Output harmonic analysis as a potential method of condition monitoring

Abstract

Condition monitoring in power electronics is critical for operational management and control in the context of prolonging the life of the power converter. This becomes even more critical in large complex systems like grid connected voltage source converters for HVDC systems. The common failure modes in power modules based on DBC substrate technology include solder pad delamination and wire-bond lift-off. Both these failure modes have the effect of increasing the junction temperature of the device since the thermal resistance and switching/conduction losses increase. Hence, monitoring the junction temperature using integrated on-chip sensors or temperature sensitive electrical parameters is an active research area. Power modules are comprised of several dies which may degrade at a non-uniform rate thus resulting non-uniform switching rates and junction temperatures between the dies in the module. In this paper, Total Harmonic Distortion (THD) analysis is investigated as a method of condition monitoring. A full bridge power module is driven and by switching the individual devices with different gate resistances, the impact of non-uniform switching losses on the output harmonics is analysed. The impact of variations in the junction temperature on output harmonics is also analysed.