Performance analysis of a bidirectional V2G charger in non ideal conditions

In the last few years, the Electrical Vehicles (EVs) market has experienced a rapid growth, as the world is moving towards a more sustainable mobility system, aiming to the electrification of road transport sector and the reduction of its carbon emissions. The storage capabilities of EVs led to the development of smart charging technologies that allow to use their batteries in the most cost-efficient way. In this scenario, Vehicle-to-Grid (V2G) is seen as a profitable market opportunity, since it enables a bidirectional flux of energy between vehicles and the network itself, providing charged power back to the grid when needed, protecting it from being overloaded in times of peak demand and thus benefitting both the vehicle owners and grid operators. The high penetration of EVs though could cause negative impacts on the power quality of the grid, so the effects of EVs stations (EVSs) must be considered. It has been demonstrated [1] that EVs integration in the grid could create voltage imbalance and reduce the transformers efficiency. The harmonic current content should be kept under the limits set by IEEE standard [2], but in the case of multiple vehicles charging/discharging together their individual harmonics could sum, getting dangerously close to the limits and generating unclean power, that would reduce the life of the equipment that’s supplied, increasing the need for maintenance. This thesis work is the result of an ongoing collaboration between Politecnico di Torino and Edison S.p.A., Italian energy company that supplied the shared laboratory with two bidirectional charging stations. The first part of this study was focused on the characterization of the performances of a single V2G DC charger in conditions close to its operational limits. Inserting the Wallbox into a thermostatic chamber, the whole temperature range has been explored, varying the supply voltage and the power setpoints both in G2V and V2G. Real time simulation, with power hardware in the loop configuration, has been used to feed the charger with a disturbed supply voltage, characterized by voltage dips of different length and depth. Afterwards, the case with two chargers connected to the same electrical node and operating together has been examined, to evaluate their mutual influence. This situation is similar to the real one that could be met, for example, in a parking lot and this study has been useful to assess how much the resulting current would be disturbed. Different configurations have been exploited, to define the most convenient one for the purpose of reducing the harmonics summation.