We describe a method for stabilizing unstable steady states in nonlinear dy
namical systems using a form of extended time-delay autosynchronization. Sp
ecifically, stabilization is achieved by applying a feedback signal generat
ed by high-pass-filtering in real time the dynamical state of the system to
an accessible system parameter or variables. Our technique is easy to impl
ement, does not require knowledge of the unstable steady state coordinates
in phase space, automatically tracks changes in the system parameters, and
is more robust to broadband noise than previous schemes. We demonstrate the
controller's efficacy by stabilizing unstable steady states in an electron
ic circuit exhibiting low-dimensional temporal chaos. The simplicity and ro
bustness of the scheme suggests that it is ideally suited for stabilizing u
nstable steady states in ultra-high-speed systems. (C) 1998 American Instit
ute of Physics. [S1054-1500(98)00704-6].