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Abstract
A challenge while applying latching control on a wave energy converter (WEC) is to find a reliable and robust control strategy working in irregular waves and handling the non-ideal behavior of real WECs. In this paper, a robust and model-free collaborative learning approach for latchable WECs in an array is presented. A machine learning algorithm with a shallow artificial neural network (ANN) is used to find optimal latching times. The applied strategy is compared to a latching time that is linearly correlated with the mean wave period: It is remarkable that the ANN-based WEC achieved a similar power absorption as the WEC applying a linear latching time, by applying only two different latching times. The strategy was tested in a numerical simulation, where for some sea states it absorbed more than twice the power compared to the uncontrolled WEC and over 30% more power than a WEC with constant latching. In wave tank tests with a 1:10 physical scale model the advantage decreased to +3% compared to the best tested constant latching WEC, which is explained by the lower advantage of the latching strategy caused by the non-ideal latching of the physical power take-off model.
Highlights
Since the electric revolution started in the 19th century, the consumption of electrical energy has risen to more than 20 PWh in 2015 [1] and is expected to rise further [2]
The three constant latching times were chosen, so that they represent a wide range of latching times and at the same time are not too close to the optimal constant latching time: Figure 8 shows the absorbed power in dependence of different latching times in the test wave sequence and sets the latching times used by the cWECs and the learning WEC (lWEC) in relation
The three constant latching times used by the cWECs during the collaborative reinforcement machine learning (CL) training phase are indicated as orange dots and the latching time chosen by the lWEC as grey diamonds
Summary
Since the electric revolution started in the 19th century, the consumption of electrical energy has risen to more than 20 PWh in 2015 [1] and is expected to rise further [2] To fulfill these demands in an environmentally friendly way, energy harvested from ocean waves may play an important role. Even after decades of research [3] and a better predictability compared to wind energy [4], the levelized costs of energy are still too high Cutting down these costs is a challenge in which this paper wants to contribute by investigating a model-free latching algorithm for wave energy converters (WECs) in arrays. The algorithm presented here is suitable for other converter designs
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