EP1257832A1 - System and method for digitally compensating frequency and temperature induced errors in amplitude and phase shift in current sensing of electronic energy meters - Google Patents
System and method for digitally compensating frequency and temperature induced errors in amplitude and phase shift in current sensing of electronic energy metersInfo
- Publication number
- EP1257832A1 EP1257832A1 EP00903407A EP00903407A EP1257832A1 EP 1257832 A1 EP1257832 A1 EP 1257832A1 EP 00903407 A EP00903407 A EP 00903407A EP 00903407 A EP00903407 A EP 00903407A EP 1257832 A1 EP1257832 A1 EP 1257832A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- phase shift
- degrees
- value
- processor
- shift value
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R22/00—Arrangements for measuring time integral of electric power or current, e.g. electricity meters
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R21/00—Arrangements for measuring electric power or power factor
- G01R21/14—Compensating for temperature change
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R21/00—Arrangements for measuring electric power or power factor
- G01R21/133—Arrangements for measuring electric power or power factor by using digital technique
Definitions
- the present invention relates in general to the field of utility meters. More particularly, the present invention relates to systems and methods for temperature-dependent and frequency-dependent phase shift compensation of low permeability current sensors in electronic energy meters.
- Programmable electronic energy meters are rapidly replacing electro-mechanical meters due to the enhanced functionality achieved using programmable logic integrated into solid-state electronic meters. Some of these meters can be used to meter various different electrical services without hardware modification. For example, meters having a voltage operating range between about 98 Vims and about 526 Vims are capable of operation with either 120 V or 480 V services.
- U.S. Patent No. 5,457,621, dated October 10, 1995, entitled SWITCHING POWER SUPPLY HAVING VOLTAGE BLOCKING CLAMP, assigned to ABB Automation Inc. discloses examples of such meters. In addition, some meters are constructed for use with any 3 -wire or any 4- wire service, also disclosed in U.S. Patent No. 5,457,621.
- Electronic energy meters are instruments that measure the flow of energy. Electronic energy meters typically do this by sensing the current and voltage. The power is derived from the sensed currents and voltages, and energy is defined as the measurement of power over time.
- Voltage and current signals are primarily sinusoidal. Voltage and current sensors are used in a meter to convert the primary signals to a signal that can be processed.
- One type of current sensor commonly used in electronic meters is a current transformer. In an ideal current transformer the secondary current is equal to the primary current divided by the turns ratio.
- current tran formers are non-ideal, having losses in the burden, the copper wire in the windings, and the core itself. These characteristics result in amplitude and phase deviations as compared to an ideal current transformer.
- the current transformer' s phase shift is predominately determined by the inductance, the winding resistance, and the burden resistance.
- the current transformer essentially behaves as a high pass filter with the inductance and the sum of the winding and burden resistances setting the break frequency.
- electronic energy meters In order to reduce this phase shift error, electronic energy meters typically use core materials having a very high relative permeability to obtain a high inductance. It is not uncommon for a core's relative permeability to be as high as 100,000 in order to achieve phase shifts of less than 0.1 degrees.
- immunity from DC current can be improved by increasing core area, by selecting alternative core materials that have a higher saturation level, and by lowering the relative permeability of the core material.
- increasing the core geometry is limited due to cost and space requirements.
- alternative core materials are nanocrystalline and amorphous materials. These materials have recently become economically feasible and reliable. Although such materials improve the DC immunity it is still necessary to lower the overall relative permeability to provide an appropriate solution. This DC immunity comes at a cost, however. As the permeability and inductance of the current sensors are reduced, the phase shift error is greater. With phase shifts greater than about 0.5 degrees, changes in the phase shift with operating conditions can no longer be ignored.
- the current transformer's inductance is a function of the line frequency and the winding resistance is a function of temperature (as a result of the copper wire).
- the phase shift is a function of temperature and frequency, and because the phase shift in low permeability materials is larger, they are more sensitive to temperature and frequency.
- the present invention is directed to a system and method for compensating for temperature-induced and/or line frequency-induced changes in the phase shift of the current sensors in an energy meter.
- a temperature reading from a temperature sensor within the energy meter is obtained.
- the temperature reading is converted to a digital signal.
- the digital signal is then converted to a degrees of phase shift value.
- a processor in the meter adjusts its output based on the degrees of phase shift value.
- a line frequency of the signals is obtained.
- the line frequency is converted to an engineering units value.
- the engineering units value is then converted to a degrees of phase shift value.
- a processor in the meter adjusts its output based on the degrees of phase shift value.
- the respective degrees of phase shift values are combined to obtain a total degrees of phase shift value.
- the processor then adjusts its output based on the total degrees of phase shift value.
- converting a digital signal or an engineering units value to a degrees of phase shift value comprises solving an associated linear equation for phase shift based on temperature or line frequency.
- the linear equation is determined by an approximation of the theoretical and experimental data.
- the output of the processor is delayed by an amount equal to the degrees of phase shift value, or by a time shift determined based on the degrees of phase shift value.
- Figure 1 is a block diagram showing the functional components of an exemplary meter and their interfaces in accordance with the present invention
- Figure 2A is a schematic diagram showing an exemplary current sensor circuit in accordance with the present invention.
- Figure 2B is a schematic diagram of an equivalent circuit of the current transformer of Figure 2 A;
- FIG. 3 is a schematic diagram of an exemplary temperature sensor in accordance with the present invention.
- Figure 4 is a flow chart of an exemplary temperature compensation method in accordance with the present invention
- Figure 5 is a flow chart of an exemplary frequency compensation method in accordance with the present invention.
- Figure 6 is a flow chart of an exemplary method of combining the temperature compensation and the frequency compensation in accordance with the present invention.
- the present invention dynamically corrects for phase shift in an electronic energy meter by obtaining temperature and frequency readings in the meter and using these readings in a digital signal processor (DSP) residing within the electronic energy meter.
- DSP digital signal processor
- the temperature and frequency readings are used to compensate for temperature and frequency-dependent phase shifts.
- the frequency and temperature compensation adjusts each phase's calibration values and the result is stored in the DSP.
- the compensation values are averaged to provide a smoothing of the data.
- Figure 1 is a block diagram showing the functional components of an exemplary meter and their interfaces in accordance with the present invention.
- a meter for metering three-phase or single phase electrical energy preferably includes a digital LCD type display 30, a meter integrated circuit (IC) 14 which preferably comprises A/D converters and a programmable DSP, and a microcontroller 16.
- the microcontroller also comprises an A/D converter.
- Analog voltage and current signals propagating over power transmission lines between the power generator of the electrical service provider and the users of the electrical energy are sensed by voltage sensors 12A, 12B, 12C and current sensor circuits 18A, 18B, 18C, respectively.
- the outputs of the voltage sensors 12A-12C and current sensor circuits 18A- 18C, or sensed voltage and current signals, are provided as inputs to meter IC 14.
- the A/D converters in the meter IC 14 convert the sensed voltage and current signals into digital representations of the analog voltage and current signals. In a preferred embodiment, the A/D conversion is carried out as described in U.S. Patent No.
- the exemplary microcontroller 16 performs numerous revenue metering functions as well as instrumentation functions. Instrumentation functions, in contrast to revenue functions, are intended to assist a technician in evaluating a service based on near-instantaneous conditions at the meter. Instrumentation measurements may include system parameters such as frequency, Watts, VARs, and VAs, and per phase information such as voltage, current, phase angles, power factor, current to voltage angle, kWatts, kVARs, kVA, and harmonic distortion related parameters.
- system parameters such as frequency, Watts, VARs, and VAs
- phase information such as voltage, current, phase angles, power factor, current to voltage angle, kWatts, kVARs, kVA, and harmonic distortion related parameters.
- the microcontroller 16 preferably interfaces with the meter IC 14 and one or more memory devices through an IIC bus 36.
- An EEPROM 35 is provided to store revenue data as well as programs and program data.
- selected programs and program data stored in the EEPROM 35 may be downloaded to program RAM and data RAM associated with the DSP in the meter IC 14.
- the DSP under the control of the microcontroller 16 processes the digital voltage and current signals in accordance with the downloaded programs and data stored in the respective program and data RAM.
- the microcontroller 16 may use voltage and current, real and apparent energy with lead/lag indication, frequency, and relative voltage or current phase angle information from the DSP.
- the meter IC 14 monitors the digital phase voltage signals and phase current signals over two line cycles (at about 50 or 60 Hz, two line cycle measurements are defined herein as RMS measurements even though they are near instantaneous) and then computes the RMS voltage and current values, real and apparent energies with lead/lag indication, average frequency, and relative voltage and current phase angle information. It should be understood that the number of line cycles is preferably programmable and a different number of line cycles, such as four line cycles for example, may be used for designated measurements.
- the RMS parameters are computed for a single phase at a time and stored in the data RAM in meter IC 14.
- the microcontroller 16 polls for data in these registers via the IIC bus 36 for requested instrumentation measurements. Because the instrumentation measurements are near-instantaneous, no values are stored other than the ones presently being requested.
- the current sensor circuits 18 A, 18B, 18C employ current transformers 40.
- Figure 2A shows a schematic diagram of an exemplary current sensor circuit
- Figure 2B shows the equivalent circuit of the current transformers as a combination of ideal parts.
- Each current transformer preferably has a low permeability core (e.g., a permeability less than about 10,000, and preferably between about 1000 and 10,000). These cores may also be constructed with nanocrystalline or amorphous material.
- a temperature sensor 50 is disposed within the meter, such as on the current sensor, though the temperature sensor could be disposed elsewhere, such as directly on the printed circuit board (PCB).
- a schematic diagram of an exemplary temperature sensor 50 is shown in Figure 3.
- the analog output voltage VT from the temperature sensor 50 is electrically connected to the A/D converter of the microcontroller 16 and is sensed in order to determine the temperature of the meter.
- the output voltage VT is non-linear.
- the following linear equations (1), (2), and (3) are good approximations and are used to determine the temperature T (in °C) based on the voltage VT:
- the temperature sensor is located on the PCB, it is assumed that the PCB temperature reasonably corresponds to the current transformers temperature. It is noted that any conventional temperature sensor can be used in accordance with the present invention and that the temperature in °C can be obtained, if not directly, then from the voltage or another measured value based on the manufacturer's data sheets.
- Equations (4) and (5) describe the relations of amplitude and phase shift to temperature and frequency. Equations (4) and (5) are based on the equivalent ideal circuit as shown in Figure 2B.
- F(T) is the error amplitude of the voltage measured at the burden of the current sensor
- ⁇ (T) is the phase shift of the secondary burden voltage relative to the primary current
- R B is the burden resistance
- R w is the resistance of the winding
- f is the frequency
- Equation (5) is the inductance of the current transformer.
- R B in the exemplary embodiment is approximately 3.3 ⁇ and is relatively immune to temperature variation.
- the R w term is a function of the copper winding and varies with temperature.
- R w is approximately 10 ⁇ at 25 °C and varies with temperature by about 0.4% per °C, which is temperature coefficient for copper.
- Equation (5) is represented by piecewise linear approximations for both temperature and frequency compensation.
- the temperature sensor 50 can also be used to improve the readability of the LCD display 30.
- the readability of the LCD display 30 is temperature-dependent.
- the LCD bias voltages are adapted or adjusted responsive to the temperature, as shown in Figure 3.
- FIG. 4 is a flow chart of an exemplary method of temperature compensation in accordance with the present invention.
- the present temperature reading is obtained from the temperature sensor.
- the temperature is converted by the A/D converter to obtain a digital signal. If desired, and if additional or continuous temperature readings are being taken, the temperature (represented by a digital signal) can be filtered in order to reduce noise.
- the optional filtering is shown in step 120.
- An exemplary filter can be an infinite impulse response filter, for example, and is given by equation (6):
- Tav g, n [( - 1 )/m]T avg , n _, + ( 1 /m)T instantaneous (6)
- T avg n _ is the past filter output and T avg n is the current filter output
- T jnstantaneous is the presently obtained temperature reading
- m is the filter constant. It is noted that the first temperature reading is not filtered (because there is no average temperature reading yet).
- the digital signal is then converted to degrees of phase shift at step 130 by solving a linear equation that has been found to be a close approximation of the temperature effect in Equation (5).
- ⁇ o sensor * s the phase shift of the specific current sensor being compensated at 25 °C (room temperature). This value is normally calibrated for each current sensor at the point of manufacture.
- the calculated value ⁇ (T) is stored in the memory of microcontroller 16 and the value is provided to the DSP in the meter IC 14, for example by the exemplary procedure described with respect to Figure 6.
- the microcontroller either uses this temperature-based phase shift compensation value alone or in conjunction with the below described frequency-based phase shift compensation value to compensate for the temperature and/or frequency induced phase shift(s) through calibration factors within the DSP.
- the meter IC 14 monitors the voltage and current signals, and then computes frequency, among other things. Varying frequency induces varying amounts of phase shift error in the low permeability current sensors according to
- Equation (5) The present invention compensates for this frequency induced phase shift error.
- FIG. 5 is a flowchart of an exemplary method of frequency compensation in accordance with the present invention.
- the actual line frequency is measured in DSP units at a predetermined rate, with each value being stored in memory, such as the data
- the line frequency is read from the meter IC by the microcontroller and converted to a value in engineering units.
- the value in engineering units is smoothed using an IIR filter, for example, similar to the one described above with respect to the temperature compensation.
- the filter is given by equation (8):
- fav g, n [(m- l)/m]f av&n ., + (l/m)f jnstamaneous (8)
- f avg> ⁇ - ⁇ is the past filter output and f avg n is the current filter output
- f instantaneous is the presently obtained frequency value
- m is the filter constant. It is noted that the first frequency reading is not filtered (because there is no average frequency reading yet).
- the value in engineering units is then converted to degrees of phase shift at step 230 by solving a linear equation that has been determined from experimental data to be a good approximation for the effect of frequency in Equation (5).
- ⁇ ( ⁇ sensor + ni ⁇ f ( ⁇ nominal Hz) (9)
- m ⁇ /f -0.126 °/Hz.
- ⁇ 0sensor represents the actual phase shift of the individual current sensor at the nominal line frequency (and room temperature).
- O 0sensor is nominally 6.18°
- 60 Hz ⁇ o sensor is nominally 5.15°.
- ⁇ 0sensor is normally calibrated for each current sensor at the point of manufacture.
- f nomina ⁇ is either 50 Hz or 60 Hz, as appropriate.
- the resulting value for ⁇ (f) is saved at step 240 in the memory of the microcontroller, and the value is provided to the DSP in the meter IC 14, for example by the exemplary procedure described with respect to Figure 6.
- the resulting value of ⁇ (f) is the phase shift resulting from an off-nominal frequency.
- FIG 6 is a flowchart of an exemplary method of compensating for the phase shift errors in accordance with the present invention.
- the temperature compensation value is obtained (from the exemplary method of Figure 4, for example) at step 300.
- the frequency compensation value is obtained (from the exemplary method of Figure 5, for example).
- the result is written back to the DSP in the IC 14 at step 330.
- a phase shift calibration value in the DSP's data memory is changed by the microcontroller to reflect the change in the compensation value.
- the DSP uses this phase shift calibration value in determining the output signals (including energy, instrumentation and potential indicator outputs) that the DSP provides to the microcontroller 16.
- the phase shift is determined to be 5.5 degrees
- an offset of 5.5 degrees is provided to the DSP, and the DSP uses this offset (incorporates a 5.5 degree delay or a time shift based on the phase shift) in providing output values to the microcontroller 16.
- the measured temperature and frequency values are applied for all current sensors.
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Measuring Instrument Details And Bridges, And Automatic Balancing Devices (AREA)
- Measurement Of Current Or Voltage (AREA)
- Indication And Recording Devices For Special Purposes And Tariff Metering Devices (AREA)
Abstract
Description
Claims
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
PCT/US2000/001663 WO2001055733A1 (en) | 2000-01-26 | 2000-01-26 | System and method for digitally compensating frequency and temperature induced errors in amplitude and phase shift in current sensing of electronic energy meters |
2003-06-19 |
Publications (2)
Publication Number | Publication Date |
---|---|
EP1257832A1 true EP1257832A1 (en) | 2002-11-20 |
EP1257832A4 EP1257832A4 (en) | 2006-01-11 |
Family
ID=21740991
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP00903407A Withdrawn EP1257832A4 (en) | 2000-01-26 | 2000-01-26 | System and method for digitally compensating frequency and temperature induced errors in amplitude and phase shift in current sensing of electronic energy meters |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP1257832A4 (en) |
AU (1) | AU2000225155A1 (en) |
BR (1) | BRPI0017072B8 (en) |
WO (1) | WO2001055733A1 (en) |
Families Citing this family (24)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7085824B2 (en) | 2001-02-23 | 2006-08-01 | Power Measurement Ltd. | Systems for in the field configuration of intelligent electronic devices |
US7249265B2 (en) | 2001-02-23 | 2007-07-24 | Power Measurement, Ltd. | Multi-featured power meter with feature key |
US6745138B2 (en) | 2001-02-23 | 2004-06-01 | Power Measurement, Ltd. | Intelligent electronic device with assured data storage on powerdown |
US6813571B2 (en) | 2001-02-23 | 2004-11-02 | Power Measurement, Ltd. | Apparatus and method for seamlessly upgrading the firmware of an intelligent electronic device |
US6871150B2 (en) | 2001-02-23 | 2005-03-22 | Power Measurement Ltd. | Expandable intelligent electronic device |
US6563697B1 (en) | 2001-02-23 | 2003-05-13 | Power Measurement, Ltd. | Apparatus for mounting a device on a mounting surface |
CA2522373A1 (en) * | 2003-07-01 | 2005-01-20 | Itron Electricity Metering, Inc. | System and method for acquiring voltages and measuring voltage into an electrical service using a non-active current transformer |
US7305310B2 (en) | 2004-10-18 | 2007-12-04 | Electro Industries/Gauge Tech. | System and method for compensating for potential and current transformers in energy meters |
US7304586B2 (en) | 2004-10-20 | 2007-12-04 | Electro Industries / Gauge Tech | On-line web accessed energy meter |
US9080894B2 (en) | 2004-10-20 | 2015-07-14 | Electro Industries/Gauge Tech | Intelligent electronic device for receiving and sending data at high speeds over a network |
US7747733B2 (en) | 2004-10-25 | 2010-06-29 | Electro Industries/Gauge Tech | Power meter having multiple ethernet ports |
US8190381B2 (en) | 2005-01-27 | 2012-05-29 | Electro Industries/Gauge Tech | Intelligent electronic device with enhanced power quality monitoring and communications capabilities |
US8160824B2 (en) | 2005-01-27 | 2012-04-17 | Electro Industries/Gauge Tech | Intelligent electronic device with enhanced power quality monitoring and communication capabilities |
US7996171B2 (en) | 2005-01-27 | 2011-08-09 | Electro Industries/Gauge Tech | Intelligent electronic device with broad-range high accuracy |
US8620608B2 (en) | 2005-01-27 | 2013-12-31 | Electro Industries/Gauge Tech | Intelligent electronic device and method thereof |
US7920976B2 (en) | 2007-03-27 | 2011-04-05 | Electro Industries / Gauge Tech. | Averaging in an intelligent electronic device |
US20130275066A1 (en) | 2007-04-03 | 2013-10-17 | Electro Industries/Gaugetech | Digital power metering system |
US9989618B2 (en) | 2007-04-03 | 2018-06-05 | Electro Industries/Gaugetech | Intelligent electronic device with constant calibration capabilities for high accuracy measurements |
US10845399B2 (en) | 2007-04-03 | 2020-11-24 | Electro Industries/Gaugetech | System and method for performing data transfers in an intelligent electronic device |
US11307227B2 (en) | 2007-04-03 | 2022-04-19 | Electro Industries/Gauge Tech | High speed digital transient waveform detection system and method for use in an intelligent electronic device |
CN103454490A (en) * | 2012-05-28 | 2013-12-18 | 湖南省电力公司科学研究院 | Intelligent metering system and intelligent metering method on basis of Blackman-harris window spectrum correction |
CN104849523B (en) * | 2015-05-15 | 2017-06-09 | 威胜集团有限公司 | The temperature compensation of single-phase electric energy meter |
FR3080457B1 (en) * | 2018-04-20 | 2020-10-23 | Sagemcom Energy & Telecom Sas | ELECTRICAL ENERGY METER CONTAINING A CURRENT MEASURING CIRCUIT AND A VOLTAGE MEASURING CIRCUIT |
CN109298236B (en) * | 2018-11-15 | 2021-05-07 | 中电科思仪科技股份有限公司 | Measuring method of microwave power measurement linear bias meter |
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US5485393A (en) * | 1990-08-30 | 1996-01-16 | Metricom, Inc. | Method and apparatus for measuring electrical parameters using a differentiating current sensor and a digital integrator |
EP0777125A2 (en) * | 1995-11-30 | 1997-06-04 | General Electric Company | Vector electricity meters and associated vector electricity metering methods |
US5640085A (en) * | 1995-02-17 | 1997-06-17 | Landis & Gyr Technology Innovation Ag | Temperature compensation circuit |
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US5017860A (en) * | 1988-12-02 | 1991-05-21 | General Electric Company | Electronic meter digital phase compensation |
US5457621A (en) * | 1992-02-21 | 1995-10-10 | Abb Power T&D Company Inc. | Switching power supply having voltage blocking clamp |
US5467012A (en) * | 1994-05-10 | 1995-11-14 | Load Controls Incorporated | Power monitoring |
-
2000
- 2000-01-26 AU AU2000225155A patent/AU2000225155A1/en not_active Abandoned
- 2000-01-26 WO PCT/US2000/001663 patent/WO2001055733A1/en active Application Filing
- 2000-01-26 EP EP00903407A patent/EP1257832A4/en not_active Withdrawn
- 2000-01-26 BR BRPI0017072A patent/BRPI0017072B8/en not_active IP Right Cessation
Patent Citations (3)
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US5485393A (en) * | 1990-08-30 | 1996-01-16 | Metricom, Inc. | Method and apparatus for measuring electrical parameters using a differentiating current sensor and a digital integrator |
US5640085A (en) * | 1995-02-17 | 1997-06-17 | Landis & Gyr Technology Innovation Ag | Temperature compensation circuit |
EP0777125A2 (en) * | 1995-11-30 | 1997-06-04 | General Electric Company | Vector electricity meters and associated vector electricity metering methods |
Non-Patent Citations (1)
Title |
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See also references of WO0155733A1 * |
Also Published As
Publication number | Publication date |
---|---|
AU2000225155A1 (en) | 2001-08-07 |
EP1257832A4 (en) | 2006-01-11 |
BR0017072B1 (en) | 2013-08-27 |
BRPI0017072B8 (en) | 2015-12-22 |
WO2001055733A1 (en) | 2001-08-02 |
BR0017072A (en) | 2005-02-09 |
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