Electric vehicle DC charger integrated within a photovoltaic power system

Mitigation of the variability in output power of renewable generators such as solar photovoltaic (PV) systems is a growing concern as these generators reach higher penetrations on electric grids. This paper presents a system where a bidirectional, highly efficient, DC-DC electric vehicle (EV) charger is placed between the high-voltage DC bus of a PV system and the EV battery. In addition to providing fast charging for the EV battery from PV or from the grid, the charger is capable of diverting fast changes in PV power output to the battery, thereby reducing the rate of change of inverter output power to a level below the ramp rate of existing grid resources. The paper addresses sizing of the charger and energy storage based on the PV system rating, the desired maximum ramp rate, and site insolation characteristics. Analysis suggests that small amounts of energy storage can accomplish large reductions in output power ramp rate. Experimental results are shown for a 10 kW, 98% efficient DC-DC charger based on bidirectional four-phase zero-voltage-switching converter.