SST vs Traditional Transformer: Key Advantages

Solid-State Transformers (SST): The Future of Intelligent Power Conversion

A solid-state transformer (SST), also known as a power electronic transformer (PET), is a static power conversion device that integrates power electronics, high-frequency transformation, and advanced control systems based on electromagnetic induction. It enables the conversion of electrical energy from one set of voltage, current, and frequency characteristics to another—while offering active control, bidirectional power flow, and enhanced functionality far beyond traditional transformers.

SSTs play a critical role in improving power system stability, enabling flexible power transmission, and supporting the development of smart grids, distributed energy resources (DERs), and multi-energy systems.

Limitations of Conventional Transformers

Traditional transformers, while reliable and widely deployed, face growing limitations in modern power systems:

• Large size and heavy weight

• Lack of active control over voltage, current, or power flow

• Mutual coupling between grid and load disturbances

• No inherent energy storage or fault isolation capability

• Dependence on insulating oil, posing environmental and maintenance challenges

These drawbacks make conventional transformers increasingly inadequate for today’s demands for reliability, flexibility, and sustainability.

Advantages of Solid-State Transformers (SST/PET)

In contrast, SSTs are compact, lightweight, and offer precise, real-time control over primary current, secondary voltage, and bidirectional power flow. They significantly improve power quality, mitigate voltage disturbances, ensure stable operation, and enable flexible, adaptive power delivery.

Beyond the power grid, SSTs are ideal for applications in:

• Electric vehicle charging systems

• Medical power supplies

• Chemical and process industries

• Aerospace and defense systems

• Data centers and microgrids

Enhanced Functionalities of Power Electronic Transformers

The SST is more than a transformer—it is a fully controllable power processing unit. In addition to the core functions of conventional transformers—voltage transformation, galvanic isolation, and energy transfer—the PET provides advanced capabilities such as:

• Power quality regulation (e.g., harmonic suppression, voltage balancing)

• Active and reactive power control

• Unity power factor operation with sinusoidal input current

• Flexible phase conversion (e.g., three-phase to two-phase or four-phase)

• Simultaneous AC and DC output for hybrid systems

• Built-in fault protection via high-speed semiconductor devices

By leveraging power electronic converters and digital control, SSTs can independently regulate the amplitude, phase, and frequency of voltages and currents on both primary and secondary sides, enabling precise power flow management tailored to system needs.

Key Features of SSTs

Compared to conventional transformers, PETs offer the following advantages:

Compact and Lightweight：Utilizes high-frequency transformers, drastically reducing size and weight—ideal for space-constrained environments.

Oil-Free and Air-Cooled Design：Eliminates the need for insulating oil, reducing environmental risk, simplifying maintenance, and enhancing operational safety.

Constant Output Voltage：Maintains stable secondary voltage under varying load and input conditions.

High Power Quality：Delivers clean, sinusoidal output voltage and input current, supporting unity power factor and low total harmonic distortion (THD).

Integrated Circuit Breaker Functionality：High-power semiconductor switches (e.g., SiC MOSFETs, IGBTs) can interrupt fault currents within microseconds, eliminating the need for external relays or mechanical breakers.

Energy Storage Integration：Can be seamlessly coupled with batteries or supercapacitors to improve supply reliability, support ride-through during outages, and enable grid-forming operation.

Multi-Function Output：Capable of delivering both AC and DC power simultaneously—ideal for hybrid AC/DC microgrids and electrified transportation.

Performance Validation: Simulation Study

A referenced simulation study compared conventional transformers with self-balancing power electronic transformers (PETs) under five critical operating conditions:

• Full-load rated operation

• Single-phase open circuit (LV side)

• Three-phase short circuit

• Unbalanced three-phase voltage (HV side)

• Input harmonic pollution

Results:

The PET demonstrated superior performance in all scenarios:

• Maintained stable output despite input imbalances or faults

• Effectively isolated disturbances between primary and secondary sides

• Preserved sinusoidal waveforms and balanced phase voltages

• Enabled fast dynamic response and self-healing capability

These results confirm that SSTs significantly outperform conventional transformers in resilience, controllability, and power quality.

Conclusion: Enabling the Next-Generation Grid

Solid-state transformers represent a transformative leap in power conversion technology. With their compact design, active control, multi-functionality, and superior fault resilience, SSTs are poised to become core components of future power systems—driving the evolution toward smarter, greener, and more reliable energy infrastructure.