A Simple Digitally Controlled Three-Phase PWM Inverter using Turn-Off Thyristors

A new pulsewidth-modulation method for a three-phase inverter is proposed. The method offers the advantages of a much simpler control logic circuitry and relatively high-quality waveforms of the output voltage. The use of high-power turn-off thyristors allows simplification of the power circuit construction and a reduction in size. The experiments using turn-off thyristors with a rating of 1200 V and 50 A show that both improved waveforms of the output current and high efficiency can be obtained. The details of the control circuits and the driver circuits of the turn-off thyristors are also presented.