State and parameter estimation for multirate systems with frequency-aliased output measurements

Proposes the adaptive parallel observer system (APOS), a multirate estimation technique for discrete time systems, to compensate for output measurements that are available only periodically and for systems whose frequency content is beyond that of the Nyquist-frequency. The APOS provides the controller with stable state and system parameter estimates, which also allow for the extraction of system damping ratios and resonant frequencies despite the presence of aliasing. A stability proof and error bounds are provided. The APOS is applied to an IBM head/disk assembly system, and the parameter estimates are used to obtain accurate values of the system damping ratio and aliased resonant frequency via a trained neural network.