Control strategy of offshore marine energy converters for improving reliability availability and cost effectiveness
Portugal Rosas, Isaac
High–energy density places in the sea are typically located some kilometres away from the shores. Harvesting energy from these sites is desirable but defiant. In these areas, one of the challenges is the harsh weather conditions, which may limit the maintenance accessibility of electrical generators. The nature of the marine resources (i.e. turbulence and wave spectrum) could create high-load patterns that may jeopardise the reliability and economic feasibility of entire projects. Thus, reliability of marine energy converters becomes a key challenge for engineers. Most marine energy devices are being designed to allow the usage of off–the–shelf electrical generators. At the cost of dismissing potential benefits of especially designed machines, developers are focusing their efforts in optimising the hydro-dynamic and aerodynamic performance of the devices. Stress-levels seen by the electrical machine are device dependant. The work here presented is focused on an oscillating water column (OWC). This is a system using a semi open chamber with one opening semi submerged under the sea and the other directed to a duct. The air pushed and sucked by the waves is forced to pass through an air turbine that extracts energy from the moving fluid. The turbine is then attached to an electrical generator for a final energy conversion. The key aspect of this work is to present a proposed methodology that could be used to extend the life of a machine. The methodology first consists on defining the life of a generator as a single variable phenomenon. Second, the methodology is assuming that a deterioration model can be used as a proxy for estimating the life of the generator. Third, the in–service load profile is calculated by modelling a generator in an OWC. Lastly, with the load profile and the life estimated from the generator, a power management technique is demonstrated.