High Power Cables in Electric Vehicles - Analysis of Optimization of High Power Cables Design for both DC and AC in Electric Vehicles

Abstract

As the demand for cleaner transportation increases around the world, passenger vehicle manufacturers are introducing electric and hybrid powertrains. However, the electric and hybrid powertrains have new issues to deal with, such as electromagnetic interference (EMI) and current ripple generated by the electric drive. To address these issues the manufacturer Volvo has started the Ripple and Electromagnetic Fields in Electric Vehicles (RIFEL) project. This thesis is a part of the project and will focus on the power cables in the Volvo XC90 plug-in hybrid. There are several methods to reduce the magnetic fields emitted by the cables, including changing the cable arrangement, shielding the cables and twisting the cables. To study and compare these methods, simulations in Comsol and a variety of measurements have been conducted. The results shows that there is a variety of possible solutions to reduce the fields depending on what frequency range the interference occurs at. For high frequencies, shielding with a highly conductive material is a very effective method as long as the shield is properly connected. However, for low frequencies a highly conductive shield has little to no affect. Here the magnetic permeability of the shield is the determining factor of the shield effectiveness. By using a high permeability material with a high conductive material as shield, the magnetic field can be reduced by 19.23 dB at 10 kHz compared to the cable currently in use. Furthermore, the results also shows that by changing the cable arrangement or twisting the cables the magnetic fields can be reduced over the full frequency spectrum from 1 Hz to 10 MHz. The work also includes modeling of the shielded cable and determination of the cable parameters. To determine the parameters simulations in Comsol and measurements on the cable was used. The results from the measurement shows that the inductance of the cable is 246 nH/m when the shield is not grounded and 94.3 nH/m when the shield is grounded. Furthermore, the simulations shows that the inductance changes with frequency when the shield is grounded. Therefore the model of the cable was made so that these effects could be accounted for.