Wave energy conversion under constrained wave-by-wave impedance matching with amplitude and phase-match limits |
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| Institution: | 1. Department of Electric Power Engineering, Norwegian University of Science and Technology, O.S. Bragstadsplass 2E, N-7491 Trondheim, Norway;2. Department of Engineering Cybernetics, NTNU, O.S. Bragstadsplass 2D, N-7491 Trondheim, Norway |
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| Abstract: | This paper investigates an approach to limit the fullness of ‘tuning’ provided by wave-by-wave impedance matching control of wave energy devices in irregular waves. A single analytical formulation based on the Lagrange multiplier approach of Evans 1] is used to limit the velocity amplitude while also limiting the closeness of the phase match between velocity and exciting force. The paper studies the effect of the present technique in concurrently limiting the device velocity and the required control/actuation force. Time domain application requires wave-profile prediction, which here is based on a deterministic propagation model. Also examined in the time domain is the effect of possible violation of the displacement constraint, which for many designs implies impacts at hard stops within the power take-off mechanism. Time domain simulations are carried out for a 2-body axisymmetric converter (with physical end-stops) in sea states reported for a site off the US east coast. It is found that the approach leads to effective power conversion in the less energetic sea states, while as desired, considerable muting of the optimal response is found in the larger sea states. Under the assumptions of this work, the end-stop collisions are found to have a minor effect on the power conversion. The present approach could be used to guide the design of power take-off systems so that their displacement stroke, maximum force, and resistive and reactive power limits are well-matched to the achievable performance of a given controlled primary energy converter. |
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| Keywords: | Wave energy conversion Constrained impedance-matching control Wave-by-wave control Relative oscillation Time-domain Irregular waves Displacement and force constraints End stops |
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