Power-to-load balancing for heaving asymmetric wave-energy converters with nonideal power take-off

• Published in: Renewable energy Vol. 131; pp. 1208 - 1225
• Main Authors: Tom, Nathan M., Madhi, Farshad, Yeung, Ronald W.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.02.2019
• Subjects: Asymmetric heave wave energy converter; Berkeley Wedge; Nonideal PTO efficiency; Power absorption control; Structural load mitigation; Structural load mitigation; Asymmetric heave wave energy converter; Power absorption control; Berkeley Wedge; Nonideal PTO efficiency
• ISSN: 0960-1481; 1879-0682
• DOI: 10.1016/j.renene.2017.11.065

The aim of this paper is to maximize the power-to-load ratio for asymmetric wave energy converters undergoing heave motion. Linear hydrodynamic theory is 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. •Review of “The Berkeley Wedge” an asymmetric wave energy converter/breakwater device.•Includes effect of power-take-off efficiency and force coefficients on power output.•Use of pseudo-spectral control theory while including structural and actuator loads.•Introduces a power-to-load ratio for evaluating wave energy converter performance.•Losses in power capture were exceeded by reductions in structural and actuator loads.