Scientists at the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg, Germany have successfully tested power transistors made of gallium nitride (GaN) in power electronic systems. By using such transistors the researchers says that, for example, the size of charging inverters in electric vehicles and the weight of power converters in aircraft can be reduced, and power supplies in server farms can be more gain efficiency.
GaN has long been in the focus of interest of many researchers, and prototype devices are now available. “With power transistors made of gallium nitride, significantly higher switching frequencies are achievable than with ordinary silicon power transistors,” says professor Bruno Burger, head of the Power Electronics department at Fraunhofer ISE. “In contrast to silicon carbide, gallium nitride is particularly suited for the lower voltage range.” In particular, resonant topologies can fully utilize the advantages of gallium nitride power transistors, he adds.
Picture 1: Developed 1MHz LLC resonant converter with rated output power of 1kW, equipped with 600V GaN power transistors.
Despite still needing substantial research, Fraunhofer ISE says that impressive results have been obtained in an internal study. A DC/DC converter with rated output power of 1kW was operated at a switching frequency of 1MHz, providing 94% peak efficiency. “With regard to the 600V gallium nitride transistor, the switching frequency and also the efficiency of the DC/DC converter could have been raised to an even higher level,” says Arne Hendrik Wienhausen, who performed the experiments. “The limiting factor was the high-frequency transformer.”
Until now, only transistors made of silicon have been used in power electronic systems with voltages up to 600V, says Fraunhofer ISE. The switching and conduction losses of these transistors are significantly higher than those of transistors made of gallium nitride. Large losses generated in the transistors hence need to be dissipated in a complex way.
Picture 2: Measured efficiency of 1MHz resonant converter for various values of output power and output voltage at an input voltage of 380V.
In addition to the higher efficiency, GaN provides the opportunity to increase the switching frequency to many times greater than the state-of-the-art. As a result, passive components such as inductors, transformers and capacitors can be much smaller, leading to more compact and lighter-weight designs. Also, expensive material can be saved.
Fraunhofer ISE predicts that GaN will permanently change the world of power electronics since, in all applications where system weight and volume are crucial, power transistors made of GaN and operated at high frequency offer great advantages over other technologies. It can be assumed that the 1MHz switching frequency demonstrated in the DC/DC converter is just a first step towards much higher switching frequencies while maintaining high efficiency, reckons Fraunhofer ISE.
