Novel parameter settings for gain-scheduled feedback control of rotational speed in a floating offshore wind turbine–generator system

Abstract

Novel parameter settings for gain-scheduled feedback control of rotational speed using collective blade pitch manipulation in a spar-buoy floating offshore wind turbine–generator system were developed in order to reduce both power-output fluctuation and platform motion. The development was conducted through numerical simulation using the aeroelastic simulation model (FAST), measured high wind speed data, and simulated irregular sea waves. In this gain-scheduled feedback control of rotational speed, a proportional-plus-integral action was employed, and the proportional gain was varied to the blade pitch angle. First, the sensitivity analysis of the control parameter settings, that is, the proportional gain, integral time, and the generator torque manipulation strategy, to the system performances was carried out. Then, a new guideline of parameter settings for the gain-scheduled feedback control was theoretically revealed by investigating the damped oscillation characteristics of the feedback control loop. Novel parameter settings yielded a natural frequency of the feedback control loop higher than that of the platform pitching motion and a damping coefficient larger than 1.0. Under these parameter settings, the platform pitching motion was similar to that under settings previously developed for this floating offshore system, while the power-output fluctuation was drastically reduced. High power–generation performance and a significant reduction in the damage equivalent fatigue loads at the main parts of the system were also obtained.