Modeling of DC-Side Dynamics in PV/Battery Grid-forming Inverter Systems

The DC-side dynamics of two-stage grid-forming (GFM) inverters are often neglected or oversimplified in power system studies, although they play a vital role in stability. Detailed models for the primary source and power converter are not practical for complexity reasons, leading usually to DC side representations that omit critical aspects such as the operational limits. To bridge this gap between accuracy and simplicity, this paper proposes for the first time an equivalent model for the DC side dynamics of GFM systems that captures all important dynamics and limits in a simple formulation. The model supports either batteries or photovoltaic arrays as a primary source and is easily parameterizable with minimal information, thus proving a useful tool for grid stability studies. Time-domain simulations validate the proposed equivalent model.