Model Following Robust Control of a Wavestar-prototype Wave Energy Converter: Part 2 Estimation and Optimal Reference Computation

Abstract

Listen

Translate article

Following the description of the model following robust control for scaled Wavestar-prototype wave energy converter (WEC) in Part 1, this paper focuses on the high-level design, the estimation of wave excitation Moment (WEM) and calculation of the optimal reference, which are of high significance for energy-maximizing tracking control. For this calculation, WEM prediction is not required, a considerable advantage over other WEC approaches. Part 1 focuses on the low-level hierarchical tracking structure, comprising a specially designed robust controller. This paper describes new work on the determination of the reference signal. For this WEC system, the WEM is an unmeasurable quantity. Hence, some alternative application-focused robust ways are outlined, to determine the best choice of observers for WEM estimation. Four approaches are compared which are relatively simple, effective, and straightforward for real application. Although the Luenberger Observer (LO) with pole-placement the simplest, the Adaptive Sliding Mode Observer (ASMO) has the strongest robustness. In the final part an Extended Kalman filter (EKF) is described to obtain the amplitude and angular frequency of the WEM used in calculation of the reference velocity.