Electric vehicle high voltage cable structure design and requirements, electric vehicle cable standardization status

June 3, 2023
Latest company news about Electric vehicle high voltage cable structure design and requirements, electric vehicle cable standardization status

1. Brief introduction of high voltage wiring harness

In recent years, with the strong support and promotion of the country, the development of new energy vehicles in China has made great progress, and various new energy vehicles have entered our daily life one after another. Simply put, new energy vehicles mainly refer to the use of unconventional vehicle fuels as power sources (or the use of conventional vehicle fuels, the use of new vehicle power devices), and the integration of advanced technologies in vehicle power control and drive. Cars with advanced principles, new technologies and new structures. It mainly includes pure electric vehicles, extended-range electric vehicles, hybrid electric vehicles, fuel cell electric vehicles, hydrogen engine vehicles, and other new energy vehicles.

But no matter what the form of new energy vehicles is, their common feature is that they use a voltage platform as high as 300V~600V or higher, involving wiring, and they all have the same basic requirements, that is, under the electromagnetic interference protection system Safely transmit high currents and voltages. The high-voltage cables are used to connect high-voltage batteries, inverters, air-conditioning compressors, three-phase generators and motors, so as to realize the transmission of power and electric energy. But it needs to be explained that the high-voltage wiring harness of electric vehicles is not equivalent to the high-voltage power transmission cables in our daily life, but only relative to the low-voltage system of conventional vehicles.

2. Requirements for electric vehicle high voltage wiring harness

1. Voltage

The basic difference from conventional automotive cables is that the structure needs to be designed for a rated voltage of 600V, and if used in commercial vehicles and buses, the rated voltage can be as high as 1000V. In contrast, even higher. Cables currently used in cars powered by internal combustion engines are designed for a rated voltage of 60V.

Under the condition that the power generated by the system (P=U×I) remains unchanged, the high voltage can reduce the power loss in the transmission system (PLOSS=I2×R) due to the use of lower current.

2. Current

High voltage cables need to carry high currents as the cables connect the battery, inverter and electric motor. Depending on the power requirements of the system components, the current can reach 250A to 450A. Such high currents are hard to find on conventionally driven vehicles. In fact, the transmission rate of the current is mainly due to the intuitive effect of the cross-section of the cable, so how to ensure the reliability of the current transmission, Keyingfa has a special testing instrument that can visually observe the contact situation of the cross-sectional area of the cable and the contact and contact of the connecting accessories. Pull test conditions, so that the current can fully guarantee the transmission.

3. Temperature

The high current transfer results in high power consumption and heating of the components. Therefore high voltage cables are designed to withstand higher temperatures. It can be seen that there is a further increase in temperature requirements.

In contrast, current vehicles typically use cables rated to 105°C, which are sufficient, as long as the cables are not used in the engine compartment or other areas that are resistant to higher temperatures. Electric vehicle high voltage cables are usually higher than this temperature, such as 125°C or 150°C.

If the route through the electric vehicle is unfavorable, the OEM will even put forward higher requirements for high temperature resistance. Such as near the exhaust pipe, in front of the motor, behind the battery, etc.

4. Working life

The automotive industry usually has a designed service life of 3000h at a specified temperature level. In recognized cable standards (such as ISO6722, ISO14572), this value is usually used for long-term aging tests. The special requirements of customers in the high-pressure application field may exceed 3000h, and the cumulative operating time at the specified temperature may even reach 12000h.

5. Shielding effect

The high-voltage cable itself does not need shielding, because it does not transmit data like a coaxial cable, but it needs to prevent or reduce the high-frequency radiation generated by the switching power supply in the system from being induced to surrounding components through the cable.

Unlike fuel-powered vehicles, three-phase alternating current to control the motors of electric vehicles becomes necessary. A sinusoidal voltage carrying energy is equivalent to a square wave pulse signal of different frequency. Due to the steep edges of the high-frequency pulses, high-energy harmonics are emitted to the surrounding area.

EMI problems can be completely solved by using proper shielding methods. In some cases, a combination of different shielding types is required to meet different requirements for shielding effects.

6. Flexibility

The challenge faced in many cases by the development of hybrid vehicles is that the existing series platforms were originally designed only to accommodate the gasoline engine and its components into the space for more electrical components. Even without wiring, space constraints can be expected. Additionally, space is required for cables and connectors to be routed through. The usual consequence is tight bend radii.

Due to the inherent design of conventional cables, high bending forces are difficult to overcome. In order to solve this problem, high-voltage cables with high flexibility are crucial. Only with a relatively flexible design, the routing through the vehicle can be easily achieved.

7. Resistant to bending

If the motor is located close to the moving parts of the vehicle, then causing continuous vibration of the connected high voltage cables, it needs to be designed to withstand high cyclic bending to ensure good bending resistance.

8. Identification

Because of the increased application risk associated with high voltage, various standards define that high-voltage cables must be visually distinguished from ordinary automotive cables, and the specified surface must be a bright orange color.

At the same time, warning content and special marks can also be printed, such as "Caution! High voltage 600V", high voltage lightning logo, etc.

3. Standardization status of electric vehicle cables

In response to the above-mentioned challenges and requirements of high-voltage cables for electric vehicle applications, it is necessary to establish new cable standards to meet the needs of suppliers, wiring harness factories and OEMs.

This work is being carried out by the Automotive Cable Working Group (ISO/TC22/SC3/WG4) of the Electrical and Electronic Subcommittee of the International Organization for Standardization Road Vehicle Technical Committee.

It can be seen on ISO6722, which is based on the common 600V cable standard and revised to meet the needs of 600V cables. Because most of its requirements are still very general, but often do not consider the special design required by high voltage cables. ISO14572 has also made similar revisions.

At present, the standardization of high-voltage cables with voltages higher than 600V is a topic of various working groups. The standard number is ISO17195.

SAE will adjust the current high-voltage (rated 600V) specification SAE J1654 for high-voltage cables and cover rated voltages from 600 to 1000V, and the newly created yet-to-be-published standard SAE J2840 will define shielded type cables.

LV is the common procurement specification of the five major automobile companies in Germany. Currently, the electric vehicle high-voltage cable standard LV216 with a rated voltage of 600V has been launched. It covers single-core and multi-core shielded cables.

my country's national automotive industry standards for high-voltage shielded cables are being formulated, and their rated voltage will reach 1000V.

4. Structural design of high-voltage cables for electric vehicles

Standard products and very specific requirements are difficult to define. The purpose of this article is to address fundamental design considerations to overcome the challenges described above by applying advanced high voltage cable construction principles.

1. Conductor design

The flexibility of high-voltage cables is mostly determined by the design of the conductors. This is why high voltage cables use special conductors with a large number of monofilaments of very small diameter. A certain number of monofilaments are bundled and twisted first, and then re-twisted concentrically to form the soft conductor required by the high-voltage cable.

Another advantage of more roots is better bending resistance. The shortened strand pitch can also improve the bending life of high voltage cables.

2. Insulation material

The choice of insulating material is mainly to consider the requirements of heat resistance and mechanical strength. The specially designed stranded conductors remain flexible due to the rational choice of softer materials than standard battery cables. Keyingfa's high-voltage wiring harness adopts new energy vehicle standard flame-retardant materials, and the cable material is orange

3. Cabled

When the cable has multiple cores, it is usually necessary to twist the cores together. In order to compensate for the deformation caused by twisting the cores of high-voltage cables, special equipment called untwisting is required. During this process, the pay-off reel equipped with the special stranding machine rotates in the opposite direction relative to the stranding direction. This is necessary to prevent deformation tension of the cable. Especially high current cables,

According to the structure of the cable, fillers are usually used to ensure a high concentricity of the shielded cable, and finally to obtain a satisfactory high-voltage cable. The use of tape on stranded cores maintains the flexibility of the cable.

4. Shield

Due to EMC (Electromagnetic Compatibility) requirements, multiple copper wires are used to form a braided shield. Tinned copper wire makes it stronger against environmental influences such as oxidation. Design flexibility can be maintained with fine copper wire

Shielding needs to have a coverage rate of more than 90% to overcome the EMI problem introduced earlier.

According to different needs of shielding effect, braided shielding can be combined with other kinds of shielding, such as aluminum-plastic composite film. The shield can be wrapped with a layer of non-woven fabric to ensure easy peeling of the jacket during assembly.

5. Sheath

Like the insulation of the core, the sheath material is selected according to thermal and mechanical requirements. Environmental properties like resistance to liquids and abrasion are also particularly important for sheaths due to direct contact. These properties depend primarily on the type of sheath material chosen and to some extent also by the sheath construction design.

If special requirements, such as overcoming the wear and tear of the installation vehicle environment, require increased wear resistance, this needs to be considered when selecting materials. Real-world conditions are often simulated using test equipment to verify these characteristics.

Choosing a softer material benefits from flexibility, which may result in lower wear resistance of the high voltage cable.

According to the relevant regulations, the extrusion jacket should be a bright orange color, and special warning signs for high voltage can also be added according to the regulations.

V. Summary

As the main carrier of power output in electric vehicles, high-voltage wiring harness is one of the key components for vehicle performance and safety. The R&D and design of high-voltage wiring harnesses should not only be considered from the perspective of the entire vehicle, but also from the perspectives of raw materials, connectors, component suppliers, etc. In the case that the industry standards are not yet standardized, we should work together to formulate a The actual use environment has an industry-forward-looking unified standard. In this way, the safety of electric vehicles can be further improved, and at the same time, it is also beneficial to reduce the design and manufacturing costs of high-voltage wiring harnesses, and make due contributions to the promotion of the development of electric vehicles.