Turn‐off analysis of FS‐IGBTs based on a simplified analytical model

Abstract

Normally for IGBTs five stages can be identified during Turn-Off transient, among which stage 3 and 4 are most complicated and time consuming in calculation, due to its intrinsically complicated physics process. In this paper, through extensive experiments, we found an interesting phenomenon that in stage 3 the slope of the driving gate voltage is linearly related to the FS-IGBT voltage and current, which greatly simplifies modeling and calculation. In stage 4, we further simplify the model by assuming (i) no interactive effects between the redistribution current and combination current; (ii) the base excess carrier density at depletion boundary far less than that at FSL boundary; (iii) The total charge in the base only relating to carrier life time. With these simplifications, equivalent circuit for each stage with less calculation efforts is developed, and the running time of the simulation under Matlab is less than one second. A double-pulse testing platform was built. The experimental results for both test beds with single IGBT and two IGBTs in series connection match the proposed model developed in Matlab pretty well, under quite different operating conditions, with the maximum error on both I L-E off and V DC-E off <17%.

Modelling and solving of IGBT's transient analysis model based on the finite state machine

“…The circuit equation of stage 6 can be expressed by Equations ( 1), ( 2) and ( 4). Therefore, the state equation at this stage can be expressed by Equation (7).…”

“…Currently, the analysis of IGBT switching transients mostly relies on some mature commercial computing software, such as Saber, Pspice and Simulink [5][6][7][8]. By calling the IGBT models from these commercial software component libraries, the switching transient characteristics of IGBTs in specific circuit topologies can be obtained.…”