This text is a part of our unique IEEE Journal Watch sequence in partnership with IEEE Xplore.
The speedy buildout of fast-charging stations for electrical automobiles is testing the bounds of immediately’s energy grid. With particular person chargers drawing 350 to 500 kilowatts (or extra), 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 quick charging stations are usually clustered in city facilities, alongside highways, and in fleet depots. As a result of the load shouldn’t be unfold evenly throughout the community, specific substations are overworked—even when total grid capability is rated to accommodate the load. Overcoming this drawback as extra charging stations, with higher energy calls for, come on-line requires energy electronics that aren’t solely compact and environment friendly, but in addition able to managing native storage and renewable inputs.
One of the vital promising applied sciences for modernizing the grid so it might sustain with the calls for of auto electrification and renewable era is the solid-state transformer (SST). An SST performs the identical primary 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 a substitute of passive magnetic coupling alone. An SST’s setup permits it to regulate energy move dynamically.
For many years, charging infrastructure has relied on line-frequency transformers (LFTs)—large 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 present 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 pricey and more and more troublesome to supply. 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 interchange.
“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 pricey (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 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.
Make Stable-State Transformers Extra Environment friendly
In a examine revealed on 20 August in IEEE Transactions on Energy 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 depend as a single-port converter whereas offering a number of independently managed DC outputs,” says Shashidhar Mathapati, the CTO of Delta Electronics. “Which means no extra battery storage, no further semiconductor gadgets, and no further medium-voltage insulation.”
The staff constructed a 1.2-kilowatt laboratory prototype to validate the design, reaching 95.3 % 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 situated on the low-voltage aspect 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 may obtain the identical outcome 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 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 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 section, which is roughly half as many as some modular multilevel converter designs. Fewer modules in the end means decrease price, easier management, and higher reliability.
Though nonetheless on the laboratory stage, the design might allow a brand new era of compact, cost-effective fast-charging hubs. By eradicating the necessity for intermediate battery storage—which provides price, complexity, and upkeep—the proposed topology might prolong the operational lifespan of EV charging stations.
Based on the researchers, this converter isn’t just for EV charging. Any utility that wants medium-voltage to multiport low-voltage conversion—equivalent to information facilities, renewable integration, or industrial DC grids—may gain advantage.
For utilities and charging suppliers going through 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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