MS Thesis Defense: Kavi Krsnadas

"Neutral-Forming Solid-State Autotransformer for Split-Phase Power Using Bidirectional GaN in a Resonant Switched Capacitor Topology"

Abstract

Inverters for residential power systems in North America often rely on line-frequency neutral-forming autotransformers to create a split-phase power configuration from a single-phase inverter output. Particularly with bidirectional electric vehicle systems, off-board neutral formation is required. Autotransformers used in these applications are based on century-old technology that suffers from poor light load efficiency and high mass. A single-stage solid-state autotransformer alternative is proposed to reduce size and standby loss compared to the line-frequency counterpart. The proposed converter builds on the 2:1 switched capacitor topology, most notably with the inclusion of bidirectional voltage blocking switches. Implications of ac-ac operation for this well-described dc-dc topology are discussed, including bidirectional switch operation and approximate loss modeling. A prototype has been designed and tested for proof-of-concept, leveraging newly available monolithic bidirectional GaN switches. The 4 kW, 240 Vac to split-phase 120 Vac prototype achieves a peak efficiency of 98.9% and power density of 7.18 kW/kg with resistive loads, using fixed timing to achieve partial zero voltage switching throughout the line cycle. A demonstration of 1 kVA operation with a nonlinear reactive load is also shown. The solid-state autotransformer prototype has 3.45x lower no-load loss and 16x smaller mass than a line-frequency autotransformer with a comparable power rating.

Thesis Committee

• (Chair) Charles R. Sullivan,
• Jason T. Stauth
• Cong Chen

Contact

For more information, contact Thayer Registrar at thayer.registrar@dartmouth.edu .