Interaction between current harmonics produced by different electric vehicles DC chargers

The need to reduce the environmental impact of transportation has driven the rapid spread of Electric Vehicles (EVs), which do not contribute to the emission of pollutants. This has led to the evolution of Electric Vehicle System Equipments (EVSEs), as the need to ensure faster charging speeds and higher performance has become more pronounced. As a result of numerous studies conducted on charging systems, some chargers on the market today allow not only the Grid-to-Vehicle (G2V) configuration of vehicle charging but also the Vehicle-to-Grid (V2G) technology by which the vehicle can be used as a generator, discharging in the grid. With this technology, the vehicle can provide electricity from the battery during off-peak periods, or can act as a load taking power from the grid during peak periods. This ensures the supply and demand balance of energy, helping to keep the grid frequency close to the nominal values of 50 or 60 Hz, that is an important condition for correct operation of the electrical systems. The operation of chargers impacts the power quality of the grid, due to the AC/DC conversion stage inducing current harmonic distortions, adversely affecting the operation of grid-connected devices. Electric vehicles can be charged in AC, where the conversion takes place in the vehicle via the on-board charger, or in DC, where the converter is internal to the charger, and this makes DC charging faster than AC charging. The distortion problem is amplified when multiple chargers operating simultaneously are connected to the same network node, such as in a parking lot. In this case, the current harmonics interact with each other by adding or subtracting at the Point of Common Coupling (PCC), where the system interface with the network. Pursuing previous thesis work, in which was examined the harmonic interaction of two identical DC chargers, this thesis aims to analyze the interaction between current harmonics due to the contemporary operation of two different DC charging stations, one unidirectional and the other bidirectional. The tests are performed within an ongoing collaboration between Politecnico di Torino and Edison S.p.A., which provides the shared laboratory with the chargers under test. The first part of the thesis work focuses on the comparison of the two different power amplifiers available in the laboratory, a linear and a nonlinear type. The objective of the comparison is to define whether the nonlinear amplifier, which must be used to supply the unidirectional charger, introduces or not excessive disturbances in powering the charger, ensuring good performance as the linear type. Afterwards, characterization tests of the unidirectional charger are performed, in order to define its performance, in terms of conversion efficiency, power factor and current harmonic distortion. The results are compared to standard limits and to the values stated in the charger datasheet. Finally, the thesis focuses on the analysis of the current harmonic interaction between the unidirectional and bidirectional charger, connected to the same electrical node. The devices are firstly supplied by the power amplifier, during which the interaction is studied once with both chargers in charging mode (G2V-G2V) and after that with the unidirectional in charging and bidirectional in discharging modes (G2V-V2G). In the final part of these tests, both chargers are powered by the grid only in G2V-G2V configuration, to confront the results with those obtained with the amplifier as power source.