Output-Constrained Individual Pitch Control using an Adaptive Leaky Integrator for Wind Turbine Blade Load Reductions

Abstract

Wind turbines are getting larger to increase power capacity. Their longer blades sample a larger area of the spatially and temporally varying turbulent wind field, leading to increased periodic blade load and fatigue damage over time. Individual pitch control (IPC) has proven effective in alleviating these loads by pitching the blades. Conventional IPC fully attenuates the periodic blade loads, which requires excessive pitching, leading to additional stresses on the pitch system. To balance pitch actuation and load alleviation, bounds can be set on the pitch signal (input-constrained IPC), or on the load (output-constrained IPC). While input-constrained IPC has been abundantly researched, little research has focused on output-constrained IPC and on the trade-off when operating between full IPC and no IPC. Therefore, we propose an output-constrained IPC method using an adaptive leaky integrator. The natural frequency of the leaky integrator is adapted on the error between the reference and resultant blade moment. This allows the control scheme to attain every load alleviation level between full and no IPC. Furthermore, in realistic turbulent wind conditions, operating close to full IPC leads to diminishing returns, showing that the proposed controller achieves a superior trade-off between load reduction and actuator effort.