A/B/C phase determination and synchrophasor measurement using common electric smart meters and wireless communications

Patent metadata

Field	Value
Publication number	US-9230429-B2
Application number	US-201313765404-A
Country	US
Kind code	B2
Filing date	Feb 12, 2013
Priority date	Aug 15, 2011
Publication date	Jan 5, 2016
Grant date	Jan 5, 2016

Abstract

Phasor Measurement Units (PMUs) tend to be specialized and expensive—relegated to only key points in power distribution networks, and are generally reliant on GPS technology. The present disclosure details how any smart meter—using wireless communication—can perform sub-microsecond-grade synchrophasor measurements. Other aspects concern smart meter-based determination of A, B or C phase of the tri-phase power network. This can involve count-stamp enabling message packets sent to and/or from a smart meter, and then associating such count-stamps to local measurements of power phase by a metrology unit. Once a network of such enabled smart meters and other devices is formed, sub-microsecond metropolitan-wide and entire region-wide synchronizing time standard can calibrate local measurements of power phase, where simple A, B and C phase determination is one low hanging fruit application of such. Low cost aggregate monitoring of metropolitan-wide synchrophasors promises a next chapter of importance for that relatively recent art.

First claim

The invention claimed is:

1. A method useful in determining an electric power phase relationship between two devices, a first device comprising a power meter device connected to a power distribution system and a second device comprising another device connected to the power distribution system, the method characterized by processing one or more messages received from the second device, together with zero crossing data generated by the first device, to determine relative timing between zero crossings of power signals sensed at said devices, wherein the method further includes count-stamping the message(s) received from the second device, by reference to clock counts from a free-running clock in the first device that runs at 100 KHz or more.

2. The method of claim 1 that further includes, from said relative timing, determining whether the power signal at the first device is (a) in phase with the power signal at the second device; (b) leads the power signal at the second device by 120 degrees; or (c) lags the power signal at the second device by 120 degrees.

3. The method of claim 1 in which both of said devices comprise power meter devices.

4. The method of claim 1 that includes determining relative timing between the zero crossing measurements to an accuracy of better than 25 microseconds.

5. The method of claim 1 wherein at least one of said devices is devoid of a GPS receiver.

6. The method of claim 1 wherein the message received from the second device is clock-stamped.

7. The method of claim 6 in which the message received from the second device is clock-stamped by the second device.

8. The method of claim 6 in which the message received from the second device is clock-stamped by the second device to indicate a zero-crossing event at the second device.

9. The method of claim 6 in which the message received from the second device is clock-stamped by the first device.

10. A method of determining phase relationship among power meters, the method comprising:
collecting count stamped messages transmitted between nodes in a network including at least two power meters, the messages including zero crossing measurements of a power signal sensed at a corresponding power meter;
from the count stamped messages, determining relative timing among clocks within the power meters;
from the relative timing and zero crossing measurements, determining relative phases between the power meters;
wherein the zero crossing measurements within a first power meter, and the count-stamping of a message by said first power meter, are made relative to a common clock within the first power meter.

11. The method of claim 10 wherein the power meters include a first clock for zero crossing measurements and a second clock for count-stamping a message communicated with another node in the network, and further including determining relative timing between said first and second clocks.

12. A power meter comprising:
a metrology unit for measuring zero crossing of a power signal; and
a communication unit, in communication with the metrology unit, for collecting zero crossing measurements, and communicating count stamped messages including the collected zero crossing measurements to a remote node for determining relative phase between the power meter and another power meter;
wherein the communication unit is in communication with a local clock for count-stamping messages upon receipt or transmission.

13. The power meter of claim 12 wherein the communication unit is in communication with a local clock for count-stamping messages upon transmission.

14. The power meter of claim 12 wherein the communication unit is in communication with a local clock for count-stamping messages upon receipt.

15. The power meter of claim 12 wherein the communication unit is in communication with a second power meter for receiving count-stamped messages and for determining phase relative to the second power meter.

16. The power meter of claim 12 including a first clock for providing time for the zero crossing and a second clock for count-stamping the messages.

17. The power meter of claim 12 including a first clock for providing time for the zero crossing and time for count-stamping messages.

18. A system comprising:
a node for collecting count stamped messages transmitted between nodes in a network, the nodes including at least first and second power meters, the count stamped messages including zero crossing measurements of a power signal sensed at the first power meter, and including count stamped zero crossing measurements of a power signal sensed at the second power meter;
a node for determining relative timing among clocks within the network nodes from the count stamped messages; and
a node for determining relative phases between the network nodes from the relative timing and zero crossing measurements.

19. The system of claim 18 wherein the node for collecting, the node for determining relative timing, and the node for determining relative phases is a common node.

20. The system of claim 19 wherein the common node comprises a server in communication with the power meters via a computer network and providing relative phase to the power meters.

21. The system of claim 20 wherein the common node is in communication with a unit whose phase serves as a reference phase from which phase is determined for network nodes, based on the reference phase and the relative phases.

22. A system including a first smart meter in digital packet communication with a second, separate smart meter, said meters including a metrology unit adapted to produce a counter or clock datum as a function of electric power phase, said meters including a communications unit adapted to produce a counter or clock datum as a function of sending and receiving communications packets, the system being configured whereby the first smart meter determines its electric power phase relative to the second smart meter by using a sent message as a common reference for two separate counters on the two separate meters.

23. A metrology unit for coupling to a power distribution network, comprising:
a zero-crossing detector;
a free-running counter; and
circuitry that outputs a value from the free-running counter when the detector senses a zero-crossing;
wherein the communication unit is in communication with a local clock for count-stamping messages upon receipt or transmission.

24. A method useful in determining an electric power phase relationship between two devices, a first device comprising a power meter device connected to a power distribution system and a second device comprising another device connected to the power distribution system, the method characterized by processing one or more messages received from the second device, together with zero crossing data generated by the first device, to determine relative timing between zero crossings of power signals sensed at said devices, wherein the message received from the second device is clock-stamped by the first device.

Assignees

• Digimarc Corp

Inventors

• Mckinley Tyler J
• Rhoads Geoffrey B

Classifications

• G08C19/12 Primary

  in which the signal transmitted is frequency or phase of AC · CPC title

• Y04S20/48

  Cross-Sectional Technologies · mapped topic

• Y04S10/265

  Cross-Sectional Technologies · mapped topic

• G01R29/18

  Indicating phase sequence; Indicating synchronism · CPC title

• G01D4/002 Primary

  Remote reading of utility meters · CPC title