Voltage Stability Improvement of Multi-Microgrid Clusters with Electrical Vehicle Loads Using Unified Power Flow Controllers

This paper investigates voltage-stability improvement of bus nodes within four microgrid clusters (MGCs) based on the IEEE 14-bus system. Wind and PV systems are added to the generator sides of the microgrids (MGs), and electric vehicle (EV) loads are added to the load sides to simulate practical power system situations. Unified power-flow controllers (UPFCs) are added to the transmission lines between neighboring MGs to improve their voltage stability. For static voltage stability, frequency-domain characteristics of the studied MGCs under different line-outage scenarios are first performed through Q-V sensitivity analysis, and the system load margin is evaluated using P-V curves. For the transmission-line stability of the studied MGCs, a critical X-R ratio index derived from an extension of the fast voltage stability index (FVSI) is proposed. © 2025 IEEE.