Abstract:
Exhaust emission control, especially in case of diesel engines, is a challenging re
search problem as the emission regulating authorities place stringent protocols
against emissions. The air management system of a diesel engine, that is fit
ted 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/cho
king. 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 pos
sible. 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 de
tection, estimation and compensation capability of unified approaches give them
an edge over passive schemes.
