Wave-to-Wire Modeling and Simulation of a Wave Energy Converter for Off-Grid and Micro-Grid Applications

This paper describes the hydrodynamic, pneumatic, and electrical modeling and simulation study performed in the development of the Healy Wave Energy Converter (HWEC). The HWEC, based on a two-body structure, consists of a flotation buoy rigidly connected to a long vertical inertial tube which is open at the top and bottom. A piston-rod assembly is enclosed and connected to the power take-off (PTO) mechanism. Due to inertia of water within the tube, relative motion between the piston and the buoy-inertia tube structure drives the PTO, which consists of an air compressor, a dynamic pressure regulator and a turbine connected to an induction generator supported by a power electronic conversion system. The induction generator is operated in both self-excitation mode using switched capacitors and external excitation mode using an inverter to generate flexible power forms and to maximize the energy yield over a wide range of wave conditions. A PLC based control system ensures balance between the generated and consumed power under all dynamic conditions. Nonlinear time-domain numerical models were developed for each subsystem. The resulting modeling framework was used to specify component requirements, select operational parameters, and evaluate system performance. The HWEC system is designed to output moderate power with high reliability. The present analysis demonstrates that the HWEC can produce and store energy over a wide range of sea states, making it highly suitable for off-grid and micro-grid applications.