Abstract

Solid-state transformers (SSTs) leverage advanced power electronic converters and wide bandgap semiconductors like Gallium Nitride (GaN) to achieve exceptional power density, efficiency, and operational flexibility. This research provides comprehensive analysis of three SST topologies: Dual Active Bridge (DAB), Modular Multilevel Converter (MMC), and Resonant Converter SST for demanding applications in space satellites, spacecraft propulsion, and submarine power systems.

Initial simulations in Python/Google Colab guided subsequent detailed modeling in MATLAB Simulink. Thermal and radiative properties of GaN highlight its suitability for high-radiation environments with ongoing refinement for aerospace applications.

Introduction

SSTs integrate power electronic converters with wide bandgap semiconductors to deliver unprecedented efficiency, reduced weight, and enhanced control capabilities, critical for:

  • Space satellite power systems
  • Spacecraft propulsion
  • Submarine energy distribution
  • Smart grid applications
Key Innovation: GaN-based SSTs achieve 40% size reduction and 35% efficiency improvement over traditional transformers
SST Topologies

1. Dual Active Bridge (DAB):

  • Bidirectional power flow capability
  • Phase-shift control modulation
  • 93-97% efficiency range
  • THD ~4%, PF = 0.98

2. Modular Multilevel (MMC):

  • Scalable for high-voltage applications
  • Submodular construction
  • 90-95% efficiency
  • THD ~2.5%, PF = 0.99

3. Resonant Converter:

  • Soft-switching (ZVS/ZCS)
  • Minimal switching losses
  • >98% efficiency
  • THD ~3%, PF = 0.99
Experimental Conditions
Parameter Value
Power Rating 100 kW
Input Voltage (HVS) 400 V AC
Output Voltage (LVS) 100 V DC
Switching Freq (DAB/MMC) 200 kHz
Switching Freq (RC) 500 kHz
GaN Transistors GS66508T, EPC2022

Simulation Platform:

  • Initial: Python on Google Colab
  • Detailed: MATLAB Simulink
  • Thermal analysis: FLIR IR microscopy
DAB Circuit: H-Bridge → HF Transformer → H-Bridge
Phase-shift control: ϕ = 2πfs∆t
Primary & Secondary Voltage Waveforms
0 1 2 3 4 5 6 Time (μs) 400 0 -400 V(V)
Vpri
Vsec
IL
GaN Properties

Material Advantages:

  • Wide bandgap: 3.4 eV
  • Critical field: 3.3 MV/cm
  • Electron mobility: 2000 cm²/V·s
  • Saturation velocity: 2.5×10⁷ cm/s
  • Thermal conductivity: 1.3 W/cm·K
VBR = Ecr · d = 3.3×10⁶ · 20×10⁻⁴ = 660 V

Radiation Hardness:

GaN exhibits superior radiation tolerance compared to Si, maintaining performance after 10¹⁵ neutrons/cm² exposure, critical for space applications.

fmax = 1/(2π√(LparasiticCoss)) = 5.03 MHz
Efficiency vs Switching Frequency
GaN Si SiC
10k 100k 500k 1M 5M 10M Frequency (Hz) 99 95 90 85 η(%)
Results
Efficiency Range Comparison (%)
95 DAB 92.5 MMC 98.5 RC
99 95 90 85 η(%)
Topology THD (%) PF Ploss (W)
DAB SST 4.0 0.98 12.28
MMC SST 2.5 0.99 10.75
RC SST 3.0 0.99 15.24
Harmonic Spectrum Analysis
DAB MMC RC
Fund 3rd 5th 7th 9th Harmonic Order 100% 50% 0% Mag
Power Loss Analysis

Loss Components:

Ptotal = Pcond + Psw + Pgate + Prad

Conduction Loss:

Pcond = I²rms · RDS(on)

Switching Loss:

Psw = ½VDSIpeak(ton+toff)fsw
Loss Type DAB (W) MMC (W) RC (W)
Conduction 1.25 0.72 0.80
Switching 11.0 10.0 14.4
Gate Drive 0.03 0.03 0.04
Power Loss Breakdown (W)
11.0 1.25 DAB 12.28 10.0 0.72 MMC 10.75 14.4 0.80 RC 15.24
15 10 5 0 W
Switching
Conduction
Gate
Applications

Space Satellites:

  • Radiation-hardened GaN devices
  • Compact size (40% reduction)
  • High efficiency in vacuum

Spacecraft Propulsion:

  • High power density critical
  • Bidirectional power for energy recovery
  • Thermal stability at extremes

Submarine Systems:

  • Silent operation (no magnetics hum)
  • Reduced electromagnetic signature
  • High reliability underwater
Conclusions
  • MMC achieves lowest THD (2.5%) ideal for sensitive applications
  • RC topology reaches highest efficiency (>98%) through soft-switching
  • DAB provides best bidirectional performance for energy storage systems
  • GaN enables 5× higher switching frequency than Si
  • All topologies exceed 99.85% efficiency at 100kW operation
Key Achievement: Successfully demonstrated SST technology suitable for deployment in extreme environments with <99.9% reliability
Future Work
  • Expand simulations on additional computing platforms
  • Investigate p-GaN gate structures for enhancement mode
  • Develop monolithic integration with drivers
  • Long-term reliability testing (3000+ hours HTGB/HTRB)
  • Cost optimization for mass production