The paper presents an approach to the modelling of a cyclic battery tester and contains observations about lithium-ion (Li-ion) batteries, charging/discharging procedures, conditions and protections which must be observed during the testing process. The main goal was to create and simulate a schematic which will be capable of cyclically testing Li-ion battery cells. Regulation of the final schematic is based on cascade connections of operation amplifiers, which work as a voltage source with current-limiting functions. The power part is created by two MOSFETs connected as a half-bridge. This topology allows current to flow in both directions (from and to the battery). Final simulation is supplemented by protections such as reverse polarity protection, short circuit protection and overvoltage protection during charging. Proper operation of the whole connection is demonstrated by the simulation outputs in the final section.

The paper describes the digital twin of a Li-ion battery cell based on the MATLAB/Simulink generic model. The digital twin is based on measured data for constant current/constant voltage charging and discharging cycles with State of Health (SoH) up to 79%, also including fast charging. Mathematical equations used for the digital twin are obtained by 3D data fitting of measured SoH, battery capacity, and battery cell current. The input to the proposed digital twin is only the measured battery cell current, and its output includes State of Charge (SoC), SoH, and battery cell voltage. The designed digital twin is tested and compared with MATLAB/Simulink generic model and battery cell measurements for constant discharging current and dynamically generated discharging current profile. The results show significant improvement in the generic MATLAB/Simulink model.

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