US 5,122,735 A · Digital power metering

Abstract

A digital power meter achieves enhanced accuracies through the utilization of a sequence of meter stage improvements. Such improvements include the utilization of a digital phase shift based cycle phase realignment following the scaling function of the meter. The cycle phase corrected signals are digitized utilizing a sampling procedure wherein two samples of both current and voltage are taken within a precisely defined sampling interval. These samples are improved by the application thereto of a truncation correction and are averaged prior to being combined to provide quantity signals such as watt, VAR, volt, amperes, and the like. By developing subinterval transfer of components of these quantities to an overflow register, errors otherwise occurring at this stage of metering are substantially eliminated.

Claims27

Dependent claims

Apparatus for metering a power supply, comprising:

scaling means connectable with said supply for deriving scaled current and voltage signals of given amplitude;
selector means actuable for selecting said scaled current and voltage signals;
converter means actuable to sample the amplitudes of said scaled current and voltage signals within predetermined regular sampling intervals for effecting the conversion thereof to corresponding uncorrected current and voltage digital values;
and
control means for actuating said selector means and said converter means, for providing predetermined intra-integer bit correction to said uncorrected current and voltage digital values to provide corrected current and voltage digital sample signals for each said sampling interval, for effecting select arithmetic treatment of said corrected current and voltage digital sample signals to derive digital power quantity signals, and for selectively accumulating said digital power quantity signals to derive pulse categorized meter output signals.

2 more elements

Apparatus for metering a power supply having current and voltage parameters exhibiting given relative cycle phase relationship, comprising:

a sampling network actuable within predetermined regular sampling intervals to provide current and voltage digital signals corresponding with said current and voltage parameters;
and
control means including first accumulator means and an overflow accumulator means having a predetermined overflow value for selectively actuating said sampling network to derive said current and voltage digital signals, for treating said current and voltage digital signals to provide predetermined electrical quantity signals of given values, for accumulating said predetermined electrical quantity signals at said first accumulator means for a predetermined interval to provide an accumulated value for said electrical quantity signals, for deriving a subinterval value representing a portion of said accumulated value corresponding with a predetermined increment of a said sampling interval, for transferring said subinterval value to said overflow accumulator means at a rate corresponding with said increment of a said sampling interval until said overflow value is reached, and for outputting a quantity pulse when said overflow value is reached.

Apparatus for monitoring an electrical power supply having first and second electrical parameters exhibiting given relative cycle phase relationship comprising:

scaling means connectable with said supply for deriving first and second electrical parameter signals for corresponding cycles of said supply having a post scaling relative cycle phase relationship;
a cycle phase shift network including a phase delay network coupled to receive a select said electrical parameter signal for effecting a phase delay thereof in correspondence with the select impedance of a variable impedance component provided as a digital-to-analog converter controllable in response to a digital input for aligning said post scaling relative cycle phase relationship to a correspondence with said given relative cycle phase relationship to provide first and second cycle phase corrected electrical parameter signals;
a sampling network actuable for sampling the amplitudes of said first and second phase corrected electrical parameter signals and deriving corresponding first and said digital sample signals;
and
control means for controlling said cycle phase shift network by providing said digital input, for actuating said sampling network within predetermined regular sampling intervals to derive said first and second digital sample signals for effecting select arithmetic treatment of said first and second digital sample signals to derive digital power quantity signals, and for selectively accumulating said digital power quantity signals to derive pulse categorized meter output signals.

2 more elements

Apparatus for monitoring an electrical power supply having first and second electrical parameters exhibiting given relative cycle phase relationship comprising:

scaling means connectable with said supply for deriving first and second electrical parameter signals for corresponding cycles of said supply having a post scaling relative cycle phase relationship;
a cycle phase shift network responsive to a select said electrical parameter signal and controllable for aligning said post scaling relative cycle phase relationship to a correspondence with said given relative cycle phase relationship to provide first and second cycle phase corrected electrical parameter signals;
a sampling network including an analog-to-digital converter actuable for sampling the amplitudes of said first and second phase corrected electrical parameter signals to provide corresponding preliminary first and second digital sample signals;
and
control means for controlling said cycle phase shift network, for actuating said sampling network within predetermined regular sampling intervals to derive said preliminary first and second digital sample signals, responsive to said preliminary first and second digital parameter signals to apply a binary digital truncation correction to said preliminary first and second digital parameter signals to derive corresponding first and second digital sample signals, for effecting select arithmetic treatment of said first and second digital sample signals to derive digital power quantity signals, and for selectively accumulating said digital power quantity signals to derive pulse categorized meter output signals.

2 more elements

Apparatus for metering a polyphase power supply with first to last elements, comprising:

scaling means connectable with said power supply for deriving scaled current and voltage signals corresponding with each said element;
a sampling network including an analog-to-digital converter actuable for sampling the amplitude of said scaled current and voltage signals to provide corresponding preliminary current and voltage digital sample signals;
and
control means for actuating said sampling network within predetermined sampling intervals to derive at least two said preliminary voltage digital sample signals and at least two said preliminary current digital sample signals within said sampling interval, responsive to said preliminary voltage and current digital sample signals to apply a binary digital truncation correction thereto to derive corresponding voltage digital sample signal and current digital sample signals, and for carrying out the averaging thereof to provide corresponding averaged voltage sample signals and averaged current sample signals, for effecting select arithmetic treatment of said averaged voltage sample signals to derive digital power quantity signals, and for selectively accumulating said digital power quantity signals to derive pulse categorized meter output signals.

1 more element

Dependencies are inferred from the claim text.

Digital power metering

Life of this patent

Digital power metering

Life of this patent

Abstract

Claims27