Hybrid Car: High-Voltage Safety
Hybrid Car: High-voltage Safety
High-voltage components are included in the BMW active hybrid models, which have voltages of over 60 V direct current voltage or 25 V AC voltage. If live high-voltage components are touched then current could flow through the human body. This could lead to serious internal burns and ventricular fibrillation. High-voltage safety is a series of measures to protect against direct and indirect touching of live high-voltage components and inhibit the occurrence of electric arcs.
Brief component description
The following components are described for high-voltage safety:
- High-voltage interlock loop
- High-voltage safety connector
- High-voltage cables
System wiring diagram: High-voltage system, high-voltage interlock loop and service disconnect
High-voltage interlock loop
The high-voltage interlock loop is a circuit that protects against dangers when working on high-voltage components if the high-voltage electrical system was not switched off correctly.
If this circuit is interrupted, the voltage supply for the high-voltage system is switched off, or the voltage supply for the high-voltage system is prevented from being switched on. The status of the high-voltage interlock loop is evaluated by the battery management electronics (SME) and the electrical machine electronics (EME) by means of the signal (square wave signal with defined frequency).
High-voltage safety connector
The high-voltage safety connector is used to switch the high-voltage system to a de-energized state. With the active hybrid 5 and active hybrid 7, it is located behind the luggage compartment trim panel to the right of the fuse carrier, and in the active hybrid 3 it is located in the luggage compartment trim panel near to the high-voltage battery unit.
Pulling the high-voltage safety connector interrupts the circuit for the high-voltage interlock loop, causing the high-voltage system to switch off.
NOTICE: Remove the high-voltage safety connector
The high-voltage safety connector must be removed when terminal 15 is switched off in order to ensure that the switch contact does not wear too quickly. If this precaution is not taken, the high-voltage system is active when terminal 15 is switched on and the switch contacts are opened under load, which shortens the service life of this component.
High-voltage cables
High-voltage cables connect the high-voltage components to one another and are designated with orange cable sheaths or insulation.
WARNING: High-voltage cables must not be repaired. If they are damaged, the cables must always be replaced.
System functions
The following system functions are described for high-voltage safety:
- Passive and active discharge
- Insulation monitoring
- Switch-off of the high-voltage system in the event of an accident
Passive and active discharge
High-voltage components store electrical energy in their internal capacitors. To ensure that the stored energy of the high-voltage circuit is discharged a short time after the high-voltage system is shut down or in the event of an error, two discharge variants have been integrated:
- Active discharge: After every shut-down of the high-voltage system, the stored energy is discharged in less than 5 seconds by means of activation of a resistance. If the electrical machine is not intended to rotate, the connections for the voltage induced by the electrical machine are inhibited by means of a short-circuit.
- If active discharging fails to work or high-voltage components are disconnected from the electrical machine electronics when they are still carrying stored energy, passive discharging cuts in. The electrical machine electronics and electric A/C compressor have a resistor which discharges the energy in less than 5 minutes.
Insulation monitoring
The insulation monitoring system is used for continuously checking the insulation resistance of the high-voltage system. It is operated by the MME battery management electronics. Insulation monitoring is active during driving if the high-voltage system is switched on, and is active after the vehicle has been stopped if the high-voltage system is switched off. This means it is possible to determine whether an insulation fault is located internally, within the high-voltage battery unit, or externally, within the high-voltage electrical system.
If an insulation fault (fault threshold) is identified, a Check Control message, "High-voltage system fault" (ID 586), is displayed in the instrument cluster:
Switch-off of the high-voltage system in the event of an accident
The safety battery terminal on the system battery (12 V vehicle electrical system) is adjusted in such a way to ensure that in the event of an accident, the battery management electronics (SME) and the electrical machine electronics (EME) can receive the information via a signal line, redundant to the CAN message.
The EME short circuits the three phases of the electrical machine and initiates the active discharging of the link capacitors. The pyrotechnic unit on the safety battery terminal also causes the voltage supply to the switch contact in the high-voltage battery unit to be interrupted, so that the high-voltage system automatically switches off.
Notes for Service department
General notes
WARNING:
Hybrid cars have an additional high-voltage electrical system which has its own safety regulations to be observed. Work on live high-voltage components is expressly prohibited. Prior to every operation which involves a high-voltage component, it is essential to disconnect the high-voltage system from the voltage supply and to secure it against unauthorized return to service.
1. Switch off ignition.
2. Remove the high-voltage safety connector.
3. Prevent the high-voltage safety connector from being reinserted.
4. Switch the ignition on.
5. Always wait 10 s until the "HV system switched-off" Check Control message (ID 636) appears in the instrument panel.
In order to switch on the high-voltage system again, plug in the high-voltage safety connector and switch on terminal 15 (where required, perform a terminal change and, in the process, allow the vehicle to enter sleep mode): If the high-voltage electrical system is OK and the circuit of the high-voltage interlock loop is closed then the high-voltage system becomes active again.
Diagnosis instructions
NOTICE: Use the service function.
The BMW diagnosis system provides the following service functions for the high-voltage safety: - Locate insulation fault - Status, high-voltage safety
Path: Service function > Body > Voltage supply > Hybrid car > High-voltage safety
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