Comparison between i_g integration and v_(gs) derivation methods dedicated to fast short-circuit 2D diagnosis for wide bandgap power transistors

摘要

This study presents and compares two original high-speed protection circuit methods, namely, i_g integration and v_(gs) derivation, against short-circuit types, referred to as, the hard switch fault and fault under load. Since the gate-drain capacitor C_(gd) of a power device depends on the drain to source voltage v_(ds),it can become an original native sensor to monitor the switching operation and so detect the unwanted v_(ds) transition or the absence of the v_(ds) transition by monitoring only v_(gs). The use of only low-voltage monitoring, such as υ_(gs), is an essential step to integrate fast and embedded new detection methods into a low-voltage application-specific integrated circuit gate driver, in particular for wide bandgap power transistors. The C_(gd) capacitor plays a major part in the two detection methods. The first method is based on dedicated two-dimensional monitoring of the gate charge transferred in a time interval combined with gate voltage monitoring. The second method consists of the reconstruction of the dv_(gs)/dt by means of a capacitive current sensing to provide the v_(gs) derivation combined with the v_(gs) monitoring. Comparison and simulation of the methods based on a C2M0025120D SiC MOSFET device under LTspice™ are made to verify the validity of the methods. In terms of detection speed of the short circuit, a detection time of 200 ns is obtained for both methods. Experimental waveforms based on C3M0120090J SiC MOSFET device were included into LTspice™ to push furthermore the methods to their limits and validate the approaches. Both methods are easy to design and to integrate. However, the robustness and the speed of detection trade-off of all these methods should be analysed and compared relative to the critical functionalities.