Investigation on PTO control of a Combined Axisymmetric Buoy-WEC(CAB-WEC)

Abstract

The Combined Axisymmetric Buoy (CAB), a vertical axisymmetric buoy, has the potential to deliver a high energy absorption power. Considering the CAB-Wave Energy Converters (WEC), in order to achieve higher efficiency, the Power Take Off (PTO) systems, which converts the float motion into energy output, needs to be properly controlled. In this paper, a PTO control method for a CAB-WEC under irregular wave conditions is proposed. Based on the semi-analytical solution obtained in the time domain, a numerical optimization is carried out. The optimal PTO damping coefficients under different wave conditions are obtained, by considering the parameter defined as "capture width ratio". The expression of the optimal PTO damping coefficient in the frequency domain is derived by an analytical method. Based on the semi-analytical solution of time domain dynamic characteristics and analytical method, a comparison between frequency domain optimization and time domain optimization is presented. In general, the two approaches arrive to very similar conclusions, even if with the time domain methodology a slightly higher capture width ratio is achieved. The experimental results have been used to validate the time domain optimization method and the variation in optimal average capture width ratio results.

Control Strategies for Power Enhancement and Fatigue Damage Mitigation of Wave Cycloidal Rotors

“…The rotor operates near the water surface but remains submerged with interaction between the foils and waves generating lift forces on the foils, which then sustains the rotation of the device to generate electric power. The use of lift forces, due to the wave hydrofoil interaction, contrasts with more traditional WECs, whose designs exploit buoyancy and/or diffraction forces [14,16,35,48,54]. At the same time, control technology is reaching a level of maturity for classical WECs [44,43], including experimental validation [10,20,29], while specific control strategies for wave cycloidal rotors are a topic of current research and development [21,22,40].…”

Energy conversion and hydrodynamic analysis of multi-degree-of-freedom wave energy converters integrated into a semi-submersible platform

“…Kim et al [11] put forward a concentric dual-buoy WEC which consists of external buoy with circular attachment and cylindrical internal buoy in moon-pool, and investigated its hydrodynamic performance under various wave conditions. Kong et al [12] analyzed numerically and experimentally the power take-off (PTO) optimization scheme of a combined axi-symmetric buoy (CAB) subjected irregular wave loads, revealing that there is an optimal PTO daming for the average energy extraction under each spectral peak period. Subsequently, Guo et al [13] presented an absorption two-degree-of-freedom (TDOF) WEC with coaxial symmetrical articulated points, and simulated the energy extraction performance generated by the coupled motions of heave and pitch using a viscous-folw model.…”

Assessment of a Hydrokinetic Energy Converter Based on Vortex-Induced Angular Oscillations of a Cylinder

“…Driven by the need to increase the percentage of renewable sources in the energy-production mix during the last decade, much research has focused on the development and advancement in science, technology, and engineering of wave, wind, and current energy converters, primarily in offshore installations [1][2][3][4]. Conventional devices harnessing the kinetic energy of water currents are usually based on propeller-like turbines, which require relatively high current speeds of above 1 m/s.…”