Vertical axis wind turbine generator case study: costs and losses associated with variable torque and variable speed strategies

This case study investigates the generator of a large offshore Vertical Axis Wind Turbine (VAWT). In particular this case study focuses on the effect of the inherent cyclic torque loading of the VAWT on the generator in terms of the costs and losses experienced. A spectrum of torque control strategies were created based on the ratio q of the allowed electrical torque variation to the mechanical torque variation. Equations relating the copper and iron losses of the generator to this q factor were established and investigated for a test turbine. In addition the relationship between the allowed variation in electrical torque and the cost of the active materials of the generator was explored.