Truck & Off-Highway Engineering - June 2022 - 26

EXECUTIVE VIEWPOINTS
Solving the challenges of
Megawatt chargers
Littelfuse executive details an alternative technique for fast and efficient highpower
charging of commercial electric vehicles.
by Dr. Martin Schulz
efficiency must be the most important design objective since power
losses can result in increased costs and wasted energy. An alternative
design, detailed in this article, is based on topologies used for electrolysis,
which substantially improves circuit efficiency, reduces system
complexity and dramatically reduces energy costs.
Magnitude of power required
CEV delivery vehicles providing intra-city services during the day
often have a central depot where overnight charging is practical.
With at least eight hours of idle time, an 8-10 kW charger is sufficient
to recharge 50-80 kWh into a vehicle's battery. A typical electric bus
will have a 250 kWh capacity and need 30-40 kW for a recharge during
a 6- to 8-hour idle timeframe. A 500 kWh charger typically serves
this charging requirement.
When the luxury of an overnight charge is not practical, such as for
vehicles traveling long distances, chargers at stations along the road
must be available. A long-haul CEV can use 500 kW delivered in under
30 minutes, and that level of energy delivery requires charging power
greater than 1 MW. As a result, standards for high-power charging stations
define power levels up to 2.2
MW and allow for options to upgrade
to 4.5 MW in the coming years.
A forced air-cooled 12-pulse thyristor stack supports 2 MW
of output power and has a smaller space requirement than a
MOSFET configuration.
T
he most significant barrier to the growth of
electric vehicles (EVs) is the battery charging
infrastructure. The availability of charging stations
and the time required to recharge vehicles
have become the critical impediment limiting
the adoption of EVs, which is particularly true for
long-haul commercial electric vehicles (CEVs). Heavyduty,
fossil-fuel vehicles such as trucks and buses contribute
about 25 percent of total vehicle emissions.
Electrification of these heavy-duty vehicles poses a
challenge for the charging infrastructure because the
vehicles operate over long distances and have random
routes. A charging station will require available
power above 1 MW to recharge a long-haul CEV in
under 30 minutes, the time a driver would find acceptable
for a meal break.
A conventional circuit design for a high-power charging
station employs wide bandgap semiconductors
such as SiC MOSFETS. However, the highest possible
26 June 2022
Dr. Martin Schulz, Global Principal,
Application Engineering, Littelfuse.
" A charging station
will require available
power above 1 MW
to recharge a longhaul
CEV in under
30 minutes, the
time a driver would
find acceptable for
a meal break. "
High-power charging
technology
Current chargers on the market,
such as passenger-car chargers,
have power levels up to 350 kW
and are often installed in groups of
six to ten charging stations. The
required power for the installation
necessitates step-down transformers
to convert 10-30 kV grid voltages
to about 690 VAC. Figure 1
shows a charging station installation
block diagram with four chargers.
The AC-DC converters achieve 350
kW by paralleling units typically
sized between 60-80 kW. The ACDC
converter consists of an input
state with boost and power factor
correction circuits and an output
DC-DC buck converter stage. The
output stage supplies a controlled
voltage suitable for the charged
vehicle battery.
TRUCK & OFF-HIGHWAY ENGINEERING
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Truck & Off-Highway Engineering - June 2022

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