Charging electric vehicles from solar energy

Abstract

Electric vehicles are only sustainable if the electricity used to charge them comes from renewable sources and not from fossil fuel based power plants. The goal of this PhD thesis is to develop a highly efficient, V2G-enabled smart charging system for electric vehicles at workplaces, that is powered by solar energy. The thesis focusses on three research elements – power converter, charging algorithms and system design.  A 10kW EV charger has been developed that enables the direct DC charging of EV from PV without converting to AC. The charger is bidirectional, so energy from the EV battery can also be fed to the grid for vehicle to grid (V2G). The charger can realize four different power flows: PV → EV, EV → Grid, Grid → EV, PV → Grid. The 10kW modules are modularly built and can be operated without solar input as a bidirectional EV charger as well. Further, several DC charger modules can be operated paralleled for fast charging up to 150kW. The charger is based on silicon carbide and quasi-resonant technology which results in high efficiency (>96%) for both full load and partial load. The integrated EV-PV solution has a lower component count, three times higher power density and lower cost than using separate EV charger and PV inverter exchanging power over AC. The charger is compatible with the CHAdeMO and CCS/Combo charging standard and is designed for implementing smart charging. New smart charging algorithms developed in the project integrate several applications together: PV forecast, EV user preferences, multiplexing of EVs, V2G demand, energy prices, regulation prices and distribution network constraints. For two case studies simulated for Netherlands and Texas, the proposed algorithms reduced the net costs by up to 427% and 651% when compared to average rate charging, respectively.