A Hierarchical Control Strategy for Maximizing EV Flexibility in a Distribution System

Increasing penetration of distributed energy resources (DER), particularly electric vehicles (EV), challenges distribution system operations with issues such as voltage instability and congestion. Effectively managing the flexibility from numerous, uncertain EVs requires advanced frameworks. This paper proposes a novel hierarchical control strategy for maximizing EV flexibility in a distribution system. The strategy features multiple layers enabling efficient upstream aggregation and downstream control allocation. Individual EV flexibility, quantified with opportunity cost, is aggregated and simplified using curve fitting. The top-level entity perform network-aware optimization considering grid constraints to determine flexibility request for lower-level entities. Subsequently, lower-level entities execute cost-effective scheduling for their EV portfolio within these targets and local constraints. Simulations on the IEEE 33-bus system validate the approach.