The rectifier portion of the rail traction system usually converts 480V, 60Hz AC power to DC power around 650VDC.
The faster switching speeds of SiC power components provide the tools for designers to create railcar power systems that are as much as 50% smaller and 30% lighter than existing systems using other power transistor devices like Si IGBTs. This reduces the weight of the entire motor system by as much as 15%, mostly due to smaller magnetics with SiC higher frequencies. The maximum voltage and current ratings of SiC devices are significantly higher than theoretical capability of Si. SiC has larger margins from failures as well.
Lighter trains are not only more efficient but can be safer as well because lower weight enables the train to stop faster. As a bonus, when SiC and/or GaN devices are also designed into the system’s auxiliary power supplies for passenger comfort devices, such as A/C, Wi-Fi, as well as interior lighting, these systems will also consume far less energy.
SiC and GaN higher operational speeds enable designers to create railcar power systems which are up to 50% smaller and 30% lighter than existing systems, reducing the weight of the entire motor system by as much as 15%. Lighter trains are not only more efficient, but can be safer, too – less weight means they can stop faster.
GaN devices have advantages of low Figure of Merit (FOM) (where the definition of FOM is ‘ON resistance x Gate charge’), and zero reverse-recovery charges (Qrr). GaN transistors are far better than Si because their switching frequency, magnetic design, and switching losses will be significantly reduced in the system.
Si MOSFETs have a typical reverse-recovery charge in the 50- to 60-nC range, depending on their size and characteristics. When the MOSFET turns off, the Qrr in the body diode produces losses that add to the total system’s switching losses. These losses rise proportionally with switching frequency, and make MOSFETs impractical for use at higher frequencies in many applications like traction converter systems.