An official website of the United States government
The escalating adoption of wide-bandgap (WBG) semiconductor devices in power electronics has led to the generation of high-frequency, high-slew-rate voltage waveforms, which exert significant stress on encapsulating materials such as silicone gel (SG). This study systematically investigates the breakdown performance of SG under DC,60 HzAC, and highfrequency square wave excitations. Breakdown voltage assessments were performed across a frequency range of 10 to 50 kHz for square pulses with 100 ns rise time, revealing a pronounced decline in dielectric strength as frequency increased. Specifically, the breakdown voltage measured under DC conditions, which was 20.6 kV, diminished by 84.9 % when subjected to a square wave excitation at 50 kHz. Furthermore, electric field simulations elucidated the phenomenon of localized field intensification occurring near the needle tip, which corresponded with the identified breakdown locations. The key revelations from this research underscore the limitations inherent in conventional testing methodologies, which fail to adequately characterize the degradation behavior of SG under realistic high-frequency fast-rise square voltage stress conditions.
more »
« less
This content will become publicly available on April 11, 2026
Impact of Frequency and Rise Time on Breakdown Voltage of Air in Needle-to-Plane Geometry Under Square Wave Voltage Pulses
Air has always been an insulation medium that mainly interfaces with solid dielectrics within power electronics building blocks (PEBBs). Equipped with wide-bandgap (WBG) and ultrawide-bandgap (UWBG) devices, air around sharp edges is stressed by high frequency, high slew rate square wave voltage pulses within PEBBs. Having a lower insulation strength than solid dielectrics, decreased dielectric strength of air due to high frequencies and high slew rates of applied voltage can lead to enhanced surface discharges at interfaces, leading to degradation of solid dielectrics and eventually their breakdown. This shows the importance of studying the rise time and frequency effect on air breakdown subjected to the square wave voltage pulses at normal pressure, which is the main objective of our research. This study focuses on understanding the air breakdown voltage behavior under a frequency range of 2.5 kHz to 75 kHz and a rise time between 50 ns and 150 ns. This study reveals that a higher breakdown voltage (BDV) occurs at longer rise times, consistent with previous research, except for 150 ns, in which the expected effect was not observed. Results showed that BDV decreases with frequency increases beyond 20 kHz. For 75 kHz and a rise time of 125 ns, BDV reduces by 30 % to that of 10 kHz.
more »
« less
- Award ID(s):
- 2306093
- PAR ID:
- 10652889
- Publisher / Repository:
- IEEE
- Date Published:
- Page Range / eLocation ID:
- 1 to 6
- Format(s):
- Medium: X
- Location:
- Arlington, TX, USA
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Emerging power electronic drives and converters, especially wide bandgap (WBG) technology-based devices, are expected to operate at high voltages and switching frequencies, potentially reaching up to several hundred kHz. These operating conditions pose significant challenges to the reliability of insulation systems in motor windings, which are critical to the longevity and safe operation of electrical machines. This study investigates the impact of high-frequency square wave voltage pulses on the lifetime of motor winding insulation by conducting lifetime tests on twisted pair magnet wire commonly used in electrical machines. The experiments were conducted in the frequency range of 100 kHz to 300 kHz, with rise times of 50 ns and 400 ns (slew rate ranging from 2.4kV/μ s to 19.2kV/μs), to simulate the conditions typical in modern power electronics and inverter-driven systems. The results show that fast rise times and high switching frequencies influence turn-to-turn insulation's aging and breakdown characteristics. The findings highlight the importance of switching frequency and rise time in determining the reliability of insulation systems, offering critical data to enhance the design and performance of electrical machines in the context of high-frequency operation.more » « less
-
Wide bandgap (WBG) and ultra-wide bandgap (UWBG)-based inverters are increasingly being adopted in More Electric Aircraft (MEA) and All Electric Aircraft (AEA) due to their ability to operate at higher switching frequencies with improved efficiency and power density. However, these advantages come with drawbacks, including increased electrical stress and exacerbation of AC losses, such as the skin effect and proximity effect. Litz wire, known for its effectiveness in mitigating these losses, is becoming a preferred conductor in highvoltage, high-frequency aerospace applications. This study investigates the breakdown voltage behavior of Litz wire insulation under square wave voltage stress across different frequencies. Twisted-pair Litz wire specimens were tested using a state-of-the-art high-voltage pulse generator with fixed rise times to emulate inverter-fed conditions. The resulting breakdown voltages were statistically analyzed using the Weibull distribution to evaluate insulation strength and failure predictability. The findings offer new insights into the insulation characteristics of Litz wire under realistic high-frequency converter stress and support the development of converter-resistant insulation systems for next-generation aerospace electrical power systems (EPS).more » « less
-
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.more » « less
-
Emerging power electronic drives and converters are planned to operate at high voltages with high switching frequencies (up to a few hundred kHz), which will affect the reliability of insulation systems of windings of electrical machines. To evaluate the insulation quality under such high-frequency pulses, lifetime test is a prominent way. For simplification of test procedure, turn-to-turn insulation samples are approved by IEC 60034-18-42. In past studies, the impact of switching frequencies has been investigated under lower frequencies (up to 20 kHz), which cannot address the challenges of next-generation wide bandgap (WBG)-based power converters. In this study, the lifetimes of turn-to-turn insulations under high switching frequencies (50 kHz) are tested at four different rise times (50 ns, 100 ns, 150 ns, 200 ns), and the impact of switching frequency on the lifetime of the insulation is analyzed.more » « less
