Medium-voltage silicon carbide power devices, due to their higher operational temperature, higher blocking voltage, and faster switching speed, promise transformative possibilities for power electronics in grid-tied applications, thereby fostering a more sustainable, resilient, and reliable electric grid. The pursuit of increasing power density, however, escalates the blocking voltage and shrinks the module size, consequently posing unique insulation challenges for the medium voltage power module packaging. The state-of-the-art solutions, such as altering the geometry of the insulated-metal-substrates or thickening or stacking them, exhibit limited efficacy, inflate manufacturing costs, raise reliability concerns, and increase thermal resistance. This dissertation explores a material-based approach that utilizes a nonlinear resistive polymer nanocomposite field-grading coating to enhance insulation performance without compromising thermal performance for medium-voltage power modules. The studied polymer nanocomposite is a mutual effort of this research and NBE Technologies. Instead of using field-grading materials as encapsulation, a thin film coating (about 20 μm) can be achieved by painting the polymer nanocomposite solution to the critical regions to grade the electric field and extend the range of the applicability of the bulk encapsulation.
A polymer nanocomposite's electrical properties were characterized and found theoretically and experimentally to be effective in improving the insulation performance or increasing the partial discharge inception voltage, of direct-bonded-copper substrates for medium-voltage power modules. By applying the polymer nanocomposite coating on the direct-bonded- copper triple-point edges, the partial discharge inception voltages of a wide range of direct-bonded-coppers increased by 50-100%. To assure its effectiveness for heated power modules during operation, this field-grading effect was then evaluated at elevated temperatures up to 200°C and found almost unchanged. The nanocomposite's long-term efficacy was further corroborated by voltage endurance tests.
Building on these promising characterizations, functional power modules were designed, fabricated, and tested, employing the latest packaging techniques, including double-sided cooling and silver-sintering. Prototypes of 10-kV and 20-kV silicon carbide diode modules confirmed the practicality and efficacy of the polymer nanocomposite. The insulation enhancements observed at the module level mirrored those at the substrate level. Moreover, the polymer nanocomposite coating enabled modules to use insulated-metal-substrates with at least 100% thinner ceramic, resulting in a reduction of at least 30% in the junction-to-case thermal resistance of the module.
Subsequently, to test the nanocomposite's performance during fast-switching transients (> 300 V/ns), 15-kV silicon carbide MOSFET modules were designed, fabricated, and evaluated. These more complex modules passed blocking tests, partial discharge tests, and double-pulse tests, further validating the feasibility of the nonlinear resistive polymer nanocomposite field-grading for medium-voltage power modules.
In summary, this dissertation presents a comprehensive evaluation of a nonlinear resistive polymer nanocomposite field-grading coating for medium-voltage power modules. The insights and demonstrations provided in this work bring the widespread adoption of this packaging concept for medium-voltage power modules significantly closer to realization. / Doctor of Philosophy / This dissertation delves into a novel approach to improving the resilience and reliability of our electric grid by employing medium-voltage silicon carbide power devices. These power devices, due to their superior performance at higher temperatures and faster switching speeds, can revolutionize grid-tied power electronics. However, the challenge lies in safely packaging these devices, given their high blocking voltage and compact size.
To address this, the study explores an innovative solution that uses a material called a nonlinear resistive polymer nanocomposite. This nanocomposite can improve insulation and endure high temperatures, promising a significant boost in performance for these power devices. The study reveals that applying this nanocomposite coating to the edges of direct- bonded-copper, a component of the power module, can enhance the insulation performance by 50-100%.
Building on these findings, we designed, made, and tested functional power modules, using cutting-edge packaging techniques that we developed. The tests confirmed the practicality and effectiveness of the polymer nanocomposite, leading to insulation improvements on both the substrate and module levels. Importantly, this coating also reduced the thermal resistance of the module by at least 30%, signifying a more efficient operation.
Then we evaluated the nanocomposite's performance during fast-switching transients in more complex silicon carbide modules. The modules passed multiple tests, further validating the feasibility of the nanocomposite coating for medium-voltage power modules.
In essence, this dissertation uncovers a promising approach to more efficient and resilient power module packaging, paving the way for potential widespread adoption in the power electronics industry.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/116244 |
| Date | 07 September 2023 |
| Creators | Zhang, Zichen |
| Contributors | Electrical Engineering, Lu, Guo Quan, Ngo, Khai D., Jia, Xiaoting, Dimarino, Christina Marie, Narumanchi, Sreekant |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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