Analysis of IGBT modules connected in series

An analysis is presented of IGBTs connected in series, with reference to the phenomenon of parasitic oscillation. A linear model is developed for use in the study. Two methods are proposed; an analytical approach and a numerical approach based on the state space analysis. The analytical approach offers insight into the effect of the various parameters, whereas the numerical approach offers greater accuracy as it makes fewer assumptions. The theoretical analysis is corroborated by the experimental results from a step-up convertor. Conclusions are drawn concerning the circuit design, and appropriate experimental results are provided, illustrating near ideal operation.