Electric Vehicle Fast DC Charging: Holistic Overview

 

AC Charging and DC Charging Concept Diagram

 AC charging is generally referred to as ‘slow charging’ due to its power limitation (22 kW at the highest end typically and the minimum necessary time to charge. The AC higher power ranges (11 – 22 kW) might occasionally be referred as ‘high power AC charging’ or ‘fast AC charging’, there is no actual definition though. On the other hand, those DC chargers with ratings as of 22 kW and spanning up to even 400 kW are considered ‘fast’. The term ‘ultrafast’ is as well used for powers above 50 kW, but there is no actual clear line or definition. The most common DC power ranges deployed nowadays range from 22 – 150 kW, with power ranges between 200 – 350 kW gaining traction. Fast and ultra−fast DC chargers are generally only available publicly at dedicated areas with access to a three−phase power connection to the grid. Charging stations, predominant so far along highways, might display multiple ultra−fast chargers ( > 150 kW each). Such facilities requires a dedicated high voltage transformer from the grid.

Charging Rates and Times

Charging time = Battery capacity (effective) *1 [kWh] / Average Charging Power [kW]

Range of a full battery = Battery capacity (effective) *1 [kWh] / Efficiency [kWh/ 100 km]

60 kWh / 100 kW = 36 min

60 kWh / (18 kWh/100 km*2) = ~ 333 km

*1 For the purpose of this exercise the complete battery capacity is considered. There might be

EVs that might pose a limitation on the full ‘effective’ capacity.

*2 Generic value, will depend on the characteristics of each vehicle. Normally will fall between

12−23 kWh/100 km

What are some of the Important Standards for DC Charging?

IEC 61851. The International Electrotechnical Commission (IEC) has developed several of

the standards listed in the previous section. The IEC 61851 refers to ‘Electric Vehicle Conductive Charging Systems’ and is the central piece of the IEC series for EV charging, focusing on different topics of electric vehicle conductive charging system, including AC and DC charging up to 1000 V and 1500 V respectively [13]. This standard defines four different charging ‘modes’, where the first three ‘modes’ (1 to 3) refer to AC charging and ‘mode’ 4 addresses DC charging. The IEC 62196 defines ‘Plugs, socket−outlets, vehicle connectors and vehicle inlets’ and the IEC 61980 addresses ‘EV wireless power transfer (WPT) systems’. The ISO17409:2020 is the foundational standard on EV charging from the International Organization for Standardization (ISO) and complements exclusively the IEC 61851 discussed above. The documentation addresses ‘Electrically propelled road vehicles — Conductive powertransfer — Safety requirements’ for charging ‘modes’ 2,3,4 defined in IEC 61851−1.