Performance Comparison of Offline and Real-Time Models of a Power Take-Off for Qualification Activities of Wave Energy Converters

This paper examines the economic advantages and disadvantages of multi-axis point absorber wave energy converters in comparison to conventional heave-only point absorbers. A multi-axis point absorber wave energy converter (MA-PAWEC) is classified as a point absorber device that has a power take off (PTO) system extracting energy from more than one mode of motion (e.g. heave and surge). The majority of existing point absorber devices operate in heave mode alone. Therefore the forces exerted along other axes must be resisted by the mooring system, any reciprocal component of which constitutes a wasted opportunity to extract energy. The economics of PAWECs are governed by the available resource, energy generated by the device, capital cost and operational cost. These factors are examined for MA-PAWECs and compared to a generic heave-PAWEC. For a performance comparison, a simple generic body PAWEC is examined under heave mode operation and multi-axis operation in a representative spectrum. The modelling is based on linear potential theory. The potential advantages of MA-PAWECS are identified as greater energy absorption, fewer installed devices for a given capacity, and greater array control. Disadvantages include higher capex, higher maintenance costs and sensitivity to PTO costs. The performance and costs are assigned an estimated economic scaling factor and are applied to a generic heave-PAWEC for an economic comparison of the two devices. This indicates that a multi-axis approach to point absorbers could offer a 21% lower cost of electricity than the incumbent heave-response devices.

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Short-term wave forecasting with AR models in real-time optimal control of wave energy converters

2010 IEEE International Symposium on Industrial Electronics ◽

10.1109/isie.2010.5637714 ◽

2010 ◽

Cited By ~ 7

Author(s):

Francesco Fusco ◽

John V. Ringwood

Keyword(s):

Optimal Control ◽

Real Time ◽

Wave Energy ◽

Time Optimal Control ◽

Short Term ◽

Wave Energy Converters ◽

Time Optimal ◽

Wave Forecasting ◽

Ar Models ◽

Energy Converters

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Real-Time Passive Control of Wave Energy Converters Using the Hilbert-Huang Transform * *This work was partially supported by CNPq-Brazil under grant number 201773/2015-5.

IFAC-PapersOnLine ◽

10.1016/j.ifacol.2017.08.2502 ◽

2017 ◽

Vol 50 (1) ◽

pp. 14705-14710 ◽

Cited By ~ 3

Author(s):

Paula B. Garcia-Rosa ◽

Geir Kulia ◽

John V. Ringwood ◽

Marta Molinas

Keyword(s):

Real Time ◽

Wave Energy ◽

Passive Control ◽

Hilbert Huang Transform ◽

Wave Energy Converters ◽

Energy Converters

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Short-Term Wave Forecasting for Real-Time Control of Wave Energy Converters

IEEE Transactions on Sustainable Energy ◽

10.1109/tste.2010.2047414 ◽

2010 ◽

Vol 1 (2) ◽

pp. 99-106 ◽

Cited By ~ 128

Author(s):

Francesco Fusco ◽

John V Ringwood

Keyword(s):

Real Time ◽

Wave Energy ◽

Real Time Control ◽

Short Term ◽

Wave Energy Converters ◽

Time Control ◽

Wave Forecasting ◽

Energy Converters

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A Real-Time Detection System for the Onset of Parametric Resonance in Wave Energy Converters

Journal of Marine Science and Engineering ◽

10.3390/jmse8100819 ◽

2020 ◽

Vol 8 (10) ◽

pp. 819

Author(s):

Josh Davidson ◽

Tamás Kalmár-Nagy

Keyword(s):

Control System ◽

Real Time ◽

Parametric Resonance ◽

Wave Energy ◽

Detection System ◽

Maximum Amplitude ◽

Recursive Least Squares ◽

Wave Energy Converters ◽

Real Time Detection ◽

Energy Converters

Parametric resonance is a dynamic instability due to the internal transfer of energy between degrees of freedom. Parametric resonance is known to cause large unstable pitch and/or roll motions in floating bodies, and has been observed in wave energy converters (WECs). The occurrence of parametric resonance can be highly detrimental to the performance of a WEC, since the energy in the primary mode of motion is parasitically transferred into other modes, reducing the available energy for conversion. In addition, the large unstable oscillations produce increased loading on the WEC structure and mooring system, accelerating fatigue and damage to the system. To remedy the negative effects of parametric resonance on WECs, control systems can be designed to mitigate the onset of parametric resonance. A key element of such a control system is a real-time detection system, which can provide an early warning of the likely occurrence of parametric resonance, enabling the control system sufficient time to respond and take action to avert the impending exponential increase in oscillation amplitude. This paper presents the first application of a real-time detection system for the onset of parametric resonance in WECs. The method is based on periodically assessing the stability of a mathematical model for the WEC dynamics, whose parameters are adapted online, via a recursive least squares algorithm, based on online measurements of the WEC motion. The performance of the detection system is demonstrated through a case study, considering a generic cylinder type spar-buoy, a representative of a heaving point absorber WEC, in both monochromatic and polychromatic sea states. The detection system achieved 95% accuracy across nearly 7000 sea states, producing 0.4% false negatives and 4.6% false positives. For the monochromatic waves more than 99% of the detections occurred while the pitch amplitude was less than 1/6 of its maximum amplitude, whereas for the polychromatic waves 63% of the detections occurred while the pitch amplitude was less than 1/6 of its maximum amplitude and 91% while it was less than 1/3 of its maximum amplitude.

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