An AC-DC coupled impedance model and stability analysis for more electric aircraft

High voltage DC systems have become one of the dominant electrical power system architectures for future applications in more electric aircraft. Accurate model and stability analysis of these systems are crucial. However, past studies typically use the DC impedance model, which may overlook some system characteristics. Additionally, the impedance model needs repetitive adjustment as the source side and the load side change. In this paper, an AC-DC coupled impedance model is proposed, which can model the overall system into submodules. The resulting converter impedance is independent of load and source-side parameters, which means that changes on the AC and DC side have no effect on the converter impedance model. Furthermore, this model is more accurate as it includes AC, DC, and AC-DC coupled terms, better aligning with actual onboard characteristics. The modelling process, frequency sweep verification, and stability analysis in MATLAB/Simulink are provided in this paper.