果冻传媒

Nowadays, the increasing energy demands along with the global imperatives toward sustainable energy resources have led to a growing need for innovative energy conversion systems. One promising technology is the solid-state transformer (SST), which is an advanced power converter that play a crucial role in smart grids, renewable energy integration, electric vehicle charging, and data centers.

Compared to traditional low-frequency transformers (LFTs), SSTs are lighter, more compact, and offer enhanced functionalities like digital control, improved fault tolerance, and the ability to handle power flow in both directions. These features are key facilitators of efficient energy management solutions, reducing carbon emissions, and reliable power delivery grids.

Medium frequency transformers

A critical component of SSTs is the medium frequency transformer (MFT), which protects electrical systems against faults by providing isolation of power distribution networks and adjusting the voltage levels.

By operating at a higher frequency, MFTs reduce the size of the magnetic components, enabling more compact and efficient designs. However, increasing the operating frequency also introduces challenges.

Higher frequencies lead to greater energy loss within the transformer windings. Additionally, the smaller size of the components reduces heat dissipation, which can affect the reliability of the system.

New designs hold the key

To tackle these challenges, researchers are exploring new designs, materials, and construction methods to enhance the performance of MFTs.

For instance, oil-immersed MFTs offer high power density and effective cooling but come with drawbacks such as environmental risks, fire hazards, and maintenance requirements. Another common solution is to use litz wire to reduce frequency-dependent losses, but this option is costly and limits the transformer鈥檚 power density due to poor thermal dissipation.

This research

In this study, developed a new approach to improve MFT design by using dry-type transformers with foil windings.

Dry-type MFTs use epoxy-filled cast windings for insulation, resulting in lighter, simpler designs. Foil conductors allow for better use of the winding鈥檚 cross-sectional area and offer a more affordable alternative to litz wire.

However, this approach comes with its own set of challenges, such as reduced heat dissipation due to thick insulation layers and increased AC losses at medium frequencies. To overcome these issues, improved loss estimation models and new winding topologies were developed to manage these elevated losses effectively.

Mathematical techniques

To improve computational efficiency and understanding of electromagnetic phenomena inside the MFT windings, a set of novel mathematical techniques was developed from Maxwell鈥檚 electromagnetic field theory.

These methods offer better computational efficiency and accuracy compared to traditional tools in estimating the winding losses and facilitate studying the coupled inductive-capacitive phenomena inside MFT windings.

To make foil conductors viable in MFT windings, a new circuit topology was proposed to mitigate the circulating currents that arise when operating at medium frequencies.

This topology effectively reduces the losses incorporated with the circulating currents between parallel windings and improves the overall efficiency of MFTs.

Designed and built

Finally, a full-scale 100 kW, 20 kHz dry-type MFT was designed and built using the proposed winding topology.

The prototype was rigorously tested, achieving a remarkable efficiency of 99.42% and successfully passing high-voltage tests without any insulation failures.

The full-scale prototype confirmed that the new design methodology significantly improves the power density and cost efficiency of MFTs, making it a promising solution for future energy conversion systems.

Title of PhD thesis: . Supervisors: Elena Lomonova and Mitrofan Curti.