With the rising of international crude oil price, the whole society pays more attention to the environmental deterioration and global warming, and the tax tilt and policy support of governments, which promotes the market share of alternative energy, especially electric vehicles, to increase all over the world.
Electric vehicles mainly include three types, namely pure electric vehicles, hybrid vehicles and fuel cell vehicles.
Pure electric vehicle and fuel cell vehicle are driven by an electric motor. Hybrid electric vehicles are supported by motors when the efficiency of internal combustion engines is not high under acceleration and low speed conditions.
Their common feature is to use up to 600V or higher drive voltage, involving wiring, they all have the same basic requirements, both in EMI (electromagnetic interference) protection system safe transmission of high current and voltage.
As a high voltage acsr cable, it is used to connect high voltage battery, inverter, air conditioning compressor, three-phase generator and motor to realize the transmission of power and electricity.
The basic principles of electric vehicles seem to be simple. But in-depth analysis, the manufacturers of the system are facing a series of challenges to overcome.
New technical requirements are put forward for the items of high voltage cable, such as flexibility, shielding, safety and size of electric vehicle, because these will affect the wiring of components with high current and high voltage. In the face of different technical points of each possible power system, different special requirements are put forward for the components needed.
It is necessary to note that the high voltage system of electric vehicles is not a typical high-voltage system. The relevant terms such as “high voltage” and “high current” must be limited to the scope of the automotive field, compared with the low-voltage system of conventional vehicles.
In other fields, reference systems adopt totally different standards, such as the definition of high voltage in the power field, which starts at thousands of volts.
2、 Requirements for high voltage cable of electric vehicle
The innovative electric vehicle design presents new challenges to high voltage cables and system components, which cannot fully adopt the existing solutions. The specific requirements are analyzed as follows.
The basic difference between the cable and the conventional vehicle is that the structure needs to be designed at 600 V rated voltage, and if used on commercial vehicles and buses, the rated voltage can be up to 1000 V. By contrast, it’s even higher. The cables used in vehicles powered by internal combustion engines are designed to have a rated voltage of 60 v.
Power generated by the system (P = u × 1) The high voltage can reduce the power loss in the transmission system (pls= I2) without change due to the use of lower current × R)2. current
Because the cables connect the battery, inverter and motor, the high voltage cable needs to transmit high current. According to the power requirements of system components, the current can reach 250A to 450A. It is difficult to find such a high current in conventional drive vehicles.
The result of high current transmission results in high power consumption and heating of components. Therefore, the high voltage cable is designed to bear higher temperature. At present, it can be seen that there is a trend of further increase in temperature requirements.
In contrast, the current vehicle usually uses a cable rated at 105 ° C, as long as it is not used in the engine compartment or other areas with high temperature resistance. High voltage cables of electric vehicles are usually higher than this temperature, such as 125 ℃ or 150 ℃.
If the routing in electric vehicles is unfavorable, the host plant will even put forward higher requirements for high temperature resistance. Such as exhaust pipe, motor front, battery back, etc.
4. working life
The automotive industry usually has a design life of 3000 hours for cables of specified temperature grade. In recognized cable standards (e.g. ISO 6722, ISO 14572), this value is usually used for long-term aging tests. The special requirements of customers in high voltage applications may exceed 3000 hours, and the cumulative operating time at the specified temperature can reach 12000 hours.
5. shielding effect
The high voltage aaac cable itself does not need to be shielded, because it does not transmit data as coaxial cable, but it is necessary to prevent or reduce the high frequency radiation generated by switching power supply in the system to be induced to the surrounding parts through the cable.
Unlike fuel driven vehicles, it is necessary to control the three-phase alternating current of the motor of the electric vehicle. The sinusoidal voltage with energy is equivalent to the square wave pulse signal with different frequencies. Because of the steep edge of high frequency pulse, it will generate strong energy harmonic emission to the surrounding area.
EMI problem can be solved by using appropriate shielding method. In some cases, different shielding types are needed to meet different requirements of shielding effect.
The challenge for the development of hybrid vehicles in many cases is that the existing series of platforms originally designed only to load gasoline engines and its components into more electrical components. Even if wiring is not considered, the space constraints can be predicted.
In addition, space is required for cables and connectors to pass through routing. The usual consequence is the bending radius that leads to tension.
Because of the inherent design of conventional cables, high bending force is difficult to overcome. In order to solve this problem, high flexibility and toughness of high voltage cable is very important. Only flexible design can be easily realized through vehicle routing.
7. bending resistance
If the motor is located near the moving part of the vehicle and then causes continuous vibration of the connected high voltage cable, it requires that it be designed to withstand high cyclic bending to ensure good bending endurance.
Because of the increased application risk caused by high voltage, various standards define that high voltage cables must be visually different from ordinary vehicle cables, and the designated surface must be bright orange.
Warning content and special marks can also be printed, such as “caution! High voltage 600V “, high voltage lightning sign, etc.
3、 The standardization status of electric vehicle cable
In view of the challenges and requirements of the high voltage cables used in the electric vehicle, it is necessary to establish new cable standards to meet the needs of suppliers, harness plants and host plants.
The international organization for Standardization (iso/tc 22/sc 3/wg4) of the electrical and electronic sub Technical Committee of the Technical Committee on road vehicles of the international organization for standardization is carrying out this work.
As can be seen on ISO 6722, revisions have been made based on the common 60 V cable standards to meet the requirements of 600V cables. Because most of its requirements are still very common, but often do not consider the special design of high voltage cable. Similar revisions have been made to ISO 14572.
At present, standardization of high voltage cable with voltage higher than 600V is a task of each working group. The standard number is ISO 17195.
SAE will adjust the current high voltage (600 V rating) specification SAE j1654 requirements for high voltage cables and cover rated voltages from 600 to 1000 V. The newly created standard SAE j2840 will be defined as shielded type cables.
LV is a common purchasing specification of five major German auto companies. At present, LV 216 is a high voltage cable standard for electric vehicles with rated voltage of 600 v. It covers shielded cables with single core and multi-core.
The national automobile industry standard of high voltage shielded cable in China is under development, and its rated voltage will reach 1000 V.
4、 The structure design of high voltage cable for electric vehicle
Standard products and very specific requirements are difficult to define. The purpose of this paper is to solve the basic design ideas and overcome the challenges mentioned above by applying advanced high voltage cable structure principle.
1. conductor design
The flexibility of high voltage cable is mostly determined by the design of conductor. That’s why high voltage cables use special conductors with a large number of very small diameter monofilament. A certain number of single wires are twisted first, then concentric rewind is carried out to form the soft conductor required by high voltage cable.
Another advantage of the number of roots is better bending resistance. The short pitch of the strand can also improve the bending life of the high voltage cable.
2. insulation materials
The selection of insulation materials mainly considers the heat resistance requirements and mechanical strength. Compared with the standard battery cable, the soft materials can be selected reasonably to keep the specially designed stranded conductor flexible.
3. cable formation
When the cable is multi-core, it is usually necessary to twist the core. In order to make up for the deformation caused by the twisted high voltage cable core, the so-called twisted special equipment is needed. In this process, the special strand machine is equipped with a set-up plate which rotates in reverse direction relative to the direction of stranding. This is necessary to prevent the deformation tension of the cable.
According to the structure of cable, filling is usually used to ensure the high concentricity of shielded cable, and finally to obtain a satisfactory high voltage cable. The use of wrapping tape in the stranded cable core can keep the cable flexible.
Due to EMC requirements, the braided shielding is made up of several copper wires. Tin plated copper wire can make it more powerful to resist environmental effects such as oxidation. The design is flexible with fine copper wire
Shielding requires a coverage of more than 90% to overcome the EMI problem described earlier.
Different shielding effects need, woven shielding can be combined with other shielding, such as aluminum plastic to meet the film. The shield can be wrapped with a layer of non-woven fabric to ensure that the sheath is easily peeled off during assembly.
As with the insulation of the core, the sheath material is selected according to the requirements of heat and mechanical properties. Environmental properties such as resistance to liquids and wear are also important for sheath due to direct contact. These characteristics are mainly determined by the type of sheath material selected, and to some extent, are affected by the design of sheath structure.
If special requirements, such as overcoming the wear of the installation vehicle environment, require increased wear resistance, this should be considered when selecting materials. Usually, test equipment is used to simulate the reality to verify these characteristics.
Choosing a softer material benefits from flexibility, which can lead to lower wear resistance of high voltage cables.
The extruded jacket shall be a bright orange as specified in the relevant specifications and special high pressure warning marks can be added as specified.