A new topology for electric all-terrain vehicle hybrid battery systems using low-frequency discrete cell switching

This paper presents an investigation into the feasibility of a novel discrete-switched topology for an electric all-terrain vehicle (e-ATV) hybrid battery system that avoids expensive and bulky DC-DC converters using a simpler discrete-switched structure together with an intelligent low-frequency switching algorithm. Hardware is simplified at the expense of more complex control. The algorithm switches cells in and out of series strings, based on their state of charge relative to other cells in the pack and the power being drawn from the pack. The principles are demonstrated using a simulated model combining lithium-titanate-oxide (LTO) and lithium-ion-phosphate (LFP) cells together in an e-ATV battery pack. Despite its simplicity, the intelligent switching algorithm, successfully allocates power to different elements of the battery and ensures that state of charge remains broadly balanced throughout discharge, with the pack ending up in good balance: the LFP cells are in balance to within 0.01% of each other, and the LTO cells within 0.1% of each other. While the paper focuses on the essential feasibility of the concept, it also identifies future research for including thermal effects, uncertainties in state estimation, cell ageing and non-uniformly, and consideration of other powertrain components, e.g. motor and power electronics.