Energy in ocean waves is distributed across a wide range of frequencies, with a challenge to optimise the loading of a WEC to maximise power capture across a range of sea states that a wave energy installation may be subject to. When using simple resistive damping control, even a well-designed device will fail to capture much of the energy in ocean waves. As such, a large number of studies have begun to investigate advanced control design and implementation for WECs; these studies have generally shown very attractive results for increased energy absorption as well as performance factors such as decreased loads and represent a key path towards lowering the levelized cost of energy (LCOE) for WECs.
While there are a significant number of studies which evaluate particular devices under particular wave excitation conditions, few studies exist which compare a number of control strategies on one (or a set of) standard device(s), with consistent wave excitation applied in each case, to level the playing field. However, controller evaluations are usually carried out in simulation, where the simulation model is often identical to that used to build the model-based controller. In such a situation, any controller sensitivities due to modelling inaccuracies are masked in the evaluation. In addition, due to the non-causal nature of the generic impedance-matching control problem, future information (available in simulation environments) is often assumed for controller. While there are ways of estimating such future information, the effects of the estimation errors are not always considered. Finally, the real-time computational requirements of WEC controllers are not always clear from simulation studies.
Despite the comparative simulation results available, there is also a desire to compare a variety of WEC control strategies under real, or at least wave tank, implementation scenarios, so that all real effects are encountered, such as nonlinear hydrodynamic and PTO effects, realistic measurement assumptions, including the presence of measurement noise and bias, and real-time computational requirements. Ironically, the challenge for WEC controllers for small-scale WECs can be greater, due to the exaggerated role of friction, and the shorter sampling rate requirements associated with faster dynamics, but these issues are, at least, consistent for each of any compared control strategies.
The objective of the currently proposed competition, which will consist of a standard WEC prototype platform, is to compare the energy capture performance of various WEC control strategies evaluated, in the first instance in simulation and then, for shortlisted entrants, on the prototype device in a wave tank environment. In order to provide a consistent simulation environment for both competitors and evaluators, the WEC-Sim simulation environment will be employed. For wave tank testing, the real-time control algorithms will be implemented using the Matlab/Simulink xPC environment.