Method for controlling a power semiconductor switch, control circuit for a power semiconductor switch and electronic circuit breaker

Abstract

Method for controlling a power semiconductor switch (14A, 14B) of an alternating current circuit which can be switched on and / or off by the power semiconductor switch (14A, 14B), comprising the following steps: a) Determining an instantaneous current value and an instantaneous voltage value of the alternating current circuit; b) Determine whether the instantaneous current value exceeds a preset maximum value and if so: c1) generating a control signal to switch off the circuit; c2) generating a control signal for switching on the circuit within a time period from generating the control signal for switching off the 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 preset maximum value that is equal to or 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 curve of a short circuit, or c4b) Determine whether the current-time curve immediately before and immediately after the next zero crossing of the instantaneous voltage value does not at least approximately correspond to an expected current-time curve, and c5) if condition c3) is met and condition c4a) or c4b) is not met, repeat steps c1), c2), c3), c4a) or c4b) and c5); d) detecting an error and permanently outputting the control signal to switch off the circuit and terminating the process if the number of repetitions of steps c1), c2), c3), c4a) or c4b), c5) exceeds a value n and / or if the 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 predeterminable maximum value or if it was determined in step c5) that condition c3) is met and condition c4a) or c4b) is not met, and continuing the method with step a).

Description

[0001] The invention relates to a method for controlling a power semiconductor switch, a control circuit for a power semiconductor switch and an electronic circuit breaker.

[0002] When connecting electronic loads, such as loads with switching power supplies and / or rectifiers, to an AC power supply, high inrush currents often occur, also known as inrush currents. Even with switching power supplies with a comparatively low power rating, for example, with a power rating of less than 100 W, current peaks of several hundred amperes can occur. These inrush currents can lead to the unwanted tripping of conventional miniature circuit breakers (MCBs).

[0003] A typical example of consumers with low continuous power and high inrush current are LED lamps, which are increasingly replacing other light sources in households and building services. LED lamps for operation on the 230V mains have, among other things, a power supply that exhibits capacitive behavior when switched on. In practice, many of these lamps are often connected in parallel and are therefore switched on simultaneously, which multiplies the inrush current accordingly and can lead to circuit overload and / or unwanted tripping of the MCB.

[0004] In addition, the high inrush current load can also cause increased wear in conventional 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 combined with the high current can then lead to brief arcing at the switching contacts, which in turn cause contact erosion and corresponding wear of the switching element, and in extreme cases, even welding of the contacts.

[0005] When using modern semiconductor circuit breakers (SCCBs for short, sometimes also Solid State Circuit Breakers, SSCBs for short; the abbreviation SCCB is used below), another problem is that such an SCCB itself can be destroyed by excessively high currents.

[0006] With conventional components, the entire circuit must be designed so that the maximum inrush current does not cause a malfunction or overload. In practice, this means that all components of the circuit must be designed for many times the intended continuous load. This results in correspondingly higher costs and also results in the circuit breaker not protecting the actual application defined by the intended continuous load, but rather a compromise between continuous load and inrush current.With conventional electromechanical MCBs, this compromise can be achieved comparatively cost-effectively by selecting the MCB's tripping characteristics. However, it remains a compromise in that the MCB is then not optimally designed for the respective application. In particular, an MCB with a slower tripping characteristic is used, which also results in higher fault currents in the event of a fault. The use of SCCBs, on the other hand, is not economically feasible in many cases.

[0007] DE 10 2008 018 619 A1 discloses a method for limiting the inrush current of a transformer. It involves using a ballast with two anti-serial transistors for each phase that can be switched off at any time, in conjunction with a load current measurement. If, after an initial switch-on, the load current measurement detects that the current is becoming too high, this phase is immediately switched off via the transistors. After a short time, for example, 1 ms, the transformer is switched on again. After several current periods and repetitions of the switch-on cycle, the transformer no longer exhibits saturation symptoms.

[0008] US 2019 / 0 123 549 A1 discloses a method for detecting and reducing inrush currents. Current, including an output current, is selectively supplied to a load. A semiconductor switching device is operated such that, in response to the detection of an overcurrent condition, it is determined whether the load is a capacitive load in a charging state and, if so, that the output current is reduced during the charging state.

[0009] JP 2007 - 236 061 A relates to an overcurrent protection device for protecting an electronic circuit from overcurrent and preventing malfunction due to a sudden inrush current or noise. A FET is inserted into a current path. If the flowing current exceeds a predetermined value, the FET is turned off for a predetermined time and then turned back on. If the number of on / off cycles within a predetermined time exceeds a predetermined value, the FET is permanently turned off.

[0010] US 2010 / 0 328 828 A1 relates to a method for protecting an electrical circuit. A value associated with a circuit in which a current flows through a switch to a load is measured and compared with a threshold value. If the measured value reaches or exceeds the threshold value, the switch is turned off and a counter is incremented. If the counter reading is below the counter limit and a predefined time period has elapsed, the switch is turned back on.

[0011] DE 10 2007 018 761 A1 discloses an arrangement for switching an inductive load. In particular, when a load current exceeds a first anomaly threshold current, a power MOSFET is immediately turned off. A threshold voltage generator initially sets the first anomaly threshold current to an initial level greater than the inrush current in preparation for an inrush current, and when a melt current is detected, it gradually reduces the level over time.

[0012] An object of the present invention is to provide an improved method for controlling a power semiconductor switch as well as 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.

[0013] This object is achieved by a method having the features of independent patent claim 1, by a control circuit having means for carrying out the method according to the invention and by an electronic circuit breaker having such a control circuit.

[0014] Advantageous further developments of the present invention are specified in the subclaims.

[0015] One advantage of the invention is that excessive inrush currents are suppressed by briefly interrupting the circuit when an excessive inrush current is detected, and then reconnecting it, with the time between switching off and on again corresponding to a maximum of one cycle. In many loads of the type discussed above, the inrush current, which is limited in time by the method, will have precharged the capacitive elements of the loads, so that the inrush current is lower during the reconnection process.Preferably, the circuit is switched on again at a(n) lower voltage value, for example at voltage values ​​that occur in a time window around the zero crossing, which begins at a phase angle of the voltage at -20° relative to the next zero crossing of the voltage and ends at a phase angle of the voltage of +20° relative to the next zero crossing of the voltage, so that the voltage values ​​when switched on again are less than approximately 35% of the peak voltage of the AC voltage. In further embodiments, smaller phase angles and thus smaller voltages are selected, for example ± 15° around the zero crossing corresponding to approximately 25% of the peak voltage or ± 10° around the zero crossing corresponding to approximately 17% of the peak voltage. In special embodiments of the invention, the circuit is switched on again before the next zero crossing of the voltage, ie before the zero crossing following the switching off.In this way, the inrush current is further limited when switching on again.

[0016] If the existing capacitances are not yet sufficiently precharged, an excessively high inrush current is again caused and detected according to the invention, and the above steps are repeated until either an excessively high inrush current no longer occurs or, after n repetitions of the method, it is determined that the inrush current is still too high and then a consumer with an excessively high capacitance, a short circuit or, more generally, a fault is detected.

[0017] In other words, the present invention reliably prevents excessive inrush currents, and unlike the prior art, it is not necessary to design the entire circuit for the high inrush currents generated by permissible loads. It is also not necessary to intentionally slow down protective switching devices, for example, by using a protective switching device with a C characteristic instead of a protective switching device with a B characteristic in order to prevent false triggering of the protective switching device when connecting a load that is permissible and functioning properly for the circuit. 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 control controls, can be dispensed with, thus saving costs on the load side.

[0018] In addition, the method according to the invention advantageously allows the use of an SCCB without the risk of destruction due to excessive inrush currents. At least in any case, a given SCCB can be extended using the method according to the invention and thus adapted to circuits with electrical loads that typically have high inrush currents and low continuous currents.

[0019] Overall, improved protection of the electrical consumers in the circuit and the entire electrical system is achieved. The method according to the invention is scalable and can be used in virtually any voltage and current range.

[0020] A particularly advantageous feature is that by repeating the switching off and on process, even loads with very high inrush currents, such as rectifiers with very large DC link capacitances, can be started up with limited currents. Only the number n of repetitions of the process needs to be adjusted accordingly.

[0021] Another advantage is that modern SCCBs already have the necessary measuring devices for recording the instantaneous current and voltage values, or they can be implemented with very little additional effort. Furthermore, a controller is usually already present, so the implementation of the present invention is often possible with existing hardware.

[0022] Another advantage is that consumers already connected to the circuit are not significantly affected by the switching-off and re-switching processes occurring within a single full cycle or, in the exemplary embodiments, within a single half cycle. With regard to ordinary household circuits, for example, it can be assumed that, for reasons of interference immunity, every electrical consumer is immune to multiple short-term switching-off and re-switching processes anyway.

[0023] Another important advantage of the present invention is that, unlike conventional soft starters, which are each assigned to a motor, there is no need for a 1:1 relationship between the load and the circuit for limiting the inrush current, which brings with it cost advantages, for example. Rather, in typical applications, a circuit breaker controlled according to the invention serves to protect a circuit with multiple loads.

[0024] In the following, embodiments of the present invention are explained in more detail with reference to drawings.

[0025] Showing: Fig. 1 is a schematic diagram of a semiconductor circuit breaker according to an embodiment of the present invention; Fig. 2 shows an exemplary time course of current and voltage in connection with the application of an embodiment of the method according to the invention; Fig. 3. an exemplary sequence of an embodiment of the method according to the invention; and Fig. 4 shows an exemplary time course of current and voltage in connection with the application of a further embodiment of the method according to the invention.

[0026] Fig. Figure 1 shows a schematic representation of a semiconductor circuit breaker (hereinafter: SCCB) 10 according to an embodiment of the present invention. SCCB 10 has line-side terminals 11A, 11B with which SCCB 10 can be connected to a power supply network (not shown). A first line-side terminal 11A serves to connect to the neutral conductor N, and a second line-side terminal 11B serves to connect to the phase conductor L.

[0027] A voltage measuring device 12 is used to measure the input voltage of the SCCB 10. The voltage values ​​determined by the voltage measuring device 12 are sent to a controller 13 (shown by a dashed line). The voltage measuring device 12 can be designed such that a signal representing the voltage between the input terminals 11A and 11B is continuously sent in analog form to the controller 13. In alternative embodiments, the voltage between the input terminals 11A and 11B is sampled by the voltage measuring device 12 at discrete times and delivered to the controller 13 as a time-discrete digital signal, wherein the sampling frequency is selected in relation to the mains frequency such that the controller 13 can determine the time profile of the voltage applied to the input terminals 11A, 11B, in particular the times of the zero crossings, from the signal sequence, if necessary by interpolation.

[0028] The neutral conductor connected to the first mains-side terminal 11A is directly connected to a first output-side or load-side terminal 18A of the SCCB 10. The phase L connected to the second mains-side terminal 11B is connected to a second output-side or load-side terminal 18B by means of a power semiconductor circuit 14A, 14B. In the example of the Fig. 1 comprises two self-commutated power semiconductor switches 14A, 14B, which are controlled by the controller 13 and connect the phase L to the second output-side or load-side terminal 18B or switch off the connection between the second mains-side terminal 11B and the second load-side terminal 18B. In embodiments of the invention, parallel-connected power semiconductors can also be used (not shown).

[0029] In the example of Fig. 1, an energy absorber 16 is connected in parallel to the power semiconductor circuit 14A, 14B, 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 to protect the power semiconductor circuit during certain switching events.

[0030] 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 serves to measure the load current in the phase conductor. The current measuring device 17 can be designed such 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 the controller 13). In alternative embodiments, the current is measured by the current measuring device 17 at discrete times and delivered to the controller 13 as a time-discrete digital signal, with the sampling frequency selected to be high enough that, for example, a sharply rising current curve caused by a short circuit can be detected in a timely manner for the respective application and converted into appropriate actions.

[0031] Three electrical loads 20, 30, and 40 are connected to the load-side terminals 18A and 18B of the SCCB 10. Loads 30 and 40 are arbitrary loads and are shown only to illustrate that the method described below for limiting the inrush current of load 20 can also be implemented if other loads 30, 40 in the respective circuit protected by the SCCB 10 are already active before load 20 is switched on, which corresponds to a typical practical application.

[0032] Consumer 20 is in the example of Fig. 1 a consumer of the type described above, i.e. a consumer with low continuous power and high inrush current, for example LED lighting for a large room comprising a plurality of individual LED lamps. This is indicated by a rectifier 21 and a capacitive load 22. In embodiments of the invention, both the rectifier 21 and the capacitive load are representative of a plurality of parallel-connected rectifiers and capacitive loads, as is the case, for example, with LED lighting in a large hall. Consumer 20 can be switched on or off by a switch 23. Switch 23 can be a mechanical wall switch operable by a user or an electronically controlled switch.

[0033] A first variant of the method according to the invention is described below in connection with Fig. 2 explained. Fig. Figure 2 shows, in a single diagram, an exemplary time profile 220 of the current I detected by current measuring device 17 (right scale axis of the diagram) and an exemplary time profile 210 of the voltage U detected by voltage measuring device 12 (left scale axis of the diagram). Purely as an example, the situation is shown for a 230 V low-voltage network, in which the peak voltage at time t = 0 of a single phase L relative to the neutral conductor N is approximately 325 V.

[0034] At time t = 0, load 20 is switched on, causing a very high inrush current 221. This current is measured by current measuring device 17 and processed by controller 13. In this exemplary embodiment, controller 13 is configured to prohibit currents exceeding 80 A. Thus, when a current value of 80 A is reached, controller 13 controls the power semiconductor circuit so that it is blocked, thus interrupting the current flow in the phase conductor L between input terminal 11B and output terminal 18B, whereupon the current and the measured current value drop to zero.

[0035] Subsequently, shortly before the zero crossing of the sinusoidal (mains) voltage U at t = 0.005 s is reached, the power semiconductor circuit is switched on by the controller 13, whereupon the measured value of the current again shows a strong increase 222, which is, however, already flatter than at t = 0, since the capacitances of the consumer 20 are already partially charged and / or since the instantaneous voltage value is low and also shows a falling tendency and thus the increase and maximum value of the current are limited independently of the consumer 20.

[0036] If consumer 20 is a consumer who, as in Fig. 1 has capacitive elements 22, then a zero-current phase 230 usually arises around the voltage zero crossing due to the already partially charged capacitances. This circumstance and the term "zero-current phase" are explained in detail below.

[0037] After the zero crossing of the voltage (here characterized 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 of 224, which is significantly higher than the normal value for the corresponding circuit, but no longer reaches the tripping value of 80 A and still during the negative half-wave of the mains voltage falls back to the low continuous current value of, for example, a few hundred milliamperes of the consumer 20, whereby the continuous current value in Fig. 2 cannot be distinguished from the current value I = 0 due to the selected scale.

[0038] Based on the fact that the current did not reach the limit of 80 A again after the restart shortly before the voltage crossed zero, the controller 13 determines that no short circuit occurred. Operation of the SCCB 10 continues with current monitoring.

[0039] In a preferred embodiment of the present invention, the time point described above as "shortly before reaching the zero crossing" for switching the power semiconductor circuit back on by the controller 13 can preferably be selected as the time point at which the phase angle of the sinusoidal mains voltage, ie 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 occurred during the positive or during the negative half-wave of the mains voltage.

[0040] The zero-sequence current phase is used to distinguish a short circuit from a switch-on process. Typically, a short circuit has a characteristic current-time curve and practically no zero-sequence current phase. This is because a short circuit exhibits resistive behavior, i.e., the current-time curve exhibits high current values ​​and is very similar to the voltage-time curve. The situation is different when a load 20, which has capacitive elements and causes a very high inrush current 221, is switched on: here, the expected current-time curve around the zero crossing of the voltage is characterized by low current values, which can be zero if no other loads in the circuit are switched on – hence the simplified term "zero-sequence current phase."

[0041] Fig. 3. illustrates the above in connection with Fig. 2, the sequence of an embodiment of the method according to the invention is described. The method starts with an initialization step 310, which provides a maximum current value, for example by reading it from a memory, and makes it available for the monitoring step 320.

[0042] 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, the power semiconductor circuit 14A, 14B remains switched on (step 330), and the method continues with step 320.

[0043] If, however, the current current value corresponds to or exceeds the maximum current value(s), the power semiconductor circuit 14A, 14B is switched off, step 340, and a check is carried out in step 350 as to whether the short circuit or fault can already be detected, for example because a counter (not shown) incremented in step 340 exceeds a certain value n.

[0044] If it is determined in step 350 that a short circuit or a fault has occurred, the method ends with step 370 and the power semiconductor circuit 14A, 14B remains switched off until, for example, the short circuit has been rectified and is manually switched back on (not shown). In embodiments of the present invention, whenever a fault or short circuit is detected, a disconnector arranged in series with the power semiconductor switch can also be switched off (not shown). This disconnector is preferably arranged on the line side of the power semiconductor switch in conductor L1, but can also be arranged on the load side of the power semiconductor switch. It is possible to use single-pole or double-pole disconnectors.

[0045] If it is determined in step 350 that the conditions for detecting a short circuit or fault are not met, the power semiconductor circuit 14A, 14B is switched on again in step 360, the time of switching on again being the same as described above with reference to Fig. The comments made in paragraph 2 apply.

[0046] Upon re-entry into monitoring step 320 from step 360, it may additionally be provided that a different, for example a lower, maximum current value is used instead of the previous maximum current value. Additionally or alternatively, upon re-entry into monitoring step 320 from step 360, it is provided that the presence of a zero current phase is detected, as in connection with Fig. 2 is monitored and a short circuit or fault is detected and the procedure is terminated if no zero current phase occurs (not shown).

[0047] A further variant of the method according to the invention is described below in connection with Fig. 4 explained. Fig. 4 shows (as Fig. 2) in a single diagram, an exemplary time profile 220A of the current I detected by the current measuring device 17 (right scale axis of the diagram) and an exemplary time profile 210 of the voltage U detected by the voltage measuring device 12 (left scale axis of the diagram). Again purely as an example, the situation is shown for a 230 V / 400 V low-voltage network, in which the peak voltage of a single phase L relative to the neutral conductor N is approximately 325 V.

[0048] At time t = 0.005 s, load 20 is again switched on, causing a very high inrush current 221. This current is measured by current measuring device 17 and processed by controller 13. In this exemplary embodiment, controller 13 is configured such that currents above 50 A are initially not permitted. Thus, when a current value of 50 A is reached, controller 13 controls the power semiconductor circuit so that it blocks, thus interrupting the current flow in the phase conductor, whereupon the measured current value returns to zero.

[0049] The control signals output to the power semiconductor circuit are shown at the bottom of the diagram in Fig. 4 is represented as a digital signal sequence 240. From t = 0 to t = 0.005 s, an ON signal is represented, from t = 0.005 s until shortly before t = 0.01 s, an OFF signal, then a very short ON signal followed by a very short OFF signal, followed by an ON signal at approximately t = 0.01 s, etc.

[0050] As can be seen from the signal sequence 240, shortly before the zero crossing of the sinusoidal voltage U at t = 0.01 s is reached, the power semiconductor circuit is switched on by the controller 13 (first re-switching on), whereupon the current and its measured value again exhibit a sharp increase 222 and again rise to over 50 A. Controller 13 therefore controls the power semiconductor circuit again so that it blocks, i.e. the current flow in the phase conductor is interrupted, whereupon the current and its measured value return to zero.

[0051] In one embodiment of the method, the controller 13 can immediately thereafter switch the power semiconductor circuit on again, still shortly before or even during the zero crossing of the voltage U (second re-switching on), whereupon, due to the diodes in the rectifier 21 and / or the partially pre-charged capacitor 22, a renewed current increase 224 only occurs when the magnitude of the voltage exceeds the threshold voltage of the diodes in the rectifier and / or the voltage of the already partially charged capacitors.

[0052] At point 224, the current also exceeds a maximum value after the second restart, whereby in the illustrated embodiment, the maximum value during the second restart was selected to be lower than the maximum value during the first restart and is, for example, 40 A.

[0053] Because the maximum value currently valid has been exceeded, the controller 13 controls the power semiconductor circuit again so that it blocks, i.e. the current flow in the phase conductor is interrupted, whereupon the current and its measured value return to zero.

[0054] At the end of the (negative) half-wave of the voltage U, the device is switched on again (third re-switching on) 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 first re-switching on, or a slightly later time, closer to the voltage zero crossing, can be selected for the third re-switching on.

[0055] The current rises sharply again (point 225) but does not exceed the maximum value, which is why the controller 13 keeps the power semiconductor circuit on. 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 so that it is blocked, thus interrupting the current flow in the phase conductor, whereupon the current and its measured value return to zero.

[0056] At the end of the (positive) half-wave of the voltage U, the power semiconductor circuit is switched on again (fourth re-switching on) by the controller 13 switching the power semiconductor circuit on. The same time interval before reaching the zero voltage crossing can be selected as for the third re-switching on, or a slightly later time, closer in time to the zero voltage crossing, can be selected for the fourth re-switching on, or a slightly earlier time, further away in time from the zero voltage crossing, can be selected for the fourth re-switching on.

[0057] In the example of Fig. 4, there is no current increase directly with the fourth re-switching on shortly before t = 0.03 s, because the switch-on time falls into a zero current phase 232 caused by the already partially reached charge of the capacity 22 of the consumer 20.

[0058] After the zero crossing and at the end of the zero current phase 232, the current at point 227 again exceeds the maximum value of 40 A, whereupon the controller 13 again controls the power semiconductor circuit so that it blocks, i.e. the current flow in the phase conductor is interrupted, whereupon the current and its measured value return to zero.

[0059] At the end of the (negative) half-wave of the voltage U, the device is switched on again (fifth re-switching on) by the controller 13 switching the power semiconductor circuit on.

[0060] In the example of Fig. 4, there is no current increase directly with the fifth re-switching on shortly before t = 0.04 s, because the switch-on time again falls into a zero current phase 233 caused by the already partially reached charge of the capacity 22 of the consumer 20.

[0061] After the zero crossing and at the end of the zero current phase 233, the current at point 228 rises sharply again, but does not reach the maximum value of 40 A. Therefore, the controller 13 leaves the power semiconductor circuit in the switched-on state and continues the process with current monitoring, 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.

[0062] More generally, the process, consisting of the steps of turning the power semiconductor off and on again, can be repeated up to n times. If the current no longer exceeds the maximum value before the nth repetition, the controller determines that the switch-on process is normal. If this does not occur, i.e., if the maximum current value is exceeded even during the nth repetition of the process, the process is terminated, and an error is detected and, if necessary, signaled to an operator.

[0063] As already explained above using the example, the maximum value can be constant for each restart or can be redefined for each restart, for example, reduced to reduce the I 2t-load of the entire system. Furthermore, the time for reconnection can be varied with respect to the zero crossing, for example, by setting the time for reconnection closer to the zero crossing with each repetition in order to achieve a lower inrush current due solely to the then lower absolute value of the voltage, while still charging the load-side capacitances, in particular the intermediate circuit capacitances of the rectifiers, or to postpone the reconnection to the zero-current phase expected for rectifier loads and to detect the short circuit if unexpectedly high currents occur during this phase.

[0064] The value n for the number of repetitions depends, among other things, on which other loads (30, 40) are connected to the circuit protected by the SCCB 10, and in particular, on how many half-cycles may fail without causing malfunctions or damage to the other loads. This can be determined from standards applicable to the respective circuit or can be determined on a case-by-case basis based on the loads typically connected.

[0065] In the example of Fig. 4, n = 5 was selected. In other embodiments, n ≤ 5 applies and in yet other 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. Likewise, the maximum current value can be made dependent on this already existing load; in particular, the initial maximum current value and all further maximum current values ​​can be selected to be smaller than the standard maximum current value if there is already a load in the circuit, in particular if this existing load is, for example, more than 50% or more than 75% or more than 90% of the nominal load or the permissible continuous current of the circuit.

[0066] In embodiments of the invention, it can be provided that, in the event of a detected error, the circuit is automatically switched on again after a configurable waiting time, which can be several milliseconds to seconds or several seconds to minutes, and that the method described above, which is then repeated, is used to determine whether the error still exists or has subsided, for example in the case of a thermally induced temporary malfunction of a consumer.

[0067] This can be implemented, for example, as follows: During the execution of the method described above, for each reconnection, it is determined whether the subsequently occurring current peak 222, 224, 226, 227, 228 is an inrush current or a short-circuit current, e.g., based on the criterion of whether or not a zero current phase can be detected around the zero crossing. If 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.

[0068] These counters are continuously compared with threshold values. If inr_cnt > n, the system will not be switched on again, as described above. After a specified time, the counter inr_cnt is gradually decremented until it reaches its starting value, for example, zero. The specified time can be, for example, one grid period, i.e., 20 ms in the case of European household grids, or several grid periods up to several seconds.

[0069] In addition, the counter sc_cnt can be compared with another limit value k and a restart after a short-circuit current event or fault event is only prevented if sc_cnt > k, so that even events classified as short-circuit current events do not immediately lead to the detection of a fault, but only when more than k short-circuit current events have been detected is a fault detected and output.

[0070] In this case, k = 0 can be selected, i.e. even the first short-circuit current event 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 gradually decremented again after a predeterminable time until it has reached its starting value, for example zero. This predeterminable time can also be one network period, for example, or it can be selected to be longer than the predeterminable time after which the counter inr_cnt is decremented. Preferably, the predeterminable time that is waited for before the counter sc_cnt is gradually decremented again is several seconds and, in certain embodiments, even minutes.

[0071] The already explained reduction of the maximum value for the current at which the power semiconductor circuit is switched off can be coupled 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 reducing the maximum value in fewer steps, for example when inr_cnt = 2 is reached for the first time and when inr_cnt = 4 is reached again.

[0072] It should be noted that in the above description of exemplary embodiments, the power consumption of the consumers 30, 40 already connected before the additional consumer 20 was connected was assumed to be low for the sake of simplicity and is therefore Fig. 2 and Fig. 4 is indistinguishable from I = 0. Likewise, the period in which the load 20 to be connected, equipped with a rectifier, does not consume any current because the forward voltage of the rectifier diodes is not reached, was simply referred to as the "zero current phase." The term "zero current phase" generally refers to the period in which the situation in Fig. 1 is not influenced by switching-on processes of the newly connected consumer 20, i.e. typically the period in which the consumer 20 causes no or no significant additional current flow, for example because the capacitances 22 are already partially charged.

[0073] The latter example is to be understood as follows: if a consumer 21 with a rectifier and parasitic capacitances or useful capacitances 22 in the DC circuit is switched on via the switch 23, then these capacitances are, as already explained, at least partially charged by the current pulse until they are switched off by the controller 13 and hold 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.

[0074] Because of this partial charging of the capacitors, a current only begins to flow into the load 20 after reconnection when the instantaneous voltage on the load side of the SCCB 10 exceeds the voltage applied to the DC side of the rectifier 21, plus the threshold voltage of the diodes in the current path. Conversely, the zero-current phase results from the fact that no charge flows into the capacitors 22 that have already been charged to a voltage defined by the previous current pulse(s) as long as the instantaneous voltage fed into the load 20 is lower than this defined voltage. Of course, this can also be easily expressed as a phase angle or time period using the sinusoidal relationship of the voltage curve; see below for details.

[0075] In certain embodiments of the present invention, this defined voltage value can be determined at least approximately by measuring the voltage between the load-side terminals 18A, 18B or can be established as a comparison criterion based on such a measurement. In other embodiments, the defined voltage value can be established based on an estimate, in particular based on an estimate based on the number of reclosing operations. The regular switching-on behavior (e.g., current, voltage, and number of required reclosing cycles) of typical loads 20 that can be connected to the specific AC circuit can be used as a basis.

[0076] For short-circuit or fault detection, the current-time curve in the expected or as defined above zero-current phase, i.e., immediately before and immediately after the zero crossing of the instantaneous voltage value, is also evaluated. The current-time curve is compared with an expected current-time curve. This expected current-time curve can, for example, be the current-time curve of a short circuit or an impermissibly high load, and the short circuit or fault is detected if the actual current-time curve at least approximately corresponds to such a short circuit or impermissible overload curve.

[0077] Alternatively, the current time curve is compared with a current-time curve that is expected when no short circuit or excessive overload occurs. Such a target current-time curve can be specified for a specific AC circuit by configuration and, for example, correspond to the current-time curve of the circuit loaded with its nominal load.

[0078] Alternatively or additionally, the target current-time curve can be selected as the current-time curve that regularly occurred before the first detection of exceeding a predefined maximum value, e.g., before the first inrush current event or short-circuit current event 221. "Regularly" here refers to the "normal case," which can be determined in various ways. For example, the time curve of the current between a selectable phase angle of the voltage before its zero crossing, e.g., -10°, to a selectable phase angle of the voltage after its zero crossing, e.g., +10°, can be saved as a reference for each zero crossing.

[0079] This reference is used when an inrush current event or short-circuit current event has been detected to compare the zero current phase after this event with the reference and, if the deviation exceeds a certain tolerance, to determine that a short-circuit current event has occurred. Otherwise, if the current trend and the reference deviate from each other by less than a certain tolerance, to determine that an inrush current event has occurred.

[0080] The said phase angles are preferably selected such that the absolute values ​​of the voltage are suitable for charging the (possibly already pre-charged) capacitances in the newly connected load, i.e., higher by a certain amount than the voltage already reached by these capacitances, which in turn can be derived, for example, from the previous course of the switching-on process. In 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, wherein this period is preferably placed symmetrically around the zero crossing, i.e., beginning 0.25 milliseconds before the zero crossing and ending 0.25 milliseconds after the zero crossing.In other embodiments or during repeated reactivation, for example, starting with the second or third repetition, this period can be selected to be longer in order to provide a higher voltage for further charging of the already partially precharged capacitors. For example, a zero-current phase of 1 millisecond can be selected, which is preferably again positioned symmetrically around the zero crossing, i.e., beginning 0.5 milliseconds before the zero crossing, corresponding to a voltage value of approximately 50 V, and ending 0.5 milliseconds after the zero crossing.

[0081] Expressed in equation form, the zero-current phase can also be described as follows: abs(I(t)) ≤ I_Lim(t). Where I(t) is the current value 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 time profile of the current in the considered time window around the zero crossing. A tolerance of, for example, 10%, 20%, 25%, or 50% of the actually expected value can be taken into account.

[0082] In other embodiments, a constant limit value can be used, to which a time-dependent value proportional to the mains voltage is added, for example I_Lim(t) = I_const + I_dyn(t), where I_const is the constant limit value and I_dyn(t) is the time-dependent value. I_dyn(t) = U(t) / R_cur can be selected, where U(t) is the instantaneous voltage value and R_cur is the ohmic resistance of a currently connected ohmic load, for example ohmic consumers 30, 40. For U(t), the value determined by the voltage measuring device 12 can easily be used, or an additional load-side voltage measuring device (not shown) can be used.

[0083] In addition to 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 with a maximum or reference value to distinguish an inrush current event from a short-circuit current event. This is particularly useful for subsequent reclosing operations in implementations where multiple repetitions of on and off operations are permitted, for example, n = 5. A capacitive load is charged slightly with each reclosing operation, so that with an increasing number of reclosing operations, a somewhat smaller increase in the current-time curve can be assumed, whereas the same increase is always to be expected for a short circuit.

[0084] In a further development, this analysis is extended to the current-time curve shape between the power semiconductor circuit being switched on again and the immediately subsequent switch-off due to exceeding the maximum value. The current-time curve shape is compared with a predefined fault curve shape. A fault / short-circuit event is detected if the current-time curve shape is at least predominantly above the fault curve shape. Otherwise, an inrush current event is detected.

[0085] It should be noted that the exemplary embodiments described above can be combined with one another as desired. Furthermore, it should be noted that the above particularly considered the case of a single-phase low-voltage circuit in a three-phase 400 V / 50 Hz supply network. Based on the above disclosure, the person skilled in the art can, without inventive step, discover variants and applications of the invention described above, for example, the application of the invention to other voltages and / or frequencies and / or to any circuits in a three-phase system, for example, for circuits connected between two phases L1, L2.

Claims

[1] Method for controlling a power semiconductor switch (14A, 14B) of an alternating current circuit which can be switched on and / or off by the power semiconductor switch (14A, 14B), comprising the following steps: a) Determining an instantaneous current value and an instantaneous voltage value of the alternating current circuit; b) Determine whether the instantaneous current value exceeds a preset maximum value and if so: c1) generating a control signal to switch off the circuit; c2) generating a control signal for switching on the circuit within a time period from generating the control signal for switching off the 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 preset maximum value that is equal to or 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 curve of a short circuit, or c4b) Determine whether the current-time curve immediately before and immediately after the next zero crossing of the instantaneous voltage value does not at least approximately correspond to an expected current-time curve, and c5) if condition c3) is met and condition c4a) or c4b) is not met, repeat steps c1), c2), c3), c4a) or c4b) and c5); d) detecting an error and permanently outputting the control signal to switch off the circuit and terminating the process if the number of repetitions of steps c1), c2), c3), c4a) or c4b), c5) exceeds a value n and / or if the 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 predeterminable maximum value or if it was determined in step c5) that condition c3) is met and condition c4a) or c4b) is not met, and continuing the method with step a). [2] Method according to claim 1, wherein in step c3) the control signal for switching on the circuit is generated 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° relative to the next zero crossing of the voltage and ends at a phase angle of the voltage of +20° relative to the next zero crossing of the voltage. [3] Method according to 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, wherein the increase is compared with a predeterminable maximum value and wherein the method is terminated, the fault is detected and the control signal for switching off the circuit is permanently output if the increase is above the maximum value. [4] Method according to one of claims 1 or 2, in which in step c3) in addition to the instantaneous current value, a waveform of the current-time curve is also determined, which is compared with a predeterminable error curve form, wherein the method is terminated, the error case is detected and the control signal for switching off the circuit is permanently output if the waveform of the current-time curve is at least predominantly above the error curve form. [5] Method according to one of the preceding claims, in which the current-time curve which was regularly present before the first detection of the exceeding of a predeterminable maximum value in step b) is used as the expected current-time curve. [6] Method according to one of the preceding claims, in which the current-time curve is evaluated in a time window around the zero crossing of the instantaneous voltage value, which is defined in that in the time window the amount of the instantaneous voltage is below a predefined value. [7] Method according to claim 6, wherein the predefined value corresponds at least approximately to the voltage present on the DC side at a rectifier (21) of a consumer (20) to be connected to the AC circuit. [8] Method according to claim 6, wherein the predefined value is determined based on a measurement of a voltage at a load-side terminal (18A, 18B) of the power semiconductor switch (14A, 14B) or based on an estimate, in particular based on an estimate based on the number of repetitions of steps c1), c2) and c3) that have already taken place for typically the load (20) that can be connected to the AC circuit. [9] Method according to one of the preceding claims, in which in step c2) the control signal for switching on the circuit is generated such that the switching on of the circuit takes place at a predeterminable 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] Control circuit (13) for a power semiconductor switch (14A, 14B) of an alternating current circuit with means for carrying out the method according to one of claims 1 to 9. [11] Electronic circuit breaker (10) for an alternating current 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 alternating current circuit; - voltage measuring means (12) for determining an instantaneous voltage value of the alternating current circuit relative to a reference potential; - a control circuit (13) controlling the power semiconductor switch (14A, 14B) according to claim 10. [12] Electronic circuit breaker (10) according to claim 11, which additionally comprises an electromechanical isolating contact arranged in series with the power semiconductor switch (14A, 14B), and means for opening the isolating contact if a fault has been detected.

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