Automotive Application - HEV Battery Charger
EV and PHEV (Plug-in Hybrid Electrical Vehicle) systems push the envelope of vehicle electrification by allowing
high voltage battery banks to recharge from the mains. A high voltage charger converts electrical power from AC to
DC, and controls the power flow to the high voltage battery. Electronics on board the car transform the wall power
into the proper form to charge the battery. The power levels for these chargers range from 3 to 10 kW, and
therefore require a front-end PFC circuit. There are 3 levels of charging that are classified by peak power
capacity. Level 1 charging enables charging from any standard electrical plug, which in the United States is 120V
and limited in peak amperage draw (8 - 15 amps) by local circuit breakers. Level 1 chargers are portable
converters that may be placed in the trunk for use anywhere a standard outlet can be found. Charging can take up
to 22 hours for a fully depleted battery. At Level 1 charging, a user might be inclined to plug in every time a
charger is available, with cumulative partial charges extending driving range on an ongoing basis.
Level 2 charging supplies 240V power that in the U.S. typically feeds an electric clothes dryer or kitchen
oven. Level 2 charging can take from 4 – 8 hours or more, depending on the battery energy level when the car is
plugged in, and charge rating capacity of the vehicle model. Presently, electronics on board the car convert
wall power to charge the battery, and each car model has its own power capacity rating, which affects charging
time. Level 3 charging is dedicated to the high current draw that an electric vehicle battery bank would need to
make an EV or PHEV practical for everyday use with rapid charging times of 2 hours. (However, charging times are
always limited by the rate of power feed that the vehicle model is designed to take.) For comparison purposes,
power ratings for EV/PHEV charging ranges from 3.3kW, 6.6kW, and 16.8kW at the present. Lower charging and
operating temperatures seem to extend the capacity-life of the batteries. Faster charging times correlate to
higher power and higher temperatures with present battery technology. But as technology evolves, charging rates
above 19kW, will become standard and significantly reduce charging times. It is guaranteed that technology will
outpace infrastructure and legislation.
In the U.S., taxation for roads comes via national gasoline sales taxes that are collected at the pump. This
taxation is avoided by early adopters of EVs and PHEVs until legislation dictates standards. Standardization of
the battery charging protocol is underway in the U.S., but not yet fixed. Standards encompass the
plug/connector, communication link, whether charging will be on-board or external to the car, and at what
physical point charging will be monitored in relation to the smart grid. Who and how electrical billing will
happen (exclusively for charging cars) is yet to be determined, and will likely be a de facto standard formed
where technology presents the most convenience.
