Solid-State Transformers Could Be Key to Scaling EV Charging
the rapid buildout of fast-charging stations for electric vehicles is testing the limits of today’s power grid. With individual chargers drawing 350 to 500 kilowatts (or more), full charging sites can reach megawatt-scale demand – enough to strain medium-voltage distribution networks.
DC fast charging stations tend to be clustered in urban centers, along highways, and in fleet depots. Because the load is not spread evenly across the network, particular substations are overworked-even when overall grid capacity is rated to accommodate the load. Overcoming this problem as more charging stations with greater power demands come online requires power electronics that are not only compact and efficient,but also capable of managing local storage and renewable inputs.
One of the most promising technologies for modernizing the grid is the solid-state transformer (SST). An SST performs the same basic function as a conventional transformer-stepping voltage up or down-but does so using semiconductors,high-frequency conversion with silicon carbide or gallium nitride switches,and digital control,rather of passive magnetic coupling. This setup allows it to control power flow dynamically.
For decades, charging infrastructure has relied on line-frequency transformers (LFTs)-massive assemblies of iron and copper that step down medium-voltage AC to low-voltage AC before or after conversion to direct current for EV batteries. A typical LFT can contain hundreds of kilograms of copper windings and tonnes of iron, making them costly and increasingly difficult to source. these systems are reliable but bulky and inefficient,especially when energy flows between local storage and vehicles.
New Solid-State Transformer Design Promises Efficient, Cost-Effective EV Charging
A new solid-state transformer (SST) design from delta Electronics and detailed in a recent research paper, offers a potentially transformative approach to electric vehicle (EV) charging and other medium-voltage applications. The design streamlines power conversion, reducing costs and complexity while improving efficiency and reliability.
According to Shashidhar Mathapati, CTO of Delta Electronics, the device functions as a “single-port converter while providing multiple independently controlled DC outputs.” This eliminates the need for additional battery storage,extra semiconductor devices,and costly medium-voltage insulation – components traditionally required in similar systems. https://www.linkedin.com/posts/delta-electronics-india_deltaelectronicsindia-designinindia-designforindia-activity-7311299447068471296-NUOX
The team successfully built and tested a 1.2-kilowatt laboratory prototype, achieving 95.3% efficiency at its rated load. Thay also modeled a larger, 400-kilowatt system operating at 11 kilovolts, divided into two 200-kilowatt ports.
A key element of the design is a multi-winding transformer positioned on the low-voltage side of the converter. This configuration allows for power balancing between ports without relying on auxiliary batteries. As the authors explain in their paper,previous multi-port converter designs based on cascaded H-bridge (CHB) topologies often required multiple battery banks or capacitor networks for load equalization. This new approach achieves the same result with a simpler, lighter, and more dependable transformer arrangement.
The system incorporates a novel modulation and control strategy that maintains a unity power factor at the grid interface. This ensures minimal energy waste, preventing current from oscillating between the source and load without performing useful work. Moreover, the SST allows each DC port to operate independently, enabling each connected vehicle to receive the optimal voltage and current without impacting other ports or the grid.
Utilizing silicon-carbide (SiC) switches connected in series, the system efficiently handles medium-voltage inputs.An 11-kilovolt grid connection requires only 12 cascaded modules per phase – approximately half the number needed by some modular multilevel converter designs. Fewer modules translate to lower costs, simplified control, and increased reliability. Silicon carbide is increasingly favored in power electronics due to its superior efficiency and thermal performance compared to customary silicon-based devices. https://spectrum.ieee.org/tag/silicon-carbide
While currently in the laboratory stage, this design holds promise for a new generation of compact and affordable fast-charging hubs. By eliminating the need for intermediate battery storage – which adds to cost, complexity, and maintenance – the proposed topology could significantly extend the lifespan of EV charging stations.
However, the applications extend beyond EV charging. Any system requiring medium-voltage to multi-port low-voltage conversion, including data centers, renewable energy integration, and industrial DC grids, could benefit from this technology. https://spectrum.ieee.org/tag/data-centers https://spectrum.ieee.org/tag/renewable-energy
For utilities and charging providers anticipating megawatt-scale demand, this streamlined solid-state transformer could facilitate a more grid-kind and faster EV charging experience.
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