Line cycle correlated spectral analysis for power measurement systems

Patent metadata

Field	Value
Publication number	US-9759751-B1
Application number	US-201313740014-A
Country	US
Kind code	B1
Filing date	Jan 11, 2013
Priority date	Jan 12, 2012
Publication date	Sep 12, 2017
Grant date	Sep 12, 2017

Abstract

In one embodiment, a system and method perform a spectral analysis in a power measurement system to determine the total harmonic distortion (“THD”) in a power signal by correlating one or more THD calculation parameters to a sensed period of a voltage input signal. In at least one embodiment, the one or more THD calculation parameters are a number of samples of a voltage, current, or voltage and current components of the power signal that correlate to the sensed period. Because, for example, the period of the power signal can vary or the clock frequency can drift over time, the power measurement system correlates the number of samples with the period and, thus, varies the count of samples over which THD is calculated when the period varies. By correlating the samples with the period, the samples more closely represent a period of the sampled component of the power signal.

First claim

What is claimed is:

1. A method comprising:
in a power measurement system:
sensing an occurrence of a period of a periodic input voltage to a load;
obtaining samples of total harmonic calculation parameters;
correlating an integer number of samples of the total harmonic distortion calculation parameters to the sensed period of the voltage input so that the integer number of samples used for determining total harmonic distortion of one or more components of power delivered to the load varies with changes in the period of the periodic input voltage;
determining the total harmonic distortion of the one or more components of power delivered to the load using the integer number of samples of the total harmonic calculation parameters that are correlated with the sensed period of the input voltage and using only an integer number of full values of the total harmonic calculation parameters for each determination of the total harmonic distortion; and
providing access to the determined total harmonic distortion.

2. The method of claim 1 further comprising:
in the power measurement system:
sampling the input voltage to the load, wherein the one or more total harmonic distortion calculation parameters comprises an integer number of samples of the input voltage that occur during X number of periods of the input voltage, wherein X is an integer greater than or equal to one; and
determining the total harmonic distortion of the one or more components of power delivered to the load using the one or more calculation parameters comprises determining the total harmonic distortion of the one or more components of power delivered to the load using the integer number of samples of the input voltage that occur during X number of periods of the input voltage.

3. The method of claim 2 wherein the one or more components of power delivered to the load comprise one or more members of a group consisting of a current to the load and the input voltage to the load.

4. The method of claim 3 wherein determining the total harmonic distortion of the one or more components of power delivered to the load comprises determining the total harmonic distortion using a Goertzel algorithm based on a fundamental line frequency of the input voltage for the integer number of samples of the input voltage that occur during X number of periods of the input voltage.

5. The method of claim 1 wherein:
sensing an occurrence of a period of a periodic input voltage to a load comprises:
detecting a beginning and an ending zero crossing of each of P cycles of the periodic input voltage, where P is an integer greater than or equal to one; and

the method further comprises:
sampling the input voltage to the load; and
tracking an integer number of samples of the input voltage to the load that occur from a beginning zero crossing of the period of the periodic input voltage to a last zero crossing of the period of the periodic voltage; and

the one or more total harmonic distortion calculation parameters comprises the integer number of samples of the input voltage that occur from the beginning zero crossing of the first of the one or more periods of the periodic input voltage to the last zero crossing of the one or more periods of the periodic voltage.

6. The method of claim 1 wherein the period of the input voltage is P cycles of the periodic input voltage, where P is an integer greater than or equal to one.

7. A method comprising:
in a power measurement system:
sensing an occurrence of a period of a periodic input voltage to a load;
obtaining an integer number of samples of total harmonic calculation parameters;
correlating the integer number of samples of the total harmonic distortion calculation parameters to the sensed period of the voltage input so that the integer number of samples used for determining total harmonic distortion of one or more components of power delivered to the load varies with changes in the period of the periodic input voltage;
determining the total harmonic distortion of the one or more components of power delivered to the load using the integer number of samples of the total harmonic calculation parameters that are correlated with the sensed period of the input voltage and using only an integer number of full values of the total harmonic calculation parameters for each determination of the total harmonic distortion; and
providing access to the determined total harmonic distortion.

8. The method of claim 7 wherein determining the total harmonic distortion of the one or more components of power delivered to the load comprises determining the total harmonic distortion of the one or more components of power delivered to the load using an integer count of samples of the input voltage that occur during X number of periods of the input voltage, wherein X is an integer greater than or equal to one.

9. The method of claim 7 wherein the one or more components of power delivered to the load comprise one or more members of a group consisting of a current to the load and the input voltage to the load.

10. The method of claim 7 wherein determining the total harmonic distortion of the one or more components of power delivered to the load comprises determining the total harmonic distortion using a Goertzel algorithm based on a fundamental line frequency of the input voltage for the integer count of the samples of the input voltage that occur during X number of periods of the input voltage, wherein X is an integer greater than or equal to one.

11. The method of claim 7 wherein:
sensing an occurrence of a period of one or more cycles of a periodic input voltage to a load comprises:
detecting a beginning and an ending zero crossing of the period; and

correlating a count of the samples to period of the input voltage comprises:
determining the integer count of the integer number of samples to equal the number of samples of the input voltage that occur from the beginning zero crossing of the period of the periodic input voltage to the last zero crossing of the period of the periodic voltage.

12. The method of claim 7 wherein the period of the input voltage is P cycles of the periodic input voltage, where P is an integer greater than or equal to one.

13. An apparatus comprising:
a power measurement system, wherein the power measurement system is configured to:
sense an occurrence of a period of a periodic input voltage to a load;
obtain samples of total harmonic calculation parameters;
correlate an integer number of samples of the total harmonic distortion calculation parameters to the sensed period of the voltage input so that the integer number of samples used for determining total harmonic distortion of one or more components of power delivered to the load varies with changes in the period of the periodic input voltage;
determine the total harmonic distortion of the one or more components of power delivered to the load using the integer number of samples of the total harmonic calculation parameters that are correlated with the sensed period of the input voltage and using only an integer number of full values of the total harmonic calculation parameters for each determination of the total harmonic distortion;
provide access to the determined total harmonic distortion.

14. The apparatus of claim 13 further comprising:
an analog-to-digital converter to sample the input voltage to the load, wherein the one or more total harmonic distortion calculation parameters comprises an integer number of samples of the input voltage that occur during X number of periods of the input voltage, wherein X is an integer greater than or equal to one; and
to d

Assignees

• Cirrus Logic Inc

Inventors

• SETHI Shruti

Classifications

• G01R21/133 Primary

  by using digital technique · CPC title

• G06F17/00

  Digital computing or data processing equipment or methods, specially adapted for specific functions (information retrieval, database structures or file system structures therefor G06F16/00) · CPC title

• G01R23/20

  Measurement of non-linear distortion · CPC title