Voltage Support using Electric Vehicles in an Islanded Resistive-Microgrid under Voltage Sags

Abstract

The number of electric vehicles connected to the grid is growing constantly due to environmental and regulatory issues. Conventionally these vehicles work as variable loads, although using them as distributed generators is a promising future functionality, known as vehicle to grid concept. Using vehicle to grid capacities to support the grid during voltage sags, emulating Low Voltage Ride Through protocols, have been studied extensively, also in the field of islanded microgrids based on power electronics converters. This work proposes a change of paradigm for low voltage islanded microgrids, where the network impedances are mainly resistive. Instead of injecting reactive currents during the sag, this work proposes the injection of unbalanced active currents with two main objectives. First, support the microgrid voltage prioritizing in the reduction of voltage unbalance to avoid over voltages in the less faulty phases. And second, collaborate in the active power injection with the distributed generators to supply the over currents that demands the system during short circuits which produce voltage sags. Selected simulation results demonstrate the effectiveness of the control proposal.