Two-Stage Charging Strategy for Plug-In Electric Vehicles at the Residential Transformer Level

In this paper, the coordinated charging control problem for plug-in electric vehicles (PEVs) with vehicle-to-grid functionality is formulated and investigated at the residential transformer level. A two-stage charging control (TSCC) strategy is proposed to shift the transformer load while achieving good charging performance for all PEVs connected to the grid. The proposed TSCC consists of an aggregator optimizer and a power distributor designed in two stages with different control functions. During the first stage, based on the dynamic aggregator concept, the optimal charging power for all PEVs in the aggregator is derived using the Pontryagin's minimum principle. During the second stage, a power distribution law is developed to allocate the aggregated power from the first stage using the fuzzy logic control approach. The TSCC framework considers the stochastic characteristics and nonlinear battery dynamics of practical vehicle charging scenarios, and therefore, is feasible for practical implementation. Finally, simulation results are presented to validate the control performance of the TSCC.