Robust Frequency Estimation of Multi-Harmonic Signals

In this paper we propose a robust estimator for the frequencies of biased multi-harmonic signals in the presence of unknown additive disturbances. The estimator consists of a continuous-time stable linear system and a discrete-time recursive least-squares identifier. In absence of additive disturbances, the proposed design guarantees global exponential convergence to the optimal (in the least-squares sense) parameter estimates. In presence of disturbances, instead, an input-to-state stability property relative to such optimal estimates holds.