Harmonic Mitigation using 36-Pulse AC-DC Converter for Direct Torque Controlled Induction Motor Drives

This paper presents the design and analysis of a transformer based 36-pulse ac-dc converters which supplies direct torque controlled induction motor drives (DTCIMD's) in order to have better power quality conditions at the point of common coupling. The converters output voltage is accomplished via two paralleled eighteen-pulse ac-dc converters each of them consisting of nine-phase diode bridge rectifier. The design procedure of magnetics is in a way such that makes it suitable for retrofit applications where a six-pulse diode bridge rectifier is being utilized. The 36-pulse structure improves power quality criteria at ac mains and makes them consistent with the IEEE-519 standard requirements for varying loads. Furthermore, near unity power factor is obtained for a wide range of DTCIMD operation. A comparison is made between 6-pulse and 36-pulse converters (Polygon, Fork, and Hexagon) from view point of power quality indices. Results show that input current total harmonic distortion (THD) is less than 4% for the 36-pulse topologies at variable loads. The Delta/Hexagon connected platform could simplify the resulted configuration for the converters and reducing the costs.