Comprehensive Loss and Thermal Analysis for Three-phase NPC Grid-tied Converters

Loss and junction temperature are key parameters for the safe operation of power semiconductor devices in power electronic systems. However, it is difficult to forecast the exact thermal stress of the device in field use. Consequently, engineers tend to use higher rated devices to maintain excessive margin, resulting in a higher cost. In this article, the loss and thermal characteristics of a three-phase neutral point clamped (NPC) converter are investigated under different operating conditions. Firstly, the loss and thermal characteristics of a three-phase converter under different modulation methods are explored, as well as the effect of positive and negative power factors on the losses. Secondly, along with the needs of the grid, the converter's loss characteristics for producing inductive and capacitive reactive power are taken into account. Finally, the loss changes during low-voltage ride-through (LVRT) are evaluated. These evaluations contribute in the rationalization of semiconductors selection and design during the early stages of converter design.