Smart rotors for next generation wind turbines

Abstract

The most visible trend in wind turbine design over the past three decades has been the increasing size of the turbines themselves. This growth has been driven by a desire for increased power production and lower generation costs, and been enabled through the incorporation of improvements to materials, aerodynamic design, and control systems. The latter feature, in the form of active aerodynamic load control, is of particular interest due to its ability to increase the lifetime and reliability of turbine components through the reduction of fatigue loads. Recent developments within literature have proposed the use of trailing edge flaps (TEFs) installed near the blade tips to effect these load reductions, with the combination of these devices along with sensors and existing individual blade pitch control (IPC) strategies forming the ‘smart-rotor’ concept. In this work, a turbine scale-invariant controller synthesis process is developed for IPC and TEFs for the purpose of reducing blade root fatigue loads. The performance of the controllers obtained using this process is evaluated on a range of current and nextgeneration turbine models using simulations over the operating range of the turbines. The controller synthesis process is then integrated into a blade optimisation procedure, wherein aerodynamic and structural design variables are selected to minimise the levelised cost of energy (LCOE). The inclusion of the controller synthesis process enables the effects of IPC and TEFs to be included in the optimisation of the wind turbine blades. The effectiveness of the controller synthesis process is demonstrated on a range of turbines with ratings from 5–20 MW, where significant and consistent blade root fatigue load reductions are obtained when IPC and TEF actuation are used on top of existing collective pitch control (CPC). The blade optimisation procedure is then run with blades from 5–20 MW turbines with combinations of CPC, IPC and TEFs. The optimisation procedure results in turbines with a lower LCOE, and lighter and cheaper blades. The inclusion of IPC and TEFs enables further reductions in the LCOE, blade mass and cost relative to blades optimised with CPC only. From the blade optimisation procedure, blade deflection, rotor thrust and flatwise extreme loads were identified as important design drivers.