# Pseudo-spectral control of a novel oscillating surge wave energy converter in regular waves for power optimization including load reduction

## Abstract

The aim of this study is to describe a procedure to maximize the power-to-load ratio of a novel wave energy converter (WEC) that combines an oscillating surge wave energy converter with variable structural components. The control of the power-take-off torque will be on a wave-to-wave timescale, whereas the structure will be controlled statically such that the geometry remains the same throughout the wave period. Linear hydrodynamic theory is used to calculate the upper and lower bounds for the time-averaged absorbed power and surge foundation loads while assuming that the WEC motion remains sinusoidal. Previous work using pseudo-spectral techniques to solve the optimal control problem focused solely on maximizing absorbed energy. This work extends the optimal control problem to include a measure of the surge foundation force in the optimization. The objective function includes two competing terms that force the optimizer to maximize power capture while minimizing structural loads. A penalty weight was included with the surge foundation force that allows control of the optimizer performance based on whether emphasis should be placed on power absorption or load shedding. Results from pseudo-spectral optimal control indicate that a unit reduction in time-averaged power can be accompanied by a greater reduction in surge-foundationmore »

- Authors:

- National Renewable Energy Lab. (NREL), Golden, CO (United States)

- Publication Date:

- Research Org.:
- National Renewable Energy Lab. (NREL), Golden, CO (United States)

- Sponsoring Org.:
- NREL Laboratory Directed Research and Development (LDRD); USDOE Office of Energy Efficiency and Renewable Energy (EERE), Wind and Water Technologies Office (EE-4W); USDOE Office of Energy Efficiency and Renewable Energy (EERE), Water Power Technologies Office (EE-4WP)

- OSTI Identifier:
- 1357747

- Alternate Identifier(s):
- OSTI ID: 1415660

- Report Number(s):
- NREL/JA-5000-65123

Journal ID: ISSN 0029-8018

- Grant/Contract Number:
- AC36-08GO28308

- Resource Type:
- Accepted Manuscript

- Journal Name:
- Ocean Engineering

- Additional Journal Information:
- Journal Volume: 137; Journal Issue: C; Journal ID: ISSN 0029-8018

- Publisher:
- Elsevier

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 16 TIDAL AND WAVE POWER; oscillating surge wave energy converter; variable structures; load shedding; convex optimization; nonlinear optimization; psuedo-spectral control

### Citation Formats

```
Tom, Nathan M., Yu, Yi -Hsiang, Wright, Alan D., and Lawson, Michael J. Pseudo-spectral control of a novel oscillating surge wave energy converter in regular waves for power optimization including load reduction. United States: N. p., 2017.
Web. doi:10.1016/j.oceaneng.2017.03.027.
```

```
Tom, Nathan M., Yu, Yi -Hsiang, Wright, Alan D., & Lawson, Michael J. Pseudo-spectral control of a novel oscillating surge wave energy converter in regular waves for power optimization including load reduction. United States. doi:10.1016/j.oceaneng.2017.03.027.
```

```
Tom, Nathan M., Yu, Yi -Hsiang, Wright, Alan D., and Lawson, Michael J. Tue .
"Pseudo-spectral control of a novel oscillating surge wave energy converter in regular waves for power optimization including load reduction". United States. doi:10.1016/j.oceaneng.2017.03.027. https://www.osti.gov/servlets/purl/1357747.
```

```
@article{osti_1357747,
```

title = {Pseudo-spectral control of a novel oscillating surge wave energy converter in regular waves for power optimization including load reduction},

author = {Tom, Nathan M. and Yu, Yi -Hsiang and Wright, Alan D. and Lawson, Michael J.},

abstractNote = {The aim of this study is to describe a procedure to maximize the power-to-load ratio of a novel wave energy converter (WEC) that combines an oscillating surge wave energy converter with variable structural components. The control of the power-take-off torque will be on a wave-to-wave timescale, whereas the structure will be controlled statically such that the geometry remains the same throughout the wave period. Linear hydrodynamic theory is used to calculate the upper and lower bounds for the time-averaged absorbed power and surge foundation loads while assuming that the WEC motion remains sinusoidal. Previous work using pseudo-spectral techniques to solve the optimal control problem focused solely on maximizing absorbed energy. This work extends the optimal control problem to include a measure of the surge foundation force in the optimization. The objective function includes two competing terms that force the optimizer to maximize power capture while minimizing structural loads. A penalty weight was included with the surge foundation force that allows control of the optimizer performance based on whether emphasis should be placed on power absorption or load shedding. Results from pseudo-spectral optimal control indicate that a unit reduction in time-averaged power can be accompanied by a greater reduction in surge-foundation force.},

doi = {10.1016/j.oceaneng.2017.03.027},

journal = {Ocean Engineering},

number = C,

volume = 137,

place = {United States},

year = {2017},

month = {4}

}

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