DC SWITCHGEAR WITH EARTH FAULT PROTECTION

Description

Beschreibung

[0001] The invention relates to a DC switching device with earth fault protection, in particular a DC switching device for coupling a DC load to a DC voltage source via a positive conductor and a negative conductor.

[0002] It is generally known from the prior art to use DC switching devices for electrically coupling DC loads to DC sources. Both a positive conductor and a negative conductor, via which the DC load is coupled to the DC source, can be routed through the DC switching device. Within the scope of the invention, the DC load does not have to be a single load, but can also be composed of a group of DC loads or be configured as a DC network with a plurality of DC loads operating across it.Such DC switching devices for electrically coupling DC loads to DC sources are becoming increasingly important, particularly at the factory level and / or in the implementation of smart grids. This is because a higher-level energy management system can be easily integrated to optimize the economic and energy efficiency of the electrically coupled DC network, and predefined current-voltage characteristics in the resulting DC devices can ensure immediate balancing of power demand and power supply. Furthermore, many components required for alternating current can be eliminated with direct current. The advantages of a direct current (DC) power supply for industrial plants are therefore obvious.Within the scope of the invention, a DC voltage load which can be electrically coupled to a DC voltage source can therefore in particular also form a logical unit and / or have components with strong functional dependencies on one another and / or contain intermediate circuit capacitances in order to keep switching frequency compensation processes between individual devices away from the DC voltage source or the DC supply, and / or via a DC voltage switching device to the.

[0003] The DC voltage source or the DC supply may be electrically coupled. EP3723223 A1 discloses such a DC voltage switch according to the preamble of claim 1.

[0004] Especially in network configurations where the earth potential is not isolated from the live conductors (e.g., TN networks), the fault location must be isolated from the rest of the network in the event of a ground fault. With sufficiently low impedance, a ground fault can, for example, lead to a ground fault current that causes an upstream fuse to blow.

[0005] The object of the invention is to provide a new and simple way of monitoring earth faults when electrically coupling a DC voltage load to a DC voltage source, which requires a small number of components

[0006] The solution according to the invention is provided by a DC switching device and a switching system with the features according to appended claims 1 and 9 respectively. Accordingly, a DC switching device for coupling a DC load to a DC voltage source via a positive conductor and a negative conductor is proposed, wherein the positive conductor and the negative conductor are guided through the DC switching device, wherein the DC switching device has a first switching element for coupling and uncoupling the DC load, which is a semiconductor-based, electronically controllable switching element integrated into the positive conductor or the negative conductor, as well as a fuse integrated in the respective other conductor and a sensor at least for detecting the current flow of the conductor in which the first switching element is integrated.Furthermore, the DC voltage switching device has an evaluation device connected to the sensor and the first switching element, which is configured to compare the detected current flow with a threshold value and to control the first switching element to decouple the DC voltage load when the threshold value is exceeded.

[0007] A key advantage of the invention is that even in the event of an earth fault, the fault location can be disconnected from the rest of the network very quickly, in particular within a few µs, so that the current to be disconnected does not become too high. The semiconductor switching element can therefore switch off the conductor in which it is integrated in just a few µs, thus isolating the DC voltage source from the fault location before the current becomes too high. Fuses with sufficient short-circuit strength are available, so that the conductor in which they are integrated can also be disconnected sufficiently quickly. If both the positive pole and the negative pole have a voltage relative to earth potential that would result in a very high fault current in the event of an earth fault, the DC switching device according to the invention has the option of safely disconnecting both the positive and negative branches even in the event of such a fault.Since a controllable semiconductor switching element is generally required in a branch (positive or negative) for operational switching anyway, this switching element can also be used for ground fault protection for this branch. This requires a sensor that at least detects the current flow in this conductor. The evaluation device, e.g., a µC (microcontroller), evaluates the sensor signal and deactivates the semiconductor switching element when the threshold value is exceeded. The switching element, the sensor, and the evaluation device thus together also form the ground fault protection for the corresponding conductor.

[0008] In the other branch, a fuse can be used for ground fault protection. Firstly, no additional semiconductor switching element is required for operational switching, which means that a current sensor in the branch containing the fuse is not absolutely necessary, and therefore no evaluation or control is required for this branch. Furthermore, the power loss of the fuse is significantly lower, which means that complex cooling, as is usually required for the semiconductor switching element, can be omitted. Accordingly, the use of a fuse also results in cost advantages.

[0009] Furthermore, such a DC switching device can be used to implement, in particular, a switching system in which the positive conductor and the negative conductor are connected to a rectified three-phase AC network or to a DC bus as a DC voltage source at an input of the DC switching device, and a DC voltage branch can be coupled to and uncoupled from the DC load at an output of the DC switching device via the positive conductor and the negative conductor.

[0010] In a first embodiment, the sensor according to the invention expediently has a sensor element arranged in series with the first switching element for detecting the current flow. In a supplementary or alternative embodiment, a sensor is arranged and configured to detect the current flow of both conductors, in particular for detecting a current flow forming the differential current or total current from the positive and negative conductors. When detecting a current flow or total current forming the differential current. In this embodiment, the sensor element arranged in series with the first switching element can therefore also be omitted and / or a sensor element connected in series for protection can also be present and / or the detection of a differential current or total current as a current flow can, for example, also be carried out by means of a sensor element that is configured to detect a magnetic field forming overall around the positive and negative conductors, such asin application No. BE2021 / 5520, filed by the applicant of the present application with the Belgian filing authority on July 5, 2021, entitled "Residual current monitoring for a DC switching device," which is therefore incorporated by reference with regard to the related disclosure. The term "difference," as used in the present description and claims, is understood to mean the difference in amount.

[0011] The invention will be described in more detail below with reference to the accompanying drawings using preferred embodiments, from which further features and advantages of the invention will become apparent. In the drawings: Fig. 1 shows a highly simplified first preferred embodiment of a DC switching device according to the invention, Fig. 2 shows a highly simplified second preferred embodiment of a DC switching device according to the invention, Fig. 3 shows a highly simplified further preferred embodiment of a first switching element which is constructed from two electronically controllable switching units connected in reverse series, Fig. 4 shows a highly simplified DC bus with positive and negative conductors as a DC voltage source with two DC branches which can be coupled to the DC bus by means of DC switching devices according to the invention, and Fig. 5 shows a highly simplified circuit diagram of a switching system according to the invention with a DC switching device and rectified three-phase AC network as a DC voltage source on the input side and connected DC load on the output side as well as with indicated earth fault from PE to the negative line at the device output.

[0012] The invention is described in more detail below with reference to the accompanying drawings using preferred embodiments.

[0013] In the Fign. 1 and 2 are shown in a highly simplified manner a first and a second preferred embodiment of a DC switching device according to the invention. In detail, Fign. 1 and 2Each of the drawings shows a DC switching device 100 which is configured to couple a DC load 200 to a DC voltage source 4 via a positive conductor 8 and a negative conductor 10. The positive conductor 8 and the negative conductor 10 are each routed through the DC switching device 100. By means of the DC switching device 100, a DC voltage branch 2 is essentially configured between the DC voltage source 4 and the DC load 200. The positive and negative conductors 8, 10 can also be arranged on a printed circuit board, i.e., in particular, be designed as conductor tracks. The DC switching device 100 comprises, i.e., contains a first switching element 101 for coupling and uncoupling the DC load 200, which is a semiconductor-based, electronically controllable switching element integrated into the positive conductor 8 or the negative conductor 10; and a fuse 103 integrated in the other conductor. Fig. 1 The semiconductor-based, electronically controllable switching element, additionally marked with "HS", is integrated into the positive conductor 8 and Fig. 2 into the negative conductor 10. Accordingly, Fig. 1 an additional fuse 103 marked "SI" in the negative conductor 10 and at Fig. 2 integrated into the positive conductor.

[0014] Furthermore, the DC voltage switching device 100 comprises a sensor 116, which is configured at least to detect the current flow of the conductor in which the first switching element 101 is integrated. Fign. 1 and 2 For this purpose, according to an expedient embodiment, the sensor 116 has a sensor element arranged in series with the first switching element 101 for detecting the current flow, i.e., the current flow of the conductor into which the first switching element 101 is also integrated. The sensor element detecting this current flow is additionally marked with "CS."

[0015] A sensor 116 and the first switching element 101 are connected to the Fign. 1 and 2 Finally, the evaluation device 118 of the DC switching device 100, marked with "Ctrl," is configured to compare the detected current flow with a threshold value and to actuate the first switching element 101 accordingly to decouple the DC load 200 when the threshold value is exceeded. The semiconductor-based switching element 101 is consequently switched off, and the DC load 200 is subsequently at least electrically decoupled and can no longer be operated via the DC voltage source 4. At least the first switching element 101, the fuse 103, and the evaluation device 118 can be contained in a common housing unit of the DC switching device 100, as in Fig. 1 indicated by the dashed outline, and in particular the fuse 103 can also be included in the DC switching device 100 in a replaceable or additional manner, so that it can be easily replaced in the event of "destruction."

[0016] Consequently, the DC switching device 100 according to the invention ensures the isolation of the fault location from the rest of the network in the event of an earth fault, particularly in network configurations in which the earth potential PE is not isolated from the active conductors, and it offers the possibility of safely isolating the fault in both the positive branch 8 and the negative branch 10.

[0017] The controllable semiconductor switching element in one of the conductors, i.e. in the positive or negative conductor, which is generally required anyway for operational switching, can switch off in a few µs and thus disconnect the DC voltage source 4 from the fault location before the current becomes too high. This semiconductor switching element is therefore expediently also used as the first switching element for the earth fault protection for this conductor, so that the separation can take place very quickly, i.e. in particular within a few µs, and the current to be switched off does not become too high. The current flow detected in relation to this conductor is evaluated by the evaluation device 118, which can contain, for example, a µC (microcontroller) or comparator circuit, and controls the first switching element 101, i.e. the semiconductor element, to decouple the DC voltage load when a threshold value is exceeded, i.e. switches it off.Together, the first switching element 101, the sensor 116 and the evaluation device 118 form the earth fault protection for the corresponding conductor.

[0018] In the other conductor, however, fuse 103 is used for earth fault protection. Fuses with sufficient short-circuit strength are available, which may react more slowly but can safely interrupt very high currents (e.g., even several 10 kA). The advantage is that no additional semiconductor switching element is required, and therefore no sensor is necessarily required to detect the current flow in the conductor into which the fuse is integrated. Related evaluation and control is also not absolutely necessary for this conductor. Furthermore, the power loss of the fuse is significantly lower, which eliminates the need for complex cooling, as is usually required for a semiconductor switching element. In any case, no additional controllable semiconductor switching element is required in the second conductor for operational switching. Accordingly, the use of a fuse also results in cost advantages.

[0019] In a variation to the Fig. 1 and 2 However, in the embodiments shown, the sensor element 116 arranged in series with the first switching element 101 could also be omitted, and the current flow of the conductor in which the first switching element 101 is integrated could be detected by means of a sensor system arranged and configured in a different way.

[0020] A useful possibility according to the invention, in addition to or as an alternative to a sensor element arranged in series with the first switching element 101, for detecting the current flow of the conductor in which the first switching element 101 is also integrated, consists in detecting the current flow of both conductors using a correspondingly arranged and configured sensor, i.e., in particular, detecting a current flow forming the differential current or sum current of the positive and negative conductors. As defined at the beginning, the term "difference," as used in the context of the present description and the claims, is to be understood as the difference in magnitude. If there is no fault current, i.e., in particular, no current flow to ground potential in the DC voltage branch, then the magnitudes of the currents in the positive and negative conductors are, in the optimal case, equal, i.e., the sum of the currents is equal to zero or the difference in magnitude is equal to zero.Consequently, in the event of an earth fault, a current flow of the conductor in which the first switching element 101 is integrated can also be (co-)detected by means of such a sensor.

[0021] For this purpose, according to a preferred embodiment, such a current flow can be detected by detecting a magnetic field that develops around the positive conductor 8 and the negative conductor 10. For this purpose, a sensor equipped with a Hall-effect sensor element can be used, in particular. For easy detection of the magnetic field that develops around these conductors, the positive conductor 8 and the negative conductor 10 can then, for example, be guided through a common through-opening of a ferrite core contained in the DC switching device, which is preferably split at one point and houses the sensor in the air gap consequently formed there. With the aid of such a ferrite core, the magnetic field lines can thus be expediently bundled and guided.For reasons of clarity, this useful possibility is not shown in detail in the figures, but reference is made to the disclosure of application No. BE2021 / 5520, filed by the applicant of the present application with the Belgian filing authority on 5 July 2021, entitled "Residual current monitoring for a DC switching device".

[0022] As in Fig. 3 shown in a very simplified way, can be modified to the Fign. 1 and 2A first switching element 101' may also be used, which comprises two electronically controllable switching units connected in series. In the case of such an anti-serial configuration, ie, in particular as a bidirectional switch, operation of the DC load, ie, the current flow required for this with a corresponding connection to the DC voltage source, is also fundamentally possible bidirectionally, and one of the anti-serially connected diodes of the semiconductor element can ensure the limitation of a respective current flow in one direction or the other.

[0023] The evaluation device 118 can have an analog circuit, a discrete circuit or preferably also a µC (microcontroller) for evaluating the detected current flow, ie in particular for comparing the detected magnetic field with a threshold value and for activating the at least one switching element 101. If, depending on the design and / or field of application, the current flow exceeds or falls below a predetermined threshold value, the switching element, ie for example the one according to Fig. 1 shown switching element 101 for decoupling the load 200 from the source 4 is activated accordingly, ie in particular switched off. The switching element for coupling and decoupling the DC load 200 can additionally also comprise a second and a third switching element 106, in particular a second and third electromechanical switching element, wherein one of the second and third switching elements 106 is integrated into the positive conductor 8 and the other into the negative conductor 10. In this way, in particular equally by means of the evaluation device 118, a galvanic decoupling of the load 200 from the source 4 can also be effected. For this purpose, the second and third switching elements 106 can consequently have relay contacts, in the Fign. 1 and 2 additionally marked with K1 or K2. However, such relay contacts are unsuitable for rapid disconnection, as the time until disconnection is in the ms range.

[0024] Consequently, if the current flow detected and evaluated by the evaluation device 118 exceeds a predetermined critical value, then, depending on the value exceeded and the specific design, the first switching element 101 or, additionally, the second and third switching elements 106 can be switched off by the evaluation device 118, thus electrically or galvanically decoupling the DC voltage branch from the DC voltage source 4. Furthermore, by switching off the second and third switching elements 106, the current flow is prevented in both directions, whereas switching off only the first switching element 101 prevents the current flow in only one direction. The second and third switching elements 106 thus always ensure reliable galvanic isolation of the DC output from the DC input.The evaluation device 118 is further preferably configured to take into account, at least for switching off the first switching element 101, when a current flow change rate predetermined by the threshold value is exceeded. In other words, alternatively or additionally, in particular to the current amplitude, the current flow change rate and / or the current direction can also be compared with a threshold value and, if exceeded, lead to the switching off of the first switching element (101). Expediently, during an evaluation against a threshold value, in particular in addition to a comparison of the current amplitude, a comparison of the current flow change rate and / or the current direction is also carried out and, if the threshold value is exceeded, leads to switching off.

[0025] In a useful development, the evaluation device 118 further comprises a signal output or a communication interface for outputting 119 a signal when the threshold value is exceeded and / or when the threshold value is not exceeded, but the detected current flow has a greater value in magnitude than a second threshold value that is smaller in magnitude than the threshold value. Thus, by comparing with a threshold value, it is extremely useful to take into account, for example, tolerable current changes, fluctuations, and / or losses during operation of the DC voltage load in a diverse and flexible manner.

[0026] Furthermore, the evaluation device 118 is expediently designed and configured not only to effect the decoupling of the DC voltage load 200 or the entire DC voltage branch 2 electrically or additionally also galvanically from the DC voltage source 4 by means of corresponding activation commands to the switching element or the switching elements, ie to switch it or them off, but also to effect the electrical and / or galvanic coupling of the DC voltage load 200 or the entire DC voltage branch 2 to the DC voltage source 4 by means of corresponding activation commands to the switching element or the switching elements, ie to switch it or them on.In particular, a command to the evaluation device 118 for effecting the switching on based thereon can, according to an expedient embodiment, also be received by the evaluation device 118, for example, via a communication interface as described above or via another input interface, in particular a digital input.

[0027] With a DC voltage switching device as described above in various embodiments, it is therefore also possible to implement, in particular, a switching system in which the positive conductor 8 and the negative conductor 10 are connected to the DC voltage source 4 at an input IN+, IN- of the DC voltage switching device 100, and a DC voltage branch can be coupled to and uncoupled from the DC voltage load 200 at an output OUT+, OUT- of the DC voltage switching device 100 via the positive conductor 8 and the negative conductor 10 (cf. Fig. 1 ).

[0028] As a rule, the DC voltage of the DC voltage source 4 is usually generated from a three-phase AC network with L1, L2, L3 by means of a rectification GR, whereby the rectification can be carried out actively with a power electronic circuit or passively with diodes. Fig. 5 shows a highly simplified circuit diagram of a switching system according to the invention with a DC switching device and rectified three-phase AC network as DC voltage source 4 on the input side IN+, IN- and connected DC voltage load 200 on the output side OUT+, OUT- as well as with indicated earth fault from PE to the negative line at the device output.

[0029] In Fig. 4 Based on this, a preferred switching system is outlined in a highly simplified manner, which has a first such DC switching device 100a, an input and an output, wherein the positive conductor and the negative conductor 10 input are connected to a DC voltage bus 4a as a DC voltage source and at the output via the positive conductor and the negative conductor a DC voltage branch 2a with a DC voltage load 200a can be coupled and uncoupled.

[0030] In accordance with the Fig. 2 further comprises at least one further such DC switching device 100b with an input and an output, wherein in this further DC switching device 100b the positive conductor 8 and the negative conductor 10 are also connected equally at the input to the DC bus 4a and at the output a further DC voltage branch 2b with a DC load 200b can be coupled and uncoupled via the positive conductor 8 and the negative conductor 10.

[0031] Taking into account the above description, the DC load does not have to be a single load, but can be composed of a group of DC loads or be designed as a DC network with a plurality of DC loads operating over it.

[0032] For the rapid decoupling of the DC voltage load or the DC voltage branch from the DC voltage source, in particular a DC voltage bus, a MOSFET ("metal-oxide-semiconductor field-effect transistor") or IGBT ("Insulated Gate Bipolar Transistor") is suitable in practical implementation for the semiconductor-based, electronically controllable switching element 101.

[0033] By means of the evaluation device 118 described above, it is therefore possible to determine, in particular, application-specifically and / or depending on the specific design Implement charging current limitation of connected DC loads, i.e. pre-charging of intermediate circuit capacitors of the connected loads to the input voltage level. Monitor various state variables, such as the input voltage, the output voltage, the load current, and leakage currents to PE (fault current). Switch off in the event of a fault, i.e. as soon as a state variable leaves the permissible range. Fault current shutdown, i.e. shutdown when the difference between the currents in the positive and negative conductors becomes too large, and / or rapid shutdown in the event of a short circuit on the output side. List of reference symbols

[0034] 2, 2a, 2b DC voltage branch 4 DC voltage source 4a DC voltage bus 8 Positive conductor 10 Negative conductor 100, 100a, 100b DC voltage switching device 101, 101' First switching element 103 Fuse 106 Second, third switching element 116 Sensor 118 Evaluation device 119 Output from signal output or communication interface 200, 200a, 200b DC voltage load

Claims

1. Direct voltage switching device (100) for coupling a direct voltage load (200) via a positive conductor (8) and negative conductor (10) to a direct voltage source (4), the positive conductor (8) and the negative conductor (10) being routed through the direct voltage switching device (100), comprising: - a first switching element (101, 101') for coupling and decoupling the direct voltage load (200), which is a semiconductor-based, electronically controllable switching element integrated in the positive conductor (8) or in the negative conductor (10); - a fuse (103) integrated in the respective other conductor; - a sensor (116), at least for detecting the current flow of the conductor in which the first switching element (101) is integrated; and - an evaluation device (118) connected to the sensor (116) and the first switching element (101), characterized in that, the evaluation device (118) is set up to compare the detected current flow with respect to a threshold value and to trigger the first switching element (101, 101') in order to disconnect the direct voltage load when the threshold value is passed.

2. Direct voltage switching device (100) according to claim 1, wherein the sensor (116) has a sensor element arranged in series with the first switching element (101) for detecting the current flow.

3. Direct voltage switching device (100) according to one of claims 1 or 2, wherein the sensor (116) is arranged and set up for detecting the current flow of both conductors, in particular is arranged and set up for detecting a current flow forming the differential current or sum current of positive and negative conductors.

4. Direct voltage switching device (100) according to any one of claims 1 to 3, comprising a second and third switching element (106) for coupling and decoupling the direct voltage load (200), in particular a second and third electromechanical switching element, wherein one of the second and third switching element (106) is integrated in the positive conductor (8) and the other is integrated in the negative conductor (10).

5. Direct voltage switching device (100) according to any one of claims 1 to 4, wherein the first switching element (101') comprises two antiserially switched, electronically controllable switching units.

6. Direct voltage switching device (100) according to one of claims 1 to 5, wherein at least the first switching element (101, 101'), the fuse (103) and the evaluation device (118) are contained in a common housing unit.

7. Direct voltage switching device (100) according to one of claims 1 to 6, wherein the positive conductor (8) and the negative conductor (10) are designed as conductor tracks on a circuit board.

8. Direct voltage switching device (100) according to one of claims 1 to 7, wherein the evaluation device (118) is set up to compare not only the current amplitude but also the current flow rate of change and / or current direction with a threshold value and to cause the first switching element (101) to be switched off if this is exceeded.

9. Switching system with a direct voltage switching device (100) according to one of claims 1 to 7, wherein the direct voltage switching device (100) has an input and an output, wherein the positive conductor (8) and the negative conductor (10) are connected at the input to a direct voltage bus as a direct voltage source (4) and a direct voltage branch with at least one direct voltage load can be connected and disconnected at the output via the positive conductor (8) and the negative conductor (10).