exceed the preset time, or when the dc arc reappears within the preset time, for example, when the time required for the dc arc to reappear does not exceed the preset time, it is necessary to further confirm whether the fault arc event is induced by the combination of the accidental arc event and the non-fault arc event. Referring to fig. 7, it is obvious that a real fault arc is considered to occur, assuming that a dc arc condition is detected in the line to be tested at a first time T1, and then a dc arc condition is detected in the line to be tested at a fifth time T5 (a time point when the dc arc occurs again). Unfortunately, however, the dc arc at the first time T1 may be a sporadic arc or a non-fault arc, and the dc arc at the fifth time T5 may also be a non-fault arc or a sporadic arc, which means that the determined real fault arc is a situation induced by a combination of a sporadic arc and a non-fault arc (see fig. 3). The combination induced pilot false fault arcs can accidentally shut down the photovoltaic system directly and cause system outage outages, which is unreasonable without doubt. After all, the arcing phenomenon of continuous combustion does not really occur, and the actual situation is that only sporadic arc events such as the arcing which is automatically extinguished after the combustion flash and harmonic interference caused by non-fault arcs such as inverters are blended and superposed, so that the false fault arc is very similar to the true arcing phenomenon of the continuous combustion at the monitoring end of the processor, and an error detection result is generated. In an alternative embodiment, such errors need to be eliminated, and the scheme is: if the direct current arc is determined to be a real fault arc event, the initial threshold ITH1, i.e., the first threshold, is further adjusted to a threshold interval with an upper limit value, e.g., a third threshold, and a lower limit value, e.g., a second threshold, and the high frequency current component representing the direct current arc condition is compared with the threshold interval, and if the high frequency current component is distributed within the threshold interval, the direct current arc is re-detected. The second threshold value, which is the lower limit value of the threshold value interval, is larger than the first threshold value, which is the initial threshold value. The third threshold value, which is the upper limit value of the threshold interval, is larger than the second threshold value, which is the lower limit value. If the high-frequency current component is distributed in the above threshold interval range to indicate that the dc arc is re-detected, it can be further discriminated whether the fault arc is induced by combination of accidental arc and non-fault arc according to the detailed conditions described below.

Referring to fig. 7, in an alternative embodiment, if the high-frequency current component is distributed in the range of the threshold interval, it indicates that the dc arc is re-detected, and the time interval during which the dc arc appears in the threshold interval is re-determined under the condition that the dc arc is re-detected, i.e. the time required for the re-determination, and when the re-determined time interval (in the threshold interval) shows a periodic characteristic, it is determined that the fault arc is not a situation induced by the combination of the incidental arc and the non-fault arc. The time interval during which the re-detected dc arc occurs characterizes a periodicity, meaning that the re-detected dc arc occurs periodically and these tasks of this embodiment may be performed by a processor. The present solution is applicable to the examples of fig. 4 to 9. When the reconfirmed time interval (within the threshold interval) does not exhibit periodic characteristics, then the fault arc is identified as a condition induced by a combination of incidental arc events and non-fault arc events; and if the direct current is required to be eliminated, the high-frequency current component is still distributed in the range of the threshold interval and indicates that the direct current arc is detected again. If the high-frequency current component is not distributed in the range of the threshold interval, the direct current arc is not detected again, and the condition that the fault arc is induced by combination of the accidental arc event and the non-fault arc event is directly indicated; it is also the case that it needs to be eliminated.

Referring to fig. 7, in an alternative embodiment, if the high frequency current component is distributed in the range of the threshold interval, it indicates that the dc arc is re-detected, the time interval during which the dc arc appears in the threshold interval is re-confirmed under the condition that the dc arc is re-detected, that is, the time required for the re-confirmation, and when the re-confirmed time interval (referred to as the second time interval) is larger than the time interval under the condition that the threshold is not adjusted up, that is, the first threshold (referred to as the first time interval), it is confirmed that the fault arc event is not a situation induced by the combination of the sporadic arc event and the non-fault arc event. The time interval (referred to as a first time interval) under the first threshold condition, which is the non-increased threshold, is a time interval between a time point when the presence of the dc arc in the line to be measured is preliminarily detected and a time point when the dc arc occurs again. These tasks are performed by a processor. The scheme has the advantages that the false fault arc phenomenon can be eliminated, the wrong detection result can be avoided, and the scheme is applicable to the examples of fig. 4 to 9 and the like. If the high-frequency current component is not distributed in the range of the threshold interval, the direct current arc is not detected again, and the condition that the fault arc is induced by combination of the accidental arc event and the non-fault arc event is directly indicated; it is also the case that it needs to be eliminated.

While the present invention has been described with reference to the preferred embodiments and illustrative embodiments, it is to be understood that the invention as described is not limited to the disclosed embodiments. Various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above description. It is therefore intended that the appended claims be interpreted as covering all alterations and modifications as fall within the true spirit and scope of the invention. Any and all equivalent ranges and contents within the scope of the claims should be considered to be within the intent and scope of the present invention.

Claims

1. A method of detecting a fault arc, comprising:

2. The method of claim 1, wherein:

the line to be tested comprises a direct current line which is used for supplying power to the inverter through the photovoltaic assembly.

3. The method of claim 2, wherein:

the cause of the non-fault arc event includes at least harmonic interference introduced by the inverter onto the dc link.

4. The method of claim 2, wherein:

the direct current line is cut off when a real fault arc event occurs, and the direct current line is not cut off when a negligible accidental arc event occurs or when a non-fault arc event occurs.

5. The method of claim 1, wherein:

detecting a high-frequency current component on the line to be detected, wherein the high-frequency current component is used for representing the condition of the direct current arc, and when the value of the high-frequency current component is not lower than a set threshold value, the high-frequency current component indicates that the direct current arc is preliminarily detected at the line to be detected.

6. A method of detecting a fault arc, comprising:

7. A method of detecting a fault arc, comprising:

8. The method of claim 7, wherein:

negligible incidental arcing events include the situation where a direct current arc causes a flash of combustion that self-extinguishes;

causes of non-fault arc events include harmonic interference introduced into the dc link by the inverter during dc to ac operation.

9. A method of detecting a fault arc, comprising:

10. A method of detecting a fault arc, comprising: