Cost and Efficiency analysis of the Secondary electric machine in a CRAFT wind turbine

Abstract Floating offshore wind turbines are ideal for deeper waters, providing access to stronger and more stable winds. The Counter-Rotating Axis Floating Tilting (CRAFT) turbine features a unique design with two counter-rotating turbines on a tilted vertical shaft and two independent electrical machines submerged below sea level. The primary generator, connected to both turbines, includes counter-rotation which doubles the relative torque, while the secondary machine controls the upper turbine. This study examines the impact of primary and secondary machine efficiency on electricity generation. The findings indicate that the primary generator’s efficiency is crucial for system stability, whereas the secondary machine’s efficiency is less critical. Reducing the secondary machine’s efficiency from 97% to 83% resulted in a 0.1% reduction in annual electricity generation. Despite the asynchronous machine’s lower efficiency, it is the economically favorable choice as the secondary machine over its synchronous counterpart due to its reduced design complexity and lower magnet costs, leading to lower overall expenses. Future research investigate how turbulent flow effects and airflow interactions between the turbines influences the model. Incorporating the cooling factor, a more comprehensive cost model and a refined dynamic stall model will also further improve the simulation’s accuracy and robustness.