Wave, tidal and off-shore wind energy compose direct and easy ways of harnessing power from the Ocean.
Among the different wave energy converters used, Oscillating Water Column devices stand out as one of the most promising ones. Schematically, the main objective of the group at this stage is the theoretical, modeling, simulation and experimental control studies on distributed wave power generation systems using an OWC converter, which is made up of the capture chamber, the Wells turbine, the double fed induction generator (DFIG) and the network. The group has currently the following research objectives:
- Background studies so as to obtain an updated state of the art on the devices that have been developed to obtain renewable energy from the sea, with special emphasis on wave energy, explaining the different existing power converters with a special interest in the OWC device. Summarize the various wave theories, so as to apply the most adequate to the characteristics of the location of the OWC drive system. Improvement of the numerical model currently used by the group -composed by the capture chamber, Wells turbine and DFIG- so as to allow for the study of the system dynamics as faithfully as possible.
- Accurately simulate the OWC operation and develop a new model of the capture chamber, which will then be implemented. Describe the main features of the Wells turbine operation to improve the modeling with the aim of implementing the controls in different structures, such as NEREIDA MOWC (in collaboration with EVE) or floating off-shore wind platform (in collaboration with UPM). Justify the choice of the doubly-fed generator (DFIG) as a link between the Wells turbine and the grid, explaining its way of operation, equations and model. Analyze the back to back converter that has been used, its component design and adaptation, in particular the rotor side converter (RSC), DC-link, and grid side converter (GSC).
- Advanced controller design in order to solve some of the problems that have been raised on distributed energy converter devices such as fault-ride-through capability during voltage drops. In the OWC system controllability of the active and reactive power is needed to fulfill the European Grid Code. Besides, different control algorithms to optimize the power output avoiding issues such as the stalling behavior of the wells turbine shall be further developed.
- The group is currently involved in a small international project involving wave mapping in order to compare the energy production of various devices when located in different areas.
The aim of the NEREIDA MOWC project, promoted by the Basque Energy, Ente Vasco de Energía-EVE, is to demonstrate the feasibility of the OWC technology with Wells turbine power take-off into a newly constructed breakwater in Mutriku (Guipuzcoa).
It consist of 16 turbines, each of them with a generation power of 18.5kW that provide a total power of 296kW.
Mutriku Wave Plant was inaugurated in July 2011 and produced 200kWh during the 1st year. The estimated production is 600kWh per year. Although the difference was mainly due to a storm that damaged the control room and kept the facility closed during the best wave months, an improvement in the power generation could highly benefit the system.
Since one of the main objectives when dealing with renewable energies is to make them economically viable to compete with fossil fuels and nuclear fission, all technological improvements are particularly welcome. In this context, this research line deals with control schemes for OWC wave power generation plants that allow to avoid the undesired stalling phenomenon present in Wells turbines while maximizing the power output. The proposed controllers appropriately adapt the rotational speed according to the pressure drop entry. The results show that the system avoids the stalling behavior and that the active power of the generator fed into the grid is significantly higher in the controlled case than in the uncontrolled one.