WO2016096044A1

WO2016096044A1 - Device and method for determining electric power

Info

Publication number: WO2016096044A1
Application number: PCT/EP2014/078789
Authority: WO
Inventors: Uli Hart; Christian Hirsbrunner; Harm de Roo
Original assignee: Abb Schweiz Ag
Priority date: 2014-12-19
Filing date: 2014-12-19
Publication date: 2016-06-23

Abstract

A current sensor device (10), a system (22), and a method for determining an electric power fed through a conductor (12) is proposed. The current sensor device (10) comprises a current sensor (14) adapted for determining an analog current signal of a current supplied through the conductor (12), a bus interface (16) adapted for receiving via a data bus (28) at least one digital voltage parameter of a voltage at the conductor (12), and a controller (18) adapted for converting the determined analog current signal into digital current values. Therein, the controller (18) is adapted for determining digital voltage values based on the at least one digital voltage parameter, and for calculating a power value based on the digital current values and the digital voltage values and/or energy values based on the power values.

Description

DESCRIPTION

DEVICE AND METHOD FOR DETERMINING ELECTRIC POWER

FIELD OF THE INVENTION

The present invention relates to a current sensor device, a system with such a current sensor device and a method for determining an electric power fed through a conductor.

BACKGROUND OF THE INVENTION

EP 2 282 321 Al and US 2011/0040506 Al disclose a module for measuring current flowing through a conductor of a low- voltage distribution board. The module comprises a current sensor for detecting current, a microprocessor circuit for processing an output signal from the current sensor, and a module housing with an opening for passing the conductor.

WO 2013/128993 Al relates to a current sensor comprising magneto-electric conversion elements disposed on a wiring board, wherein the magneto-electric conversion elements are adapted for detecting magnetism generated when a current flows through a current path to be measured.

WO 2014/026963 Al describes a measuring device for a contactless current measurement on an electric conductor through which a current is flowing. The device comprises a field-sensitive magnetic field sensor as a current measurement sensor. The measuring device further comprises an electronic analyzing device arranged in a housing with cut-out sections, through which an insertable conductor passes. By connecting a measuring pin to the conductor, a voltage at the conductor may be determined, which may allow to provide an energy analysis via the analyzing device.

DESCRIPTION OF THE INVENTION

It is an object of the invention to provide a device and a method for determining an electric power fed through a conductor. This object is achieved by the subject-matter of the independent claims. Further exemplary embodiments are evident from the dependent claims and the following description.

An aspect of the present invention relates to a current sensor device adapted for determining an electric power fed through a conductor. The electric power may flow through the conductor to an electrical load, wherein the conductor may denote a cable, a wire, an electrical line, and/or any other current carrying element.

According to an embodiment of the invention, the current sensor device comprises a current sensor adapted for determining and/or measuring an analog current signal of a current supplied through the conductor. The current may be an alternating current (AC) of arbitrary frequency or a direct current (DC). The current may be a single phase current or a multi-phase current.

The current sensor device further comprises a bus interface adapted for receiving via a data bus at least one digital voltage parameter of a voltage at the conductor. The voltage may be an alternating voltage of arbitrary frequency or a direct voltage. The voltage may be a single phase voltage or a multi-phase voltage.

The current sensor device further comprises a controller adapted for converting the determined analog current signal into digital current values, wherein the controller is adapted for determining digital voltage values based on the at least one digital voltage parameter, and for calculating power values based on the digital current values and the digital voltage values.

The current sensor device and/or the controller may for this purpose comprise e.g. an analog digital converter, and the controller may comprise a microcontroller, a microcontroller circuit, and/or a data processing device for processing the digital voltage parameter, the digital voltage values, the digital current values, and/or the analog current signal. The power values may comprise and/or correlate with absolute or relative effective power values, active power values, apparent power values, at least one power factor, and/or at least one efficiency factor. Each power value may generally denote a value of the electric power fed through the conductor at a certain point in time and/or during a certain time interval.

By determining power values of the electric power fed through the conductor, e.g. an energy consumption and/or a power consumption of an electrical load connected to the conductor may be determined and/or analyzed, in a time-resolved or a non-time-resolved manner.

In order to precisely determine the power values in a time-resolved manner, the current sensor device may quantize the current supplied through the conductor and/or the analog current signal in terms of instantaneous current values during certain time intervals, and the digital current values may be generated accordingly. In other words, the digital current values may be determined with a certain sampling rate. According to the Nyquist-Shannon sampling theorem, the sampling rate may be at least twice the frequency of a periodic function in order to gain comprehensive information about the function. Accordingly, the sampling rate may range from about 10 Hz to about 100 kHz, wherein a sampling rate of about 10 Hz may be sufficient e.g. for a slowly varying DC current. For example, the sampling rate may range from about 1 kHz to about 10 kHz; preferably the sampling rate may be about 5 kHz.

The digital voltage parameter may be digitally transmitted and received by the current sensor device as one or more data packets via the data bus and/or via the bus interface. The digital voltage parameter may comprise information about and/or represent a shape and/or a strength of the voltage at the conductor. In other words, the digital voltage parameter and/or its value may correlate with the shape and/or the strength of the voltage. Generally, the digital voltage parameter may comprise and/or correlate with a variable and/or an observable characterizing the voltage at the conductor, such that based on the voltage parameter e.g. a variation of the voltage in time and/or in phase may be determined and/or such that e.g. voltage values may be determined and/or calculated for an arbitrary instant or point in time. For example, the digital voltage parameter may comprise and/or correlate with an amplitude of the voltage, a voltage frequency, a voltage strength, an instantaneous voltage value, an absolute voltage value, a relative voltage value, and/or an effective voltage value. The digital voltage parameter may alternatively or additionally comprise information about a basic course of the voltage at the conductor with respect to time and/or phase, such as e.g. a sinusoidal variation, a rectangular variation, or a triangular variation. The voltage parameter may also comprise information about a plurality of phases in a multi-phase electric supply grid, such as for instance a phase shift and/or a phasing between at least two phases of the voltage. By representing the voltage and/or its time dependence by the digital voltage parameter, a data traffic on the data bus may be reduced. Further, compared to transmitting e.g. an analog voltage signal via the data bus, material costs, production costs, and/or maintenance costs may be reduced, in particular in case of a multi-phase electric supply grid, which may require to transmit an analog voltage signal for each phase via a separate cable to the current sensor device.

A further aspect of the invention relates to a system for determining an electric power fed through a conductor, wherein the system comprises at least one current sensor device as described in the above and in the following.

Yet a further aspect of the invention relates to a method for calculating an electric power fed through a conductor.

It has to be understood that features of the method as described in the above and in the following may be features of the current sensor device and/or the system as described in the above and in the following. Vice versa, features of the current sensor device and/or the system as described in the above and in the following may be features of the method.

According to an embodiment of the invention, the current sensor device is adapted for receiving a trigger signal via the data bus and/or via the bus interface, wherein the controller is adapted for determining an instant of time of a zero-crossing and/or a phasing of the voltage at the conductor based on the trigger signal. In other words, the controller may be adapted to determine a point in time of the zero-crossing of the voltage, in which the voltage at the conductor may equal 0 V. Alternatively or additionally the phasing of the voltage may be determined allowing to calculate the point of time of the zero-crossing e.g. based on a frequency and/or a wavelength of the voltage. The phasing may denote a relative phasing of the current supplied through and the voltage at the conductor. However, in order to determine the relative phasing between current and voltage, the current and/or its course with respect to time may be approximated with a periodic function such as e.g. a sine function. Such approximation may be required due to the fact that the current's course may not be a stable sinusoidal function. Time information about the zero-crossing may be implicitly inferred by a transmission time, in which the trigger signal may be transmitted and/or received by the current sensor device.

To precisely determine the point in time of the zero-crossing and/or the phasing, the controller may also take into account a latency time and/or a reaction time and/or a dead time of the transmission of the trigger signal via the data bus, which may comprise amongst others a certain time period for the transmission itself and/or e.g. a time period for the current sensor device to process and/or interpret the trigger signal as well as a time period potentially required for generating and sending the trigger signal.

The trigger signal may for instance be based on a data packet transmitted and/or received by the current sensor device via the data bus. Alternatively or additionally the trigger signal may be based on a change in an impedance of at least one of a data line of the data bus, such as e.g. switching the line to a high-impedance state.

Generally, determining the point in time of the zero-crossing and/or the phasing, may enable the current sensor device to synchronize the digital current values and the digital voltage values in order to precisely calculate the power value. In other words, the trigger signal may enable the current sensor device to timely match value pairs of the digital voltage values and the digital current values.

According to an embodiment of the invention, the current sensor device is adapted for receiving a time-offset via the bus interface, wherein the controller is adapted for determining an instant of time of a zero-crossing and/or a phasing of the voltage at the conductor based on the trigger signal and the time-offset. The time-offset may be transmitted as a data packet via the data bus and it may for example denote a time period between a determination time, in which the zero-crossing of the voltage may be determined, and a transmission time, in which the trigger signal is transmitted to and/or received by the current sensor device. This may allow transmitting the trigger signal and the time-offset at an arbitrary time, thereby increasing a flexibility in terms of a communication and a data traffic via the data bus.

According to an embodiment of the invention, the trigger signal is based on receiving a data packet and/or wherein the time-offset is encoded in the data packet. In other words, the data packet may be digitally transmitted via the data bus, wherein the time-offset may be contained in the data packet. The trigger signal may be a receiving time of an edge of a (for example first) bit of the data packet.

However, the time-offset may also be transmitted as a separate data packet.

According to an embodiment of the invention, the calculated power values comprise active power values of the electric power fed through the conductor. The controller may be adapted to calculate energy values of an energy fed through the conductor based on the power values. The energy values and/or the energy may be determined by integration of the active power values with respect to time. Determining the active power values may allow determining a real power consumption and/or energy consumption of an electrical load at the conductor, e.g. in contrast to an apparent power.

According to an embodiment of the invention, the digital voltage parameter is based on and/or comprises at least one of an amplitude and a frequency of the voltage at the conductor. For instance, a value of the digital voltage parameter may refer to and/or correlate with at least one of the amplitude and the frequency.

By way of example, the voltage at the conductor may be a periodical function, such as e.g. a sine function. Accordingly, the voltage may be represented as a sine function having a certain amplitude, a certain frequency and phasing. Hence, providing e.g. the amplitude and the frequency as well as information about the phase and/or a zero-crossing of the voltage may enable the current sensor device to determine and/or calculate precise voltage values for an arbitrary point in time.

Further, this may enable the current sensor device to calculate the voltage congruently to the current measurements, which may be conducted with a certain sampling rate and which may timely differ from voltage measurement. Thus, the current sensor device may be enabled to precisely calculate the power values of the electric power fed through the conductor.

The digital voltage parameter may be transmitted and/or received as data packet encoding at least one of the amplitude and the frequency of the voltage. However, the amplitude, the frequency and potentially further quantities may also be transmitted separately as separate data packets.

According to an embodiment of the invention, the current sensor device further comprises a memory for storing at least one of the digital current values and the digital voltage values. The memory may denote a data storage device for storing the digital current values and/or the digital voltage values. Also other quantities such as e.g. the digital voltage parameter, a value of the digital parameter, and/or the power values may be stored in the memory. This way, all information potentially required for determining and/or processing the power values may be stored in the memory, which may be accessed for example by the controller without requiring further data traffic on the data bus.

According to an embodiment of the invention, the controller is adapted for determining the digital voltage values based on the at least one digital voltage parameter and on a lookup table. The look-up table may for instance comprise numerical values of a function representing a course of the voltage. By way of example, in case the course of the voltage at the conductor is sinusoidal, numerical values of a basic sine function may be stored in the look-up table, which values may be accessed by the controller for calculating and/or determining a digital voltage value for an arbitrary point in time without requiring to calculate a corresponding value of the sine function. Consequently, a computing time for determining and/or calculating the digital voltage values may be reduced. Further, in the look-up table a number of values may correspond to a number of samples per period of the voltage, i.e. the number of values in the look-up table may correspond to a sampling rate, with which the digital current values and/or the digital voltage values may be determined and/or quantized. However, the look-up table may not necessarily comprise values for an entire period, i.e. a full cycle period, of the voltage. Preferably, the look-up table may comprise values corresponding to a part of the full cycle period, e.g. a quarter period, of an alternating voltage at the conductor, and the remaining part of the full cycle period, e.g. the remaining three quarters of the period, may be extrapolated and/or determined based on the part of the period stored in the look-up table.

According to an embodiment of the invention, the controller is adapted for transmitting the power values via the bus interface to a control device. The control device may store and/or further process and/or analyze the power values. Based on the power values the control device may be adapted for determining and/or calculating and/or storing e.g. absolute or relative effective power values, active power values, apparent power values, at least one power factor, and/or at least one efficiency factor. This may allow comprehensive analysis of an energy and/or power consumption of the electrical load at the conductor.

According to an embodiment of the invention, the data bus is a fieldbus, and/or wherein the data bus is a RS-485 bus. For instance the data bus may be a Common Industrial Protocol (CIP) bus, an Ethernet bus, a Local Area Network (LAN), a Wireless Local Area Network (WLAN), a P-Net, an INTERBUS, a Modbus, a Modbus/TCP, a CANbus, an EtherCAT, or any other appropriate data bus. According to an embodiment of the invention, the current sensor device is configured as a slave with respect to the data bus and is connectable via the data bus with a control device configured as a master. In other words, the data bus, a communication via the data bus, and/or a data transmission via the data bus may be hierarchically managed in a master-slave system, wherein the current sensor device may be a slave and the control device may be a master. This may allow a centralized control of the communication and/or data sharing and/or data transmission between components and/or devices connected to the data bus, thereby avoiding any collisions.

According to an embodiment of the invention, the current sensor device is galvanically separated from the conductor. The current sensor device and the conductor may be electrically isolated against each other. Accordingly, the current sensor device may not be affected by potential short-circuit currents and/or fault currents. This may increase a safety, reliability and a life-time of the current sensor device.

According to an embodiment of the invention, the voltage at the conductor is a low- voltage or a medium-voltage. For an alternating low-voltage a maximum voltage value may be around 1 kV, whereas for a direct low- voltage a maximum voltage value may be about 1.5 kV. On the other hand, the term medium voltage may denote a voltage above approximately 1 kV, at least concerning an alternating voltage. By way of example, the voltage at the conductor may be below 1 kV.

According to an embodiment of the invention, a supply power of the current sensor device is provided via the bus interface. This may reduce material costs, production costs and maintenance costs of the current sensor device and it may simplify an installation and retrofit of the current sensor device.

A further aspect of the invention relates to a system for determining an electric power fed through at least one conductor. The system comprises a control device, at least one current sensor device as described in the above and in the following, a voltage sensor device for determining and/or measuring an analog voltage signal at and/or applied at the at least one conductor, and a data bus interconnecting the at least one current sensor device, the voltage sensor device and the control device. The inventive system may e.g. be a part of and/or it may be integrated in a voltage distribution board connecting several electrical loads in parallel to a main conductor and/or power supply cable, thereby allowing to determine a power consumption of each load separately.

According to an embodiment of the invention, the voltage sensor device is adapted for converting the analog voltage signal into the at least one digital voltage parameter and for sending the at least one digital voltage parameter via the data bus to the at least one current sensor device and/or to the control device. The voltage sensor device may be adapted for deriving the digital parameter from the analog voltage signal and/or it may be adapted for determining the at least one digital voltage parameter based on the analog voltage signal. The voltage sensor device may comprise an analog digital converter for converting the analog voltage signal into a digital voltage signal.

According to an embodiment of the invention, the voltage sensor device is adapted for sending a digital voltage signal based on the analog voltage signal via the data bus to the control device, and the control device is adapted for converting the digital voltage signal into the at least one digital voltage parameter and for sending the at least one digital voltage parameter to the at least one current sensor device. The control device may be adapted for generating and/or deriving the at least one digital voltage parameter from the digital voltage signal received from the voltage sensor device.

According to an embodiment of the invention the voltage sensor device and the at least one current sensor device lack a common clock signal, and/or wherein the data bus is non time critical. Generally, this may allow to retrofit the inventive system to any other system using any non time critical data bus. Further, by avoiding to share a clock signal via the data bus, data traffic may be reduced.

According to an embodiment of the invention, the voltage sensor device is integrated in the control device, and/or wherein the voltage sensor device is configured as a slave connected to the data bus. Integration of the voltage sensor device in the control device may advantageously reduce a number of components of the system and material costs as well as it may simplify an installation and/or a set-up of the entire system.

According to an embodiment of the invention, the control device and/or the voltage sensor device is adapted for sending a trigger signal to the current sensor device via the data bus, the trigger signal indicating a zero-crossing of the voltage at the conductor.

According to an embodiment of the invention, the system comprises a plurality of current sensor devices interconnected via the data bus with the control device, wherein each current sensor device is adapted for determining power values of an electric power fed through a respective conductor. In other words, the system may comprise a plurality of current sensor devices each determining and/or measuring an analog current signal of a current supplied through the respective conductor to an electrical load. The electrical loads and/or the conductors may be connected in parallel to a main conductor, to which the voltage sensor device may be connected to and/or at which the voltage sensor device may determine and/or measure the analog voltage signal, wherein the analog voltage signal at the main conductor may correspond to the actual voltage at the respective conductors, to which the loads and the current sensor devices are connected to. This way the analog voltage signal may be centrally determined for all current sensor devices of the system at a measurement location differing from measurement locations of the current sensor devices. This may allow to provide a compact and comprehensive system at low production costs, which may for instance easily be installed and/or retrofit to a voltage distribution board. According to an embodiment of the invention, the control device and/or the voltage sensor device is adapted for broadcasting the digital voltage parameter via the data bus to a plurality of current sensor devices. This may ensure that all current sensor devices may receive the digital voltage parameter, based on which the power values may be determined, while reducing a data traffic on the data bus.

According to an embodiment of the invention, the control device and/or the voltage sensor device is adapted for broadcasting a trigger signal via the data bus to the plurality of current sensor devices, the trigger signal indicating a zero-crossing of the voltage at the conductor. This may ensure that all current sensor devices may be enabled to determine, based on the trigger signal, the point in time of the zero-crossing of the voltage, which may be required to synchronize the digital current values determined by each of the current sensor devices and the digital voltage values determined by the controller of the current sensor devices.

A further aspect of the invention relates to a method for calculating an electric power fed through a conductor, the method comprises the steps of measuring, with a current sensor device, an analog current signal of a current supplied through the conductor; converting, with the current sensor device, the measured analog current signal into digital current values; receiving, with the current senor device, via a data bus at least one digital voltage parameter of a voltage at the conductor; determining, with the current sensor device, digital voltage values based on the digital voltage parameter; and calculating with the current sensor device power values based on the digital current values and the digital voltage values.

According to an embodiment of the invention, the step of determining digital voltage values further comprises receiving, with the current sensor device, a trigger signal indicating a zero-crossing of the voltage at the conductor, and determining, with the current sensor device, an instant of time of the zero-crossing and/or a phasing of the voltage at the conductor based on the trigger signal.

According to an embodiment of the invention, the method further comprises updating the digital voltage parameter. The digital voltage parameter may be updated after a predefined and/or definable time interval. The digital parameter may also be updated dynamically, e.g. accounting for any variation or change of a currently determined digital voltage parameter to a previously determined digital voltage parameter. Generally, updating the digital voltage parameter may comprise determining and/or measuring an analog or digital voltage signal and deriving the digital voltage parameter from the analog or digital voltage signal. Thus, updating the digital voltage parameter may allow to compensate for e.g. any variations in a frequency, an amplitude, a time dependence, and/or a phasing of the voltage at the conductor. It is to be noted that also the trigger signal indicating the voltage's zero-crossing may be repeatedly sent in order to update the instant of time of the zero-crossing and/or in order to provide an updated information about the instant of time of the zero-crossing.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

The subject-matter of the invention will be explained in more detail in the following text with reference to exemplary embodiments which are illustrated in the attached drawings.

Fig. 1 shows a current sensor device according to an embodiment of the invention. Fig. 2 shows a system for determining an electric power with a plurality of current sensor devices of Fig. 1 according to an embodiment of the invention.

Fig. 3 shows a flow chart illustrating steps of a method for determining an electric power according to an embodiment of the invention.

The reference symbols used in the drawings, and their meanings, are listed in summary form in the list of reference symbols. In principal, identical parts are provided with the same reference symbols in the figures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Fig. 1 shows a current sensor device 10 for determining an electric power fed through a conductor 12 according to an embodiment of the invention.

The current sensor device 10 comprises a current sensor 14 adapted for determining and/or measuring an analog current signal of a current supplied through the conductor 12 to an electrical load. The current sensor 14 may be galvanically separated and/or electrically isolated from the conductor 12. By way of example, the current sensor 14 may be based on a field-sensitive magnetic field sensor detecting a magnetic field generated by the current flowing through the conductor 12, such as e.g. a Hall sensor, a magneto- resistive sensor or a giant magneto-resistive sensor. The current sensor 14 may also be induction based, such as e.g. a transformer-based sensor or a sensor based on a Rogowski coil. Further, the current sensor 14 may also be based on a current clamp sensor, a resistor sensor or a fiber-optic current sensor using an interferometer.

The current supplied through the conductor 12 may be a single phase or a multi-phase AC current of arbitrary frequency or it may be a DC current. Accordingly, the current sensor 14 may be adapted for determining an analog current signal for each phase of a multi-phase AC current. The analog current signal may correlate with and/or be proportional to the current supplied through the conductor 12. The analog current signal may comprise e.g. a frequency, an amplitude, a phase, a strength, an instantaneous current value, an intensity, an amperage, a current rating, a relative current value, an absolute current value, and/or an effective current value.

The current sensor device 10 further comprises a controller 18 for converting the determined and/or measured analog current signal into digital current values, which may be accomplished by means of an analog digital converter. In other words, the controller 18 and/or the current sensor device 10 may comprise an analog digital converter. The current sensor device 10 and/or the controller 18 may generate and/or determine the digital current values based on the analog current signal with a certain sampling rate, which sampling rate may be definable, predefined, and/or adjustable according to e.g. a frequency of the current supplied through conductor 12. For example a sampling rate ranging from 1 kHz to 50 kHz may be conceivable. By way of example, the sampling rate may be about 5 kHz, which may be suitable for a common AC supply network/grid with a frequency of about 50 Hz. Consequently, the controller 18 may determine and/or generate about 100 digital current values during one full cycle period of the alternating current supplied through conductor 12.

The current sensor device 10 further comprises a memory 20, in which, amongst other quantities, the digital current values may be at least temporarily stored for further processing. The current sensor device 10 further comprises a bus interface 16 for connecting the current sensor device 10 to a data bus 28 (see Fig. 2) and/or for interconnecting the current sensor device 10 with various other components of the system 22 as shown in Fig. 2.

Fig. 2 shows a system 22 for determining an electric power with a plurality of current sensor devices 10 of Fig. 1. In Fig. 2 only three current sensor devices lOa-c are shown, but basically the system 22 may comprise an arbitrary number of current sensor devices 10, lOa-c as indicated by the dots in Fig. 2. The system 22 may for example be part of and/or it may be integrated in a voltage distribution board.

The system 22 comprises a control device 24 with a control module and/or a control unit 24a. The system 22 further comprises a voltage sensor device 26, which may either be integrated in the control device 24 or which may be a separate component and/or member of the system 22.

The system 22 further comprises a data bus 28 interconnecting the current sensor devices lOa-c and the control device 24 as well as the voltage sensor device 26. The control device 24, each current sensor device lOa-c and the voltage sensor device 26 are connected to the data bus 28 by a bus interface 16, respectively. However, if the voltage sensor device 26 is integrated in the control device 24, both the control device 24 and the voltage sensor device 26 may alternatively be connected to the data bus 26 via a single common bus interface 16.

For interconnecting the control device 24, the current sensor devices lOa-c, and optionally the voltage sensor device 26, the data bus 28 may comprises e.g. a ribbon cable 29, which ribbon cable 29 may comprise four data lines. At least one of the data lines may provide a supply power for at least one of the current sensor devices lOa-c, the voltage sensor device 26, and/or the control device 24.

Generally, the data bus 28 of the system 22 shown in Fig. 2 is a fieldbus. More specifically, the data bus 28 is a RS-485 bus. The data bus 28 may be a non-time-critical data bus 28, i.e. the data bus 28 may not provide a common clock signal for the components connected to it and/or no common clock signal may be shared via the data bus 28 by the components or members of the system 22 connected to the data bus 28. However, the invention may not be restricted to a fieldbus and/or the RS-485 bus, but rather the data bus 28 may be any other appropriate data bus 28, such as e.g. a Common Industrial Protocol (CIP) bus, an Ethernet bus, a Local Area Network (LAN), a Wireless Local Area Network (WLAN), a P-Net, an INTERBUS, a Modbus, a Modbus/TCP, a CANbus, and/or an EtherCAT.

The data bus 28, a communication via the data bus 28, and/or a data transmission via the data bus 28 is hierarchically managed in a master-slave system, wherein the current sensor devices lOa-c are each configured as slave and the control device 24 is configured as master. If not integrated in the control device 24, the voltage sensor device 26 is configured as further slave in the master-slave system provided by the data bus 28. A communication protocol utilized for communicating via the data bus 28 may be based on a standard bus protocol, such as e.g. a standard RS-485 protocol, which protocol may be modified according to specific needs of the system 22 as described in more detail in the above and in the following.

The voltage sensor device 26 is adapted for determining and/or measuring an analog voltage signal at a main conductor 11, which main conductor 11 may denote a power supply cable of a voltage distribution board and which main conductor 11 exemplary branches out into three conductors 12a-c as shown in Fig. 2. Each of the conductors 12a-c may be connected to an electrical load. Accordingly, the electrical loads and/or the conductors 12a-c are connected in parallel to the main conductor 11. Hence, a voltage and/or the analog voltage signal measured at the main conductor 11 by the voltage sensor device 26 may equal a voltage and/or an analog voltage signal at each of the conductors 12a-c. The voltage sensor device 26 may be based on and/or may be designed as e.g. a resistive voltage divider.

On the other hand, a current supplied through each of the conductors 12a-c to the respective electrical load may depend on a power consumption of the respective electrical load. The system 22 allows to measure and/or determine the current supplied through each conductor 12a-c independently. In combination with the determination of the voltage at the main conductor 11 by the voltage sensor device 26, an electric power fed through each of the conductors 12a-c is determinable with the inventive system 22 and/or the current sensor devices lOa-c as described in detail in the following.

For example, the system 22 may be part of a smart meter near an electrical building connection. The conductors 12a-c may be electrical lines from the electrical building connection to loads inside the building. In such a way, the system 22 or the smart meter may determine the active power of the loads inside the building and may report these values to a grid operator, which for example may use these values to forecast a power consumption of the building. Based on the analog voltage signal measured by voltage sensor device 26, the voltage sensor device 26 may determine at least one digital voltage parameter. In other words, the voltage sensor device 26 may be adapted for converting the analog voltage signal into the digital voltage parameter. For this purpose, the voltage sensor device 26 may comprise an analog digital converter for converting the analog voltage signal into a digital voltage signal, which digital voltage signal may be further processed e.g. by a processing device of the voltage sensor device 26 in order to derive the digital voltage parameter. However, the analog voltage signal may also be directly processed by the voltage sensor device 26 to determine the digital voltage parameter. Alternatively, the voltage sensor device 26 may be adapted for sending the digital voltage signal via the data bus 28 to the control device 24 and the control device 24 may process the digital voltage signal and convert it into and/or derive the digital voltage parameter from the digital voltage signal, e.g. by means of a processing device of the control device 24.

Generally, the digital voltage parameter may comprise information about and/or represent a shape and/or a strength of the voltage at the conductor, such that based on the voltage parameter e.g. a variation of the voltage in time and/or in phase may be determined and/or such that e.g. voltage values may be determined and/or calculated for an arbitrary instant of time or point in time. By way of example, in case a direct voltage is applied at the main conductor 11, the digital voltage parameter may comprise e.g. a voltage strength, a mean voltage strength, either as absolute or relative quantity. Further, assuming a common AC supply grid at 50 Hz alternating voltage is connected to the main conductor 11, the voltage may usually have a rather stable sinusoidal course with respect to time and/or phase. In this case, the voltage sensor device 26 and/or the control device 24 may determine at least one of a frequency and/or an amplitude of that sinusoidal voltage. Accordingly, the digital voltage parameter may comprise at least one of the amplitude and the frequency of the voltage and/or the digital voltage parameter may at least be based on at least one of the frequency and the amplitude.

When determined, the digital parameter may be provided and/or digitally transmitted as a data packet via the data bus to each of the current sensor devices lOa-c. If determined by the control device 24 itself, the control device 24 configured as master may the digital voltage parameter to each of the current sensor device s lOa-c, wherein the control device 24 may either send the digital voltage parameter separately to each of the current sensor devices lOa-c or the control device 24 may send the digital voltage parameter by a broadcast simultaneously to all current sensor devices lOa-c. Alternatively, if the digital voltage parameter is determined by the voltage sensor device 26, the voltage sensor device 26 may transmit the digital voltage parameter directly to the current sensor devices lOa-c, which may also be done separately or simultaneously via a broadcast. In the latter case, the control device 24 may instruct and/or allow all current sensor devices lOa-c (configured as slave) to receive the digital voltage parameter from the voltage sensor device 26 (also configured as slave), e.g. by sending an appropriate data signal and/or instruction signal via the data bus 28.

As described above, each current sensor device lOa-c measures an analog current signal at each the respective conductor 12a-c and determines corresponding digital current values. In order to determine the corresponding electric power fed through each of the conductors 12a-c, the current sensor devices lOa-c require information about e.g. a phasing between the voltage and the current at each conductor 12a-c. The phasing may be determinable if for example an instant of time and/or a point in time of a zero-crossing of the voltage is known by each of the current sensor devices lOa-c.

This may be accomplished in an approach based on the bus protocol of the data bus 28, as described in the following. The control device 24 as master may broadcast an initiating trigger signal to all current sensor devices lOa-c, which initiating trigger signal may permit each of the current sensor devices lOa-c to receive a trigger signal from the voltage sensor device 26 (which may be part of the control device 24). The initiating trigger signal may also give permission to the voltage sensor device 26 to transmit the trigger signal to the current sensor devices lOa-c, if the voltage sensor device 26 is configured as further slave. In other words, the initiating trigger signal, which may be a data packet sent via the data bus 28, may switch the current sensor devices lOa-c to a listening mode, in which the actual trigger signal may be received from the voltage sensor device 26.

The trigger signal may comprise a data packet sent via the data bus 28 and it may be regarded as a custom function broadcast message sent by the voltage sensor device 26, which message may indicate, with a known latency time and/or dead time and/or reaction time, the instant of time of the zero-crossing of the voltage. The latency time may for instance denote a time interval required for data processing and/or for the transmission of the trigger signal via the data bus 28, which latency time may be rather precisely known. The trigger signal may for instance comprise a number of processor cycles of a processor of the voltage sensor device's 26 processing device, wherein the number of cycles may be the number of elapsed cycles between the initiating trigger signal and a cycle, in which the voltage sensor device 26 determined the zero-crossing of the voltage. The cycle, in which the voltage sensor device 26 determined the zero-crossing of the voltage, may be regarded as determination time of the zero-crossing. Optionally, the trigger signal may comprise a time-offset, which may denote a time interval between the determination time and a transmission time, in which the trigger signal is transmitted and/or sent by the voltage sensor device 26. The time-offset may also be given as a number of processor cycles.

Based on the trigger signal each of the current sensor devices lOa-c is able to determine the instant of time of the zero-crossing of the voltage, for example by interpreting the number of processor cycles comprised in the trigger signal in terms of processor cycles of the controllers 18 of each current sensor device lOa-c. Accordingly, based on the trigger signal each of the current sensor devices lOa-c is able to calculate and/or determine the voltage at the conductors 12a-c as a function of time and/or as a function of phase, and consequently the relative phasing between the current supplied through and the voltage at the conductors 12a-c is determinable by each of the current sensor devices lOa-c, respectively. Corresponding to the sampling rate, with which the current sensor devices lOa-c determine the digital current values, each of the current sensor devices lOa-c calculates, with the controllers 18, digital voltage values based on the digital voltage parameter and based on the time information inferred by the trigger signal. In other words, each of the current sensor devices lOa-c and/or the respective controllers 18 calculates digital voltage values, which are timely matched and/or synchronized with the digital current values.

It is to be noted here that the trigger signal and the digital voltage parameter may be transmitted as a signal sequence via the data bus 28 to each of the current sensor devices lOa-c, thereby providing comprehensive information about the voltage and enabling each current sensor device lOa-c to calculate the digital voltage values. The signal sequence and/or the digital voltage parameter may in this context comprise e.g. the frequency of the voltage, which may equal 0 Hz in case of a direct voltage, an effective voltage value, the latency time, the instant of time of the voltage's zero-crossing, which may be implicitly provided by the transmission time of the trigger signal, and/or the time-offset. Further, it is to be noted that such information may also be provided to the current sensor devices lOa-c e.g. via a signal modulated on a power supply line, a data line of the data bus 28, and/or another appropriate channel.

In order to reduce a processing time potentially required to calculate and/or determine the digital voltage values, numerical values of a function representing a basic course of the voltage with respect to time and/or phase may be utilized and/or accessed by the current sensor devices lOa-c and/or the respective controllers 18. The numerical values may for instance be stored in a look-up table in the memory 20 of each current sensor device lOa-c. By way of example, if the voltage is sinusoidal, numerical values of a sine function may be stored in the look-up table and accessed by the controllers 18 of each current sensor device lOa-c. The look-up table may comprise numerical values distributed over a full cycle period of the sine function (or a full cycle of the voltage) or values over a part of the full cycle period. Preferably, the look-up table comprises values of a quarter period of the sine function, or generally a quarter period of the voltage. The remaining part of the full cycle period may be extrapolated based on the part of the period stored in the look-up table, e.g. based on the quarter period. Further, also values between values stored in the look-up table may be determined via interpolation of the values stored in the look-up table. By way of example, in case a sampling rate of 5 kHz is used for determining the digital current and/or voltage values of a 50 Hz alternating sinusoidal voltage as usually the case in a common AC supply grid, a number of 25 numerical values for a quarter period of the sine function may be stored in the look-up table.

By multiplication of corresponding value pairs of the digital current values and the digital voltage values, power values are calculated by each of the current sensor devices lOa-c. The power values particularly comprise active power values of the electric power fed through the respective conductor 12a-c, but also other power values may be determined, such as e.g. apparent power values, power factors, and/or effective power values.

An alternative exemplary approach for determining a phasing between the voltage and the current at each conductor 12a-c and/or an alternative approach of providing the instant of time of the voltage's zero-crossing to the current sensor devices lOa-c may be a hardware based approach. Therein, at least one data line of the data bus 28 may be utilized as a synchronization data channel. Also in this approach, the voltage sensor device 26 may gain permission to send the trigger signal to the current sensor devices lOa-c via the data bus 28, and the current sensor devices lOa-c may be instructed and/or gain permission to receive the trigger signal from the voltage sensor device 26.

For this purpose, at least one of the data lines may be set to a high-impedance state, which state may denote an unlocked and/or active state of the data line. This state may be maintained for a definable or predefined time, during which the voltage sensor device 26 may gain control over the at least one data line. Setting the at least one data line to the unlocked state may thus be regarded as the initial trigger signal. If required, the voltage sensor device 26 may also set the data line to a preparing state, thereby indicating the current sensor devices lOa-c that the trigger signal may be transmitted. Therein, the trigger signal may for example be transmitted by the voltage sensor device 26, at the instant of time where the zero-crossing of the voltage is detected, via a defined change of a state of the data line, such as e.g. a change in a level of the data line.

The detection of the change of state of the data line may be accomplished by means of a direct access of a detection circuit of the voltage sensor device 26 to a transceiver of the data bus 28, which may allow to bypass e.g. a micro-controller circuit of the voltage sensor device 26 with its sometimes variable latency time.

Upon detecting and/or determining the high-impedance unlocked and/or active state of the at least one data line, and optionally after detecting the preparing state, each of the current sensor devices lOa-c detects the trigger signal indicating the zero-crossing of the voltage and processes the trigger signal. Preferably the trigger signal is directly processed e.g. via an interrupt control of the controllers 18. Based on the trigger signal and the digital voltage parameter, which may be transmitted separately, each current sensor device lOa-c is enabled to calculate the digital voltage values timely matched with the digital current values, and the power values may be calculated by multiplication of these values.

After determination and/or calculation of the power values, the current sensor devices lOa-c may transmit the power values via the bus interfaces 16 and the data bus 28 to the control device 24 for further processing and/or evaluation and/or analysis. The current sensor devices lOa-c and/or the respective controllers 18 may also calculate further quantities based on the power values, such as e.g. an electrical energy supplied through the conductors 12a-c by integrating the determined power values over a certain time period. However, also the control device 26 may calculate such quantities based on the power values received by each current sensor device lOa-c. The control device 26 may further process and/or evaluate the data and/or values received from the current sensor devices lOa-c, and it may e.g. display them on a graphical user interface.

It is to be noted that in case the system 22 and/or the main conductor 11 is connected to a multi-phase AC supply grid, the above-described approach and/or method of determining the power values may be conducted for each phase separately.

The system 22 shown in Fig. 2 may further comprise an interface for transmitting information to the system 22, e.g. for setting-up the system 22, and/or for transmitting information, such as e.g. the determined power values and/or energy values, from the system 22 to for example an operational unit. The interface may for example be an Ethernet interface, such as a RJ-45 interface, which may be connected to a local area network and/or the Internet. However, the interface may also be any other appropriate interface, such as a serial port, a USB port, or the like.

Fig. 3 shows a flow chart illustrating steps of a method for determining an electric power fed through a conductor 12 according to an embodiment of the invention. Features and/or steps of the method may be features and/or steps conducted by the current sensor devices 10, lOa-c of Figs. 1 and 2 and/or by the system 22 of Fig. 2. Vice versa, features and/or steps conducted by the current sensor devices 10, lOa-c of Figs. 1 and 2 and/or by the system 22 of Fig. 2 may be features and/or steps of the method.

In a first step S 1 the analog current signal of the current supplied through the conductor 12 is measured by the current sensor device 10 and/or the current sensor 14 of the current sensor device 10. The measured analog current signal is then converted into the digital current values, which may be stored in a memory 20 of the current sensor device 10.

Simultaneously, before, or after step SI, the voltage sensor device 26 determines the analog voltage signal of the voltage at the conductor 12 and derives and/or determines the digital voltage parameter, which may be temporarily stored in a memory of the voltage sensor device 26. Alternatively, the analog voltage signal may be converted to a digital voltage signal, which may be transmitted to the control device 24, and the control device 24 may determine the digital voltage parameter based on the digital voltage signal.

In a second step S2 the current sensor device 10 receives via the data bus 28 the digital voltage parameter, which may comprise at least one of a frequency and an amplitude of the voltage. The digital voltage parameter may be transmitted by the control device 24 and/or the voltage sensor device 26. The digital voltage parameter may further be stored in memory 20 of the current sensor device 26. Simultaneously, before, or after receiving the digital voltage parameter, the trigger signal indicating the zero-crossing of the voltage is transmitted by the voltage sensor device 26 and/or the control device 24 via the data bus 28 to the current sensor device 10, and/or the trigger signal is received by the current sensor device 10. Also the time information regarding the zero-crossing of the voltage may be stored in memory 20 of the current sensor device 10.

In a further step S3 the current sensor device 10 determines the digital voltage values based on the digital voltage parameter and/or based on the trigger signal. As described in the above, based on the trigger signal and optionally based on the time-offset the instant of time of the voltage's zero-crossing may be determined by the current sensor device 10, thereby allowing to synchronize the measured current and the voltage. In other words, based on the instant of time of the voltage's zero-crossing, as determined by the current sensor device 10, digital voltage values may be determined with the current sensor device 10, which digital voltage values timely correspond to the digital current values.

Based on the timely corresponding digital current values and the digital voltage values, power values are calculated by the current sensor device 10 and/or its controller 18 in a step S4. The power values may then be transmitted via the data bus 28 to the control device 24 for further processing and/or evaluation. Further, energy values may be determined based on the power values, e.g. by integrating a plurality of the power values over time, which energy values may also be transmitted via the data bus 28 to the control device 24 for further processing and/or evaluation.

After a predefined, a definable, and/or a dynamically adjustable period of time the digital voltage parameter and/or the trigger signal indicating the voltage's zero-crossing may be repeatedly determined by the voltage sensor device 26 and transmitted to the current sensor device 10, thereby updating the previous digital voltage parameter and/or the instant of time of the zero-crossing as determined by the current sensor device 10 based on the previous trigger signal.

While the invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art and practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or features, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims are not to be construed to as limiting the scope.

LIST OF REFERENCE SYMBOLS

10, lOa-c current sensor device

11 main conductor

12, 12a-c conductor

14 current sensor

16 bus interface

18 controller

20 memory

22 system

24 control device

26 voltage sensor device

28 data bus

29 ribbon cable

Claims

1. A current sensor device (10) adapted for determining an electric power fed through a conductor (12), the current sensor device (10) comprising:

a current sensor (14) adapted for determining an analog current signal of a current supplied through the conductor (12);

a bus interface (16) adapted for receiving via a data bus (28) at least one digital voltage parameter of a voltage at the conductor (12); and

a controller (18) adapted for converting the determined analog current signal into digital current values,

wherein the controller (18) is adapted for determining digital voltage values based on the at least one digital voltage parameter, and for calculating power values based on the digital current values and the digital voltage values.

2. The current sensor device (10) according to claim 1,

wherein the current sensor device (10) is adapted for receiving a trigger signal via the bus interface (16), and

wherein the controller (18) is adapted for determining an instant of time of a zero- crossing and/or a phasing of the voltage at the conductor (12) based on the trigger signal.

3. The current sensor device (10) according to claim 2,

wherein the current sensor device (10) is adapted for receiving a time-offset via the bus interface (16), and

wherein the controller (18) is adapted for determining an instant of time of a zero- crossing and/or a phasing of the voltage at the conductor (12) based on the trigger signal and the time-offset.

The current sensor device (10) according to claim 2 or 3,

wherein the trigger signal is based on receiving a data packet; and/or

wherein the time-offset is encoded in the data packet.

5. The current sensor device (10) according to one of the preceding claims,

wherein the calculated power values comprise active power values; and/or wherein the controller (18) is adapted to calculate energy values of an energy fed through the conductor (12) based on the power values.

6. The current sensor device (10) according to one of the preceding claims,

wherein the digital voltage parameter is based on at least one of an amplitude and a frequency of the voltage at the conductor (12).

7. The current sensor device (10) according to one of the preceding claims, further comprising a memory (20) for storing at least one of the digital current values and the digital voltage values.

8. The current sensor device (10) according to one of the preceding claims,

wherein the controller (18) is adapted for determining the digital voltage values based on the at least one digital voltage parameter and on a lookup table.

9. The current sensor device (10) according to one of the preceding claims,

wherein the controller (18) is adapted for transmitting the power values via the bus interface (16) to a control device (24).

10. The current sensor device (10) according to one of the preceding claims,

wherein the data bus (28) is a fieldbus, and/or

wherein the data bus (28) is a RS-485 bus; and/or

wherein the current sensor device (10) is configured as a slave with respect to the data bus (28) and is connectable via the data bus (28) with a control device (24) configured as a master.

11. The current sensor device (10) according to one of the preceding claims,

wherein the current sensor device (10) is galvanically separated from the conductor (12); and/or

wherein the voltage at the conductor (12) is a low- voltage or a medium- voltage.

12. The current sensor device (10) according to one of the preceding claims,

wherein a supply power of the current sensor device (10) is provided via the bus interface (16).

13. A system (22) for determining an electric power fed through at least one conductor (12a-c), the system (22) comprising:

a control device (24);

at least one current sensor device (lOa-c) according to one of the preceding claims; a voltage sensor device (26) for determining an analog voltage signal at the at least one conductor (12a-c); and

a data bus (28) interconnecting the at least one current sensor device (lOa-c), the voltage sensor device (26) and the control device (24).

14. The system (22) according to claim 13,

wherein the voltage sensor device (26) is adapted for converting the analog voltage signal into the at least one digital voltage parameter and for sending the at least one digital voltage parameter via the data bus (28) to the at least one current sensor device (lOa-c) and/or to the control device (24); and/or

wherein the voltage sensor device (26) is adapted for sending a digital voltage signal based on the analog voltage signal via the data bus (28) to the control device (26), and the control device (26) is adapted for converting the digital voltage signal into the at least one digital voltage parameter and for sending the at least one digital voltage parameter to the at least one current sensor device (lOa-c).

15. The system (22) according to one of claims 13 or 14,

wherein the control device (24) and/or the voltage sensor device (26) is adapted for sending a trigger signal to the at least one current sensor device (lOa-c) via the data bus (28), the trigger signal indicating a zero-crossing of the voltage at the conductor (12a-c).

16. The system (22) according to one of claims 13 to 15,

wherein the system (22) comprises a plurality of current sensor devices (lOa-c) interconnected via the data bus (28) with the control device (24);

wherein each current sensor device (lOa-c) is adapted for determining power values of an electric power fed through a respective conductor (12a-c).

17. The system (22) according to one of claims 13 to 16, wherein the control device (24) and/or the voltage sensor device (26) is adapted for broadcasting the digital voltage parameter via the data bus (28) to a plurality of current sensor devices (lOa-c).

18. The system (22) according to one of claims 13 to 17,

wherein the control device (24) and/or the voltage sensor device (26) is adapted for broadcasting a trigger signal via the data bus (28) to the plurality of current sensor devices (lOa-c), the trigger signal indicating a zero-crossing of the voltage at the conductor (12a-c).

19. A method for calculating an electric power fed through a conductor (12), the method comprising the steps of:

measuring, with a current sensor device (10), an analog current signal of a current supplied through the conductor (12);

converting, with the current sensor device (10), the measured analog current signal into digital current values;

receiving, with the current sensor device (10), via a data bus (28) at least one digital voltage parameter of a voltage at the conductor (12);

determining, with the current sensor device (10), digital voltage values based on the digital voltage parameter;

calculating, with the current sensor device (10), power values based on the digital current values and the digital voltage values.

The method according to claim 19, further comprising the step of:

updating the digital voltage parameter.