Detailed explanation of high-voltage interlock, one of the high-voltage
safety technologies of electric vehicles
What is high-voltage interlock
High-voltage interlock refers to the use of low-voltage signals to check the connection integrity of all branches connected to the high-voltage bus on electric vehicles, including power battery packs, controllers, high-voltage distribution boxes, etc. The lock pin is generally in the middle of the high-voltage plug. When the high-voltage plug falls off, the whole vehicle can be controlled to power off at high voltage at the moment the plug falls off without making pins.
Characteristics of high-voltage interlock
1. The HVIL circuit must be able to effectively, in real time and continuously monitor the on-off status of the entire high-voltage circuit.
2. All high-voltage connectors cannot be connected or disconnected without human intervention.
3. All connectors should have mechanical interlocking devices, and the HVIL should be disconnected first when the high-voltage connector is disconnected, and connected last when connected.
4. The high-voltage interlock circuit should be able to directly detect the HVIL circuit through the BMS under special circumstances and directly disconnect the high-voltage circuit.
5. When an abnormality is detected in the HVIL, the vehicle must alarm and indicate to remind the driver.
Classification of high-voltage interlock circuits
(1) Series type
Through a low-voltage line, the high-voltage connector at the unit end of the main high-voltage unit and the high-voltage connector at the harness end are short-circuited and connected. The VCU can know the integrity of the high-voltage component connection by detecting the signal on this line.
(2) Parallel type
The high-voltage interlock circuit is integrated inside the high-voltage control unit, and there is no external wiring harness. Each high-voltage connector interlock circuit is detected by the unit separately. If a high-voltage connector connection fails, the unit will immediately determine the fault location, which is convenient for detection and maintenance.
Detection of high-voltage interlock
If the high-voltage interlock fails, will it cause a short circuit or open circuit and then report a fault? When repairing, we can start from two aspects:
First, external inspection
External inspection is relatively simple: 1. Check whether the interlock plug has a pin withdrawal 2. Check whether the contacts of the interlock device are dirty 3. Check whether the power connection of the interlock device is normal. These can be judged by the naked eye. If there is no problem with the above, then internal inspection is required to see if the circuit is faulty.
The second is internal detection
Method 1: Use the DC voltage of an external meter to measure the two pin angles of the interlock line. If the voltage is normal, the voltage at the detection point A is about 9 volts, and the voltage at the detection point A is about 0 volts.
Method 2: Detect the PWM waveform, introduce a switch controlled by a PWM signal, and measure it with an external meter. After measuring the waveform signal on this terminal inside the VCU, compare it with the stored normal waveform signal. If the amplitude and frequency of the waveform signal are normal, the VCU confirms that the high-voltage system circuit is complete. If the amplitude and frequency of the waveform signal are abnormal, or if there is a fault, in order to prevent safety accidents, the vehicle system will prohibit high-voltage power-on and generate a fault code at the same time.
