On the impedance and stability analysis of dual-active-bridge-based input-series output-parallel converters in DC systems

Dual-active-bridge-based (DAB-based) input-series output-parallel (ISOP) converters have become increasingly popular due to their promising features made up of the advantages of the modular power electronics and the DAB converter. The modeling of the DAB converter and the DAB-based ISOP converter has been widely explored for control design in order to analyze the stability and improve the performance of the converter itself such as the voltage balancing and power sharing of DAB submodules. However, the modeling on the impedance of the DAB-based ISOP converter, which can be quite useful for system-level stability analysis and optimization, has not been addressed sufficiently so far. To solve this issue, this paper presents comprehensive impedance modeling of the DAB-based ISOP converter, where the output voltage control and the input voltage balancing control are applied to the converter to achieve the equal power sharing of the submodules. The proposed input impedance model and output impedance model of the DABbased ISOP converter are validated through the frequencydomain sweep in simulation and experiment. With the validated impedance models, the instability phenomenon and the frequency of the main harmonic component in oscillating waveforms can be accurately predicted at the source side and at the load side of the converter respectively.