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Title: Power-to-load balancing for asymmetric heave wave energy converters with nonideal power take-off

The aim of this study is to maximize the power-to-load ratio for asymmetric heave wave energy converters. Linear hydrodynamic theory was used to calculate bounds of the expected time-averaged power (TAP) and corresponding surge-restraining force, pitch-restraining torque, and power take-off (PTO) control force with the assumption of sinusoidal displacement. This paper formulates an optimal control problem to handle an objective function with competing terms in an attempt to maximize power capture while minimizing structural and actuator loads in regular and irregular waves. Penalty weights are placed on the surge-restraining force, pitch-restraining torque, and PTO actuation force, thereby allowing the control focus to concentrate on either power absorption or load mitigation. The penalty weights are used to control peak structural and actuator loads that were found to curb the additional losses in power absorption associated with a nonideal PTO. Thus, in achieving these goals, a per-unit gain in TAP would not lead to a greater per-unit demand in structural strength, hence yielding a favorable benefit-to-cost ratio. Demonstrative results for 'The Berkeley Wedge' in the form of output TAP, reactive TAP needed to drive WEC motion, and the amplitudes of the surge-restraining force, pitch-restraining torque, and PTO control force are shown.
Authors:
 [1] ;  [2] ; ORCiD logo [2]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  2. Univ. of California, Berkeley, CA (United States)
Publication Date:
Report Number(s):
NREL/JA-5000-68167
Journal ID: ISSN 0960-1481
Grant/Contract Number:
AC36-08GO28308
Type:
Accepted Manuscript
Journal Name:
Renewable Energy
Additional Journal Information:
Journal Name: Renewable Energy; Journal ID: ISSN 0960-1481
Publisher:
Elsevier
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), NREL Laboratory Directed Research and Development (LDRD)
Country of Publication:
United States
Language:
English
Subject:
16 TIDAL AND WAVE POWER; asymmetric heave wave energy converter; power absorption control; structural load mitigation; nonideal PTO efficiency; Berkeley Wedge
OSTI Identifier:
1416257