The Role of Medium-Frequency Transformers in Solid-State Transformers

Solid-state transformers (SSTs) are often described as the future of power distribution, promising higher efficiency, smaller footprints, and greater control compared to conventional transformers. But at the heart of every SST is a component that ultimately determines how far these benefits can scale: the medium-frequency transformer (MFT).

While semiconductors and control architectures often receive the spotlight, the MFT is a key enabler of scalable medium-voltage SSTs.

From Line Frequency to Medium Frequency

Traditional transformers operate at 50/60 Hz, relying on large magnetic cores to transfer energy efficiently at low frequency. SSTs fundamentally change this paradigm.

Instead of stepping voltage up or down directly at line frequency, SSTs:

1. Rectify incoming AC power to DC

2. Switch the DC polarity at higher frequencies (typically 10 kHz–100 kHz)

3. Use a medium-frequency transformer to provide isolation and voltage transformation

This shift to higher frequency enables dramatic reductions in size, weight, and copper usage, but it also introduces entirely new design challenges.

What the MFT Must Deliver

Within an SST, the MFT must perform core electrical functions while supporting the system-level performance, controllability, and integration requirements that shape overall system viability.

Core functions

• Provide electrical isolation between primary and secondary systems

• Deliver voltage transformation at elevated switching frequencies

Key design requirements

• Support high power density within a compact system footprint

• Manage thermal loads under high-current, high-frequency operation

Unlike traditional transformers, the MFT must deliver this performance under fast switching waveforms, high dv/dt, and medium-voltage insulation constraints—making magnetics design a central system-level discipline in SST development.

This combination puts the MFT at the center of the SST’s technical risk profile.

Why Magnetics Become the Bottleneck

As SST power and voltage scale up to meet emerging power delivery needs in medium-voltage applications, the difficulty of MFT design increases disproportionately. Several factors converge:

1. Insulation at Medium Voltage

Providing reliable isolation at kV levels while maintaining compact size is one of the most challenging problems in SST design.

2. Frequency vs. Loss Tradeoffs

Higher switching frequencies reduce magnetic size but increase core and copper losses. Finding the optimal balance is not trivial, especially as system power scales to hundreds of kilowatts and above.

3. Thermal Constraints

Compact, high-density designs concentrate losses in smaller volumes, making heat removal more difficult. Poor thermal design can limit lifetime or force derating.

4. Manufacturability at Scale

A lab prototype may fail to translate into a repeatable, production-ready component. Design for manufacturing and performance becomes an essential requirement.

In practice, the MFT is often the component that determines whether SST performance goals can be realized in a manufacturable, reliable, and cost-effective system. That makes CorePower’s expertise in advanced magnetics and manufacturable transformer design central to enabling successful SST deployment.

The MFT as an Enabling Technology

When properly designed, the MFT unlocks the advantages that make SSTs compelling:

• Compact form factors for space- and weight-constrained applications

• Higher efficiency through optimized magnetic and thermal design

• Modular architectures that support scaling and redundancy

• Advanced system control enabled by high-frequency conversion and close integration between power electronics and the MFT

For companies pursuing SST platforms, magnetics is not just a supporting component; it is the driving force, and one where CorePower’s expertise in advanced magnetics and manufacturable transformers provides a lower time to market and a clearer path to reliable, scalable commercialization.

Applications Driving SST Adoption

The importance of MFTs is increasingly becoming evident in emerging medium-voltage applications, including:

• Grid modernization and solid-state substations

• Traction and transportation electrification

• Industrial power systems and large drives

• Data center and high‑power DC architectures

In each case, the value of SSTs depends heavily on whether the underlying MFT can meet demanding electrical, thermal, and reliability requirements.

Designing Beyond the Datasheet

For OEMs and system integrators, successfully deploying SSTs requires looking beyond conventional transformer specifications. Key considerations include:

• How the transformer design preserves insulation reliability

• How insulation systems perform under fast-switching operating conditions

• Whether the design is validated for long‑term reliability

• How scalable the manufacturing approach is for volume production

  
  

This is where CorePower takes a different approach, with medium-frequency magnetics developed around the realities of SST operation by integrating insulation design, high-frequency electromagnetic performance, thermal management, and manufacturability from the outset. That means transformer solutions that are not only optimized for performance targets, but also engineered for long-term reliability under fast-switching, medium-voltage conditions and for repeatable production at scale.

A Critical Piece of the SST Puzzle

As solid-state transformers transition from research to real-world infrastructure, the medium-frequency transformer will play an outsized role in determining success.

It is more than a component; it is the element that ties together voltage isolation, power density, efficiency, and manufacturability. For organizations investing in next-generation power systems, understanding the role of the MFT is essential, not only for designing SSTs, but for unlocking their full potential. This is where CorePower’s expertise becomes a key enabler, helping SST developers turn ambitious performance targets into manufacturable, reliable, and commercially viable systems.