Maximum switching frequency choice for IGBT used in ZCS mode

Develops quasi-resonant converters using ZCS (zero current switching) mode. In these converters, operating at medium power and frequency range (a few kW and about 100 kHz), the authors used the IGBT (Insulated Gate Bipolar Transistor) as a resonant thyristor. The experiment shows a frequency limit: higher frequencies lead to component failure by thermal instability for punch-through IGBT. The frequency limitation is due to a thermal phenomenon occurring in the bipolar transistor part of the IGBT: The charges injected into the component during the conduction phase have not all disappeared by recombination when the voltage is applied to the component. The authors have studied the variation of these charges and of the losses versus the temperature of the component in order to explain the thermal instability. The results allow one to predict the maximum working frequency of the IGBT in ZCS mode, while avoiding failure of the studied component. The results are discussed and an IGBT, included in a forward resonant converter, has been experimentally studied to check the results. First, the authors show the different behaviours of punch-through ad non-punch-through components with temperature, in ZCS. The behaviour of NPT components is reliable in opposition to PT components. Thermal instability is impossible with NPT components. Such a study is shown to be the most efficient way of choosing the best adapted component to high frequency applications