Technical and economical evaluation of reactive power service from aggregated EVs

In this paper we present a novel framework to evaluate the capability and cost of providing reactive power service by electric vehicles (EVs). EVs are becoming a promising reactive power service provider because of their short response time and little or no battery degradation during this service. The presented framework is flexible enough to be easily integrated in different market structures proposed in the literature. A linear program is developed to minimize the operating cost of an EV under a range of practical constraints. These constraints include owner's desired state of charge, battery degradation, and limitation in the current ripple from the DC-link capacitor of the EV charger. The developed framework yields optimal charging/discharging schedules for EVs. We also present an algorithm to calculate the reactive power supply function (RPSF) of the EV, as a step-wise ascending function of reactive power, in real-time. The RPSF is calculated based on the price of electricity provided by the grid operator, scheduled charging/discharging activities, and constraints on the EV charger. Simulation results clearly show an opportunity to provide reactive power service by EVs with low marginal cost, especially during on-peak periods when the need of reactive power is high.