Extraction of Single Cell Impedance from Battery Pack Measurement by Simulation-Based Multiport De-Embedding

Battery cell modeling is becoming increasingly important for EMC simulation, because batteries are a fundamental part of many modern electric networks, such as electric vehicle powertrains or powerline communication systems. The battery's impedance and reaction on transient events can have a dominant impact on electromagnetic distortions and susceptibility of the overall network to electromagnetic interference. Simulation models which depict the interior of a battery pack are usually composed of models of the individual cells, whereas the cell impedance data is obtained by measurement on single cells. However, when individual cells are not accessible, the single cell impedance needs to be extracted from measurement of the complete pack. This work describes a solution to this problem by combining numerical multiport de-embedding with measured pack impedance and 3D simulation of the pack assembly. For validation of the approach, cell impedances obtained by pack measurement and subsequent de-embedding are compared to single cell measurement results for frequencies from 9 kHz to 1 GHz. The demonstration is conducted with a commercial PP3 9V battery made of six closely packed LR61 alkaline cells.