BMW I01 Product Information page 180

I01￿High-voltage￿Components
12.￿Technical￿Safety￿Precautions
3 The￿voltage￿in￿the￿high-voltage￿circuit￿is￿increased￿continuously
4 The￿contacts￿of￿the￿switch￿contactors￿are￿fully￿closed.
The￿high-voltage￿electrical￿system￿is￿mainly￿checked￿by￿the￿EME￿control￿unit￿and￿the￿SME￿control
unit.￿Criteria￿relevant￿for￿safety,￿for￿example￿the￿circuit￿of￿the￿high-voltage￿interlock￿loop￿or￿the￿isolation
resistance,￿are￿checked.￿Functional￿preconditions￿such￿as￿the￿operating￿readiness￿of￿all￿subsystems
must￿also￿be￿fulfilled￿for￿starting.
As￿the￿high-voltage￿circuit￿capacitors￿have￿high￿capacity￿values￿(link￿capacitors￿in￿the￿power
electronics),￿the￿contacts￿of￿the￿electromechanical￿switch￿contactors￿cannot￿be￿easily￿closed.
Extremely￿high￿current￿pulses￿would￿damage￿both￿the￿high-voltage￿battery￿and￿the￿link￿capacitors
and￿the￿contacts￿of￿the￿switch￿contactors.￿First￿of￿all,￿the￿switch￿contactor￿of￿the￿ground￿cable￿in￿the
high-voltage￿battery￿is￿closed.￿In￿order￿to￿restrict￿the￿switch-on￿current,￿there￿is￿a￿current￿path￿with
resistance￿in￿the￿positive￿wire￿(connected￿parallel￿to￿the￿switch￿contactor).￿This￿is￿now￿activated￿and
a￿switch-on￿current￿restricted￿by￿the￿resistance￿charges￿the￿link￿capacitors.￿If￿the￿voltage￿of￿the￿link
capacitors￿has￿reached￿the￿approximate￿value￿of￿the￿battery￿voltage,￿the￿last￿contact￿of￿the￿switch
contactor￿at￿the￿positive￿terminal￿of￿the￿high-voltage￿battery￿unit￿is￿closed.￿The￿high-voltage￿system￿is
now￿fully￿operational.
If￿there￿is￿no￿fault￿in￿the￿high-voltage￿system,￿the￿entire￿starting￿of￿the￿high-voltage￿system￿is
completed￿in￿about￿0.5￿seconds.￿There￿is￿thus￿no￿disadvantage￿for￿the￿customer￿in￿comparison￿to
vehicles￿with￿a￿conventional￿engine.
The￿SME￿control￿unit￿communicates￿successful￿starting￿via￿the￿PT-CAN2￿to￿the￿EME￿control￿unit.
Fault￿statuses￿are￿also￿communicated￿in￿the￿same￿way,￿if,￿for￿example,￿a￿contact￿of￿a￿switch￿contactor
was￿unable￿to￿be￿closed.
12.2.2.￿Shutting￿off￿the￿high-voltage￿system
When￿it￿comes￿to￿shutting￿off￿the￿high-voltage￿system￿a￿distinction￿is￿made￿between￿regular￿shut-
off￿and￿fast￿shut-off.￿The￿regular￿shutdown￿described￿here￿protects￿all￿respective￿components￿on￿the
one￿hand,￿and,￿on￿the￿other￿hand,￿includes￿the￿monitoring￿of￿components￿of￿the￿high-voltage￿system
which￿are￿relevant￿for￿safety.
Regular￿shutdown
If￿the￿following￿preconditions￿or￿criteria￿are￿present,￿the￿high-voltage￿system￿is￿shutdown￿in￿the￿regular
manner:
• Terminal￿15￿is￿switched￿off￿by￿the￿driver￿and￿the￿after-running￿period￿is￿expired￿(controlled￿by
EME)
• End￿of￿the￿functions￿"stationary￿cooling",￿"auxiliary￿heater"￿or￿"conditioning￿of￿the￿high-
voltage￿battery"
• End￿of￿the￿charging￿procedure￿for￿the￿high-voltage￿battery.
The￿sequence￿for￿the￿regular￿shutdown￿is￿generally￿the￿same￿irrespective￿of￿the￿trigger.￿The￿individual
steps￿are:
1 EME￿orders￿the￿shutdown￿after￿the￿after-running￿period￿has￿expired￿via￿bus￿signals￿at￿the￿PT-
CAN/PT-CAN2
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