Abstract
This visual presentation dives into the realm of heaving Wave Energy Converter (WEC) optimal control, employing a highly graphical methodology to expound the trajectories derived from various control algorithms within the position, velocity, and power take-off (PTO) force phase space. By visualizing these trajectories, we aim to provide a clearer understanding of how different control strategies influence the performance of WECs.
To enhance our analysis, we combine average power flow Sankey diagrams that investigate the performance from wave to wire with dynamic graphical animations informed by instantaneous trajectories. These animations vividly illustrate the interactions between key variables in real-time, allowing viewers to grasp the complexities of operating WECs. This visual representation not only enhances comprehension but also engages the audience, making the intricate nature of WEC control more accessible.
The power flow diagrams serve as critical tools for understanding how energy is captured, converted, or reflected, reinforcing the importance of effective control strategies in maximizing the output of usable energy. Our control strategies encompass both passive and active approaches, including damping as a passive control method, proportional-damping, and numerically optimal control strategies that incorporate reactive components. We emphasize the necessity of using average electrical power as the objective function in optimal control scenarios.
Further, we present compelling examples that illustrate the sometimes counterintuitive relationship between PTO efficiency and average usable power. Notably, we demonstrate that higher PTO efficiency does not always correlate with increased average electrical power output; in some instances, a control approach with lower PTO efficiency may lead to more effective hydrodynamic power absorption, particularly through the use of reactive power.
Our objective is to further demystify the use of reactive power in WEC systems. All dynamic models utilized in this work are based on empirical data from the WaveBot in its heave mode. We provide a high-level overview of how to obtain the numeric models, including the hydrodynamic impedance derived from tank tests and the PTO dynamics characterized by bi-variate PTO power loss measured during bench tests. We compute the optimal control trajectories for various regular wave scenarios and the underlying dynamics using WecOptTool.
In summary, this presentation aims to provide a comprehensive and visually engaging exploration of optimal control in heaving WECs, highlighting the critical interplay between control strategies, energy capture, and the importance of average electrical power as a performance metric. Through our visualizations and empirical foundations, we aspire to contribute to the intuitive understanding of WEC control within the research community, paving the way for more effective wave energy systems in the future.
Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525.
This paper describes objective technical results and analysis.
Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government.