Dynamics of an integrated solar photovoltaic and battery storage nanogrid for electric vehicle charging

In this paper, the performance of a renewable Solar Photovoltaic (PV) nanogrid - here defined as a small-scale power system, which comprises a single domain for control, reliability, and power quality - is assessed for Electric Vehicle (EV) charging. A nanogrid testbed, containing PV as the power supply, twenty EV charging stations, a Battery Energy Storage System (BESS), and a smart-inverter is connected to a primary feeder on the University of California, Irvine (UCI) Microgrid. We present four different smart-inverter control algorithms that govern battery dispatch for different energy management goals. The control algorithms were evaluated with respect to four figures of merit: (1) Renewable Penetration, (2) Voltage Profiles, (3) Net Power Flows, and (4) PV curtailed. A steady-state power flow model of the nanogrid was developed to study the local power quality. The control algorithms were able to successfully use the battery to shift the nanogrid peak load and also limit the nanogrid demand to a given threshold. It is shown that the nanogrid was able to offset the EV daily charging loads completely. In this same mode, the renewable contribution to EV charging was 80%, and the overall solar penetration (accounting for export and battery charge) was 89%.