24- Pulse Fork Autotransformer Based Converter for Improvement of Power Quality Indices

In this paper, a 24-pulse ac-dc converter is designed, modeled and simulated based on a fork autotransformer to improve power quality indices. The use of autotransformer results in reduced kVA rating of the proposed topology as compared with the transformer based 24-pulse converter. Due to the proper flexibility of the proposed topology, it can be simply utilized in other similar applications. Also the proposed converter has a better performance in power quality improvements as compared with the transformer based 24-pulse converters. Whereas the total harmonic current distortion for the given converter is between 2% in light load to 5% at full load, the same index in regular transformer based 24-pulse converter is varied from 4% to 8%. In this paper various power quality indices and kVA rating resulting in total construction cost of the 24-pulse transformer/ autotransformer based converters are compared. The investigated converters used in induction motor drive systems are modeled and simulated using multi-winding transformer block of Matlab/Simulink software. Simulation results confirmed that power quality indices related to the proposed converter are similar to those achieved by fork transformer based converter but better than existing transformer based converters, indicating its ability to fulfill the criteria required by IEEE 519 standard (THDi < 5%) under various loading conditions. Also, power factor reaches near unity under various ranges of converter operation. The kVA rating for the 24-pulse fork transformer based converter is about 146.62% of the nominal load rating comparing with 87.12% of the proposed converter topology resulting in reduced size, weight and finally cost of the proposed converter with respect to the conventional transformer based 24-pulse converters.