In-Situ EV Battery Electrochemical Impedance Spectroscopy with Pack-Level Current Perturbation from a 400V-to-12V Triple-Active-Bridge

Abstract

A GaN-based, 4-kW, 400V-to-12V triple-active-bridge dc-dc converter is proposed to impose a variable-frequency sinusoidal perturbation between two EV battery half-packs for Electrochemical Impedance Spectroscopy (EIS). The proposed architecture performs EIS on the high-voltage battery at arbitrarily low test frequencies, requiring only a few cycles of operation and no additional means of energy-storage. This allows for fast, opportunistic, in-situ EIS measurements during EV operation. In-situ impedance measurements can help maximize the EV battery performance with respect to its local environment. Full integration into the existing high-voltage to low-voltage dc-dc EV converter results in a compact and low-cost system. A cell-level voltage-response sensor with automatic dc-offset calibration is implemented with integrated signal processing to measure cell-level voltage responses, thereby accurately capturing cell-to-cell impedance variations in the EV battery. Impedance measurements from a fully custom liquid-cooled 350-V lithium-ion EV battery pack are collected between 0.1 Hz and 200 Hz, from 15° C to 25° C, demonstrating simultaneous in-situ pack-level EIS perturbation and cell-level response measurement.