Time and Fuel Optimal Power Response of a Diesel-Electric Powertrain

Optimal control policies for a diesel-electric powertrain in transient operation are studied. In order to fully utilize the extra degree of freedom available in a diesel-electric powertrain, compared to a conventional powertrain, the engine-speed is allowed to vary freely. The considered transients are steps from idle to target power. A non-linear four state-three input mean value engine model, incorporating the important turbocharger dynamics, is used for this study. The study is conducted for two different criteria, fuel optimal control and time optimal control. The results from the optimization show that the optimal controls for each criteria can be divided into two categories, one for high requested powers and one for low requested powers. For high power transients the controls for both criteria follow a similar structure, a structure given by the maximum torque line and the smoke-limiter. The main difference between the criteria is the end point and how it is approached. The fuel optimal control builds more kinetic energy in the turbocharger, reducing the necessary amount of kinetic energy in the system to produce the requested power. For low power transients the optimal controls deal with the turbocharger dynamics in a fundamentally different way.