Voltage Stability Assessment of Transmission System with Electric Vehicles as Virtual Power Plants

The proposition of Electric Vehicles (EVs) for mobility is gaining prominence due to foreseen depletion of fossil fuels as well as the ease of charging them at home or in parking lots from renewable energy sources. Aggregators with smart communication facilitate the utilization of batteries of EVs as portable power plants for emergency and ancillary services as well as for daily load scheduling which helps to increase the reliability of the existing grid. But the penetration of such power sources from the distribution side should also ensure the stability of the existing power system. This paper investigates the voltage stability of a power system with participation of EVs in grid scheduling. A cost model of battery of EV to schedule the available active and reactive power is proposed. A hierarchical control strategy to aggregate the capacities of EV batteries is also proposed in this paper. Optimal scheduling of modified IEEE 9 bus test system is done in MATPOWER with EVs as virtual power plants (VPP). To evaluate the voltage stability of the system, L-indices of the load buses with and without the participation of EVs are determined using MATLAB.