Electronic meter digital phase compensation

• US 5,017,860 A
• Filed: 06/25/1990
• Issued: 05/21/1991
• Est. Priority Date: 12/02/1988
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Ouellette, Maurice J., Germer, Warren R., Negahban-Hagh, Mehrdad
• Primary Examiner(s): Wieder, Kenneth
• Assistant Examiner(s): BURNS, WILLIAM
• Application Number:
  US07/542,668
• Time in Patent Office: 330 Days
• Field of Search: 324/107, 324/141, 324/142, 324/77 R, 324/83 D, 324/74, 364/483, 364/487, 73/660
• US Class Current: 324/142
• CPC Class Codes: G01R 21/133 by using digital technique

Abstract

An electronic watthour meter for metering the consumption of electrical energy on power lines includes phase compensation means for compensating for leading and lagging phase differences between line current and voltage, whereby sampling times of the current and voltage are shifted to compensate for phase errors between the current and voltage by controlling timing signals provided to current and voltage analog to digital converters. Digital output signals from the analog to digital converters proportional to current and voltage are multiplied to provide an accurate representation of energy consumption as a result of the compensation.

Claims

1. In an electronic watthour meter for metering the consumption of electrical energy in polyphase power lines, the combination comprising:

a first analog to digital converter for providing a first digital signal in response to current flow in each line of said power lines;

a second analog to digital converter for providing a second digital signal in response to voltage applied to each of said power lines;

a multiplier for multiplying said first digital signal and said second digital signal to derive an indication of electrical energy consumption on said power lines; and

compensation means for providing a first timing signal to said first analog to digital converter and a second timing signal to said second analog to digital converter, said compensation means including phase shifting means for lead or lag phase errors by shifting the direction and amount of timing of said first timing signal relative to that of said second timing signal to provide said first and second digital signals to said multiplier substantially in time phase for all current and voltage phases of said polyphase power lines through use of a single adjustment.

2. In an electronic watthour meter for metering the consumption of electrical energy in polyphase power lines, the combination comprising:

a first analog to digital converter for providing a first digital signal in response to current flow in each line of said power lines;

a second analog to digital converter for providing a second digital signal in response to voltage applied to each of said power lines;

a multiplier for multiplying said first digital signal and said second digital signal to derive an indication of electrical energy consumption on said power lines; and

first compensation means for providing a first timing signal to said first analog to digital converter and a second timing signal to said second analog to digital converter,

said first compensation means including phase shifting means for lead or lag phase errors by shifting the direction and amount of timing of said first timing signal relative to that of said second timing signal,

to provide said first and second digital signals to said multiplier substantially in time phase for all current and voltage phases of said polyphase power lines through use of a single adjustment; and

additional compensation means providing insensitivity of said electronic watthour meter to power line frequency variations;

whereby phase compensation is provided for phase differences in the power line and in the watthour meter circuitry and additional compensation is provided for power line frequency variations.

3. The electronic watthour meter in accordance with claim 2 wherein said phase shifting means includes means for providing a fixed timing offset plus means for shifting the timing of one of said first and second timing signals to correspond with a shift in the phase of either one of said power line currents and voltages, and said additional compensation includes a phase locked loop.

4. The electronic watthour meter of claim 3 wherein

said first compensation means further includes means for cross switching the timing signals provided to said analog to digital converters, and the frequency of said first and second timing signals are very high compared to the frequency on said power lines.

5. The electronic watthour of claim 4 wherein a current scaling and isolation circuit is adapted to be connected in circuit with each phase of said power lines;

and a current multiplexer is provided to combine the outputs of each current scaling and isolation circuit for provision of a multiplexed analog current signal to said first analog to digital converter; and

a voltage scaling and isolation circuit is adapted to be connected in circuit with each phase of said power lines; and

a voltage multiplexer is provided to combine the outputs of each voltage scaling and isolation circuit for provision of a multiplexed analog voltage signal to second analog to digital converter.

6. The electronic watthour meter of claim 5 wherein a current to voltage converter converts said multiplexed analog current signal to a voltage signal proportional to the multiplexed analog current before said multiplexed analog current signal is applied to said first analog to digital converter.

7. The electronic watthour meter of claim 6 wherein an adjustable gain circuit is provided to adjust the amplitude of the proportional voltage signal prior to the application thereof to said first analog to digital converter.

8. The electronic watthour meter of claim 7 wherein a precision voltage reference source provides a voltage reference signal to said first analog to digital converter and to said second analog to digital converter.

9. The electronic watthour meter of claim 8 wherein said precision voltage reference source includes a zener diode.

10. The electronic watthour meter of claim 9 wherein said first and second timing signals are derived from an oscillator.

11. In an electronic watthour meter for metering the consumption of electrical energy in polyphase power lines the combination comprising:

means for providing a multiplexed current signal, in response to the current flow in each of the lines of said power lines;

means for providing a multiplexed voltage signal, in response to the voltage applied to each of the lines of said power lines;

a multiplier for multiplying said multiplexed current signal and said multiplexed voltage signal to provide a signal proportional to electrical energy consumption in said polyphase power lines;

means for sampling said multiplexed current signal and said multiplexed voltage signal prior to the multiplication thereof by said multiplier;

means to compensate for phase difference errors between said multiplexed current signal and said multiplexed voltage signal by adjusting the timing of the sampling of said multiplexed current and voltage signals;

said means for sampling including a current analog to digital converter for converting said multiplexed current signal to a first digital signal prior to multiplication by said multiplier;

a voltage analog to digital converter for converting said multiplexed voltage signal to a second digital signal prior to multiplication by said multiplier;

said means to compensate including means for providing a separate timing signal to each of said first and second analog to digital converters;

means for adjusting the timing of one of said timing signals relative to the other of said timing signals;

said timing signals being derived from an oscillator;

said oscillator including a phase locked loop whereby the accuracy of said oscillator is made equal to the frequency accuracy of the frequency of said power lines; and

the timing signal provided to said current analog to digital converter may be adjusted relative to the timing signal provided to said voltage analog to digital converter; and

said means to compensate further includes means for cross switching the timing signals provided to said analog to digital converters.

12. The electronic watthour meter of claim 11 wherein said oscillating is a high frequency oscillator.

13. The electronic watthour meter of claim 12 wherein the adjustment of the timing signal provided to said current analog to digital converter is performed by a binary coded switch.

14. The electronic watthour meter of claim 13 wherein a fixed timing offset between said timing signals is provided, which timing offset may then be modified by adjustment of said binary coded switch.

15. The electronic watthour meter of claim 14 wherein said binary coded switch provides at least a 4-bit binary code.

16. The electronic watthour meter of claim 15 wherein the frequency of said oscillator is very high compared to the frequency on said power lines, and includes;

means for providing high frequency pulses to each of said current and voltage analog to digital converters to provide high frequency sampling of the multiplexed current and voltage signals during the periods when the timing signals are provided to said current and voltage analog to digital converters.

17. The electronic watthour meter of claim 16 wherein said means to compensate includes means responsive to outputs from said binary coded switch to indicate whether said multiplexed current signal is leading or lagging said voltage multiplexed signal.

18. The electronic watthour meter of claim 17 wherein said binary coded switch may be actuated to change the timing of the sampling of said multiplexed current signal relative to said multiplexed voltage signal to compensate for the phase difference error therebetween.

19. The electric watthour meter of claim 11 wherein a fixed offset is provided to the timing of said timing signals and said means for adjusting the timing is binary coded to enable adjustment for both lead and lag phase differences.

20. The electronic watthour meter of claim 19 wherein a fixed offset is provided to the timing of one of said timing signals and said means for adjusting the timing is a binary coded switch to enable adjustment for both lead and lag phase difference.

21. The electronic watthour meter of claim 11 wherein the frequency of said oscillator is divided by counter circuit to provide said timing signals at a sub-multiple frequency of said oscillator, which sub-multiple frequency is much higher than the line frequency of said power lines.

22. The electronic watthour meter of claim 21 wherein a decoding logic circuit provides a signal to selectively control the application of said timing signals to said current and voltage analog to digit converters.

24. The electronic watthour meter of claim 22 wherein the frequency of said oscillator is in excess of 400 kilohertz and said counter circuit divides said oscillator frequency by 12.

25. The electronic watthour meter of claim 14 wherein the rate of said timing signals are equal at said fixed timing offset.

23. In an electronic watthour meter for metering the consumption of electrical energy in polyphase power lines the combination comprising:

means for providing a multiplexed current signal, in response to the current flow in each of the lines of said power lines;

means for providing a multiplexed voltage signal, in response to the voltage applied to each of the lines of said power lines;

a multiplier for multiplying said multiplexed current signal and said multiplexed voltage signal to provide a signal proportional to electrical energy consumption in said polyphase power lines;

means for sampling said multiplexed current signal and said multiplexed voltage signal prior to the multiplication thereof by said multiplier;

means to compensate for phase difference errors between said multiplexed current signal and said multiplexed voltage signal by adjusting the timing of the sampling of said multiplexed current and voltage signals;

said means for sampling including a current analog to digital converter for converting said multiplexed current signal to a first digital signal prior to multiplication by said multiplier;

a voltage analog to digital converter for converting said multiplexed voltage signal to a second digital signal prior to multiplication by said multiplier;

means to compensate including means for providing a separate timing signal to each of said first and second analog to digital converters;

means for adjusting the timing of one of said timing signals relative to the other of said timing signals;

same timing signals being derived from an oscillator;

the frequency of said oscillator is divided by a counter circuit to provide said timing signals at a sub-multiple frequency of said oscillator, which sub-multiple frequency is much higher than the line frequency of said power lines;

a decoding logic circuit provides a signal to selectively control the application of said timing signals to said current and voltage analog to digital converters; and

the contents of a counter in said counter circuit are compared with the binary coded outputs from said decoding logic circuit to provide the amount of delay and direction of change of at least one of said timing signals to compensate for phase differences between the multiplexed current and voltage signals.