Hybrid Energy Storage System With Active Power-Mix Control in a Dual-Chemistry Battery Pack for Light Electric Vehicles

This paper demonstrates a hybrid energy storage system (HESS), comprised of lithium-ion (LI) and lead-acid (PbA) batteries, for a utility light electric vehicle. While LI batteries have superior energy density, lower internal resistance, and longer lifetime than PbA batteries, the module cost is typically three times higher. The objective of this paper is to design an HESS that: 1) is cost competitive with a PbA single energy storage system (SESS) and 2) maintains most of the performance benefits of a conventional LI SESS. This is done by minimizing the Peukert effect and thus increasing the usable energy of the PbA battery. The proposed modular multiphase dc-dc converter achieves stable interleaving operation, and the traditional noninverting buck-boost converter is modified to allow intermodule balancing. A simple power-mix algorithm with active intramodule state-of-charge balancing is proposed, and the modular hybrid battery system is demonstrated experimentally with low-cost embedded hardware. The cost and the performance of the HESS are assessed side by side with PbA and LI SESS configurations. The HESS has a total projected cost midway between the SESS PbA cost and the SESS Li cost, while providing 23% efficiency (range/kWh) increases over the SESS PbA vehicle.