Mitigating High-Frequency Overvoltage on Motor Windings: An Adaptive Approach

This paper examines the non-uniform overvoltage distribution on stator windings in AC motors driven by SiC-based inverters. The first coil of the stator winding experiences particularly severe overvoltage stress. To address this challenge, the paper suggests employing a circuit with adaptive impedance across the first coil. Surge impedance mismatch between the cable and motor has been identified as a cause of voltage reflection, leading to high-magnitude and high-frequency voltage ringing at the motor terminals. These overvoltage ringings/spikes pose a risk of insulation failure in the windings. To address this issue, the proposed adaptive circuit mainly includes a capacitor and a bidirectional gallium nitride (GaN) switch across the first coil. The purpose of this circuit is to ensure uniform voltage distribution by efficiently suppressing the occurrence of overvoltage spikes. A comprehensive experimental analysis is conducted to evaluate the effectiveness of the capacitor in mitigating voltage spikes, and the results are discussed in depth. The experimental setup involves a 2 hp, 460 V motor powered by a SiC-based inverter, connected through 4/C 10 AWG 30m and 18m cables. Preliminary experiments demonstrate that inserting a small capacitor during the initial few cycles effectively reduces overvoltage stress across the first coil by approximately 47%.