Active-gate-control for Snubberless IGBTs connected in Series

Abstract

High voltage IGBT converters require an IGBT series connection. To reduce converter loss and simplify converter configuration, snubber circuits should be omitted. In this paper we introduce our snubberless IGBT series connection technique with active-gate-control.
In the active-gate-control IGBT, gate-voltage is set to increase with collector-voltage. Due to increased gate-voltage, IGBT impedance drops and the collector-voltage is limited. The collector-voltages of IGBTs connected in series can be balanced by uniting the collector-voltages of each single IGBTs independently. In the active-gate-control, the gate is charged before the collector-voltage reaches the clamping voltage. So fast control can be performed and surge voltages at the recovery state can be clamped. In the control the clamping voltage increases with tum-off current and it is saturated for further larger currents. By increasing the clamping voltage with tum-off current, the increase of tum-off loss caused by collector voltage clamping is limited. Saturating the clapping voltage for further higher currents prevents overvoltage failure.