high voltage cable assemblies for electric vehicles

high voltage cable assemblies for electric vehicles

• 2025-03-03 09:00:43
• by Admin

I. Overview

The rising price of international crude oil, the increased concern of the whole society about environmental degradation and global warming, coupled with the tilting of taxes and policy support from governments, have contributed to the growing market share of alternative energy sources, especially electric vehicles, around the world. Electric vehicles mainly include three categories, namely pure electric vehicles, hybrid vehicles and fuel cell vehicles. Pure electric vehicles and fuel cell vehicles are driven entirely by an electric motor, while hybrid vehicles combine an internal combustion engine with an electric motor, which is supported by an electric motor when the internal combustion engine is not efficient under acceleration and low speed conditions. Their common characteristic is the use of drive voltages of up to 600V or higher, and when it comes to wiring, they all share the same basic requirements, both in terms of the safe transmission of high currents and voltages under EMI (Electro Magnetic Interference) protection systems. As high-voltage cables are used to connect high-voltage batteries, inverters, air conditioning compressors, three-phase generators and electric motors for the transmission of power electrical energy. The fundamentals of electric vehicles seem simple. But analyzed in depth, manufacturers of the system are facing a series of challenges to overcome. New technical requirements are being placed on electric vehicle high-voltage cables, their flexibility, shielding, safety, dimensions, and other items that can affect the wiring of high-current and high-voltage components. And faced with the different technical points of each possible powertrain, there are also different special requirements for the required components. It should be noted that the high-voltage system of an electric vehicle is not a typical high-voltage system, and the terms “high voltage” and “high current” must be restricted to the automotive sector only, as opposed to the low-voltage system of a conventional vehicle. In other areas the reference systems are based on completely different criteria, e.g. the definition of high voltage in the power sector starts at a level of a few kilovolts.

II. Requirements for high-voltage cables for electric vehicles

Innovative electric vehicle designs present new challenges for high-voltage cables and system components, requirements that cannot be fully met with existing solutions. The specific requirements are analyzed as follows.1 The basic difference between voltage and conventional automotive cables is that the structures need to be designed for rated voltages of 600 V, whereas for use in commercial vehicles and buses, the rated voltages can be as high as 1,000 V. By comparison, they can be even higher. The cables currently used in vehicles driven by internal combustion engines are designed for a rated voltage of 60 V. The system produces a constant power (P = U x I), and the high voltage reduces the power losses in the transmission system (PLOSS = I2 x R) due to the use of lower currents.2 CURRENT CURRENT Since the cables connect the batteries, the inverters, and the electric motors, the high-voltage cables need to transmit high currents. Depending on the power requirements of the system components, currents can reach 250 A to 450 A. Such high currents are difficult to find in conventionally driven vehicles.3 Temperature The result of high current transmission leads to high power consumption and heating of the components. High-voltage cables are therefore designed to withstand high temperatures. A trend towards a further increase in temperature requirements can currently be observed. In contrast, current vehicles usually use cables rated up to 105°C as long as the cables are not used in engine compartments or other areas that are resistant to higher temperatures. High-voltage cables for electric vehicles are typically rated for temperatures higher than this, such as 125°C or 150°C. OEMs may even demand higher temperature resistance if the routing through the EV is unfavorable. For example near the exhaust pipe, in front of the motor, at the back of the battery, etc.4 Operating lifeThe automotive industry usually designs cables for a service life of 3000 h at specified temperature levels.In recognized cable standards (e.g. ISO 6722, ISO 14572), this value is usually used for long-term aging tests. Customer-specific requirements in high-voltage applications may exceed 3000 h, with cumulative operating times at specified temperatures even reaching up to 12000 h. 5 Shielding effects High-voltage cables do not need to be shielded per se, since they do not transmit data as coaxial cables do, but it is necessary to prevent or minimize the high-frequency radiation generated by switching power supplies in the system from being induced through the cable into the peripheral components. Unlike fuel-driven vehicles, three-phase AC power to control the motor of an electric vehicle becomes necessary. The sinusoidal voltage carrying the energy corresponds to square wave pulse signals of different frequencies. Since high frequency pulses have steep edges, very energetic harmonics are emitted into the surrounding area. The EMI problem can be completely solved by using appropriate shielding methods. In some cases a combination of different shielding types is required to meet different requirements for shielding effectiveness.6 Flexible Hybrid Vehicle Development The challenge in many cases is that existing series platforms originally designed to carry only the gasoline engine and its components have space to incorporate additional electrical components. Space constraints can be expected even without considering wiring. In addition, cables and connectors routed through also require space. The usual consequence is a tight bending radius. Due to the inherent design of conventional cables, high bending forces are difficult to overcome. To solve this problem, high flexibility of high voltage cables is essential. Only with a more flexible design can routing through the vehicle be easily achieved.7 Bending resistanceIf the motor is located close to a moving part of the vehicle, which then causes continuous vibration of the connected HV cable, it is required to be designed to withstand high cyclic bending to ensure good bending resistance.8 MarkingBecause of the increased risk of applications due to high voltages, various standards define that HV cables have to be visually distinguishable from normal automotive cables, specifying that the surface must be brightly colored. The cable must be visually distinguishable from ordinary automotive cables, and the specified surface must be bright orange in color. It is also possible to print warnings and special markings such as “Caution! High Voltage 600V”, high voltage lightning bolts, etc.