Control co-design and optimization of oscillating-surge wave energy converter

Ocean wave energy has the potential to play a crucial role in the shift to renewable energy. In order to improve wave energy conversion performance, it is necessary to break through the traditional sequential design process due to the coupling of subsystems such as the wave capture structure geometry, power take-off (PTO), and control systems. A co-design optimization is introduced in this paper to include effects of all subsystems with one outer and one inner optimization loop in order to reach a fully optimal design of an oscillating surge wave energy converter (OSWEC). A width and height sweep serves as an outer loop geometry optimization while power take-off components and control parameters are optimized efficiently in an inner loop for each geometry. An investigation into electrical power and mechanical power maximization also outlines the contrasting nature of the two objectives to illustrate the importance of electrical power maximization for identifying optimality. The co-design optimization leads to an optimal design with a width of 12 m and a height of 10 m which achieves an improvement in the normalized power value of over 60% when compared to sequential design. A sensitivity analysis of the PTO system enhances understanding of the impact of PTO component value changes to support detailed-design of relevant components including drivetrain and generator. Lastly, the effect of the wave height and period on the optimal design is explored. Through the optimization and sensitivity analysis, a greater understanding on the effects of applying control co-design principles on surface piercing OSWECs is achieved and the importance of control co-design methods is demonstrated.