Shorter distances save energy
With many types of electrical energy use, the first step is to convert the alternating voltage available from the low-voltage grid and the socket (230 or 400 volts) into a direct current voltage required by the end device.
Because a small part of the energy is lost as heat here, it would make sense for larger systems to draw power directly from the medium-voltage grid. This is the next higher grid level, which is responsible for the coarse distribution of the electrical power and works with alternating voltages of many kilovolts. If the alternating voltage of the medium-voltage grid is converted directly into a direct voltage adapted to the end device, one conversion step could be skipped and the associated energy loss saved. Researchers at ETH Zurich have implemented this concept with the help of a new semiconductor technology – recently developed “solid-state transformers” (SST) with power electronic converter stages based on silicon carbide with which voltage and frequency can be arbitrarily changed and protective functions can be implemented.
The researchers based their work on the case of data centre – a type of large consumer experiencing strong growth. They developed a solid-state transformer that can supply a single server cabinet with 25 kilowatts of power and convert an alternating voltage of 3.8 kilovolts into a direct voltage of 400 volts. This takes place in two stages, the first stage producing a constant direct current voltage of 7 kilovolts and the second stage transforming the voltage down to 400 volts at medium frequency using an isolated circuit.