Computer modelling of GTO series strings in megawatt inverters

In order to study the effect of differences in GTO turn-on in series strings, semi-empirical SPICE models of the GTO and snubber diode have been used which were based on experimental data. The GTO model was derived using a two stage device/circuit interaction which is believed to accurately represent turn-on behaviour under these conditions. The computer runs have given useful quantitative data on the effects of varying turn-on differences, etc., on device switching losses. These results may be used to tolerance GTO turn-on characteristics and `optimise´ gate drive parameters in order to minimise turn-on switching losses. The modelling of complete inverters, consisting of devices connected in series to increase voltage capabilities, can give useful information on the operation of the circuit. Component ratings can be adequately assessed whilst reaching a compromise between solution accuracy and program execution time