Detection of and responses to time delays in networked control systems

Patent metadata

Field	Value
Publication number	US-2017060102-A1
Application number	US-201514842447-A
Country	US
Kind code	A1
Filing date	Sep 1, 2015
Priority date	Sep 1, 2015
Publication date	Mar 2, 2017
Grant date	—

Abstract

To ameliorate the detrimental effects of time delays, techniques and systems are disclosed for detecting time delays in a plant, facility, or environment (such as a power system) controlled by an NCS, and for providing more resilient control capabilities for adapting to the detected time delays. A time delay estimate can be determined by comparing the expected state of the plant, calculated from a plant model, with the state of the plant described by its telemetry data. Techniques for adapting to a time delay include: switching to an emergency controller and acting in accordance with a local reference model; sending adjusted control commands in accordance with an expected plant state; and instructing a transmitter to transmit subsequent communications packets over multiple redundant communication channels.

First claim

What is claimed is:

1 . A method of controlling the effect of time delays in a networked control system (NCS), the method comprising:
receiving a communication packet containing telemetry data from one or more devices in the NCS; detecting a time delay event from an analysis of the communication packet; sending, to at least one of the one or more devices in the NCS, a control signal determined in accordance with the time delay event.

2 . The method of claim 1 , wherein detecting the time delay event comprises:
determining whether a timestamp of the communication packet differs from a reference time value of the NCS by more than a stability value.

3 . The method of claim 1 , wherein detecting the time delay event comprises:
computing a time delay estimate; and comparing the time delay estimate to a stability value.

4 . The method of claim 1 , wherein detecting the time delay event comprises:
computing an estimated plant state from a plant model; and comparing a received plant state, indicated by the telemetry data, to the estimated plant state.

5 . The method of claim 1 , wherein the control signal comprises a control instruction to transfer NCS control to a local controller.

6 . The method of claim 1 , wherein determining the control signal comprises:
(A) computing a current plant state from the telemetry data and a plant model; (B) computing an estimated plant state based on the plant model, a performance error estimate, and a model error, (C) computing a time delay estimate; (D) determining an iteration trial control signal for a controller type; and (E) repeating steps (A)-(D) until the performance error estimate is lower than an error tolerance value, and setting the control signal to the iteration trial control signal.

7 . The method of claim 1 , wherein the control signal is an instruction to transmit one or more subsequent communication packets over a plurality of redundant communication channels.

8 . A system for controlling the effect of time delays in a networked control system (NCS), the system comprising:
one or more computer readable storage media; and program instructions for a delay detector stored on at least one of the one or more computer readable storage media that, when executed by a processing system, direct the processing system to: in response to receiving one or more communication packets containing telemetry data from one or more devices in the NCS: detect a time delay event from an analysis of the one or more communication packets; and send, to at least one of the one or more devices in the NCS, a control signal determined in accordance with the time delay event.

9 . The system of claim 8 , wherein the program instructions to detect the time delay event comprise instructions that direct the processing system to:
determine whether a timestamp of the one or more communication packets differs from a reference time value of the NCS by more than a stability value.

10 . The system of claim 8 , wherein the program instructions to detect the time delay event comprise instructions that direct the processing system to:
compute a time delay estimate; and compare the time delay estimate to a stability value.

11 . The system of claim 8 , further comprising a plant model for determining an estimated plant state from the telemetry data.

12 . The system of claim 11 , wherein the program instructions to detect the time delay event comprise instructions that direct the processing system to:
compute the estimated plant state from the plant model; and compare a received plant state, indicated by the telemetry data, to the estimated plant state.

13 . The system of claim 11 , wherein the program instructions to determine the control signal comprise instructions that direct the processing system to:
(A) compute a current plant state from the telemetry data and the plant model; (B) compute the estimated plant state based on the plant model, a performance error estimate, and a model error; (C) compute a time delay estimate; (D) determine an iteration trial control signal for a controller type; and (E) repeat steps (A)-(D) until the performance error estimate is lower than an error tolerance value, and set the control signal to the iteration trial control signal.

14 . The system of claim 8 , wherein the control signal comprises a control instruction to transfer control from a networked controller to a local controller having a local reference model.

15 . The system of claim 8 , further comprising an NCS transmitter that, in response to receiving the control signal from the delay detector when the time delay event is detected, transmits one or more subsequent communication packets over a plurality of redundant communication channels.

16 . The system of claim 8 , wherein the NCS is a power system, a water system, a wastewater system, or a transportation system.

17 . An apparatus for time delay switch response in a networked control system (NCS):
one or more computer readable storage media; a system model for determining the system state from the telemetry data stored on the one or more computer readable storage media; a controller; a transmitter, program instructions stored on the one or more computer readable storage media that, when executed by a processing system, direct the processing system to: in response to receiving one or more communication packets containing telemetry data from one or more devices in the NCS, identify a time delay event by one or more of:
determining that a timestamp of the one or more communication packets differs from a reference time value of the NCS by more than a stability value, and
computing a time delay estimate and determining that the time delay estimate exceeds a stability value, and
computing a transmitted state of the NCS from the telemetry data and the system model, computing an estimated state of the NCS from the system model, computing a modeling error by comparing the transmitted state to the estimated state, and determining that the modeling error exceeds a tolerable error value; and in response to the time delay event, instructing the transmitter to transmit one or more subsequent communication packets over a plurality of redundant communication channels.

18 . The apparatus of claim 17 , further comprising program instructions for sending, from the controller, a control signal determined in accordance with the estimated state, wherein the controller sends the control signal to at least one of the one or more devices in the NCS.

19 . The apparatus of claim 17 , wherein the controller is an optimal controller or a proportional-integral-derivative controller.

20 . The apparatus of claim 17 , wherein the NCS comprises a multi-area power system and the controller performs a load frequency control (LFC) activity.

Assignees

• Sargolzaei Arman
• Abdelghani Mohamed
• Yen Kang K
• Univ Florida Int

Inventors

• Sargolzaei Arman
• Abdelghani Mohamed
• Yen Kang K

Classifications

• G05B13/021 Primary

  in which a variable is automatically adjusted to optimise the performance · CPC title

• G05B13/047 Primary

  the criterion being a time optimal performance criterion · CPC title

• G05B2219/34413

  Add time stamp to command message · CPC title

• G05B2219/25404

  Command order is delayed as function of expected and real delay · CPC title