Tech Briefs Magazine - February 2022 - BT-10

Battery Testing
The high-power inverter technology is
crucial to this testing platform. It provides
the modular power conversion, taking
the plant's main AC power and converting
to DC, then delivers power efficiently
to DC/DC inverters on a common
DC bus. DC/DC inverter set(s) are connected
to the battery pack being tested,
interfacing with the test computer and
BMS to carry out the discharge, recharge
and full charge cycles as dictated by the
testing program.
Bosch Rexroth's IndraDrive ML scalable range of inverters enables effective solutions for battery
pack and e-axle testing, with a versatile DC/DC drive design that provides the smallest
footprint and weight to save valuable control cabinet space. (Photo: Bosch Rexroth)
able energy/charge in the pack. The BMS
also controls the energy discharge (when
the EV demands energy) and recharge
(when power is fed back into the battery
via regeneration and/or full charging).
End-of-line battery and e-axle testing
systems must take into consideration the
challenges associated with high-output
mass production of vehicles using them -
by one estimate, a plant producing 50 EVs
per hour would have a new battery pack
to test every 72 seconds. Battery packs
and e-axles are complex devices, with
size and weight dimensions that
require careful handling to move
efficiently through testing systems.
In response to these challenges, a
new generation of battery and eaxle
testing systems is being developed,
built around a combination of
advanced testing software modules
and the latest generation of highperformance
industrial inverter
drives. These high-power inverters,
such as the modular and scalable
Bosch Rexroth IndraDrive ML, provide
the safe, controlled, and rapid
delivery of DC power to the test
stands, in order to supply/remove the
correct amount of power to battery
packs and e-axles according to the
testing program's requirements.
The system topology for the battery
charging and e-axle testing sys10
tems
is similar, although not completely
identical. The EV manufacturer creates the
master testing program, which typically
runs on an industrial PC, and controls the
specific charge and load cycles. These
cycles are designed to match real world
demand specifications for driving, regeneration
and charging, and to verify
that the e-axle and battery performs
as designed, by comparing
the command and actual data
point, as well as EV equipment data.
The DC/DC inverter and the BMS provide
the real-time data the testing system
needs to evaluate whether the battery
pack or e-axle is performing according
to specifications: the BMS computes,
tracks and monitors the available energy/charge
and the EV's computer computes
the available range, based on the
vehicle's drives and electric motors.
The testing system inverter power supply
can report real-time voltage, current
and power as each battery pack or e-axle
is cycled through the testing sequences.
The versatility of the Rexroth IndraDrive ML platform makes
it easier for EV manufacturers to select one common inverter
power stack for power supply, inverter, and DC/DC converter
to support both battery pack and e-axle testing systems.
(Photo: Bosch Rexroth)
Key Inverter Features for EV
Testing Systems
To support the rigorous, high-throughput
testing demands for these systems, the
scalable inverter technology and system
plays a central role. They need to
be efficient to support very dynamic
current ramps into the EV inverters
and/or battery, charging and discharging
power at the required
voltage, and also exercise tight
control of the power flow.
The most crucial performance
consideration for testing system
inverters is their ability to support
a broad range of DC output
voltages and currents. One reason
this is critical is that EV manufacturers
have been increasing
their battery pack storage and
output capacities. Older battery
packs were often limited to
approximately 420 volts (DC),
and the charging systems were
limited in power (typically 11 kW
to 50 kW). These could take too
long to charge from 20 percent
to 80 percent.
EV manufacturers are moving
to more powerful packs - in the
800 V to 900 V DC range - so it
Battery & Electrification Technology, February 2022
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Tech Briefs Magazine - February 2022

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