ELECTRONIC SWITCH WITH SURGE PROTECTOR

Abstract

An electronic switch includes a turn-off semiconductor switch, a capacitor, a varistor, with the capacitor and the varistor being arranged in a first series circuit which is arranged in parallel with the turn-off semiconductor switch, a switch, and a resistor, with the switch and the resistor being arranged in parallel with the turn-off semiconductor switch and with the first series circuit.

Claims

1.-7. (canceled)

8. An electronic switch, comprising: a turn-off semiconductor switch; a capacitor; a varistor, with the capacitor and the varistor being arranged in a first series circuit which is arranged in parallel with the turn-off semiconductor switch; a switch; and a resistor, with the switch and the resistor being arranged in parallel with the turn-off semiconductor switch and with the first series circuit.

9. The electronic switch of claim 8, comprising at least two of said turn-off semiconductor switch, with a first one of the two turn-off semiconductor switches being arranged such as to enable turning off a current from a first connection of the electronic switch to a second connection of the electronic switch, and with a second one of the two turn-off semiconductor switches being arranged such as to enable turning off a current from the second connection of the electronic switch to the first connection of the electronic switch, said capacitor being designed as a bipolar capacitor.

10. The electronic switch of claim 8, further comprising a discharge resistor arranged in parallel with the capacitor.

11. The electronic switch of claim 8, further comprising a further capacitor arranged in parallel with the varistor.

12. The electronic switch of claim 10, further comprising a further discharge resistor arranged in parallel with the varistor.

13. A method for operating an electronic switch as set forth in claim 8, said method comprising switching on the switch before the turn-off semiconductor switch is switched on.

14. The method of claim 13, further comprising switching off the switch when a voltage at the capacitor falls below a voltage threshold value.

15. The method of claim 13, further comprising: turning off a current from a first connection of the electronic switch to a second connection of the electronic switch by the turn-off semiconductor switch; and turning off a current from the second connection of the electronic switch to the first connection of the electronic switch by another turn-off semiconductor switch.

16. The method of claim 13, wherein the capacitor is designed as a bipolar capacitor.

17. The method of claim 13, further comprising arranging a discharge resistor in parallel with the capacitor.

18. The method of claim 13, further comprising arranging a further capacitor in parallel with the varistor.

19. The method of claim 17, further comprising arranging a further discharge resistor in parallel with the varistor.

Description

[0030] The invention is described and explained in more detail in the following text using the exemplary embodiments illustrated in the figures. In the figures:

[0031] FIG. 1 shows a DC network with an electronic switch, and

[0032] FIG. 2 to FIG. 4 show exemplary embodiments of an electronic switch with overvoltage protection.

[0033] FIG. 1 shows a DC network 33, which is also referred to as a DC voltage network. Said network supplies power to a load 31 from a DC source 30, also referred to as a DC voltage source. This load may be, for example, a drive with a converter, wherein the converter with its intermediate circuit is connected to the DC source 30 via an electronic switch 1. The lines between DC source 30 and load 31 can assume very different properties with regard to their inductive behavior. This inductive behavior is illustrated in the illustration with the aid of inductances 32. These can take on very low values, as there is no transformer that has a current-limiting effect with its inductance. On the other hand, the inductances can also assume very high values due to the long cable lengths that are permissible due to the energy transfer with direct current. The requirements that result therefrom for the electronic switch are that, due to the low inductance and the associated large current changes, especially in the event of a short circuit, it should have a very rapid switching behavior so that impermissibly high currents, such as those generated in the event of a short circuit, for example, can be safely controlled. Furthermore, the switch must also be able to function reliably in the case of high inductances. Then, although there is no problem with excessive current increases, the inductance causes high voltages, which result from the change in current during turn-off. These must also be safely managed and must not damage the electronic switch 1 and its components located in it.

[0034] FIG. 1 here shows the basic structure of an electronic switch 1. Arranged in its power path between its first connection 12 and its second connection 13 there is at least one turn-off semiconductor switch 2, which can turn off a current through the switch. Depending on the type of turn-off semiconductor switch 2, it can turn off a current in only one direction or in both directions between the first and the second connection 12, 13. It is advantageous to use two turn-off semiconductor switches 2, which can each switch off the current for one direction. If these are reverse blocking, they are arranged in an anti-parallel circuit. In the event that the turn-off power semiconductor switches are reverse conductive, which can be identified at the diode parallel to the switching element of the turn-off semiconductor switch 2, 21, 22, the arrangement, as shown in FIG. 1, takes place in a series circuit, in which the first turn-off semiconductor switch 21 and the second turn-off semiconductor switch 22 of the two turn-off semiconductor switches are connected to one another in anti-series.

[0035] FIG. 2 shows an exemplary embodiment of an electronic switch 1 with overvoltage protection. To avoid repetition, reference is made to the description relating to FIG. 1 and to the reference symbols introduced there. A first series circuit 10 is arranged in parallel with the first and second turn-off semiconductor switches 21, 22. This first series circuit 10 has a capacitor 3 and a varistor 4, which are arranged in a series circuit. If one of the two turn-off semiconductor switches 21, 22 turns off the current between the connections 12, 13 of the electronic switch 1, the current driven by the inductances is commutated onto the first series circuit 10. Because of the voltages that arise, the varistor becomes conductive, also referred to as the breakdown of the varistor, and the capacitor 3 absorbs the energy from the inductances. This reduces the voltages that arise at the switch, which result from the large decrease in current when the switch is turned off, and prevents damage to the switch. At the same time, the service life of the switch is increased, since the turn-off semiconductor switches are not loaded with excessively high voltage.

[0036] When the electronic switch 1 is switched on again, the capacitor 3 is discharged via the turn-off semiconductor switches 2, 21, 22. This is the case, in particular, when the period of time between turning off and switching on the electronic switch again is so short that self-discharge of the capacitor has not yet been able to take place or has not been able to take place sufficiently. In order to avoid this, in the exemplary embodiment of the electronic switch 1 in FIG. 3, a second series circuit 11 composed of switch 5 and resistor 6 is inserted, which is arranged in parallel with the first series circuit. To avoid repetition, reference is made to the description relating to FIGS. 1 and 2 and to the reference symbols introduced there. With this second series circuit 11, the capacitor 3 can be discharged by closing the switch 5 before the turn-off semiconductor switches 2, 21, 22 are switched on again. At the same time, this resistor 6 can be used as a precharging resistor for a load 31 which, due to high inrush currents, is usually connected to the DC source via a precharging resistor. An example of such a load is a converter whose intermediate circuit capacitor is usually charged via a precharging resistor.

[0037] The switch can be realized in this case as a mechanical switch or with the aid of a semiconductor. Both turn-off semiconductors or else non-turn-off semiconductors, such as thyristors, can be used here.

[0038] In the exemplary embodiment of FIG. 4, further measures for voltage limitation are shown, which can be used both individually or else in their entirety. To avoid repetition, reference is made to the description relating to FIGS. 1 to 3 and to the reference symbols introduced there. As a first measure, a discharge resistor 7 can be arranged in parallel with the capacitor 3. This ensures that after the electronic switch 1 has been turned off, the capacitor 3, which has absorbed the energy from the inductances 32, is quickly discharged again and that it can be switched on again without having to switch on the resistor 6 beforehand.

[0039] As a second measure, a further capacitor 8 is arranged in parallel with the varistor 4. This improves the inductive response behavior of the varistor 4 when the current is commutated from the turn-off semiconductor switches onto the current path through the capacitor 3. In this way, even short-term voltage peaks at the turn-off semiconductor switches can be avoided. This also has a positive effect on the service life of the electronic switch 1.

[0040] As a third measure, a further discharge resistor 9 can be arranged in parallel with the varistor 4. The voltage drop across the varistor 4 is reduced by the resulting voltage divider composed of the discharge resistor 7 and the further discharge resistor 9. This takes place both when the electronic switch 1 is switched on and when it is switched off and increases the service life of the varistor 4 and therefore also of the electronic switch 1. At the same time, the further discharge resistor 9 makes it possible for the capacitor 3 to be discharged moderately when the electronic switch 1 is switched on again. As a result, the second series circuit 11 can also be dispensed with. When used with the second series circuit 11, the voltage loading of the electronic switch 1 during switching can be further reduced and the service life thereof can be further increased as a result.

[0041] These three measures can be carried out separately or in any desired combination in order to improve the switching behavior of the electronic switch 1.

[0042] In summary, the invention relates to an electronic switch, having at least one turn-off semiconductor switch, wherein the electronic switch has a capacitor and a varistor, wherein the capacitor and the varistor are arranged in a first series circuit, wherein the first series circuit composed of the capacitor and the varistor is arranged in parallel with the turn-off semiconductor switch. To improve the electronic switch, in particular with respect to the switching behavior thereof, it is proposed that the electronic switch has a switch and a resistor, wherein the switch and the resistor are arranged in a second series circuit, wherein the second series circuit composed of the switch and the resistor is arranged in parallel with the turn-off semiconductor switch and with the first series circuit. The invention further relates to a method for operating such an electronic switch, wherein the switch is switched on before the turn-off semiconductor switch is switched on.