Prevention of Iron Core Saturation in Multi-Winding Transformers for DC-DC Converters

This paper deals with prevention of saturation in the iron core of a multi-winding transformer. It is a substantial part of dc-dc converters used in resistance spot welding systems. The discussed resistance spot welding system consists of a semiconductor input converter, a single-phase welding transformer with one primary coil and two secondary coils, and a full-wave output rectifier connected to the transformer´s secondary coils. The paper shows that the interaction among magnetically nonlinear behavior of the iron core combined with unbalanced parameters of the circuits with the two transformer´s secondary coils can cause iron core saturation even when elements connected to coils are passive elements. The first part of the paper focuses on analysis of saturation phenomena in multi-winding transformers. It is performed on specially designed laboratory transformer composed of the iron core in the form of two C-shaped segments and modular coils used to form the single-coil primary winding and two-coil secondary winding. Knowledge acquired on the laboratory transformer is applied to develop two different solutions for active prevention of the iron core saturation in multi-winding welding transformers. Both solutions are presented in the second part of the paper.