Spatial and Temporal Instabilities in High Voltage Power Devices
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Beschreibung
During the turn-off process of high voltage bipolar devices, e.g. IGBTs and power diodes, dynamic avalanche may result in spatial instabilities of the homogeneous current density and the formation of current filaments. In the first part of this PhD thesis, using the device simulation results, the underlying physical mechanisms of the filament dynamic are investigated. An analytical model for the filament velocity is presented. It is shown how the weak boundary conditions and self-heating may turn the electrically triggered filament into a thermal filament and a consequent thermal runaway.
In the second part, IGBT under short-circuit conditions is considered. A basic small-signal model shows that, even without considering stray inductances or the interaction of parallel devices, oscillatory and unstable behaviors are possible. The criteria for oscillation and their dependence on parameters of the device and external circuit are derived and the apparent negative gate capacitance is explained. These results can be considered as design criteria to avoid instabilities.
Autor*in
Saeed Milady