What is a high-voltage interlock system?
1. What is a high-voltage interlock?
The high-voltage interlock of new energy vehicles refers to a safety protection measure that uses low-voltage signals to check the integrity (continuity) of high-voltage components, lines, high-voltage wiring harness connectors, and protective covers in the entire high-voltage circuit, identify abnormal disconnections in the high-voltage circuit, and disconnect the high-voltage electricity within milliseconds.
2. The functions of the high-voltage interlock are as follows
(1) Ensure the integrity of the entire high-voltage circuit, so that the high-voltage electricity runs in a closed loop, thereby improving the safety of the entire vehicle.
(2) During vehicle operation, when the high-voltage circuit is disconnected or its integrity is damaged, a fault signal is issued, so that the vehicle control system starts the corresponding safety protection.
(3) Prevent arcing when plugging and unplugging the high-voltage wiring harness connector under power.
3. Structure of high-voltage interlock
The high-voltage interlock circuit runs on low-voltage signals, so the high-voltage interlock wires need to be isolated from the high-voltage wires. High-voltage wiring harness connectors should have a high-voltage interlock function. When disconnecting the high-voltage wiring harness connector, the high-voltage interlock circuit should be disconnected first, followed by the high-voltage circuit. When connecting the high-voltage wiring harness connector, the high-voltage circuit should be connected first, followed by the high-voltage interlock circuit to prevent current surges from high-voltage electricity.
4. High-Voltage Interlock Principle
The high-voltage interlock circuit monitoring signal is generally emitted from the BMS or vehicle control unit (VCU), passing through the high-voltage wiring harness connector or high-voltage control box to complete the circuit.
The high-voltage interlock utilizes a control unit (BMS or VCU) and low-voltage wiring to form a closed circuit, which is responsible for checking the integrity of the circuit. If a short circuit or open circuit in the high-voltage circuit indicates a potential hazard, the high-voltage output of the power battery will be shut off.
Currently, pulse width modulation (PWM) is the most commonly used method for high-voltage interlock detection signals. In this PWM scheme, the control unit is responsible for sending and receiving PWM signals. Under normal circumstances, this PWM signal passes through high-voltage components such as the PTC heater, high-voltage control box, and electric compressor before reaching the control unit. The control unit checks the received PWM signal parameters (such as the duty cycle) to determine the integrity of the high-voltage circuit, the connection status of the high-voltage wiring harness, and the operating status of each high-voltage component. If the control unit does not receive the returned PWM signal, direct or potential hazards may arise, such as a misconnected high-voltage wiring harness connector (exposed high-voltage cable), damaged high-voltage components, or a failed protective structure.
Because the PWM scheme uses PWM signals, the control unit can detect high-voltage circuit faults even if a short or open circuit occurs in the high-voltage interlock circuit. This prevents the undetected exposure of high voltage caused by a low-voltage wiring harness fault, thus providing a higher level of safety. This scheme can utilize a single circuit or several relatively independent circuits. The latter approach offers the advantage of quickly identifying the fault location and selectively isolating it based on the fault condition, thus meeting the user's basic vehicle usage needs.
5. High-Voltage Interlock Control Strategy
Fault Alarm: When the high-voltage interlock system detects a hazard, regardless of the vehicle's state, the control unit must issue an alarm, alerting the driver through audible or visual signals, alerting them to the abnormality and allowing them to promptly address it to avoid a safety hazard.
Cutting off the high-voltage power supply: When the vehicle is stopped, if the high-voltage interlock system detects a dangerous condition in the high-voltage circuit, in addition to issuing a fault alarm, it also notifies the vehicle control system to disconnect the high-voltage contactor, thereby shutting off the high-voltage output of the power battery, avoiding potential high-voltage hazards and ensuring safety.
Reduced power operation: While the vehicle is traveling at high speed, if the high-voltage interlock system detects a dangerous condition in the high-voltage circuit, the vehicle control system cannot immediately shut off the high-voltage output of the power battery. Instead, it must notify the driver with an alarm and then reduce the operating power of the drive motor to slowly slow the vehicle down, ensuring that the driver can control the vehicle to a safe stop. At the same time, the load on the high-voltage system is reduced, thereby reducing the probability of a high-voltage safety accident.
