Switching device for disconnecting a power path

Description

[0001] The invention relates to a switching device for separating a current path of a DC voltage network comprising source-side and load-side inductances.

[0002] A switching device designed to break a DC path with source- and load-side inductances must be able to handle the recovery or dissipation of energy from the DC voltage network. During rapid disconnection, high voltages build up, which must be dissipated via a protective circuit to prevent damage to the switching device's components.

[0003] From EP 3 367 567 A1 a switching device according to the preamble of claim 1 is known. A disadvantage of this circuit is an oscillating current flow, i.e. an oscillation, after a switch-off process, as in the Figure 4 This oscillation has time constants in the range of 10-50 milliseconds, meaning it lasts a comparatively long time.

[0004] The object of the invention is to provide an improved switching device for separating a current path of a DC voltage network comprising source- and load-side inductances, which is structurally and / or functionally improved. In particular, the switching device is intended to prevent oscillating currents after a shutdown process.

[0005] This object is achieved by a switching device having the features of patent claim 1. Advantageous embodiments emerge from the dependent claims.

[0006] The switching device according to the invention for interrupting a current path of a DC voltage network comprising source- and load-side inductances comprises at least two switching modules connected in series. Each of the switching modules comprises at least one controllable semiconductor switching element, with which a series circuit comprising a resistor and a capacitor is connected in parallel. The switching device is designed such that, in order to interrupt the current path and dissipate the energy stored in the inductances, the controllable semiconductor switching element of at least one of the switching modules is switched on with a duty cycle. The duty cycle is formed using the difference between the actual voltage across the semiconductor switching element and a target voltage across the semiconductor switching element, and the target voltage is formed at least from the system voltage of the DC voltage network and the number of switching modules.

[0007] Such a switching device enables a "soft" shutdown process, in which the current flow in the current path is reduced gradually rather than abruptly. A countervoltage is generated in the current path by at least one of the at least two switching modules. This is achieved by operating the respective semiconductor switching element of the switching modules at a duty cycle. Thus, the high power loss during shutdown is not dissipated in the semiconductor switching element of the respective switching modules, but primarily in the resistance of the respective switching modules. The switching device can thus dispense with voltage-limiting components such as varistors, which are expensive, heavy, and space-intensive. The semiconductor switching element in the respective switching modules assumes the role of the braking chopper.At the same time, the respective capacitors of the switching modules can be dimensioned small, since they do not have to absorb the entire energy stored in the source- and load-side inductances, but only a small portion due to the clocked operation of the semiconductor switching element of the respective switching modules. The total energy to be dissipated is therefore not limited by the semiconductor switching element of the respective switching modules. The shutdown process simply takes longer with larger source- and load-side inductances.

[0008] Duty cycle operation refers to a change between the on and off states of the semiconductor switching element at a predetermined frequency, i.e., period duration. Within a period, the semiconductor switching element is switched on once, i.e., turned on, and off once, i.e., turned off. The duty cycle specifies the proportion of the period duration during which the semiconductor switching element is switched on. During the time in which the controllable semiconductor switching element of the respective switching module is switched off, the current in this switching module can only flow via the parallel path of the RC element. This charges the capacitor of the RC element.

[0009] A particular advantage of operation with a duty cycle that depends on the difference between the actual voltage and the target voltage is the slowing down of energy dissipation towards the end of a turn-off process. This prevents the current from reaching zero crossing as quickly as possible. As a result, oscillations after the turn-off process are almost completely eliminated. With other methods, at the first current zero crossing, the total capacitor voltage across the switching device is higher than the system voltage of the DC voltage network due to the source and load-side inductances. As a result, the current zero crossing is followed by a current backflow and a subsequent oscillation process whose duration can be ten times the duration of the turn-off process. By contrast, operation with a duty cycle only delays the turn-off process by, for example, 25%.

[0010] The switching device is particularly advantageous in ships, especially in medium-voltage DC grids. A fast and safe DC switch enables the safe isolation of DC zones, for example, in the event of flooding or other shutdown scenarios. This also generally applies to the operation of other island grids, where different zones must remain safely and quickly separable.

[0011] Advantageous embodiments of the switching device according to the invention emerge from the dependent claims. The embodiment according to the independent claims can be combined with the features of one of the subclaims or, preferably, with those of several subclaims. Accordingly, the following additional features can be provided: All switching modules are expediently operated with a duty cycle. Since the duty cycle depends on the actual voltage across the semiconductor switching element, which corresponds to the voltage across the series of resistor and capacitor in the same switching module, each switching module has its own time-varying duty cycle. At most times, this will be different from those of the other switching modules. In other words, all semiconductor switching elements of the switching modules switch at a predetermined frequency, which is expediently selected to be the same for all switching modules. However, the length of time within a switching period for a semiconductor switching element to be switched on is determined separately for each switching module. Expediently, the switching device comprises a control device for controlling the semiconductor switching elements of the switching modules. The control device is designed to determine an actual voltage for each of the switching modules.The target voltage is expediently stored in the control device or, in an alternative embodiment, can also be determined by measurement. The control device controls the switching times of the semiconductor switching elements. Several semiconductor switching elements connected in series can be present per switching module. The duty cycle is expediently directly proportional to the difference between the actual voltage and the target voltage. It is also expedient to select the system voltage of the DC voltage network divided by the number of switching modules as the target voltage. In this way, the control directly strives for the final state after shutdown, in which the system voltage of the DC voltage network is evenly distributed among the switching modules. It is advantageous if the duty cycle is directly proportional to the difference between a maximum voltage for the controllable semiconductor switching element, i.e. the blocking capability, and the target voltage.This enables adaptation to the current-carrying and blocking capacity of the semiconductor switching elements, i.e. the design of the switching device. It is advantageous if the duty cycle is limited to an upper limit selected so that the voltage across the switching device does not fall below the system voltage of the DC voltage network during a switch-off process. This prevents the control system from creating a situation during the highly dynamic switch-off process in which a current to be switched off, possibly even a short-circuit current, increases again. The upper limit can be fixed and stored or determined dynamically. The control of the semiconductor switching elements expediently comprises a proportional controller, whereby the proportional controller receives at least the actual value and the setpoint of the voltage as control inputs.It is advantageous if the switching frequency of the controllable semiconductor switching element is at least 5 kHz, in particular at least 20 kHz. The higher the switching frequency, the smaller the fluctuations in the charge of the capacitors resulting from outflow and inflow during a switching period. In other words, the current ripple is lower. As a result, the capacitors used can have a smaller capacitance at high switching frequencies, which also results in a smaller overall size. Since the capacitors typically contribute a significant proportion to the overall size, this advantage can be considerable. If so-called wide bandgap switches, in particular SiC switches or GaN switches, are used as controllable semiconductor switching elements and a switching frequency of at least 50 kHz, in particular at least 200 kHz, is used, a further reduction in the size of the capacitors can be achieved.A further expedient embodiment provides that, during operation of the switching device, the semiconductor switching elements of different switching modules are switched on and off at different times to break the current path until the energy stored in the inductances is dissipated. In other words, the switching modules are clocked offset from one another. This avoids or reduces simultaneous switching on or off of the switching modules as well as overlapping of the duty cycles, and minimizes voltage fluctuations across the switching device. A further expedient embodiment provides that, in the path of the controllable semiconductor switching element of a respective switching module, another controllable semiconductor switching element is connected anti-serially to the controllable semiconductor switching element.This provides a bidirectionally operable switching module, so that the switching device can ultimately switch off the current path regardless of the prevailing current direction.

[0012] A practical embodiment according to a first variant provides that the parallel circuit comprising the at least one controllable switching element and the series circuit comprising the resistor and the capacitor is connected between a first switching module connection and a second switching module connection of the respective switching module. A plurality of serially connected switching modules can then be connected such that a first switching module connection of one switching module is connected to the second switching module connection of a preceding switching module. The first switching module connection of a first switching module is connected to a DC voltage source via a source-side inductance, and a second switching module connection of a last switching module of the plurality of switching modules is connected to a load via a load-side inductance.Such a switching module, in which at least one controllable semiconductor switching element, a resistor and a capacitor are provided, requires a minimal number of components.

[0013] A further expedient embodiment according to a second variant provides that the parallel circuit comprising precisely one controllable semiconductor switching element and the series circuit comprising the resistor and the capacitor (so-called basic module) is connected between a first rectification connection and a second rectification connection of a rectifier bridge of the respective switching module. The first rectification connection is a first node of the rectifier bridge, to which cathode connections of two rectification elements are connected to one another. The second rectification connection is a second node of the rectifier bridge, to which anode connections of two further rectification elements are connected to one another. If a unidirectional basic module, i.e. a switching module that comprises only a single semiconductor switching element, is provided in the rectifier bridge, the switching module can be used for both current directions.Current reversal is realized by the rectifier bridge, which in the simplest case is a diode bridge.

[0014] According to this embodiment, any number of switching modules can be connected in series. The series connection is implemented such that a third rectification terminal of one switching module is connected to a fourth rectification terminal of a preceding switching module. The third rectification terminal is a third node of the rectifier bridge, at which a cathode terminal of one rectification element is connected to an anode terminal of another rectification element. Similarly, the fourth rectification terminal is a fourth node of the rectifier bridge, at which a cathode terminal of one rectification element is connected to a cathode terminal of another rectification element.

[0015] A further advantageous embodiment provides that, during operation of the switching device for breaking the current path, the controllable semiconductor switching element of at least one switching module is switched off until the energy stored in the source- and load-side inductances is dissipated at a given time. This prevents, for example, the short-circuit current from building up again via the switching device during a breaking process due to a load-side short circuit.

[0016] The controllable semiconductor switching element is advantageously a turn-off semiconductor switching element. In addition to the aforementioned GaN or SiC switches, IGBTs, MOSFETs, IGCTs, or thyristors with a turn-off device (so-called quenching circuit) can also be used. The blocking capability of the controllable semiconductor switching element is advantageously at least 400 V, in particular at least 1 kV.

[0017] The switching device described is intended in particular for use in a direct current network with a voltage of more than 400 V, in particular more than 1000 V. In particular, the switching device can be used in high-voltage direct current transmission lines. Depending on the voltage prevailing in the direct current network, a suitable number of switching modules of the switching device must be selected. The higher the voltage to be controlled in the direct current network, the greater the number of switching modules selected – assuming the same semiconductor switching elements. For DC networks in the medium-voltage range, IGBTs or MOSFETs can be used in particular. At even higher voltages, thyristors with a shutdown device or IGCTs are used.A further embodiment provides that the switching device of the type described here is used as a short-circuit-proof circuit breaker.

[0018] The invention is explained in more detail below using exemplary embodiments in the drawings. They show: Fig. 1 is an electrical equivalent circuit diagram showing the structure of a single unidirectional switching module for a switching device according to the invention; Fig. 2 is an electrical equivalent circuit diagram of a serial connection of three in Fig. 1shown switching modules; Fig. 3 an electrical equivalent circuit diagram of a switching device according to the invention in a DC voltage network with source and load side inductances; Fig. 4 a diagram showing the time course of voltage and current during a disconnection process of the switching device according to the invention with eight switching modules; Fig. 5 a diagram showing the time course of the voltage occurring across eight serially connected switching modules; Fig. 6 an embodiment of a bidirectional switching module according to the invention; and Fig. 7 an electrical equivalent circuit diagram of a switching device according to the invention in a DC voltage network, in which the switching device consists of two modified switching modules with a bridge rectifier.

[0019] In the following description, identical elements are provided with identical reference numerals.

[0020] Fig. 1shows the schematic structure of a switching module 10 of a switching device 1 according to the invention for separating a current path 6 comprising source-side and load-side inductances. The switching module 10 comprises a controllable semiconductor switching element 13. The controllable semiconductor switching element 13 can be an IGBT or another type of turn-off semiconductor switch. The load terminals of the controllable semiconductor switching element 13 are connected between a first switching module terminal 11 and a second switching module terminal 12. Furthermore, a series circuit comprising a resistor 14 and a capacitor 15 is arranged between the first and second switching module terminals 11, 12. In other words, an RC element formed from the resistor 14 and the capacitor 15 is connected in parallel to the load terminals of the controllable switching element 13.

[0021] The basic functionality of such an individual switching module of the switching device 1 according to the invention is as follows: If the switching device 1 is to conduct current, the controllable semiconductor switching element 13 is switched to the conducting state. As soon as the current path 6 is to be interrupted by the switching device 1, the controllable semiconductor switching element 13 is switched to the blocking state by a control device not shown in the figures. As a result, the current I flowing in the current path 6 can only continue to flow via the RC element formed by the resistor 14 and the capacitor 15. The capacitor 15 charges as a result of the current I flowing into it.

[0022] Subsequently, the controllable semiconductor switching element 13 is operated by the control device with a duty cycle, i.e., it is switched on and off again in regular sequence. A fixed switching frequency, such as 10 kHz, is used for this. This results in a period of 100 µs. Within this period, the controllable semiconductor switching element 13 is switched on once, i.e., switched on, and off again once, i.e., switched off. The duty cycle determines for what proportion of the period the controllable semiconductor switching element 13 remains conductive. A duty cycle of 0 represents a completely off-state circuit, while a duty cycle of 30% means that the controllable semiconductor switching element 13 is switched on for 30 µs within each period of 100 µs. It is advantageous to use the highest possible frequency, such as 25 kHz, as the switching frequency.The resulting shortest possible period and the associated faster switching between conducting and blocking states reduce the resulting charging and discharging, i.e., the voltage ripple, and the capacitors can be designed for lower voltages. This saves space for the circuit.

[0023] To determine the current duty cycle for one of the switching modules 10, the actual voltage across the switching module 10 is first determined. This actual voltage can be measured or calculated. A current measurement is advisable, which must be done anyway, for example, for short-circuit detection. The voltage of the switching module can be calculated from the current and the duty cycle of each switching module, i.e., the duty cycle. The controller then attempts to regulate this voltage to the system voltage divided by the number of switches connected in series. Various controller approaches can be used for this purpose.

[0024] One example is a proportional controller (P controller). A proportional integrating controller (PI controller) can also be used. The duty cycle (control level) of each of the switch modules 10 is composed as follows: a i = U i − U S N ⋅ k p

[0025] The duty cycle (0 to 100%) corresponds to the measured or calculated switching voltage U i for the i-th semiconductor switching element 13 in the i-th switching module 10 minus the system voltage U s divided by the number of switching modules N, multiplied by the controller constant kp . The term U s / N can be viewed as the target voltage across each of the switching modules 10 in the off state. The controller constant kp can be calculated as follows: k p = U max − U S N ⋅ a max

[0026] Here, U max corresponds to the maximum switching voltage that may occur across a semiconductor switching element 13, and a max corresponds to the maximum duty cycle for which the system is designed. The maximum duty cycle represents a design parameter for the semiconductor switching element 13. The larger this value, the larger the currents and lower the voltages for which the system is designed; the smaller the value, the larger the voltages and lower the currents for which it is designed.

[0027] With this type of control, the short-circuit current represents a disturbance. The energy flowing from the capacitors when the switch is closed is also not taken into account in this control and represents a disturbance. With this design, it can happen that the duty cycle is set too high, so that the voltage built up across the entire switch becomes, on average, smaller than the system voltage and the current would continue to rise. However, this should be prevented. For this reason, it is advisable to add a limiting element after the proportional controller. This limits the maximum duty cycle in such a way that the voltage drop across the entire switch does not become, on average, smaller than the system voltage. However, short-term undershoots of the system voltage are possible and can be Figures 4 to 7 to recognize.

[0028] Fig. 2shows an electrical equivalent circuit diagram of a serial connection of n switching modules 10-1, 10-2, ..., 10-n (generally: 10-i, where i = 1 to n). Each of the switching modules 10-i is arranged as in Fig. 1 The serial connection of the switching modules 10-i is such that the second switching module connection 12-1 of the first switching module 10-1 is connected to the first switching module connection 11-2 of the subsequent switching module 10-2, and so on. The first switching module connection 11-1 of the first switching module 10-1 is, as shown in Fig. 3 shown, connected to a DC voltage source 2 via a source-side inductance 3. The DC voltage source 2 can be, for example, an energy generation unit, e.g., a photovoltaic system, a storage system, a battery charger, a wind turbine, a rectifier, and the like. The second switching module terminal 12-n of the last switching module 10-n is, as shown in Fig. 3shown, connected to a load 4 via a load-side inductance 6. The load 4 can, for example, be a drive of a DC voltage network or similar.

[0029] Fig. 3 shows the electrical equivalent circuit diagram of a switching device 1 according to the invention, which consists of two serially connected switching modules 10-1 and 10-2, each as in Fig. 1 The switching device 1 is connected to the DC voltage source 2 via the aforementioned source-side inductance 3. On the output side, the switching device 1 is connected to the load 4 via the load-side inductance 5. The source- and load-side inductances 3, 5 do not necessarily have to be physical components of the DC voltage network. The source- and load-side inductances 3, 5 can also be line inductances.

[0030] The functionality of the Fig. 3The switching device shown is as follows: When the load 4 is to be supplied with current from the DC voltage source 2, the controllable semiconductor switching elements 13-1, 13-2 (generally: 13-i, i = 1 to 2) of the switching modules 10-1, 10-2 (generally: 10-i, i = 1 to 2) are switched to the conductive state. As soon as the current path 6 is to be interrupted, e.g. due to a short circuit on the load side, a switch is made to duty cycle operation in which the controllable semiconductor switching elements 13-i switch between the conductive and blocking states at a fixed frequency, as already described. The controllable semiconductor switching elements 13-i are expediently controlled in an offset manner so that their switch-on times overlap as little as possible.By controlling the duty cycle as a function of the respective switch voltage and the target voltage, it is ensured that a total voltage U ges is present across both controllable semiconductor switching elements 13-i, with which the current flow and thus the energy stored in the inductors 3, 5 is reduced.

[0031] Unlike when using a single switching module, when multiple switching modules are used, a countervoltage (i.e., a voltage directed opposite to the direction of the DC voltage source 2) is always present in the DC voltage network. If the number n of switching modules connected in series is very large, the brief short-circuiting of a switching module is negligible, as a result of which the current gradually dissipates. The described procedure is carried out accordingly, regardless of the number n of switching modules connected in series.

[0032] Fig. 4shows the time course of the voltage 42 and the current 41 for a switching device 1, which comprises eight switching modules 10. In the diagram of the Fig. 4A nominal voltage of 6 kV and a current of 2 kA are assumed. The source-side inductance in the illustrated embodiment is 1 mH, whereas no load-side inductance was used for this simulation. In real environments, inductances are typically present on both sides, whereby these can be formed by discrete components or be parasitic, or both. It is clearly visible that the current path is broken at a time t ≈ 0.6 ms. The voltage 42 that drops across the switching device 1 before turn-off is determined by the conduction losses of the controllable semiconductor switching element 13. Due to the turn-off at time t ≈ 0.6 ms, the voltage rises to just under 10 kV.The clocked switching on and off of the controllable semiconductor switching element results in a waveform remaining between 4 kV and 12 kV until time t ≈ 4 ms, whereby the current I is reduced by the counter voltage within about 2.5 ms.

[0033] Fig. 5 shows a diagram in which the temporal progression of the voltages during a switch-off process of the switching device 1 with eight switching modules connected in series is shown in higher temporal resolution. In the simulation, which corresponds to the diagram of the Fig. 5is based, two of the eight switching modules at the same time, so that only four separate voltage waveforms 51...54 - for four pairs of switching modules 10 - can be seen. The time segment shown between 1.5 ms and 4.5 ms clearly shows the clocking of the controllable semiconductor switching elements of the switching modules 10 with a fixed switching frequency of 5 kHz. It can also be seen that the four pairs of switching modules switch out of phase with one another and that at least one controllable semiconductor switching element 13-i is switched off at a given time. Initially, i.e. at a high duty cycle, the switch-on periods nevertheless overlap due to their respective length, i.e. due to the still high duty cycle. From around 2 ms, the switch-on periods no longer overlap.From about 3 ms onwards it can be seen that the duty cycles become small and the semiconductor switching elements 13-i are only switched on for short periods of time, but still at the same frequency.

[0034] In the diagram of the Figure 5 Two of the four pairs of switching modules 10 operate with a lower voltage 53, 54 than the other two pairs. This is an artifact of the simulation. Such control is possible in principle. However, it is expedient and advantageous for the entire switch if all switching modules 10 are operated in the same way, i.e., operate with the same voltage load. Due to the different voltage levels 51...54 of the switching modules 10 in Figure 5Different duty cycles also occur, which can be seen in the range of t = 3 ms. Furthermore, the switching modules 10 with the lower voltage also switch off completely somewhat earlier, at approximately t = 3.5 ms. The complete switch-off of a switching module 10 is triggered when the current drops below a definable threshold, such as 50 A, and the voltage across the switching module 10, i.e., the voltage of the capacitor 15-i, is close to the system voltage, i.e., the difference to the system voltage falls below a threshold.

[0035] Due to the described control of the duty cycle as a function of the difference between the actual voltage and the target voltage for each of the switching modules 10-i, the duty cycle depends significantly on the currently present inductively induced overvoltage across the entire switching device. If this approaches 0 V, as in Figure 4 and Figure 5From a time of approximately 2.5 ms, the duty cycle decreases accordingly. However, since there is still a short on-time, the capacitors 15-i are still able to discharge. Therefore, when the overvoltage disappears, ie after the energy has dissipated, there is no longer any significant overvoltage in the capacitors 15-i, which would cause a current backflow and thus a current oscillation. Subsequent oscillations are calculated as in Figure 4 clearly visible, almost completely avoided. A comparatively weak and short-lasting backflow, which nevertheless exists, is Figure 5 From approximately t = 3 ms, this can be seen in the fact that the voltage across capacitors 15-i decreases instead of increasing when semiconductor switching element 13-i is switched off. From this point on, the current reaches 0 A for the first time, while the total voltage across the switching device is still slightly higher than the nominal voltage of 6 kV.

[0036] Fig. 6shows a modification of the Fig. 1 shown switching module 10. In addition to the semiconductor switching element 13, a further semiconductor switching element 16 is connected anti-serially to the controllable semiconductor switching element 13. The controllable semiconductor switching element 13 and the further controllable semiconductor switching element 16 can be of the same type, e.g., IGBTs. The behavior of this bidirectionally operable switching module 10 corresponds to the behavior of the switching module from Fig. 1 The current flow can be Fig. 6 The bidirectional switching module 10 shown can be directed in both directions. One of the two controllable semiconductor switching elements 13, 16 is switched to conducting mode, and the other to blocking mode. The current flow is ensured by a respective anti-parallel-connected diode 17 or 18.

[0037] Fig. 7shows a further electrical equivalent circuit diagram of a switching device 1 according to the invention, which comprises two switching devices 10-1 and 10-2 as an example. These are as in Fig. 3 between a source-side inductance 3 and a load-side inductance 5. The switching modules 10-1 and 10-2 (generally: 10-i, where i = 1 to 2) are capable of processing a bidirectional current flow. For this purpose, a Fig. 1 The basic module shown is integrated into a rectifier bridge 20-1 and 20-2 (generally: 20-i, where i = 1 to 2). The structure is described using the switching module 10-1, whereby the structure of the switching module 10-2 is identical.

[0038] The rectifier bridge 20-1 is implemented as a diode bridge with four diodes 21-1, 22-1, 23-1, and 24-1. A first rectifier terminal 25-1 is formed between the cathodes of the diodes 21-1 and 23-1. A second rectifier terminal 26-1 is formed between the anode terminals of the diodes 22-1 and 24-1. The Fig. 1 The switching module constructed is connected between the first rectifier terminal 25-1 and the second rectifier terminal 26-1. A third rectifier terminal 27-1 is formed between the anode of the diode 21-1 and the cathode of the diode 22-1. The third rectifier terminal 27-1 is connected to the DC voltage source 2 via the source-side inductance 3. A fourth rectifier terminal 28-1 is formed between an anode of the diode 23-1 and a cathode of the diode 24-1. The fourth rectifier terminal 28-1 is connected to the first rectifier terminal 27-2 of the second switching module 10-2.

[0039] Thus, a unidirectional base module is arranged in the rectifier bridge 20-1, which together form the switching module 10-1. This is used for both current directions, with the current reversal being realized by the elements of the rectifier bridge 20-i. For the sake of simplicity, Fig. 7 Only the DC voltage source 2 on the left and the load 4 on the right of the switching device 1 are shown. For bidirectional operation, the arrangement has another DC voltage source on the right and another load 4 on the left of the switching device 1.

[0040] As in Fig. 7 As shown, any number of switching modules 10-i can be connected in series. List of reference symbols

[0041] 1Switching device 2DC voltage source 3Source-side inductance 4Load 5Load-side inductance 6Current path 10, 10-iSwitching module 11, 11-iSwitching module connection 12, 12-iSwitching module connection 13, 13-iControllable semiconductor switching element 14, 14-iResistor 15, 15-iCapacitor 16Further controllable semiconductor switching element 17Diode 18Diode 20-iRectifier bridge 21-i...24-iDiode 25-iRectifier connection 26-iRectifier connection 27-i, 28-iRectifier connection 41Switch current 42Switch voltage 51...54Switching module voltages

Claims

1. Switching apparatus (1) for disconnecting a current path (6) of a DC voltage network, which current path comprises source-side and / or load-side inductances (3, 5), comprising at least two switching modules (10) connected in series, wherein each of the switching modules (10) comprises at least one controllable semiconductor switching element (13, 16) with which a series circuit comprising a resistor (14) and a capacitor (15) is connected in parallel, wherein the switching apparatus is configured in such a manner that, during disconnection of the current path (6), in order to reduce the energy stored in the inductances (3, 5), the semiconductor switching element (13, 16) of at least one of the switching modules (10) is turned on with a duty factor, characterized in that the duty factor is formed using the difference between the actual voltage across the semiconductor switching element and a setpoint voltage across the semiconductor switching element, and wherein the setpoint voltage is formed at least from the system voltage of the DC voltage network and the number of switching modules (10).

2. Switching apparatus (1) according to Claim 1, in which the duty factor is directly proportional to the difference between the actual voltage and the setpoint voltage.

3. Switching apparatus (1) according to one of the preceding claims, in which the setpoint voltage is equal to the system voltage of the DC voltage network divided by the number of switching modules (10).

4. Switching apparatus (1) according to one of the preceding claims, configured in such a manner that the duty factor is limited to an upper limit value which is selected in such a manner that the voltage across the switching apparatus (1) during a switching-off process does not become lower on temporal average than the system voltage of the DC voltage network.

5. Switching apparatus (1) according to one of the preceding claims, having in each case a proportional controller for controlling the controllable semiconductor switching elements (13, 16), wherein the proportional controller receives, as control inputs, at least the actual value and the setpoint value of the voltage.

6. Switching apparatus (1) according to one of the preceding claims, configured in such a manner that the switching frequency of the controllable semiconductor switching element (13, 16) is at least 5 kHz, in particular at least 20 kHz.

7. Switching apparatus (1) according to one of the preceding claims, wherein the controllable semiconductor switching element (13, 16) is a wide bandgap switch, in particular an SiC switch or a GaN switch, and the switching frequency is at least 50 kHz, in particular at least 200 kHz.

8. Switching apparatus (1) according to one of the preceding claims, in which the parallel circuit comprising the at least one controllable semiconductor switching element (13, 16) and the series circuit comprising the resistor (14) and the capacitor (15) is connected between a first rectifying connection (25) and a second rectifying connection (26) of a rectifier bridge (20) of the respective switching module (10), wherein the first rectifying connection (25) is a first node of the rectifier bridge (20), at which cathode connections of two rectifying elements (21, 23) are connected to one another, and wherein the second rectifying connection (26) is a second node (26) of the rectifier bridge (20), at which anode connections of two further rectifying elements (22, 24) are connected to one another.

9. Switching apparatus (1) according to one of the preceding claims, in which, during operation of the switching apparatus (1) for disconnecting the current path (6) until the energy stored in the inductances (3, 5) has been reduced, the controllable semiconductor switching element (13, 16) of a first portion of switching modules (10) is turned off at a given time and a second portion of switching modules (10) is turned on.

10. Switching apparatus (1) according to one of the preceding claims, in which, during operation of the switching apparatus (1) for disconnecting the current path (6) until the energy stored in the inductances (3, 5) has been reduced, the semiconductor switching elements (1, 16) of different switching modules (10) are switched on and off at different times.

11. Switching apparatus (1) according to one of the preceding claims, in which a further controllable semiconductor switching element (16) is reverse-connected in series with the controllable semiconductor switching element (13) in the path of the controllable semiconductor switching element (13) of a respective switching module (10).

12. Switching apparatus (1) according to one of the preceding claims, in which the controllable semiconductor switching element (13, 16) has a blocking capability of at least 400 V, in particular at least 1000 V.

13. DC voltage network having a system voltage of at least 400 V, in particular at least 1 kV, having a switching apparatus (1) according to one of the preceding claims.

14. Use of the switching apparatus (1) according to one of Claims 1 to 12 as a short-circuit-proof circuit breaker.