Super twisting controller-based unified FDI and FTC scheme for air path of diesel engine using the certainty equivalence principle

This paper proposes a combination of higher order sliding mode and adaptive control for unified fault detection and isolation and fault tolerant control (FTC) of the air path of a diesel engine. Current diesel engines are equipped with features such as variable geometry turbochargers (VGT) and exhaust gas recirculation (EGR) for exhaust emission control. Since EGR and VGT systems are present in the exhaust channel, they are strongly coupled and are prone to both structured as well as unstructured faults. The proposed controller detects and estimates the structured faults by means of adaptation laws, designed by making use of the certainty equivalence principle. Fault effects are compensated by repositioning the actuators. This allows relaxation of the boundedness condition of the super twisting algorithm, as sliding mode controller gains are required to dominate the unstructured parts only, which consequently reduces chattering. A nonlinear multi-input multi-output reduced state control-oriented model has been employed for working out the FTC strategy for EGR and VGT actuators. The stability of the overall system has been analysed using the Lyapunov stability criterion. Faults and proposed controllers are simulated using a fully validated industrial scale diesel engine model to establish the effectiveness of the algorithm.