Analytical Solution to Energy Management Guaranteeing Battery Life for Hybrid Trucks

This paper considers a parallel hybrid electric truck where the tractive force delivered to the wheels can be provided by a conventional internal combustion engine (ICE) and/or a motor generator (MG). This hybrid truck is equipped with a clutch system that is capable of decoupling the ICE and the MG from the drivetrain to improve the fuel reduction performance, compared with a hybrid truck without a separate clutch for the MG. In the considered hybrid truck, the energy management strategy utilizes the battery to reduce the fuel consumption and the associated emissions. As the battery life is limited, the vehicle owner will suffer from extra costs for battery replacement. Henceforth, it is necessary to guarantee sufficient battery life. This paper develops a quasi-static battery cycle-life model and formulates a model-based integrated energy management (IEM) strategy. This IEM strategy optimizes the power split (between the ICE and the MG) and the operation of the clutch system to minimize the hybrid truck fuel consumption while guaranteeing the requested battery life. The problem of fuel minimization with battery life guarantee is analytically solved using optimal control theory. Mathematical and physical arguments are used to explain the compromise between fuel reduction and battery life preservation. Simulation results demonstrate that the IEM strategy will guarantee the requested battery life for different driving cycles while allowing appropriate hybrid powertrain operations for fuel minimization. Moreover, the results also show the fuel reduction improvement from decoupling the MG from the drivetrain using the clutch system.