GOALI: 1.2 kV Vertical GaN FETs enabled Novel Ultra-High-Density Bidirectional Soft-switching Dc-Dc Charger Architecture with Scalable Electronic-embedded Transformer

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The electrification of land vehicles, including personal cars and transport/freight trucks, plays a critical role to accelerate the transformation of energy eco-system from fossil-fuel to zero-carbon-emission based renewable energies system. The high-efficient, high-density onboard battery charging system propels such electrification transformation. Inside the onboard charger, the galvanic isolation transformer represents one of the biggest and heaviest components, occupying about 50% of the total system size and weight. To increase the power density by an order of magnitude, the power transformer operation frequency has to reach MHz range meanwhile efficiently delivering tens of kW and even hundreds of kW power. This poses a huge challenge and many fundamental knowledge gaps need to be addressed, including high-efficient ultra-fast switching devices and ultra-high-frequency high power transformer. This NSF GOALI program proposes to investigate and develop a novel bi-directional high-power dc-dc onboard charger system with ultra-high-power density and scalability operating beyond MHz by adopting novel medium-voltage vertical GaN field-effect transistors (FETs) and proposed electronic-embedded transformer (EET) concepts. The team from Virginia Tech will carry out the proposed research tasks. The program will collaborate with researchers/technologists from two industry partners: Carrier Corporation and NexGen Power Systems.To enable the order-of-magnitude power density improvement in onboard battery charger, this proposal proposes four critical areas and scientific gaps: 1. Design and demonstrate 1.2 kV GaN-on-GaN vertical GaN field-effect transistor (FETs) based high-frequency power converters which operates over 1 MHz with over 800 V input. 2. Investigate a novel ultra-high-frequency “Electronic-embedded Transformer (EET)” concept for ease of transformer integration and paralleling operation for high power applications. 3. Investigate soft-switching (zero-voltage switching, and close to zero-current switching) circuit operation with auto-tuned operation point for high-efficiency operation over entire operation life. 4. Characterize MV vertical GaN FETs static and dynamic performance, establish device physics-based models, and create a comprehensive reliability assessment of vertical GaN FETs under repetitive short circuit and surge energy for automobile industry. The innovation circuit solutions and fundamental knowledge can be applied to a wide range of applications, like solid-state transformer; EV battery charger, commercial and utility energy storage system, PV string optimizer, etc. The device modeling and characterization, circuit operation, and reliability evaluation will offer the in-depth knowledge of understanding vertical GaN technology and its comparison with SiC MOSFET for both power semiconductor and power electronics industries.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.