Patent Grant
11280810
The present invention generally relates to a meter apparatus for measuring parameters (e.g., amplitude and/or phase shift) of electrical quantities (e.g., electric voltage and/or electric current). In particular, the present invention relates to a meter apparatus for effectively measuring parameters of electrical quantities of any wire in operation without the use of batteries and in a non-intrusive manner.
In modern society, electric power is critical to daily life. Therefore, measurement of parameters (such as amplitude and/or phase shift) of electrical quantities (such as electric voltage and/or electric current) in wires (such as in line and/or neutral wires) in operation is of the utmost importance for achieving efficient control on power usage of electric loads in residential households and buildings.
For example, determining the amplitude of the electric voltage and of the electric current in line and neutral wires in an electrical distribution system permits to determine harmonic distortion in that electrical distribution system. Harmonic distortion typically affects electric loads (such as personal computers, laser printers, battery chargers, and other small appliances) powered by “Switched-Mode Power Supply” (SMPS) modules, and may cause, inter alia, large load currents in the neutral wire of a three-phase electrical distribution system (which can cause potential fire hazards, as only the line wire is usually protected by circuit breakers), overheating (which may shorten the life of the electronic devices), poor power factor of the electric loads (e.g. power factor lower than 0.9, which could result in monthly utility penalty fees), resonance (which produces over-current surges), false tripping of circuit breakers, and electric load malfunctions.
In order to measure (and monitor) electric load consumption, information sensors, and respective meter apparatuses, have been developed.
Most of the existing solutions of meter apparatuses are substantially based on two approaches, namely a single-sensor approach and a multi-sensor approach.
A meter apparatus based on single-sensor approach allows monitoring an electrical circuit that contains a number of electric loads which switch on and off independently, and makes use of an on-site analysis of the electric current and electric voltage waveforms for estimating the number of electric loads, the nature of each electric load, the energy consumption of each electric load, and other relevant statistics such as time-of-day variations. Although meter apparatuses based on single-sensor approach are easier to deploy, they nevertheless rely on expensive custom hardware, and require either a priori knowledge about the electric loads and their electrical characteristics or a complex training phase involving the user (where the apparatus learns about the specific electrical characteristics of the electric loads). A-priori knowledge is difficult to obtain, and to keep updated, in a modern context of fast changing small appliances, and training procedures discourage users.
A meter apparatus based on multi-sensor approach comprises a current sensor installed in-line with each load (such as a commercially available smart power outlet) for measuring the power consumption at the point where the electric load is placed, or measure point, and a central gateway for gathering (and possibly displaying) the measured power consumption from each electric load.
S. Ahmad, “Smart metering and home automation solutions for the next decade” in Proc. of the international conference on Emerging Trends in Networks and Computer Communications, 2011(ETNCC 2011), Apr. 22-24 2011, pp. 200-204, discloses the use of the smart metering and home automation technologies for efficient utilization of energy, thus paving the way for a cleaner and greener environment for future generations. This paper presents an overview on Information and Communications Technology (ICT) used for Smart Metering and Home Automation based on Short distance Radio Frequency (RF) technologies like ZigBee, Z-Wave, Low Power Radio and Distribution Line Carrier (DLC).
F. Cai, E. Farantatos, R. Huang, A. P. Sakis Meliopoulos, J. Papapolymerou, “Self-powered smart meter with synchronized data” in Proc. Of the IEEE Radio and Wireless Symposium (RWS 2012), Jan. 15-18 2012, pp. 395-398, discloses a meter apparatus with real-time data detection capability, high reliability, self-powered and with low fabrication cost, intended for use in smart grid applications. Compared with the old local grid, knowing the system status in real time is achieved as a first step to control a smart grid reliably. The proposed framework provides insights about an energy harvesting sensor network to monitor the smart grid's power distribution. This provides the information needed to make a compromise between efficiency and reliability of the whole grid system. The meter apparatus design shown in this document operates automatically and is considered with installation difficulties and environmental effects such as position displacement due to weather, electrical and magnetic field interaction and so on. Each meter apparatus collects current, voltage and associated phase angles and proceed to carry a two-way communication to form a sensors net using which a RF commercial communication module.
U.S. Pat. No. 6,825,649 discloses a measurement method for measuring an AC voltage applied to a conductor, without contacting the conductor, using a detection probe, provided with a detection electrode capable of covering part of a surface of insulation for insulating the conductor and a shield electrode for covering the detection electrode, and an oscillator for outputting a signal having a certain frequency, wherein one end of each of a core wire and a sheath wire of a shield cable are connected to the detection electrode and the shield electrode, and a floating capacitance effect is substantially made zero by establishing an imaginary short-circuit state between each of the other ends. The measurement method comprises the steps of measuring impedance between the detection electrode and the conductor by applying the signal from an oscillator to the detection electrode via the shield cable, measuring a current discharged from the detection electrode attributable to the voltage applied to the conductor, and obtaining the applied voltage based on the measured impedance and current.
The Applicant has recognized that none of the cited prior-arts solutions is satisfactory.
The Applicant has found that current meter apparatuses based on multi-sensor approach achieve a consumption breakdown, but need a large number of sensors in the residential environment. This leads to high costs, and discourages their use.
According to the Applicant, in “Self-powered smart meter with synchronized data” paper, each meter apparatus is arranged for collecting current, voltage and associated phase angles in an intrusive manner, which makes measurements not fully reliable. Moreover, the Applicant has understood that this paper does not face any issue that affects real measurements, such as wire geometry (which may also significantly differ from a measure point to another one) and wire spatial geometry or arrangement (indeed, a wire at a measure point cannot be approximated as a rectilinear conductor if, for example, it is bent).
The Applicant has noticed that U.S. Pat. No. 6,825,649 only discloses a voltage monitoring, without taking into account parameters relating to phase shift (such as Power Factor). Moreover, the Applicant has understood that U.S. Pat. No. 6,825,649, similarly to the “Self-powered smart meter with synchronized data” paper, does not face any issue that affects real measurements, such as wire geometry and wire spatial geometry or arrangement.
In view of the above, the Applicant has faced the issue of determining the electric voltage and/or electric current waveforms (or relevant parameters thereof) of an AC signal in a non-intrusive manner, and independently from wire geometry and from wire spatial geometry or arrangement at the measure point, and, in order to achieve that, has devised a low cost and effective meter apparatus (and method) addressing this issue.
One or more aspects of the present invention are set out in the independent claims, with advantageous features of the same invention that are indicated in the dependent claims, whose wording is enclosed herein verbatim by reference (with any advantageous feature being provided with reference to a specific aspect of the present invention that applies mutatis mutandis to any other aspect).
More specifically, an aspect of the present invention relates to a meter apparatus for determining parameters of an AC electric signal in first and second wires, the AC electric signal comprising an AC electric current and an AC electric voltage. The meter apparatus comprises:
a measurement section configured for providing first and second measure signals each one indicative of the AC electric voltage based on a first capacitive coupling with the first wire and on a second capacitive coupling with the second wire, the first and second measure signals depending on capacitance values of the first and second capacitive couplings. The meter apparatus also comprises a control unit configured for:
determining said capacitance values of the first and second capacitive couplings according to the first and second measure signals, and
determining the amplitude of the AC electric voltage according to the first or second measure signal, and to the capacitance values of the first and second capacitive couplings.
According to an embodiment of the present invention, the meter apparatus further comprises a further measurement section configured for providing a third measure signal indicative of the AC electric current based on an inductive coupling with the first or second wire. Preferably, the control unit is further configured for:
determining a phase shift between the AC electric voltage and the AC electric current according to a phase shift between the first and third measure signals.
According to an embodiment of the present invention, the meter apparatus further comprises first and second capacitive elements for performing said first and second capacitive couplings. Said first and second capacitive elements preferably comprise at least a portion of said first and second wires.
According to an embodiment of the present invention, said measurement section further comprises first and second input capacitive elements electrically coupleable to the first and second capacitive elements, respectively. Preferably, the first and second capacitive elements and, respectively, the first and second input capacitive elements define, when coupled to each other, an impedance voltage divider for providing said first measure signal from said AC electric voltage, the first measure signal being in phase with respect to said AC electric voltage.
According to an embodiment of the present invention, said measurement section comprises further first and further second capacitive elements electrically coupleable to the first and second capacitive elements, respectively. The first and second capacitive elements and, respectively, the further first and further second capacitive elements preferably define, when coupled to each other, an impedance voltage divider providing said second measure signal from said AC electric voltage, the first and second measure signals being in phase with respect to each other.
According to an embodiment of the present invention, said measurement section comprises first and second circuit arrangements electrically coupleable to the first and second capacitive elements, respectively. The first and second capacitive elements and, respectively, the first and second circuit arrangements preferably define, when coupled to each other, a differentiator arrangement providing said second measure signal from said AC electric voltage.
According to an embodiment of the present invention, the control unit is arranged for determining said capacitance values of the first and second capacitive couplings according to amplitudes of the first and second measure signals. Preferably, the control unit is further arranged for determining the amplitude of the AC electric voltage according to the amplitudes of first or second measure signal and to the capacitance values of the first and second capacitive couplings.
According to an embodiment of the present invention, the first and second measure signals have a phase shift with respect to each other, said phase shift between the first and second measure signals depending on the capacitance values of the first and second capacitive couplings. Preferably, the control unit is further arranged for:
determining said phase shift between the first and second measure signals,
determining said capacitance values of the first and second capacitive couplings according to said phase shift between the first and second measure signals, and
determining the amplitude of the AC electric voltage according to the first or second measure signal, and to the capacitance values of the first and second capacitive couplings.
According to an embodiment of the present invention, said measurement section comprises first and second resistive elements electrically coupleable to the first and second capacitive elements, respectively. Preferably, the first and second capacitive elements and, respectively, the first and second resistive elements define, when coupled to each other, a high-pass filter providing said second measure signal from said AC electric voltage.
According to an embodiment of the present invention, the further measurement section comprises an energy harvesting module for harvesting energy from said inductive coupling. Preferably, the further measurement section also comprises a switching device selectively operable in a first configuration allowing energy harvesting by said energy harvesting unit or in a second configuration allowing provision of the third measure signal and preventing said energy harvesting.
According to an embodiment of the present invention, the further measurement section further comprises a charge storage element for storing electric charge according to said energy harvesting and for supplying said electric charge to the measurement section, to the further measurement section, and to the control unit.
According to an embodiment of the present invention, the further measurement section comprises a current clamp device for performing said inductive coupling with the first or second wires.
According to an embodiment of the present invention, the current clamp device comprises a split core current transformer.
According to an embodiment of the present invention, said measurement section comprises first and second electrically conductive layers adapted to be provided on portions of the first and second wires, respectively. Preferably, the portion of the first wire and the first electrically conductive layer thereon define said first capacitive element between the first wire and the measurement section, and, preferably, the portion of the second wire and the second electrically conductive layer thereon define said second capacitive element between the second wire and the measurement section.
Another aspect of the present invention relates to a corresponding method for determining said parameters of the AC electric signal.
The present invention allows determining electric voltage and/or electric current waveforms (i.e., amplitude and phase shift) of an AC signal (for example, the AC signal in the line and neutral wires of an electrical distribution system) by using inductive and capacitive couplings. Thanks to inductive and capacitive couplings, the electric voltage and/or electric current waveforms are determined in a non-intrusive manner (i.e., without altering the overall load of the electrical distribution system) and independently from wire geometry (which may also significantly differ from a measure point to another one) and from wire spatial geometry or arrangement (i.e., regardless of whether the wire is bent or twisted), thus providing highly precise measurements.
Moreover, the proposed meter apparatus features a simple circuit implementation requiring low cost hardware, so that it can profitably be implemented based on the multi-sensor approach.
These and other features and advantages of the present invention will be made apparent by the following description of some exemplary and non-limitative embodiments thereof; for its better intelligibility, the following description should be read making reference to the attached drawings, wherein:
With reference to the drawings,
The meter apparatus 100 is preferably arranged for determining one or more parameters of an “Alternate Current” (AC) electric signal (hereinafter, AC signal) in one or more wires, preferably line L and neutral N wires of an electrical distribution system (the electrical distribution system being not shown).
As schematically represented in the figure, the line L and neutral N wires are preferably intended to supply electric power to one or more electric loads (for example, electric loads in residential households and buildings), such as the electric load 105. The electric load 105 may for example comprise a small appliance (such as personal computers, laser printers, battery chargers), the electric load 205 being for example powered by a “Switched-Mode Power Supply” (SMPS) module. A SMPS module is typically configured for efficiently transferring electric power through the electrical distribution system to the electric load 205, while minimizing wasted energy by continually switching between low-dissipation, high-dissipation and no-dissipation states.
The AC signal comprises an AC electric current (hereinafter, AC current) IAC through the L and neutral N wires and an AC electric voltage (hereinafter, AC voltage) VAC across the L and neutral N wires, and the AC signal parameters to be determined preferably comprise at least one among:
The AC signal parameters may act as feedback information about energy consumption of the electric load 205, which can be used to promote energy awareness to residents. Indeed, timely electrical consumption feedback information through real-time metering may reduce electrical consumption by a fraction of 10-30%, and may lead to bill saving (indeed, the feedback information may be used to change energy consumption, for example by enabling the use of one or more appliances when it is least expensive).
Moreover, determining the amplitude of the AC voltage VAC and/or of the AC current IAC in the line L and neutral N wires allows determining harmonic distortion in the electrical distribution system. Harmonic distortion typically affects electric loads powered by SMPS modules, and may cause, inter alia, large load currents in the neutral wire N of a three-phase electrical distribution system (which can cause potential fire hazards, as only the line wire L is usually protected by circuit breakers), overheating (which may shorten the life of the electronic devices), poor power factor of the electric loads (e.g. power factor lower than 0.9, which could result in monthly utility penalty fees), resonance (which produces over-current surges), false tripping of circuit breakers, and electric load malfunctions.
Broadly speaking, the meter apparatus 100 in its widest conception preferably comprises:
In the preferred, not limiting, embodiment herein discussed, the meter apparatus 100 also comprises a current measurement section 110 configured for providing a signal VIS indicative of the AC current IAC (hereinafter, current measure signal VIS) based on an inductive coupling with the line L and neutral N wires. Preferably, as discussed below, the current measurement section 110 is such that the current measure signal VIS is in a respective predetermined phase relationship (the current measure signal VIS being for example in phase) with respect to the AC current IAC, and the control unit 120 is also configured for determining the phase shift between the AC current IAC and the AC voltage VAC according to the phase shift between the current measure signal VIS from the current measurement section 110 and the first voltage measure signal VVS1 from the voltage measurement section 115 (and, when provided, according to the predetermined phase relationships).
The control unit 120 (and, preferably, also the ADC module) is preferably supplied by means of one or more supply voltages VSUPPLY (for example including an upper supply voltage, e.g. +5V, and a lower supply voltage, e.g. −5V) with respect to a reference voltage (such as a 0V or ground voltage).
Preferably, as illustrated, the current measurement section 110 comprises a current sensing arrangement 110CS for sensing the AC current IAC through the line L and neutral N wires based on said inductive coupling—the current sensing arrangement 110CS, not limitative for the present invention, is illustrated as a generic oval block in the figure. More preferably, the current sensing arrangement 110CS comprises a non-invasive (or non-intrusive) current sensor, the current sensing arrangement 110CS being for example based on a current clamp device (not shown). A current clamp device is an electrical device having two jaws which open to allow clamping around a wire (e.g. the line wire L, as conceptually illustrated in the figure by the oval block 110CS intercepting the line wire L). This allows the AC current IAC through the line L and neutral N wires to be sensed, and hence measured, without having to make direct physical contact with them in an intrusive manner (such as by interrupting or cutting the wires). Even more preferably, the current clamp device is (or comprises) a so-called split core current transformer. Broadly speaking, a split core current transformer comprises a split ring of ferrite or soft iron, and a wire coil wound round one or both halves, which form one winding of the current transformer—with the wire around which it is clamped (the line wire L in the example at issue) that forms the other winding. In this way, when sensing the AC current IAC, the clamped wire (the line wire L in the example at issue) forms the primary winding and the coil forms the secondary winding of the current transformer.
According to the disclosed embodiment, the AC current sensed by the current sensing arrangement 110CS (hereinafter, sensed current IS) depends on the AC current IAC through the line L and neutral N wires and on the winding turns ratio of the current transformer.
Preferably, the current measurement section 110 also comprises a conversion module 110C for converting the sensed current IS into the current measure signal VIS, which is adapted to be processed by the control unit 120 for determining the AC signal parameters (as better discussed in the following). Assuming, as usual, that the ADC module of the control unit 120 carries out a voltage conversion, the current measure signal VIS is advantageously a voltage signal—in any case, the possibility that the ADC module of the control unit 120 carries out the conversion of a different electrical quantity, such as a current conversion, is not excluded, in which case the conversion module 110C may be omitted or simplified.
More preferably, the current measure signal VIS is adapted to (i.e., it is within) the full scale range at which the control unit 120 (and, particularly, the ADC module thereof) is allowed to operate (i.e., between the upper and lower supply voltages). In order to achieve that, the conversion module 110C preferably comprises a voltage divider (e.g., a resistive voltage divider), not shown. However, in case that the ADC module of the control unit 120 carries out a current conversion, and the current measure signal VIS is therefore a current signal, the conversion module 110C preferably comprises a current divider (e.g., a resistive current divider), not shown.
Preferably, as mentioned above, the current measure signal VIS features a predetermined phase relationship with respect to the AC current IAC (for example, by purposely adding the predetermined phase shift in the conversion module 110C). Even more preferably, the current measure signal VIS is in phase with respect to the AC current IAC.
Preferably, as illustrated, the current measurement section 110 further comprises an energy harvesting module 110H for harvesting energy from said inductive coupling (and, hence, from the sensed current IS) when the conversion module 110C (and the subsequent processing by the control unit 120) is not enabled. Even more preferably, the current measurement section 110 also comprises a power supply module 125 having one or more charge storage elements (not shown), such as a battery, a capacitor, or, preferably, as herein assumed, a super capacitor, for storing electric charge according to the harvested energy and for supplying such a stored electric charge to the control unit 120 (and, preferably, to the current 110 and voltage 115 measurement sections in a selective way, as discussed below) for powering thereof. According to the exemplary considered embodiment, such a stored electric charge is supplied to the control unit 120 (and, preferably, to the current 110 and voltage 115 measurement sections) in the form of said supply voltages VSUPPLY.
In order to achieve that, the current measurement section 110 preferably comprises a switching device SW110,A, which is preferably switchable (i.e., selectively operable) between a first configuration enabling electrical coupling (e.g., direct connection) between the current sensing arrangement 110CS and the energy harvesting module 110H thereby allowing energy harvesting from the sensed current IS, and a second configuration enabling electrical coupling (e.g., direct connection) between the current sensing arrangement 110CS and the conversion module 110C thereby preventing energy harvesting and allowing conversion of the sensed current IS into the corresponding current measure signal VIS.
Preferably, the switching of the switching device SW110,A in the first or second configuration is commanded by a command signal S110 from the control unit 120, the command signal S110 being for example a digital signal taking high or low logic levels (e.g. equal to the upper supply voltage or to the ground voltage, respectively).
According to the preferred, but not limiting, illustrated embodiment, the current measurement section 110 also comprises a further switching device SW110,B, which is preferably switchable (i.e., selectively operable) between a first, or open, configuration preventing electrical coupling between the power supply module 125 and the conversion module 110C (thus preventing powering, and hence operation, thereof) and a second, or closed, configuration enabling electrical coupling (e.g., direct connection) between the power supply module 125 and the conversion module 110C (thus allowing operation thereof, and, hence, conversion of the sensed current IS into the current measure signal VIS).
Advantageously, although not necessarily, the switching of the switching device SW110,B in the open or closed configuration is commanded by the command signal S110 (i.e., the same command signal S110 that also commands the switching of the switching device SW110,A), so that the conversion module 110C is powered only when required, i.e. only when the sensed current IS has to be converted into the current measure signal VIS for determining the AC signal parameters. This allows achieving a non-negligible power saving.
Preferably, as illustrated, the voltage measurement section 115 comprises a voltage sensing arrangement 115VS for sensing the AC voltage VAC across the line L and neutral N wires—the voltage sensing arrangement 115VS, not limitative for the present invention, is illustrated as a generic oval block in the figure. More preferably, the voltage sensing arrangement 115VS comprises a non-invasive voltage sensor, being for example a voltage sensor based on capacitive coupling. In order to achieve that, as visible in the exemplary voltage sensing arrangement 115VS of
Assuming, as usual, that the line L and neutral N wires are cylindrical in shape, the first ECLL and second ECLN electrically conductive layers are advantageously provided around the sensed portion of the line wire L and the sensed portion of the neutral wire N, respectively (so as to form cylindrical conductive layers), such that the first and second sensing capacitors result in cylindrical first and second capacitors—although this should not be construed in a restrictive manner.
Preferably, the first ECLL and second ECLN electrically conductive layers are copper sheets (or tapes). More preferably, the first ECLL and second ECLN electrically conductive layers are self-adhesive copper sheets adapted to be wrapped around the sensed portion of the line wire L and the sensed portion of the neutral wire N, respectively.
The first ECLL and second ECLN electrically conductive layers preferably have same length and thickness.
According to an embodiment of the present invention, the length of the first ECLL and second ECLN electrically conductive layers is of the order of a few centimeters (for example between 1 cm and 5 cm, such as 1.25 cm), which descends from the measurement sensitivity achieved by the conditioning module 115C (as discussed below). This very short length of the first ECLL and second ECLN electrically conductive layers (especially compared to known solutions of voltage sensors based on capacitive coupling) implies that the AC voltage VAC and/or the AC current IAC waveforms are determined independently from wire geometry (which may also significantly differ from a measure point to another one) and from wire spatial geometry or arrangement (i.e., regardless of whether the wire is bent or twisted).
According to an embodiment of the present invention, the thickness of the first ECLL and second ECLN electrically conductive layers is of the order of the hundredths of millimeters (for example, between 0.01 mm and 0.1 mm, such as 0.35 mm), so that when they are wrapped around the sensed portion of the line wire L and the sensed portion of the neutral wire N, respectively, substantially no additional space occupation arises. This very low space occupation of the first ECLL and second ECLN electrically conductive layers implies the adaptability of the voltage sensing arrangement 115VS (and, hence, of the meter apparatus 100) to substantially any measure point.
In the circuit representations of
Assuming, as usual, that the permittivity of the insulating material is the same in both line L and neutral N wires and that the radius is the same for both the line L and neutral N wires, and considering same length and thickness for the first ECLL and second ECLN electrically conductive layers, the first C1 and second C2 sensing capacitors feature a same capacitance value CS (although this should not be construed in a restrictive manner).
In this arrangement, a first voltage forms at the first electrically conductive layer ECLL (or, equivalently, at the second terminal T2C1 of the first sensing capacitor C1) according to the AC voltage VAC in the sensed portion of the line wire L and to the capacitance value CS, and a second voltage forms at the second electrically conductive layer ECLN (or, equivalently, at the second terminal T2C2 of the second sensing capacitor C2) according to the AC voltage VAC in the sensed portion of the neutral wire N and to the capacitance value CS. This equals to say that, as visible in the circuit representation of
The capacitance value CS, which depends on the wire size, is unknown a priori, as it depends on geometrical and electrical features of the wires at the measure point where the meter apparatus 100 is intended to be used. However, as will be understood from the following discussion, thanks to the present invention, the amplitude of the AC voltage VAC (as well as the phase shift between AC voltage VAC and the AC current IAC, when the current measurement section 110 is provided) is independent from the capacitance value CS (or from the capacitance values, when different capacitance values for the first C1 and second C2 sensing capacitors are expected), and hence from the measure point.
Back to
More preferably, as conceptually illustrated in the figures, the voltage measure signals VVS1,VVS2 are single-ended voltage signals, i.e. voltage signals referred to proper reference voltages, and adapted to (i.e., it is within) the full scale range at which the ADC module of the control unit 120 is allowed to operate. Even more preferably, the voltage measure signals VVS1,VVS2 are both referred to a common reference voltage, the common reference voltage being for example between the supply voltages VSUPPLY (such as the ground voltage).
Broadly speaking, as better discussed in the following, the conditioning module 115C according to the considered embodiment comprises first and second conditioning branches (for the AC voltage VAC) for providing the first VVS1 and second VVS2 voltage measure signals, respectively.
In order to achieve that, the voltage measurement section 115 preferably comprises a switching device SW115,A, which is preferably switchable between a first configuration electrically coupling the voltage sensing arrangement 115VS to the first conditioning branch of the conditioning module 115C (thereby allowing it to provide the first voltage measure signal VVS1 and, hence, allowing the control unit 120 to determine the phase shift between the AC current IAC and the AC voltage VAC according to the phase shift between the first voltage measure signal VVS1 and the current measure signal VIS), and a second configuration electrically coupling the voltage sensing arrangement 115VS to the second branch of the conditioning module 115C (thereby allowing it to provide the second voltage measure signal VVS2 and, hence, allowing the control unit 120 to determine the capacitance value CS according to the first VVS1 and second VVS2 voltage measure signals, and the amplitude of the AC voltage VAC according to the first VVS1 or second VVS2 voltage measure signal, and to the determined capacitance value CS, as detailed below).
In order to take into account the differential nature of the AC voltage VAC, which requires to condition both the voltage at the first terminal T1C1 of the first sensing capacitor C1 (referred to as AC voltage VAC+) and the voltage at the first terminal T1C2 of the second sensing capacitor C2 (referred to as AC voltage VAC−, with the AC voltage VAC that thus corresponds to the difference between the AC voltage VAC+ and the AC voltage VAC−), the first conditioning branch (for the AC voltage VAC) preferably comprises a first sub-branch for receiving the AC voltage VAC+ and a second sub-branch for receiving the AC voltage VAC−, and, more preferably, the second conditioning branch preferably comprises a first sub-branch for receiving the AC voltage VAC+ and a second sub-branch for receiving the AC voltage VAC−. In this exemplary arrangement, the switching device SW115,A preferably comprises two switching elements, namely (as better illustrated in
Preferably, the switching of the switching device SW115,A in the first or second configuration is commanded by a proper command signal S115,A from the control unit 120, the command signal S115,A being for example a digital signal (e.g., similar to the command signal S110). The command signal S115,A preferably commands both the switching elements of the switching device SW115,A concurrently.
According to the preferred, but not limiting, illustrated embodiment, the voltage measurement section 115 also comprises a further switching device SW115,B, which is preferably switchable (i.e., selectively operable) between a first, or open, configuration preventing electrical coupling between the power supply module 125 and the conditioning module 115C (thus preventing powering, and hence operation, thereof) and a second, or closed, configuration enabling electrical coupling (e.g., direct connection) between the power supply module 125 and the conditioning module 115C (thus allowing operation thereof, and hence conditioning of the sensed voltage VS into the corresponding voltage measure signals VVS1,VVS2).
The switching of the switching device SW115,B in the open or closed configuration is advantageously commanded by a command signal S115,B different from the command signal S115,A that commands the switching of the switching device SW115,A, such that, regardless of the switching device SW115,A configuration, the conditioning module 115C is energized only when required, i.e. only when the sensed voltage VS has to be conditioned into the voltage measure signals VVS1,VVS2 for determining the AC signal parameters.
According to a preferred, but not limitative, embodiment of the present invention, the command signals S110, S115,B are synchronized to each other, e.g. such that the conversion module 110C in the current measurement section 110 and the conditioning module 115C in the voltage measurement section 115 are both powered (and, hence, enabled) during a predetermined measurement period (e.g., of the order of milliseconds or even second) in order to provide the current VIS and voltage VVS1, VVS2 measure signals to the control unit 120 within a measurement time window (with the command signal S115,A that, within the measurement period, sequentially enables the first and second sub-branches of the first and second conditioning branches for providing the voltage measure signals VVS1,VVS2). However, according to the AC signal parameters to be determined and/or to the specific application, the command signals S110,S115,B may also be independent from each other (at least in part).
Preferably, during the predetermined measurement time window:
Advantageously, during the time periods between two consecutive measurements time windows (hereinafter, referred to as harvesting time periods), each one of the order of minutes, hours, days or even months according to the AC signal parameters to be determined and/or to the specific application of the meter apparatus 100, the conversion module 110C in the current measurement section 110 and the conditioning module 115C in the voltage measurement section 115 are both unpowered and hence disabled (switching devices SW110,B and SW115,B both in the open configuration), and the switching device SW110,A in the second configuration enables energy harvesting by the energy harvesting module 110H.
Finally, the meter apparatus 100 preferably comprises a wireless network communication interface 130 for receiving the AC signal parameters determined by the control unit 120 (or an indication thereof) and for wirelessly transmitting them to a proper receiving apparatus (e.g., by means of short distance radio frequency technologies).
Thanks to the present invention, the AC voltage VAC and/or the AC current IAC waveforms (i.e., amplitude and phase shift) are determined by using inductive and capacitive couplings, thus in a non-intrusive manner (i.e., without altering the overall electric load of the electrical distribution system). Moreover, thanks to capacitive coupling, and to the measurement sensitivity of the conditioning module 115C (as discussed below), the length of the first ECLL and second ECLN conductive layers, and hence of the sensing capacitors C1, C2 thereby obtained, may be very short (e.g., in the order of a few centimeters, such as 1.25 cm). The very short length of the sensing capacitors C1,C2 implies that the AC voltage VAC and/or the AC current IAC waveforms are determined independently from wire geometry (which may also significantly differ from a measure point to another one) and from wire spatial geometry or arrangement (i.e., regardless of whether the wire is bent or twisted), thus providing highly precise measurements.
Moreover, the proposed meter apparatus 100 features a simple circuit implementation requiring low cost hardware (as will be apparent from the following discussion of preferred embodiments of the conditioning module 115C illustrated in
For the sake of ease, the electronic components of the conditioning module 115C′ have been considered referred to the ground voltage (as conceptually illustrated in the figure by the conventional electrical symbol of a ground terminal providing the ground voltage). Anyway, according to specific design options, the electronic components of the conditioning module 115C′ (or at least a part thereof) may be referred to one or more different reference voltages (such the upper supply voltage and/or the lower supply voltage).
Preferably, the conditioning module 115C′ comprises, in the first conditioning branch, a first input stage for processing (e.g., scaling) the AC voltage VAC and a first output stage for providing the first voltage measure signal VVS1 from the scaled AC voltage, and, in the second conditioning branch, a second input stage for processing the AC voltage VAC and a second output stage for providing the second voltage measure signal VVS2 from the processed AC voltage VAC (the specific implementation of the second input stage determining the processing on the AC voltage VAC).
Even more preferably, as illustrated, the first input stage comprises a first input capacitive element (e.g., a capacitor) C3 having a first terminal T1C3 electrically coupled to the second terminal T2C1 of the first sensing capacitor C1 when the switching device SW115,A is in the first configuration (the first terminal T1C3 of the first input capacitor C3 being for example electrically floating when the switching device SW115,A is in the second configuration), and a second terminal T2C3 electrically coupled to the ground terminal, and a second input capacitive element (e.g., a capacitor) C4 having a first terminal T1C4 electrically coupled to the second terminal T2C2 of the second sensing capacitor C2 when the switching device SW115,A is in the first configuration (the first terminal T1C4 of the second input capacitor C4 being for example electrically floating when the switching device SW115,A is in the second configuration), and a second terminal T2C4 electrically coupled to the ground terminal.
Thus, the first sensing capacitor C1 and the first input capacitor C3 define, when electrically coupled to each other, an impedance voltage divider, in particular a capacitive voltage divider for the AC voltage VAC+, whereas the second sensing capacitor C2 and the second input capacitor C4 define, when electrically coupled to each other, a capacitive voltage divider for the AC voltage VAC− (with the first C1 and second C2 sensing capacitors and, respectively, the first C3 and second C4 input capacitors that, when electrically coupled to each other, define as a whole a capacitive voltage divider for the AC voltage VAC). Anyway, nothing prevents from implementing one or more impedance voltage dividers other than the capacitive voltage dividers, such as inductive voltage dividers, resistive voltage dividers or a combination thereof.
Assuming, as discussed above, a same capacitance value CS for both the first C1 and second C2 sensing capacitors, and assuming a same capacitance value CI for both the first C3 and second C4 input capacitors (the capacitance value CI being preferably chosen according to the smallest value of the AC voltage VAC that the conditioning module 115C′ is required to discern, and/or according to the full scale range at which the ADC module of the control unit 120 is allowed to operate), the voltage at the first terminal T1C3 of the first input capacitor C3 is:
and the voltage at the first terminal T1C4 of the second input capacitor C4 is:
Thanks to the impedance voltage dividers C1,C3 and C2,C4, no phase shift is introduced in the voltages VIC3 and VIC4 with respect to the AC voltages VAC+ and VAC−, respectively.
Preferably, the first output stage of the conditioning module 115C′ is arranged for providing the first voltage measure signal VVS1 according to a difference between the voltage VIC3 from the first sub-branch of the first conditioning branch (or a voltage corresponding thereto) and the voltage VIC4 from the first sub-branch of the second conditioning branch (or a voltage corresponding thereto).
This is advantageously achieved by means of a differential amplifier circuit. Preferably, the differential amplifier circuit of the first output stage is conceived such that no phase shift is introduced in the first voltage measure signal VVS1 with respect to the voltages VIC3 and VIC4 (and, hence, with respect to the AC voltage VAC)—in any case, as discussed above, the possibility that a predetermined phase shift is introduced in the first input stage and/or in the first output stage is not excluded.
According to the illustrated embodiment, not limiting for the present invention, the differential amplifier circuit of the first output stage comprises:
In this exemplary configuration, the first voltage measure signal VVS1 is (the resistance values of the resistors R3, R4, R5 and R6 being denoted by R3, R4, R5 and R6, respectively):
Therefore, the first voltage measure signal VVS1 has no (or ideally no) phase shift with respect to the AC voltage VAC, such that the control unit 120 is allowed to determine the phase shift between the AC current IAC and the AC voltage VAC based on the current measure signal VIS and on the first voltage measure signal VVS1—in any case, when a predetermined phase shift is introduced in the first input stage and/or in the first output stage, the control unit 120 is allowed to determine the phase shift between the AC current IAC and the AC voltage VAC also based on the predetermined phase shift.
Preferably, although not necessarily, the phase shift between the AC current IAC and the AC voltage VAC is determined by the control unit 120 according to a zero-crossing technique. Broadly speaking, zero-crossing is a point where the sign of a function, such as a sinusoidal waveform, changes (e.g., from positive to negative or vice versa), and is defined by a crossing of the axis representing the zero value in the graph of the function. In the considered context, the control unit 120 is configured for determining the zero-crossing of the current measure signal VIS (i.e., the time instant at which the current measure signal VIS is zero), and corresponding to the zero crossing of the AC current IAC (by virtue of the absence of phase shifting between the AC current IAC and the current measure signal VIS), and the zero-crossing of the first voltage measure signal VVS1 (i.e., the time instant at which the first voltage measure signal VVS1 is zero), and corresponding to the zero crossing of the AC voltage VAC (by virtue of the absence of phase shifting between the AC voltage VAC and the first voltage measure signal VVS1), and the phase shift according to a difference between the time instant at which zero-crossing of the current measure signal VIS takes place and the time instant at which zero-crossing of the first voltage measure signal VVS1 takes place (the phase shift being expressed as time shift or angular shift).
Therefore, the meter apparatus 100 so far discussed allows determining the AC current IAC waveform and the phase shift between the AC voltage VAC and the AC current without the need of external power supply (indeed, thanks to the energy harvesting module 110H, the meter apparatus 100 is a self-powering apparatus), with no direct electrical contact to the line L and neutral N wires (indeed, the current 110CS and voltage 115VS sensing arrangements are “applied” externally to the wires, without direct physical contact with them in an intrusive manner, such as by interrupting or cutting the wires), and regardless of wire size, i.e. without requiring calibration because of the wire size (indeed, the capacitance value CS, which depend on the wire size, is not involved in determining the current measure signal VIS in the current measurement section 110, nor it affects the phase of the first voltage measure signal VVS1 in the voltage measurement section 115 thanks to the capacitive voltage dividers C1,C3 and C2,C4 and to the resistor-based differential amplifier circuit OA1,R3-R6).
According to the illustrated embodiment, the first and second input stages comprise first R1,R2 and second R7,R8 input resistors electrically coupleable to the first C1 and second C2 sensing capacitors, respectively. Preferably, the first input resistor R1 has a first terminal T1R1 electrically coupled to the second terminal T2C1 of the first sensing capacitor C1 when the switching device SW115,A is in the second configuration (the first terminal T1R1 of the first input resistor R1 being for example electrically floating when the switching device SW115,A is in the first configuration), and the first input resistor R2 has a first terminal T1R2 electrically coupled (e.g., directly connected) to a second terminal T2R1 of the first input resistor R1 and a second terminal T2R2 electrically coupled to the ground terminal. The second input resistor R7 has a first terminal T1R7 electrically coupled to the second terminal T2C2 of the second sensing capacitor C2 when the switching device SW115,A is in the second configuration (the first terminal T1R7 of the second input resistor R7 being for example electrically floating when the switching device SW115,A is in the first configuration), and the second input resistor R8 has a first terminal T1R8 electrically coupled (e.g., directly connected) to a second terminal T2R7 of the second input resistor R7 and a second terminal T2R8 electrically coupled to the ground terminal.
In other words, the first R1,R2 and second R7,R8 input resistors are in series to the first C1 and second C1 sensing capacitors, respectively, when the switching device SW115,A is in the second configuration. Thus, when the switching device SW115,A is in the second configuration, the first sensing capacitor C1 and the first input resistors R1,R2 define a high-pass filter for the AC voltage VAC+, whereas the second sensing capacitor C2 and the second input resistors R7,R8 define a high-pass filter for the AC voltage VAC− (or, otherwise stated, the first C1 and second C2 sensing capacitors and, respectively, the first R1,R2 and second R7,R8 input resistors, when electrically coupled to each other, define as a whole a high-pass filter for the AC voltage VAC).
Assuming, as discussed above, a same capacitance value CS for both the first C1 and second C2 sensing capacitors, and assuming a same resistance value R1 for both the first R1 and second R7 input resistors and a same resistance value R2 for both the first R2 and second R8 input resistors (the resistance values R1 and R2 being preferably chosen according to the smallest value of the AC voltage VAC that the conditioning module 115C′ is required to discern, i.e. for maximizing the span and optimizing the accuracy, and/or according to the full scale range at which the ADC module of the control unit 120 is allowed to operate), the voltage at the first terminal T1R2 of the second input resistor R2 (denoted by VT1R2) and the voltage at the first terminal T1R8 of the second input resistor R8 (denoted by VT1R8) are:
The cut-off frequency fcut-off, and the module |H| and phase φ of the transfer function of the high-pass filter are:
Preferably, the cut-off frequency fcut-off is sufficiently lower than 50 Hz, so that the AC voltage VAC of the electrical mains is allowed to be transferred with a phase shift across the second sub-branches of the first and second conditioning branches (so that the resulting second voltage measure signal VVS2 has a phase shift with respect to the first voltage measure signal VVS1, as better discussed below).
Back to
This is advantageously achieved by means of a differential amplifier circuit.
Preferably, the differential amplifier circuit of the second output stage is conceived such that no phase shift is introduced in the second voltage measure signal VVS2 with respect to the voltages V1R2 and V1R8 (so that the phase of the second voltage measure signal VVS2 only depends on the phase φ of the transfer function of the high-pass filter, whereby the control unit 120 is allowed to easily determine the, unknown, capacitance value CS of the first C1 and second C2 sensing capacitors, as discussed herebelow). In any case, nothing prevents from adding a further phase shift in the second output stage.
Even more preferably, the differential amplifier circuit of the second output stage is identical (e.g., in terms of architecture) to the differential amplifier circuit of the first output stage.
According to the illustrated embodiment, not limiting for the present invention, the differential amplifier circuit of the second output stage comprises:
In this exemplary configuration, the second voltage measure signal VVS2 is (the resistance values of the resistors R9, R10, R11 and R12 being denoted by R9, R10, R11 and R12, respectively):
According to a preferred, not limiting embodiment of the present invention, the structure of the differential amplifier circuit of the second output stage is identical to the structure of the differential amplifier circuit of the first output stage (or substantially identical, as the possibility of including structural differences, e.g. for taking into account manufacturing tolerances or non-idealities of specific electronic components, is not excluded). Moreover, the resistance values R9, R10, R11 and R12 of the resistors R9, R10, R11 and R12 and the electrical properties of the respective operational amplifier OA2 are preferably identical to the resistance values R3, R4, R5 and R6 of the resistors R3, R4, R5 and R6 and to the electrical properties of the operational amplifier OA1, respectively (or substantially identical, as the possibility of including structural differences, e.g. for taking into account manufacturing tolerances or non-idealities of specific electronic components, is not excluded).
Thus, the second voltage measure signal VVS2 has a phase shift with respect to the first voltage measure signal VVS1, which phase shift is detected and measured by the control unit 120 (e.g., still by means of the zero-crossing technique). In its turn, such a phase shift, which thus is known, depends on the capacitance value CI of the first C3 and second C4 input capacitors, which is known, and by the capacitance value CS of the first C1 and second C2 sensing capacitors, which instead is unknown (and depends, inter alia, on wire geometry). Therefore, in the considered embodiment, upon reception of the first VVS1 and second VVS2 voltage measure signals, the control unit 120 is configured for determining the capacitance value CS according to the phase shift between the first VVS1 and second VVS2 voltage measure signals (e.g., by reversing the above equation for the phase φ of the transfer function of the high-pass filter), and thus the amplitude of the AC voltage VAC according to the first VVS1 or second VVS2 voltage measure signals and to the capacitance value CS (e.g., by reversing the above equation for the first voltage measure signal VVS1 or for the second voltage measure signal VVS2). In this way, with contact-less sensors around the wire under test, the meter apparatus 100 is capable of determining the relevant AC signal parameters (namely, the amplitude of the AC current IAC, the amplitude of the AC voltage VAC and the phase shift between the AC current IAC and the AC voltage VAC) regardless of wire geometry (namely, without calibration).
As should be readily understood, as both the first VVS1 and second VVS2 voltage measure signals depend on the amplitude of the AC voltage VAC and on the capacitance value CS, in principle either the equation for first voltage measure signal VVS1 or the equation for the second voltage measure signal VVS2 may be reversed for determining the amplitude of the AC voltage VAC. In any case, in practical scenarios, the equation for the voltage measure signal to be reversed may be chosen according to the actual implementation of the conditioning module and/or according to design options and/or criteria (for example, the equation for the voltage measure signal implying lower computational capability may be reversed).
Back to
With reference now to
The conditioning module 115C″ is almost entirely similar to the conditioning module 115C′, for which reason same elements will not be discussed again.
The conditioning module 115C″ differs from the conditioning module 115C′ in that the first and second input stages comprise, instead of the high-pass filter (defined by the first C1 and second C2 sensing capacitors and, respectively, the first R1,R2 and second R7,R8 input resistors, as discussed above), an impedance voltage divider for the AC voltage VAC. In the example at issue wherein the voltage measurement section 115 is configured for providing the first VVS1 and/or second VVS2 voltage measure signals based on capacitive coupling with line L and neutral N wires, the impedance voltage divider is advantageously a capacitive voltage divider.
In the exemplary illustrated embodiment, the first input stage comprises a further first input capacitive element, e.g. a capacitor (hereinafter referred to as first input capacitor, for the sake of conciseness) C5 electrically coupleable to the first sensing capacitor C1 and, preferably, the second input stage comprises a further second input capacitive element, e.g. a capacitor (hereinafter referred to as second input capacitor, for the sake of conciseness) C6 electrically coupleable to the second sensing capacitor C2. In this way, the first C1 and second C2 sensing capacitors and, respectively, the first C5 and second C6 input capacitors define, when coupled to each other, an impedance voltage divider for the AC voltage VAC (i.e., a first capacitive voltage divider C1,C5 for the AC voltage VAC+ and a second capacitive voltage divider C2,C6 for the AC voltage VAC−).
Preferably, as illustrated, the first input capacitor C5 has a first terminal T1C5 electrically coupled to the second terminal T2C1 of the first sensing capacitor C1 when the switching device SW115,A is in the second configuration (the first terminal T1C5 of the first input capacitor C5 being for example electrically floating when the switching device SW115,A is in the first configuration) and to the resistor R9 (for example, by interposition of the voltage buffer OA4), and a second terminal T1C5 electrically coupled (e.g., directly connected) to the ground terminal. Similarly, the second input capacitor C6 has a first terminal T1C6 electrically coupled to the second terminal T2C2 of the second sensing capacitor C2 when the switching device SW115,A is in the second configuration (the first terminal T1C6 of the second input capacitor C6 being for example electrically floating when the switching device SW115,A is in the first configuration) and to the resistor R11 (for example, by interposition of the voltage buffer OA6), and a second terminal T2C6 electrically coupled to the ground terminal.
Assuming, as discussed above, a same capacitance value CS for both the first C1 and second C2 sensing capacitors, and assuming a same capacitance value CIN for both the first C5 and second C6 input capacitors (the capacitance value CIN being preferably chosen according to the smallest value of the AC voltage VAC that the conditioning module 115C″ is required to discern, i.e. for maximizing the span and optimizing the accuracy, and/or according to the full scale range at which the ADC module of the control unit 120 is allowed to operate), the voltage at the first terminal T1C5 of the first input capacitor CS (denoted by VIC5) and the voltage at the first terminal T1C6 of the second input capacitor C6 (denoted by VIC6) are:
Assuming, as illustrated, that the second output stage has the same circuit implementation of the previous embodiment, then the second voltage measure signal VVS2 resulting from the conditioning module 115C″ is (the resistance values of the resistors R9, R10, R11 and R12 being again denoted by R9, R10, R11 and R12, respectively):
Moreover, assuming, similarly to the above discussion, that the structure (as well as the values and the electrical properties of electronic components) of the differential amplifier circuit of the second output stage is preferably identical to the structure (and, respectively, to the values and the electrical properties of electronic components) of the differential amplifier circuit of the first output stage (or substantially identical, as the possibility of including structural differences, e.g. for taking into account manufacturing tolerances or non-idealities of specific electronic components, is not excluded), the first voltage measure signal VVS1 is (the resistance values of the resistors R3, R4, R5 and R6 being denoted by R3, R4, R5 and R6, respectively):
The above assumption implies that:
In the considered embodiment, thanks to the impedance voltage divider, the second voltage measure signal VVS2 is in phase (i.e., it has no, or substantially no, phase shift) with respect to the first voltage measure signal VVS1, so that the capacitance value CS can be easily determined based on the first VVS1 and second VVS2 voltage measure signals (i.e., based on the amplitudes thereof as detected by the control unit 120, as discussed herebelow). In any case, similarly to the above discussion, the provision of predetermined phase shifts to the first voltage measure signal VVS1 and/or to the second voltage measure signal VVS2, and/or to the current measure signal VIS does not affect the principles of the present invention.
More particularly, in the considered embodiment and under the above assumptions, upon reception of the first VVS1 and second VVS2 voltage measure signals, the control unit 120 is configured for determining the capacitance value CS according to a difference between the first VVS1 and second VVS2 voltage measure signals (i.e., according to the amplitudes thereof detected by the control unit 120), e.g. by reversing the above equation for the first VVS1 and second VVS2 voltage measure signals as follows:
and hence for determining the amplitude of the AC voltage VAC according to the first voltage measure signal VVS1 or to the second voltage measure signal VVS2 (i.e., according to the amplitudes thereof as detected by the control unit 120), and to the capacitance value CS (e.g., by reversing the above equation for the first voltage measure signal VVS1 or the above equation for the second voltage measure signal VVS2, as discussed above).
As should be readily understood from the above equation of the capacitance value CS, in the considered example of symmetrical structure of the first and second conditioning branches, the capacitance values CI and CIN are advantageously set different from each other (in order to avoid numerator zeroing and, hence, the impossibility of determining the capacitance value CS itself).
In this way, the meter apparatus 100 is capable of determining the relevant AC signal parameters (namely, the amplitude of the AC current IAC, the amplitude of the AC voltage VAC and the phase shift between the AC current IAC and the AC voltage VAC) regardless of the size of the wires (namely, without calibration because of the size of the wires).
Moreover, with respect to the previous embodiment, the conditioning module 115C″ allows avoiding the determination of the phase shift between the first VVS1 and second VVS2 voltage measure signals, which could be a relevant source of error in some applications.
With reference now to
The conditioning module 115C′″ is almost entirely similar to the conditioning module 115C′, for which reason same elements will not be discussed again.
The conditioning module 115C′″ differs from the conditioning module 115C′ in that it comprises, instead of the high-pass filter (which, in the conditioning module 115C′, is defined by the first C1 and second C2 sensing capacitors and, respectively, the first R1,R2 and second R7,R8 input resistors, as discussed above), a differentiator arrangement for the AC voltage VAC.
In the exemplary illustrated embodiment, the first and second input stages comprise first R13 and second R14 input resistors electrically coupleable to the first C1 and second C2 sensing capacitors, respectively, and first OA7 and second OA8 operational amplifiers electrically coupled to the first R13 and second R14 input resistors, respectively (the operational amplifiers OA7,OA8 preferably having same electrical characteristics, for example the same electrical characteristics as the operational amplifiers OA1-OA6 and being preferably powered with the supply voltages VSUPPLY upon closing of the switching device SW115,B).
Preferably, as visible in the figure, the first input resistor R13 has a first terminal T1R13 electrically coupled (e.g., electrically connected) to the second terminal T2C1 of the first sensing capacitor C1 when the switching device SW115,A is in the second configuration (the first terminal T1R13 of the first input resistor R13 being for example electrically floating when the switching device SW115,A is in the first configuration) and electrically coupled (e.g., electrically connected) to a an inverting input terminal of the first operational amplifier OA7, and a second terminal T2R13 electrically coupled (e.g., electrically connected) to an output terminal of the first operational amplifier OA7 and electrically coupled to the first terminal T1R9 of the resistor R9 (for example, by interposition of the voltage buffer OA4). In other words, the first input resistor R13 is electrically coupled (e.g., electrically connected) across the (inverting) input terminal and the output terminal of the first operational amplifier OA7 (with the non-inverting input terminal of the first operational amplifier OA7 that is instead electrically coupled, e.g. electrically connected, to the ground terminal).
Preferably, as visible in the figure, the second input resistor R14 has a first terminal T1R14 electrically coupled (e.g., electrically connected) to the second terminal T2C2 of the second sensing capacitor C2 when the switching device SW115,A is in the second configuration (the first terminal T1R14 of the second input resistor R14 being for example electrically floating when the switching device SW115,A is in the first configuration) and electrically coupled (e.g., electrically connected) to a an inverting input terminal of the first operational amplifier OA8, and a second terminal T2R14 electrically coupled (e.g., electrically connected) to an output terminal of the second operational amplifier OA8 and electrically coupled to the first terminal T1R11 of the resistor R11 (for example, by interposition of the voltage buffer OA6). In other words, the second input resistor R14 is electrically coupled (e.g., electrically connected) across the (inverting) input terminal and the output terminal of the second operational amplifier OA8 (with the non-inverting input terminal of the second operational amplifier OA8 that is instead electrically coupled, e.g. electrically connected, to the ground terminal).
Thus, when the switching device SW115,A is in the second configuration, the first sensing capacitor C1, the first input resistor R13 and the first operational amplifier OA7 define a differentiator arrangement (or differentiator) for the AC voltage VAC+, whereas the second sensing capacitor C2, the second input resistor R14 and the second operational amplifier OA8 define a differentiator for the AC voltage VAC− (or, otherwise stated, the first C1 and second C2 sensing capacitors and, respectively, the first R13 and second R14 input resistors and the associated first OA7 and second OA8 operational amplifiers, when electrically coupled to each other, define as a whole a differentiator for the AC voltage VAC). In any case, as should be readily understood, circuit arrangements other than those formed by the operational amplifiers OA7, OA8 and the input resistors R13,R14 can be used to for implementing the differentiator.
Assuming, as discussed above, a same capacitance value CS for both the first C1 and second C2 sensing capacitors, and assuming a same resistance value RIN for both the first R13 and second R14 input resistors (the resistance value RIN being preferably chosen according to the smallest value of the AC voltage VAC that the conditioning module 115C is required to discern, i.e. for maximizing the span and optimizing the accuracy, and/or according to the full scale range at which the ADC module of the control unit 120 is allowed to operate), the voltage at the second terminal T2R13 of the first input resistor R13 (denoted by V2R13), and hence at the output terminal of the first operational amplifier OA7, and the voltage at the second terminal T2R14 of the second input resistor R14 (denoted by V2R14), and hence at the output terminal of the second operational amplifier OA8, are:
Assuming, as illustrated, that the second output stage has the same circuit implementation of the previous embodiment, then the second voltage measure signal VVS2 resulting from the conditioning module 115C′″ is (the resistance values of the resistors R9, R10, R11 and R12 being again denoted by R9, R10, R11 and R12, respectively):
Moreover, assuming that the AC voltage VAC is in the form:
VAC=A sin(2πft)
wherein A is the amplitude of the AC voltage VAC to be determined, then the second voltage measure signal VVS2 resulting from the conditioning module 115C′″ is:
In addition, assuming, similarly to the above discussion, that the structure (as well as the values and the electrical properties of electronic components) of the differential amplifier circuit of the second output stage is preferably identical to the structure (and, respectively, to the values and the electrical properties of electronic components) of the differential amplifier circuit of the first output stage (or substantially identical, as the possibility of including structural differences, e.g. for taking into account manufacturing tolerances or non-idealities of specific electronic components, is not excluded), the first voltage measure signal VVS1 is (the resistance values of the resistors R3, R4, R5 and R6 being denoted by R3, R4, R5 and R6, respectively):
Thus, from the equation above it follows that
In the considered embodiment, the capacitance value CS can be easily determined based on the first VVS1 and second VVS2 voltage measure signals (i.e., based on the amplitudes thereof as detected by the control unit 120) from the above equations.
More particularly, in the considered embodiment and under the above assumptions, upon reception of the first VVS1 and second VVS2 voltage measure signals, the control unit 120 is configured for determining the capacitance value CS according to a difference between the first VVS1 and second VVS2 voltage measure signals, e.g. by reversing the above equation for the first VVS1 and second VVS2 voltage measure signals as follows:
and hence for determining the amplitude A of the AC voltage VAC according to the first voltage measure signal VVS1 or the second voltage measure signal VVS2, and to the capacitance value CS (e.g., by reversing the above equation for the first voltage measure signal VVS1 or the above equation for the second voltage measure signal VVS2, as discussed above), as follows:
As should be readily understood, the amplitude A of the AC voltage VAC is advantageously determined by taking into account a number of samples, the samples being preferably sufficiently far from the “risky” points in which the above equation is not valid (e.g., π/6, π/4, π/3 and kπ/20).
In this way, the meter apparatus 100 is capable of determining the relevant AC signal parameters (namely, the amplitude of the AC current IAC, the amplitude of the AC voltage VAC and the phase shift between the AC current IAC and the AC voltage VAC) regardless of the size of the wires (namely, without calibration because of the size of the wires).
Moreover, with respect to the first embodiment, the conditioning module 115C′″ allows avoiding the determination of the phase shift between the first VVS1 and second VVS2 voltage measure signals, which could be a relevant source of error in some applications. In particular, this approach significantly improves the amplitude measurement with an error lower than 5%.
In addition, with respect to the conditioning module 115C″, wherein the ADC module should exhibit a very high sensitivity (i.e., a resolution of the order of μV) thus determining relatively high complexity and costs, the conditioning module 115C′″ allows achieving very low costs and reliability.
Naturally, in order to satisfy local and specific requirements, a person skilled in the art may apply to the solution described above many logical and/or physical modifications and alterations. More specifically, although the present invention has been described with a certain degree of particularity with reference to preferred embodiments thereof, it should be understood that various omissions, substitutions and changes in the form and details as well as other embodiments are possible. In particular, different embodiments of the invention may even be practiced without the specific details set forth in the preceding description for providing a more thorough understanding thereof; on the contrary, well-known features may have been omitted or simplified in order not to encumber the description with unnecessary details. Moreover, it is expressly intended that specific elements and/or method steps described in connection with any disclosed embodiment of the invention may be incorporated in any other embodiment.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2016/062303 | 5/31/2016 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2017/207037 | 12/7/2017 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5473244 | Libove | Dec 1995 | A |
| 20100156441 | Moliton et al. | Jun 2010 | A1 |
| 20100318306 | Tierney | Dec 2010 | A1 |
| 20160061864 | White | Mar 2016 | A1 |
| Entry |
|---|
| International Search Report and Written Opinion dated Feb. 7, 2017, in PCT/EP2016/062303, filed May 31, 2016. |
| Office Action dated Apr. 20. 2021 in corresponding Chinese Patent Application No. 201680087418.8 (with English Translation), 6 pages. |
| Number | Date | Country | |
|---|---|---|---|
| 20200278383 A1 | Sep 2020 | US |
