PASSIVITY-BASED NUMERICAL MODELING AND GRID INTEGRATION STRATEGIES FOR WAVE ENERGY CONVERTER ARRAYS

Abstract

The body of work presented here develops numerical time-domain models of Wave Energy Converter (WEC) arrays or wave farms. It will be shown here that a cluster of WECs can be more effective in extracting oceanic energy, can facilitate deployment logistics, and help with grid integration. The objectives of this work are: (i) developing a theoretical metric to evaluate the energy extraction potential of a WEC array, (ii) developing an algorithm that ensures the stability of the time-domain models of WEC arrays, and (iii) identifying strategies that facilitate grid integration and power management of a WEC array. In the process of developing the theoretical performance metric, the potential theory was used to develop expressions for wave potentials as the incoming wave reflects by and transmits through the WEC array. Decomposing the wave potential in horizontal and vertical parts enabled the application of boundary conditions based on continuity in terms of velocities and potentials. Incorporation of the hydrodynamic terms showed an increase of up to 28% in the low-frequency range. The knowledge of the wave potentials in and around the WEC array helped the application of robust system identification strategies that accurately described the physical phenomenon and ensured the numerical stability of the numerical models. The dissipative nature of the system enabled the application of the passivity property for system identification. The proposed approach could guarantee the numerical stability of time-domain modeling of WEC arrays while also ensuring high accuracy of the emulated hydrodynamics and the motions of the bodies. For the case studies considered, the identified systems calculated the motion time-histories with > 95% accuracy for WEC array cases and > 99% accuracy for the single isolated body case. Finally, the dissertation addresses the grid integration and power management issues associated with the power generated by WEC arrays. The oscillatory nature of ocean waves introduces variability in the total power produced. This work develops the conditions that exploit the phase offsets in the wave received at individual WECs at any given time. The conditions developed here will result in constant power by imposing polyphase power profiles for the WECs in the array. Continuously constant power is desirable for grid integration and power management. Additionally, the objectives for an ideal power controller are developed that can make the overall produced by the WEC array constant.