Modeling and Stability Analysis of CCIs- and VCIs-Based Hybrid Microgrids Operating in Grid-Connected Modes

Converters serving as power interfaces between distributed generation (DG) sources and loads can operate in current-controlled modes (CCMs) and voltage-controlled modes (VCMs) together in a microgrid. This paper studies the stability issues in a grid-connected hybrid microgrid represented by a current-controlled inverter (CCI) and a voltage-controlled inverter (VCI), whose inner control loops would interact with each other because of the grid line impedance. The impedance and admittance-based passivity stability criterion is applied to analyze the stability issues, so output admittances of the CCI and output impedances of the VCI are modeled and analyzed, respectively. Additionally, a stability analysis model is also developed for multiparallel grid-connected inverters to reveal the instability phenomena between the inverters and the grid. Theoretical and simulation results show that the studied VCI can help to mitigate near-synchronous oscillations and cannot damp harmonic oscillations in higher frequencies.