Design aspects of an electrostatic shield in an electric machine for hybrid electric vehicles

This paper is about the design of an electrostatic shield in an electric machine for hybrid electric vehicles and other applications. A parasitic shaft to ground voltage is responsible for bearing currents and disturbances in the radio frequency range. Hence, a slot-embedded shield is used to mitigate the capacitive coupling of stator and rotor thereby reducing these effects. With an ideal shield the shaft voltage can be reduced to zero, but this results in major losses and less output power of the machine due to circulating currents in the solution. Based on the first results an one-sided insulated shield is analysed to avoid the circulating currents. This design does not require a reduction of the output power, but still eddy currents occur in the electromagnetic interference (EMI) mitigation technique. This current heat loss causes thermal heating and life time issues of the shield. To decrease the eddy current losses, the shield is then segmented in radial direction of the machine. This proposed design, one-sided insulated and segmented, suppresses the EMI and shows still a good shielding characteristic of the parasitic electric field in a wide frequency range. All results are simulated with FEA and shown in the following contribution.