Title:  Topologies and Controls of Medium-Voltage Soft-Switching Solid-State Transformer

Committee: 

Dr. Divan, Advisor        

Dr. Saeedifard, Chair

Dr. Habetler

Abstract: The objective of the proposed research is to push the boundary of existing state-of-the-art solid-state transformer (SST) in terms of efficiency, power density, voltage balancing control across series-connected modules, and grid compatibility from both topology and control perspectives. The SST is a promising solution in the future grid as a replacement of line-frequency transformer for renewable energy integration, EV fast charging, etc. Single-stage SST topologies are proposed for reduced conduction loss and auxiliary counts, which indicate higher efficiency, higher power density, lower cost, and complexity, compared to the existing solution. Predictive control methods are proposed to achieve robust and stable operation of this stacked low-inertia (reduced dc-link) converter under extreme grid events and allow active power decoupling to buffer double line-frequency power ripple, which enables reduced passive for high power density and high robustness. Moreover, the multiport power flow and the dc-link current are steered to realize optimal efficiency using the predictive control. To verify the effectiveness of the concepts above, a 5 kV-600 V DC SST prototype has been built and tested and a 7.2 kV SST prototype is being built and is under test.