Two-component HPPC pulse approximation for lithium-ion LiFePO₄ cell identification tests

During the identification of lithium-ion cell equivalent circuit parameters based on HPPC (Hybrid Pulse Power Characterization) measurement results, time constants of the recorded voltage transients are identified. A significant practical problem is that the identified time constants, in the case of LFP (LiFePO₄) cells, are longer than the test pulse duration. Therefore, a solution to this problem was proposed by including in the identification process the transient recorded after the test pulse ceases, during the significantly longer cell relaxation period. This resulted in an identification method based on two components, enabling more precise identification of cell time constants.