Title :
Discrete-time Frequency-Locked-Loop filters for exact asymptotic rejection of sinusoidal disturbances
Author :
Tedesco, Francesco ; Casavola, Alessandro ; Fedele, Giuseppe
Author_Institution :
Dipt. di Ing. Inf., Modellistica, Elettron. e Sist. (DIMES), Univ. degli Studi della Calabria, Rende, Italy
Abstract :
The paper proposes a discrete-time adaptive control scheme for the asymptotical rejection of unknown and possibly time-varying sinusoidal disturbances acting on a plant. The approach is based on a recently proposed discrete-time Frequency-Locked-Loop (FLL) nonlinear filter which is used in the scheme as an adaptive frequency tracker. The properties of the scheme are fully analyzed and it is shown that standard discretization techniques fail to provide discrete-time FLL filters that exhibit the same good properties of their continuous-time counterparts. In particular, unlike continuous-time FLL filters, biased estimates are usually produced by these discrete-time FLL filters and the corresponding rejection properties of the scheme are poor. In order to overcome this drawback, a Tustin discretization technique equipped with an adaptive pre-warping mechanism consisting of properly adjusting the pre-warping frequency on-line is shown to be sufficient to solve the problem and recover the rejection performance of the continuous-time schemes. Several final examples are provided for assessment purposes.
Keywords :
discrete time systems; filtering theory; frequency locked loops; Tustin discretization technique; adaptive frequency tracker; adaptive pre-warping mechanism; discrete-time FLL filters; discrete-time adaptive control scheme; discrete-time frequency-locked-loop filters; exact asymptotic rejection; time-varying sinusoidal disturbances; Convergence; Difference equations; Estimation; Frequency estimation; Frequency locked loops; Resonant frequency; Time-frequency analysis; Estimation; Indirect adaptive control;
Conference_Titel :
American Control Conference (ACC), 2014
Conference_Location :
Portland, OR
Print_ISBN :
978-1-4799-3272-6
DOI :
10.1109/ACC.2014.6858944