Power quality and grid integration of direct wave energy converters – QUALIPHE

Among all the marine renewable energies, « wave energy » represents a significant part. However, despite the large number of past and present proposed technologies for wave energy conversion, none of these has proven yet its superiority over the others and has been acknowledged as the best solution. There are various reasons for that, resulting to a large extent from direct wave energy converter specific issues : hydrodynamical, mechanical, electrical, control aspects etc. In this project, we will focus on strongly coupled energy transfer featuring different natural dynamics and thus increasing the complexity of energy recovery and power quality control.
We consider here, wave energy converters (WEC) with direct hydro-mechanical conversion (i.e. except for overtopping and oscillating water column devices, but also systems with oleo-pneumatic storage) which constitute the broad majority of currently developed devices and the most promising long term. In this case, one major problem concerns power quality due to the highly fluctuating power resource. An electrical solution is to use electrical energy storage systems, embarked on-board or shared in a farm, in order to smooth the produced electrical power without losing energy productivity. But, in order to consider the problem of power quality in its entirety, one must also consider the smoothing due to spatial dispersion of many converters in a wave farm. A centralized energy storage systems can be considered such as separated embedded energy storage systems centrally managed. The proposed work consist, considering life cycle, in maximizing energy productivity and power quality with an optimized sizing and management of the storage system and optimal control of the wave energy converter.
For the hydrodynamic aspect, the problem mainly concerns the modeling of large amplitude motions of wave energy converters, not only in survival conditions but also in operational conditions.

Then, planned work focuses on
• Sizing methodologies and energy management of supercapacitor based energy storage system for smoothing the electrical output and improve the quality of power, considering for example flicker level as a constraint. The problem will be considered for only one WEC but also for a full farm, and the strong coupling between hydrodynamical, electrical and control aspects will require the use of advances hydrodynamical models even if in a first stage, simplified models will be used.
• The definition of qualitative and quantitative electrical power quality criteria for grid integration (beyond of only flicker).
• Development of waves prediction methods and wave energy converter control in order to optimize the amount and the quality of electrical energy produced
• Development of innovating hydrodynamic numerical simulation tools in order to integrate them in a global energetic model of a direct wave energy converter. According to the dynamics of the machine response, modeling approaches will be based either on linear potential or on non-linear methods.