SST Technology: Full-Scenario Analysis in Power Generation, Transmission, Distribution, and Consumption

I. Research Background

Power System Transformation Needs

Changes in energy structure are placing higher demands on power systems. Traditional power systems are transitioning toward new-generation power systems, with the core differences between them outlined as follows:

Ⅱ.Core Application Scenarios of Solid-State Transformers (SST)

Under the backdrop of new power systems, active support, grid integration regulation, flexible interconnection, and supply-demand interaction have become key requirements for spatiotemporal energy complementarity. SSTs permeate all stages—generation, transmission, distribution, and consumption—with specific applications as follows:

• Generation Side:Direct-connected grid-tied converters, grid-forming equipment, medium-voltage DC transformers for integrating wind, solar, and storage.

• Transmission Side:Medium- and high-voltage DC distribution transformers, flexible DC interconnection devices.

• Distribution Side:Medium- and low-voltage flexible interconnection units, flexible distribution power electronic transformers (PET), DC transformers for electrified transportation.

• Consumption Side:DC power supplies for hydrogen/aluminum production, direct-connected charging systems, direct-connected data center power sources.

(1) Rail Transit Traction — 25kV Traction PETT

SST-based converter systems are core equipment for building next-generation power grids.

Key Technical Breakthroughs:

• High-isolation high-frequency topology conversion and high-power high-frequency transformer technologies

• High-voltage (AC25kV direct connection) and high-insulation technology under compact design (withstand voltage: 85kV/1min)

• Adaptation to strong impact and vibration environments, efficient phase-change cooling

• High-frequency, high-efficiency conversion topologies and driving techniques, high-frequency modulation control with smooth switching

Application Results:

• Installed and tested on a 140 km/h EMU in 2020, outputting DC1800V

• Rated efficiency of 96.7% (2% higher than existing systems), 20% increase in power density

• Fully controlled grid side enables active filtering, reactive power compensation, zero magnetizing inrush current and no standby losses

• World’s first 25kV-SST product to achieve vehicle-mounted dynamic testing

(2) Urban Rail Power Supply — Multi-port Energy Router for Metro Systems

Core Design:
Four-port isolated structure supporting traction power, auxiliary power, energy storage, and PV integration.

Key Technologies:

• Two-level full-bridge LLC circuit topology based on IGBTs

• SiC-based DAB circuit topology with series-parallel DC configuration

• Soft-switching technology for power devices (branch efficiency ≥98.5%)

• Shared 12-pulse transformer connected to AC grid, eliminating circulating currents when paralleled with diode rectifiers

Application Advantages:

• Eliminates bulky line-frequency regenerative transformers; 26% smaller footprint, reducing installation space and construction costs

• No transformer no-load losses, enabling retrofitting of existing lines

• Integrates rectification, energy feedback, reactive compensation, and harmonic filtering for precise multi-port power flow control

(3) Charging & Battery Swap — 10kV Direct-Connected SST for EV Charging

System Configuration:

• 10kV medium-voltage direct connection, 1MVA capacity: 1 direct-charging module + 2 shared-bus networking modules

• Configured with 300kW ultra-fast charging and six 120kW fast chargers; compatible with PV-storage integration and medium-voltage grid connection

Core Functions:

• Integrates transformer and charging modules; wide-range voltage regulation enables direct charging, system efficiency ≥97% (peak 98.3%)

• Provides grid support and power quality management, enabling bidirectional V2G (vehicle-to-grid) and G2V (grid-to-vehicle) interaction

(4) Park Power Supply — Low-Carbon Park Energy Router (PV-Storage-Charging Integration)

System Architecture:
10kV direct-connected energy router based on SST, featuring AC10kV and DC750V ports, with battery storage, DC charging interfaces, and DC protection devices on the output side.

Core Configuration:
315kW SST cabinet, 976.12kWp PV, 0.5MW/1.3MWh energy storage, 10 DC charging stations.

Application Value:

• Reduces electricity costs through PV generation and energy storage peak-shaving arbitrage

• Lowers station capacity demand, buffers grid impact, and offers excellent scalability

• Output-side "solid-state DC circuit breaker + disconnect switch" combination ensures fault isolation for storage and charging stations

(5) Renewable Energy Integration — DC/DC Energy Router for PV-to-Hydrogen

Core Parameters:

• 5MW isolated DC/DC converter: input DC800–1500V, output DC0–850V, connected to hydrogen electrolyzer busbar

• Single cabinet capacity: 3/6MVA, scalable from 3–20MVA; output voltage adaptable to DC0–1300V/2000V

Technical Advantages:

• Reduces conversion stages compared to AC transmission; overall efficiency 96%–98%

• High-frequency isolated DC transformers with flexible series-parallel topologies, suitable for PV, storage, rail power, hydrogen/aluminum production

• Modular, configurable platform tailored to diverse industry-specific DC grid needs

(6) Distribution Network Optimization

Medium- and Low-Voltage Flexible Interconnection Device:

• Addresses load imbalance, rising distributed PV, EV charger expansion, and reliability enhancement

• Normal operation: asynchronous grid interconnection with active/reactive power flow control, improved renewable integration, and power quality isolation

• Fault condition: rapid isolation and automatic switchover to prevent outages

10kV Direct-Connected Energy Storage System:

• Medium/high-voltage grid connection reduces line losses

• Two-stage conversion enables wide-range voltage regulation

• Modular PCS and battery configuration

• More flexible capacity vs. cascaded H-bridge topology, ensuring battery insulation safety and full-chain power flow control

(7) Grid Connection on Generation Side — 10kV Direct-Connected Photovoltaic New Grid Interface

Technical Features:

• High-frequency isolation + cascaded CHB main circuit topology

• Capacity: N×315kVA (scalable), output compatible with 1500V systems, efficiency >98.3%

Core Advantages:

• Medium-voltage direct connection with isolated DC-DC performing MPPT (Maximum Power Point Tracking) and isolation/voltage regulation

• Simplified two-stage architecture, highly efficient; responds directly to grid demands at 10kV level

• Applicable to industrial, commercial, and rural distributed PV scenarios

(8) Load Side — Data Center Power Supply Based on SST

10kV Direct-Connection Solution:

• 2.5MW power (315kW × 8), system efficiency 98.3%, using high-frequency isolated conversion

• 400VDC DC ring network on DC side

• Full PWM control achieves grid-side power factor >0.99, harmonics <3%

Future Outlook

Centered on AC/DC distribution networks, extending to renewables, transportation, power supply, energy management, and fault protection, SSTs enable an integrated system solution encompassing:

• AC/DC hybrid power supply

• Source-grid-load-storage integration

• Optimized energy management and power flow dispatch
  Supporting the construction of next-generation power systems.

III. Application Challenges and Discussion

(1) Relay Protection Compatibility Challenge
Research is needed on the compatibility between power electronic transformers and traditional distribution systems, especially for short-circuit, ground, and open-circuit faults. Clear control strategies during fault ride-through and coordination mechanisms for relay protection must be established.

(2) Dispatch, Management, and Monitoring Integration Challenges
The widespread adoption of new power electronic equipment raises adaptation issues in dispatch and monitoring, requiring solutions to three core needs:

• Dispatch Rules & Market Mechanisms: The traditional “source-follows-load” logic cannot accommodate bidirectional “load-source-grid” interactions. Multi-directional power flow market mechanisms must be developed.

• Standardization & Interoperability: Diverse device interface protocols lead to poor interoperability among vendors. Standardized communication protocols and control command sets must be promoted.

• Cross-Regional Coordinated Dispatch: Flexible interconnection breaks traditional zoning boundaries. Unified responsibility allocation, reserve sharing, and cross-regional coordinated dispatch frameworks must be established.

These challenges require unified standards and monitoring execution mechanisms to resolve.