GB2566044A

GB2566044A - A device and method for generating a measurement signal for an AC current in a phase line

Info

Publication number: GB2566044A
Application number: GB1713944.5A
Authority: GB
Inventors: Bolz Stephan
Original assignee: Bombardier Primove GmbH
Current assignee: Bombardier Primove GmbH
Priority date: 2017-08-31
Filing date: 2017-08-31
Publication date: 2019-03-06
Also published as: GB201713944D0

Abstract

A device and method for generating a measurement signal (Vm, DS) for an AC current i in a phase line, wherein the device 1 comprises at least one decoupling means 2 for decoupling a current signal from the phase line, wherein the device further comprises at least one burden resistance element 5 electrically connected to the decoupling means, wherein the measurement signal is provided by the voltage falling across the at least one burden resistance element or by a signal which is a function of the voltage falling across the at least one burden resistance element, characterized in that the device further comprises at least one rectifying means 11, wherein the at least one burden resistance element is electrically connected to the decoupling means via the at least one rectifying means such that a rectified decoupled current signal is provided to at least one terminal T1 of the burden resistance element. The decoupling means may be a current transformer and the rectifying means may be a bridge rectifier.

Description

A device and method for generating a measurement signal for an AC current in a phase line

In the field of inductive power transfer as well as many other technical fields, an isolated, high frequency current measurement and current level detection is desirable, e.g. for control purposes and I or for safety purposes. In an inductive power transfer application, it is e.g. desired to measure the current for controlling a converter which provides the alternating current to energize the primary winding structure. In particular, the measured current can be used as a feedback signal for a controller which controls the energy to be transferred inductively. Further, a current level detection can be used, in particular for instantaneous detection of abnormal or potentially safety relevant levels which may require immediate response, e.g. a system shut down. The system shut down can e.g. performed by executing a hardware - based function.

Figure 1 shows a schematic circuit diagram of a device 1 for generating a measurement signal Vm (see Fig. 7a) for an alternating current (AC current) in a phase line PL according to the state of the art. The device 1 comprises a current transformer 2, wherein the current transformer 2 comprises a first winding 3 and a second winding 4. The first and the second winding 3, 4 are inductively coupled, but galvanically isolated. The device 1 further comprises a burden resistor 5 which is electrically connected to the second winding 4 of the current transformer 2. In particular, a first terminal T1 of the burden resistor 5 is electrically connected to a first terminal of the secondary winding 4 and a second terminal T2 of the burden resistor 5 is electrically connected to a further terminal of the second winding 4 of the current transformer 2.

Further shown is that the device 1 comprises a voltage source 6 which provides a reference voltage Vref, e.g. 2.5 V. The reference voltage Vref is a direct current (DC) voltage and is provided to the second terminal T2 of the burden resistor 5.

Further shown is a phase current i which flows through the phase line PL and a potential Vi of the first terminal T1 of the burden resistor 5. The potential Vi is measured relative to a reference potential RP.

The measurement signal Vm corresponds to the voltage falling across the burden resistor 5 and thus to the difference between the potential Vi and the reference voltage Vref.

Figure 2 shows exemplary time courses for signals provided within the circuit diagram shown in Figure 1. In the first row, a schematic time course of the phase current i is shown, wherein the phase current i flows through the first winding 3 of the current transformer 2. It is shown that a peak amplitude of the phase current i is equal to +/- 40 A.

In the second row, a so-called decoupled current i_d, i.e. translated current, is shown, wherein the decoupled current i_d flows through the second winding 4 of the current transformer 2. Due to the transformer ratio of the current transformer 2, a peak amplitude of the decoupled current i_d is equal to +/- 200 mA.

In the third row, a schematic time course of the measurement signal Vm is shown, wherein the measurement signal Vm corresponds to the voltage falling across the burden resistor 5. It is shown that an offset value of the measurement signal Vm corresponds to the reference voltage Vref provided by the voltage source 6. Further shown is that the voltage level is within a predetermined interval from 0 V to 5 V.

Figure 3 shows a schematic circuit diagram of a detection signal generating section according to the state of the art.

It is shown that the potential Vi of the first terminal T1 of the burden resistor 5 (see Figure 1) is provided to a first terminal of a first comparator 7 and to a first terminal of a second comparator 8. Further shown are a first comparing voltage generating means 9 and a second comparing voltage generating means 10. The first comparing voltage generating means 9 provides a DC voltage with a predetermined first level to a second terminal of the first comparator 7 (high voltage level). The second comparing voltage generating means 10 provides another DC voltage with another voltage level to a second terminal of the second comparator 8 (low level). The first level is higher than the other level.

The voltage generating means 9, 10 provide voltages such that the difference between the potential Vi of the first terminal T1 of the burden resistor 5 and the reference voltage Vref, i.e. the measurement signal Vm, is compared to desired threshold values.

An output terminal of the comparators 7, 8 is connected to input terminals of an AND-gate

19. The first comparator 7 provides a high level output signal if the potential Vi of the first terminal T1 of the burden resistor 5 is higher than the voltage provided by the first comparing voltage generating means 9. The second comparator 8 provides a high level output signal if the voltage provided by the second comparing voltage generating means 9 is higher than the potential Vi of the first terminal T1 of the burden resistor 5.

As a result, a high level detection signal DS is generated if the voltage falling across the burden resistor 5 is higher than a desired threshold value or lower than a further threshold value as an output signal of the AND-gate 19. This detection signal DS can e.g. be used for error state detection. If such an error state is detected, safety measures can be conducted, in particular a system shut down by a hardware-based function.

The disadvantage of the measurement signal generation according to Figure 1 is the need for at least two A/D converter inputs and the effort needed for calculating the actual voltage falling across the burden resistor 5 which is usually done by software, requiring consecutive steps and adding an undesired delay time to a feedback control loop.

The disadvantage of the detection signal generation according to Figure 3 is the need for at least two voltage comparators 7, 8 and at least two voltage generating means 9, 10 and a logic combining means 19. This hardware effort triples in three phase applications.

A further disadvantage is that two comparators 7, 8 and two comparing voltage generating means 9, 10 are required in order to reliably generate the detection signal DS, e.g. for detecting an error state.

There is the technical problem of providing a device for generating a measurement signal AC current in a phase line as well as for a method for generating such a signal which allow a fast, computationally efficient and cost effective generation of the measurement signal or the detection signal, in particular in a digital form.

The solution to said technical problem is provided by the subject-matter with the features of claim 1 and claim 10. Further advantages embodiments are provided by the subjectmatter of the sub claims.

This invention can be based on the assumption that a sign information of the AC current in the phase line is not required for control purposes for monitoring purposes.

A device for generating a measurement signal for an AC current in a phase line is proposed. The phase line can be an electric line carrying a feeding voltage or a power supply voltage for an arbitrary load. In particular, the phase line can be a phase line of a primary unit or a secondary unit of a system for inductive power transfer. In particular, the phase line can be electrically connected to a primary winding structure or to a secondary winding structure of said units.

The measurement signal can e.g. be proportional to the current level or amplitude of the AC current in the phase line. Alternatively, the measurement signal can also be a detection signal, wherein the detection signal represents a certain state of the measurement signal, e.g. if the measurement signal level is higher than a predetermined threshold value or lower than a predetermined threshold value or if the measurement signal level is within a predetermined value interval.

The measurement signal can be used for control purposes, in particular for controlling the AC current or quantities depending on the AC current in the phase line, e.g. the transferred power in case of the system for inductive power transfer. Further, the measurement signal can be used for monitoring purposes, e.g. for fault detection.

This means that a control function can be executed as a function of at least the measurement signal. Alternatively or in addition, a safety function can be executed as a function of at least the measurement signal.

The device comprises at least one decoupling means for decoupling a current signal from the phase line. The decoupling means can be configured such that a decoupled signal is generatable, wherein the decoupled signal is a function of the AC current in the phase line, in particular is proportional to said AC current in the phase line. Preferably, the decoupled signal is generated in a galvanically isolated way. More preferably, the decoupling means is a current transformer. The current transformer has been explained before. In particular, the current transformer can comprise a first winding which is electrically connected to the phase line and second winding which is inductively coupled to the first winding, but not electrically connected to the phase line. The current transformer can have a predetermined transformer ratio.

Further, the device comprises at least one burden resistance element, preferably at least one burden resistor. The burden resistance element can have a predetermined resistance. As will be explained later, the resistance value can be chosen according to system requirements.

Further, the at least one burden resistance element is electrically connected to the decoupling means. In particular, the at least one burden resistance element is electrically connected to the decoupling means such that the decoupled current signal, e.g. the current flowing through the second winding of the current transformer, can flow to at least one terminal of the burden resistance element. The electrical connection between the burden resistance element and the decoupling means can be such that the decoupled current signal generated by the decoupling means flows through the first terminal of the burden resistance element.

Further, the measurement signal is provided by the voltage falling across the at least one burden resistance element. In this case, the measurement signal is proportional to the level of AC current in the phase line.

Alternatively, the measurement signal is provided by a signal which is a function of the voltage falling across the at least one burden resistance element. In this case, the measurement signal can be a detection signal.

According to the invention, the device further comprises at least one rectifying means. The at least one burden resistance element is electrically connected to the decoupling means via the at least one rectifying means such that a rectified decoupled current signal is provided to at least one terminal, in particular the first terminal, of the burden resistance element. In other words, the rectifying means is designed and I or arranged such that the AC decoupled current signal is rectified by the rectifying means, wherein the rectified current signal is provided to the burden resistance element, in particular flows through the first terminal of the burden resistance element.

A second terminal of the burden resistance element can e.g. be connected to a predetermined reference potential or ground potential. The reference potential can e.g. be the reference potential of the phase line or the reference potential of another electric system.

The proposed device advantageously allows the generation of a measurement signal for control or monitoring purposes which can be processed quickly and computationally efficient, in particular in a digital form, e.g. by a microcontroller. In particular, the device does not need an extra voltage source for providing a reference voltage in addition to the reference voltage of an A/D converter, wherein the reference voltage needs to be digitalized in addition to the measurement signal.

The invention is based on the insight that the decoupling means, in particular the current transformer, has mainly properties of an ideal AC current source. This, in turn, means that the voltage which falls across the burden resistance element is to some extend independent of the presence of other electric components, e.g. resistive components, inductive components and I or capacitive components which are arranged in between the decoupling means and the burden resistance element. The properties of the ideal AC current source are based on the transformer ratio of the current transformer which is usually a high ratio of up to 1:200, 1:200 or larger than 1:200. This has the effect that the voltage induced in the first winding of the current transformer due the current flow in the second winding is much smaller than the phase line voltage falling across the first winding during a current flow of the phase current.

This means that rectifying means which is arranged between the decoupling means and the burden resistance element will also not or only minimally impede the flow of the decoupled current signal. This again means that rectification of the decoupled current signal is possible without falsifying any signal information. A rectified signal, however, greatly simplifies its measurement as no reference voltage needs to be used and a level detection since only one comparing voltage value needs to be used.

In a preferred embodiment, the decoupling means is a current transformer. This and corresponding advantages have been explained before. The current transformer can have a transformation ratio equal to or larger 1:200. The higher the ratio, the more equal are the properties of the current transformer to the properties of a constant current source.

In another embodiment, a first winding of a current transformer is electrically connected to the phase line. The first winding can therefore be also referred to as high level winding.

Further, a second winding of the current transformer is connected to the at least one rectifying means. The second winding can also be referred to as low level winding. In particular, a first terminal of the second winding can be connected to a first AC terminal of the rectifying means. A second terminal of the second winding can be connected to a second AC terminal of the rectifying means.

A first DC terminal of the rectifying means can be connected to a first terminal of the burden resistance element. A second DC terminal of the rectifying means as well as a second terminal of the burden resistance element can be electrically connected to a reference potential, in particular of the phase line.

This advantageously provides a simple set up of the device which reduces installation space requirements as well as manufacturing costs and provides a robust and reliable operation and generation of the measurement signal.

In another embodiment, the at least rectifying means is a bridge rectifier. The bridge rectifier can e.g. comprise a first leg with a series connection of a first diode and a second diode. Further, the bridge rectifier can comprise a second leg with a series connection of a first diode and a second diode. The legs can be electrically connected in parallel. Conducting directions of the diodes in one leg can be oriented in the same direction. A section connecting the first and the second diode in one leg can provide an AC terminal of the bridge rectifier. A section connecting the first diodes of each leg, in particular the anodes of the first diodes, can provide a first DC terminal of the bridge rectifier. A section connecting the second diodes of each leg, in particular cathodes of these second diodes, can provide another DC terminal of the bridge rectifier. The first DC terminal can e.g. be connected to the reference potential as mentioned before, wherein the further DC terminal can be electrically connected to the first terminal of the burden resistance element.

This advantageously allows a simple and robust rectification of the signal wherein the manufacturing cost and installation space requirements for the corresponding circuit are minimized.

In another embodiment, the resistance of the at least one burden resistance element is chosen such that the level of the measurement signal corresponds to a predetermined voltage level if the absolute value of the current amplitude in the phase line is maximal or minimal. The resistance can e.g. be chosen such that the said level of the measurement signal corresponds to a maximum admissible voltage level of a system which further processes the measurements signal, e.g. of a microcontroller and I or an A/D converter. The level can e.g. be equal 5 V or a predetermined percentage of 5 V, in particular 80% or 90% of 5 V.

This has the technical effect of providing a high resolution of the level of the AC current in the phase line. As the decoupled signal is rectified, there is no need represent negative levels of the AC current by the measurement signal. This, in turn, can be used for increasing the voltage range of the measurement signal which represents positive levels of the AC current in the phase line.

In another embodiment, the predetermined voltage level can be chosen systemdependent. In particular, the predetermined voltage level can be chosen such that a maximum level of the measurement signal does not exceed a maximum admissible operating voltage of an electric or electronic element to which the measurement signal is provided. This advantageously allows a safe and reliable operation of the device.

In a preferred embodiment, a further terminal of the burden resistance is electrically connected to a reference potential. The reference potential is the reference potential of the phase line, e.g. the potential against which a phase voltage is measured. In particular, the second terminal of the burden resistance element is not connected to a voltage source which provides a reference voltage different from said reference potential.

In another embodiment the device comprises at least one comparing means, e.g. a comparator. Further, the voltage falling across the at least one burden resistance element is provided to the at least comparing means, in particular to one input terminal of the at least comparing means. Further, the at least one comparing means generates a measurement signal if the voltage falling across the at least one burden resistance element is higher than a predetermined threshold value or if the voltage falling across the at least one burden resistance element is lower than a predetermined threshold value or if the voltage falling across the at least burden resistance element is within a predetermined voltage interval.

In this case, the measurement signal is a detection signal. The detection signal can have two states, in particular a high level state and a low level state. Generating a detection signal can e.g. mean generating a voltage with the high level state or with a low level state.

The device can comprise at least one threshold voltage generating means, e.g. provided by a voltage source. This threshold voltage generating means can also be electrically connected to the at least one comparing means, in particular to a further terminal of the comparing means. The threshold voltage generating means can e.g. provide the aforementioned threshold values or boundary values of the voltage interval.

This advantageously allows a robust and reliable generation of detection signal, in particular for monitoring purposes.

It is, for instance, possible to execute a safety function if a detection signal is generated. The safety function can e.g. be executed by a control unit. It is possible that the device comprises the control unit. Alternatively or in addition, the device can electrically be connected to the control unit. Alternatively, the safety function can be a hardware-based safety function. In this case, the detection signal can trigger the execution of the hardware-based function. The safety function can e.g. execute a shutdown of the system. Other safety function are, however, possible.

In another embodiment, the device comprises one threshold voltage generating means per comparing means, in particular exactly one threshold voltage generating means per comparing means. Further, the threshold value generating means generates a voltage with a voltage level. This and corresponding advantages have been explained before.

Further proposed is a method for generating a measurement signal for an AC current in a phase line. The method can be executed by a device according to one of embodiments described therein, in particular using such a device. This means, that the device is configured such that a method according to one of the embodiments described therein can be performed by the device.

In particular, a decoupled current signal is generated by decoupling the current signal from the phase line, in particular using a current transformer. Further, the decoupled current signal is provided to at least one terminal of a burden resistance element. Further, the measurement signal is provided by the voltage falling across the at least one burden resistance element or by a signal which is a function of the voltage falling across the at least one burden resistance element.

According to the invention, the decoupled current signal is rectified and the rectified decoupled current signal is provided to at least one terminal of the burden resistance element.

This and corresponding advantages have been explained before.

In another embodiment, the voltage falling across the at least one burden resistance element is provided to at least one comparing means, e.g. a comparator. Further, the at least one comparing means generates a measurement signal if the voltage falling across the at least one burden resistance element is higher than a predetermined threshold value or if the voltage falling across the at least one burden resistance element is lower than a predetermined threshold value or if the voltage falling across the at least one burden resistance elements is within a predetermined voltage interval.

The device can be part of a primary unit or of a secondary unit of a system for inductive power transfer, in particular to a vehicle. Further described is therefore a primary unit or a secondary unit of a system for inductive power transfer, in particular to a vehicle.

In case of a primary unit, the phase line can be an electric line which connects an AC output terminal of a converter to an AC input terminal of a primary winding structure. A control unit can e.g. control the operation of the converter, in particular such that a desired amount of power or energy is transferred. The control performed by the control unit can e.g. be based on the measurement signal.

In case of a secondary unit the phase line can be an electric line which connects AC output terminal of a secondary winding structure to an AC input terminal of a secondarysided rectifier.

The invention, however, is not restricted to the use of the device in a primary or secondary unit of the system for inductive power transfer.

The invention will be described with reference to the attached figures. The figures show:

Figure 1: A schematic circuit diagram of a device for generating a measurement signal according to the state of the art,

Figure 2: A schematic time course of current and voltage signals according to the state of the art,

Figure 3: A schematic circuit diagram of a detection signal generating section according to the state of the art,

Figure 4: A schematic circuit diagram of a device for generating a measurement signal according to the invention,

Figure 5: A schematic time course of current and voltage signals according to the invention,

Figure 6: A schematic circuit diagram of a detection signal generating section according to the invention,

Figure 7: A schematic circuit diagram of a primary unit of a system for inductive power transfer,

Fig. 8a: A schematic flow diagram of a signal processing for generating the measurement signal Vm according to the state of the art and

Fig. 8b: A schematic flow diagram of a signal processing for generating the measurement signal Vm according to the invention.

In the following, the same reference numerals denote the same or similar technical elements.

Figure 4 shows a schematic circuit diagram of a device 1 for generating measurement signal Vm according to the invention. The device 1 shown in Fig. 4 is essentially similar to the device 1 which is shown in Figure 1. In contrast to the embodiment according to the state of the art shown in figure 1, the device 1 comprises a bridge rectifier 11 which provides a rectifying means according to the invention. The bridge rectifier 11 comprises a first leg with a series connection of a first diode D1 and a second diode D2. Further, the bridge rectifier 11 comprises a second leg with a series connection of a third diode D3 and a fourth diode D4.

Anodes of the first and the third diode D1, D3 are electrically connected. Further, cathodes of the second and the fourth diode D2, D4 are electrically connected. Further, a cathode of the first diode D1 is electrically connected to an anode of the second diode D2. Correspondingly, a cathode of the third diode D3 is electrically connected to an anode of the fourth diode D4.

The section of the first leg of the bridge rectifier 11 which connects the cathode of the first diode D1 to the anode of the second diode D2 provides a first AC input terminal of the bridge rectifier 11 which is electrically connected to a first terminal of the second winding 4 of the current transformer 2. Correspondingly, the section of the second leg of the bridge rectifier 11 which connects the cathode of the third diode D3 to the anode of the fourth diode D4 provides a second AC input terminal of the bridge rectifier 11, wherein said second terminal is electrically connected to a second terminal of the second winding 4 of the current transformer 2.

The section of the bridge rectifier 11 which electrically connects the anodes of the first diode D1 and the third D3 provide a first DC terminal of the bridge rectifier 11 and is electrically connected to a reference potential RP. The section of the bridge rectifier 11 which electrically connects the cathodes of the second diode D2 and the fourth diode D4 provides a second DC terminal of the bridge rectifier 11 which is electrically connected to a first terminal T1 of the burden resistor 5. A second terminal T2 of the burden resistor 5 is connected to the reference potential RP. The voltage falling across the burden resistor 5 provides the measurement signal Vm. In this case, the measurement signal Vm corresponds to the voltage Vi at the first terminal T1 of the burden resistor 5 which is measured relative to the reference potential RP.

Figure 5 shows a schematic time course of current and voltage signals according to the invention. The first and the second row of figure 5 correspond to the first and the second row shown in figure 2. This means that the time course of the phase current i and the decoupled current i_d flowing through the second winding 4 of the current transformer 2 are equal to the corresponding time courses shown in figure 2.

The third row of figure 5, however, shows time course of the voltage falling across the burden resistor 5. It can be seen, in contrast to the time course shown in figure 2, that the measurement voltage Vm only comprises positive voltage levels.

Further, the resistance value of the burden resistor 5 shown in figure 4 is chosen different, in particular higher, than the resistance value of the burden resistor 5 shown in figure 1. In particular, the resistance of the burden resistor 5 in figure 4 is chosen such that the level of the measurement signal Vm corresponds to a predetermined voltage level, namely 4.0 V, if the absolute value of the current amplitude in the phase line PL is maximal, e.g. equal to 40 A.

Figure 6 shows a schematic circuit diagram of a detection signal generating section of the device 1. The detection voltage generating section comprises one comparator 12, in particular exactly one comparator 12. The measurement voltage Vm, i.e. the voltage falling across the burden resistor 5 shown in figure 5 is provided to a first input terminal of the comparator 12. Further shown is that the detection signal generating section 13 comprises a threshold voltage generating means 14 which is e.g. provided by a voltage source. In particular, the detection signal generating section comprises exactly one threshold voltage generating means 14 per comparator.

As the decoupled current signal is rectified, a detection signal DS, in particular with a high state, is generated if the voltage falling across the burden resistor 5 is higher than a predetermined threshold value which is e.g. equal to the voltage provided by the threshold voltage generating means 14. This means that the detection signal DS is provided if the level of the AC current in the phase line PL is either higher than a predetermined threshold value or lower than a predetermined threshold value.

Figure 7 shows a schematic circuit diagram of a primary unit 14 of a system for inductive power transfer. The primary unit 14 comprises a primary winding structure 15 with one transfer winding L per phase line PL1, PL2, PL3. These transfer winding structures L generate an electromagnetic field for a power transfer if they are energised by phase currents i1, i2, i3. The primary winding structure 14 comprises three phase lines PL1, PL2,

PL3 which electrically connect AC output terminals of a converter 16 to the transfer winding L.

Further, the primary unit 14 comprises one device 1 for generating a measurement signal Vm per phase line PL1, PL2, PL3. This means that one device 1 is used for generating a measurement signal Vm for the phase current i1 in the first phase line, a second device 1 is used for generating a measurement signal Vm for the phase current i2 in the second phase PL2 and a third device 1 is used for generating a measurement signal Vm for the phase current i3 in the third phase line PL3.

For illustration purposes only, the devices 1 for generating a measurement signal for the phase currents i2, i3 of the second and third phase line PL2, PL3 are not shown completely.

In particular, only current transformers 2 with the first and second winding 2, 3 of these devices are indicated.

The device 1 for generating a measurement signal Vm for the phase current i3 in the third phase line PL3 is shown completely. In particular shown is the bridge rectifier 11 and the detection signal generating section 13.

The determined signal Vi is provided to a control unit 17, which is e.g. a micro controller. The control unit 17 can control the operation of the converter 16 depending on measurement signal Vm, wherein the measurement signal Vm represents the phase current i3 in the third phase PL3. Further shown is that the detection signal DS which can be generated by the detection signal generating section 13 is provided to a switch element

18. If a detection signal DS is generated, the switch element 18 can interrupt the third phase line PL3, e.g. by executing a hardware-based function.

The same functionality holds for the first and the second phase line PL1, PL2.

As explained before, it is possible that the detection signal generating section 13 comprises one or more comparing means for generating a detection signal DS. Further, one detection signal generating section 13 can comprise, in particular exactly, one threshold voltage generating means per comparing means. It is, however, also possible that the primary unit 14 comprises one or more common threshold voltage generating means, wherein a common threshold voltage generating means generates a threshold voltage for at least two comparing means of different detection signal generating sections

13. In other words, it is possible that a threshold voltage generating means for one comparing means of a detection signal generating section 13 of a device 1 for generating a measurement signal Vm for an AC current in a first phase line PL1 also provides a threshold voltage generating means for one comparing means of a detection signal generating section 13 of a device 1 for generating a measurement signal Vm for an AC current in a further phase line PL2, PL3.

Fig. 8a shows a schematic flow diagram of a signal processing for generating the measurement signal Vm if device 1 shown in Fig. 1 is used.

In a first step S1, the potential Vi of the first terminal T1 of the burden resistor 5 is digitized, e.g. by an A/D converter. Further, the reference voltage Vref is digitized, e.g. by the A/D converter or another A/D converter. In a second step S2, the digitized potential/voltage values are stored, e.g. in one or more memory units. In a third step S3, a difference between the stored, digitized potential Vi of the first terminal T1 of the burden resistor 5 and the stored, digitized reference voltage Vref is determined. This difference corresponds to the measurement signal Vm. In a fourth step S4, this measurement signal Vm is stored. Consequently, the following steps have to be performed: A/D conversion and storing of the potential Vi of the first terminal T1, A/D conversion and storing of the reference voltage Vref, difference determination, storing of the difference. Only after the last step, the measurement signal Vm is available for further processing steps, e.g. control purposes.

Fig. 8b shows a schematic flow diagram of a signal processing for generating the measurement signal Vm if a device 1 according to the invention is used.

In a first step S1, the potential Vi of the first terminal T1 of the burden resistor 5 is digitized, e.g. by an A/D converter. As explained before, the potential Vi corresponds to the measurement signal Vm. In a second step S2, the measurement signal Vm is stored, e.g. in a memory unit. Consequently, the only two and thus less steps than in the signal processing shown in Fig. 7a have to be performed: A/D conversion and storing of the potential Vi of the first terminal T1. Thus, the measurement signal Vm is available faster for further processing steps, e.g. control purposes.

Claims

1. A device (1) for generating a measurement signal (Vm, DS) for an AC current (i) in a phase line (PL, PL1, PL2, PL3), wherein the device (1) comprises at least one decoupling means for decoupling a current signal from the phase line (PL, PL1, PL2, PL3), wherein the device (1) further comprises at least one burden resistance element (5), wherein the at least one burden resistance element (5) is electrically connected to the decoupling means, wherein the measurement signal (Vm, DS) is provided by the voltage falling across the at least one burden resistance element (5) or by a signal which is a function of the voltage falling across the at least one burden resistance element (5), characterized in that the device (1) further comprises at least one rectifying means (11), wherein the at least one burden resistance element (5) is electrically connected to the decoupling means via the at least one rectifying means (11) such that a rectified decoupled current signal is provided to at least one terminal (T1) of the burden resistance element.

2. The device according to claim 1, characterized in that the decoupling means is a current transformer (2).

3. The device according to claim 1 or 2, characterized in that a first winding (3) of the current transformer (2) is electrically connected to the phase line (PL, PL1, PL2, PL3), wherein a second winding (4) of the current transformer (2) is connected to the at least one rectifying means (11).

4. The device according to one of the claims 1 to 3, characterized in that the at least one rectifying means is a bridge rectifier (11).

5. The device according to one of the claims 1 to 4, characterized in that a resistance of the at least one burden resistance element (5) is chosen such that the level of the measurement signal (Vm) corresponds to a predetermined voltage level if the absolute value of the current amplitude in the phase line (PL, PL1, PL2, PL3) is maximal or minimal.

6. The device according to claim 5, characterized in that the predetermined voltage level can be chosen system-dependent.

7. The device according to one of the claims 1 to 6, characterized in that a further terminal (T2) of the burden resistance element (5) is electrically connected to a reference potential (RP) of the phase line (PL, PL1, PL2, PL3) or another electric system.

8. The device according to one of the claims 1 to 7, characterized in that the device (1) comprises at least one comparing means (12), wherein the voltage falling across the at least one burden resistance element is provided to the at least comparing means (12), wherein the at least one comparing means (12) generates a measurement signal (DS) if the voltage falling across the at least one burden resistance element (5) is higher than a predetermined threshold value or if the voltage falling across the at least one burden resistance element (5) is lower than a predetermined threshold value or if the voltage falling across the at least one burden resistance element (5) is within a predetermined voltage interval.

9. The device according to claim 8, characterized in that the device comprises one threshold voltage generating means (14) per comparing means (12).

10. A method for generating a measurement signal (Vm, DS) for an AC current (i) in a phase line (PL, PL1, PL2, PL3), wherein a decoupled current signal is generated by decoupling the current signal from the phase line (PL, PL1, PL2, PL3), wherein the decoupled current signal is provided to at least one terminal (T1) of a burden resistance element (5), wherein the measurement signal (Vm, DS) is provided by the voltage falling across the at least one burden resistance element (5) or by a signal which is a function of the voltage falling across the at least one burden resistance element (5), characterized in that the decoupled current signal is rectified and the rectified decoupled current signal is provided to at least one terminal (T1) of the burden resistance element (5).

11. The method according to claim 10, characterized in that the voltage falling across the at least one burden resistance element (5) is provided to at least one comparing means (12), wherein the at least one comparing means (12) generates a measurement signal (DS) if the voltage falling across the at least one burden resistance element (5) is higher than a predetermined threshold value or if the voltage falling across the at least one burden resistance element (5) is lower than a predetermined threshold value or if the voltage falling across the at least one burden resistance element (5) is within a predetermined voltage interval.