solid-State Transformers Poised to Revolutionize EV Charging Infrastructure
A new design promises to overcome cost adn complexity hurdles, paving the way for more efficient and grid-amiable fast-charging hubs.
The rapid expansion of electric vehicle (EV) fast-charging stations is placing unprecedented strain on existing power grids. As chargers capable of delivering 350 to 500 kilowatts – and even more – become commonplace, enabling EV charging times comparable to gasoline fill-ups, charging sites are reaching megawatt-scale demand. This surge in power consumption
One of the most promising solutions lies in the progress of the solid-state transformer (SST). Unlike conventional transformers that rely on passive magnetic coupling, an SST utilizes semiconductors, high-frequency conversion with materials like silicon carbide or gallium nitride, and advanced digital control to step voltage up or down. This setup allows for dynamic control of power flow, a critical capability for managing the fluctuating demands of EV charging.
For decades, line-frequency transformers (LFTs) – bulky and heavy assemblies of iron and copper – have been the standard for stepping down medium-voltage AC to the low-voltage AC needed for EV charging. A typical LFT can weigh several tonnes and contain hundreds of kilograms of copper. While reliable, these systems are increasingly expensive due to material costs and logistical challenges, and they are particularly inefficient when managing energy flow between storage and vehicles. SSTs offer a considerably smaller and lighter choice.
“Our solution achieves the same semiconductor device count as a single-port converter while providing multiple independently controlled DC outputs,” explained a CTO at Delta Electronics. However, previous multiport SST designs have been hampered by high costs – typically five to ten times that of LFTs – and a reliance on auxiliary battery banks, which further increase expense and reduce reliability. These factors have slowed the adoption of solid-state technology despite its clear advantages.
Researchers at the Indian Institute of Science and Delta Electronics India in Bengaluru have recently unveiled a new SST design that aims to overcome these limitations.Published on August 20 in IEEE Transactions on Power Electronics, their work details a cascaded H-bridge (CHB)-based multiport SST that eliminates the need for costly components and complex configurations.
The team successfully built and tested a 1.2-kilowatt laboratory prototype, achieving 95.3% efficiency at its rated load.They also modeled a full-scale 11-kilovolt, 400-kilowatt system, divided into two 200-kilowatt ports. At the heart of the system is a multi-winding transformer on the low-voltage side, which eliminates the need for expensive medium-voltage insulation and enables power balancing between ports without requiring auxiliary batteries.
“Previous CHB-based multiport designs needed multiple battery banks or capacitor networks to even out the load,” the authors wrote in their paper. “We’ve shown you can achieve the same result with a simpler, lighter, and more reliable transformer arrangement.”
A key innovation is a new modulation and control strategy that maintains a unity power factor at the grid interface, minimizing energy waste. The SST also allows each DC port to operate independently, ensuring that each connected vehicle receives the appropriate voltage and current without impacting other vehicles or the grid. Utilizing silicon-carbide switches in series, the system efficiently handles medium-voltage inputs with a reduced module count – requiring just 12 cascaded modules per phase for an 11-kilovolt connection, roughly half the number needed by some modular multilevel converter designs. Fewer modules translate to lower costs,simplified control,and improved reliability.
While still in the laboratory stage, this design holds the potential to unlock a new generation of compact and cost-effective fast-charging hubs. By removing the need for intermediate battery storage, the proposed topology could also extend the operational lifespan of EV charging stations. The researchers emphasize that the applications extend beyond EV charging, encompassing data centers, renewable energy integration, and industrial DC grids – any scenario requiring medium-voltage to multiport low-voltage conversion.
for utilities and charging providers grappling with megawatt-scale demand, this streamlined solid-state transformer could be instrumental in making the EV revolution more sustainable and accelerating charging speeds for drivers.
