Frequency-Domain Subspace Identification of Linear Time-Periodic (LTP) Systems

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Uyanık İ., Saranlı U., Ankaralı M. M., Cowan N., Morgül Ö.

IEEE TRANSACTIONS ON AUTOMATIC CONTROL, vol.64, pp.2529-2536, 2019 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 64
  • Publication Date: 2019
  • Doi Number: 10.1109/tac.2018.2867360
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.2529-2536
  • Keywords: Linear time-periodic (LTP) systems, subspace methods, system identification, time-varying systems, MODEL IDENTIFICATION, ALGORITHMS
  • Middle East Technical University Affiliated: Yes


This paper proposes a new methodology for subspace-based state-space identification for linear time-periodic (LTP) systems. Since LTP systems can be lifted to equivalent linear time-invariant (LTI) systems, we first lift input-output data from an unknown LTP system as if they were collected from an equivalent LTI system. Then, we use frequency-domain subspace identification methods to find the LTI system estimate. Subsequently. we propose a novel method to obtain a time-periodic realization for the estimated lifted LTI system by exploiting the specific parametric structure of Fourier series coefficients of the frequency-domain lifting method. Our method can be used to obtain state-space estimates for unknown LTP systems as well as to obtain Floquet transforms for known LTP systems.