6Poincaré-based control of delayed measured systems: Limitations and Improved Control 1 Jens Christian Claussen
IntroductionWhat is the effect of measurement delay on Ott, Grebogi, and Yorke (OGY) chaos control? Which possibilities exists for improved control? These questions are addressed within this chapter, and the OGY control case is considered as well as a related control scheme, difference control; both together form the two main Poincaré-based chaos control schemes, where the control amplitude is computed once during the orbit after crossing the Poincaré section.If the stabilization of unstable periodic orbits or fixed points by the method given by Ott, Grebogi, Yorke [23] and Hübler [15] can only be based on a measurement delayed by τ orbit lengths, resulting in a control loop latency, the performance of unmodified OGY control is expected to decay. For experimental considerations, it is desired to know the range of stability with minimal knowledge of the system. In section 6.3, the area of stability is investigated both for OGY control and for difference control, yielding a delay-dependent maximal Lyapunov number beyond which control fails. Sections 6.3.4 to 6.4.3 address the question how the control of delayed measured chaotic systems can be improved, i.e., what extensions must be considered if one wants to stabilize fixed points with a higher Lyapunov number. Fortunately, the limitation can be overcome most elegantly by linear control methods that employ memory terms, as linear predictive logging control (Sec. 6.4.1) and memory difference control (Sec. 6.4.3). In both cases, one is equipped with an explicit deadbeat control scheme that allows, within linear approximation, to perform control without principal limitations in delay time, dimension, and Ljapunov numbers.
The delay problem -time-discrete caseFor fixed point stabilization in time-continuous control, the issue of delay has been investigated widely in control theory, dating back at least to the Smith predictor [31].