Range Extension of Electric Vehicles through Improved Battery Capacity Utilization: Potentials, Risks and Strategies

Among the biggest challenges battery electric vehicles (BEVs) face is their limited range and higher price compared to conventionally powered vehicles. One underlying reason is the operation strategy of the battery pack. To reduce aging and avoid deep discharge, state of the art battery management employs strict and conservative operational limits, leaving a significant amount of energy in the battery unused, directly translating into a loss of possible range. Additionally, this strategy leads to a sudden and, for the driver unpredictable, power derating at a low state-of-charge (SOC). This paper proposes an approach for defining the operational limits of the vehicle's battery and a strategy for using most of the available capacity and power at a low SOC, increasing the vehicle's capabilities with no additional hardware. The benefits of this approach are shown by a theoretical assessment of selected BEVs. The limitations of current implementations are analyzed by an experimental study of a Volkswagen e-Golf on a chassis dynamometer and under real driving conditions. The impact of an extension of the battery's operational limits is discussed with a study of relevant literature and supported by measurements of lithium-ion battery behavior. The strategies presented in this paper are implemented, simulated and evaluated under consideration of the behavior of a single cell within the battery pack, as well as the whole electric drivetrain.