DC network

Abstract

The present invention relates to a DC network, which has an electrical conductor and a switching unit arranged at one end of the conductor, the switching unit being used to separate an electrical connection via the conductor, wherein the switching unit comprises at least one controllable power semiconductor connected in series in a current path of the conductor, wherein, starting from the switching unit, the conductor is divided into a first and a second section, a first overvoltage protection device is connected between a connection point of the first and the second section and a second pole of the DC network, and a second overvoltage protection device is connected between an end of the second section remote from the switching unit and the second pole, and the overvoltage protection devices each have a capacitor.

Description

Technical Field

[0001] The invention relates to a DC network having a first pole, a second pole and at least one switching unit for separating a conductor of the first pole. Background Art

[0002] In future industrial facilities, DC networks should reduce losses, ensure direct energy exchange between converters, storage and motors, and achieve improved robustness. This type of network may have very different cable lengths between different load outlets and power sources (Einspeisungen). Here, the existing short cable length leads to very small longitudinal inductance in the feeder, so that the fault current may have a very steep current rise. As a result, very fast fault identification and fault disconnection are required. Because mechanical separation switches cannot meet the requirements for switching speed, power semiconductors are used. After the fault is identified, the power semiconductor disconnects the fault within a few hundred nanoseconds. Because the current through the load inductance now has no freewheeling path, a voltage may be generated on the power semiconductor, which may damage the power semiconductor in some cases. In order to deal with this problem, the switch can have an overvoltage limit. Disadvantageously, the overvoltage limit must be designed for each switch for the actual existing line length or feeder inductance, that is, the switch must be adapted to the existing feeder, or the switch is only allowed to be used before a specific line length, because otherwise there will be a risk of insufficient overvoltage limitation. Summary of the invention

[0003] The object of the present invention is to provide a DC network which alleviates or solves the problems mentioned at the outset. This object is achieved by a DC network having the features of claim 1 .

[0004] The DC network according to the invention has an electrical conductor and a switching unit arranged at one end of the conductor, the switching unit being used to disconnect an electrical connection via the conductor. The switching unit comprises at least one controllable power semiconductor connected in series in a current path of the conductor.

[0005] Starting from the switching unit, the conductor is divided into a first and a second section. In other words, the first section extends from the switching unit to the connecting point of the first section and the second section. The second section extends from the connecting point.

[0006] A first overvoltage protection device is connected between the connection point of the first and second sections and the second pole of the DC network. That is, the conductor forms the first pole of the DC network. A second overvoltage protection device is connected between the end of the second section remote from the switching unit and the second pole. That is, the first and second overvoltage protection devices are connected in parallel; however, between their connection point with the conductor, i.e. with the first pole of the DC network, there is a conductor piece with the length of the second section. Between the connection point of the first overvoltage protection device and the switching unit, there is a conductor piece with the length of the first section.

[0007] The overvoltage protection devices each have a capacitor.

[0008] In this case, the length of the first and second section is expediently at least greater than 1 m, in particular greater than 10 m, and in a particular embodiment greater than 50 m.

[0009] The invention advantageously makes it possible to protect the switching unit by means of an overvoltage protection device arranged at a distance on the conductor from overvoltages that occur during the disconnection process by the switching unit and have damaging or destructive effects on the power semiconductor. In this case, the switching unit itself only has to be designed for overvoltages caused by the inductance of the closest segment, namely the first segment. In contrast, the inductance of the second segment no longer plays a role in this.

[0010] The invention recognizes that instead of adapting the switching units, an adaptation of the conductors in the form of overvoltage protection devices can be used. Thus, preferably similar protection devices and similar switching units can be used in the DC network. This means that, compared to a network using adapted switching units, more components are used, but only similar components are used for this purpose, which reduces the cost and increases the reliability. As a result, the DC network can be better planned and controlled.

[0011] An overvoltage protection device with a capacitor between the poles of a DC network advantageously provides voltage stability and regulation reserve. Since the capacitor forms an oscillatory system with the line inductance, a series resistor is present as damping.

[0012] Advantageous embodiments of the DC network according to the invention are derived from the dependent claims of claim 1. In this case, the embodiment according to claim 1 can be combined with the features of one of the dependent claims or preferably also with the features from a plurality of dependent claims. Accordingly, the following features can also be provided in addition:

[0013] The DC network may include one or more loads, a plurality of further switching units and a plurality of further electrical conductors, wherein the further conductors connect the switching units and the loads. The further conductors are also divided into sections, wherein for the connection points of two connected sections of the further conductors, an overvoltage protection device is connected between the respective connection point and the second pole. That is, in the case of a large DC network, the further switching units are also protected against excessive overvoltages by embedding the overvoltage protection device in the conductor.

[0014] Preferably, the switching cells and the further switching cells in the DC network are designed identically. In other words, only one type of switching cell is used which is designed for the maximum voltage to be blocked. The length or the inductance of the segments is advantageously selected in this case so that the overvoltage which is formed when disconnecting by one of the switching cells remains below the breakdown voltage of the controllable power semiconductor. In general, this means that only two different types of components are advantageously used for disconnection in the DC network, namely one switching cell and one overvoltage protection device.

[0015] The switch unit may comprise a switch unit capacitor which is connected between the first pole and the second pole of the DC network and has a capacitance of at least 10 μF, in particular at least 50 μF, in particular at least 100 μF. Thus, the switch itself also has an inherent ability to absorb overvoltages of a certain conductor inductance without damage.

[0016] The capacitors of the overvoltage protection device can each have a capacitance of at least 10 μF, in particular at least 50 μF, in particular at least 100 μF. A sufficiently large capacitance acts on the voltage sufficiently stably to effectively relieve the switching unit.

[0017] - The overvoltage protection devices can each have a resistor connected in series with the capacitor for oscillation damping, in particular a resistance of less than 10 ohms. As a result, oscillations are avoided in an oscillatory system consisting of capacitor and line inductance, while at the same time the possibility of rapid charging of the capacitor is ensured due to the low resistance.

[0018] - The overvoltage protection device may comprise a diode connected in series with the capacitor, wherein the diode is connected so as to block the flow of current from the capacitor to the first pole of the DC network. Such a connection enables energy to be absorbed quickly by the capacitor in the event of a disconnection in the event of a short circuit. Furthermore, a discharge is suitably allowed but slowed down by the resistor.

[0019] The overvoltage protection device may include a spark gap connected in series with a capacitor. When an impermissibly high voltage is formed across a resistor, this generates a low-resistance current path which allows the energy to be absorbed quickly via the capacitor.

[0020] The overvoltage protection device can have a controllable power semiconductor, in particular a thyristor, connected in parallel with a resistor, thereby making it possible to switch a low-resistance current path.

[0021] The overvoltage protection device can comprise an overvoltage element, in particular a varistor, connected in parallel with the capacitor. Furthermore, a discharge resistor can be present in parallel with the capacitor, wherein the discharge resistor is in particular greater than 1 kOhm, in particular greater than 10 kOhm or greater than 100 kOhm. This supports the discharge of the capacitor by dissipating energy in the event of an overvoltage across the capacitor and making the overvoltage protection device quickly ready for use again in the event of repeated triggering.

[0022] The switching device may include a second power semiconductor, wherein two power semiconductors are connected in anti-series or anti-parallel. The power semiconductor may be an IGBT, for example. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Further advantages and features are apparent from the following description of exemplary embodiments with reference to the drawings. In the drawings, the same reference numerals denote the same components and functions.

[0024] Figure 1 A DC network with a switching unit for separating electrical conductors and an overvoltage protection device is shown,

[0025] Figures 2 to 6 Variants of the overvoltage protection device are shown. DETAILED DESCRIPTION

[0026] Figure 1 A DC network 10 is schematically shown. The DC network 10 comprises a DC voltage source 11 and a load 16, which are connected to one another via electrical conductors 121 ... 123. Here, two first conductors 121, 122 together form a first pole of the DC network 10, and a third conductor 123 forms a second pole. The two first conductors 121, 122 are connected in series with one another, wherein a switching unit 19 is arranged at their connection point.

[0027] The switch unit 19 serves as an interrupter of the electrical connection from the DC voltage source 11 to the load 16. For example, if a fault, i.e. a short circuit, occurs in the area of ​​the load 16 and a very large current flows from the DC voltage source 11 to the short circuit, then an interruption may be required. The switch unit 19 includes at least one power semiconductor, which is connected in series between two first conductors 121, 122 and can interrupt the current path through these conductors. In an alternative design, the switch unit 19 can also include two power semiconductors connected in reverse series.

[0028] Because there is no freewheeling path for the current when the current path is interrupted by the switching unit 19, an excessively high voltage is formed on the switching unit 19, that is, on the power semiconductor, shortly after the interruption. The magnitude of this excessively high voltage is particularly related to the magnitude of the inductance storing the electrical energy. The magnitude of the inductance is decisively determined by the inductance of the two first conductors 121, 122 adjacent to the switching unit. The longer these conductors 121, 122 are, the greater their inductance. In order not to need to adapt the switching unit 19 to the conductor length, the two first conductors 121, 122 are divided into sections 141...146. Here, in this example, the sections 141...146 are selected so that the conductor length of each section 141...146 does not exceed 100m. Therefore, the maximum inductance of each of the sections 141...146 is determined. In an alternative design, the sections 141...146 are selected according to a determined maximum inductance of, for example, 50μH. In this variant, it is advantageously not necessary to pay attention to whether the conductors 121 , 122 are similar or whether different electrical conductors are used in order to maintain a maximum inductance for each section 141 . . . 146 .

[0029] An overvoltage protection device 181 ... 184 is arranged at the connection point between each two adjacent sections 141 ... 146. Here, the overvoltage protection device 181 ... 184 is connected between the following connection point and the second pole in the form of the third conductor 123, which connection point is located in the two first conductors 121, 122 and is therefore part of the first pole of the DC network 10. That is, the overvoltage protection devices 181, 182 in the first conductor 121 are connected in parallel, except for the inductance 152 of the second section 142 located in the middle. Similarly, the overvoltage protection devices 183, 184 in the second conductor 122 are connected in parallel, except for the inductance 155 of the fifth section 145 located in the middle.

[0030] The overvoltage protection devices 181 ... 184 ensure that when the current flow is interrupted by the switching unit 19, the formation of overvoltages in the conductors 121, 122 is prevented or delayed in sections. As a result, the overvoltage generated at the switching unit 19 is limited to act on the inductance of the sections 141, 144 directly located at the switching unit 19. The switching unit 19 is suitably designed for such overvoltages. That is, it is achieved that the switching unit 19 can also be used in an unsuitable situation when the adjacent electrical conductors 121, 122 are significantly longer than the length allowed for the maximum inductance value for the switching unit 19. That is, instead of changing the switching unit 19, the design of the conductors 121, 122 is adjusted, and the overvoltage protection devices 181 ... 184 are provided for the conductors 121, 122. The switching unit itself has an overvoltage protection (not shown), which is sufficient for the line length or inductance of the adjacent switching unit, for example, an overvoltage protection for an inductance of 100 μH is sufficient.

[0031] A real DC network 10 in an industrial environment is generally more complex and comprises a plurality of loads 16, a plurality of electrical conductors 121 ... 123, partly of different lengths, and a plurality of switching units 19. In addition, it may also have branches. Figure 1 The DC network 10 is regarded as a simplified section of a real DC network. However, the present invention makes it possible to use only a single structure of switching units 19 in a large DC network 10. The overvoltage protection devices 181 . . . 184 also preferably have only one structure.

[0032] exist Figures 2 to 6 184. In principle and as the simplest embodiment variant, a capacitor 30 is sufficient as an overvoltage protection device 181 ... 184. The capacitor 30 provides voltage stability and regulation reserve. However, since this capacitor 30 forms an oscillating system with the line inductance 151 ... 156, a series resistor 31 as a damping is advantageous. Figure 2 Such an overvoltage protection device 20 is shown in FIG.

[0033] Figure 3 Shown according to Figure 2 An extended overvoltage protection device 21 of the embodiment of the invention is provided, wherein a diode 32 is present in parallel with the series resistor 31. The diode 32 enables the capacitor 30 to absorb energy very quickly, which is achieved according to the embodiment of the invention. Figure 2 The embodiment of is limited by the series resistor 31. Especially when opening the short circuit, it is important to absorb the energy very quickly. However, the discharge continues to decay via the series resistor 31.

[0034] Figure 4 An alternative to the use of diode 32 is shown. Figure 4 In the overvoltage protection device 22 of FIG. 3 , a spark gap 33 is arranged in parallel with the series resistor 31 to provide a low-ohmic current path when an impermissibly high voltage is generated across the series resistor 31. If the voltage across the spark gap 33 becomes sufficiently low, the arc in the spark gap 33 is extinguished again. The capacitor 30 is discharged again via the series resistor 31.

[0035] exist Figure 5 Another alternative is shown in . In this overvoltage protection device 23, a low-ohmic current path can be switched by a triggered semiconductor component, for example, in this example, by a thyristor 34. If the current through the thyristor 34 is less than its holding current, the thyristor 34 becomes high-ohmic again. The capacitor 30 is again discharged via the series resistor 31.

[0036] In accordance with Figure 6 In the overvoltage protection device 24 of FIG. 1 , the discharge of the capacitor 30 is supported by a discharge resistor 35 and an overvoltage element, such as a varistor 36 shown here, in order to discharge energy when the voltage across the capacitor 30 is too high and to make the protection circuit quickly ready for use again in the event of repeated triggering. In this case, the discharge resistor 35 and the varistor 36 are arranged in parallel with the capacitor 30. In this example, a diode 32 is arranged in series with the capacitor 30. However, this example can also be connected with Figures 3 to 5 , ie, here, too, a series resistor 31 or a spark gap 33 can be used in series with the capacitor 30.

[0037] Reference numerals list

[0038] 10 DC network

[0039] 121…123 Electrical wiring

[0040] Segment 141…146

[0041] Inductance of the segment 151…156

[0042] 11 DC voltage source

[0043] 19 Switching unit

[0044] 16 Load

[0045] 181…186 Overvoltage protection devices

[0046] 20…24 Variants of overvoltage protection devices

[0047] 30 Capacitor

[0048] 31 Series resistance

[0049] 32 diode

[0050] 33 Spark Gap

[0051] 34 Thyristor

[0052] 35 Discharge resistor

[0053] 36 Rheostat

Claims

1. A direct current network (10), comprising an electrical conductor (121, 122) and a switch unit (19) arranged at one end of the electrical conductor (121, 122), the switch unit being used to separate an electrical connection via the electrical conductor (121, 122), wherein: The switching unit (19) comprises at least one controllable power semiconductor connected in series in the current path of the electrical conductor (121, 122), wherein: - proceeding from the switching unit (19), the electrical conductor (121, 122) is divided into a first and a second section (141, 142, 144, 145), - a first overvoltage protection device (181, 183) is connected between the connection point of the first and second sections (141, 142, 144, 145) and the second pole of the DC network (10), - a second overvoltage protection device (182, 184) is connected between an end of the second section (142, 145) away from the switching unit (19) and the second pole, - if the inductance (152, 155) of a section of the electrical conductor (121, 122) which is located between the first overvoltage protection device (181, 183) and the second overvoltage protection device (182, 184) is not taken into account, the first overvoltage protection device (181, 183) and the second overvoltage protection device (182, 184) are connected in parallel, The overvoltage protection devices (181 . . . 184) each have a capacitor (30).

2. A DC network (10) according to claim 1, comprising at least one load (16), a plurality of further switching units and a plurality of further electrical conductors, the further electrical conductors connecting the switching units and the load (16) and being divided into sections, wherein: For the connection point of the two connected sections of the further electrical conductor in each case, an overvoltage protection device is connected between the connection point and the second pole.

3. A DC network (10) according to claim 2, wherein: The switching unit (19) is designed identically to the further switching unit.

4. The DC network (10) according to claim 1, wherein: The length or inductance of the sections (141 . . . 146) is selected such that an overvoltage which is generated when the switching unit (19) is switched off remains below a breakdown voltage of the controllable power semiconductor.

5. The DC network (10) according to claim 1, wherein: The switching unit (19) comprises a switching unit capacitor which is connected between the first pole and the second pole of the DC network and has a capacitance of at least 10 μF.

6. The DC network (10) according to claim 1, wherein: The switching unit (19) comprises a switching unit capacitor which is connected between the first pole and the second pole of the DC network and has a capacitance of at least 50 μF.

7. The DC network (10) according to claim 1, wherein: The switching unit (19) comprises a switching unit capacitor which is connected between the first pole and the second pole of the DC network and has a capacitance of at least 100 μF.

8. A DC network (10) according to any one of claims 1 to 7, wherein: The capacitors (30) of the overvoltage protection devices (181 . . . 184) each have a capacitance of at least 10 μF.

9. A DC network (10) according to any one of claims 1 to 7, wherein: The capacitors (30) of the overvoltage protection devices (181 . . . 184) each have a capacitance of at least 50 μF.

10. A DC network (10) according to any one of claims 1 to 7, wherein: The capacitors (30) of the overvoltage protection devices (181 . . . 184) each have a capacitance of at least 100 μF.

11. A DC network (10) according to any one of claims 1 to 7, wherein: The overvoltage protection devices (181 . . . 184) each have a resistor (31) connected in series with the capacitor (30) for oscillation damping.

12. A DC network (10) according to any one of claims 1 to 7, wherein: The overvoltage protection devices (181 . . . 184) each have a resistor (31) connected in series with the capacitor (30) for oscillation damping, the resistor being less than 10 ohms.

13. A DC network (10) according to any one of claims 1 to 7, wherein: The overvoltage protection devices (181 . . . 184) respectively include a diode (32) connected in series with the capacitor (30), wherein the diode (32) is connected to block the flow of current from the capacitor (30) to the first pole.

14. A DC network (10) according to any one of claims 1 to 7, wherein: The overvoltage protection device (181 . . . 184) comprises a spark gap (33) connected in series with a capacitor (30).

15. A DC network (10) according to any one of claims 1 to 7, wherein: The overvoltage protection device (181 . . . 184) has a controllable power semiconductor connected in series with a capacitor (30).

16. A DC network (10) according to any one of claims 1 to 7, wherein: The overvoltage protection device (181 . . . 184) has a thyristor (34) connected in series with a capacitor (30).

17. A DC network (10) according to any one of claims 1 to 7, wherein: The overvoltage protection device (181 . . . 184) includes an overvoltage element connected in parallel with the capacitor (30).

18. A DC network (10) according to any one of claims 1 to 7, wherein: The overvoltage protection device (181 . . . 184) includes a varistor (36) connected in parallel with the capacitor (30).

19. A DC network (10) according to any one of claims 1 to 7, wherein: The overvoltage protection device (181 . . . 184) includes a discharge resistor (35) connected in parallel with the capacitor (30).

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