Experimental Investigation on the Turn-Off Current Redistribution Characteristics of IGCT Based on an Isolated Anode Design

The integrated gate commutated thyristor (IGCT) is promising in dc grids nowadays. However, to meet the increasing demands for handling high fault currents, the turn-off capability of IGCT still needs to be optimized, which is affected by transient turn-off current redistribution significantly. This article proposes an experiment method based on an isolated anode design for detecting the turn-off current redistribution characteristics of IGCT. Influences of on-state current density and commutation impedance distribution on IGCT's turn-off current redistribution characteristics are explored in detail. The results show that when IGCT's turn-off process satisfies the "hard" gate drive condition, the anode current redistribution gets changed mainly in the current commutation period and the anode voltage rising period of the turn-off process, before IGCT's dynamic avalanche phenomenon happens. Though the anode current distribution experiences large fluctuations during the commutation period, it will achieve a new balancing state at the end of this period, which almost does not affect the following periods. When IGCT goes into the anode voltage rising period, the on-state current density distribution will affect the turn-off current redistribution. Under the effects of carrier extraction speed differences, the current density distribution throughout the chip tends to reduce its initial difference, which leads to the phenomenon of "current self-balancing." Meanwhile, the region with the highest on-state current density dominates the anode voltage's building-up speed. To increase IGCT's turn-off capability, improving the on-state anode current density uniformity utilizing an optimized layout or cell structure is one of the effective methods.