Individual pitch control with two azimuth offsets in the reverse multiblade coordinate transformation for reducing periodic blade loads in wind turbines

Individual pitch control (IPC) is commonly used to mitigate periodic blade loads in wind turbines, relying on the multiblade coordinate (MBC). Although the transformed axes are theoretically decoupled, practical implementations exhibit persistent interactions. Prior studies have shown that introducing an azimuth offset in the reverse MBC transform or applying static inverted decoupling reduces these interactions. This study proposes an extended IPC formulation that introduces two independent azimuth offsets in the MBC transformation, enabling separate phase compensation of the tilt and yaw components. The approach is analytically shown to be equivalent to static inverted decoupling, providing a unified interpretation of decoupling-based IPC strategies. Design expressions based on the steady-state gain matrix of the 2 × 2 IPC process are provided, along with practical guidelines for upgrading existing IPCs by adjusting controller gains when offsets or decoupling are introduced. The proposed methods are evaluated on the IEA 15-MW reference wind turbine using OpenFAST at a nominal operating point. Multi-objective optimization is employed to tune several IPC schemes and assess the trade-off between blade fatigue reduction and pitch actuator activity. Results show that optimized azimuth offset IPC reduces blade damage equivalent loads by 6–9% with control effort comparable to conventional IPC, while steady-state based designs achieve 4–6% reductions. The two-offset scheme provides the greatest flexibility, although improvements over a single offset remain modest due to similar optimal offset values.