EP4091250A1

EP4091250A1 - Method for actuating a semiconductor power switch, actuation circuit for a semiconductor power switch, and electronic circuit breaker

Info

Publication number: EP4091250A1
Application number: EP21823774.1A
Authority: EP
Inventors: Marvin TANNHÄUSER; Fabian Döbler
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2020-12-21
Filing date: 2021-11-22
Publication date: 2022-11-23
Also published as: DE102020216405A1; CN115244853A; WO2022135808A1; US20230344424A1

Abstract

The invention relates to a method for actuating a semiconductor power switch (14A, 14B) of an AC circuit which can be activated or deactivated by the semiconductor power switch. The method has the following steps: a) ascertaining the present current value and the present voltage value of the AC circuit; b) ascertaining whether the present current value exceeds a specifiable maximum value and if so, c1) generating an actuation signal for deactivating the current circuit, c2) generating an actuation signal for activating the current circuit within a period of time after generating the actuation signal for deactivating the current circuit, wherein the period of time is less than or equal to the period duration of the voltage, and c3) ascertaining whether the present current value exceeds a specifiable maximum value, which corresponds to the previous maximum value or is less than the previous maximum value, after activating the current circuit. If so, steps c1), c2), and c3) are repeated. In step d), a malfunction is detected, and the actuation signal is permanently output in order to disconnect the current circuit, and the method is terminated if the number of repetitions of steps c1), c2), and c3) exceeds a value n. Otherwise, in step e), the actuation signal for activating the current circuit is continued to be generated if, in step b) or step c3), it was ascertained that the present current value exceeds the respective maximum value, and the method is continued with step a).

Description

description

Method for driving a power semiconductor switch, driving circuit for a power semiconductor switch and electronic circuit breaker

The invention relates to a method for driving a power semiconductor switch, a driving circuit for a power semiconductor switch and an electronic protective switch.

When switching on electronic loads, such as loads that have switched-mode power supplies and/or rectifiers, to an AC voltage supply, high inrush currents often occur, which are also referred to as inrush currents. Current peaks of several hundred amperes can occur even in the case of switched-mode power supplies with a comparatively low rated power, for example switched-mode power supplies with a rated power of less than 100 W. These inrush currents can lead to the undesired triggering of conventional miniature circuit breakers (MCB for short).

A typical case for consumers with low continuous power and high inrush current are LED lamps, which are increasingly displacing other lamps in households and in building technology. LED lamps for operation on the 230V mains have, among other things, a power pack which has a capacitive behavior when it is switched on. In practice, many of these light sources are often connected in parallel and are therefore switched on at the same time, which means that the inrush current is multiplied accordingly and can lead to an overload of the circuit and/or to the MCB being triggered undesirably.

In addition, the high inrush current load can also lead to increased wear in classic switching devices such as relays, Contactors or switches, for example when the high inrush current occurs in combination with the bouncing of a mechanical contact. The bouncing in connection with the high current can then lead to short-term arcing at the switching contacts, which in turn result in contact erosion and corresponding wear of the switching element and, in extreme cases, cause the contacts to weld.

When using modern semiconductor miniature circuit breakers (English: Semiconductor Circuit Breaker, SCCB for short, sometimes also Solid State Circuit Breaker, SSCB for short; the abbreviation SCCB is used below) there is another problem in that such an SCCB itself can be damaged by excessive currents can be destroyed.

With conventional components, the entire circuit must be designed in such a way that the maximum inrush current that occurs does not lead to any malfunction or overload, which in practice means that all components of the circuit must be designed for a multiple of the intended continuous load. This entails correspondingly higher costs and also means that the circuit breaker does not protect the actual application defined by the intended continuous load, but rather a compromise between continuous load and inrush current. In the case of classic electromechanical MCBs, this compromise can be achieved comparatively inexpensively by selecting the tripping characteristics of the MCB, but there is still a compromise to the effect that the MCB is then not optimally designed for the respective application, i.e. that an MCB with a slower tripping characteristic is used in particular is, whereby, however, in the event of a fault, higher fault currents also occur. In many cases, however, the use of SCCB is not economically viable.

One object of the present invention is therefore to provide an improved method for driving a power semiconductor specify conductor switch and an improved control circuit for a power semiconductor switch and an improved electronic circuit breaker, which are suitable for use in circuits with potentially very high inrush currents.

This object is achieved by a method having the features of independent claim 1, by a control circuit with means for executing the method according to the invention, and by an electronic circuit breaker that has such a control circuit.

Advantageous developments of the present invention are specified in the dependent claims.

An advantage of the invention can be seen in the fact that excessive inrush currents are suppressed by briefly interrupting the circuit when an inrush current that is too high is detected and then switching it on again, with the time between switching off and switching on again being a maximum of one period is equivalent to . In the case of many consumers of the type discussed at the outset, the inrush current that is limited by the method precharges the capacitive elements of the consumers, so that the inrush current is lower when the system is switched on again. It is preferably switched on again at a low (er) voltage value, for example at voltage values that occur in a time window around the zero crossing, which starts at a phase angle of the voltage at -20° relative to the next zero crossing of the voltage and at a phase angle of the voltage of +20 ° in relation to the next zero crossing of the voltage ends , so that the voltage values are less than approx . 35% of the peak voltage of the AC voltage is . In further refinements, smaller phase angles and thus smaller voltages are selected, for example ±15° around the zero crossing, corresponding to approx. 25% of the peak voltage or ± 10° around the zero crossing corresponding to approx. 17% of the peak voltage. In special embodiments of the invention, the circuit is switched on again before the next, d. H . before the zero crossing of the voltage following switch-off. In this way, the inrush current is additionally limited when switching on again.

If the existing capacities are not yet sufficiently precharged, an excessively high inrush current is caused again and detected according to the invention, and the aforementioned steps are repeated until either the inrush current is no longer too high or it is determined after n repetitions of the method that the inrush current is still increasing is high and as a result a consumer with too large a capacity, a short circuit or, more generally speaking, an error is detected.

In other words, excessive inrush currents are reliably prevented by means of the present invention and, unlike in the prior art, it is not necessary to design the entire circuit for high inrush currents generated by permissible consumers. It is also not necessary to deliberately slow down protective switching devices, for example using a protective switching device with a C characteristic instead of a protective switching device with a B characteristic, in order to prevent the protective switching device from tripping incorrectly when a properly functioning consumer that is permissible for the circuit is connected. In exemplary embodiments, the inrush current is advantageously limited centrally by the SCCB, so that special components for inrush current limitation such as DALI circuits and phase angle controls can be dispensed with, which means that costs can be saved on the consumer side.

In addition, the method according to the invention can advantageously ensure that an SCCB can be used at all without the risk of the SCCB being destroyed by excessively high inrush currents. At least a given SCCB can be expanded by the method according to the invention and thus adapted to circuits with electrical loads that typically have a high inrush current and a low continuous current.

Overall, improved protection of the electrical loads in the circuit and of the entire electrical system is achieved. The method according to the invention can be scaled as desired and can be used in almost any voltage and current range.

It is particularly advantageous that by repeating switching off and on again, loads with very large inrush currents, for example rectifiers with very large intermediate circuit capacitances, can also be started up with limited currents. Only the number n of repetitions of the method has to be adjusted accordingly.

A further advantage is that in modern SCCBs the necessary measuring equipment for detecting the instantaneous values for current and voltage is already available or can be implemented with very little additional effort. Furthermore, a controller is usually present anyway, so that the present invention can often be implemented with existing hardware.

It is also advantageous that consumers already connected to the circuit are in exemplary embodiments, switching off and switching on processes that take place within a single half-wave are not significantly affected. With regard to ordinary household circuits, for example, it can be assumed that, for reasons of immunity to interference, every electrical consumer is immune to several short-term switching off and on again.

Another important advantage of the present invention can be seen in the fact that, unlike classic soft start tern, which are each assigned to a motor, no 1: 1 relationship between consumers and the circuit for limiting the inrush current must exist, which brings cost advantages, for example. Rather, in a typical application, a circuit breaker controlled according to the invention is used to protect a circuit with several consumers.

In the following, exemplary embodiments of the present invention are explained in more detail with reference to drawings.

show in it :

Fig. 1 shows a schematic representation of a semiconductor circuit breaker according to an exemplary embodiment of the present invention;

Fig. FIG. 2 shows an exemplary time course of current and voltage in connection with the application of an exemplary embodiment of the method according to the invention; FIG.

Fig. 3 . an exemplary sequence of an exemplary embodiment of the method according to the invention; and

Fig. FIG. 4 shows an example of current and voltage over time in connection with the use of a further exemplary embodiment of the method according to the invention.

Fig. 1 shows a schematic representation of a semiconductor miniature circuit breaker (hereinafter: SCCB) 10 according to an embodiment of the present invention. SCCB 10 has network-side terminals 11A, 11B, with which SCCB 10 can be connected to a power supply network (not shown). A first line-side terminal 11A is used to connect to the neutral conductor N, and a second line-side terminal 11B is used to connect to the phase conductor L .

A voltage measuring device 12 serves to measure the voltage on the input side of the SCCB 10 . The voltage values determined by the voltage measuring device 12 are sent to a controller 13 (represented by a dashed line). Included For example, the voltage measuring device 12 can be designed in such a way that a signal representing the voltage between the input-side terminals 11A and 11B is continuously fed to the controller 13 in analog form. In alternative configurations, the voltage between the input-side terminals 11A and 11B is sampled by the voltage measuring device 12 at discrete points in time and supplied to the controller 13 as a time-discrete digital signal, with the sampling frequency being selected in relation to the mains frequency in such a way that the controller 13 can Signal follow the time course of the voltage present at the input-side terminals 11A, 11B, in particular the times of the zero crossings, can determine, if necessary. by interpolation.

The neutral conductor connected to the first mains-side terminal 11A is connected directly to a first output-side or connected to the load side terminal 18A of the SCCB 10 . The applied to the second mains-side terminal 11B phase L is by means of a power semiconductor circuit 14A, 14B with a second output side or. consumer-side terminal 18B connected. The power semiconductor circuit has in the example of FIG. 1 two self-commutated power semiconductor switches 14A, 14B, which are controlled by the controller 13 and the phase L to the second output side or. Switch through terminal 18B on the consumer side or switch off the connection between the second network-side terminal 11B and the second consumer-side terminal 18B. In exemplary embodiments of the invention, power semiconductors connected in parallel can also be used (not shown).

In the example of FIG. 1, the power semiconductor circuit 14A, 14B is connected in parallel with an energy absorber 16, which is connected between a mains-side bridging terminal 15A and a load-side bridging terminal 15B and serves to limit the voltage and thus protect the power semiconductor circuit during certain switching events. A current measuring device 17 is arranged in the phase conductor between the power semiconductor circuit 14A, 14B and the second load-side terminal 18B and is used to measure the load current in the phase conductor. The current measuring device 17 can be designed in such a way that a signal representing the current flowing in the phase conductor is continuously transmitted in analog form to the controller 13 (indicated by the dashed line between the current measuring device 17 and controller 13). In alternative configurations, the current is recorded by the current measuring device 17 at discrete points in time and supplied to the controller 13 as a time-discrete digital signal, with the sampling frequency being selected so high that, for example, a sharply rising current curve caused by a short circuit is detected in good time for the respective application and can be translated into appropriate actions.

Three electrical loads 20 , 30 , 40 are connected to the load-side terminals 18A, 18B of the SCCB 10 . Consumers 30 and 40 are any consumers, which are only shown to make it clear that the method described below for limiting the inrush current of the consumer 20 can also be carried out if other consumers 30, 40 in the respective circuit that is through the SCCB 10 is secured, are already active before the consumer 20 is turned on, which corresponds to a typical practical application.

Consumer 20 is in the example of FIG. 1 a consumer of the type described above, i. H . a consumer with low continuous power and high inrush current, for example LED lighting for a larger room comprising a plurality of individual LED light sources. This is indicated by a rectifier 21 and a capacitive load 22 . In exemplary embodiments of the invention, both the rectifier 21 and the capacitive load are representative of a plurality of rectifiers and capacitive loads connected in parallel, as is the case, for example, with LED lighting in FIG a large hall is the case. Consumer 20 can be switched on or off by a switch 23 . Switch 23 can be a mechanical wall switch that can be actuated by a user or an electronically controlled switch.

A first variant of the method according to the invention is described below in connection with FIG. 2 explained . Fig. 2 shows in a single diagram an exemplary time profile 220 of the current I recorded by the current measuring device 17 (right scale axis of the diagram) and an exemplary time profile 210 of the voltage U recorded by the voltage measuring device 12 (left scale axis of the diagram). The situation for a 230 V low-voltage network is shown purely as an example, in which the peak voltage at time t=0 of a single phase L compared to the neutral conductor N is approx. 325V is .

At time t=0, consumer 20 is switched on, causing a very high inrush current 221 . This current is determined by the current measuring device 17 and processed by the controller 13 . In this exemplary embodiment, controller 13 is set up in such a way that currents over 80 A are not permitted. When a current value of 80 A is reached, controller 13 controls the power semiconductor circuit in such a way that it blocks, the current flow in phase conductor L between input terminal 11B and output terminal 18B is interrupted, whereupon the current and also the measured current value drop to zero.

Shortly before the zero crossing of the sinusoidal (mains) voltage U is reached at t=0.005 s, the power semiconductor circuit is switched on by the controller 13, whereupon the measured value of the current again shows a sharp rise 222, which is however already flatter than at t=0, since the capacities of the consumer 20 are already partially charged and/or since the instantaneous voltage value is low and also tends to fall, and thus Increase and maximum value of the current are limited regardless of the consumer 20.

If consumer 20 is a consumer that, as shown in FIG. 1 has capacitive elements 22 , then a zero-current phase 230 usually occurs around the voltage zero crossing due to the already partially charged capacitances. This circumstance and the term “zero current phase” are explained in detail further below.

After the zero crossing of the voltage (characterized here by the entry into the negative half-wave) and at the end of the zero-current phase 230, the current rises again to a value 224, which is significantly higher than the normal value for the corresponding circuit, but no longer the trigger value of 80 A is reached and during the negative half-wave of the mains voltage it returns to the low continuous current value of, for example, a few hundred milliamps of the consumer 20, the continuous current value in FIG. 2 cannot be distinguished from the current value 1=0 due to the selected scale.

Based on the fact that the current has not reached the limit value of 80 A again shortly before the voltage crosses zero after being switched on again, the controller 13 decides that there was no short circuit. The SCCB 10 continues to operate by monitoring the current.

In a preferred exemplary embodiment of the present invention, the time described above with "shortly before reaching the zero crossing" for switching on the power semiconductor circuit again by the controller 13 can preferably be selected as the time at which the phase angle of the sinusoidal mains voltage, d. H . at the input terminals 11A, 11B of the SCCB 10, is between 160° and 170° or between 340° and 350°, depending on whether the interruption of the circuit by the controller during the positive or during the negative half-wave of the mains voltage.

The zero-current phase can be used in exemplary embodiments of the present invention to distinguish a short circuit from a switch-on process. This is because a short circuit typically shows a characteristic current-time profile and practically no zero-current phase, because a short circuit exhibits ohmic behavior, i. H . the current-time curve shows high values for the current and is very similar to the voltage-time curve. The case is different when a load 20 is switched on, which has capacitive elements and causes a very high inrush current 221: here the expected current-time curve around the zero crossing of the voltage is characterized by low current values, which can be zero if otherwise no consumers are switched on in the circuit - hence the term "zero current phase" used here for simplification.

Fig. 3 . illustrates the above in connection with FIG. 2 described sequence of an exemplary embodiment of the method according to the invention. The method starts with an initialization step 310, which provides a maximum current value, for example by reading it out from a memory, and makes it available for the monitoring step 320.

In monitoring step 320 the current current value is compared with the maximum current value. If the current current value does not exceed the maximum current value, then the power semiconductor circuit 14A, 14B remains switched on, step 330, and the method continues with step 320.

If, on the other hand, the current current value corresponds to or exceeds the maximum current value, then the power semiconductor circuit 14A, 14B is switched off, step 340, and it is checked in step 350 whether the short circuit or Error can be detected because, for example, in step 340 incremented counter (not shown) exceeds a certain value n.

If it is determined in step 350 that there is a short circuit or an error, the method ends with step 370 and the power semiconductor circuit 14A, 14B remains switched off until, for example, the short circuit has been eliminated and it is switched on again manually (not shown). In exemplary embodiments of the present invention, whenever the error or the case of a short circuit is detected, in addition, a disconnector arranged in series with the power semiconductor switch can be switched off (not shown). This isolating switch is preferably arranged on the network side of the power semiconductor switch in the conductor LI, but can also be arranged on the load side of the power semiconductor switch. It is possible to use single-pole or two-pole disconnectors.

If it is determined in step 350 that the conditions for determining a short circuit or a fault have not been met, the power semiconductor circuit 14A, 14B is switched on again in step 360, with the above with reference to FIG. 2 made remarks apply.

When re-entering monitoring step 320 from step 360, it can also be provided that another, for example a lower, maximum current value is used instead of the previous maximum current value. Additionally or alternatively, when re-entering monitoring step 320 from step 360, it can be provided that the presence of a zero-current phase as in connection with FIG. 2 is monitored and a short circuit or fault is detected and the method is terminated if no zero-current phase occurs (not shown).

A further variant of the method according to the invention is described below in connection with FIG. 4 explained . Fig. 4 shows (like Fig. 2) in a single diagram an exemplary time profile 220A of the current I recorded by the current measuring device 17 (right-hand scale axis of the diagram) and an exemplary time profile 210 of the voltage U recorded by the voltage measuring device 12 (left-hand scale axis of the diagram). Again, purely as an example, the situation for a 230 V / 400 V low-voltage network is shown, in which the peak voltage of a single phase L compared to the neutral conductor N is approx. 325 V.

At time t=0.005 s, consumer 20 is switched on again, causing a very high inrush current 221 . This current is determined by current measuring device 17 and processed by controller 13 . In this exemplary embodiment, controller 13 is set up in such a way that currents over 50 A are initially not permitted. When a current value of 50 A is reached, controller 13 controls the power semiconductor circuit in such a way that it blocks, ie the current flow in the phase conductor is interrupted, whereupon the measured value for the current returns to zero.

The control signals output to the power semiconductor circuit are shown as a digital signal sequence 240 at the lower edge of the diagram in FIG. An ON signal is shown from t=0 to t=0.005 s, an OFF signal from t=0.005 s until just before t=0.01 s, then a very short ON signal followed by a very short OFF signal , followed by an ON signal at about t = 0.01 s, etc.

As can be seen from the signal sequence 240, shortly before the zero crossing of the sinusoidal voltage U is reached at t = 0.01 s by the controller 13, the power semiconductor circuit is switched on (first switching on again), whereupon the current and its measured value again exhibit a sharp rise 222 and again rise to over 50 A. Controller 13 thus controls the power semiconductor circuit again in such a way that it blocks the current flow in the phase conductor i.e. is interrupted, whereupon the current and its measured value return to zero.

In one embodiment of the method, the power semiconductor circuit can be switched on again immediately afterwards by the controller 13, still shortly before or even during the zero crossing of the voltage U (second switching on again), whereupon, due to the diodes in the rectifier 21 and/or the partially already precharged capacitance 22 a new increase in current 224 only occurs when the amount of the voltage exceeds the threshold voltage of the diodes in the rectifier and/or the voltage of the already partially charged capacitances.

The current also exceeds a maximum value at point 224 after the second switch-on, the maximum value on the second switch-on being selected to be lower than the maximum value on the first switch-on again in the illustrated exemplary embodiment and being, for example, 40 A.

Because the currently valid maximum value is exceeded, the controller 13 controls the power semiconductor circuit again so that it blocks, the current flow in the phase conductor is thus interrupted, whereupon the current and its measured value return to zero.

At the end of the (negative) half-cycle of the voltage U, it is switched on again (third switch-on again) by the controller 13 switching the power semiconductor circuit on. In this case, the same time interval before reaching the voltage zero crossing can be selected as when switching on again for the first time, or a somewhat later point in time, closer to the zero crossing of the voltage, can be selected for the third switching on again.

The current rises sharply again, point 225, but does not exceed the maximum value, which is why the controller 13 allows the power semiconductor circuit to be switched on. All- However, after the zero crossing at the end of a zero-current phase 231, the current again exceeds the maximum value of 40 A at point 226, whereupon the controller 13 again controls the power semiconductor circuit in such a way that it blocks, the current flow in the phase conductor is thus interrupted, whereupon the current and its measured value go back to zero.

At the end of the (positive) half-wave of the voltage U, it is switched on again (fourth switch-on again) by the controller 13 switching the power semiconductor circuit on. The same time interval before reaching the voltage zero crossing can be selected as for the third restart, or a slightly later point in time, closer to the zero crossing of the voltage, can be selected for the fourth restart, or a slightly earlier point in time, further from the zero crossing, can also be selected the point in time away from zero voltage can be selected for the fourth switch-on again.

In the example of FIG. 4, there is no current rise directly with the fourth switch-on again shortly before t=0.03 s, because the switch-on time falls in a zero-current phase 232 caused by the charge of the capacitance 22 of the consumer 20 having already been partially reached.

After the zero crossing and at the end of the zero current phase 232, the current in point 227 again exceeds the maximum value of 40 A, whereupon the controller 13 again controls the power semiconductor circuit in such a way that it blocks, the current flow in the phase conductor is thus interrupted, whereupon the current and its measured value go back to zero.

At the end of the (negative) half-cycle of the voltage U, it is switched on again (fifth switch-on again) by the controller 13 switching the power semiconductor circuit on. In the example of FIG. 4, there is no current rise directly with the fifth switch-on again shortly before t=0.04 s, because the switch-on time again falls in a zero-current phase 233 caused by the already partially reached charge of the capacitance 22 of the consumer 20.

After the zero crossing and at the end of the zero current phase 233, the current rises sharply again at point 228, but does not reach the maximum value of 40 A. The controller 13 therefore leaves the power semiconductor circuit in the switched-on state and continues the process with monitoring the current, using the original maximum value of 50 A instead of the modified maximum value of 40 A either immediately or after a definable time has elapsed.

Expressed more generally, the method consisting of the steps of switching the power semiconductor off and on again can be repeated up to n times. If, before the nth repetition is reached, the current no longer exceeds the maximum value, then the controller determines a normal switch-on process. If this case does not occur, ie if the maximum value for the current is also exceeded the nth time the process is repeated, the process is terminated and an error is detected and, if necessary, signaled to an operator.

As already explained above using the example, the maximum value can be constant for each switch-on again or can be redefined for each switch-on again, for example reduced in order to limit the I ² t load on the overall system. Furthermore, the point in time for switching on again can be varied with respect to the zero crossing, for example by setting the point in time for switching on again closer to the zero crossing with each repetition, in order to achieve a lower inrush current simply because of the then lower absolute value of the voltage, which nevertheless loads on the consumer side, in particular the intermediate circuit capacitances of the rectifiers, or to to shift the restart to the zero-current phase expected for rectifier consumers and to determine the short-circuit case if unexpectedly high currents occur in this phase.

The value n for the number of repetitions depends on u . a. according to which other consumers 30, 40 are connected to the circuit secured by the SCCB 10 and in particular according to how many half-waves may fail without malfunctions or damage occurring to the other consumers. This can result from standards that apply to the respective circuit, or can be decided on a case-by-case basis based on the typically connected consumers.

In the example of FIG. 4 was chosen n = 5 . In other exemplary embodiments, n<5 applies, and in still other exemplary embodiments, n<10 applies. The number n can depend not only on the type of consumer, as explained above, but also on the total load already present in the circuit in the specific case, which is caused by the other active consumers 30 , 40 . The maximum current value can also be made dependent on this load that is already present, in particular the initial maximum current value and all other maximum current values can be selected to be smaller than the standard maximum current value if there is already a load in the circuit, especially if this existing load is more than 50% or more, for example more than 75% or more than 90% of the nominal load or . of the permissible continuous current of the circuit is .

In exemplary embodiments of the invention, it can be provided that, when an error is detected, the circuit is switched on again automatically after a configurable waiting time, which can be several milliseconds to seconds or several seconds to minutes, and using the method described above, which then runs again, to determine whether the error is still present or has subsided, for example in the case of a thermally induced temporary malfunction of a consumer.

This can be implemented as follows, for example: during the course of the method described above, it is determined for each switch-on whether the current peak 222, 224, 226, 227, 228 that subsequently occurs is an inrush current or a short-circuit current, e.g. B. based on the criterion of whether or not a zero-current phase can be detected around the zero crossing. When an inrush current event is detected, a counter inr_cnt is incremented. If a short-circuit current event is detected, a counter sc_cnt is incremented.

These counters are continuously compared with limit values. If inr_cnt>n, it is no longer switched on again, as described above, with the counter inr_cnt being decremented step by step after a predefinable time, until it has reached its starting value, for example zero. The predefinable time can be, for example, one network period, ie 20 ms in the case of European household networks, or also several network periods up to several seconds.

In addition, the counter sc_cnt can be compared with another limit value k and restarting after a short-circuit current event or Error event is only suppressed when sc_cnt > k, so that events classified as short-circuit current events do not immediately lead to the detection of an error, but only when more than k short-circuit current events have been detected, an error is detected and output.

Here, k = 0 can be chosen, d . H . the first short-circuit current event already leads to the detection of a fault, or k>0 can be selected, preferably 0<k<n. It can also be specified for the counter sc_cnt that it is decremented step by step after a definable time until it reaches its starting value, for example zero , has reached . This predefinable time can also be one mains period, for example, or it can be selected to be longer than the predefinable time after which the counter inr_cnt is decremented. The predefinable time that is awaited before the counter sc_cnt is decremented step by step is preferably several seconds and, in certain exemplary embodiments, also minutes.

The already explained lowering of the maximum value for the current at which the power semiconductor circuit is switched off can be linked to the values of the counters inr_cnt and/or sc_cnt, for example by reducing the maximum value with each increment of one of these values or by increasing the maximum value in fewer stages is reduced, for example when reaching inr_cnt = 2 for the first time and when reaching inr_cnt = 4 again.

It should be pointed out that in the above description of exemplary embodiments, the power consumption of consumers 30, 40 that were already switched on before the further consumer 20 was switched on was assumed to be low for the sake of simplicity and is therefore shown in FIG. 2 and figs. 4 is indistinguishable from 1 = 0. Likewise, the time period in which the load 20 that is equipped with a rectifier and is to be switched on does not consume any current because the forward voltage of the rectifier diodes was not reached is simply referred to as the “zero current phase”. What is meant by the term "zero current phase" is generally the period in which the situation in FIG. 1 circuit shown is not influenced by switch-on processes of the newly connected consumer 20, that is typically the period in which the consumer 20 has no or does not cause any significant additional current flow, for example because the capacitances 22 are already partially charged.

The latter example is to be understood as follows: a consumer 21 with a rectifier and parasitic capacitances or useful capacitances 22 in the DC circuit via the switch 23 switched on, then these capacitances, as already explained, are at least partially charged by the current pulse until they are switched off by the controller 13 and maintain this voltage completely or partially for the short period of time until the power semiconductor circuit is switched on again at the latest at the end of the current half-wave of the voltage .

Because of this partial charging of the capacitances, a current only begins to flow into the load 20 after switching on again when the instantaneous value of the voltage on the load side of the SCCB 10 exceeds the value of the voltage present on the DC voltage side at the rectifier 21, plus the threshold voltage of the diodes located in the current path. exceeds . Conversely, the zero-current phase results from the fact that no charge flows to a voltage of the capacitors 22 already defined by the previous current pulse(s) as long as the instantaneous value of the voltage fed into the consumer 20 is lower than this defined voltage. Of course, this can also be easily expressed as a phase angle or time span using the sine relationship of the voltage curve, see below for details.

In certain exemplary embodiments of the present invention, this defined voltage value can be determined or calculated at least approximately by measuring the voltage between the load-side terminals 18A, 18B. based on such a measurement as a comparison criterion. In other exemplary embodiments, the defined voltage value can be established based on an estimate, in particular based on an estimate based on the number of restart processes. This can be based on the regular switch-on behavior (e.g. course of current, voltage and number of required switch-on cycles) of typical loads 20 that can be connected to the specific AC circuit. For the short-circuit or In exemplary embodiments of the invention, error detection can also be based on the current-time profile in the expected zero-current phase or as defined above, d. H . immediately before and immediately after the zero crossing of the instantaneous voltage value. The current time profile of the current is compared with the current-time profile. This expected current-time profile can be, for example, the current-time profile of a short circuit or an impermissibly high load, and the short circuit or A fault is detected when the actual current-time profile corresponds at least approximately to such a short-circuit or impermissible overload profile.

In other exemplary embodiments, the current time profile of the current is compared with a current-time profile that is expected when there is no short circuit or impermissible overload case. Such a desired current-time profile can be predetermined for a specific AC circuit by configuration and can correspond, for example, to the current-time profile of the circuit loaded with its nominal load.

Alternatively or in addition, the target current-time profile can be selected as the current-time profile before the first determination that a predetermined maximum value, ie z. B. before the first inrush current event or Short-circuit current event 221, was present regularly. At this point, “regularly” means the “regular case”, which can be determined in various ways. For example, the time course of the current between a selectable phase angle of the voltage before its zero crossing, z. B. - 10 °, up to a selectable phase angle of the voltage after crossing zero, e.g. B. + 10°, can be stored again as a reference for each zero crossing.

This reference is used when an inrush current event or Short-circuit current event was detected in order to compare the zero-current phase after this event with the reference and to exceed a certain tolerance tending deviation to make the determination that a short-circuit current event is present and otherwise, so if the current curve and the reference differ less than a certain tolerance, to make the determination that an inrush current event is present.

The phase angles mentioned are preferably selected in such a way that the absolute values of the voltage are suitable for charging the (possibly already pre-charged) capacitances in the consumer to be newly connected, i.e. by a certain amount higher than the voltage of these capacitances that has already been reached, which in turn, for example, comes from the previous course of the switch-on process can be derived. In exemplary embodiments, in particular those with a mains frequency of 50 Hz, the zero current phase is defined as a period of 0.5 milliseconds around the zero crossing of the voltage, this period preferably being placed symmetrically around the zero crossing, i.e. beginning 0.25 milliseconds before the zero crossing and ends 0.25 milliseconds after the zero crossing. In other exemplary embodiments or in the case of repetitions of switching back on, for example after the second or third repetition, this period of time can be chosen to be longer in order to provide a higher voltage for further charging of the already partially precharged capacitances. For example, a zero-current phase of 1 millisecond can be selected, which is preferably in turn placed symmetrically around the zero crossing, ie begins 0.5 milliseconds before the zero crossing corresponding to a voltage value of approximately 50 V and ends 0.5 milliseconds after the zero crossing.

Expressed in terms of equations, the zero-current phase can also be described as follows: abs (I (t) ) < l_Lim(t) . I(t) is the value of the current in the SCCB 10 determined by the current measuring device 17, I_Lim(t) is the current expected during the zero current phase and abs( ) is the absolute value. I_Lim(t) can be constant, i.e. independent of t. In the general case, I Lim(t) describes the expected course of the current mes in the considered time window around the zero crossing. A tolerance of, for example, 10% or 20% or 25% or 50% of the actually expected value can also be taken into account.

In other exemplary embodiments, a constant limit value can be used, to which a time-dependent value proportional to the mains voltage is added, e.g. I_Lim ( t ) = I_const + I_dyn ( t ) , where I_const is the constant limit value and I_dyn ( t ) the time-dependent limit value Is worth . In this case, I_dyn(t)=U(t)/R_cur can be selected, where U(t) is the instantaneous value of the voltage and R_cur is the ohmic resistance of a currently connected ohmic load, for example ohmic consumers 30, 40. The value determined by the voltage measuring device 12 can be used without further ado for U(t), or an additional load-side voltage measuring device is used (not shown).

In addition or as an alternative to the methods described above for distinguishing an inrush current event from a short-circuit current event, the increase in the current-time curve can also be compared to a maximum or reference value in order to distinguish an inrush current event from a short-circuit current event. This is particularly useful for subsequent switch-on processes in implementations in which several repetitions of switch-on and switch-off processes are permitted, for example n=5. A capacitive load is slightly charged with each reclosing process, so that with an increasing number of reclosing processes, a slightly lower increase in the current-time curve can be assumed, while the same increase can always be expected in the case of a short circuit.

In a further development, this consideration is extended to the curve shape of the current-time profile between switching the power semiconductor circuit on again and switching it off immediately thereafter because the maximum value . The curve shape of the current-time profile is compared with a predefinable error curve shape. A fault/short-circuit event is recognized when the curve shape of the current-time curve runs at least predominantly above the fault curve shape. Otherwise an inrush current event is detected.

It should be noted that the exemplary embodiments described above can be combined with one another as desired. It should also be pointed out that the case of a single-phase low-voltage circuit in a three-phase 400 V/50 Hz supply network was considered in particular above. On the basis of the disclosure above, the person skilled in the art can find variants and applications of the invention described above without any inventive activity, for example the application of the invention to other voltages and/or frequencies and/or to any circuits in the three-phase system, for example for between two phases LI , L2 switched circuits .

Claims

25 patent claims

1 . Method for driving a power semiconductor switch (14A, 14B) of an AC circuit, which can be switched on and/or off by the power semiconductor switch, having the following steps: a) determining an instantaneous current value and an instantaneous voltage value of the AC circuit; b) determining whether the instantaneous current value exceeds a predeterminable maximum value and if so: cl) generating a control signal for switching off the electric circuit; c2) generation of a control signal for switching on the electric circuit within a time period from generation of the control signal for switching off the electric circuit, the time period being less than or equal to the period of the voltage; c3) determine whether the instantaneous current value after switching on the circuit exceeds a predeterminable maximum value which corresponds to the previous maximum value or is less than the previous maximum value, and either c4a) determine whether the current-time curve immediately before and immediately after the next zero crossing of the instantaneous voltage value corresponds at least approximately to an expected current-time profile of a short circuit, or c4b) determining whether the current-time profile directly before and immediately after the next zero crossing of the instantaneous voltage value does not at least approximately correspond to an expected current-time profile , and c5 ) if condition c3 ) is met and condition c4a ) is not met or . condition c4b) is not met, repeating steps cl), c2), c3), c4a) or c4b ) and c5 ) ; d) Recognition of an error and permanent output of the control signal to switch off the circuit and end that of the method if the number of repetitions of steps c1), c2), c3), c4a) or c4b), c5) exceeds a value n and/or if condition c4a or c4b is met; e) continued generation of the control signal for switching on the circuit if it was determined in step b) that the instantaneous current value falls below the predefinable maximum value or if it was determined in step c5) that condition c3) is met and condition c4a) is not met or the condition c4b) is not met, and continuation of the method with step a).

2. The method as claimed in claim 1, in which in step c3) the control signal for switching on the circuit before the next zero crossing of the voltage and/or within a time window which begins at a phase angle of the voltage at −20° in relation to the next zero crossing of the voltage and ends at a phase angle of the voltage of +20° with respect to the next zero crossing of the voltage.

3. The method according to any one of the preceding claims, in which in step c3), in addition to the instantaneous current value, an increase in a current-time curve is also determined, the increase being compared with a predeterminable maximum value and the method being ended, the error detected and the Control signal to turn off the circuit is output continuously when the increase is above the maximum value.

4. The method according to claim 3, in which, instead of the increase, a curve shape of the current-time profile is determined, which is compared with a predeterminable error curve shape, the method being terminated, the error case being recognized and the control signal for switching off the circuit being output continuously, if the curve shape of the current-time profile runs at least predominantly above the error curve shape.

5. The method according to any one of the preceding claims, in which the current-time curve is used as the expected current-time curve, which was regularly present before the first detection of the exceeding of a predetermined maximum value in step b).

6. The method according to any one of the preceding claims, in which the current-time profile is evaluated in a time window around the zero crossing of the instantaneous voltage value, which is defined in that the absolute value of the instantaneous voltage is below a predefined value in the time window.

7 . Method according to Claim 6 , in which the predefined value corresponds at least approximately to the voltage which is present on the DC voltage side at a rectifier ( 21 ) of a consumer ( 20 ) to be connected to the AC circuit .

8th . Method according to one of Claims 6 or 7, in which the predefined value is based on a measurement of a voltage at a load-side connection (18A, 18B) of the power semiconductor switch or based on an estimate, in particular based on an estimate based on the number of repetitions that have already taken place Steps cl ) , c2 ) and c3 ) are typically fixed to the load ( 20 ) that can be connected to the AC circuit .

9. The method according to any one of the preceding claims, in which in step c2) the control signal for switching on the circuit is generated in such a way that the circuit is switched on at a predefinable or predetermined phase angle of the voltage, in particular at a phase angle of the voltage of 10° - 20° before the next zero crossing.

10 . 10. Control circuit (13) for a power semiconductor switch (14A, 14B) of an AC circuit with means for carrying out the method according to one of Claims 1 to 9. 28

11. Electronic circuit breaker (10) for an AC circuit, comprising:

- a power semiconductor switch (14A, 14B), in particular a self-commutated power semiconductor switch for switching the AC circuit on and/or off,

- Current measuring means (17) for determining an instantaneous current value of a current flowing in the AC circuit;

- Voltage measuring means (12) for determining an instantaneous voltage value of the AC circuit with respect to a reference potential;

- a drive circuit (13) controlling the power semiconductor switch according to claim 10.

12. Electronic circuit breaker according to claim 11, which additionally has an electromechanical isolating contact which is arranged in series with the power semiconductor switch, and means for opening the isolating contact if a fault has been detected.