Methods and apparatus for phase compensation in electronic energy meters

• US 6,759,837 B2
• Filed: 08/28/2001
• Issued: 07/06/2004
• Est. Priority Date: 08/28/2001
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Gandhi, Guljeet S.
• Primary Examiner(s): Cuneo, Kamand
• Assistant Examiner(s): PATEL, PARESH H
• Application Number:
  US09/940,779
• Publication Number:
  US 20030042886A1
• Time in Patent Office: 1,043 Days
• Field of Search: 324/76.48, 324/74, 324/76.54, 324/130, 324/76.52, 324/142, 702/85, 702/106, 702/66, 702/71, 702/89, 702/72, 702/80, 702/60
• US Class Current: 324/74
• CPC Class Codes: G01R 21/133 by using digital technique
• CPC Class Codes: G01R 35/005 Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references G01R33/0035, G01R35/002 take precedence

Abstract

An electronic meter includes a sensing circuit for sensing voltage and current values of a waveform, an analog-to-digital converter for converting the sensed voltage and current values to digital voltage and current values, a digital filter for delaying one or both of the digital voltage and current values to compensate for a phase shift error in the sensing circuit, and a computation circuit for computing one or more parameters of the waveform in response to the phase compensated voltage and current values. The electronic meter may be calibrated by applying to the meter a test waveform having a known phase shift, measuring the phase shift using the electronic meter, determining a phase shift error based on the difference between the known phase shift and the measured phase shift and determining digital filter coefficients to produce a digital filter delay that corresponds to the phase shift error.

Claims

1. A method for calibrating an electronic meter, comprising the steps of:

(a) applying to an input of the electronic meter a test waveform having a known phase shift between voltage and current;

(b) measuring a phase shift between the voltage and the current of the test waveform using the electronic meter;

(c) determining a phase shift error based on the difference between the known phase shift and the measured phase shift;

(d) determining digital filter coefficients to produce a digital filter delay that corresponds to the phase shift error; and

(e) saving digital filter coefficients to compensate for the phase shift error during normal metering operation.

3. A method as defined in claim 1 wherein steps (a), (b), (c), (d) and (e) are repeated for predetermined current ranges to provide a set of digital filter coefficients for each of the predetermined current ranges.

4. A method as defined in claim 1 wherein the step of determining digital filter coefficients is performed in a computing device external to the electronic meter and wherein the digital filter coefficients are downloaded from the external computing device to the electronic meter.

5. A method as defined in claim 4 wherein the electronic meter includes a digital signal processor and wherein the digital filter coefficients are downloaded to the digital signal processor.

6. A method as defined in claim 4 wherein step (b) comprises measuring the power factor of the test waveform with the electronic meter, sending the measured power factor to the external computing device and determining the measured phase shift from the measured power factor in the external computing device.

7. A method as defined in claim 1 wherein step (a) comprises applying a test waveform to an input of an electronic watthour meter.

2. A method as defined in claim wherein step (a) comprises applying waveforms of a polyphase power line to the input of the electronic meter and wherein steps (b), (c), (d) and (e) are repeated for each phase of the polyphase power line.