Abstract
Ocean energy is a field of growing interest when it comes to renewable energy thanks to its high density of energy per unit area, and to the high predictability. Conversion of hydrokinetic energy, found in marine currents, is the utilization of the energy in free-flowing water for conversion to electric energy. This thesis presents experimental data from a test site with a marine current converter.
The converter system features a vertical axis turbine directly connected to a permanent magnet synchronous generator placed on the riverbed. The converter is controlled by an electrical system. The focus of the work is to evaluate power control methods and turbine performance.
Results of a simple voltage control system is presented and compared with operation without control. The turbine type in the converter system is not self-starting. The startup power and energy has been investigated through experiments. The converter system has been connected to the local electric utility grid and the first experimental results are presented.
The performance of the turbine for a range of water speeds is investigated. The range of experiments are limited by the water velocity at the experimental site. To address the issue, a simulation model coupling the electrical system and hydrodynamic model into one has been validated. One factor affecting the turbine's power capture is the angle of the blade pitch relative to the water flow. The influence of blade pitch on turbine performance is studied with experiments and two 3D simulation models.
The possibilities of powering a desalination plant using marine current converters is discussed. Water speed data from outside the east coast of South Africa has been used for a case study. The study investigates how many people can early be supplied with freshwater using the converter system at the experimental site as a model.