A Review of Solid-State Transformer-Based Ultra-Fast Charging Station Technologies: Topologies, Control, and Grid Interaction
Abstract
1. Introduction
2. Functional Demand-Driven Evolution of SST Topologies
2.1. High-Efficiency Energy Conversion Demand
2.1.1. Classical Topologies and Their Bottlenecks
2.1.2. High-Frequency Innovative Topologies
2.2. Modularity and Scalability Demand
2.3. Grid Interaction Capability Demand
3. SST Control Strategies and Grid Interaction
3.1. Inner Control Layer
3.1.1. Modulation Optimization and Soft-Switching Control
3.1.2. Decoupling and Model Reconstruction Control Strategies
3.1.3. Ripple-Suppression and Energy-Buffering Techniques
3.2. Middle Control Layer
3.2.1. Power Balancing and Voltage Coordination
3.2.2. Dynamic Power Scheduling and Efficiency Optimization for Multi-Module/Multi-Port Systems
3.2.3. Grid Support and Abnormal Condition Adaptability
3.3. Outer Control Layer
3.3.1. System Architecture and Module-Level Communication Support
3.3.2. System-Level Power Scheduling and Grid-Adaptive Control
3.4. Control Optimization Under Complex Conditions
3.4.1. Robust Control Under Weak Grid Conditions and Parameter Uncertainty
3.4.2. Dynamic Control Under Grid Faults and Overload Conditions
3.5. Topology–Control Co-Design and Synergy Analysis
4. System Performance Evaluation and Challenges
4.1. Efficiency and Loss Analysis
4.2. Reliability and Engineering Challenges
4.2.1. Thermal Management and Electro-Thermal Coordination
4.2.2. Device Aging and Lifetime-Oriented Optimization
4.2.3. Device-System Co-Design and Packaging Integration
4.3. Commercialization Progress and Engineering Challenges
4.4. Future Trends and Research Directions
5. Conclusions
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Topology Type | Technical Features | Efficiency and THD (%) | Bottlenecks | Cases |
---|---|---|---|---|
Vienna Rectifier [9,11,12,13,14,15] | • Three-level structure • Unidirectional | >95% <1 | • Does not support V2G • Neutral-point balancing issues | Texas Instruments Level 3 Commercial Fast Charging (120–350 kW) [16] |
NPC Rectifier (Neutral Point Clamped) [9,14,15] | • Three-level topology • Supports V2G | >97% <1 | • Neutral-point balancing issues | NPC-Based Bi-Directional Rapid EV Charging Prototype (30 kW) [17] |
SWISS RECTIFIER [14,18] | • Eight-switch bridgeless structure • Unidirectional | >96% <1 | • Does not support V2G • Limited power capability •Complex control | Swiss-Rectifier-Based EV Charging Prototype (10 kW) [19] |
CHB Rectifier (Cascaded H-Bridge Rectifier) [9,13,14] | • Multi-module series-connected topology | >95% <1 | • Low efficiency under light load • Complex control | CHB + Three-level CLLC Resonant Converter [20] |
Standard Multi-Level/Boost-Type Rectifiers (TLB, TLI, MCB, AFE, etc.) [9] | • Boost-type structure • Mature technology, compatible with standard PFC control schemes | - | • Neutral-point balancing issues • Large neutral-point support capacitor | - |
Topology Type | Main Technical Features | Efficiency | Existing Bottlenecks | Application Cases |
---|---|---|---|---|
LLC Resonant Converter [9,13,14,15] | • Resonant soft-switching structure, suitable for improving light-load efficiency • High power-density topology design • Includes enhanced CLLC variant to improve light-load efficiency and gain control | >95% | • Poor light-load efficiency | Texas Instruments Level 3 Commercial Fast Charging (120–350 kW) [16] |
DAB [9,13,14,15] | • Symmetrical dual-bridge structure • Supports ZVS soft-switching • Sensitive to parasitic parameters | >95% | • Sensitive to parasitic parameters • Challenges in thermal management and resonant control | SiC-Based Medium-Voltage Fast Charger Prototype (200 kW) [21] |
PSFB (Phase-Shifted Full Bridge) [9,14,15] | • Simple control logic | >95% | • Secondary hard switching affects efficiency • Not suitable for complex grid-side feedback | PSFB with Center-Tapped Clamp Prototype (3.3 kW) [22] |
Non-Isolated Boost/Buck Converter [14,15] | • Simple structure, low cost | - | • No galvanic isolation • Limited voltage capability • Lack of isolation leads to large ripple and strong interference | NPC-Based Bi-Directional Rapid EV Charging Prototype (30 kW) [17] |
Core Topology Combination | Power Rating | System Characteristics |
---|---|---|
Three-level active front-end rectifier + LLC resonant converter + hybrid-switch inverter [34] | 15 kV/25 kW | - Natural cooling - High voltage regulation - Foundational architecture for SST |
TLB + ANPC-DAB [35] | 12.47 kV/350 kW | - High-voltage direct connection - Compact structure - Well-suited for SiC devices |
ISOP + Three-level boost PFC + Half-bridge LLC [36] | 3.8 kV input/16 kW (4 × 4 kW) | - Modular redundancy - Harmonic optimization |
QAB + Wide-voltage direct connection structure [37] | MV input/4 kW | - Three-phase self-balancing - Adaptable to various EVs |
CHB + Three-level CLLC resonant converter [20] | 13.2 kV/400 kW | - High efficiency - Commercially deployable topology |
Topology Type | Grid Interaction Capability | Key Technical Features | Loss Characteristics |
---|---|---|---|
Modular Multilevel Converter (MMC) [9,13,14,15] | • V2G • Grid–vehicle interaction | • Multi-level modular structure • High-voltage output and fault tolerance | • Loss sharing |
Modular Push–Pull Converter (MPC) [9,14,15] | • V2G | • Three-phase center-tapped structure eliminates DC bias | • Parallel architecture reduces conduction loss |
Cascaded H-Bridge (CHB) [9,13,14] | • V2G • Grid–vehicle interaction • Low harmonic pollution | • Each submodule has self-sustained capacitor voltage balancing | • Circulating current loss is controllable |
Multiport Modular SST (MPMSST) [13,14] | • V2X • Large-scale deployment | • Multiport modular parallel power distribution • MPC-based power flow optimization | • Multiport optimization reduces overall losses |
Control Method | Applicable Topologies | Advantages | Areas for Improvement |
---|---|---|---|
Dual-Loop Control [13,18] | - TPSSBR - Vienna | -Simple structure - high reliability | -Sampling delay -Poor light-load performance |
Proportional Resonant Control (PR) [13,18] | - Vienna - NPC multilevel | - No steady - state error | - Parameter sensitivity - Complex computation |
SVM voltage balancing in closed-loop [18] | - NPC - CHB multilevel | - Utilizes redundant switching states | - High control complexity |
Voltage-Oriented Control (VOC) [13,14,18] | - Vienna - Multilevel | - Easy PFC implementation - Compatible with SVPWM | - Requires PLL |
Sliding Mode Control (SMC) [13] | - Vienna rectifier | - Fast response - Strong robustness | - Switching chattering issue |
Model Predictive Control (MPC) [13] | - CHB - TLT | - High dynamic performance | - High computational burden |
Control Method | Applicable Topologies | Advantages | Improvement Direction |
---|---|---|---|
PI Cascade Control [13,18] | - Multi-phase interleaved topology | - Simple and easy to implement | - Low light-load efficiency |
Model Predictive Control (MPC) [13,18] | - MMC - three-level DC/DC | - Multi-objective optimization - High dynamic performance | - High computational complexity |
Burst-Mode Control [18] | - LLC - PSFB | - Low light-load loss | - Output voltage ripple suppression |
Mixed PFM + PWM control [14,18] | - LLC | - Extended soft-switching range | - Complex control logic |
Phase-Shift Control [13,14,18] | - DAB - PSFB | - Low backflow and switching loss | - SPS cannot achieve soft switching at light load |
Control Method | Application Scenario | Implementation Mechanism | Advantages |
---|---|---|---|
Droop Control [18] | Multi-charger parallel operation | Simulates droop characteristics of synchronous generators | Communication-independent |
Zero-Sequence Circulating Current Suppression [14] | Parallel AC/DC modules | Zero-sequence current feedback loop ([79]) | - No need for extra sensors - >90% suppression rate |
Distributed Voltage Balancing Control [13] | ISOP/IPOS structures | - Local controller exchanges voltage error - Independently adjusts PWM duty cycle | - No central controller - Single-point failure does not affect the whole system |
Target Function | Applicable SST Structure | Typical Application Scenario/Limitations |
---|---|---|
Harmonic compensation, reactive power regulation, partial power processing (PPP) [90] | Hybrid SST | - Effective for low-voltage distribution grids |
Enhanced reactive power support under light load, extended ZVS region [91] | Single-stage DAB electronic transformer | - Designed for light-load and weak grid conditions - Experimental validation confirms improved ZVS region and reduced THD |
Frequency support and inertia emulation under weak grid conditions [92] | B2B-structured simulated SST (AC–DC–AC) | - Offers practical potential for low-inertia systems with a high share of renewables |
Control Method | Targeted Special Operating Conditions | Solution Approach and Key Measures | Applicable Scenarios |
---|---|---|---|
Adaptive ZSV Compensation (AZSVCS)+ PNS Harmonic Injection(PNSMMHZSVIS) [110] | - Active power backflow during interphase faults. - Modulation instability under low power/deep voltage sag | - Dynamically adjust zero-seq coefficient for power balance - Inject harmonic zero-seq voltage to reshape modulation - Hierarchical control to reduce latency | - High dynamic power scenarios - Deep voltage sag scenarios |
Frequency-Based Overload Control (FBOC) [111] | - Current approaching the hard limit and exceeds the set security threshold | - ST actively lowers grid frequency - Activates DG droop controllers to increase active power injection - Resets nominal frequency when current recovers | - LV grids with droop-controlled DG |
Typical Topologies and Their Features | Corresponding Control Strategies | Synergistic Performance Benefits | Assessment (Complexity, Stability, Comparison) |
---|---|---|---|
• DAB and Variants - Natural bidirectionality - Wide ZVS capability [71,72,73,74] | • Online Analytical Modulation • Minimum-Backflow-Power Scheme (MEPS) | • Efficiency: 96–98.5% (wide load range) • THD: 0.8–1.6% (grid-side) • Power Density: 2.4–3.8 kW/L • Full-range ZVS achieved | - Computational load, model dependency - Model sensitivity, light-load oscillation risk - High efficiency and flexibility vs. highest control complexity |
• LLC and Variants - Resonant soft-switching - High peak efficiency [24,25,26] | • Hybrid Control (PFM+PWM) • Adaptive Dead-Time Control | • Efficiency: 97.5–99% • Innate Bidirectionality • EMI: Low | - Medium-Low control algorithm complexity - Inherently high stability - efficiency and superior EMI performance vs. narrower gain range |
• Other Front-End Topologies - Multi-level, PFC capability - MV direct connection [35,36] | • Hybrid Feedforward Control | • THD: <3.75% • Efficiency: 98% • Robust MV grid adaptation | - Requires precise modeling - High robustness to grid disturbance - Excellent PFC and cost-effective solutions vs. complex modeling |
Typical Topologies and Their Features | Corresponding Control Strategies | Synergistic Performance Benefits | Assessment (Complexity, Stability, Comparison) |
---|---|---|---|
• DAB and Modular Variants - Fundamental building block for scaling [84,85,86] | • Multi-objective Optimal Control (MOC) • Modulated Coupled Inductor Control | • <5% power sharing accuracy • Significant reduction in turn-off and RMS current • Enables high-power system scaling (MW-level) | - Requires fast online parameter estimation and communication sync - Good hot-swap support - Achieving modularity vs. high complexity |
• Modularized Bridge Rectifier (mBR) - Ultra-simplified hardware architecture [39,40,41,42] | • ΣΔ-Vector Control | • THD < 1% • Efficiency > 98% | - Complexity: Medium - High robustness to parameter changes - High power density and low cost vs. unidirectional power flow |
• Modular Multilevel Converter (MMC) [78] - Superior waveform quality for MV connection | • Power Fluctuation Delivery (PFD) Control | • Capacitor volume reduced by 90% • Power density increased by 50% | - No additional hardware required - Stable operation - Ideal for compact high-power scenarios vs. higher submodule count |
Typical Topologies and Their Features | Corresponding Control Strategies | Synergistic Performance Benefits | Assessment (Complexity, Stability, Comparison) |
---|---|---|---|
• DAB and Variants - Provides galvanic isolation - Compact structure [91] | • Reduced Frequency Modulation (RFM) | • Enhanced light-load reactive power support • THD reduced from 5.2% to 2.5% • Light-load efficiency improved | -Low complexity - Good for light-load/weak grid conditions - Effective solution for extending operating range |
• Cascaded H-Bridge (CHB) - Excellent fault voltage tolerance [110] | • Dynamic Comp. and Harmonic Modulation (AZSVCS and PNSMMHZSVIS) | • Suppresses active power backflow during faults • Rapid DC bus stabilization (<250 ms) | - High complexity - Enhanced robustness in asymmetric faults - Superior for fault ride-through in high-power applications |
• Others (HSST, etc.) - Full controllability [87,90,92,93,95,111] | • Multi-function Control Strategies - Harmonic/reactive comp. and PPP - Adaptive VSM and FBOC - LV side voltage/frequency regulation | • Multi-dimensional power quality regulation • Frequency support in weak grids • Dynamic overload management • Cost-effective solutions | - High complexity - Cost-effective and full ancillary services |
Commercial Case Name | Power Rating | Voltage Range | Peak Efficiency | Interface Protocols | Year |
---|---|---|---|---|---|
ABB HVC360 [123] | 360 kW | 150–850 V DC | 96% | • CCS2 | 2024 |
Terra 360 [124] | 360 kW | 150–920 V DC | >95% | • CCS2 • CHAdeMO 1.2 | 2021 |
Siemens Sicharge D 400 [125] | 400 kW | 150–1000 V DC | 96% | • CCS2 | 2024 |
Tritium TRI-FLEX [126] | 400 kW | 150–1000 V DC | 97.20% | • CCS1 • CCS2 • NACS | 2025 |
XCharge C7 Ultra-Fast Charger [127] | 400 kW | 200–1000 V DC | ≥94% | • CCS2 | 2024 |
Huawei Fusion Charge [128] | 600 kW | 200–1000 V DC | ≥96% | • CCS2 • GB/T • CHAdeMO | 2024 |
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Xiao, H.; Prasad, K.; Kilby, J. A Review of Solid-State Transformer-Based Ultra-Fast Charging Station Technologies: Topologies, Control, and Grid Interaction. Energies 2025, 18, 4705. https://doi.org/10.3390/en18174705
Xiao H, Prasad K, Kilby J. A Review of Solid-State Transformer-Based Ultra-Fast Charging Station Technologies: Topologies, Control, and Grid Interaction. Energies. 2025; 18(17):4705. https://doi.org/10.3390/en18174705
Chicago/Turabian StyleXiao, Hanbing, Krishnamachar Prasad, and Jeff Kilby. 2025. "A Review of Solid-State Transformer-Based Ultra-Fast Charging Station Technologies: Topologies, Control, and Grid Interaction" Energies 18, no. 17: 4705. https://doi.org/10.3390/en18174705
APA StyleXiao, H., Prasad, K., & Kilby, J. (2025). A Review of Solid-State Transformer-Based Ultra-Fast Charging Station Technologies: Topologies, Control, and Grid Interaction. Energies, 18(17), 4705. https://doi.org/10.3390/en18174705