Energy Management Strategies for Diesel Hybrid Electric Vehicle

Abstract

This paper focuses on hybrid energy management for a Diesel Hybrid Electric Vehicle (HEV) with a parallel architecture. The proposed strategy focuses on the reduction of Nitric Oxides (NOx) emissions that represents a key issue to meet Diesel emissions standards. The strategy is split in two separated functions aiming at limiting the NOx in steady-state and transient operating conditions. The first functions, control the torque split between the engine and the electric motor. This energy management is based on the Equivalent Consumption Minimization Strategy (ECMS) where an additional degree of freedom is introduced to tune the optimization trade-offs from the pure fuel economy case to the pure NOx limitation case. The second function adapts the torque split ratio between the motor and the engine, initially computed from the optimal control strategy during transient operations where NOx are produced. The engine torque correction relies on mean value models for the EGR system dynamics and for the NOx formation. This paper applies a methodology based on Software in the Loop (SiL) and Hardware in the Loop (HiL) simulations in order to understand the system performance according to the powertrain configurations and also to tune the proposed energy management strategy. The simulation results are confirmed by experiments performed on Hybrid-Hardware in the Loop (Hy-HiL) test bench. This work shows the potential of using the hybrid architecture to limit NOx emissions by choosing the best operating point and by limiting the engine dynamics. The NOx reduction has limited impact on fuel consumption.