Optimization-Based Battery Thermal Management for Improved Regenerative Braking in CEP Vehicles

Abstract

The courier express parcel service industry (CEP industry) has experienced significant changes in the recent years due to increasing parcel volume. At the same time, the electrification of the vehicle fleets poses additional challenges. A major advantage of battery electric CEP vehicles compared to internal combustion engine vehicles is the ability to regenerate the kinetic energy of the vehicle in the frequent deceleration phases during parcel delivery. If the battery is cold, the maximum regenerative power of the powertrain is limited by a reduced chemical reaction rate inside the battery. In general, the maximum charging power of the battery depends on the state of charge and the battery temperature. Due to the low power demand for driving during CEP operation, the battery self-heating is comparably low. Without active conditioning of the battery, potential of regenerating energy is partially lost because the friction brake needs to absorb kinetic energy whenever the cold battery’s limit is exceeded. This paper proposes an optimization-based strategy for the battery thermal management of CEP vehicles. The tradeoff between the cost of battery heating and the benefit of regenerative braking is investigated under cold ambient conditions. For this purpose, a nonlinear model predictive control approach is developed to maximize the overall vehicle efficiency depending on the upcoming driving task by selective battery heating. The evaluation shows that the increase in overall efficiency depends on the electric efficiency of the battery heating system, the ambient conditions, the intensity and frequency of the deceleration phases, and the usage behavior of the vehicle. Based on the assumption that the driving cycle and ambient conditions can be accurately predicted, the model-in-the-loop simulation indicates a reduction in energy consumption of up to 3.3 % with an electric coolant heater and up to 9.6 % with an ambient heat pump.