This text is a part of our unique IEEE Journal Watch series in partnership with IEEE Xplore.
The fast buildout of fast-charging stations for electric vehicles is testing the boundaries of right this moment’s power grid. With particular person chargers drawing 350 to 500 kilowatts (or more), which makes charging occasions for EVs now functionally equal to the fill-up time for a gasoline or diesel car, full charging websites can attain megawatt-scale demand. That’s sufficient to pressure medium-voltage distribution networks—the phase of the grid that hyperlinks high-voltage transmission strains with the low-voltage strains that serve finish customers in properties and companies.
DC fast charging stations are typically clustered in city facilities, alongside highways, and in fleet depots. As a result of the load will not be unfold evenly throughout the community, specific substations are overworked—even when general grid capability is rated to accommodate the load. Overcoming this downside as extra charging stations, with larger energy calls for, come on-line requires power electronics that aren’t solely compact and environment friendly, but additionally able to managing native storage and renewable inputs.
One of the promising applied sciences for modernizing the grid so it may sustain with the calls for of car electrification and renewable technology is the solid-state transformer (SST). An SST performs the identical primary perform as a traditional transformer—stepping voltage up or down. But it surely does so utilizing semiconductors, high-frequency conversion with silicon carbide or gallium nitride switches, and digital management, as an alternative of passive magnetic coupling alone. An SST’s setup permits it to manage energy circulation dynamically.
For many years, charging infrastructure has relied on line-frequency transformers (LFTs)—huge assemblies of iron and copper that step down medium-voltage AC to low-voltage AC earlier than or after exterior conversion from alternating present to the direct current that EV batteries require. A typical LFT can include as a lot as a couple of hundred kilograms of copper windings and some tonnes of iron. All that steel is costly and increasingly difficult to source. These programs are dependable however cumbersome and inefficient, particularly when power flows between native storage and automobiles. SSTs are a lot smaller and lighter than the LFTs they’re designed to switch.
“Our resolution achieves the identical semiconductor gadget depend as a single-port converter whereas offering a number of independently managed DC outputs.” –Shashidhar Mathapati, Delta Electronics
However most multiport SSTs developed to this point have been too complicated or expensive (between 5 and 10 occasions the upfront price of LFTs). That distinction—plus SSTs’ reliance on auxiliary battery banks that add extra expense and cut back reliability—explains why solid-state’s apparent advantages haven’t but incentivized shifting to the expertise from LFTs.
Surjakanta Mazumder, Saichand Kasicheyanula, Harisyam P.V. and Kaushik Basu maintain their SST prototype in a lab.Harisyam P.V., Saichand Kasicheyanula, et al.
The best way to Make Stable-State Transformers Extra Environment friendly
In a study printed on 20 August in IEEE Transactions on Power Electronics, researchers at the Indian Institute of Science and Delta Electronics India, each in Bengaluru, proposed what’s referred to as a cascaded H-bridge (CHB)–based mostly multiport SST that eliminates these compromises. “Our resolution achieves the identical semiconductor gadget depend as a single-port converter whereas offering a number of independently managed DC outputs,” says Shashidhar Mathapati, the CTO of Delta Electronics. “Meaning no extra battery storage, no further semiconductor gadgets, and no further medium-voltage insulation.”
The group constructed a 1.2-kilowatt laboratory prototype to validate the design, reaching 95.3 % effectivity at rated load. Additionally they modeled a full-scale 11-kilovolt, 400-kilowatt system divided into two 200-kilowatt ports.
On the coronary heart of the system is a multi-winding transformer positioned on the low-voltage aspect of the converter. This configuration avoids the necessity for expensive, cumbersome medium-voltage insulation and permits energy balancing between ports with out auxiliary batteries. “Earlier CHB-based multiport designs wanted a number of battery banks or capacitor networks to even out the load,” the authors wrote of their paper. “We’ve proven you’ll be able to obtain the identical consequence with a less complicated, lighter, and extra dependable transformer association.”
A brand new modulation and management technique maintains a unity energy issue on the grid interface, that means that none of the present coming from the grid goes to waste by oscillating forwards and backwards between the supply and the load with out doing any work. The SST described by the authors additionally permits every DC port to function independently. In sensible phrases, every car related to the charger would have the ability to obtain the suitable voltage and present, with out affecting neighboring ports or disturbing the grid connection.
Utilizing silicon-carbide switches related in sequence, the system can deal with medium-voltage inputs whereas sustaining excessive effectivity. An 11-kilovolt grid connection would require simply 12 cascaded modules per part, which is roughly half as many as some modular multilevel converter designs. Fewer modules in the end means decrease price, less complicated management, and larger reliability.
Though nonetheless on the laboratory stage, the design may allow a brand new technology of compact, cost-effective fast-charging hubs. By eradicating the necessity for intermediate battery storage—which provides price, complexity, and upkeep—the proposed topology may lengthen the operational lifespan of EV charging stations.
Based on the researchers, this converter isn’t just for EV charging. Any software that wants medium-voltage to multiport low-voltage conversion—corresponding to data centers, renewable integration, or industrial DC grids—may gain advantage.
For utilities and charging suppliers dealing with megawatt-scale demand, this streamlined solid-state transformer may assist make the EV revolution extra grid-friendly, and quicker for drivers ready to cost.
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