Online Battery Pack Electrochemical Impedance Spectroscopy Measurement Using a Three-Phase Neutral Point Clamped Converter

This article proposes an online battery pack Electrochemical Impedance Spectroscopy (EIS) measurement integrated within the control scheme of a three-phase three-level neutral point clamped (NPC) converter. This is achieved by adding zero-sequence voltages over a range of frequencies to the three-phase reference voltages of the converter’s controller, which has the effect of injecting corresponding frequency current perturbations into the battery without impacting the output three-phase current. A lock-in amplifier is used to extract the corresponding current and voltage perturbation signals and calculate the battery’s impedance. The proposed method is verified using detailed simulation of an NPC inverter with a 10 kHz switching frequency. The results show a close agreement between the online EIS measurement and actual values over the range of 0.01 Hz – 3 kHz, which covers the useful EIS spectrum of most Lithium batteries. The proposed method can be used for online battery diagnosis, battery protection and management using the existing power electronic interface without additional ancillary electronic circuits.