Robust control design for suspension system in LIGO

Abstract

In this article, we present a relatively new state-space methodology, called synthesis, to design a robust controller for a subsystem of the Laser Interferometer Gravitational Wave Observatory. In particular, we examine the quadruple pendulum subsystem, which is simplified for the purpose of the study to a two wire simple pendulum system. Structured and unstructured uncertainties are considered in the modelling, though the structured ones are incorporated in the unstructured framework based on a design philosophy presented in the literature. Incorporating weighting functions that emphasize the spectral band of the uncertainties as well as the band in which disturbances are to be attenuated, we design a robust control law using the coprime factorization technique of the paradigm.