Dynamic Model and Nonlinear Control for a Two Degrees of Freedom First Generation Tidal Energy Converter

Several manufacturers have developed devices with which to harness tidal currents power in areas where depth does not exceed 40 meters. These are the so-called first generation tidal energy converters (TEC). The maintenance tasks carried out on these devices therefore require them to he extracted from their bases to the sea surface at and subsequently placed back on the bases. Special high performance ships are required for these tasks, signifying high maintenance costs. The automation of emersion and immersion maneuvers will undoubtedly lead to lower costs, given that ships with less demanding requirements will be required for the aforementioned maintenance tasks. This work presents a very simple dynamic modeling for a first generation TEC composed of only two lumped masses, which are handled solely by hydrostatic forces (conceived as volume-increasing devices). We propose a nonlinear control law based on friction terms compensation for closed loop depth and/or orientation control in order to ensure an adequate behavior when the TEC performs emersion and immersion maneuvers with only passive hydrosta,tic forces. A control scheme based on nonlinear input transformation, a proportional-derivative (PD) linear action mid nonlinear compensation term are also proposed in order to ensure a global asymptotic stability of the TEC posture Finally, the effectiveness of the dynamic model and the controller approach is demonstrated by means of numerical simulations when the TEC is carrying out an emersion maneuver for the development of blade-cleaning maintenance tasks. (C) 2016, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.