The model of a three-degree-of-freedom Wave Energy
Converter can be simplified as a linear time-varying system.
In this model, the heave mode parametrically excites the pitch
mode, which in turn excites the surge mode. The heave mode,
however, is independent to the other two modes when the motion
is small. The purpose of this paper is to design a controller to
maximize the energy harvested over a receding time horizon.
We also want to demonstrate that, with proper design of the
control, it is possible to exploit this nonlinear coupling between
the modes so as to harvest more energy. The controller selected is
the linear quadratic Gaussian optimal control. The prediction of
excitation forces is constructed based on the estimation where the
estimations are obtained by using extended Kalman Filter. The
prediction of excitation force is fed into the controller to compute
the time-varying linear quadratic optimal control. Constraints on
the WEC motion are accounted for in computing the control. The
results show that the energy captured by three-degree-of-freedom
Wave Energy Converter is 3:56 times the energy extracted in
heave mode only. Higher energy harvesting is demonstrated when
the linear time-varying model is used in control design.
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Control of Wave Energy Converters Using A Simple Dynamic Model
This paper derives a control law within the context of optimal control theory for a heaving wave energy converter (WEC) and presents its implementation procedure. The proposed control assumes the availability of measurements of pressure distribution on the buoy surface, buoy position, and buoy velocity. This control has two main characteristics. First, this control is derived based on a simple dynamic model. The forces on the WEC are modeled as one total force, and hence there is no need to compute excitation or radiation forces. Second, this control can be applied to both linear and nonlinear WEC systems. The derived control law is optimal, yet its implementation requires estimation of some force derivatives which render the obtained control force sub-optimal. Numerical testing demonstrates in this paper that the proposed simple model control can achieve levels of harvested energy close to the maximum theoretical limit predicted by singular arc control in the case of linear WEC systems.
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- Award ID(s):
- 1635362
- NSF-PAR ID:
- 10081489
- Date Published:
- Journal Name:
- IEEE Transactions on Sustainable Energy
- ISSN:
- 1949-3029
- Page Range / eLocation ID:
- 1 to 1
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1109/TSTE.2018.2838768
