Restricted Complexity Control Design for Wave Energy Converters

This thesis introduces various control system designs for wave energy converters. It describes optimal conditions for maximizing the energy absorbed from wave energy converters. Feedback realisation of complex-conjugate control and velocity-tracking control are used to create these conditions. Also, passive loading control and latching control, which correspond to non-optimal conditions, are both discussed here. Several different ways of overcoming the non-causal problem of optimal conditions are also discussed. Firstly, prediction of wave elevation or excitation force can be used to solve the non-causal problem. Several predictive approaches’ performances are compared. A new approach, called multi-steps predictive identification, has been shown that have better performance than other approaches. Secondly, the prediction error method, which is used to find a constant approximation of a model’s performance can be also used to overcome the non-causal problem. The most important aim of this project is to maximize absorbed energy. The design of a Power Takeoff (PTO) device of a wave energy conversion system here involved direct optimization of the parameters of a mechanical network using the Nelder–Mead method can be linked to power absorption performance. Approximate transfer functions are realized with different admittances are here compared. Real ocean data sets were tested in terms of admittances. Their advantages and disadvantages of each method are presented in this thesis.