Sliding Mode Framework Based Fault Tolerant Control for Air Path Actuators of a Turbocharged Diesel Engine.
Exhaust emission control, especially in case of diesel engines, is a challenging research problem as the emission regulating authorities place stringent protocols against emissions. The air management system of a diesel engine, that is fitted with Variable Geometry Turbocharger (VGT) and Exhaust Gas Recirculation (EGR) actuators, is among the sub-systems, whose effective control ensures that emissions are kept to minimum. Both EGR and VGT sub-systems are located in the engine exhaust channel, hence, they are strongly coupled and exposed to high temperatures, un-burnt hydrocarbons and lubricants and thus prone to faults/choking. One way to increase tolerance against faults is to have redundancy. Diesel engines do not have high number of identical actuators to preserve satisfactory operation, but, still have prospects for enhancing the reliability of these control loops by constructing algorithms, that are capable of performing online detection, diagnosis, estimation and compensation of faults. This research investigates the possible options for development of Fault Tolerant Control (FTC) schemes for coordinated control of air management system actuators of diesel engine. The dynamic nature of a control system and real time environment of Fault Detection and Isolation (FDI) and controller re-configuration requires FTC system to be capable of detecting, identifying and accommodating the faults as swiftly as possible. To meet the purpose, unified and systematic design techniques need to be developed to guarantee swift integration of FDI and FTC schemes, such that, the faults are handled in an early design phase by extending the control system with additional modules, i.e., FDI module. The model used in this research is a fully validated industrial scale Mean Value Model of a diesel engine that is equipped with VGT and EGR actuators. It has eight states and three control inputs. Two types of approaches i.e., passive FTC and unified FDI and FTC with further two algorithms of each have been proposed based on the sliding mode framework. The simulation results have shown that the proposed controllers can comfortably meet strict emission regulations even in the event of system faults. Specially fault detection, estimation and compensation capability of unified approaches give them an edge over passive schemes.