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EP-4735902-A1 - ELECTRIC METER AND METHOD FOR MEASURING ELECTRIC POWER

EP4735902A1EP 4735902 A1EP4735902 A1EP 4735902A1EP-4735902-A1

Abstract

An electric meter (100) comprising a non-invasive voltage measurement sensor (12), one or more non-invasive current measurement sensors (14A-14C) for measuring one or more phase currents, and a digital processing unit (10). The voltage measurement sensor (12) and the current measurement sensors (14A-14C) are connected or connectable to the processing unit (10). The processing unit (10) is configured, in a calibration mode, to determine phase shift values between a first voltage sensor signal and first current sensor signals, and to store the phase shift values into a memory. The processing unit (10) is configured, in an operation mode, to determine a second voltage sensor signal, determine voltage estimates based on the second voltage sensor signal and the stored phase shifts, and determine, based on the voltage estimates and second current sensor signals determined by the current measurement sensors (14A-14C), respectively, one or more electric power values.

Inventors

  • ALHONEN, Antti

Assignees

  • Robustco Oy

Dates

Publication Date
20260506
Application Date
20240620

Claims (15)

  1. 1. An electric meter (100), comprising: a non-invasive voltage measurement sensor (12), one or more non-invasive current measurement sensors (14A-14C) for measuring one or more phase currents, and a digital processing unit (10), wherein the non-invasive voltage measurement sensor (12) and the one or more non-invasive current measurement sensors (14A-14C) are connected or connectable to the processing unit (10) for providing voltage and current sensor signals to the processing unit (10); wherein the processing unit (10) is configured, in a calibration mode, to determine one or more phase shift values between a first voltage sensor signal and one or more first current sensor signals, respectively, and to store the phase shift values into a memory, and wherein the processing unit (10) is configured, in an operation mode, to: determine, by the non-invasive voltage measurement sensor (12), a second voltage sensor signal, determine one or more voltage estimates based on the second voltage sensor signal and the stored phase shifts, and determine, based on the one or more voltage estimates and one or more second current sensor signals determined by the one or more current non-invasive current measurement sensors (14A-14C), respectively, one or more electric power values; wherein, in the calibration mode, the determination of the one or more phase shift values includes utilizing a known, estimated, or received power factor value for an electric load (30) or source, and the processing unit (10) is configured in the calibration mode: to execute a zero crossing detection with respect to the first voltage sensor signal and the one or more first current sensor signals for determining the phase shifts, or to execute a zero crossing detection with respect to the first voltage sensor signal and to determine a voltage estimate based on the zero crossing detection, and to determine the one or more phase shift values by calculating a plurality of electric power values based on the voltage estimate and the one or more first current sensor signals, such as by a dot product therebetween, relative to a plurality of different simulated phase shifts between the voltage estimate and the one or more first current sensor signals, and to select a phase shift or shifts providing the highest electric power value or values as the one or more phase shift values.
  2. 2. The electric meter (100) of claim 1, wherein the processing unit (10) generates a common clock signal for the first voltage sensor signal and the one or more first current sensor signals, wherein the phase shifts are determined with respect to the common clock signal.
  3. 3. The electric meter (100) of claim 1 or 2, wherein the processing unit (10) is configured, in the calibration mode, to adapt the selected phase shift or shifts providing the highest electric power value or values based on the known, estimated, or received power factor of the load or source used during the calibration mode.
  4. 4. The electric meter (100) of claims 1-3, wherein the processing unit (10) is configured to execute a phase-locked loop to determine a voltage clock signal and to synchronize the voltage clock signal with respect to the second voltage sensor signal.
  5. 5. The electric meter (100) of claim 4, wherein the processing unit (10) is configured to generate the one or more voltage estimates based on the voltage clock signal and the stored phase shifts for corresponding phase current.
  6. 6. The electric meter (100) of any of claim 1-5, wherein the processing unit (10) is configured to accumulate determined electric power values over a measurement period.
  7. 7. The electric meter (100) of claim 6, wherein the processing unit (10) is configured to determine one or more of the following during the measurement period: a real power value, a reactive power value, an apparent power value, one or more root-mean-square current values, a power factor value.
  8. 8. The electric meter (100) of any of claims 1-7, wherein the voltage estimates, the one or more second current sensor signals, and the electric power values represent instantaneous voltage and power values, respectively; or the voltage estimates, the one or more second current sensor signals, and the electric power values represent average voltage and power values, respectively, over an averaging time period, such as the measurement period.
  9. 9. The electric meter (100) of any one of claims 1-8, wherein the non-invasive voltage measurement sensor (12) is based on capacitive coupling, such as being a capacitive sensor.
  10. 10. The electric meter (100) of claim 9, wherein the non-invasive voltage measurement sensor (12) includes a conductor including at least a measurement portion (13) without a grounding shield layer (103), wherein the measurement portion (13) is adapted to be arranged adjacent or even in contact with an outer layer of a phase line (21-23).
  11. 11. The electric meter (100) of any one of claims 1-10, wherein the one or more current non-invasive current measurement sensors (14A-14C) include one or more current clamp sensors, such as one or more split core sensors or one or more Rogowski coil sensors.
  12. 12. The electric meter (100) of any one of claims 1-11, wherein the one or more current non-invasive current measurement sensors (14A-14C) include one or more Halleffect current sensors.
  13. 13. The electric meter (100) of any one of claim 1-12, wherein the processing unit (10) is configured to sample the voltage and current values by analog-to-digital converters at a sampling rate of at least 1000 Hz, preferably at least 3000 Hz, most preferably at least 6000 Hz per measurement.
  14. 14. The electric meter (100) of any one of claim 1-13, wherein the processing unit (10) is configured to detect if, in the calibration mode, a power factor value is higher than 0.95 and direction of real power is towards an electric load, the electric power of which is being determined.
  15. 15. A method for measuring electric power, the method comprising, in a calibration mode (301), determining (310) one or more phase shifts between a first voltage sensor signal determined by a non-invasive voltage measurement sensor (12) and one or more first current sensor signals determined by one or more non-invasive current measurement sensors (14A-14C), respectively, and to store the phase shifts into a memory of a processing unit (10), wherein, in the calibration mode, the determination (310) of the one or more phase shift values includes utilizing a known, estimated, or received power factor value for an electric load (30) or source, and: executing, by the processing unit (10), a zero crossing detection with respect to the first voltage sensor signal and the one or more first current sensor signals for determining the phase shifts, or executing, by the processing unit (10), a zero crossing detection with respect to the first voltage sensor signal and to determine a voltage estimate based on the zero crossing detection, and determining the one or more phase shift values by calculating a plurality of electric power values based on the voltage estimate and the one or more first current sensor signals, such as by a dot product therebetween, relative to a plurality of different simulated phase shifts between the voltage estimate and the one or more first current sensor signals, and to select a phase shift or shifts providing the highest electric power value or values as the one or more phase shift values; and wherein the method further comprises, in an operation mode (302), determining (320), by the non-invasive voltage measurement sensor, a second voltage sensor signal, determining (330) one or more voltage estimates based on the second voltage sensor signal and the stored phase shifts, and determining (340), based on the voltage estimates and one or more second current sensor signals determined by the one or more current non-invasive current measurement sensors, one or more electric power values.

Description

ELECTRIC METER AND METHOD FOR MEASURING ELECTRIC POWER FIELD OF THE INVENTION The present invention relates in general to electric meters. BACKGROUND Known electric meters typically require an electrician to install the meter into its intended position. This often, if not always, requires switching off electricity in order to ensure safety. Furthermore, the installing of the electric meter requires manual labor so that the sensors of the meter can be galvanically connected to right positions or portions of the electric system. SUMMARY An objective of the present invention is to provide an electric meter and a method for measuring electric. Another objective of the present invention is that the electric meter and the method provide an easy and convenient, yet accurate enough solution for measuring electric power without the need to invade to electrical portions of the target system or device. The objectives of the invention are reached by an electric meter and a method as defined by the respective independent claims. According to a first aspect, an electric meter is provided. The electric meter comprises a non-invasive voltage measurement sensor, one or more (at least one) non-invasive current measurement sensors for measuring one or more phase currents, and a digital processing unit. The non-invasive voltage measurement sensor and the one or more non- invasive current measurement sensors are connected or connectable, such as removable, to the processing unit, such as via input ports thereof, for providing voltage and current sensor signals to the processing unit. The processing unit is configured, in a calibration mode, to determine one or more phase shifts between a first voltage sensor signal and one or more first current sensor signals, respectively, and to store the phase shifts into a memory. One phase shift may be determined for each phase current represented by the one or more first current sensor signals. In the calibration mode, the determination of the one or more phase shift values includes utilizing a known, estimated, or received power factor value for an electric load or source, for example, but not limited to, a resistive heater or a photovoltaic inverter. The processing unit is configured in the calibration mode: to execute a zero crossing detection with respect to the first voltage sensor signal and the one or more first current sensor signals for determining the phase shifts, or to execute a zero crossing detection with respect to the first voltage sensor signal and to determine a voltage estimate, such as a voltage vector, a voltage waveform, or a voltage time series, based on the zero crossing detection, such as an ideal voltage sinewave^) that is(/are) phase-locked relative to the first voltage sensor signal, and to determine the one or more phase shift values by calculating a plurality of electric power values based on the voltage estimate and one or more first current sensor signals, such as by a dot product therebetween, relative to a plurality of different simulated phase shifts between the voltage estimate and the one or more first current sensor signals, and to select a phase shift or shifts providing the highest electric power value or values (such as one per phase) as the one or more phase shift values. Regarding the simulated phase shifts between the voltage estimate and the one or more first current sensor signals, the processing unit may be configured to vary a phase angle of the current or currents relative to that of the voltage estimate, such as by steps of one, five or ten degrees, for instance. For every simulated phase shift, that is an angle difference, the electric power is then calculated by the dot product of the voltage estimate and the current or currents, for instance. Alternatively, the electric power may be calculated by varying the phase angle of the voltage estimate relative to the current(s). As a result, a plurality of electric power values is obtained for each simulated phase shift. The phase shift with the maximum power value is then selected. Furthermore, in the calibration mode, the processing unit may be configured to adapt, such as subtract a further phase shift from or add a further phase shift to, the selected phase shift or shifts providing the highest electric power value or values based on the known, estimated, or received power factor of the load or source used during the calibration mode. The processing unit may be configured to determine, in the calibration mode, which of the first current sensor signals corresponds to the determined voltage sensor signal in the sense that they are determined of the same phase. For example, the phase shift between the first voltage sensor signal and the first current sensor signal of the same phase should be either close to zero or close to 180 degrees (such as within an angle of 0-10 or 0-20 degrees thereof), depending which direction is the current sensor measuring positive current. On the other hand, in