High-voltage interlock design is used in automotive circuit design as a monitoring method for electric vehicle high-voltage systems. During the operation of electric vehicle high-voltage systems, the biggest risk is that the vehicle suddenly loses power and loses power. There are many reasons for the loss of vehicle power, one of which is the loosening and disconnection of the high-voltage circuit connection position. The high-voltage interlock design can monitor the continuity of the circuit and send an alarm signal to the VCU before the high-voltage power is cut off, so that the VCU can take countermeasures for the entire vehicle system.
Another type of risk point for electric vehicles is manual disconnection of the high-voltage connector due to human error during the operation of the system. At the moment of disconnection, the entire circuit voltage is applied to both ends of the connector terminal, and the high-voltage connector itself does not have the ability to break. The voltage breaks through the air and produces a strong arc between the two devices, which may cause damage to personnel and equipment around the breakpoint. The existence of the high-voltage interlock design can disconnect the output of the power battery at the same time when the connector is disconnected to avoid electric shock.
01 High-voltage interlock analysis
1.1 Definition of high-voltage interlock
High-voltage interlock (HVIL) is a safety design method that uses low-voltage signals to monitor the integrity and continuity of high-voltage circuits. The high-voltage interlocking design can identify abnormal disconnection or damage of the high-voltage circuit and disconnect the high-voltage electricity in time. In theory, the low-voltage monitoring circuit is disconnected before the high-voltage circuit and connected later, and the necessary advance amount is maintained in the middle. The length of time can be determined according to the specific strategy of the vehicle model.
1.2 Principle of high-voltage interlocking
All high-voltage connector connection positions of the whole vehicle require a high-voltage interlocking signal circuit, but the interlocking circuit and the high-voltage circuit are not necessarily related. On the whole vehicle, electrical appliances A and B form a complete circuit. However, the high-voltage interlocking design may set a separate interlocking signal circuit for electrical appliance A, and also set a separate interlocking signal circuit for electrical appliance B; it is also possible to connect the interlocking signals of A and B in series in one circuit. That is, the interlocking circuit can be designed in parallel mode or in series mode.
The high-voltage system of the whole vehicle uses the power battery as the power source, and the low-voltage circuit also needs a detection power source to allow the low-voltage signal to be transmitted along the closed low-voltage circuit. When the low-voltage signal is interrupted, it means that a high-voltage connector is loose or detached. The basic principle of high-voltage interlocking is shown in Figure 1/Figure 2. Based on the high-voltage interlock signal loop, a monitoring point or monitoring loop is designed to transmit the status of the high-voltage interlock signal loop to the BMS.
1.3 Composition of the high-voltage interlock loop
The implementation of the high-voltage interlock design requires the following equipment: high-voltage interlock connector and high and low voltage wires, closed low-voltage power signal loop, high-voltage interlock monitoring loop and monitoring module (the monitoring module can be a battery management system BMS, or a vehicle controller VCU), and a high-voltage relay controlled by the monitoring module according to the high-voltage interlock monitoring results.
The high-voltage connector with high-voltage interlock function consists of a shell, a high-voltage conductive part, a low-voltage signal conductive part, a monitoring module and a monitoring circuit. The high-voltage interlock connector is generally implemented by fixing a pair of high-voltage connectors and a pair of low-voltage connectors on a pair of male and female ends. When the high-voltage plug-in is in the disconnected state, the low-voltage circuit is cut off; when the high-voltage plug-in is in the connected state, the low-voltage circuit is also connected to form a complete circuit.
02 High-voltage interlocking case
2.1 High-voltage interlocking design
The electric vehicle adopts a series connection method, which leads the high-voltage interlocking low-voltage detection line from the positive pole of the BMS, passes through the PDU-DCDC-ACCM-PTC and then returns to the negative pole of the BMS to form an interlocking loop. Under normal power-on conditions, the output voltage of the interlocking loop is generally ≥5V and ≤9V. When it is necessary to check whether there is a problem with the high-voltage interlocking, detect the voltage of the two pins of the BMS input and output. If it is within the design voltage range, it is normal. Or directly measure the loop resistance. Theoretically, the resistance value of the loop is 0Ω, and anything below 5Ω can be regarded as 0Ω.
Each high-voltage electrical device is connected in series by a low-voltage interlocking loop. When the high-voltage wiring harness is connected to the high-voltage electrical appliance, a connector with a high-voltage interlocking structure is used to connect the entire loop. As long as the high-voltage plug-in is not connected or disconnected, the entire low-voltage interlocking loop will be disconnected, the BMS will stop providing high-voltage output, and external operators will not be in danger of electric shock. As shown in Figure 4, the schematic diagram of the high-voltage electrical appliance interlocking loop connection.
2.2 High-voltage interlock troubleshooting
Take a certain electric vehicle as an example, to determine whether the vehicle has a high-voltage interlock fault, two conditions must be met:
First: the power battery fault indicator light in the instrument cluster is always on;
Second: the message $1D8:BMS_General_Status_1::HVInterLoStat=False sent by the BMS on the CAN line.
When both conditions are met at the same time, it can be determined as a high-voltage interlock fault. At this time, according to the electrical principle of the high-voltage interlock in Figure 3, a logical troubleshooting method is formulated.
Interlock circuit troubleshooting: First, disconnect the 12V low-voltage power supply of the vehicle. Then disconnect the low-voltage plug-in connecting the BMS to the power battery, and use a multimeter to measure the resistance value between the BMS positive output X2-10 and the negative input X2-11 pins. If the resistance value is greater than 5Ω, it is necessary to check the continuity of the entire high-voltage circuit.
a) Check all high-voltage plug-ins for missing or weak connections;
b) Check the interlocking paper clips of the high-voltage plug-ins for bending or breaking;
c) Check the low-voltage 4 modules (PDU-DC/DC-ACCM-PTC) for missing or weak connections;
If the circuit is confirmed to have the above faults, it can be solved directly. If the circuit check does not have the above faults, it can be located as a problem with the wiring harness or the internal problem of the electrical module, and further investigation is required.
d) According to the above high-voltage interlock electrical principle, the faulty module is located by elimination method;
e) Start from the DC/DC wiring harness end and check in sections.
Check whether K to X2-10 and J to X2-11 are conductive. If any section is not conductive, it can be locked as a faulty module.
If the resistance value is less than or equal to 5Ω, it is necessary to check whether the entire high-voltage circuit is short-circuited.
a) If the resistance value is less than 5Ω, it means that the circuit is conductive. It is necessary to check whether X2-10 is short-circuited to the ground. b) Check if X2-10 is short-circuited to the power supply. If the above faults are confirmed, they can be solved directly. If the above faults are not found, it can be located as an internal problem of the PACK and needs to be further investigated. c) Check if the MSD under the passenger seat is missing, the interlocking pin is bent or broken. d) Check if the interlocking paper clip of the high-voltage connector of the BMS is bent or broken. If the above faults are confirmed, they can be solved directly. If the above faults are not found, it can be located as an internal problem of the BMS.
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