Reduced-Order Model for Wind-Solar Multi-Microgrids Considering Time-Scale Coupling

A computationally efficient and accurate reduced-order model (ROM) that characterizes the time-scale coupling caused by the high penetration of power-electronic converters in microgrids (MGs) is crucial to system stability analysis. When such MGs are interconnected into multi-microgrids (MMGs), the coupling between fast and slow dynamics will be more complicated due to the interactions among each MG. The traditional ROM without concerning dynamic coupling may lead to low accuracy and even misjudgment of system stability. In this paper, by considering primary energy dynamics of renewable energy sources, e.g., doubly-fed induction generator (DFIG) and photovoltaic (PV), a small-signal model that characterizes the practical multi-timescale of MMGs is firstly presented. Then with the division of the entire MMGs into fast and slow dynamic subsystems based on the assumption of time-scale separating, the coupling dynamics are identified via the residues-based method. Finally, a ROM considering coupling dynamics and preserving physical meaning is proposed by reconfiguring the fast and slow dynamic subsystems based on singular perturbation. The accuracy of the proposed ROM is verified by comparing it with the detailed model under different control parameters, wind speeds and irradiance conditions. The time-domain simulation is employed to validate the dynamic response of the proposed ROM.