Characteristics and optimization of high voltage cable for electric vehicles

- Oct 06, 2019-

The perfect complex design and the use of high quality materials result in costly cable costs. Experience has shown that specific high-voltage cables can often be tailored to the cross-section, temperature requirements, flexibility and shielding effectiveness. Weight and cost savings can be seen, over-sized and excessive components can be avoided.

1. Optimization of cross-sectional area and temperature class

The choice of cable is mostly based on the ambient temperature and the current transfer. In this respect, the most important characteristics are the "cable section" and the "heat resistance rating of the material used for the cable".

The voltage drop of the conductor is converted into a conductor of a high-voltage cable that is heated by thermal energy. This heat can be partially transferred to the environment, causing the wire to operate at a lower temperature. Lower temperature gradients can transfer less heat. Cables with continuous load current can be subjected to the highest rated temperatures. This temperature can cause aging of the materials used.

Cable designers face the challenge of designing the most suitable cable for use: Excessive conductor specifications can result in increased cost and weight, and larger outside diameter. In the worst case, considering only the highest possible load current and ambient temperature will result in the use of large cross-section cables, high temperature resistant materials such as organic fluorine or silicon materials.

Determining the relationship between current and load ambient temperature makes sense from a technical and economic point of view. The true dynamic peak current of the driver should be considered, allowing for a reasonable definition of the worst case load current and peak current.

A prerequisite for a good design is an understanding of the basic conditions, such as the need to first determine the ambient temperature and cable load. Generally, large-section high-voltage cables have large inertia in terms of temperature changes, so the peak current of the vehicle's acceleration or deceleration does not cause a large conductor temperature. Allowing for short-term temperature peaks to exceed the cable temperature levels defined above, the ability of high-voltage cables to handle these peaks is usually defined by thermal overload performance. Therefore, the cable does not need to be designed for a higher operating temperature class, and it is not necessary to use a cable that exceeds the specified operating temperature. The resident load current as well as the single pulse or series of pulses can be considered together with various parameters such as ambient temperature.

The combination of the theoretical foundation and the experience gained in the real world allows for the initial determination, selection and optimization of high-voltage cables that are suitable for the application.

2. Flexibility optimization

The available space for cable routing of the vehicle deserves careful consideration. A tight bend radius only in a specific area of the vehicle requires an increase in the flexibility requirements of the overall cable. If it is possible to make small changes in the overall design, it is very meaningful to avoid tight bending problems.

It is not necessary for the cable to have the highest flexibility. The exact definition of the bending force, combined with the structure and the corresponding test equipment, allows the cable designer to create the design for the most appropriate application. Especially for cables with larger cross-sections, replacing the highly flexible design with a more flexible or conventional structural design can significantly reduce costs.

3. Shielding optimization

The shielding effect defined in a certain frequency range is very necessary for the development of the cable. There is no shielding effect on frequency information that is not very useful, which can lead to solutions that use excessive size and use expensive combination shielding, which is technically unnecessary.

Normally, the development and design phase of the electric vehicle cable can be theoretically calculated to give an expected effect value for consideration. Then, the physical shielding method is used to verify the shielding effect of the high-voltage cable.