2023-09 SUSTAINABLE BUS

OUTLOOKS
32
HOW OPERATORS CAN ENSURE EFFICIENT AND SAFE OPERATIONS
LIKE A FLOCK
OF SHEEPS
What a flock of sheep has in common with
a battery system? Why is BMS crucial in
maintaining the health and performance of EV
batteries? How can diagnostic tools help?
Batteries are maintenance free –
that’s what’s generally said. No
oil change, no cylinder head
gaskets, almost no brake wear,
no consumables, no exhaust: perfect for
24/7 operation. Also, technological progress
just makes them better and stronger.
But is that true? Not necessarily. The
quest for longer range rather led to a decline
in lifetime. Early NMC-based batteries
lasted more than 2,000 cycles before
end-of-warranty (that is not equal to end
of life!) – far too much for cars (more than
300,000 km). Automotive technology has
thus approached the 1,000-cycle mark,
also impacting the bus industry and thus
THE AUTHOR
Claudius Jehle is CEO of
volytica diagnostics GmbH.
The company has the
mission of «providing an
easy-to-integrate battery
remote monitoring and
diagnostics solution to enable
a sustainable mobility
future». He cooperates with
Sustainable Bus on a series
of knowledge articles on a
series of topics around Li-
Ion Batteries.
Credit opening picture: BVG
raising the importance of lifetime management
and careful operation.
Are batteries ‘maintenance free’?
But even more important in daily business
is availability and safety. A battery
is like a flock of hundreds of single cells,
with delicate cables, electronics and
sensors tying them together. We know
from diesel engines how vulnerable such
clockworks are to component issues – but
here, something is peculiarly different:
the cells themselves.
Does the weakest sheep determine the behaviour
of the entire flock?
Any difference in quality or property
among the flock of cells will impact the
performance of the entire
herd. The battery management
system (BMS)
is there to handle such
deviations: asymmetries
in voltage/state of charge
are ‘balanced’ out to
some degree, e.g. during
idling after charging. But
if the asymmetry has become
too pronounced, or
if the BMS is unable to
sense it (a huge problem
of LFP), a battery can
just shut down or show unexpected behaviour,
such as sudden standstill, erratic
jumps in State of Charge or significantly
reduced range.
But why do such ‘evil’ asymmetries arise
in the first place?
On balancing, BMS, diagnostics
Balancing works best during rest, so heavy
use reduces balancing efficiency,
especially for LFP. Also, small quality
differences will intensify due to imperfect
cooling. Standard BMS can handle
normal spreads, but outliers always exist.
Also, the electronics can only detect an
existing problem and are limited in predicting
them. All of that is amplified by
strong usage conditions like fast charging
or low temperatures that make it even
worse, raising the likelihood of safety critical,
cell-internal damages.
Fine precursors for these bad things can
be sensed in the interplay of voltages,
currents and temperatures (but: temperature
is the last to react!), but they are
often too subtle and gradual for any BMS
to spot unambiguously and without being
too squeamish. Online diagnostic tools
can give early indications on things that
BVG’S WAY IN DEALING WITH BATTERY TECHNOLOGY
BVG aims to decarbonize its entire bus As a transport company, we want to
fleet with approx. 1,750 electrically deal with this ourselves in order to build
powered buses by 2030. As early as up internal expertise. In doing so, we are
2023, 228 e-buses will be on the roads of looking for supportive and experienced
Berlin. A vehicle tender for a framework partners».
contract for new electrically powered
What tangible results have you already
articulated buses is currently underway.
been able to achieve with battery diagnostics?
Kevin Doãn, battery technologist at
BVG, outlines the challenges of the battery
technology for electric buses.
Besides charging infrastructure, what
worries you the most?
Doãn: «The battery technology
of buses is subject to very
dynamic development and is
therefore a key component
of new vehicles. In addition
to passenger safety concerns
and compliance with the extensive
warranty conditions,
we are confronted with a
complex electromobility system.
At present, volatile general
conditions are a constant companion
and make future planning difficult.
Electromobility is currently associated
with high costs, as there is currently no
1:1 replacement of vehicles».
Regarding the battery, which responsibilities
do you see for the manufacturer
and which for the PTOs respectively
owners?
«The vehicle manufacturers are rarely
the battery manufacturers themselves.
So, the high-voltage battery is a subsystem
that the vehicle manufacturers
integrate into their vehicle concepts,
and the responsibility must lie with the
battery manufacturers to monitor the
production process accordingly. As the
operator of the vehicles, I see the responsibility
to ensure the safe operation
of all components, whether through
maintenance intervals or battery diagnostics.
A ‘defective’ battery cell can be
detected much earlier than when it fails.
«Although for the time being only a
small part of our electrically powered
vehicle fleet is being monitored by external
partners, we have already had our
first taste of success. A few months ago,
an anomaly was detected that indicated
a problem with individual cells, with the
potential for vehicle failure. The anomaly
detection allowed the vehicle to be
taken out of service and the battery system
to be repaired by the vehicle manufacturer
within the warranty period».
What does this mean for day-to-day
operations?
«Not only can we convey safety to our
passengers, but we can also prove and
ensure it. By detecting deviations at an
early stage, a technical defect could be
detected, checked, and remedied. This
indirectly increases vehicle availability
in daily operation. Another important
aspect of decarbonisation for us is the
sustainability factor: with battery diagnostics,
the charging management can
be analysed and adjusted to extend the
life of the battery».
Does this incident have any influence
on future decisions?
«Yes. From this case study we have seen
the possibilities that battery diagnostics
/ battery monitoring offer. As BVG, we
must continue to work intensively on
the topic of battery diagnostics, which
means both building up internal knowhow
and working continuously with
partners in the areas of battery, charging
and drive technology».
33