Smart Charging, Vehicle-to-Grid, and Reactive Power Support from Electric Vehicles in Distribution Grids: A Performance Comparison

This paper compares different charging strategies for electric vehicles (EVs) and mechanisms to support local distribution grids. First, a general scheduling problem for EVs based on convex optimization and linearized power grid models is presented. Then, it is shown how it can be adapted to model different charging strategies. These include: i) uncoordinated charging, where EVs maximize a local utility function regardless of grid constraints; ii) smart charging, where a charge schedule of all EVs is determined by maximizing their utility function subject to grid constraints; iii) vehicle-to-grid, where bidirectional power from the EVs is allowed; and iv) reactive power support, where 2- and 4-quadrant EV chargers can provide reactive power. The performance of these strategies are investigated considering the CIGRE benchmark system for medium-voltage distribution grids. It shows that, in the proposed scenario, smart charging with reactive power support is conducive to the shortest global recharging time.