High speed power analyzer

• US 5,606,510 A
• Filed: 12/21/1994
• Issued: 02/25/1997
• Est. Priority Date: 12/13/1991
• Status: Expired due to Fees

• Current Assignee: The Dow Chemical Company (Dow, Inc.)
• Original Assignee: The Dow Chemical Company (Dow, Inc.)
• Inventors: Glaser, R. Steven, Bade, Jeffrey M.
• Primary Examiner(s): Voeltz, Emanuel T.
• Assistant Examiner(s): VO, HIEN XUAN
• Application Number:
  US08/362,471
• Time in Patent Office: 797 Days
• Field of Search: 364/483, 364/484, 364/492, 364/550, 324/76.19, 324/76.21, 324/76.22
• US Class Current: 702/60
• CPC Class Codes: G01R 19/02 Measuring effective values, i.e. root-mean-square values
• CPC Class Codes: G01R 21/133 by using digital technique

Abstract

A method and apparatus for rapidly and continuously sampling AC voltage and current signals in a power system. The sampled signals are then analyzed in a sine board computer to derive a number of fundamental electrical variables. These variables include frequency, RMS volts, RMS amps and a phase angular relationship between the voltage and currents in the system. The computer also performs calibration and compensation functions. From these fundamental variable, other useful parameters can be calculated such as watts, watt-hours, VARS, and power factor.

Claims

1. A high speed power analyzer for measuring electrical parameters in an alternating waveform power system, comprising:

input means for receiving a plurality of analog input signals which represent electrical parameters of the power system, where at least one of said analog input signals represents a voltage signal and another of said analog input signals represents a current signal;

multiplexer means connected to said input means for sampling each of said analog input signals by individually transmitting selected ones of said analog input signals;

converter means, connected to said multiplexer means, for converting sampled analog input signals received from said multiplexer means into a digital representation of said analog input signals; and

processor circuit means, coupled to said multiplexer means and said converter means, for controlling the sampling of said analog input signals by said multiplexer means in accordance with a predetermined sampling schedule which is nonsynchronous with the waveform of said power system, and for processing said digital representations of said analog input signals received from said converter means to produce a plurality of output signals which are indicative of predetermined electrical variables related to the power being used in said power systems wherein said predetermined variables include the phase difference between said voltage and current signals, the frequency of said voltage signal, and the RMS values of each of said analog input signals.

2. The invention according to claim 1, wherein said analog input signals vary sinusoidally an a given frequency, and said analog input signals include at least one voltage signal and a plurality of current signals.

3. The invention according to claim 2, wherein said predetermined sampling schedule requires that each of said analog input signals be sampled over 1000 times per second.

4. The invention according to claim 3, wherein the sampling frequency of said predetermined sampling schedule is not a multiple of the given frequency of said analog input signals.

15. The invention according to claim 1, wherein said processor circuit means includes means for compensating for the difference between the times that said analog input signals are sampled.

5. A high speed power analyzer for measuring electrical parameters in an alternating waveform power system, comprising:

input means for receiving a plurality of analog input signals which represent electrical parameters of the power system, where at least one of said analog input signals represents a voltage signal and another of said analog input signals represents a current signal;

multiplexer means connected to said input means for sampling each of said analog input signals by individually transmitting selected ones of said analog input signals;

converter means, connected to said multiplexer means, for converting sampled analog input signals received from said multiplexer means into a digital representation of said analog input signals; and

processor circuit means, coupled to said multiplexer means and said converter means, for controlling the sampling of said analog input signals by said multiplexer means in accordance with a predetermined sampling schedule, and for processing said digital representations of said analog input signals received from said converter means to produce a plurality of output signals which are indicative of predetermined electrical variables related to the power being used in said power system, said processor circuit means including means for determining a zero crossing time in the waveform of at least two of said analog input signals by first detecting that a predetermined number of sampled data points of one numeric sign for an analog input signal have followed a predetermined number of sampled data points of the opposite numeric sign for said analog input signal, and then determining said zero crossing time from a linear extrapolation between the two sampled data points closest to the zero crossing of said analog input signal.

6. The invention according to claim 5, wherein said one numeric sign is positive and said other numeric sign is negative.

7. The invention according to claim 5, wherein said predetermined number of sampled data points for both of said numeric signs is two.

10. The invention according to claim 5, wherein said predetermined sampling schedule is nonsynchronous with the waveform of said power system.

16. The invention according to claim 5, wherein said processor circuit means includes means for compensating for the difference between the times that said analog input signals are sampled.

8. A high speed power analyzer for measuring electrical parameters in an alternating waveform power system, comprising:

input means for receiving a plurality of reference signals and a plurality of analog input signals which represent electrical parameters of the power system, where at least one of said analog input signals represents a voltage signal and another of said analog input signals represents a current signal;

multiplexer means connected to said input means for sampling each of said analog input signals by individually transmitting selected ones of said analog input signals;

amplifier means, connected to said multiplexer means, for amplifying the magnitude of sampled analog input signals received from said multiplexer means;

converter means, connected to said amplifier means, for converting sampled analog input signals received from said amplifier means into a digital representation of said analog input signals; and

processor circuit means, coupled to said multiplexer means and said converter means, for controlling the sampling of said reference signals and said analog input signals by said multiplexer means in accordance with a predetermined sampling schedule, and for processing said digital representation of said analog input signals received from said converter means to produce a plurality of output signals which are indicative of predetermined electrical variables related to the power being used in said power system, said processor circuit means including means for calibrating the conversion coefficients of said converter means by sampling said reference signals in accordance with said predetermined sampling schedule, adjusting said conversion coefficients when said adjustments are within a predetermined limit, and generating an error signal when said adjustments exceed said predetermined limit.

9. The invention according to claim 8, wherein said reference signals are sampled at least once per second.

11. The invention according to claim 8, wherein said predetermined sampling schedule is nonsynchronous with the waveform of said power system.

12. The invention according to claim 11 wherein said processor circuit means includes means for determining a zero crossing time in the waveform of at least two of said analog input signals by first detecting that a predetermined number of sampled data points of one numeric sign for an analog input signal have followed a predetermined number of sampled data points of the opposite numeric sign for said analog input signal, and then determining said zero crossing time from a linear extrapolation between the two sampled data points closest to the zero crossing of said analog input signal.

13. The invention according to claim 8, wherein said processor circuit means includes means for determining a zero crossing time in the waveform of at least two of said analog input signals by first detecting that a predetermined number of sampled data points of one numeric sign for an analog input signal have followed a predetermined number of sampled data points of the opposite numeric sign for said analog input signal, and then determining said zero crossing time from a linear extrapolation between the two sampled data points closest to the zero crossing of said analog input signal.

14. The invention according to claim 9, wherein said predetermined sampling schedule requires that each of said analog input signals be sampled over 1000 times per second.

17. The invention according to claim 8, wherein said processor circuit means includes means for compensating for the difference between the times that said analog input signals are sampled.

18. A method of measuring electrical parameters in an alternating waveform power system, comprising the steps of:

receiving a plurality of analog input signals which represent electrical parameters of the power system, where at least one of said analog input signals represents a voltage signal and another of said analog input signals represents a current signal;

sampling each of said analog input signals in accordance with a predetermined sampling schedule which is nonsynchronous with the waveform of said power system;

converting said sampled analog input signals into a digital representation of said analog input signals; and

producing a plurality of output signals which are indicative of predetermined electrical variables related to the power being used in said power system.

19. The invention according to claim 18, further including the step of determining a zero crossing time in the waveform of at least two of said analog input signals.

20. The invention according to claim 19, wherein said zero crossing time is determined by first detecting that a predetermined number of sampled data points of one numeric sign for an analog input signal have followed a predetermined number of sampled data points of the opposite numeric sign for said analog input signal, and then performing a linear extrapolation between the two sampled data points closest to the zero crossing of said analog input signal.

21. The invention according to claim 18, further including the steps of periodically sampling a plurality of reference signals, calibrating the coefficients used during said analog to digital conversion step from the measurement of said reference signals, adjusting said conversion coefficients when said adjustments are within a predetermined limit, and generating an error signal when said adjustments exceed said predetermined limit.

22. The invention according to claim 18, further including the steps of sampling said analog input signals at different times, and compensating for the difference in times that said analog signals are sampled.

23. The invention according to claim 18, wherein said predetermined variables include the phase difference between said voltage and current signals, the frequency of said voltage, and the RMS values of each of said analog input signals.

24. A method of measuring electrical parameters in an alternating waveform power system, comprising the steps of:

receiving a plurality of analog input signals which represent electrical parameters of the power system, where at least one of said analog input signals represents a voltage signal and another of said analog input signals represents a current signal;

sampling each of said analog input signals in accordance with a predetermined sampling schedule, said analog input signals being sampled at different times;

converting said sampled analog input signals into a digital representation of said analog input signals;

compensating for the difference in times that said analog signals are sampled; and

producing a plurality of output signals which are indicative of predetermined electrical variables related to the power being used in said power system.

25. The invention according to claim 24, wherein said predetermined variables include the phase difference between said voltage and current signals, the frequency of said voltage, and the RMS values of each of said analog input signals.

26. A method of measuring electrical parameters in an alternating waveform power system, comprising the steps of:

receiving a plurality of analog input signals which represent electrical parameters of the power system, where at least one of said analog input signals represents a voltage signal and another of said analog input signals represents a current signal;

sampling each of said analog input signals in accordance with a predetermined sampling schedule;

converting said sampled analog input signals into a digital representation of said analog input signals;

determining a zero crossing time in the waveform of at least two of said analog input signals by first detecting that a predetermined number of sampled data points of one numeric sign for an analog input signal have followed a predetermined number of sampled data points of the opposite numeric sign for said analog input signal, and then performing a linear extrapolation between the two sampled data points closest to the zero crossing of said analog input signal; and

producing a plurality of output signals which are indicative of predetermined electrical variables related to the power being used in said power system.

27. The invention according to claim 26, wherein said predetermined variables include the phase difference between said voltage and current signals, the frequency of said voltage, and the RMS values of each of said analog input signals.

28. A method of measuring electrical parameters in an alternating waveform power system, comprising the steps of:

receiving a plurality of analog input signals which represent electrical parameters of the power system, where at least one of said analog input signals represents a voltage signal and another of said analog input signals represents a current signal;

sampling each of said analog input signals in accordance with a predetermined sampling schedule;

converting said sampled analog input signals into a digital representation of said analog input signals;

periodically sampling a plurality of reference signals, calibrating the coefficients used during said analog to digital conversion step from the measurement of said reference signals, adjusting said conversion coefficients when said adjustments are within a predetermined limit, and generating an error signal when said adjustments exceed said predetermined limit; and

producing a plurality of output signals which are indicative of predetermined electrical variables related to the power being used in said power system.

29. The invention according to claim 28, wherein said predetermined variables include the phase difference between said voltage and current signals, the frequency of said voltage, and the RMS values of each of said analog input signals.