Adaptive holdover timing error estimation and correction

• US 9,425,652 B2
• Filed: 06/16/2014
• Issued: 08/23/2016
• Est. Priority Date: 06/16/2014
• Status: Active Grant

• Current Assignee: Schweitzer Engineering Laboratories, Incorporated
• Original Assignee: Schweitzer Engineering Laboratories, Incorporated
• Inventors: Rippon, Daniel B., Achanta, Shankar V.
• Primary Examiner(s): LE, TOAN M
• Application Number:
  US14/305,608
• Publication Number:
  US 20150364953A1
• Time in Patent Office: 799 Days
• US Class Current: 1/1
• CPC Class Codes: H02J 13/00001 characterised by the display of information or by user interaction, e.g. supervisory control and data acquisition systems [SCADA] or graphical user interfaces [GUI]
• CPC Class Codes: H02J 13/00002 characterised by monitoring
• CPC Class Codes: H02J 13/00028 involving the use of Internet protocols
• CPC Class Codes: H02J 13/00034 the elements or equipment being or involving an electric power substation
• CPC Class Codes: H02J 13/0004 involved in a protection system
• CPC Class Codes: H03L 1/02 against variations of temperature only
• CPC Class Codes: H04J 3/0667 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 Class Codes: H04J 3/0688 Change of the master or reference, e.g. take-over or failure of the master
• CPC Class Codes: Y02E 60/00 Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
• CPC Class Codes: Y04S 10/30 State monitoring, e.g. fault, temperature monitoring, insulator monitoring, corona discharge
• CPC Class Codes: Y04S 10/40 Display of information, e.g. of data or controls

Abstract

Disclosed herein are a variety of various systems and method for adaptive holdover time error estimation. In one embodiment a system may include a local time source configured to generate a local time signal and an external time source interface configured to receive an external time signal. A time source subsystem may be configured to compare the local time signal and the external time signal and to determine a temperature-dependent signal drift rate of the local time signal relative to the external time signal. The time source subsystem may be a time-dependent signal drift rate of the local time signal relative to the external time signal. A holdover subsystem may detect a loss of reception of the external time signal during a holdover period and may estimate a total maximum error based on an estimated maximum time-dependent error and an estimated maximum temperature-dependent error.

Claims

1. A system for adaptive holdover time error estimation, comprising:

a local time source configured to generate a local time signal;

an external time source interface configured to receive an external time signal;

a temperature determination subsystem configured to determine a plurality of temperature measurements in proximity to the local time source at a corresponding plurality of times;

a temperature-dependent model subsystem configured to develop a temperature-dependent model based on the plurality of temperature measurements and comparison of the local time signal to the external time signal at a corresponding plurality of times;

a time-dependent model subsystem configured to develop a time-dependent model based on a plurality of comparisons of the local time signal to the external time signal at a corresponding plurality of times;

a holdover subsystem configured to;

detect a loss of reception of the external time signal during a holdover period;

estimate a maximum time-dependent error based on the time-dependent model and a duration of the holdover period;

estimate a maximum temperature-dependent error based on the temperature-dependent model;

determine an estimated total maximum error based on the estimated maximum time-dependent error and the estimated maximum temperature-dependent error; and

a communication system configured to transmit the local time signal and the estimated total maximum error to at least one receiving device.

2. A method of adaptive holdover duration time error estimation, the method comprising:

generating a local time signal using a local time source;

receiving an external time signal;

losing reception of the external time signal during a holdover period;

estimating a maximum time-dependent error based on a duration of the holdover period;

estimating a maximum temperature-dependent error based on a current temperature;

determining an estimated total maximum error based on the estimated maximum time-dependent error and the estimated maximum temperature-dependent error; and

transmitting the local time signal and the estimated total maximum error to a receiving device.

3. The method of claim 2, further comprising:

generating a temperature-dependent model of the local time source based on a plurality of temperature measurements and comparison of the local time signal to the external time signal at a corresponding plurality of times; and

wherein the temperature-dependent model is used in estimating the maximum temperature-dependent error.

4. The method of claim 3, further comprising:

determining an average of the plurality of temperature measurements; and

using the average of the plurality of temperature measurements to estimate the maximum temperature-dependent error.

5. The method of claim 2, further comprising:

generating a time-dependent model of the local time source based on a comparison of the local time signal to the external time signal over a temporal period; and

wherein the time-dependent model is used in determining the maximum time-dependent error.

6. The system of claim 2, wherein the local time source comprises one of a voltage-controlled temperature compensated crystal oscillator, a phase locked loop oscillator, a time locked loop oscillator, a rubidium oscillator, a cesium oscillator, a microelectromechanical oscillator, an oven controlled crystal oscillator, and temperature compensated crystal oscillator.

7. The method of claim 2, wherein the external time signal comprises at least one of a Global Navigation Satellite System and a National Institute of Science and Technology radio broadcast.

8. The method of claim 2, wherein transmitting the local time signal and the estimated total maximum error to the receiving device comprises transmitting the local time signal according to a protocol chosen from one of the group consisting of an Inter-Range Instrumentation Group protocol, an IEEE 1588 protocol, a Network Time Protocol, a Simple Network Time Protocol, and a synchronous transport protocol.

9. The method of claim 2, wherein the estimated total maximum error is transmitted in a clock accuracy enumeration field.

10. The method of claim 2, further comprising:

the receiving device receiving the local time signal and the estimated total maximum error;

determining that the estimated total maximum error exceeds an accuracy requirement; and

disregarding the local time signal.

11. The method of claim 2, further comprising:

determining a temperature-dependent signal drift rate of the local time signal relative to the external time signal; and

determining a time-dependent signal drift rate of the local time signal relative to the external time signal;

wherein estimating the maximum time-dependent error is further based on the temperature-dependent signal drift rate and estimating the maximum temperature-dependent error is further based on the time-dependent signal drift rate.

12. The method of claim 2, further comprising:

determining that the current temperature falls outside of a bounded range; and

applying an adjustment to the maximum temperature-dependent error.

13. The method of claim 2, further comprising correcting the local time signal based on the estimated maximum time-dependent error and the estimated maximum temperature-dependent error.

14. A system configured for adaptive holdover time error estimation, comprising:

a local time source configured to generate a local time signal;

an external time source interface configured to receive an external time signal;

a holdover subsystem configured to;

detect a loss of reception of the external time signal during a holdover period;

estimate a maximum time-dependent error based on a duration of the holdover period;

estimate a maximum temperature-dependent error based on a current temperature;

determine an estimated total maximum error based on the estimated maximum time-dependent error and the estimated maximum temperature-dependent error;

a communication system configured to transmit the local time signal and the estimated total maximum error to at least one receiving device.

15. The system of claim 14, wherein the external time source interface comprises a Global Navigation Satellite System input;

and

wherein the external time signal is received via the Global Navigation Satellite System interface.

16. The system of claim 14, wherein the external time source interface comprises an Inter-Range Instrumentation Group (IRIG) input;

and

wherein the external time signal is received via the IRIG input.

17. The system of claim 14, wherein the communication system comprises:

a network communication port configured to distribute the local time signal and the estimated total maximum error to the at least one receiving device.

18. The system of claim 14, wherein the local time signal and the estimated total maximum error are distributed to the at least one receiving device using a protocol selected from the group consisting of an Inter-Range Instrumentation Group protocol, an IEEE 1588 protocol, a Network Time Protocol, a Simple Network Time Protocol, and a synchronous transport protocol.

19. The system of claim 14, wherein the local time source comprises one of a voltage-controlled temperature compensated crystal oscillator, a phase locked loop oscillator, a time locked loop oscillator, a rubidium oscillator, a cesium oscillator, a microelectromechanical oscillator, an oven controlled crystal oscillator, and temperature compensated crystal oscillator.

20. The system of claim 14, wherein the holdover subsystem is further configured to determine whether the current temperature falls outside of a bounded range and to apply an adjustment to the maximum temperature-dependent error when the current temperature falls outside of the bounded range.

21. The system of claim 14, wherein the time source subsystem is further configured to correct the local time signal based on the estimated maximum time-dependent error and the estimated maximum temperature-dependent error.

22. The system of claim 14, further comprising:

a time source subsystem configured to compare the local time signal and the external time signal and determine;

a temperature-dependent signal drift rate of the local time signal relative to the external time signal;

a time-dependent signal drift rate of the local time signal relative to the external time signal; and

wherein the holdover subsystem is further configured to estimate the maximum time-dependent error is further based on the temperature-dependent signal drift rate and estimating the maximum temperature-dependent error is further based on the time-dependent signal drift rate.

23. The system of claim 22, further comprising:

a temperature determination subsystem configured to determine a plurality of temperature measurements in proximity to the local time source at a corresponding plurality of times;

wherein the time source subsystem is configured to utilize the plurality of temperature measurements to determine the temperature-dependent signal drift rate.

24. The system of claim 22, further comprising:

a temperature-dependent model subsystem configured to develop a temperature-dependent model based on a plurality of temperature measurements and comparison of the local time signal to the external time signal at a corresponding plurality of times; and

wherein the time source subsystem uses the temperature-dependent model to determine the maximum temperature-dependent error.

25. The system of claim 22, further comprising:

a time-dependent model subsystem configured to develop a time-dependent model based on a plurality of comparisons of the local time signal to the external time signal at a corresponding plurality of times; and

wherein the time source subsystem uses the time-dependent model to determine the maximum time-dependent error.