Model based coordinated control of dual-loop EGR and VGT in a turbocharged diesel engine air-path system

Abstract

This paper deals with the design of coordinated controllers for dual-loop exhaust gas recirculation (EGR) and variable geometry turbine (VGT) in a diesel engine air-path system. The technique of model-based control is adopted for the controller design to handle the coupling properties of the air-path system effectively. As for the control of the air-path, it is very important to select control states considering physical importance of them and practical aspects. In most papers about the control of air-path with dual-loop EGR, states of air fraction or burnt gas fraction are controlled to satisfy the target set-point. However, controlling fraction states is not practical because sensors for the fraction states are not available on the production engine. In this paper, model-based controllers are designed only based on pressure and flow states, which are easily measured or estimated even in the production engine. Robust nonlinear control methods such as sliding mode control or input-output linearization are applied to design the controllers of the air-path system which is a highly nonlinear system with strong coupling effects. The control performance of the proposed control schemes is verified through simulation of the valid 10th order plant model based on a 6,000cc heavy duty diesel engine and also using the GT-POWER program which is a well-known engine simulation tool. This paper also suggests estimation methods of pressure states which are not measurable on the production engine such as exhaust manifold pressure, compressor inlet pressure, and turbine outlet pressure. The estimation performance of each estimator is verified experimentally based on the target diesel engine in various operating points.