Frequency-Dependent Bearing Voltage Model for Squirrel-Cage Induction Motors

This work describes a frequency-dependent bearing voltage model for squirrel-cage induction motors. Previous research related to bearing voltages commonly considered the bearing voltage ratio (BVR) as a constant. However, it is important to analyze the frequency-dependent behavior of the BVR when dealing with systems excited by high-switching-frequency pulsewidth modulation voltages. First, we measure the BVR characteristic for a 1.5-kW test motor. The measurement data show that, in the mid-frequency range (100 kHz-6 MHz), the BVR values are smaller than the conventional low-frequency constant value, and at higher frequencies, the BVR value increases above the low-frequency value. Considering this BVR characteristic, an equivalent circuit has been built and analyzed from the perspective of the BVR. The proposed equivalent circuit has been verified by comparing simulation data with measurement data. Based on the analysis results of the equivalent circuit, a parametric study was done to examine the effects of motor system parameters on the bearing voltage. For the study, variations of the bearing voltage on the changes of the input voltage waveforms and the winding-to-stator capacitance are analyzed by using measurement and simulation data.