Direct DC-DC electric vehicle charging with a grid connected photovoltaic system

Abstract

The Electric VehicldPhotovoltaic Demonstration and Evahmtion Program being conducted at the University of South Florida (USF) includes a 20 kW (peak) photovoltaic (PV) system in which PV panels form the roof of a 12 bay carport. A 6 kW (peak) segment of the PV system can be simultaneously distributed between computer controlled direct DC-DC charging and power grid interconnection.The DC-DC charger (DC-DAS) controls the charging current of a battery pack with minimal power waste, by computer control of current flow direction of each of four source circuits. It demonstrates superior efficiency, dependability and safety for DC-DC charging over DC-AC-DC charging and has greater control over the last 20% of charge than traditional PV DC-DC chargers. PV SYSTEM CONFIGURATIONThe 12 bay photovoltaic carport at USF uses Siemens Solar M55 High Efficiency Power PV Modules that can achieve a peak output of 53 Watts (Vmm=17.4V & I-=3.05A @ 75°F & 1000W/m2) each. A total of 377 M55 modules are used which provide a peak power of 19,981 Watts. By properly connecting the modules in series and in parallel, modules can be interhxd with the Electric Vehicles (Ev's) directly or through the power grid. AC-DC chargers are available for charging when solar power is unavailable or insufficient. DC-DC CHARGER CONFIGURATIONA 1 17 module segment of the PV array has been configured for both direct DC-DC charging and power grid interconnection and is capable of delivering a 41.6A maximum current. The segment consists of four source circuits which in turn are comprised of series circuits. A series circuit consists of nine PV modules wired in series to provide a peak power voltage of 13OV-156V (depending upon the PV module temperature) and a current of about 3.2A at 1000W/mz. A source circuit is formed by connecting a number of series circuits in parallel. Source circuit #l (SC#l) has one series circuit, SC#2 has two series circuits, SC#3 has three series circuits, and SC#4 has seven series circuits. The DC-DAS coni3guration is shown in (FSgure 1). The source circuits are switched between the charging vehicle and the power grid (via two 3kW inverters) by computer controlled relays. The 124V to 156V charging voltage range of the electric vehicle battery pack is within the power knee of these source circuits (Figure 2). DC-DC CHARGING (DC-DAS) PROCEDUREThe DC-DAS is able to control the charging current of a battery pack with minimal power waste and can achieve an efficient 100% state of charge (SOC). This is made possible by properly utilizing the 4 source Circuits (SC#l-SC#4) of the PV array (Figure 1). With source circuits of 1, 2 ,3 and 7 series circuits, any number of series circuits from 1 to 13 can be employed. Each source circuit can provide 3.2A at 148.5V and 75°F. This will allow any integral multiple of 3.2A from 3.2 A to 41.6A. DC-DC charging is accomplished using USF developed software, which monitors the battery temperature, voltage, and charging current along with the array irradiance. The DC-DAS analyzes these parameters to determi...

A critical review of electric vehicle charging using solar photovoltaic

“…without the involvement of utility (grid) as shown in Figure 7 [78]. It is more efficient because of the fewer power conversion stages [79,80]. However, the PV array must be sufficiently large to fulfil the charging requirement for the designated number of vehicles [81].…”

Comparison of system architecture and converter topology for a solar powered electric vehicle charging station

“…The PV and EV converters are both DC/DC converters that have MPPT control and charge control respectively. The DC interconnection facilitates the direct use of the DC power of PV for DC charging of EV, which results in higher efficiency [5]- [7]. An (optional) central inverter connects the DC grid with the AC gird and provides for V2G operation and facilitates the feeding/drawing of the power difference between PV generation and EV demand.…”

Control and Management of PV Integrated Charging Facilities for PEVs

“…Based on the imbalance between the PV power and the load demand, various possible scenarios are described. In case of [45], the power flow in a PV parking lot is managed through a set of computer controlled relays. PV panels of different ratings are interfaced with PEV chargers and the power grid through computer controlled relays.…”