Influence of pulse width modulated auxiliary consumers on battery aging in electric vehicles

Abstract

The number of electric vehicles is increasing worldwide. Due to the high energy density of their Li-ion batteries, these vehicles are gaining acceptance among customers. Nevertheless, Li-ion batteries experience calendric and cyclic aging over the lifetime of the vehicle, leading to a reduction in performance and range. For economical and sustainable vehicles, battery aging must be minimized. Numerous studies have focused on analyzing and influencing battery aging by performing tests on battery cells and packs with a DC current. However, the battery is exposed to high-frequency perturbations in electric vehicles. In recent years, more focus has been placed on the influence of the current ripples generated by the traction power electronics with contradictory results. High-voltage auxiliary loads also cause high-frequency loads due to pulse-width modulation. The scope of this study is to investigate whether pulse-width modeled auxiliary consumers have an impact on battery aging and which frequencies are detrimental. For this purpose, battery cells were loaded with a discharge frequency of 400 Hz of a serial heater. In addition, 10 Hz and 5,000 Hz were chosen as further test points and cells were discharged with direct current as a reference. The results show a significant acceleration of the capacity fade and the internal resistance increase under load with a 10 Hz discharge current. On the other hand, the aging of the cells discharged by high frequencies does not show any abnormalities compared to the DC cells. Differential voltage analysis demonstrates increased aging of the anode compared to the cathode for all cells. An influence of the frequencies on the aging of the different electrodes is not observed but suspected by the different corner frequencies of the double layer capacities. Low frequencies should therefore be avoided in the control design of auxiliary consumers in electric vehicles.