Application of pulse multiplication in autotransformer based AC-DC converters for direct torque control induction motor drives

Power quality improvement has been achieved using a 24 pulse autotransformer based ac-dc converter. The idea is to use an autotransformer based 12-pulse ac-dc converter and incorporating pulse doubling method for improving power quality ac mains for feeding a direct torque controlled induction motor drive (DTCIMD) load. The scheme uses a star connected autotransformer to produce 12-pulses with flexibility to adjust its voltage ratio which makes it suitable for retrofit application where a 6-pulse diode bridge rectifier is being used. Using the proposed 24-pulse AC-DC convertor, harmonic currents up to 21st order has been eliminated in the AC mains currents. A set of power quality indices on input AC mains for the proposed ac-dc converter feeding DTCIMD are also presented to compare its performance with 6-pulse and 12 pulse ac-dc converters. Also the effect of load variation on DTCIMD fed 24-pulse ac-dc converter is studied to demonstrate the effectiveness of the proposed ac-dc converter.