in the next few minutes I'll explain the
main components of the BMS modeled in
Simulink we can use this model for
desktop simulations where we can for
example reproduce diverse usage cycles
and environmental conditions to evaluate
the system's response to a potentially
unsafe condition for example a
temperature voltage or current outside
the recommended limits let's say this
battery system is part of an electric
vehicle powertrain say the battery is
75% charged and the outside temperature
is 15 degrees Celsius in these
conditions we start driving for a while
and stop and charge the battery finally
the battery is at rest and the balancing
cycle kicks in how do we know that
during these three typical usage stages
the battery pack remains within
recommended electrical and thermal
limits what if the temperature is 40
degrees Celsius instead of 15 how about
if the initial state of charge is 30%
well an aggressive drive cycle will
cause an under voltage situation a model
allows the vehicle designer to test all
these situations in simulation without
risking causing damage to the real
battery this is the BMS model in
simulink the battery and its management
system are inside this model reference
on the top left we define a different
driving scenarios that determine the
test sequence provided by the subsystem
on the bottom left the green lights at
the top right indicates whether there
has been a fault for example any cell
has reached an over temperature
condition the system itself has a model
reference representing the BMS ECU with
its various monitoring and control
algorithms connected to a block with a
representation of the battery pack and
associated circuitry and peripherals
this model contains two versions of the
battery pack a small one with just six
cells connected in series and a larger
one with 16 modules
each module containing the six Celsius
string in all cases we model just one
parallel string let's start with a
description of the battery pack and
spare Ferrell's the variant subsystem on
the Left contains the two versions of
the battery pack mentioned before the
one with six cells and the large one
with 96 cells let's take a look at the
small one first this battery pack is
model in sim scape where the component
color tells us its physical domain for
example blue indicates electrical an
orange indicates the thermal we can see
that the six cells are connected in
series and can exchange heat with one
another the thermal layout is
asymmetrical with cell number six at the
bottom
insulated on one side so no heat can
dissipate in that direction and cell
number one at the top exposed to the
outside atmosphere and therefore getting
rid of the heat by convection this
asymmetry will be responsible for a
significant temperature difference among
the six cells so what makes each unit
cell representative of a real-life
little man chemistry say nickel
manganese cobalt or NMC well inside each
cell there's an equivalent circuit whose
topology and parameters should give me a
response equivalent to the one I would
observe experimentally the equivalent
circuit components should also include
temperature SOC and possibly aging
dependencies if you are interested in
cell characterization a detailed account
on how to perform this parameter
estimation on battery cells is available
on website searching for battery
modeling next to the battery pack
there's a subsystem with a passive
balancing circuitry commanded by the
balancing logic from the BMS algorithm
these switches selectively closed when
their corresponding cell needs a partial
discharge to lower its associ
maintaining the battery cell modules
imbalance allows me to better utilize
its total storage capacity as we will
see in a few minutes another important
element of the plant model is the set of
charger and inverter contactor circuitry
prior to connecting a battery back to a
charger it is important to pre connect
them via a resistor to prevent an
excessively high current from rushing
into the pack and potentially damage it
this pre connection needs a special
sequence that we will show and we
describe the BMS algorithm finally the
last piece of the battery plan that we
model here are the charger and the load
both simply represented here by current
sources commanded to follow the charging
and driving profiles from the source
block at the model top level