Optimal Utilization of Bidirectional EVs for Grid Frequency Support in Power Systems

Bidirectional onboard chargers introduce electric vehicles (EVs) as flexible actors in the power grids that can operate in grid-to-vehicle (G2V) and vehicle-to-grid (V2G) modes. Despite the benefits of the bidirectional EVs in the event of grid contingencies, they may have adverse impacts on the normal operation of the power systems. This article investigates the impacts of bidirectional EVs on power quality, voltage profile, and frequency stability of the power grid. For this purpose, a detailed model of practical bidirectional onboard charger is presented to measure the total harmonic distortion (THD) in the grid current caused by the EVs. The proposed study accounts for various EV power levels, grid voltage levels, and EV modes of operation. Furthermore, an optimal frequency support strategy is developed that takes advantage of available EVs in V2G mode to improve the frequency stability of the grid in the event of frequency fluctuations. The effects of bidirectional EVs on the voltage profile is also explored by implementing current summation method (CSM)-derived power flow analysis for IEEE 33-Bus radial distribution system. The results show that with an optimal planning of EVs, it is possible to improve voltage profile and frequency stability of the grid while the power quality of the grid is maintained in the allowed range according to the IEEE 519-2014 standard.