IEEE Electrification Magazine - March 2017 - 57

cells parallel, which is called 200s 2p. With this configuration, the maximum possible charging voltage is 830 V. In
this case, the maximum current limit of the two cells in
parallel with each at a 150-A max-charge-current leads
to a max total charge current of 300 A, which is well
below the maximum of the CCS contact system, resulting in a max-charging power of 249 kW.
The resulting charge power of about 249 kW enables a
charge time of 15 or 14 min less charging time than the
system with a 400-V configuration. However, in the highvoltage system, the cells are charged at a much higher
current (max 150 versus 87.5 A). Considering the limits
regarding aging and thermal characteristics, cell-power
degradation will appear at an earlier point of time. Furthermore, the thermal system of the vehicle has to be
designed carefully. Assuming a simplified internal cell
resistance of 1 mΩ, the thermal losses in a 400-V system
will be about 3 kW, and the discussed 800-V system will

Charge Times

90
80

400 V
800 V

Charge Time for
80% SoC at
400 km/250 mi

60
Min

50
40
30
20
10
0
Trend
50 kW 100 kW 150 kW 150 kW First
at
800 V
at
State of
800 V Passenger 800 V
the Art
Vehicle

Charging Characteristics
Comparison 800 V Versus 400 V

350
300
250
200
150
100
50
0

15 20 25
Time (min)

Power at 800 V
SoC at 800 V

100
90
80
70
60
50
40
30
20
10
0

SoC (%)

Figure 7. An overview over charging times.

Power (kW)

connection between the infrastructure and the internal
battery voltage is used.
Although the standardization allows voltages up to
1,000 V in the European Union (EU) or 600 V in the United
States (see Figure 4), the installed infrastructure delivers
up to 500 V due to the limitation imposed by the 600-V
IGBT modules. In addition, the installed power of the commonly installed infrastructure offers a maximum charge
power of 50 kW. All major regions are expanding the
applied standards (orange bar in Figure 4) to increase the
current, the voltage, or both for the charge connectors. The
CCS connector is already standardized to the maximum
voltage of 1,000 V with a planned current increase in
application, and similar activities can be recognized
regarding the GBT connector in China. Additionally, a limited increase of the charge power is possible with the
CHAdeMO connector. For example, in the summer of 2016,
a new initiative called CHAdeMO 2.0 started working on
an extension of this system to 1,000 V and 350 A.
The charge time for a typical electric vehicle using a
50-kW dc fast charging station is about 80 min (Figure 7).
Tesla has installed a fast charging infrastructure that is
able to recharge to 80% state of charge (SoC) or 400 km
with an average electric charge power of about 100 kW,
which reduces the charging time by half to a more attractive charge time of 40 min.
However, the dc fast charging stations of today can only
deliver a maximum voltage of about 500 V, whereas the discussed vehicle needs a charging voltage range between 600
and 830 V. Until a broad availability of 800-V compatible
infrastructure is ensured, an additional interface component in the 800-V vehicle is necessary. The dc-booster
shown in Figure 2 allows power transfer between a 400-V
charging station and an 800-V vehicle. Fast charging with an
800-V compatible charging station offers multiple advantages, and a simplified schematic is illustrated in Figure 5.
Two limits, charge current and cell voltage, determine
the maximum charge rate of the system infrastructure
and vehicle. The maximum charge current is limited by
the connection system between infrastructure and vehicle. In the case of the CCS connector, the current is limited
to 350 A. Battery systems as illustrated here show a typical
assumed maximum charge current of 150 A per cell.
Assuming a battery system with a 100s 4p configuration and the maximum charge voltage is 4.15 V per cell
(depending on the used chemistry) results in a max pack
voltage of 415 V. This leads to a maximum charge power of
about 145 kW, resulting in a charge time of about 29 min for
80% of SoC. While the principal charge power over time is
shown in Figure 8, the limits defined by the cell supplier
regarding aging and temperature must be considered. Due
to these limits, the shown simplified charge power (Figure 8)
will decrease at a certain point in time.
Reconfiguring the battery system to an 800-V system,
while keeping the same number of cells and capacity,
leads to a configuration of 200 cells in series with two

Power at 400 V
SoC at 400 V

Figure 8. The principal characteristics of charge power and SoC over
time.

IEEE Electrific ation Magazine / march 2 0 1 7

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