Method and system for detecting arcs in a DC grid

Abstract

A method and system for detecting the occurrence of an arc in a DC grid, wherein an electric device is connectable to the DC grid, the method comprising providing at least one detector unit in the DC grid, the detector unit configured to measure an arc noise voltage superimposed on the DC grid voltage without direct measurement of a current flowing through the arc itself, the arc noise voltage being associated with the occurrence of an arc in the DC grid, and a minimum impedance range within a predefined frequency range being ensured for each of the electric devices connected to the DC grid.

Description

Technical Field

[0001] The present invention relates to monitoring a direct current (DC) grid. The present invention also relates to a method and system for detecting the occurrence of an arc in a DC grid to which an electrical device can be connected.

Background Art

[0002] DC power systems can be used in renewable energy power generation systems, DC load systems, electric vehicles, and the like. Such DC power systems can provide higher energy efficiency, better power quality, and more flexible operating modes. A DC power system or so-called DC grid can comprise one or more DC voltage sources that supply a DC voltage to a DC load via various DC connections. For example, a plurality of solar panels and / or batteries can be connected to a power electronics load. In some cases, the DC power can also function as a DC load such as a battery cell / module when being charged.

[0003] The occurrence of DC arcs in DC systems (such as photovoltaics, battery storage, EV charging, etc.) can pose a serious safety hazard. DC arcs can be caused by loose terminals / contacts, aging of insulation materials, damage to electrical components or devices, mechanical work, improper installation, or animal bites. Depending on the location of the arc within the DC power system, the DC arc can be a series arc, a line-to-line parallel arc, or an arc to ground.

[0004] An arc can be a luminous discharge of electricity across an insulating medium and usually involves partial volatilization of the electrodes. A large amount of heat is released to the surroundings in a relatively short time, which can carbonize or even ignite surrounding insulation materials and other combustibles. Therefore, arc detection is an important protection measure for DC microgrids.

[0005] However, unlike alternating current (AC) arc current, DC arc current has no zero crossing point. Conventional zero-crossing protection may not be applicable. Also, since a DC arc can be considered as a variable resistor embedded in the circuit, the circuit current decreases during a series arc. Overcurrent protection typically used in the art may not be able to appropriately detect an arc within a DC grid. It is desired to provide an appropriate arc detection method / system that can be used to suppress an arc before several incidents occur.

[0006] On the other hand, power electronics is widely used in DC microgrids. Since power electronics uses a switch-mode converter, it emits noise or so-called switching harmonics into the DC power system. Switching harmonics may increase electrical losses, overheat devices, or cause component failures / malfunctions due to interference with control logic. For example, it is necessary to filter excessive harmonics to ensure the reliability of arc detection.

[0007] The presence of switching harmonics is a challenge to the efficiency and reliability of current arc detection methods. Existing arc detection methods can be classified into the following three categories. · Methods based on physical characteristics such as arc detection based on sound and light. However, the relevant sensors need to be installed in an appropriate location, usually near the location where an arc fault may occur. As a result, the application of such methods is limited to some small spaces such as closed cabinets. · Time-domain signal-based methods. This type of method measures the change in the magnitude, average, or ratio of a specific current or voltage to determine whether an arc has occurred. · Frequency-domain signal-based methods such as wavelet and fast Fourier transform (FFT). The behavior of the arc depends on factors such as temperature, humidity, corrosion of the contactor, and load conditions, and is uncertain. As a result, a large amount of conductive electrical noise is generated during arc combustion, typically in a wide bandwidth (e.g., 2 kHz to 150 kHz). For example, refer to the publication "Low Frequency Conducted Emissions Caused by Series Arc Faults" (C. Rose, D. W. P. Thomas, C. Smartt, P. Meng) in Proc. 2019 International Symposium on Electromagnetic Compatibility - EMC EUROPE held in Barcelona, Spain from September 2 to 6, 2019.

[0008] However, time-domain signals and frequency-domain signals are inevitably susceptible to the influence of harmonics / noise in the DC microgrid. For example, excessive noise present in the same bandwidth for arc detection covers the noise generated by arcing, making it difficult to distinguish between the two.

[0009] Publication EP3599693A1 describes the detection of arcs by an external signal injected by a single transmitting device. A communication transformer is inserted in series with the PV circuit, and a large DC current flows through the primary coil. Publication US10291016B2 detects arcs by performing a fast Fourier analysis (FFA) of the arc current signal measured on the output side of the solar cell array. In this publication, a current converter for a specific PV application that measures the total current of the PV panel is required. Generally, prior art for arc detection uses an arc current detector. However, since the current detector needs to be sized based on the maximum current of the grid, this can be bulky in some cases.

[0010] In particular, in complex DC grids having multiple loads and sources or multiple devices, it is highly desirable to ensure that DC arcs are properly detected against background noise. There is a need to provide a reliable arc detection method / system that can be easily applied to a wide variety of DC networks in a cost-effective manner. It would also be beneficial if arc occurrences within a large-scale microgrid could be detected regardless of where a single arc detector is connected or located. Having selective arc detection in a complex DC grid can also sometimes be beneficial, which means that arc detection can be performed in different segments of the grid, allowing a defective segment to be disconnected while keeping another segment operational. In this way, while performing arc detection, the DC grid can be made more redundant and faults can be prevented.

[0011] Also, several arcs occur between the voltage terminals of the DC grid and the protective earth. To improve fault diagnosis, a combination with an insulation monitoring device (IMD) that detects insulation faults between voltage conductors and earth within the DC grid may be beneficial. An example of an IMD is disclosed in patent EP1265076.

SUMMARY OF THE INVENTION

[0012] An object of the present invention is to provide a method and system that eliminate at least one of the above-mentioned drawbacks.

[0013] Additionally or alternatively, an object of the present invention is to improve the detection of arcs within a DC grid.

[0014] Additionally or alternatively, an object of the present invention is to provide a method / system that can more reliably ensure that DC arcs are properly detected even against background (electrical) noise.

[0015] Additionally or alternatively, an object of the present invention is to improve the safety of operation of the DC grid.

[0016] For this purpose, the present invention provides a method for detecting the occurrence of an arc in a DC grid, wherein an electrical device is connectable to the DC grid, and the method includes providing at least one detector unit in the DC grid, the detector unit being configured to measure an arc noise voltage superimposed on the DC grid voltage without involving direct measurement of the current flowing through the arc itself, the arc noise voltage being associated with the occurrence of an arc in the DC grid, and a minimum impedance range within a predefined frequency range being ensured for each of the electrical devices connected to the DC grid.

[0017] Advantageously, it is a method that does not depend on arc current measurement, depends only on DC bus ripple voltage measurement, and can operate in a complex DC environment having a plurality of electrical loads and / or sources with high flexibility, where the detection system is installed in the DC grid. Since there is no need to measure the current flowing through the arc, there is also no need to use a current transformer and / or a shunt.

[0018] It has also been found that arc detection can be reliably performed based on measuring the arc noise voltage superimposed on the DC grid voltage, provided that all electrical devices connected to the DC microgrid have a minimum impedance within the frequency range of the arc noise. Advantageously, there is no need to directly measure the current flowing through the arc itself. The minimum impedance of the electrical device serves two purposes. First, it ensures that the current ripple of the arc noise is converted to a voltage level at which measurement is easier. Second, the impedance of each load must be high enough relative to the line impedance of the electrical network, which is typically mainly inductive and typically 5 - 50 μH, so as not to attenuate the arc voltage signal and to enable easy detection anywhere in the DC grid regardless of the location of the detector.

[0019] As a result, the present invention requires that the impedance of all electrical devices connected to the DC grid exceeds a predefined minimum impedance or impedance threshold within a predefined frequency range. Compliance with the predefined minimum impedance requirements for electrical devices within the DC grid can be checked by compliance measurement or, alternatively, by placing a default or predefined minimum series inductor in the electrical device such that the impedance exceeds the minimum threshold in any case.

[0020] This method provides improved detection of arcs within the DC grid. Arc formation can be sensed in a highly reliable and robust manner, significantly improving the operational safety of the DC grid. Advantageously, for a DC grid having multiple loads and sources, coherent and relatively cost-effective arc detection can be provided. The arc detection can be easily used for large-scale and / or complex DC grids. The resulting arc detector unit can be easily connected in parallel to the sources and loads where an arc is assumed to occur.

[0021] For example, a typical line impedance according to standard CISPR16 is 50 μH equal to j.ω.L or an impedance at 30 kHz of j.2.pi.30 kHz.0.05 mH or 9.4 Ohm. Therefore, taking this into account, based on experiments, optionally, each electrical attachment unit is configured to set a minimum impedance range greater than 0.5 Ohm, more preferably greater than 2 Ohm, in a frequency range of 40 kHz to 300 kHz, more preferably in a frequency range of 40 kHz to 100 kHz. The minimum impedance range can generally be selected based on the power supply and cables of the DC grid, depending on the application. Generally, the higher the impedance of the load, the better the arc detection functions in this new concept, which is also referred to as the minimum impedance requirement or threshold.

[0022] Optionally, a minimum impedance range is imposed on all electrical devices connected to the DC grid.

[0023] Accordingly, each device connected to the DC grid must meet the minimum impedance range. In this way, arc detection can be significantly improved and the safety of the operation of the DC grid can be enhanced.

[0024] Optionally, the minimum impedance compliance of an electrical device connected to the DC grid is ensured by at least one of determining compliance based on the characteristics of the device and / or by performing a compliance measurement, or connecting the electrical device to the DC grid via an electrical attachment unit configured to guarantee a minimum impedance range within a predefined frequency range for the electrical device.

[0025] Compliance can be ensured without any change to the electrical device circuit after reconfiguration or in response to the compliance measurement results. In some examples, the device connected to the DC grid can be checked for compliance before actually connecting the electrical device to the DC grid. In some cases, the device can be reconfigured and / or another unit can be used to meet the minimum impedance requirements.

[0026] For compliance, in some cases, an electrical attachment unit is added between the grid connection and an electrical device connected to the DC grid. The electrical attachment unit can be, for example, a minimum series inductor. However, various other devices suitable for providing minimum impedance can be used. The electrical device of the DC grid can be any of an electrical load (e.g., a lamp, a motor, etc.) and a source (e.g., a PV panel, a battery, etc.). However, it will be understood that in some cases, such an electrical attachment unit may not be required, for example, due to pre-estimation of compliance in the case of a simple resistive load having a resistance value exceeding the minimum impedance.

[0027] In principle, a higher impedance can be beneficial for arc detection. However, on the one hand, since the electrical attachment unit may be too bulky, the selection of the minimum threshold is an act of balancing and a compromise between better arc detection and the size of the electrical attachment unit. In some advantageous examples, the minimum impedance threshold can be between 0.5 and 50 Ohm in a frequency range of 40 to 300 kHz, preferably 40 to 100 kHz.

[0028] Therefore, some devices connected to or to be connected to a DC grid may not require an electrical attachment unit according to the related disclosure. For example, in the case of LED devices with relatively low power consumption (small wattage), their impedance may already exceed the threshold. Such electrical devices may not require an associated electrical attachment unit to ensure a minimum impedance range. These electrical devices can be directly connected to the DC grid. Only devices with too low impedance, i.e., a subset of electrical devices, can be indirectly connected to the DC grid by an electrical attachment unit between them. Another example enabling direct connection is a specific case of a DC / DC switching converter that already incorporates a filter for suppressing switching noise to comply with the minimum impedance requirement, for example, by using a sufficiently large inductor.

[0029] Optionally, the configuration of the electrical attachment unit associated with an electrical device that is connected to or to be connected to a DC grid is based on the electrical device. The configuration of the electrical attachment unit can be based on measurements providing an indication of the impedance of the electrical device connected to the DC grid. In this way, the electrical attachment unit can be used to ensure a minimum impedance.

[0030] The electrical attachment unit can be a minimum impedance network / circuit added in series to the electrical device to comply with the minimum impedance requirement.

[0031] The electrical attachment unit can be a minimum impedance unit having various electrical components. For example, the electrical attachment unit can include an electrical circuit. Optionally, the electrical attachment unit is a low-pass filter. For example, the electrical attachment unit can include at least one series inductor. For example, a simple arrangement of the minimum impedance circuit is a series inductor and thus also a low-pass filter that enables the supply current to pass through the electrical device. Of course, this can be a more complex circuit that enables compliance with band-pass filter or minimum impedance requirements. Thus, according to Ohm's law, by connecting a sufficiently large inductor in series, compliance with the minimum impedance requirements can be achieved. For example, if the minimum requirement is 2 Ohm at 40 - 100 kHz, adding a 10 μH series inductor provides compliance because it is greater than j.2.pi.40 kHz.0,01 mH, or 2.51 Ohm.

[0032] The inductor within the electrical attachment unit can include at least one electrical coil element. In some examples, the electrical circuit of the electrical attachment unit includes two inductors, or one inductor in series having a positive supply terminal and another inductor in series with the negative supply terminal of the electrical device connected to the DC grid.

[0033] In some examples, the electrical circuit of the electrical attachment unit has a first side and a second side opposite the first side, the second side is connected to the electrical device with which the electrical attachment unit is associated, the first side is connected to one or more lines of the DC grid, and the electrical circuit of the electrical attachment unit has an inductor on the first side directly connected to one or more lines of the DC grid.

[0034] In some examples, the electrical circuit of the electrical attachment unit includes at least one capacitor and at least one inductor arranged to obtain a high-order filter.

[0035] The electrical attachment unit can be any filter device configured to ensure that the minimum impedance requirements of the connected device or a device connected to a DC grid are met. In some examples, the filter comprises two inductors arranged in a straight line. In some examples, the filter is a low-pass filter having at least two inductors connected to each other. Various implementations of the electrical attachment unit are envisioned.

[0036] Optionally, when directly connected to a DC grid, a subset of electrical devices that do not comply with the established minimum impedance requirements are connected to the DC grid via their associated electrical attachment units, each electrical attachment unit being arranged in series with each respective electrical device to which it is associated, and each electrical attachment unit being configured to set a minimum impedance range within a predefined frequency range so as to meet the minimum impedance requirements.

[0037] In some examples, electrical devices having capacitors are prevented from being directly connected to the DC grid. Connecting such an electrical device directly to the DC grid can result in filtering of the arc voltage signal and prevent the voltage detector unit from detecting signals generated by arc formation. Such an electrical device can be connected to an electrical attachment unit configured to provide a minimum impedance. For example, a filter including an inductor can be used as described above.

[0038] Optionally, the low-pass filter comprises a circuit having one or more inductors and capacitors configured to achieve higher-order filtering. Advantageously, this can further enhance arc detection.

[0039] Optionally, the arc detector unit is arranged to measure, for example, the voltage ripple between two poles of a DC grid. Thus, there is no direct arc current measurement. The detector unit can be configured to perform voltage measurements without using any current transformers.

[0040] Optionally, the DC grid includes at least a first branch and a second branch, an electrical device is connectable to each of the first branch and the second branch, each branch includes at least one detector unit, and a low-pass filter is added between the branches to support selective arc detection and to identify the affected branch.

[0041] This method can be used for complex DC grids.

[0042] Optionally, the DC grid includes a branch separation unit configured to block the propagation of arc noise from the first branch to the second branch and / or vice versa.

[0043] The detector units can be arranged in a plurality of branches. In some examples, the detector units are arranged in each branch of the DC grid. In some examples, the power supply to each branch can be controlled. In this way, when arc formation is detected in one branch, the operability of the other branch of the DC grid can be maintained. The other parts of the DC grid can remain operational if arc formation is detected only on one branch.

[0044] Accordingly, if an arc is detected where it is formed within the DC grid, the controller may disable only a portion of the DC grid where the arc is detected. For this purpose, the electrical noise induced by the arc can be blocked for each branch. In other words, the arc noise in one particular branch is limited to that particular branch only, and the propagation of electrical noise to other branches can be substantially prevented. To effectively isolate the branches within the DC grid so as to prevent the electrical noise from propagating to other branches, the DC capacitor can be used in combination with an additional branch separation unit described below. The capacitor can be arranged to avoid the inter-branch voltage ripple. This provides an easy way to prevent signals related to arc formation from moving from one branch to another, thereby enabling selectivity. Advantageously, the localized arc noise detection can be performed at least at the branch level.

[0045] Optionally, the branch separation unit comprises a capacitor.

[0046] Optionally, at least one breaker unit is provided for each branch configured to cut off and / or disable one or more portions of the DC grid, and the one or more portions are selected based on the detection of the occurrence of an arc within the DC grid by at least one detector unit.

[0047] After detection, there can be actions to suppress arc formation. In some examples, the detection can be used to interrupt the voltage supply to stop the arc discharge and prevent further escalation. For example, various types of breaker units can be used, such as an electromechanical breaker configured to cut off at least a portion of the circuit of the DC grid (e.g., a portion of a solar power generation cell), which can also be a solid-state switch.

[0048] Optionally, the breaker unit comprises at least one switch for cutting off one or more portions of the DC grid.

[0049] Optionally, the circuit breaker unit is configured to selectively disconnect at least one of the first branch and the second branch.

[0050] Optionally, a blocking capacitor is provided to filter the DC voltage component, and then a band - pass filter is provided to enable only noise electrical signals within a predetermined frequency range associated with the occurrence of arcs in the DC grid to pass towards the detector unit.

[0051] Optionally, the blocking capacitor is a band - pass filter comprising at least one capacitor.

[0052] Optionally, the electrical device is an electrical load device or a power supply device.

[0053] Optionally, the DC grid is configured such that new devices can be added to the circuit and / or at least a subset of the devices arranged in the circuit are electrically removable.

[0054] Optionally, the detector unit is configured to further monitor an insulation fault between the voltage terminal of the DC grid and the protective earth.

[0055] In addition to arc detection in the DC grid, the detector unit can be configured to perform insulation detection to provide protection against electric shock. Advantageously, by providing a single device for this purpose, the diagnosis of the operation of the DC grid can be improved. There are various types of arcs, and some arcs are advantageously reflected in combined measurements, further improving the reliability of arc detection. For example, arcs passing through the housing or its protective earth can be detected better. Additionally, a simpler and more cost - effective design can be obtained.

[0056] This arc detection based on voltage measurement is good for complementing an insulation monitoring device (IMD) according to EP1265076, can be implemented on the same processor, and can perform all at least three voltage measurements with the same analog-to-digital converter and voltage reference. Since series arcs can be distinguished from arc faults on the protective earth, combining the IMD and arc fault detection can provide better fault diagnosis.

[0057] Optionally, the detector unit for measuring insulation faults measures the DC bus voltage, the DC bus ripple voltage available for arc noise detection, where a block capacitor is used to perform operations such as filtering the DC voltage, the first electrical voltage (Vi’) related to a first electrical network connected to the protective earth such as a resistive voltage divider resistor network, and a second electrical voltage (Vi’’) related to a second electrical network connected to the protective earth such as another resistive voltage divider network having the same high voltage resistor as the first electrical network but different low voltage resistors.

[0058] Optionally, the switch is used to measure insulation faults by connecting the first electrical network by setting the switch to the first state and connecting the second electrical network by setting the switch to the second state, the DC bus voltage, the first voltage (Vi’) and the second voltage (Vi’’) are measured with respect to the same reference voltage such as the negative voltage of the DC bus, and the insulation fault resistance value is calculated based on the DC bus voltage, the first voltage (Vi’) and the second voltage (Vi’’).

[0059] The grid code can define some constraints of electrical equipment. For example, the grid code can improve the electromagnetic compatibility between multiple electrical devices and at least partially prevent the electrical devices from interfering with the operation of other electrical devices. Advantageously, by associating an electrical attachment unit with an electrical device connected to or to be connected to a DC grid, it is possible to prevent the electrical device from preventing reliable arc detection by a detector unit.

[0060] According to one aspect, the present invention provides a method for monitoring arc faults in a DC grid having a plurality of loads and a protection device based on the measurement of conducted emissions, wherein for the loads and / or sources used in the DC grid, a grid code is implemented that partially limits the conducted voltage and / or current noise in the frequency band of 1 to 500 kHz, wherein the arc detection device is configured to measure the electrical signal noise in the frequency band of 1 to 500 kHz, and the measured electrical signal can be either a current signal or a voltage signal. This avoids interference and false signals in arc detection.

[0061] Optionally, the load and / or source also has a minimum impedance requirement in the frequency band of 500 kHz to allow for a large enough noise to flow through the arc detector. A minimum impedance greater than 2 Ohm can be used in the frequency range of 40 kHz to 300 kHz.

[0062] Optionally, the load and / or source has a minimum series inductance requirement.

[0063] Optionally, the requirements for conducted emissions depend on the frequency bandwidth and the type of load or source.

[0064] Optionally, two predefined frequency bands are allocated for arc detection and power line communication.

[0065] Optionally, an analog and / or digital filter is added to the measurement signal for arc detection and tuned to the emission limit such that a specific portion of the frequency with relatively high limits is filtered.

[0066] Optionally, the arc detection filter filters a predefined frequency band.

[0067] Optionally, the arc detection circuit is connected in parallel to the DC bus.

[0068] Optionally, the arc parallel detection circuit includes a coupling transformer in series with a capacitor. One side of the transformer is connected to the DC grid and the other is connected to the detector. Such a transformer can be added to provide galvanic isolation between the detector unit and the DC grid.

[0069] Optionally, it is a detector unit installed in a bipolar DC microgrid. In a bipolar grid, a neutral point or conductor is added. The positive and negative polarities are regarded as two DC voltage sources.

[0070] To monitor the arcs of the positive and negative lines, the detector unit can be connected in parallel on the source side between the positive pole and the neutral point, and also between the negative pole and the neutral point.

[0071] In each arc detection branch within the bipolar DC microgrid, one block capacitor can be used to prevent DC current from flowing through the detector unit. Thus, one detector unit can detect arc faults on both the positive line, negative line, and neutral line. Optionally, for a bipolar DC grid, a coupling transformer can also be used in the arc detector to provide galvanic insulation between the detector unit and the grid. Optionally, for a bipolar DC grid, analog and / or digital filters are added to the measurement signal for arc detection and tuned to the emission limit such that specific portions of frequencies with relatively high limits are filtered.

[0072] According to one aspect, the present invention provides a system for detecting the occurrence of an arc in a DC grid having one or more connectable electrical devices, the system including at least one detector unit connectable to the DC grid, the detector unit being configured to measure an arc noise voltage superimposed on the DC grid voltage without involving direct measurement of the current flowing through the arc itself, the arc noise voltage being associated with the occurrence of an arc in the DC grid, and the system being configured to ensure a minimum impedance range within a predefined frequency range for each of the electrical devices connected to the DC grid.

[0073] Advantageously, the system provides highly reliable and robust arc detection for an adaptive DC grid. The design of the DC grid can be flexible (non-fixed design), and electrical devices can be added / removed without the need for changes to the detector unit. This provides a cost-effective and universally applicable method for arc detection in DC grids that can be easily implemented in existing DC grids.

[0074] Even if the number of electrical devices and / or the configuration of the electrical devices within the DC grid are changed, arc detection can still be guaranteed to be reliable. For example, the DC grid can be dynamically scaled up or down with connectable electrical devices. New devices connected to the DC grid can first be subjected to compliance tests to ensure minimum impedance. If necessary, for example, if the impedance is too low for an electrical device to be connected, an electrical attachment unit can be provided for that device. The electrical attachment unit is configured to ensure the minimum impedance requirement.

[0075] Advantageously, an inexpensive detector design can be obtained. In some examples, the detector unit includes a microcontroller configured to sample a voltage and calculate a (frequency) spectrum. Advantageously, since the voltage signal is processed to identify the presence of signal components associated with the formation of an arc somewhere in the DC grid, there is no need to use a current transformer. Such a current transformer should be sized within a DC grid where the load is unknown because it can remove and / or add various loads. Therefore, using a current detector may require redesign or reconfiguration of the transformer when other loads are added / removed. Therefore, monitoring the voltage provides significant advantages. Advantageously, according to the method / system of the present disclosure, arc detection can be performed using voltage sampling measurements, and electrical devices connected to the DC grid comply with the minimum impedance requirement. Electrical devices that would not comply (e.g., by performing compliance measurements) can be provided with an electrical attachment unit placed between the electrical device and the DC grid line to ensure the established minimum impedance requirement. For example, such electrical devices can be provided with a low-pass filter. Alternatively, electrical devices that would not comply can be reconfigured to meet the minimum impedance requirement when their electrical circuits are known, enabling this reconfiguration.

[0076] Optionally, the compliance measurement includes determining an impedance metric by superimposing a test signal on the voltage of the DC grid, wiring an impedance measurement bridge circuit in series with the electrical device being tested, measuring the amplitude voltage resulting from the impedance measurement bridge circuit, and comparing the resulting amplitude voltage with a reference voltage curve corresponding to the minimum impedance.

[0077] Optionally, the reference voltage curve corresponds to the voltage measured at the minimum impedance.

[0078] This compliance method can be used, for example, to identify electrical devices that require an electrical attachment unit or to reconfigure an electrical circuit to comply with a minimum impedance requirement threshold.

[0079] According to one aspect, the present invention provides a method for determining the compliance of an electrical device connected to a DC grid, wherein an impedance metric of the electrical device is determined to check whether the electrical device meets a predefined minimum impedance range, and the method includes superimposing a test signal on the voltage of the DC grid, wiring an impedance measurement bridge circuit to the electrical device being tested, measuring the amplitude voltage resulting from the impedance measurement bridge circuit, and comparing the resulting amplitude voltage with a reference voltage curve corresponding to the minimum impedance.

[0080] The test setup can be used to verify the minimum impedance compliance requirement. For identifying electrical devices that require an electrical attachment unit (and / or reconfiguration) to comply with the minimum impedance requirement threshold, the compliance test can be simply performed within a predefined frequency range.

[0081] For example, an AC signal (e.g., 1V) can be superimposed on the DC signal, and the frequency can be changed in the range of 40 kHz to 300 kHz. The AC signal used can mimic an arc signal. Output voltage Vac_load Let it be an indicator representing the load impedance. In particular, V ac_load is a fraction of the well - defined input voltage V ac_test coming from the signal generator. It is calculated as follows according to Kirchhoff's law. V ac_load =V ac_test xZ L / (Z L +Z LI )(1)

[0082] Here, Z L represents the load impedance, and Z LI represents the line impedance.

[0083] In the DC grid, the larger Z L is, the larger V ac_loadが is. Therefore, the load impedance is estimated by comparing V ac_load with a reference voltage curve corresponding to the impedance threshold. When V ac_load is greater than the reference voltage, the device impedance is considered to be greater than the impedance threshold.

[0084] According to one aspect, the present invention provides a DC grid including the system according to the present disclosure. The band - pass filter can be used to pass only the voltage noise within a predefined frequency range (refer to the bandwidth). It is expected that arc formation generates a signal having frequency components within the predefined frequency range.

[0085] Furthermore, the transformer of such a current detector may have to be sized based on the grid arrangement / configuration. By using a voltage detector unit and ensuring the minimum impedance of the electronic device connected to or to be connected to the DC grid, and by arranging the electrical attachment unit, a reliable distinction can be made between the detection of actual arc formation and other signals detected in the electrical circuit.

[0086] Advantageously, a plurality of identical voltage arc detector units can be used in a DC grid without the need to adapt the detector units based on the configuration of the DC grid. Further, the detector units can continue to operate even if the DC grid configuration is changed.

[0087] According to one aspect, the present invention provides a method and system for improving power line communication in a DC grid, wherein an electrical device is connectable to the DC grid, and the method includes providing at least one power line communication unit in the DC grid, the power line communication unit being configured to enable communication via the DC grid voltage, and ensuring a minimum impedance range within a predefined frequency range for each of the electrical devices connected to the DC grid. Similar to arc detection, minimum impedance compliance provides an improvement in power line communication in the DC grid.

[0088] It will be understood that any of the aspects, features, and optional features described in connection with the method are equally applicable to the system, the described device, and the DC grid. It will also be apparent that any one or more of the above aspects, features, and optional features can be combined.

Brief Description of the Drawings

[0089] The present invention will be further described based on exemplary embodiments shown in the drawings. The exemplary embodiments are shown as non-limiting illustrations. Note that these figures are merely schematic representations of the embodiments shown as non-limiting examples.

[0090]

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DETAILED DESCRIPTION OF THE INVENTION

[0091] FIG. 1 shows a schematic diagram of an embodiment of a system 1 configured to detect the occurrence of an arc in a DC grid 3 having a DC power supply P and connectable electrical devices 5. In this example, only two electrical devices 5 are shown, but more electrical devices can be connected. The system 1 includes at least one detector unit 7 connectable to the DC grid 3. The detector unit 7 is configured to measure the arc noise voltage superimposed on the DC grid voltage without directly measuring the current flowing through the arc itself. The arc noise voltage is associated with the occurrence of an arc in the DC grid 3. A minimum impedance range within a predefined frequency range is ensured for each of the electrical devices and the power supply P connected to the DC grid. In this embodiment, the power supply P is a specific type of electrical device 5 that is essential for providing a DC voltage to the grid. In principle, various power supplies can be connected in parallel within the DC grid. The detector unit 7 does not need to be installed near the power supply P, but can be installed at various locations within the grid, for example, near an electrical unit 5.

[0092] The detector unit 7 is configured to perform measurements of one or more electrical signals, such as detecting arc noise within the one or more signals. In some examples, a subset of the electrical devices 5 can be connected to the DC grid via the electrical attachment unit 9 associated therewith. Each electrical attachment unit 9 can be arranged in series with each respective electrical device 5 with which it is associated. Further, each electrical attachment unit 9 can be configured to set a preselected impedance range so as to ensure a minimum impedance. However, some electrical devices 5 may already comply with the minimum impedance. This can be determined, for example, by performing a test measurement. Such compliant electrical devices 5 may not be provided with an electrical attachment unit 9.

[0093] In some advantageous examples, arc noise voltage is measured instead of arc noise current and / or DC current. This electrical attachment unit can enable conversion of an arc noise current signal into an arc noise voltage signal that can be picked up by the detector unit. The electrical attachment unit can be regarded as a minimum impedance device. When there is an arc, inductive arc noise propagates through the DC grid. If one of the electrical devices has an impedance smaller than a threshold impedance, the arc current can flow through the electrical device and not through the line connected to the detector unit. By setting the minimum impedance of each electrical device connected to or to be connected to the DC grid, it can be ensured that arc noise always reaches the detector unit. The electrical attachment unit can be configured to increase the impedance to a value greater than the minimum value.

[0094] This system enables highly reliable arc fault detection (e.g., arc noise in the frequency range of 10 - 200 kHz) and can reduce electromagnetic interference in the DC grid. Highly reliable arc detection can be achieved even in complex (adaptive) DC grids. The electrical attachment unit associated with a subset of electrical devices can effectively avoid attenuation of the arc (voltage) signal in the DC grid. The electrical attachment unit provides a minimum impedance to the DC voltage source or load. In some examples, this is implemented by a series inductor (>10 μH) for each power source or load (refer to the subset of electrical devices).

[0095] In some examples, the detector unit 7 is configured to monitor voltage noise. Since it is measured by the voltage noise generated by the inductor of the electrical attachment unit, it is not necessary to measure the complete arc current itself. Advantageously, the voltage arc detector 7 may not require a large current transformer to measure the arc current. In principle, one (unipolar DC) or two detector units (bipolar DC) are sufficient to detect arcs even in complex topologies. In some examples, the measurement circuit can be combined with a power line modem.

[0096] The test system can be configured to check whether the impedance of the electrical devices connected to the DC grid meets the minimum impedance requirement above a predefined frequency range, preferably above 40 kHz. Based on the results of the compliance test, the corresponding electrical attachment unit can be selectively configured to increase the impedance to a value above the threshold minimum so that the voltage signal induced by arc formation can be effectively picked up by the detector unit.

[0097] Figure 2 shows a schematic diagram of an embodiment of a system 1 with a DC power supply P. The DC grid 3 has two branches, namely, a first branch 2a and a second branch 2b. A plurality of electrical attachment units 9 are arranged to ensure minimum impedance. The detector unit 7 can detect an arc in the DC grid by ensuring a minimum impedance range within a predefined frequency range for each of the electrical devices 5 connected to the DC grid, so that the DC grid always has a minimum impedance between all connected loads or sources. In some cases, for electrical devices 5 that do not comply with the minimum impedance, the electrical devices 5 are reconfigured to comply with them, or the electrical attachment units 9 are arranged to guarantee minimum impedance when the associated electrical devices 5 are connected to the DC grid. The detector unit 7 can be configured to measure one or more values indicating the arc noise voltage. In this example, a capacitor 13 is used to block the DC voltage so that only the arc noise voltage can pass towards the detector unit.

[0098] A subset of the electrical devices can include any load / source in the DC grid 3 that has an impedance below a certain threshold (e.g., >2 Ohm.j.2.phi.f) within a frequency range of 40 to 300 kHz, preferably within a frequency range of 40 to 100 kHz. For example, a small resistive LED device with a low wattage can be directly connected without the need to provide reconfiguration and / or additional electrical attachment units 9 because it has an impedance above the 2 Ohm threshold.

[0099] Advantageously, in this example, a capacitor 8 is provided that enables selectivity, which means that arc formation can be detected in one branch of the network without interfering with the other branch. Optionally, additional electrical attachment units 9', 9'' can be provided for each branch.

[0100] Figure 3 shows a schematic diagram of an embodiment of system 1. In this example, the electrical attachment unit 9 is associated with only a subset of the electrical devices 5a to ensure minimum impedance. In this example, the electrical attachment unit is not associated with the electrical device 6. Since this electrical device 6 may already meet the minimum impedance requirement, it may not require a minimum impedance network. The electrical device 6 can be, for example, an LED device, a low-power electrical device, etc.

[0101] When an arc is formed in the DC grid, the ultrasonic frequency signal can be effectively detected by the detector unit, and the effect of suppressing the generated signal due to the arrangement of one or more electrical devices in the DC grid can be effectively prevented by ensuring the minimum impedance requirement. If the connected device does not comply with the minimum impedance requirement, the device can be reconfigured before connection to the DC grid and / or one or more electrical attachment units (connected to the non-compliant electrical device) can be used to ensure the minimum impedance requirement.

[0102] The system is configured to have a minimum impedance requirement for each electrical device (e.g., electrical load or voltage source) connected to the DC grid. It can be initially determined, for example, by performing a compliance measurement, whether the electrical devices (e.g., photovoltaic panels, converters, loads, battery modules, etc.) connected to the DC grid meet the established minimum impedance requirement. For these electrical devices that do not meet such a minimum impedance requirement, electrical attachment units such as series inductors can be provided at the input or output, depending on whether the associated electrical device is a voltage source or a load. The detector unit can be configured to measure a voltage signal that provides a cost-effective and compact design.

[0103] Additionally, the placement of the electrical attachment units can enable proper communication of signals via the DC grid wiring and prevent the communication signals from being suppressed by the connected devices.

[0104] Optionally, each electrical device of a subset of the electrical devices (when directly connected to the DC grid and not compliant with the minimum impedance requirement) is connected to the DC grid via respective electrical attachment units. In some examples, each of the subset of the electrical devices can be indirectly connected to the DC grid via respective electrical attachment units 9.

[0105] FIG. 4 shows a schematic diagram of one embodiment of a graph illustrating an exemplary frequency spectrum and conducted emission limits of a DC device, such as an electrical device including a power source that is part of the DC grid.

[0106] Various electrical devices can be connected to a DC grid, and different conducted emission limits can be set for PLCs, and switched power converters and arc detection can be set, in order to avoid EMC interference between them, as well as interference with power line communication (PLC), switched power converters, and arc detection. Specific frequency bands can be reserved for arc detection (40 - 100 kHz) and power line communication (120 kHz - 300 kHz). In this example, the frequency band used for arc detection is 40 kHz to 100 kHz. This supports arc detection while still enabling switched-mode power converters below 40 kHz without generating interference. Thus, loads and sources such as switched power converters within the DC grid can have restrictive requirements in these frequency ranges. In some examples, less restrictive requirements can be imposed between 100 kHz and 120 kHz, which means, for example, less restrictive filtering requirements for the third harmonic (3 × 37 kHz) of a switched-mode power converter having a switching frequency of 37 kHz. In some examples, power line communication can operate from 120 kHz up to 300 kHz, and thus has more relaxed emission limits in this frequency range.

[0107] Power line communication may also suffer from voltage signal attenuation when the grid impedance is low. For example, when a capacitor is placed in parallel on a DC grid, the capacitor can filter the power line modem signal. Thus, the minimum line impedance for the load or generator is provided using one or more electrical attachment units to facilitate power line communication in addition to arc detection. For example, the minimum impedance may be required to be greater than 2 Ohm in the frequency range of 40 kHz to 300 kHz. Thus, this can be achieved by adding a series input filter inductor of 10 μH or typically twice 4.7 μH on the DC load side, which is equal to j.2.π.40 kHz.10 μH or j2.5 Ohm. Briefly, this means that the minimum impedance requirement proposed for arc detection is also beneficial for power line communication when applied to the frequency range of the power line modem.

[0108] Typically, in an electrical DC grid, the impedance of the arc detection branch is related to the cable inductance and, within the frequency range of 10 to 300 kHz, this is 5 to 50 μH depending on the type and length of the cable used.

[0109] FIG. 5 shows a schematic diagram of one embodiment of a system comprising an arc detector unit arranged on the DC voltage source side. The possibility of an arc phenomenon is indicated by A. The arc phenomenon can occur anywhere within the DC microgrid. The minimum impedance requirement can be imposed by inductor 20.

[0110] In this example, the arc detection circuits 30, 40, 50 are arranged in parallel with the electrical grid and are configured to detect arcs regardless of where the arcs occur, even when a more complex grid is connected. For arc detection, a large current transformer for measuring the current flowing through the arc is not necessary. By using a relatively small optional transformer 40, it can be easily electrically isolated from the electrical grid, which means that the detection circuit can be safely isolated from the DC grid voltage. The optional transformer 40 can be provided to provide additional safety insulation.

[0111] In this example, the DC voltage source 10 supplies power to the load 70, and both 10 and 70 are so-called electrical devices of the DC grid. The DC voltage source can be a PV, a battery storage unit, etc. The arc detector 50 is connected in parallel to the DC voltage source via the DC voltage blocking capacitor 30 and the coupling transformer 40. The DC voltage blocking capacitor is configured to prevent DC current from flowing into the arc detector. As an advantage, the DC current does not flow through the coupling transformer and can thus remain relatively small. This helps to reduce heat loss and the cost of the transformer.

[0112] Only the noise signal can flow through the capacitor 30 and the coupling transformer 40. The arc noise can be first filtered by a band-pass filter, which allows only the noise present in the passband with a bandwidth of 40 kHz to 100 kHz. Such a filter can be analog or digital.

[0113] The filtered arc noise can be sent to the microprocessor for arc detection, and an arc detection algorithm is created. Time domain characteristics (such as magnitude, change in voltage or current ratio, etc.) or frequency domain characteristics (such as frequency spectrum, etc.) can be used to determine whether an arc occurs. The detection algorithm compares the time domain / frequency domain characteristics before and after the arc to determine whether an arc occurs in the downstream microgrid connected to this DC voltage source.

[0114] As indicated by the symbol marked by A, when an arc occurs, due to the parallel connection between the arc detector and the DC voltage source, arc noise may flow through the DC voltage source and the DC arc detector. If the impedance of the DC voltage source in the bandwidth of 40 kHz to 100 kHz is the same as or smaller than the impedance of the arc detection branch, only a very small part (for example, less than 50%) of the arc noise may flow through the arc detection branch, which is disadvantageous for arc detection. The arc noise measured by the detector may be covered by background noise. In this case, it is difficult to distinguish between the two. Therefore, the impedance of the DC source in the range of 40 kHz to 100 kHz needs to be greater than the impedance of the arc detection branch. If the impedance of the DC source or electrical equipment is too small, a specific line impedance is installed in series between the DC voltage source and the arc detection branch. The minimum impedance on the DC voltage source side is proposed to be 2 Ohm. Depending on the actual application, this impedance can be increased. Typically, in an electrical DC grid, the impedance of the arc detection branch is related to the cable inductance and is 5 to 50 μH within the frequency range of arc detection. Therefore, imposing a minimum impedance on a sufficiently large connected device facilitates arc detection by voltage measurement. If the minimum impedance threshold is small, the arc voltage noise is attenuated, which may result in unreliable detection. Therefore, the proposed minimum impedance threshold (for example, 2 Ohm) is found accordingly and experimentally checked.

[0115] The band - pass filter and the microprocessor, if present, can be embedded in the PLC module. In this way, the arc detector and the PLC share one coupling transformer. Since DC current does not pass through the coupling transformer, the nominal current of the coupling transformer is small and is determined by the arc noise. Therefore, it is possible to select a transformer with a small coil. This helps to reduce the installation cost of the arc detector. Also, the arc detection algorithm can be programmed into the same processor used by the PLC. If a digital filter is employed, it can be programmed in the PLC processor. This can further reduce the cost of the arc detector.

[0116] When an arc occurs, the conduction noise can flow through the DC - blocking capacitor and the coupling transformer. It is measured on the secondary coil and can be further filtered by the band - pass filter. The monitored arc noise is greater than the background noise. By comparing the arc noise and the background noise, the arc detector can determine whether an arc has occurred.

[0117] FIG. 6 shows a schematic diagram of an embodiment of a system comprising an arc detector in a bipolar DC microgrid.

[0118] The bipolar DC microgrid has a neutral line, which can provide improved supply flexibility and resilience compared to a unipolar DC microgrid. Source 10 is connected to load 70. Transformer 40 provides galvanic insulation and additional safety to the detector unit.

[0119] The arc detector units are separately connected in parallel on the DC voltage source side between the positive electrode and the neutral point, and between the negative electrode and the neutral point. In the bipolar model, two arc detector units can independently detect arcs on the positive and negative cables. Even if one pole is not functioning, the arc detector connected to the other pole can still operate normally.

[0120] To repeat, a minimum impedance is required for the DC voltage source and the DC load so that the magnitude of the arc noise flowing through the coupling transformer is large enough for arc detection. If the DC source / load impedance is too small, a specific line impedance is connected in series between the arc detector and the voltage source / load. In this example, the minimum impedance required for the positive / negative DC source and the load is selected as 2 Ohm. However, other values shown in the present disclosure may be used.

[0121] A band-pass analog / digital filter is installed to allow only arc noise within a specific bandwidth to enter the arc detection processor. The arc detector determines the arc based on the differences in the time domain / frequency domain characteristics of the arc.

[0122] The filter and the arc detector share a coupling transformer and can be embedded in the PLC existing on the DC source / load side to reduce the arc detection cost.

[0123] A subset of the electrical devices can each be associated with an electrical mounting unit configured to ensure a minimum impedance so that the arc (voltage) noise signal can effectively reach the (voltage) detector unit.

[0124] By providing an electrical attachment unit (e.g., a low-pass filter) to a subset of electrical devices, the formation of arcs in a DC grid can be detected better. The subset of electrical devices is not directly connected to one or more lines of the DC grid. Instead, the electrical attachment unit can be provided between the electrical devices of the subset of electrical devices and one or more lines of the DC grid. The electrical attachment unit can be adapted to set a minimum impedance that exceeds a predefined minimum impedance threshold.

[0125] Additionally, this method enables more reliable power line communication (PLC) and avoids interference with arc detection.

[0126] Additionally, it is possible to sum the arc noise of both poles and use a detector unit having two coupling capacitors (30) with only a single voltage measurement value, but this will clearly provide less information about where the arc occurred.

[0127] FIG. 7 shows a schematic diagram of one embodiment of a test setup 2 for compliance measurement. The compliance measurement can be performed to verify compliance with a minimum impedance requirement in a predefined frequency range. Taking a load as an example of an electrical device, the aim is to verify whether the load impedance meets the minimum impedance requirement in a specific frequency range when powered on. Alternatively, the so-called load can also be a voltage source, a battery, etc. The principle of the proposed compliance measurement method is shown in the following figure and is based on a so-called impedance measurement bridge circuit. For the identification of electrical devices that require an electrical attachment unit to comply with the minimum impedance requirement threshold, the compliance test can be simply performed within a predefined frequency range.

[0128] For compliance measurement, a high-frequency signal V test is a DC voltage (V dc) For example, it is superimposed on a sine wave frequency sweep signal of 40 kHz to 100 kHz. Obviously, it can also be other types of signals as long as its frequency spectrum covers the frequency range of the minimum impedance requirement.

[0129] The concept of the impedance measurement bridge circuit uses a predefined series impedance (Z L ) having a load (Z L1 ) during the test.

[0130] As a result, the voltage V test_load is relative to the load impedance. In particular, V test_ load is a fraction of the clearly defined input voltage, V test , coming from the signal generator. According to Kirchhoff's law, V test_ load is calculated as follows. V test_load =V test ×Z L / (Z L +Z LI )(1)

[0131] Here, Z L represents the load impedance, and Z LI represents the line impedance.

[0132] According to this formula, the larger Z L is, the larger V test_load is, so it can be simply used for compliance testing. Therefore, the load impedance threshold limit can be verified by comparing V test_load with the reference voltage curve corresponding to the impedance threshold. If V test_load is greater than the reference voltage defined by the reference voltage curve, the device impedance is greater than the impedance threshold and thus compliant. This has been verified by experiments in the laboratory. This method can operate, for example, at a sine wave frequency where the measured voltage (V test_load ) at each frequency is compared with the reference voltage curve. Alternatively, V test_When the load signal is measured in the time domain (t) and then converted to its amplitude in the frequency domain using mathematical calculations based on the Fourier transform (FT), the method can operate faster. In this case, V test should be a signal that covers the frequency range of the minimum impedance requirement, for example, any signal having a frequency range of 40 to 100 kHz. The reference voltage curve for the test can be easily obtained by performing a calibration test on a resistor instead of a load (Z L ), for example, a 2 Ohm calibration resistor for testing the minimum impedance requirement of 2 Ohm of the load.

[0133] Figure 8 shows a schematic diagram of a method for determining the compliance of an electrical device connected to a DC grid. It may be important to obtain a reliable voltage reference. A modified line impedance network configured to simulate the wiring in the DC grid can be used. A load having differential characteristics (resistance, inductance, etc.) and an impedance value is tested to obtain a voltage reference.

[0134] Compliance measurement may include determining an impedance metric by superimposing an AC signal on a DC network including a DC power supply, wiring, and the electrical device being tested, measuring the resulting voltage, and comparing the resulting voltage with a reference voltage linked to the minimum impedance described above.

[0135] The test setup can generate an output voltage having a DC component (e.g., 1V) and an AC component (e.g., within a frequency range of 40 kHz to 300 kHz, or 40 kHz to 100 kHz). The generated output voltage can be applied to the device under test (referring to the device connected to the DC grid), and then the impedance is calculated. It is possible to identify whether the connected device suppresses the applied generated signal (e.g., the simulated arc signal), thereby preventing the signal from reaching the detector unit when the device is directly connected to the DC grid.

[0136] FIG. 9 shows a schematic diagram of an embodiment of system 1. In this example, the detector unit is configured to further monitor an insulation fault between the voltage terminal of the DC grid and the protective earth. The detector unit measures the DC bus voltage, the DC bus ripple voltage that can be used for arc noise detection and where a block capacitor is used to perform operations such as filtering the DC voltage, the first electrical voltage (Vi') related to a first electrical network connected to the protective earth such as a resistive voltage divider resistor network, and a second electrical voltage (Vi'') related to a second electrical network connected to the protective earth such as another resistive voltage divider network that has the same high-voltage resistor as the first electrical network but a different low-voltage resistor.

[0137] In some examples, a switch is used that connects the first electrical network by setting the switch to a first state and connects the second electrical network by setting the switch to a second state. The DC bus voltage, the first voltage (Vi'), and the second voltage (Vi'') are measured with respect to the same reference voltage such as the negative voltage of the DC bus, and the insulation fault resistance value is calculated based on the DC bus voltage, the first voltage (Vi'), and the second voltage (Vi'').

[0138] Advantageously, the detector unit may provide a combination of arc detection and insulation monitoring devices in a cost-effective manner. The connections A1, A2 are arc detection connections, and the connections A1, A3, A4 are insulation monitoring connections.

[0139] The occurrence of a DC arc may coincide with insulation failure. Therefore, for the purpose of better diagnosis and the cost of protection equipment, it is interesting to combine an arc detection method and / or circuit with an insulation monitoring device (IMD). In particular, a floating DC grid uses an IMD as a safety measure to ensure proper electrical insulation between the DC grid and the protective earth. The IMD functions to provide protection against electrocution. Therefore, in addition to arc detection within the DC grid, the detector unit may be configured to perform an IMD. Advantageously, a single device can result in an improvement in the diagnosis of the operation of the DC grid. There are various types of arcs, and some arcs can be advantageously reflected in the combined measurements. In particular, those connecting to the protective earth will benefit the most, such as an arc passing through the protective housing. Additionally, a simpler and more cost-effective design can be obtained.

[0140] The arc detection method included in the present invention based on voltage measurement has been found to be a good complement to the IMD described in EP1265076, which is also based on voltage measurement and can be combined with the same device, for example. Typically, the same processor can perform all three minimum voltage measurements for the same voltage reference, such as the negative DC voltage of the grid, using the same analog-to-digital converter.

[0141] Therefore, an advantageous combination extends the arc detector unit that requires measurement of the DC bus voltage itself (A3&A1) and arc voltage ripple measurement (A1&A2) using at least one additional measurement channel (A4) for connection to the protective earth. This measurement channel (A4) is a high-impedance connection for constituting itself as insulation failure. The connection (A1) is the reference voltage connection for the measurement channels (A2), (A3), and (A4).

[0142] FIG. 10 shows a schematic diagram of an embodiment of system 1. Similar to the embodiment shown in FIG. 9, the detector unit is configured to further monitor an insulation fault between the voltage terminal of the DC grid and the protective earth. The detector unit can be used for a cost-effective and easy method for performing arc detection monitoring and insulation monitoring, and significantly improves the safety of system 1.

[0143] For the calculation of the insulation fault measurement channel (A4), first, it is necessary to measure the voltage (Vi’) related to the first electrical network connected to the protective earth, and second, it is necessary to measure another voltage (Vi’’) related to the second electrical network connected to the protective earth. Therefore, the switch can be used by connecting the first electrical network by placing the switch in the first state and, in another step, connecting the second electrical network by placing the switch in the second state. The DC bus voltage, Vi’ and Vi’’ are measured with respect to the same reference voltage, such as the negative voltage of the DC bus, and then the insulation fault resistance value is calculated based on the DC bus voltage, Vi’ and Vi’’.

[0144] Various embodiments may be implemented using hardware elements, software elements, or a combination of both. Examples of hardware elements can include processors, microprocessors, circuits, application specific integrated circuits (ASICs), programmable logic devices (PLDs), digital signal processors (DSPs), field programmable gate arrays (FPGAs), logic gates, registers, semiconductor devices, microchips, chip sets, and the like. Examples of software can include software components, programs, applications, computer programs, application programs, system programs, machine programs, operating system software, mobile apps, middleware, firmware, software modules, routines, subroutines, functions, computer implemented methods, procedures, software interfaces, application program interfaces (APIs), methods, instruction sets, computing code, computer code, and the like.

[0145] In this specification, the present invention has been described with reference to specific examples of embodiments of the invention. However, it will be apparent that various modifications, variations, alternatives, and changes can be made therein without departing from the essence of the invention. For purposes of clarity and concise description, features are described herein as part of the same or separate embodiments, but alternative embodiments having all or some combination of the features described in these separate embodiments are also contemplated and understood to fall within the framework of the invention as outlined by the claims. Accordingly, this specification, the drawings, and the examples are to be regarded in an illustrative rather than a limiting sense. The present invention is intended to embrace all alternatives, modifications, and variations within the scope of the appended claims. Further, many of the elements described are functional entities that can be implemented as separate or distributed components or in any suitable combination and location, or in combination with other components.

[0146] In the claims, any reference signs placed in parentheses shall not be construed as limiting the claims. The word "comprising" does not exclude the presence of other features or steps than those listed in a claim. Further, the words "a" and "an" are not to be construed as limited to only one, but are used in the sense of "at least one", and do not exclude a plurality. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used advantageously.

Claims

1. A method for detecting the occurrence of an arc in a DC grid, wherein an electrical device is connectable to the DC grid, and the method includes providing at least one detector unit in the DC grid, wherein the detector unit is configured to measure an arc noise voltage superimposed on the DC grid voltage without directly measuring the current flowing through the arc itself, the arc noise voltage is associated with the occurrence of the arc in the DC grid, and a minimum impedance range within a predefined frequency range is ensured for each of the electrical devices connected to the DC grid. The minimum impedance compliance of the electrical device connected to the DC grid is To determine compliance based on the characteristics of the aforementioned device and / or by performing compliance measurements, A method that ensures at least one of the following: connecting the electrical device to the DC grid via an electrical mounting unit configured to guarantee the minimum impedance range within the predefined frequency range for the electrical device.

2. The method according to claim 1, wherein the minimum impedance range is selected to be greater than 0.5 ohms and more preferably greater than 2 ohms in a frequency range of 40 kHz to 300 kHz, more preferably in a frequency range of 40 kHz to 100 kHz.

3. The method according to claim 1 or 2, wherein the minimum impedance range is imposed on all electrical devices connected to the DC grid.

4. The aforementioned compliance measurement, Superimposing a test signal onto the voltage of the DC grid, The impedance measurement bridge circuit is wired in series with the electrical device to be tested, To measure the amplitude voltage resulting from the impedance measurement bridge circuit, The method according to claim 1, comprising comparing the resulting amplitude voltage with a reference voltage curve corresponding to the minimum impedance, thereby determining the impedance index.

5. The method according to claim 1, wherein, when directly connected to the DC grid, a subset of electrical devices that do not conform to the predetermined minimum impedance requirement are connected to the DC grid via the electrical mounting units associated with them, each electrical mounting unit is arranged in series with each of the electrical devices to which it is associated, and each electrical mounting unit is configured to set the minimum impedance range within the predefined frequency range so as to satisfy the minimum impedance requirement.

6. The method according to claim 1, wherein the electrical mounting unit is a low-pass filter adapted to ensure compliance with the predetermined minimum impedance requirement.

7. The method according to claim 6, wherein the low-pass filter comprises a circuit having one or more inductors and capacitors configured to achieve higher-order filtering.

8. The method according to claim 1, wherein the DC grid includes at least a first branch and a second branch, an electrical device is connectable to each of the first branch and the second branch, each branch includes at least one detector unit, and a low-pass filter is added between the branches to support selective arc detection and to identify the affected branch.

9. The method according to claim 1, wherein a block capacitor is provided to filter out DC voltage components, and then a bandpass filter is provided to allow only noise electrical signals within a defined frequency range associated with the generation of the arc in the DC grid to pass toward the detector unit.

10. The method according to claim 1, wherein the detector unit is configured to further monitor for an insulation fault between the voltage terminal of the DC grid and the protective earth.

11. The detector unit, DC bus voltage and A DC bus ripple voltage usable for arc noise detection, wherein a block capacitor is used to filter the DC voltage, and A first electrical voltage (Vi') related to the first electrical network connected to the protective earth, such as a resistor divider resistor network, The method according to claim 10, configured to measure a second electrical voltage (Vi'') associated with a second electrical network connected to the protective earth, such as another resistor divider network having the same high-voltage resistors as the first electrical network but different low-voltage resistors.

12. The method according to claim 11, wherein a switch is used, the switch being moved to a first state to connect a first electrical network, and the switch being moved to a second state to connect a second electrical network, the DC bus voltage, the first voltage (Vi'), and the second voltage (Vi'') are measured against the same reference voltage, for example, a negative voltage of the DC bus, and the insulation fault resistance is calculated based on the DC bus voltage, the first voltage (Vi'), and the second voltage (Vi'').

13. A system for detecting the occurrence of an arc in a DC grid having one or more connectable electrical devices, wherein the system includes at least one detector unit connectable to the DC grid, the detector unit is configured to measure an arc noise voltage superimposed on the DC grid voltage without direct measurement of the current flowing through the arc itself, the arc noise voltage is associated with the occurrence of the arc in the DC grid, and the system is configured to ensure a minimum impedance range within a predefined frequency range for each of the electrical devices connected to the DC grid. The minimum impedance compliance of the electrical device connected to the DC grid is A system that ensures compliance by determining compliance based on the characteristics of the device and / or by performing compliance measurements, or by connecting the electrical device to the DC grid via an electrical mounting unit configured to ensure the minimum impedance range within the predefined frequency range for the electrical device.

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