Turbocharged engines often suffer from significant intake manifold pressure response delay due to so-called turbo-lag. Many technologies have been investigated to combat this phenomenon, and combinations of them are often utilized together. The addition of these technologies to already complicated modern engines presents a significant control challenge due to significant system nonlinearity, especially when considering the large operating range of engine speeds and loads. In this dissertation a Ford 6.7L 8-cylinder diesel engine equipped with a variable geometry turbocharger (VGT) and exhaust gas recirculation (EGR) is additionally augmented with an external electric compressor, or eBoost, along with a bypass valve to mitigate turbo-lag without negatively impacting emissions. The air charge system has two control targets, intake manifold pressure and EGR rate. First, a dual-output proportional-integral-derivative (PID) controller is proposed for controlling the boost pressure using both VGT and eBoost to reduce turbo-lag, and a transition logic is developed to detect transient operating conditions for activating the eBoost as well as closing and opening the bypass valve. The EGR rate PID control remains unchanged from the production control scheme. The addition of the eBoost is shown to experimentally improve transient response time by up to 55% and reduce transient NOx emissions by up to 42% during transitional operations without negatively impacting steady-state engine performance or emissions. Second, a model-based control strategy is developed to illustrate the benefit of a modern coordinated control strategy as compared to the production-style PID control scheme. A multiple-input and multiple-output (MIMO) Linear Quadratic Tracking with Integral (LQTI) control strategy, along with its gain-scheduling logic, and transition logic, is developed for the diesel engine air charge system. Multiple model-based LQTI controllers were designed at different engine operational conditions based on the associated linearized models, and the control outputs are scheduled based upon the engine load condition and bypass valve position. The developed control strategy is validated in both simulation and experimental studies, and the experimental test results show a reduction in engine response time by up to 81.36% in terms of reaching target intake manifold pressure following a load step-up, compared with the production configuration without eBoost and bypass valve with no significant impact on NOx emissions. The LQTI strategy is additionally compared with the dual-output PID control strategy, and is shown to improve intake manifold response speed by up to 57%. Finally, a model-based, gain-scheduling control strategy is developed utilizing a constrained H2 linear parameter-varying (LPV) control strategy. The nonlinear eBoost air charge system is modeled as a function of two scheduling parameters, engine load and bypass valve position, for this study, and three LPV controllers are designed for the defined operating range of these parameters. LPV controllers and a controller switching logic for implementation of the LPV control strategy onto the experimental setup are developed, and the transition logic previously developed for the LQTI strategy is adapted for use by the LPV system. The LPV control strategy is validated in simulation and experimental studies, and is shown to experimentally achieve a reduction in intake manifold response time of up to 84% compared to the production control strategy without eBoost following a load step-up, with no significant impact on NOx emissions. The LPV control strategy is also shown to improve intake manifold pressure response speed by up to 65% compared with the dual-output PID control strategy, and achieve close performance to the LQTI control strategy while providing additional benefits in terms of performance and stability guarantees and simplicity of implementation.
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