Active fault tolerant control design for uncertain strict-feedback non-linear systems

This study proposes an active fault tolerant control (FTC) scheme for uncertain strict-feedback non-linear systems. Changes in the system dynamics due to faults are modelled as unknown non-linear functions of the measurable state variables. The scheme is composed of fault detection and estimation (FDE) module, accommodation mechanism and nominal controller based on the dynamic surface control (DSC). The FDE module, composed of a diagnostic estimator and an adaptive non-linear-in parameter (NLIP) approximator, generates the residual signal, detects and estimates fault simultaneously. Robust adaptive laws are derived for learning all parameters of an adaptive NLIP approximator. After FDE, accommodation mechanism uses the generated fault information to construct the corrective control law to compensate the fault effects. The proposed active FTC system detects and estimates unknown fault and constructs a corrective control law to reduce the effects of fault on the system without the need for fault isolation module. Unlike most of the traditional active FTC schemes, the proposed scheme requires no prior knowledge about the faulty situations, offline computational cost and fault isolation module. It is proven that all signals of the closed loop system are uniformly ultimately bounded. Simulation results illustrate the effectiveness of the proposed scheme.