Model Predictive Control of an Air Path System for Multi-Mode Operation in a Diesel Engine

A supervisory model predictive control system is developed for the air system of diesel engine. The diesel air system is complicated, composing of many components and actuators, with significant nonlinear behavior. Furthermore, the engine usually often operates in various modes, for example to activate catalyst regeneration like LNT or DPF. Model predictive control (MPC) is based on a dynamical model of the controlled system and it features predicted actuator path optimization. MPC has been previously successfully applied to the diesel air path control problem, however, most of these applications were developed for a single operating mode (often called normal operating mode) which has only one set of high-level set point values. In reality, each engine operating mode requires a different set of set point maps in order to meet the various system requirements such as, HP-EGR modes for cold start purposes, heat-up modes for after-treatment conditioning, rich operation for catalyst purging and normal modes. Air mass and its composition requirement are heavily depending on each specific mode. This large array of mode specific set points is not easy to control with a linear MPC since linearized modeling is challenging at all the different demand set points. Engine air system is highly nonlinear and therefore significant number of local linear models (or real-time linearization) would be needed in order to achieve the required performance targets. A new scheme is proposed which aims to combine the benefits of a simple linear MPC controller with nonlinear, low-level local compensators. These nonlinear compensators are based on a dynamic inversion of the local system, using efficient real-time linearization of the component under consideration. The MPC controller acts as a supervisory controller to ensure the high level set points are achieved with good tracking performance. It is demonstrated that the proposed scheme can be used with the very significant benefit that no mode specific calibration is required.