Aggregated Modeling and Power Hardware-in-the-Loop Emulation of Grid Impedance

The rapid growth of renewable energy production increases the number of grid-connected inverters in the power system. The interface between the inverter and the grid may face stability issues, which can be assessed using impedance-based stability criterion. The frequency-dependent grid impedance is often an unknown parameter, and vastly simplified grid impedance models are widely used. Most common modeling approach is to use series-connected inductor as the grid impedance. However, measurements on real grids have shown the grid to be more complex, resonant, and time-variant. This paper introduces a grid-impedance model based on aggregation of sub-models, which drastically simplifies complex grid modeling, while still accurately captures resonances and possible time-variant behavior. Numerical sensitivity analysis is carried out for grid parameters to illustrate the significance of separate grid elements. Lastly, impedance measurements are shown for emulated full-order and aggregated impedance models in an experimental power hardware-in-the-loop setup.