Investigations on the shaft currents of an electric vehicle traction system in dynamic operation

Abstract

As a result of the power train electrification in electric and hybrid vehicles the electromagnetic compatibility of these vehicles is comprehensively affected. To ensure the electromagnetic compatibility of these vehicles the traction system is built up completely shielded and isolated from the vehicle chassis. Considering the shielding of the propulsion system the shaft of the traction drive represents a weak point. Due to stray capacitances of the drive's bearings the high frequent portions of the stator current can couple onto the shaft. These currents can flow through the gear box in direction of the wheels and possibly affect sensors of the 12V system. For EMC testing on component level, normally the common mode current on the cables between the inverter and the drive and between the inverter and the propulsion battery is considered. For the disturbances occurring on the battery cables alternatively the unsymmetrical voltage is measured using a high voltage coupling network. Considering the actual standard, a measurement of the shaft currents is actually not provided. Another point is that the measurements are normally tested in constant operating points, not representing the typical operation of a vehicle. Thus in this paper the shaft currents occurring in the traction system of an electric vehicle are investigated for constant and dynamic operation. For the investigation, a Hardware in the Loop (HiL) setup of an electric vehicle traction system with the ability to variably simulate dynamic drive scenarios is used. For the detection of the shaft currents, an inductive measurement transducer is used. The occurring EMI are measured using a Time Domain EMI Measurement system to analyze the EMI behavior and to indentify critical operating points during the dynamic operation of an electric vehicle.