Solid State Transformers
February 2026
9 / 9
Overview
Solid State Transformers (SSTs) are power electronic devices that convert AC voltage levels using high-frequency semiconductor switching, filtering, and a small medium-frequency transformer. SSTs can convert AC power at one voltage level to DC and back to AC at another voltage level, or convert directly from one AC voltage level to another without the DC stage.
These devices serve a role similar to conventional transformers, which use magnetic cores to transfer energy. SSTs are envisioned to replace conventional transformers in distribution systems[1].
Benefits
Power Quality and Control
SSTs can regulate voltages with greater precision and can quickly respond to voltage fluctuations, unlike conventional transformers. They can suppress harmonics and enable power factor correction, thereby improving power quality[2]. Contrary to conventional transformers, SSTs can send power in both directions (bi-directional power transfer), allowing for flexible grid integration of variable resources and batteries. Bi-directional power flow is crucial for enabling flexibility and resiliency in future power grids[3].
Efficiency, Portability, and Integration
SSTs have higher efficiencies under partial loads, a considerable improvement over conventional transformers[4]. They are smaller and lighter, an advantage due to high frequency switching, which allows them to use smaller transformers as opposed to conventional transformers. They can integrate communication links for smart grid applications, an essential feature of future power grids. SSTs’ DC links can facilitate direct connections to DC grids and battery banks for inter-area power transmission and integration of variable generation. Currently, DC breakers, which are used in DC networks, are starting to come to market scale, but this can be a risk associated with SSTs.
Fault Isolation and Broad Applications
SSTs can isolate faults in networks, enhancing grid resilience. They are scalable and allow redundancy. Unlike conventional transformers, they can be applied broadly to electric charging, microgrids, data centers, and traction systems[5].
Removal of Inrush Current
Unlike conventional transformers, SSTs do not require significant levels of inrush current to facilitate energization of the transformer. Inrush current can be several times that of full load current and require significant levels of reactive power when a conventional transformer is energized. SSTs remove this need as energization is based on startup of power electronics.
Technology Readiness Level (TRL)
- System proven in real operations
- Full range of operating conditions
- Deployed in production environment
- Fully mature technology
The components of SSTs, namely power supplies that convert AC power efficiently to a given DC level and inverters that take DC energy sources and form an AC power output, have been in use for decades meaning that overall, the technology has a TRL of 9. However, widespread adoption of SSTs is still limited due to high cost and other technical challenges such as concerns about the reliability and longevity of their electronic components under grid stress[6]. New features and enhancements are being incorporated, and proof-of-value trials are underway, like those by Amperesand.
Adoption Readiness Level (ARL)
Value Proposition
Delivered Cost
Medium Risk
Current SSTs remain cost-premium hardware due to the high expense of wide-bandgap (SiC) devices and medium-voltage packaging[7]. However, in targeted applications—such as utility-direct fast charging—SSTs can reduce site balance-of-system costs by eliminating low-voltage equipment and reducing spatial requirements. Demonstration systems have achieved conversion efficiencies exceeding 96.5%.
SSTs require significant upfront capital due to their semiconductor-based architecture, high-frequency components, and advanced control systems. While long-term operational gains—such as improved efficiency, controllability, and lower maintenance—can offset these costs, initial acquisition and integration expenses remain higher than those of conventional transformers.
Some sectors, including microgrids and EV charging infrastructure, are expected to adopt SSTs in the near term[8]. Additionally, SSTs have been proposed as solutions within data center applications, highlighting benefits like smaller footprints, increased efficiency, and less equipment like switchgear and wiring. This alsoalso translates to higher reliability due to the reduction in equipment that could break[9]. Other applications will require further technological and economic development before broader implementation is feasible.
Functionality Performance
Low Risk
SSTs provide grid-support services such as voltage regulation, reactive power compensation, and harmonic mitigation. Their native AC/DC ports allow configurations like medium-voltage to DC for applications such as depots and data centers. This is something conventional transformers can’t do without extra equipment like switchgear and wiring. SSTs also offer high switching speeds, low conversion losses, high power density, and advanced control capabilities[10]. These functional attributes are well-established in power electronics and have been successfully deployed across various grid environments.
Compared to conventional transformers, power-electronic devices—including SSTs—tend to exhibit lower intrinsic reliability, particularly under thermal stress, surge conditions, and extended medium-voltage grid operations. While SSTs deliver high functionality, their long-term performance under demanding grid conditions is still under development. However, the funcionalities are highly recognized in this promising technology.
Ease of Use/Complexity
Medium Risk
Operationally, SSTs are active power-electronics systems rather than passive iron-and-oil assets. They require specialized protection schemes, control systems, and operations and maintenance protocols[4]. Medium-voltage insulation coordination and device reliability remain active engineering challenges, increasing integration complexity relative to legacy equipment[6].
SSTs introduce new operational modes, including different switching frequencies, cybersecurity requirements, and coordination with existing protection systems[4][11]. While these factors add complexity, SSTs leverage established power-electronics design and manufacturing practices. Integration into existing converter-based systems is generally straightforward. Although replacing medium-voltage transformers introduces additional engineering considerations, the underlying operational principles are familiar to professionals experienced with inverters and power-conversion technologies.
Market Acceptance
Demand Maturity/Market Openness
Low Risk
Utility procurement tends to be conservative, and standards for medium-voltage SSTs are still evolving, which slows adoption beyond pilot deployments. Nonetheless, SSTs have been included in DOE’s advanced transformer initiatives, signaling institutional interest and potential policy support.
Market success will depend on clearly defined functional advantages. Sectors such as microgrids and EV charging infrastructure are expected to reach commercialization in the near term[12]. Broader adoption is supported by growing demand for grid modernization, integration of DER, and energy-efficient power conversion. In the advanced energy and storage sector, its applications are particularly strong drivers, as SST capabilities align with the control, flexibility, and bidirectional power flow requirements of inverter-based systems[9].
The market is competitive and open, with multiple vendors contributing to technology development and deployment.
Market Size
Low Risk
The transformer market is large and expanding, driven by an aging asset base and electrification equipments. EV infrastructure introduces a parallel demand channel, where medium-voltage SSTs can reduce site development costs by minimizing the need for low-voltage equipment. National Laboratory of the Rockies (NLR) analyses indicate sustained scaling of charging networks, reinforcing this demand trajectory[12].
The global power electronics market is well-established and rapidly growing, driven by increasing demand for energy-efficient, flexible, and compact interface technologies. SSTs are positioned to benefit from this growth, particularly in applications requiring bidirectional power flow, advanced grid support, and integration with inverter-based systems[4].
Downstream Value Chain
Low Risk
For utility replacements, SSTs align with existing transmission and distribution (T&D) value chains and fit within established procurement and deployment channels. In EV charging, integrators and site hosts already plan around medium-voltage service using tools such as those developed by NLR; SST adoption in this context primarily shifts the configuration of on-site equipment rather than the overall planning process.
Recent supply chain disruptions have affected the availability and lead times of liquid-filled transformers (LFTs), increasing interest in alternative technologies such as SSTs. SSTs also support a broad portfolio of downstream applications—including motor drives, inverters and converters for variable generation, and energy storage interfaces—which further support their market potential[13].
However, deployment at higher voltage levels entails greater cost and engineering complexity than in low- and medium-voltage applications, where integration is more technically and economically feasible.
Resource Maturity
Capital Flow
Low Risk
Public investment in the U.S. has supported SST development, though it remains targeted rather than broad-based. Programs such as ARPA-E’s wide-bandgap (WBG) device initiatives and the DOE Vehicle Technologies Office’s extreme-fast-charging demonstrations have helped de-risk key technologies. However, these efforts have not yet established commodity-level financing norms for utility-scale SST deployments.
Economies of scale and established manufacturing processes in the power electronics industry have reduced costs for low-voltage SST applications, improving accessibility. While high-voltage SST technologies are technically mature, they require significantly more capital investment. Funding remains a challenge due to the relative novelty of medium- and high-voltage SSTs in utility environments.
Project Development, Integration, and Management
Low Risk
Interconnection guidelines for power-electronic grid assets (e.g., IEEE 1547) reduce execution risk by providing standardized control, testing, and cyber-security requirements[14][11]. Nonetheless, medium-voltage SST integration into substations typically requires first-of-its-kind engineering at most utilities, involving custom protection schemes, thermal assessments, and interoperability validation.
Infrastructure
Low Risk
SSTs can be deployed using existing medium-voltage distribution networks. For applications such as EV fast charging, shifting the conversion from low-voltage to medium-voltage levels can reduce the need for costly low-voltage feeder reconductoring, representing a notable infrastructure advantage where medium-voltage service is available.
Manufacturing and Supply Chain
Low Risk
As SST technology continues to mature, careful selection of materials, components, and design strategies remains essential to avoid performance limitations. These challenges are expected to diminish as advanced power semiconductor technologies are incorporated into next-generation SST designs.
The power electronics supply chain is mature and global, with established vendors producing converters, semiconductor modules, and control systems at scale. Multiple SST designs and power ratings are already commercially available. However, the supply chain for silicon carbide (SiC) devices—critical for high-performance SSTs—is still scaling and remains capacity-constrained and internationally concentrated[15]. This leads to considerations relative to current lead times and risk of extension in a non-mature supply chain for SSTs. DOE supply chain reviews have identified semiconductors as strategic components, and actions are underway to mitigate potential schedule and cost sensitivities during scale-up.
Materials Sourcing
Medium Risk
LFTs, which rely on mature manufacturing processes with relatively low environmental impact, SSTs depend on advanced power semiconductor materials. The extraction and processing of these materials, particularly silicon carbide (SiC), entail higher primary energy consumption. Additionally, the high component count in SSTs raises concerns around equipment maintenance and end-of-life recycling.
SST production is heavily reliant on SiC semiconductors, which are listed on the DOE’s Critical Materials List[16]. This designation signals elevated supply-chain risk through 2035 unless domestic manufacturing capacity expands[15]. This constraint may pose a barrier to high-volume SST deployment, particularly in utility-scale applications.
Workforce
Low Risk
The absence of established standards for SST design, performance metrics, testing procedures, and grid interconnection requirements impedes interoperability, utility acceptance, and system comparability. Standardization will be critical to enabling broader deployment and integration across diverse grid environments.
SSTs offer significant technological and societal benefits by enabling adaptive and efficient operation under a wide range of conditions. However, workforce readiness remains a constraint. Medium-voltage power electronics, protection, controls, and cybersecurity expertise are limited relative to projected growth across the energy sector[11]. DOE has identified workforce development as a cross-cutting bottleneck in scaling energy related technologies.
However, the existing workforce possesses strong competencies in power electronics design, manufacturing, and maintenance. Incremental training and targeted education programs are generally sufficient to prepare technicians and engineers for SST deployment in most applications.
License to Operate
Regulatory Environment
Low Risk
The integration of grid-following and grid-forming functionalities positions SSTs as a foundational technology for smart grids, offering adaptability, flexibility, scalability, and reliable power regulation across all stages of energy conversion[3]. Compared to conventional transformers, SSTs enable more adaptive and efficient operation under diverse conditions. These capabilities support broader energy system resilience and align with global sustainability and energy efficiency goals, positioning SSTs as a transformative solution for modern power systems.
However, SSTs intersect multiple regulatory and standards regimes, combining utility equipment requirements with converter interconnection practices. While IEEE 1547 standards facilitate the integration of DERs, medium-voltage SSTs—particularly in substation applications—often require utility-specific qualification and type-testing[14]. Regulatory frameworks generally support the deployment of energy-efficient, low-voltage power electronic devices, and some regions offer incentives for their adoption. In contrast, high-voltage DC (HVDC) and medium-voltage SST applications face stricter regulatory scrutiny, which has limited large-scale deployment in the U.S. to date.
Policy Environment
Low Risk
Federal programs are directionally supportive of SST development and deployment. Initiatives such as the Office of Electricity’s TRAC program on advanced transformers, ARPA-E’s WBG semiconductor efforts, and the DOE Vehicle Technologies Office’s fast-charging R&D help reduce policy risk for pilot projects and early-stage procurement[17][18].
The technology offers improvements across multiple application areas; however, interoperability with existing grid infrastructure remains a challenge due to the absence of standardized protocols and regulatory compliance frameworks. The lack of universal technical standards continues to delay commercialization and complicate system integration.
Policies that support grid modernization, DER integration, and electrification strengthen the business case for SST adoption at low-and medium-voltage levels. At higher voltages, however, more stringent environmental review requirements and complex permitting processes can extend deployment timelines and increase project risk.
Permitting & Siting
Low Risk
SSTs are typically installed within existing converter stations, substations, or equipment enclosures, and most applications follow permitting processes similar to those used for other power electronics systems. Behind-the-fence utility upgrades generally proceed through internal utility procedures. In contrast, public fast-charging sites are subject to local permitting timelines, where NLR research shows that standardized workflows can reduce soft costs and accelerate approvals.
While SST technology offers improvements across multiple application areas, interoperability with existing grid infrastructure remains challenging due to the absence of standardized protocols and regulatory compliance frameworks. The absence of universal technical standards continues to pose barriers to commercialization and system integration.
Environmental & Safety
Low Risk
Compared to oil-filled equipment, SSTs reduce reliance on large volumes of flammable dielectric fluids, shifting operational risks toward semiconductor reliability, insulation coordination, and thermal management. Ongoing DOE and Oak Ridge National Laboratory (ORNL) research focuses on improving these protections[19]. Where quantified, IEEE studies indicate that SST-based medium-voltage-to-DC interfaces may reduce both equipment mass and embodied carbon.
While SSTs offer significant advantages in grid flexibility, control precision, and integration with emerging technologies, they also introduce new environmental considerations[9]. Unlike conventional LFTs, SSTs rely on advanced power semiconductor materials, such as silicon carbide (SiC), whose extraction and processing result in higher CO₂ emissions and increased primary energy consumption[20]. The high component count in SSTs also raises concerns about maintenance and end-of-life recycling.
As with all semiconductor-based systems, SSTs can experience electrical leakage or failure due to material imperfections or improper operation. However, when manufactured to standard and operated in accordance with appropriate safety protocols, SSTs pose no greater risk than other grid-scale power-electronic systems.
While SSTs still face economic and regulatory challenges, their long-term potential as a cornerstone of sustainable smart grids is reinforced by their ability to support adaptive, efficient, and resilient power systems operations.
Community Perception
Low Risk
For utility sites, SSTs are generally not salient to the public, as they are deployed within existing substations or within fenced infrastructure. At public-facing locations, such as EV charging sites, streamlined local permitting processes and clear communication regarding safety and physical footprint—per NLR guidance—can help mitigate concerns. Community-facing issues are typically minimal, as SSTs are most often installed in non-residential or utility environments.
Moreover, SSTs contribute positively to public perception by enhancing grid reliability, enabling better equipment monitoring, and supporting the integration of other energy resources. These attributes align with broader societal goals related to energy resilience, thereby reinforcing the value of SSTs in modern grid infrastructure.
Case Studies & Implementation
EPRI Laboratory Evaluation — 25 kVA Distribution SST Prototype
This project evaluates the novel 35-kVA SST through laboratory testing to characterize its performance, identify deployment challenges, and establish requirements for safe, reliable operation on the distribution grid. Unlike conventional transformers, SSTs can enable bidirectional power flow, integrate AC and DC systems, support locally sourced energy generation systems, and provide built-in sensing, monitoring and voltage regulations. This work aims to develop robust test protocols and application guidance to support utility decision-making and accelerate adoption of SST technology as the grid transitions toward greater electrification, flexibility, and resilience.
https://www.epri.com/research/products/000000003002030242
Eaton Acquires Resilient Power Systems to Expand Solid-State Transformer Technology
In August 2025, Eaton acquired Resilient Power Systems, a Texas-based developer of medium-voltage SST technology. Resilient’s ultra-compact SSTs have already been deployed in EV charging depots that integrate directly with distribution grids, enabling quicker and more cost-effective installation compared to traditional setups. SSTs consolidate voltage conversion, power conditioning, and grid support into a single device.
References
- CIGRE. Welcome to the World of CIGRE. CIGRE. [Online] https://www.cigre.org/.
- Solid-State Transformer: The Catalyst for Resilient and Sustainable Smart Grids. Coelho, Sergio, et al. s.l. : Energy, 2025, Vol. 327. https://doi.org/10.1016/j.energy.2025.136321.
- Zhu, Charles. High-Efficiency, Medium Voltage Input, Solid-State, Transformer-Based 400-kW/1000-V/400-A Extreme Fast Charger for Electric Vehicles. [Slide Deck] s.l. : DELTA, 2020. DE-EE0008361.
- Solid State Transformers: A Comprehensive Review of Technology, Topologies, Applications, Research Gaps, and Future Directions. Ramesh Chandran, Deepak, Kumar, Sanath and Sanath, Deepashri. 6, s.l. : Journal of Power and Energy Engineering, 2025, Vol. 13. https://doi.org/10.4236/jpee.2025.136003.
- Insulation Coordination Design for Grid-Connected Solid-State Transformers. Xu, Chunmeng, et al. s.l. : IEEE Journal of Emerging and Selected Topics in Power Electronics, 2021. Digital Object Identifier: 10.1109/JESTPE.2022.3125708.
- Office of Electricity. Energy Department Advances U.S. Electric Grid Resilience and Reliability with New Transformer and Silicon Carbide Packaging Project. [Online] U.S. Department of Energy, December 3, 2024. [Cited: February 24, 2026.] https://www.energy.gov/oe/articles/energy-department-advances-us-electric-grid-resilience-and-reliability-new-transformer.
- Kaplar, Robert, et al. Reliability of Wide-Bandgap Power Electronics: Devices to Systems. [Online] August 7, 2024. [Cited: February 24, 2026.] https://www.sandia.gov/app/uploads/sites/82/2024/08/PR2024_902_Kaplar_Bob_PowerElectronics-1.pdf. SAND No. SAND2024-10046C.
- Desai, Ranjit, et al. EVSE Soft Costs. [Online] June 6, 2024. [Cited: February 24, 2026.] https://docs.nlr.gov/docs/fy25osti/89856.pdf.
- Evaluating EV Charging Stations Operation with Medium Voltage Solid-State Transformer: Grid Performance and Value Analysis. Paudyal, Pritti, et al. Seattle, WA : 024 IEEE Power & Energy Society General Meeting (PESGM), 2024. https://doi.org/10.1109/PESGM51994.2024.10689200.
- Soft-Switching Solid-State Transformer with Reduction Conduction Loss. Zheng, Liran, Prasad Kandula, Rajendra and Divan, Deepak. 5, s.l. : IEEE Transactions on Power Electronics, 2021, Vol. 36. https://doi.org/10.1109/TPEL.2020.3030795.
- Office of Cybersecurity, Energy Security, and Emergency Response. Protecting Energy Infrastructure: CESER, Partners Publish Cybersecurity Guidance to Mitigate Cyber-Attacks. [Online] U.S. Department of Energy, January 17, 2025. [Cited: February 24, 2026.] https://www.energy.gov/ceser/articles/protecting-energy-infrastructure-ceser-partners-publish-cybersecurity-guidance.
- National Laboratory of the Rockies. EVI-X Modeling Suite of Electric Vehicle Charging Infrastructure Analysis Tools. [Online] National Laboratory of the Rockies, February 3, 2026. [Cited: February 24, 2026.] https://www.nlr.gov/transportation/evi-x.
- U.S. Department of Energy. Advanced Transformers Workshop Report. Washington, D.C. : U.S. Department of Energy, 2023.
- Ingram, Michael. Updating Interconnection Procedures and Incorporating IEEE-1547. [Online] February 9, 2020. [Cited: February 24, 2026.] https://docs.nlr.gov/docs/fy20osti/75969.pdf.
- U.S. Department of Energy. Critical Materials Assessment. Washington, D.C. : U.S. Department of Energy, 2023.
- —. Notice of Final Determination on 2023 DOE Critical Materials List. Federal Register. [Online] U.S. Department of Energy, August 4, 2023. [Cited: February 26, 2026.] https://www.federalregister.gov/documents/2023/08/04/2023-16611/notice-of-final-determination-on-2023-doe-critical-materials-list. 2023-16611 (88 FR 51792).
- Office of Electricity. Solid State Power Substation Technology Roadmap. Washington, D.C. : U.S. Department of Energy, 2020.
- —. Transformer Resilience and Advanced Components (TRAC) Program. [Online] U.S. Department of Energy. [Cited: February 24, 2026.] https://www.energy.gov/oe/transformer-resilience-and-advanced-components-trac-program.
- Zheng, Liran, Kandula, Rajendra Prasad and Divan, Deepak. Soft-Switching Solid-State Transformer with Reduced Conduction Loss. Oak Ridge, TN : Oak Ridge National Laboratory, 2021. https://doi.org/10.1109/TPEL.2020.3030795.
- Office of Critical Minerals and Energy Innovation. Permitting Processes for Electric Vehicle Charging Infrastructure. Alternative Fuels Data Center. [Online] U.S. Department of Energy. [Cited: February 24, 2026.] https://afdc.energy.gov/fuels/electricity-permitting-processes.
If you have any updates or would like to suggest a new technology, please let us know by filling out this form.