A three-phase AC-DC GTO thyristor converter employing equal pulse-width modulation (EPWM)

A comparative study of equal, triangular, stepped, sinusoidal, and inverted sinusoidal pulse-width modulation (PWM) schemes on the source and load performances of a three-phase AC-DC gate turn-off (GTO) thyristor converter-fed DC motor is presented. The two-quadrant GTO thyristor converter employing an equal pulse-width modulation (EPWM) scheme is studied in detail. This scheme has been found to offer better overall performance among the PWM schemes considered. A new symmetrical gate pulse pattern that reduces the total number of switchings and allows switching GTOs an equal number of times in each supply cycle is reported. The symmetrical gate pulse pattern has a beneficial effect on the switching loss, especially when the switching frequency is high. Smooth and continuous transition is obtained between rectification and inversion with a single GTO converter. The proposed converter was designed, constructed, and tested using a 3 HP laboratory-sized separately excited DC motor. The exponential results are shown to be in good agreement with the theory