Book excerpt: This book is an all-in-one resource on the development and application of variable frequency transformers to power systems and smart grids. It introduces the main technical issues of variable frequency transformers (VFT) systematically, including its basic construction, theory equations, and simulation models. Readers will then gain an in-depth discussion of its control system, operation performance, low frequency power oscillation, and technical economics, before proceeding to practical implementation and future developments. The related concepts of energy revolution, third generation grids, and power system interconnection are discussed as well. The first, comprehensive introduction to variable frequency transformers (VFT) An in-depth look at the construction of VFT, with simulations and applications Demonstrates how to assess the control system and overall system performance Analyses future developments, energy revolution and power system interconnections Variable Frequency Transformers for Large Scale Power Systems is a timely overview of the state of the art for VFT as it is increasingly adopted in smart grids. It is intended for engineers and researchers specializing in power system planning and operation, as well as advanced students and industry professionals of power engineering.