A phase-lock-loop-based control system for suppressing periodic vibration in smart structural systems

Abstract

This paper presents a simple, effective and economical system capable of suppressing periodic vibration (external or self-induced) affecting a structure or payload. The approach used integrates piezoelectric materials/actuators, sensors and low-cost electronics in a novel way. The key innovation is the use of phase-lock loops (PLLs) and switch-capacitor filters (SCFs) for the on-line identification, tracking and control of periodic vibration. This method concentrates its control action at those frequencies where periodic vibration is detected. Among the advantages of this approach are the following: it is conceptually simple, easily expandable and modular; the controller does not rely on a model of the structure and it only needs some approximate notion of the frequency range where the periodic disturbances are expected to occur; it is robust and can be operated at high gain without loss of stability; it is not significantly affected by the presence of random vibration or sensor noise and it can be implemented with inexpensive electronics. The effectiveness of this new approach was experimentally evaluated using a test unit consisting of a simple structure, accelerometers and Terfenol-D actuators. The structure was excited by driving one of the actuators with sinusoidal and random signals. The resulting periodic disturbances were measured using the accelerometers. The acceleration signals were passed though a bank of PLLs and associated SCFs to detect the fundamental frequency and harmonics. This information was used to drive another actuator that rejected the original disturbances, and attenuation levels as high as 30 dB were achieved.

Rejection of periodic disturbances of unknown and time‐varying frequency

“…Although the frequency of the disturbance was known, a modification of algorithm (20) was found to be the most successful approach, among a few that were tried. The algorithm of Algrain et al [34] is also similar in concept to the one proposed in Reference [30]. It was applied to the vibration control of smart structures, but no stability analysis was provided that would predict the dynamic behaviour of the adaptive system.…”

A vibration suppression approach based on enhanced phase locked loop harmonic tracking

“…A batch of PLLs is used as a comb filter to suppress all the frequency components but the frequencies of the observed modes, proving that the PLL is an effective method to control a single or a set of vibration modes avoiding spillover (Niezrecki and Cudney (1997)). A different approach is to associate a bank of PLLs to switch-capacitor filters to generate square waves with the same frequency as the disturbances to suppress, which are used to identify the frequency in real-time and to tune the band-pass filters accordingly and the control gains (Algrain et al (1997)).…”