Abstract
A numerical model for a hydraulic wave energy converter power take-off is developed in this study. The system architecture is described and the mathematical model for each component is presented. The accumulators are not used as energy storage devices. Instead, they are used to reduce the stiffness of the system, increase the response time, and improve the controllability. The numerical model was implemented using MATLAB/Simulink. The design variables selected for this study are the maximum displacement in the hydraulic motors, and the shaft inertia. The effect of these design variables on system performance is studied using latin-hypercube sampling to generate the cases to be simulated. The displacement in the hydraulic devices is used as a control input to adjust the pressure in the hydraulic cylinder and then change the force acting on the floating body. The desired force is calculated by a high level controller that estimates the force value to achieve impedance matching in the WEC. The torque in the electric generator is used to control the shaft speed. The system was designed to actively use reactive power flow to maximize the electric power output in the generator. The model developed in this study is a complete wave-to-wire model based on a co-design approach that considers the effect of all the different subsystems on the dynamic behavior of the whole WEC system. Twelve different wave conditions were tested. The most critical metric for this study is the electric power in the generator, which is the objective function of the optimization that was performed for all the wave conditions defined as case study. The wave-to-wire efficiency, which includes the complete wave energy to electrical energy conversion chain, is also calculated in this work.