Individual pitch controller with static inverted decoupling for periodic blade load reduction on monopile offshore wind turbines

Abstract

Individual pitch control (IPC) is a technique used to reduce periodic blade loads in wind turbines. It generally uses the multiblade coordinate transformation to convert blade load measurements from a rotating frame into a two-axes non-rotating frame. Although these non-rotating axes are assumed to be decoupled, studies reveal persistent interactions. Reducing this coupling, such as by introducing an azimuth offset, enhances IPC performance. This study explores the impact of static inverted decoupling, which decouples the process in the steady state, on IPC performance. The proposed IPCs are adaptive, scheduling controller and decoupling gains based on operational conditions. In such IPC designs, the integral gains of the diagonal controllers and the decoupling elements can either be the same or different. These methods were validated on a simulated 15 MW wind turbine. Controller parameter optimization was accomplished through genetic algorithms to minimize blade fatigue loads, measured via the damage equivalent load (DEL). Results indicate that incorporating static inverted decoupling into IPC improves blade load reduction without increasing pitch actuator effort. IPCs with similar integral gains and matching absolute values in decoupling elements achieved the best balance between DEL reduction and complexity with minimal actuator effort, while additional optimization parameters provided negligible improvements.