Modified current source inverter for sq. cage motor drive

The conventional analysis of a current source inverter configuration with series diodes, assumes that the diodes are reverse-biased after the current through them has been commutated. This paper presents an improved method of analysis which shows that, under some operating conditions, e.g. high slip frequency, the series diodes may be forward biased during a part of the cycle and the inverter-induction motor drive may be unstable. Therefore, a modified current source inverter in which the series diodes have been replaced by thyristors has been proposed. The operation of the new configuration has been verified on an experimental 3 HP a.c. drive system. The experimental results have been given and compared with those predicted by the analysis.