Fault‐tolerant individual pitch control of floating offshore wind turbines via subspace predictive repetitive control

Abstract

Individual pitch control (IPC) is an effective and widely used strategy to mitigate blade loads in wind turbines. However, conventional IPC fails to cope with blade and actuator faults, and this situation may lead to an emergency shutdown and increased maintenance costs. In this paper, a fault‐tolerant individual pitch control (FTIPC) scheme is developed to accommodate these faults in floating offshore wind turbines (FOWTs), based on a Subspace Predictive Repetitive Control (SPRC) approach. To fulfill this goal, an online subspace identification paradigm is implemented to derive a linear approximation of the FOWT system dynamics. Then, a repetitive control law is formulated to attain load mitigation under operating conditions, both in healthy and faulty conditions. Since the excitation noise used for the online subspace identification may interfere with the nominal power generation of the wind turbine, a novel excitation technique is developed to restrict excitation at specific frequencies. Results show that significant load reductions are achieved by FTIPC, while effectively accommodating blade and actuator faults and while restricting the energy of the persistently exciting control action.

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

“…In (6), λ is a forgetting factor (0 λ ≤ 1) to alleviate the effect of past data, and adapt to the varying system dynamics online. In this paper, a value close to 1, i.e., λ = 0.99999, is chosen for the optimization process.…”

“…2. In summary, the Markov matrix Ξk is obtained by solving the RLS optimization in an online recursive manner (6). Then, the constrained repetitive control law is formulated in (9) by solving an MPC optimization problem ( 13)- (19).…”

“…In general, the majority of the loads on wind turbine rotors, showing a periodic nature, is caused by wind shear, tower shadow, turbulence and gravity [6]. Individual Pitch Control *This research was supported by the European Union via a Marie Sklodowska-Curie Action (Project EDOWE, grant 835901).…”

“…The basic idea of SPRC was initially proposed by van Wingerden et al [9], which showed promising results in numerical study [10] and in wind tunnel experiments [11], [12]. Since it is a fully data-driven approach consisting of subspace identification [13] and repetitive control, it was also extended for adaptive fault-tolerant control [6], [14], [15]. The subspace identification, based on an online solution, is used to derive a linear approximation of wind turbine dynamics.…”

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

“…The basic idea of SPRC was initially proposed by van Wingerden et al [9], which showed promising results in numerical study [10] and in wind tunnel experiments [11], [12]. Since it is a fully data-driven approach consisting of subspace identification [13] and repetitive control, it was also extended for adaptive fault-tolerant control [6], [14], [15]. The subspace identification, based on an online solution, is used to derive a linear approximation of wind turbine dynamics.…”