What should be paid attention to in the design and selection of high-voltage connectors (top)?

The high-voltage electrical connection system mainly includes high-voltage wiring harnesses and connectors. The electrical connection system accounts for a certain proportion of the vehicle failure report, and the electrical connection has become a weaker link in the high-voltage system.

In the electrical connection system, the quality of the connector is particularly important, which has become a vital factor to ensure the safety and reliability of the electrical connection. When the connector is selected and applied, it needs to be based on the component’s use environment (such as temperature, humidity, altitude, etc.) and installation location (Vibration conditions, volume structure, sealing level requirements), current-carrying characteristics, cost accounting and other reasonable selection of products. The ideal expectation for high-voltage connectors is that the products have a higher level of safety protection, high temperature resistance, large current-carrying, low power consumption, grease resistance, small size, light weight, long life cycle and low cost.

1. Security

The safety protection of the connector mainly refers to the electrical performance meeting the design requirements, such as insulation, withstand voltage, electrical clearance, creepage distance, foolproof, and anti-finger (insulating material around the terminal, higher than the terminal height or the terminal with a plastic cap) design In addition to the above performance, it is necessary to pay attention to the connector HVIL, sealing protection, and EMC performance during application.

1) High Voltage Interlock

The high-voltage interlock uses electrical signals to confirm the integrity of the high-voltage system connection, and can also be used as a cover open detection.

When designing high-voltage connectors, consider the high-voltage safety protection during plugging and unplugging. For example, when disconnecting, the HVIL is disconnected first, and then the high-voltage terminals are disconnected; the opposite is true when connecting. HVIL connectors generally have a built-in type and an external type in structural design . Because the built-in type is compact and small in size, the built-in type is commonly used at present, and the high-voltage interlock circuit is installed between the high-voltage terminals.

In applications, some built-in connectors lack the CPA (Connector position assurance) of the interlocking device. If the connector structure is not well designed, under certain harsh conditions, some suppliers’ products will cause the displacement of the interlocking device. The discontinuity of the interlock signal brings unnecessary problems to vehicle debugging and safe driving.

Figure 1 built-in type high-voltage interlock connector

In the actual use process, HVIL loop is mainly detected by signal (such as level, PWM signal) injection method, and the failure mode mainly considers HVIL circuit fault short-circuit (including short-circuit to power supply and ground. Level detection is used. The system may not be able to Risk of correct judgment) or disconnection (the product must ensure that the interlock device does not move).

In addition, the connector HVIL device contact resistance and wiring harness loop resistance should be considered when the connector is selected and designed to avoid HVIL detection failure due to signal voltage drop.

2) Protection level requirements

High-pressure connector sealing generally requires at least IP67, and even IP6K9K is required in the selection of some special occasions in the car to ensure that the use requirements are met even during high-pressure washing.

The current product protection requirements and verification methods mainly refer to GB4208, and the parts or connectors are placed at a depth of 1m in the water tank to detect whether the protection level IP67 is passed , but in actual use, whether this can simulate the performance of the vehicle The actual working conditions are debatable.

The actual working conditions of the vehicle need to experience fatigue loads and face the problem of material aging (see Figure 2). For example, long-term exposure to vibration conditions; extreme weather conditions, extreme cold and extreme heat; when wading, the water contains other impurities and needs to deal with corrosive conditions. In order to ensure the product performance throughout the life cycle, in actual use, it is important that the seal is good or bad when the vehicle is approaching the end of its life.

he water-dust and dust-proof test of the connector in the laboratory cannot fully simulate the actual environment of the vehicle connector. The connector product is tested for mechanical fatigue, vibration, thermal shock, salt spray, etc., and then tested for IP67, which can estimate the sealing performance of the system at the end of the life as completely as possible.

In addition, it is worth noting that the sealing material is generally made of rubber, which itself faces life degradation. At present, there is a lack of effective risk reports in the application of connector products. In the system design, it is also necessary to consider how to prevent problems caused by the life degradation of the sealing material.

If the sealing performance can be guaranteed during the whole life cycle of the product, the following points should be considered in the application design of the connector sealing: between the connector and the component (mainly involving the control of component structure design), between the connector and the cable (the product guarantees the seal The position of the ring does not move and the assembly accuracy is controlled during the production of the wiring harness), between the male and female ends of the connector (the product structure process and the integrity of the assembly).

3) EMC

As new energy vehicles use a large number of power electronic devices, the electromagnetic field generated by high voltage and large current will cause electromagnetic interference to other communication equipment, and the whole vehicle and parts must have the ability to resist interference and radiation.

When designing a high-voltage electrical connection system, the connector is required to have a 360°shielding layer and effectively connect to the cable shielding layer. The shielding layer covers the entire length of the connector to ensure sufficient shielding function and minimize the resistance between the shielding interfaces. During the product life cycle, the shield connection contact resistance is less than 10mΩ.

For high-voltage connectors made of plastic, the shielding must be realized with a metal surface.