High-Voltage Interlock System

Overview

As EVs rely on high-voltage power systems ranging from 200V to over 800V, ensuring user and technician safety is critical. The High-Voltage Interlock System (HVIL) is designed to prevent accidental exposure to dangerous electrical currents.

This system continuously monitors connections within the high-voltage circuit, including the battery pack, inverter, motor, and charging systems. If a connector is unplugged, damaged, or improperly installed, the HVIL signals the Battery Management System (BMS) or safety relays to instantly cut power.

In short, HVIL functions as a protective “watchdog” that ensures no one comes into contact with live high-voltage parts, reinforcing the safety and reliability of electric mobility.

How Does It Work?

The HVIL operates through a low-voltage monitoring circuit integrated into high-voltage connectors and components:

1. Continuous Monitoring – A small voltage loop runs through all critical connectors in the high-voltage system.

2. Interruption Detection – If a connector is unplugged, broken, or tampered with, the loop is interrupted.

3. Automatic Shutdown – The HVIL sends a signal to the Battery Disconnect Unit (BDU) or BMS, which instantly opens the high-voltage contactors, isolating the battery.

4. Fail-Safe Operation – This ensures that no live high-voltage electricity is present when maintenance, repairs, or emergency responses are underway.

By combining simple monitoring with instant response, the HVIL adds a crucial layer of safety to complex EV systems.

Features of High-Voltage Interlock System

1. Connector-Level Protection

   Detects any disconnection or tampering in high-voltage connectors.

2. Automatic Isolation

   Cuts off high-voltage power instantly, preventing accidental shock or arc flash.

3. System-Wide Coverage

   Integrated across the battery, inverter, charger, and motor circuits.

4. Failsafe Redundancy

   Works with relays, fuses, and the BMS to enhance overall safety.

5. Simple Yet Effective Design

   Uses a low-voltage loop to monitor high-voltage systems without adding complexity.

Applications in EV

• Passenger Vehicles: Ensures safe operation by disconnecting high-voltage power during faults or maintenance.

• Commercial EV Fleets: Protects technicians working on buses, trucks, and delivery vans with large battery packs.

• Charging Systems: Monitors connectors during fast charging to prevent unsafe conditions.

• Crash Safety: In case of accidents, HVIL contributes to automatic isolation of high-voltage circuits.

• Servicing & Repairs: Provides a safe working environment for mechanics by guaranteeing de-energized systems.

Conclusion

The High-Voltage Interlock System is a fundamental safeguard in electric vehicles, ensuring that high-voltage circuits remain safe under all conditions. By providing automatic disconnection during faults, crashes, or improper handling, HVIL protects both drivers and technicians while reinforcing trust in EV technology. As battery capacities and voltages rise, HVIL will remain a cornerstone of safe and scalable electric mobility.