Non-Linear Model Predictive Control Applied to a Generic Ocean-Wave Energy Extractor

Tom, Nathan; Yeung, Ronald W.

doi:10.1115/omae2013-11247

Cited by 12 publications

(27 citation statements)

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“…These papers acknowledge that practical constraints imposed by the PTO system must be studied to a greater extent. Similar conclusions are drawn by [11], which demonstrates the potentials of MPC in a simulation study of a model-scale point absorber albeit unrealistic performance requirements for the PTO system are obtained due to the simplicity of the used PTO model. [10] reports a study of both a centralized MPC and decentralized MPCs applied to a small array of three WECs and concludes that MPC can improve the energy absorption compared to a linear fixed damping controller.…”

Section: Introductionsupporting

confidence: 77%

“…Recently, WPEA's based on the idea of Model Predictive Control (MPC) have attained increasing focus from the wave energy research community, see e.g., [4][5][6][7][8][9][10][11], and initial results are encouraging: MPC may lead to increased energy output of a WEC compared to e.g., reactive control WPEA. In the early work of [4,6,8], a linear MPC has been developed and simulated on ideal PTO systems harvesting energy of point absorber WEC's.…”

Section: Introductionmentioning

confidence: 99%

“…Traditionally, a controller is tuned off-line based on ideas such as reactive control [2] 127 and mapping techniques are used to accommodate quantization of the controller output [11].…”

mentioning

confidence: 99%

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Model Predictive Control of a Wave Energy Converter with Discrete Fluid Power Power Take-Off System

Hansen¹,

Asmussen

Bech³

2018

Energies

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Wave power extraction algorithms for wave energy converters are normally designed without taking system losses into account leading to suboptimal power extraction. In the current work, a model predictive power extraction algorithm is designed for a discretized power take of system. It is shown how the quantized nature of a discrete fluid power system may be included in a new model predictive control algorithm leading to a significant increase in the harvested power. A detailed investigation of the influence of the prediction horizon and the time step is reported. Furthermore, it is shown how the inclusion of a loss model may increase the energy output. Based on the presented results it is concluded that power extraction algorithms based on model predictive control principles are both feasible and favorable for use in a discrete fluid power power take-off system for point absorber wave energy converters.

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Section: Introductionsupporting

confidence: 77%

Section: Introductionmentioning

confidence: 99%

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Model Predictive Control of a Wave Energy Converter with Discrete Fluid Power Power Take-Off System

Hansen¹,

Asmussen

Bech³

2018

Energies

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“…The use of model-predictive control (MPC) allows for the optimization over any number of state constraints, such as the amplitude of motion [25], [26] or power-takeoff (PTO) capacity [27]. Nonlinear-model-predictive control (NMPC) has also been used to account for the nonlinear dynamics from mooring lines [28] as well as the optimization of a time-varying PTO damper [29], [30]. However, the results from [29] include an active control force in addition to a time-varying PTO damper that allows for energy flow reversal, whereas Tom and Yeung [30] rely on the time-varying PTO damping as the only control input preventing a reverse in energy flow.…”

Section: Introductionmentioning

confidence: 99%

“…Nonlinear-model-predictive control (NMPC) has also been used to account for the nonlinear dynamics from mooring lines [28] as well as the optimization of a time-varying PTO damper [29], [30]. However, the results from [29] include an active control force in addition to a time-varying PTO damper that allows for energy flow reversal, whereas Tom and Yeung [30] rely on the time-varying PTO damping as the only control input preventing a reverse in energy flow. The results from both sources suggest a damping input following a strongly bang-bang time history [31].…”

Section: Introductionmentioning

confidence: 99%

Experimental Confirmation of Nonlinear-Model- Predictive Control Applied Offline to a Permanent Magnet Linear Generator for Ocean-Wave Energy Conversion

Tom

Yeung

2016

IEEE J. Oceanic Eng.

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To further maximize power absorption in both regular and irregular ocean wave environments, nonlinear-modelpredictive control (NMPC) was applied to a model-scale point absorber developed at . The NMPC strategy requires a power-takeoff (PTO) unit that could be turned on and off, as the generator would be inactive for up to 60% of the wave period. To confirm the effectiveness of this NMPC strategy, an in-house-designed permanent magnet linear generator (PMLG) was chosen as the PTO. The time-varying performance of the PMLG was first characterized by dry-bench tests, using mechanical relays to control the electromagnetic conversion process. The on/off sequencing of the PMLG was tested under regular and irregular wave excitation to validate NMPC simulations using control inputs obtained from running the choice optimizer offline. Experimental results indicate that successful implementation was achieved and absorbed power using NMPC was up to 50% greater than the passive system, which utilized no controller. Previous investigations into MPC applied to wave energy converters have lacked the experimental results to confirm the reported gains in power absorption. However, after considering the PMLG mechanical-to-electrical conversion efficiency, the electrical power output was not consistently maximized. To improve output power, a mathematical relation between the efficiency and damping magnitude of the PMLG was inserted in the system model to maximize the electrical power output through continued use of NMPC which helps separate this work from previous investigators. Of significance, results from latter simulations provided a damping time series that was active over a larger portion of the wave period requiring the actuation of the applied electrical load, rather than on/off control.

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Model-Predictive Control Strategy for an Array of Wave-Energy Converters

Qian¹,

Yeung²

2019

J. Marine. Sci. Appl.

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To facilitate the commercialization of wave energy in an array or farm environment, effective control strategies for improving energy extraction efficiency of the system are important. In this paper, we develop and apply model-predictive control (MPC) to a heaving point-absorber array, where the optimization problem is cast into a convex quadratic programming (QP) formulation, which can be efficiently solved by a standard QP solver. We introduced a term for penalizing large slew rates in the cost function to ensure the convexity of this function. Constraints on both range of the states and the input capacity can be accommodated. The convex formulation reduces the computational hurdles imposed on conventional nonlinear MPC. For illustration of the control principles, a point-absorber approximation is adopted to simplify the representation of the hydrodynamic coefficients among the array by exploiting the small devices to wavelength assumption. The energycapturing capabilities of a two-cylinder array in regular and irregular waves are investigated. The performance of the MPC for this two-WEC array is compared to that for a single WEC, and the behavior of the individual devices in head or beam wave configuration is explained. Also shown is the reactive power required by the power takeoff system to achieve the performance.

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Non-Linear Model Predictive Control Applied to a Generic Ocean-Wave Energy Extractor

Cited by 12 publications

References 0 publications

Model Predictive Control of a Wave Energy Converter with Discrete Fluid Power Power Take-Off System

Model Predictive Control of a Wave Energy Converter with Discrete Fluid Power Power Take-Off System

Experimental Confirmation of Nonlinear-Model- Predictive Control Applied Offline to a Permanent Magnet Linear Generator for Ocean-Wave Energy Conversion

Model-Predictive Control Strategy for an Array of Wave-Energy Converters

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