Model Predictive Control of a Nonlinear 2-Body Point Absorber Wave Energy Converter With Estimated State Feedback

Abstract

Ocean wave energy has the potential to significantly contribute to sustainable power generation in coastal regions. Much of the research effort has gone into developing time domain state space models of point absorber wave energy converters (WECs) and subsequently into model-based optimal control to efficiently harvest the maximum possible amount of energy. The resulting controllers require knowledge of the states of the WEC in order to achieve the design goals. The purpose of this paper is to design and apply an extended Kalman filter-based estimation algorithm to a nonlinear two-body WEC model and to evaluate its performance in conjunction with a model predictive controller (MPC), which maximizes energy yield while satisfying operational constraints.Index Terms-Kalman filter, model predictive control (MPC), nonlinear point absorber, wave energy converters (WECs).

Optimal control, MPC and MPC-like algorithms for wave energy systems: An overview

“…However, the authors of Richter et al (2013) indicate that, if required, a full WEC model could be used in the MPC formulation, based on a linear state-space approximation as in (17) (the reader is referred to Richter (2011) for further details). Another noteworthy study is Amann et al (2015) , where a nonlinear mooring model, as described in Section 5.1 , is considered. The authors claim that "the radiation forces, [...], are negligibly small and can be excluded for the given device".…”

“…a non-zero feed-through matrix appears in (17) . Another alternative discretisation method is used in Amann et al 2015, where a second-order truncated Taylor series around the current time step is used, since the authors in Amann et al (2015) report that the nonlinearities present in their model are not well approximated with the first derivative. A similar approach is also used in Richter (2011) .…”

A Vertical Flux-Switching Permanent Magnet Based Oscillating Wave Power Generator with Energy Storage

“…Recently, oscillating wave power generation has become popular [9][10][11] and the idea that linear direct drive generators demonstrate good performance has not been rejected by investigations in [12]. Because they can directly capture oscillating wave energy in one dimension without intermediate translators, more and more investigations reveal the advantages of linear direct drive generation methods which have simple power take-off structures with relatively high power efficiency.…”

Control of a Point Absorber Using Reinforcement Learning

“…On the other hand, at each time instant, model predictive control applies the force that results in maximum future energy extraction over a pre-defined time horizon, whilst still respecting any constraints on the motions or loading of the device [10]- [12]. Whereas latching control is difficult to scale to array problems, model predictive control has been successfully applied to multi-body devices and even small array problems [13]- [15]. However, the greatest problem with the latter strategy is that the optimization process is not guaranteed to converge, so that alternative solutions may be required.…”