An Equivalent Circuit Modeling Approach for Hybrid AC/DC Microgrids with Bilateral Inertia Sharing

The bus voltage of DC grids and frequency of AC grids are two important parameters that affect hybrid AC/DC microgrids (MGs). Bilateral inertia sharing (BIS) control strategy, which can simultaneously mitigate DC voltage and AC frequency variations, is applied to hybrid AC/DC MGs to enhance the dynamic responses of the entire system. The bidirectional interlinking converter (BIC) enables mutual sharing of inertia in both directions within hybrid AC/DC microgrids. However, a quantitative analysis or modeling method for BIS control strategy has not been yet investigated in literatures. To fill up this gap, a systematic analysis framework of bilateral inertia through a dynamic circuit model (DCM) is proposed in this paper. In the framework, load disturbances, frequency, voltage deviations, and inertia emulation control across the hybrid system are represented by circuit quantities. DC and AC subgrids integrated with virtual inertia control (VIC) are modeled as dynamic Thevenin's equivalent circuits. Thanks to the bidirectional power transfer by BIC under normalization control, the two circuits can be connected in parallel, which characterizes a complete dynamic circuit model that helps to quantify the inertia transferred between the two subgrids. The feasibility of proposed framework is verified by Bode diagrams in frequency domain and time domain simulations.