Investigation of a High Frequency Coupling Path Between HV and Shaft of an Electric Machine

Electrification of the drivetrain in modern vehicles brings new problems to the front line. High power electronics, high capacity high voltage batteries and electric machines with vast power density are now common attributes for vehicles. Existing low voltage (LV) on-board power network was extended with a high voltage (HV) drivetrain, which made a great impact on electromagnetic compatibility compliance testing. Low voltage supply conducted and radiated emission limits were adapted by to fit new emissions with their much higher amplitudes. In order to fulfill new limits for HV systems the drivetrain must be fully shielded. Due to construction restrains, an application of a shield around the electric shaft of the powertrain is not feasible. Existing magnetic field inside the stator and insulation breakdowns inside of the bearings make coupling to the shaft very effective, which is resulting in undesirable shaft currents. Hence the drivetrain must comply with defined limits for the electromagnetic compatibility of low voltage on-board power systems. In order to comply, the coupling path between HV side and the shaft of the machine should fulfill the limits for coupling attenuation defined in the international standard International Special Committee on Radio Interference 25 (CISPR 25) [1]. This publication describes a method to obtain coupling attenuation of the machine in the operating state and presents results compared with the corresponding limits described in CISPR 25.