Optimal design of star-connected autotransformer applied to large current rectifier

To improve the power density of large current rectifier, this study designs optimally a star-connected autotransformer which is used in large current rectifier. From the viewpoint of minimising the kVA rating of phase-shift transformer and conduction loss of rectification devices, it is concluded that the ideal large current rectifier is a combination of dual three-phase half-wave rectifiers and a star-connected autotransformer which is used to be the phase-shift transformer. To design optimally the star-connected autotransformer, the winding configurations of the star-connected autotransformer are analysed, and the corresponding expressions and waveforms of current through windings at different winding configurations are also obtained. Consequently, the kVA rating expressions of the autotransformer under different winding configurations are calculated, which describe the relationship between the winding configuration and load power. From the expressions, the optimal winding configuration, which has the least kVA rating and winding numbers, is obtained. Some simulations and experiments are carried out to verify the theoretical analysis.