Investigation on the influence of the shielding concept on the disturbances from the propulsion system of an electric vehicle

In electric and hybrid vehicles power trains with a total output power ranging up to the 100 kW range and batteries with terminal voltages up to 800 V are used. In these vehicles, compared to conventional motor vehicles, higher emissions because of the higher power level are observed. These interferences must be regarded as a critical disturbance. Therefore a closer look is needed. Normally the electric propulsion system is built as an IT network. It is totally isolated and thoroughly screened. This screening and the conventional 12 V electrical system are both connected to vehicle ground. The power semiconductors, which are used in the drive inverters, cause high frequency interference voltages during switching operations. These interferences can couple through the stray capacitances and mutual inductances in other areas of the electrical system and affect it. In this paper the pulsed voltages on the phasing lines between electric machine and inverter are investigated. The combination of the connection lines and the stator windings of the motor represent a resonant system. Regarding the three phase motor cables, there are currently two screening designs used. On the one hand there are separately shielded cables and on the other hand connection cables with a total shield for all three phases are used. The interferences can be mapped by a simple simulation model consisting of a source (inverter), the shielded cables and the motor. In this paper the effects of the different shielding concepts on the interferences in the electrical driving system are studied in time and frequency domain. Furthermore the simulation results are verified with measurements of a power train system, consisting of components which are used in current electric vehicles.