TITLE:
Solid State Transformers: A Comprehensive Review of Technology, Topologies, Applications, Research Gaps, and Future Directions
AUTHORS:
Deepak Ramesh Chandran, Sanath Kumar, Deepashri Sanath
KEYWORDS:
Solid State Transformer (SST), Power Electronic Transformer (PET), Smart Grid, Medium Frequency Transformer (MFT), Wide Bandgap (WBG) Semiconductors, SiC, GaN, Power Electronics, Renewable Energy Integration, Electric Vehicle Charging, Microgrids, Power Quality, Multilevel Converters
JOURNAL NAME:
Journal of Power and Energy Engineering,
Vol.13 No.6,
June
26,
2025
ABSTRACT: Solid-State Transformers (SSTs), or Power Electronic Transformers (PETs), are emerging as transformative components in modern electric grids, capable of intelligent power flow control, AC/DC interfacing, and multi-level voltage regulation. While SSTs promise substantial advantages over conventional Low-Frequency Transformers (LFTs) in terms of compactness, bidirectional power flow, and integration with renewable energy sources and electric vehicles, their adoption necessitates a critical reevaluation of grid protection paradigms and communication infrastructure. Unlike passive LFTs, SSTs contribute minimal fault current due to fast-switching semiconductors, challenging conventional protection schemes based on overcurrent detection. Furthermore, their deployment requires robust, low-latency communication frameworks to coordinate with utility systems, raising pressing concerns regarding protocol standardization and cybersecurity resilience. This review advances the state of SST literature by offering a thematic and evaluative perspective—one that synthesizes converter-level advancements with system-level integration challenges. Specifically, we critique current SST architectures through a multi-criteria lens involving efficiency, cost, protection compatibility, and fault ride-through, supported by comparative matrices and taxonomy frameworks. A novel contribution of this work lies in identifying the disparity between component-level maturity and system-level readiness, especially in fault isolation, thermal resilience, and coordinated control. Rather than a broad technical survey, this paper adopts a focused perspective on SSTs as enablers of hybrid AC/DC smart grids. It emphasizes key innovations—such as advanced modulation for fault limitation, grid-compatible communication protocols, and modular multilevel topologies and maps them against evolving utility requirements. In doing so, we bridge the gap between technical feasibility and operational viability and propose a future research roadmap aligned with practical deployment milestones. The synthesis culminates in a revised classification of SST readiness for distinct grid applications and outlines unresolved technical bottlenecks that warrant targeted investigation.