Reduction of Shaft Voltage of IPMSM According to the Shape of the Novel Shield Ring

Recently, the motor drive system of electric vehicles (EVs) has been increased to high voltage to enhance the output and efficiency of the motor. However, higher voltage exacerbates common-mode voltage (CMV), which is the main cause of bearing faults. Due to the CMV component, shaft voltage is generated in the motor, shortening the life of the bearing and, in severe cases, causing serious motor faults due to bearing damage. Therefore, it is very important to reduce the shaft voltage of the motor. This paper proposes a method for reducing shaft voltage by applying a shield ring with a novel structure to the stator part of the interior permanent magnet synchronous motor (IPMSM). First, the parasitic capacitance and shaft voltage equivalent circuit model of the IPMSM are analyzed. The effect of shaft voltage based on the material of the shield ring is then analyzed. In addition, changes in shaft voltage magnitude are analyzed according to the shape of the shield ring. Finally, the proposed method is verified through experiments.