Method for operating an electronic circuit breaker, and electronic circuit breaker

Abstract

A method for operating an electronic circuit breaker having a semiconductor switch that is connected between a voltage input and a load output and that is driven as a function of the output voltage sensed at the load output during the switching on and/or cutting in of a capacitive load, wherein the output voltage is compared with a stored voltage threshold value, wherein when the voltage threshold value is reached or negatively exceeded, a current limit, to which a load current carried by the semiconductor switch is limited, is increased from a nominal value to a first step value increased therefrom, wherein the current limit is reduced stepwise from the first step value to the original nominal value, and wherein the semiconductor switch is opened if the output voltage does not reach the voltage threshold during a triggering time after the stepwise reduction of the current limit.

Claims

1. A method for operating an electronic circuit breaker having a semiconductor switch that is connected between a voltage input and a load output and that is driven during the switching on and/or cutting in of a capacitive load as a function of the output voltage sensed at the load output, the method comprising: comparing the output voltage with a stored voltage threshold value; increasing, when the threshold value is reached or negatively exceeded, a current limit to which a load current carried by the semiconductor switch is limited from a nominal value to a first step value increased therefrom; reducing stepwise the current limit from the first step value to the original nominal value; and opening the semiconductor switch if the output voltage does not reach the voltage threshold during a triggering time after the stepwise reduction of the current limit.

2. The method according to claim 1, wherein at least one second step value, to which the current limit is set in the stepwise reduction, is provided between the first step value and the nominal value.

3. The method according to claim 1, wherein the current limit is reduced to the next value after an applicable step time.

4. The method according to claim 3, further comprising equal-length step times of the individual step values.

5. The method according to claim 3, further comprising a triggering time that is equal to the sum of the individual step times.

6. The method according to claim 1, wherein the current limit is increased to a first step value that is equal to a multiple or a multiple of three of the nominal value.

7. An electronic circuit breaker comprising a semiconductor switch that is connected between a voltage input and a load output and is routed on the control side to a controller that is provided and equipped for carrying out the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

(2) FIG. 1 is a schematic block diagram of an electronic circuit breaker with a semiconductor switch arranged in the positive path of a current controller and with a controller that drives it;

(3) FIG. 2 is a flow chart of the method sequence of the operating method of the electronic protective circuit during a switching on or cutting in of a capacitive load;

(4) FIG. 3 is a diagram of current vs. time, the curve of a charging current of the capacitive load during a stepwise current limiting of the circuit breaker;

(5) FIG. 4 is a diagram of current and voltage vs. time, the curve of an output voltage and a load current, limited by the current limiting, of the circuit breaker in the event of a continuing overload current;

(6) FIG. 5 is a diagram of current and voltage vs. time, the curve of the output voltage and the load current of the circuit breaker during a turn-on process of the capacitive load in which the circuit breaker is not triggered; and

(7) FIG. 6 is a diagram of current and voltage vs. time, the curve of the output voltage and the load current of the circuit breaker during a turn-on process of the capacitive load in which the circuit breaker is triggered.

DETAILED DESCRIPTION

(8) The electronic circuit breaker 2 shown schematically in FIG. 1 is connected in a circuit between a current source or voltage source of a power supply 4 and a capacitive load 6. The circuit breaker 2 includes a power transistor or semiconductor switch 8 in the form of a MOSFET that is connected in a current path 10, namely in the positive path of the electronic circuit breaker 2.

(9) The current path 10 extends between an operating voltage terminal or voltage input 12 and a positive load terminal or load output 14. The positive pole of the load 6 that is to be switched is connected to the load output 14, while a negative pole is to be connected to a corresponding negative load terminal 16 of the circuit breaker 2. This load terminal 16 is routed to ground GND in the exemplary embodiment shown.

(10) The operating or input voltage V.sub.e generated by the current source or voltage source of the power supply 4, for example in the form of a DC voltage at 24 V (DC), is applied to the voltage input 12 of the electronic circuit breaker 2.

(11) With the power supply 4 connected and load 6 connected, in operation of the circuit breaker 2, an output current or load current I.sub.L starting from the voltage input 12 flows through the current path 10, and thus through the drain-source section of the semiconductor switch 8 and through the load 6, to the reference potential or ground GND. The load voltage or output voltage V.sub.a dropping across the load 6 is sensed between the load outputs 14 and 16 by means of a voltage sensor 18 integrated into the circuit breaker 2.

(12) The semiconductor switch 8 is connected into the current path 10 by means of a drain terminal 20 and a source terminal 22. A gate terminal 24 of the semiconductor switch 8 is routed on the drive side to a controller 26 of the circuit breaker 2. The controller 26, implemented as a microcontroller, for example, is coupled by a signal to the voltage sensor 18. During normal operation, the controller 26 limits the load current I.sub.L or the source-drain current flowing through the semiconductor switch 8 by means of current limiting to a current limit I.sub.g, which is equal, for example, to a nominal value I.sub.N of a nominal current of the electronic circuit breaker 2.

(13) An operating method that is appropriate, in particular even in the case of turn-on of the electronic circuit breaker 2 on a capacitive load 6, or in the case of addition of a capacitive load 6, is illustrated in the flow chart shown in FIG. 2. After a start 28, which means for example at the turn-on of the electronic circuit breaker 2, a query or a threshold comparison 30 takes place as to whether the sensed output voltage V.sub.a is less than a stored voltage threshold V.

(14) If the output voltage V.sub.a falls below the voltage threshold V.sub.s, the current limit I.sub.g is increased to a first step value I.sub.s1 in a method step 32. The step value I.sub.s1 here has a higher value than the original nominal value I.sub.N. In particular, the step value I.sub.s1 is a multiple of the nominal value I.sub.N, which is to say, for example, I.sub.s1=a*I.sub.N, wherein a=3 in one possible embodiment. The current limiting of the circuit breaker 2 is subsequently carried out for a step time T.sub.s1, which means that the load current I.sub.L is limited to the current limit I.sub.g=I.sub.s1 for the step time T.sub.s1. To this end, after method step 32 a timer or clock is started that measures a time t and monitors whether the time t has reached the step time T.sub.s1.

(15) After the step time T.sub.s1, in a method step 34 the current limit is lowered to a second step value I.sub.s2. The second step value I.sub.s2 here is lower than the previous step value I.sub.s1 and higher than the original nominal value I.sub.N. In particular, the step value I.sub.s2 is a multiple of the nominal value I.sub.N, which is to say, e.g., I.sub.s2=b*I.sub.N, wherein b=2.65 in one possible embodiment, for example. Next, a timer is started anew that monitors whether the time t has reached the step time T.sub.s2.

(16) The current limit I.sub.g is then successively lowered or reduced stepwise until in a method step 36 the current limit I.sub.g is set to the original nominal value I.sub.N, thus I.sub.g=I.sub.N. In a threshold comparison 38 that follows this, a test is made as to whether the output voltage V.sub.a remains below or has again fallen below the voltage threshold V.sub.s. If the output voltage V.sub.a is lower than the voltage threshold value V.sub.s, another timer is started for a triggering time T.sub.a. During the triggering time T.sub.a, a test is repeatedly made as to whether the output voltage V.sub.a is lower than the voltage threshold value V.sub.s.

(17) If the output voltage V.sub.a does not exceed the voltage threshold V.sub.s during the triggering time T.sub.a, the circuit breaker 2 is triggered in a method step 40. To this end, the semiconductor switch 8 is opened or switched to a blocking state by the controller 26. The method is then ended in a method step 42.

(18) The action of the above-described method is explained in detail below on the basis of FIGS. 3 to 6.

(19) FIG. 3 shows, in a diagram of current vs. time, a schematic curve of the charging current I.sub.L of the capacitive load 6 during a turn-on process with a stair-step current limiting of the circuit breaker 2. The time t is plotted along the horizontal abscissa axis (x-axis). The current I is plotted along the vertical ordinate axis (y-axis).

(20) The capacitive load 6 is uncharged at the time of turn-on or cut-in, and hence can take on a large number of electrons. Consequently, the resistance of the capacitive load 6 at turn-on is very low, as a result of which a high current arises that is comparable to a short-circuit current. The high current loading results in a collapse of the output voltage V.sub.a of the circuit breaker 2. As a result, in the method step 30 the output voltage V.sub.a drops below the voltage threshold V.sub.s, so the current limiting is raised to the step value I.sub.s1 by means of the current limit I.sub.g.

(21) In this exemplary embodiment, after the step time T.sub.s1 the current limit I.sub.g is then lowered or reduced in a stair-step or stepwise manner to a step value I.sub.s2 for a step time T.sub.s2 and to a step value I.sub.s3 for a step time T.sub.s3 and to a step value I.sub.s4 for a step time T.sub.s4. After the step time T.sub.s4, the current limit I.sub.g is finally set to the nominal value I.sub.N. The original nominal value I.sub.N is then maintained for the triggering time T.sub.a. The resulting stair-step current limiting 44 substantially representsas can be seen comparatively clearly in FIG. 3an envelope over the actual current curve of the load current I.sub.L during turn-on or addition of the capacitive load 6. In this embodiment, the step times T.sub.s1, T.sub.s2, T.sub.s3 and T.sub.s4 preferably are all dimensioned to be of equal length.

(22) The exemplary embodiment from FIG. 4 shows, in a diagram of current and voltage vs. time, a curve of the load current I.sub.L of the capacitive load 6 and a curve of the output voltage V.sub.a in the event of a fault. The time t is plotted here along the horizontal abscissa axis (x-axis). The current I and the voltage U are plotted along the vertical ordinate axis (y-axis).

(23) In this exemplary embodiment, the circuit breaker has a nominal current of approximately 2 A (amperes). At a point in time t.sub.0, the circuit breaker 2 is loaded with a current I of approximately 8 A. This causes a collapse of the output voltage V.sub.a. As a result, the current limit I.sub.g is set to the step value I.sub.s1 for the step time T.sub.s1. The first step value I.sub.s1 in this exemplary embodiment has a value of 6 A. In the exemplary embodiment, the current switch 2 is continuously loaded with the 8 A, so the current limiting to the step value T.sub.s1 is not sufficient to raise the output voltage V.sub.a again. After the step time T.sub.s1, which is dimensioned at 122 ms, for example, the current limit I.sub.g is reduced to the step value I.sub.s2 of approximately 5.3 A. Next, the current limit is reduced to the step value I.sub.s3 of approximately 4.5 A, and the step value I.sub.s4 3.7 A is reduced stepwise to the nominal value I.sub.N, which in this exemplary embodiment is dimensioned at 2.8 A. The nominal value I.sub.N is maintained during the triggering time T.sub.a of approximately 500 ms, and it is tested whether the output voltage V.sub.a continues to be below the voltage threshold V. Since the output voltage V.sub.a is still collapsed after the triggering time T.sub.a, the circuit breaker 2 then triggers.

(24) In the exemplary embodiment from FIG. 5, a curve of the load current I.sub.L of the capacitive load 6 and a curve of the output voltage V.sub.a are shown in a diagram of current and voltage vs. time in the event of an addition of the capacitive load 6.

(25) In the exemplary embodiment from FIG. 5, the circuit breaker 2 has a nominal value of 4 A and is loaded with a base load of approximately 2.4 A. At the point in time t.sub.0 a capacitance of 43000 F is added as a load 6. The output voltage V.sub.a initially collapses, as a result of which the stair-step current limiting 44 is initiated. Since the output voltage V.sub.a is sufficiently reestablished during the triggering time T.sub.a, and thus exceeds the voltage threshold V.sub.s, the circuit breaker 2 does not trigger, so the load 6 was added without causing other loads in the circuit to be switched off or changed to a passive state.

(26) In the exemplary embodiment from FIG. 6, the triggering time T.sub.a is approximately equal to the time of the stair-step current limiting 44. In this embodiment the circuit breaker 2 has a nominal value of 3 A and is loaded with a base load of approximately 2.4 A. At the point in time t.sub.0 a capacitance of 43000 F is added as a load 6. The output voltage V.sub.a initially collapses, as a result of which the stair-step current limiting 44 is initiated. Since the output voltage V.sub.a is not sufficiently reestablished during the triggering time T.sub.a, and thus does not exceed the voltage threshold V.sub.s, the circuit breaker 2 triggers.

(27) The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.