Abstract
Control of wave energy converters (WECs) has been very often limited to hydrodynamic control to absorb the maximum energy possible from ocean waves. This generally ignores or significantly simplifies the performance of real power take-off (PTO) systems. However, including all the required dynamics and constraints in the control problem may considerably vary the control strategy and the power output. Therefore, this paper considers the incorporation into the model of all the conversion stages from ocean waves to the electricity network, referred to as wave-to-wire (W2W) models, and identifies the necessary components and their dynamics and constraints, including grid constraints. In addition, the paper identifies different control inputs for the different components of the PTO system and how these inputs are articulated to the dynamics of the system. Examples of pneumatic, hydraulic, mechanical or magnetic transmission systems driving a rotary electrical generator, and linear electric generators are provided.
Highlights
The increasing penetration of renewable energy sources into the power grid, especially wind and solar energy, poses a daunting challenge to both renewable energy plants and the electricity network, due to the variability of the renewable sources and the rigorous restrictions of the network.Wave energy is expected to contribute to the future power supply
The main challenge for the technologies to be implemented in this transmission stage is to reliably and efficiently convert the power absorbed by the wave energy converters (WECs), dealing with the extreme variations between maximum power peaks and average power flow
The objective of this paper is to examine the current literature and available W2W models for wave energy devices to see if a complete W2W model, suitable for advanced control studies is available, or can be assembled
Summary
The increasing penetration of renewable energy sources into the power grid, especially wind and solar energy, poses a daunting challenge to both renewable energy plants and the electricity network, due to the variability of the renewable sources and the rigorous restrictions of the network. Apart from the grid restrictions, each of the components used in the power conversion can add constraints to the conversion process, such as force, displacement or speed limitations These components are designed to efficiently perform close to nominal values, but lose performance as soon as operation conditions move away from these nominal values. The absorption stage comprises the conversion of wave motion into oscillating motion of the WEC This absorbed energy is transmitted into hydraulic energy in the transmission stage and converted into electrical energy in the generation stage. Models that incorporate all these stages from waves to the grid are known in the literature as wave-to-wire (W2W) models
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