BMW I01 Product Information page 182

I01￿High-voltage￿Components
12.￿Technical￿Safety￿Precautions
If￿a￿cell￿supervision￿circuit￿identifies￿extreme￿under-voltage,￿over-voltage￿or￿excess
temperature￿at￿a￿battery￿cell,￿this￿also￿leads￿to￿a￿hard￿opening￿of￿the￿electromechanical￿switch
contactors￿-￿controlled￿by￿the￿SME￿control￿unit.￿Although￿this￿may￿lead￿again￿to￿increased
wear￿at￿the￿contacts,￿this￿quick￿shutdown￿is￿necessary￿to￿prevent￿destroying￿the￿respective
battery￿cells.
Malfunction￿of￿the￿12 V￿voltage￿supply￿of￿the￿high-voltage￿battery￿unit:
•
In￿this￿case￿the￿battery￿management￿electronics￿control￿unit￿no￿longer￿works￿and￿it
is￿no￿longer￿possible￿to￿monitor￿the￿battery￿cells.￿For￿this￿reason￿the￿contacts￿of￿the
electromechanical￿switch￿contactors￿also￿open￿here￿automatically.
12.2.3.￿Charging￿the￿high-voltage￿battery
The￿SME￿control￿unit￿also￿plays￿an￿important￿role￿in￿the￿charging￿of￿the￿high-voltage￿battery￿with
energy￿supply￿from￿an￿external￿power￿network.￿Using￿the￿state￿of￿charge￿and￿the￿temperature￿of
the￿battery￿cells,￿the￿SME￿control￿unit￿defines￿the￿maximum￿electrical￿power￿which￿the￿high-voltage
battery￿can￿currently￿use.￿This￿value￿is￿transmitted￿in￿the￿form￿of￿a￿bus￿signal￿via￿the￿PT-CAN2￿to￿the
EME￿control￿unit.￿The￿"High-voltage￿power￿management"￿function￿coordinates￿the￿individual￿power
requirements￿and￿forwards￿the￿total￿value￿to￿the￿electrical￿machine￿electronics￿(and￿from￿there￿to￿the
convenience￿charging￿electronics).
During￿charging￿the￿SME￿control￿unit￿constantly￿identifies￿the￿state￿of￿charge￿already￿reached￿and
monitors￿all￿sensor￿signals￿of￿the￿high-voltage￿battery.￿In￿order￿to￿ensure￿optimal￿progress￿of￿the
charging￿procedure,￿the￿SME￿control￿unit￿constantly￿calculates￿current￿values￿for￿the￿maximum
charging￿power￿based￿on￿these￿values￿and￿communicates￿these￿to￿the￿EME￿control￿unit.￿The￿heating/
cooling￿system￿of￿the￿high-voltage￿battery￿is￿also￿continuously￿controlled￿by￿the￿SME￿control￿unit
during￿the￿charging￿procedure￿which￿contributes￿to￿a￿quick￿and￿efficient￿charging￿procedure.
12.3.￿Pinpointing￿isolation￿faults
The￿SME￿control￿unit￿reliably￿identifies￿when￿the￿isolation￿resistance￿in￿the￿high-voltage￿electrical
system￿drops￿below￿the￿specified￿values.￿A￿fault￿code￿entry,￿a￿Check￿Control￿message￿and,￿if￿required,
the￿shutdown￿of￿the￿high-voltage￿system,￿are￿automatically￿effected.￿The￿isolation￿monitoring￿in￿the
SME￿control￿unit￿alone￿cannot￿determine￿the￿actual￿location￿of￿the￿fault￿in￿the￿high-voltage￿electrical
system.￿Instead,￿an￿isolation￿fault￿must￿be￿pinpointed￿by￿using￿a￿test￿schedule￿in￿the￿diagnosis￿system.
Several￿systematic￿test￿steps￿are￿required￿in￿order￿to￿determine￿the￿components￿or￿the￿high-voltage
cable￿causing￿the￿isolation￿fault.
12.4.￿Start-up￿of￿the￿high-voltage￿system
If￿in￿the￿event￿of￿a￿repair￿high-voltage￿components￿are￿removed￿or￿replaced,￿it￿is￿imperative￿to￿ensure
that
• all￿high-voltage￿connectors
• all￿potential￿compensation￿lines￿and￿connections￿for￿potential￿compensation
• all￿signal￿connectors
• all￿coolant￿or￿refrigerant￿lines￿and
• all￿mechanical￿connections￿are￿properly￿connected.
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