Fault estimation and fault-tolerant control of the FAST NREL 5-MW reference wind turbine using a proportional multi-integral observer

A proportional multi-integral (PMI) observer scheme is used to reconstruct actuator and sensor faults in large-scale wind turbines. For the nonlinear full-load region, a PMI observer in Takagi-Sugeno form is used. Two different methods are proposed for the observer design: a Lyapunov-based and a modified linear quadratic regulator approach, where the stability is ensured by a negative derivative of the Lyapunov function candidate. The actuator and sensor faults are directly reconstructed from an augmented state-space vector. The control inputs and measurement signal are then modified with the reconstructed fault signals to achieve fault-tolerant control in the presence of faults with a similar behavior to the fault-free case. It is shown by extensive simulation studies that the PMI observer is able the reconstruct offset and ramp-shaped faults with high accuracy. The performance of the fault reconstruction and fault-tolerant control scheme based on a 4-degree-of-freedom observer model is tested in simulations by a high-order 24-degree-of-freedom model with the aeroelastic code FAST by the National Renewable Energy Laboratory. The new results are also compared with those of the previously published fault reconstruction scheme using Takagi-Sugeno sliding-mode observers.