EPFL researchers from Lausanne, Switzerland have developed a compact and efficient medium-frequency transformer (MFT), which should enhance the flexibility and efficiency of tomorrow's smart grids and DC power distribution networks.

The researchers have designed and tested a working MFT prototype, rated for 100 kW and operated at 10 kHz.

MFTs are one of the key enabling technologies for solid-state transformers (SSTs), which will be essential in achieving the transition to DC grids that can facilitate the smart grids concept.

"We can be highly flexible and quickly alter the power flow - and we can do that very efficiently," explains Marko Mogorovic, one of the device's designers. "This will be very important when it comes to integrating the intermittent energy generation from renewable sources into tomorrow's smart grids."

The reduced size of these transformers will be particularly useful in traction systems where the device would transform the AC from the railway lines into DC for the traction/propulsion chain.

Drazen Dujic, director of Power Electronics Laboratory explains: "In an AC system, the frequency at which transformers operate depends on that of the surrounding grid. In Europe, that frequency is fixed at 50Hz."

"In a DC system, however, transformers operate within converters at very high frequencies of up to several tens of kilohertz, thanks to power electronics. And the higher the frequency, the more compact the device," says Dujic.

The railway grid in Switzerland operates at 16.7 Hz, which until now has translated into rather bulky transformers inside the locomotives.

 
Source: EPFL