Outbound detector system and method

• US 4,914,418 A
• Filed: 01/03/1989
• Issued: 04/03/1990
• Est. Priority Date: 01/03/1989
• Status: Expired due to Term

• Current Assignee: Distribution Control Systems Inc (Hubbell, Inc.)
• Original Assignee: Emerson Electric Company
• Inventors: Hatton, Ray C. Jr., Takach, David S., Mak, Sioe T.
• Primary Examiner(s): Crosland, Donnie L.
• Application Number:
  US07/293,181
• Time in Patent Office: 455 Days
• Field of Search: 340/310 R, 340/310 A, 340/310 CP, 375/76, 375/99, 375/104, 358/138, 358/166, 370/6
• US Class Current: 370/201
• CPC Class Codes: H02J 13/00009 using pulsed signals
• CPC Class Codes: H02J 13/0001 using modification of a parameter of the network power signal
• CPC Class Codes: H02J 13/00034 the elements or equipment being or involving an electric power substation
• CPC Class Codes: H04B 2203/5416 by adding signals to the wave form of the power source
• CPC Class Codes: H04B 2203/542 using zero crossing information
• CPC Class Codes: H04B 2203/5425 improving S/N by matching impedance, noise reduction, gain control
• CPC Class Codes: H04B 2203/5433 Remote metering
• CPC Class Codes: H04B 2203/5491 using filtering and bypassing
• CPC Class Codes: H04B 2203/5495 having measurements and testing channel
• CPC Class Codes: H04B 3/542 the information being in digital form
• CPC Class Codes: Y02B 90/20 Smart grids as enabling technology in buildings sector smart grids supporting the management or operation of end-user stationary applications in general, or like technologies with no associated climate change mitigation effect Y04S20/00
• CPC Class Codes: Y02E 60/00 Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
• CPC Class Codes: Y04S 10/52 Outage or fault management, e.g. fault detection or location
• CPC Class Codes: Y04S 40/121 using the power network as support for the transmission

Abstract

Outbound signals carried over an electric power network are detected and crosstalk is rejected by sampling the waveform in three segments of each cycle. In the first segment valid signals are always absent. Valid signals appear at the same time in both the second and third segments. Sample waveform values from alternate half cycles are compared to detect differences indicative of outbound signal information. The energy in each of the three segments is compared with an energy threshold for that segment and a cycle under test is rejected when the energy in the first segment exceeds the threshold for that first segment. A cycle under test is also rejected if the energy in the third segment greatly exceeds the energy in the second segment. Signal detection thresholds for both signal strength and energy in the segments are set recursively using actual samples acquired at the outbound detection site. These thresholds are sensitive to dynamic network changes.

Claims

1. Apparatus for detecting outbound signals carried by cyclic waveforms over an electric power distribution network comprising:

means for rectifying cyclic waveforms transmitted from a central site over an electric power distribution network to create a rectified cyclic waveform of successive half cycles;

means for sampling the rectified waveform to obtain sample waveform values, said sampling occurring in three segments of each cycle of said waveform, a first segment being a region of the cycle in which valid signals are always absent, a second segment being a region of the cycle in which valid signals appear, and a third segment distinct from the second segment being a region in which valid signals appear; and

means for detecting the presence of outbound signal information as a function of the sample waveform values in the three segments.

2. The apparatus as set forth in claim 1 wherein the sample waveform values represent the energy in the waveform in the three segments, the sample values being rejected as containing other than valid signal information when the energy values in the first segment exceed a threshold value.

3. The apparatus as set forth in claim 2 wherein the detecting means includes means for setting the first segment threshold value from sample values for the first segments of previous cycles of the cyclic waveform.

4. The apparatus as set forth in claim 1 wherein the sample waveform values represent the energy in the waveform in the three segments, the sample values being rejected when the energy values in one of the second or third segments exceed the energy values in the other of the second or third segments by a factor of approximately fifty.

5. The apparatus as set forth in claim 1 wherein the sample waveform values are time differences representing the difference between the times the voltage of an unmodulated voltage waveform would have reached predetermined points and the times the voltage of the sampled waveform actually reached said predetermined points.

6. The apparatus as set forth in claim 5 wherein the squares of said time differences are representative of the energy in said sampled waveform.

7. The apparatus as set forth in claim 5 further including means for deriving a DC voltage value from the rectified waveform, the magnitude of the DC voltage value representing the average magnitude of the cyclic waveform and varying with variations in the average magnitude of the cyclic waveform.

8. The apparatus as set forth in claim 7 further including means responsive to the DC voltage value to modify the predetermined points as a function of the DC voltage value to compensate for changes in the average magnitude of the cyclic waveform.

9. The apparatus as set forth in claim 5 wherein the rectified waveform instantaneous voltage is compared with one predetermined point at a time, further including means for changing the predetermined point with which the instantaneous voltage is compared once the instantaneous voltage reaches the previous predetermined point.

10. The apparatus as set forth in claim 9 including means for generating a stop signal when the instantaneous voltage reaches a predetermined point, further including counter means responsive to said signal for continuously counting and for latching the time upon receipt of the stop signal.

11. The apparatus as set forth in claim 10 wherein the predetermined point changing means is responsive to the stop signal to change the predetermined point with which the instantaneous voltage is compared.

12. Apparatus for detecting outbound signals carried by cyclic waveforms over an electric power distribution network comprising:

means for rectifying cyclic waveforms transmitted from a central site over an electric power distribution network to create a rectified cyclic waveform of successive half cycles;

means for sampling the rectified waveform to obtain sample waveform values, said sampling occuring in three segments of each cycle of each waveform, a first segment being a region of the cycle in which valid signals are always absent, a second segment being a region of the cycle in which valid signals appear, and a third segment distinct from the second segment being a region in which valid signals appear; and

means for comparing sample waveform values from alternate half cycles of the rectified waveform to detect differences indicative of outbound signal information in the three segments.

13. A method of detecting outbound information carried by cyclic waveforms over an electric power distribution network comprising the steps of:

sampling a cyclic waveform originating at a central site and transmitted over an electric power distribution network to obtain a plurality of samples for each cycle of the waveform, at least some of said samples having a first expected value in the absence of an outbound signal and having a second expected value in the presence of an outbound signal on the waveform;

setting a signal detection threshold from a predetermined number, N, of samples taken; and

modifying the signal detection threshold if the value of the (N+1)st sample exceeds a predetermined fraction of the previously set signal detection threshold.

14. The method as set forth in claim 13 wherein the samples are time differences, further including the steps of deriving energy samples from the time differences, partitioning the energy samples into three groups representative of three different segments of a cycle of the cyclic waveform, the first group representing a first segment of the cycle in which valid signals are absent, setting a threshold for energy in said first segment from energy samples taken from the first segments of preceding cycles, and rejecting the samples for that cycle if the energy samples in the first group exceed the threshold for the first segment.

15. The method as set forth in claim 14 wherein the threshold of the first segment is obtained by averaging the total energy samples for the first segment and omitting from that average samples from any cycle in which the total energy in the first segment samples greatly exceeds the average.

16. The method as set forth in claim 13 wherein the samples are time differences and the threshold is a function of the time differences of previously sampled cycles.

17. The method as set forth in claim 13 wherein the predetermined fraction is approximately one-half.

18. The method as set forth in claim 13 wherein the signal detection threshold is an average of samples taken from previous cycles, each of said samples being included in the average only if they exceeded the predetermined fraction of the threshold which existed at the time said sample was taken.

19. The method as set forth in claim 18 wherein the average of previous accepted samples is reset after a predetermined number of samples are included to allow response to dynamic network changes.

20. A method of rejecting crosstalk in outbound information flow along a multi-phase electric distribution network comprising:

for at least one phase of a multi-phase electric distribution network, dividing a cyclic waveform associated with that phase into at least three segments per cycle, a first of said three segments being selected such that outbound information is absent from the first segment unless crosstalk has occurred, a second of said segments being selected such that outbound information appears in said second segment, and a third of said segments being selected such that outbound information also appears in said third segment;

comparing the energy in each segment with an energy threshold for that segment; and

rejecting a cycle under test for the presence of signal when the energy in the first segment exceeds the threshold for said first segment.

21. The method as set forth in claim 20 further including the step of rejecting a cycle under test for the presence of signal when the energy in the third segment greatly exceeds the energy in the second segment.

22. The method as set forth in claim 21 wherein the cycle under test is rejected if the energy in the third segment exceeds the energy in the second segment by a factor of at least fifty.

23. A method of detecting outbound information in a multi-phase electric distribution network comprising:

deriving a waveform from the voltage on at least one phase of a multi-phase electric distribution network, which derived waveform includes at least a cyclic carrier component;

partitioning cycles of the waveform into at least three segments per cycle, a first of said segments being before a valid signal would appear on the waveform, a second of said segments being in the area where a valid signal could appear but before a zero crossing of the waveform, and a third of said segments being in an area where a valid signal could appear but after a zero crossing of the waveform;

comparing the energy in at least the first segment with an energy threshold for that segment; and

identifying the presence of a signal in the cycle under test only if the energy in the first segment falls below the threshold for that segment and the energy in the second and third segments is indicative of the presence of a signal in that cycle.

24. The method as set forth in claim 23 wherein the indicating step results in the indication of signal presence only if the energy in the second segment and the energy in the third segment together exceed a threshold for those segments together.

25. The method as set forth in claim 23 wherein the energy comparing step includes measuring differences between the times when the unmodulated waveform would reach predetermined voltages and the times the actual waveform reaches said predetermined voltages, said energy being a function of the sum of the squares of said time differences.

26. The method as set forth in claim 23 further including the step of determining the signal strength in the second and third segments and comparing said signal strength with a signal strength threshold, said signal strength threshold being a function of signal strengths in the second and third segments for previous cycles.

27. The method as set forth in claim 26 wherein the signal strength threshold is modified by each successive cycle signal strength if the signal strength for said successive cycle exceeds a predetermined fraction of the pre-existing signal strength threshold.

28. The method as set forth in claim 26 in which the threshold determining function is an average of signal strengths in the second and third segments for previous cycles.

29. The method as set forth in claim 28 wherein said average omits signal strengths which fall below a predetermined fraction of the signal strength threshold existing at the time the signal strength under consideration was taken.

30. The method as set forth in claim 26 wherein the signal strength is determined by sampling the waveform during the second and third segments and selecting extreme values for each segment for determination of signal strength.