Abstract
The ISWEC (inertial sea wave energy converter) is presented, its control problems are stated, and an optimal control strategy is introduced. As the aim of the device is energy conversion, the mean absorbed power by ISWEC is calculated for a plane 2D irregular sea state. The response of the WEC (wave energy converter) is driven by the sea-surface elevation, which is modeled by a stationary and homogeneous zero mean Gaussian stochastic process. System equations are linearized thus simplifying the numerical model of the device. The resulting response is obtained as the output of the coupled mechanic-hydrodynamic model of the device. A stochastic suboptimal controller, derived from optimal control theory, is defined and applied to ISWEC. Results of this approach have been compared with the ones obtained with a linear spring-damper controller, highlighting the capability to obtain a higher value of mean extracted power despite higher power peaks.
Highlights
Oceans represent a wide, distributed reservoir of energy and, in them, waves are by far the most conspicuous form of energy
The first use of gyroscopes for wave energy extraction is due to Salter, who invented the Duck device at the University of Edinburgh in the 1970s [7, 8]; the ISWEC belongs to the last generation of this kind of energy converters
The main issue is the “reaction problem”: in order to generate an action on the power take-off (PTO: the component aimed at the power conversion, e.g., the electric generator) to generate energy, a reaction is needed and has to be given by either the seabed, the water, inertia, or other structures [11]
Summary
Oceans represent a wide, distributed reservoir of energy and, in them, waves are by far the most conspicuous form of energy. Since a lot of devices have been conceived and developed while a few of them arrived to the precommercial stage [4] Among these machines, a considerable role is played by gyroscopic converters. Many problems have still to be solved in order to develop a reliable and economically sustainable wave energy converter (WEC). The main issue is the “reaction problem”: in order to generate an action on the power take-off (PTO: the component aimed at the power conversion, e.g., the electric generator) to generate energy, a reaction is needed and has to be given by either the seabed, the water, inertia, or other structures [11]. The effect of the maximum PTO torque constraint is analyzed in order to take into account the real machine limits
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