This book presents novel contributions in the development of solid-state-transformer (SST) technology both for medium-voltage (MV) and low-voltage (LV) utility grid interfaces, which can potentially augment the grid modernization process in the evolving power system paradigm. For the MV interface, a single-stage AC-DC SST submodule topology has been proposed, and its modulation and soft-switching possibilities are analysed, experimentally validated and adequately benchmarked. A control scheme with power balance capability among submodules is developed for MV grid-connected single-stage AC-DC SST for smooth operation under inevitable parameter drift scenario, and experimental validation shows excellent performance under drastic load change conditions. A novel machine learning-aided multi-objective design optimization framework for grid-connected SST is developed and experimentally validated, which equips a power electronics design engineer with meagre computational resources to find out the most optimal SST design in a convenient time-frame. This book has also contributed towards the development of dual-active-bridge (DAB)-type and non-DAB-type LV grid-interfaced isolated AC-DC converters by providing solutions to specific topology and modulation-related shortcomings in these two types of topologies. A comprehensive comparison of the DAB and non-DAB-type LVAC-LVDC converters reveals the superiority of DAB-type conversion strategy.
Author(s): Jaydeep Saha
Series: Springer Theses
Publisher: Springer
Year: 2022
Language: English
Pages: 294
City: Singapore
Supervisor’s Foreword
Summary
Preface
Declaration
List of Publications
Acknowledgements
Contents
Abbreviations
List of Figures
List of Tables
1 Introduction
1.1 The Changing Paradigm of Power Systems
1.2 Medium-Voltage AC-Low-Voltage DC (MVAC-LVDC) and Low-Voltage AC-Low-Voltage DC (LVAC-LVDC) Interfacing with Utility-Grid
1.2.1 Microgrid and Nanogrid
1.2.2 Conventional Line-Frequency-Transformer (LFT)
1.3 Grid-Connected Solid-State-Transformers (SSTs)
1.3.1 Broad Classification of SST Topologies
1.3.2 Relevance of SSTs for Grid-Connected Applications
1.4 Three-Phase Isolated LVAC-LVDC Power Converters
1.5 Problem Definition
1.6 Contributions of the Thesis
1.7 Organization of Thesis
1.8 Summary
References
2 Selection of Submodule Topology in MVAC-LVDC Modular SST
2.1 Introduction
2.2 Cascaded Modular SST Submodules
2.2.1 Conventional Two-Stage (IBE Type)
2.2.2 Front-End Indirect-Matrix (FE-IM) Based
2.2.3 Isolated Front-End (IFE) or Swiss-SST (S3T) Type
2.2.4 Single-Stage AC-DC Dual-Active-Bridge (DAB) Type
2.2.5 FE Matrix Converter + BE Current Doubler Rectifier (MC-CDR) Type
2.2.6 FE Matrix Converter + BE 6-Switch Converter (MC-6Sw) Type
2.3 Comparative Evaluation of Submodules
2.4 Modulation of Front-End Direct Matrix-Based AC-DC DAB Type Submodules
2.4.1 MB-DAB Topologies and Modulation
2.4.2 Analysis of Modulation Boundaries
2.4.3 Simulation Results
2.4.4 Experimental Verification
2.5 Summary
References
3 Half-Bridge Matrix-Based Dual-Active-Bridge
3.1 Introduction
3.2 Topology and Modulation Modes
3.2.1 Half-Bridge MB-DAB AC-DC Converter
3.2.2 ZCS Constrained Modulation Modes
3.2.3 ZVS Constrained Modulation Modes
3.3 Analysis of Modulation Modes
3.3.1 Modulation Mode Boundaries Due to SCAPT Limits
3.3.2 Simulation Results
3.3.3 Possible Modulation Schemes
3.4 Multi-objective Optimal Design
3.4.1 Converter Modelling and Design Optimization
3.4.2 η-ρ Design Optimization Results
3.4.3 Experimental Prototype and Results
3.5 ZVS Modulation Scheme
3.5.1 Modulation Modes and ZVS Capabilities
3.5.2 Proposed Analytical ZVS Modulation
3.6 Converter Modelling, Simulation Results and Experimental Validation
3.6.1 Converter Loss Modelling
3.6.2 Simulation Results and Discussions
3.6.3 Experimental Results
3.7 Summary
References
4 Machine Learning Aided Design Optimization Framework for Medium-Voltage Grid-Connected Solid-State-Transformers
4.1 Introduction
4.2 Modular SST and Component Modelling
4.2.1 MVAC-LVDC Modular SST Topology
4.2.2 Modelling of Relevant Components
4.3 Design Optimization Framework for SST
4.3.1 Local Design Optimization of Submodule and AC Filter
4.3.2 Learning the Local η-ρ Optimization
4.3.3 Pareto-Optimal Design of the Three-Phase SST
4.4 Optimization Routine for CMB-DAB SST
4.4.1 Modelling of Components for CMB-DAB SST
4.4.2 Local and Global Optimization Strategies
4.5 Optimization Results and Discussion
4.5.1 Results for CMB-DAB SST Using Proposed Algorithm
4.5.2 Laboratory Level Prototype Design
4.6 Summary
References
5 Power Balance Control Scheme for a Cascaded Matrix-Based Dual-Active-Bridge (CMB-DAB) Converter
5.1 Introduction
5.2 Cascaded Matrix-Based Dual-Active-Bridge
5.2.1 Converter Topology and Operation
5.2.2 Converter Modeling
5.2.3 Power Imbalance Issue
5.3 Closed-Loop-Control Strategy for CMB-DAB with Power Balance Controllers
5.3.1 LVDC Bus Voltage Controller
5.3.2 Power Balance Controller (PBC)
5.3.3 Stability Analysis of CMB-DAB's Control
5.4 Simulation Results and Discussion
5.5 Experimental Verification
5.6 Summary
References
6 Three-Phase Matrix-Based Isolated AC-DC Conversion
6.1 Introduction
6.2 Non-DAB Type Three-Phase Matrix-Based Isolated AC-DC Converter
6.2.1 Topology and Modulation
6.2.2 Simulation Results
6.3 DAB Type Three-Phase Matrix-Based Isolated AC-DC Converter
6.3.1 Topology and Modulation
6.3.2 Simulation Results
6.4 Modeling and Design
6.4.1 Converter Loss Modelling
6.4.2 Design Guidelines
6.4.3 Efficiency Comparison
6.5 Experimental Results
6.5.1 Non-DAB Type Matrix-Based Isolated AC-DC Converter
6.5.2 DAB Type Matrix-Based Isolated AC-DC Converter
6.5.3 Comparison of Efficiency and Harmonic Distortion
6.6 Summary
References
7 Conclusions and Future Work
7.1 Inferences and Conclusions
7.2 Recommendations for Future Work
References
Appendix A Investigated Novel Single-Stage Single-Phase AC-DC Converter Possibilities
A.1 Introduction
A.2 FE MC + BE CDR Type Submodule
A.3 FE MC + BE 6Sw Type Submodule
Appendix B Integrated Medium-Frequency Transformer (iMFT) for Dual-Active-Bridge (DAB) type Converters
B.1 Introduction
B.2 Dual-Active-Bridge Converters
B.2.1 DC-DC, AC-DC and AC-AC DAB Configurations
B.2.2 Integrated Medium-Frequency-Transformer (iMFT) and Its Functionality for DAB Converters
B.3 Leakage Inductance Design for iMFT
B.4 FEM Simulations and Experimental Characterization of MFT Prototypes
B.5 AC-DC MB-DAB Converter Simulation
B.6 Summary
Appendix C Loss and Volume Models of Converter Components
C.1 Introduction
C.2 Semiconductor Devices
C.3 Heat Sink and Auxiliary Power Supply
C.4 Medium Frequency Transformer (MFT)
C.5 AC and DC Filter Inductors
C.6 AC and DC Capacitors
Appendix References
