Analysis of electrical drive speed control limitations of a power take-off system for wave energy converters

The active control of wave energy converters with oil-hydraulic power take-off systems presents important demands on the electrical drives attached to their pumps, in particular on the required drive accelerations and rotational speeds. This work analyzes these demands on the drives and designs reliable control approaches for such drives by simulating a wave-to-wire model in a hardware in-the-loop simulation test rig. The model is based on a point absorber wave energy converter, being the wave, hydrodynamic and oil-hydraulic part simulated in a computer that sends and receives signals from the real embedded components, such as the drive generator, controller and back-to-back converter. Three different control strategies are developed and tested in this test rig and the results revealed that despite the drive limitations to acceleration levels, well above 1 × 104 rpm/s, these do not significantly affect the power take-off efficiency, because the required acceleration peaks rarely achieve these values. Moreover this drive is much more economical than an oil-hydraulic and equivalent one that is able to operate at those peaks of acceleration.This work was performed within the Strategic Research Plan of the Center for Marine Technology and Ocean Engineering, which is financed by Portuguese Foundation for Science and Technology (Fundacao para a Ciencia e Tecnologia-FCT) and the project "Generic hydraulic power take-off system for wave energy converters" funded by the Portuguese Foundation for Science and Technology (FCT) under contract PTDC/EMS-SIS-1145/2014. The testing has received support from MARINET, a European Community - Research Infrastructure Action under the FP7 "Capacities" Specific Programme, grant agreement nr. 262552. The research leading to these results is also part of the OceaNET project, which has received funding from the European Union's Seventh Framework Programme for research, technological development and demonstration under grant agreement nr. 607656

A review of fault tolerant design in wave energy converters

The main objective of this pape is to presente a review on typical faults including the actual development and application of the fault tolerant design techniques in WEC systems and subsystems. Also, various WEC devices are studied and categorized in three diferente maintenance levels based on the defined criteria in maintenance standard. In this paper, the oscillating body and structure, power take-off system and transmission units, control,safety and survivability units are considered as the essencial componentes of the WEC for fault and failure study. Moreover, several faults are identified and fault tolerant design techniques are proposed for these systems. Moreover, several faults are identified and fault tolerant design techniques are proposed for these systems.info:eu-repo/semantics/publishedVersio

Numerical and experimental analysis of a hybrid wind-wave offshore floating platform’s hull

This paper presents a study regarding a novel hybrid concept for both wind and wave energy offshore. The concept resembles a semi-submersible wind platform with a larger number of columns. Wave Energy Devices such as point absorbers are to be displayed around the unit, capturing wave energy while heaving and also enhancing the stability of the platform. In this paper, a first numerical study of the platform’s hull, without Wave Energy Converters, is carried out. Experiments in wave basin regarding the same unit have been conducted and the results are presented and compared to the numerical ones. Both stability and seakeeping performances are assessed and compared.info:eu-repo/semantics/publishedVersio

Prototyping and wave tank testing of a floating platform with point absorbers

The main aim of this paper is to present the experimental results of a concept of a platform, with several point energy absorbers. A floating circular array of point absorbers, in 1-27 scale, was tested in the wave tank. The hydrodynamic behavior of the platform was studied in different configurations. Moreover, the performance of the platform was assessed in different sea states with and without point absorbers attached to the platform.info:eu-repo/semantics/publishedVersio

On the experimental study of a concentric wave energy array adapted to an offshore floating platform

Experimental results of the dynamics of a small scale concentric wave energy converter array adapted to a floating offshore platform are presented. A small scale prototype is tested without and with twelve conical heaving point absorbers. The free decay and regular wave tests are carried out in an ocean basin to understand the hydrodynamic interactions between various elements of the floating offshore platform and wave energy converter array. Meanwhile, the heave motions of the buoys are observed in regular waves with and without dampers for the initial estimation of power take-off damping as a pitch control module. The results show the improvements in heave, pitch, and roll performance of the platform due to the interaction between the buoys and platform.info:eu-repo/semantics/publishedVersio