The High Voltage Interlock Loop (HVIL) monitors all components connected to the high-voltage cables in an electric vehicle via low-voltage signals. It detects the integrity of the electrical connections in the high-voltage system circuit and activates safety measures when the circuit is broken.
In high-voltage systems, potential leakage currents or connection failures pose risks to both the vehicle’s electronics and users. HVIL instantly detects such conditions and initiates a power cutoff. This ensures that during an accident, the vehicle’s high-voltage system is rapidly deactivated, protecting both occupants and first responders. It also safeguards technicians during maintenance and repair operations. Standards such as IEC 61851 and ISO 26262 mandate the use of HVIL.
The battery management system may know quite a lot about the HV system. For example, it probably hosts the HV isolation monitoring function or the HVIL function. It will certainly know if any of its contactors are welded or stuck open.
When designing a battery pack / system it is important to think about and describe the safety concept. This needs to be considered in a systematic way.
See also: ISO 6469-3, Battery Disconnect Unit