A plug-in hybrid electric vehicle (PHEV) requires a power electronic system between the power grid and the high-voltage battery pack located inside the vehicle. This electronic system is split into two parts: a charging station, which is also called electric vehicle service equipment (EVSE) or an off-board charger, and an onboard charger inside the vehicle.
A charging station is part of the grid infrastructure installed along a street, parking lot or in a home garage; its primary purpose is to supply the power to the PHEV for charging the battery. An onboard charger is responsible for the final stage of charging the battery pack. It takes the AC power source from the EVSE and transforms the power into the required battery-charging profile.
Despite having separate functions for charging a vehicle, similarities in the naming conventions (“on-” and “off-” board chargers) have caused general confusion about these two types of systems. While the onboard charger has to condition (convert to high-voltage DC) power from the off-board AC charger before supplying it to the battery management system (BMS), the off-board DC charger works without an onboard charger and interfaces directly with the BMS.