Coordination of Electric Vehicle Aggregators: A Coalitional Approach

Given the rapid rise of electric vehicles (EVs) worldwide, and the ambitious targets set for the near future, the smart charging of an EV fleet must be seen as a priority. Specifically, we study a scenario where EV charging is managed through self-interested EV aggregators (e.g. car parks or electricity suppliers) who compete in the day-ahead market in order to purchase the electricity needed to meet their clients' requirements. In order to reduce electricity costs and lower the impact on electricity markets, we study the possibility of inter-aggregator cooperation. Specifically, we model the system as a coalitional game and prove that the resulting game is superadditive and balanced, hence having a non-empty core. However, due to the game not being convex, the Shapley value is not guaranteed to lie in the core. As an alternative, we propose employing the payment mechanism provided by the least-core, which we show to be in the core in our setting. Furthermore, a realistic empirical evaluation is presented, using real market and driver data from the Iberian Peninsula. The simulations show that large payment reductions can be achieved when using the coordination mechanism. Moreover, we show that the individual payments of the least-core are very close to the Shapley value, suggesting that the payment mechanism is both fair and stable.