Adaptive clock offset estimation for protection devices without time-based synchronization

Patent metadata

Field	Value
Publication number	US-12556358-B2
Application number	US-202419003067-A
Country	US
Kind code	B2
Filing date	Dec 27, 2024
Priority date	Jan 2, 2024
Publication date	Feb 17, 2026
Grant date	Feb 17, 2026

Abstract

A system for determining channel delay or communication link asymmetry in an electric power system. The delay or asymmetry uses local clock signals instead of an external time source. Prediction errors are calculated using communications among the devices. A prediction algorithm compares the predicted channel delay against a measured channel delay. When the prediction error changes abruptly, the channel delay or communication asymmetry is detected.

First claim

What is claimed:

1 . A system for protection of electric power equipment, comprising:
an oscillator configured to provide a time signal used to timestamp a first stream of data comprising a plurality of local measurements; a communications interface configured to receive a second stream of data comprising a plurality of remote measurements from a remote source through a communication channel, the second stream of data from the remote source comprising a plurality of timestamps associated with a plurality of measurements; a clock offset estimation subsystem to determine a plurality of clock offset values based on the second stream of data from the remote source, and configured to:
analyze the second stream of data from the remote source;
identify a plurality of valid raw clock offset values within the second stream of data;
generate a prediction error based on the plurality of valid raw clock offset values; and
generate an enhanced clock offset value based on the prediction error; and
a data alignment subsystem configured to:
generate an adjusted timestamp in the second stream of data from the remote source based on the clock offset value; and
time-align the first stream of data and the second stream of data based on the adjusted timestamp;
a synchronization subsystem configured to identify a lack of synchronization of the communication channel; wherein the system is further configured to suspend normal operation based on the lack of synchronization of the communication channel.

2 . The system of claim 1 , wherein the oscillator comprises a high-stability oscillator capable of providing a stability of at least 10 PPM.

3 . The system of claim 1 , further comprising:
an asymmetry detection and estimation subsystem configured to:
identify an asymmetry in the communication channel; and
generate an estimate of the asymmetry in the communication channel;
wherein the clock offset value comprises the estimate of the asymmetry in the communication channel.

4 . The system of claim 3 , wherein the asymmetry detection and estimation subsystem is further configured to identify the asymmetry by comparing the clock offset value to an average of a prior plurality of predicted clock offsets.

5 . The system of claim 3 , wherein the asymmetry in the communication channel is caused by a path-switching event.

6 . The system of claim 1 , wherein the synchronization subsystem is further configured to adjust the clock offset value based on one of a low-precision synchronization condition and a high-precision synchronization condition.

7 . The system of claim 1 , further comprising an adaptive filter configured to apply an adaptive gain to the prediction error based on conditions of the communication channel.

8 . The system of claim 7 , wherein the adaptive filter comprises a Kalman filter.

9 . The system of claim 1 , wherein the system lacks time-based synchronization with the remote source.

10 . The system of claim 1 , wherein the system comprises an intelligent electronic device (IED) in electrical communication with a portion of an electric power system.

11 . A method of protecting electric power equipment, comprising:
providing, using an oscillator, a time signal used to timestamp a first stream of data comprising a plurality of local measurements; receiving, using a communications interface, a second stream of data comprising a plurality of remote measurements from a remote source through a communication channel, the second stream of data from the remote source comprising a plurality of timestamps associated with a plurality of measurements; determining, using a clock offset estimation subsystem, a plurality of clock offset values based on the second stream of data from the remote source; analyzing, using the clock offset estimation subsystem, the second stream of data from the remote source; identifying, using the clock offset estimation subsystem, a plurality of valid raw clock offset values within the second stream of data; generating, using the clock offset estimation subsystem, a prediction error based on the plurality of valid raw clock offset values; generating, using the clock offset estimation subsystem, a clock offset value based on the prediction error; generating, using a data alignment subsystem, an adjusted timestamp in the second stream of data from the remote source based on the clock offset value; time-aligning, using the data alignment subsystem, the first stream of data and the second stream of data based on the adjusted timestamp; identifying, using a synchronization subsystem, a lack of synchronization of the communication channel; and suspending normal operation based on the lack of synchronization of the communication channel.

12 . The method of claim 11 , further comprising:
identifying, using an asymmetry detection and estimation subsystem, an asymmetry in the communication channel; and generating, using the asymmetry detection and estimation subsystem, an estimate of the asymmetry in the communication channel; wherein the clock offset value comprises the estimate of the asymmetry in the communication channel.

13 . The method of claim 12 , further comprising:
identifying, using the asymmetry detection and estimation subsystem, the asymmetry by comparing the clock offset value to an average of a prior plurality of predicted clock offsets.

14 . The method of claim 12 , wherein the asymmetry in the communication channel is caused by a path-switching event.

15 . The method of claim 11 , further comprising:
adjusting, using the synchronization subsystem, the clock offset value based on one of a low-precision synchronization condition and a high-precision synchronization condition.

16 . The method of claim 11 , further comprising applying, using an adaptive filter, an adaptive gain to the prediction error based on conditions of the communication channel.

17 . The method of claim 16 , wherein the adaptive filter comprises a Kalman filter.

18 . The method of claim 11 , further comprising generating the clock offset value without time-based synchronization with the remote source.

Assignees

• Schweitzer Engineering Lab Inc

Inventors

• Ravi Anirudhh
• Skendzic Veselin
• Yedidi Vinod K
• Kulkarni Pallavi
• Hartshorn Jay
• Janarthanan Balaji
• D'Aversa Angelo
• Fischer Normann

Classifications

• H04L25/0202 Primary

  Channel estimation · CPC title

• H04J3/0667

  Bidirectional timestamps, e.g. NTP or PTP for compensation of clock drift and for compensation of propagation delays (arrangements for monitoring round trip delays in packet switching networks H04L43/0864) · CPC title

• H02H7/263

  involving transmissions of measured values (comparison of currents or voltages using pilot wires H02H3/30) · CPC title

• H04L25/0272

  Arrangements for coupling to multiple lines, e.g. for differential transmission · CPC title

• H04L7/0016 Primary

  correction of synchronization errors · CPC title