| Summary: | Both the frequency domain Nyquist curve of electrochemical impedance spectroscopy (EIS) and time domain simulation of DC equivalent first principle linear circuit (<i>FPLC<sub>DCequ</sub></i>) are some of the fundamentals of lead-acid batteries management system design. The Nyquist curve is used to evaluate batteries’ state of health (SoH), but the curve does not distinguish charging/discharging impedances on electrode−electrolyte interfaces in the frequency domain. <i>FPLC<sub>DCequ</sub></i> is used to simulate batteries’ terminal electrical variables, and the circuit distinguishes charging/discharging impedances on electrode−electrolyte interfaces in the time domain. Therefore, there is no direct physical relationship between Nyquist and <i>FPLC<sub>DCequ</sub></i> This paper proposes an AC equivalent first principle linear circuit (<i>FPLC<sub>ACequ</sub></i>) by average switch modeling, and the novel circuit distinguishes charging/discharging impedances on electrode−electrolyte interfaces in Nyquist. The novel circuit establishes a physical bridge between Nyquist and <i>FPLC<sub>DCequ</sub></i> for lead-acid batteries management system design.
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