Platform Pitch Motion Suppression for Floating Offshore Wind Turbine in Above-Rated Wind Speed Region

Abstract

A novel control strategy of platform pitch motion suppression is presented for floating offshore wind turbines (FOWTs). System analysis shows that the platform pitch motion acts as unstable zero dynamics, resulting in non-minimum phase characteristics. The proposed strategy consists of a nonlinear generator torque compensator and a multiplicative feedback-based gain-scheduled proportional-integral (GSPI) blade pitch controller. The proposed torque compensator directly compensates the non-minimum phase system to a minimum phase one. It breaks the limitation of the platform pitch motion on the bandwidth of the blade pitch controller. Moreover, the simultaneous multiplicative feedback of rotor speed and platform pitch angular velocity is proposed as a new framework for platform pitch suppression. It gets rid of the requirements by cascade control for decoupled dynamics of dual loops. Meanwhile, a GSPI controller is used to determine the blade pitch angle. Stability proof is given for the proposed method. Compared with the traditional methods, such as PI gain-detuning and cascade control, simulation results demonstrate that the proposed control strategy performs better in platform pitch suppression.