Electronic circuit breaker and method for operating the circuit breaker

Abstract

Electronic circuit breaker (1) with a line (9) running between an input (E) and an output (A), into which line a semiconductor switch (4) with "source" and "drain" connections is connected, and with a control unit (6), wherein an ammeter (3) is arranged in the line (9) between the input (E) and the output (A), wherein an output of the ammeter (3) is connected to an input of the control unit (6) so that an output signal for controlling the semiconductor switch (4) is formed from the input parameter of the current, and wherein an output of the control unit (6) is connected to the gate connection of the semiconductor switch (4), characterized in that when switched on, a voltage (U) at the output (A) is gradually increased according to a ramp (10) and the state of a load (L1 to L5) connected to the output (A) is determined during the course of the voltage increase by continuously measuring the current.

Description

The invention relates to an electronic circuit breaker of the type specified in the preamble of claim 1 and to a method for operating the circuit breaker.In a voltage supply system, electronic circuit breakers are used in order to reliably disconnect the current path from loads, for example in the form of actuators, sensors or interfaces in the event of a defect, for example a short circuit, and thus to protect the loads. A defective load frequently results in an overload current, as a result of which electrical lines and components are exposed to increased loading and are possibly damaged or destroyed. In the event of a short circuit in a connected load with, for example, 24 V DC voltage, a current of approximately 100 A or more can flow in the current path to be monitored. For active current limiting, semiconductor switches in the form of a MOSFET or IGBT are usually used. Such semiconductor switches take up a substantial portion of the supply voltage, that is to say that the semiconductor switch can be exposed to a high current and high voltage in the event of a fault in the current path. The greater the supply voltage, the greater the load on the semiconductor switch. However, the MOSFETs or IGBTs mentioned have a region called SOA (Save Operation Area) which is formed by the current, the voltage and the time together. The SOA of a semiconductor switch must not be exceeded, since otherwise the operational reliability of the electronic circuit breaker and thus of the entire voltage supply system would be endangered.It is known for the state detection of a connected load to provide a current limitation at a predetermined level. If the predefined level of the current is exceeded for a specific duration, a defect or short circuit in the load is presumed and the protective function in the circuit breaker is triggered by activation of the semiconductor switch. Since, depending on the load type of the load, different conditions with respect to the current must be taken into account when switching on the load, in particular because some loads require a large starting current for a certain time during starting, the triggering time of the circuit breaker must not be set too short. This leads to no higher supply voltages being used in order not to exceed the SOA of the semiconductor switch.Electronic circuit breakers according to the preamble of claim 1 are known from the documents US 2011 / 0 242 716 A1, EP 1 150 410 A2, WO 2009 / 123 615 A1, DE 197 12 261 A1, US 2011 / 0 221 404 A1 and DE 10 2004 057 119 A1.DE 695 33 383 T2 discloses a driver circuit for a power device in which the gate voltage is immediately raised to a high level without simultaneous measurement of the current.DE 103 49 629 A1 discloses an electronic circuit for providing a suitable load voltage for supplying a control unit of a motor vehicle even during predetermined fault cases which do not require a fuse. In the path of the load current, a transistor is arranged, the gate voltage of which rises with a delay buffered via a capacitor.U.S. Pat. No. 5,374,887 A relates to an electronic circuit breaker in which the voltage first assumes a constant value. Starting from this constant value, a voltage rise takes place in the form of a ramp.The object of the present invention is to provide an electronic circuit breaker of the generic type which enables a reliable disconnection of a current path more quickly. It is a further object of the invention to provide a method of operating the circuit breaker which permits diagnosis in various operating states.This object is achieved by an electronic circuit breaker having the features of claim 1 and by a method having the features of claim 8.The present invention provides an electronic circuit breaker which is applicable to various types of loads. To diagnose the state, the current is continuously measured and a corresponding signal is supplied to a control unit, which generates signals for driving the semiconductor switch on the basis of this value. When switching on, the voltage is gradually increased according to a ramp and the state of the load connected to the output is determined in the course of the voltage increase. With this circuit breaker, it becomes possible to reliably detect a fault in a connected load within ≤3 ms. The circuit breaker according to the invention allows the operating reliability of the voltage supply system to be significantly increased. In addition, the circuit breaker provides additional functions, namely diagnosis, state archiving, active current limiting, remote control, etc. The invention makes it possible to effectively use electronic circuit breakers in an "unsmooth" voltage supply system (higher voltage, steep current rises, strong fluctuations). The semiconductor switch is operated in a safe area. Preferably, in addition to the current, the voltage is also continuously measured and a corresponding signal is supplied to the control unit. A microcontroller is considered as the control unit, but it can alternatively comprise an operational amplifier or a flip-flop.In connection with renewable energy, direct current networks play an essential role. Solar or battery voltage suppliers do not have inherent current protection, thus requiring an external circuit breaker. The present invention is particularly suitable for use as an electronic circuit breaker in such supply systems, since it can react more quickly in the event of a fault. The requirements with respect to a steep current rise, severe voltage fluctuations and also greater voltage or current are thus taken into account.An exemplary embodiment of the invention is explained in more detail below with reference to the drawings. The drawing shows: FIG. 1 shows a block diagram of an electronic circuit breaker with different loads which can be connected to its output, FIG. 2 shows a voltage profile during a new connection of a load connected to the output of the circuit breaker with ohmic load and a current profile given via the time axis, FIG. 3 shows a voltage profile during the new connection of a load connected to the output of the circuit breaker and having a capacitive load, and a current profile given over the time axis, FIG. 4 shows a voltage profile when switching on a load connected to the output of the circuit breaker in the event of a short circuit in the load and a corresponding current profile, FIG. 5 shows a voltage profile in the case of a short circuit during the operation of a connected load and associated current profile, FIG. 6 shows a voltage profile when a capacitive load of a connected load is connected during operation and associated current profile, FIG. 7 shows a voltage profile in the case of a short circuit occurring at a high voltage and associated current profile.Referring now to FIG. 1, there is shown a block diagram of an electronic circuit breaker 1 having an input E and an output A. A line 9 forming a current path extends between the input E and the output A, into which line a semiconductor switch 4 in the form of a MOSFET or IGBT is connected with its source and drain connections. Starting from the input E, a fuse 2 is first connected into the line 9 and an ammeter 3 is connected between the fuse and the semiconductor switch 4, which in turn is connected to the semiconductor switch 4. Connected to the input E is a circuit 5 for the internal supply of the electronic circuit breaker 1, which circuit is connected to a control unit 6 in order to provide the required energy to the latter. In the exemplary embodiment of FIG. 1, a microcontroller 6 is provided as the control unit, which is referred to as such in the following description. A voltmeter 7 is also provided which measures the voltage between input E and output A. An output of the ammeter 3 and an output of the voltmeter 7 are each connected to an input of the microcontroller 6. The respective output signals of the ammeter 3 and the voltmeter 7 are supplied to the microcontroller 6, which forms an output signal from these input parameters, which is supplied to a driver 8, which in turn is connected to a gate terminal of the semiconductor switch 4 (MOSFET or IGBT). A load is connected to the output A, which is generally referred to as load L, wherein this load can represent quite different loads at the output of the electronic circuit breaker 1, for example a short circuit L 1, an inductive load L 2, an ohmic load L 3 and a capacitive load L 4 or another load L 5.With the illustrated circuit breaker 1, it is possible to identify the different load types as such, since both the voltage between input and output and the current flowing through the semiconductor switch are continuously measured and the corresponding signals are processed in the microcontroller 6 to generate a signal for driving the gate of the MOSFET or IGBT.FIG. 2 shows the profile of the voltage U and of the current I when a load with ohmic load connected to the output of the electronic circuit breaker (L 3 in FIG. 1 ) is switched on anew. In order to determine whether a defect is present in the load, for example a short circuit which could cause damage, in particular to the semiconductor switch (MOSFET or IGBT), the voltage U is gradually increased starting from zero, as shown in FIG. 2, this increase being referred to as ramp 10. Accordingly, the current I also gradually increases in the same relation. This rise in the voltage U takes place-if no defect is present-until the full operating voltage (rated voltage) is reached, wherein at the same time the current I reaches its predefined level (rated current). This time is designated t' in FIG. 2. The slope of the ramp 10 is adjustable, which is simple in the case of a MOSFET as a semiconductor switch, because for this purpose only the control 8 in FIG. 1 has to have the gate voltage rise according to a corresponding ramp. In general, a precise ramp 10 of the voltage U at the output A can be generated by forming a closed loop. The slope of the ramp is also variable as the current increases so as to optimize the voltage / current response for speed and accuracy.FIG. 3 shows the profile of voltage U and current I when a load with capacitive load (L 4 in FIG. 1 ) connected to the output of the electronic circuit breaker is switched on again. It can be seen that the voltage U is gradually increased according to the ramp 10, as is described with reference to FIG. 2. Due to the capacitive load (L 4 in FIG. 1 ), a steep increase of the current I takes place until the maximum charging current of the capacitance is reached. As the voltage U at the ramp 10 rises, the maximum charging current I runs at a constant level until it drops steeply toward zero approximately at the time when the rated voltage is reached. The electronic circuit breaker according to FIG. 1 recognizes, on the basis of the simultaneous voltage and current measurement and the inclusion of the corresponding signals in the drive of the MOSFET or IGBT, that the strong increase in the current with an increase in the voltage according to ramp 10 is not due to a defect, but is due to the capacitive load (L 4 in FIG. 1 ).FIG. 4 shows the profile of the voltage U and of the current I when a load which is connected to the output of the electronic circuit breaker and is defective as a result of a short circuit is switched on anew, that is to say with a load L 1 according to FIG. 1. Even with a small increase in the voltage U at the start of the ramp 10, the current I rises abruptly to a value which corresponds to a multiple of the rated current and is therefore identified as a short-circuit current. It is clear from FIG. 4 that the circuit breaker detects the defect of the connected load already at a very low voltage U and disconnects the current path (line 9 in FIG. 1 ) by driving the MOSFET or IGBT. As shown in FIG. 4, the voltage U collapses and thus no longer flows a current I. If a considerable defect is present in the load, such as a short circuit, the circuit breaker can react even at a very low output voltage and disconnect the current path. This may be the case after a very short time, for example within 3 ms.FIGS. 2 to 4 clearly show that the state of the respective load or of the load formed by it is determined at low voltage U. In this way, it is ensured that the semiconductor switch is not operated in a range hazardous to this area and thus the SOA of the semiconductor switch is not exceeded.FIG. 5 shows a curve of the voltage U and of the current I in the event of a short circuit during the operation of a load connected to the output of the circuit breaker. At a time t 1, the short circuit occurs, i.e. the current rises sharply abruptly, which is detected by the ammeter 3 in FIG. 1 and immediately triggers the disconnection of the current path. As a result, the voltage U collapses and no current I flows. At a time t 2, the state of the load is tested once again and a gradual increase of the voltage U in the form of the ramp 10 begins. Since the short circuit in the connected load is still present as a defect, the current I rises again very steeply and exceeds a permissible level, as a result of which the circuit breaker disconnects the current path and the voltage U and the current I at the output are thus "zero". The time interval between t1 and t2 should preferably be <5 ms.FIG. 6 shows the profile of the voltage U and of the current I during the operation of a connected load when a capacitive load (L 4 in FIG. 1 ) is switched on. At a time t 1, a sudden current rise occurs, which is detected by the ammeter and drives the semiconductor switch that disconnects the current path. As a result, the voltage U collapses and no current I flows. At the time t 2, a test is carried out as to whether the sudden current increase is attributable to a defect in the load or whether another fault was the cause of the shutdown. Therefore, at t 2, the output voltage is gradually increased according to the ramp 10. Since the connected load is a capacitive load, a steep but still permissible increase in the current I takes place until the maximum charging current of the capacitance is reached. With a further rising voltage U according to ramp 10, the charging current initially remains at this level and drops to the level of the predefined operating current approximately at the time when the rated voltage is reached.FIG. 7 shows the curve of the voltage U and of the current I in the case of such a defect in which the fault only occurs at a higher voltage, for example when an insulation is no longer sufficient and a short circuit only arises when a higher voltage is reached. The voltage U gradually rises according to the ramp 10 and the current I also rises at the corresponding ratio. Even before the rated voltage is reached, a short circuit occurs in the connected load, so that a larger short-circuit current flows abruptly, which initiates the protective function of the circuit breaker already described above and therefore the voltage U and the current I are at "zero". At the time t 2, it is tested once again whether the cause of the shutdown is attributable to a defect in the consumer. In this case, the voltage U is increased again according to the ramp 10, as a result of which a current increase also takes place. Since the short circuit again occurs when the voltage level is reached, as in the previous rise, the current path is disconnected as already described. It is thus established that the consumer is defective.The electronic circuit breaker illustrated in FIG. 1 and described above ensures that the current path is very rapidly disconnected at high current both during switching on and during operation, and the load is thus switched off. The time required for this is extremely short and for t' in FIGS. 2 to 4 or t 1 in FIGS. 5 to 7 is in the range of <3 ms, preferably 1 ms. It is also possible to test, by increasing the voltage again according to the ramp, whether a defect is actually present in the connected load. Depending on the situation, the load is either switched off or put back into operation. The determination of the voltage rise or the steepness of the ramp 10 is such that the output voltage rises slowly enough so that the state of the load can already be determined before the semiconductor switch is subjected to too great a load. On the other hand, the output voltage must not rise too slowly, since otherwise the semiconductor switch absorbs too great a power loss. The ramp should therefore be in a range between 0.2V / ms and 50V / ms.

Claims

Electronic circuit breaker (1) having a line (9) running between an input (E) and an output (A), into which a semiconductor switch (4) having terminals "source" and "drain" is connected, and having a control unit (6), wherein a current meter (3) is arranged in the line (9) between input (E) and output (A), wherein an output of the current meter (3) is connected to an input of the control unit (6), such that an output signal for driving the semiconductor switch (4) is formed from the input parameter of the current, and wherein an output of the control unit (6) is connected to the gate terminal of the semiconductor switch (4), characterized in that, that, upon switching on, a voltage (U) at the output (A) is gradually increased according to a ramp (10), and the state of a load (L1 to L5) connected to the output (A) is determined in the course of the voltage increase by continuous measurement of the current.Circuit breaker according to Claim 1, characterized in that a voltmeter (7) is connected to the input (E) and to the output (A), and an output of the voltmeter (7) is connected to an input of the control unit (6), with the result that an output signal for driving the semiconductor switch (4) is formed from the input parameters of current and voltage.Circuit breaker according to Claim 1 or 2, characterized in that the output of the control unit (6) is connected to a control (8), which in turn is connected to the gate connection.Circuit breaker according to one of Claims 1 to 3, characterized in that the control unit is a microcontroller (6).Circuit breaker according to one of Claims 1 to 3, characterized in that the control unit comprises an operational amplifier.Circuit breaker according to one of Claims 1 to 3, characterized in that the control unit comprises at least one flip-flop.Circuit breaker according to one of Claims 1 to 6, characterized in that a fuse (2) is provided in the line (9) between the input (E) and the ammeter (3).Method for actuating an electronic circuit breaker (1) which comprises an input (E) and an output (A) and a semiconductor switch (4) connected therebetween, and a control unit (6) for driving the semiconductor switch (4), characterized in that the current (I) flowing between the input (E) and the output (A) is continuously measured and a corresponding signal is transmitted to the control unit (6) as an input parameter, said signal forming an output signal from this signal for driving the semiconductor switch (4) and driving a gate terminal of the semiconductor switch (4) accordingly, wherein the voltage (U) at the output (A) is gradually increased according to a ramp (10) when it is switched on, and the state of a load (L1 to L5) connected to the output (A) is determined by continuous measurement of the current in the course of the voltage increase.Method according to Claim 8, characterized in that the voltage lying between the input (E) and the output (A) is continuously measured and a corresponding signal is fed as input parameter to the control unit (6) and the output signal is formed from both signals of current (I) and voltage.Method according to claim 8 or 9, characterized in that the ramp (10) has an increase which is in the range of 0.2V / ms to 50V / ms.Method according to one of Claims 8 to 10, characterized in that, after the semiconductor switch (4) has been switched off by actuating the gate terminal after an impermissible operating state, a renewed rise in the voltage (U) takes place according to the ramp (10) at a predefined time interval, wherein this time interval is preferably <5 ms.

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