Modeling, control design and technical grid analysis of V2G and G2V systems

Abstract

The integration of renewable energies as power generators in the electricity grid is necessary to overcome the dependence and pollution linked to fossil fuels. Nevertheless, the variability of these renewable resources limits their quantity in the system. In addition, there exists a trend to change the transport sector by means of the electrification of the existing conventional vehicles based on internal combustion engine (ICE). A solution to mitigate the mentioned variability and to enable a higher integration is the use of energy storage systems, such as batteries and supercapacitors (SCs). Nonetheless, batteries are nowadays very expensive, so using them only for this back-up function is unviable. Electric Vehicles’ batteries could be used for this purpose and be consequently repaid sooner. In order to provide this support service, the chargers of the electric vehicles (EVs) should work with a bidirectional power flow, in two modes: as dynamic loads, when they are charging, which corresponds to Grid-to-Vehicle (G2V) mode; or as generators, when they are discharging, which corresponds to Vehicle-to-Grid (V2G) or Vehicle-to-Home (V2H) modes. Even if this first mode is broadly deployed, the V2G and V2H modes are still in developing process and they are not commercialized yet. This thesis is mainly focused on designing, modeling and simulating two different chargers that connect a battery pack to either a single-phase grid for low power applications or to a three-phase grid for high power applications, in which both G2V and V2G/V2H modes are implemented. An assessment of the most typical AC/DC and DC/DC converters’ topologies is carried out, and their benefits and drawbacks are highlighted. Different control strategies are employed and tested, and a harmonics study of the grid current and voltage is performed.