  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 operational 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.
