Design and Optimization of a Novel GaN-Based High-Power-Density Online Uninterruptible Power Supply

This work presents a comprehensive design and optimization methodology for a novel GaN-based transformerless online uninterruptible power supply (UPS) topology that enables universal input/output operation with a common neutral and a single DC bus. The topology, featuring a multi-mode operation, allows the bus voltage to be lower than the peak line voltage, enabling the use of commercially available 650-V GaN devices. This enhances switching performance, reduces system size, and improves potential battery integration. A design tool using the proposed system-level design methodology is developed to sweep key variables—including bus voltage, switching frequency, GaN device, number of parallel devices, inductance values, core material/shape, and heatsinks—while computing loss, volume, and cost for each design point. Pareto-optimal fronts are used to identify the best trade-offs amongst loss, volume, and cost. A 1.1-kVA prototype is designed, built and tested achieving 96.6% dc-ac efficiency. The developed methodology for the first-of-its-kind topology enhances UPS performance, and enables efficient, data-driven UPS design tailored to practical performance, size, and cost constraints.