Coordinated dispatch of electric vehicle charging and discharging resources for emergency power supply in distribution transformer areas

Abstract

Electric vehicles with vehicle-to-grid capability can provide distributed and rapidly deployable support for distribution transformer areas during emergency supply shortages. However, emergency use of electric vehicle resources should not be treated as unrestricted battery discharge, because vehicle availability, user travel demand, transformer loading, and voltage security may jointly limit the feasible support capacity. This paper proposes a coordinated charging and discharging method for electric vehicle clusters participating in the emergency power supply of a distribution transformer area. Electric vehicle resources are aggregated into clusters, and their available emergency flexibility is evaluated according to state of charge, charging and discharging power limits, minimum state-of-charge requirements, and departure energy requirements. A priority-load-oriented dispatch model is then formulated to coordinate electric vehicle discharging, charging recovery, and emergency load shedding while considering transformer loading and voltage constraints. A comparative simulation with four cases is conducted, including emergency operation without electric vehicle support, uncoordinated electric vehicle discharging, coordinated dispatch without network constraints, and the proposed network-constrained coordinated control. The results show that the proposed method increases the critical-load supply rate from 96.27% to 98.84%, reduces critical unserved energy from 66.74 kWh to 20.83 kWh, maintains 100% state-of-charge target satisfaction, and avoids transformer and voltage violations. These results indicate that coordinated electric vehicle charging and discharging can improve emergency supply capability while preserving user mobility and distribution network security.