<p>One of the widely studied power take-off (PTO) units of wave energy converters (WECs) is the direct drive system, which typically applies a linear electrical machine (LEM). As far as the control algorithm is concerned, passive control is usually applied, given that it is simple and robust. However, energy production is not maximized without using active control, which requires a PTO unit that is able to supply reactive power. Therefore, a permanent magnet linear electrical machine (PMLEM) PTO unit is implemented in this paper, which can be controlled to provide the required reactive power. A shape-based (SB) optimal control is implemented in this paper to maximize the wave energy production (mechanical side) with the employment of PTO constraints and power losses. Further, the LEM design is optimized such that the electrical power output can be maximized (e.g., reduced power losses).</p><p>The numerical simulations are conducted using MATLAB Simulink and Simscape. The linear wave theory is applied in modeling the WEC dynamics. Additionally, the PTO unit (built by Simscape) is composed of a PMLEM, an ideal inverter, and an ideal energy storage system that is connected to a direct current circuit.&nbsp;The numerical experiment is first conducted to evaluate the performance of the optimal control in terms of energy production. The simulation results show the mechanical power output (with the consideration of the PTO unit) is nearly the same as the power output predicted by the ideal model (without the consideration of the PTO unit). That indicates the proposed PTO unit can track the optimal control signal accurately.&nbsp;While the simulation results also show the actual electrical power output is poor due to significant power losses (very high current). Then, the performance of the optimal control is numerically simulated with an optimized LEM design. The results show the electrical power output can be significantly improved by limiting the current in the PTO unit. Considering the tracking of the optimal control signal will be jeopardized by limiting the current, the electrical energy production is compared with different levels of current limitations, and an optimal limitation is thus identified. Finally, the energy produced by the proposed system is compared with the energy absorbed by a passive control. The results show the wave energy extraction can be significantly improved by using optimal control and the introduced PTO system (with optimal design).</p>

Control of Wave Energy Converter With Losses in Electrical Power Take-Off System

Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2021/volume/85109

ASME 2021 Power Conference (POWER2021)

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