The role of high voltage interlocking
A safe design method for monitoring the integrity of high voltage circuits with low voltage signals. In theory, the low-voltage monitoring loop is connected first and then disconnected than the high-voltage one, and the necessary advance is maintained in the middle. The length of time can be determined according to the specific situation of the project, such as 150ms, roughly in this order of magnitude. Specific high voltage interlock implementation form, different projects may have different designs. The target is an electrical interface such as a high-voltage connector that requires manual operation to open or disconnect a circuit
Reasons for high voltage interlocking of electric vehicles
From the perspective of system function security, each possible risk needs to be monitored by corresponding security technical means to reduce the probability of risk occurrence. From this perspective, high voltage interlocking, as a safety measure for the safety of high voltage system of electric vehicles, is used in circuit design.
One of the risk points for high-voltage systems in electric vehicles is a sudden power outage and loss of power. There are a few things that can cause a car to lose power, one of which is a loose high voltage loop. High voltage interlocking can detect this sign and provide an alarm to the vehicle controller before the high voltage power outage, allowing the vehicle system time to take action.
Another risk point for electric vehicles is human misoperation, which manually disconnects high-voltage connections while the system is working. If there is no high-voltage interlocking design, the entire circuit voltage is applied to both ends of the breakpoint at the moment of disconnection, which is very dangerous for high-voltage connectors and other devices that do not have the ability to break. The voltage breakdown air pulls the arc between the two devices for a short time, but can be very high, which may cause injury to personnel and equipment around the breakpoint.
There are several different theories about the specific purpose of high voltage interlocking. Some people believe that high voltage interlock mainly plays a role before the vehicle on the trolley. If the circuit is detected to be incomplete, the system cannot be powered on to avoid accidents caused by virtual connection and other problems. It is also believed that the high voltage interlock mainly plays a role in the collision blackout process, and the collision signal triggers the high voltage interlock signal to power off the system. However, in the critical situation after the collision, the steps to perform power outage should be as few as possible, and the collision signal is directly transmitted to the VCU, which is more logical.
Design principles of high voltage interlocking
1. The HVIL loop must be able to effectively, real-time and continuously monitor the on-off status of the entire high voltage loop.
2. All high voltage connectors shall be equipped with mechanical interlocking devices, and HVIL will disconnect the high voltage connector first when it is disconnected; When engaged, connect HVIL later.
3. All high-voltage connectors cannot be connected or disconnected in non-human conditions
4. The high voltage interlock loop shall be equipped with the ability to detect the HVIL loop directly through the BMS and disconnect the high voltage loop directly under special circumstances
5.When HVIL is identified as abnormal, the vehicle must give an alarm indication, such as instrument indicator light or sound or light to alert the driver.
Working principle
When there is an emergency disconnect, the monitoring point 1 directly feeds the detection result to the BMS, which disconnects the three high-voltage relays. When the high voltage connector of the motor and DCU are well connected, the low voltage relay 2 is connected, and the 12V of the BMS is connected. When the high voltage connector is not well connected, the low voltage relay 2 is disconnected from the BMS to realize the power failure function. The other HVIL components check their Hvil status by checking points 3, 4, and 5 respectively and report back to VCU.
Advantages and disadvantages
Each high voltage component has its own HVIL test. If a fault occurs, it is easy to troubleshoot. The HVIL status of the motor and the DCU can directly determine whether the BMS work and reduce the risk. The disadvantage is that the low-voltage relay is added to control the BMS power supply, which makes the wiring harness design more complicated and increases the total mass of the wiring harness. In addition, if the low-voltage relay 2 is attached, the VCU can only indirectly disconnect the high-voltage components through the BMS.
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