Method for protecting external circuits from surge voltages

Abstract

The invention relates to a method for protecting an external circuit (2) against surge voltages by means of a protection circuit (1), the protection circuit (1) comprising a protection unit (3) with a semiconductor switch (4) and a voltage regulator (6), in which a set voltage (U_SOLL) and the actual voltage (U_IST) of the external circuit (2) are specified to the voltage regulator (6), and a gate voltage (U_GATE) is supplied to the semiconductor switch (4) by the voltage regulator (6) depending on the difference between the set voltage (U_SOLL) and the extracted actual voltage (U_IST). The invention also relates to a protection circuit (1) for carrying out this method.

Description

[Technical field]

[0001] The invention relates to a method for protecting an external circuit against surge voltages by means of a protection circuit according to the preamble of claim 1. The invention also relates to a protection circuit for carrying out this method. [Background technology]

[0002] To limit surge voltage peaks in electronic circuits, protection circuits with suppressor diodes or TVS diodes (TVS, transient voltage suppressor) are often used. However, TVS diodes are generally optimized for very short peaks (μs to ms) and are often not robust enough for high surge voltages even at low power. Thus, for example in separately excited synchronous machines, the surge voltage peaks can be long in the event of a fault or when the power demand on the synchronous machine changes in dynamic operating conditions. In this case, protection circuits with TVS diodes cannot switch off the surge voltage peaks safely enough.

[0003] The subject of the present invention is therefore to describe improved, or at least alternative, embodiments of methods and protection circuits of the general kind, whereby the mentioned drawbacks are overcome. Summary of the Invention

[0004] According to the invention, this object is solved by the subject matter of the independent claims. Preferred embodiments are the subject matter of the dependent claims.

[0005] A method for protecting an external circuit against a surge voltage by means of a protection circuit is provided. The protection circuit comprises a protection unit connected in parallel with the external circuit and equipped with a semiconductor switch that can be switched, and a voltage regulator. In this method, a set voltage corresponding to a rated voltage of the external circuit is assigned to the voltage regulator. In addition, the voltage regulator taps an actual voltage of the external circuit, which corresponds to a current voltage of the external circuit. Depending on the difference between the assigned set voltage and the tapped actual voltage, the voltage regulator provides a gate voltage to the semiconductor switch of the protection unit. When the gate voltage is applied, the semiconductor switch consumes a current flowing in the external circuit, thus changing the current voltage in the external circuit.

[0006] In the method according to the invention, the gate voltage is adjusted on the semiconductor switch, so that the resistance of the semiconductor switch changes. When the resistance changes, the current drawn from the semiconductor switch changes and, accordingly, the current voltage in the external circuit also changes. In effect, the protection circuit acts as a parallel path with a controlled resistance to receive the excess energy.

[0007] The resistance of the semiconductor switch decreases as the gate voltage increases and increases as the gate voltage decreases. When the gate voltage increases and the resistance decreases, the current consumed by the semiconductor switch in the external circuit increases more. When the gate voltage decreases and the resistance increases, the current consumed by the semiconductor switch in the external circuit decreases more. Thus, the gate voltage of the semiconductor switch is adjusted so that the current drawn from the semiconductor switch reduces the current voltage in the external circuit below the rated voltage of the switching circuit. In other words, the gate voltage of the semiconductor switch is adjusted so that the current flowing through the semiconductor switch is sufficient to limit the peak value of the current voltage in the external circuit. When the current voltage in the circuit is below the rated voltage, the semiconductor switch can be completely turned off.

[0008] In the method according to the invention, a reduction in long-term power losses and a better control of power operation can be advantageously achieved, in addition, costs can be reduced compared to protection circuits with conventional TVS diodes.

[0009] Advantageously, the method may be suitable for different applications. For example, the external circuit may be a contactless rotor power supply for a separately excited synchronous machine. The protection circuit may also be used as a controlled dissipative series resistor. Here, the protection circuit may be integrated into a circuit protection switch, for example for pre-charging applications or for resonant energy dumping of the rotor of a separately excited synchronous machine in case of a short circuit of the stator inverter.

[0010] In a protection circuit, the actual voltage corresponds to the current voltage and the set voltage corresponds to the rated voltage. It should be understood that in both cases the correspondence is the same. For example, the actual voltage of the current voltage and the set voltage of the rated voltage may be the same. Alternatively, the actual voltage may differ from the current voltage by a multiplication factor and the set voltage may differ from the rated voltage by a multiplication factor.

[0011] The protection unit may therefore comprise a voltage divider connected in parallel to the semiconductor switch. In this way, the current voltage in the external circuit may thus be divided by the voltage divider by a factor specified by the voltage divider. The voltage divider may thus extract the divided current voltage as an actual voltage. A set voltage, which essentially corresponds to the rated voltage of the external circuit, pre-divided by the factor, is thus specified to the voltage regulator. The voltage divider may comprise two resistive elements with different electrical resistances. The factor is thus defined by the ratio of the resistance values ​​of the two resistive elements to each other and may be larger or smaller as required depending on the application case. Advantageously, the factor may be adapted to the set voltage.

[0012] In this method, it may be provided that the voltage regulator comprises an impedance converter. The actual voltage taken from the external circuit may thus be conducted by the impedance converter and therefore decoupled from the external circuit. By means of the impedance converter, interactions between the voltage regulator and the external circuit may be eliminated. The impedance converter may be designed as known to the person skilled in the art. Preferably, the impedance converter may comprise at least one resistive element and an operational amplifier. The at least one resistive element may be connected to the inverting input and to the output of the operational amplifier.

[0013] Advantageously, it may be provided that the voltage regulator comprises a PID control loop, in which way the setpoint voltage and the actual voltage may thus be assigned to the PID control loop of the voltage regulator.

[0014] Depending on the difference between the set voltage and the actual voltage, the PID control loop may thus provide a gate voltage for the semiconductor switch. The PID control loop may be designed as known to those skilled in the art. Preferably, the PID control loop may comprise an integrator circuit and an operational amplifier. The integrator circuit may be designed as known to those skilled in the art and comprises at least one capacitor and at least one resistive element connected in parallel with each other. The integrator circuit may be connected to the inverting input and the output of the operational amplifier. The set voltage may be applied to the inverting input of the operational amplifier and the actual voltage may be applied to the non-inverting input of the operational amplifier. The gate voltage for the semiconductor switch may be provided to the output of the operational amplifier.

[0015] As mentioned above, the resistance of the semiconductor switch decreases / increases as the gate voltage increases / decreases, and the current through the semiconductor switch changes. Thus, the current voltage in the external circuit also changes. The gate voltage in turn depends on the current voltage in the circuit. Advantageously, the gate voltage provided by the PID control loop now settles the current voltage in the external circuit to the value required to bring the current voltage in the external circuit to the rated voltage of the external circuit.

[0016] As soon as the current voltage of the external circuit falls below the rated voltage of the external circuit, the semiconductor switch can be turned off by the voltage regulator. In particular, a clear difference between the setpoint voltage and the actual voltage at the two inputs is no longer required by the PID control of the voltage regulator, and therefore no gate voltage is provided by the PID control. Therefore, no gate voltage is applied to the semiconductor switch, which is turned off.

[0017] Preferably, the protection circuit may include a current protection unit and a current regulator for adjusting the current protection unit. In this way, the external circuit may also be protected from the surge current. Thus, a power limiting system that can operate for a long period of time may be formed.

[0018] The invention also relates to a protection circuit for protecting an external circuit from surge currents, the protection circuit comprising a protection unit with a semiconductor switch and a voltage regulator. According to the invention, the protection circuit is designed to perform the above-mentioned method.

[0019] Preferably, the semiconductor switches of the protection units are bipolar transistors with insulated gate electrodes.

[0020] The protection unit may include a voltage divider having at least two electrical resistive elements for specifying a multiplication factor for the actual voltage. The voltage divider may be connected in parallel with the semiconductor switch.

[0021] The voltage divider may include an impedance converter, which is directly connected to the protection unit of the protection circuit. The impedance converter may be designed as known to those skilled in the art. Preferably, the impedance converter may include at least one resistive element and an operational amplifier.

[0022] The voltage divider may include a PID control loop interconnected with an external circuit for deriving an actual voltage, an external source for deriving a set voltage, and a semiconductor switch for specifying a gate voltage. The PID control loop may be designed as known to those skilled in the art. Preferably, the PID control loop may include an integrator circuit and an operational amplifier.

[0023] To avoid repetition, reference is made here to the above description.

[0024] Further important features and advantages of the invention emerge from the dependent claims, the drawings and the associated figure description by the drawings.

[0025] It is to be understood that the features mentioned above, and those further described below, can be used not only in the respective combinations described, but also in other combinations or alone without departing from the scope of the present invention.

[0026] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred exemplary embodiments of the present invention are illustrated in the drawings and will be described in more detail in the following description, where like reference numbers refer to identical, similar, or functionally identical components. [Brief description of the drawings]

[0027] Each case is shown diagrammatically. [Figure 1] FIG. 1 shows a schematic diagram of a protection circuit according to the invention with an external circuit. [Diagram 2] FIG. 2 shows the time course of voltage and current in the circuit according to FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] 1 shows a circuit diagram of a protection circuit 1 according to the present invention, comprising an external circuit 2. The external circuit 2 comprises a current source Q1, a capacitor C1 and a resistive element R1. The current source Q1, the capacitor C1 and the resistive element R1 are connected in parallel with each other. It should be understood that the external circuit 2 shown is merely exemplary. The external circuit 2 shown is not part of the present invention.

[0029] The protection circuit 1 according to the invention comprises a protection unit 3 with a semiconductor switch 4 and a voltage divider 5, which is formed from resistive elements R2 and R3. The voltage divider 5 determines a multiplication factor determined by the ratio of the electrical resistances of the two resistive elements R2 and R3. In addition, the protection circuit 1 comprises a voltage regulator 6 with an impedance converter 7 and a PID control loop 8. The impedance converter 7 comprises a first operational amplifier OP1 and resistive elements R4, R5, R11 and R15. The PID control loop 8 comprises an integrator circuit 9, which comprises two capacitors C2 and C3 and a resistive element R14. In addition, the PID control loop 8 comprises a second operational amplifier OP2 and two resistive elements R9 and R10.

[0030] The current source Q1 generates a current I1, and a current voltage U_AKTUELL is applied to the elements of the external circuit 2. In the voltage divider 5, an actual voltage U_IST is applied, which corresponds to the current voltage U_AKTUELL divided by the multiplication factor. The actual voltage U_IST is taken from the voltage regulator and decoupled from the external circuit 2 by an impedance converter 7. Following this, the actual voltage U_IST is conducted to a second operational amplifier OP2 of a PID control loop 8. In addition, a set voltage U_SOLL is applied to the second operational amplifier OP2 of the PID control loop 8, which corresponds to the nominal voltage of the external circuit 2 divided by the multiplication factor.

[0031] Depending on the difference between the actual voltage U_IST and the set voltage U_SOLL at its input terminals, the second operational amplifier OP2 outputs a gate voltage U_GATE, which in turn is applied to the semiconductor switch 4. When the actual voltage U_IST exceeds the set voltage U_SOLL, the semiconductor switch 4 is turned on, otherwise it is turned off. The gate voltage U_GATE rises and falls depending on the above-mentioned difference, and as a result, depending on this, the resistance of the semiconductor switch 4 also changes. The resistance of the semiconductor switch 4 decreases when the gate voltage U_GATE rises and increases when the gate voltage U_GATE falls. When the gate voltage U_GATE rises, the resistance of the semiconductor switch 4 decreases and it consumes more current in the external circuit 2. Thus, the current voltage U_AKTUELL in the external circuit 2 falls. When the gate voltage U_GATE falls, the resistance of the semiconductor switch 4 increases and it consumes less current in the external circuit 2. Thus, the current voltage U_AKTUELL in the external circuit 2 rises. The gate voltage and thus the resistance value of the semiconductor switch 4 settle at a value such that the current voltage U_AKTUELL corresponds exactly to the rated voltage of the external circuit.

[0032] The two operational amplifiers OP1 and OP2 are each supplied with a supply voltage U_AMP of the power supply. It is conceivable that the two operational amplifiers OP1 and OP2 are supplied with the supply voltage U_AMP from the same power supply. The power supply may additionally also provide a set voltage U_SOLL. For this purpose, the supply voltage U_AMP of the power supply may be divided by a further voltage divider. It may further be envisaged that the two operational amplifiers OP1 and OP2 are arranged, fixed or integrated in a common component.

[0033] The protection circuit 1 is designed to carry out a method 10 according to the invention, which is explained in more detail by means of FIG.

[0034] 2 shows the time courses of voltages and currents in the circuit according to FIG. 1, corresponding to a simulation of the method 10 according to the invention. In the partial image A, the time courses of the current I1 of the current source Q1 and the current I_4 drawn from the semiconductor switch 4 are shown. In the partial image B, the time courses of the gate voltage U_GATE are shown. In the partial image C, the time courses of the actual voltage U_IST and the time courses of the set voltage U_SOLL are shown. In the partial image D, the time courses of the current voltage U_AKTUELL in the external circuit 2 are shown.

[0035] During the simulation, exemplary values ​​are set: Here, the current source Q1 supplies a current I1 of 200 mA. The resistive element R1 is a 5 kΩ resistor. The voltage divider 5 divides the current voltage U_AKTUELL in the external circuit 2 to the actual voltage U_IST with a factor equal to 100. The rated voltage of the external circuit 2 is set to 420 V. The set voltage U_SOLL corresponds to the rated voltage of the external circuit 2 divided by the factor 100 and amounts to 4.2 V. The voltage regulator is therefore set to a rated voltage of 420 V.

[0036] At a current voltage U_AKTUELL of 400 V, the resistive element R1 with a resistance of 5 kΩ consumes a current of 80 mA. However, the current source Q1 supplies a current I1 of 200 mA. Thus, the current voltage U_AKTUELL at the resistive element R1 rises. When the current voltage U_AKTUELL becomes higher than 420 V, i.e. the actual voltage becomes higher than 4.2 V, the second operational amplifier OP2 applies the gate voltage U_GATE to the semiconductor switch 4. Thus, the semiconductor switch 4 is turned on. The gate voltage U_GATE settles to a value at which the semiconductor switch 4 consumes just the extra current of 120 mA in the external circuit 2. This behavior corresponds to the operation of a conventional TVS diode, but allows for reduced long-term power losses and better control of the system operation.

Claims

1. A method for protecting an external circuit (2) from surge voltage by means of a protection circuit (1), wherein the protection circuit (1) is connected in parallel with the external circuit (2) and comprises a protection unit (3) with a semiconductor switch (4) that can be switched, and a voltage regulator (6), a set voltage (U_SOLL) corresponding to the rated voltage of the external circuit (2) is specified for the voltage regulator (6), the voltage regulator (6) extracts the actual voltage (U_IST) of the external circuit (2) corresponding to the current voltage (U_AKTUELL) of the external circuit (2), the voltage regulator (6) supplies a gate voltage (U_GATE) to the semiconductor switch (4) of the protection unit (3) according to the difference between the specified set voltage (U_SOLL) and the extracted actual voltage (U_IST), at the applied gate voltage (U_GATE), the semiconductor switch (4) consumes the current (I1) flowing through the external circuit (2), thereby changing the current voltage (U_AKTUELL) in the external circuit, Method.

2. The protection unit (3) comprises a voltage divider (5) connected in parallel with the semiconductor switch (4), the current voltage (U_AKTUELL) in the external circuit (2) is divided by the voltage divider (5) according to a magnification specified by the voltage divider (5), and is extracted from the voltage regulator (6) as the actual voltage (U_IST), the voltage regulator (6) is specified with a set voltage (U_SOLL) corresponding to the rated voltage of the external circuit (2) pre-divided by the magnification, The method according to claim 1.

3. The voltage regulator (6) comprises an impedance converter (7), and the actual voltage (U_IST) taken out in the external circuit (2) is conducted by the impedance converter (7) and thus decoupled from the external circuit (2). The method according to claim 1.

4. The voltage regulator (6) comprises a PID control loop (8), and the PID control loop (8) is specified with the set voltage (U_SOLL) and the actual voltage (U_IST). Depending on the difference between the set voltage (U_SOLL) and the actual voltage (U_IST), the PID control loop (8) supplies the gate voltage (U_GATE) in the semiconductor switch (4). The method according to claim 1.

5. The voltage regulator (6) comprises an impedance converter (7), and the actual voltage (U_IST) taken out in the external circuit (2) is conducted by the impedance converter (7) and thus decoupled from the external circuit (2). The actual voltage (U_IST) decoupled by the impedance converter (7) is supplied to the PID control loop (8). The method according to claim 4.

6. The gate voltage (U_GATE) supplied by the PID control loop (8) is adjusted to a value necessary to set the current voltage (U_AKTUELL) in the external circuit (2) to the rated voltage of the external circuit (2). The method according to claim 4.

7. The magnification corresponds to the set voltage (U_SOLL). The method according to claim 2.

8. As soon as the current voltage (U_AKTUELL) of the external circuit (2) falls below the rated voltage of the external circuit (2), the semiconductor switch (4) is turned off by the voltage regulator (6). The method according to claim 1.

9. A protection circuit (1) for protecting the external circuit (2) from a surge voltage, The protection circuit (1) comprises the protection unit (3) having the semiconductor switch (4) and the voltage regulator (6), The protection circuit (1) is designed to execute the method according to claim 1. Protection circuit (1).

10. The semiconductor switch (4) of the protection unit (3) is a bipolar transistor having an insulated gate electrode. The protection circuit according to claim 9.

11. The protection unit (3) comprises a voltage divider (5) having at least two resistor elements (R2, R3) for specifying a magnification factor for the actual voltage (U_IST), and the voltage divider (5) is connected in parallel with the semiconductor switch (4). The protection circuit according to claim 9.

12. The voltage regulator (6) comprises an impedance converter (7), and the impedance converter (7) is directly connected to the protection unit (3) of the protection circuit (1). The protection circuit according to claim 9.

13. The voltage regulator (6) comprises a PID control loop (8), and the PID control loop (8) is interconnected with the external circuit (2) for taking out the actual voltage (U_IST), an external source for taking out the set voltage (U_SOLL), and the semiconductor switch (4) for specifying the gate voltage (U_GATE). The protection circuit according to claim 9.

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