IEEE Electrification Magazine - March 2017 - 58

show a thermal loss of 9 kW at a 249-kW charging rate.
This thermal loss needs to be managed by the thermal
capacity and the cooling system of the vehicle. The
boundary conditions of battery temperature and cooling
requirements in this case lead to a vehicle thermal design
with coolers similar in size to coolers of today's conventional combustion vehicles.
The previous discussion demonstrates that an infrastructure for 400-V class vehicles is already at its technical design limits, while the 800-V system shows potential
for further improvement. Calculations verify that the
minimum charge time of a battery system in a 400-V system is about 29 min. An 800-V vehicle including a dc
booster can gain two minutes in charging time, because
the infrastructure does not have to follow the characteristic voltage curve of the battery. This results in a minimum charge time of 27 min, which is shown in Figure 7
(the 150 kW at 800 V bar). Additionally, the 800-V charge
stations are downward compatible and can serve cars
with 400-V technology.
As discussed in the beginning of this section, the
800-V technology leaves room for further improvement
in charging time and charging power. Right now, the
battery technology limits the charge power, but battery
advancements in the coming years will allow charge
time improvements. The short charge times can become
an important commercial advantage that brands can
use to advertise their vehicles.
A fast-charging infrastructure with a charge power up
to 350 kW will probably make sense, especially at rest stations along long-distance travel routes. Thus, to provide
sufficient coverage in main markets, 500 fast-charging stations per continent are necessary. If each charge station is
equipped with four to eight 350-kW charge points, then
500 charge stations in each of the 50 United States and the
EU would provide sufficient coverage.
A further advantage of 350-kW charging stations is a
possible higher throughput. Due to faster charging rates,
the throughput can be increased by about 70% compared to a 400-V station. In contrast, the cost increase
for providing a charge station serving 400- and 800-V
systems is incremental. The reason is that the charge
station installation cost is mostly driven by the installed
maximum current capacity, which does not change for
the 800-V system.

advantages for the customer
Ultimately, introducing a new technology must lead to a
substantial advantage for the customer for a successful
introduction to the market. In the long term, a cost reduction is expected by transitioning from a 400-V system to
an 800-V system, because less physical material is necessary in a car designed for higher voltage. In contrast, first
generations of these vehicles must carry the financial
burden of the initial development cost. Also, converted
designs and vehicles in the lower segment can utilize the

I E E E E l e c t r i f i c ati o n M agaz ine / march 2017

advantages but not in the early component generations.
A classic top-down introduction for high-performance
products will probably be observed in the market.
The possible weight reduction of an 800-V system will
lead to slightly increased efficiency of the electric vehicle.
This improved efficiency is the needed motivation to
introduce these systems first in sports cars. Nevertheless,
the battery weight still dominates the overall weight of the
car in the 800-V system.
The customer will see a substantially decreased charging
time. Short charging stops will become common, since
recharging 100 km in 5 min will be possible. This may make
electric vehicles more attractive to owners who do not own
a fixed parking lot, especially in large cities, since the owners
can simply have a short refueling stop on the way home. For
comparison, the median time a driver spends at a European
rest stop for refueling is approximately 12 min.
Using high power at the HV level lowers the necessary
charge current, and this reduces the necessary cross section of the charge wire at the charging station. Consequently, the charge handle for 800 V should be much more
comfortable than the handle for high-power charging at
low-voltage levels (400 V) that is typically made with a
heavy, high-gauge wire, which the flexibility and ease of
handling a 120 mm2 charge cable in the winter in Detroit,
Michigan, or Beijing, China, are not great. Liquid cooled
charge cables (under development) appear to be a step forward toward development of a lightweight and comfortable charging system.

Outlook
For electric vehicles to be successful in the market, comparable requirements regarding use and handling of
today's cars have to be fulfilled. The customer expects a
vehicle without any major limitations, especially range,
charging times, and comfortable handling. Exclusive use
in the city may satisfy limitations in range and charging
time, but this only applies for a limited time and limited
pool of customers. Similar to today's vehicles, many customers expect the ability to use the vehicle for traveling
long distances without a negative impact on the refueling time. Charging times of 40 min for 400 km is far from
this expectation.
The 800-V technology overcomes some of this limitation. Products that are to be introduced in 2019 will have
a charge time of 15 min. Additionally, the 800-V technology offers a possibility of further charge-time reductions.
Multiple advantages of the 800-V technology lead to a
substantial advantage in the vehicle design if the design
process allows for system-wide optimization and not an
individual component optimization design approach.

Biography
Christian Jung (cjung07@me.com) is a senior director of
electronics at Faraday Future, Gardena, California.

Table of Contents for the Digital Edition of IEEE Electrification Magazine - March 2017