In this Letter, a dynamical delayed output-feedback (DDOF) control strategy
is proposed for stabilizing unstable periodic orbits (UPOs) of chaotic sys
tems. Using the Floquet theory, a separation principle is established which
gives a necessary and sufficient stability condition for DDOF UPO stabiliz
ing control systems. The new principle shows that the so-called "odd number
limitation" for delayed state-feedback control systems also applies to DDO
F control. (C)\ 2001 Published by Elsevier Science B.V.