Abstract
Maximising average power over a whole tidal cycle will increase revenue, and reducing unexpected maintenance will reduce operation and maintenance cost. Both of these help to reduce levelized cost of energy, in order to enhance tidal energy competitiveness. This paper presents a novel control strategy which aims to reduce the loadings on tidal current turbines, while still enabling a significant amount of the available power to be extracted. The control strategy is based on adjusting the axial induction factor, in which the tip-speed ratio and blade pitch angle degrees are altered from optimum point simultaneously based on the temporally-variable incoming flow speed. A detailed electromechanical model of a 1.5MW three-bladed variable-pitch horizontal-axis tidal turbine, from resource to the grid, is established in MATLAB/Simulink to test this control strategy. The impact of non-optimum operation on electrical subsystems is studied. Results show that the variation in torque and thrust force on turbine blades can be reduced by increasing the rotor speed and blade pitch angle. In addition, fatigue loading mitigation does not cause adverse effects on power generation.