A Sliding Mode-Based Tracking Observer for Excitation Force Estimation in Wave Energy Systems

Accurate excitation force estimation is essential for wave energy control. Over the past two decades, multiple proposals have been developed, ranging from linear to nonlinear observers, and from simple Kalman-based estimators to a wide range of statistical approaches. In particular, sliding mode unknown input observers are an attractive alternative to this problem, offering finite time convergence, and robustness to uncertainties. In this paper, a second-order sliding mode observer, based on a reference tracking controller structure, is developed. To evaluate the performance of the developed algorithm, illustrative numerical examples and comparisons against observers based on linear tracking controllers are presented and analysed.