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Fast construction fast charging stations for electric vehicles tests the limits of today's capabilities power grid. With individual chargers ranging from 350 to 500 kilowatts (or more), which increases charging time electric cars is now functionally equivalent to the time it takes to fill up with petrol or diesel vehicles, full charging stations can reach megawatt-scale demand. It's enough to make you tense medium voltage distribution networks– The network segment that connects high-voltage power lines to low-voltage lines serving end users in homes and businesses.
DC fast charging stations tend to be clustered in city centers, along highways and in car parks. Because the load is distributed unevenly across the network, individual substations become overloaded, even if the overall network capacity is designed to handle the load. Overcoming this problem is more charging stationswith higher power requirements, Internet access requires power electronics which are not only compact and efficient, but also capable of managing local storage and renewable resources.
One of the most promising technologies for upgrading the network to meet vehicle requirements. electrification and renewable generation is solid state transformer (SST). An SST performs the same basic function as a regular transformer – it increases or decreases voltage. But he does this using semiconductorshigh frequency conversion with silicon carbide or gallium nitride switches and digital control, not just passive magnetic coupling. The SST setting allows it to dynamically control the power flow.
For decades, charging infrastructure has relied on line frequency transformers (LFT) – Massive assemblies of iron and copper that step down medium-voltage alternating current to low-voltage alternating current before or after external AC-to-AC conversion. D.C. What batteries for electric vehicles demand. A typical LFT can contain up to several hundred kilograms of copper windings and several tons of iron. All this metal expensive and increasingly difficult to obtain. These systems are reliable but bulky and inefficient, especially when energy flows between local storage and vehicles. SSTs are much smaller and lighter than the LFTs they are intended to replace.
“Our solution provides the same number of semiconductor devices as a single-port converter while providing multiple independently controlled DC outputs.” – Shashidhar Mathapati, Delta Electronics
But most multiport SSTs developed so far have been too complex or expensive (5 to 10 times the original cost of LFT). This difference plus the dependence of SST on the auxiliary battery. banks which increase costs and reduce reliability – explains why the obvious advantages of semiconductor transistors have not yet been realized. stimulated transition to LFT technology.
Surjakanta Mazumder, Saichand Kasicheyanula, Harisyam P.V. and Kaushik Basu holding their first prototype in the laboratory.Harisyam P.V., Saichand KASICHYANLA, ETL.
How to Make Solid State Transformers More Efficient
IN study published August 20 in IEEE Transactions on Power Electronicsresearchers from Indian Institute of Science And Delta Electronics Indiaboth from Bangalore, have proposed a so-called cascaded H-bridge (CHB)-based multiport SST that eliminates these trade-offs. “Our solution provides the same number of semiconductor devices as a single-port converter, while providing multiple independently controlled DC outputs,” says Shashidhar MathapatiTechnical Director of Delta Electronics. “This means no additional batteries, no additional semiconductors, and no additional medium voltage insulation.”
To test the design, the team built a 1.2-kilowatt laboratory prototype, achieving 95.3 percent efficiency at rated load. They also simulated a full-scale 11-kilowatt and 400-kilowatt system divided into two 200-kilowatt ports.
The heart of the system is a multi-winding transformer located on the low voltage side of the converter. This configuration avoids the need for costly and bulky medium voltage isolation and allows power to be balanced between ports without auxiliary devices. batteries. “Previous CHB-based multiport designs required multiple battery banks or capacitor strings for load balancing,” the authors write in their paper. “We have shown that you can achieve the same result with a simpler, lighter and more reliable transformer.”
The new modulation and control strategy maintains a uniform power factor at the grid interface, meaning that no current from the grid is wasted by oscillating back and forth between source and load without doing any work. The SST described by the authors also allows each DC port to operate independently. In practice, each vehicle connected to the charger will be able to receive the appropriate voltage and current without affecting adjacent ports or disrupting the network connection.
Using series-connected silicon carbide switches, the system can handle medium voltage inputs while maintaining high efficiency. To connect to an 11 kV network, only 12 cascade modules per phase are required, which is approximately half as much as some modular multilevel converters. Fewer modules ultimately mean lower cost, easier management and greater reliability.
Although this design is still in the laboratory stage, it could enable the creation of a new generation of compact and cost-effective fast charging hubs. By eliminating the need for intermediate storage of batteries, which increases cost, complexity and maintenance, the proposed topology can extend the life of electric vehicle charging stations.
According to the researchers, this converter is not just for charging electric vehicles. Any application requiring medium voltage to multiport low voltage conversion, e.g. data centersintegration of renewable energy sources or industrial DC grids—can bring benefits.
For utilities and charger providers facing megawatt-scale demand, this optimized solid-state transformer could help make the electric vehicle revolution easier on the grid and faster for drivers waiting to charge.
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