Advanced

LQG-Based Real-Time Scheduling and Control Codesign

Xu, Yang LU (2017)
Abstract
Having multiple control tasks concurrently running on a single computing platform increases the processor utilization but degrades the control performance due to delay and jitter. In scheduling and control codesign, the objective is to optimize the combined performance of all the controllers, subject to a schedulability constraint. The codesign procedure consists of selecting task parameters, e.g., periods and priorities, as well as designing the controllers so that the scheduling-induced delay and jitter are taken into account.

In the thesis, four linear-quadratic-Gaussian (LQG) codesign methods are proposed: stochastic, periodic, harmonic, and robust LQG codesign. In stochastic LQG codesign, the delay distributions are... (More)
Having multiple control tasks concurrently running on a single computing platform increases the processor utilization but degrades the control performance due to delay and jitter. In scheduling and control codesign, the objective is to optimize the combined performance of all the controllers, subject to a schedulability constraint. The codesign procedure consists of selecting task parameters, e.g., periods and priorities, as well as designing the controllers so that the scheduling-induced delay and jitter are taken into account.

In the thesis, four linear-quadratic-Gaussian (LQG) codesign methods are proposed: stochastic, periodic, harmonic, and robust LQG codesign. In stochastic LQG codesign, the delay distributions are calculated at design-time. Then LQG controllers are designed assuming these delay distributions. The obtained task periods generally give rise to infinite hyperperiods. This can be avoided by perturbing the periods slightly in order to obtain a finite hyperperiod, yielding a periodic delay pattern for the control loops. The periodicity is then accounted for by using periodic LQG control design, resulting in a periodic sequence of feedback gains for each controller. In harmonic LQG codesign, again the task periods are perturbed, but this time to make the periods harmonic. The scheduling-induced delays will be constant and standard LQG design can be applied. Finally, a robust LQG codesign method is presented. The design is based on convex optimization and guarantees system robustness in the presence of delay and jitter. A new rule of thumb for initial sampling period assignment is proposed. We propose a jitter-aware priority and period assignment codesign method to optimize the overall system performance.

A large evaluation of the proposed four codesign methods is performed using the Jitterbug toolbox. All of the four methods lead to improved control performance compared to earlier work. The harmonic scheduling and control codesign shows the largest overall improvements. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Cela, Arben, ESIEE Paris, France
organization
publishing date
type
Thesis
publication status
published
subject
keywords
LQG control, Real-time system, Scheduling, Time-delay system
publisher
Department of Automatic Control, Lund Institute of Technology, Lund University
defense location
Lecture hall M:B, building M, Ole Römers väg 1, Lund University, Faculty of Engineering LTH, Lund
defense date
2017-12-15 10:15
ISBN
978-91-7753-515-7
978-91-7753-516-4
language
English
LU publication?
yes
id
ca00ea30-30ce-4d62-9b2f-6718d09591c0
date added to LUP
2017-11-20 10:51:05
date last changed
2018-03-12 22:54:38
@phdthesis{ca00ea30-30ce-4d62-9b2f-6718d09591c0,
  abstract     = {Having multiple control tasks concurrently running on a single computing platform increases the processor utilization but degrades the control performance due to delay and jitter. In scheduling and control codesign, the objective is to optimize the combined performance of all the controllers, subject to a schedulability constraint. The codesign procedure consists of selecting task parameters, e.g., periods and priorities, as well as designing the controllers so that the scheduling-induced delay and jitter are taken into account.<br/><br/>In the thesis, four linear-quadratic-Gaussian (LQG) codesign  methods are proposed: stochastic, periodic, harmonic, and robust LQG codesign. In stochastic LQG codesign, the delay distributions are calculated at design-time. Then LQG controllers are designed assuming these delay distributions. The obtained task periods generally give rise to infinite hyperperiods. This can be avoided by perturbing the periods slightly in order to obtain a finite hyperperiod, yielding a periodic delay pattern for the control loops. The periodicity is then accounted for by using periodic LQG control design, resulting in a periodic sequence of feedback gains for each controller. In harmonic LQG codesign, again the task periods are perturbed, but this time to make the periods harmonic. The scheduling-induced delays will be constant and standard LQG design can be applied. Finally, a robust LQG codesign method is presented. The design is based on convex optimization and guarantees system robustness in the presence of delay and jitter. A new rule of thumb for initial sampling period assignment is proposed. We propose a jitter-aware priority and period assignment codesign method to optimize the overall system performance.<br/><br/>A large evaluation of the proposed four codesign methods is performed using the Jitterbug toolbox. All of the four methods lead to improved control performance compared to earlier work. The harmonic scheduling and control codesign shows the largest overall improvements.},
  author       = {Xu, Yang},
  isbn         = {978-91-7753-515-7},
  keyword      = {LQG control,Real-time system,Scheduling,Time-delay system},
  language     = {eng},
  month        = {11},
  publisher    = {Department of Automatic Control, Lund Institute of Technology, Lund University},
  school       = {Lund University},
  title        = {LQG-Based Real-Time Scheduling and Control Codesign},
  year         = {2017},
}