New Energy Vehicle High Voltage Connector Technology

In recent years, world-renowned connector companies have moved their production bases to China. China has become the world’s largest connector production base. After years of technology accumulation, my country’s connectors have met the technical level required for high-voltage connectors for new energy vehicles in terms of design capabilities and automated production capabilities. On the premise that downstream manufacturers are localized and have sufficient technical capabilities, domestic manufacturers have occupied the highest point in high-voltage connectors for new energy vehicles, such as Sichuan Yonggui, AVIC Optoelectronics, Basba and other well-known companies.

Layout diagram of high-voltage connectors used in automobiles

1-Technical analysis of high-voltage connectors:
1.1 Application of high-voltage connectors in vehicle systems
Compared with traditional high-voltage and high-current connectors, the usage conditions of connectors for new energy vehicles are more complex and changeable, requiring higher reliability of the connector;
Compared with traditional low-voltage automotive connectors, due to the increase in voltage level (currently mainstream voltages are higher than 300V DC), the risk of human body being injured by electric shock has increased, and the safety requirements for connectors are higher. Therefore, the insulation and protection requirements of the product are higher than those of traditional low-voltage plug-ins.
The main function of connectors for new energy vehicles is to ensure the high-voltage interconnection system of the entire vehicle. That is, building a bridge where the internal circuit is blocked or isolated to allow current to flow.
The composition of new energy vehicle connectors can generally be divided into three parts: auxiliary structures such as shells and seals, insulating parts, and conductive contact pairs. Through the insertion and mutual cooperation between the plug sheath and the socket sheath, the functions of connection and conduction can be achieved.
High-voltage connectors are mainly used in high-voltage and high-current circuits of new energy vehicles, and work simultaneously with conductive cables to transport the energy of the battery pack to various components in the vehicle system through different electrical circuits. Such as battery packs, motor controllers, DCDC converters, chargers and other body power units.
Figure: Layout diagram of high-voltage connectors used in vehicle systems.

Temperature rise and derating curves of high-voltage connectors

1.2 Analysis of key items in high-voltage connector design
1.2.1 Temperature rise and derating curve values
Temperature rise is one of the most important design critical items in connector design. Abnormal temperature rise will cause the connector to ablate due to excessive temperature rise.
The temperature rise of the connector is affected by the following factors:
1. Contact resistance: used for conductive connection, resistance between two contact carriers. Such as pinhole-to-pin contact resistance, crimp resistance between pinhole tail and wire, and contact resistance between threaded connection copper plates.
2. Material environment heating: When the connector is in a high temperature environment for a long time, the materials used in the connector are engineering plastics, metal, rubber, etc. In particular, engineering plastics require a maximum working temperature of 140°C. However, when the ambient temperature of the product is too high, the connector generates heat due to its own contact internal resistance and reaches thermal equilibrium. In addition, the ambient temperature is higher than the maximum allowable operating temperature of the material. At this time, if the connector is in this environment for a long time and the internal pinhole part of the connector heats up and the internal temperature cannot be discharged, the internal temperature will continue to rise and the connector will generate a lot of heat. This can lead to connector ablation and vehicle burning, which is a very serious problem. Both rubber materials and metal materials have maximum operating temperature limits, which need to be considered during design.

Derating curve chart of high voltage connector

3. Connection of plate ends: If bolts are required during design, preventive measures must be taken to prevent loosening during delivery; at the same time, when connecting bolts, torque testing must be performed according to operating specifications. In the case of screw connections of conductive parts, one of the main failure modes is that the tightening torque is not controlled according to the torque requirements, resulting in abnormal temperature rise and ablation of the connection parts.
4. Derating curve: Now let’s discuss the derating curve. In my understanding, the derating curve is like choosing a product that should be used in a specific environment. At this time, when selecting a product, you must determine which range of products you choose based on an attribute value of the product. The derating curve of high-voltage connectors is to provide customers with a menu, and customers can choose their own appropriate dishes according to their own tastes based on this menu.
The derating curve is the different values corresponding to different currents at different working ambient temperatures. These values are obtained by plotting a curve graph. With this derating curve graph, the usage conditions of this connector can be seen more intuitively.

Connector locking structure diagram

Figure: Illustration of temperature rise and derating curves – temperature rise curve graph

header mating connector

Figure: Illustration of temperature rise and derating curve – derating curve graph
1.2.2 High Voltage Interlock (HVIL)
For the entire high-voltage interconnection system, in order to ensure the safety of the high-voltage system when powering on and off, the concept of high-voltage interlocking is introduced in the connection design.
A simple description is that when the connector is plugged in and connected, the high-voltage circuit first contacts and conducts, and then the high-voltage interlock signal circuit conducts. When breaking, the high-voltage interlock signal is broken first, and then the high-voltage circuit is broken.
Most connector manufacturers will place the high-voltage interlock design inside the connector, and some manufacturers will place the high-voltage interlock outside the mating cavity through auxiliary structural design. It is very important to ensure the stability of the high-voltage interlock loop.
If the high-voltage interlocking is discontinuous, the possible consequences will be severe. For example, while the vehicle is driving, the high-voltage interlock circuit signal suddenly becomes abnormal, causing the vehicle to suddenly lose power and fail to operate normally, which may cause a traffic accident.
1.2.3 Locking structure
Understand that the real secondary lock does not have a secondary protection function, but it must protect it effectively. The real meaning of this is that after the primary lock, if the primary lock fails or there is no operation verification, the secondary lock is to ensure that the primary lock is locked and the first lock is protected. This is a very important role.
The most commonly used secondary locking structure combined with the primary lock is the force arm mechanism. Because one-time locking is related to the insertion and extraction force, a form similar to a force arm mechanism is required according to the mechanical design concept, so as to save labor and easily insert the connector into place.
Regarding the requirements for the moment arm, USCAR talks a lot about the ergonomic operability of the moment arm. USCAR also stipulates the force requirements for the relevant primary locks and secondary locks in the inserted and non-inserted situations. In fact, we all think that USCAR is the standard for connectors, but I think the USCAR standard is not only a technical standard, but also guides designers to make the structure reliable during the design process. How to provide customers with a better product experience on the premise of reliable structure and performance.
Picture: Pictures of relatively common locking structure products

Connector wire end seal

1.2.4 Protection level
The protection of connectors is mainly divided into three arrangements:
The first is the board end seal: the board end is the connector socket end which is installed mechanically with four screws. This is a more commonly used structure, but there are also some more special structures.

The second is the head-base plug-in seal: the head-base plug-in means that the male end includes the female end, or the female end includes the male end, and rubber parts are used in the middle for radial and axial protection.

IPI67 protection for high voltage connectors

The third is the line end seal, the protective seal between the line end connector and the cable.

For high-voltage connectors for electric vehicles, with the development of the market, the performance requirements of OEMs for product protection are also constantly improving. In the early stages of industry development, the protection requirements of IPI67 can already meet the vast majority of customers. However, as the protection of connector products appeared on the market later, there were more and more cases of water leakage, insulation failure, and even ablation.
The gradual improvement of protection requirements has become the development trend of electric vehicles. The current IP67 requirements cannot meet the normal use requirements. Of course, this is not absolute, and it also depends on the location of the connector on the car.
According to the layout of the entire vehicle, the high-voltage circuit will be suspended under the chassis of the vehicle. It is a principle that high pressure is not allowed to enter the cabin. Therefore, most high-voltage connectors are located on the chassis close to the ground, or close to the wheel hub.
When there is severe weather, such as severe weather, heavy rainstorms or some severe cold weather, the water brought up by your tires will actually impact these connectors. If you are familiar with testing, there is no such thing as IP6K9K in domestic standards. You will find that if it is IP67, the impact pressure of the high-pressure water gun is actually not as high as 6k9k.

High voltage connector selection process

1.2.5 Electromagnetic shielding of high-voltage connectors
Electric vehicles have many electronic devices, and current will generate magnetic fields. The vehicle parts must have anti-interference capabilities. In particular, electric vehicles are now used as a carrier, and autonomous driving will be developed more on this basis, so this technical issue is very important. For high-voltage systems, shielded connectors and cables are very important, but we must give priority to system-level layout, which is a prerequisite. If your OBC, the location you arrange, including the DCDC in the system, may have some inherent problems. No matter how well-made the connector is, there will still be various signal interference problems.
Therefore, we must first consider the system level, and secondly consider the component level. For connector shielding effectiveness, two methods are generally used.
The first way is that we have a metal shield on some plastic connectors, and the cable shield will be connected to the shield of the metal shell to form an effective 360° shield.
In the second method, most high-voltage and low-current connections will not have secondary connections and will be connected to the shielding layer of the cable. This method is also commonly used by existing manufacturers, including some well-known domestic OEMs, which are also considering this method. We call it spring contact (English), which is actually a spring connection. There are also many benefits to this structure, because the size and space will be smaller, and it will have more contact points;
There are many manufacturers of this structure, mainly represented by companies such as BMW Spring in Switzerland and Basel in the United States. They have many practical and mature application cases in this area. In most cases, we will use metal inner and outer rings for crimping the connection between the wires and the shielding layer. The shielding layer is placed between the two metal rings, and the shielding layer and the metal rings are tightly fixed through cold pressing and deformation. In addition, we also have a shielding method that uses a structure similar to a watch strap spring to replace the spring connection. This structure is often used in military products and the technology is mature; we have done relevant tests and all can meet the design requirements. This structure is used in the shielding of new energy electric vehicles, which can not only meet the performance requirements, but is also a stamped part, suitable for mass production, and has high cost performance.
1.2.6 Connector material

Application of connectors on different high-voltage electrical appliances

The connector insulating material is generally made of PA66, PBT, ABS, PC, etc. The contact materials are generally made of brass, phosphor bronze, beryllium copper, etc., but now the material used more abroad is copper-nickel-silicon material.
Connector shell materials are generally divided into two types: plastic and metal. Regarding how to choose plastic or metal materials, there are generally the following reference points:
1. Lightweight
Due to the demand for lightweight vehicles, especially passenger car manufacturers, on the premise of meeting product performance, they will try their best to choose plastic connectors to control the weight of the vehicle.
2. Product usage environment
Because the mechanical strength of metal materials is better than that of plastics. Therefore, in some harsh environments, metal connectors will be more suitable. For example, special vehicles, dump trucks, and electrical connection parts that are not protected during the layout of the entire vehicle. At this time, metal connectors are slightly better than plastic connectors in terms of environmental impact and mechanical strength.
3. Shielding implementation method
For shielded connectors, the shell of the metal connector itself is used to conduct shielding and form a carrier for shielding protection. Generally speaking, metal connectors are easier to achieve better shielding performance than plastic connectors, and their appearance and structure are more compact.

1.2.7 Connector selection
1.2.7.1 Connector selection process (see the figure below)

1.2.7.2 Interpretation of common technical parameters of connectors
(1) Location of use: As the name suggests, the connector is selected for its application location on different high-voltage electrical appliances in the vehicle.

(2) Rated voltage: the maximum voltage at which electrical equipment (including electricity and power supply equipment) can work stably for a long time.
The rated voltage is proportional to the creepage distance & clearance. In other words, the higher the voltage rating required, the larger or longer the connector. Creepage distance & clearance design standards are in accordance with GBT 16935.1 (IEC 60664-1),
(3) Rated current: The rated current of electrical equipment refers to the maximum current allowed to pass for a long time when the heat generation does not exceed the allowable long-term heating temperature under the reference ambient temperature and rated voltage working conditions.
For electric vehicles, P=UI, the rated current is determined based on the power P of the electrical equipment and the output voltage U.
Peak current: The maximum current value generated by an electric vehicle at the moment of rapid acceleration, climbing, or overloading.
The current-carrying cross-sectional area is proportional to the rated current of the connector. In other words, the larger the pin/hole/wire cross-section, the greater the current it can pass, and the larger the connector.

The connection of the power terminal indicates good contact

(4) HVIL (high voltage interlock)
(4.1) Design HVIL functional purpose
Confirm the integrity of the entire high voltage system. When the high-voltage system circuit is disconnected or the integrity is damaged, the safety measures of the entire vehicle are triggered.
(4.2) Implementation of HVIL function
a. The entire system is required and must be designed into the system during system development;
b. Mainly done through connectors;
c.HVIL circuit is a low-voltage circuit and is independent from the power circuit.
(4.3) Principle of connector HVIL function implementation
Power and signal terminals should meet:
——When connecting, the power terminal is connected first, followed by the signal terminal.
——When disconnecting, the signal terminal is disconnected first, followed by the power terminal.
Special note: The connection of the power terminals indicates good contact, and virtual contact is unacceptable.
(5) Shielding
Alternating electric field shielding: In order to reduce the coupling interference voltage of the alternating electric field to sensitive circuits, a metal shield with good conductivity can be set up between the interference source and the sensitive circuit, and the metal shield can be grounded.
The main difference between shielded and unshielded connectors is whether there is a metal shield with good conductivity.

(6) Protection level
The IP protection level is composed of two numbers. The first marked number indicates the level of dust-proofing and protection against intrusion of foreign objects by the appliance. The second marked number indicates the degree of sealing of the appliance against moisture and water intrusion. The higher the number, the higher the protection level.

(7) Outgoing method
Mainly refers to the angle between the cable outlet angle at the end of the electrical connector plug and the normal direction of the socket installation surface. According to this classification, the common ones are 90° (angled) and 180° (straight) outlet electrical connectors.
(8) Socket installation method
In order to meet the needs of OEM designers for different layouts of connectors, the installation methods of electrical connector sockets are subdivided into the following four types:

1.6.2.3 Option Notes
(1) Voltage selection needs to match: the rated voltage of the vehicle after load calculation should be less than or equal to the rated voltage of the connector. If the working voltage of the vehicle exceeds the rated voltage of the connector for a long time, the electrical connector is at risk of creepage and ablation.
(2) Current selection needs to match: the rated current of the vehicle after load calculation should be less than or equal to the rated current of the connector. If the operating current of the vehicle exceeds the rated current of the connector for a long period of time, the electrical connector is at risk of overload ablation.
(3) Cable selection needs to match: The cable selection and matching of the entire vehicle is divided into cable current-carrying matching and cable and connector sealing matching. Regarding the current carrying capacity of cables, each OEM has dedicated electrical engineers to carry out matching design, which will not be explained here.
Sealing matching: The connector and cable seal rely on the elastic compression of the rubber seal to provide contact pressure between them, thereby achieving reliable protection performance, such as IP67. According to calculations, achieving a specific contact pressure relies on a specific amount of compression of the seal. Based on this, if reliable protection is required, the sealing protection of the connector has specific size requirements for the cable at the beginning of the design;
Cables with the same specifications of current-carrying cross-section can have different outer diameters, such as shielded cables and unshielded cables, national standard cables and LV216 standard cables. The specific matching cables and connector selection specifications are clearly stated. Therefore, when selecting connectors, special attention must be paid to the cable specification requirements to prevent connector sealing failure.
(4) The entire vehicle requires flexible wiring: For vehicle wiring, each OEM now has bending radius and slack requirements; according to the connector in the vehicle
For use cases, it is recommended that after the harness assembly is complete, the connector terminals themselves are not stressed. Only when the entire wire harness is subject to vibration, impact and relative displacement of the vehicle body due to the operation of the car, the purpose of strain relief can be achieved through wire harness flexibility. Even if a small amount of strain is transmitted to the connector terminal, the resulting stress does not exceed the terminal’s design retention force in the connector.