An Energy-Maximising Linear Time Invariant Controller (LiTe-Con) for Wave Energy Devices

A Linear Time Invariant (LTI) energy-maximising control strategy for Wave Energy Converters (WECs) is proposed in this paper. Using the fundamental requirement of impedance-matching, the controller is tuned to maximise the energy obtained under polychromatic wave excitation. Given the LTI nature of the proposed controller, the design and implementation procedure is significantly simpler than well-established energy-maximising controllers, including state-of-the-art numerical optimisation routines, which are predominant in this field. Additionally, a LTI constraint handling mechanism is provided. The effectiveness of both the LTI control strategy and the constraint handling mechanism are assessed using regular and irregular waves in unconstrained and constrained cases. The resulting performance is compared to those obtained using existing WEC optimal control strategies. Finally, the benefits, in terms of power production, for both the controller and the constraint handling mechanism are explicitly highlighted by means of an application case.

[1]  John Ringwood,et al.  An Analytical and Numerical Sensitivity and Robustness Analysis of Wave Energy Control Systems , 2020, IEEE Transactions on Control Systems Technology.

[2]  Fernando Daniel Bianchi,et al.  Model selection: From LTI to switched-LPV , 2012, 2012 American Control Conference (ACC).

[3]  Bart De Moor,et al.  N4SID: Subspace algorithms for the identification of combined deterministic-stochastic systems , 1994, Autom..

[4]  John V. Ringwood,et al.  Numerical Optimal Control of Wave Energy Converters , 2015, IEEE Transactions on Sustainable Energy.

[5]  John Ringwood,et al.  Optimal control, MPC and MPC-like algorithms for wave energy systems: An overview , 2017, IFAC J. Syst. Control..

[6]  John Ringwood,et al.  A high-fidelity wave-to-wire simulation platform for wave energy converters: Coupled numerical wave tank and power take-off models , 2018, Applied Energy.

[7]  Torgeir Moan,et al.  A Comparison of Selected Strategies for Adaptive Control of Wave Energy Converters , 2011 .

[8]  Michel Gevers,et al.  Identification for Control: From the Early Achievements to the Revival of Experiment Design , 2005, Proceedings of the 44th IEEE Conference on Decision and Control.

[9]  John Ringwood,et al.  A Model for the Sensitivity ofNon-Causal Control of Wave Energy Converters toWave Excitation Force Prediction Errors , 2011 .

[10]  A. Clément,et al.  Optimal Latching Control of a Wave Energy Device in Regular and Irregular Waves , 2006 .

[11]  John Ringwood,et al.  A Critical Comparison of Excitation Force Estimators for Wave-Energy Devices , 2020, IEEE Transactions on Control Systems Technology.

[12]  T. Moan,et al.  Constrained Optimal Control of a Heaving Buoy Wave-Energy Converter , 2011 .

[13]  F. Fusco,et al.  A Simple and Effective Real-Time Controller for Wave Energy Converters , 2013, IEEE Transactions on Sustainable Energy.

[14]  John Ringwood,et al.  Finite-order hydrodynamic model determination for wave energy applications using moment-matching , 2018, Ocean Engineering.

[15]  João C. C. Henriques,et al.  Reactive versus latching phase control of a two-body heaving wave energy converter , 2009, 2009 European Control Conference (ECC).

[16]  Ted K.A. Brekken,et al.  Power optimisation of a point absorber wave energy converter by means of linear model predictive control , 2014 .

[17]  Bart De Moor,et al.  Subspace Identification for Linear Systems: Theory ― Implementation ― Applications , 2011 .

[18]  Lennart Ljung,et al.  System Identification: Theory for the User , 1987 .

[19]  John V. Ringwood,et al.  Energy-Maximizing Control of Wave-Energy Converters: The Development of Control System Technology to Optimize Their Operation , 2014, IEEE Control Systems.

[20]  Michel Guglielmi,et al.  Declutching control of a wave energy converter , 2009 .

[21]  A H Clément,et al.  Discrete control of resonant wave energy devices , 2012, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences.

[22]  Gordon Lightbody,et al.  Maximisation of Energy Capture by a Wave-Energy Point Absorber using Model Predictive Control , 2011 .

[23]  J. Falnes.  Ocean Waves and Oscillating Systems: Linear Interactions Including Wave-Energy Extraction , 2002 .

[24]  John V. Ringwood,et al.  Energy-maximising control of wave energy converters using a moment-domain representation , 2018, Control Engineering Practice.

[25]  R. H. Hansen.  Design and Control of the PowerTake-Off System for a Wave Energy Converter with Multiple Absorbers , 2013 .

[26]  John Ringwood,et al.  Energy maximising robust control for spectral and pseudospectral methods with application to wave energy systems , 2019, Int. J. Control.

[27]  Søren Nielsen,et al.  Stochastic control of wave energy converters for optimal power absorption with constrained control force , 2019, Applied Ocean Research.

[28]  Guang Li,et al.  Model predictive control of sea wave energy converters – Part II: The case of an array of devices , 2014 .

[29]  T. Barnett,et al.  Measurements of wind-wave growth and swell decay during the Joint North Sea Wave Project (JONSWAP) , 1973 .

[30]  Joseba Jokin Quevedo Casín,et al.  Identification and control : the gap between theory and practice , 2007 .

[31]  Johannes Falnes,et al.  A REVIEW OF WAVE-ENERGY EXTRACTION , 2007 .