Browsing by Author "Ferragut, Andres"
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- ItemDynamic load balancing of selfish drivers between spatially distributed electrical vehicle charging stations(2023) Paganini, Fernando; Ferragut, AndresThis paper considers an electrical vehicle recharging infrastructure made up of physically separate stations serving spatially distributed requests for charge. Arriving EVs receive feedback on transport times to each station, and waiting times at congested stations, based on which they make a selfish selection. We present a fluid model of the resulting dynamics, in particular modeling queueing delays as a function of fluid queues, and two different models of client departures: given sojourn times, or given service times. In each case, the joint load balancing dynamics is related to a convex program, suitable variant of a centralized optimal transport problem. In particular, we use Lagrange duality to show the correspondence between equilibrium points and optima, and to analyze the convergence properties of the dynamics. The results have similarities and differences with classical work on selfish routing for transportation networks. We present illustrative simulations, which also explore the alidity of the model beyond the fluid assumption.
- ItemQueueing analysis of imbalance between multiple server pools with an application to 3-phase EV charging(2023) Ferragut, Andres; Paganini, FernandoWe consider systems where multiple servers operate in parallel, with a particular feature: servers are classified into d classes, and we wish to keep approximate balance between the load allocated to each class. We introduce a relevant imbalance metric, and study its behavior under stochastic demands with different task routing policies. For random routing, we analyze two cases of interest, depending on whether capacity constraints are operative: we obtain expressions for the stationary distribution and analyze the scaling behavior of our metric as a function of system size. Subsequently, we analyze active routing to the least loaded class, obtaining sharp bounds for the imbalance metric. As a practical application, we study the problem of imbalance between d = 3 phases, for the service of electrical vehicle charging. We show the engineering relevance of our imbalance metric in this context, and validate the theoretical results with simulations and real traces from EV charging data.