Improved disturbance rejection and tracking control of time-delayed systems: Application to engine air-fuel ratio control

Many dynamic systems contain output time delays due to transport or process elements or other phenomena. This work explores the use of time-delay system control techniques for controlling the air-fuel ratio behavior of an internal combustion engine. Effective disturbance rejection and tracking are critical to maximizing the engine air-fuel ratio's effect on catalyst performance and emissions. The state of the art in engine air-fuel ratio control is reviewed (which includes consideration of the exhaust system's aftertreatment) and compared to a controller derived from directly addressing the engine's time delay elements. During the analysis of control structures for time delay systems, many improvements to past work are demonstrated toward improved tracking and disturbance rejection for both SISO and MIMO systems. Applying the new control structure and design resulting from this analysis, it was experimentally shown that improvements in tracking and disturbance rejection are possible over the current state of the art. Considering the time-varying nature of the engine plant, a novel method of state equation augmentation is demonstrated to account for rapid plant parameter changes in reference plant models with feedthrough terms. Finally, the new controller is simulated with a validated, detailed catalyst model to show the improved catalyst control flexibility in the presence of input disturbances.