Time series analysis-based adaptive tuning techniques for a heaving wave energy converter in irregular seas

Abstract

The paper presents a time domain model of a heaving buoy wave-energy converter and investigates the tuning problem in irregular seas. The tuning issue is addressed by employing both fixed (passive) and adaptive (active) power-take-off settings. The fixed power-take-off tuning approach includes models based on tuning the device natural frequency to either the energy frequency or peak frequency of the sea-state or a weighted average of several peak frequencies. The adaptive tuning approaches employ a sliding discrete Fourier transform frequency analysis, or a time-series analysis of the measured wave elevation and device velocity to estimate a localized dominant wave frequency and hence calculate power-take-off settings. The paper presents details of these tuning techniques by discussing issues related to the modelling, simulation, and predicted power captures for each method. A comparative study of each method along with practical implications of the results and recommendations are also presented.

Large-scale ocean wave energy plant modeling

“…Yavuz et. al also modeled a single heaving buoy to compare different PTO tuning strategies [14], [15]. These papers were used as a point of reference for their overall model structure, but were limited in that they only modeled one body with the PTO connected directly to the sea floor, and did not include external mooring forces.…”

“…Assuming the nitrogen gas to be isentropic, the pressure in each accumulator as a function of time can be determined using the relationship defined in Eq. (15).…”

“…(12), (14) and (15) is shown in Figure 6. The LP Accumulator subsystem is very similar to Figure 6, except it implements Eqs.…”

Developments, expectations of wave energy converters and mooring anchors in the UK

“…A number of devices have been conceived and studied, including the Lancaster Flexible Bag (Chaplin and French, 1980), the Flounder, the Frog, the PS Frog (Aggidis et al, 2005;McCabe et al, 2006), and the Frond (Taylor et al, 2002), and generic research has been carried out into the theory of WECs, their systematic design and economic study (Budal and Falnes, 1980;French and Bracewell, 1995;Yavuz et al, 2007;Stallard et al, 2007).…”

A resistance emulation approach to optimize the wave energy harvesting for a direct drive point absorber

“…In this type of tuning, the sea state is taken into account to calculate the optimal damping coefficient. On the other hand, active tuning is based on estimating the dominant wave frequency by an analysis of measured wave elevation and device velocity [11]. The fact that the incoming wave has to be known brings some difficulty to this method.…”