PWM thyristor inverter with one bypass GTO utilizing line and device commutations

The waveforms and power factor of an ordinary line-commutated thyristor inverter can be improved by adding one bypass GTO (gate-turn-off) thyristor and a small AC filter unit. Possible transitions between the switching states of the inverter are investigated on the basis of instantaneous voltage and current vectors. The extended freedom from adding the GTO is clearly shown. Restrictions for the pulse width-modulation (PWM) pattern are also shown, and an example pattern is deduced. A criterion for the design of the AC filter parameters is given. The validity of the method is confirmed by simulation and experimental results. >