This text is a part of our unique IEEE Journal Watch series in partnership with IEEE Xplore.
The speedy buildout of fast-charging stations for electric vehicles is testing the boundaries of right now’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 section 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 usually clustered in city facilities, alongside highways, and in fleet depots. As a result of the load is just not unfold evenly throughout the community, explicit 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 in addition able to managing native storage and renewable inputs.
Some of the promising applied sciences for modernizing the grid so it could possibly sustain with the calls for of car electrification and renewable technology is the solid-state transformer (SST). An SST performs the identical fundamental operate as a standard transformer—stepping voltage up or down. However it 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 regulate energy movement 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 techniques are dependable however cumbersome and inefficient, particularly when vitality flows between native storage and autos. SSTs are a lot smaller and lighter than the LFTs they’re designed to switch.
“Our resolution achieves the identical semiconductor gadget rely 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 pricey (between 5 and 10 occasions the upfront value 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 know-how 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.
Learn how to Make Stable-State Transformers Extra Environment friendly
In a study revealed 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)–primarily based multiport SST that eliminates these compromises. “Our resolution achieves the identical semiconductor gadget rely 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 additional semiconductor gadgets, and no additional medium-voltage insulation.”
The crew constructed a 1.2-kilowatt laboratory prototype to validate the design, reaching 95.3 p.c effectivity at rated load. In addition 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 facet of the converter. This configuration avoids the necessity for pricey, 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 end result with an easier, 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 backwards and forwards 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 be capable to obtain the suitable voltage and present, with out affecting neighboring ports or disturbing the grid connection.
Utilizing silicon-carbide switches related in collection, 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 finally means decrease value, less complicated management, and larger reliability.
Though nonetheless on the laboratory stage, the design might allow a brand new technology of compact, cost-effective fast-charging hubs. By eradicating the necessity for intermediate battery storage—which provides value, complexity, and upkeep—the proposed topology might prolong the operational lifespan of EV charging stations.
In line with the researchers, this converter isn’t just for EV charging. Any software that wants medium-voltage to multiport low-voltage conversion—resembling 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 might assist make the EV revolution extra grid-friendly, and quicker for drivers ready to cost.
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