PRODUCTS & SERVICES
Faster on-board charging
In the coming years, battery
electric (BEV) and plug-in
hybrid (PHEV) vehicles will shape
the cityscape much more than
they do today. Both use lithium-ion
battery packs with a capacity of
40kWh to 80kWh (BEV) or around
10kWh (PHEV). With BEVs, charging
from an external source is a basic
requirement; with PHEVs, it is in
addition to recuperating kinetic
energy, for example during braking.
There are three basic charging
scenarios, which each have di erent
charging power requirements.
Main Harbor Charging refers
to charging at locations where the
vehicle is kept for a long duration,
typically at home and at work.
Charging time plays a minor role,
so the available installation is used
and provides power levels up to
1.9kW (120V, 16A, ‘AC level-1’) in the
US or 3.6kW (230V, 16A) in the EU.
To charge a battery with a
capacity greater than 40kWh
overnight or during working hours,
the charger will require an output
power of 11kW or more, which
necessitates three-phase power
inputs. Main Harbor Charging
is where the on-board charger
(OBC) in the car comes into play,
converting AC from the external
power source to DC to charge
Destination Charging occurs
at locations such as car parks at
supermarkets and shopping centers.
It lasts for a shorter time and is
usually used to recharge the battery
su iciently, rather than fully. This
requires a higher charging power
and, today, most charging stations
are still based on AC level-2, which
reaches up to 43kW of charging
power. AC-DC conversion is carried
out by the vehicle’s onboard charger,
which also limits charging speed,
depending on its maximum power.
Therefore, the trends goes to DC
the active power factor correction
stage (PFC) and the DC-DC voltage
converter (DC-DC). The PFC stage
secures an active power factor of
>0.9 on the line side, implements
the rectification of the AC line
voltage to an intermediate DC
circuit voltage and communicates
with the charging station.
The DC-DC converter controls
the battery charging current and
separates the mains from the
battery side by galvanic isolation.
182 // January 2020 // www.electrichybridvehicletechnology.com
Various topologies are available
for each option, but choice is limited
in the automotive sector to meet
cost and space requirements: boost
converter or totem pole for the PFC,
as well as LLC or ZVS phase shift
for the DC-DC.
In addition to the topology,
the focus in system design is
on the power semiconductors.
They impact power dissipation,
maximum achievable switching
frequency and robustness. This
in turn a ects power density, cost
and e iciency.
Each of the circuit topologies
mentioned requires di erent types
of semiconductors. For example, the
high switching frequency of an LLC
converter (up to 500 kHz) means
MOSFETs are the best choice.
A totem pole PFC operating
in continuous conduction mode
requires fast switching IGBTs due
to hard switching of the devices,
while silicon carbide (SiC) MOSFETs
and diodes can increase e iciency.
Infineon Technologies o ers the full
range of power semiconductors
specifically designed for OBC
systems as well as suitable driver
ICs and microcontrollers.
Cost and space limitations make on-board charging tricky, but
semiconductors make for compact and cost-efficient chargers
The three basic charging scenarios for BEVs and PHEVs
FREE READER INQUIRY SERVICE
To learn more about Infi neon,
fast-charging stations that integrate
the power conversion, enabling
charging at 50kW and more.
With Range Extension Charging,
the battery is charged in the
shortest possible time to enable
longer distances for BEVs. The
respective DC fast-charging stations
feature today power in the range of
50kW to 120kW. For the near future
up to 350kW are planned.
The OBC combines the
conversion from AC to DC voltage
and the control of the battery
charging, which means it needs
to ensure compatibility with single
and three-phase power networks
in addition to the various required
communication protocols. At the
same time, active power factor,
isolation and EMC requirements
need to be met in the input side,
as well as supplying the proper
charging current and voltage
on the output side.
An on-board charging system
will consist of two subsystems:
Onboard charging comprises two subsystems: PFC and the DC-DC converter