Fraunhofer ISE

Silicon carbide for partial load efficiency

One of the challenges with residential PV storage systems is that they need to be charged within a few hours when the sun is intense, and discharged over a longer period of time when the electricity is consumed at partial load. Therefore, battery inverters should have a high conversion efficiency over a broad power range. Fraunhofer ISE has just concluded a project in partnership with Kaco New Energy and STS, developing a 6 kW hybrid inverter comprised of silicon carbide components. The researchers say that by implementing new wide band-gap semiconductors, the inverter maintains high efficiency even at partial loads, while also reaching a high power density. Underlining the crucial role of power electronics and their significance to the development of storage systems, Fraunhofer ISE is one of the five Gigawatt winners of this year’s competition.

A special highlight of the engineered innovation is the battery charger’s DC-DC converter with a three-leg interleaved synchronized topology, that switches the silicon carbide module to make use of its three distinct control input legs.

In serial production, the institute says that the device built from silicon carbide components would not cost more than today’s battery inverters. When compared to particularly poor-performing inverters on the market, savings could amount to €150-250 per year. However, as conventional devices have improved in the past, final potential savings may depend on the choice of comparison.

Jury comments

Xavier Daval: “The main benefit of Wide Band Gap power transistors is a strong reduction of switching losses. By providing faster commutation capabilities, this new generation of Power Semiconductors are the components expected to build more efficient DC-DC converters for storage. The Fraunhofer-Kaco partnership is providing a new generation of charge controllers delivering a significant improvement in efficiency, especially at low power level.”

Nina Munzke: “Very high efficiencies in the partial power range, which is very important for residential storage.”