CROSS-REFERENCES TO RELATED APPLICATIONS

This application is the U.S. National Stage of International Application No. PCT/EP2020/051514, filed Jan. 22, 2020, which designated the United States and has been published as International Publication No. WO 2020/156905 A1 and which claims the priority of European Patent Application, Serial No. 19154819.7, filed Jan. 31, 2019, pursuant to 35 U.S.C. 119(a)-(d).

BACKGROUND OF THE INVENTION

The invention relates to an electronic switch for disconnecting a current flow between a first and a second connection with a semiconductor switch. The invention further relates to an electrical network with at least one electronic switch of this kind and an energy source. The invention further relates to a method for operating an electronic switch of this kind or an electrical network of this kind.

An electronic switch, also referred to as an electronic switching device or a semiconductor-based switching device, is understood as a component that has at least one semiconductor switch and can switch, especially switch off, a current. Transistors such as IGBTs, MOSFETS, IGCTs etc. are examples of a semiconductor switch.

In practice semiconductor-based switching devices are implemented with series-connected conventional fuses, in order, on failure of the semiconductor switch, still to be able to have access to a safe fallback level. The fuse is designed and dimensioned so that it only triggers with a short-circuit current through the semiconductor switch and a failure of the semiconductor switch to switch off. The task of the fuse is to protect the connected load or the connected subnetwork with its lines etc.

A series circuit is understood as the serial arrangement of components, wherein the voltages at the individual components add up. Thus a star circuit has a number of (at least three) series circuits.

The underlying object of the invention is to improve an electronic switch.

SUMMARY OF THE INVENTION

This object is achieved by an electronic switch for disconnecting a current flow between a first and a second connection, having a third connection, a semiconductor switch, a fuse and a short-circuiter, wherein a series circuit of the fuse and the semiconductor switch is arranged between the first connection and the second connection and a series circuit of the fuse and the short-circuiter is arranged between the first connection and the third connection, wherein the fuse has a trigger threshold with a current limit value, wherein the current limit value has a value between a permanently permitted current of the semiconductor switch and a maximum permitted current of the semiconductor switch. This object is further achieved by an electrical network with at least one electronic switch of this kind and an energy source, wherein the energy source is connected to the first connection and the third connection of the electronic switch. This object is further achieved by a method for operating an electronic switch of this kind or an electrical network of this kind wherein, on overloading of the semiconductor switch, the short-circuiter is closed for at least part of the time.

Further advantageous embodiments of the invention are specified in the dependent claims.

The knowledge underlying the invention is that a short-circuit current can be created by the series circuit of fuse and short-circuiter, which leads to the fuse triggering and thus protects the semiconductor switch and a load connected to the electronic switch or a number of loads connected there from overload. In this case an energy source, for example an energy-providing DC bus, can be connected to the first and third connection of the electronic switch and the loads or a subnetwork with different loads is connected to the second and third connection. The triggering of a fuse is also referred to a tripping of the fuse.

If the semiconductor switch is threatened with an overload, the semiconductor switch is reduced to zero current as quickly as possible. This is achieved by the short-circuiter being put into the conductive state and driving a short-circuit current via the fuse from the connected energy source. As a consequence the fuse triggers and the semiconductor switch is at zero current. In this way the transmission of electrical energy to the loads connected to the electronic switch is also interrupted and these loads are protected from overloading. Instead of a number of loads, just one load, a consumer or a subnetwork can also be connected to the electronic switch.

Among other things, the danger in an overloading of the semiconductor switch lies in the fact that it can no longer open or sustains damage when opening. Through the triggering of the fuse this danger, i.e. both of a switching failure and also of damage during the switching-off process, can be avoided, since the current is switched off by the fuse. After resetting or replacing the fuse the electronic switch is ready for use again. Furthermore, the fuse likewise protects the loads and lines connected thereto from overloading.

An overload or the threat of an overload can be detected with the aid of a criterion. For example the overload can be determined on the basis of a current value through the semiconductor switch or by evaluating the current value. In this case it is also possible for example to recognize the overload or the threat of an overload on the basis of a temperature, in particular the junction temperature, of the semiconductor of the semiconductor switch. The current value can also be employed for determining the temperature, in particular on the basis of a temperature model.

By way of the method described, the semiconductor switch is reliably protected from being destroyed or damaged, so that after replacement or resetting of the fuse and possibly after rectification of the error causing the overload, further operation is possible without replacing the expensive semiconductor.

There are thus many ways in which damage to or destruction of the semiconductor switch can be avoided, by which cost savings can essentially be realized. Moreover a second triggering option also exists for the fuse, so that redundancy exists for the semiconductor switch, which ensures that it is switched off safely.

A further advantage of the electronic switch lies in the function of the electronic switch, even in the event of a malfunction in the semiconductor switch, being able to realize a safe opening of the electronic switch. Then, by closing the short-circuiter and the subsequent triggering, i.e. opening of the fuse, the consumer, the load or a connected subnetwork, which is connected to the second connection of the electronic switch, can be disconnected from the energy source, which is connected to the first connection.

If the switch in the short-circuiter can block a voltage with different polarity and can conduct a current with different polarity, which can be realized in a simple way by using two semiconductors that are connected in an antiserial or antiparallel circuit, then the switch can be used both for AC voltage applications as an AC voltage switch or also for DC voltage applications with both polarities as a DC voltage switch.

The electronic switch is thus able to be used as an AC voltage switch and also as a DC voltage switch for different polarities provided the short-circuiter can block a voltage with different polarity and conduct a current with different polarity.

It has proved especially advantageous for the fuse to have a trigger threshold with a current value that lies between a permanently permitted current value for the semiconductor switch and a maximum permitted value for the semiconductor switch. Such a trigger value enables the fuse to carry out a number of safety functions safely and independently of one another. On the one hand an impermissibly high current is already avoided solely by the fuse, since such a current would lead to the fuse being triggered. Furthermore, the semiconductor switch with this arrangement can simultaneously be briefly overloaded, since the trigger threshold is set suitably high, i.e. above the permanently permitted current value of the semiconductor. The loading of the semiconductor can be monitored in this case by means of a closed-loop/open-loop control or protection apparatus. If the monitoring is triggered the semiconductor switch can be opened. Only on overload, in which the semiconductor switch can sustain damage by opening it, does the short-circuiter come into use. This drives through the fuse such a high current, which lies above the maximum permitted current value of the semiconductor switch, and thus causes the fuse to be triggered.

The particular advantage of this trigger threshold thus lies in the synergetic collaboration between the protection function of the fuse against overcurrent and the regulation, which controls the short-circuiter and thus can intervene in a protective manner via the fuse.

In this case the energy source of the electrical network, in particular in respect of its short-circuit performance, should be powerful enough to be able to create a current greater than the maximum permitted current of the semiconductor switch.

In an advantageous embodiment of the invention a further short-circuiter is arranged between the second connection and the third connection. If the load is capable of feedback or has an energy store, this can also result in a current from the load or the number of loads in the direction of the electronic switch. Then, through the conducting short-circuiter a current arises from the load or the loads via the semiconductor switch through the short-circuiter. The further short-circuiter serves to exclude a current flow that comes from the load side through the semiconductor switch. In this case the further short-circuiter is closed at least temporarily when the short-circuiter will be closed or is closed, The closing of the further short-circuiter can thus occur at the same time with a time delay from the closing of the short-circuiter, in order safely to be able to exclude a current flow from the energy source through the semiconductor switch and the further short-circuiter.

Thus it has proved advantageous, for the protection of the semiconductor switch, to close the further short-circuiter, provided the connected load permits such a short-circuit, in order to avoid, or even exclude completely, a current flow through the semiconductor switch.

In a further advantageous embodiment of the invention the short-circuiter is embodied as a thyristor. Thyristors are available at low cost on the market and at the same time have a very-high short-term overload capability. This is important to enable a high short-circuit current to be briefly conducted, without damaging the short-circuiter, in this case the thyristor. The disadvantage of a thyristor, that it cannot switch off a current, is not a factor, since the switching-off is done by the fuse and thus the current through the thyristor comes to a halt after a brief period.

If the short-circuiter is formed as a switch by pairs of anti-parallel connected thyristors, then such a switch can be used as an AC voltage switch and/or as a DC voltage switch with both polarities.

As well as thyristors, other switchable semiconductor elements can be used, provided these can bear the high short-circuit current and, in doing so, can keep the voltage via themselves sufficiently small.

In a further advantageous embodiment of the invention a further fuse is arranged between the semiconductor switch and the second connection in such a way that a series circuit of the further short-circuiter and the further fuse is arranged between the second connection and the third connection. Such an embodiment allows two subnetworks to be connected to one another. With an overload of the switch the short-circuiter and the further short-circuiter can be dosed simultaneously, so that the fuse and the further fuse are triggered and the exchange of energy between the two subnetworks is interrupted. The semiconductor switch, with the simultaneous closing of the short-circuiter and the further short-circuiter, is not subjected to any short-circuit current and is thus not subject to any further load, but is quickly put into a voltage-free and current-free state.

Furthermore, the electronic switch in this version is symmetrically constructed, so that it is versatile and suitable for all applications, in particular for any given combinations of subnetworks and electrical consumers and does not require any specific adaptation. Moreover the two fuses mean that redundancy is available, which makes the electronic switch especially safe.

In a further advantageous embodiment of the invention the further short-circuiter is dosed when the short-circuiter is dosed and a current through the semiconductor switch exceeds a predeterminable limit value or when the amount of the current through semiconductor switch exceeds the predeterminable limit value. Since the closing of the further short-circuiter could readily represent a load on the connected loads, it has proved useful to only dose said short-circuiter when a load for the semiconductor switch would actually be produced by a feedback of the load. In this case the triggering is advantageously made dependent on a current through the semiconductor switch. if this measured current value or the amount of the measured current value or the effective value of the measured current value exceeds a predeterminable limit value, then the further short-circuiter will be closed provided the short-circuiter has already been closed.

