Long-term Evaluation of the State-of-Health of Traction Lithium-ion Batteries in Operational Buses

Abstract

In this paper, we present and evaluate a novel methodol¬ogy to estimate the usable capacity and state-of-health (SOH) of lithium-ion batteries in battery-electric buses (BEV). This methodology is designed to be applicable to any BEV in nor-mal operation, independently of battery chemistry, and with-out requiring complex electrochemical models or large data sets. We have tested the proposed methodology on two vehi-cle fleets with a total of 105 vehicles, for which we have been acquiring data for up to three years. Additionally, we have analysed the operation of the fleets in terms of daily distance driven and the charging strategies chosen by the operators. The monitored vehicles are part of fleets currently in nor¬mal operation in Europe. The data collection is done with a third-party data logger that is connected to the vehicles’ Communication Area Network (CAN) buses, and no addi-tional changes were made to the vehicle’s hardware or soft-ware. The results show that the proposed methodology shows significantly lower variance in SOH estimation than the alter-native methodologies. It also shows similar accuracy in the long-term and smaller short-term deviations from the typical capacity fade model.