Analysis of power cycling for semiconductor devices in modular multilevel converters

This paper presents a numerical analysis of the temperature profiles within the semiconductor devices of modular multilevel converters (MMCs). These temperature profiles are essential for assessing the power-cycling lifetime of IGBT modules, which influences the converter reliability. An electro-thermal simulation model has been established, combining a dynamic thermal model of the semiconductor devices with a detailed model of the MMC topology and its associated control loops. Conduction losses and switching losses in the semiconductors are calculated online in the simulation, using the instantaneous voltages and currents in the devices. The presented simulation results reveal low losses and limited thermal stresses in terms of peak-to-peak temperature variations in the devices, for both a 200-level MMC operating under staircase modulation, as well as for a 20-level MMC operating with pulsewidth modulation (PWM). This indicates that the application of conventional IGBT modules in high power MMCs is mainly constrained by the current switching capability and not by the power-cycling lifetime.