Online battery electrochemical impedance spectroscopy using a neutral point clamped inverter

Abstract

Electrochemical Impedance Spectroscopy (EIS) is a widely used method for assessing the state of charge (SOC) and state of health (SOH) on batteries and fuel cells. While previously limited to research laboratories, the increasing demand for fuel cells and battery storage due to the growth of electric vehicles (EVs) and renewable energy has prompted research into online measurement. This thesis investigates the integration of online EIS within the control and measurement system of a neutral point clamped (NPC) inverter. This is accomplished by applying zero-sequence voltage injection to the NPC control. Connecting the battery midpoint to the neutral point of the inverter results in a perturbation current flowing into the battery. The battery voltage and current are measured, and subsequent spectral analysis is used to calculate its impedance. A simulation model using different excitation signals (single-sine, multi-sine, and broadband) demonstrates close alignment of the proposed EIS measurement with theoretical values from the battery equivalent circuit. Furthermore, a test rig was developed, and the experimental results were compared with the offline benchmark for validation. This demonstrates the feasibility and effectiveness of the proposed method for online battery measurement.

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Identifiers

ORCID for Kai-Ping Liu: orcid.org/0009-0003-4092-4558

ORCID for Suleiman Sharkh: orcid.org/0000-0001-7335-8503

ORCID for Andrew Cruden: orcid.org/0000-0003-3236-2535

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