Method for arc detection and inverter for carrying out the method

Abstract

The right of protection describes a method for detecting an arc (50) in a DC circuit, having the following steps: - operating a DC / DC converter (21, 22) of a two-stage inverter (10) in a first operating mode (BM1) with a first intermediate circuit voltage (UZWK, 1) applied to a DC intermediate circuit (31), - checking values of current and / or voltage associated with a DC connection (11, 12) of the inverter (10) for the presence of an indication of an arc (50) in the first operating mode (BM1) of the DC / DC converter (21, 22), wherein, if the values of current and / or voltage indicate an arc (50), the DC / DC converter (21, 22) is operated in a second operating mode (BM2) with a second intermediate circuit voltage (UZWK, 2), which is greater than the first intermediate circuit voltage (UZWK, 1) and which is greater than or equal to the open-circuit voltage (ULL) of the DC source (60), and wherein the following is carried out in the second operating mode (BM2): - deactivating the DC / DC converter (21, 22) connected to the DC connection (11, 12) in the second operating mode (BM2) of the DC / DC converter (21, 22).

Description

[0001] ARC DETECTION METHOD AND INVERTER FOR IMPLEMENTING THE METHOD

[0002] Technical area

[0003] The application relates to a method for detecting an arc in a DC circuit, in particular a DC circuit formed between a DC source and a connected inverter, possibly also including the DC source and parts of the inverter. The application further relates to an inverter designed to implement the method.

[0004] State of the art

[0005] Under certain conditions, arcs can form during operation of electrical systems. This is particularly the case with systems that operate at high voltages and / or high currents, such as photovoltaic (PV) systems. If the arcs go undetected, they can lead to fires that can damage not only the affected electrical system but also its surroundings and possibly even people. Arcs are particularly critical in direct current (DC) circuits because, unlike alternating current (AC) circuits, these circuits do not usually have a zero crossing of the electrical voltage and / or current during operation, which can lead to the arc being extinguished. For this reason, a method for detecting and, if necessary, extinguishing an arc in DC circuits is desired.

[0006] Documents WO 2021 / 144434 A1 and DE 10 2020 100838 B4 each disclose a method for detecting an arc in a photovoltaic (PV) system having a DC load, a DC source, and a circuit arrangement arranged between the DC source and the DC load. A power flow between the DC source and the DC load at an output of the circuit arrangement is cyclically interrupted by means of the switching unit, so that the power flow is enabled in an active time window with the first time duration and suppressed in a deactive time window with the second time duration. In the method, a current and / or a voltage is detected in two consecutive active time windows. By comparing the detected current and / or voltage values ​​from the active time window with the corresponding detected values ​​from the previous active time window, it can be concluded that an arc has occurred.A similar method for arc detection is also disclosed in WO 2021 / 144462 A1.

[0007] The known methods can be advantageously used in a PV system, particularly when it has a two-stage inverter with a boost-operating DC / DC converter and a downstream DC / AC converter. However, the use of this method also has disadvantageous effects. Firstly, the constant cyclical interruption of the power flow is associated with a certain, albeit limited, loss of yield. Secondly, it is necessary that a voltage in a direct current (DC) intermediate circuit always reaches or exceeds an open-circuit voltage of the DC source (in this case: the PV string), which otherwise does not necessarily have to be the case. When using the method in conjunction with a multi-string inverter, it is even necessary, or at least advantageous, that the voltage of the DC intermediate circuit is above the open-circuit voltage of each of the connected PV strings.Therefore, the inverter components connected to the DC link are always subjected to a higher voltage and therefore age faster than would be the case without the process. However, the higher DC voltage at the DC link also results in increased conversion losses within the DC / DC converter and the DC / AC converter, resulting in a certain loss of yield.

[0008] The document DE 10 2014 204253 B4 discloses a device for detecting a serial arc in an electrical system, which comprises an electrical DC voltage source and an inverter connected to the DC voltage source. A monitoring unit of the device is configured to monitor an electrical voltage for voltage changes and / or an electrical current for current changes in the electrical system. An evaluation unit of the device is configured to evaluate the detected voltage and current changes to detect the serial arc. A determination unit of the device serves to determine whether a spontaneous change in a current intended operating state exists, in which both the electrical voltage and the electrical current are reduced.

[0009] Document EP 3783762 A1 discloses a method for protecting an electrical network against direct current arcs. The electrical network comprises a direct current supply system, an alternating current system, and an inverter arranged between the direct current supply system and the alternating current system. The method comprises detecting a direct current arc in the direct current supply system and performing an arc extinguishing process in which the inverter is controlled to change the voltage at its input.

[0010] Task

[0011] The object of the application is to provide a method for detecting and extinguishing an arc that prevents, or at least reduces, the aforementioned disadvantages. Furthermore, the application aims to provide an inverter suitable for implementing the method.

[0012] Solution

[0013] The object of providing a method of the type mentioned above is achieved by a method having the features of independent patent claim 1. The object of providing an inverter for implementing the method is achieved by an inverter having the features of independent claim 13. Advantageous embodiments of the method are recited in claims 2 to 12. Advantageous embodiments of the inverter are recited in claims 14 to 18.

[0014] Description

[0015] A two-level inverter has a DC / DC converter and a DC / AC converter. The DC / DC converter is arranged between a DC terminal of the inverter and the DC / AC converter and is connected to the DC / AC converter via a DC intermediate circuit. A DC source is connected to the DC terminal. A DC circuit has the DC source connected to the DC terminal and the DC / DC converter connected to the DC terminal. A method for detecting an arc in the DC circuit comprises: i. operating the DC / DC converter in a first operating mode BM1 with a first intermediate circuit voltage applied to the DC intermediate circuit; ii. checking current and / or voltage values ​​assigned to the DC terminal of the inverter for the presence of an indication of an arc in the first operating mode of the DC / DC converter; iii.wherein, if the current and / or voltage values ​​indicate an arc, the DC / DC converter is operated in a second operating mode with a second intermediate circuit voltage, wherein the second intermediate circuit voltage is greater than the first intermediate circuit voltage and the second intermediate circuit voltage is greater than or equal to the open circuit voltage of the DC source, and wherein the following steps iv) - vi) are carried out in the second operating mode: iv. Deactivating the DC / DC converter connected to the DC terminal in the second operating mode of the DC / DC converter, v. Re-checking the current and / or voltage values ​​associated with the DC terminal for the presence of further indication of an arc in the second operating mode of the DC / DC converter, vi. Signaling an arc if the re-checking of the current and / or voltage values ​​associated with the DC terminal in the second operating mode also indicates an arc.

[0016] In the second operating mode, the DC / DC converter is operated with an intermediate circuit voltage that matches or exceeds the open-circuit voltage of the DC source located in the same DC circuit. The DC / DC converter is typically a boost converter designed to step up a DC voltage applied to the DC terminal of the inverter to an intermediate circuit voltage applied to the DC link. The voltage conditions at the DC / DC converter are therefore such that it is possible to interrupt the power flow of the DC source by deactivating the DC / DC converter. Such an interruption of the power flow is desirable for treating an arc, as this not only allows any arc present in the DC circuit to be detected but can also advantageously be extinguished.This treatment can be enabled by the method, in particular the method steps iv) and v) that occur at the second intermediate circuit voltage. Such a voltage ratio is not guaranteed in the first operating mode; therefore, advantageous treatment of an arc cannot be ensured in the first operating mode. In contrast to the second operating mode, interruption of the power flow by deactivating the DC / DC converter is not guaranteed in the first operating mode of the DC / DC converter.

[0017] A benefit of this method is that the DC / DC converter is only deactivated when the higher second intermediate circuit voltage is present at the DC link. This voltage is higher than the open-circuit voltage of the DC source. This allows for an interruption of the power flow and prevents unwanted reversals of the inverter's power flow.

[0018] In the first operating mode, which corresponds to normal operating mode, an interruption of the power flow from the DC source by deactivating the DC / DC converter is not guaranteed. This is a consequence of the voltage conditions at the DC / DC converter, which operates in a step-up mode towards the DC intermediate circuit. Specifically, if the first intermediate circuit voltage falls below the open-circuit voltage of the DC source, the voltage of the DC source would rise upon deactivation of the DC / DC converter. When the voltage of the DC source reaches or (slightly) exceeds the value of the first intermediate circuit voltage, an uncontrollable power flow into the DC intermediate circuit would begin, which would persist even if the DC / DC converter was deactivated.In the second operating mode, however, due to the voltage ratios of the DC voltages applied to the DC connection on the one hand and to the DC intermediate circuit on the other hand, an interruption of the power flow of the DC source can be ensured by deactivating the DC / DC converter.

[0019] When the DC / DC converter is deactivated in the second operating mode, it is possible that the power flow P is interrupted anywhere in the DC circuit, i.e. along the entire path between the DC source and a connection of the DC / DC converter facing the DC link. However, this is not absolutely necessary. Rather, it is sufficient if the power flow is only interrupted along a section between the DC source and the DC link connection of the DC / DC converter. In concrete terms, for example, if the power flow is only interrupted along a section between the DC source and the DC link connection of the DC / DC converter, decaying charging processes of capacitances present there can still occur in the remaining section of the DC circuit.However, by suppressing the power flow along one section of the DC circuit, the power flow along the remaining section of the affected DC circuit is at least largely reduced. This is sufficient to perform the desired treatment of any arc that may be present in the DC circuit.

[0020] The DC / DC converter is therefore operated in the first operating mode with the first intermediate circuit voltage applied to the DC intermediate circuit, and in the second operating mode with the second intermediate circuit voltage applied to the DC intermediate circuit, which is greater than the first intermediate circuit voltage and greater than or equal to the open circuit voltage of the DC source. In the second operating mode, the DC / DC converter is deactivated. Deactivating the DC / DC converter interrupts the power flow between the DC connection and the AC connection. Deactivating the DC / DC converter simultaneously causes a current decrease in the DC circuit, which also affects any arc that may be present there. This leads to a current value in the DC circuit below which is sufficient to maintain the arc, so that any arc that may be present there is interrupted or extinguished.At the same time, current and / or voltage values ​​at the DC connection can be recorded even when the power is interrupted and / or the DC / DC converter is deactivated. These re-recorded values ​​can then provide further information about the presence of an arc.

[0021] At the same time, the method enables the inverter to be operated continuously for an extended period with the DC / DC converter in the first operating mode. This has the advantage that the first intermediate circuit voltage can be lower, thus resulting in fewer losses. The higher second intermediate circuit voltage can only be set when there is an initial indication of an arc in the DC circuit. This reduces power loss and increases the service life of the components. The period during which the DC / DC converter is operated in the first operating mode can typically range from a few minutes to a few hours. It is also possible that if there is no initial indication of an arc, the DC / DC converter will only operate in the first operating mode or not in the second operating mode for a day, or even several days.The inverter is designed to convert electrical DC power absorbed via the DC connection into AC power and output it via an AC connection. The inverter converts DC power provided by the DC source via the DC connection. The DC / AC converter is located between an AC connection of the inverter and the DC / DC converter. The DC / AC converter is connected to the DC / DC converter via the DC intermediate circuit.

[0022] In one embodiment of the method, the DC / DC converter is operated in the first operating mode with an intermediate circuit voltage that is below the open-circuit voltage of the DC source located in the same DC circuit. The power flow of the DC source cannot therefore be interrupted by deactivating the DC / DC converter.

[0023] In one embodiment of the method, during the check in the first operating mode of the DC / DC converter, it is determined whether the current and / or voltage values ​​exhibit unexpected values, or whether the temporal changes in current and / or voltage exhibit unexpected values. If such unexpected values ​​occur, this is the first indication of an arc. When the first indication of an arc is present, the DC / DC converter transitions to the second operating mode. In the second operating mode, the voltage at the DC intermediate circuit is set to the second intermediate circuit voltage, which is greater than the first intermediate circuit voltage.

[0024] The indication of an arc can be determined, for example, by comparing the current and / or voltage values ​​with the characteristic curve behavior of the DC source, e.g., a PV system. Furthermore, the formation and extinction of an arc are usually accompanied by a sudden change in the current and / or voltage. Such jumps in the current and / or voltage, which are characteristic of an arc, would therefore be reflected, in particular, in unexpected values ​​in the temporal changes of the current and / or voltage. Examples of the detection of such indications are described, for example, in EP2729821 B1.

[0025] In one embodiment of the method, during the recheck in the second operating mode of the DC / DC converter, it is determined whether the current assigned to the DC terminal exhibits an abrupt current drop when the DC / DC converter is deactivated. As also described in WO 2021 / 144462 A1, deactivating the DC / DC converter leads to a decrease in the current in the DC circuit. If the decrease in current extinguishes an existing arc, this is associated with an abrupt current drop. Therefore, if the current value exhibits such an abrupt current drop, this is further indication of an arc.

[0026] In one embodiment of the method, operating the DC / DC converter in the second operating mode comprises reactivating the DC / DC converter, wherein the reactivation occurs after a period of time has elapsed, which begins with the previous deactivation of the DC / DC converter. This has the advantage that any arc that may be present can be extinguished by deactivating the DC / DC converter, and at the same time, the behavior of the inverter after reactivation in the second operating mode of the DC / DC converter can be examined. In particular, the current values ​​and / or voltage values ​​at the DC terminal can be recorded in the reactivated state and checked for further indications of an arc.

[0027] In one embodiment of the method, during the retest in the second operating mode of the DC / DC converter, the current and / or voltage values ​​are determined both before the DC / DC converter is deactivated and after the DC / DC converter is reactivated. The values ​​determined during the retest after the DC / DC converter is reactivated are compared with the values ​​determined before the DC / DC converter is deactivated. An indication of an arc can be obtained from the comparison.

[0028] In one embodiment of the method, an indication of an arc is present during the renewed check in the second operating mode of the DC / DC converter if the comparison shows that the values ​​determined after the DC / DC converter has been reactivated differ by a predefinable threshold value from the values ​​determined before the DC / DC converter has been deactivated.

[0029] It is within the scope of the invention that, in the second operating mode, the reactivation of the DC / DC converter, as well as the deactivation of the DC / DC converter, occurs not only once, but multiple times and sequentially. In this case, the current values ​​and / or voltage values ​​at the DC terminal can be recorded in a reactivated state that occurs before the DC / DC converter is deactivated. These values ​​can be compared with the current values ​​and / or voltage values ​​at the DC terminal recorded when the DC / DC converter is reactivated after its deactivation in order to check whether further indications of an arc are present.

[0030] In the activated phases of the DC / DC converter, current values ​​and / or voltage values ​​are detected. Between the activated phases there is a phase in which the DC / DC converter was deactivated and which may, for example, have had an influence on any arc present in the DC circuit, e.g. by extinguishing any arc that may have been present there. This means that further evidence can be obtained if, for example, the current values ​​detected in two consecutive activated phases differ from one another by more than a predefined threshold. Alternatively or cumulatively, further evidence can also be obtained if, for example, voltage values ​​detected in two consecutive activated phases differ from one another by more than a predefined threshold.

[0031] In one embodiment of the method, the DC / DC converter is then operated again in the first operating mode with the first intermediate circuit voltage if, upon renewed checking of the current and / or voltage values ​​assigned to the DC connection in the second operating mode of the DC / DC converter, there is no further indication of an arc. In the first operating mode, the DC / DC converter is operated with the first intermediate circuit voltage, which is lower than the second intermediate circuit voltage. This allows the inverter to be operated again with the first intermediate circuit voltage, which has lower losses and is gentler on the components. The second intermediate circuit voltage can only be set for a limited time. In this way, the method steps can be repeated again, starting with method step i) and the first intermediate circuit voltage.When repeating the method steps, the first intermediate circuit voltage can be the same value that existed before the DC / DC converter was switched to the second operating mode. However, this is not mandatory. Rather, the first intermediate circuit voltage can also differ from that which existed before the DC / DC converter was switched to the second operating mode. In one embodiment of the method, the DC source comprises a photovoltaic string or a battery. Furthermore, an AC grid can be connected to the AC connection, into which electrical power from the DC source can be fed via the inverter.

[0032] In one embodiment of the method, the inverter is designed as a multi-string inverter with multiple DC connections. Each DC connection is connected to the DC intermediate circuit via a separate DC / DC converter. The DC / DC converters are connected in parallel to one another to the same DC intermediate circuit. One advantage of a multi-string inverter is that the DC sources connected to the DC connections are decoupled from one another via the DC / DC converters assigned to the DC connections and, in particular, can be operated at different voltages. The method is carried out, for example, for one of the DC connections of the inverter. The method can therefore be carried out at just one of the multiple DC connections of the multi-string inverter.For example, in a hybrid inverter where the DC sources include batteries, the procedure may be performed for the DC circuits that have a PV generator and not, for example, for those DC circuits that have only a battery.

[0033] The respective operating mode of each DC / DC converter refers to a combination of DC / DC converter and DC link. It can vary for different DC / DC converters in an inverter. If multiple DC / DC converters are connected in parallel within an inverter and connected to the same DC link, they operate with the same DC link voltage. However, since the voltage on the other side of the DC / DC converter is influenced by the connected DC source, this can correspond to different operating modes.For example, it is possible that one or some of the DC / DC converters of the multi-string inverter are operating in a second operating mode at the first intermediate circuit voltage due to a relatively low open-circuit voltage of their associated DC source, while others of the DC / DC converters are operating in the first operating mode at the first intermediate circuit voltage due to a higher open-circuit voltage of their connected DC source. Taking the above into account, it is therefore possible that certain constellations exist in a multi-string inverter that do not allow all process steps to be carried out by each of the DC / DC converters. Nevertheless, even in a multi-string inverter there is usually one, and often several, DC / DC converters or DC connections at which the process can be carried out simultaneously.Therefore, in embodiments, the method is performed for a plurality of the DC terminals and optionally for each of the DC terminals. If, due to an indication of an arc at one of the DC terminals, one of the DC / DC converters is already operating in the second operating mode, method steps i) and ii) for the remaining DC terminals for which the method is performed are also performed in the second operating mode of the respective DC / DC converters at the second intermediate circuit voltage.

[0034] In one embodiment of the method, the multi-string inverter can have one or more DC terminals, each connected to a DC source whose open-circuit voltage is already less than or equal to the first intermediate circuit voltage. Therefore, the DC / DC converter(s) is / are capable of interrupting the power flow at its respective assigned DC terminal upon deactivation, even at the first intermediate circuit voltage. Therefore, these DC / DC converters are already in the second operating mode at the first intermediate circuit voltage, in which an interruption of the power flow is ensured by deactivating the corresponding DC / DC converter.In this case, it is not necessary to put the DC / DC converter(s) in question into their second operating mode by increasing the intermediate circuit voltage from the first intermediate circuit voltage to the larger second intermediate circuit voltage, since they are already in their second operating mode at the first intermediate circuit voltage, which ensures an interruption of the power flow by deactivation.

[0035] In one embodiment of the method, the first intermediate circuit voltage is lower than the open-circuit voltage of a DC source connected to the inverter, optionally also lower than the open-circuit voltage of several or each of the DC sources connected to the inverter. This enables low-loss operation of the inverter. The described method also avoids deactivating DC / DC converters at the first intermediate circuit voltage, i.e., in the first operating mode.

[0036] A two-stage inverter according to the invention has the DC connection for connecting the inverter to the DC source and the AC connection for connecting the inverter to the AC grid. The two-stage inverter further has the DC / AC converter connected to the AC connection and the DC / DC converter connected to the DC connection, which is connected to the DC / AC converter via the DC intermediate circuit. The two-stage inverter further has a control unit designed to control the inverter and configured to operate the inverter in a state connected to the AC grid and the DC source according to the described method.

[0037] In one embodiment, the inverter is designed as a multi-string inverter with a plurality of DC terminals for connecting a respective DC source. Each DC terminal is assigned a respective DC / DC converter. The multiple DC / DC converters are connected in parallel to one another via the common DC link to the DC / AC converter. The inverter is designed to perform the method for one or more of the DC terminals, optionally for each of the DC terminals.

[0038] The described inverter can be designed as a bidirectional inverter with regard to its power flow. A bidirectional inverter allows power to flow in both directions, i.e. from the DC terminal(s) to the AC terminal and vice versa. In a multi-string inverter, one or more DC terminals can be designed for bidirectional operation, while one or more of its DC terminals are designed for unidirectional operation. For this purpose, one or more of the DC / DC converters can each be designed as a bidirectional DC / DC converter, while one or more of its DC terminals can each be designed as a unidirectional DC / DC converter. The DC / AC converter of the multi-string inverter can be designed as a unidirectional DC / AC converter or as a bidirectional DC / AC converter.In one embodiment, the described inverter may comprise one or more elements from the following group: a battery inverter having one or more DC terminals each designed to connect a battery; a photovoltaic (PV) inverter having one or more DC terminals each designed to connect a PV string; a hybrid inverter having one or more DC terminals each designed to connect a battery and one or more DC terminals each designed to connect a PV string.

[0039] In one embodiment, the inverter has a communication interface and / or a visual and / or acoustic alarm device and / or an electrical signal output for signaling the detected arc. The detected arc can thus be signaled visually and / or acoustically. Alternatively or additionally, the detected arc can be signaled via the communication interface to a more remote location, e.g., to the inverter operator.

[0040] In one embodiment, the control unit is designed to permanently deactivate the inverter upon detection of an arc, or to permanently deactivate only the DC terminal at which the arc was detected. If the DC terminal is permanently deactivated, only the power flow between the respective DC terminal and the AC terminal of the inverter is interrupted. If the inverter is permanently deactivated, the power flow between each of its DC terminals and the AC terminal is interrupted.

[0041] Permanent deactivation of the inverter after a detected arc can, in particular, mean deactivation of the inverter for a period of time that is greater than the deactivation of the DC / DC converter or the DC / DC converter in the second operating mode. Permanent deactivation can mean that the inverter is deactivated until a waiting period predefined by a standard, for example, several minutes, in particular 5 minutes, has elapsed. Alternatively or additionally, permanent deactivation can mean that the inverter is or remains deactivated until a qualified electrician has verified that the system is in proper working order and acknowledges this. In this way, a qualified electrician can be given the opportunity to identify and, if necessary, repair any damage to the DC circuit caused by the detected arc.In contrast, the deactivation of the DC / DC converter(s) in the second operating mode, which is performed for the purpose of detecting and extinguishing any arc that may be present, only lasts for a short period of time. This period is typically less than 1 second, and advantageously less than 0.1 second.

[0042] The described method and the described inverter make it possible to detect arcs in good time and extinguish them if necessary. This can prevent damage caused by arcs. Such damage can cause considerable damage to electrical systems, which can, for example, lead to a fire in the electrical system or in the building containing the system. Personal injuries are also possible. For this reason, the detection of an arc is an advantage in electrical systems. This is particularly true for electrical systems with a DC circuit, since in a DC circuit, unlike an AC circuit, there is usually no zero crossing of an electrical voltage that can extinguish a burning arc, or at least facilitate its extinguishing.

[0043] Typically, two different types of arcs are distinguished. A parallel arc occurs when there is a contact fault, for example, when a cable or plug comes loose, but the contacts are so close that a high electric field strength is present locally in the gap between the contacts. Another example of a parallel arc is a switching arc that occurs between the contacts of a relay during a switching operation. Parallel arcs are less common and occur, for example, when the positive and negative wires of an electrical system are run close together and their insulation becomes damaged. Here, too, a high field strength can be present locally between the damaged conductors.

[0044] The described method and inverter can be used in particular for the detection of light arcs. Brief description of the figures

[0045] The application is illustrated below with the help of figures.

[0046] Fig. 1 shows a first embodiment of an inverter according to the invention within a PV system;

[0047] Fig. 2 shows a second embodiment of an inverter according to the invention within a PV system;

[0048] Fig. 3a is a flowchart of a first embodiment of a method according to the invention for detecting an arc;

[0049] Fig. 3b is a flowchart of a second embodiment of a method according to the invention for detecting an arc.

[0050] The same reference numerals are used throughout the figures for identical or similar elements. The illustrations in the figures may not be to scale.

[0051] Figure description

[0052] Fig. 1 schematically shows a first embodiment of a PV system 100 with a first embodiment of an inverter 10. The inverter 10 is designed as a two-stage inverter 10. A first stage comprises a DC / DC converter 21, in particular a DC / DC converter that boosts toward a DC / AC converter 30. A second stage comprises the DC / AC converter 30.

[0053] A DC connection 11 of the inverter 10 has two input connections 11.1, 11.2, via which a DC source 60 can be connected to the inverter 10. An AC network 40, for example a public supply network, can be connected to the inverter 10 via an AC connection 15 of the inverter 10. The inverter 10 is designed to transfer electrical power from the DC connection 11 to the AC connection 15. In this case, direct electrical power is converted into alternating electrical power, which is suitable for being fed into the AC network 40. Optionally, the inverter 10 can also be designed to transfer electrical power from the AC connection 15 to the DC connection 11, wherein alternating electrical power is converted into direct electrical power. The AC network 40 can be designed as a single-phase or multi-phase, e.g. three-phase, AC network 40.The AC connection 15 of the inverter 10 can be single-phase and have a phase conductor connection and a neutral conductor connection. Alternatively, it can also be multi-phase and have several, for example, two or three, phase conductor connections and optionally a neutral conductor connection.

[0054] The DC / DC converter 21 is connected to the DC terminal 11. The DC / DC converter 21 is connected to the DC / AC converter 30 via a DC intermediate circuit 31. The DC / AC converter 30 is connected to the AC terminal 15 of the inverter 10. The inverter 10 has a control unit 35 that controls the inverter 10. In particular, the control unit 35 is designed to control power semiconductor switches (not explicitly shown in Fig. 1) of the DC / DC converter 21 and the DC / AC converter 30.

[0055] The DC intermediate circuit 31 can have an electrical energy storage device, e.g., a capacitor for storing electrical charge. An intermediate circuit voltage UZWK is applied to the DC intermediate circuit 31.

[0056] The DC source 60 can comprise at least one PV string 1 or a parallel connection of several PV strings 1. Alternatively, the DC source 60 can comprise at least one battery 2 or a parallel connection of several batteries 2. A bidirectional inverter with a bidirectional DC / DC converter 21 and a bidirectional DC / AC converter 30 is particularly advantageous when the DC source 60 comprises a battery 2.

[0057] A DC circuit of the PV system 100 includes the DC source 60 connected to the DC terminal 11 and the DC / DC converter 21 connected to the DC terminal 11. In Fig. 1, an arc 50 is shown as an example in the DC circuit of the PV system 100.

[0058] A method for detecting the arc 50 in the DC circuit comprises: i. Operating the DC / DC converter 21 in a first operating mode BM1 with a first intermediate circuit voltage UZWK=UZWK,1 applied to the DC intermediate circuit 31; ii. Checking the current and / or voltage values ​​assigned to the DC terminal 11 of the inverter 10 for the presence of an indication of an arc 50 in the first operating mode BM1 of the DC / DC converter 21; iii. wherein, when the values ​​of current and / or voltage indicate an arc 50, the DC / DC converter 21 is operated in a second operating mode BM2 with a second intermediate circuit voltage UZWK=UZWK,2, wherein the second intermediate circuit voltage UZWK,2 is greater than the first intermediate circuit voltage UZWK,1 and the second intermediate circuit voltage UZWK,2 is greater than or equal to an open circuit voltage ULL of the DC source 60, and wherein in the second operating mode BM2 the following steps iv) - vi) are carried out: iv.Deactivating the DC / DC converter 21 connected to the DC terminal 11 in the second operating mode BM2 of the DC / DC converter 21, v. Re-checking the current and / or voltage values ​​assigned to the DC terminal 11 for the presence of a further indication of an arc 50 in the second operating mode BM2 of the DC / DC converter 21, vi. Signaling an arc 50 if the re-checking of the current and / or voltage values ​​assigned to the DC terminal 11 in the second operating mode BM2 also indicates an arc 50.

[0059] The control unit 35 has a processor, memory, and interfaces. The control unit 35 is designed to execute the described method and operate the inverter 10 according to the method.

[0060] In step ii), for example, there is an indication of an arc 50 if the values ​​of current and / or voltage have unexpected values ​​and / or if the temporal changes of current and / or voltage have unexpected values.

[0061] In step v), for example, a further indication is present if the current assigned to the DC terminal 11 exhibits an abrupt drop in current when the DC / DC converter 21 is deactivated. Alternatively, the DC / DC converter 21, 22 assigned to the DC terminal 11, 12 potentially affected by the arc can be reactivated. Current and / or voltage values ​​can be detected upon reactivation of the DC / DC converter 21, 22 and compared with their respective corresponding values ​​determined before the DC / DC converter 21, 22 was deactivated. This comparison can also be used as a further indication of the arc 50.

[0062] Fig. 2 schematically shows a second embodiment of the PV system 100 with a second embodiment of the inverter 10. The inverter 10 is designed as a two-stage multi-string inverter 10. A first stage has, for example, two DC / DC converters 21, 22, and a second stage has the DC / AC converter 30.

[0063] The DC connection 11 of the inverter 10 has two input connections 11.1, 11.2, via which a DC source 60 can be connected to the inverter 10. A further DC connection 12 of the inverter 10 has two input connections 12.1, 12.2, via which a further DC source 60 can be connected to the inverter 10. The AC grid 40, for example a public supply grid, can be connected to the inverter 10 via the AC connection 15 of the inverter 10. The inverter 10 is designed to transfer electrical power from each of the DC connections 11, 12 to the AC connection 15. In this case, direct electrical power is converted into alternating electrical power, which is suitable for being fed into the AC grid 40.For one or more of the DC connections 11, 12, and optionally also for each of the DC connections 11, 12, the inverter 10 can additionally be designed to transfer electrical power from the AC connection 15 to the respective one of the DC connections 11, 12, wherein alternating electrical power is converted into direct electrical power. The AC network 40 can be designed as a single-phase or multi-phase, e.g., three-phase, AC network 40. By way of example, Fig. 2 shows the AC connection 15 of the inverter 10 as a three-phase AC connection 15 to which a three-phase AC network 40 is connected. In general, however, the same applies to this second embodiment of the inverter 10 with regard to the number of phase conductors of the AC network and the design of the AC connection as already mentioned in Fig. 1, which is why reference is made here to the explanations there.

[0064] The DC / DC converter 21 is connected to the DC connection 11. The further DC / DC converter 22 is connected to the further DC connection 12. On their other sides, the two DC / DC converters 21, 22 are connected in parallel to one another to the DC intermediate circuit 31 and via the DC intermediate circuit 31 to the DC / AC converter 30. The DC / AC converter 30 is connected to the AC connection 15 of the inverter 10. The inverter 10 has a control unit 35 which controls the inverter 10. In particular, the control unit 35 is designed to control power semiconductor switches of the DC / DC converters 21, 22 and the DC / AC converter 30.

[0065] The second embodiment of the inverter 10 shown in Fig. 2 has a communication interface 36 connected to the control unit 35. A communicative connection of the control unit 35 to the outside is possible via the communication interface 36. The communication interface 36 can be configured, for example, for wired and / or wireless communication.

[0066] The DC intermediate circuit 31 can have an electrical energy storage device, e.g., a capacitor for storing electrical charge. The intermediate circuit voltage UZWK is applied to the DC intermediate circuit 31.

[0067] At least one PV string 1 or at least one battery 2 can be used as the DC source 60 connected to one of the DC terminals 11, 12. Although this is explicitly symbolized only for the DC terminal 12 in Fig. 2, it can also apply to the DC terminal 12. By way of example, in Fig. 2, a PV string 1 is connected to each of the DC terminals 11, 12.

[0068] The DC circuit of the PV system 100 comprises the DC sources 60 connected to the DC terminals 11, 12 and the DC / DC converters 21, 22 connected to the DC terminals 11, 12. In Fig. 2, an arc 50 at the DC terminal 11 is shown as an example in the DC circuit of the PV system 100.

[0069] The method for detecting the arc 50 in the DC circuit of the multi-string inverter 10 shown in Fig. 2 comprises: i. Operating the DC / DC converters 21, 22 in the first operating mode BM1 with a first intermediate circuit voltage UZWK=UZWK,1 applied to the DC intermediate circuit 31; ii. Checking the current and / or voltage values ​​assigned to the DC terminals 11, 12 of the inverter 10 for the presence of an indication of an arc 50 in the first operating mode BM1 of the DC / DC converters 21, 22; iii.wherein, when the values ​​of current and / or voltage at at least one of the DC connections 11, 12 indicate an arc 50, both DC / DC converters 21, 22 are operated in the second operating mode BM2 with the second intermediate circuit voltage UZWK=UZWK,2, wherein the second intermediate circuit voltage UZWK,2 is greater than the first intermediate circuit voltage UZWK,1 and the second intermediate circuit voltage UZWK,2 is greater than or equal to each of the open-circuit voltages ULL of the DC sources 60, and wherein in the second operating mode BM2 the following steps iv) - vi) are carried out for that DC / DC converter 21, 22 for whose assigned DC connection 11, 12 the indication of the arc 50 was determined in ii): iv. Deactivating the DC / DC converter 21, 22 connected to the DC connection 11, 12 affected by the notice in the second operating mode BM2 of the DC / DC converter 21, 22, v.Rechecking the current and / or voltage values ​​assigned to the affected DC connection 11, 12 for the presence of a further indication of an arc 50 in the second operating mode BM2 of the DC / DC converter 21, 22, vi. Signaling an arc 50 if the rechecking of the current and / or voltage values ​​assigned to the affected DC connection 11, 12 in the second operating mode BM2 also indicates an arc 50.

[0070] The control unit 35 has a processor and a memory (not explicitly shown in Fig. 2). It is connected for control purposes to the DC / DC converters 21, 22, the DC / AC converter 30, and the communication interface (symbolized by dashed lines in Fig. 2). The control unit 35 is designed to execute the described method and to operate the multi-string inverter 10 according to the method. The signaling of the arc 50 can be performed, for example, via the communication interface 36.

[0071] In step ii), for example, an indication of an arc 50 exists if the current and / or voltage values ​​exhibit unexpected values, and / or if the temporal changes in current and / or voltage exhibit unexpected values. The DC terminal 11, 12 at which the unexpected values ​​occurred is then the DC terminal 11, 12 potentially affected by the arc 50.

[0072] In step v), for example, a further indication is present if the current assigned to the DC connection 11, 12 potentially affected by the arc 50 exhibits an abrupt current drop when the DC / DC converter 21, 22 is deactivated. Alternatively, the DC / DC converter 21, 22 assigned to the DC connection 11, 12 potentially affected by the arc 50 can be reactivated. In this case, current and / or voltage values ​​can be detected upon reactivation of the DC / DC converter 21, 22 and compared with their respective corresponding values ​​that were determined before the DC / DC converter 21, 22 was deactivated. This comparison can also be used as a further indication of the arc 50.

[0073] Fig. 3a shows a flowchart of a first embodiment of the method for detecting an arc. The method can be executed by one of the DC / DC converters 21, 22 or by both.

[0074] In step S1, the DC / DC converter 21, 22 is in the first operating mode BM1 or in the second operating mode BM2. In step S1, a check is made as to whether another DC / DC converter 21, 22 is in the second operating mode BM2 and still requires this second operating mode BM2. For example, operation of the other DC / DC converter 21, 22 in the second operating mode BM2 at the second intermediate circuit voltage UZWK,2 may still be required because an initial indication of an arc was previously detected at a DC connection 11, 12 assigned to it. If yes, the DC / DC converter 21, 22 is also operated in step S2 in the second operating mode BM2 with the second intermediate circuit voltage UZWK,2. If no, the DC / DC converter 21, 22 is operated in step S3 in the first operating mode BM1 with the first intermediate circuit voltage UZWK,1.

[0075] In step S4, a check is performed to determine whether an indication of an arc 50 occurs during operation in the first or second operating mode BM1, BM2. This check can be performed by monitoring current and / or voltage values ​​at the DC connection 11, 12. Unexpected current and / or voltage values ​​or unexpected temporal changes in current and / or voltage can be such a first indication of an arc 50 in the DC circuit connected to the respective DC connection 11, 12. To determine unexpected values, the determined values ​​can be checked, for example, to determine whether they lie within a predeterminable range.

[0076] If no first indication of the presence of an arc 50 is found in step S4, the method continues with step S1.

[0077] If step S4 reveals that a first indication of an arc 50 is present, then in step S5 the affected DC / DC converter 21, 22, which is located in the DC circuit with the indication of the arc 50, is operated in the second operating mode BM2 with the second intermediate circuit voltage UZWK,2. The second intermediate circuit voltage UZWK,2 is greater than or equal to the open-circuit voltage ULL of the DC source 60 that is located in the DC circuit with the first indication of the arc 50 and is connected to the affected DC / DC converter 21, 22.

[0078] In step S6, the affected DC / DC converter 21, 22 is deactivated. The affected DC / DC converter 21, 22 is the DC / DC converter 21, 22 located in the DC circuit with the reference to the arc 50.

[0079] In step S7, the affected DC source 60 is operated at idle or near idle. Near idle means that a current of the affected DC source 60 falls below a threshold value required to maintain an arc, so that any arc present in the DC circuit is extinguished. The DC source 60 comprises, for example, generators or sub-generators that generate electrical energy. These are operated at idle or near idle in step S7. The affected DC source 60 is the DC source 60 located in the DC circuit with the reference to the arc 50.

[0080] If, during idle operation of the affected DC source 60, a further indication of the arc 50 at the associated DC terminal 11, 12 is detected in step S8, the arc 50 is detected in step S9. If no further indication is detected in step S8, the method returns to step S1.

[0081] A further indication of an arc 50 can be, for example, an abrupt current interruption at the DC terminal 11, 12 in the DC circuit with the first indication of the arc 50. Thus, if both the first indication of an arc 50 from S4 and the further indication of an arc 50 from S8 are present, the arc 50 is detected in S9.

[0082] After the arc 50 is detected in S9, the arc 50 is then signaled in S10 and / or the DC connection 11, 12 affected by the arc 50 is permanently deactivated, and if necessary the inverter 10 is also permanently deactivated.

[0083] The arc 50 can be signaled acoustically and / or visually, for example. Alternatively or additionally, the arc 50 can be signaled via the communication interface 36, e.g., via data communication.

[0084] Fig. 3b shows a flowchart of a second embodiment of the method for detecting an arc 50. The method can be executed by one of the DC / DC converters 21, 22 or by both.

[0085] In step S11, the DC / DC converter 21, 22 is in the first operating mode BM1 or in the second operating mode BM2. In step S11, a check is carried out to determine whether another DC / DC converter 21, 22 is in the second operating mode BM2 and still requires this second operating mode BM2. For example, operation of the other DC / DC converter 21, 22 in the second operating mode BM2 at the second intermediate circuit voltage UZWK,2 may still be required because a first indication of an arc was previously detected at a DC connection 11, 12 assigned to it. If so, the DC / DC converter 21, 22 is operated in step S12 in the second operating mode BM2 with the second intermediate circuit voltage UZWK,2. If not, the DC / DC converter 21, 22 is operated in step S13 in the first operating mode BM1 with the first intermediate circuit voltage UZWK,1.

[0086] In step S14, a check is performed to determine whether a first indication of an arc 50 occurs during operation in the first or second operating mode BM1, BM2. This check can be performed by monitoring current and / or voltage values ​​at the DC connection 11, 12. Unexpected current and / or voltage values ​​or unexpected temporal changes in current and / or voltage can be such a first indication of an arc 50 in the DC circuit connected to the respective DC connection 11, 12. To determine unexpected values, the determined values ​​can be checked, for example, to determine whether they lie within a predeterminable range.

[0087] If no first indication of the presence of an arc 50 is found in step S14, the method continues with step S11.

[0088] If step S14 reveals that a first indication of the arc 50 is present, then in step S15 the affected DC / DC converter 21, 22, which is located in the DC circuit with the first indication of the arc 50, is operated in the second operating mode BM2 with the second intermediate circuit voltage UZWK,2. The second intermediate circuit voltage UZWK,2 is greater than or equal to the open-circuit voltage ULL of the DC source 60 that is located in the DC circuit with the first indication of the arc 50 and is connected to the affected DC / DC converter 21, 22.

[0089] In step S16, the affected DC / DC converter 21, 22 is deactivated. The affected DC / DC converter 21, 22 is the DC / DC converter 21, 22 located in the DC circuit with the reference to the arc 50.

[0090] In step S17, the affected DC source 60 is operated at idle, or at least near idle. Near idle means that a current of the affected DC source 60 falls below a threshold value required to maintain an arc, so that any arc present in the DC circuit is extinguished. The DC source 60 comprises, for example, generators or sub-generators that generate electrical energy. These are operated at idle or near idle in step S7. The affected DC source 60 is the DC source 60 that is located in the DC circuit with the reference to the arc 50.

[0091] In step S18, the affected DC / DC converter 21, 22 is then reactivated after a time period Δt. It is operated in the second operating mode BM2 with the second intermediate circuit voltage UZWK,2.

[0092] If, during operation in the reactivated state of the affected DC / DC converter 21, 22 in the second operating mode BM2, a further indication of the arc 50 at the associated DC terminal 11, 12 is detected in step S19, the arc 50 is detected in step S20. If no further indication is detected in step S19, the method returns to step S11.

[0093] The further indication can be determined, for example, from the fact that the current values ​​and / or voltage values ​​determined in step S18 differ from the current values ​​and / or voltage values ​​determined in step S15 at the affected DC terminal 11, 12 by at least a predetermined threshold value. Thus, if both the first indication from S14 and the further indication from S19 are present, the arc 50 is detected in S20.

[0094] After the arc 50 is detected in S20, the arc 50 is then signaled in S21 and / or the DC connection 11, 12 affected by the arc 50 is permanently deactivated and / or the inverter 10 is permanently deactivated.

[0095] The arc 50 can be signaled acoustically and / or visually, for example. Alternatively or additionally, the arc 50 can be signaled via the communication interface 36, e.g., via data communication.

[0096] List of reference symbols

[0097] 1 PV string

[0098] 2 batteries

[0099] 10 inverters

[0100] 11 DC connector

[0101] 11.1 , 11.2 Input connection

[0102] 12 DC connection

[0103] 12.1 , 12.2 Input connection

[0104] 15 AC connection

[0105] 21 DC / DC converters

[0106] 22 DC / DC converters

[0107] 30 DC / AC converters

[0108] 31 DC link

[0109] 35 Control unit

[0110] 36 Communication interface

[0111] 40 AC network

[0112] 50 arcs

[0113] 60 DC source

[0114] 100 PV systems

[0115] BM1 First operating mode

[0116] BM2 Second operating mode

[0117] S1 - S8 process step

[0118] S11 - S19 Process step

[0119] At duration

[0120] UZWK.1 , UZWK,2 intermediate circuit voltage

[0121] BM1 , BM2 operating mode

[0122] ULL open circuit voltage

Claims

Patent claims 1 . Method for detecting an arc (50) in a DC circuit, wherein the DC circuit has a DC source (60) connected to a DC terminal (11, 12) of a two-stage inverter (10) and a DC / DC converter (21, 22) of the inverter (10) connected to the DC terminal (11, 12), wherein the DC / DC converter (21, 22) is connected via a DC intermediate circuit (31) to a DC / AC converter (30) of the inverter (10), comprising the steps of: i) operating the DC / DC converter (21, 22) in a first operating mode (BM1) with a first intermediate circuit voltage (UZWK,1) applied to the DC intermediate circuit (31), ii) checking the DC terminal (11, 12) of the inverter (10) assigned values ​​of current and / or voltage for the presence of an indication of an arc (50) in the first operating mode (BM1) of the DC / DC converter (21, 22), iii) wherein, if the values ​​of current and / or voltage indicate an arc (50), the DC / DC converter (21,22) is operated in a second operating mode (BM2) with a second intermediate circuit voltage (UZWK,2) which is greater than the first intermediate circuit voltage (UZWK,1) and which is greater than or equal to an open-circuit voltage (ULL) of the DC source (60), and wherein in the second operating mode (BM2) the following steps iv) - vi) are carried out: iv) Deactivating the DC / DC converter (21, 22) connected to the DC connection (11, 12) in the second operating mode (BM2) of the DC / DC converter (21, 22), v) Re-checking the values ​​of current and / or voltage assigned to the DC connection (11, 12) for the presence of a further indication of an arc (50) in the second operating mode (BM2) of the DC / DC converter (21, 22), vi) Signaling an arc (50), even if the re-checking the values ​​of current and / or voltage assigned to the DC connection (11, 12) in the second operating mode (BM2) indicate an arc (50).

2. The method according to claim 1, wherein during the checking in the first operating mode (BM1) of the DC / DC converter (21, 22) it is determined whether the values ​​of current and / or voltage have unexpected values, or whether the temporal changes of current and / or voltage have unexpected values.

3. The method according to claim 1 or 2, wherein during the re-check in the second operating mode (BM2) of the DC / DC converter (21, 22) it is determined whether the current assigned to the DC terminal (11, 12) has an abrupt current drop when the DC / DC converter (21, 22) is deactivated.

4. The method according to claim 1 or 2, wherein the operation of the DC / DC converter (21, 22) in the second operating mode (BM2) includes a reactivation of the DC / DC converter (21, 22), wherein the reactivation takes place after the expiration of a time period (At) which begins with the deactivation of the DC / DC converter (21, 22).

5. The method according to claim 4, wherein during the re-checking in the second operating mode (BM2) of the DC / DC converter (21, 22), the values ​​of current and / or voltage are determined both before the deactivation of the DC / DC converter (21, 22) and after the re-activation of the DC / DC converter (21, 22), and wherein during the re-checking, the values ​​determined after the re-activation of the DC / DC converter (21, 22) are compared with the values ​​determined before the deactivation of the DC / DC converter (21, 22).

6. The method according to claim 5, wherein upon renewed checking in the second operating mode (BM2) of the DC / DC converter (21, 22), an indication of an arc is present if the comparison shows that the values ​​determined after the renewed activation of the DC / DC converter (21, 22) differ by a predeterminable threshold value from the values ​​determined before the deactivation of the DC / DC converter (21, 22).

7. Method according to one of the preceding claims, wherein when there is no indication of an arc when the values ​​of current and / or voltage assigned to the DC connection (11, 12) are checked again in the second operating mode (BM2) of the DC / DC converter (21, 22), the DC / DC converter (21, 22) is switched back to the first operating mode (BM1) with the first intermediate circuit voltage (UZWK, 1 ) which is lower than the second intermediate circuit voltage (UZWK, 2).

8. Method according to one of the preceding claims, wherein the DC source (60) comprises a photovoltaic string (1) or a battery (2).

9. Method according to one of the preceding claims, wherein the inverter (10) is designed as a multi-string inverter with a plurality of DC terminals (11, 12), each of which is connected to the common DC intermediate circuit (31) via a separate DC / DC converter (21, 22), and wherein the method is carried out for one of the DC terminals (11, 12) of the inverter (10).

10. The method according to claim 9, wherein the method is carried out for a plurality of the DC connections (11, 12), optionally for each of the DC connections (11, 12), and wherein if, due to an indication at one of the DC connections (11, 12), one of the DC / DC converters (21, 22) is already being operated in the second operating mode (BM2), the method steps i) and ii) for the remaining DC connections (11, 12) for which the method is carried out are also carried out in the second operating mode (BM2) of the respective DC / DC converters (21, 22) at the second intermediate circuit voltage (UZWK, 2).

11. Method according to claim 9 or 10, wherein one or more of the DC terminals (11, 12) of the inverter (10) are each connected to a DC source (60) whose open-circuit voltage (ULL) is less than or equal to the first intermediate circuit voltage (UZWK,1), wherein at the one or more DC terminals (11, 12) an interruption of the power flow of the DC source (60) connected thereto takes place by deactivating the relevant DC / DC converter (21, 22) at the first intermediate circuit voltage (UZWK,1).

12. Method according to one of the preceding claims, wherein the first intermediate circuit voltage (UZWK,1 ) is smaller than the open circuit voltage (ULL) of a DC source (60) connected to the inverter (10), optionally also smaller than the open circuit voltage (ULL) of several or each of the DC sources (60) connected to the inverter (10).

13. Two-stage inverter (10) comprising: a DC connection (11, 12) for connecting the inverter (10) to a DC source (60), an AC connection (15) for connecting the inverter (10) to an AC network (40), a DC / AC converter (30) connected to the AC connection (15), and a DC / DC converter (21, 22) connected to the DC connection (11, 12) and connected to the DC / AC converter (30) via a direct current (DC) intermediate circuit (31), a control unit (35) for controlling the inverter (10), characterized in that the control unit (35) is designed to operate the inverter (10) in a state connected to the AC network (40) and the DC source (60) according to the method according to one of the preceding claims.

14. Inverter (10) according to claim 13, characterized in that the inverter (10) is designed as a multi-string inverter with a plurality of DC connections (11, 12) for the respective connection of a DC source (60), wherein each DC connection (11, 12) is assigned a DC / DC converter (21, 22), and the plurality of DC / DC converters (21, 22) are connected in parallel to one another via the common DC intermediate circuit (31) to the DC / AC converter (30), and wherein the inverter (10) is designed to carry out the method at one or more of the DC connections (11, 12), optionally at each of the DC connections (11, 12).

15. Inverter according to claim 13 or 14, characterized in that the inverter (10) is designed as a bidirectional inverter with respect to its power flow.

16. Inverter (10) according to one of claims 13 to 15, characterized in that the inverter (10) comprises one or more elements from the following group: a battery inverter with one or more DC connections (11, 12) each designed to connect a battery (2); a photovoltaic (PV) inverter with one or more DC connections (11, 12) each designed to connect a PV string (1); a hybrid inverter having one or more DC terminals (11, 12) each designed for connecting a battery and one or more DC terminals (11, 12) each designed for connecting a PV string (1).

17. Inverter (10) according to one of claims 13 to 16, characterized in that the inverter (10) includes a communication interface (36) and / or a visual and / or acoustic alarm device and / or an electrical signal output for signaling a detected arc (50).

18. Inverter (10) according to one of claims 13 to 17, characterized in that the control unit (35) is designed to permanently deactivate the inverter (10) when an arc (50) is detected or to permanently deactivate only that DC connection (11, 12) at which the arc (50) was detected.

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