Usability and limitations of behavioural component models in IGBT short-circuit modelling

Abstract

Power electronic device design and electrical system analysis can be enhanced by applying modern simulation tools, which make it possible to decrease the use of costly and time-consuming prototypes. One very critical component to be modelled is the semiconductor switch (e.g. an insulated gate bipolar transistor, IGBT) which significantly contributes to the circuit behaviour in power converter systems.

This doctoral dissertation studies behavioural IGBT circuit simulation models and their applicability to the analysis of device short-circuit operation. Commonly, short-circuit operation is modelled with complex device models, but also quite simple models can be used for this purpose. The aim of the study is to develop an IGBT model that can describe the component behaviour especially in short-circuit operation, while the characterization of the model can be performed with commercially available information. Moreover, an existing behavioural IGBT model is used as a reference model. The limitations of both the models in terms of short-circuit operation are analysed.

The IGBT short-circuit behaviour is investigated as a function of several external circuit parameters with circuit simulations, and the simulation results are compared with experimental results to validate the usability of the models and define their limitations. The busbar structure of the switching circuit is modelled with numerical methods, and the busbar model is implemented into the circuit simulator model that is used to model the rest of the switching circuit.

The simplicity of the models produces some inaccuracy in the simulation results, which can be seen particularly when the IGBT operating point deviates from the reference point. However, even with a simple model structure, the main points of an IGBT short-circuit can be described if the model characterization is carried out appropriately. According to the results of the study, the modelling accuracy of the IGBT capacitances and its thermal behaviour are the main contributors to the overall short-circuit modelling accuracy.

Taking into account the reported limitations, the models can be used for instance for short-circuit analysis of busbar structures of power converters or investigation of short-circuit protection functions in hardware-in-loop systems.