Periodic Load Rejection for Floating Offshore Wind Turbines via Constrained Subspace Predictive Repetitive Control

TL;DR

This paper presents a constrained Subspace Predictive Repetitive Control method for floating offshore wind turbines that effectively reduces blade loads while respecting pitch actuator safety limits, enhancing reliability and lifespan.

Contribution

It introduces a data-driven, model predictive control approach that incorporates physical actuator constraints into load mitigation control for offshore wind turbines.

Findings

Reduces pitch activity during turbulent conditions.

Prevents future actuator constraint violations.

Extends pitch system lifespan and reliability.

Abstract

Individual Pitch Control (IPC) is an effective control strategy to mitigate the blade loads on large-scale wind turbines. Since IPC usually requires high pitch actuation, the safety constraints of the pitch actuator should be taken into account when designing the controller. This paper introduces a constrained Subspace Predictive Repetitive Control (SPRC) approach, which considers the limitation of blade pitch angle and pitch rate. To fulfill this goal, a model predictive control scheme is implemented in the fully data-driven SPRC approach to incorporate the physical limitations of the pitch actuator in the control problem formulation. An optimal control law subjected to constraints is then formulated so that future constraint violations are anticipated and prevented. Case studies show that the developed constrained SPRC reduces the pitch activities necessary to mitigate the blade loads when experiencing wind turbulence and abrupt wind gusts. More importantly, the approach allows the wind farm operator to design conservative bounds for the pitch actuator constraints that satisfies safety limitations, design specifications and physical restrictions. This will help to alleviate the cyclic fatigue loads on the actuators, increase the structural reliability and extend the lifespan of the pitch control system.