  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.
