  Motivated by the increasing concerns over environmental challenges such as
global warming and the exhaustion of fossil-fuel reserves, the renewable energy
industry has become the most demanded electrical energy production source
worldwide. In this context, wind energy conversion systems (WECSs) are the most
dominant and fastest-growing alternative energy production technologies,
playing an increasingly vital role in renewable power generation. To tackle the
pitch control problem of WECSs, this thesis proposes an optimal fault-tolerant
fractional-order pitch control strategy for pitch angle regulation of WT blades
subjected to sensor, actuator, and system faults. To showcast the effects of
faults, changes in the system parameters are considered as a result of sensor,
actuator and system faults with various levels of severity.} Furthermore,
taking advantage of the favourable merits of higher-order SMCs and fractional
calculus, this thesis develops a fault-tolerant fractional-calculus-based
higher-order sliding mode controller for optimum rotor speed tracking and power
production maximization of WECSs. \textcolor{black}{The partial loss of the
generator output torque is considered as an actuator failure, leading to loss
of partial actuation power. Moreover, active fault-tolerant fractional-order
higher-order SMC strategies are developed for rotor current regulation and
speed trajectory tracking of doubly-fed induction generator (DFIG) -driven
WECSs subjected to model uncertainties and rotor current sensor faults. The
developed controllers are augmented with two state observers, an algebraic
state estimator and a sliding mode observer, to estimate the rotor current
dynamics during sensors' faults.
