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A vast majority of research on (U)WBG power modules has been going on to implement nonlinear resistive field grading material on metal-brazed substrates in reducing the electric field that is maximum at triple points (TPs). However, nearly all investigations have been conducted under either DC or 50/60 HZ sinusoidal AC voltages, even though the actual operation of envisioned (U)WBG power modules involves high-frequency square voltages with high slew rates. It has been validated by several studies that fast rise times of square voltages rapidly degrade the breakdown strength of insulation materials, leading to premature failure. Therefore, this paper introduces a nonlinear resistive field grading material or field-dependent conductivity (FDC) layer around the TP and metal edges to evaluate the electric field mitigation under a high frequency and high slew rate square voltage. The modeling and simulation of both coated and uncoated (U)WBG substrates were performed in COMSOL Multiphysics to assess the electric field reduction with the nonlinear FDC layer. The improvement of reduction in electric field under 100 kHz high slew rate square voltage is compared with that of 60 Hz. The results reveal a significant decrease in field stress at the TP, even under square voltages with fast rise times and high frequencies, when applying a nonlinear FDC coating, as opposed to the uncoated substrate. The influence of switching field (Eb) and nonlinearity coefficient (α) of nonlinear FDC layer is studied under 100 kHz square voltage, and it is concluded that α and Eb should be more than 10 and less than 8 kV/mm, respectively to achieve effective performance of resistive field grading material.
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This content will become publicly available on August 24, 2026
Comparison of Electric Field Suppression Techniques in (U)WBG Power Modules Under Unipolar and Bipolar Square Voltages at Varying High Frequencies
Most research involving resistive field grading materials or nonlinear field-dependent conductivity (FDC) layers has predominantly concentrated on DC or sinusoidal AC voltages, even though (U)WBG power electronic modules typically operate under high-frequency square wave voltages. To bridge this existing research gap, the present study systematically investigates the efficacy of an FDC coating in alleviating electric field stress when subjected to high-frequency, high-slew-rate square wave voltages. The findings indicate that applying a nonlinear FDC layer significantly reduces electric field stress, even under stringent conditions involving elevated operating frequencies. Furthermore, the influence of the square wave voltage type—the distinction between unipolar and bipolar square waveforms—on electric field stress remains inadequately understood despite substantial progress in breakdown and PD experiments related to these phenomena. Consequently, this study undertakes a comparative analysis of nonlinear FDC layers' performance under unipolar (+27.5 kV) and bipolar (±27.5 kV) square wave voltages. In doing so, this investigation contributes valuable insights into the interplay between high-frequency operation, the polarity of square waveforms, and the efficacy of nonlinear FDC layers in mitigating electric field stress within (U)WBG power module packages.
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- Award ID(s):
- 2306093
- PAR ID:
- 10652884
- Publisher / Repository:
- IEEE
- Date Published:
- Page Range / eLocation ID:
- 1 to 7
- Format(s):
- Medium: X
- Location:
- Dallas, TX, USA
- Sponsoring Org:
- National Science Foundation
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