Dynamically allocated individual pitch control for fatigue load reduction in wind turbines

Abstract

This article presents multivariable control designs to improve performance and reduce fatigue loads in wind turbines using torque control, Collective Pitch Control (CPC), and Individual Pitch Control (IPC). Two multi-input, multi-output (MIMO) control structures are proposed in this study. The first approach uses force distribution on blades to design the IPC, while the second uses the Relative Gain Array (RGA), which quantifies the level of interactions between inputs and outputs, to design the IPC. Both approaches use the same torque control and CPC. This work emphasizes the second approach, i.e., the RGA-based IPC. A novel aspect of this approach is the dynamic allocation of IPC, which refers to the change in the input–output pairing as a function of the rotor azimuth angle. The frequency-dependent characteristics of this allocation facilitate fatigue load reduction at targeted frequencies. Extensive simulations show that the RGA-based IPC controller outperforms the first controller in reducing cyclic loads on the blade root bending moment, tower side-to-side, and tower fore-aft bending moments at the frequencies of interest. Moreover, it has no detrimental effects on the rotor speed and power generation, which are regulated by the CPC and torque controller. A Control-oriented, Reconfigurable, and Acausal Floating Turbine Simulator (CRAFTS), developed in-house, is used for design, implementation, and evaluation.