Wave energy converter control by wave prediction and dynamic programming

Abstract

This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. b s t r a c tWe demonstrate that deterministic sea wave prediction (DSWP) combined with constrained optimal control can dramatically improve the efficiency of sea wave energy converters (WECs), while maintaining their safe operation. We focus on a point absorber WEC employing a hydraulic/electric power take-off system. Maximizing energy take-off while minimizing the risk of damage is formulated as an optimal control problem with a disturbance input (the sea elevation) and with both state and input constraints. This optimal control problem is non-convex, which prevents us from using quadratic programming algorithms for the optimal solution. We demonstrate that the optimum can be achieved by bangebang control. This paves the way to adopt a dynamic programming (DP) algorithm to resolve the on-line optimization problem efficiently. Simulation results show that this approach is very effective, yielding at least a two-fold increase in energy output as compared with control schemes which do not exploit DSWP. This level of improvement is possible even using relatively low precision DSWP over short time horizons. A key finding is that only about 1 second of prediction horizon is required, however, the technical difficulties involved in obtaining good estimates necessitate a DSWP system capable of prediction over tens of seconds.

Error bounds in the gap metric for dissipative balanced approximations

“…Mass-spring-damper arrangements are a key ingredient in many mechanical systems (a novel application, for instance, is in renewable wave energy [17]) and are the mechanical equivalent of a resistor-inductorcapacitor (RLC) circuit, ubiquitous in electrical systems. Figure 2.1 demonstrates two masses connected in series.…”

Technological cost-reduction pathways for attenuator wave energy converters in the marine hydrokinetic environment.

“…16 Although the body of research on controls specific to offshore WAB attenuators is small, there has been considerable research into the use of controls on other WEC types. [31][32][33][34][35][36] This research has consistently shown the potential for large increases, on the order of hundreds of percent, in absorbed power with the use of advanced controls.…”

“…Although much of the literature focusing on reactive and bang-bang controls is applied to single body point absorbers or dual body point absorbers, there is nothing fundamentally limiting application of this research to WAB attenuator devices. 32,[34][35][36] Reactive controls involve applying forces to the device in phase with the wave motion that can then be tuned for maximum energy absorption at the peak frequencies that correspond to different incoming wave spectra. Bang-bang controls include latching and clutching, and allow the control output to jump between two values, a low and a high.…”

Energy capture optimization for an adaptive wave energy converter

“…The proposed solution relies on mathematical optimization (Bertsekas 1999, Papalambros & Wilde 2000, which aims at maximizing the extracted energy from the waves. In (Li, Weiss, Mueller, Townley, & Belmont 2012) the applicability of MPC for optimizing a single non-adaptable WEC is discussed -by non-adaptability we mean that the WEC operation is restricted to a certain wave height. In (Feng & Kerrigan 2013) optimization-based techniques were also used for control of WECs.…”