Understanding the Impact of Coalitions between EV Charging Stations

The rapid growth of electric vehicles (EVs) is driving the expansion of charging infrastructure globally. This expansion, however, places significant charging demand on the electricity grid, impacting grid operations and electricity pricing. While coordination among all charging stations is beneficial, it may not be always feasible. However, a subset of charging stations, which could be jointly operated by a company, could coordinate to decide their charging profile. In this paper we investigate whether such coalitions between charging stations is better than no coordination. We model EV charging as a non-cooperative aggregative game, where each station's cost is determined by both monetary payments tied to reactive electricity prices on the grid and its sensitivity to deviations from a nominal charging profile. We consider a solution concept that we call $\mathcal{C}$-Nash equilibrium, which is tied to a coalition $\mathcal{C}$ of charging stations coordinating to reduce their cumulative costs. We provide sufficient conditions, in terms of the demand and sensitivity of charging stations, to determine when independent (uncoordinated) operation of charging stations could result in lower overall costs to charging stations, the coalition, and charging stations outside the coalition. Somewhat counter to intuition, we demonstrate scenarios where allowing charging stations to operate independently is better than coordinating as a coalition. Jointly, these results provide operators of charging stations insights into how to coordinate their charging behavior, and open several research directions.