Relative MTTF evaluation for present and future MV VFD topologies on ships

This work evaluates how redundancy and device voltage rating affects the reliability of the neutral-point piloted (NPP) and modular multilevel converter (MMC) topologies in medium voltage variable-frequency drive (VFD) applications. Reliability block diagrams are used along with relative Failure in Time (FIT) rates to look at the effect redundancy and reduced parts count due to higher voltage devices has on overall VFD reliability. The analysis demonstrates that MMC converters with redundancy are very competitive in terms or reliability despite increased parts count. Additionally, the results indicate that 10kV wide bandgap semiconductor devices with FIT values approximately twice as high as today´s 4.5kV devices may still make sense in niche applications for the NPP due to the reduced parts count at higher voltages.